Complementary action of the PGC-1 coactivators in mitochondrial biogenesis and brown fat differentiation

Mitochondria play an essential role in the ability of brown fat to generate heat, and the PGC-1 coactivators control several aspects of mitochondrial biogenesis. To investigate their specific roles in brown fat cells, we generated immortal preadipocyte lines from the brown adipose tissue of mice lacking PGC-1α. We could then efficiently knockdown PGC-1β expression by shRNA expression. Loss of PGC-1α did not alter brown fat differentiation but severely reduced the induction of thermogenic genes. Cells deficient in either PGC-1α or PGC-1β coactivators showed a small decrease in the differentiation-dependant program of mitochondrial biogenesis and respiration; however, this increase in mitochondrial number and function was totally abolished during brown fat differentiation when both PGC-1α and PGC-1β were deficient. These data show that PGC-1α is essential for brown fat thermogenesis but not brown fat differentiation, and the PGC-1 coactivators play an absolutely essential but complementary function in differentiation-induced mitochondrial biogenesis. Affymetrix microarray analysis of total RNA from wt, PGC-1α KO and PGC-1α KO cells expressing an RNAi specific for PGC-1β knockdown was performed. Of the 461 mitochondrial genes analyzed, 181 were found to be at least 20% different between wt and defective PGC-1α and β adipocytes (p < 0.05). More than 85% of these genes were downregulated in cells deficient for PGC-1alpha and PGC-1beta. Keywords: Analysis of mitochondrial gene expression Brown preadipocytes that were either WT, KO for PGC-1alpha, or KO for PGC-1alpha and deficient for PGC-1beta (knockdown through siRNA expression) were differentiated for seven days. RNA was made from biological replicates of the three different types of brown adipocytes (WT, KO expressing a control siRNA, KO expressing a siRNA specific for PGC-1beta knockdown).