Cold stress modulates redox signalling in murine fresh bone marrow cells and promotes osteoclast transformation

Enhanced bone healing using local cryostimulation: In vivo rat study

A short-term intense cooling through the skin causes a response of the body. Potentially, it can be used to enhance bone healing. The aim of this study is to evaluate an effectiveness of a bone defect cryostimulation in the Wistar rat model in vivo. Through holes with a diameter of 2.15 mm were formed in the cortical layer of the diaphysis of the hind paws of rats. Further animals were subjected to cryotherapy 1 and 2 times a week (up to 6 weeks). The local average skin surface temperature dropped from 28 to 14 °C. The decrease in temperature in a control point inside the biological tissue was 5.3 °C. Micro CT and histological analyses showed that cryostimulation twice a week is efficient treatment. In this case, there was an acceleration of maturation of the newly formed bone tissue replacing the defect region. In the control, the newly formed immature bone with a large number of osteocytes and vessels was detected. In the experiment, the newly formed bone had a more mature structure with signs of a compact bone (formation of Haversian canals, reduction in the number of osteocytes, appearance of gluing lines). Morphometric analysis has showed a 2-fold decrease of the relative vessels area near the defect region and an increase of 30% in the content of mast cells in the entire bone marrow and especially near the site of osteogenesis. Generally, the complete filling of the critical size defect and almost complete mineralization have been observed. This information is expected to be useful for understanding the effect-exposure correlation of the cryotherapy and in the design of the cryotherapy protocols.

Cold Exposure Induces Intestinal Barrier Damage and Endoplasmic Reticulum Stress in the Colon via the SIRT1/Nrf2 Signaling Pathway

Ambient air temperature is a key factor affecting human health. Long-term exposure to a cold environment can cause various diseases, while the impact on the intestine, the organ which has the largest contact area with the external environment, cannot be ignored. In this study, we investigated the effect of chronic cold exposure on the colon and its preliminary mechanism of action. Mice were exposed to 4°C for 3 hours a day for 10 days. We found that cold exposure damaged the morphology and structure of the colon, destroyed the tight junctions of the colonic epithelial tissue, and promoted inflammation of the colon. At the same time, cold exposure also activated the unfolded protein response (UPR) in the colon and promoted apoptosis in intestinal epithelial cells. Chronic cold exposure induced oxidative stress in vivo, but also significantly enhanced the response of the Nrf2 pathway that promotes an anti-oxidant effect. Furthermore, we demonstrated that chronic cold exposure promoted p65 acetylation to aggravate the inflammatory response by inhibiting SIRT1. Similar results were observed following SIRT1 knock-down by shRNA in Caco-2 cells treated with Thapsigargin (Tg). Knock-down of SIRT1 promoted nuclear localization of Nrf2, and increased the level of Nrf2 acetylation. Taken together, our study indicates that cold exposure may aggravate endoplasmic reticulum stress and damage epithelial tight junctions in the colon by inhibiting SIRT1, which promotes nuclear localization of Nrf2 and induces an anti-oxidant response to maintain intestinal homeostasis. These findings suggest that SIRT1 is a potential target for regulating intestinal health under cold exposure conditions.

Hibernator-Derived Cells Show Superior Protection and Survival in Hypothermia Compared to Non-Hibernator Cells

Mitochondrial failure is recognized to play an important role in a variety of diseases. We previously showed hibernating species to have cell-autonomous protective mechanisms to resist cellular stress and sustain mitochondrial function. Here, we set out to detail these mitochondrial features of hibernators. We compared two hibernator-derived cell lines (HaK and DDT1MF2) with two non-hibernating cell lines (HEK293 and NRK) during hypothermia (4 °C) and rewarming (37 °C). Although all cell lines showed a strong decrease in oxygen consumption upon cooling, hibernator cells maintained functional mitochondria during hypothermia, without mitochondrial permeability transition pore (mPTP) opening, mitochondrial membrane potential decline or decreased adenosine triphosphate (ATP) levels, which were all observed in both non-hibernator cell lines. In addition, hibernator cells survived hypothermia in the absence of extracellular energy sources, suggesting their use of an endogenous substrate to maintain ATP levels. Moreover, hibernator-derived cells did not accumulate reactive oxygen species (ROS) damage and showed normal cell viability even after 48 h of cold-exposure. In contrast, non-hibernator cells accumulated ROS and showed extensive cell death through ferroptosis. Understanding the mechanisms that hibernators use to sustain mitochondrial activity and counteract damage in hypothermic circumstances may help to define novel preservation techniques with relevance to a variety of fields, such as organ transplantation and cardiac arrest.

Corticosterone Excess-Mediated Mitochondrial Damage Induces Hippocampal Neuronal Autophagy in Mice Following Cold Exposure

Simple Summary

In this study, the phenomenon of ‘autophagy’ was demonstrated in the hippocampus following cold exposure. Persistent neuronal stimulation of the hippocampus after corticosterone (CORT) treatment induced mitochondrial damage and autophagy by activating the AMPK/mTOR signaling pathway, which did not rely on glucocorticoid receptors (GRs). The phenomenon in the hippocampus of the cold stress mice was also a sex-related difference in the response to cold stress; the phenomenon of autophagy was more severe in males. These findings provided a new understanding of the underlying mechanisms of the cold stress response, which may influence the selection of animal models in future stress-related studies.

Abstract

Cold stress can induce autophagy mediated by excess corticosterone (CORT) in the hippocampus, but the internal mechanism induced by cold stress is not clear. In vivo, male and female C57BL/6 mice were stimulated in 4 °C, 3 h per day for 1 week to build the model of cold sress. In vitro, hippocampal neuronal cell line (HT22) cells were incubated with or without mifepristone (RU486) for 1 h, then treated with 400 μM cortisol (CORT) for 3 h. In vivo, autophagy was measured by western blotting. In vitro, monodansylcadaverine staining, western blotting, flow cytometry, transmission electron microscopy, and immunofluorescence were used to characterize the mechanism of autophagy induced by excess CORT. Autophagy was shown in mouse hippocampus tissues following cold exposure, including mitochondrial damage, autophagy, and 5’ AMP-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway activation after CORT treatment. Autophagy did not rely on the glucocorticoid receptor. In addition, autophagy in male mice was more severe. The study would provide new insight into the mechanisms and the negative effect of the cold stress response, which can inform the development of new strategies to combat the effects of hypothermia.