Abstract 2384: Calcineurin-mediated Activation of the Human PPARγ Coactivator-1α (PGC-1α) Gene promoter is Influenced by Haplotype
Recent evidence implicates an important role for the inducible transcriptional coactivator PGC-1α in the adaptive regulation of cardiac and skeletal muscle energy metabolism in diabetes and heart failure. Common genetic variants within the human PGC-1α gene have been linked to insulin resistance and obesity. We sought to determine whether distinct haplotypic differences within the human PGC-1α promoter region conferred functional effects in cardiac myocytes. Human PGC-1α promoter region fragments containing 5 independent human PGC-1α promoter haplotypes blocks (HAPs) fused to luciferase reporters were transfected into primary rat cardiac myocytes. The 5 HAPs (1000, 0001, 0010, 0101, 0000) consisted of unique combinations of major (0) or minor (1) alleles at each of 4 previously identified tagged SNPs representing 8 variants over a span of approximately 4.0 kb of 5′-flanking DNA. The transcriptional activity of the PGC-1α-promoter HAP-specific reporters was assessed under basal conditions and following stimulation by calcineurin A (CnA). CnA signaling has been shown to mediate stress responses relevant to cardiac hypertrophy and failure and is a known activator of PGC-1α expression. HAP 1000 demonstrated significantly impaired calcineurin-stimulated expression (p<0.01). This difference represented a combination of lower basal expression and impaired activation by CnA compared to the other HAPs (1.96 mean fold activation vs. 2.47, 2.40, 2.5, and 2.9 fold activation, p value for interaction between CnA and HAP = 0.014). This resulted in CnA-stimulated activities <50% for HAP 1000 compared to all other HAPs. This finding is notable given that clinical associations, specifically impaired glucose tolerance and earlier age of onset of diabetes, have been found with individual SNPs within the HAP 1000 as well as with haplotype analysis. Inspection of the DNA sequences of the 5 HAPs revealed that HAP 1000 is unique in that it contains a G to A substitution within a putative MEF-2 site, a known target of CnA signaling. These results suggest that common genetic variants within the human PGC-1α gene influence its promoter activity and could explain genotype-phenotype correlations recently observed for this key regulator of striated muscle energy metabolism.