MG53, A Tissue Repair Protein with Broad Applications in Regenerative Medicine

Fracture haematoma proteomics

Aims

The aim of this study was to determine the fracture haematoma (fxH) proteome after multiple trauma using label-free proteomics, comparing two different fracture treatment strategies.

Methods

A porcine multiple trauma model was used in which two fracture treatment strategies were compared: early total care (ETC) and damage control orthopaedics (DCO). fxH was harvested and analyzed using liquid chromatography-tandem mass spectrometry. Per group, discriminating proteins were identified and protein interaction analyses were performed to further elucidate key biomolecular pathways in the early fracture healing phase.

Results

The early fxH proteome was characterized by immunomodulatory and osteogenic proteins, and proteins involved in the coagulation cascade. Treatment-specific proteome alterations were observed. The fxH proteome of the ETC group showed increased expression of pro-inflammatory proteins related to, among others, activation of the complement system, neutrophil functioning, and macrophage activation, while showing decreased expression of proteins related to osteogenesis and tissue remodelling. Conversely, the fxH proteome of the DCO group contained various upregulated or exclusively detected proteins related to tissue regeneration and remodelling, and proteins related to anti-inflammatory and osteogenic processes.

Conclusion

The early fxH proteome of the ETC group was characterized by the expression of immunomodulatory, mainly pro-inflammatory, proteins, whereas the early fxH proteome of the DCO group was more regenerative and osteogenic in nature. These findings match clinical observations, in which enhanced surgical trauma after multiple trauma causes dysbalanced inflammation, potentially leading to reduced tissue regeneration, and gained insights into regulatory mechanisms of fracture healing after severe trauma.

MG53/GMs/HA-Dex neural scaffold promotes the functional recovery of spinal cord injury by alleviating neuroinflammation

The adverse microenvironment, including neuroinflammation, hinders the recovery of spinal cord injury (SCI). Regulating microglial polarization to alleviate neuroinflammation at the injury site is an effective strategy for SCI recovery. MG53 protein exerts obvious repair ability on multiple tissues damage, but with short half-life. In this study, we composited an innovative MG53/GMs/HA-Dex neural scaffold using gelatin microspheres (GMs), hyaluronic acid (HA), and dextran (Dex) loaded with MG53 protein. This novel neural scaffold could respond to MMP-2/9 protein and stably release MG53 protein with good physicochemical properties and biocompatibility. In addition, it significantly improved the motor function of SCI mice, suppressed M1 polarization of microglia and neuroinflammation, and promoted neurogenesis and axon regeneration. Further mechanistic experiments demonstrated that MG53/GMs/HA-Dex hydrogel inhibited the JAK2/STAT3 signaling pathway. Thus, this MG53/GMs/HA-Dex neural scaffold promotes the functional recovery of SCI mice by alleviating neuroinflammation, which provides a new intervention strategy for the neural regeneration and functional repair of SCI.

Alkylation Repair Homolog 5 Regulates N(6)-methyladenosine (m6A) Methylation of Mitsugumin 53 to Attenuate Myocardial Infarction by Inhibiting Apoptosis and Oxidative Stress

ABSTRACT

N(6)-methyladenosine (m6A) methylation modification is involved in the progression of myocardial infarction (MI). In this study, we investigated the effects of demethylase alkylation repair homolog 5 (ALKBH5) on cell apoptosis and oxidative stress in MI. The ischemia/reperfusion (I/R) injury mouse model and hypoxia/reoxygenation (H/R) cell model were established. The levels of ALKBH5 and mitsugumin 53 (MG53) were measured by quantitative real-time polymerase chain reaction, immunohistochemical, and immunofluorescence analysis. Apoptosis was evaluated by TUNEL assay, flow cytometry, and western blot. Oxidative stress was assessed by antioxidant index kits. Methylation was analyzed by RNA binding protein immunoprecipitation (RIP), MeRIP, and dual-luciferase reporter assay. We observed that ALKBH5 and MG53 were highly expressed in MI. Overexpression of ALKBH5 inhibited H/R-induced cardiomyocyte apoptosis and oxidative stress in vitro, and it inhibited I/R-induced collagen deposition, cardiac function, and apoptosis in vivo. ALKBH5 could bind to MG53, inhibit m6A methylation of MG53, and increase its mRNA stability. Silencing of MG53 counteracted the inhibition of apoptosis and oxidative stress induced by ALKBH5. In conclusion, ALKBH5 suppressed m6A methylation of MG53 and inhibited MG53 degradation to inhibit apoptosis and oxidative stress of cardiomyocytes, thereby attenuating MI. The results provided a theoretical basis that ALKBH5 is a potential target for MI treatment.

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.

MG53 alleviates airway inflammatory responses by regulating nuclear factor-κB pathway in asthmatic mice

BACKGROUND

Asthma is a common lung disease with increasing incidence and prevalence globally, thereby imposing a substantial global health and economic burden. Recently, studies have shown that Mitsugumin 53 (MG53) exhibits multiple biological functions and plays a protective role in a variety of diseases. However, the role of MG53 in asthma remained unknown; hence, in the present study we aimed to explore the functioning of MG53 in asthma.

METHODS

Using ovalbumin and aluminum hydroxide adjuvant, an OVA-induced asthmatic animal model was constructed and administered with MG53. After establishing mice model, inflammatory cell counts and the levels of type 2 inflammatory cytokines were examined and histological staining of lung tissues were performed. The levels of key factors associated with the nuclear factor-κB (NF-κB) pathway were detected.

RESULTS

Asthmatic mice displayed a remarkable accumulation of white blood cells, neutrophils, macrophages, lymphocytes, and eosinophils in bronchoalveolar lavage fluid, compared to control mice. MG53 treatment lowered the number of these inflammatory cells in asthmatic mice. The level of type 2 cytokines in asthmatic mice was higher than that in control mice, and was lessened by MG53 intervention. In asthmatic mice, airway resistance was elevated, which was reduced by MG53 treatment. In addition, inflammatory cell infiltration and mucus secretion were aggravated in the lung tissues of asthmatic mice, and both were attenuated by MG53 intervention. The levels of phosphorylated p65 and phosphorylated inhibitor of nuclear factor kappa-B kinase were elevated in asthmatic mice, but were downregulated by MG53 supplement.

CONCLUSION

The aggravated airway inflammation was observed in asthmatic mice; however, MG53 treatment suppressed airway inflammation by targeting the NF-κB pathway.

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.

TRIM72 Alleviates Muscle Inflammation in mdx Mice via Promoting Mitophagy-Mediated NLRP3 Inflammasome Inactivation

Chronic muscle inflammation exacerbates the pathogenesis of Duchenne muscular dystrophy (DMD), which is characterized by progressive muscle degeneration and weakness. NLRP3 (nucleotide-binding domain and leucine-rich repeat pyrin domain containing 3) inflammasome plays a key role in the inflammatory process, and its abnormal activation leads to a variety of inflammatory or immune diseases. TRIM72 (MG53) is a protective myokine for tissue repair and regeneration. However, little is known about the potential impact of TRIM72 in the crosstalk between mitophagy and inflammatory process of DMD. Here, 10-week-old male mdx mice were injected intramuscularly with adeno-associated virus (AAV-TRIM72) to overexpress TRIM72 protein for 6 weeks. Then, skeletal muscle samples were collected, and relevant parameters were measured by histopathological analysis and molecular biology techniques. C2C12 cell line was transfected with lentivirus (LV-TRIM72) to overexpress or siRNA (si-TRIM72) to suppress the TRIM72 expression for the following experiment. Our data firstly showed that the TRIM72 expression was decreased in skeletal muscles of mdx mice. Then, we observed the increased NLRP3 inflammasome and impaired mitophagy in mdx mice compared with wild type mice. In mdx mice, administration of AAV-TRIM72 alleviated the accumulation of NLRP3 inflammasome and the consequent IL-18 and IL1β maturation by inducing autophagy, while this protective effect was reversed by chloroquine. Mitochondrial reactive oxygen species (mtROS), as a recognized activator for NLRP3 inflammasome, was attenuated by TRIM72 through the induction of mitophagy in C2C12 cells. Additionally, we proposed that the TRIM72 overexpression might promote mitophagy through both the early stage by PI3K-AKT pathway and the late stage by autolysosome fusion. In conclusion, the current study suggests that TRIM72 prevents DMD inflammation via decreasing NLRP3 inflammasomes and enhancing mitophagy. Collectively, our study provides insight into TRIM72 as a promising target for therapeutic intervention for DMD.

Deficient Sarcolemma Repair in ALS: A Novel Mechanism with Therapeutic Potential

The plasma membrane (sarcolemma) of skeletal muscle myofibers is susceptible to injury caused by physical and chemical stresses during normal daily movement and/or under disease conditions. These acute plasma membrane disruptions are normally compensated by an intrinsic membrane resealing process involving interactions of multiple intracellular proteins including dysferlin, annexin, caveolin, and Mitsugumin 53 (MG53)/TRIM72. There is new evidence for compromised muscle sarcolemma repair mechanisms in Amyotrophic Lateral Sclerosis (ALS). Mitochondrial dysfunction in proximity to neuromuscular junctions (NMJs) increases oxidative stress, triggering MG53 aggregation and loss of its function. Compromised membrane repair further worsens sarcolemma fragility and amplifies oxidative stress in a vicious cycle. This article is to review existing literature supporting the concept that ALS is a disease of oxidative-stress induced disruption of muscle membrane repair that compromise the integrity of the NMJs and hence augmenting muscle membrane repair mechanisms could represent a viable therapeutic strategy for ALS.

A cell membrane repair protein-based nanoformulation with multiple actuators for scarless wound healing

Diabetic wounds remain a major contributor to disability worldwide due to their difficulty of healing, and their primary etiologic factor involves impaired cell membrane repair. Additionally, ideal wound repair should prevent excessive scar formation from affecting tissue function following reconstruction. Therefore, the development of a therapeutic strategy for promoting rapid wound healing and reduced scar formation is urgently needed. In this study, a remote light-controlled thermosensitive nanoformulation was developed, which integrated the photothermal conversion performance of a photosensitizer and cell membrane repair protein (rhMG53). The nanoformulation not only protected rhMG53 from being degraded by proteases at the lesion site but also efficiently released this protein through photothermal stimulation. The nanoformulation remained stable at physiological temperatures and released approximately 80% rhMG53 at 45 °C. More protein was effectively delivered to tissue cells, achieving synergistic therapy with photothermal and rhMG53. By utilizing this approach, increased wound closure rate, reduced extent of cell membrane damage and inflammation, and improved cell function were observed in diabetic wounds. More importantly, rhMG53@TSCL3 treatment inhibited excessive skin fibrosis and angiogenesis, indicating a reduction in scar formation. Collectively, this work reveals a promising strategy for high-quality wound repair and provides a new route for rapid scarless wound healing.

Cellular and molecular mechanisms underlying plasma membrane functionality and integrity

The plasma membrane not only protects the cell from the extracellular environment, acting as a selective barrier, but also regulates cellular events that originate at the cell surface, playing a key role in various biological processes that are essential for the preservation of cell homeostasis. Therefore, elucidation of the mechanisms involved in the maintenance of plasma membrane integrity and functionality is of utmost importance. Cells have developed mechanisms to ensure the quality of proteins that inhabit the cell surface, as well as strategies to cope with injuries inflicted to the plasma membrane. Defects in these mechanisms can lead to the development or onset of several diseases. Despite the importance of these processes, a comprehensive and holistic perspective of plasma membrane quality control is still lacking. To tackle this gap, in this Review, we provide a thorough overview of the mechanisms underlying the identification and targeting of membrane proteins that are to be removed from the cell surface, as well as the membrane repair mechanisms triggered in both physiological and pathological conditions. A better understanding of the mechanisms underlying protein quality control at the plasma membrane can reveal promising and unanticipated targets for the development of innovative therapeutic approaches.

TRIM72 exerts antitumor effects in breast cancer and modulates lactate production and MCT4 promoter activity by interacting with PPP3CA

A hypoxic tumor microenvironment (TME) promotes cancer progression, yet its value as a therapeutic target remains underexploited. Tripartite motif-containing 72 (TRIM72) may protect cells against various stresses including hypoxia. Recently, low TRIM72 expression has been implicated in cancer progression. However, the biological role and molecular mechanism of TRIM72 in breast cancer (BC) remain unclear. Herein, we analyzed the TRIM72 expression in BC tissue and cell lines by western blot (WB) and quantitative reverse transcription-PCR. We established the overexpression of TRIM72 using plasmids and lentiviral-mediated upregulation, as well as downregulation of protein phosphatase 3 catalytic subunit alpha (PPP3CA) by siRNA. The tumor-suppressive roles of TRIM72 were assessed on BT549 and MDA-MB-231 cells by MTS, Transwell, and flow cytometry assays in vitro and in xenografted tumors in vivo. The molecular mechanism of TRIM72 was investigated by luciferase reporter and co-immunoprecipitation (Co-IP) assay. Lactate production was measured by ELISA under hypoxic environments induced by CoCl2. Moreover, the expression of PI3K/Akt/mTOR pathway-associated proteins was detected by WB in BC cells. Results showed that TRIM72 was downregulated in BC. Overexpression of TRIM72 inhibited tumor proliferation and invasion in vitro and in a xenograft tumor model. Mechanistically, PPP3CA altered the inhibitory effects of TRIM72 on hypoxia-induced lactate production and monocarboxylate transporter 4-promoter activity, as well as the effect of the PI3K/Akt/mTOR signaling pathway. Our study suggests that TRIM72 modulates the TME and plays tumor-suppressive roles in BC progression. Therefore, TRIM72 may serve as a potential therapeutic target in BC.

The Sarcoplasmic Reticulum of Skeletal Muscle Cells: A Labyrinth of Membrane Contact Sites

The sarcoplasmic reticulum of skeletal muscle cells is a highly ordered structure consisting of an intricate network of tubules and cisternae specialized for regulating Ca2+ homeostasis in the context of muscle contraction. The sarcoplasmic reticulum contains several proteins, some of which support Ca2+ storage and release, while others regulate the formation and maintenance of this highly convoluted organelle and mediate the interaction with other components of the muscle fiber. In this review, some of the main issues concerning the biology of the sarcoplasmic reticulum will be described and discussed; particular attention will be addressed to the structure and function of the two domains of the sarcoplasmic reticulum supporting the excitation-contraction coupling and Ca2+-uptake mechanisms.

The Emerging Roles of Tripartite Motif Proteins (TRIMs) in Acute Lung Injury

Acute lung injury (ALI) is an inflammatory disorder of the lung that causes high mortality and lacks any pharmacological intervention. Ubiquitination plays a critical role in the pathogenesis of ALI as it regulates the alveolocapillary barrier and the inflammatory response. Tripartite motif (TRIM) proteins are one of the subfamilies of the RING-type E3 ubiquitin ligases, which contains more than 80 distinct members in humans involved in a broad range of biological processes including antivirus innate immunity, development, and tumorigenesis. Recently, some studies have shown that several members of TRIM family proteins play important regulatory roles in inflammation and ALI. Herein, we integrate emerging evidence regarding the roles of TRIMs in ALI. Articles were selected from the searches of PubMed database that had the terms "acute lung injury," "ubiquitin ligases," "tripartite motif protein," "inflammation," and "ubiquitination" using both MeSH terms and keywords. Better understanding of these mechanisms may ultimately lead to novel therapeutic approaches by targeting TRIMs for ALI treatment.

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.

Muscle multiorgan crosstalk with MG53 as a myokine for tissue repair and regeneration

Through stress and injury to tissues, the cell membrane is damaged and can lead to cell death and a cascade of inflammatory events. Soluble factors that mitigate and repair membrane injury are important to normal homeostasis and are a potential therapeutic intervention for regenerative medicine. A myokine is a type of naturally occurring factors that come from muscle and have impact on remote organs. MG53, a tripartite motif-containing family protein, is such a myokine which has protective effects on lungs, kidneys, liver, heart, eye, and brain. Three mechanisms of action for the beneficial regenerative medicine potential of MG53 have been identified and consist of 1) repair of acute injury to the cellular membrane, 2) anti-inflammatory effects associated with chronic injuries, and 3) rejuvenation of stem cells for tissue regeneration. As such, MG53 has the potential to be a novel and effective regeneration medicine therapeutic.

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.