Enhanced nuclear localization of phosphorylated MLKL predicts adverse events in patients with dilated cardiomyopathy

Necroptosis: a significant and promising target for intervention of cardiovascular disease

Due to changes in dietary structures, population aging, and the exacerbation of metabolic risk factors, the incidence of cardiovascular disease continues to rise annually, posing a significant health burden worldwide. Cell death plays a crucial role in the onset and progression of cardiovascular diseases. As a regulated endpoint encountered by cells under adverse stress conditions, the execution of necroptosis is regulated by classicalpathways, the calmodulin-dependent protein kinases (CaMK) pathway, and mitochondria-dependent pathways, and implicated in various cardiovascular diseases, including atherosclerosis, myocardial infarction, myocardial ischemia-reperfusion injury (IRI), heart failure, diabetic cardiomyopathy, dilated cardiomyopathy, hypertrophic cardiomyopathy, chemotherapy drug-induced cardiomyopathy, and abdominal aortic aneurysm (AAA). To further investigate potential therapeutic targets for cardiovascular diseases, we also analyzed the main molecules and their inhibitors involved in necroptosis in an effort to uncover insights for treatment.

Inflammatory adhesion mediates myocardial segmental necroptosis induced by mixed lineage kinase domain-like protein in acute myocardial infarction

PURPOSE

Cardiomyocyte death is a major cytopathologic response in acute myocardial infarction (AMI) and involves complex inflammatory interactions. Although existing reports indicating that mixed lineage kinase domain-like protein (MLKL) is involved in macrophage necroptosis and inflammasome activation, the downstream mechanism of MLKL in necroptosis remain poorly characterized in AMI.

METHODS

MLKL knockout mice (MLKLKO), RIPK3 knockout mice (RIPK3KO), and macrophage-specific MLKL conditional knockout mice (MLKLM-KO) were established. AMI was induced by coronary artery ligation. The role of MLKL in regulating myocardial morphological necroptosis was evaluated using immunofluorescence staining, flow cytometry, qRT-PCR, Western blot, CCK-8 assay, and ELISA.

RESULTS

Our findings revealed that myocardial segmental necroptosis (MSN), a unique morphological characteristics of cell death observed post-AMI, was promoted by intercellular inflammatory adhesion mediated by MLKL. The key features of MSN included localized cytomembrane perforation, segmental attenuation of myofilaments, MLKL-mediated filling, and macrophage inflammatory adhesion. In a mouse model of AMI, we observed MSN, which was absent in immunosuppressed mice. Pharmacological depletion of macrophages or genetic knockout of macrophage-specific MLKL (MLKLM-KO) reduced the occurrence of MSN. This reduction was reversed upon reinfusion of wild-type macrophages. Additionally, myocardial injury was significantly ameliorated in MLKLM-KO mice following AMI. In a macrophage-cardiomyocyte co-culture system, MLKLM-KO attenuated hypoxia-induced MSN and inhibited macrophage-mediated inflammatory adhesion. Furthermore, MLKL was found to trigger the formation of membrane pores and the polymerization of integrin αvβ1, thereby enhancing inflammatory adhesion in the co-culture system. Notably, MLKL-enhanced inflammatory adhesion was not entirely dependent on RIPK3.

CONCLUSION

Our study demonstrates that MLKL is directly involved in myocardial segmental necroptosis by interacting with macrophages through inflammatory adhesion, and possibly independently of RIPK3.

Prognostic signature and therapeutic drug identification for dilated cardiomyopathy based on necroptosis via bioinformatics and experimental validation

Necroptosis, a type of programmed cell death, has been increasingly linked to cardiovascular disease development, yet its role in dilated cardiomyopathy (DCM) remains unclear. In this study, we analyzed the GSE5406 dataset from the GEO database to explore necroptosis-related prognostic signatures in DCM using LASSO regression. We identified five necroptosis-related genes (BID, CAMK2B, GLUL, HSP90AB1, CHMP5) that define a necroptosis-related signature with strong predictive value, evidenced by ROC curve areas of 0.852 and 0.957 in training and test sets, respectively. Our analyses, including GO and GSEA enrichment, focused on pathways associated with high necroptosis-related scores (NRS) and revealed significant immune cell infiltration. Notably, nTreg and iTreg cells were enriched in the high NRS group, while CD8 naive T cells and CD8 T cells positively correlated with NRS. Small molecule drugs fenofibrate, procyclidine, and tienilic acid emerged as potential therapeutic agents for high-risk patients, with fenofibrate showing efficacy in inhibiting DCM progression in an inflammatory animal model. These findings underscore the clinical relevance of necroptosis-related genes in assessing DCM progression and prognosis and highlight their potential for targeted therapeutic development.

Contribution of MLKL to the development of doxorubicin-induced cardiomyopathy and its amelioration by rapamycin

Necroptosis, necrosis characterized by RIPK3-MLKL activation, has been proposed as a mechanism of doxorubicin (DOX)-induced cardiomyopathy. We showed that rapamycin, an mTORC1 inhibitor, attenuates cardiomyocyte necroptosis. Here we examined role of MLKL in DOX-induced myocardial damage and protective effects of rapamycin. Cardiomyopathy was induced in mice by intraperitoneal injections of DOX (10 mg/kg, every other day) and followed for 7 days. DOX-treated mice showed a significant decline in LVEF assessed by cardiac MRI (45.5 ± 5.1% vs. 65.4 ± 4.2%), reduction in overall survival rates, and increases in myocardial RIPK3 and MLKL expression compared with those in vehicle-treated mice, and those changes were prevented by administration of rapamycin (0.25 mg/kg) before DOX injection. In immunohistochemical analyses, p-MLKL signals were detected in the cardiomyocytes of DOX-treated mice, and the signals were reduced by rapamycin. Mlkl+/- and Mlkl-/- mice were similarly resistant to DOX-induced cardiac dysfunction, indicating that a modest reduction in MLKL level is sufficient to prevent the development of DOX-induced cardiomyopathy. However, evidence of cardiomyocyte necrosis assessed by C9 immunostaining, presence of replacement fibrosis, and electron microscopic analyses was negligible in the myocardium of DOX-treated mice. Thus, MLKL-mediated signaling contributes to DOX-induced cardiac dysfunction primarily by a necrosis-independent mechanism, which is inhibitable by rapamycin.

Luteolin-7-O-β-d-glucuronide Ameliorates Cerebral Ischemic Injury: Involvement of RIP3/MLKL Signaling Pathway

Luteolin-7-O-β-d-glucuronide (LGU) is a major active flavonoid glycoside compound that is extracted from Ixeris sonchifolia (Bge.) Hance, and it is a Chinese medicinal herb mainly used for the treatment of coronary heart disease, angina pectoris, cerebral infarction, etc. In the present study, the neuroprotective effect of LGU was investigated in an oxygen glucose deprivation (OGD) model and a middle cerebral artery occlusion (MCAO) rat model. In vitro, LGU was found to effectively improve the OGD-induced decrease in neuronal viability and increase in neuronal death by a 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and a lactate dehydrogenase (LDH) leakage rate assay, respectively. LGU was also found to inhibit OGD-induced intracellular Ca2+ overload, adenosine triphosphate (ATP) depletion, and mitochondrial membrane potential (MMP) decrease. By Western blotting analysis, LGU significantly inhibited the OGD-induced increase in expressions of receptor-interacting serine/threonine-protein kinase 3 (RIP3) and mixed lineage kinase domain-like protein (MLKL). Moreover, molecular docking analysis showed that LGU might bind to RIP3 more stably and firmly than the RIP3 inhibitor GSK872. Immunofluorescence combined with confocal laser analyses disclosed that LGU inhibited the aggregation of MLKL to the nucleus. Our results suggest that LGU ameliorates OGD-induced rat primary cortical neuronal injury via the regulation of the RIP3/MLKL signaling pathway in vitro. In vivo, LGU was proven, for the first time, to protect the cerebral ischemia in a rat middle cerebral artery occlusion (MCAO) model, as shown by improved neurological deficit scores, infarction volume rate, and brain water content rate. The present study provides new insights into the therapeutic potential of LGU in cerebral ischemia.

Regulated cell death pathways in cardiomyopathy

Heart disease is a worldwide health menace. Both intractable primary and secondary cardiomyopathies contribute to malignant cardiac dysfunction and mortality. One of the key cellular processes associated with cardiomyopathy is cardiomyocyte death. Cardiomyocytes are terminally differentiated cells with very limited regenerative capacity. Various insults can lead to irreversible damage of cardiomyocytes, contributing to progression of cardiac dysfunction. Accumulating evidence indicates that majority of cardiomyocyte death is executed by regulating molecular pathways, including apoptosis, ferroptosis, autophagy, pyroptosis, and necroptosis. Importantly, these forms of regulated cell death (RCD) are cardinal features in the pathogenesis of various cardiomyopathies, including dilated cardiomyopathy, diabetic cardiomyopathy, sepsis-induced cardiomyopathy, and drug-induced cardiomyopathy. The relevance between abnormity of RCD with adverse outcome of cardiomyopathy has been unequivocally evident. Therefore, there is an urgent need to uncover the molecular and cellular mechanisms for RCD in order to better understand the pathogenesis of cardiomyopathies. In this review, we summarize the latest progress from studies on RCD pathways in cardiomyocytes in context of the pathogenesis of cardiomyopathies, with particular emphasis on apoptosis, necroptosis, ferroptosis, autophagy, and pyroptosis. We also elaborate the crosstalk among various forms of RCD in pathologically stressed myocardium and the prospects of therapeutic applications targeted to various cell death pathways.

A year in heart failure: updates of clinical and preclinical findings

We witnessed major advances in the management of heart failure (HF) in 2022. Results of recent clinical and preclinical investigations aid preventive strategies, diagnostic efforts, and therapeutic interventions, and collectively, they hold promises for a more effective HF care for the near future. Accordingly, currently available information extends the 2021 European Society of Cardiology guidelines and provides a solid background for the introduction of improved clinical approaches in the number of HF-related cases. Elaboration on the relationships between epidemiological data and risk factors lead to better understanding of the pathophysiology of HF with reduced ejection fraction and HF with preserved ejection fraction. The clinical consequences of valvular dysfunctions are increasingly interpreted not only in their haemodynamic consequences but also in association with their pathogenetic factors and modern corrective treatment possibilities. The influence of coronavirus disease 2019 pandemic on the clinical care of HF appeared to be less intense in 2022 than before; hence, this period allowed to refine coronavirus disease 2019 management options for HF patients. Moreover, cardio-oncology emerges as a new subdiscipline providing significant improvements in clinical outcomes for oncology patients. Furthermore, the introduction of state-of-the-art molecular biologic methods, multi-omic approaches forecast improved phenotyping and precision medicine for HF. All above aspects are addressed in this article that highlights a selection of papers published in ESC Heart Failure in 2022.

Progress in study on the final executor of necroptosis MLKL and its inhibitors

Necroptosis is one of the regulated cell death, which involves receptor interacting protein kinase (RIPK) 1/RIPK3/mixed lineage kinase domain like protein (MLKL) signaling pathway. Among them, MLKL is the final execution of necroptosis. The formation of RIPK1/RIPK3/MLKL necrosome induces the phosphorylated MLKL, and the activated MLKL penetrates into the membrane bilayer to form membrane pores, which damages the integrity of the membrane and leads to cell death. In addition to participating in necroptosis, MLKL is also closely related to other cell death, such as NETosis, pyroptosis, and autophagy. Therefore, MLKL is involved in the pathological processes of various diseases related to abnormal cell death pathways (such as cardiovascular diseases, neurodegenerative diseases and cancer), and may be a therapeutic target of multiple diseases. Understanding the role of MLKL in different cell death can lay a foundation for seeking various MLKL-related disease targets, and also guide the development and application of MLKL inhibitors.

Nuclear translocation of MLKL enhances necroptosis by a RIP1/RIP3-independent mechanism in H9c2 cardiomyoblasts

Accumulating evidence suggests that necroptosis of cardiomyocytes contributes to cardiovascular diseases. Lethal disruption of the plasma membrane in necroptosis is induced by oligomers of mixed lineage kinase domain-like (MLKL) that is translocated to the membrane from the cytosol. However, the role played by cytoplasmic-nuclear shuttling of MLKL is unclear. Here, we tested the hypothesis that translocation of MLKL to the nucleus promotes the necroptosis of cardiomyocytes. Activation of the canonical necroptotic signaling pathway by a combination of TNF-α and zVAD (TNF/zVAD) increased nuclear MLKL levels in a RIP1-activity-dependent manner in H9c2 cells, a rat cardiomyoblast cell line. By use of site-directed mutagenesis, we found a nuclear export signal sequence in MLKL and prepared its mutant (MLKL-L280/283/284A), though a search for a nuclear import signal was unsuccessful. MLKL-L280/283/284A localized to both the cytosol and the nucleus. Expression of MLKL-L280/283/284A induced necroptotic cell death, which was attenuated by GppNHp, an inhibitor of Ran-mediated nuclear import, but not by inhibition of RIP1 activity or knockdown of RIP3 expression. GppNHp partly suppressed H9c2 cell death induced by TNF/zVAD treatment. These results suggest that MLKL that is translocated to the nucleus via RIP1-mediated necroptotic signaling enhances the necroptosis of cardiomyocytes through a RIP1-/RIP3-independent mechanism.