TRPM8 inhibition reduces the size but increases the number of lipid droplets in mature adipocytes in vitro

Understanding the processes and/or the key factors involved in the formation as well as degradation of lipid droplets (LDs) within the adipocytes is of immense importance, especially in the context of health, obesity, cancer, and other diseases. While cold temperature and/or menthol (an edible cooling agent), seem to have diverse and confounding effects on obesity and/or thermogenesis, so far there is no direct evidence that specific pharmacological modulation of the Transient Receptor Potential cation channel subfamily Melastatin member 8 (TRPM8), a cold-temperature-activated ion channel, can indeed affect LD status within the mature adipocytes. Here, we used highly specific antagonists and agonists of TRPM8 to modulate TRPM8 in cultured adipocyte cells in vitro and monitored the expression of TRPM8 as well as other adipogenic functions. Our results indicate that specific activation of TRPM8 in mature adipocytes by a specific agonist, that is, WS12 ((1R∗,2S∗)-N-(4-methoxyphenyl)-5-methyl-2-(1-methylethyl)cyclohexanecarboxamide), results in increased expression of PPARγ protein. However, TRPM8 inhibition by N-(3-aminopropyl)-2-[(3-methylphenyl)methoxy]-N-(2-thienylmethyl)benzamidehydrochloride results in no change in the PPARγ expression, yet causes decreased Oil Red O intensity, a reduction in LD sizes, and an increase in LD numbers. BODIPY (4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene) labeling in live cells also suggests the same findings. Altogether, data suggest that in the absence of any confounding factors, specific inhibition of TRPM8 results in either less fusion of LDs or enhanced fragmentation of LDs in vitro. These findings may have broad implications in the field of adipogenesis and in cancer.