Temporal regulation of protein O-GlcNAc levels during pressure-overload cardiac hypertrophy.

Protein posttranslational modifications (PTMs) by O-linked β-N-acetylglucosamine (O-GlcNAc) rise during pressure-overload hypertrophy (POH) to affect hypertrophic growth. The hexosamine biosynthesis pathway (HBP) branches from glycolysis to make the moiety for O-GlcNAcylation. It is speculated that greater glucose utilization during POH augments HBP flux to increase O-GlcNAc levels; however, recent results suggest glucose availability does not primarily regulate cardiac O-GlcNAc levels. We hypothesize that induction of key enzymes augment protein O-GlcNAc levels primarily during active myocardial hypertrophic growth and remodeling with early pressure overload. We further speculate that downregulation of protein O-GlcNAcylation inhibits ongoing hypertrophic growth during prolonged pressure overload with established hypertrophy. We used transverse aortic constriction (TAC) to create POH in C57/Bl6 mice. Experimental groups were sham, 1-week TAC (1wTAC) for early hypertrophy, or 6-week TAC (6wTAC) for established hypertrophy. We used western blots to determine O-GlcNAc regulation. To assess the effect of increased protein O-GlcNAcylation with established hypertrophy, mice received thiamet-g (TG) starting 4 weeks after TAC. Protein O-GlcNAc levels were significantly elevated in 1wTAC versus Sham with a fall in 6wTAC. OGA, which removes O-GlcNAc from proteins, fell in 1wTAC versus sham. GFAT is the rate-limiting HBP enzyme and the isoform GFAT1 substantially rose in 1wTAC. With established hypertrophy, TG increased protein O-GlcNAc levels but did not affect cardiac mass. In summary, protein O-GlcNAc levels vary during POH with elevations occurring during active hypertrophic growth early after TAC. O-GlcNAc levels appear to be regulated by changes in key enzyme levels. Increasing O-GlcNAc levels during established hypertrophy did not restart hypertrophic growth.