The immunoproteasome subunit ß2i ameliorates myocardial ischemia/reperfusion injury by regulating Parkin-Mfn1/2-mediated mitochondrial fusion.

Mitochondrial dynamics are critical for maintaining mitochondrial morphology and function during cardiac ischemia and reperfusion (I/R). The immunoproteasome complex is an inducible isoform of the proteasome that plays a key role in modulating inflammation and some cardiovascular diseases, but the importance of immunoproteasome catalytic subunit ß2i (also known as LMP10 or MECL1) in regulating mitochondrial dynamics and cardiac I/R injury is largely unknown. Here, using ß2i-knockout (KO) mice and rAAV9-ß2i-injected mice, we discovered that ß2i expression and its trypsin-like activity were significantly attenuated in the mouse I/R myocardium and in patients with myocardial infarction (MI). Moreover, ß2i-KO mice exhibited greatly enhanced I/R-mediated cardiac dysfunction, infarct size, myocyte apoptosis and oxidative stress accompanied by excessive mitochondrial fission due to Mfn1/2 and Drp1 imbalance. Conversely, cardiac overexpression of ß2i in mice injected with recombinant adeno-associated virus 9 (rAAV9)-ß2i ameliorated cardiac I/R injury. Mechanistically, I/R injury reduced ß2i expression and activity, which increased the expression of the E3 ligase Parkin protein and promoted the degradation of mitofusin 1/2 (Mfn1/2), leading to excessive mitochondrial fission. In conclusion, our data suggest for the first time that ß2i exerts a protective role against cardiac I/R injury and that increasing ß2i expression may be a new therapeutic option for cardiac ischemic disease in clinical practice. Graphical abstract showing how the immunoproteasome subunit ß2i ameliorates myocardial I/R injury by regulating Parkin-Mfn1/2-mediated mitochondrial fusion.

TCH-165 attenuates cardiac ischaemia/reperfusion injury by balancing mitochondrial dynamics via increasing proteasome activity.

The proteasome is the main complex responsible for maintaining intracellular protein homeostasis, impairment of which is associated with cardiac ischaemia/reperfusion (I/R) injury. The small molecule TCH-165 has been found to activate the 20S proteasome to remove disordered proteins in multiple myeloma and glioblastoma. However, the preventive effect of TCH-165 against I/R-mediated cardiac impairment in mice remains largely unknown. Here, a cardiac I/R model was established in mice. Heart function was assessed with echocardiography. Cardiac infarction, myocyte death, and superoxide level were evaluated by 2,3,5-triphenyltetrazolium chloride (TTC)-Evans blue staining, terminal deoxynucleotidyl transferase-mediated dUTP nick and labelling (TUNEL) assay and immunostaining, respectively. Our results showed that TCH-165 treatment markedly ameliorated I/R-mediated cardiac dysfunction and decreased the infarct size, apoptosis, and superoxide levels. Mechanistically, TCH-165 increased immunoproteasome subunit expression/activity, increasing pro-fission protein dynamin-1-like protein (DNM1L, also known as DRP1) degradation and the expression of the pro-fusion proteins mitofusin 1/2 (Mfn1/2) and thereby leading to mitochondrial fission/fusion balance. In vitro experiments confirmed that inhibition of proteasome activity by epoxomicin abolished the protective effect of TCH-165 against hypoxia/reoxygenation (H/R)-induced increases in cardiomyocyte apoptosis, superoxide production and mitochondrial fission. In summary, TCH-165 is a newly discovered inducer of immunoproteasome activity that exerts a preventive effect against cardiac I/R damage by targeting Drp1 degradation, indicating that it may be as a potential therapeutic candidate for ischaemic heart disease.

MK-886 protects against cardiac ischaemia/reperfusion injury by activating proteasome-Keap1-NRF2 signalling.

Oxidative stress is considered a key factor contributing to the initiation and development of cardiac injury following ischaemia‒reperfusion (I/R). Arachidonate 5-lipoxygenase (ALOX5) is a rate-limiting enzyme for leukotriene biosynthesis. MK-886 is an inhibitor of ALOX5 that exhibits anti-inflammatory and antioxidant activities. However, the significance of MK-886 in preventing I/R-mediated cardiac injury and the underlying mechanism remain unclear. Cardiac I/R model was produced by ligation/release of the left anterior descending artery. MK-886 (20 mg/kg) was administered intraperitoneally into mice at 1 and 24 h before I/R. Our results indicated that MK-886 treatment significantly attenuated I/R-mediated cardiac contractile dysfunction and decreased the infarct area, myocyte apoptosis, and oxidative stress accompanied with reduction of Kelch-like ECH-associated protein 1 (keap1) and upregulation of nuclear factor erythroid 2-related factor 2 (NRF2). Conversely, administration of the proteasome inhibitor epoxomicin and NRF2 inhibitor ML385 greatly abrogated MK-886-mediated cardioprotection after I/R injury. Mechanistically, MK-886 enhanced the expression of the immunoproteasome subunit ß5i, which interacted with keap1 and enhanced its degradation, leading to activation of the NRF2-dependent antioxidant response and improvement of mitochondrial fusion-fission balance in the I/R-treated heart. In summary, our present findings indicated that MK-886 could protect the heart against I/R injury and highlight that MK-886 may represent a promising therapeutic candidate for preventing ischaemic disease.