STIM2β is a Ca signaling modulator for the regulation of mitotic clonal expansion and PPARG2 transcription in adipogenesis.

Intracellular Ca is crucial in the regulation of adipocyte lipid metabolism and adipogenesis. In this study, we aimed to investigate the regulation mechanism of intracellular Ca levels ([Ca]) during adipocyte differentiation. We found that the expression of stromal interaction molecule 2 beta (STIM2β), which is the inhibitor of store-operated Ca entry (SOCE), is upregulated throughout the differentiation process. Evaluation of [Ca] in 3 T3-L1 and primary stromal vascular fraction (SVF) cells revealed that the basal Ca level is downregulated after differentiation. Knockout (KO) of STIM2β in 3T3-L1 and primary SVF cells showed increased [Ca], indicating the involvement of STIM2β in the regulation of [Ca] during adipogenesis. We further evaluated the function of STIM2β-mediated [Ca] in early and terminal differentiation of adipogenesis. Analysis of cell proliferation rate during mitotic clonal expansion (MCE) in wild-type and STIM2β KO 3T3-L1 cell lines revealed that a larger population of KO cells underwent G1 arrest, suggesting that reduced [Ca] by STIM2β induces MCE. Additionally, ablation of STIM2β increased differentiation efficiency, with more lipid accumulation and rapid transcriptional activation of adipogenic genes, especially proliferator-activator receptor γ2 (PPARG2). We found that PPARG2 transcription is regulated by store-operated calcium entry (SOCE) downstream transcription factors, confirming that increased [Ca] by STIM2β ablation promotes PPARG2 transcription during adipogenesis. Additionally, STIM2β KO mice showed hypertrophic adipose tissue development. Our data suggest that STIM2β-mediated [Ca] plays a pivotal role in the regulation of mitotic clonal expansion and PPARG2 gene activation and provides evidence that MCE is not a prerequisite process for terminal differentiation during adipogenesis.