Aging Reduces an ERRalpha-Directed Mitochondrial Glutaminase Expression Suppressing Glutamine Anaplerosis and Osteogenic Differentiation of Mesenchymal Stem Cells

Aging deteriorates osteogenic capacity of mesenchymal stem/stromal cells (MSCs), contributing to imbalanced bone remodeling and osteoporosis. Glutaminase (Gls) catabolizes glutamine into glutamate at the first step of mitochondrial glutamine (Gln)-dependent anaplerosis which is essential for MSCs upon osteogenic differentiation. Estrogen-related receptor alpha (ERR alpha) regulates genes required for mitochondrial function. Here, we found that ERR alpha and Gls are upregulated by osteogenic induction in human MSCs (hMSCs). In contrast, osteogenic differentiation capacity and glutamine consumption of MSCs, as well as ERR alpha, Gls and osteogenic marker genes are significantly reduced with age. We demonstrated that ERR alpha binds to response elements on Gls promoter and affects glutamine anaplerosis through transcriptional induction of Gls. Conversely, mTOR inhibitor rapamycin, ERR alpha inverse agonist compound 29 or Gls inhibitor BPTES leads to reduced Gln anaplerosis and deteriorated osteogenic differentiation of hMSCs. Importantly, overexpression of ERR alpha or Gls restored impairment by these inhibitors. Finally, we proved that compensated ERR alpha or Gls expression indeed potentiated Gln anaplerosis and osteogenic capability of elderly mice MSCs in vitro. Together, we establish that Gls is a novel ERR alpha target gene and ERR alpha/Gls signaling pathway plays an important role in osteogenic differentiation of MSCs, providing new sights into novel regenerative therapeutics development. Our findings suggest that restoring age-related mitochondrial Gln-dependent anaplerosis may be beneficial for degenerative bone disorders such as osteoporosis.