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‐α‐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) α, peroxisome proliferator‐activated receptor γ, glucose transporter 4, C/EBPβ, and Cx43 were measured by real‐time polymerase chain reaction. The protein levels of C/EBPβ 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/EBPα, peroxisome proliferator‐activated receptor γ, and glucose transporter 4 were markedly reduced in AGA‐treated adipocytes. The mRNA levels of C/EBPβ did not decrease; however, C/EBPβ [liver‐enriched transcriptional activator protein (LAP)] expression and the C/EBPβ (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/EBPβ (LAP) and inhibited adipogenesis.

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