# Photoperiod influences visceral adiposity and the adipose molecular clock independent of temperature in wild‐derived Peromyscus leucopus

## TL;DR

Extended artificial light increases visceral fat in mice without affecting body weight or temperature, suggesting a link between artificial light and obesity.

## Contribution

Demonstrates that photoperiod alone, independent of temperature, influences visceral adiposity and molecular clock genes in mice.

## Key findings

- Mice in long photoperiods developed greater visceral WAT mass without changes in subcutaneous WAT or BAT.
- Clock genes Per1, Per2, and Nr1d1 showed altered expression in visceral WAT with photoperiod.
- Adrβ3 and Ucp1 mRNA levels in visceral WAT decreased under long photoperiod conditions.

## Abstract

Physiology is closely synchronized to daily and seasonal light/dark cycles. Humans artificially extend daylight and experience irregular light schedules, resulting in dysregulation of metabolism and body mass. In rodents, winter‐like conditions (cold and short photoperiod) can alter energy balance and adipose tissue mass. To determine if photoperiod alone, independent of temperature, is a strong enough signal to regulate adiposity, we compared the effects of long and short photoperiod at thermoneutrality on adiposity and WAT gene expression in photoperiod‐sensitive, F1 generation wild‐derived adult male white‐footed mice (Peromyscus leucopus). Mice were housed in long‐day (16:8 light:dark) or short‐day (8:16 light:dark) photoperiod conditions at thermoneutrality (27°C) for 4 weeks with the extended light being provided through artificial lighting. Photoperiod did not impact body weight or calorie consumption. However, mice housed in long photoperiod with extended artificial light selectively developed greater visceral WAT mass without changing subcutaneous WAT or interscapular BAT mass. This was accompanied by a decrease in Adrβ3 and Ucp1 mRNA expression in visceral WAT with no change in Pgc1a, Lpl, or Hsl. Expression of Per1, Per2, and Nr1d1 mRNA in visceral WAT differed between long and short photoperiods over time when aligned to circadian time but not onset of darkness, indicating alterations in clock gene expression with photoperiod. These findings suggest that extended photoperiod through artificial light can promote visceral fat accumulation alone, independent of temperature, supporting that artificial light may play a role in obesity.

Physiology is closely synchronized to daily and seasonal light/dark cycles. Wild‐derived white‐footed mice were housed in long‐day (LD – 16L:8D) or short‐day (SD – 8L:16D) photoperiods at thermoneutrality (27°C). LD selectively increased visceral WAT mass and decreased Adrβ3 and Ucp1 expression while inducing misalignment of clock genes compared to SD. Thus, extended photoperiod through artificial light can promote visceral fat accumulation alone, independent of temperature, supporting that artificial light may play a role in obesity.