Heat Acclimation and Cross‐Tolerance: Changes in the Mitochondrial Proteome
Authors: Horowitz Michal , Smeir Elia , Gerstenblith Gary 
Published: November 2023

Accumulating evidence suggests that the remodeling of mitochondrial function is important in heat acclimation (AC) and heat acclimation mediated cross‐tolerance (HACT). Cross‐tolerance is the phenomenon by which acclimation to one environmental stressor confers protection to novel stressors. In the ischemic AC heart, the protective role of the mitochondria include decreased trafficking of cytochrome C to the cytosol, elevated PDK1 levels and a switch of the COX4.2/COX4.1 ratio optimizing complex IV function. In order to investigate the orchestrated role of the mitochondria in HACT, mitochondria‐enriched fractions (sucrose gradient procedure) from hearts of control (C) and AC rats (1mo, 34°C) before and after subjection to: 10′ 20′ and 30′ global ischemia were exposed to a ‘label free’ quantification ‐ mass spectrometry technique. The experimental design enabled analyses of baseline differences between the groups and within group protein kinetics during progressive global ischemia. For bioinformatics, we used software including Spotfire (for clustering), Genecodis, Onto‐express, String and GeneCard. The clustering analysis of the identified proteins showed significant differences between the C and the AC groups, at baseline and following ischemia. Clustering by mutual functions clearly showed that in AC mitochondria, molecular functions associated with ATP production and transport are enhanced. The kinetics of the proteins during progressive ischemia also differed. There was a down‐regulation of proteins in C and a marked up‐regulation in AC hearts. Among the 1113 identified proteins 360 were mitochondrial proteins of which 90 were significantly changed at least in one group. In addition to energy metabolism associated proteins (e.g. up‐regulation of ATPase subunit 8, NADH subunit 4) in AC hearts, supporting metabolic efficiency per se, our analyses revealed new players in HACT for example (i) elevation of HSP27 during ischemia. This protein is involved with the prevention of trafficking cytochrome c and its elevation in the cytosol, fitting with the anti‐apoptotic features of the AC heart. (ii) Dynamin 1 causes mitochondrial fission. AC caused a down–regulation of this protein i.e. an additional stress protective feature. (iii) Significant changes were found in the subunits of the TOM (TOM5) and TIM (Tim 23) complex, which are involved in the translocation of proteins through the mitochondrial membrane for use, primarily in oxidative phosphorylation. TOM is the outer mitochondrial membrane transporter complex, and TIM is the inner. (iv) CRA‐b, identified as a deleterious functional protein, is significantly upregulated in C ischemic mitochondria only. Collectively, the findings of our examination of the mitochondrial protein profile during subjection to global ischemia are in congruence with our principal hypothesis that the acclimated mitochondria have enhanced functioning during ischemic insult. This fits with physiological features of HACT identified in previous studies.Support or Funding InformationBinetional Science Foundation US‐Israel (BSF)