Amelioration of ischemia-reperfusion-induced muscle injury by the recombinant human MG53 protein

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.

MyoV: a deep learning-based tool for the automated quantification of muscle fibers

Accurate approaches for quantifying muscle fibers are essential in biomedical research and meat production. In this study, we address the limitations of existing approaches for hematoxylin and eosin-stained muscle fibers by manually and semiautomatically labeling over 660 000 muscle fibers to create a large dataset. Subsequently, an automated image segmentation and quantification tool named MyoV is designed using mask regions with convolutional neural networks and a residual network and feature pyramid network as the backbone network. This design enables the tool to allow muscle fiber processing with different sizes and ages. MyoV, which achieves impressive detection rates of 0.93-0.96 and precision levels of 0.91-0.97, exhibits a superior performance in quantification, surpassing both manual methods and commonly employed algorithms and software, particularly for whole slide images (WSIs). Moreover, MyoV is proven as a powerful and suitable tool for various species with different muscle development, including mice, which are a crucial model for muscle disease diagnosis, and agricultural animals, which are a significant meat source for humans. Finally, we integrate this tool into visualization software with functions, such as segmentation, area determination and automatic labeling, allowing seamless processing for over 400 000 muscle fibers within a WSI, eliminating the model adjustment and providing researchers with an easy-to-use visual interface to browse functional options and realize muscle fiber quantification from WSIs.

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.

Molecular Mechanisms of Rhabdomyolysis-Induced Kidney Injury: From Bench to Bedside

Rhabdomyolysis-induced acute kidney injury (RIAKI) occurs following damage to the muscular sarcolemma sheath, resulting in the leakage of myoglobin and other metabolites that cause kidney damage. Currently, the sole recommended clinical treatment for RIAKI is aggressive fluid resuscitation, but other potential therapies, including pretreatments for those at risk for developing RIAKI, are under investigation. This review outlines the mechanisms and clinical significance of RIAKI, investigational treatments and their specific targets, and the status of ongoing research trials.

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.

MG53 Inhibits Necroptosis Through Ubiquitination-Dependent RIPK1 Degradation for Cardiac Protection Following Ischemia/Reperfusion Injury

Rationale

While reactive oxygen species (ROS) has been recognized as one of the main causes of cardiac injury following myocardial infarction, the clinical application of antioxidants has shown limited effects on protecting hearts against ischemia–reperfusion (I/R) injury. Thus, the precise role of ROS following cardiac injury remains to be fully elucidated.

Objective

We investigated the role of mitsugumin 53 (MG53) in regulating necroptosis following I/R injury to the hearts and the involvement of ROS in MG53-mediated cardioprotection.

Methods and Results

Antioxidants were used to test the role of ROS in MG53-mediated cardioprotection in the mouse model of I/R injury and induced human pluripotent stem cells (hiPSCs)-derived cardiomyocytes subjected to hypoxia or re-oxygenation (H/R) injury. Western blotting and co-immunoprecipitation were used to identify potential cell death pathways that MG53 was involved in. CRISPR/Cas 9-mediated genome editing and mutagenesis assays were performed to further identify specific interaction amino acids between MG53 and its ubiquitin E3 ligase substrate. We found that MG53 could protect myocardial injury via inhibiting the necroptosis pathway. Upon injury, the generation of ROS in the infarct zone of the hearts promoted interaction between MG53 and receptor-interacting protein kinase 1 (RIPK1). As an E3 ubiquitin ligase, MG53 added multiple ubiquitin chains to RIPK1 at the sites of K316, K604, and K627 for proteasome-mediated RIPK1 degradation and inhibited necroptosis. The application of N-acetyl cysteine (NAC) disrupted the interaction between MG53 and RIPK1 and abolished MG53-mediated cardioprotective effects.

Conclusions

Taken together, this study provided a molecular mechanism of a potential beneficial role of ROS following acute myocardial infarction. Thus, fine-tuning ROS levels might be critical 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.

MG53 attenuates nitrogen mustard-induced acute lung injury

Nitrogen mustard (NM) is an alkylating vesicant that causes severe pulmonary injury. Currently, there are no effective means to counteract vesicant‐induced lung injury. MG53 is a vital component of cell membrane repair and lung protection. Here, we show that mice with ablation of MG53 are more susceptible to NM‐induced lung injury than the wild‐type mice. Treatment of wild‐type mice with exogenous recombinant human MG53 (rhMG53) protein ameliorates NM‐induced lung injury by restoring arterial blood oxygen level, by improving dynamic lung compliance and by reducing airway resistance. Exposure of lung epithelial and endothelial cells to NM leads to intracellular oxidative stress that compromises the intrinsic cell membrane repair function of MG53. Exogenous rhMG53 protein applied to the culture medium protects lung epithelial and endothelial cells from NM‐induced membrane injury and oxidative stress, and enhances survival of the cells. Additionally, we show that loss of MG53 leads to increased vulnerability of macrophages to vesicant‐induced cell death. Overall, these findings support the therapeutic potential of rhMG53 to counteract vesicant‐induced lung injury.

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.

Recombinant Human MG53 Protein Protects Against Alkaline-Induced Corneal Injuries in Mice

INTRODUCTION

The current study was designed to test the potential role of recombinant human MG53 (rhMG53) protein on protecting against alkaline-induced corneal injury in mice.

MATERIALS AND METHODS

A round filter paper with 2-mm diameter was soaked in 1 mol/L of NaOH solution. The mouse alkaline injury was generated by placing the filter paper directly on the cornea for 30 seconds and washed with 30-mL saline; 10 µL of rhMG53 solution (20 µg/mL) or saline control was topically administrated on the mouse corneas (twice per day for 10 days). Re-epithelialization was measured by fluorescein staining and imaged by a slit lamp equipped with a digital camera. Clinical neovascularization and opacity scores were measured every day after injury. Ten days after injury, mice were sacrificed and corneas were dissected out for flat mount staining of CD31 for neovascularization.

RESULTS

MG53 was present in both dog aqueous humor and human tears. mg53-/- corneas were more susceptible to alkaline-induced corneal injury. Topical treatment of rhMG53 improved re-epithelialization, suppressed neovascularization, and fibrosis induced by alkaline injury.

CONCLUSIONS

rhMG53 may be an effective means to treat corneal wounding.

MG53 as a Novel Therapeutic Protein to Treat Acute Lung Injury

INTRODUCTION

Lung injury has several inciting etiologies ranging from trauma (contusion and hemorrhage) to ischemia reperfusion injury. Reflective of the injury, tissue and cellular injury increases proportionally with the injury stress and is an area of potential intervention to mitigate the injury. This study aims to evaluate the therapeutic benefits of recombinant human MG53 (rhMG53) protein in porcine models of acute lung injury (ALI).

MATERIALS AND METHODS

We utilized live cell imaging to monitor the movement of MG53 in cultured human bronchial epithelial cells following mechanical injury. The in vivo efficacy of rhMG53 was evaluated in a porcine model of hemorrhagic shock/contusive lung injury. Varying doses of rhMG53 (0, 0.2, or 1 mg/kg) were administered intravenously to pigs after induction of hemorrhagic shock/contusive induced ALI. Ex vivo lung perfusion system enabled assessment of the isolated porcine lung after a warm ischemic induced injury with rhMG53 supplementation in the perfusate (1 mg/mL).

RESULTS

MG53-mediated cell membrane repair is preserved in human bronchial epithelial cells. rhMG53 mitigates lung injury in the porcine model of combined hemorrhagic shock/contusive lung injury. Ex vivo lung perfusion administration of rhMG53 reduces warm ischemia-induced injury to the isolated porcine lung.

CONCLUSIONS

MG53 is an endogenous protein that circulates in the bloodstream. Therapeutic treatment with exogenous rhMG53 may be part of a strategy to restore (partially or completely) structural morphology and/or functional lung integrity. Systemic administration of rhMG53 constitutes a potential effective therapeutic means to combat ALI.

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

Under natural conditions, injured cells can be repaired rapidly through inherent biological processes. However, in the case of diabetes, cardiovascular disease, muscular dystrophy, and other degenerative conditions, the natural repair process is impaired. Repair of injury to the cell membrane is an important aspect of physiology. Inadequate membrane repair function is implicated in the pathophysiology of many human disorders. Recent studies show that Mitsugumin 53 (MG53), a TRIM family protein, plays a key role in repairing cell membrane damage and facilitating tissue regeneration. Clarifying the role of MG53 and its molecular mechanism are important for the application of MG53 in regenerative medicine. In this review, we analyze current research dissecting MG53′s function in cell membrane repair and tissue regeneration, and highlight the development of recombinant human MG53 protein as a potential therapeutic agent to repair multiple-organ injuries.

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.

MG53 Does Not Manifest the Development of Diabetes in db/db Mice

MG53 is a member of the TRIM protein family that is predominantly expressed in striated muscles and participates in cell membrane repair. Controversy exists regarding MG53's role in insulin signaling and manifestation of diabetes. We generated db/db mice with either whole-body ablation or sustained elevation of MG53 in the bloodstream in order to evaluate the physiological function of MG53 in diabetes. To quantify the amount of MG53 protein in circulation, we developed a monoclonal antibody against MG53 with high specificity. Western blot using this antibody revealed lower or no change of serum MG53 levels in db/db mice or patients with diabetes compared with control subjects. Neither whole-body ablation of MG53 nor sustained elevation of MG53 in circulation altered insulin signaling and glucose handling in db/db mice. Instead, mice with ablation of MG53 were more susceptible to streptozotocin-induced dysfunctional handling of glucose compared with the wild-type littermates. Alkaline-induced corneal injury demonstrated delayed healing in db/db mice, which was restored by topical administration of recombinant human (rh)MG53. Daily intravenous administration of rhMG53 in rats at concentrations up to 10 mg/kg did not produce adverse effects on glucose handling. These findings challenge the hypothetical function of MG53 as a causative factor for the development of diabetes. Our data suggest that rhMG53 is a potentially safe and effective biologic to treat diabetic oculopathy in rodents.

Enhancing membrane repair increases regeneration in a sciatic injury model

Various injuries to the neural tissues can cause irreversible damage to multiple functions of the nervous system ranging from motor control to cognitive function. The limited treatment options available for patients have led to extensive interest in studying the mechanisms of neuronal regeneration and recovery from injury. Since many neurons are terminally differentiated, by increasing cell survival following injury it may be possible to minimize the impact of these injuries and provide translational potential for treatment of neuronal diseases. While several cell types are known to survive injury through plasma membrane repair mechanisms, there has been little investigation of membrane repair in neurons and even fewer efforts to target membrane repair as a therapy in neurons. Studies from our laboratory group and others demonstrated that mitsugumin 53 (MG53), a muscle-enriched tripartite motif (TRIM) family protein also known as TRIM72, is an essential component of the cell membrane repair machinery in skeletal muscle. Interestingly, recombinant human MG53 (rhMG53) can be applied exogenously to increase membrane repair capacity both in vitro and in vivo. Increasing the membrane repair capacity of neurons could potentially minimize the death of these cells and affect the progression of various neuronal diseases. In this study we assess the therapeutic potential of rhMG53 to increase membrane repair in cultured neurons and in an in vivo mouse model of neurotrauma. We found that a robust repair response exists in various neuronal cells and that rhMG53 can increase neuronal membrane repair both in vitro and in vivo. These findings provide direct evidence of conserved membrane repair responses in neurons and that these repair mechanisms can be targeted as a potential therapeutic approach for neuronal injury.

EFFECTS OF CONTUSION AND EXHAUSTIVE EXERCISE ON MG53, PTRF IN SKELETAL MUSCLE OF RATS

ABSTRACT Objectives To study the effects of contusion and exhaustive exercise on gene expression of MG53, PTRF, Pax7 and β-catenin in skeletal muscle of rats, and reveal the repair mechanism of skeletal muscle injury. Methods Forty-two male Wistar rats were randomly divided into 7 groups, with 6 rats in each group. All groups were euthanized at different time points after exhaustive exercise and contusion, respectively, while the control group was euthanized in resting state. The right gastrocnemius muscles were measured for mRNAs of MG53, PTRF, Pax7 and β-catenin by real time PCR. Results MG53 mRNA and PTRF mRNA of skeletal muscle in groups immediately after exhaustive exercise and after contusion increased significantly (p<0.05), while the two indices decreased constantly at 24 and 48 hours after injury with a similar change trend. Compared with the control group, Pax7 mRNA of skeletal muscle as a marker showed no significant difference in exhaustive exercise groups, but decreased at 48 hours after contusion (p<0.05). β-catenin mRNA of skeletal muscle down-regulated significantly over 24 hours after injury, then activated with an increased value at 48 hours after contusion (p<0.05). As a whole, the variations in the above indices in the contusion groups covered a wider range than in the exhaustive exercise groups. Conclusion The cytomembrane repair mechanism of MG53 and PTRF began immediately after the end of exhaustive exercise and contusion. Activation of Pax7 as the satellite cell marker took longer, and Wnt/β-catenin pathway showed first a decrease and then an increase resulting from the time-dependent gene expression during the repair of skeletal muscle injury. Level of evidence III, Therapeutic studies investigating the results of treatment.

Sustained elevation of MG53 in the bloodstream increases tissue regenerative capacity without compromising metabolic function

MG53 is a muscle-specific TRIM-family protein that presides over the cell membrane repair response. Here, we show that MG53 present in blood circulation acts as a myokine to facilitate tissue injury-repair and regeneration. Transgenic mice with sustained elevation of MG53 in the bloodstream (tPA-MG53) have a healthier and longer life-span when compared with littermate wild type mice. The tPA-MG53 mice show normal glucose handling and insulin signaling in skeletal muscle, and sustained elevation of MG53 in the bloodstream does not have a deleterious impact on db/db mice. More importantly, the tPA-MG53 mice display remarkable dermal wound healing capacity, enhanced muscle performance, and improved injury-repair and regeneration. Recombinant human MG53 protein protects against eccentric contraction-induced acute and chronic muscle injury in mice. Our findings highlight the myokine function of MG53 in tissue protection and present MG53 as an attractive biological reagent for regenerative medicine without interference with glucose handling in the body.

MG53 is a protein that regulates the cell membrane repair process, and it’s been suggested that it might play a role in diabetes. Here, the authors demonstrate that circulating MG53 functions as a myokine to facilitate tissue injury-repair and regeneration without impacting glucose handling.

Mitochondrial transplantation ameliorates acute limb ischemia

OBJECTIVE

Acute limb ischemia (ALI), the most challenging form of ischemia-reperfusion injury (IRI) in skeletal muscle tissue, leads to decreased skeletal muscle viability and limb function. Mitochondrial injury has been shown to play a key role in skeletal muscle IRI. In previous studies, we have demonstrated that mitochondrial transplantation (MT) is an efficacious therapeutic strategy to replace or to augment mitochondria damaged by IRI, allowing enhanced muscle viability and function in cardiac tissue. In this study, we investigated the efficacy of MT in a murine ALI model.

METHODS

C57BL/6J mice (male, 10-12 weeks) were used in a model of ALI. Ischemia was induced by applying a tourniquet on the left hindlimb. After 2 hours of ischemia, the tourniquet was released, and reperfusion of the hindlimb was re-established; either vehicle alone (n = 15) or vehicle containing mitochondria (n = 33) was injected directly into all the muscles of the hindlimb. Mitochondria were delivered at concentrations of 1 × 10⁶ to 1 × 10⁹ per gram wet weight to each muscle, and the animals were allowed to recover. Sham mice received no ischemia or injections but were anesthetized for 2 hours and allowed to recover. After 24 hours of recovery, limb function was assessed by DigiGait (Mouse Specifics Inc, Boston, Mass), and animals were euthanized; the gastrocnemius, soleus, and vastus medialis muscles were collected for analysis.

RESULTS

After 24 hours of hindlimb reperfusion, infarct size (percentage of total mass) and apoptosis were significantly decreased (P < .001, each) in the gastrocnemius, soleus, and vastus medialis muscles in MT mice compared with vehicle mice for all mitochondrial concentrations (1 × 10⁶ to 1 × 10⁹ per gram wet weight). DigiGait analysis at 24 hours of reperfusion showed that percentage shared stance time was significantly increased (P < .001) and stance factor was significantly decreased (P = .001) in vehicle compared with MT and sham mice. No significant differences in percentage shared stance time (P = .160) or stance factor (P = .545) were observed between MT and sham mice.

CONCLUSIONS

MT ameliorates skeletal muscle injury and enhances hindlimb function in the murine model of ALI.

Fresh whole blood resuscitation does not exacerbate skeletal muscle edema and long-term functional deficit after ischemic injury and hemorrhagic shock

BACKGROUND

Hemorrhagic shock caused by extremity vascular injuries is common in combat injuries. Fluid resuscitation is the standard treatment for severe hemorrhage (HEM). Tourniquets (TKs) used for HEM control cause ischemia-reperfusion (I/R) injury that induces edema formation in the injured muscle. Resuscitation fluids affect edema formation; however, its effect on long-term functional response remains unknown. The objectives of this study are to (1) compare acute muscle damage; (2) determine long-term functional recovery of ischemic muscle; and (3) compare local and systemic inflammatory response including the expression of junctional proteins following early resuscitation with Hextend and fresh whole blood using a rodent model of combined HEM and TK-induced limb I/R.

METHODS

Anesthetized Sprague-Dawley rats underwent 42.5% arterial HEM, followed by 3 hours of TK application. Animals were either not resuscitated or resuscitated with Hextend or fresh whole blood. Two time points were evaluated, 2 and 28 days. Plasma cytokine concentrations were determined at baseline and end resuscitation. At 2 days, edema formation, expression of junctional proteins, and tissue level cytokines concentrations were evaluated. At 28 days, in vivo muscle contractile properties were determined. At both time points, routine histology was performed and graded using a semiquantitative grading system.

RESULTS

All animals developed hemorrhagic hypovolemia; the mortality rate was 100% in nonresuscitated rats. Hextend resuscitation exacerbated muscle edema (~11%) and muscle strength deficit (~20%). Fresh whole blood resuscitation presented edema and muscle strength akin to TK only. Fresh whole blood resuscitation upregulated expression of junctional proteins including proangiogenic factors and dampened the inflammatory response.

CONCLUSION

Fresh whole blood resuscitation does not exacerbate either TK-induced edema or muscle strength deficit. Fresh whole blood resuscitation may reduce both acute and long-term morbidity associated with extremity trauma. To our knowledge, this is the first study to demonstrate the nature of the resuscitation fluid administered following HEM impacts short- and long-term indices of I/R in skeletal muscle.

MG53 promotes corneal wound healing and mitigates fibrotic remodeling in rodents

The cornea plays an important role in transmitting light and providing protection to the eye, but is susceptible to injury and infection. Standard treatments for corneal wounds include topical lubricants, antibiotics, bandage contact lens, and surgery. However, these measures are often ineffective. Here we show that MG53, a protein with an essential role in cell membrane repair, contributes to the corneal injury-repair process. Native MG53 is present in the corneal epithelia, tear film, and aqueous humor, suggesting its potential function in corneal homeostasis. Knockout of MG53 in mice causes impaired healing and regenerative capacity following injury. Exogenous recombinant human MG53 (rhMG53) protein protects the corneal epithelia against mechanical injury and enhances healing by promoting migration of corneal fibroblasts. Using in vivo alkaline-induced injury to the rat cornea, we show that rhMG53 promotes re-epithelialization and reduces post-injury fibrosis and vascularization. Finally, we show that rhMG53 modulates TGF-β-mediated fibrotic remodeling associated with corneal injury. Overall, our data support the bi-functional role of MG53 in facilitating corneal healing and maintaining corneal transparency by reducing fibrosis and vascularization associated with corneal injuries.

Heather Chandler, Tao Tan, Chunlin Yang et al. find that the cell membrane repair protein MG53 plays a key role in repairing cornea injury. Using mouse and rat models, they show that recombinant human MG53 protects the cornea against injury and enhances healing.

Role of a TRIM72 ADP-ribosylation cycle in myocardial injury and membrane repair

Mono-ADP-ribosylation of an (arginine) protein catalyzed by ADP-ribosyltransferase 1 (ART1) - i.e., transfer of ADP-ribose from NAD to arginine - is reversed by ADP-ribosylarginine hydrolase 1 (ARH1) cleavage of the ADP-ribose-arginine bond. ARH1-deficient mice developed cardiomyopathy with myocardial fibrosis, decreased myocardial function under dobutamine stress, and increased susceptibility to ischemia/reperfusion injury. The membrane repair protein TRIM72 was identified as a substrate for ART1 and ARH1; ADP-ribosylated TRIM72 levels were greater in ARH1-deficient mice following ischemia/reperfusion injury. To understand better the role of TRIM72 and ADP-ribosylation, we used C2C12 myocytes. ARH1 knockdown in C2C12 myocytes increased ADP-ribosylation of TRIM72 and delayed wound healing in a scratch assay. Mutant TRIM72 (R207K, R260K) that is not ADP-ribosylated interfered with assembly of TRIM72 repair complexes at a site of laser-induced injury. The regulatory enzymes ART1 and ARH1 and their substrate TRIM72 were found in multiple complexes, which were coimmunoprecipitated from mouse heart lysates. In addition, the mono-ADP-ribosylation inhibitors vitamin K1 and novobiocin inhibited oligomerization of TRIM72, the mechanism by which TRIM72 is recruited to the site of injury. We propose that a mono-ADP-ribosylation cycle involving recruitment of TRIM72 and other regulatory factors to sites of membrane damage is critical for membrane repair and wound healing following myocardial injury.

Altered membrane integrity in the progression of muscle diseases

Sarcolemmal integrity is orchestrated through the interplay of preserving membrane strength and fast tracking the membrane repair process during an event of compromised membrane fragility. Several molecular players have been identified that act in a concerted fashion to maintain the barrier function of the muscle membrane. Substantial research findings in the field of muscle biology point out the importance of maintaining membrane integrity as a key contributory factor to cellular homeostasis. Innumerable data on the progression of membrane pathology associated with compromised muscle membrane integrity support targeting sarcolemmal integrity in skeletal and cardiac muscle as a model therapeutic strategy to alleviate some of the pathologic conditions. This review will discuss strategies that researchers have undertaken to compensate for an imbalance in sarcolemma membrane fragility and membrane repair to maintain muscle membrane integrity.

A Bioinspired Alginate-Gum Arabic Hydrogel with Micro-/Nanoscale Structures for Controlled Drug Release in Chronic Wound Healing

Biopolymeric hydrogels have drawn increasing research interest in biomaterials due to their tunable physical and chemical properties for both creating bioactive cellular microenvironment and serving as sustainable therapeutic reagents. Inspired by a naturally occurring hydrogel secreted from the carnivorous Sundew plant for trapping insects, here we have developed a bioinspired hydrogel to deliver mitsugumin 53 (MG53), an important protein in cell membrane repair, for chronic wound healing. Both chemical compositions and micro-/nanomorphological properties inherent from the natural Sundew hydrogel were mimicked using sodium alginate and gum arabic with calcium ion-mediated cross-linking. On the basis of atomic force microscopy (AFM) force measurements, an optimal sticky hydrogel scaffold was obtained through orthogonal experimental design. Imaging and mechanical analysis showed the distinct correlation between structural morphology, adhesion characteristics, and mechanical properties of the Sundew-inspired hydrogel. Combined characterization and biochemistry techniques were utilized to uncover the underlying molecular composition involved in the interactions between hydrogel and protein. In vitro drug release experiments confirmed that the Sundew-inspired hydrogel had a biphasic-kinetics release, which can facilitate both fast delivery of MG53 for improving the reepithelization process of the wounds and sustained release of the protein for treating chronic wounds. In vivo experiments showed that the Sundew-inspired hydrogel encapsulating with rhMG53 could facilitate dermal wound healing in mouse model. Together, these studies confirmed that the Sundew-inspired hydrogel has both tunable micro-/nanostructures and physicochemical properties, which enable it as a delivery vehicle for chronic wounding healing. The research may provide a new way to develop biocompatible and tunable biomaterials for sustainable drug release to meet the needs of biological activities.

Plasma membrane wounding and repair in pulmonary diseases

Various pathophysiological conditions such as surfactant dysfunction, mechanical ventilation, inflammation, pathogen products, environmental exposures, and gastric acid aspiration stress lung cells, and the compromise of plasma membranes occurs as a result. The mechanisms necessary for cells to repair plasma membrane defects have been extensively investigated in the last two decades, and some of these key repair mechanisms are also shown to occur following lung cell injury. Because it was theorized that lung wounding and repair are involved in the pathogenesis of acute respiratory distress syndrome (ARDS) and idiopathic pulmonary fibrosis (IPF), in this review, we summarized the experimental evidence of lung cell injury in these two devastating syndromes and discuss relevant genetic, physical, and biological injury mechanisms, as well as mechanisms used by lung cells for cell survival and membrane repair. Finally, we discuss relevant signaling pathways that may be activated by chronic or repeated lung cell injury as an extension of our cell injury and repair focus in this review. We hope that a holistic view of injurious stimuli relevant for ARDS and IPF could lead to updated experimental models. In addition, parallel discussion of membrane repair mechanisms in lung cells and injury-activated signaling pathways would encourage research to bridge gaps in current knowledge. Indeed, deep understanding of lung cell wounding and repair, and discovery of relevant repair moieties for lung cells, should inspire the development of new therapies that are likely preventive and broadly effective for targeting injurious pulmonary diseases.

Dual function of MG53 in membrane repair and insulin signaling

MG53 is a member of the TRIM-family protein that acts as a key component of the cell membrane repair machinery. MG53 is also an E3-ligase that ubiquinates insulin receptor substrate-1 and controls insulin signaling in skeletal muscle cells. Since its discovery in 2009, research efforts have been devoted to translate this basic discovery into clinical applications in human degenerative and metabolic diseases. This review article highlights the dual function of MG53 in cell membrane repair and insulin signaling, the mechanism that underlies the control of MG53 function, and the therapeutic value of targeting MG53 function in regenerative medicine. [BMB Reports 2016; 49(8): 414-423]

Caveolin-1/-3: therapeutic targets for myocardial ischemia/reperfusion injury

Myocardial ischemia/reperfusion (I/R) injury is a major cause of morbidity and mortality worldwide. Caveolae, caveolin-1 (Cav-1), and caveolin-3 (Cav-3) are essential for the protective effects of conditioning against myocardial I/R injury. Caveolins are membrane-bound scaffolding proteins that compartmentalize and modulate signal transduction. In this review, we introduce caveolae and caveolins and briefly describe the interactions of caveolins in the cardiovascular diseases. We also review the roles of Cav-1/-3 in protection against myocardial ischemia and I/R injury, and in conditioning. Finally, we suggest several potential research avenues that may be of interest to clinicians and basic scientists. The information included, herein, is potentially useful for the design of future studies and should advance the investigation of caveolins as therapeutic targets.

Non-canonical roles for caveolin in regulation of membrane repair and mitochondria: implications for stress adaptation with age

Many different theories of ageing have been proposed but none has served the unifying purpose of defining a molecular target that can limit the structural and functional decline associated with age that ultimately leads to the demise of the organism. We propose that the search for a molecule with these unique properties must account for regulation of the signalling efficiency of multiple cellular functions that degrade with age due to a loss of a particular protein. We suggest caveolin as one such molecule that serves as a regulator of key processes in signal transduction. We define a particular distinction between cellular senescence and ageing and propose that caveolin plays a distinct role in each of these processes. Caveolin is traditionally thought of as a membrane-localized protein regulating signal transduction via membrane enrichment of specific signalling molecules. Ultimately we focus on two non-canonical roles for caveolin - membrane repair and regulation of mitochondrial function - which may be novel features of stress adaptation, especially in the setting of ageing. The end result of preserving membrane structure and mitochondrial function is maintenance of homeostatic signalling, preserving barrier function, and regulating energy production for cell survival and resilient ageing.

Above the fray: Surface remodeling by secreted lysosomal enzymes leads to endocytosis-mediated plasma membrane repair

The study of plasma membrane repair is coming of age. Mirroring human adolescence, the field shows at the same time signs of maturity and significant uncertainty, confusion and skepticism. Here we discuss concepts that emerged from experimental data over the years, some of which are solidly established while others are still subject to different interpretations. The firmly established concepts include the critical requirement for Ca(2+) in wound repair, and the role of rapid exocytosis of intracellular vesicles. Lysosomes are being increasingly recognized as the major vesicles involved in injury-induced exocytosis in many cell types, as a growing number of laboratories detect markers for these organelles on the cell surface and lysosomal hydrolases in the supernatant of wounded cells. The more recent observation of massive endocytosis following Ca(2+)-triggered exocytosis initially came as a surprise, but this finding is also being increasingly reported by different groups, shifting the discussion to the mechanisms by which endocytosis promotes repair, and whether it operates or not in parallel with the shedding of membrane blebs. We discuss how the abundant intracellular vesicles that undergo homotypic fusion close to wound sites, previously interpreted as exocytic membrane patches, actually acquire extracellular tracers demonstrating their endocytic origin. We also suggest that an initial, temporary patch that prevents cytosol loss until the bilayer is restored might result not from vesicular fusion, but from rapid Ca(2+)-dependent crosslinking and aggregation of cytosolic proteins. Finally, we propose that cell surface remodeling, orchestrated by the extracellular release of lysosomal hydrolases and perhaps also cytosolic molecules, may represent a key aspect of the plasma membrane repair mechanism that has received little attention so far.