Calpain system regulates the differentiation of adult primitive mesenchymal ST-13 adipocytes

Endocrinology. 2006 Oct;147(10):4811-9. doi: 10.1210/en.2005-1647. Epub 2006 Jul 20.

Abstract

The activity of calpain, a calcium-activated protease, is required during the mitotic clonal expansion phase of 3T3-L1 embryonic preadipocyte differentiation. Here we examined the role of calpain in the adipogenesis of ST-13 preadipocytes established from adult primitive mesenchymal cells, which do not require mitotic clonal expansion. After exposure to the calpain inhibitor, N-benzyloxycarbonyl-L-leucyl-L-leucinal or overexpression of calpastatin, a specific endogenous inhibitor of calpain, ST-13 preadipocytes acquired the adipocyte phenotype. Overexpression of calpastatin in ST-13 adipocytes stimulated the expression of adipocyte-specific CCAAT/enhancer-binding protein-alpha (C/EBPalpha), peroxisome proliferator-activated receptor (PPAR)-gamma, sterol regulatory element-binding protein 1, and the insulin signaling molecules, insulin receptor alpha, insulin-receptor substrates, and GLUT4. However, insulin-stimulated glucose uptake was reduced by approximately 52%. The addition of calpain to the nuclear fraction of ST-13 adipocytes resulted in the Ca(2+)-dependent degradation of PPARgamma and C/EBPalpha but not sterol regulatory element-binding protein 1. Exposing ST-13 adipocytes to A23187 also led to losses of endogenous PPARgamma and C/EBPalpha. Under both conditions, calpain inhibitors almost completely prevented C/EBPalpha cleavage but partially blocked the decrease of PPARgamma. Two ubiquitous forms of calpain, mu- and m-calpain, localized to the cytosol and the nucleus, whereas the activated form of mu- but not m-calpain was found in the nucleus. Finally, stable dominant-negative mu-calpain transfectants showed accelerated adipogenesis and increase in the levels of PPARgamma and C/EBPalpha during adipocyte program. These results support evidence that the calpain system is involved in regulating the differentiation of adult primitive mesenchymal ST-13 preadipocytes.

MeSH terms

  • Adipocytes / physiology*
  • Adipose Tissue / growth & development
  • Antimetabolites / metabolism
  • Blotting, Northern
  • CCAAT-Enhancer-Binding Protein-alpha / antagonists & inhibitors
  • Calcimycin / pharmacology
  • Calcium-Binding Proteins / biosynthesis
  • Calpain / antagonists & inhibitors
  • Calpain / biosynthesis
  • Calpain / physiology*
  • Cell Differentiation / drug effects
  • Cell Differentiation / physiology*
  • DNA, Complementary / biosynthesis
  • DNA, Complementary / genetics
  • Deoxyglucose / metabolism
  • Dipeptides / pharmacology
  • Humans
  • Stem Cells / drug effects
  • Sterol Regulatory Element Binding Protein 1 / biosynthesis
  • Sterol Regulatory Element Binding Protein 1 / physiology
  • Subcellular Fractions / physiology

Substances

  • Antimetabolites
  • CCAAT-Enhancer-Binding Protein-alpha
  • Calcium-Binding Proteins
  • DNA, Complementary
  • Dipeptides
  • Sterol Regulatory Element Binding Protein 1
  • benzyloxycarbonylleucyl-leucine aldehyde
  • Calcimycin
  • calpastatin
  • Deoxyglucose
  • Calpain
  • m-calpain
  • mu-calpain