The Protective Effects on Ischemia–Reperfusion Injury Mechanisms of the Thoracic Aorta in Daurian Ground Squirrels (Spermophilus dauricus) over the Torpor–Arousal Cycle of Hibernation

Abstract

Hibernators are a natural model of vascular ischemia–reperfusion injury; however, the protective mechanisms involved in dealing with such an injury over the torpor–arousal cycle are unclear. The present study aimed to clarify the changes in the thoracic aorta and serum in summer-active (SA), late-torpor (LT) and interbout-arousal (IBA) Daurian ground squirrels (Spermophilus dauricus). The results show that total antioxidant capacity (TAC) was unchanged, but malondialdehyde (MDA), hydrogen peroxide (H2O2), interleukin-1β (IL-1β) and tumor necrosis factor α (TNFα) were significantly increased for the LT group, whereas the levels of superoxide dismutase (SOD) and interleukin-10 (IL-10) were significantly reduced in the LT group as compared with the SA group. Moreover, the levels of MDA and IL-1β were significantly reduced, whereas SOD and IL-10 were significantly increased in the IBA group as compared with the SA group. In addition, the lumen area of the thoracic aorta and the expression of the smooth muscle cells (SMCs) contractile marker protein 22α (SM22α) were significantly reduced, whereas the protein expression of the synthetic marker proteins osteopontin (OPN), vimentin (VIM) and proliferating cell nuclear antigen (PCNA) were significantly increased in the LT group as compared with the SA group. Furthermore, the smooth muscle layer of the thoracic aorta was significantly thickened, and PCNA protein expression was significantly reduced in the IBA group as compared with the SA group. The contractile marker proteins SM22α and synthetic marker protein VIM underwent significant localization changes in both LT and IBA groups, with localization of the contractile marker protein α-smooth muscle actin (αSMA) changing only in the IBA group as compared with the SA group. In tunica intima, the serum levels of heparin sulfate (HS) and syndecan-1 (Sy-1) in the LT group were significantly reduced, but the serum level of HS in the IBA group increased significantly as compared with the SA group. Protein expression and localization of endothelial nitric oxide synthase (eNOS) was unchanged in the three groups. In summary, the decrease in reactive oxygen species (ROS) and pro-inflammatory factors and increase in SOD and anti-inflammatory factors during the IBA period induced controlled phenotypic switching of thoracic aortic SMCs and restoration of endothelial permeability to resist ischemic and hypoxic injury during torpor of Daurian ground squirrels.

Integrated transcriptomics and metabolomics reveal protective effects on heart of hibernating Daurian ground squirrels

“…All procedures were in accordance with the guidelines of the Experimental Animal Management Committee of the Ministry of Health of the People's Republic of China (approval number: SL2012‐42). Daurian ground squirrels were housed and treated as previously described by our laboratory (Han et al, 2022; Miao et al, 2022). Two groups of ground squirrels were studied.…”

“…Hibernation is a remarkable survival strategy employed by many mammals to withstand seasonal food shortages, prolonged low temperatures, and other environment extremes (Andrews, 2019). During hibernation, small mammalian hibernators such as ground squirrels exhibit a remarkable drop in body temperature (often to just 2–10°C), reduced metabolic rate, slower heartbeat, and significantly lower organ perfusion rates (often less than 10% of normal) (Han et al, 2022; Horii et al, 2018). Despite these extreme physiological changes, ground squirrels experience brief interbout arousal (IBA) periods every few days or weeks that are characterized by a rapid return to euthermic body temperature and normal organ perfusion rates, before sinking into another torpor bout within ~24 h. Such torpor‐arousal cycles are repeated multiple times over the hibernation season (Miao et al, 2022).…”

“…Despite these extreme physiological changes, ground squirrels experience brief interbout arousal (IBA) periods every few days or weeks that are characterized by a rapid return to euthermic body temperature and normal organ perfusion rates, before sinking into another torpor bout within ~24 h. Such torpor‐arousal cycles are repeated multiple times over the hibernation season (Miao et al, 2022). Hence, over the annual hibernation cycle, tissues and organs undergo repeated bouts ischemia‐reperfusion (I/R) and major changes in body temperature, but ground squirrels have evolved mechanisms to resist the damage that often arises from such conditions in non‐hibernators, including humans (Andrews, 2007; Han et al, 2022; Otis et al, 2017)…”

“…Despite these extreme physiological changes, ground squirrels experience brief interbout arousal (IBA) periods every few days or weeks that are characterized by a rapid return to euthermic body temperature and normal organ perfusion rates, before sinking into another torpor bout within ~24 h. Such torpor-arousal cycles are repeated multiple times over the hibernation season (Miao et al, 2022). Hence, over the annual hibernation cycle, tissues and organs undergo repeated bouts ischemiareperfusion (I/R) and major changes in body temperature, but ground squirrels have evolved mechanisms to resist the damage that often arises from such conditions in non-hibernators, including humans (Andrews, 2007;Han et al, 2022;Otis et al, 2017) Compared with non-hibernators, the heart of hibernating species is highly protected, showing a strong resistance to myocardial ischemia, allowing animals to be protected from I/R injury, which is similar to protection against ischemia that can be achieved with preconditioning (Yan et al, 2015). For instance, Hong Li and colleagues employed proteomic analysis to investigate the myocardium of Arctic ground squirrels (Spermophilus undulatus) versus rats following in vivo coronary artery ligation, and showed that markers of apoptosis (TUNEL and caspase-3) are lower in ground squirrels than in rats, whereas upregulation of sirtuin-3 and MnSOD, that are known to protect against ischemic injury, played a cardio-protective role (Yan et al, 2015).…”