Necroptosis contributes to myofiber death in idiopathic inflammatory myopathies

Mitochondrial defects in sporadic inclusion body myositis-causes and consequences

Sporadic inclusion body myositis (sIBM) is a distinct subcategory of Idiopathic Inflammatory Myopathies (IIM), characterized by unique pathological features such as muscle inflammation, rimmed vacuoles, and protein aggregation within the myofibers. Although hyperactivation of the immune system is widely believed as the primary cause of IIM, it is debated whether non-immune tissue dysfunction might contribute to the disease's onset as patients with sIBM are refractory to conventional immunosuppressant treatment. Moreover, the findings that mitochondrial dysfunction can elicit non-apoptotic programmed cell death and the subsequent immune response further support this hypothesis. Notably, abnormal mitochondrial structure and activities are more prominent in the muscle of sIBM than in other types of IIM, suggesting the presence of defective mitochondria might represent an overlooked contributor to the disease onset. The large-scale mitochondrial DNA deletion, aberrant protein aggregation, and slowed organelle turnover have provided mechanistic insights into the genesis of impaired mitochondria in sIBM. This article reviews the disease hallmarks of sIBM, the plausible contributors of mitochondrial damage in the sIBM muscle, and the immunological responses associated with mitochondrial perturbations. Additionally, the potential application of mitochondrial-targeted chemicals as a new treatment strategy to sIBM is explored and discussed.

The role of ZBP1 in eccentric exercise-induced skeletal muscle necroptosis

This study aimed to explore the occurrence of necroptosis in skeletal muscle after eccentric exercise and investigate the role and possible mechanisms of ZBP1 and its related pathway proteins in the process, providing a theoretical basis for the study of exercise-induced skeletal muscle injury and recovery. Forty-eight male adult Sprague-Dawley rats were randomly divided into a control group (C, n = 8) and an exercise group (E, n = 40). The exercise group was further divided into 0 h (E0), 12 h (E12), 24 h (E24), 48 h (E48), and 72 h (E72) after exercise, with 8 rats in each subgroup. At each time point, gastrocnemius muscle was collected under general anesthesia. The expression levels of ZBP1 and its related pathway proteins were assessed using Western blot analysis. The colocalization of pathway proteins was examined using immunofluorescence staining. After 48 h of eccentric exercise, the expression of necroptosis marker protein MLKL reached its peak (P < 0.01), and the protein levels of ZBP1, RIPK3, and HMGB1 also peaked (P < 0.01). At 48 h post high-load eccentric exercise, there was a significant increase in colocalization of ZBP1/RIPK3 pathway proteins, reaching a peak (P < 0.01). (1) Eccentric exercise induced necroptosis in skeletal muscle, with MLKL, p-MLKLS358, and HMGB1 significantly elevated, especially at 48 h after exercise. (2) After eccentric exercise, the ZBP1/RIPK3-related pathway proteins ZBP1, RIPK3, and p-RIPK3S232 were significantly elevated, particularly at 48 h after exercise. (3) Following high-load eccentric exercise, there was a significant increase in the colocalization of ZBP1/RIPK3 pathway proteins, with a particularly pronounced elevation observed at 48 h post-exercise.

TWEAK and Fn14 are overexpressed in immune-mediated necrotizing myopathy: implications for muscle damage and repair

OBJECTIVES

TNF-like weak inducer of apoptosis (TWEAK) and its sole receptor fibroblast growth factor-inducible 14 (Fn14) are involved in various inflammatory conditions. This study was performed to investigate the potential role of TWEAK/Fn14 in immune-mediated necrotizing myopathy (IMNM).

METHODS

Muscle biopsies from patients with IMNM (n = 37) and controls (n = 11) were collected. Human muscle cells were treated with TWEAK in vitro. Muscle biopsies and cultured muscle cells were analysed by immunostaining and quantitative PCR. Serum levels of TWEAK and Fn14 were detected by ELISA.

RESULTS

TWEAK and Fn14 were overexpressed in IMNM muscle biopsies. The percentage of Fn14-positive myofibers correlated with disease severity, myonecrosis, regeneration and inflammation infiltrates. Fn14-positive myofibers tended to be surrounded or invaded by CD68+ macrophages. TWEAK treatment had a harmful effect on cultured muscle cells by inducing the production of multiple chemokines and pro-inflammatory cytokines. Serum Fn14 levels were increased in patients with IMNM and correlated with muscle weakness.

CONCLUSIONS

TWEAK/Fn14 signalling was activated in IMNM, most likely aggravating muscle damage via amplifying inflammatory response and macrophages chemotaxis. Fn14 seems to be a biomarker for assessing disease severity in IMNM. In addition, Fn14 may also contribute to muscle injury repair.

The role of neutrophil extracellular traps and proinflammatory damage-associated molecular patterns in idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) are a group of systemic autoimmune diseases characterized by immune-mediated muscle injury. Abnormal neutrophil extracellular traps (NETs) can be used as a biomarker of IIM disease activity, but the mechanism of NET involvement in IIMs needs to be elucidated. Important components of NETs, including high-mobility group box 1, DNA, histones, extracellular matrix, serum amyloid A, and S100A8/A9, act as damage-associated molecular patterns (DAMPs) to promote inflammation in IIMs. NETs can act on different cells to release large amounts of cytokines and activate the inflammasome, which can subsequently aggravate the inflammatory response. Based on the idea that NETs may be proinflammatory DAMPs of IIMs, we describe the role of NETs, DAMPs, and their interaction in the pathogenesis of IIMs and discuss the possible targeted treatment strategies in IIMs.

Muscle fiber necroptosis in pathophysiology of idiopathic inflammatory myopathies and its potential as target of novel treatment strategy

Idiopathic inflammatory myopathies (IIMs), which are a group of chronic and diverse inflammatory diseases, are primarily characterized by weakness in the proximal muscles that progressively leads to persistent disability. Current treatments of IIMs depend on nonspecific immunosuppressive agents (including glucocorticoids and immunosuppressants). However, these therapies sometimes fail to regulate muscle inflammation, and some patients suffer from infectious diseases and other adverse effects related to the treatment. Furthermore, even after inflammation has subsided, muscle weakness persists in a significant proportion of the patients. Therefore, the elucidation of pathophysiology of IIMs and development of a better therapeutic strategy that not only alleviates muscle inflammation but also improves muscle weakness without increment of opportunistic infection is awaited. Muscle fiber death, which has been formerly postulated as "necrosis", is a key histological feature of all subtypes of IIMs, however, its detailed mechanisms and contribution to the pathophysiology remained to be elucidated. Recent studies have revealed that muscle fibers of IIMs undergo necroptosis, a newly recognized form of regulated cell death, and promote muscle inflammation and dysfunction through releasing inflammatory mediators such as damage-associated molecular patterns (DAMPs). The research on murine model of polymyositis, a subtype of IIM, revealed that the inhibition of necroptosis or HMGB1, one of major DAMPs released from muscle fibers undergoing necroptosis, ameliorated muscle inflammation and recovered muscle weakness. Furthermore, not only the necroptosis-associated molecules but also PGAM5, a mitochondrial protein, and reactive oxygen species have been shown to be involved in muscle fiber necroptosis, indicating the multiple target candidates for the treatment of IIMs acting through necroptosis regulation. This article overviews the research on muscle injury mechanisms in IIMs focusing on the contribution of necroptosis in their pathophysiology and discusses the potential treatment strategy targeting muscle fiber necroptosis.

Identification of featured necroptosis-related genes and imbalanced immune infiltration in sepsis via machine learning

Background: The precise diagnostic and prognostic biological markers were needed in immunotherapy for sepsis. Considering the role of necroptosis and immune cell infiltration in sepsis, differentially expressed necroptosis-related genes (DE-NRGs) were identified, and the relationship between DE-NRGs and the immune microenvironment in sepsis was analyzed.

Methods: Machine learning algorithms were applied for screening hub genes related to necroptosis in the training cohort. CIBERSORT algorithms were employed for immune infiltration landscape analysis. Then, the diagnostic value of these hub genes was verified by the receiver operating characteristic (ROC) curve and nomogram. In addition, consensus clustering was applied to divide the septic patients into different subgroups, and quantitative real-time PCR was used to detect the mRNA levels of the hub genes between septic patients (SP) (n = 30) and healthy controls (HC) (n = 15). Finally, a multivariate prediction model based on heart rate, temperature, white blood count and 4 hub genes was established.

Results: A total of 47 DE-NRGs were identified between SP and HC and 4 hub genes (BACH2, GATA3, LEF1, and BCL2) relevant to necroptosis were screened out via multiple machine learning algorithms. The high diagnostic value of these hub genes was validated by the ROC curve and Nomogram model. Besides, the immune scores, correlation analysis and immune cell infiltrations suggested an immunosuppressive microenvironment in sepsis. Septic patients were divided into 2 clusters based on the expressions of hub genes using consensus clustering, and the immune microenvironment landscapes and immune function between the 2 clusters were significantly different. The mRNA levels of the 4 hub genes significantly decreased in SP as compared with HC. The area under the curve (AUC) was better in the multivariate prediction model than in other indicators.

Conclusion: This study indicated that these necroptosis hub genes might have great potential in prognosis prediction and personalized immunotherapy for sepsis.

Anti-SRP immune-mediated necrotizing myopathy: A critical review of current concepts

Purpose of review

This review aims to describe clinical and histological features, treatment, and prognosis in patients with anti-signal recognition particle (SRP) autoantibodies positive immune-mediated necrotizing myopathy (SRP-IMNM) based on previous findings.

Previous findings

Anti-SRP autoantibodies are specific in IMNM. Humoral autoimmune and inflammatory responses are the main autoimmune characteristics of SRP-IMNM. SRP-IMNM is clinically characterized by acute or subacute, moderately severe, symmetrical proximal weakness. Younger patients with SRP-IMNM tend to have more severe clinical symptoms. Patients with SRP-IMNM may be vulnerable to cardiac involvement, which ought to be regularly monitored and cardiac magnetic resonance imaging is the recommended detection method. The pathological features of SRP-IMNM are patchy or diffuse myonecrosis and myoregeneration accompanied by a paucity of inflammatory infiltrates. Endoplasmic reticulum stress-induced autophagy pathway and necroptosis are activated in skeletal muscle of SRP-IMNM. Treatment of refractory SRP-IMNM encounters resistance and warrants further investigation.

Summary

Anti-SRP autoantibodies define a unique population of IMNM patients. The immune and non-immune pathophysiological mechanisms are involved in SRP-IMNM.

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

AIMS

The role of necroptosis in dilated cardiomyopathy (DCM) remains unclear. Here, we examined whether phosphorylation of mixed lineage kinase domain-like protein (MLKL), an indispensable event for execution of necroptosis, is associated with the progression of DCM.

METHODS AND RESULTS

Patients with DCM (n = 56, 56 ± 15 years of age; 68% male) were enrolled for immunohistochemical analyses of biopsies. Adverse events were defined as a composite of death or admission for heart failure or ventricular arrhythmia. Compared with the normal myocardium, increased signals of MLKL phosphorylation were detected in the nuclei, cytoplasm, and intercalated discs of cardiomyocytes in biopsy samples from DCM patients. The phosphorylated MLKL (p-MLKL) signal was increased in enlarged nuclei or nuclei with bizarre shapes in hypertrophied cardiomyocytes. Nuclear p-MLKL level was correlated negatively with septal peak myocardial velocity during early diastole (r = -0.327, P = 0.019) and was correlated positively with tricuspid regurgitation pressure gradient (r = 0.339, P = 0.023), while p-MLKL level in intercalated discs was negatively correlated with mean left ventricular wall thickness (r = -0.360, P = 0.014). During a median follow-up period of 3.5 years, 10 patients (18%) had adverse events. To examine the difference in event rates according to p-MLKL expression levels, patients were divided into two groups by using the median value of nuclear p-MLKL or intercalated disc p-MLKL. A group with high nuclear p-MLKL level (H-nucMLKL group) had a higher adverse event rate than did a group with low nuclear p-MLKL level (L-nucMLKL group) (32% vs. 4%, P = 0.012), and Kaplan-Meier survival curves showed that the adverse event-free survival rate was lower in the H-nucMLKL group than in the L-nucMLKL group (P = 0.019 by the log-rank test). Such differences were not detected between groups divided by a median value of intercalated disc p-MLKL. In δ-sarcoglycan-deficient (Sgcd-/- ) mice, a model of DCM, total p-MLKL and nuclear p-MLKL levels were higher than in wild-type mice.

CONCLUSION

The results suggest that increased localization of nuclear p-MLKL in cardiomyocytes is associated with left ventricular diastolic dysfunction and future adverse events in DCM.

Macrophage Subsets and Death Are Responsible for Atherosclerotic Plaque Formation

Cardiovascular diseases, the notorious killer, are mainly caused by atherosclerosis (AS) characterized by lipids, cholesterol, and iron overload in plaques. Macrophages are effector cells and accumulate to the damaged and inflamed sites of arteries to internalize native and chemically modified lipoproteins to transform them into cholesterol-loaded foam cells. Foam cell formation is determined by the capacity of phagocytosis, migration, scavenging, and the features of phenotypes. Macrophages are diverse, and the subsets and functions are controlled by their surrounding microenvironment. Generally, macrophages are divided into classically activated (M1) and alternatively activated (M2). Recently, intraplaque macrophage phenotypes are recognized by the stimulation of CXCL4 (M4), oxidized phospholipids (Mox), hemoglobin/haptoglobin complexes [HA-mac/M(Hb)], and heme (Mhem). The pro-atherogenic or anti-atherosclerotic phenotypes of macrophages decide the progression of AS. Besides, apoptosis, necrosis, ferroptosis, autophagy and pyrotopsis determine plaque formation and cardiovascular vulnerability, which may be associated with macrophage polarization phenotypes. In this review, we first summarize the three most popular hypotheses for AS and find the common key factors for further discussion. Secondly, we discuss the factors affecting macrophage polarization and five types of macrophage death in AS progression, especially ferroptosis. A comprehensive understanding of the cellular and molecular mechanisms of plaque formation is conducive to disentangling the candidate targets of macrophage-targeting therapies for clinical intervention at various stages of AS.