Effect of +36T>C in intron 1 on the glutamine: fructose-6-phosphate amidotransferase 1 gene and its contribution to type 2 diabetes in different populations

Cardiomyocyte protein O-GlcNAcylation is regulated by GFAT1 not GFAT2

In response to cardiac injury, increased activity of the hexosamine biosynthesis pathway (HBP) is linked with cytoprotective as well as adverse effects depending on the type and duration of injury. Glutamine-fructose amidotransferase (GFAT; gene name gfpt) is the rate-limiting enzyme that controls flux through HBP. Two protein isoforms exist in the heart called GFAT1 and GFAT2. There are conflicting data on the relative importance of GFAT1 and GFAT2 during stress-induced HBP responses in the heart. Using neonatal rat cardiac cell preparations, targeted knockdown of GFPT1 and GFPT2 were performed and HBP activity measured. Immunostaining with specific GFAT1 and GFAT2 antibodies was undertaken in neonatal rat cardiac preparations and murine cardiac tissues to characterise cell-specific expression. Publicly available human heart single cell sequencing data was interrogated to determine cell-type expression. Western blots for GFAT isoform protein expression were performed in human cardiomyocytes derived from induced pluripotent stem cells (iPSCs). GFPT1 but not GFPT2 knockdown resulted in a loss of stress-induced protein O-GlcNAcylation in neonatal cardiac cell preparations indicating reduced HBP activity. In rodent cells and tissue, immunostaining for GFAT1 identified expression in both cardiac myocytes and fibroblasts whereas immunostaining for GFAT2 was only identified in fibroblasts. Further corroboration of findings in human heart cells identified an enrichment of GFPT2 gene expression in cardiac fibroblasts but not ventricular myocytes whereas GFPT1 was expressed in both myocytes and fibroblasts. In human iPSC-derived cardiomyocytes, only GFAT1 protein was expressed with an absence of GFAT2. In conclusion, these results indicate that GFAT1 is the primary cardiomyocyte isoform and GFAT2 is only present in cardiac fibroblasts. Cell-specific isoform expression may have differing effects on cell function and should be considered when studying HBP and GFAT functions in the heart.

Molecular characterization, chromosomal location, alternative splicing and polymorphism of porcine GFAT1 gene

Glutamine: fructose-6-phosphate amidotransferase (GFAT) is the rate-limiting enzyme of the hexosamine synthesis pathway, which plays important roles in insulin resistance and glucose toxicity. GFAT1 is one of the two isoenzymes of GFAT. In the present study, we cloned cDNA sequence of the porcine GFAT1 gene and identified a GFAT1 splice variant (designed GFAT1-L) that contains a 54 bp insertion within the coding region. Nested RT-PCR revealed that GFAT1 was ubiquitously expressed in all tested tissues, but GFAT1-L was only expressed in skeletal muscle and heart, not in liver, spleen, lung, kidney, small intestine, stomach and fat tissue, suggested that GFAT1-L was selectively expressed in striate muscle in pig. Using both the somatic cell hybrid panel and radiation hybrid panel, the GFAT1 gene was mapped to porcine chromosome 3q21-q27, in which several significant QTLs for carcass traits were found. Among the SNPs we found in porcine GFAT1 gene, only the g. 101A>G polymorphism which located in intron 8 was polymorphic in two pig populations we investigated in the study. Association analyses revealed that the g. 101A>G polymorphism has a significant effect on lean meat percentage (P < 0.05), corrected backfat thickness (P < 0.05) and backfat at the rump (P < 0.05).