Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1a) is a tissue-specific coactivator that enhances the activity of many nuclear receptors and coordinates transcriptional programs important for energy metabolism and energy homeostasis. Inappropriate increases in PGC-1a activity have been linked to a number of pathological conditions including heart failure and diabetes. PGC-1a is highly expressed in metabolically active tissues including brown fat, skeletal muscle and heart. PGC-1a has been implicated in mitochondrial biogenesis in the heart and increased mitochondrial respiration in brown fat. PGC-1a is a coactivator for many factors including, CBP, Scr-1, PPARa, GR (glucocorticoid receptor), THR (thyroid hormone receptor), several orphan receptors and MEF2. This pathway illustrates two of the cofactor regulatory factors MEF2 and PPARa) and an example orphan receptor feedback inhibition loop. Glut4 is used as an example of the downstream elements leading to changes in metabolism. Ichida et al discovered the ERRa repression of PGC-1a. Their results suggest a novel mechanism of transcriptional control wherein ERR-a can function as a specific molecular repressor of PGC-1a. This suggests that other co-activators might also have specific repressors, adding another layer of combinatorial complexity in transcriptional regulation. Czubryt et al identified PGC-1 a as a key target of the MEF2/HDAC regulatory pathway and demonstrated this pathway's importance in maintenance of cardiac mitochondrial function. The linking of MEF2/HDAC provides an potential explanation for the increase in mitochondrial number observed in response to CaMK signaling.
