Inflammation is an important process involved in several cardiovascular diseases (CVDs), and nod‐like receptor family pyrin domain containing 3 (NLRP3) inflammasome is a vital player in innate immunity and inflammation. In this review, we aim to provide a comprehensive summary of the current knowledge on the role and involvement of NLRP3 inflammasome in the pathogenesis and treatment of CVDs. NLRP3 inflammasome functions as a molecular platform, and triggers the activation of caspase‐1 and cleavage of pro‐IL‐1β, pro‐IL‐18, and gasdermin D (GSDMD). Cleaved NT‐GSDMD forms pores in the cell membrane and initiates pyroptosis, inducing cell death and release of many intracellular pro‐inflammatory molecules. NLRP3 inflammasome activation is triggered via inter‐related pathways downstream of K⁺ efflux, lysosomal disruption, and mitochondrial dysfunction. In addition, the Golgi apparatus and noncoding RNAs are gradually being recognized to play important roles in NLRP3 inflammasome activation. Many investigations have revealed the association between NLRP3 inflammasome and CVDs, including atherosclerosis, ischemia/reperfusion (I/R) injury and heart failure induced by pressure overload or cardiomyopathy. Some existing medications, including orthodox and natural medicines, used for CVD treatment have been newly discovered to act via NLRP3 inflammasome. In addition, NLRP3 inflammasome pathway components such as NLRP3, caspase‐1, and IL‐1β may be considered as novel therapeutic targets for CVDs. Thus, NLRP3 inflammasome is a key molecule involved in the pathogenesis of CVDs, and further research focused on development of NLRP3 inflammasome‐based targeted therapies for CVDs and the clinical evaluation of these therapies is essential.

Treatment options for myocarditis are currently limited. Inhibition of calpains has been shown to prevent Coxsackievirus B3 (CVB3)-induced cardiac injuries, but the underlying mechanism of action of calpains has not been elucidated. We investigated whether NOD-, LRR-, and pyrin domain-containing 3 (NLRP3) inflammasome participated in CVB3-induced myocarditis, and investigated the effects of calpain-1 on CVB3-induced cardiac injury. NLRP3 inflammasome was activated in CVB3-infected hearts, evidenced by elevated protein levels of NLRP3, N-terminal domain of Gasdermin D, and cleaved caspase-1, and the increased co-localization of NLRP3 and apoptosis-associated speck-like protein. The intraperitoneal administration of MCC950, a selective inhibitor of the NLRP3 inflammasome, led to decreased levels of serum creatine kinase-MB, cardiac troponin I, lactate dehydrogenase, interleukin-18, interleukin-1β, prevention of the infiltration of inflammatory cells, and improvement of cardiac function under CVB3 infection. Transgenic mice overexpressing the endogenous calpain inhibitor calpastatin (Tg-CAST mice) exhibited not only decreased apoptosis, inflammation, fibrosis, and enhanced cardiac function but also inhibition of NLRP3 inflammasome and pyroptosis. The selective inhibition of calpain-1 using PD151746 protected cardiomyocytes in vitro from CVB3 infection by downregulating NLRP3 inflammasome and, thus, preserved cell viability. Mechanistically, we showed that mitochondrial dysfunction preceded inflammatory response after CVB3 treatment and elimination of mitochondrial reactive oxygen species (ROS) using mitochondria-targeted antioxidants (mito-TEMPO) recapitalized the phenotype observed in Tg-CAST mice. Furthermore, the promotion or inhibition of calpain-1 activation in vitro regulated the mitochondrial respiration chain. Mito-TEMPO reversed calpain-1-mediated NLRP3 inflammation activation and cell death. We also found that mitochondrial calpain-1, which was increased after CVB3 stimulation, activated the NLRP3 inflammasome and resulted in cell death. Furthermore, ATP synthase-α (ATP5A1) was revealed to be the cleaving target of calpain-1 after CVB3 treatment. Downregulating ATP5A1 using ATP5A1-small interfering RNA impaired mitochondrial function, decreased cell viability, and induced NLRP3 inflammasome activation. In conclusion, CVB3 infection induced calpain-1 accumulation in mitochondria, and led to subsequent ATP5A1 cleavage, mitochondrial ROS overproduction, and impaired mitochondrial function, eventually causing NLRP3 inflammasome activation and inducing pyroptosis. Therefore, our findings established the role of calpain in viral myocarditis and unveiled its underlying mechanism of its action. Calpain appears as a promising target for the treatment of 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.

Backgrounds: Inflammation underlies the mechanism of different kinds of heart disease. Cytoplasmic membrane localized N‐terminal fragment of gasdermin‐D (GSDMD‐N) could induce inflammatory injury to cardiomyocyte. However, effects and dynamic changes of GSDMD during the process of lipopolysaccharide (LPS) related inflammatory stress induced cardiomyocyte injury are barely elucidated to date. In this study, LPS related cardiomyocyte injury was investigated based on potential interaction of GSDMD‐N induced mitochondrial injury and mitophagy mediated mitochondria quality control.Methods: HL‐1 cardiomyocytes were treated with LPS and Nigericin to induce inflammatory stress. The dual‐fluorescence‐labelled GSDMD expressed HL‐1 cardiomyocytes were constructed to study the translocation of GSDMD. The mitochondrial membrane potential (MMP) was measured by JC‐1 staining. Mitophagy and autophagic flux were recorded by transmission electron microscopy and fluorescent image.Results: GSDMD‐N showed a time‐dependent pattern of translocation from mitochondria to cytoplasmic membrane under LPS and Nigericin induced inflammatory stress in HL‐1 cardiomyocytes. GSDMD‐N preferred to localize to mitochondria to permeablize its membrane and dissipate the MMP. This effect couldn't be reversed by cyclosporine‐A (mPTP inhibitor), indicating GSDMD‐N pores as alternative mechanism underlying MMP regulation, in addition to mitochondrial permeability transition pore (mPTP). Moreover, the combination between GSDMD‐N and autophagy related Microtubule Associated Protein 1 Light Chain 3 Beta (LC3B) was verified by co‐immunoprecipitation. Besides, mitophagy alleviating GSDMD‐N induced mitochondrial injury was proved by pre‐treatment of autophagy antagonist or agonist in GSDMD‐knock out or GSDMD‐overexpression cells. A time‐dependent pattern of GSDMD translocation and mitochondrial GSDMD targeted mitophagy were verified.Conclusion: Herein, our study confirmed a crosstalk between GSDMD‐N induced mitochondrial injury and mitophagy mediated mitochondria quality control during LPS related inflammation induced cardiomyocyte injury, which potentially facilitating the development of therapeutic target to myocardial inflammatory disease. Our findings support pharmaceutical intervention on enhancing autophagy or inhibiting GSDMD as potential target for inflammatory heart disease treatment.

Exploring the immune mechanism of coxsackievirus B3 (CVB3)-induced myocarditis may provide a promising therapeutic strategy. Here, we investigated the regulatory role of macrophage CAPN4 in the phenotypic transformation of macrophages and NOD-like receptor protein 3 (NLRP3) inflammasome activation. We found that CAPN4 was the most upregulated subtype of the calpain family in CVB3-infected bone marrow-derived macrophages (BMDMs) and Raw 264.7 cells after CVB3 infection and was upregulated in cardiac macrophages from CVB3-infected mice. Conditional knockout of CAPN4 (CAPN4^flox/flox; LYZ2-Cre, CAPN4-cKO mice) ameliorated inflammation and myocardial injury and improved cardiac function and survival after CVB3 infection. Enrichment analysis revealed that macrophage differentiation and the interleukin signaling pathway were the most predominant biological processes in macrophages after CVB3 infection. We further found that CVB3 infection and the overexpression of CAPN4 promoted macrophage M1 polarization and NLRP3 inflammasome activation, while CAPN4 knockdown reversed these changes. Correspondingly, CAPN4-cKO alleviated CVB3-induced M1 macrophage transformation and NLRP3 expression and moderately increased M2 transformation in vivo. The culture supernatant of CAPN4-overexpressing or CVB3-infected macrophages impaired cardiac fibroblast function and viability. Moreover, macrophage CAPN4 could upregulate C/EBP-homologous protein (chop) expression, which increased proinflammatory cytokine release by activating the phosphorylation of transducer of activator of transcription 1 (STAT1) and 3 (STAT3). Overall, these results suggest that CAPN4 increases M1-type and inhibits M2-type macrophage polarization through the chop-STAT1/STAT3 signaling pathway to mediate CVB3-induced myocardial inflammation and injury. CAPN4 may be a novel target for viral myocarditis treatment.