MG53-induced IRS-1 ubiquitination negatively regulates skeletal myogenesis and insulin signalling

TRIM32 regulates insulin sensitivity by controlling insulin receptor degradation in the liver

Impaired insulin receptor signaling is strongly linked to obesity-related metabolic conditions like non-alcoholic fatty liver disease (NAFLD) and Type 2 diabetes (T2DM). However, the exact mechanisms behind impaired insulin receptor (INSR) signaling in obesity induced by a high-fat diet remain elusive. In this study, we identify an E3 ubiquitin ligase, tripartite motif-containing protein 32 (TRIM32), as a key regulator of hepatic insulin signaling that targets the insulin receptor (INSR) for ubiquitination and proteasomal degradation in high-fat diet (HFD) mice. HFD induces the nuclear translocation of SREBP-1c (Sterol Regulatory Element-Binding Protein 1c), resulting in increased expression of TRIM32 in hepatocytes. TRIM32 ubiquitylates INSR and facilitates its proteasomal degradation, leading to severe insulin resistance and fat accumulation within the liver of high-fat diet induced obese (DIO) mice. Conversely, liver-specific knockdown of TRIM32 enhances INSR expression and hepatic insulin sensitivity. Reduced AMPK signaling and phosphorylation of SREBP-1c at S372 in high-fat DIO mice promotes the nuclear translocation of SREBP-1c, leading to increased TRIM32 expression. In conclusion, our results demonstrate that TRIM32 promotes diet-induced hepatic insulin resistance by targeting the INSR to degradation.

Deciphering molecular crosstalk mechanisms between skeletal muscle atrophy and KRAS-mutant pancreatic cancer: a literature review

Background and Objective

Cachexia-induced skeletal muscle atrophy is a critical manifestation in Kirsten rat sarcoma viral oncogene homologue (KRAS)-mutant pancreatic cancer (PC) patients, predominantly characterized by a shift in metabolic equilibrium towards catabolism that accelerates protein degradation in myofibers and leads to muscle atrophy. This metabolic reprogramming not only supports tumor growth but also precipitates energy depletion in skeletal muscle tissues. Exploring these mechanisms reveals potential therapeutic targets in the metabolic and proteolytic pathways associated with KRAS-mutant PC.

Methods

A comprehensive search for literature was conducted in PubMed, Web of Science, Google Scholar and other search engines up to May 21st, 2024. Studies on PC models and patients were included.

Key Content and Findings

The crosstalk between KRAS-mutant PC and skeletal muscle atrophy can be categorized into four principal domains: (I) KRAS-driven metabolic reprogramming in cancer cells leads to the depletion of muscle energy reserves, thereby influencing the reallocation of myofiber energy towards fueling cancer cell; (II) KRAS-mutant cancer cells rely on nutrient-scavenging pathways, resulting in altered cytokine profiles, increased ubiquitin mRNA expression and autophagy-lysosome pathway, which facilitate myotube degradation and inhibit muscle regeneration, thereby disrupting muscular homeostasis and causing a one-way nutrient flux; (III) tumor-induced oxidative stress inflicts damage on myotubes, highlighting the detrimental effects of reactive oxygen species on muscle structure; (IV) KRAS-mutant cancer cells remodulate immune cell dynamics within the tumor environment, thereby reshaping host immunity. Together, these findings illuminate the intricate interplay between KRAS-mutant PC and skeletal muscle atrophy, mapping the pathophysiological framework that is crucial for understanding sarcopenia and related disorders.

Conclusions

This comprehensive analysis advances our understanding of the complex etiology of cancer cachexia and stimulates the development of targeted therapeutic strategies.

Friend or Foe: The Paradoxical Roles of MG53 in Diabetes

MG53 is predominantly expressed in striated muscles. The role of MG53 in diabetes has gradually been elucidated but is still full of controversy. Some reports have indicated that MG53 is upregulated in animal models with metabolic disorders and that muscle-specific MG53 upregulation is sufficient to induce whole-body insulin resistance and metabolic syndrome through targeting both the insulin receptor (IR) and insulin receptor substrate 1 (IRS-1) for ubiquitin-dependent degradation. Additionally, MG53 has been identified as a myokine/cardiokine that is secreted from striated muscles into the bloodstream, and circulating MG53 has further been shown to trigger insulin resistance by binding to the extracellular domain of the IR, thereby allosterically inhibiting insulin signaling. Conversely, findings have been reported from other studies that contradict these results. Specifically, no significant change in MG53 expression in striated muscles or serum has been observed in diabetic models, and the MG53-mediated degradation of IRS-1 may be insufficient to induce insulin resistance due to the compensatory roles of other IRS subtypes. Furthermore, sustained elevation of MG53 levels in serum or systemic administration of recombinant human MG53 (rhMG53) has shown no impact on metabolic function. In this article, we will fully characterize these two disparate views, strive to provide critical insights into their contrasts, and propose several specific experimental approaches that may yield additional evidence. Our goal is to encourage the scientific community to elucidate the effects of MG53 on metabolic diseases and the molecular mechanisms involved, thereby providing the theoretical basis for the treatment of metabolic diseases and the applications of rhMG53.

The Potential Role of Cardiokines in Heart and Kidney Diseases

As the engine that maintains blood circulation, the heart is also an endocrine organ that regulates the function of distant target organs by secreting a series of cardiokines. As endocrine factors, cardiokines play an indispensable role in maintaining the homeostasis of the heart and other organs. Here, we summarize some of the cardiokines that have been defined thus far and explore their roles in heart and kidney diseases. Finally, we propose that cardiokines may be a potential therapeutic target for kidney diseases.

MG53 suppresses tumor growth via transcriptional inhibition of KIF11 in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) poses a formidable challenge in oncology due to its limited treatment options and poor long-term survival rates. Our previous work identified MG53, a member of the tripartite motif family protein (TRIM72), as a key player in tissue repair with potential applications in regenerative medicine. Despite the focus on MG53's cytosolic functions, its nuclear role in suppressing pancreatic cancer remains unknown. Through orthotopic and subcutaneous transplantation studies in mice, we observed enhanced tumor growth in MG53-deficient mice compared to wild-type counterparts. The overexpression of KIF11, a motor protein crucial for cell mitosis regulation, has been linked to the aggressive proliferation of pancreatic cancer cells. Confocal imaging confirmed MG53's presence in the nucleus of human pancreatic cancer cells, while functional assays demonstrated its impact on KIF11 expression and subsequent cell proliferation. Mechanistically, we revealed MG53's transcriptional control over KIF11, leading to cell cycle arrest. Our findings position MG53 as a promising tumor suppressor in PDAC, offering a novel avenue for therapeutic intervention by regulating KIF11 expression.

MG53's non-physiologic interaction with insulin receptor: lack of effect on insulin-stimulated Akt phosphorylation in muscle, heart and liver tissues

Rationale

MG53's known function in facilitating tissue repair and anti-inflammation has broad applications to regenerative medicine. There is controversy regarding MG53's role in the development of type 2 diabetes mellitus.

Objective

This study aims to address this controversy - whether MG53's myokine function contributes to inhibition of insulin signaling in muscle, heart, and liver tissues.

Study design

We determined the binding affinity of the recombinant human MG53 (rhMG53) to the insulin receptor extracellular domain (IR-ECD) and found low affinity of interaction with Kd (>480 nM). Using cultured C2C12 myotubes and HepG2 cells, we found no effect of rhMG53 on insulin-stimulated Akt phosphorylation (p-Akt). We performed in vivo assay with C57BL/6J mice subjected to insulin stimulation (1 U/kg, intraperitoneal injection) and observed no effect of rhMG53 on insulin-stimulated p-Akt in muscle, heart and liver tissues.

Conclusion

Overall, our data suggest that rhMG53 can bind to the IR-ECD, however has a low likelihood of a physiologic role, as the Kd for binding is ~10,000 higher than the physiologic level of MG53 present in the serum of rodents and humans (~10 pM). Our findings question the notion proposed by Xiao and colleagues - whether targeting circulating MG53 opens a new therapeutic avenue for type 2 diabetes mellitus and its complications.

Diabetes-induced muscle wasting: molecular mechanisms and promising therapeutic targets

Diabetes has become a serious public health crisis, presenting significant challenges to individuals worldwide. As the largest organ in the human body, skeletal muscle is a significant target of this chronic disease, yet muscle wasting as a complication of diabetes is still not fully understood and effective treatment methods have yet to be developed. Here, we discuss the targets involved in inducing muscle wasting under diabetic conditions, both validated targets and emerging targets. Diabetes-induced skeletal muscle wasting is known to involve changes in various signaling molecules and pathways, such as protein degradation pathways, protein synthesis pathways, mitochondrial function, and oxidative stress inflammation. Recent studies have shown that some of these present potential as promising therapeutic targets, including the neuregulin 1/epidermal growth factor receptor family, advanced glycation end-products, irisin, ferroptosis, growth differentiation factor 15 and more. This study's investigation and discussion of such pathways and their potential applications provides a theoretical basis for the development of clinical treatments for diabetes-induced muscle wasting and a foundation for continued focus on this disease.

Unveiling the emerging role of curcumin to alleviate ochratoxin A-induced muscle toxicity in grass carp (Ctenopharyngodon idella): in vitro and in vivo studies

BACKGROUND

Ochratoxin A (OTA), a globally abundant and extremely hazardous pollutant, is a significant source of contamination in aquafeeds and is responsible for severe food pollution. The developmental toxicity of OTA and the potential relieving strategy of natural products remain unclear. This study screened the substance curcumin (Cur), which had the best effect in alleviating OTA inhibition of myoblast proliferation, from 96 natural products and investigated its effect and mechanism in reducing OTA myotoxicity in vivo and in vitro.

METHODS

A total of 720 healthy juvenile grass carp, with an initial average body weight of 11.06 ± 0.05 g, were randomly assigned into 4 groups: the control group (without OTA and Cur), 1.2 mg/kg OTA group, 400 mg/kg Cur group, and 1.2 mg/kg OTA + 400 mg/kg Cur group. Each treatment consisted of 3 replicates (180 fish) for 60 d.

RESULTS

Firstly, we cultured, purified, and identified myoblasts using the tissue block culture method. Through preliminary screening and re-screening of 96 substances, we examined cell proliferation-related indicators such as cell viability and ultimately found that Cur had the best effect. Secondly, Cur could alleviate OTA-inhibited myoblast differentiation and myofibrillar development-related proteins (MyoG and MYHC) in vivo and in vitro and improve the growth performance of grass carp. Then, Cur could also promote the expression of OTA-inhibited protein synthesis-related proteins (S6K1 and TOR), which was related to the activation of the AKT/TOR signaling pathway. Finally, Cur could downregulate the expression of OTA-enhanced protein degradation-related genes (murf1, foxo3a, and ub), which was related to the inhibition of the FoxO3a signaling pathway.

CONCLUSIONS

In summary, our data demonstrated the effectiveness of Cur in alleviating OTA myotoxicity in vivo and in vitro. This study confirms the rapidity, feasibility, and effectiveness of establishing a natural product screening method targeting myoblasts to alleviate fungal toxin toxicity.

MG53/TRIM72: multi-organ repair protein and beyond

MG53, a member of the tripartite motif protein family, possesses multiple functionalities due to its classic membrane repair function, anti-inflammatory ability, and E3 ubiquitin ligase properties. Initially recognized for its crucial role in membrane repair, the therapeutic potential of MG53 has been extensively explored in various diseases including muscle injury, myocardial damage, acute lung injury, and acute kidney injury. However, further research has revealed that the E3 ubiquitin ligase characteristics of MG53 also contribute to the pathogenesis of certain conditions such as diabetic cardiomyopathy, insulin resistance, and metabolic syndrome. Moreover, recent studies have highlighted the anti-tumor effects of MG53 in different types of cancer, such as small cell lung cancer, liver cancer, and colorectal cancer; these effects are closely associated with their E3 ubiquitin ligase activities. In summary, MG53 is a multifunctional protein that participates in important physiological and pathological processes of multiple organs and is a promising therapeutic target for various human diseases. MG53 plays a multi-organ protective role due to its membrane repair function and its exertion of anti-tumor effects due to its E3 ubiquitin ligase properties. In addition, the controversial aspect of MG53's E3 ubiquitin ligase properties potentially causing insulin resistance and metabolic syndrome necessitates further cross-validation for clarity.

Post-translational modifications in diabetic cardiomyopathy

The increasing attention towards diabetic cardiomyopathy as a distinctive complication of diabetes mellitus has highlighted the need for standardized diagnostic criteria and targeted treatment approaches in clinical practice. Ongoing research is gradually unravelling the pathogenesis of diabetic cardiomyopathy, with a particular emphasis on investigating various post-translational modifications. These modifications dynamically regulate protein function in response to changes in the internal and external environment, and their disturbance of homeostasis holds significant relevance for the development of chronic ailments. This review provides a comprehensive overview of the common post-translational modifications involved in the initiation and progression of diabetic cardiomyopathy, including O-GlcNAcylation, phosphorylation, methylation, acetylation and ubiquitination. Additionally, the review discusses drug development strategies for targeting key post-translational modification targets, such as agonists, inhibitors and PROTAC (proteolysis targeting chimaera) technology that targets E3 ubiquitin ligases.

Sea buckthorn oil regulates primary myoblasts proliferation and differentiation in vitro

Skeletal muscle is the main edible part of meat products, and its development directly affects the yield and palatability of meat. Sea buckthorn oil (SBO) contains plenty of bioactive substances and has been recognized as a potential functional food product. The study aimed to explore the effects and possible mechanisms of SBO on sheep primary myoblast proliferation and myogenic differentiation. The results implied that SBO exhibited a pro-proliferative effect on primary myoblasts, along with up-regulated proliferating cell nuclear antigen (PCNA) and Cyclin D1/cyclin-dependent kinase 4 (CDK4) abundances. And, SBO promoted myotube formation by increasing the expression of myogenin. Meanwhile, we found that SBO inhibited the expression of miRNA-292a. Moreover, the regulatory effect of SBO on myogenic differentiation of myoblasts was attenuated by miRNA-292a mimics. Of note, SBO activated protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway and augmented glucose uptake and glucose transporter 4 (GLUT4) content, which might be attributed to AMP-activated protein kinase (AMPK) activation. Additionally, the results were shown that SBO increased the abundance of antioxidative enzymes, including glutathione peroxidase 4 (Gpx4) and catalase. In summary, these data suggested that SBO regulated the proliferation and myogenic differentiation of sheep primary myoblasts in vitro, which might potentiate the application of SBO in muscle growth.

TRIM72 restricts lyssavirus infection by inducing K48-linked ubiquitination and proteasome degradation of the matrix protein

The tripartite motif (TRIM) protein family is the largest subfamily of E3 ubiquitin ligases, playing a crucial role in the antiviral process. In this study, we found that TRIM72, a member of the TRIM protein family, was increased in neuronal cells and mouse brains following rabies lyssavirus (RABV) infection. Over-expression of TRIM72 significantly reduced the viral titer of RABV in neuronal cells and mitigated the pathogenicity of RABV in mice. Furthermore, we found that TRIM72 over-expression effectively prevents the assembly and/or release of RABV. In terms of the mechanism, TRIM72 promotes the K48-linked ubiquitination of RABV Matrix protein (M), leading to the degradation of M through the proteasome pathway. TRIM72 directly interacts with M and the interaction sites were identified and confirmed through TRIM72-M interaction model construction and mutation analysis. Further investigation revealed that the degradation of M induced by TRIM72 was attributed to TRIM72's promotion of ubiquitination at site K195 in M. Importantly, the K195 site was found to be partially conserved among lyssavirus's M proteins, and TRIM72 over-expression induced the degradation of these lyssavirus M proteins. In summary, our study has uncovered a TRIM family protein, TRIM72, that can restrict lyssavirus replication by degrading M, and we have identified a novel ubiquitination site (K195) in lyssavirus M.

Multisite phosphorylation dictates selective E2-E3 pairing as revealed by Ubc8/UBE2H-GID/CTLH assemblies

Ubiquitylation is catalyzed by coordinated actions of E3 and E2 enzymes. Molecular principles governing many important E3-E2 partnerships remain unknown, including those for RING-family GID/CTLH E3 ubiquitin ligases and their dedicated E2, Ubc8/UBE2H (yeast/human nomenclature). GID/CTLH-Ubc8/UBE2H-mediated ubiquitylation regulates biological processes ranging from yeast metabolic signaling to human development. Here, cryoelectron microscopy (cryo-EM), biochemistry, and cell biology reveal this exquisitely specific E3-E2 pairing through an unconventional catalytic assembly and auxiliary interactions 70-100 Å away, mediated by E2 multisite phosphorylation. Rather than dynamic polyelectrostatic interactions reported for other ubiquitylation complexes, multiple Ubc8/UBE2H phosphorylation sites within acidic CK2-targeted sequences specifically anchor the E2 C termini to E3 basic patches. Positions of phospho-dependent interactions relative to the catalytic domains correlate across evolution. Overall, our data show that phosphorylation-dependent multivalency establishes a specific E3-E2 partnership, is antagonistic with dephosphorylation, rigidifies the catalytic centers within a flexing GID E3-substrate assembly, and facilitates substrate collision with ubiquitylation active sites.

Role of the tripartite motif-containing (TRIM) family of proteins in insulin resistance and related disorders

Emerging evidence suggests that the ubiquitin-mediated degradation of insulin-signalling-related proteins may be involved in the development of insulin resistance and its related disorders. Tripartite motif-containing (TRIM) proteins, a superfamily belonging to the E3 ubiquitin ligases, are capable of controlling protein levels and function by ubiquitination, which is essential for the modulation of insulin sensitivity. Recent research has indicated that some of these TRIMs act as key regulatory factors of metabolic disorders such as type 2 diabetes mellitus, obesity, nonalcoholic fatty liver disease, and atherosclerosis. This review provides a comprehensive overview of the latest evidence linking TRIMs to the regulation of insulin resistance and its related disorders, their roles in regulating multiple signalling pathways or cellular processes, such as insulin signalling pathways, peroxisome proliferator-activated receptor signalling pathways, glucose and lipid metabolism, the inflammatory response, and cell cycle control, as well as recent advances in the development of TRIM-targeted drugs.

MG53 alleviates hypoxia/reoxygenation-induced cardiomyocyte injury by succinylation and ubiquitination modification

BACKGROUND

Mitsugumin 53 (MG53) is a membrane repair factor that is associated with acute myocardial infarction. This study aimed to investigate the effects of MG53 on cardiomyocyte injury and the posttranslational modification of MG53.

METHODS

Cardiomyocyte injury was evaluated by enzyme-linked immunosorbent assay and flow cytometry. The succinylation and ubiquitination levels of MG53 were examined by immunoprecipitation (IP) and western blot. The relationship between MG53 and KAT3B or SIRT7 was assessed by co-IP and immunofluorescence.

RESULTS

The results showed that overexpression of MG53 inhibited inflammation response and apoptosis of cardiomyocytes induced by hypoxia/reoxygenation (H/R). Succinylation and protein levels of MG53 were downregulated in H/R-induced cells, which was inhibited by SIRT7 and promoted by KAT3B. SIRT7 aggravated and KAT3B alleviated MG53-mediated cardiomyocyte injury. Moreover, MG53 was succinylated and ubiquitinated at K130.

CONCLUSION

SIRT7 inhibited/KAT3B promoted succinylation of MG53 at K130 sites, which suppressed ubiquitination of MG53 and upregulated its protein levels, thereby alleviating H/R-induced cardiomyocyte injury. The findings suggested that MG53 may be a potential therapy for myocardial infarction.

Is MG53 a potential therapeutic target for cancer?

Cancer treatment still encounters challenges, such as side effects and drug resistance. The tripartite-motif (TRIM) protein family is widely involved in regulation of the occurrence, development, and drug resistance of tumors. MG53, a member of the TRIM protein family, shows strong potential in cancer therapy, primarily due to its E3 ubiquitin ligase properties. The classic membrane repair function and anti-inflammatory capacity of MG53 may also be beneficial for cancer prevention and treatment. However, MG53 appears to be a key regulatory factor in impaired glucose metabolism and a negative regulatory mechanism in muscle regeneration that may have a negative effect on cancer treatment. Developing MG53 mutants that balance the pros and cons may be the key to solving the problem. This article aims to summarize the role and mechanism of MG53 in the occurrence, progression, and invasion of cancer, focusing on the potential impact of the biological function of MG53 on cancer therapy.

Structure and activation of the RING E3 ubiquitin ligase TRIM72 on the membrane

Defects in plasma membrane repair can lead to muscle and heart diseases in humans. Tripartite motif-containing protein (TRIM)72 (mitsugumin 53; MG53) has been determined to rapidly nucleate vesicles at the site of membrane damage, but the underlying molecular mechanisms remain poorly understood. Here we present the structure of Mus musculus TRIM72, a complete model of a TRIM E3 ubiquitin ligase. We demonstrated that the interaction between TRIM72 and phosphatidylserine-enriched membranes is necessary for its oligomeric assembly and ubiquitination activity. Using cryogenic electron tomography and subtomogram averaging, we elucidated a higher-order model of TRIM72 assembly on the phospholipid bilayer. Combining structural and biochemical techniques, we developed a working molecular model of TRIM72, providing insights into the regulation of RING-type E3 ligases through the cooperation of multiple domains in higher-order assemblies. Our findings establish a fundamental basis for the study of TRIM E3 ligases and have therapeutic implications for diseases associated with membrane repair.

MG53 does not mark cardiovascular risk and all-cause mortality in subjects with type 2 diabetes: A prospective, observational study

AIMS

Subjects with type 2 diabetes (T2D) are characterized by a high cardiovascular morbidity and mortality. MG53, a marker of peripheral insulin resistance, has been linked with impaired β-cell function and decreased β-cell survival, and its circulating levels are increased in T2D. Its relationship with the cardiovascular risk profile and mortality in T2D is currently unknown.

METHODS

In this longitudinal study, MG53 was measured in serum samples collected at baseline for 296 Caucasian participants in the MIND.IT study, relating its circulating levels with the cardiovascular risk profile and all-cause mortality over a 17-years follow up.

RESULTS

As compared to a reference cohort of 234 healthy subjects, MG53 levels were higher in T2D individuals (p < 0.001), and higher in T2D women than in men (p = 0.001). In the whole study cohort, MG53 levels were directly related to HbA1c (r2 0.029; p = 0.006) and systolic blood pressure (r2 0.032; p = 0.004). There was no difference in baseline MG53 levels between deceased and alive participants, neither predict all-cause mortality.

CONCLUSIONS

MG53 does not mark the cardiovascular risk profile neither predict long-term mortality in Caucasian T2D individuals.

Activation of MG53 Enhances Cell Survival and Engraftment of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes in Injured Hearts

BACKGROUND AND OBJECTIVE

Our previous studies demonstrated that MG53 protein can protect the myocardium, but its use as a therapeutic is challenging due to its short half-life in blood circulation. This study aimed to investigate the cardioprotective role of MG53 on human induced pluripotent stem cell-derived cardiomyocytes (HiPSC-CMs) in the context of myocardial ischemia/reperfusion (I/R).

METHODS

In vitro: HiPSC-CMs were transfected with adenoviral MG53 (HiPSC-CMsMG53), in which the expression of MG53 can be controlled by doxycycline (Dox), and the cells were then exposed to H2O2 to mimic ischemia/reperfusion injury. In vivo: HiPSC-CMsMG53 were transplanted into the peri-infarct region in NSG™ mice after I/R. After surgery, mice were treated with Dox (+ Dox) to activate MG53 expression (sucrose as a control of -Dox) and then assessed by echocardiography and immunohistochemistry.

RESULTS

MG53 can be expressed in HiPSC-CMMG53 and released into the culture medium after adding Dox. The cell survival rate of HiPSC-CMMG53 was improved by Dox under the H2O2 condition. After 14 and 28 days of ischemia/reperfusion (I/R), transplanted HiPSC-CMsMG53 + Dox significantly improved heart function, including ejection fraction (EF) and fractional shortening (FS) in mice, compared to HiPSC-CMsMG53-Dox, and reduced the size of the infarction. Additionally, HiPSC-CMMG53 + Dox mice demonstrated significant engraftment in the myocardium as shown by staining human nuclei-positive cells. In addition, the cell survival-related AKT signaling was found to be more active in HiPSC-CMMG53 + Dox transplanted mice's myocardium compared to the HiPSC-CMMG53-Dox group. Notably, the Dox treatment did not cause harm to other organs.

CONCLUSION

Inducible MG53 expression is a promising approach to enhance cell survival and engraftment of HiPSC-CMs for cardiac repair.

Association of MG53 with presence of type 2 diabetes mellitus, glycemic control, and diabetic complications

OBJECTIVES

Mitsugumin 53 (MG53) is a myokine that acts as a membrane repair protein in tissues. Data on the effect of MG53 on insulin signaling and type 2 diabetes mellitus (T2 DM) are still unknown; most are from preclinical studies. Nevertheless, some researchers have argued that it may be a new pathogenic factor, and therapies targeting MG53 may be a new avenue for T2 DM. Our study aims to evaluate the relationship of circulating MG53 levels with the presence of diabetes, diabetic complications, and glycemic control.

METHODS

We conducted a case-control study with 107 patients with T2 DM and 105 subjects without insulin resistance-related disease. Concurrent blood samples were used for serum MG53 levels and other biochemical laboratory data. MG53 concentration was measured using Human-MG53, an enzyme-linked immunosorbent assay kit (Cat# CSB-EL024511HU).

RESULTS

We found no difference in MG53 levels between the diabetic and control groups (p = 0.914). Furthermore, when the subjects were divided into tertiles according to their MG53 levels, we did not find any difference between the groups in terms of the presence of diabetes (p = 0.981). Additionally, no correlation was observed between weight, BMI, waist circumference, systolic and diastolic blood pressure, fasting blood glucose, HbA1c, albumin excretion in the urine, e-GFR levels, and MG53. Finally, MG53 levels were similar between the groups with and without microvascular and macrovascular complications of diabetes.

CONCLUSION

Our research finding provides insightful clinical evidence of lack of association between the levels of MG53 and T2 DM or glycemic control, at least in the studied population of Turkeys ethnicity. However, further clinical studies are warranted to establish solid evidence of the link between MG53, insulin resistance and glycemic control in a wider population elsewhere in the world.

E3 ligase MG53 suppresses tumor growth by degrading cyclin D1

Due to the essential role of cyclin D1 in regulating transition from G1 to S phase in cell cycle, aberrant cyclin D1 expression is a major oncogenic event in many types of cancers. In particular, the dysregulation of ubiquitination-dependent degradation of cyclin D1 contributes to not only the pathogenesis of malignancies but also the refractory to cancer treatment regiments with CDK4/6 inhibitors. Here we show that in colorectal and gastric cancer patients, MG53 is downregulated in more than 80% of tumors compared to the normal gastrointestinal tissues from the same patient, and the reduced MG53 expression is correlated with increased cyclin D1 abundance and inferior survival. Mechanistically, MG53 catalyzes the K48-linked ubiquitination and subsequent degradation of cyclin D1. Thus, increased expression of MG53 leads to cell cycle arrest at G1, and thereby markedly suppresses cancer cell proliferation in vitro as well as tumor growth in mice with xenograft tumors or AOM/DSS induced-colorectal cancer. Consistently, MG53 deficiency results in accumulation of cyclin D1 protein and accelerates cancer cell growth both in culture and in animal models. These findings define MG53 as a tumor suppressor via facilitating cyclin D1 degradation, highlighting the therapeutic potential of targeting MG53 in treating cancers with dysregulated cyclin D1 turnover.

The Activation Mechanism of the Insulin Receptor: A Structural Perspective

The insulin receptor (IR) is a type II receptor tyrosine kinase that plays essential roles in metabolism, growth, and proliferation. Dysregulation of IR signaling is linked to many human diseases, such as diabetes and cancers. The resolution revolution in cryo-electron microscopy has led to the determination of several structures of IR with different numbers of bound insulin molecules in recent years, which have tremendously improved our understanding of how IR is activated by insulin. Here, we review the insulin-induced activation mechanism of IR, including (a) the detailed binding modes and functions of insulin at site 1 and site 2 and (b) the insulin-induced structural transitions that are required for IR activation. We highlight several other key aspects of the activation and regulation of IR signaling and discuss the remaining gaps in our understanding of the IR activation mechanism and potential avenues of future research.

Islr regulates insulin sensitivity by interacting with Psma4 to control insulin receptor alpha levels in obese mice

Insulin resistance is the leading cause of type 2 diabetes (T2D), and dysfunctional insulin receptor signaling is a major manifestation of this insulin resistance. In T2D, the corresponding insulin receptor levels are aberrantly down-regulated, which is one of the major factors underlying obesity-induced insulin resistance in adipose tissue. However, the precise mechanism of insulin receptor impairment in obese individuals remains unclear. In the current study, we established that immunoglobulin superfamily containing leucine-rich repeat (Islr) is highly expressed in adipocytes of mice fed a high-fat diet. We further demonstrated that Islr mediates the ubiquitin-independent proteasomal degradation of insulin receptor alpha (Insrα) by specifically interacting with proteasome subunit alpha type 4 (Psma4). Islr knockout increased the corresponding Insrα subunit levels and enhanced insulin sensitivity in adipocytes, ultimately improving systemic metabolism. Further, siRNA-mediated down-regulation of Islr expression in the white adipose tissue of obese mice increased insulin sensitivity. Overall, Islr regulates insulin sensitivity by interacting with Psma4 to control the ubiquitin-independent proteasomal degradation of Insrα in obese mice, indicating that Islr may be a potential therapeutic target for ameliorating insulin resistance.

Structural basis for TRIM72 oligomerization during membrane damage repair

Tripartite Motif Protein 72 (TRIM72, also named MG53) mediates membrane damage repair through membrane fusion and exocytosis. During injury, TRIM72 molecules form intermolecular disulfide bonds in response to the oxidative environment and TRIM72 oligomers are proposed to connect vesicles to the plasma membrane and promote membrane fusion in conjunction with other partners like dysferlin and caveolin. However, the detailed mechanism of TRIM72 oligomerization and action remains unclear. Here we present the crystal structure of TRIM72 B-box-coiled-coil-SPRY domains (BCC-SPRY), revealing the molecular basis of TRIM72 oligomerization, which is closely linked to disulfide bond formation. Through structure-guided mutagenesis, we have identified and characterized key residues that are important for the membrane repair function of TRIM72. Our results also demonstrate that TRIM72 interacts with several kinds of negatively charged lipids in addition to phosphatidylserine. Our work provides a structural foundation for further mechanistic studies as well as the clinical application of TRIM72.

MG53: A potential therapeutic target for kidney disease

Ensuring cell survival and tissue regeneration by maintaining cellular integrity is important to the pathophysiology of many human diseases, including kidney disease. Mitsugumin 53 (MG53) is a member of the tripartite motif-containing (TRIM) protein family that plays an essential role in repairing cell membrane injury and improving tissue regeneration. In recent years, an increasing number of studies have demonstrated that MG53 plays a renoprotective role in kidney diseases. Moreover, with the beneficial effects of the recombinant human MG53 (rhMG53) protein in the treatment of kidney diseases in different animal models, rhMG53 shows significant therapeutic potential in kidney disease. In this review, we elucidate the role of MG53 and its molecular mechanism in kidney disease to provide new approaches to the treatment of kidney disease.

The insulin receptor endocytosis

Insulin signaling controls multiple aspects of animal physiology. At the cell surface, insulin binds and activates the insulin receptor (IR), a receptor tyrosine kinase. Insulin promotes a large conformational change of IR and stabilizes the active conformation. The insulin-activated IR triggers signaling cascades, thus controlling metabolism, growth, and proliferation. The activated IR undergoes internalization by clathrin- or caveolae-mediated endocytosis. The IR endocytosis plays important roles in insulin clearance from blood, and distribution and termination of the insulin signaling. Despite decades of extensive studies, the mechanism and regulation of IR endocytosis and its contribution to pathophysiology remain incompletely understood. Here we discuss recent findings that provide insights into the molecular mechanisms and regulatory pathways that mediate the IR endocytosis.

Blocking MG53S255 Phosphorylation Protects Diabetic Heart From Ischemic Injury

BACKGROUND

As an integral component of cell membrane repair machinery, MG53 (mitsugumin 53) is important for cardioprotection induced by ischemia preconditioning and postconditioning. However, it also impairs insulin signaling via its E3 ligase activity-mediated ubiquitination-dependent degradation of IR (insulin receptor) and IRS1 (insulin receptor substrate 1) and its myokine function-induced allosteric blockage of IR. Here, we sought to develop MG53 into a cardioprotection therapy by separating its detrimental metabolic effects from beneficial actions.

METHODS

Using immunoprecipitation-mass spectrometry, site-specific mutation, in vitro kinase assay, and in vivo animal studies, we investigated the role of MG53 phosphorylation at serine 255 (S255). In particular, utilizing recombinant proteins and gene knock-in approaches, we evaluated the potential therapeutic effect of MG53-S255A mutant in treating cardiac ischemia/reperfusion injury in diabetic mice.

RESULTS

We identified S255 phosphorylation as a prerequisite for MG53 E3 ligase activity. Furthermore, MG53^S255 phosphorylation was mediated by GSK3β (glycogen synthase kinase 3 beta) and markedly elevated in the animal models with metabolic disorders. Thus, IR-IRS1-GSK3β-MG53 formed a vicious cycle in the pathogenesis of metabolic disorders where aberrant insulin signaling led to hyper-activation of GSK3β, which in turn, phosphorylated MG53 and enhanced its E3 ligase activity, and further impaired insulin sensitivity. Importantly, S255A mutant eliminated the E3 ligase activity while retained cell protective function of MG53. Consequently, the S255A mutant, but not the wild type MG53, protected the heart against ischemia/reperfusion injury in db/db mice with advanced diabetes, although both elicited cardioprotection in normal mice. Moreover, in S255A knock-in mice, S255A mutant also mitigated ischemia/reperfusion-induced myocardial damage in the diabetic setting.

CONCLUSIONS

S255 phosphorylation is a biased regulation of MG53 E3 ligase activity. The MG53-S255A mutant provides a promising approach for the treatment of acute myocardial injury, especially in patients with metabolic disorders.

Protective role of MG53 against ischemia/reperfusion injury on multiple organs: A narrative review

Ischemia/reperfusion (I/R) injury is a common clinical problem after coronary angioplasty, cardiopulmonary resuscitation, and organ transplantation, which can lead to cell damage and death. Mitsugumin 53 (MG53), also known as Trim72, is a conservative member of the TRIM family and is highly expressed in mouse skeletal and cardiac muscle, with minimal amounts in humans. MG53 has been proven to be involved in repairing cell membrane damage. It has a protective effect on I/R injury in multiple oxygen-dependent organs, such as the heart, brain, lung, kidney, and liver. Recombinant human MG53 also plays a unique role in I/R, sepsis, and other aspects, which is expected to provide new ideas for related treatment. This article briefly reviews the pathophysiology of I/R injury and how MG53 mitigates multi-organ I/R injury.

Central role of Prominin-1 in lipid rafts during liver regeneration

Prominin-1, a lipid raft protein, is required for maintaining cancer stem cell properties in hepatocarcinoma cell lines, but its physiological roles in the liver have not been well studied. Here, we investigate the role of Prominin-1 in lipid rafts during liver regeneration and show that expression of Prominin-1 increases after 2/3 partial hepatectomy or CCl₄ injection. Hepatocyte proliferation and liver regeneration are attenuated in liver-specific Prominin-1 knockout mice compared to wild-type mice. Detailed mechanistic studies reveal that Prominin-1 interacts with the interleukin-6 signal transducer glycoprotein 130, confining it to lipid rafts so that STAT3 signaling by IL-6 is effectively activated. The overexpression of the glycosylphosphatidylinsositol-anchored first extracellular domain of Prominin-1, which is the domain that binds to GP130, rescued the proliferation of hepatocytes and liver regeneration in liver-specific Prominin-1 knockout mice. In summary, Prominin-1 is upregulated in hepatocytes during liver regeneration where it recruits GP130 into lipid rafts and activates the IL6-GP130-STAT3 axis, suggesting that Prominin-1 might be a promising target for therapeutic applications in liver transplantation.

Cryo-EM structure of human MG53 homodimer

MG53 is a tripartite motif (TRIM) family E3 ligase and plays important biological functions. Here we present the cryo-EM structure of human MG53, showing that MG53 is a homodimer consisting of a "body" and two "wings". Intermolecular interactions are mainly distributed in the "body" which is relatively stable, while two "wings" are more dynamic. The overall architecture of MG53 is distinct from those of TRIM20 and TRIM25, illustrating the broad structural diversity of this protein family.

The E3 ubiquitin ligase MG53 inhibits hepatocellular carcinoma by targeting RAC1 signaling

Ras-related C3 botulinum toxin substrate 1 (RAC1) overexpressiosn and hyperactivation are correlated with aggressive growth and other malignant characteristics in a wide variety of cancers including hepatocellular carcinoma (HCC). However, the regulatory mechanism of RAC1 expression and activation in HCC is not fully understood. Here, we demonstrated that E3 ubiquitin ligase MG53 (also known as tripartite motif 72, TRIM72) acted as a direct inhibitor of RAC1, and it catalyzed the ubiquitination of RAC1 and further inhibited RAC1 activity in HCC cells. Mechanistically, MG53 directly bound with RAC1 through its coiled-coil domain and suppressed RAC1 activity by catalyzing the Lys48 (K48)-linked polyubiquitination of RAC1 at Lys5 residue in HCC cells. We further demonstrated that MG53 significantly suppressed the malignant behaviors of HCC cells and enhanced the chemosensitivity of HCC cells to sorafenib treatment by inhibiting RAC1-MAPK signaling axis. In summary, we identified MG53 as a novel RAC1 inhibitor and tumor suppressor in HCC, and it suppressed HCC progression by inducing K48-linked polyubiquitination of RAC1 and further inhibiting the RAC1-MAPK signaling. Altogether, our investigation provided a new therapeutic strategy for RAC1 overactivated tumors by modulating MG53.

The Insulin Receptor: An Important Target for the Development of Novel Medicines and Pesticides

The insulin receptor (IR) is a transmembrane protein that is activated by ligands in insulin signaling pathways. The IR has been considered as a novel therapeutic target for clinical intervention, considering the overexpression of its protein and A-isoform in multiple cancers, Alzheimer's disease, and Type 2 diabetes mellitus in humans. Meanwhile, it may also serve as a potential target in pest management due to its multiple physiological influences in insects. In this review, we provide an overview of the structural and molecular biology of the IR, functions of IRs in humans and insects, physiological and nonpeptide small molecule modulators of the IR, and the regulating mechanisms of the IR. Xenobiotic compounds and the corresponding insecticidal chemicals functioning on the IR are also discussed. This review is expected to provide useful information for a better understanding of human IR-related diseases, as well as to facilitate the development of novel small-molecule activators and inhibitors of the IR for use as medicines or pesticides.

Ubiquitin Ligases in Longevity and Aging Skeletal Muscle

The development and prevalence of diseases associated with aging presents a global health burden on society. One hallmark of aging is the loss of proteostasis which is caused in part by alterations to the ubiquitin-proteasome system (UPS) and lysosome-autophagy system leading to impaired function and maintenance of mass in tissues such as skeletal muscle. In the instance of skeletal muscle, the impairment of function occurs early in the aging process and is dependent on proteostatic mechanisms. The UPS plays a pivotal role in degradation of misfolded and aggregated proteins. For the purpose of this review, we will discuss the role of the UPS system in the context of age-related loss of muscle mass and function. We highlight the significant role that E3 ubiquitin ligases play in the turnover of key components (e.g., mitochondria and neuromuscular junction) essential to skeletal muscle function and the influence of aging. In addition, we will briefly discuss the contribution of the UPS system to lifespan. By understanding the UPS system as part of the proteostasis network in age-related diseases and disorders such as sarcopenia, new discoveries can be made and new interventions can be developed which will preserve muscle function and maintain quality of life with advancing age.

MG53 preserves mitochondrial integrity of cardiomyocytes during ischemia reperfusion-induced oxidative stress

Ischemic injury to the heart induces mitochondrial dysfunction due to increasing oxidative stress. MG53, also known as TRIM72, is highly expressed in striated muscle, is secreted as a myokine after exercise, and is essential for repairing damaged plasma membrane of many tissues by interacting with the membrane lipid phosphatidylserine (PS). We hypothesized MG53 could preserve mitochondrial integrity after an ischemic event by binding to the mitochondrial-specific lipid, cardiolipin (CL), for mitochondria protection to prevent mitophagy. Fluorescent imaging and Western blotting experiments showed recombinant human MG53 (rhMG53) translocated to the mitochondria after ischemic injury in vivo and in vitro. Fluorescent imaging indicated rhMG53 treatment reduced superoxide generation in ex vivo and in vitro models. Lipid-binding assay indicated MG53 binds to CL. Transfecting cardiomyocytes with the mitochondria-targeted mt-mKeima showed inhibition of mitophagy after MG53 treatment. Overall, we show that rhMG53 treatment may preserve cardiac function by preserving mitochondria in cardiomyocytes. These findings suggest MG53's interactions with mitochondria could be an attractive avenue for developing MG53 as a targeted protein therapy for cardioprotection.

Reduced Sarcolemmal Membrane Repair Exacerbates Striated Muscle Pathology in a Mouse Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a common X-linked degenerative muscle disorder that involves mutations in the DMD gene that frequently reduce the expression of the dystrophin protein, compromising the structural integrity of the sarcolemmal membrane and leaving it vulnerable to injury during cycles of muscle contraction and relaxation. This results in an increased frequency of sarcolemma disruptions that can compromise the barrier function of the membrane and lead to death of the myocyte. Sarcolemmal membrane repair processes can potentially compensate for increased membrane disruptions in DMD myocytes. Previous studies demonstrated that TRIM72, a muscle-enriched tripartite motif (TRIM) family protein also known as mitsugumin 53 (MG53), is a component of the cell membrane repair machinery in striated muscle. To test the importance of membrane repair in striated muscle in compensating for the membrane fragility in DMD, we crossed TRIM72/MG53 knockout mice into the mdx mouse model of DMD. These double knockout (DKO) mice showed compromised sarcolemmal membrane integrity compared to mdx mice, as measured by immunoglobulin G staining and ex vivo muscle laser microscopy wounding assays. We also found a significant decrease in muscle ex vivo contractile function as compared to mdx mice at both 6 weeks and 1.5 years of age. As the DKO mice aged, they developed more extensive fibrosis in skeletal muscles compared to mdx. Our findings indicate that TRIM72/MG53-mediated membrane repair can partially compensate for the sarcolemmal fragility associated with DMD and that the loss of membrane repair results in increased pathology in the DKO mice.

Cytoplasmic HDAC4 regulates the membrane repair mechanism in Duchenne muscular dystrophy

BACKGROUND

Histone deacetylase 4 (HDAC4) is a stress-responsive factor that mediates multiple cellular responses. As a member of class IIa HDACs, HDAC4 shuttles between the nucleus and the cytoplasm; however, HDAC4 cytoplasmic functions have never been fully investigated. Duchenne muscular dystrophy (DMD) is a genetic, progressive, incurable disorder, characterized by muscle wasting, which can be treated with the unspecific inhibition of HDACs, despite this approach being only partially effective. More efficient strategies may be proposed for DMD only after the different HDAC members will be characterized.

METHODS

To fully understand HDAC4 functions, we generated dystrophic mice carrying a skeletal muscle-specific deletion of HDAC4 (mdx;KO mice). The progression of muscular dystrophy was characterized in mdx and age-matched mdx;KO mice by means of histological, molecular, and functional analyses. Satellite cells (SCs) from these mice were differentiated in vitro, to identify HDAC4 intrinsic functions influencing the myogenic potential of dystrophic SCs. Gain-of-function experiments revealed the cytoplasmic functions of HDAC4 in mdx;KO muscles.

RESULTS

Histone deacetylase 4 increased in the skeletal muscles of mdx mice (~3-fold; P < 0.05) and of DMD patients (n = 3, males, mean age 13.3 ± 1.5 years), suggesting that HDAC4 has a role in DMD. Its deletion in skeletal muscles importantly worsens the pathological features of DMD, leading to greater muscle fragility and degeneration over time. Additionally, it impairs SC survival, myogenic potential, and muscle regeneration, ultimately compromising muscle function (P < 0.05-0.001). The impaired membrane repair mechanism in muscles and SCs accounts for the mdx;KO phenotype. Indeed, the ectopic expression of Trim72, a major player in the membrane repair mechanism, prevents SC death (~20%; P < 0.01) and increases myogenic fusion (~40%; P < 0.01) in vitro; in vivo it significantly reduces myofibre damage (~10%; P < 0.005) and improves mdx;KO muscle function (P < 0.05). The mdx;KO phenotype is also fully rescued by restoring cytoplasmic levels of HDAC4, both in vitro and in vivo. The protective role of HDAC4 in the cytoplasm of mdx;KO muscles is, in part, independent of its deacetylase activity. HDAC4 expression correlates with Trim72 mRNA levels; furthermore, Trim72 mRNA decays more rapidly (P < 0.01) in mdx;KO muscle cells, compared with mdx ones.

CONCLUSIONS

Histone deacetylase 4 performs crucial functions in the cytoplasm of dystrophic muscles, by mediating the muscle repair response to damage, an important role in ensuring muscle homeostasis, probably by stabilizing Trim72 mRNA. Consequently, the cytoplasmic functions of HDAC4 should be stimulated rather than inhibited in muscular dystrophy treatments, a fact to be considered in future therapeutic approaches.

Membrane-delimited signaling and cytosolic action of MG53 preserve hepatocyte integrity during drug-induced liver injury

BACKGROUND & AIMS

Drug-induced liver injury (DILI) remains challenging to treat and is still a leading cause of acute liver failure. MG53 is a muscle-derived tissue-repair protein that circulates in the bloodstream and whose physiological role in protection against DILI has not been examined.

METHODS

Recombinant MG53 protein (rhMG53) was administered exogenously, using mice with deletion of Mg53 or Ripk3. Live-cell imaging, histological, biochemical, and molecular studies were used to investigate the mechanisms that underlie the extracellular and intracellular action of rhMG53 in hepatoprotection.

RESULTS

Systemic administration of rhMG53 protein, in mice, can prophylactically and therapeutically treat DILI induced through exposure to acetaminophen, tetracycline, concanavalin A, carbon tetrachloride, or thioacetamide. Circulating MG53 protects hepatocytes from injury through direct interaction with MLKL at the plasma membrane. Extracellular MG53 can enter hepatocytes and act as an E3-ligase to mitigate RIPK3-mediated MLKL phosphorylation and membrane translocation.

CONCLUSIONS

Our data show that the membrane-delimited signaling and cytosolic dual action of MG53 effectively preserves hepatocyte integrity during DILI. rhMG53 may be a potential treatment option for patients with DILI.

LAY SUMMARY

Interventions to treat drug-induced liver injury and halt its progression into liver failure are of great value to society. The present study reveals that muscle-liver cross talk, with MG53 as a messenger, serves an important role in liver cell protection. Thus, MG53 is a potential treatment option for patients with drug-induced liver injury.

Exercise mediates ubiquitin signalling in human skeletal muscle

Physical activity or regular exercise provides many beneficial effects towards human health, helping prevent and ameliorate metabolic diseases. However, certain molecular mechanisms that mediate these health benefits remain poorly understood. Parker et al. provided the first global analysis of exercise‐regulated ubiquitin signalling in human skeletal muscle, revealing post‐translational modification cross‐talk. As a result of their analysis, NEDDylation is thought to promote ubiquitin signalling for the removal of damaged proteins following exercise. The proteomic dataset generated from their study is invaluable for researchers in this field to validate new mechanistic hypotheses. To further reveal molecular mechanisms regulated by exercise, future research could employ more sensitive mass spectrometry‐based workflows that increase the detection of both ubiquitylated sites and peptides and subsequently identify more exercise‐regulated ubiquitin signalling pathways.

MG53 E3 Ligase-Dead Mutant Protects Diabetic Hearts From Acute Ischemic/Reperfusion Injury and Ameliorates Diet-Induced Cardiometabolic Damage

Cardiometabolic diseases, including diabetes and its cardiovascular complications, are the global leading causes of death, highlighting a major unmet medical need. Over the past decade, mitsugumin 53 (MG53), also called TRIM72, has emerged as a powerful agent for myocardial membrane repair and cardioprotection, but its therapeutic value is complicated by its E3 ligase activity, which mediates metabolic disorders. Here, we show that an E3 ligase-dead mutant, MG53-C14A, retains its cardioprotective function without causing metabolic adverse effects. When administered in normal animals, both the recombinant human wild-type MG53 protein (rhMG53-WT) and its E3 ligase-dead mutant (rhMG53-C14A) protected the heart equally from myocardial infarction and ischemia/reperfusion (I/R) injury. However, in diabetic db/db mice, rhMG53-WT treatment markedly aggravated hyperglycemia, cardiac I/R injury, and mortality, whereas acute and chronic treatment with rhMG53-C14A still effectively ameliorated I/R-induced myocardial injury and mortality or diabetic cardiomyopathy, respectively, without metabolic adverse effects. Furthermore, knock-in of MG53-C14A protected the mice from high-fat diet-induced metabolic disorders and cardiac damage. Thus, the E3 ligase-dead mutant MG53-C14A not only protects the heart from acute myocardial injury but also counteracts metabolic stress, providing a potentially important therapy for the treatment of acute myocardial injury in metabolic disorders, including diabetes and obesity.

Hyperuricemia contributes to glucose intolerance of hepatic inflammatory macrophages and impairs the insulin signaling pathway via IRS2-proteasome degradation

AIM

Numerous reports have demonstrated the key importance of macrophage-elicited metabolic inflammation in insulin resistance (IR). Our previous studies confirmed that hyperuricemia or high uric acid (HUA) treatment induced an IR state in several peripheral tissues to promote the development of type 2 diabetes mellitus (T2DM). However, the effect of HUA on glucose uptake and the insulin sensitivity of macrophages and its mechanism is unclear.

METHODS

To assess systemic IR, we generated hyperuricemic mice by urate oxidase knockout (UOX-KO). Then, glucose/insulin tolerance, the tissue uptake of 18F-fluorodeoxyglucose, body composition, and energy balance were assessed. Glucose uptake of circulating infiltrated macrophages in the liver was evaluated by glucose transporter type 4 (GLUT-4) staining. Insulin sensitivity and the insulin signaling pathway of macrophages were demonstrated using the 2-NBDG kit, immunoblotting, and immunofluorescence assays. The immunoprecipitation assay and LC-MS analysis were used to determine insulin receptor substrate 2 (IRS2) levels and its interacting protein enrichment under HUA conditions.

RESULTS

Compared to WT mice (10 weeks old), serum uric acid levels were higher in UOX-KO mice (WT, 182.3 ± 5.091 μM versus KO, 421.9 ± 45.47 μM). Hyperuricemic mice with metabolic disorders and systemic IR showed inflammatory macrophage recruitment and increased levels of circulating proinflammatory cytokines. HUA inhibited the nuclear translocation of GLUT-4 in hepatic macrophages, restrained insulin-induced glucose uptake and glucose tolerance, and blocked insulin IRS2/PI3K/AKT signaling. Meanwhile, HUA mediated the IRS2 protein degradation pathway and activated AMPK/mTOR in macrophages. LC-MS analysis showed that ubiquitination degradation could be involved in IRS2 and its interacting proteins to contribute to IR under HUA conditions.

CONCLUSION

The data suggest that HUA-induced glucose intolerance in hepatic macrophages contributed to insulin resistance and impaired the insulin signaling pathway via IRS2-proteasome degradation.

MG53 Preserves Neuromuscular Junction Integrity and Alleviates ALS Disease Progression

Respiratory failure from progressive respiratory muscle weakness is the most common cause of death in amyotrophic lateral sclerosis (ALS). Defects in neuromuscular junctions (NMJs) and progressive NMJ loss occur at early stages, thus stabilizing and preserving NMJs represents a potential therapeutic strategy to slow ALS disease progression. Here we demonstrate that NMJ damage is repaired by MG53, an intrinsic muscle protein involved in plasma membrane repair. Compromised diaphragm muscle membrane repair and NMJ integrity are early pathological events in ALS. Diaphragm muscles from ALS mouse models show increased susceptibility to injury and intracellular MG53 aggregation, which is also a hallmark of human muscle samples from ALS patients. We show that systemic administration of recombinant human MG53 protein in ALS mice protects against injury to diaphragm muscle, preserves NMJ integrity, and slows ALS disease progression. As MG53 is present in circulation in rodents and humans under physiological conditions, our findings provide proof-of-concept data supporting MG53 as a potentially safe and effective therapy to mitigate ALS progression.

MG53 suppresses tumor progression and stress granule formation by modulating G3BP2 activity in non-small cell lung cancer

Background

Cancer cells develop resistance to chemotherapeutic intervention by excessive formation of stress granules (SGs), which are modulated by an oncogenic protein G3BP2. Selective control of G3BP2/SG signaling is a potential means to treat non-small cell lung cancer (NSCLC).

Methods

Co-immunoprecipitation was conducted to identify the interaction of MG53 and G3BP2. Immunohistochemistry and live cell imaging were performed to visualize the subcellular expression or co-localization. We used shRNA to knock-down the expression MG53 or G3BP2 to test the cell migration and colony formation. The expression level of MG53 and G3BP2 in human NSCLC tissues was tested by western blot analysis. The ATO-induced oxidative stress model was used to examine the effect of rhMG53 on SG formation. Moue NSCLC allograft experiments were performed on wild type and transgenic mice with either knockout of MG53, or overexpression of MG53. Human NSCLC xenograft model in mice was used to evaluate the effect of MG53 overexpression on tumorigenesis.

Results

We show that MG53, a member of the TRIM protein family (TRIM72), modulates G3BP2 activity to control lung cancer progression. Loss of MG53 results in the progressive development of lung cancer in mg53^-/- mice. Transgenic mice with sustained elevation of MG53 in the bloodstream demonstrate reduced tumor growth following allograft transplantation of mouse NSCLC cells. Biochemical assay reveals physical interaction between G3BP2 and MG53 through the TRIM domain of MG53. Knockdown of MG53 enhances proliferation and migration of NSCLC cells, whereas reduced tumorigenicity is seen in NSCLC cells with knockdown of G3BP2 expression. The recombinant human MG53 (rhMG53) protein can enter the NSCLC cells to induce nuclear translation of G3BP2 and block arsenic trioxide-induced SG formation. The anti-proliferative effect of rhMG53 on NSCLC cells was abolished with knockout of G3BP2. rhMG53 can enhance sensitivity of NSCLC cells to undergo cell death upon treatment with cisplatin. Tailored induction of MG53 expression in NSCLC cells suppresses lung cancer growth via reduced SG formation in a xenograft model.

Conclusion

Overall, these findings support the notion that MG53 functions as a tumor suppressor by targeting G3BP2/SG activity in NSCLCs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-021-01418-3.

MG53 inhibits angiogenesis through regulating focal adhesion kinase signalling

Mitsugumin 53 (MG53), which is expressed predominantly in striated muscle, has been demonstrated to be a myokine/cardiokine secreted from striated muscle under specific conditions. The important roles of MG53 in non-striated muscle tissues have also been examined in multiple disease models. However, no previous study has implicated MG53 in the control of endothelial cell function. In order to explore the effects of MG53 on endothelial cells, human umbilical vein endothelial cells (HUVECs) were stimulated with recombinant human MG53 (rhMG53). Then, rhMG53 uptake, focal adhesion kinase (FAK)/Src/Akt/ERK1/2 signalling pathway activation, cell migration and tube formation were determined in vitro. The efficacy of rhMG53 in regulating angiogenesis was also detected in postnatal mouse retinas. The results demonstrated that rhMG53 directly entered into endothelial cells in a cholesterol-dependent manner. The uptake of rhMG53 directly bound to FAK in endothelial cells, which resulted in a significant decrease in FAK phosphorylation at Y397. Accompanied by the dephosphorylation of FAK, rhMG53 uncoupled FAK-Src interaction and reduced the phosphorylation of Src at Y416. Consequently, the activation of FAK/Src downstream signalling pathways, such as Akt and ERK1/2, was also significantly inhibited by rhMG53. Furthermore, rhMG53 remarkably decreased HUVEC migration and tube formation in vitro and postnatal mouse retinal angiogenesis in vivo. Taken together, these data indicate that rhMG53 inhibits angiogenesis through regulating FAK/Src/Akt/ERK1/2 signalling pathways. This may provide a novel molecular mechanism for the impaired angiogenesis in ischaemic diseases.

Cardiac effects and clinical applications of MG53

Heart disease remains the leading cause of mortality globally, so further investigation is required to identify its underlying mechanisms and potential targets for treatment and prevention. Mitsugumin 53 (MG53), also known as TRIM72, is a TRIM family protein that was found to be involved in cell membrane repair and primarily found in striated muscle. Its role in skeletal muscle regeneration and myogenesis has been well documented. However, accumulating evidence suggests that MG53 has a potentially protective role in heart tissue, including in ischemia/reperfusion injury of the heart, cardiomyocyte membrane injury repair, and atrial fibrosis. This review summarizes the regulatory role of MG53 in cardiac tissues, current debates regarding MG53 in diabetes and diabetic cardiomyopathy, as well as highlights potential clinical applications of MG53 in treating cardiac pathologies.

Role of UPP pathway in amelioration of diabetes-associated complications

Type 2 diabetes (T2D) is one of the most widely spread metabolic disorder also called as "life style" disease. Due to the alarming number of patients, there is great need to therapies targeting functions which can help in maintaining the homeostasis of glucose levels and improving insulin sensitivity. Detailed analysis was done through various research and review papers which was searched using MEDLINE, BIOSIS, and EMBASE using various keywords. This search retrieved the most appropriate content on these molecules targeting UPP pathway. From this extensive review involving UPP pathway, it was concluded that the role of ubiquitin's is not only limited to neurodegenerative disorders but also plays a critical role in progression of diabetes including obesity, insulin resistance, and various neurogenerative disorders but it also targets proteasomal degradation including mediation of cellular signaling pathways. Thus, drugs targeting UPP not only may show effect against diabetes but also are therapeutically beneficial in the treatment of diabetes-associated complications which may be obtained. Thus, based on the available information and data on UPP functions, it can be concluded that regulation of UPP pathway via downstream regulators mainly E1, E2, and E3 may bring promising results. Drugs targeting these transcriptional factors may emerge as a novel therapy in the treatment of diabetes and diabetes-associated complications.

Photobiomodulation therapy ameliorates hyperglycemia and insulin resistance by activating cytochrome c oxidase-mediated protein kinase B in muscle

Ameliorating hyperglycemia and insulin resistance are major therapeutic strategies for type 2 diabetes. Previous studies have indicated that photobiomodulation therapy (PBMT) attenuates metabolic abnormalities in insulin-resistant adipose cells and tissues. However, it remains unclear whether PBMT ameliorates glucose metabolism in skeletal muscle in type 2 diabetes models. Here we showed that PBMT reduced blood glucose and insulin resistance, and reversed metabolic abnormalities in skeletal muscle in two diabetic mouse models. PBMT accelerated adenosine triphosphate (ATP) and reactive oxygen species (ROS) generation by elevating cytochrome c oxidase (CcO) activity. ROS-induced activation of phosphatase and tensin homolog (PTEN)/ protein kinase B (AKT) signaling after PBMT promoted glucose transporter GLUT4 translocation and glycogen synthase (GS) activation, accelerating glucose uptake and glycogen synthesis in skeletal muscle. CcO subunit III deficiency, ROS elimination, and AKT inhibition suppressed the PBMT effects of glucose metabolism in skeletal muscle. This study indicated amelioration of glucose metabolism after PBMT in diabetic mouse models and revealed the metabolic regulatory effects and mechanisms of PBMT on skeletal muscle.

MG53 is not a critical regulator of insulin signaling pathway in skeletal muscle

In type 2 diabetes (T2D), both muscle and liver are severely resistant to insulin action. Muscle insulin resistance accounts for more than 80% of the impairment in total body glucose disposal in T2D patients and is often characterized by an impaired insulin signaling. Mitsugumin 53 (MG53), a muscle-specific TRIM family protein initially identified as a key regulator of cell membrane repair machinery has been suggested to be a critical regulator of muscle insulin signaling pathway by acting as ubiquitin E3 ligase targeting both the insulin receptor and insulin receptor substrate 1 (IRS1). Here, we show using in vitro and in vivo approaches that MG53 is not a critical regulator of insulin signaling and glucose homeostasis. First, MG53 expression is not consistently regulated in skeletal muscle from various preclinical models of insulin resistance. Second, MG53 gene knock-down in muscle cells does not lead to impaired insulin response as measured by Akt phosphorylation on Serine 473 and glucose uptake. Third, recombinant human MG53 does not alter insulin response in both differentiated C2C12 and human skeletal muscle cells. Fourth, ectopic expression of MG53 in HEK293 cells lacking endogenous MG53 expression fails to alter insulin response as measured by Akt phosphorylation. Finally, both male and female mg53 -/- mice were not resistant to high fat induced obesity and glucose intolerance compared to wild-type mice. Taken together, these results strongly suggest that MG53 is not a critical regulator of insulin signaling pathway in skeletal muscle.

Negative regulation of AMPK signaling by high glucose via E3 ubiquitin ligase MG53

As a master regulator of metabolism, AMP-activated protein kinase (AMPK) is activated upon energy and glucose shortage but suppressed upon overnutrition. Exaggerated negative regulation of AMPK signaling by nutrient overload plays a crucial role in metabolic diseases. However, the mechanism underlying the negative regulation is poorly understood. Here, we demonstrate that high glucose represses AMPK signaling via MG53 (also called TRIM72) E3-ubiquitin-ligase-mediated AMPKα degradation and deactivation. Specifically, high-glucose-stimulated reactive oxygen species (ROS) signals AKT to phosphorylate AMPKα at S485/491, which facilitates the recruitment of MG53 and the subsequent ubiquitination and degradation of AMPKα. In addition, high glucose deactivates AMPK by ROS-dependent suppression of phosphorylation of AMPKα at T172. These findings not only delineate the mechanism underlying the impairment of AMPK signaling in overnutrition-related diseases but also highlight the significance of keeping the yin-yang balance of AMPK signaling in the maintenance of metabolic homeostasis.

Multi-Cellular Functions of MG53 in Muscle Calcium Signaling and Regeneration

Since its identification in 2009, multiple studies have indicated the importance of MG53 in muscle physiology. The protein is produced in striated muscles but has physiologic implications reaching beyond the confines of striated muscles. Roles in muscle regeneration, calcium homeostasis, excitation-contraction coupling, myogenesis, and the mitochondria highlight the protein's wide-reaching impact. Numerous therapeutic applications could potentially emerge from these physiologic roles. This review summarizes the current literature regarding the role of MG53 in the skeletal muscle. Therapeutic applications are discussed.