Inhibition of chymotrypsin-like activity of the proteasome by ixazomib prevents mitochondrial dysfunction during myocardial ischemia

Quercetin inhibits cardiomyocyte apoptosis via Sirt3/SOD2/mitochondrial reactive oxygen species during myocardial ischemia-reperfusion injury

Background

Myocardial ischemia/reperfusion injury (MI/RI) can lead to impaired cardiac function. Quercetin (Que) has a positive effect and improves MI/RI. Sirtuin-3 (Sirt3) is a deacetylase that ameliorates oxidative stress and is associated with MI/RI. This study aimed to investigate the molecular mechanism by which Que protects cardiac function against MI/RI through the Sirt3 signaling pathway.

Methods

We conducted experiments by constructing hypoxia/reoxygenation (H/R) cardiomyocytes and MI/RI rat models. H9C2 cells were transfected with siRNA-Sirt3. Cardiomyocyte apoptosis was examined by TUNEL and Western blotting. The oxidative stress index was also determined. Mitochondrial reactive oxygen species (ROS) activity assays, ATP assays and mitochondrial membrane potential assays were performed. Evans Blue/TTC staining was used to examine surviving myocardial tissue.

Results

In the constructed H/R cells and MI/RI animal models, it was found that myocardial cell apoptosis increased (Bcl-2 expression was downregulated; Bax and cleaved caspase-3/8/9 expression were upregulated). In addition, oxidative stress levels increased (MDA levels increased; SOD, CAT, GSH-Px levels decreased), myocardial tissue was damaged (LDH, CK content increased), Sirt3 expression was downregulated, acetylation levels of superoxide dismutase 2 (SOD2) increased (AC-SOD2), and mitochondrial ROS increased. Que treatment alleviated the effects of MI/RI on cardiomyocytes and rats. Sirt3 expression and activity were upregulated, SOD2 acetylation was decreased, and mitochondrial ROS production was reduced by Que treatment. After Sirt3 was knocked down, we found that AC-SOD2 expression was upregulated and mitochondrial ROS were increased in H/R cardiomyocytes, further increased the degree of injury, while Que treatment attenuated the effect of Sirt3 knockdown on H/R cardiomyocytes.

Conclusion

Que inhibits cardiomyocyte apoptosis, reduces oxidative stress levels, protects mitochondrial function and prevents the impairment of cardiac function during MI/RI via the Sirt3/SOD2/mitochondrial ROS pathway.

Targeting the immunoproteasome in hypothalamic neurons as a novel therapeutic strategy for high-fat diet-induced obesity and metabolic dysregulation

OBJECTIVE

Obesity represents a significant global health challenge characterized by chronic low-grade inflammation and metabolic dysregulation. The hypothalamus, a key regulator of energy homeostasis, is particularly susceptible to obesity's deleterious effects. This study investigated the role of the immunoproteasome, a specialized proteasomal complex implicated in inflammation and cellular homeostasis, during metabolic diseases.

METHODS

The levels of the immunoproteasome β5i subunit were analyzed by immunostaining, western blotting, and proteasome activity assay in mice fed with either a high-fat diet (HFD) or a regular diet (CHOW). We also characterized the impact of autophagy inhibition on the levels of the immunoproteasome β5i subunit and the activation of the AKT pathway. Finally, through confocal microscopy, we analyzed the contribution of β5i subunit inhibition on mitochondrial function by flow cytometry and mitophagy assay.

RESULTS

Using an HFD-fed obese mouse model, we found increased immunoproteasome levels in hypothalamic POMC neurons. Furthermore, we observed that palmitic acid (PA), a major component of saturated fats found in HFD, increased the levels of the β5i subunit of the immunoproteasome in hypothalamic neuronal cells. Notably, the increase in immunoproteasome expression was associated with decreased autophagy, a critical cellular process in maintaining homeostasis and suppressing inflammation. Functionally, PA disrupted the insulin-glucose axis, leading to reduced AKT phosphorylation and increased intracellular glucose levels in response to insulin due to the upregulation of the immunoproteasome. Mechanistically, we identified that the protein PTEN, a key regulator of insulin signaling, was reduced in an immunoproteasome-dependent manner. To further investigate the potential therapeutic implications of these findings, we used ONX-0914, a specific immunoproteasome inhibitor. We demonstrated that this inhibitor prevents PA-induced insulin-glucose axis imbalance. Given the interplay between mitochondrial dysfunction and metabolic disturbances, we explored the impact of ONX-0914 on mitochondrial function. Notably, ONX-0914 preserved mitochondrial membrane potential and attenuated mitochondrial ROS production in the presence of PA. Moreover, we found that ONX-0914 reduced mitophagy in the presence of PA.

CONCLUSIONS

Our findings strongly support the pathogenic involvement of the immunoproteasome in hypothalamic neurons in the context of HFD-induced obesity and metabolic disturbances. Targeting the immunoproteasome highlights a promising therapeutic strategy to mitigate the detrimental effects of obesity on the insulin-glucose axis and cellular homeostasis. This study provides valuable insights into the mechanisms driving obesity-related metabolic diseases and offers potential avenues for developing novel therapeutic interventions.

MgIG exerts therapeutic effects on crizotinib-induced hepatotoxicity by limiting ROS-mediated autophagy and pyroptosis

Crizotinib (CRIZO) has been widely employed to treat non‐small‐cell lung cancer. However, hepatic inflammatory injury is the major toxicity of CRIZO, which limits its clinical application, and the underlying mechanism of CRIZO‐induced hepatotoxicity has not been fully explored. Herein, we used cell counting kit‐8 assay and flow cytometry to detect CRIZO‐induced cytotoxicity on human hepatocytes (HL‐7702). CRIZO significantly reduced the survival rate of hepatocytes in a dose‐dependent manner. Furthermore, the reactive oxygen species (ROS) assay kit showed that CRIZO treatment strongly increased the level of ROS. In addition, CRIZO treatment caused the appearance of balloon‐like bubbles and autophagosomes in HL‐7702 cells. Subsequently, Western blotting, quantitative real‐time PCR and ELISA assays revealed that ROS‐mediated pyroptosis and autophagy contributed to CRIZO‐induced hepatic injury. Based on the role of ROS in CRIZO‐induced hepatotoxicity, magnesium isoglycyrrhizinate (MgIG) was used as an intervention drug. MgIG activated the Nrf2/HO‐1 signalling pathway and reduced ROS level. Additionally, MgIG suppressed hepatic inflammation by inhibiting NF‐κB activity, thereby reducing CRIZO‐induced hepatotoxicity. In conclusion, CRIZO promoted autophagy activation and pyroptosis via the accumulation of ROS in HL‐7702 cells. MgIG exerts therapeutic effects on CRIZO‐induced hepatotoxicity by decreasing the level of ROS.

Identification of the metabolic remodeling profile in the early-stage of myocardial ischemia and the contributory role of mitochondrion

Cardiac remodeling is the primary pathological feature of chronic heart failure. Prompt inhibition of remodeling in acute coronary syndrome has been a standard procedure, but the morbidity and mortality are still high. Exploring the characteristics of ischemia in much earlier stages and identifying its biomarkers are essential for introducing novel mechanisms and therapeutic strategies. Metabolic and structural remodeling of mitochondrion is identified to play key roles in ischemic heart disease. The mitochondrial metabolic features in early ischemia have not previously been described. In the present study, we established a mouse heart in early ischemia and explored the mitochondrial metabolic profile using metabolomics analysis. We also discussed the role of mitochondrion in the global cardiac metabolism. Transmission electron microscopy revealed that mitochondrial structural injury was invoked at 8 minutes post-coronary occlusion. In total, 75 metabolites in myocardium and 26 in mitochondria were screened out. About 23% of the differentiated metabolites in mitochondria overlapped with the differentiated metabolites in myocardium; Total 81% of the perturbed metabolic pathway in mitochondria overlapped with the perturbed pathway in myocardium, and these pathways accounted for 50% of the perturbed pathway in myocardium. Purine metabolism was striking and mechanically important. In conclusion, in the early ischemia, myocardium exacerbated metabolic remodeling. Mitochondrion was a contributor to the myocardial metabolic disorder. Purine metabolism may be a potential biomarker for early ischemia diagnosis. Our study introduced a perspective for prompt identification of ischemia.

Communication Between Cardiomyocytes and Fibroblasts During Cardiac Ischemia/Reperfusion and Remodeling: Roles of TGF-β, CTGF, the Renin Angiotensin Axis, and Non-coding RNA Molecules

Communication between cells is a foundational concept for understanding the physiology and pathology of biological systems. Paracrine/autocrine signaling, direct cell-to-cell interplay, and extracellular matrix interactions are three types of cell communication that regulate responses to different stimuli. In the heart, cardiomyocytes, fibroblasts, and endothelial cells interact to form the cardiac tissue. Under pathological conditions, such as myocardial infarction, humoral factors released by these cells may induce tissue damage or protection, depending on the type and concentration of molecules secreted. Cardiac remodeling is also mediated by the factors secreted by cardiomyocytes and fibroblasts that are involved in the extensive reciprocal interactions between these cells. Identifying the molecules and cellular signal pathways implicated in these processes will be crucial for creating effective tissue-preserving treatments during or after reperfusion. Numerous therapies to protect cardiac tissue from reperfusion-induced injury have been explored, and ample pre-clinical research has attempted to identify drugs or techniques to mitigate cardiac damage. However, despite great success in animal models, it has not been possible to completely translate these cardioprotective effects to human applications. This review provides a current summary of the principal molecules, pathways, and mechanisms underlying cardiomyocyte and cardiac fibroblast crosstalk during ischemia/reperfusion injury. We also discuss pre-clinical molecules proposed as treatments for myocardial infarction and provide a clinical perspective on these potential therapeutic agents.

Hydroxysafflor Yellow A Ameliorates Myocardial Ischemia/Reperfusion Injury by Suppressing Calcium Overload and Apoptosis

Myocardial ischemia/reperfusion injury (MI/RI) is an urgent problem with a great impact on health globally. However, its pathological mechanisms have not been fully elucidated. Hydroxysafflor yellow A (HSYA) has a protective effect against MI/RI. This study is aimed at further clarifying the relationship between HSYA cardioprotection and calcium overload as well as the underlying mechanisms. We verified the protective effect of HSYA on neonatal rat primary cardiomyocytes (NPCMs) and human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from hypoxia-reoxygenation (HR) injury. To explore the cardioprotective mechanism of HSYA, we employed calcium fluorescence, TUNEL assay, JC-1 staining, and western blotting. Finally, cardio-ECR and patch-clamp experiments were used to explain the regulation of L-type calcium channels (LTCC) in cardioprotection mediated by HSYA. The results showed that HSYA reduced the levels of myocardial enzymes and protected NPCMs from HR injury. HSYA also restored the contractile function of hiPSC-CMs and field potential signal abnormalities caused by HR and exerted a protective effect on cardiac function. Further, we demonstrated that HSYA protects cardiomyocytes from HR injury by decreasing mitochondrial membrane potential and inhibiting apoptosis and calcium overload. Patch-clamp results revealed that MI/RI caused a sharp increase in calcium currents, which was inhibited by pretreatment with HSYA. Furthermore, we found that HSYA restored contraction amplitude, beat rate, and field potential duration of hiPSC-CMs, which were disrupted by the LTCC agonist Bay-K8644. Patch-clamp experiments also showed that HSYA inhibits Bay-K8644-induced calcium current, with an effect similar to that of the LTCC inhibitor nisoldipine. Therefore, our data suggest that HSYA targets LTCC to inhibit calcium overload and apoptosis of cardiomyocytes, thereby exerting a cardioprotective effect and reducing MI/RI injury.

Bortezomib alleviates myocardial ischemia reperfusion injury via enhancing of Nrf2/HO-1 signaling pathway

Bortezomib is a classical proteasome inhibitor and previous researches have reported its roles of anti-oxidation and anti-inflammatory functions in various diseases. However, the role of Bortezomib in myocardial ischemia reperfusion injury (MIRI) is unclear. Thus, our research seeks to reveal the protective effects of Bortezomib pretreatment in the mice model of MIRI. First, by the optimization of Bortezomib concentration and pretreatment timepoints, we found that 0.5 mg/kg Bortezomib pretreatment 2 h before MIRI significantly attenuated pathological damage and neutrophil infiltration. Then we found that pretreatment with Bortezomib obviously increased myocardial systolic function ((left ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS)) and decreased infarct size, as well as serum Troponin T levels. Meanwhile, Bortezomib pretreatment also remarkably augmented oxidative stress related protein levels of Superoxide dismutase [Cu-Zn] (SOD1), Catalase (CAT) and Glutathione (GSH), while reactive oxygen species (ROS) contents and Malonaldehyde (MDA) protein level were significantly reduced. Mechanistically, Bortezomib pretreatment significantly promoted nuclear translocation of transcriptional factor nuclear factor erythroid 2-related factor 2(Nrf2) and Heme Oxygenase 1(HO-1) expression. Interestingly, co-treatment with ML-385, a new type and selective Nrf2 inhibitor, counteracted antioxidative effects induced by Bortezomib pretreatment. In conclusion, Bortezomib pretreatment mitigates MIRI by inhibiting oxidative damage which is regulated by Nrf2/HO-1 signaling pathway.

The ubiquitin-proteasome system and its crosstalk with mitochondria as therapeutic targets in medicine

The ubiquitin-proteasome system constitutes a major pathway for protein degradation in the cell. Therefore the crosstalk of this pathway with mitochondria is a major topic with direct relevance to many mitochondrial diseases. Proteasome dysfunction triggers not only protein toxicity, but also mitochondrial dysfunction. The involvement of proteasomes in the regulation of protein transport into mitochondria contributes to an increase in mitochondrial function defects. On the other hand, mitochondrial impairment stimulates reactive oxygen species production, which increases protein damage, and protein misfolding and aggregation leading to proteasome overload. Concurrently, mitochondrial dysfunction compromises cellular ATP production leading to reduced protein ubiquitination and proteasome activity. In this review we discuss the complex relationship and interdependence of the ubiquitin-proteasome system and mitochondria. Furthermore, we describe pharmacological inhibition of proteasome activity as a novel strategy to treat a group of mitochondrial diseases.