Thyroid hormone and vitamin D regulate VGF expression and promoter activity

Area of Science:

• Neuroendocrinology
• Metabolic Regulation
• Circadian Biology

Background:

• Siberian hamsters exhibit profound seasonal body weight loss during winter.
• Hypothalamic tanycytes play a key role in mediating seasonal adaptations.
• Short photoperiods alter thyroid hormone and retinoic acid (RA) signaling in tanycytes.

Purpose of the Study:

• To elucidate the mechanisms linking tanycyte signaling to seasonal appetite and energy expenditure.
• To investigate the role of VGF expression in photoperiodic regulation of body weight.

Main Methods:

• In silico analysis of the VGF promoter for response elements.
• In vitro studies using SH-SY5Y cells to assess VGF expression and promoter activity under various hormonal treatments (RA, vitamin D, T3).
• In vivo experiments involving intra-hypothalamic administration of T3 in Siberian hamsters to evaluate its effect on VGF expression.

Main Results:

• Retinoic acid (RA) and 1,25-dihydroxyvitamin D3 increased VGF expression and promoter activity in vitro.
• Triiodothyronine (T3) decreased VGF expression and promoter activity in vitro.
• Intra-hypothalamic T3 administration blocked the short-day induced increase in VGF expression in Siberian hamsters.

Conclusions:

• VGF expression is a likely target of photoperiod-induced changes mediated by tanycyte signaling.
• VGF may function as a regulator of seasonal appetite and energy expenditure in Siberian hamsters.