Melanopsin mediates thermal activation of molecular clock genes in murine preadipocytes.

In mammals, melanopsin (OPN4) is a retinal photopigment found on a subset of intrinsically photosensitive ganglion cells, which synchronize the central circadian clock with the light-dark cycle. Peripheral tissues have also been found to express melanopsin, but its function remains to be explored. In this study, we investigated whether cold temperature pulses (34°C) could modulate clock gene expression in murine 3T3-L1 preadipocytes and the role of melanopsin in regulating this response. We detected the presence of the cone opsin (OPN1SW), rhodopsin (OPN2), and melanopsin (OPN4) using immunocytochemistry. We demonstrated the role of OPN4 in the upregulation of the clock gene Per1 in 3T3-L1 cells in response to cold-temperature pulses (34°C), through a pharmacological assay employing a well-established OPN4 antagonist. Then, we determined the profile of the clock gene Per1, using luciferase as the bioluminescence reporter. Per1::Luc 3T3-L1 cells subjected to constant temperature (37°C) or repeated cold-temperature pulses (34°C) exhibited an oscillatory bioluminescence profile. The cold-temperature pulses induced an increase in the amplitude of Per1 bioluminescence and a phase delay in comparison to control cells. These findings suggest that temperature detection through melanopsin could be an important pathway for peripheral clock modulation, with direct implications for metabolism control.