Matrix metalloproteinases in inflammatory myopathies: enhanced immunoreactivity near atrophic myofibers

Space Omics and Tissue Response in Astronaut Skeletal Muscle after Short and Long Duration Missions

The molecular mechanisms of skeletal muscle adaptation to spaceflight are as yet not fully investigated and well understood. The MUSCLE BIOPSY study analyzed pre and postflight deep calf muscle biopsies (m. soleus) obtained from five male International Space Station (ISS) astronauts. Moderate rates of myofiber atrophy were found in long-duration mission (LDM) astronauts (~180 days in space) performing routine inflight exercise as countermeasure (CM) compared to a short-duration mission (SDM) astronaut (11 days in space, little or no inflight CM) for reference control. Conventional H&E scout histology showed enlarged intramuscular connective tissue gaps between myofiber groups in LDM post vs. preflight. Immunoexpression signals of extracellular matrix (ECM) molecules, collagen 4 and 6, COL4 and 6, and perlecan were reduced while matrix-metalloproteinase, MMP2, biomarker remained unchanged in LDM post vs. preflight suggesting connective tissue remodeling. Large scale proteomics (space omics) identified two canonical protein pathways associated to muscle weakness (necroptosis, GP6 signaling/COL6) in SDM and four key pathways (Fatty acid β-oxidation, integrin-linked kinase ILK, Rho A GTPase RHO, dilated cardiomyopathy signaling) explicitly in LDM. The levels of structural ECM organization proteins COL6A1/A3, fibrillin 1, FBN1, and lumican, LUM, increased in postflight SDM vs. LDM. Proteins from tricarboxylic acid, TCA cycle, mitochondrial respiratory chain, and lipid metabolism mostly recovered in LDM vs. SDM. High levels of calcium signaling proteins, ryanodine receptor 1, RyR1, calsequestrin 1/2, CASQ1/2, annexin A2, ANXA2, and sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA1) pump, ATP2A, were signatures of SDM, and decreased levels of oxidative stress peroxiredoxin 1, PRDX1, thioredoxin-dependent peroxide reductase, PRDX3, or superoxide dismutase [Mn] 2, SOD2, signatures of LDM postflight. Results help to better understand the spatiotemporal molecular adaptation of skeletal muscle and provide a large scale database of skeletal muscle from human spaceflight for the better design of effective CM protocols in future human deep space exploration.

Role of Matrix Metalloproteinases in Musculoskeletal Diseases

Musculoskeletal disorders include rheumatoid arthritis, osteoarthritis, sarcopenia, injury, stiffness, and bone loss. The prevalence of these conditions is frequent among elderly populations with significant mobility and mortality rates. This may lead to extreme discomfort and detrimental effect on the patient’s health and socioeconomic situation. Muscles, ligaments, tendons, and soft tissue are vital for body function and movement. Matrix metalloproteinases (MMPs) are regulatory proteases involved in synthesizing, degrading, and remodeling extracellular matrix (ECM) components. By modulating ECM reconstruction, cellular migration, and differentiation, MMPs preserve myofiber integrity and homeostasis. In this review, the role of MMPs in skeletal muscle function, muscle injury and repair, skeletal muscle inflammation, and muscular dystrophy and future approaches for MMP-based therapies in musculoskeletal disorders are discussed at the cellular and molecule level.

A Complete and Versatile Protocol: Decoration of Cell-Derived Matrices with Mass-Encoded Peptides for Multiplexed Protease Activity Detection

This article provides guidance toward a platform technology for monitoring enzyme activity within the extracellular matrix (ECM) assessed by quantifying reporters secreted into the cell culture supernatant and analyzed by tandem mass spectrometry. The reporters are enzymatically and covalently bound to the ECM by transglutaminases (TG) using the peptide sequence of human insulin-like growth factor I's (IGF-I) D-domain which is known to be bound to the ECM by transglutaminase. The IGF-I D-domain sequence is followed by a peptide sequence cleaved by the intended target protease. This protease-sensitive peptide sequence (PSS) is cleaved off the ECM and can be used to monitor target-enzyme activity by employing a downstream mass tag designed according to isobaric mass encoding strategies, i.e., the combination of isotopically labeled, heavy amino acids. Thereby, cleavage events are linked to the appearance of encoded mass tags, readily allowing multiplexing. This article presents the design and synthesis of these mass reporters. It further aims at detailing the search for peptide sequences responding to target proteases to facilitate future work on enzyme activity measurement for enzymatic activities of hitherto unknown enzymes. In conclusion, the goal of this article is to arm scientists interested in measurements of local enzymatic activities within the ECM with robust protocols and background knowledge.

Cytokine and Growth Factor Response in a Rat Model of Radiation Induced Injury to the Submental Muscles

Submental muscles (i.e., mylohyoid and geniohyoid) play a vital role during swallowing, protecting the airway from ingested material. To design therapies to reduce the functional deficits associated with radiation treatment relies in part on our understanding of the changes in the cytokine and growth factor response that can impact muscle function. The purpose of this study is to quantify changes in the inflammatory, pro-fibrotic, and pro-angiogenic factors following 48 Gy of fractionated radiation to the mylohyoid muscle. We hypothesized that (1) irradiation will provoke increases in TGF-1β and MMP-2 mRNA in the mylohyoid muscle; and (2) muscles surrounding the target location (i.e., geniohyoid and digastric muscles) will exhibit similar alterations in their gene expression profiles. Rats were exposed to 6 fractions of 8 Gy using a 6 MeV electron beam on a clinical linear accelerator. The highest dose curve was focused at the mylohyoid muscle. After 2- and 4-weeks post-radiation, the mylohyoid, geniohyoid, and digastric muscles were harvested. Expression of TNF-α, IFNγ, IL-1β, IL-6, TGF-1β, VEGF, MMP-2, and MMP-9 mRNA was analyzed via PCR and/or RT-PCR. TGF-1β, MMP-2, and IL-6 expression was upregulated in the irradiated mylohyoid compared to non-irradiated controls. No notable changes in TNF-α, IFNγ, and IL-1β mRNA expression were observed in irradiated muscles. Differing expression profiles were found in the surrounding muscles post-radiation. Results demonstrated that irradiation provokes molecular signals involved in the regulation of wound healing, which could lead to fibrosis or atrophy in the swallowing muscle after radiation.

Matrix Metalloproteinases and Tissue Inhibitor of Metalloproteinases in Inflammation and Fibrosis of Skeletal Muscles

In skeletal muscles, levels and activity of Matrix MetalloProteinases (MMPs) and Tissue Inhibitors of MetalloProteinases (TIMPs) have been involved in myoblast migration, fusion and various physiological and pathological remodeling situations including neuromuscular diseases. This has opened perspectives for the use of MMPs' overexpression to improve the efficiency of cell therapy in muscular dystrophies and resolve fibrosis. Alternatively, inhibition of individual MMPs in animal models of muscular dystrophies has provided evidence of beneficial, dual or adverse effects on muscle morphology or function. We review here the role played by MMPs/TIMPs in skeletal muscle inflammation and fibrosis, two major hurdles that limit the success of cell and gene therapy. We report and analyze the consequences of genetic or pharmacological modulation of MMP levels on the inflammation of skeletal muscles and their repair in light of experimental findings. We further discuss how the interplay between MMPs/TIMPs levels, cytokines/chemokines, growth factors and permanent low-grade inflammation favor cellular and molecular modifications resulting in fibrosis.

Skeletal muscle cells actively shape (auto)immune responses

Histopathological analyses of muscle specimens from myositis patients indicate that skeletal muscle cells play an active role in the interaction with immune cells. Research over the last few decades has shown that skeletal muscle cells exhibit immunobiological properties that perfectly define them as non-professional antigen presenting cells. They are able to present antigens via major histocompatibility complex molecules, exhibit costimulatory molecules and secrete soluble molecules that actively shape the immune response in an either pro- or anti-inflammatory manner. Skeletal muscle cells regulate both innate and adaptive immune responses and are essentially involved in the pathophysiological processes of idiopathic inflammatory myopathies. Understanding the role of skeletal muscle cells might help to identify new therapeutic targets for these devastating diseases. This review summarizes the immunobiological features of skeletal muscle cells, especially in the context of idiopathic inflammatory myopathies, and discusses shortcomings and limitations in skeletal muscle related research providing potential perspectives to overcome them in the future.

IL-15 up-regulates the MMP-9 expression levels and induces inflammatory infiltration of macrophages in polymyositis through regulating the NF-kB pathway

This study was aimed to research the effects of IL-15 on inducing inflammatory infiltration of macrophages in polymyositis (PM) through the NF-kB pathway, and whether IL-15 was able to further regulate MMP-9 expression levels. Prepared PM cells, collected from the patients suffering from PM, were administered to SD rats. Also, a group of healthy SD rats was undergoing the same treatment as the control group. The test animals were treated with either anti-IL-15, IL-15, MMP-9 siRNA or ERK1/2 inhibitor. The blood toxicological parameters creatine kinase (CK) and CD163 were tested by using ELISA and immunohistochemistry assay. In addition, NF-kB expression in macrophages was measured by immunocytochemical assay. To measure the degree of cell infiltration the Transwell assay was performed. Lastly, western blot and zymography were carried out to compare MMP-9 and ERK expression levels between the two groups, both in vivo and in vitro. The results showed that S-CK, IL-15 and IL-15Rα levels increased rapidly after the conventional treatment was introduced to the PM infected SD rats. The PM model establishment and IL-15 treatment significantly increased the expressions of IL-15Rα, MMP-9, p-ERK and p-IKBα. However, the same effect can be suppressed by using anti-IL-15, MMP-9 siRNA or ERK1/2 inhibitor (P < 0.05). In addition, IL-15 is proved to increase cell migration and nucleus expression of NF-kB in the macrophages. IL-15 is able to significantly regulate the inflammatory infiltration of macrophages in PM patients through affecting the NF-kB pathway and MMP-9 expression levels.

A new modified animal model of myosin-induced experimental autoimmune myositis enhanced by defibrase

INTRODUCTION

We investigated the effect of defibrase (a proteolytic enzyme extraction of Agkistrodon halys venom) on experimental autoimmune myositis (EAM) in guinea pigs and explored the option of using a modified pig model of EAM to enhance the study of this disease.

MATERIAL AND METHODS

Guinea pigs were divided into 3 groups: group A (control group) was immunized with complete Freund adjuvant (CFA), then received 6 injections of saline weekly; group B (EAM group) was immunized with partially purified rabbit myosin emulsified with CFA, then received an injection of saline; group C (EAM + defibrase group) was immunized with purified rabbit myosin emulsified with CFA, then received an injection of defibrase. The animals were observed for their general health condition and the body weight was measured daily. Plasma levels of fibrinogen and creatine kinase (CK) were determined. Muscle tissues were examined histologically.

RESULTS

After immunizations for 6 weeks, incidence of EAM in groups A, B and C was 0 (0/7), 83.3% (10/12) and 100% (15/15), respectively. Guinea pigs with EAM presented angeitis symptoms of muscle weakness. Histological analysis revealed a significant difference. Muscles with EAM had scattered or diffuse inflammatory manifestations, which are also common pathological features of human idiopathic polymyositis (IPM). Defibrase-treated animals displayed extensive inflammation and fiber necrosis compared with the EAM group (histological score: 2.80 ±1.15 vs. 1.88 ±1.32, p < 0.05). Severity of inflammation of group B was mainly mild to moderate; 16.7% (2/12) of animals developed severe inflammation. Incidence of severe inflammation with a score up to 4 in group C was 40% (6/15).

CONCLUSIONS

Defibrase can exacerbate myosin-induced EAM; thus a new modified model was generated.

Wasting mechanisms in muscular dystrophy

Muscular dystrophy is a group of more than 30 different clinical genetic disorders that are characterized by progressive skeletal muscle wasting and degeneration. Primary deficiency of specific extracellular matrix, sarcoplasmic, cytoskeletal, or nuclear membrane protein results in several secondary changes such as sarcolemmal instability, calcium influx, fiber necrosis, oxidative stress, inflammatory response, breakdown of extracellular matrix, and eventually fibrosis which leads to loss of ambulance and cardiac and respiratory failure. A number of molecular processes have now been identified which hasten disease progression in human patients and animal models of muscular dystrophy. Accumulating evidence further suggests that aberrant activation of several signaling pathways aggravate pathological cascades in dystrophic muscle. Although replacement of defective gene with wild-type is paramount to cure, management of secondary pathological changes has enormous potential to improving the quality of life and extending lifespan of muscular dystrophy patients. In this article, we have reviewed major cellular and molecular mechanisms leading to muscle wasting in muscular dystrophy. This article is part of a Directed Issue entitled: Molecular basis of muscle wasting.

Decrease of MMP-9 activity improves soleus muscle regeneration

The regeneration of skeletal muscles relies on the function of satellite cells that are quiescent myogenic precursors associated with adult skeletal muscle fibers. Upon injury, the satellite cells are activated, divide extensively, and differentiate into new myofibers. These events are accompanied by the remodeling of the surrounding extracellular matrix, which is mediated by variety of factors, including matrix metalloproteinases (MMPs). Regeneration of certain type of muscles, such as Soleus slow twitch muscle, is often inefficient and hindered by the development of fibrosis. Here, we studied the effect of inhibition of MMP-9 and MMP-2 activity on the Soleus muscle regeneration in vivo and on the in vitro differentiation of myoblasts derived from this muscle. Using in situ and in-gel zymography, we tested the activity of these two MMPs in vivo, during regeneration of the muscle, and in vitro, during differentiation of the myoblasts. We also analyzed the histology of regenerating muscles and morphology of differentiating myoblasts. All these analyses showed that treatment with doxycycline and anti-MMP-9, but not MMP-2 antibody, significantly improved Soleus muscle regeneration and ameliorated development of excessive fibrosis, as well as delayed myoblast proliferation and differentiation in vitro.

Human matrix metalloproteinases: an ubiquitarian class of enzymes involved in several pathological processes

Human matrix metalloproteinases (MMPs) belong to the M10 family of the MA clan of endopeptidases. They are ubiquitarian enzymes, structurally characterized by an active site where a Zn(2+) atom, coordinated by three histidines, plays the catalytic role, assisted by a glutamic acid as a general base. Various MMPs display different domain composition, which is very important for macromolecular substrates recognition. Substrate specificity is very different among MMPs, being often associated to their cellular compartmentalization and/or cellular type where they are expressed. An extensive review of the different MMPs structural and functional features is integrated with their pathological role in several types of diseases, spanning from cancer to cardiovascular diseases and to neurodegeneration. It emerges a very complex and crucial role played by these enzymes in many physiological and pathological processes.

Effects of 660 and 780 nm low-level laser therapy on neuromuscular recovery after crush injury in rat sciatic nerve

BACKGROUND AND OBJECTIVE

Post-traumatic nerve repair is still a challenge for rehabilitation. It is particularly important to develop clinical protocols to enhance nerve regeneration. The present study investigated the effects of 660 and 780 nm low-level laser therapy (LLLT) using different energy densities (10, 60, and 120 J/cm²) on neuromuscular and functional recovery as well as on matrix metalloproteinase (MMP) activity after crush injury in rat sciatic nerve.

MATERIALS AND METHODS

Rats received transcutaneous LLLT irradiation at the lesion site for 10 consecutive days post-injury and were sacrificed 28 days after injury. Both the sciatic nerve and tibialis anterior muscles were analyzed. Nerve analyses consisted of histology (light microscopy) and measurements of myelin, axon, and nerve fiber cross-sectional area (CSA). S-100 labeling was used to identify myelin sheath and Schwann cells. Muscle fiber CSA and zymography were carried out to assess the degree of muscle atrophy and MMP activity, respectively. Statistical significance was set at 5% (P≤0.05).

RESULTS

Six hundred sixty nanometer LLLT either using 10 or 60 J/cm² restored muscle fiber, myelin and nerve fiber CSA compared to the normal group (N). Furthermore, it increased MMP-2 activity in nerve and decreased MMP-2 activity in muscle and MMP-9 activity in nerve. In contrast, 780 nm LLLT using 10 J/cm² decreased MMP-9 activity in nerve compared to the crush group (CR) and N; it also restored normal levels of myelin and nerve fiber CSA. Both 60 and 120 J/cm² decreased MMP-2 activity in muscle compared to CR and N. 780 nm did not prevent muscle fiber atrophy. Functional recovery in the irradiated groups did not differ from the non-irradiated CR.

CONCLUSION

Data suggest that 660 nm LLLT with low (10 J/cm²) or moderate (60 J/cm²) energy densities is able to accelerate neuromuscular recovery after nerve crush injury in rats.

The Ras antagonist, farnesylthiosalicylic acid (FTS), decreases fibrosis and improves muscle strength in dy/dy mouse model of muscular dystrophy

The Ras superfamily of guanosine-triphosphate (GTP)-binding proteins regulates a diverse spectrum of intracellular processes involved in inflammation and fibrosis. Farnesythiosalicylic acid (FTS) is a unique and potent Ras inhibitor which decreased inflammation and fibrosis in experimentally induced liver cirrhosis and ameliorated inflammatory processes in systemic lupus erythematosus, neuritis and nephritis animal models. FTS effect on Ras expression and activity, muscle strength and fibrosis was evaluated in the dy^2J/dy^2J mouse model of merosin deficient congenital muscular dystrophy. The dy^2J/dy^2J mice had significantly increased RAS expression and activity compared with the wild type mice. FTS treatment significantly decreased RAS expression and activity. In addition, phosphorylation of ERK, a Ras downstream protein, was significantly decreased following FTS treatment in the dy^2J/dy^2J mice. Clinically, FTS treated mice showed significant improvement in hind limb muscle strength measured by electronic grip strength meter. Significant reduction of fibrosis was demonstrated in the treated group by quantitative Sirius Red staining and lower muscle collagen content. FTS effect was associated with significantly inhibition of both MMP-2 and MMP-9 activities. We conclude that active RAS inhibition by FTS was associated with attenuated fibrosis and improved muscle strength in the dy^2J/dy^2J mouse model of congenital muscular dystrophy.

Basement membrane remodelling and segmental fibrosis in sporadic inclusion body myositis

Sporadic inclusion body myositis (sIBM) is a debilitating idiopathic inflammatory myopathy. Little is known about the pathogenetic mechanisms that lead to myofiber degeneration. In the present study, we evaluated the integrity of the myofiber basement membrane in non-necrotic myofibers invaded by inflammatory infiltrates. We used 100 ten mum thick serial sections obtained from biopsies of 5 patients suffering from sIBM. Biopsies from 5 patients suffering from polymyositis served as controls. We performed sequential HE staining and immunolabeling using anti-CD68, -CD8, -merosin, -laminin alpha4 chain, and -collagen IV antibodies. In sIBM, we detected a total of 89 non-necrotic myofibers that were invaded by inflammatory cells. The invasive process and its sequelae were segmental in nature and included destruction of the myofiber basement membrane, and eventually, partial replacement by fibrosis of the invaded myofiber. In polymyositis, we found only two myofibers that were affected in this way. In sIBM, basement membrane remodelling and irreversible replacement by fibrosis of myofibers appear to represent the end result of a process in which the balance between injury and repair are disrupted.

Matrix metalloproteinases in neuromuscular disease

Matrix metalloproteinases (MMPs), a family of zinc-dependent endoproteinases, are effector molecules in the breakdown of the blood-brain and blood-nerve barrier, and promote neural tissue invasion by leukocytes in inflammatory diseases of the central and peripheral nervous systems. Moreover, MMPs play an important role in synaptic remodeling, neuronal regeneration, and remyelination. Recent work concerning MMPs in patients with neuropathy, myopathy, spinal cord injury, and amyotrophic lateral sclerosis (ALS), and in corresponding animal models, is discussed in this review.

Tumor necrosis factor-alpha augments matrix metalloproteinase-9 production in skeletal muscle cells through the activation of transforming growth factor-beta-activated kinase 1 (TAK1)-dependent signaling pathway

We have investigated the effect of tumor necrosis factor-alpha (TNF-alpha) on the production of extracellular matrix-degrading proteases in skeletal muscles. Using microarray, quantitative PCR, Western blotting, and zymography, we found that TNF-alpha drastically increases the production of matrix metalloproteinase (MMP)-9 from C2C12 myotubes. In vivo administration of TNF-alpha in mice increased the transcript level of MMP-9 in skeletal muscle tissues. Although TNF-alpha activated all the three MAPKs (i.e. ERK1/2, JNK, and p38), inhibition of ERK1/2 or p38 but not JNK blunted the TNF-alpha-induced production of MMP-9 from myotubes. Inhibition of Akt also inhibited the TNF-alpha-induced production of MMP-9. TNF-alpha increased the activation of transcription factors NF-kappaB and AP-1 but not SP-1 in myotubes. Overexpression of a dominant negative inhibitor of NF-kappaB or AP-1 blocked the TNF-alpha-induced expression of MMP-9 in myotubes. Similarly, point mutations in AP-1- or NF-kappaB-binding sites in MMP-9 promoter inhibited the TNF-alpha-induced expression of a reporter gene. TNF-alpha increased the activity of transforming growth factor-beta-activating kinase-1 (TAK1). Furthermore, overexpression of a dominant negative mutant of TAK1 blocked the TNF-alpha-induced expression of MMP-9 and activation of NF-kappaB and AP-1. Our results also suggest that TNF-alpha induces MMP-9 expression in muscle cells through the recruitment of TRAF-2, Fas-associated protein with death domain, and TNF receptor-associated protein with death domain but not NIK or TRAF-6 proteins. We conclude that TAK1-mediated pathways are involved in TNF-alpha-induced MMP-9 production in skeletal muscle cells.

Activation and localization of matrix metalloproteinase-2 and -9 in the skeletal muscle of the muscular dystrophy dog (CXMDJ)

Background

Matrix metalloproteinases (MMPs) are key regulatory molecules in the formation, remodeling and degradation of all extracellular matrix (ECM) components in both physiological and pathological processes in various tissues. The aim of this study was to examine the involvement of gelatinase MMP family members, MMP-2 and MMP-9, in dystrophin-deficient skeletal muscle. Towards this aim, we made use of the canine X-linked muscular dystrophy in Japan (CXMD_J) model, a suitable animal model for Duchenne muscular dystrophy.

Methods

We used surgically biopsied tibialis cranialis muscles of normal male dogs (n = 3) and CXMD_J dogs (n = 3) at 4, 5 and 6 months of age. Muscle sections were analyzed by conventional morphological methods and in situ zymography to identify the localization of MMP-2 and MMP-9. MMP-2 and MMP-9 activity was examined by gelatin zymography and the levels of the respective mRNAs in addition to those of regulatory molecules, including MT1-MMP, TIMP-1, TIMP-2, and RECK, were analyzed by semi-quantitative RT-PCR.

Results

In CXMD_J skeletal muscle, multiple foci of both degenerating and regenerating muscle fibers were associated with gelatinolytic MMP activity derived from MMP-2 and/or MMP-9. In CXMD_J muscle, MMP-9 immunoreactivity localized to degenerated fibers with inflammatory cells. Weak and disconnected immunoreactivity of basal lamina components was seen in MMP-9-immunoreactive necrotic fibers of CXMD_J muscle. Gelatinolytic MMP activity observed in the endomysium of groups of regenerating fibers in CXMD_J did not co-localize with MMP-9 immunoreactivity, suggesting that it was due to the presence of MMP-2. We observed increased activities of pro MMP-2, MMP-2 and pro MMP-9, and levels of the mRNAs encoding MMP-2, MMP-9 and the regulatory molecules, MT1-MMP, TIMP-1, TIMP-2, and RECK in the skeletal muscle of CXMD_J dogs compared to the levels observed in normal controls.

Conclusion

MMP-2 and MMP-9 are likely involved in the pathology of dystrophin-deficient skeletal muscle. MMP-9 may be involved predominantly in the inflammatory process during muscle degeneration. In contrast, MMP-2, which was activated in the endomysium of groups of regenerating fibers, may be associated with ECM remodeling during muscle regeneration and fiber growth.

The cell-specific expression of metalloproteinase-disintegrins (ADAMs) in inflammatory myopathies

Inflammatory cell invasion and cytokine activation are important steps in the pathogenesis of immune-mediated diseases of muscle. Metalloproteinase-disintegrins (ADAMs) are considered to play a critical role in leukocyte migration by promoting cellular adhesion, cleavage of molecules of the extracellular matrix and shedding of membrane bound cytokines. Here, we report the expression patterns of ADAM8, ADAM9, ADAM10, ADAM12, ADAM17 and ADAM19 in cultured human myoblasts and peripheral blood mononuclear cells (PBMCs) in vitro, as well as in biopsies from patients suffering from polymyositis (PM), dermatomyositis (DM), inclusion body myositis (IBM) and non-inflammatory controls. We observed an in vitro downregulation of the RNAs of ADAM10, ADAM17 and ADAM19 in myoblasts after stimulation with various pro- and anti-inflammatory mediators, whereas in PBMCs an RNA upregulation of ADAM9, ADAM10, ADAM17 and ADAM19 was detectable under identical conditions. In human muscle biopsies, invading CD3+ T lymphocytes expressed ADAM17 and ADAM19, whereas macrophages co-localized to ADAM8, as detected by immunohistochemistry. Transfection of PBMCs with ADAM19 single interfering RNA and incubation with a metalloproteinase inhibitor suggest proteolytic activity of ADAM19 and involvement in the shedding of tumor necrosis factor-alpha. No differences in the cellular expression profiles between PM, DM and IBM were found, whereas the sections from non-inflammatory controls did not reveal any positive immunoreactivity for ADAMs, except for ADAM10, which is localized exclusively to muscle fibres. Our results suggest that certain ADAMs are expressed by specific cell populations during the genesis of immune-mediated diseases of human muscle.

Tumor necrosis factor-alpha in inflammatory myopathies: pathophysiology and therapeutic implications

OBJECTIVES

To present, in an organized fashion, data from the medical literature on the possible role of tumor necrosis factor (TNF)-alpha in the pathogenesis of dermatomyositis (DM) and polymyositis (PM), as well as recent clinical studies where TNF-inhibition was used as a treatment for myositis.

METHODS

PUBMED was searched from 1966 to the present using the terms: TNF-alpha, TNF-inhibitors, dermatomyositis, polymyositis, myositis, and inflammatory myopathy. In addition, relevant abstracts from major recent rheumatology meetings were retrieved.

RESULTS

Several studies that employed immunostaining and polymerase chain reaction analysis in muscle biopsy specimens from patients with inflammatory myopathies showed increased presence of TNF-alpha and its soluble receptors in inflamed muscle. One genetic study proposed an association between DM and the -308A TNF polymorphism. Abnormally high levels of TNF-alpha in the muscle may be directly toxic to myofibers, while preventing muscle regeneration. Furthermore, TNF-alpha may induce, or augment, the production of other pro-inflammatory cytokines such as interleukin (IL)-1, monocyte chemotactic protein-1, IL-6, and IL-8. These findings have prompted some investigators to use off-label, TNF-inhibitors in DM/PM patients, especially if they had failed corticosteroids, immune gamma-globulin, and traditional immunosuppressive agents. The results from these early, uncontrolled, studies have been promising.

CONCLUSION

TNF-alpha may have a role in the pathogenesis of the myositis and has emerged as a possible therapeutic target. Larger, carefully controlled studies are needed to confirm the results from early studies and clearly define the efficacy and safety of anti-TNF agents in the treatment of inflammatory myopathies.

Serum Levels of Matrix Metalloproteinases-2 and -9 and Their Tissue Inhibitors in Inflammatory Neuromuscular Disorders

We monitored serum levels of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) before and during intravenously applied immunoglobulin (IVIG) therapy in 33 patients with chronic immune-mediated neuropathies and myopathies and 15 controls. Baseline MMP-2 and TIMP-2 serum levels were lower and MMP-9 and TIMP-1 serum levels higher in all patients compared to age-matched controls. Eight days after IVIG treatment, MMP-2, TIMP-2, and TIMP-1 serum levels increased, while MMP-9 serum levels decreased, indicating tissue repair. After 60 days, MMP-9 levels increased, MMP-2 approached normal levels, while TIMP-1 and TIMP-2 serum levels were below day 8 levels, indicating relapsing tissue damage. Comparing the MMP/TIMP results with the clinical courses, IVIG treatment tended to change MMP/TIMP levels in a way that paralleled clinical improvement and relapse. In sum, during a distinct time period, IVIG therapy seems to be able to modulate MMP-mediated tissue repair.

Pathogenesis of idiopathic inflammatory myopathies

The idiopathic inflammatory myopathies, myositis, are characterized by a chronic course with decreased muscle endurance and by infiltrates of T lymphocytes and macrophages in muscle tissue. Treatment with immunosuppressives rarely leads to recovery of muscle function, despite abolishment of inflammatory cell infiltrates in muscle tissue. Therefore, other mechanisms than immune-mediated muscle fiber damage are likely to contribute to the pathogenesis. One such non-immune-mediated muscle dysfunction could be caused by a disturbed microcirculation due to capillary loss or to phenotypically changed endothelial cells in the capillaries. These aberrations may affect the micro-environment of muscle tissue and lead to local tissue hypoxia with development of a secondary metabolic myopathy. Another possible non-immune-mediated mechanism leading to muscle dysfunction is the newly identified endoplasmatic reticulum (ER) stress response in myositis. The ER stress response is thought to be a consequence of the up-regulation of major histocompatibility complex class I in muscle fibers. These newly identified molecular pathways could play a major role in the pathogenesis of myositis and could be important targets in the development of new therapies.

Regulation of TIMP-2, MT1-MMP, and MMP-2 expression during C2C12 differentiation

Matrix metalloproteinases (MMPs) are zinc-dependent proteases capable of degrading extracellular matrix components. The activity of these proteases is tightly regulated through the actions of the tissue inhibitors of metalloproteinases (TIMPs). Although the regulation of MMPs and TIMPs during physiological and pathological remodeling has been investigated in a number of systems, almost nothing is known about their role in skeletal muscle differentiation. To investigate the role of MMP-mediated proteolysis during myogenesis, the regulation of TIMP-2, MT1-MMP, and MMP-2 expression was investigated during differentiation of the mouse myoblastic C2C12 cell line. We show that this trio is upregulated coincident with myogenesis. The more diffuse spatial distribution of TIMP-2 relative to MT1-MMP and MMP-2 suggests that TIMP-2 may exert MMP-independent functions during myogenesis. Elucidating the regulation of these molecules during muscle differentiation in vitro may lead to a better understanding of their role in pathological processes in muscle tissue in vivo.

Role and function of matrix metalloproteinases in the differentiation and biological characterization of mesenchymal stem cells

Matrix metalloproteinases (MMPs), known as matrixins, are Ca- and Zn-dependent endoproteinases involved in a wide variety of developmental and disease-associated processes, proving to be crucial protagonists in many physiological and pathological mechanisms. The ability of MMPs to alter, by limited proteolysis and through the fine control of tissue inhibitors of metalloproteinases, the activity or function of numerous proteins, enzymes, and receptors suggests that they are also involved in various important cellular functions during development. In this review, we focus on the differentiation of mesenchymal stem cells (including those of the myoblastic, osteoblastic, chondroblastic, neural, and apidoblastic lineages) and the possible, if unexpected, biological significance of MMPs in its regulation. The MMP system has been implicated in several differentiation events that suggests that it mediates the proliferative and prodifferentiating effect of the matrixin proteolytic cascade. We summarize these regulatory effects of MMPs on the differentiation of mesenchymal stem cells and hypothesize on the function of MMPs in the stem cell differentiation processes.

Specific matrix metalloproteinase expression in focal myositis: an immunopathological study

OBJECTIVES

The aim of our study was to investigate immunoexpression of matrix metalloproteinases MMP2, MMP7 and MMP9 in muscle specimens from patients with focal myositis (FM) vs polymyositis (PM) and dermatomyositis.

MATERIALS AND METHODS

We studied muscle biopsy samples from seven patients affected by FM; samples from five patients each with PM and dermatomyositis were studied as disease controls.

RESULTS

MMP2 immunoreactivity was present in PM and dermatomyositis, MMP7 only in PM, and MMP9 in PM, dermatomyositis and FM.

CONCLUSIONS

Our results confirm that increased MMP9 immunoreactivity in muscle fibres is a common feature of all inflammatory myopathies and suggest that MMP2 and MMP7 cannot be implicated in the inflammatory events of FM.

Proteolysis of beta-dystroglycan in muscular diseases

Alpha-dystroglycan is a cell surface peripheral membrane protein which binds to the extracellular matrix (ECM), while beta-dystroglycan is a type I integral membrane protein which anchors alpha-dystroglycan to the cell membrane via the N-terminal extracellular domain. The complex composed of alpha-and beta-dystroglycan is called the dystroglycan complex. We reported previously a matrix metalloproteinase (MMP) activity that disrupts the dystroglycan complex by cleaving the extracellular domain of beta-dystroglycan. This MMP creates a characteristic 30 kDa fragment of beta-dystroglycan that is detected by the monoclonal antibody 43DAG/8D5 directed against the C-terminus of beta-dystroglycan. We also reported that the 30 kDa fragment of beta-dystroglycan was increased in the skeletal and cardiac muscles of cardiomyopathic hamsters, the model animals of sarcoglycanopathy, and that this resulted in the disruption of the link between the ECM and cell membrane via the dystroglycan complex. In this study, we investigated the proteolysis of beta-dystroglycan in the biopsied skeletal muscles of various human muscular diseases, including sarcoglycanopathy, Duchenne muscular dystrophy (DMD), Becker muscular dystrophy, Fukuyama congenital muscular dystrophy, Miyoshi myopathy, LGMD2A, facioscapulohumeral muscular dystrophy, myotonic dystrophy and dermatomyositis/polymyositis. We show that the 30 kDa fragment of beta-dystroglycan is increased significantly in sarcoglycanopathy and DMD, but not in the other diseases. We propose that the proteolysis of beta-dystroglycan may contribute to skeletal muscle degeneration by disrupting the link between the ECM and cell membrane in sarcoglycanopathy and DMD.

Matrix metalloproteinases and skeletal muscle: A brief review

Matrix metalloproteinases (MMPs) are a family of zinc- dependent proteolytic enzymes that function mainly in the extracellular matrix, where they contribute to the development, functioning, and pathology of a wide range of tissues. This mini-review describes the MMPs and tissue inhibitors of MMPs (TIMPs) in skeletal muscle, and considers their involvement in muscle development, ischemia, myonecrosis, angiogenesis, denervation, exercise-induced injuries, disuse atrophy, muscle repair and regeneration, and inflammatory myopathies and dystrophies. Despite the very limited information currently available on MMPs and their inhibitors in skeletal muscle, it is becoming increasingly clear that they have important physiological functions in maintenance of the integrity and homeostasis of muscle fibers and of the extracellular matrix. Understanding the roles of MMPs and TIMPs may lead to the development of new drug-related treatments for various muscle disorders based on suppression or upregulation of their expression.

Growth factor stimulation of matrix metalloproteinase expression and myoblast migration and invasion in vitro

We investigated the role of growth factors and fibronectin on matrix metalloproteinase (MMP) expression and on migration and invasion of mouse skeletal myoblasts in vitro. None of the growth factors tested significantly affected MMP-1 or MMP-2 activity as revealed by gelatin zymography, but both basic FGF (bFGF) and tumor necrosis factor (TNF)-alpha significantly increased MMP-9 activity (10- and 30-fold, respectively). The increase in secreted MMP-9 activity with TNF-alpha stimulation was due at least in part to an increase in MMP-9 gene transcription, because an MMP-9 promoter construct was approximately fivefold more active in TNF-alpha-treated myoblasts than in control myoblasts, as well as an increase in MMP-9 proteolytic activation. However, whereas fibronectin, bFGF, hepatocyte growth factor, and TGF-beta1 significantly augmented migration of mouse myoblasts, TNF-alpha did not, nor did PDGF-BB or IGF-I. Fibronectin and bFGF also significantly augmented invasion of myoblasts across a Matrigel barrier, and plasmin cotreatment potentiated whereas N-acetyl cysteine suppressed the effects of bFGF and fibronectin on myoblast migration and invasion. Finally, transient transfection with an MMP-9 overexpression construct had only minimal effects on myoblast migration/invasion, whereas overexpression of either MMP-2 or MMP-1 significantly augmented myoblast migration and invasion. These observations support the hypothesis that MMP activity is a necessary component of growth factor-mediated myoblast migration but suggest that other consequences of growth factor signaling are also necessary for migration to occur.