Low temperature decreases bone mass in mice: Implications for humans

Area of Science:

• Paleoanthropology
• Skeletal Biology
• Environmental Physiology

Background:

• Human bone morphology shows ecogeographic variation, but the impact of environmental temperature on bone is not fully understood.
• Low temperatures may cause bone loss via sympathetic nervous system activation, potentially counteracted by nonshivering thermogenesis (NST) involving UCP1 in brown adipose tissue (BAT).

Purpose of the Study:

• To investigate if low temperatures impair cortical and trabecular bone acquisition in mice.
• To determine if UCP1 expression, a marker of NST, correlates with the degree of low-temperature exposure.

Main Methods:

• Male C57BL/6J mice were housed at thermoneutral (26°C), standard (22°C), or cool (20°C) temperatures from 3 to 6 or 12 weeks of age.
• Bone microarchitecture and cortical area were analyzed, alongside UCP1 expression in brown adipose tissue.

Main Results:

• Mice housed at 20°C exhibited significantly lower trabecular bone volume, thickness, connectivity, and cortical bone area compared to those at 26°C.
• UCP1 expression in brown adipose tissue was inversely related to ambient temperature, indicating increased NST activity in cooler conditions.

Conclusions:

• Chronic exposure to low temperatures detrimentally affects bone acquisition and impairs bone architecture.
• While NST increases in response to cold, it is insufficient to prevent cold-induced bone loss, suggesting climate is a factor in skeletal phenotypic variation.