Mitochondrial metabolism and oxidative stress in tropical cockroach under fluctuating thermal regimes.

The cockroach Gromphadorinha coquereliana can survive under low temperature and extensive periods of cold stress. To assess energy management and insect adaptation in response to cold, we measured mitochondrial activity and oxidative stress in muscle and fat body tissues from G. coquereliana -under a fluctuating thermal regime (FTR, stressed at 4°C for 3-h on 3 consecutive days, with or without 24-h recovery after last exposure). Compared to our earlier work showing that a single exposure to cold significantly affects mitochondrial parameters, here, repeated exposure to cold triggered an acclimatory response, resulting in unchanged mitochondrial bioenergetics. Immediately after cold exposure, we observed an increase in the overall pool of ATP and a decrease in typical antioxidant enzyme activity. We also observed decreased activity of uncoupling protein 4 in muscle mitochondria. After 24-h of recovery, we observed an increase in antioxidant enzymes expression in muscle and fat body and a significant increase in the expression of UCP4 and HSP in the latter. This indicates that processes related to energy conversion and disturbance under cold stress may trigger different protective mechanisms in these tissues, and these mechanisms must be activated to restore insect homeostasis. In conclusion, the measured mitochondrial parameters and the enzymatic assays results suggest that mitochondria are not affected during FTR but oxidative stress markers are decreased, and a 24-h recovery period allows for the restoration of redox and energy homeostasis, especially in the fat body. This confirms the crucial role of the fat body in intermediary metabolism and energy management in insects and in the response to repeated thermal stress.