Transient receptor potential vanilloid 2 mediates the inhibitory effect of far-infrared irradiation on adipogenic differentiation of tonsil-derived mesenchymal stem cells

Abstract

Background & Aim Far-infrared (FIR) irradiation inhibits adipogenic differentiation of tonsil-derived mesenchymal stem cells (TMSCs) by activating protein phosphatase 2B through enhancing intracellular Ca2+ mobilization, but its upsteam mechanism remains unclear. Transient receptor potential vanilloid (TRPV) is a well-known calcium-permeable channel located in the cell membrane. It has been reported that certain isotypes of TRPV could regulate adipogenesis in (pre)adipocytes. Here, we investigated whether or how the TRPV channel is involved in the inhibitory effect of FIR irradiation on the adipogenic differentiation of TMSCs. Methods, Results & Conclusion Methods TMSCs were exposed to FIR irradiation with or without TRPV inhibitors at room temperature for 30 min followed by adipogenic differentiation for 14 days. At the end of the differentiation, the degree of adipogenesis was assessed by staining lipid droplets with Oil red O solution, and by measuring the protein expressions of adipocyte-specific markers (peroxisome proliferator-activated receptor γ and fatty acid-binding protein 4) using Western blotting. Total RNA was extracted from TMSCs and mRNA transcript levels were measured by reverse transcript (RT)-PCR analysis. Results Exposure to FIR irradiation or a calcium ionophore ionomycin inhibited adipogenic differentiation of TMSCs. Treatment with ruthenium red, a pan-TRP channel inhibitor, reversed the FIR irradiation-inhibited adipogenesis. RT-PCR analysis revealed that TMSCs expressed all the TRPV channels except TRPV5. Based on the previous studies showing an involvement of TRPV1, 2, and 4 in adipogenesis, we tested specific inhibitors of these three TRPV isotypes and found that among those tested, only tranilast, a specific TRPV2 inhibitor, significantly attenuated the effects of FIR irradiation, such as increase of intracellular Ca2+ levels and inhibition of adipogenic differentiation of the TMSCs. When the TMSCs were transfected with small interfering RNA against TRPV2 to silence the TRPV2 gene, the observed effects of FIR irradiation on adipogenic differentiation were also completely reversed. Additionally, we also found that the probenecid, a TRPV2 activator, decreased the adipogenic differentiation of TMSCs. Conclusion Our data demonstrate that FIR irradiation increases intracellular Ca2+ levels through TRPV2 activation, thereby suppressing the adipogenic differentiation of TMSCs.