Photoperiod-Induced Increases in Bone Mineral Apposition Rate in Siberian Hamsters and the Involvement of Seasonal Leptin Changes

Abstract

The adipokine leptin regulates energy balance, appetite, and reproductive maturation. Leptin also acts on bone growth and remodeling, but both osteogenic and anti-osteogenic effects have been reported depending on experimental conditions. Siberian hamsters (Phodopus sungorus) have natural variation in circulating leptin concentrations, where serum leptin is significantly decreased during the short day (SD)-induced winter state. In summer long day (LD) photoperiods, appetite and body adiposity increase with associated central leptin insensitivity. This natural change in leptin secretion was exploited to investigate leptin’s effect on bone growth. Hamsters were injected with calcium-chelating fluorescent dyes to measure bone mineral apposition rate (MAR). Measurements were initially obtained from 5-week and 6-month-old animals maintained in low leptin (SD) or high leptin (LD) states. A further study investigated effects of chronic administration of recombinant mouse leptin to hamsters housed in SD and LD conditions; growth plate thickness and bone density were also assessed. As expected, a reduction in body mass was seen in hamsters exposed to SD, confirming the phenotype change in all studies. Serum leptin concentrations were significantly reduced in SD animals in all studies. MAR was reproducibly and significantly increased in the femurs of SD animals in all studies. Vitamin D and growth plate thickness were significantly increased in SD animals at 6 months. No effect on bone density was observed in any study. Taken together these data suggest that bone growth is associated with the low leptin, winter, lean state. In leptin-treated animals, there was a significant interaction effect of leptin and photoperiod. In comparison to their vehicle counterparts, SD animals had decreased and LD animals had increased MAR, which was not apparent prior to leptin administration. In conclusion, increased MAR was associated with low serum leptin levels in early life and sustained over 6 months, implying that leptin has a negative effect on bone growth in this model. The unexpected finding that MAR increased after peripheral leptin administration in LD suggests that leptin exerts different effects on bone growth dependent on initial leptin status. This adds further weight to the hypothesis that leptin-treated LD animals display central leptin resistance.

Effects of a Diet Low in Vitamin and Mineral Complex and Darkness on the Growth Performance, Mineralization and Femur Histological Structure of Broiler Chickens

“…Chickens in experimental group 2 exposed to low light showed a reduction in cortical thickness and density compared with the control group. However, this result conflicts with the study by Kokolski et al (2017), which showed that low light in fast-growing animals does not affect cortical thickness and tibial density.…”

“…Chickens in experimental group 2 had higher lengths of both zones (proliferative and hypertrophic) compared to control chickens. This result agrees with Kokolski et al (2017), who demonstrated that photoperiod significantly impacted bone growth characteristics, including growth plate size. The research revealed a clear increase in proliferative and hypertrophic zones, as well as a considerable increase in overall growth plate width under short-day conditions.…”

Bone Structural, Biomechanical and Histomorphometric Characteristics of the Postcranial Skeleton of the Marsh Rice Rat (Oryzomys palustris)

“…Indeed, when female animals of this species are exposed to short photoperiods, they experienced ovarian function suppression. Furthermore, a long photoperiod is a potent environmental stimulus to increase bone mineral apposition rate in the skeleton of a closed-related species, the Siberian hamsters (Kokolski et al, 2017). Postmenopausal osteoporosis is a condition characterized by decreased bone mass associated with reduced serum levels of estrogens.…”