Effects of Palmitate on Mitochondrial Number and PGC1α Splicing in Primary Human Myocytes

PGC1α is an epigenetically regulated transcriptional coactivator that promotes mitochondrial biogenesis. Long chain fatty acids (LCFA), such as palmitate, decrease PGC1α expression in association with decreased mitochondrial function and increased insulin resistance in primary myocytes. Several splice variants of PGC1α have been identified and may compensate for the loss of full length PGC1α; yet, it is unclear if these variants are epigenetically regulated or altered by LCFA treatment in skeletal muscle. Here, we determined the effects of 48h of palmitate treatment on known PGC1α splice variant mRNA levels in cultured and differentiated primary human myocytes (Life Technologies). Genomic DNA and total RNA were isolated and mitochondrial number and PGC1α splice variants' expression, respectively, were determined by real time‐PCR. Palmitate treatment tended to increase mitochondrial number (P = 0.14), despite a significant decrease in the combined expression of all <a name=“OLE_LINK1”>PGC1α</a> splice variants (P < 0.05). The decrease in combined PGC1α splice variant expression appeared to be due to specific decreases in the unspliced PGC1α and A4 variants, although these were not significantly decreased on their own. In contrast, we observed a significant increase in the A2 splice variant (P < 0.05) and a trend towards an increase in N‐truncated PGC1α (P = 0.11). Palmitate had no significant effect on other PGC1α splice variants. N‐truncated PGC1α has been shown to compensate for loss of unspliced PGC1α. We propose that palmitate‐induced upregulation of A2 and N‐truncated PGC1α may be sufficient to acutely increase mitochondrial number, leading to compensatory increases in the cellular capacity for beta oxidation of LCFA.