UC San Diego

The NAD+ dependent protein deacetylase sirtuin 1 (SIRT1) and the acetyltransferase general control of amino acid synthesis 5 (GCN5) are proposed to regulate glucose homeostasis and mitochondrial biogenesis through their reciprocal regulation of the acetylation status of peroxisome proliferator activated receptor-γ coactivator-α (PGC1α). However, the precise contribution of these two enzymes to glucose homeostasis and mitochondrial biogenesis in skeletal muscle, remains to be fully defined. To address this gap in knowledge, this

Thesis investigated whether overexpression of SIRT1 and knockout of GCN5 in skeletal muscle would enhance glucose homeostasis and mitochondrial biogenesis. To do this, we used

Cre-LoxP methodology to generate double transgenic (dTG) mice with inducible, skeletal muscle-specific overexpression of SIRT1 and knockout of GCN5. We assessed skeletal muscle insulin sensitivity by 2-deoxy-glucose uptake, glucose tolerance via an oral glucose tolerance test, exercise capacity, and muscle maximal respiratory function by high-resolution respirometry and compared findings in dTG mice to those in wildtype littermate controls (WT). As expected, there was robust overexpression of SIRT1 and knockout of GCN5 in skeletal muscle of dTG compared to WT mice, and this was accompanied by increased gene expression of some mitochondrial proteins and citrate synthase activity in dTG versus WT mice. Despite these changes, there was no genotype difference in maximal respiratory function of skeletal muscle. Moreover, oral glucose tolerance and skeletal muscle insulin sensitivity were comparable between genotypes. Taken together, these results demonstrate that concurrent overexpression of SIRT1 and knockout of GCN5 does not impact skeletal muscle glucose homeostasis or mitochondrial function.