CX3CR1
CX3C chemokine receptor 1 (C-X3-C CKR-1) (CX3CR1) (Beta chemokine receptor-like 1) (CMK-BRL-1) (CMK-BRL1) (Fractalkine receptor) (G-protein coupled receptor 13) (V28) [CMKBRL1] [GPR13]
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Short-term (3-day) consumption of a high fat diet (HFD) rich in saturated fats is associated with a neuroinflammatory response and subsequent cognitive impairment in aged, but not young adult, male rats. This exaggerated effect in aged rats could be due to a "primed" microglial phenotype observed in the normal aging process in rodents in which aged microglia display a potentiated response to immune challenge. Here, we investigated the impact of HFD on microglial priming and lipid composition in the hippocampus and amygdala of young and aged rats. Furthermore, we investigated the microglial response to palmitate, the main saturated fatty acid (SFA) found in HFD that is proinflammatory. Our results indicate that HFD increased gene expression of microglial markers of activation indicative of microglial priming, including CD11b, MHCII, CX3CR1, and NLRP3, as well as the pro-inflammatory marker IL-1β in both hippocampus and amygdala-derived microglia. Furthermore, HFD increased the concentration of SFAs and decreased the concentration of polyunsaturated fatty acids (PUFAs) in the hippocampus. We also observed a specific decrease in the anti-inflammatory PUFA docosahexaenoic acid (DHA) in the hippocampus and amygdala of aged rats. In a separate cohort of young and aged animals, isolated microglia from the hippocampus and amygdala exposed to palmitate in vitro induced an inflammatory gene expression profile mimicking the effects of HFD in vivo. These data suggest that palmitate may be a critical nutritional signal from the HFD that is directly involved in hippocampal and amygdalar inflammation. Interestingly, microglial activation markers were increased in response to HFD or palmitate in an age-independent manner, suggesting that HFD sensitivity of microglia, under these experimental conditions, is not the sole mediator of the exaggerated inflammatory response observed in whole tissue extracts from aged HFD-fed rats.
Keywords
- DHA
- High-fat diet
- Lipid composition
- Neuroinflammation
- Normal aging
- PUFA
Age-related changes at the cellular level include the dysregulation of metabolic and signaling pathways. Analyses of blood leukocytes have revealed a set of alterations that collectively lower their ability to fight infections and resolve inflammation later in life. We studied the transcriptomic, epigenetic, and metabolomic profiles of monocytes extracted from younger adults and individuals over the age of 65 years to map major age-dependent changes in their cellular physiology. We found that the monocytes from older persons displayed a decrease in the expression of ribosomal and mitochondrial protein genes and exhibited hypomethylation at the HLA class I locus. Additionally, we found elevated gene expression associated with cell motility, including the CX3CR1 and ARID5B genes, which have been associated with the development of atherosclerosis. Furthermore, the downregulation of two genes, PLA2G4B and ALOX15B, which belong to the arachidonic acid metabolism pathway involved in phosphatidylcholine conversion to anti-inflammatory lipoxins, correlated with increased phosphatidylcholine content in monocytes from older individuals. We found age-related changes in monocyte metabolic fitness, including reduced mitochondrial function and increased glycose consumption without the capacity to upregulate it during increased metabolic needs, and signs of increased oxidative stress and DNA damage. In conclusion, our results complement existing findings and elucidate the metabolic alterations that occur in monocytes during aging.
Keywords
- DNA methylation
- aging
- glucose metabolism
- monocytes
- phosphatidylcholines
- transcriptome
Postoperative cognitive dysfunction (POCD) is a major complication affecting patients of any age undergoing surgery. This syndrome impacts everyday life up to months after hospital discharge, and its pathophysiology still remains unclear. Translational research focusing on POCD is based on a wide variety of rodent models, such as the murine tibial fracture, whose severity can limit mouse locomotion and proper behavioral assessment. Besides, influence of skeletal muscle injury, a lesion encountered in a wide range of surgeries, has not been explored in POCD occurrence. We propose a physical model of muscle injury in CX3CR1 mice (displaying green fluorescent microglial cells) to study POCD, with morphological, behavioral and molecular approaches. We highlighted: alteration of short- and long-term memory after muscle regeneration, wide microglial reactivity in the brain, including hippocampus area, 24 hours after muscle injury, and an alteration of central brain derived neurotrophic factor (BDNF) and nerve growth factor (NGF) balance, 28 days after muscle injury. Our results suggest for the first time that muscle injury can have early as well as late impacts on the brain. Our CX3CR1 model can also facilitate microglial investigation, more specifically their pivotal role in neuroinflammation and synaptic plasticity, in the pathophysiology of POCD.
MeSH Terms
- Aging
- Animals
- Brain
- Brain-Derived Neurotrophic Factor
- CX3C Chemokine Receptor 1
- Cytokines
- Disease Models, Animal
- Hippocampus
- Humans
- Male
- Mice
- Microglia
- Muscle, Skeletal
- Nerve Growth Factor
- Postoperative Cognitive Complications
- Postoperative Complications
The functional status of dynamic microglial cells plays an important role in maintaining homeostasis of microenvironment in CNS. In a previous study, we reported that microglia phenotype might be involved in stress vulnerability and depression recurrence. Here, we aimed to clarify a character of microglia exposed persistently to glucocorticoid (GC), which is representative a stress hormone, in primary cultured microglial cells. Five nanomolars of dexamethasone (DEX, GC agonist) for 72 h decreased CX3CR1 and CD200R expression and induced ramified form of microglial cells in similar morphology to in vivo resident microglia. However, the ramified form of microglia did not increase microglia signature genes such as P2RY12, OLFML3, TMEM119, and TGFBR1. In addition, DEX-treated microglia showed a reduction of phagocytosis function, pro-and anti-inflammatory cytokine production, and cell proliferation. DEX washout did not restore these changes. Based on transcriptomic analysis and functional characters of DEX-treated microglia, we performed senescence-associated beta-galactosidase (SA-β gal) assay in DEX-treated microglia and DEX-treated microglia showed more SA-β gal activity with alteration of cell cycle-related genes. Thus, our results suggest that DEX can induce a specific phenotype of microglia (like-senescence).
MeSH Terms
- Animals
- Anti-Inflammatory Agents
- Cell Proliferation
- Cells, Cultured
- Dexamethasone
- Microglia
- Phagocytosis
- Phenotype
- Rats, Sprague-Dawley
Keywords
- Depression
- Microglia
- Senescence
- Stress hormone
Age is the most prominent risk factor for the development of postoperative cognitive dysfunction. The present study investigated the role of CX3CL1-CX3CR1 signaling in age-related differences in surgery-induced cognitive deficits and neuroinflammation. Adult and aged male Sprague-Dawley rats were subjected to partial hepatectomy or partial hepatectomy with intracerebroventricular infusion of CX3CL1. On postoperative days 3, 7, and 14, the rats were subjected to an open field test and the Morris water maze test. Hippocampal interleukin-1β, CX3CL1, CX3CR1, brain derived neurotrophic factor (BDNF), ionized calcium-binding adapter molecule 1 (Iba-1), and Arginase-1 (Arg1) levels were measured. Age exacerbated cognitive impairment and increased neuroinflammation following surgery. Surgery-induced decreases in CX3CL1 and CX3CR1 proteins were accompanied by increased microglial activation, as indicated by increased Iba-1 expression. Corresponding decline in Arg1 and BDNF levels were observed. Treatment with CX3CL1 decreased proinflammatory cytokines expression, increased BDNF and Arg1 levels in the brain, and enhanced behavioral recovery. The surgery-induced decreases in CX3CL1 and CX3CR1 expression exacerbated postoperative cognitive deficits and exaggerated neuroinflammatory responses in this rodent model. Treatment with CX3CL1 attenuated these effects, at least partly by inhibiting microglial activation, decreasing the associated production of proinflammatory cytokines, and enhancing BDNF expression.
MeSH Terms
- Aging
- Animals
- Brain
- CX3C Chemokine Receptor 1
- Chemokine CX3CL1
- Cognitive Dysfunction
- Hepatectomy
- Liver
- Male
- Maze Learning
- Random Allocation
- Rats
- Rats, Sprague-Dawley
- Signal Transduction
Microglia have been discovered to undergo repopulation following ablation. However, the functionality of repopulated microglia and the mechanisms regulating microglia repopulation are unknown. We examined microglial homeostasis in the adult mouse retina, a specialized neural compartment containing regular arrays of microglia in discrete synaptic laminae that can be directly visualized. Using in vivo imaging and cell-fate mapping techniques, we discovered that repopulation originated from residual microglia proliferating in the central inner retina that subsequently spread by centrifugal migration to fully recapitulate pre-existing microglial distributions and morphologies. Repopulating cells fully restored microglial functions including constitutive "surveying" process movements, behavioral and physiological responses to retinal injury, and maintenance of synaptic structure and function. Microglial repopulation was regulated by CX3CL1-CX3CR1 signaling, slowing in CX3CR1 deficiency and accelerating with exogenous CX3CL1 administration. Microglial homeostasis following perturbation can fully recover microglial organization and function under the regulation of chemokine signaling between neurons and microglia.
MeSH Terms
- Aging
- Animals
- CX3C Chemokine Receptor 1
- Calcium-Binding Proteins
- Cell Movement
- Cell Proliferation
- Chemokine CX3CL1
- Mice, Transgenic
- Microfilament Proteins
- Microglia
- Retina
- Signal Transduction
Immunophenotyping by multi-color flow cytometry is arguably the best tool to identify and quantify distinct cell lineages from the peripheral blood and other biological fluids/tissues. Effective in both clinical and research settings, it can be used to estimate the frequency of a given cell type or measure its phenotypic or functional properties. Normally, immunophenotyping is performed in fresh or fractionated blood (i.e., PBMCs) the same day, or within 24 hours of collection; however, this may not be feasible for all study designs. We have previously shown that cryopreserved blood, a biospecimen that is simple and inexpensive to prepare, is comparable to fresh blood for the enumeration of major leukocyte cell types. For the following study, we sought to extend these observations to distinct subsets of: monocytes (classical, intermediate, and non-classical), T-cells (CD4/CD8 naïve, central and effector memory, senescent, and terminally differentiated, and regulatory T-cells), and NK-cells (CD56 bright and dim); we also examined the expression of monocyte cell-surface receptors CX3CR1, CCR2, TLR2, and TLR4. Our results indicate that cryopreserved blood is comparable to fresh blood; with exception to relatively rare subsets and lowly expressed receptors, the absolute or relative frequency of cell subsets generally correlated >0.80 between blood types, while monocyte receptor expressed was mostly >0.70. Furthermore, the day-to-day coefficient of variation for most cell subsets and parameters was below 20%. Given these findings, we suggest that cryopreserved peripheral blood be given greater consideration for studies in which the quantification of distinct leukocyte subsets is required. © 2018 International Society for Advancement of Cytometry.
MeSH Terms
- Aged
- Aged, 80 and over
- Canada
- Cryopreservation
- Female
- Flow Cytometry
- Humans
- Immunophenotyping
- Killer Cells, Natural
- Longitudinal Studies
- Lymphocyte Subsets
- Male
- Middle Aged
- Monocytes
- T-Lymphocytes
Keywords
- Canadian Longitudinal Study on Aging (CLSA)
- T-cells
- blood
- flow cytometry
- immunophenotyping
- monocytes
- natural killer cells
- regulatory T-cells
Depending on the species, microglial cells represent 5-20% of glial cells in the adult brain. As the innate immune effector of the brain, microglia are involved in several functions: regulation of inflammation, synaptic connectivity, programmed cell death, wiring and circuitry formation, phagocytosis of cell debris, and synaptic pruning and sculpting of postnatal neural circuits. Moreover, microglia contribute to some neurodevelopmental disorders such as Nasu-Hakola disease (NHD), and to aged-associated neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and others. There is evidence that human and rodent microglia may become senescent. This event determines alterations in the microglia activation status, associated with a chronic inflammation phenotype and with the loss of neuroprotective functions that lead to a greater susceptibility to the neurodegenerative diseases of aging. In the central nervous system (CNS), Triggering Receptor Expressed on Myeloid Cells 2-DNAX activation protein 12 (TREM2-DAP12) is a signaling complex expressed exclusively in microglia. As a microglial surface receptor, TREM2 interacts with DAP12 to initiate signal transduction pathways that promote microglial cell activation, phagocytosis, and microglial cell survival. Defective TREM2-DAP12 functions play a central role in the pathogenesis of several diseases. The CX3CL1 (fractalkine)-CX3CR1 signaling represents the most important communication channel between neurons and microglia. The expression of CX3CL1 in neurons and of its receptor CX3CR1 in microglia determines a specific interaction, playing fundamental roles in the regulation of the maturation and function of these cells. Here, we review the role of the TREM2-DAP12 and CX3CL1-CX3CR1 axes in aged microglia and the involvement of these pathways in physiological CNS aging and in age-associated neurodegenerative diseases.
MeSH Terms
- Adaptor Proteins, Signal Transducing
- Aging
- Animals
- Brain
- CX3C Chemokine Receptor 1
- Central Nervous System
- Chemokine CX3CL1
- Gene Expression Regulation
- Humans
- Membrane Glycoproteins
- Membrane Proteins
- Microglia
- Neurodegenerative Diseases
- Receptors, Immunologic
- Signal Transduction
Keywords
- CX3CL1
- CX3CR1
- DAP12
- TREM2
- aged microglia
- aging
The study investigated strain specificities in age-related differences in CD8 T cell- and microglial cell-mediated mechanisms implicated in induction/perpetuation and/or control of neuroinflammation in experimental autoimmune encephalomyelitis (EAE) in Albino Oxford (AO) and Dark Agouti (DA) rats exhibiting age-related changes in the susceptibility to EAE in the opposite direction (increase in relatively resistant AO rats vs decrease in DA rats). In the inductive phase of EAE, the greater number of fully differentiated effector CD8 T lymphocytes was found in draining lymph nodes (dLNs) from aged rats of both strains than in strain-matched young rats, but this was particularly prominent in AO rats, which exhibited milder EAE of prolonged duration compared with their DA counterparts. Consistently, dLN IFN-γ and IL-17 CD8 T cell counts were greater in aged AO than in DA rats. Additionally, the magnitudes of myelin basic protein (MBP)-induced rise in the frequency of IFN-γ and IL-17 CD8 T cells (providing important help to neuroantigen-specific CD4 T cells in EAE models characterized by clinically mild disease) were greater in dLN cell cultures from aged AO rats. Consistently, the magnitudes of MBP-induced rise in the frequency of both IFN-γ and IL-17 CD8 T cells were greater in spinal cord mononuclear cell cultures from aged AO rats compared with their DA counterparts. Besides, with aging CD4 CD25 Foxp3 /CD8 CD25 Foxp3 regulatory T cell ratio changed in spinal cord in the opposite direction. Consequently, in aged AO rats it was shifted towards CD8 CD25 Foxp3 regulatory T cells (exhibiting lower suppressive capacity) when compared with DA rats. Moreover, the frequency of CX3CR1 cells among microglia changed with aging and the disease development. In aged rats, in the effector phase of EAE it was lower in AO than in DA rats. This was accompanied by higher frequency of cells expressing IL-1β (whose down-regulation is central for CX3CR1-mediated neuroprotection), but lower that of phagocyting cells among microglia from aged AO compared their DA counterparts. The study indicates the control points linked with strain differences in age-related changes in EAE pathogenesis.
MeSH Terms
- Aging
- Animals
- CD8-Positive T-Lymphocytes
- CX3C Chemokine Receptor 1
- Encephalomyelitis, Autoimmune, Experimental
- Interferon-gamma
- Interleukin-17
- Leukocyte Count
- Lymph Nodes
- Microglia
- Neuroprotection
- Rats
- Spinal Cord
Keywords
- Aging
- CD8 T cells
- CX3CR1
- EAE
- Protective microglia
- Strain differences
To close the gap in our knowledge of sex influence on age-related changes in inflammation-oxidation state in spinal cord (SC) relevant to inflammation/oxidative-stress associated neuropathologies, 2-3 month-old (young) and 18-20 month-old (old) rats, exhibiting increased level of IL-6, a commonly used marker of inflamm-aging, were examined for inflammatory/redox status, and the underlying regulatory networks' molecules expression. With age, rat SC microglia became sensitized ("primed"), while SC tissue shifted towards mild inflammatory state, with increased levels of proinflammatory IL-1β (key marker of microglial systemic inflammation-induced neurotoxicity), which was more prominent in males. This, most likely, reflected age- and sex-related impairment in the expression of CX3CR1, the receptor for fractalkine (CX3CL1), the soluble factor which regulates microglial activation and diminishes production of IL-1β (central for fractalkine neuroprotection). Considering that (i) age-related changes in SC IL-1β expression were not followed by complementary changes in SC IL-6 expression, and (ii) the reversal in the direction of the sex bias in circulating IL-6 level and SC IL-1β expression, it seems obvious that there are tissue-specific differences in the proinflammatory cytokine profile. Additionally, old male rat SC exhibited greater oxidative damage than female, reflecting, most likely, their lower capacity to maintain the pro-oxidant-antioxidant balance. In conclusion, these findings, apart from highlighting the significance of sex for age-associated changes in SC inflammation-oxidation, may be relevant for understating sex differences in human inflammation/oxidative-stress related SC diseases, and consequently, for optimizing their prevention/therapy.
MeSH Terms
- Aging
- Animals
- Female
- Inflammation
- Interleukin-6
- Male
- Oxidation-Reduction
- Rats
- Sex Factors
- Spinal Cord
Keywords
- Aging
- CX3CR1
- Inflammatory state
- Oxidation state
- Spinal cord
Age-related alterations in immunity have been linked to increased incidence of infections and decreased responses to vaccines in the aging population. Human peripheral blood monocytes are known to promote Ag presentation and antiviral activities; however, the impact of aging on monocyte functions remains an open question. We present an in-depth global analysis examining the impact of aging on classical (CD14 CD16 ), intermediate (CD14 CD16 ), and nonclassical (CD14 CD16 ) monocytes. Monocytes sorted from nonfrail healthy adults (21-40 y) and old (≥65 y) individuals were analyzed after stimulation with TLR4, TLR7/8, and retinoic acid-inducible gene I agonists. Our data showed that under nonstimulated conditions, monocyte subsets did not reveal significant age-related alternations; however, agonist stimulated-monocytes from adults and old subjects did show differences at the transcriptional and functional levels. These alternations in many immune-related transcripts and biological processes resulted in reduced production of IFN-α, IFN-γ, IL-1β, CCL20, and CCL8, and higher expression of CX3CR1 in monocytes from old subjects. Our findings represent a comprehensive analysis of the influence of human aging on pattern recognition receptors signaling and monocyte functions, and have implications for strategies to enhance the immune response in the context of infection and immunization.
MeSH Terms
- Adult
- Aged
- Aged, 80 and over
- Aging
- Cytokines
- Female
- GPI-Linked Proteins
- Gene Expression Profiling
- Humans
- Immunity, Innate
- Interferons
- Lipopolysaccharide Receptors
- Male
- Middle Aged
- Monocytes
- Receptors, IgG
- Receptors, Pattern Recognition
- Toll-Like Receptor 4
- Toll-Like Receptor 7
- Toll-Like Receptor 8
- Transcription, Genetic
- Young Adult
Microglia are essential for CNS homeostasis and innate neuroimmune function, and play important roles in neurodegeneration and brain aging. Here we present gene expression profiles of purified microglia isolated at autopsy from the parietal cortex of 39 human subjects with intact cognition. Overall, genes expressed by human microglia were similar to those in mouse, including established microglial genes CX3CR1, P2RY12 and ITGAM (CD11B). However, a number of immune genes, not identified as part of the mouse microglial signature, were abundantly expressed in human microglia, including TLR, Fcγ and SIGLEC receptors, as well as TAL1 and IFI16, regulators of proliferation and cell cycle. Age-associated changes in human microglia were enriched for genes involved in cell adhesion, axonal guidance, cell surface receptor expression and actin (dis)assembly. Limited overlap was observed in microglial genes regulated during aging between mice and humans, indicating that human and mouse microglia age differently.
MeSH Terms
- Aging
- Axons
- Brain
- CD11b Antigen
- Cell Cycle
- Gene Expression
- Gene Expression Profiling
- Humans
- Microglia
Aging is associated with a progressive loss of the CD28 costimulatory molecule in CD4 lymphocytes (CD28 T cells), which is accompanied by the acquisition of new biological and functional properties that give rise to an impaired immune response. The regulatory mechanisms that govern the appearance and function of this cell subset during aging and in several associated inflammatory disorders remain controversial. Here, we present the whole-genome DNA methylation and gene expression profiles of CD28 T cells and its CD28 counterpart. A comparative analysis revealed that 296 genes are differentially methylated between the two cell subsets. A total of 160 genes associated with cytotoxicity (e.g. GRZB, TYROBP, and RUNX3) and cytokine/chemokine signaling (e.g. CX3CR1, CD27, and IL-1R) are demethylated in CD28 T cells, while 136 de novo-methylated genes matched defects in the TCR signaling pathway (e.g. ITK, TXK, CD3G, and LCK). TCR-landscape analysis confirmed that CD28 T cells have an oligo/monoclonal expansion over the polyclonal background of CD28 T cells, but feature a Vβ family repertoire specific to each individual. We reported that CD28 T cells show a preactivation state characterized by a higher level of expression of inflammasome-related genes that leads to the release of IL-1β when activated. Overall, our results demonstrate that CD28 T cells have a unique DNA methylation landscape, which is associated with differences in gene expression, contributing to the functionality of these cells. Understanding these epigenetic regulatory mechanisms could suggest novel therapeutic strategies to prevent the accumulation and activation of these cells during aging.
MeSH Terms
- Apoptosis
- CD28 Antigens
- CD4 Antigens
- CD4-Positive T-Lymphocytes
- Cellular Senescence
- CpG Islands
- Cytotoxicity, Immunologic
- DNA Methylation
- Gene Expression Regulation
- Genome, Human
- Humans
- Immunity
- Inflammasomes
- Phenotype
- Receptors, Antigen, T-Cell
- Reproducibility of Results
- Signal Transduction
Keywords
- CD4 CD28null T cells
- DNA methylation
- TCR signaling
- aging
- gene expression
- inflammation
Traumatic brain injury (TBI) is a major risk factor for the development of multiple neurodegenerative diseases, including Alzheimer's disease (AD) and numerous recent reports document the development of dementia after TBI. Age is a significant factor in both the risk of and the incidence of acquired brain injury. TBI-induced inflammatory response is associated with activation of brain resident microglia and accumulation of infiltrating monocytes, which plays a pivotal role in chronic neurodegeneration and loss of neurological function after TBI. Despite the extensive clinical evidence implicating neuroinflammation with the TBI-related sequelae, the specific role of these different myeloid cells and the influence of age on TBI-initiated innate immune response remain unknown and poorly studied. We used gene profiling and pathway analysis to define the effect of age on inflammatory response at the time of injury. The recruitment of peripheral CCR2( ) macrophages was delineated using the CX3CR1 (GFP/ ) CCR2 (RFP/ ) reporter mouse. These responses were examined in the context of CCR2/5 antagonism using cenicriviroc. Unsupervised gene clustering and pathway analysis revealed that age predisposes exacerbated inflammatory response related to the recruitment and activation of peripheral monocytes to the injured brain. Using a unique reporter animal model able to discriminate resident versus peripherally derived myeloid cells, we demonstrate that in the aged brain, there is an increased accumulation of peripherally derived CCR2( ) macrophages after TBI compared to young animals. Exaggerated recruitment of this population of cells was associated with an augmented inflammatory response in the aged TBI animals. Targeting this cellular response with cenicriviroc, a dual CCR2/5 antagonist, significantly ameliorated injury-induced sequelae in the aged TBI animals. Importantly, these findings demonstrate that peripheral monocytes play a non-redundant and contributing role to the etiology of trauma-induced inflammatory sequelae in the aged brain.
MeSH Terms
- Aging
- Animals
- Brain Injuries, Traumatic
- Cluster Analysis
- Disease Models, Animal
- Female
- Flow Cytometry
- Inflammation
- Macrophages
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Mutant Strains
- Real-Time Polymerase Chain Reaction
- Receptors, CCR2
- Receptors, CCR5
Keywords
- Aging
- Antagonist
- CCR2
- Chemokine
- Macrophage
- Microglia
- Neurotrauma
Healthy elderly individuals are particularly prone to catastrophic events at any moment of their lives. One stressful event for individuals aged 65 and older is a fall that results in a fracture of the hip (HF). HF causes a state of inflammation that may affect immune responses. In this connection, we have reported that HF induced alterations in neutrophil functions. To assess the impact of HF on classical (cM), intermediate (iM) and non-classical (ncM) monocyte subsets. Distribution, functions (chemotaxis, phagocytosis, superoxide production and cytokine production), phenotype and activation (NF-x03BA;B and PI3K) were evaluated in monocyte subsets before surgery and 6 weeks and 6 months after the event. The distribution of cM and ncM was unchanged, but iM transiently increased before surgery. Sustained increases (iM response to CCL2 and CX3CL1) and decreases (cM and ncM response to CCL2) in chemotaxis were observed. Phagocytosis and superoxide production were impaired in cM but not in iM or ncM. Sustained expression of HLA-DR occurred in cM but not in iM and ncM. Sustained decreased expression of CD11b occurred only in ncM. Sustained decreases (cM and ncM) and increases (iM) in CCR2 expression were observed. An elevated expression of CX3CR1 was found only in iM. cM produced elevated quantities of TNFα. There was a transient oxidative burst of production before surgery in iM and a sustained decrease in ncM. IL-10 production was severely impaired in cM and decreased in iM prior to surgery. Sustained activation (cM), inhibition (ncM) and transient activation (iM) of NF-x03BA;B were observed. Activation of PI3K was severely impaired in cM and ncM but was sustained in iM. HF had more impact on cM and ncM functions than on iM. HF triggered a switch in cM functions from phagocytic to inflammatory elevated TNFα-producing cells. These changes may impact clinical outcomes of HF with respect to inflammation, opportunistic infections and physical recovery.
MeSH Terms
- Aged
- Aging
- Chemotaxis
- Cytokines
- Female
- Hip Fractures
- Humans
- Longitudinal Studies
- Male
- Monocytes
- Perioperative Period
- Phagocytosis
- Phosphatidylinositol 3-Kinases
- Superoxides
- Tumor Necrosis Factor-alpha
In Alzheimer's disease (AD), β-amyloid (Aβ) plaques are tightly enveloped by microglia processes, but the significance of this phenomenon is unknown. Here we show that microglia constitute a barrier with profound impact on plaque composition and toxicity. Using high-resolution confocal and in vivo two-photon imaging in AD mouse models, we demonstrate that this barrier prevents outward plaque expansion and leads to compact plaque microregions with low Aβ42 affinity. Areas uncovered by microglia are less compact but have high Aβ42 affinity, leading to the formation of protofibrillar Aβ42 hotspots that are associated with more severe axonal dystrophy. In ageing, microglia coverage is reduced leading to enlarged protofibrillar Aβ42 hotspots and more severe neuritic dystrophy. CX3CR1 gene deletion or anti-Aβ immunotherapy causes expansion of microglia coverage and reduced neuritic dystrophy. Failure of the microglia barrier and the accumulation of neurotoxic protofibrillar Aβ hotspots may constitute novel therapeutic and clinical imaging targets for AD.
MeSH Terms
- Aging
- Amyloid
- Amyloid beta-Peptides
- Animals
- Astrocytes
- Brain
- CX3C Chemokine Receptor 1
- Coloring Agents
- Diffusion
- Female
- Gene Deletion
- Humans
- Immunization
- Male
- Mice
- Microglia
- Neurites
- Neuroprotective Agents
- Neurotoxins
- Peptide Fragments
- Plaque, Amyloid
- Receptors, Chemokine
- Solubility
- Staining and Labeling
Circulating myeloid cells are important mediators of the inflammatory response, acting as a major source of resident tissue antigen presenting cells and serum cytokines. They represent a number of distinct subpopulations whose functional capacity and relative concentrations are known to change with age. Little is known of these changes in the very old and physically frail, a rapidly increasing proportion of the North American population. In the following study the frequency and receptor expression of blood monocytes and dendritic cells (DCs) were characterized in a sample of advanced-age, frail elderly (81-100 yrs), and compared against that of adults (19-59 yrs), and community-dwelling seniors (61-76 yrs). Cytokine responses following TLR stimulation were also investigated, as well as associations between immunophenotyping parameters and chronic diseases. The advanced-age, frail elderly had significantly fewer CD14( ) and CD14( )CD16( ), but not CD14( )CD16( ) monocytes, fewer plasmacytoid and myeloid DCs, and a lower frequency of monocytes expressing the chemokine receptors CCR2 and CX3CR1. At baseline and following stimulation with TLR-2 and -4 agonists, monocytes from the advanced-age, frail elderly produced more TNF than adults, although the overall induction was significantly lower. Finally, monocyte subset frequency and CX3CR1 expression was positively associated with dementia, while negatively associated with anemia and diabetes in the advanced-age, frail elderly. These data demonstrate that blood monocyte frequency and phenotype are altered in the advanced-age, frail elderly and that these changes correlate with certain chronic diseases. Whether these changes contribute to or are caused by these conditions warrants further investigation.
MeSH Terms
- Adult
- Aged
- Aged, 80 and over
- Aging
- Chronic Disease
- Cytokines
- Dendritic Cells
- Female
- Frail Elderly
- Humans
- Immunophenotyping
- Lipopolysaccharide Receptors
- Male
- Middle Aged
- Monocytes
- Toll-Like Receptor 2
- Toll-Like Receptor 4
- Young Adult
Platelet microparticles (PM) are the most abundant cell-derived microparticles in the blood, and accumulate in thrombo-inflammatory diseases. Platelets produce PM upon aging via an apoptosis-like process and by activation with strong agonists. We previously showed that long-term treatment of monocytic cells with apoptosis-induced PM (PMap) promotes their differentiation into resident macrophages. Here we investigated shorter term effects of various types of PM on monocyte signalling and function. Flow cytometry and scanning electron microscopy revealed that PM formed upon platelet aging (PMap) or ultra-sonication (PMsonic) expressed activated αIIbβ3 integrins and tended to assemble into aggregates. In contrast, PM formed upon platelet activation with thrombin (PMthr) or Ca(2 ) ionophore (PMiono) had mostly non-activated αIIbβ3 and little aggregate formation, but had increased CD63 expression. PM from activated and sonicated platelets expressed phosphatidylserine at their surface, while only the latter were enriched in the receptors CD40L and CX3CR1. All PM types expressed P-selectin, interacted with monocytic cells via this receptor, and were internalised into these cells. The various PM types promoted actin cytoskeletal rearrangements and hydrogen peroxide production by monocytic cells. Markedly, both aging- and activation-induced PM types stimulated the phosphoinositide 3-kinase/Akt pathway, suppressing apoptosis induced by several agonists, in a P-selectin-dependent manner. On the other hand, the PM types differentially influenced monocyte signalling in eliciting Ca(2 ) fluxes (particularly PMap) and in releasing secondary mediators (complement factor C5a with PMap, and pro-inflammatory tumour necrosis factor-α with PMthr). In spite of their common anti-apoptotic potential via Akt activation, aging- and activation-induced PM cause different Ca(2 ) signalling events and mediator release in monocytic cells. By implication, aging and activated platelets may modulate monocyte function in different way by the shedding of different PM types.
Keywords
- Aging
- apoptosis
- microparticles
- monocytes
- platelet activation
- tumour necrosis factor
Here, we demonstrate that the fractalkine (FKN)/CX3CR1 system represents a regulatory mechanism for pancreatic islet β cell function and insulin secretion. CX3CR1 knockout (KO) mice exhibited a marked defect in glucose and GLP1-stimulated insulin secretion, and this defect was also observed in vitro in isolated islets from CX3CR1 KO mice. In vivo administration of FKN improved glucose tolerance with an increase in insulin secretion. In vitro treatment of islets with FKN increased intracellular Ca(2 ) and potentiated insulin secretion in both mouse and human islets. The KO islets exhibited reduced expression of a set of genes necessary for the fully functional, differentiated β cell state, whereas treatment of wild-type (WT) islets with FKN led to increased expression of these genes. Lastly, expression of FKN in islets was decreased by aging and high-fat diet/obesity, suggesting that decreased FKN/CX3CR1 signaling could be a mechanism underlying β cell dysfunction in type 2 diabetes.
MeSH Terms
- Adult
- Aging
- Animals
- CX3C Chemokine Receptor 1
- Cadaver
- Chemokine CX3CL1
- Diet, High-Fat
- Gene Expression
- Glucose
- Humans
- Hyperglycemia
- Insulin
- Insulin Secretion
- Insulin-Secreting Cells
- Islets of Langerhans
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Middle Aged
- Receptors, Chemokine
- Signal Transduction
Changes to innate cells, such as macrophages and myeloid-derived suppressor cells (MDSCs), during aging in healthy or tumor-bearing hosts are not well understood. We compared macrophage subpopulations and MDSCs from healthy young (6-8 weeks) C57BL/6J mice to those from healthy geriatric (24-28 months) mice. Spleens, lymph nodes, and bone marrow of geriatric hosts contained significantly more M2 macrophages and MDSCs than their younger counterparts. Peritoneal macrophages from geriatric, but not young, mice co-expressed CD40 and CX3CR1 that are usually mutually exclusively expressed by M1 or M2 macrophages. Nonetheless, macrophages from geriatric mice responded to M1 or M2 stimuli similarly to macrophages from young mice, although they secreted higher levels of TGF-β in response to IL-4. We mimicked conditions that may occur within tumors by exposing macrophages from young vs. geriatric mice to mesothelioma or lung carcinoma tumor cell-derived supernatants. While both supernatants skewed macrophages toward the M2-phenotype regardless of age, only geriatric-derived macrophages produced IL-4, suggesting a more immunosuppressive tumor microenvironment will be established in the elderly. Both geriatric- and young-derived macrophages induced allogeneic T-cell proliferation, regardless of the stimuli used, including tumor supernatant. However, only macrophages from young mice induced T-cell IFN-γ production. We examined the potential of an IL-2/agonist anti-CD40 antibody immunotherapy that eradicates large tumors in young hosts to activate macrophages from geriatric mice. IL-2-/CD40-activated macrophages rescued T-cell production of IFN-γ in geriatric mice. Therefore, targeting macrophages with IL-2/anti-CD40 antibody may improve innate and T-cell immunity in aging hosts.
MeSH Terms
- Aging
- Animals
- CD4-Positive T-Lymphocytes
- CD40 Antigens
- CD8-Positive T-Lymphocytes
- CX3C Chemokine Receptor 1
- Cell Line, Tumor
- Cell Proliferation
- Cellular Senescence
- Culture Media, Conditioned
- Immunity, Innate
- Interferon-gamma
- Interleukin-2
- Interleukin-4
- Lung Neoplasms
- Lymphocyte Activation
- Macrophages
- Mesothelioma
- Mice
- Mice, Inbred C57BL
- Receptors, Chemokine
- Transforming Growth Factor beta
- Tumor Microenvironment
Macrophages or activated microglia in the subretinal space are considered a hallmark of some retinal pathologies. We investigated the effects of age, pigmentation and CX(3)CR1 deficiency on the accumulation of macrophages/activated microglia in the outer retina of young and old Cx(3)cr1(gfp/gfp) (CX(3)CR1-deficient) or Cx(3)cr1(gfp/ ) mice on either a pigmented (C57BL/6) or albino (BALB/c) background. Quantitative analysis of immunostained retinal-choroidal whole mounts revealed an increase in subretinal macrophage (SRMΦ) numbers in young Cx(3)cr1(gfp/gfp) mice compared with Cx(3)cr1(gfp/ ) mice, however the increase was more marked in albino Cx(3)cr1(gfp/gfp) mice. In aged mice, large numbers of SRMΦ/activated microglia replete with autofluorescent debris were noted in both old pigmented Cx(3)cr1(gfp/gfp) and Cx(3)cr1(gfp/ ) mice proving this accumulation was not CX(3)CR1-dependent. While CX(3)CR1 deficiency leads to an early onset of SRMΦ accumulation, our data reveal that this change occurs in both aged Cx(3)cr1(gfp/ ) and Cx(3)cr1(gfp/gfp) pigmented mice in the absence of marked retinal degeneration and is likely a normal response to aging.
MeSH Terms
- Aging
- Animals
- CX3C Chemokine Receptor 1
- Female
- Macrophages
- Male
- Mice
- Mice, Knockout
- Microglia
- Receptors, Chemokine
- Retina
- Retinal Pigments
Fractalkine (CX(3)CL1) to fractalkine receptor (CX(3)CR1) interactions in the brain are involved in the modulation of microglial activation. Our recent findings indicate that there is microglial hyperactivity in the aged brain during an inflammatory challenge. The underlying cause of this amplified microglial response in the aged brain is unknown. Therefore, the purpose of this study was to determine the degree to which age-associated impairments of CX(3)CL1 and CX(3)CR1 in the brain contribute to exaggerated microglial activation after intraperitoneal (i.p.) injection of lipopolysaccharide (LPS). Here we show that CX(3)CL1 protein was reduced in the brain of aged (18-22 mo) BALB/c mice compared to adult (3-6 mo) controls. CX(3)CL1 protein, however, was unaltered by LPS injection. Next, CX(3)CR1 levels were determined in microglia (CD11b( )/CD45(low)) isolated by Percoll density gradient separation at 4 and 24h after LPS injection. Flow cytometric and mRNA analyses of these microglia showed that LPS injection caused a marked decrease of CX(3)CR1 and a simultaneous increase of IL-1β at 4h after LPS injection. While surface expression of CX(3)CR1 was enhanced on microglia of adult mice by 24h, it was still significantly downregulated on a subset of microglia from aged mice. This protracted reduction of CX(3)CR1 corresponded with a delayed recovery from sickness behavior, prolonged IL-1β induction, and decreased TGFß expression in the aged brain. In the last set of studies BV2 microglia were used to determine effect of TGFß on CX(3)CR1. These results showed that TGFβ enhanced CX(3)CR1 expression and attenuated the LPS-induced increase in IL-1β expression.
MeSH Terms
- Aging
- Animals
- Brain
- CD11b Antigen
- CX3C Chemokine Receptor 1
- Cell Count
- Cells, Cultured
- Chemokine CX3CL1
- Down-Regulation
- Enzyme-Linked Immunosorbent Assay
- Flow Cytometry
- Injections, Intraperitoneal
- Interleukin-1beta
- Leukocyte Common Antigens
- Lipopolysaccharides
- Male
- Mice
- Mice, Inbred BALB C
- Microglia
- Polymerase Chain Reaction
- RNA, Messenger
- Receptors, Chemokine
- Transforming Growth Factor beta
- Up-Regulation
Dendritic cells (DCs) have recently been found in atherosclerosis-predisposed regions of arteries and have been proposed to be causal in atherosclerosis. The chemokine receptor CX3CR1 is associated with arterial injury and atherosclerosis. We sought to determine whether a link exists between arterial DC accumulation, CX3CR1, and atherosclerosis. Mouse aortas were isolated and subjected to en face immunofluorescence analysis. We found that DCs were located predominantly in the intimal regions of arterial branch points and curvatures. Consistent with the increased accumulation of intimal DCs in aged and ApoE-/- aortas compared with young WT aortas (P=0.004 and 0.05, respectively), the incidence of atherosclerosis was 88.9% for aged WT and 100% for ApoE-/- mice compared with 0% for young WT mice. CX3CR1 was expressed on intimal DCs and DC numbers were decreased in CX3CR1-deficient aortas of young, aged, and ApoE-/- mice (P=0.0008, 0.013, and 0.0099). The reduced DC accumulation in CX3CR1-deficiency was also correlated with decreased atherosclerosis in these animals. The accumulation of intimal DC increases in aged and ApoE-/- aortas and correlates with the generation of atherosclerosis. CX3CR1-deficiency impairs the accumulation of DC in the aortic wall and markedly reduces the atherosclerotic burden.
MeSH Terms
- Aging
- Animals
- Aorta
- Apolipoproteins E
- Atherosclerosis
- CX3C Chemokine Receptor 1
- Dendritic Cells
- Mice
- Mice, Knockout
- Microscopy, Confocal
- Receptors, Chemokine
- Tunica Intima
Senescent Ccl2(-/-) mice are reported to develop cardinal features of human age-related macular degeneration (AMD). Loss-of-function single-nucleotide polymorphisms within CX3CR1 are also found to be associated with AMD. The authors generated Ccl2(-/-)/Cx3cr1(-/-) mice to establish a more characteristic and reproducible AMD model. Single Ccl2- and Cx3cr1-deficient mice were crossbred to obtain Ccl2(-/-)/Cx3cr1(-/-) mice. Funduscopy, histopathology, retinal A2E quantification, proteomics, RT-PCR gene expression assay, immunochemistry, and Western blotting were used to examine the retina and to evaluate gene expression within the retinal tissue. By 6 weeks of age, all Ccl2(-/-)/Cx3cr1(-/-) mice developed AMD-like retinal lesions, including drusen, retinal pigment epithelium alteration, and photoreceptor degeneration. Furthermore, choroidal neovascularization occurred in 15% of the mice. These degenerative lesions progressed with age. A2E, a major lipofuscin fluorophore that accumulated during AMD progression, was significantly higher in the Ccl2(-/-)/Cx3cr1(-/-) retina than in the wild-type retina. Complement cofactor was higher in the Ccl2(-/-)/Cx3cr1(-/-) RPE. Proteomics data indicated that four proteins were differentially expressed in Ccl2(-/-)/Cx3cr1(-/-) retina compared with control. One of these proteins, ERp29, an endoplasmic reticulum protein, functions as an escort chaperone and in protein folding. The authors concluded that Ccl2(-/-)/Cx3cr1(-/-) mice develop a broad spectrum of AMD abnormalities with early onset and high penetrance. These observations implicate certain chemokines and endoplasmic reticulum proteins in AMD pathogenesis. Similar to the mechanism of neurodegeneration caused by dysfunction of endoplasmic reticulum proteins, decreased chaperoning may cause misfolded protein accumulation, leading to drusen formation and retinal degeneration.
MeSH Terms
- Aging
- Animals
- CX3C Chemokine Receptor 1
- Chemokine CCL2
- Complement C3b
- Complement C4b
- Disease Models, Animal
- Endoplasmic Reticulum
- Female
- Heat-Shock Proteins
- Humans
- Macular Degeneration
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Microglia
- Microscopy, Electron, Transmission
- Pyridinium Compounds
- Receptors, Chemokine
- Retina
- Retinal Drusen
- Retinoids
This study examined the association between the sequence variation/expression of CX3CR1, a chemokine receptor, and age-related macular degeneration (AMD). Peripheral blood from 85 AMD patients and 105 subjects without AMD (controls), as well as ocular tissue from 40 pathological sections with AMD and two normal eye sections, were screened for V249I and T280M, two single nucleotide polymorphisms (SNPs) in CX3CR1. An increased prevalence, with the highest odds ratio of 3.57, of the I249 and M280 carriers was found among the AMD cases as compared with the controls. When comparing CX3CR1 expression in the archived eye sections, CX3CR1 transcripts were not detectable in the maculae of AMD eyes bearing T/M280; however, transcripts were detected in the maculae of normal eyes bearing T/T280 or T/M280 as well as in the AMD maculae bearing T/T280. Furthermore, lower CX3CR1 protein expression was observed in the maculae of AMD eyes bearing T/M280 compared with the controls bearing T/T280. The I249 and M280 alleles result in a lowered number of receptor binding sites and a decreased ligand affinity. Our data suggest that a decrease, caused by sequence variation and/or lower CX3CR1 expression, in CX3CR1-induced cellular activities could contribute to AMD development.
MeSH Terms
- Aged
- Aging
- Amino Acid Substitution
- Blood Donors
- CX3C Chemokine Receptor 1
- Case-Control Studies
- Chemotaxis
- European Continental Ancestry Group
- Eye Proteins
- Female
- Gene Expression Regulation
- Gene Frequency
- Genetic Predisposition to Disease
- Genetic Testing
- Heterozygote
- Humans
- Macular Degeneration
- Male
- Membrane Proteins
- Middle Aged
- Mutation, Missense
- Odds Ratio
- Polymorphism, Restriction Fragment Length
- Polymorphism, Single Nucleotide
- RNA, Messenger
- Receptors, Chemokine
- Risk Factors