Gap-junctional Communication Is Required for Mitotic Clonal Expansion During Adipogenesis

Obesity (Silver Spring). 2007 Mar;15(3):572-82. doi: 10.1038/oby.2007.547.

Abstract

Objective: Gap-junctional communication (GJC) plays critical roles in cell growth and differentiation. Several studies have demonstrated the involvement of GJC in myogenesis and osteogenesis; however, the role of GJC in adipogenesis has not been fully studied. Thus, we investigated the role of GJC in adipogenesis.

Research methods and procedures: 3T3-L1 preadipocytes were differentiated in the presence of gap junction inhibitor, 18-alpha-glycyrrhetinic acid (AGA), and accumulation of cytoplasmic triglycerides was measured. 3T3-L1 cells were transfected with 100 nM small interfering RNA duplexes targeting connexin (Cx) 43. The mRNA levels of CCAAT/enhancer-binding protein (C/EBP) alpha, peroxisome proliferator-activated receptor gamma, glucose transporter 4, C/EBPbeta, and Cx43 were measured by real-time polymerase chain reaction. The protein levels of C/EBPbeta were quantitated by Western blotting. The cell proliferation was measured by counting cell numbers, and DNA synthesis was measured by bromodeoxyuridine incorporation.

Results: AGA inhibited adipocyte differentiation dose-dependently. The lipid accumulation and the mRNA levels of C/EBPalpha, peroxisome proliferator-activated receptor gamma, and glucose transporter 4 were markedly reduced in AGA-treated adipocytes. The mRNA levels of C/EBPbeta did not decrease; however, C/EBPbeta [liver-enriched transcriptional activator protein (LAP)] expression and the C/EBPbeta (LAP)-to-C/EBP [liver-enriched transcriptional inhibitory protein (LIP)] ratio were reduced by AGA treatment. The increase in both cell number and DNA synthesis, which occurs during mitotic clonal expansion, was reduced by AGA in a dose-dependent fashion. The major component of gap junctions in 3T3-L1 cells was Cx43. Down-regulation of Cx43 using small interfering RNA reduced the expression of C/EBPbeta (LAP) and inhibited adipogenesis.

Discussion: Our data suggest that GJC plays some important roles in adipogenesis through inhibiting mitotic clonal expansion and modulating C/EBPbeta (LAP) expression.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3T3-L1 Cells
  • Adipocytes / drug effects
  • Adipocytes / metabolism
  • Adipogenesis / physiology*
  • Animals
  • Cell Communication / drug effects
  • Cell Communication / physiology*
  • Cell Proliferation*
  • Connexin 43 / antagonists & inhibitors
  • Connexin 43 / metabolism
  • Gap Junctions / drug effects
  • Gap Junctions / physiology*
  • Glycyrrhetinic Acid / pharmacology
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mitosis / drug effects
  • Mitosis / physiology*
  • RNA, Small Interfering / pharmacology

Substances

  • Connexin 43
  • RNA, Small Interfering
  • Glycyrrhetinic Acid