FKBP51 Controls Cellular Adipogenesis through p38 Kinase-Mediated Phosphorylation of GRα and PPARγ

Abstract

Glucocorticoid receptor-α (GRα) and peroxisome proliferator-activated receptor-γ (PPARγ) are critical regulators of adipogenic responses. We have shown that FK506-binding protein 51 (FKBP51) represses the Akt-p38 kinase pathway to reciprocally inhibit GRα but stimulate PPARγ by targeting serine 112 (PPARγ) and serines 220 and 234 (GRα). Here, this mechanism is shown to be essential for GRα and PPARγ control of cellular adipogenesis. In 3T3-L1 cells, FKBP51 was a prominent marker of the differentiated state and knockdown of FKBP51 showed reduced lipid accumulation and expression of adipogenic genes. Compared with wild-type (WT), FKBP51 knockout (51KO) mouse embryonic fibroblasts (MEFs) showed dramatic resistance to differentiation, with almost no lipid accumulation and greatly reduced adipogenic gene expression. These features were rescued by reexpression of FKBP51 in 51KO cells. 51KO MEFs exhibited reduced fatty acid synthase activity, increased sensitivity to GRα-induced lipolysis, and reduced PPARγ activity at adipogenic genes (adiponectin, CD36, and perilipin) but elevated GRα transrepression at these same genes. A p38 kinase inhibitor increased lipid content in WT cells and also restored lipid levels in 51KO cells, showing that elevated p38 kinase activity is a major contributor to adipogenic resistance in the 51KO cells. In 51KO cells, the S112A mutant of PPARγ and the triple S212A/S220A/S234A mutant of GRα both increased lipid accumulation, identifying these residues as targets of the FKBP51/p38 axis. Our combined investigations have uncovered FKBP51 as a key regulator of adipogenesis via the Akt-p38 pathway and as a potential target in the treatment of obesity and related disorders.

Bilirubin Binding to PPARα Inhibits Lipid Accumulation

“…Adipogenic differentiation of 3T3-L1 cells was achieved by treatment with 1 μM Dex, 830 nM insulin, and 100 μM isobutylmethylxanthine in 10% FBS until Day 9 [ 20 – 22 ]. Upon differentiation, cells were stained with Nile Red to visualize lipid content, and densitometry was used as a direct measure.…”

Biliverdin Reductase A (BVRA) Knockout in Adipocytes Induces Hypertrophy and Reduces Mitochondria in White Fat of Obese Mice

“…Louis, MO, USA, Cat No: C3228) that contained protease inhibitor cocktail (Millipore Sigma, St. Louis, MO, USA, Cat No: P2714-1BTL) and Halt phosphatase inhibitor (Thermo Fisher Scientific, Wilmington, DE, USA, product # 1862495) using a Qiagen TissueLyser LT (Qiagen, Germantown, MD, USA) with a setting of 50 oscillations per second for 3 min. As previously described [31,[34][35][36][37][38][39], lysates were centrifuged at 100,000× g for 7 min and the supernatant removed and measured for protein concentration by BCA Protein Assay Kit (Thermo Fisher Scientific, Wilmington, DE, USA). Protein specimens were resolved by SDS polyacrylamide gel electrophoresis and electrophoretically transferred to Immobilon FL membranes.…”

Emerging Risk Biomarkers in Cardiovascular Diseases and Disorders

“…Moreover, knockdown of FKBP51 showed reduced lipid accumulation and expression of adipogenic genes. It acts as a key regulator of adipogenesis via the Akt/p38 pathway and as a potential target in the treatment of obesity and related disorders [ 235 ] ( Table 2 ).…”