The Adiponectin Pathway Regulates ERRα Activity to Modulate Mitochondrial Gene Expression and Metabolism in Skeletal Myocytes
Authors: Hamilton Angelica , Kim Susanna , Tang Jonathan , Huss Janice 
Published: April 2020

Adiponectin is a fat‐derived hormone that promotes insulin sensitivity in skeletal muscle. Activation of the adiponectin receptors (AdipoR) in skeletal muscle turns on multiple metabolic signaling pathways, including AMP‐activated kinase (AMPK), and drives changes in metabolic gene expression and mitochondrial function by activating key transcription factors. The orphan nuclear receptor Estrogen‐related Receptor α (ERRα) plays a central role in regulating mitochondrial energy metabolism and is essential for mediating skeletal muscle metabolic remodeling in response to exercise. We previously showed that ERRα activity and expression are increased by AMPK. Based on the overlap between adiponectin and AMPK signaling and regulation of muscle metabolism, we investigated the involvement of ERRα in adiponectin mediated regulation of metabolic gene expression and function in myocytes. Using C2C12 myocytes and CV1 kidney cells, we compared the effects of adiponectin and AMPK pathway activation, using AdipoRon (adipoR agonist) and AICAR, respectively, on ERRα chromatin binding by ChIP and transcriptional activity using reporter assays. We also used siRNA knockdown to test whether the effects of adiponectin and AMPK on metabolic gene expression and mitochondrial metabolism are dependent on ERRα in C2C12 myotubes. We observed that endogenous ERRα binding at chromatin sites proximal to known ERRα target genes, including Acadm, Idh3, Pdk4, Esrra and Stk11, increased in cells that were treated with AICAR for 30 min. Consistent with these acute effects, we showed using live‐cell imaging that fluorescence intensity and nuclear accumulation of a transiently expressed GFP‐ERRα fusion protein increased within 30 min and progressively over 2.5 h after AdipoRon or AICAR treatment. In addition, cycloheximide chase assays revealed that the t1/2 of endogenous ERRα protein in C2C12 myotubes treated with AdipoRon increased by 38% (1.8 h DMSO vs. 2.5 h AdipoRon‐treated). Thus, adiponectin signaling may acutely regulate ERRα protein, in part, by increasing stability, but the post‐translational mechanisms by which adiponectin signaling controls ERRα localization and stability are not yet known. In functional assays we observed that AdipoRon and AICAR stimulated (>2‐fold) ERRα activation of its target gene reporters, including Pdk4 and Dusp1. Additionally, 24 h AdipoRon or AICAR treatment increased mitochondrial activity as determined by MitoTracker staining in both CV1 and C2C12 cells. Finally, activation of ERRα target gene reporters and endogenous metabolic transcripts in response to AdipoRon was blunted with ERRα knockdown in C2C12 myotubes. Collectively, our data support that the effects of adiponectin on gene expression and metabolism in myocytes are mediated via regulation of ERRα. Although in vivo studies are essential, these findings suggest that the ERRα transcriptional pathway may play an important role in mediating adiponectin regulation of skeletal muscle metabolism.Support or Funding InformationAmerican Diabetes Association Innovative Basic Science Award (1‐18‐IBS‐103), City of Hope, Diabetes and Metabolic Research Institute (DMRI) Pilot Award