Promotion of apoptosis and cytochrome c depletion by a low-temperature environment in hindlimb-unloading rats.

Objective: This study aimed to clarify the influence of a low-temperature environment on muscle atrophy and apoptosis.

Methods: Wistar rats were divided into four groups: two groups of hindlimb-unloading rats maintained in a normal (25°C, HU) or low-temperature (10°C, HU+LT) environment for 3 weeks and two corresponding control groups (CON; normal temperature, CON+LT; low-temperature).

Results: The soleus muscle wet weight and muscle-to-body mass ratio were lower in the experimental groups than in the control groups. The cross-sectional areas of myofibers in the HU+LT and HU groups were significantly decreased than those in the CON and CON+LT groups. Ubiquitin ladder levels from soleus muscle lysates were significantly increased in the HU+LT group. Caspase-3-activated myofibers were observed only in the HU+LT group. Decreased cytochrome c levels were present in these caspase-3-activated myofibers. Meanwhile, cytochrome c levels were increased significantly in CON+LT rats but unchanged in HU+LT rats.

Conclusion: Our results suggest that apoptosis caused by hindlimb unloading at low temperatures is associated with a lack of cytochrome c in myofibers. This indicates that long-term hindlimb unloading at low temperatures did not suppress muscle atrophy. We conclude that low-temperature stimulation should not be used as a long-term treatment for preventing disuse atrophy.