Evidence for a direct effect of melatonin on mitochondrial genome expression of Siberian hamster brown adipocytes

Photoperiod variations are known to participate in the regulation of energy balance in different rodent species via melatonin, a neurosecretory product synthesized by the pineal gland during the night. A direct effect of melatonin on adipose tissue has been suggested since binding sites for the indole have been described on brown adipocytes. The aim of this study was to investigate a genetic effect of melatonin on isolated Siberian hamster brown adipocytes using differential display RT-PCR (DDRT-PCR). Brown adipose cells were isolated from brown adipose tissue and treated for 3 hr with 0.1 and 10 microM melatonin. Total RNA was extracted and DDRT-PCR experiments were performed. A differential band, which disappeared after melatonin treatment, was detected. After confirmation and cloning, the corresponding cDNA fragment B18 was sequenced. B18 had 85 and 81% similarity with a portion of rat and mouse cytochrome b mRNA, respectively, suggesting that B18 corresponds to hamster cytochrome b. This hypothesis was confirmed by the close parallel between the changes in mRNA content, detected by B18, and by cytochrome b mRNA content, detected by a rat probe. Cytochrome b mRNA is encoded by the mitochondrial genome, suggesting a similar effect of melatonin on the whole mitochondrial transcripts. Indeed, 3 hr of treatment with melatonin (10 nM and 0.1 microM) decreased by 44% mitochondrial transcript contents. This work constitutes the first evidence of a direct biological effect of melatonin on Siberian hamster brown adipocytes.