Transcriptional coactivator NT-PGC-1α promotes gluconeogenic gene expression and enhances hepatic gluconeogenesis

Abstract

The transcriptional coactivator PGC-1α plays a central role in hepatic gluconeogenesis. We previously reported that alternative splicing of the PGC-1α gene produces an additional transcript encoding the truncated protein NT-PGC-1α. NT-PGC-1α is co-expressed with PGC-1α and highly induced by fasting in the liver. NT-PGC-1α regulates tissue-specific metabolism, but its role in the liver has not been investigated. Thus, the objective of this study was to determine the role of hepatic NT-PGC-1α in the regulation of gluconeogenesis. Adenovirus-mediated expression of NT-PGC-1α in primary hepatocytes strongly stimulated the expression of key gluconeogenic enzyme genes (PEPCK and G6Pase), leading to increased glucose production. To further understand NT-PGC-1α function in hepatic gluconeogenesis in vivo, we took advantage of a previously reported FL-PGC-1α−/− mouse line that lacks full-length PGC-1α (FL-PGC-1α) but retains a slightly shorter and functionally equivalent form of NT-PGC-1α (NT-PGC-1α254). In FL-PGC-1α−/− mice, NT-PGC-1α254 was induced by fasting in the liver and recruited to the promoters of PEPCK and G6Pase genes. The enrichment of NT-PGC-1α254 at the promoters was closely associated with fasting-induced increase in PEPCK and G6Pase gene expression and efficient production of glucose from pyruvate during a pyruvate tolerance test in FL-PGC-1α−/− mice. Moreover, FL-PGC-1α−/− primary hepatocytes showed a significant increase in gluconeogenic gene expression and glucose production after treatment with dexamethasone and forskolin, suggesting that NT-PGC-1α254 is sufficient to stimulate the gluconeogenic program in the absence of FL-PGC-1α. Collectively, our findings highlight the role of hepatic NT-PGC-1α in stimulating gluconeogenic gene expression and glucose production.