GAMT
Guanidinoacetate N-methyltransferase (EC 2.1.1.2)
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The ontogeny of intestinal CRT, AGAT and GAMT was investigated in foetuses, newborn, suckling, weaning and adult rats. In the colon, CRT mediates creatine transport because it was Na( )- and Cl(-) dependent and inhibited by creatine and GPA. In addition, Northern assays showed two CRT transcripts (2.7-kb and 4.2-kb) and the in situ hybridisation revealed that CRT mRNA is restricted to the colon epithelial cells. The immunohistochemistry revealed that CRT protein was at the apical membrane of colon epithelia. Maturation decreased colonic CRT activity to undetectable levels and increased CRT mRNA abundance. Western assays revealed 57-, 65-, 80- and 116-kDa polypeptides at the intestinal apical membrane. The abundance of the 65-, 80- and 116-kDa polypeptides decreased with age, and that of 57-kDa was only observed in adult rats. The small and large intestine express AGAT and GAMT mRNAs. Maturation decreased AGAT mRNA abundance without affecting that of GAMT. For comparison, renal AGAT mRNA levels were measured and they were increased with age. The study reports for the first time that: i) the apical membrane of rat colon have an active CRT, ii) development down-regulates CRT activity via post-transcriptional mechanism(s), iii) the intestine might synthesize creatine and iv) intestinal and renal creatine synthesis is ontogenically regulated at the level of AGAT gene expression.
MeSH Terms
- Aging
- Amidinotransferases
- Animals
- Animals, Newborn
- Animals, Suckling
- Blotting, Northern
- Blotting, Western
- Creatine
- Energy Metabolism
- Guanidinoacetate N-Methyltransferase
- Immunohistochemistry
- Intestinal Absorption
- Intestine, Large
- Intestine, Small
- Membrane Transport Proteins
- Rats
- Reverse Transcriptase Polymerase Chain Reaction
High-resolution magnetic resonance imaging (cine-MRI) is well suited for determining global cardiac function longitudinally in genetically or surgically manipulated mice, but in practice it is seldom used to its full potential. In this study, male and female guanidinoacetate N-methyltransferase (GAMT) knockout, and wild type littermate mice were subjected to a longitudinal cine-MRI study at four time points over the course of one year. GAMT is an essential enzyme in creatine biosynthesis, such that GAMT deficient mice are entirely creatine-free. Since creatine plays an important role in the buffering and transfer of high-energy phosphate bonds in the heart, it was hypothesized that lack of creatine would be detrimental for resting cardiac performance during ageing. Measurements of cardiac structure (left ventricular mass and volumes) and function (ejection fraction, stroke volume, cardiac output) were obtained using high-resolution cine-MRI at 9.4 T under isoflurane anaesthesia. There were no physiologically significant differences in cardiac function between wild type and GAMT knockout mice at any time point for male or female groups, or for both combined (for example ejection fraction: 6 weeks (KO vs. WT): 70 /- 6% vs. 65 /- 7%; 4 months: 70 /- 6% vs. 62 /- 8%; 8 months: 62 /- 11% vs. 62 /- 6%; 12 months: 61 /- 7% vs. 59 /- 11%, respectively). These findings suggest the presence of comprehensive adaptations in the knockout mice that can compensate for a lack of creatine. Furthermore, this study clearly demonstrates the power of cine-MRI for accurate non-invasive, serial cardiac measurements. Cardiac growth curves could easily be defined for each group, in the same set of animals for all time points, providing improved statistical power, and substantially reducing the number of mice required to conduct such a study. This technique should be eminently useful for following changes of cardiac structure and function during ageing.
MeSH Terms
- Aging
- Animals
- Creatine
- Female
- Guanidinoacetate N-Methyltransferase
- Heart
- Image Processing, Computer-Assisted
- Longitudinal Studies
- Magnetic Resonance Imaging, Cine
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
Glutamate plays a central role in the excitatory synaptic transmission and is important for brain development and functioning. Increased glutamate levels in the synaptic cleft are related to neuronal damage associated with excitotoxicity. Guanidinoacetate methyltransferase (GAMT) deficiency is an inherited neurometabolic disorder biochemically characterized by tissue accumulation of guanidinoacetate (GAA) and depletion of creatine. Affected patients present epilepsy and mental retardation whose pathogeny is unclear. In the present study we investigated the in vitro and in vivo (intrastriatal administration) effect of GAA on glutamate uptake by striatum slices of developing and adult rats. Results showed that GAA significantly inhibited in vitro glutamate uptake at 50 microM and 100 microM in all ages tested. We also tested the effect of taurine on the inhibition of glutamate uptake caused by GAA. Taurine significantly attenuated the inhibitory effect caused by 50 microM GAA, but did not alter that provoked by 100 microM GAA. Furthermore, intrastriatal administration of a solution of 30 microM GAA (0.06 nmol/striatum) significantly inhibited glutamate uptake by rat striatum slices. Our results suggest that the inhibition of striatal glutamate uptake caused by GAA might be involved in the neuropathology and especially in the acute neurological features present in patients with GAMT-deficiency.
MeSH Terms
- Aging
- Animals
- Glutamic Acid
- Glycine
- Microinjections
- Neostriatum
- Nerve Tissue Proteins
- Rats
- Rats, Wistar
- Taurine