Preconditioning with endoplasmic reticulum stress alleviated heart ischemia/reperfusion injury via modulating IRE1/ATF6/RACK1/PERK and PGC-1α in diabetes mellitus

Lipid droplets, autophagy, and ER stress as key (survival) pathways during ischemia-reperfusion of transplanted grafts

Ischemia-reperfusion injury is an event concerning any organ under a procedure of transplantation. The early result of ischemia is hypoxia, which causes malfunction of mitochondria and decrease in cellular ATP. This leads to disruption of cellular metabolism. Reperfusion also results in cell damage due to reoxygenation and increased production of reactive oxygen species, and later by induced inflammation. In damaged and hypoxic cells, the endoplasmic reticulum (ER) stress pathway is activated by increased amount of damaged or misfolded proteins, accumulation of free fatty acids and other lipids due to inability of their oxidation (lipotoxicity). ER stress is an adaptive response and a survival pathway, however, its prolonged activity eventually lead to induction of apoptosis. Sustaining cell functionality in stress conditions is a great challenge for transplant surgeons as it is crucial for maintaining a desired level of graft vitality. Pathways counteracting negative consequences of ischemia-reperfusion are autophagy and lipid droplets (LD) metabolism. Autophagy remove damaged organelles and molecules driving them to lysosomes, digested simpler compounds are energy source for the cell. Mitophagy and ER-phagy results in improvement of cell energetic balance and alleviation of ER stress. This is important in sustaining metabolic homeostasis and thus cell survival. LD metabolism is connected with autophagy as LD are degraded by lipophagy, a source of free fatty acids and glycerol-thus autophagy and LD can readily remove lipotoxic compounds in the cell. In conclusion, monitoring and pharmaceutic regulation of those pathways during transplantation procedure might result in increased/improved vitality of transplanted organ.

Induction mechanisms of autophagy and endoplasmic reticulum stress in intestinal ischemia-reperfusion injury, inflammatory bowel disease, and colorectal cancer

In recent years, the incidence of intestinal ischemia-reperfusion injury (II/RI), inflammatory bowel disease (IBD), and colorectal cancer (CRC) has been gradually increasing, posing significant threats to human health. Autophagy and endoplasmic reticulum stress (ERS) play important roles in II/RI. Damage caused by ischemia and cellular stress can activate ERS, which in turn initiates autophagy to clear damaged organelles and abnormal proteins, thereby alleviating ERS and maintaining the intestinal environment. In IBD, chronic inflammation damages intestinal tissues and activates autophagy and ERS. Autophagy is initiated by upregulating ATG genes and downregulating factors that inhibit autophagy, thereby clearing abnormal proteins, damaged organelles, and bacteria. Simultaneously, persistent inflammatory stimulation can also trigger ERS, leading to protein imbalance and abnormal folding in the ER lumen. The activation of ERS can maintain cellular homeostasis by initiating the autophagy process, thereby reducing inflammatory responses and cell apoptosis in the intestine. In CRC, excessive cell proliferation and protein synthesis lead to increased ERS. The activation of ERS, regulated by signaling pathways such as IRE1α and PERK, can initiate autophagy to clear abnormal proteins and damaged organelles, thereby reducing the negative effects of ERS. It can be seen that autophagy and ERS play a crucial regulatory role in the development of intestinal diseases. Therefore, the progress in targeted therapy for intestinal diseases based on autophagy and ERS provides novel strategies for managing intestinal diseases. In this paper, we review the advances in regulation of autophagy and ERS in intestinal diseases, emphasizing the potential molecular mechanisms for therapeutic applications.

Evaluation of linagliptin and insulin combined therapy on unfolded protein response in type 1 diabetic mouse heart

The aim of this study is to reveal the effects of the use of linagliptin, a DPP-4 inhibitor due to its beneficial cardiovascular effects, on endoplasmic reticulum stress (ERS) signaling, which is involved in the pathogenesis of cardiovascular complications related to type 1 diabetes. BALB/c female mice (n = 72) were divided into six groups: control, diabetes+insulin, diabetes+linagliptin, diabetes+linagliptin+insulin, diabetes+TUDCA, and diabetes+TUDCA+insulin. Immunohistochemistry and western blot method, qRT-PCR, ELISA method, and malondialdehyde (MDA) measurements were performed. Linagliptin administered to the type 1 diabetic mouse heart significantly reduced the expression levels of the total and cleaved forms of ATF6, ATF4, and p-JNK, caspase 3. Immunohistochemical and western blot analyses revealed that cleaved caspase 3 protein expression was significantly increased in the diabetes+insulin group compared to the other groups. According to ELISA findings, TUDCA was more effective in reducing NOX 1 and MDA levels than linagliptin. While linagliptin decreased the Chop mRNA level, no change was observed in the Grp78 mRNA level. Our findings showed that there was not much difference between the administration of linagliptin alone or in combination with insulin. Our study reveals that linagliptin is an effective therapeutic agent on ERS and apoptotic UPR in type 1 diabetic hearts.

Botulinum toxin type A activates protective autophagy by modulating endoplasmic reticulum stress in hypoxia/reoxygenation-treated endothelial cells

Botulinum toxin type A (BTXA) previously protected endothelial cells in free skin flaps from ischemia/reperfusion injury by inducing autophagy. Endoplasmic reticulum (ER) stress-autophagy activation may have a role in BTXA-antagonized ischemia/reperfusion damage in human dermal microvascular endothelial cells (HDMECs), however, this has yet to be proven. HDMECs were pretreated with BTXA at various concentrations for 12 h before being subjected to hypoxia and reoxygenation (H/R). Cell Count Kit 8 (CCK8) and Western blot (WB) data showed that H/R treatment significantly increased the expression of ER stress (GRP78, CHOP) and autophagy (LC3II/I, Beclin-1) proteins. The optimal BTXA pretreatment concentration was 1.6 U/mL, which resulted in the highest levels of cell survival and expression of ER stress and autophagy. Following pretreatment with 1.6 U/mL BTXA and the addition of the ER stress inducer Thapsigargin (Tg), the ER stress inhibitor 4-phenylbutyrate (4-PBA), and the inhibitor of autophagy Bafilomycin A1 (Baf A1), respectively, HDMECs were then subjected to H/R treatment. Cell survival and the percentage of ethynyldeoxyuridine-labeled cells in the BTXA pretreatment groups were reduced by the addition of Tg, 4-PBA, and Baf A1. While the expression of GRP78, CHOP, and LC3 was upregulated by Tg and Baf A1, it was downregulated by 4-PBA. The findings showed that ER stress produced by BTXA pretreatment triggers protective autophagy and protects HDMECs from H/R damage. There were no cytoprotective effects from either excessive activation or reduction of ER stress. Our results are consistent with the notion that autophagy and moderate ER stress are critical for cellular longevity and, consequently, functional integrity and may represent a potential therapeutic target.

ER stress induces upregulation of transcription factor Tbx20 and downstream Bmp2 signaling to promote cardiomyocyte survival

In the mammalian heart, fetal cardiomyocytes proliferate prior to birth; however, they exit the cell cycle shortly after birth. Recent studies show that adult cardiomyocytes re-enters the cell cycle postinjury to promote cardiac regeneration. The endoplasmic reticulum (ER) orchestrates the production and assembly of different types of proteins, and a disruption in this machinery leads to the generation of ER stress, which activates the unfolded protein response. There is a very fine balance between ER stress-mediated protective and proapoptotic responses. T-box transcription factor 20 (Tbx20) promotes embryonic and adult cardiomyocyte proliferation postinjury to restore cardiac homeostasis. However, the function and regulatory interactions of Tbx20 in ER stress-induced cardiomyopathy have not yet been reported. We show here that ER stress upregulates Tbx20, which activates downstream bone morphogenetic protein 2 (Bmp2)-pSmad1/5/8 signaling to induce cardiomyocyte proliferation and limit apoptosis. However, augmenting ER stress reverses this protective response. We also show that increased expression of tbx20 during ER stress is mediated by the activating transcription factor 6 arm of the unfolded protein response. Cardiomyocyte-specific loss of Tbx20 results in decreased cardiomyocyte proliferation and increased apoptosis. Administration of recombinant Bmp2 protein during ER stress upregulates Tbx20 leading to augmented proliferation, indicating a feed-forward loop mechanism. In in vivo ER stress, as well as in diabetic cardiomyopathy, the activity of Tbx20 is increased with concomitant increased cardiomyocyte proliferation and decreased apoptosis. These data support a critical role of Tbx20-Bmp2 signaling in promoting cardiomyocyte survival during ER stress-induced cardiomyopathies.

Resveratrol promotes liver cell survival in mice liver-induced ischemia-reperfusion through unfolded protein response: a possible approach in liver transplantation

Background

Ischemia-reperfusion (I/R) of the liver is a multifactorial condition that happens during transplantation and surgery. The deleterious effects of I/R result from the acute production of reactive oxygen species (ROS), which can trigger immediate tissue damage and induce a series of destructive cellular responses, including apoptosis organ failure and inflammation. The production of ROS in the I/R process can damage the antioxidant system and cause liver damage. Resveratrol has been shown to have antioxidant properties in several investigations. Here, we address the therapeutic effect of resveratrol on I/R-induced liver injury by focusing on unfolded protein response (UPR) signaling pathway.

Methods

Five minutes before reperfusion, resveratrol was injected into the tail vein of mice. They were ischemic for 1 h and then re-perfused for 3 h before being slaughtered (I/R). The activity of liver enzymes and the expression levels of genes involved in the unfolded protein response pathway were used to measure the hepatic damage.

Results

Our results revealed that the low dose of resveratrol (0.02 and 0.2 mg/kg) post-ischemic treatment significantly reduced the ALT and AST levels. In addition, compared with the control group, the expression of UPR pathway genes GRP78, PERK, IRE1α, CHOP, and XBP1 was significantly reduced in the resveratrol group. In the mice that received lower doses of resveratrol (0.02 and 0.2 mg/kg), the histopathological changes induced by I/R were significantly improved; however, the highest dose (2 mg/kg) of resveratrol could not significantly protect and solve the I/R damage.

Conclusion

The findings of this study suggest that hepatic ischemia occurs after liver transplantation and that receiving low-dose resveratrol treatment before reperfusion may promote graft survival through inhibition of UPR arms, especially PERK and IRE1α.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40360-022-00611-4.

Amelioration of myocardial ischemia/reperfusion injury in diabetes: A narrative review of the mechanisms and clinical applications of dexmedetomidine

Mechanisms contributing to the pathogenesis of myocardial ischemia-reperfusion (I/R) injury are complex and multifactorial. Many strategies have been developed to ameliorate myocardial I/R injuries based on these mechanisms. However, the cardioprotective effects of these strategies appear to diminish in diabetic states. Diabetes weakens myocardial responses to therapies by disrupting intracellular signaling pathways which may be responsible for enhancing cellular resistance to damage. Intriguingly, it was found that Dexmedetomidine (DEX), a potent and selective α2-adrenergic agonist, appears to have the property to reverse diabetes-related inhibition of most intervention-mediated myocardial protection and exert a protective effect. Several mechanisms were revealed to be involved in DEX’s protection in diabetic rodent myocardial I/R models, including PI3K/Akt and associated GSK-3β pathway stimulation, endoplasmic reticulum stress (ERS) alleviation, and apoptosis inhibition. In addition, DEX could attenuate diabetic myocardial I/R injury by up-regulating autophagy, reducing ROS production, and inhibiting the inflammatory response through HMGB1 pathways. The regulation of autonomic nervous function also appeared to be involved in the protective mechanisms of DEX. In the present review, the evidence and underlying mechanisms of DEX in ameliorating myocardial I/R injury in diabetes are summarized, and the potential of DEX for the treatment/prevention of myocardial I/R injury in diabetic patients is discussed.

Plasma-derived extracellular vesicles transfer microRNA-130a-3p to alleviate myocardial ischemia/reperfusion injury by targeting ATG16L1

Extracellular vesicles (EVs) are implicated in myocardial ischemia/reperfusion (I/R) injury as modulators by shuttling diverse cargoes, including microRNAs (miRNAs). The current study was initiated to unravel the potential involvement of plasma-derived EVs carrying miR-130a-3p on myocardial I/R injury. Rats were induced with moderate endoplasmic reticulum stress, followed by isolation of plasma-derived EVs. Then, an I/R rat model and hypoxia/reoxygenation (H/R) cardiomyoblast model were established to simulate a myocardial I/R injury environment where miR-130a-3p was found to be abundantly expressed. miR-130a-3p was confirmed to target and negatively regulate autophagy-related 16-like 1 (ATG16L1) in cardiomyoblasts. Based on a co-culture system, miR-130a-3p delivered by EVs derived from plasma protected H/R-exposed cardiomyoblasts against H/R-induced excessive cardiomyoblast autophagy, inflammation, and damage, improving cardiac dysfunction as well as myocardial I/R-induced cardiac dysfunction and tissue injury. The mechanism underlying the functional role of EVs-loaded miR-130a-3p was found to be dependent on its targeting relation with ATG16L1. The protective action of EV-carried miR-130a-3p was further re-produced in a rat model serving as in vivo validation as evidenced by improved cardiac function, tissue injury, myocardial fibrosis, and myocardial infarction. Collectively, miR-130a-3p shuttled by plasma-derived EVs was demonstrated to alleviate excessive cardiomyoblast autophagy and improve myocardial I/R injury.

Myocardiocyte autophagy in the context of myocardiocytes regeneration: a potential novel therapeutic strategy

Background

The regeneration strategy involves several aspects, such as reprogramming aspects, targeting pathophysiological processes, and inducing the physiological one. Autophagy targeting is a potential physiological/pathogenetic strategy to enhance myocardiocytes' function. Myocardiocytes' injury-related death remains to be the highest in our era. Unfortunately, myocardiocytes have a limited proliferation capacity to compensate for what was lost by infarction. However, partially injured myocardiocytes can be preserved by improving the autophagy process of myocardiocytes.

Main text

Autophagy induction involved controlling the cellular and subcellular environment as well as gene expression. Autophagy is well known to prolong the longevity of cell and human life. Inhibition of the mTOR receptor, proapoptotic gene Bnip3, IP3, and lysosome inhibitors, inhibition of microRNA-22 and overexpression of microRNA-99a, modulators of activated protein kinase with adenosine monophosphate, resveratrol, sirtuin activators, Longevinex and calcium lowering agents can promote physiological myocardiocyte autophagy and improve post-myocardial modulation and recovery speed. The paper aimed to assess autophagy role in myocardiocytes regeneration modulation.

Conclusions

The autophagy strategy can be applied to infarcted myocardiocytes, as well as heart failure. However, cell self-eating is not the preferred therapy for preserving injured myocardiocytes or causing regeneration.

Ischemic brain injury in diabetes and endoplasmic reticulum stress

Diabetes is a widespread disease characterized by high blood glucose levels due to abnormal insulin activity, production, or both. Chronic diabetes causes many secondary complications including cardiovascular disease: a life-threatening complication. Cerebral ischemia-related mortality, morbidity, and the extent of brain injury are high in diabetes. However, the mechanism of increase in ischemic brain injury during diabetes is not well understood. Multiple mechanisms mediate diabetic hyperglycemia and hypoglycemia-induced increase in ischemic brain injury. Endoplasmic reticulum (ER) stress mediates both brain injury as well as brain protection after ischemia-reperfusion injury. The pathways of ER stress are modulated during diabetes. Free radical generation and mitochondrial dysfunction, two of the prominent mechanisms that mediate diabetic increase in ischemic brain injury, are known to stimulate the pathways of ER stress. Increased ischemic brain injury in diabetes is accompanied by a further increase in the activation of ER stress. As there are many metabolic changes associated with diabetes, differential activation of the pathways of ER stress may mediate pronounced ischemic brain injury in subjects suffering from diabetes. We presently discuss the literature on the significance of ER stress in mediating increased ischemia-reperfusion injury in diabetes.

Hydrogen Sulfide Ameliorates Angiotensin II-Induced Atrial Fibrosis Progression to Atrial Fibrillation Through Inhibition of the Warburg Effect and Endoplasmic Reticulum Stress

Atrial fibrosis is the basis for the occurrence and development of atrial fibrillation (AF) and is closely related to the Warburg effect, endoplasmic reticulum stress (ERS) and mitochondrion dysfunctions-induced cardiomyocyte apoptosis. Hydrogen sulfide (H₂S) is a gaseous signalling molecule with cardioprotective, anti-myocardial fibrosis and improved energy metabolism effects. Nevertheless, the specific mechanism by which H₂S improves the progression of atrial fibrosis to AF remains unclear. A case-control study of patients with and without AF was designed to assess changes in H₂S, the Warburg effect, and ERS in AF. The results showed that AF can significantly reduce cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate thiotransferase (3-MST) expression and the H₂S level, induce cystathionine-β-synthase (CBS) expression; increase the Warburg effect, ERS and atrial fibrosis; and promote left atrial dysfunction. In addition, AngII-treated SD rats had an increased Warburg effect and ERS levels and enhanced atrial fibrosis progression to AF compared to wild-type SD rats, and these conditions were reversed by sodium hydrosulfide (NaHS), dichloroacetic acid (DCA) or 4-phenylbutyric acid (4-PBA) supplementation. Finally, low CSE levels in AngII-induced HL-1 cells were concentration- and time-dependent and associated with mitochondrial dysfunction, apoptosis, the Warburg effect and ERS, and these effects were reversed by NaHS, DCA or 4-PBA supplementation. Our research indicates that H₂S can regulate the AngII-induced Warburg effect and ERS and might be a potential therapeutic drug to inhibit atrial fibrosis progression to AF.

Downregulation of RIP3 Improves the Protective Effect of ATF6 in an Acute Liver Injury Model

Background

Activating transcription factor 6 (ATF6) and receptor-interacting protein 3 (RIP3) are important signaling proteins in endoplasmic reticulum (ER) stress and necroptosis, respectively. However, their regulatory relationship and clinical significance are unknown. We investigate the impact of ATF6 on RIP3 expression, and its role in hepatocyte necroptosis in an acute liver injury model.

Methods

In vivo and in vitro experiments were carried out. LO2 cells were treated with thapsigargin (TG). In vivo, male BALB/c mice were treated with carbon tetrachloride (CCl₄, 1 mL/kg) or tunicamycin (TM, 2 mg/kg). Then, the impact of ATF6 or RIP3 silencing on liver injury, hepatocyte necroptosis, and ER stress-related protein expression was examined.

Results

TG induced ER stress and necroptosis and ATF6 and RIP3 expression in LO2 cells. The knockdown of ATF6 significantly decreased RIP3 expression (p < 0.05) and increased ER stress and necroptosis. The downregulation of RIP3 significantly reduced necroptosis and ER stress (p < 0.05). Similar results were observed in CCl₄ or the TM-induced mouse model. The knockdown of ATF6 significantly decreased CCl₄-induced RIP3 expression and increased liver injury, necroptosis, and ER stress in mice livers (p < 0.05). In contrast, the downregulation of RIP3 significantly reduced liver injury, hepatocyte necroptosis, and ER stress.

Conclusions

Hepatocyte ATF6 has multiple roles in acute liver injury. It reduces hepatocyte necroptosis via negative feedback regulation of ER stress. In addition, ATF6 can upregulate the expression of RIP3, which is not helpful to the recovery process. However, downregulating RIP3 reduces hepatocyte necroptosis by promoting the alleviation of ER stress. The findings suggest that RIP3 could be a plausible target for the treatment of liver injury.

Temporal Transcript Profiling Identifies a Role for Unfolded Protein Stress in Human Gut Ischemia-Reperfusion Injury

BACKGROUND & AIMS

Intestinal ischemia-reperfusion injury is a serious and life-threatening condition. A better understanding of molecular mechanisms related to intestinal ischemia-reperfusion injury in human beings is imperative to find therapeutic targets and improve patient outcome.

METHODS

First, the in vivo dynamic modulation of mucosal gene expression of the ischemia-reperfusion-injured human small intestine was studied. Based on functional enrichment analysis of the changing transcriptome, one of the predominantly regulated pathways was selected for further investigation in an in vitro human intestinal organoid model.

RESULTS

Ischemia-reperfusion massively changed the transcriptional landscape of the human small intestine. Functional enrichment analysis based on gene ontology and pathways pointed to the response to unfolded protein as a predominantly regulated process. In addition, regulatory network analysis identified hypoxia-inducing factor 1A as one of the key mediators of ischemia-reperfusion-induced changes, including the unfolded protein response (UPR). Differential expression of genes involved in the UPR was confirmed using quantitative polymerase chain reaction analysis. Electron microscopy showed signs of endoplasmic reticulum stress. Collectively, these findings point to a critical role for unfolded protein stress in intestinal ischemia-reperfusion injury in human beings. In a human intestinal organoid model exposed to hypoxia-reoxygenation, attenuation of UPR activation with integrated stress response inhibitor strongly reduced pro-apoptotic activating transcription factor 4 (ATF4)-CCAAT/enhancer-binding protein homologous protein (CHOP) signaling.

CONCLUSIONS

Transcriptome analysis showed a crucial role for unfolded protein stress in the response to ischemia-reperfusion in human small intestine. UPR inhibition during hypoxia-reoxygenation in an intestinal organoid model suggests that downstream protein kinase R-like ER kinase (PERK) signaling may be a promising target to reduce intestinal ischemia-reperfusion injury. Microarray data are available in GEO (https://www.ncbi.nlm.nih.gov/gds, accession number GSE37013).

Integrated Stress Response Couples Mitochondrial Protein Translation With Oxidative Stress Control

BACKGROUND

The integrated stress response (ISR) is an evolutionarily conserved process to cope with intracellular and extracellular disturbances. Myocardial infarction is a leading cause of death worldwide. Coronary artery reperfusion, the most effective means to mitigate cardiac damage of myocardial infarction, causes additional reperfusion injury. This study aimed to investigate the role of the ISR in myocardial ischemia/reperfusion (I/R).

METHODS

Cardiac-specific gain- and loss-of-function approaches for the ISR were used in vivo. Myocardial I/R was achieved by ligation of the cardiac left anterior descending artery for 45 minutes followed by reperfusion for different times. Cardiac function was assessed by echocardiography. Cultured H9c2 cells, primary rat cardiomyocytes, and mouse embryonic fibroblasts were used to dissect underlying molecular mechanisms. Tandem mass tag labeling and mass spectrometry was conducted to identify protein targets of the ISR. Pharmacologic means were tested to manipulate the ISR for therapeutic exploration.

RESULTS

We show that the PERK (PKR-like endoplasmic reticulum resident kinase)/eIF2α (α subunit of eukaryotic initiation factor 2) axis of the ISR is strongly induced by I/R in cardiomyocytes in vitro and in vivo. We further reveal a physiologic role of PERK/eIF2α signaling by showing that acute activation of PERK in the heart confers robust cardioprotection against reperfusion injury. In contrast, cardiac-specific deletion of PERK aggravates cardiac responses to reperfusion. Mechanistically, the ISR directly targets mitochondrial complexes through translational suppression. We identify NDUFAF2 (NADH:ubiquinone oxidoreductase complex assembly factor 2), an assembly factor of mitochondrial complex I, as a selective target of PERK. Overexpression of PERK suppresses the protein expression of NDUFAF2 and PERK inhibition causes an increase of NDUFAF2. Silencing of NDUFAF2 significantly rescues cardiac cell survival from PERK knockdown under I/R. We show that activation of PERK/eIF2α signaling reduces mitochondrial complex-derived reactive oxygen species and improves cardiac cell survival in response to I/R. Moreover, pharmacologic stimulation of the ISR protects the heart against reperfusion damage, even after the restoration of occluded coronary artery, highlighting clinical relevance for myocardial infarction treatment.

CONCLUSIONS

These results suggest that the ISR improves cell survival and mitigates reperfusion damage by selectively suppressing mitochondrial protein synthesis and reducing oxidative stress in the heart.

Long non-coding RNA MALAT1 enhances the protective effect of dexmedetomidine on acute lung injury by sponging miR-135a-5p to downregulate the ratio of X-box binding proteins XBP-1S/XBP-1U

Acute lung injury (ALI) is the common and clinically severe complication. Dexmedetomidine (DEX) can protect against lipopolysaccharide (LPS)-induced ALI through anti-apoptosis, anti-inflammatory and immune regulatory actions. It is well documented that major causes of LPS-induced ALI are endoplasmic reticulum stress (ERS) and abnormally elevated CHOP. Moreover, XBP-1 can enhance CHOP expression. XBP-1S can aggravate ERS and XBP-1 U can repress ERS. By querying Starbase, miR-135a-5p interacts with XBP-1 and lncRNA MALAT1 sponges miR-135a-5p. It has been reported that MALAT1 interference markedly promoted the apoptosis of pulmonary microvascular endothelial cells in ALI rats by activating TLR4/NF-κB pathway. miR-135a-5p inhibitor remarkably alleviated LPS-induced A549 cell injury through suppressing cell apoptosis. In the present work, LPS was dripped into the nasal cavity of SD rats to establish the rat model of ALI and LPS was also applied to stimulate BEAS-2B cells to imitate ALI in vitro. Then, the pathology, lung function indexes, levels of inflammatory factors, apoptosis of lung tissues in SD rats and apoptotic level of BEAS-2B cells were measured, so as to confirm whether upregulation of lncRNA MALAT1 was able to suppress ERS, thus enhancing the protective effect of DEX against ALI. Herein, overexpression of lncRNA MALAT1 strengthened the remission effects of DEX on LPS-triggered ALI, severe pulmonary edema, inflammatory response and cell apoptosis of lung tissues in SD rats and reinforced the anti-apoptosis effect of DEX on LPS-stimulated BEAS-2B cells. Mechanically, lncRNA MALAT1 enhanced the protective effect of DEX against ALI by downregulating the ratio of XBP-1S/XBP-1U to repress ERS.

Unfolded protein response during cardiovascular disorders: a tilt towards pro-survival and cellular homeostasis

The endoplasmic reticulum (ER) is an organelle that orchestrates the production and proper assembly of an extensive types of secretory and membrane proteins. Endoplasmic reticulum stress is conventionally related to prolonged disruption in the protein folding machinery resulting in the accumulation of unfolded proteins in the ER. This disruption is often manifested due to oxidative stress, Ca²⁺ leakage, iron imbalance, disease conditions which in turn hampers the cellular homeostasis and induces cellular apoptosis. A mild ER stress is often reverted back to normal. However, cells retaliate to acute ER stress by activating the unfolded protein response (UPR) which comprises three signaling pathways, Activating transcription factor 6 (ATF6), inositol requiring enzyme 1 alpha (IRE1α), and protein kinase RNA-activated-like ER kinase (PERK). The UPR response participates in both protective and pro-apoptotic responses and not much is known about the mechanistic aspects of the switch from pro-survival to pro-apoptosis. When ER stress outpaces UPR response then cell apoptosis prevails which often leads to the development of various diseases including cardiomyopathies. Therefore, it is important to identify molecules that modulate the UPR that may serve as promising tools towards effective treatment of cardiovascular diseases. In this review, we elucidated the latest advances in construing the contribution imparted by the three arms of UPR to combat the adverse environment in the ER to restore cellular homeostasis during cardiomyopathies. We also summarized the various therapeutic agents that plays crucial role in tilting the UPR response towards pro-survival.

Cardioprotective effects of azilsartan compared with that of telmisartan on an in vivo model of myocardial ischemia-reperfusion injury

Azilsartan is found to be more potent than other angiotensin receptor blockers in reducing blood pressure. However, its effect on the heart following myocardial infarction remains to be established. For the first time, we investigated the peroxisome proliferator-activated receptor-γ (PPAR-γ) agonistic and cardioprotective properties of azilsartan. Computational modeling studies of interactions between azilsartan and PPAR-γ revealed azilsartan as an agonist of PPAR-γ and showed the mechanism of azilsartan in cardioprotection. Our study compared the cardioprotective potential of telmisartan to that of azilsartan in a murine model of myocardial ischemia-reperfusion injury by comparing their antioxidant, ant apoptotic, anti-inflammatory, mitogen-activated protein kinase (MAPK)-modulating ability, and PPAR-γ agonistic activity. Male Wistar rats were grouped into four to receive vehicle (dimethyl sulfoxide [0.05%] 2 ml/kg) telmisartan (10 mg/kg p.o.), azilsartan (10 mg/kg p.o.) or azilsartan with specific PPAR-γ blocker, GW 9662 for 28 days. Ischemia was induced for 45 min on the 29th day followed by 60 min of reperfusion. Telmisartan and azilsartan pretreatment significantly nearly normalized cardiac parameters and preserved structural changes. Both drugs inhibited oxidative burst, inflammation, as well as cell death by modulating apoptotic protein expression along with reduction in 4',6-diamidino-2-phenylindole/terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells. An increment in pro-survival kinase ERK paralleled with a reduction in p38 and JNK was also revealed by MAPK pathway studies, after administration of these drugs. Interestingly, the aforementioned changes induced by both drugs were reversed by administration of the specific PPAR-γ antagonist, GW9662. However, we found that azilsartan upregulated PPAR-γ to a lesser extent as compared to telmisartan and the latter may be preferred in hypertensive patients at risk of myocardial infarction.

Mechanism of long non‑coding RNA metastasis‑associated lung adenocarcinoma transcript 1 in lipid metabolism and inflammation in heart failure

Heart failure (HF) is a serious threat to human health. Long noncoding RNAs (lncRNAs) are critical regulators of HF. The aim of the study was to investigate the molecular mechanism of MALAT1 in HF rats. MALAT1 expression was detected in serum of normal volunteers and HF patients, HF rats and isoproterenol (ISO)-induced H9C2 cells, and its diagnostic value was evaluated in HF patients. Indexes related to cardiac functions and hemodynamics, myocardial injury, lipid metabolism, lipid oxidation, and inflammation were detected. Moreover, the downstream mechanism of MALAT1 was predicted and verified and in vivo experiments were further performed in ISO-induced H9C2 cells to verify the effects of MALAT1 in HF. MALAT1 was highly expressed in serum of HF patients, HF rats and ISO-induced H9C2 cells and was valuable in predicting HF. Inhibition of MALAT1 increased cardiac function and anti-inflammation and alleviated myocardial injury, lipid metabolism, lipid oxidation and apoptosis rates. Inhibition of MALAT1 reduced H9C2 cell injury. MALAT1 competitively bound to microRNA (miR)-532-3p to upregulate LDLR protein. Inhibition of miR-532-3p weakened the protective effect of downregulated MALAT1 against H9C2 cell injury. We concluded that MALAT1 upregulated LDLR expression by competitively binding to miR-532-3p, thereby increasing pathological injury in HF.

Luman/CREB3 knock-down inhibit hCG induced MLTC-1 apoptosis

Luman has been reported to be involved in the formation of COP II-mediated transport vesicles that affect protein transportation and secretion. Western blotting, immunohistochemistry, immunofluorescence, and RT-qPCR indicated that Luman is widely expressed in the male mouse reproductive system. In sperm, Luman was mainly located in the sperm tail, and the expression level increased with sperm maturity. In the testis, Luman was located in Leydig cells. In MLTC-1, a high-concentration hCG treatment significantly increased GRP78, ATF6, p-IRE1, and p-EIF2S1 expression but had no effect on Luman expression. To investigate the role of Luman in hCG-induced ER stress (ERS), experiments were conducted to examine the consequences of short hairpin RNA (shRNA)-mediated Luman knockdown in MLTC-1 cells. Luman knockdown decreased the percentage of S phase cells and up-regulated Cyclin A1, Cyclin B1, and Cyclin D2 expression. ELISA and WB results showed that with Luman knockdown, Cyp11a1, p-IRE1, and p-EIF2S1 expression and testosterone secretion were significantly increased, while GRP78 and CHOP expression were decreased. Flow cytometry results showed that Luman knockdown reduced MLTC-1 cell apoptosis. RT-qPCR and WB results showed that Luman knockdown significantly up-regulated BCL-2 expression and decreased Caspase-3 and BAX expression. These data suggest that Luman is widely expressed in the male mouse reproductive system. In MLTC-1 cells, Luman knockdown up-regulated p-IRE1, p-EIF2S1, and BCL-2 expression and decreased GRP78, CHOP, BAX, and Caspase-3 expression. We propose that Luman knockdown reduces cell apoptosis through the ERS pathway, thereby promoting cell survival and testosterone secretion. These findings provide new insights into the role of Luman in hCG-induced ERS.

Nobiletin alleviates ischemia/reperfusion injury in the kidney by activating PI3K/AKT pathway

Recent studies have demonstrated that nobiletin (NOB) displays anti-oxidative and anti-apoptotic efficacies against multiple pathological insults. However, the potential effects of NOB on the injury caused by ischemia and reperfusion (I/R) in the kidney remain undetermined. In the present study, I/R injury was elicited by right kidney removal and left renal pedicel clamping for 45 min, followed by reperfusion for 24 h. NOB was added at the start of reperfusion. Histological examination, detection of biomarkers in plasma, and measurement of apoptosis induced by endoplasmic reticulum stress (ERS) were used to evaluate renal injury. Additionally, the PI3K/AKT inhibitor LY294002 was also used in mechanistic experiments. NOB pre-treatment significantly reduced renal damage caused by I/R injury, as indicated by decreased serum levels of creatine, blood urea nitrogen and tubular injury scores. Furthermore, NOB inhibited elevated ERS-associated apoptosis, as evidenced by reduced apoptotic rates and ERS-related signaling molecules (such as, C/EBP homologous protein, caspase-12 and glucose-regulated protein of 78 kDa). NOB increased phosphorylation of proteins in the PI3K/AKT pathway. The inhibition of PI3K/AKT signaling with pharmacological inhibitors could reverse the beneficial effects of NOB during renal I/R insult. In conclusion, NOB pre-treatment may alleviate I/R injury in the kidney by inhibiting reactive oxygen species production and ERS-induced apoptosis, partly through the PI3K/AKT signaling pathway.

Circulating Cardiac Biomarkers in Diabetes Mellitus: A New Dawn for Risk Stratification-A Narrative Review

The aim of this narrative review is to update the current knowledge on the differential choice of circulating cardiac biomarkers in patients with prediabetes and established type 2 diabetes mellitus (T2DM). There are numerous circulating biomarkers with unconfirmed abilities to predict clinical outcomes in pre-DM and DM individuals; the prognostication ability of the cardiac biomarkers reported here has been established, and they are still being studied. The conventional cardiac biomarkers, such as natriuretic peptides (NPs), soluble suppressor tumorigenisity-2, high-sensitivity circulating cardiac troponins and galectin-3, were useful to ascertain cardiovascular (CV) risk. Each cardiac biomarker has its strengths and weaknesses that affect the price of usage, specificity, sensitivity, predictive value and superiority in face-to-face comparisons. Additionally, there have been confusing reports regarding their abilities to be predictably relevant among patients without known CV disease. The large spectrum of promising cardiac biomarkers (growth/differential factor-15, heart-type fatty acid-binding protein, cardiotrophin-1, carboxy-terminal telopeptide of collagen type 1, apelin and non-coding RNAs) is discussed in the context of predicting CV diseases and events in patients with known prediabetes and T2DM. Various reasons have been critically discussed related to the variable findings regarding biomarker-based prediction of CV risk among patients with metabolic disease. It was found that NPs and hs-cTnT are still the most important tools that have an affordable price as well as high sensitivity and specificity to predict clinical outcomes among patients with pre-DM and DM in routine clinical practice, but other circulating biomarkers need to be carefully investigated in large trials in the future.

PERK Overexpression-Mediated Nrf2/HO-1 Pathway Alleviates Hypoxia/Reoxygenation-Induced Injury in Neonatal Murine Cardiomyocytes via Improving Endoplasmic Reticulum Stress

Reperfusion processes following acute myocardial infarction (AMI) have been reported to induce additional cardiomyocyte death, known as ischemia-reperfusion (I/R) injury. Endoplasmic reticulum (ER) stress is reported to be involved in the development of I/R injury. There is evidence that PERK exerts beneficial roles in alleviating ER stress. Here, we investigated whether upregulation of PERK improved cardiomyocytes injury induced by I/R. Specific siRNAs or adenovirus vectors were incubated with isolated neonatal cardiomyocytes (NCMs) to regulate expression levels of target genes including PERK, Nrf2, and HO-1. Afterwards, hypoxia and subsequent reoxygenation (H/R) administration was performed as the in vitro model of I/R injury. MTT assay showed that H/R intervention decreased the viability of cells, yet PERK overexpression increased the cellular proliferative rate. Moreover, the upregulation of Nrf2 or HO-1 elevated the growth rate of cells, while gene silencing of Nrf2 or HO-1 reduced the viability of NCMs treated with PERK-rAAV9. In addition, we observed that the apoptotic index of cells with H/R stimulation was reduced when NCMs were pretreated with PERK-rAAV9, Nrf2-rAAV9, or HO-1-rAAV9. After cells were incubated with Nrf2-siRNA or HO-1-siRNA, the upregulation of PERK had no roles in affecting the apoptosis rate of NCMs damaged by H/R. Then, our findings indicated that there was a level decrease of GRP78, CRT, CHOP, and Caspase-12 in NCMs of the PERK-rAAV9 group compared to that of the H/R group. Both Nrf2 overexpression and HO-1 upregulation reduced the expression of ER stress-related proapoptotic factors, yet the expression suppression of Nrf2 and HO-1 increased levels of GRP78, CRT, CHOP, and Caspase-12 in NCMs treated with PERK-rAAV9. Taken together, our results suggested that the effects of PERK against H/R injury might be attributed to the upregulation of Nrf2/HO-1 cascade, followed by the inhibition of ER stress-related apoptotic pathway.