Activating transcription factor 5 (ATF5) is a member of the activating transcription factor/cyclic adenosine monophosphate response element binding protein (ATF/CREB) family. As a stress-induced transcription factor, ATF5 plays a crucial role in cellular inflammatory stress responses. Under cellular inflammatory stress conditions, ATF5 maintains cell homeostasis and survival by regulating key genes in the mitochondrial unfolded protein response (UPR^mt) and endoplasmic reticulum stress (ERS). As a key regulator in UPR^mt, ATF5 senses mitochondrial stress and translocate to the nucleus to activate the transcription of UPR^mt-related genes, thereby promoting mitochondrial function recovery. Meanwhile, in ERS, ATF5 maintains endoplasmic reticulum homeostasis by regulating the expression of genes related to protein folding, degradation, and apoptosis, determining cell survival or death. ATF5 plays a vital role in various cellular inflammatory stress responses. In infectious inflammation, ATF5 plays an important role in alleviating neuroinflammation and maintaining intestinal barrier function by regulating UPR^mt. In inflammation related to degenerative diseases, ATF5 improves intervertebral disc degeneration and delays the progression of osteoarthritis by regulating UPR^mt. In metabolic inflammation such as diabetes and obesity, ATF5 regulates UPR^mt and ERS to maintain the function of pancreatic β-cells, controlling their survival or inducing apoptosis, thus influencing the progression of diabetes. ATF5 protects mitochondria in the kidneys, adipose tissue, and pancreas, slows the progression of diabetic nephropathy, and improves insulin sensitivity. Furthermore, in immune-related inflammation, ATF5 alleviates glomerulonephritis and promotes tissue repair by enhancing immune tolerance in dendritic cells. In summary, ATF5, as a key regulator in cellular inflammatory stress responses, maintains cell homeostasis through regulating UPR^mt and ERS and determines cell fate. Its critical regulatory role in cellular inflammatory stress responses makes ATF5 a potential clinical therapeutic target. This article summarizes the structural features and translational regulatory mechanisms of ATF5, focusing on its role in cellular inflammatory stress responses, particularly its regulatory mechanisms in UPR^mt and ERS, aiming to provide a theoretical basis for understanding ATF5's role in cell and organ protection and to offer new insights into the treatment of related inflammatory diseases.
Humans ; Endoplasmic Reticulum Stress ; Inflammation/metabolism* ; Activating Transcription Factors/metabolism* ; Unfolded Protein Response ; Mitochondria/metabolism* ; Apoptosis ; Animals

Zishen Huoxue decoction (ZSHX) enhances cardiomyocyte viability following hypoxic stress; however, its upstream therapeutic targets remain unclear. Network pharmacology and RNA sequencing analyses revealed that ZSHX target genes were closely associated with mitophagy and apoptosis in the mitochondrial pathway. In vitro, ZSHX inhibited pathological mitochondrial fission following hypoxic stress, regulated FUN14 domain-containing protein 1 (FUNDC1)-related mitophagy, and increased the levels of mitophagy lysosomes and microtubule-associated protein 1 light chain 3 beta II (LC3II)/translocase of outer mitochondrial membrane 20 (TOM20) expression while inhibiting the over-activated mitochondrial unfolded protein response. Additionally, ZSHX regulated the stability of beta-tubulin through Sirtuin 5 (SIRT5) and could modulate FUNDC1-related synergistic mechanisms of mitophagy and unfolded protein response in the mitochondria (UPR^mt) via the SIRT5 and -β-tubulin axis. This targeting pathway may be crucial for cardiomyocytes to resist hypoxia. Collectively, these findings suggest that ZSHX can protect against cardiomyocyte injury via the SIRT5-β-tubulin axis, which may be associated with the synergistic protective mechanism of SIRT5-β-tubulin axis-related mitophagy and UPR^mt on cardiomyocytes.
Mitophagy/drug effects* ; Tubulin/genetics* ; Animals ; Myocytes, Cardiac/metabolism* ; Drugs, Chinese Herbal/pharmacology* ; Sirtuins/genetics* ; Unfolded Protein Response/drug effects* ; Myocardial Ischemia/genetics* ; Rats ; Humans ; Rats, Sprague-Dawley ; Apoptosis/drug effects* ; Male

Epilepsies are a group of chronic neurological disorders characterized by spontaneous recurrent seizures caused by abnormal synchronous firing of neurons and transient brain dysfunction. The underlying mechanisms are complex and not yet fully understood. Endoplasmic reticulum (ER) stress, as a condition of excessive accumulation of unfolded and/or misfolded proteins in the ER lumen, has been considered as a pathophysiological mechanism of epilepsy in recent years. ER stress can enhance the protein processing capacity of the ER to restore protein homeostasis through unfolded protein response, which may inhibit protein translation and promote misfolded protein degradation through the ubiquitin-proteasome system. However, persistent ER stress can also cause neuronal apoptosis and loss, which may aggravate the brain damage and epilepsy. This review has summarized the role of ER stress in the pathogenesis of genetic epilepsy.
Humans ; Endoplasmic Reticulum Stress/genetics* ; Unfolded Protein Response ; Endoplasmic Reticulum/pathology* ; Apoptosis ; Epilepsy/genetics*

Non-alcoholic fatty liver disease (NAFLD) is one of the main diseases of metabolic syndrome. With the increasing popularity of NAFLD in the world, the prevention and therapy of NAFLD are facing great challenges. In recent years, scholars at home and abroad have carried out a large number of studies on NAFLD, but its pathogenesis is still unclear. Endoplasmic reticulum stress (ERS) is caused by the accumulation of unfolded or misfolded proteins. In response to ERS, cells help restore normal endoplasmic reticulum function by initiating a protective mechanism known as the unfolded protein response (UPR). Abnormal accumulation of lipids in hepatocytes, aggravated inflammatory response, increased apoptosis of hepatocytes and insulin resistance (IR) are the main pathogenic factors and characteristics of NAFLD, which are closely related to hepatic ERS. A large number of studies have shown that exercise, as a low-cost treatment, can prevent and improve NAFLD effectively, and its mechanism is related to exercise regulating the level of ERS. This paper reviews the research progress on the mechanism of exercise improving NAFLD from the point of view of ERS. The mechanism of exercise improving NAFLD is related to the regulation of hepatocyte lipid metabolism, alleviation of inflammatory reaction, reduction of hepatocyte apoptosis and improvement of IR through regulating ERS.
Humans ; Non-alcoholic Fatty Liver Disease ; Endoplasmic Reticulum Stress ; Exercise ; Unfolded Protein Response ; Insulin Resistance

Endoplasmic reticulum (ER) is an important organelle where folding and post-translational modification of secretory and transmembrane proteins take place. During virus infection, cellular or viral unfolded and misfolded proteins accumulate in the ER in an event called ER stress. To maintain the equilibrium homeostasis of the ER, signal-transduction pathways, known as unfolded protein response (UPR), are activated. The viruses in turn manipulate UPR to maintain an environment favorable for virus survival and replication. Herpesviruses are enveloped DNA viruses that produce over 70 viral proteins. Modification and maturation of large quantities of viral glycosylated envelope proteins during virus replication may induce ER stress, while ER stress play both positive and negative roles in virus infection. Here we summarize the research progress of crosstalk between herpesvirus infection and the virus-induced ER stress.
Endoplasmic Reticulum/metabolism* ; Endoplasmic Reticulum Stress ; Herpesviridae ; Signal Transduction ; Unfolded Protein Response

The mitochondrial unfolded protein response is an important component of the mitochondrial protein quality control program. It can effectively remove unfolded or misfolded proteins under stress, and maintain a stable and healthy mitochondrial pool. The mitochondrial unfolded protein response is coordinated by multiple signaling pathways. The classical ATF4/ATF5-CHOP pathway is induced by accumulation of unfolded or misfolded proteins in the mitochondrial matrix, which reduces stress toxicity by regulating molecular chaperones and proteases. Sirt3-FOXO3a-SOD2 pathway, located in the mitochondrial matrix, plays an important role in anti-oxidative damage. The ERα-NRF1-HTRA2 pathway mainly removes unfolded proteins in the mitochondrial membrane space and improves the quality control of mitochondrial proteins. These three signaling pathways work both independently and cooperatively to enhance mitochondrial capacity and maintain health under stress.
Mitochondria ; Mitochondrial Proteins/metabolism* ; Oxidative Stress ; Signal Transduction ; Unfolded Protein Response

Endoplasmic reticulum (ER) is an important organelle for protein folding, post-transcriptional modification and transport, which plays an important role in maintaining cell homeostasis. A variety of internal and external environmental stimuli can cause the accumulation of misfolded or unfolded proteins in the endoplasmic reticulum, and then result in ER stress. ER stress activates the unfolded protein response (UPR) and initiates a cluster of downstream signals to maintain ER homeostasis. However, severe and persistent ER stress activates UPR, which eventually leads to apoptosis and diseases. In recent years, a lot of researches suggest that ER stress plays an important role in the pathogenesis of various cardiovascular diseases (CVD), including ischemic heart disease, diabetic cardiomyopathy, heart failure, atherosclerosis and vascular calcification, high blood pressure and aortic aneurysm. ER stress might be one of the important targets for treatment of multiple CVD. Herein, the regulation mechanism of ER stress by activating UPR pathways in various common CVD and the new research advances in relationship of ER stress and CVD are briefly reviewed.
Apoptosis ; Cardiovascular Diseases ; physiopathology ; Endoplasmic Reticulum ; Endoplasmic Reticulum Stress ; Humans ; Unfolded Protein Response

Despite considerable efforts to prevent and treat cardiovascular disease (CVD), it has become the leading cause of death worldwide. Cardiac mitochondria are crucial cell organelles responsible for creating energy-rich ATP and mitochondrial dysfunction is the root cause for developing heart failure. Therefore, maintenance of mitochondrial quality control (MQC) is an essential process for cardiovascular homeostasis and cardiac health. In this review, we describe the major mechanisms of MQC system, such as mitochondrial unfolded protein response and mitophagy. Moreover, we describe the results of MQC failure in cardiac mitochondria. Furthermore, we discuss the prospects of 2 drug candidates, urolithin A and spermidine, for restoring mitochondrial homeostasis to treat CVD.
Adenosine Triphosphate ; Cardiovascular Diseases ; Cause of Death ; Heart Failure ; Heart ; Homeostasis ; Mitochondria ; Mitochondrial Degradation ; Organelles ; Quality Control ; Spermidine ; Unfolded Protein Response

Endoplasmic reticulum (ER) stress is mediated by disturbance of Ca²⁺ homeostasis. The store-operated calcium (SOC) channel is the primary Ca²⁺ channel in non-excitable cells, but its participation in agent-induced ER stress is not clear. In this study, the effects of tunicamycin on Ca²⁺ influx in human umbilical vein endothelial cells (HUVECs) were observed with the fluorescent probe Fluo-4 AM. The effect of tunicamycin on the expression of the unfolded protein response (UPR)-related proteins BiP and CHOP was assayed by western blotting with or without inhibition of Orai1. Tunicamycin induced endothelial dysfunction by activating ER stress. Orai1 expression and the influx of extracellular Ca²⁺ in HUVECs were both upregulated during ER stress. The SOC channel inhibitor SKF96365 reversed tunicamycin-induced endothelial cell dysfunction by inhibiting ER stress. Regulation of tunicamycin-induced ER stress by Orai1 indicates that modification of Orai1 activity may have therapeutic value for conditions with ER stress-induced endothelial dysfunction.
Blotting, Western ; Calcium ; Endoplasmic Reticulum ; Endoplasmic Reticulum Stress ; Endothelial Cells ; Homeostasis ; Human Umbilical Vein Endothelial Cells ; Tunicamycin ; Unfolded Protein Response

PURPOSE: Protein overloading in the endoplasmic reticulum (ER) leads to endoplasmic reticulum stress, which exacerbates various disease conditions. Emodin, an anthraquinone compound, is known to have several health benefits. The effect of emodin against palmitic acid (PA) - induced ER stress in HepG2 cells was investigated. METHODS: HepG2 cells were treated with varying concentrations of palmitic acid to determine the working concentration that induced ER stress. ER stress associated genes such as ATF4, XBP1s, CHOP and GRP78 were checked using RT- PCR. In addition, the expression levels of unfolded protein response (UPR) associated proteins such as IRE1α, eIF2α and CHOP were checked using immunoblotting to confirm the induction of ER stress. The effect of emodin on ER stress was analyzed by treating HepG2 cells with 750 µM palmitic acid and varying concentrations of emodin, then analyzing the expression of UPR associated genes. RESULTS: It was evident from the mRNA and protein expression results that palmitic acid significantly increased the expression of UPR associated genes and thereby induced ER stress. Subsequent treatment with emodin reduced the mRNA expression of ATF4, GRP78, and XBP1s. Furthermore, the protein levels of p-IRE1α, p-elF2α and CHOP were also reduced by the treatment of emodin. Analysis of sirtuin mRNA expression showed that emodin increased the levels of SIRT4 and SIRT7, indicating a possible role in decreasing the expression of UPR-related genes. CONCLUSION: Altogether, the results suggest that emodin could exert a protective effect against fatty acid-induced ER stress and could be an agent for the management of various ER stress related diseases.
Emodin ; Endoplasmic Reticulum Stress ; Endoplasmic Reticulum ; Hep G2 Cells ; Immunoblotting ; Insurance Benefits ; Palmitic Acid ; Polymerase Chain Reaction ; RNA, Messenger ; Sirtuins ; Unfolded Protein Response