Adipogenic differentiation is characterized by an increase in two major transcription factors: peroxisome proliferator-activated receptor gamma (PPARγ) and the CCAAT/enhancer binding protein alpha (C/EBPα). These two signals are influenced by C/EBPβ and C/EBPδ and cross-regulate each other's expression during the initial stages of adipogenesis. Melatonin has been known to act as not only a direct scavenger of free radicals but also an inhibitor of glycogen synthase kinase 3β (GSK-3β). Here, we report that melatonin inhibits the adipogenic differentiation of human mesenchymal stem cells (hMSCs) which is due to the regulations of C/EBPβ in the early stage of adipogenic differentiation. Melatonin reduced the lipid accumulation, adiponectin, and lipoprotein lipase (LPL) during the adipogenic differentiation of hMSCs. Since C/EBPβ has been associated with the activation of PPARγ and the consensus site of ERK/GSK-3β, PPARγ and β-catenin were detected by immunofluorescence staining after pretreatment of melatonin. Melatonin blocked the activation of PPARγ which induced the degradation of β-catenin. Melatonin also decreased the levels of cyclic adenosine-3,5-monophosphate (cAMP) and reactive oxygen species (ROS). The cAMP triggered the activity of C/EBPβ which is a critical inducer of PPARγ and C/EBPα activation in the early stage of adipogenic differentiation, and this is further affected by ROS production. The adipogenic marker proteins such as PPARγ, C/EBPα, C/EBPβ, and pERK were also decreased by melatonin. In summary, melatonin inhibited the cAMP synthesis through ROS reduction and the phosphorylation of the ERK/GSK-3β site which is known to be responsible for C/EBPβ activation for adipogenic differentiation in hMSCs.
Keywords: Adipogenesis; C/EBPβ; GSK3β/ERK; Melatonin; ROS; hMSC.