Metabolism dynamics in tropical cockroach during a cold-induced recovery period

Insects are poikilothermic organisms, meaning their body heat comes entirely from their surroundings. This influences their metabolism, growth, development, and behavior. Cold tolerance is considered an important factor in determining the geographic distribution of insects. The tropical cockroach Gromphadorhina coquereliana is capable of surviving exposure to cold. To determine the dynamics of metabolic adjustments occurring in the insect body under cold stress, we subjected the cockroach to 4°C for 3 h, followed by recovery periods of 3, 8, and 24 h. We then determined the levels of glycogen, proteins, lipids, amino acids, and carbohydrates. We also measured gene expression and the activity of the main enzymes of metabolic cycles responsible for energy conversion, namely, phosphofructokinase (PFK), hydroxyacyl-CoA dehydrogenase (HADH), and lactic acid dehydrogenase (LDH). All these analyses were conducted in different tissues: hemolymph, fat body, and muscle.

Our results show that in the fat body, protein degradation and an increase in unsaturated fatty acids (UFA) and cholesterol are observed, which likely allows membranes to maintain their functions. The high levels of lactic acid and LDH expression and activity indicate that anaerobic metabolic pathways are triggered. In the hemolymph, cold stress induces an increase in the levels of cryoprotective substances such as amino acids and sugars, which can also be used as a source of energy. On the other hand, muscle metabolism slows down (LDH, HADH), except for an increase in glucose, which may result from the gluconeogenesis process. During the recovery period, increased activity and expression of LDH, PFK, and HADH, as well as increased levels of UFA, lactic acid, glycerol, and TAG, were observed in fat body tissue, while in the hemolymph, increased levels of cryoprotectants still occurred.

G. coquereliana shows partial freeze tolerance, combining traits of both freeze-intolerant and freeze-tolerant insects. This adaptation helps it survive brief cold periods and suggests an evolutionary move towards complete freeze tolerance. Although cold stress challenges G. coquereliana in maintaining metabolic homeostasis, these insects exhibit deep biochemical adjustments to cope with adverse environmental stressors such as low temperature.