Modulation of the endoplasmic reticulum stress and unfolded protein response mitigates the behavioral effects of early-life stress

Cross-species analysis uncovers the mitochondrial stress response in the hippocampus as a shared mechanism in mouse early life stress and human depression

Depression, or major depressive disorder, poses a significant burden for both individuals and society, affecting approximately 10.8% of the general population. This psychiatric disorder leads to approximately 800,000 deaths per year. A combination of genetic and environmental factors such as early life stress (ELS) increase the risk for development of depression in humans, and a clear role for the hippocampus in the pathophysiology of depression has been shown. Nevertheless, the underlying mechanisms of depression remain poorly understood, resulting in a lack of effective treatments. To better understand the core mechanisms underlying the development of depression, we used a cross-species design to investigate shared hippocampal pathophysiological mechanisms in mouse ELS and human depression. Mice were subjected to ELS by a maternal separation paradigm, followed by RNA sequencing analysis of the adult hippocampal tissue. This identified persistent transcriptional changes linked to mitochondrial stress response pathways, with oxidative phosphorylation and protein folding emerging as the main mechanisms affected by maternal separation. Remarkably, there was a significant overlap between the pathways involved in mitochondrial stress response we observed and publicly available RNAseq data from hippocampal tissue of depressive patients. This cross-species conservation of changes in gene expression of mitochondria-related genes suggests that mitochondrial stress may play a pivotal role in the development of depression. Our findings highlight the potential significance of the hippocampal mitochondrial stress response as a core mechanism underlying the development of depression. Further experimental investigations are required to expand our understanding of these mechanisms.

Exploring Epigenetic and Genetic Modulation in Animal Responses to Thermal Stress

There is increasing evidence indicating that global temperatures are rising significantly, a phenomenon commonly referred to as 'global warming', which in turn is believed to be causing drastic changes to the global climate. Global warming (GW) directly impacts animal health, reproduction, production, and welfare, presenting several challenges to livestock enterprises. Thermal stress (TS) is one of the key consequences of GW, and all animal species, including livestock, have diverse physiological, epigenetic and genetic mechanisms to respond to TS. As a result, TS can significantly affect an animals' health, immune responsiveness, metabolic pathways etc. which can also influence the productivity, performance, and welfare of animals. Moreover, prolonged exposure to TS can lead to transgenerational and intergenerational changes that are mediated by epigenetic changes. For example, in several animal species, the effects of TS are encoded epigenetically during the animals' growth or productive stage, and these epigenetic changes can be transmitted intergenerationally. Such epigenetic changes can affect animal productivity by changing the phenotype so that it aligns with its ancestors' environment, irrespective of its immediate environment. Furthermore, epigenetic and genetic changes can also help protect cells from the adverse effects of TS by modulating the transcriptional status of heat-responsive genes in animals. This review focuses on the genetic and epigenetic modulation and regulation that occurs in TS conditions via HSPs, histone alterations and DNA methylation.

Elevated Expression of HSP72 in the Prefrontal Cortex and Hippocampus of Rats Subjected to Chronic Mild Stress and Treated with Imipramine

The HSP70 and HSP90 family members belong to molecular chaperones that exhibit protective functions during the cellular response to stressful agents. We investigated whether the exposure of rats to chronic mild stress (CMS), a validated model of depression, affects the expression of HSP70 and HSP90 in the prefrontal cortex (PFC), hippocampus (HIP) and thalamus (Thal). Male Wistar rats were exposed to CMS for 3 or 8 weeks. The antidepressant imipramine (IMI, 10 mg/kg, i.p., daily) was introduced in the last five weeks of the long-term CMS procedure. Depressive-like behavior was verified by the sucrose consumption test. The expression of mRNA and protein was quantified by real-time PCR and Western blot, respectively. In the 8-week CMS model, stress alone elevated HSP72 and HSP90B mRNA expression in the HIP. HSP72 mRNA was increased in the PFC and HIP of rats not responding to IMI treatment vs. IMI responders. The CMS exposure increased HSP72 protein expression in the cytosolic fraction of the PFC and HIP, and this effect was diminished by IMI treatment. Our results suggest that elevated levels of HSP72 may serve as an important indicator of neuronal stress reactions accompanying depression pathology and could be a potential target for antidepressant strategy.