Targeted inhibition of calpain in mitochondria alleviates oxidative stress-induced myocardial injury

Integration of network pharmacology and proteomics analysis to identify key target pathways of Ginsenoside Re for myocardial ischemia

BACKGROUND

Clinically, various diseases cause myocardial ischemia (MI), which further induces severe cardiac injury and leads to high mortality in patients. Ginsenoside Re, one of the major ginsenosides in ginseng, can regulate the level of oxidative stress in the injured myocardium. Thus, it may attenuate MI injury, but the related mechanism has not been comprehensively studied.

PURPOSE

This study aimed to investigate the anti-MI effect and comprehensively mechanisms of Ginsenoside Re.

STUDY DESIGN/METHODS

Oxygen-glucose deprivation (OGD), oxidative-induced cardiomyocyte injury, and isoproterenol-induced MI mice were used to explore their protective effect of Ginsenoside Re. An integrated approach of network pharmacology, molecular docking, and tandem mass tag proteomics was applied to determine the corresponding common potential targets of Ginsenoside Re against MI, such as target proteins and related pathways. The major anti-MI target proteins and related pathways were validated by immunofluorescence (IF) assay and Western blotting (WB).

RESULTS

Ginsenoside Re (1.32-168.93 µM) had low toxicity to normal cardiomyocytes, and increased the survival of oxidative stress-injured (OGD-induced injury or H2O2-induced injury) cardiomyocytes in this concentration range. It regulated the reactive oxygen species (ROS) level in OGD-injured cardiomyocytes; stabilized the nuclear morphology, mitochondrial membrane potential (MMP), and mitochondrial function; and reduced apoptosis. Meanwhile, Ginsenoside Re (5-20 mg/kg) alleviated cardiac injury in MI mice and maintained cardiac function. Through network pharmacology and proteomics, the relevant mechanisms revealed several key pathways of Ginsenoside Re anti-MI, including inhibition of MAPK pathway protein phosphorylation, downregulation of phosphorylated PDPK1, AKT, and STAT3, and upregulation of TGF-β3, ferroptosis pathway (upregulation of GPX4 and downregulation of phosphorylation level of MDM2) and AMPK pathway (regulating the synthesis of cholesterol in the myocardium by downregulation of HMGCR). The key proteins of these target pathways were validated by IF and/or WB.

CONCLUSION

Ginsenoside Re may target MAPK, AKT, ferroptosis pathways and AMPK pathway to prevent and/or treat MI injury and protect cardiomyocytes from oxidative damage.

N-Terminomic Identification of Intracellular MMP-2 Substrates in Cardiac Tissue

Proteases are enzymes that induce irreversible post-translational modifications by hydrolyzing amide bonds in proteins. One of these proteases is matrix metalloproteinase-2 (MMP-2), which has been shown to modulate extracellular matrix remodeling and intracellular proteolysis during myocardial injury. However, the substrates of MMP-2 in heart tissue are limited, and lesser known are the cleavage sites. Here, we used degradomics to investigate the substrates of intracellular MMP-2 in rat ventricular extracts. First, we designed a novel, constitutively active MMP-2 fusion protein (MMP-2-Fc) that we expressed and purified from mammalian cells. Using this protease, we proteolyzed ventricular extracts and used subtiligase-mediated N-terminomic labeling which identified 95 putative MMP-2-Fc proteolytic cleavage sites using mass spectrometry. The intracellular MMP-2 cleavage sites identified in heart tissue extracts were enriched for proteins primarily involved in metabolism, as well as the breakdown of fatty acids and amino acids. We further characterized the cleavage of three of these MMP-2-Fc substrates based on the gene ontology analysis. We first characterized the cleavage of sarco/endoplasmic reticulum calcium ATPase (SERCA2a), a known MMP-2 substrate in myocardial injury. We then characterized the cleavage of malate dehydrogenase (MDHM) and phosphoglycerate kinase 1 (PGK1), representing new cardiac tissue substrates. Our findings provide insights into the intracellular substrates of MMP-2 in cardiac cells, suggesting that MMP-2 activation plays a role in cardiac metabolism.

Triphenyl phosphate induces cardiotoxicity through myocardial fibrosis mediated by apoptosis and mitophagy of cardiomyocyte in mice

Triphenyl phosphate (TPHP) is an organophosphorus flame retardant, but its cardiac toxicity has not been adequately investigated. Therefore, in the current study, the effect of TPHP on the heart and the underlying mechanism involved was evaluated. C57BL/6 J mice were administered TPHP (0, 5, and 50 mg/kg/day) for 30 days. In addition, H9c2 cells were treated with three various concentrations (0, 50, and 150 μM) of TPHP, with and without the reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine or the mitochondrial fusion promoter M1. TPHP caused cardiac fibrosis and increased the levels of CK-MB and LDH in the serum. TPHP increased the levels of ROS, malondialdehyde (MDA), and decreased the level of superoxide dismutase (SOD) and Glutathione peroxidase (GSH-Px). Furthermore, TPHP caused mitochondrial damage, and induced fusion and fission disorders that contributed to mitophagy in both the heart of C57BL/6 J mice and H9c2 cells. Transcriptome analysis showed that TPHP induced up- or down-regulated expression of various genes in myocardial tissue and revealed enriched apoptosis pathways. It was also found that TPHP could remarkably increase the expression levels of Bax, cleaved Caspase-9, cleaved Caspase-3, and decreased Bcl-2, thereby causing apoptosis in H9c2 cells. Taken together, the results suggested that TPHP promoted mitophagy through mitochondria fusion dysfunction resulting from oxidative stress, leading to fibrosis by inducing myocardial apoptosis.

Remote ischemic preconditioning reduces mitochondrial apoptosis mediated by calpain 1 activation in myocardial ischemia-reperfusion injury through calcium channel subunit Cacna2d3

Remote Ischemic Preconditioning (RIPC) can reduce myocardial ischemia-reperfusion injury, but its mechanism is not clear. In order to explore the mechanism of RIPC in myocardial protection, we collected myocardial specimens during cardiac surgery in children with tetralogy of Fallot for sequencing. Our study found RIPC reduces the expression of the calcium channel subunit cacna2d3, thereby impacting the function of calcium channels. As a result, calcium overload during ischemia-reperfusion is reduced, and the activation of calpain 1 is inhibited. This ultimately leads to a decrease in calpain 1 cleavage of Bax, consequently inhibiting increased mitochondrial permeability-mediated apoptosis. Notably, in both murine and human models of myocardial ischemia-reperfusion injury, RIPC inhibiting the expression of the calcium channel subunit cacna2d3 and the activation of calpain 1, improving cardiac function and histological outcomes. Overall, our findings put forth a proposed mechanism that elucidates how RIPC reduces myocardial ischemia-reperfusion injury, ultimately providing a solid theoretical foundation for the widespread clinic application of RIPC.

Landscape of molecular crosstalk between SARS-CoV-2 infection and cardiovascular diseases: emphasis on mitochondrial dysfunction and immune-inflammation

BACKGROUND

SARS-CoV-2, the pathogen of COVID-19, is a worldwide threat to human health and causes a long-term burden on the cardiovascular system. Individuals with pre-existing cardiovascular diseases are at higher risk for SARS-CoV-2 infection and tend to have a worse prognosis. However, the relevance and pathogenic mechanisms between COVID-19 and cardiovascular diseases are not yet completely comprehended.

METHODS

Common differentially expressed genes (DEGs) were obtained in datasets of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) infected with SARS-CoV-2 and myocardial tissues from heart failure patients. Further GO and KEGG pathway analysis, protein-protein interaction (PPI) network construction, hub genes identification, immune microenvironment analysis, and drug candidate predication were performed. Then, an isoproterenol-stimulated myocardial hypertrophy cell model and a transverse aortic constriction-induced mouse heart failure model were employed to validate the expression of hub genes.

RESULTS

A total of 315 up-regulated and 78 down-regulated common DEGs were identified. Functional enrichment analysis revealed mitochondrial metabolic disorders and extensive immune inflammation as the most prominent shared features of COVID-19 and cardiovascular diseases. Then, hub DEGs, as well as hub immune-related and mitochondria-related DEGs, were screened. Additionally, nine potential therapeutic agents for COVID-19-related cardiovascular diseases were proposed. Furthermore, the expression patterns of most of the hub genes related to cardiovascular diseases in the validation dataset along with cellular and mouse myocardial damage models, were consistent with the findings of bioinformatics analysis.

CONCLUSIONS

The study unveiled the molecular networks and signaling pathways connecting COVID-19 and cardiovascular diseases, which may provide novel targets for intervention of COVID-19-related cardiovascular diseases.

Nicotinamide mononucleotide as a therapeutic agent to alleviate multi-organ failure in sepsis

BACKGROUND

Sepsis-caused multi-organ failure remains the major cause of morbidity and mortality in intensive care units with limited therapeutics. Nicotinamide mononucleotide (NMN), a precursor of nicotinamide adenine dinucleotide (NAD+), has been recently reported to be protective in sepsis; however, its therapeutic effects remain to be determined. This study sought to investigate the therapeutic effects of NMN in septic organ failure and its underlying mechanisms.

METHODS

Sepsis was induced by feces-injection-in-peritoneum in mice. NMN was given after an hour of sepsis onset. Cultured neutrophils, macrophages and endothelial cells were incubated with various agents.

RESULTS

We demonstrate that administration of NMN elevated NAD+ levels and reduced serum lactate levels, oxidative stress, inflammation, and caspase-3 activity in multiple organs of septic mice, which correlated with the attenuation of heart dysfunction, pulmonary microvascular permeability, liver injury, and kidney dysfunction, leading to lower mortality. The therapeutic effects of NMN were associated with lower bacterial burden in blood, and less ROS production in septic mice. NMN improved bacterial phagocytosis and bactericidal activity of macrophages and neutrophils while reducing the lipopolysaccharides-induced inflammatory response of macrophages. In cultured endothelial cells, NMN mitigated mitochondrial dysfunction, inflammation, apoptosis, and barrier dysfunction induced by septic conditions, all of which were offset by SIRT3 inhibition.

CONCLUSION

NAD+ repletion with NMN prevents mitochondrial dysfunction and restrains bacterial dissemination while limiting inflammatory damage through SIRT3 signaling in sepsis. Thus, NMN may represent a therapeutic option for sepsis.

Calpain and Cardiometabolic Diseases

Calpain is defined as a member of the superfamily of cysteine proteases possessing the CysPC motif within the gene. Calpain-1 and -2, which are categorized as conventional isozymes, execute limited proteolysis in a calcium-dependent fashion. Accordingly, the calpain system participates in physiological and pathological phenomena, including cell migration, apoptosis, and synaptic plasticity. Recent investigations have unveiled the contributions of both conventional and unconventional calpains to the pathogenesis of cardiometabolic disorders. In the context of atherosclerosis, overactivation of conventional calpain attenuates the barrier function of vascular endothelial cells and decreases the immunosuppressive effects attributed to lymphatic endothelial cells. In addition, calpain-6 induces aberrant mRNA splicing in macrophages, conferring atheroprone properties. In terms of diabetes, polymorphisms of the calpain-10 gene can modify insulin secretion and glucose disposal. Moreover, conventional calpain reportedly participates in amino acid production from vascular endothelial cells to induce alteration of amino acid composition in the liver microenvironment, thereby facilitating steatohepatitis. Such multifaceted functionality of calpain underscores its potential as a promising candidate for pharmaceutical targets for the treatment of cardiometabolic diseases. Consequently, the present review highlights the pivotal role of calpains in the complications of cardiometabolic diseases and embarks upon a characterization of calpains as molecular targets.

Ginsenoside Rg1 attenuates diabetic vascular endothelial dysfunction by inhibiting the calpain-1/ROS/PKC-β axis

AIMS

Vascular endothelial dysfunction (VED) is the onset event of cardiovascular complications in type 2 diabetes mellitus. Ginsenoside Rg1 (Rg1) can improve the cardiovascular system, but its mechanism in diabetic vascular endothelial dysfunction has received little attention.

MAIN METHODS

Male calpain-1-knockout and wild-type C57BL/6 J mice were intraperitoneally injected with streptozotocin and treated with Rg1 (10 and 20 mg/kg) for 8 weeks. Human aortic endothelial cells (HAECs) were incubated with high glucose (HG) and were pretreated with Rg1 (10, 20 μM), MDL-28170 (calpain-1 inhibitor), LY-333531 (PKC-β inhibitor), NAC (ROS inhibitor) and calpain-1 overexpression. Then, factors related to mitochondrial dysfunction, oxidative stress and VED were measured.

KEY FINDINGS

The administration of Rg1 and calpain-1 knockout ameliorated diabetic mitochondrial dysfunction, oxidative stress and VED and inhibited the calpain-1/ROS/PKC-β axis. LY-333531 and NAC treatment restored destructive endothelium-dependent vasodilation in mice with diabetes, while pyrogallol (ROS agonist), PMA (PKC-β agonist) or L-NAME (eNOS inhibitor) treatment abrogated the protective effect of Rg1 against diabetic endothelial dysfunction. The administration of Rg1, MDL-28170, LY-333531 and NAC improved mitochondrial dysfunction, oxidative stress and VED, whereas the overexpression of calpain-1 amplified mitochondrial dysfunction, oxidative stress and VED and further upregulated the expression of PKC-β in HAECs exposed to HG. Overexpression of calpain-1 abrogated the protective effect of Rg1 against HG-induced oxidative stress and VED.

SIGNIFICANCE

These findings reveal that Rg1 can protect against VED by suppressing the calpain-1/ROS/PKC-β axis and alleviating the development of mitochondrial dysfunction and oxidative stress.

Augmentation of Cathepsin Isoforms in Diabetic db/db Mouse Kidneys Is Associated with an Increase in Renal MARCKS Expression and Proteolysis

The expression of the myristoylated alanine-rich C-kinase substrate (MARCKS) family of proteins in the kidneys plays an important role in the regulation of the renal epithelial sodium channel (ENaC) and hence overall blood pressure regulation. The function of MARCKS is regulated by post-translational modifications including myristoylation, phosphorylation, and proteolysis. Proteases known to cleave both ENaC and MARCKS have been shown to contribute to the development of high blood pressure, or hypertension. Here, we investigated protein expression and proteolysis of MARCKS, protein expression of multiple protein kinase C (PKC) isoforms, and protein expression and activity of several different proteases in the kidneys of diabetic db/db mice compared to wild-type littermate mice. In addition, MARCKS protein expression was assessed in cultured mouse cortical collecting duct (mpkCCD) cells treated with normal glucose and high glucose concentrations. Western blot and densitometric analysis showed less abundance of the unprocessed form of MARCKS and increased expression of a proteolytically cleaved form of MARCKS in the kidneys of diabetic db/db mice compared to wild-type mice. The protein expression levels of PKC delta and PKC epsilon were increased, while cathepsin B, cathepsin S, and cathepsin D were augmented in diabetic db/db kidneys compared to those of wild-type mice. An increase in the cleaved form of MARCKS was observed in mpkCCD cells cultured in high glucose compared to normal glucose concentrations. Taken together, these results suggest that high glucose may contribute to an increase in the proteolysis of renal MARCKS, while the upregulation of the cathepsin proteolytic pathway positively correlates with increased proteolysis of MARCKS in diabetic kidneys, where PKC expression is augmented.

SEVERE BURN-INDUCED MITOCHONDRIAL RECRUITMENT OF CALPAIN CAUSES ABERRANT MITOCHONDRIAL DYNAMICS AND HEART DYSFUNCTION

ABSTRACT

Mitochondrial damage is an important cause of heart dysfunction after severe burn injury. However, the pathophysiological process remains unclear. This study aims to examine the mitochondrial dynamics in the heart and the role of μ-calpain, a cysteine protease, in this scenario. Rats were subjected to severe burn injury treatment, and the calpain inhibitor MDL28170 was administered intravenously 1 h before or after burn injury. Rats in the burn group displayed weakened heart performance and decreased mean arterial pressure, which was accompanied by a diminishment of mitochondrial function. The animals also exhibited higher levels of calpain in mitochondria, as reflected by immunofluorescence staining and activity tests. In contrast, treatment with MDL28170 before any severe burn diminished these responses to a severe burn. Burn injury decreased the abundance of mitochondria and resulted in a lower percentage of small mitochondria and a higher percentage of large mitochondria. Furthermore, burn injury caused an increase in the fission protein DRP1 in the mitochondria and a decrease in the inner membrane fusion protein OPA1. Similarly, these alterations were also blocked by MDL28170. Of note, inhibition of calpain yielded the emergence of more elongated mitochondria along with membrane invagination in the middle of the longitude, which is an indicator of the fission process. Finally, MDL28170, administered 1 h after burn injury, preserved mitochondrial function and heart performance, and increased the survival rate. Overall, these results provided the first evidence that mitochondrial recruitment of calpain confers heart dysfunction after severe burn injury, which involves aberrant mitochondrial dynamics.

Calpain: the regulatory point of myocardial ischemia-reperfusion injury

Calpain is a conserved cysteine protease readily expressed in several mammalian tissues, which is usually activated by Ca²⁺ and with maximum activity at neutral pH. The activity of calpain is tightly regulated because its aberrant activation will nonspecifically cleave various proteins in cells. Abnormally elevation of Ca²⁺ promotes the abnormal activation of calpain during myocardial ischemia-reperfusion, resulting in myocardial injury and cardiac dysfunction. In this paper, we mainly reviewed the effects of calpain in various programmed cell death (such as apoptosis, mitochondrial-mediated necrosis, autophagy-dependent cell death, and parthanatos) in myocardial ischemia-reperfusion. In addition, we also discussed the abnormal activation of calpain during myocardial ischemia-reperfusion, the effect of calpain on myocardial repair, and the possible future research directions of calpain.

Rosmarinic acid protects against lipopolysaccharide-induced cardiac dysfunction via activating Sirt1/PGC-1α pathway to alleviate mitochondrial impairment

Sepsis-induced cardiomyopathy is a decisive factor that plays a critical role in the high mortality of septic patients in the critically ill. Mitochondrial dysfunction occurring during sepsis is a vital contributor to the pathogenesis of myocardial damage. Rosmarinic acid (RA), a natural poly-phenolic compound, has showed cardio-protective and mitochondrial protective effect. The present study was aimed to investigate the effect of RA on sepsis-induced cardiomyopathy. Adult mice were subjected to intraperitoneal injection of saline (control) or lipopolysaccharide (LPS, 5 mg/kg) to mimic sepsis-induced cardiomyopathy. Immediately after LPS challenge, vehicle or RA (100 mg/kg/day) was administrated via gavage. Cardiac function was examined with echocardiographic analyses 12 hours after LPS challenge and cumulative survival of mice was recorded for 8 days. Heart tissues were harvested 12 hours after LPS challenge to perform histological analyses and determine mitochondrial function. We found RA significantly improved cardiac function and survival of LPS-injected mice. Histologically, RA attenuated LPS-mediated cardiomyocyte damage, indicated by decreased cardiomyocyte apoptosis and improved myocardial swollen and disarrangement. Moreover, RA attenuated LPS-mediated myocardial mitochondrial dysfunction, indicated by improved mitochondrial ultrastructure, increased mitochondrial membrane potential (MMP), synthesis of adenosine triphosphate (ATP), markedly decreased reactive oxygen species (ROS) level and alleviated oxidative stress in heart tissues. RA treatment downregulated protein expression of Sirt1 and peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), and Sirt1 inhibition blocked protective effect of RA on LPS-induced myocardial damage and mitochondrial dysfunction. Collectively, RA attenuates LPS-induced cardiac dysfunction via activating Sirt1/PGC-1α pathway to alleviate mitochondrial impairment. It may be a promising cardio-protective drug to be used for septic patients.

Rosuvastatin Improves Endothelial Dysfunction in Diabetes by Normalizing Endoplasmic Reticulum Stress via Calpain-1 Inhibition

BACKGROUND

Rosuvastatin contributes to the improvement of vascular complications in diabetes, but the protective mechanisms remain unclear. The aim of the present study was to investigate the effect and mechanism of rosuvastatin on endothelial dysfunction induced by diabetes.

METHODS

Calpain-1 knockout (Capn1 EK684-/-) and C57BL/6 mice were intraperitoneally injected with STZ to induce type 1 diabetes. Human umbilical vein endothelial cells (HUVECs) were incubated with high glucose in this study. The function of isolated vascular rings, apoptosis, and endoplasmic reticulum stress (ERS) indicators were measured in this experiment.

RESULTS

The results showed that rosuvastatin (5 mg/kg/d) and calpain-1 knockout improved impaired vasodilation in an endothelial-dependent manner, and this effect was abolished by an ERS inducer. Rosuvastatin administration inhibited calpain-1 activation and ERS induced by high glucose, as well as apoptosis and oxidative stress both in vivo and in vitro. In addition, an ERS inducer (tunicamycin) offset the beneficial effect of rosuvastatin on endothelial dysfunction and ERS, which was accompanied by increased calpain-1 expression. The ERS inhibitor showed a similar improvement in endothelial dysfunction with rosuvastatin but could not increase the improvement in endothelial function of rosuvastatin.

CONCLUSION

These results suggested that rosuvastatin improves endothelial dysfunction by suppressing calpain- 1 and normalizing ERS, subsequently decreasing apoptosis and oxidative stress.

Serum level of calpains product as a novel biomarker of acute lung injury following cardiopulmonary bypass

OBJECTIVE

The aim of this study was to test the hypothesis whether serum level of calpains could become a meaningful biomarker for diagnosis of acute lung injury (ALI) in clinical after cardiac surgery using cardiopulmonary bypass (CPB) technology.

METHODS AND RESULTS

Seventy consecutive adults underwent cardiac surgery with CPB were included in this prospective study. Based on the American-European Consensus Criteria (AECC), these patients were divided into ALI (n = 20, 28.57%) and non-ALI (n = 50, 71.43%) groups. Serum level of calpains in terms of calpains' activity which was expressed as relative fluorescence unit (RFU) per microliter and measured at beginning of CPB (baseline), 1 h during CPB, end of CPB as well as 1, 12, and 24 h after CPB. Difference of serum level of calpains between two groups first appeared at the end of CPB and remained different at subsequent test points. Univariate and multivariate logistic regression analysis indicated that serum level of calpains 1 h after CPB was an independent predictor for postoperative ALI (OR 1.011, 95% CI 1.001, 1.021, p = 0.033) and correlated with a lower PaO₂/FiO₂ ratio in the first 2 days (The first day: r = -0.389, p < 0.001 and the second day: r = -0.320, p = 0.007) as well as longer mechanical ventilation time (r = 0.440, p < 0.001), intensive care unit (ICU) length of stay (LOS) (r = 0.419, p < 0.001) and hospital LOS (r = 0.297, p = 0.013).

CONCLUSION

Elevated serum level of calpains correlate with impaired lung function and poor clinical outcomes, indicating serum level of calpains could act as a potential biomarker for postoperative ALI following CPB in adults.

CLINICAL TRIAL REGISTRATION

[https://clinicaltrials.gov/show/NCT05610475], identifier [NCT05610475].

The mitochondrial electron transport chain contributes to calpain 1 activation during ischemia-reperfusion

Activation of calpain1 (CPN1) contributes to mitochondrial dysfunction during cardiac ischemia (ISC) - reperfusion (REP). Blockade of electron transport using amobarbital (AMO) protects mitochondria during ISC-REP, indicating that the electron transport chain (ETC) is a key source of mitochondrial injury. We asked if AMO treatment can decrease CPN1 activation as a potential mechanism of mitochondrial protection during ISC-REP. Buffer-perfused adult rat hearts underwent 25 min global ISC and 30 min REP. AMO (2.5 mM) or vehicle was administered for 1 min before ISC to block electron flow in the ETC. Hearts in the time control group were untreated and buffer perfused without ISC. Hearts were collected at the end of perfusion and used for mitochondrial isolation. ISC-REP increased both the cleavage of spectrin (indicating cytosolic CPN1 activation) in cytosol and the truncation of AIF (apoptosis inducing factor, indicating mitochondrial CPN1 activation) in subsarcolemmal mitochondria compared to time control. Thus, ISC-REP activated both cytosolic and mitochondrial CPN1. AMO treatment prevented the cleavage of spectrin and AIF during ISC-REP, suggesting that the transient blockade of electron transport during ISC decreases CPN1 activation. AMO treatment decreased the activation of PARP [poly(ADP-ribose) polymerase] downstream of AIF that triggers caspase-independent apoptosis. AMO treatment also decreased the release of cytochrome c from mitochondria during ISC-REP that prevented caspase 3 activation. These results support that the damaged ETC activates CPN1 in cytosol and mitochondria during ISC-REP, likely via calcium overload and oxidative stress. Thus, AMO treatment to mitigate mitochondrial-driven cardiac injury can decrease both caspase-dependent and caspase-independent programmed cell death during ISC-REP.

Calpain Inhibitor Calpeptin Alleviates Ischemia/Reperfusion-Induced Acute Kidney Injury via Suppressing AIM2 Inflammasome and Upregulating Klotho Protein

Renal ischemia/reperfusion injury is a major contributor of acute kidney injury (AKI), leading to renal cell necrosis, apoptosis, and inflammation. Calpains, a family of Ca²⁺-dependent cysteine proteases, play a pivotal role in the pathogenesis of renal diseases. Several studies have reported calpain inhibitors showing remarkable reno-protective effects against proteinuria and α-klotho deficiency-induced renal aging symptoms, particularly against glomerulus injury. However, little is known about the role of the calpain inhibitor calpeptin in acute kidney injury. The present study aims to investigate the potential mechanism of downregulation of Calpain 1 and 2 activity by calpeptin in the ischemia/reperfusion (IR)-induced AKI model. Firstly, we observed that the contents of Calpain 1 and 2 were significantly increased in the renal biopsy of clinical AKI patients, especially in the diseased tubules space. To investigate the impacts of calpain activity inhibition, we further pretreated with calpeptin in both the IR mouse model and in the HK-2 cells hypoxia model. We found that the calpain inhibitor calpeptin improved renal functional deterioration, attenuated pathological structure damage, and decreased tubular cell apoptosis in the IR injury-induced AKI mice model. Mechanistically, calpeptin significantly suppressed the AIM2 (absent in melanoma 2) and NLRP3 (NOD-like receptor protein 3) inflammasome signaling pathways and increased Klotho protein levels. Furthermore, immunofluorescence assays demonstrated that the application of calpeptin effectively inhibited Calpain 1 activation and gasdermin D (GSDMD) cleavage in the renal tubules of IR mice. Taken together, our both in vivo and in vitro experiments suggest that calpeptin conveyed reno-protection in AKI might be mediated by the inhibition of AIM2 inflammasome activation and upregulation of Klotho protein. As such, we provide new evidence that Calpain 1 and 2 activation may be closely associated with the pathogenesis of clinical AKI. The calpain-mediated AIM2 inflammasome signaling pathway and distinct interaction between calpain and Klotho may provide a potential novel preventative and therapeutic target for acute kidney injury.

Calpain-mediated protein targets in cardiac mitochondria following ischemia-reperfusion

Calpain 1 and 2 (CPN1/2) are calcium-dependent cysteine proteases that exist in cytosol and mitochondria. Pharmacologic inhibition of CPN1/2 decreases cardiac injury during ischemia (ISC)-reperfusion (REP) by improving mitochondrial function. However, the protein targets of CPN1/2 activation during ISC-REP are unclear. CPN1/2 include a large subunit and a small regulatory subunit 1 (CPNS1). Genetic deletion of CPNS1 eliminates the activities of both CPN1 and CPN2. Conditional cardiomyocyte specific CPNS1 deletion mice were used in the present study to clarify the role of CPN1/2 activation in mitochondrial damage during ISC-REP with an emphasis on identifying the potential protein targets of CPN1/2. Isolated hearts from wild type (WT) or CPNS1 deletion mice underwent 25 min in vitro global ISC and 30 min REP. Deletion of CPNS1 led to decreased cytosolic and mitochondrial calpain 1 activation compared to WT. Cardiac injury was decreased in CPNS1 deletion mice following ISC-REP as shown by the decreased infarct size compared to WT. Compared to WT, mitochondrial function was improved in CPNS1 deletion mice following ischemia-reperfusion as shown by the improved oxidative phosphorylation and decreased susceptibility to mitochondrial permeability transition pore opening. H2O2 generation was also decreased in mitochondria from deletion mice following ISC-REP compared to WT. Deletion of CPNS1 also resulted in less cytochrome c and truncated apoptosis inducing factor (tAIF) release from mitochondria. Proteomic analysis of the isolated mitochondria showed that deletion of CPNS1 increased the content of proteins functioning in regulation of mitochondrial calcium homeostasis (paraplegin and sarcalumenin) and complex III activity. These results suggest that activation of CPN1 increases cardiac injury during ischemia-reperfusion by impairing mitochondrial function and triggering cytochrome c and tAIF release from mitochondria into cytosol.

Calpain-mediated cleavage of mitochondrial fusion/fission proteins in acetaminophen-induced mice liver injury

Mitochondrial dysfunction was considered to be a critical event in acetaminophen (APAP) -induced hepatotoxicity. Recent studies suggest that abnormal mitochondrial dynamics contributes to mitochondrial dysfunction in APAP-induced liver injury, yet the underlying mechanisms responsible for deregulated mitochondrial dynamics remains elusive. In this study, C57BL/6 mice were used to establish a model of acute liver injury via intraperitoneal (i.p.) injection with overdose of APAP. Furthermore, calpain intervention experiments were achieved by the inhibitors ALLN or calpeptin. The activity of serum enzymes and pathological changes of APAP-treated mice were evaluated, and the critical molecules in mitochondrial dynamics and calpain degradative pathway were determined by electron microscopy, immunoblot and calpain activity kit. The results demonstrated that APAP overdose resulted in a severe liver injury, mitochondrial damage and an obvious cleavage of fusion/fission proteins. Meanwhile, the activation of calpain degradative machinery in liver were observed following APAP. By contrast, pretreatment of calpain inhibitors significantly inhibited the activation of calpains. Our further investigation found that ALLN or calpeptin administration significantly suppresses the changes of mitochondrial dynamics in APAP-treated mice and finally protected against APAP-induced hepatoxicity. Overall, these results suggest that calpain-mediated cleavage of mitochondrial dynamics proteins was involved in the pathogenic process of mitochondrial dysfunction and thus present a potential molecular coupling APAP-induced hepatotoxicity.

On the PHLPPside: Emerging roles of PHLPP phosphatases in the heart

PH domain leucine-rich repeat protein phosphatase (PHLPP) is a family of enzymes made up of two isoforms (PHLPP1 and PHLPP2), whose actions modulate intracellular activity via the dephosphorylation of specific serine/threonine (Ser/Thr) residues on proteins such as Akt. Recent data generated in our lab, supported by findings from others, implicates the divergent roles of PHLPP1 and PHLPP2 in maintaining cellular homeostasis since dysregulation of these enzymes has been linked to various pathological states including cardiovascular disease, diabetes, ischemia/reperfusion injury, musculoskeletal disease, and cancer. Therefore, development of therapies to modulate specific isoforms of PHLPP could prove to be therapeutically beneficial in several diseases especially those targeting the cardiovascular system. This review is intended to provide a comprehensive summary of current literature detailing the role of the PHLPP isoforms in the development and progression of heart disease.

Azathioprine pretreatment ameliorates myocardial ischaemia reperfusion injury in diabetic rats by reducing oxidative stress, apoptosis, and inflammation

This study was presented to observe the therapeutic effects of azathioprine (AZA) pretreatment on myocardial ischaemia reperfusion (I/R) damage in diabetic rats. All rats were randomly separated into control + sham operation; control +I/R; diabetes mellitus (DM) +I/R and DM +I/R + AZA groups. Diabetic rat models were established by intraperitoneally injecting 60 mg/kg streptozotocin (STZ). Diabetic rats were given 3 mg/kg AZA daily by gavage for 5 days. Then, myocardial I/R rat models were constructed. Myocardial infarction size and myocardial damage were respectively detected by TTC and H&E staining. Cardiac injury markers (CK-MB and MPO) and oxidative stress factors (SOD and MDA) were measured via ELISA. The protein expression of apoptotic markers (Caspase8, Caspase3, BAX and Bcl2), inflammatory factors (TLR4 and TNF-α) and AKT1/GSK3β in myocardial tissues was measured by western blot, immunohistochemistry or immunofluorescence. Data showed that AZA pretreatment could lessen myocardial infarction size and myocardial damage, and could down-regulate serum CK-MB, MPO, SOD and MDA levels in diabetic rats under I/R. Furthermore, AZA pretreatment decreased Caspase8, Caspase3, BAX, TLR4 and TNF-α expression, and increased Bcl2 expression in myocardial tissues of diabetic rats following I/R. Also, AZA pretreatment lowered AKT1, p-AKT1, GSK3β and p-GSK3β expression in diabetic heart after I/R. This study found that AZA may reduce myocardial injury in diabetic rats following I/R via reducing oxidative stress, cardiomyocyte apoptosis, and inflammatory response, which could be related to AKT1/GSK3β pathway inactivation.

Inhibition of calpain reduces cell apoptosis by suppressing mitochondrial fission in acute viral myocarditis

Cardiomyocyte apoptosis is critical for the development of viral myocarditis (VMC), which is one of the leading causes of cardiac sudden death in young adults. Our previous studies have demonstrated that elevated calpain activity is involved in the pathogenesis of VMC. This study aimed to further explore the underlying mechanisms. Neonatal rat cardiomyocytes (NRCMs) and transgenic mice overexpressing calpastatin were infected with coxsackievirus B3 (CVB3) to establish a VMC model. Apoptosis was detected with flow cytometry, TUNEL staining, and western blotting. Cardiac function was measured using echocardiography. Mitochondrial function was measured using ATP assays, JC-1, and MitoSOX. Mitochondrial morphology was observed using MitoTracker staining and transmission electron microscopy. Colocalization of dynamin-related protein 1 (Drp-1) in mitochondria was examined using immunofluorescence. Phosphorylation levels of Drp-1 at Ser637 site were determined using western blotting analysis. We found that CVB3 infection impaired mitochondrial function as evidenced by increased mitochondrial ROS production, decreased ATP production and mitochondrial membrane potential, induced myocardial apoptosis and damage, and decreased myocardial function. These effects of CVB3 infection were attenuated by inhibition of calpain both by PD150606 treatment and calpastatin overexpression. Furthermore, CVB3-induced mitochondrial dysfunction was associated with the accumulation of Drp-1 in the outer membrane of mitochondria and subsequent increase in mitochondrial fission. Mechanistically, calpain cleaved and activated calcineurin A, which dephosphorylated Drp-1 at Ser637 site and promoted its accumulation in the mitochondria, leading to mitochondrial fission and dysfunction. In summary, calpain inhibition attenuated CVB3-induced myocarditis by reducing mitochondrial fission, thereby inhibiting cardiomyocyte apoptosis.

Calpain-Mediated Mitochondrial Damage: An Emerging Mechanism Contributing to Cardiac Disease

Calpains belong to the family of calcium-dependent cysteine proteases expressed ubiquitously in mammals and many other organisms. Activation of calpain is observed in diseased hearts and is implicated in cardiac cell death, hypertrophy, fibrosis, and inflammation. However, the underlying mechanisms remain incompletely understood. Recent studies have revealed that calpains target and impair mitochondria in cardiac disease. The objective of this review is to discuss the role of calpains in mediating mitochondrial damage and the underlying mechanisms, and to evaluate whether targeted inhibition of mitochondrial calpain is a potential strategy in treating cardiac disease. We expect to describe the wealth of new evidence surrounding calpain-mediated mitochondrial damage to facilitate future mechanistic studies and therapy development for cardiac disease.

Therapeutic potential of targeting oxidative stress in diabetic cardiomyopathy

Even in the absence of coronary artery disease and hypertension, diabetes mellitus (DM) may increase the risk for heart failure development. This risk evolves from functional and structural alterations induced by diabetes in the heart, a cardiac entity termed diabetic cardiomyopathy (DbCM). Oxidative stress, defined as the imbalance of reactive oxygen species (ROS) has been increasingly proposed to contribute to the development of DbCM. There are several sources of ROS production including the mitochondria, NAD(P)H oxidase, xanthine oxidase, and uncoupled nitric oxide synthase. Overproduction of ROS in DbCM is thought to be counterbalanced by elevated antioxidant defense enzymes such as catalase and superoxide dismutase. Excess ROS in the cardiomyocyte results in further ROS production, mitochondrial DNA damage, lipid peroxidation, post-translational modifications of proteins and ultimately cell death and cardiac dysfunction. Furthermore, ROS modulates transcription factors responsible for expression of antioxidant enzymes. Lastly, evidence exists that several pharmacological agents may convey cardiovascular benefit by antioxidant mechanisms. As such, increasing our understanding of the pathways that lead to increased ROS production and impaired antioxidant defense may enable the development of therapeutic strategies against the progression of DbCM. Herein, we review the current knowledge about causes and consequences of ROS in DbCM, as well as the therapeutic potential and strategies of targeting oxidative stress in the diabetic heart.