Blockage of heart blood flow leads to myocardial ischemia. Persistent ischemia causes myocardial infarctions, resulting in profound myocyte death, irreversible myocardial damage, and a permanent loss of contractile mass. The death of cardiomyocytes cannot be supplemented by newly generated cells. Reperfusion can trigger further damage to the myocardium; i.e., I/R injury via reactive oxygen species-induced oxidative stress, calcium overload, or calpain activation [56,57,58].

Cao et al. reported that MG53 is downregulated in cardiac I/R injury and increase of MG53 expression appears cardioprotective on I/R-, hypoxia-, or oxidative stress-induced myocardial damage [11]. mg53^−/− mice suffered exaggerated I/R injury, but over-expression of MG53 was sufficient to protect cardiomyocytes against hypoxia- and oxidative stress-induced cell death. The interaction between MG53 and CaV3 can activate pro-survival kinases and further promote cardioprotection [11]. The genetic ablation of mg53 increases susceptibility to I/R-induced myocardial damage with decelerated membrane resealing compared with wild-type controls [4,16]. Routinely, stress conditions such as myocardial I/R injury can lead to loss of mitochondrial function and subsequent irreplaceable loss of cardiomyocytes. Wang et al. proved that the cardiac protection of the MG53-mediated membrane repair is cholesterol-dependent against these stress conditions with important therapeutic implications [16]. MG53 and the CaV3 complex is required for the p85 subunit of phosphoinositide 3-kinase (p85-PI3K) via PostC-mediated activation of the reperfusion injury salvage kinase (RISK) pathway [4].

In δ-SG-deficient TO-2 hamsters with severe cardiac dysfunction and dilated congestive heart failure, muscle-specific overexpression of human MG53 gene via adeno-associated virus (AAV), and systemic delivery of rhMG53, enhanced membrane repair in the cardiomyocytes via ameliorated pathology with significant improvement of heart functions in the genetically modified hamsters [17]. The overexpressed MG53 increased the dysferlin expression and facilitated its trafficking to damaged muscle membrane. The cardiac function improvement promotes phosphorylation ERK1/2, Akt, and glycogen synthase kinase (GSK) expression, and reduces the pro-apoptotic genes’ expression in the MG53 cardiomyocytes [17]. The rhMG53, introduced into the injured cardiomyocytes via perfusion, directly triggers activation of the PI3K survival pathway for cardiac protection in pigs [12].

S-nitrosylation can reduce IR-induced MG53 degradation along with infarct size in a perfused heart [54,55] and the mono-ADP-ribosylation cycle is essential for oligomerization of MG53 at the I/R injury site [53]. While the ADP-ribosylated MG53 would be considered as a rapid and abundant biomarker of cardiac ischemic injury, MG53 not only facilitates plasma membrane repair, but also further activates the intracellular RISK pathway for cardioprotection. Although cardioprotective roles for endogenous myocardial MG53 could not be extrapolated from rodents to humans, potential therapeutic application of rhMG53 for myocardial membrane injury prevails [59].

Within the routine contraction and relaxation of skeletal muscle, sarcolemma injury occurs under physiological conditions in an average life span. Impaired membrane repair capacity has been linked to many different disease states, such as muscular dystrophy. Cai et al. reported mg53^−/− mice showed progressive myopathy and reduced exercise capability associated with defective membrane-repair capacity [3]. For the tPA-MG53 mice, exercise-induced muscle injury was less than that in the controls, and tPA-MG53 muscles recovered faster in the presence of sustained elevation of MG53 in blood circulation [9]. MG53 significantly improved muscle satellite cell (mSC) proliferation and increased regenerative capacity related to muscle injury [9].

Another protein related to skeletal muscle membrane repair, dysferlin, is recognized as a fusion protein involved in restoration of muscle membrane integrity after muscle injury [60,61,62]. MG53-mediated active trafficking of intracellular vesicles to sarcolemma involves the movement of dysferlin to injured sites on cell membranes during repair patch formation [8]. Another repair-related protein, Cav3, is critical to damage recovery in cell membranes repaired by MG53. P104L and R26Q mutations of Cav3 resulted in their remaining in the Golgi apparatus. This defect resulted in the dis-localization of both MG53 and dysferlin, leading to defects in the membrane repair. These data indicate that dysferlin, Cav3, and MG53 are essential in repairing damage to muscle membrane by forming a molecular complex in muscle and heart [8].

Dystrophic muscle pathology is mainly thought to involve δ-sarcoglycan (δ-SG). TO-2 hamsters with δ-SG deletion develop chronic damage of muscle fibers along with leakage of sarcolemma [63]. He et al. demonstrated that muscle-specific overexpression of human MG53 enhanced the membrane repair of δ-SG deficient TO-2 hamsters with significantly improved pathological conditions and amended muscle function [17]. Application of rhMG53 through multiple approaches including intramuscular injection (IM), intravenous injection (IV), and subcutaneous injection (SC) can all improve the membrane repair capacity of skeletal muscle fibers, as well as ameliorate some of the pathology associated with muscular dystrophy in animal studies with dystrophin-deficient mdx mouse [10].

rhMG53 applied via IV to the wild-type mice protected I/R injured muscle and improved pathologic syndrome of skeletal muscle dystrophy [64]. However, rhMG53 did not protect against I/R injury in rat skeletal muscle. This was likely due to the fact that the serum concentrations of MG53 in mouse and human are significantly lower than that in rat, which makes rat muscle less sensitive to the therapeutic effects of rhMG53 [64].

Burn injury induced a severe failure of plasma membrane repair, resulting in skeletal muscle membrane injury. Burn-induced inactivation of disulfide isomerase can inhibit MG53 dimerization and result in failure of musculoskeletal membrane repair [65]. Gushchina et al. proved that short-term rhMG53 treatment is able to increase sarcolemma integrity, independent of the canonical dysferlin-mediated and Ca²⁺-associated pathway, which is important for sarcolemmal membrane repair in the dysferlin-deficient mouse model. rhMG53 improves muscle fiber survival, which could be beneficial for patients with type 2B limb girdle muscular dystrophy (LGMD2B) [66].

As a small molecule native to striated muscle, MG53 can be released into the extracellular space to directly reboot resealing capacity of local membrane of the tissue. Thus, circulating MG53 might play a role in muscle injury-induced regeneration. Targeting the extracellular MG53 function could promote beneficial effects on human diseases associated with defective membrane repair capacity within the entire body. The above findings suggest that MG53 could be translated into a treatment for use in human patients to target cell membrane repair in regenerative medicine.

In addition to MG53′s protective role in cardiac and muscular pathology, MG53-mediated repair machinery protects against injury to non-muscle organs including I/R or contrast-induced acute kidney injury [5,15], stress-induced damage in lungs [6,13,14,67], chronic skin wounds [68], and hepatic I/R injury in liver transplantation and hepatic resections [20]. The most recent publication on the function of MG53 predicts more involvement of the protein in other diseases [69].

Various pathological stresses including sepsis, trauma pneumonia, and blood transfusion can cause acute lung injury (ALI) [72]. We have shown that mg53^−/− mice display abnormal lung structure and function under basal conditions, a finding consistent with the observation that MG53 is present in the alveolar epithelia, where ablation of the MG53 gene leads to defective alveolar structure in the mutant mice [6]. Upon ventilation-induced lung injury, mg53^−/− mice show exacerbated damage responses compared to wild-type littermates [6].

rhMG53, when administered either intravenously or via aerosolization, has the ability to effectively mitigate lung ischemia-reperfusion injury, lipopolysaccharide (LPS) induced inflammation, and porcine pancreatic elastase (PPE)-induced emphysema in rodents. rhMG53 protects against stress-induced injury to both lung epithelial and endothelial cells. Repetitive administration of rhMG53 improves pulmonary structure associated with chronic lung injury in mice [6]. Published data from other investigators also confirm the beneficial effects of inhalational rhMG53 to treat lung injury [13,67].

As one of the world’s greatest public health challenges, influenza causes 1 billion cases resulting in 290,000 to 650,000 influenza-related deaths globally every year [73]. Recently, the therapeutic potential activity of MG53 coupling its anti-inflammasome properties with lung regeneration has not only provided a promising approach to develop MG53 to combat the lethal influenza virus H1N1, but also a strong potential treatment for the lethal Covid-19 SARS-CoV-2 virus [74].

Several other TRIM proteins have antiviral effects [75,76,77,78]. However, Sermersheim et al. have demonstrated that MG53 does not have an impact on influenza viral titers; however, it does have a protective impact through mitigation of pyroptosis [74]. By knockdown inhibition of MG53 in cultured THP-1 cells, they demonstrated that macrophages deficient in MG53 secreted increased levels of interferon-β and interleukin-1β. The MG53 knockdown cell displayed nearly a twofold increase in phosphorylation of p65 at serine 536, a well-known NF-κB activation marker. Immunofluorescent imaging revealed that along with elevated p-p65, MG53 suppression correspondingly resulted in more p65 localization to the nucleus. These observations lead one to conclude that MG53 serves as a negative regulator of NF-kB and the potential mechanism of modulation of inflammatory mediators, which are critical to an infectious response [69].

Kenney and Li et al. [74] found that exogenous injection of rhMG53 through the tail vein protected mice from the lethal influenza virus strain A/PR/8/34 (H1N1) infection. Twenty-four hours after being infected with influenza virus, mice were injected with rhMG53 (2 mg/kg) or saline via tail vein as a control daily for up to 14 days. All control group mice injected with saline died within 9 days post-infection. In sharp contrast, the mice treated with rhMG53 had a survival rate of 92% and recovered to normal body weight by day 14 post-infection [74]. A separate cohort of infected and treated mice was sacrificed 7 days post-infection to assess the protective role of rhMG53 during virus infection. Histological evaluation at 7 days post-infection demonstrated that the alveolar structure of the rhMG53 treatment group was significantly preserved along with lung injury score decrease. The infiltrating CD11b positive lymphocytes were significantly reduced in the rhMG53 treatment group. ELISA quantification showed that inflammatory cytokines of IFNβ, IL-6, and IL-1β were significantly lower in lung tissues derived from rhMG53-treated mice compared with saline control mice. Protein expression analysis of lung tissue showed that the NLRP3 was significantly increased after viral infection, but was significantly reduced by rhMG53 treatment subsequently along with significant reduction of the key protein of cell pyroptosis [79], GSDMD-N terminal, after rhMG53 treatment.

rhMG53 develops a promising host-directed therapeutic for infectious lung injury by suppressing cytokine storm and virus-induced tissue damage [74]. It seems that the current life-threatening COVID-19 pandemic shares the same immunoreaction mechanism with that of the lethal influenza H1N1 virus, which exposes a unique opportunity to design MG53-associated treatment to heal lung damage resulting from the COVID-19 pandemic.

As the world knows, diabetes mellitus (DM) is a systemic disease that has enormous impact on multiple organ systems, quality of life, and economics. It has been proposed that modulation of circulating MG53 levels through administration of monoclonal antibodies may have a role in treating DM [22]. While it is worrisome that elevated MG53 levels may contribute to glucose insensitivity, the approach to assessment of the antibody levels necessitates more in-depth analysis and refinement of assessment modalities [80].

Wang and colleagues worked to understand any contribution of MG53 in development of DM [24]. In their elegant research published in Diabetes [24], they were able to demonstrate a null impact of whole-body ablation of MG53 or sustained elevation on glucose handling and insulin signaling. In that work, Wang et al. created diabetic MG53 knockout mice (db/db-mg53^−/−) and diabetic mice with constitutively overexpressed MG53 (db/db-tPA-MG53) though murine husbandry by crossbreeding db/db^+/− with either mg53^−/− or tPA-MG53 mice. Through comparison of the six strains of mice (wild-type, mg53^−/−, tPA-MG53, db/db^−/−, db/db-mg53^−/− and db/db-tPA-MG53), they demonstrated that diabetic mice strains (db/db, db/db-mg53^−/− and db/db-tPA-MG53) exhibited increased weight gain over 32 weeks, as compared to the non-db/db strains. The three DM strains demonstrated significantly elevated glucose levels through glucose tolerance testing at both 18 and 30 weeks of age, as compared to the three non-DM strains of mice [24]. Additionally, in comparing DM and non-DM mice, there were no differences in levels of MG53 (p = 0.113). While there is interdependence on skeletal muscle and muscle mass on insulin resistance, it does not appear that either whole-body ablation of MG53 (mg53^−/− mice) or sustained constitutively overexpressed MG53 (tPA-MG53) has an impact on glucose handling and DM.

Many studies have identified MG53 as an essential character of cell membrane repair which could be applied to treat injuries for multiple organs including myocardial infarction, muscular dystrophy, and damage in non-muscle organs including kidney, lung, skin and cornea. Muscle-derived MG53 can function as a myokine to facilitate repair of injury to remote organs. Sustained elevation of MG53 in circulation is safe in animal models, and does not impact glucose metabolism. While studies with rodents and large animal models support the therapeutic benefits of rhMG53 to treat acute injury to multiple organs, it remains to be established how protection against acute tissue injury can be translated to improvement in long-term function of the targeted organs. Moreover, studies targeting rhMG53 to treat chronic organ dysfunction or aging-related organ failure represent a potential area of future translational research. The recent establishment of an anti-inflammation function of MG53, in addition to its tissue repair function, opens a further area of therapeutic development of rhMG53 to treat both acute and chronic tissue injuries that are associated with inflammation.