Cold-acclimation induces life stage-specific responses in the cardiac proteome of Western painted turtles (Chrysemys picta bellii): implications for anoxia tolerance

Abstract

Western painted turtles (Chrysemys picta bellii) are the most anoxia-tolerant tetrapod. Survival time improves at low temperature and during ontogeny, such that adults acclimated to 3°C survive far longer without oxygen than either warm-acclimated adults or cold-acclimated hatchlings. Since protein synthesis is rapidly suppressed to save energy at the onset of anoxia exposure, this study tested the hypothesis that cold-acclimation would evoke preparatory changes in protein expression that would support enhanced anoxia survival in adult but not hatchling turtles. To test this, adult and hatchling turtles were acclimated to either 20°C (warm) or 3°C (cold) for 5 weeks, and then the heart ventricles were collected for quantitative proteomic analysis using labeled isobaric tags and mass spectrometry. The relative abundances of 1316 identified proteins were compared between temperatures and developmental stages. The effect of cold-acclimation on the cardiac proteome was most evident when life stage was included as a covariable, suggesting that ontogenic differences in anoxia tolerance may be predicated on successful maturation of the heart from its hatchling to adult form and, only after this maturation occurs, will cold-acclimation induce protein expression changes appropriate for supporting heart function during prolonged anoxia. The main differences between the hatchling and adult cardiac proteomes reflect an increase in metabolic scope that included more myoglobin and increased investment in both aerobic and anaerobic energy pathways. Mitochondrial structure and function were key targets of life stage- and temperature-induced changes to the cardiac proteome, including reduced complex II proteins in cold-acclimated adults that may help down-regulate the electron transport system and avoid succinate accumulation during anoxia. Therefore, targeted cold-induced changes to the cardiac proteome may be a contributing mechanism for stage-specific anoxia tolerance in turtles.

Cytoskeletal Arrest: An Anoxia Tolerance Mechanism

“…Taken together, anoxic protein expression suggests that actin dynamics and scaffolding may be inhibited in anoxic turtle brain. A proteome for 3 °C-acclimated painted turtle heart was recently made available as a pre-print [ 65 ], and RhoA was downregulated to 20 °C heart, although this trend was not present in 3 °C-acclimated hatchlings, perhaps due a need for RhoA in development. RhoA protein downregulation in mature overwintering lends further weight to the idea that actin dynamics are arrested during turtle overwintering.…”

“…Motor proteins are powered by ATPase activity, and how a reduction of peripheral structure, and therefore trafficking, might impact cellular ATP consumption is unexamined. Interestingly, the proteome of mature 10 °C-acclimated painted turtle heart has decreased protein abundance of dynactin subunit 2 [ 65 ]. Dynactin is required for the functional attachment of dynein to cargo and also contributes to kinesin trafficking activity [ 251 ].…”

“…Dynactin is required for the functional attachment of dynein to cargo and also contributes to kinesin trafficking activity [ 251 ]. The depression of this protein with cold acclimation hints at regulation of intracellular trafficking; however, this depression was not present in cold-acclimated hatching turtles [ 65 ]. A reduction in trafficking of cellular cargo would be consistent with the reduction in protein turnover seen in anoxic turtles, as evidenced by reduced protein degradation and protein synthesis [ 8 , 63 , 64 ].…”