J G Tidball

University of California, Los Angeles, Los Angeles, California, United States

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Publications (107)525.03 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We examined the hypothesis that regulatory T cells (Tregs) modulate muscle injury and inflammation in the mdx mouse model of Duchenne muscular dystrophy (DMD). Although Tregs were largely absent in the muscle of wild-type mice and normal human muscle, they were present in necrotic lesions, displayed an activated phenotype, and showed increased expression of interleukin-10 (IL-10) in dystrophic muscle from mdx mice. Depletion of Tregs exacerbated muscle injury and the severity of muscle inflammation, which was characterized by an enhanced interferon-γ (IFN-γ) response and activation of M1 macrophages. To test the therapeutic value of targeting Tregs in muscular dystrophy, we treated mdx mice with IL-2/anti-IL-2 complexes and found that Tregs and IL-10 concentrations were increased in muscle, resulting in reduced expression of cyclooxygenase-2 and decreased myofiber injury. These findings suggest that Tregs modulate the progression of muscular dystrophy by suppressing type 1 inflammation in muscle associated with muscle fiber injury, and highlight the potential of Treg-modulating agents as therapeutics for DMD.
    Science translational medicine 10/2014; 6(258):258ra142. · 10.76 Impact Factor
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    James G. Tidball, Michelle Wehling‐Henricks
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    ABSTRACT: The secondary loss of neuronal nitric oxide synthase (nNOS) that occurs in dystrophic muscle is the basis of numerous, complex and interacting features of the dystrophic pathology that affect not only muscle itself, but also influence the interaction of muscle with other tissues. Many mechanisms through which nNOS-deficiency contributes to misregulation of muscle development, blood flow, fatigue, inflammation and fibrosis in dystrophic muscle have been identified, suggesting that normalization in NO production could greatly attenuate diverse aspects the pathology of muscular dystrophy through multiple regulatory pathways. However, the relative importance of the loss of nNOS from the sarcolemma versus the importance of loss of total nNOS from dystrophic muscle remains unknown. Although most current evidence indicates that nNOS localization at the sarcolemma is not required to achieve NO-mediated reductions of pathology in muscular dystrophy, the question remains open concerning whether membrane localization would provide a more efficient rescue from features of the dystrophic phenotype.This article is protected by copyright. All rights reserved
    The Journal of Physiology 09/2014; · 4.38 Impact Factor
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    ABSTRACT: Much of the focus in muscle regeneration has been placed on the identification and delivery of stem cells to promote regenerative capacity. As those efforts have advanced, we have learned that complex features of the microenvironment in which regeneration occurs can determine success or failure. The immune system is an important contributor to that complexity and can determine the extent to which muscle regeneration succeeds. Immune cells of the myeloid lineage play major regulatory roles in tissue regeneration through two general, inductive mechanisms: instructive mechanisms that act directly on muscle cells; and permissive mechanisms that act indirectly to influence regeneration by modulating angiogenesis and fibrosis. In this article, recent discoveries that identify inductive actions of specific populations of myeloid cells on muscle regeneration are presented, with an emphasis on how processes in muscle and myeloid cells are co-regulated.
    Development 03/2014; 141(6):1184-96. · 6.60 Impact Factor
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    ABSTRACT: Sarcopenia, the age-related loss of muscle mass, is a highly-debilitating consequence of aging. In this investigation, we show sarcopenia is greatly reduced by muscle-specific overexpression of calpastatin, the endogenous inhibitor of calcium-dependent proteases (calpains). Further, we show that calpain cleavage of specific structural and regulatory proteins in myofibrils is prevented by covalent modification of calpain by nitric oxide (NO) through S-nitrosylation. We find that calpain in adult, non-sarcopenic muscles is S-nitrosylated but that aging leads to loss of S-nitrosylation, suggesting that reduced S-nitrosylation during aging leads to increased calpain-mediated proteolysis of myofibrils. Further, our data show that muscle aging is accompanied by loss of neuronal nitric oxide synthase (nNOS), the primary source of muscle NO, and that expression of a muscle-specific nNOS transgene restores calpain S-nitrosylation in aging muscle and prevents sarcopenia. Together, the findings show that in vivo reduction of calpain S-nitrosylation in muscle may be an important component of sarcopenia, indicating that modulation of NO can provide a therapeutic strategy to slow muscle loss during old age.
    Aging cell 09/2012; · 7.55 Impact Factor
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    ABSTRACT: We examined the function of IL-10 in regulating changes in macrophage phenotype during muscle growth and regeneration following injury. Our findings showed that the Th1 cytokine response in inflamed muscle is characterized by high levels of expression of CD68, CCL-2, TNF-α, and IL-6 at 1 d postinjury. During transition to the Th2 cytokine response, expression of those transcripts declined, whereas CD163, IL-10, IL-10R1, and arginase-1 increased. Ablation of IL-10 amplified the Th1 response at 1 d postinjury, causing increases in IL-6 and CCL2, while preventing a subsequent increase in CD163 and arginase-1. Reductions in muscle fiber damage that normally occurred between 1 and 4 d postinjury did not occur in IL-10 mutants. In addition, muscle regeneration and growth were greatly slowed by loss of IL-10. Furthermore, myogenin expression increased in IL-10 mutant muscle at 1 d postinjury, suggesting that the mutation amplified the transition from the proliferative to the early differentiation stages of myogenesis. In vitro assays showed that stimulation of muscle cells with IL-10 had no effect on cell proliferation or expression of MyoD or myogenin. However, coculturing muscle cells with macrophages activated with IL-10 to the M2 phenotype increased myoblast proliferation without affecting MyoD or myogenin expression, showing that M2 macrophages promote the early, proliferative stage of myogenesis. Collectively, these data show that IL-10 plays a central role in regulating the switch of muscle macrophages from a M1 to M2 phenotype in injured muscle in vivo, and this transition is necessary for normal growth and regeneration of muscle.
    The Journal of Immunology 08/2012; 189(7):3669-80. · 5.52 Impact Factor
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    William H Foster, James G Tidball, Yibin Wang
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    ABSTRACT: p38γ kinase is highly enriched in skeletal muscle and is implicated in myotube formation. However, the activation status of p38γ in muscle is unclear. p38γ activity in slow and fast adult mouse skeletal muscle tissue was examined, as was the impact of p38γ deficiency on muscle development and gene expression. p38γ is preferentially activated in slow muscle, but it is inactive in fast muscle types. Furthermore, the loss of p38γ in mice led to decreased muscle mass associated with a smaller myofiber diameter in slow muscle, but there was no impact on fast muscle in either mass or myofiber diameter. Finally, p38γ-deficient muscle showed selective changes in genes related to muscle growth in slow muscle fibers. This study provides evidence that p38γ is selectively activated in slow skeletal muscle and is involved in the normal growth and development of a subset of skeletal muscle.
    Muscle & Nerve 02/2012; 45(2):266-73. · 2.31 Impact Factor
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    ABSTRACT: Duchenne muscular dystrophy is a degenerative disorder that leads to death by the third decade of life. Previous investigations have shown that macrophages that invade dystrophic muscle are a heterogeneous population consisting of M1 and M2 macrophages that promote injury and repair, respectively. In the present investigation, we tested whether IFN-γ worsens the severity of mdx dystrophy by activating macrophages to a cytolytic M1 phenotype and by suppressing the activation of proregenerative macrophages to an M2 phenotype. IFN-γ is a strong inducer of the M1 phenotype and is elevated in mdx dystrophy. Contrary to our expectations, null mutation of IFN-γ caused no reduction of cytotoxicity of macrophages isolated from mdx muscle and did not reduce muscle fiber damage in vivo or improve gross motor function of mdx mice at the early, acute peak of pathology. In contrast, ablation of IFN-γ reduced muscle damage in vivo during the regenerative stage of the disease and increased activation of the M2 phenotype and improved motor function of mdx mice at that later stage of the disease. IFN-γ also inhibited muscle cell proliferation and differentiation in vitro, and IFN-γ mutation increased MyoD expression in mdx muscle in vivo, showing that IFN-γ can have direct effects on muscle cells that could impair repair. Taken together, the findings show that suppression of IFN-γ signaling in muscular dystrophy reduces muscle damage and improves motor performance by promoting the M2 macrophage phenotype and by direct actions on muscle cells.
    The Journal of Immunology 11/2011; 187(10):5419-28. · 5.52 Impact Factor
  • James G Tidball
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    ABSTRACT: Skeletal muscle continuously adapts to changes in its mechanical environment through modifications in gene expression and protein stability that affect its physiological function and mass. However, mechanical stresses commonly exceed the parameters that induce adaptations, producing instead acute injury. Furthermore, the relatively superficial location of many muscles in the body leaves them further vulnerable to acute injuries by exposure to extreme temperatures, contusions, lacerations or toxins. In this article, the molecular, cellular, and mechanical factors that underlie muscle injury and the capacity of muscle to repair and regenerate are presented. Evidence shows that muscle injuries that are caused by eccentric contractions result from direct mechanical damage to myofibrils. However, muscle pathology following other acute injuries is largely attributable to damage to the muscle cell membrane. Many feaures in the injury-repair-regeneration cascade relate to the unregulated influx of calcium through membrane lesions, including: (i) activation of proteases and hydrolases that contribute muscle damage, (ii) activation of enzymes that drive the production of mitogens and motogens for muscle and immune cells involved in injury and repair, and (iii) enabling protein-protein interactions that promote membrane repair. Evidence is also presented to show that the myogenic program that is activated by acute muscle injury and the inflammatory process that follows are highly coordinated, with myeloid cells playing a central role in modulating repair and regeneration. The early-invading, proinflammatory M1 macrophages remove debris caused by injury and express Th1 cytokines that play key roles in regulating the proliferation, migration, and differentiation of satellite cells. The subsequent invasion by anti-inflammatory, M2 macrophages promotes tissue repair and attenuates inflammation. Although this system provides an effective mechanism for muscle repair and regeneration following acute injury, it is dysregulated in chronic injuries. In this article, the process of muscle injury, repair and regeneration that occurs in muscular dystrophy is used as an example of chronic muscle injury, to highlight similarities and differences between the injury and repair processes that occur in acutely and chronically injured muscle. © 2011 American Physiological Society. Compr Physiol 1:2029-2062, 2011.
    Comprehensive Physiology. 10/2011; 1(4):2029-62.
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    ABSTRACT: Mice lacking Cu,Zn superoxide dismutase (SOD1) show accelerated, age-related loss of muscle mass. Lack of SOD1 may lead to increased superoxide, reduced nitric oxide (NO), and increased peroxynitrite, each of which could initiate muscle fiber loss. Single muscle fibers from flexor digitorum brevis of wild-type (WT) and Sod1(-/-) mice were loaded with NO-sensitive (4-amino-5-methylamino-2',7'-difluorofluorescein diacetate, DAF-FM) and superoxide-sensitive (dihydroethidium, DHE) probes. Gastrocnemius muscles were analyzed for SOD enzymes, nitric oxide synthases (NOS), and 3-nitrotyrosine (3-NT) content. A lack of SOD1 did not increase superoxide availability at rest because no increase in ethidium or 2-hydroxyethidium (2-HE) formation from DHE was seen in fibers from Sod1(-/-) mice compared with those from WT mice. Fibers from Sod1(-/-) mice had decreased NO availability (decreased DAF-FM fluorescence), increased 3-NT in muscle proteins indicating increased peroxynitrite formation and increased content of peroxiredoxin V (a peroxynitrite reductase), compared with WT mice. Muscle fibers from Sod1(-/-) mice showed substantially reduced generation of superoxide in response to contractions compared with fibers from WT mice. Inhibition of NOS did not affect DHE oxidation in fibers from WT or Sod1(-/-) mice at rest or during contractions, but transgenic mice overexpressing nNOS showed increased DAF-FM fluorescence and reduced DHE oxidation in resting muscle fibers. It is concluded that formation of peroxynitrite in muscle fibers is a major effect of lack of SOD1 in Sod1(-/-) mice and may contribute to fiber loss in this model, and that NO regulates superoxide availability and peroxynitrite formation in muscle.
    Aging cell 03/2011; 10(5):749-60. · 7.55 Impact Factor
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    ABSTRACT: M1 macrophages play a major role in worsening muscle injury in the mdx mouse model of Duchenne muscular dystrophy. However, mdx muscle also contains M2c macrophages that can promote tissue repair, indicating that factors regulating the balance between M1 and M2c phenotypes could influence the severity of the disease. Because interleukin-10 (IL-10) modulates macrophage activation in vitro and its expression is elevated in mdx muscles, we tested whether IL-10 influenced the macrophage phenotype in mdx muscle and whether changes in IL-10 expression affected the pathology of muscular dystrophy. Ablation of IL-10 expression in mdx mice increased muscle damage in vivo and reduced mouse strength. Treating mdx muscle macrophages with IL-10 reduced activation of the M1 phenotype, assessed by iNOS expression, and macrophages from IL-10 null mutant mice were more cytolytic than macrophages isolated from wild-type mice. Our data also showed that muscle cells in mdx muscle expressed the IL-10 receptor, suggesting that IL-10 could have direct effects on muscle cells. We assayed whether ablation of IL-10 in mdx mice affected satellite cell numbers, using Pax7 expression as an index, but found no effect. However, IL-10 mutation significantly increased myogenin expression in vivo during the acute and the regenerative phase of mdx pathology. Together, the results show that IL-10 plays a significant regulatory role in muscular dystrophy that may be caused by reducing M1 macrophage activation and cytotoxicity, increasing M2c macrophage activation and modulating muscle differentiation.
    Human Molecular Genetics 02/2011; 20(4):790-805. · 7.69 Impact Factor
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    Michelle Wehling-Henricks, James G Tidball
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    ABSTRACT: Survival of dystrophin/utrophin double-knockout (dko) mice was increased by muscle-specific expression of a neuronal nitric oxide synthase (nNOS) transgene. Dko mice expressing the transgene (nNOS TG+/dko) experienced delayed onset of mortality and increased life-span. The nNOS TG+/dko mice demonstrated a significant decrease in the concentration of CD163+, M2c macrophages that can express arginase and promote fibrosis. The decrease in M2c macrophages was associated with a significant reduction in fibrosis of heart, diaphragm and hindlimb muscles of nNOS TG+/dko mice. The nNOS transgene had no effect on the concentration of cytolytic, CD68+, M1 macrophages. Accordingly, we did not observe any change in the extent of muscle fiber lysis in the nNOS TG+/dko mice. These findings show that nNOS/NO (nitric oxide)-mediated decreases in M2c macrophages lead to a reduction in the muscle fibrosis that is associated with increased mortality in mice lacking dystrophin and utrophin. Interestingly, the dramatic and beneficial effects of the nNOS transgene were not attributable to localization of nNOS protein at the cell membrane. We did not detect any nNOS protein at the sarcolemma in nNOS TG+/dko muscles. This important observation shows that sarcolemmal localization is not necessary for nNOS to have beneficial effects in dystrophic tissue and the presence of nNOS in the cytosol of dystrophic muscle fibers can ameliorate the pathology and most importantly, significantly increase life-span.
    PLoS ONE 01/2011; 6(10):e25071. · 3.53 Impact Factor
  • James G Tidball, S Armando Villalta
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    ABSTRACT: Recent discoveries reveal complex interactions between skeletal muscle and the immune system that regulate muscle regeneration. In this review, we evaluate evidence that indicates that the response of myeloid cells to muscle injury promotes muscle regeneration and growth. Acute perturbations of muscle activate a sequence of interactions between muscle and inflammatory cells. The initial inflammatory response is a characteristic Th1 inflammatory response, first dominated by neutrophils and subsequently by CD68(+) M1 macrophages. M1 macrophages can propagate the Th1 response by releasing proinflammatory cytokines and cause further tissue damage through the release of nitric oxide. Myeloid cells in the early Th1 response stimulate the proliferative phase of myogenesis through mechanisms mediated by TNF-alpha and IL-6; experimental prolongation of their presence is associated with delayed transition to the early differentiation stage of myogenesis. Subsequent invasion by CD163(+)/CD206(+) M2 macrophages attenuates M1 populations through the release of anti-inflammatory cytokines, including IL-10. M2 macrophages play a major role in promoting growth and regeneration; their absence greatly slows muscle growth following injury or modified use and inhibits muscle differentiation and regeneration. Chronic muscle injury leads to profiles of macrophage invasion and function that differ from acute injuries. For example, mdx muscular dystrophy yields invasion of muscle by M1 macrophages, but their early invasion is accompanied by a subpopulation of M2a macrophages. M2a macrophages are IL-4 receptor(+)/CD206(+) cells that reduce cytotoxicity of M1 macrophages. Subsequent invasion of dystrophic muscle by M2c macrophages is associated with progression of the regenerative phase in pathophysiology. Together, these findings show that transitions in macrophage phenotype are an essential component of muscle regeneration in vivo following acute or chronic muscle damage.
    AJP Regulatory Integrative and Comparative Physiology 03/2010; 298(5):R1173-87. · 3.28 Impact Factor
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    ABSTRACT: Duchenne muscular dystrophy (DMD) is the most common, lethal disease of childhood. One of 3500 new-born males suffers from this universally-lethal disease. Other than the use of corticosteroids, little is available to affect the relentless progress of the disease, leading many families to use dietary supplements in hopes of reducing the progression or severity of muscle wasting. Arginine is commonly used as a dietary supplement and its use has been reported to have beneficial effects following short-term administration to mdx mice, a genetic model of DMD. However, the long-term effects of arginine supplementation are unknown. This lack of knowledge about the long-term effects of increased arginine metabolism is important because elevated arginine metabolism can increase tissue fibrosis, and increased fibrosis of skeletal muscles and the heart is an important and potentially life-threatening feature of DMD. We use both genetic and nutritional manipulations to test whether changes in arginase metabolism promote fibrosis and increase pathology in mdx mice. Our findings show that fibrotic lesions in mdx muscle are enriched with arginase-2-expressing macrophages and that muscle macrophages stimulated with cytokines that activate the M2 phenotype show elevated arginase activity and expression. We generated a line of arginase-2-null mutant mdx mice and found that the mutation reduced fibrosis in muscles of 18-month-old mdx mice, and reduced kyphosis that is attributable to muscle fibrosis. We also observed that dietary supplementation with arginine for 17-months increased mdx muscle fibrosis. In contrast, arginine-2 mutation did not reduce cardiac fibrosis or affect cardiac function assessed by echocardiography, although 17-months of dietary supplementation with arginine increased cardiac fibrosis. Long-term arginine treatments did not decrease matrix metalloproteinase-2 or -9 or increase the expression of utrophin, which have been reported as beneficial effects of short-term treatments. Our findings demonstrate that arginine metabolism by arginase promotes fibrosis of muscle in muscular dystrophy and contributes to kyphosis. Our findings also show that long-term, dietary supplementation with arginine exacerbates fibrosis of dystrophic heart and muscles. Thus, commonly-practiced dietary supplementation with arginine by DMD patients has potential risk for increasing pathology when performed for long periods, despite reports of benefits acquired with short-term supplementation.
    PLoS ONE 01/2010; 5(5):e10763. · 3.53 Impact Factor
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    ABSTRACT: Cell-based therapy is a possible avenue for the treatment of Duchenne muscular dystrophy (DMD), an X-linked skeletal muscle-wasting disease. We have demonstrated that cultured myogenic progenitors derived from the adult skeletal muscle side population can engraft into dystrophic fibers of non-irradiated, non-chemically injured mouse models of DMD (mdx(5cv)) after intravenous and intraarterial transplantation, with engraftment rates approaching 10%. In an effort to elucidate the cell-surface markers that promote progenitor cell extravasation and engraftment after systemic transplantation, we found that expression of the chemokine receptor CXCR4, whose ligand SDF-1 is overexpressed in dystrophic muscle, enhances the extravasation of these cultured progenitor cells into skeletal muscle after intraarterial transplantation. At 1 day post-transplantation, mice that received CXCR4-positive enhanced green fluorescent protein (eGFP)-positive cultured cells derived from the skeletal muscle side population displayed significantly higher amounts of eGFP-positive mononuclear cells in quadriceps and tibialis anterior than mice that received CXCR4-negative eGFP-positive cells derived from the same cultured population. At 30 days posttransplantation, significantly higher engraftment rates of donor cells were observed in mice that received CXCR4-positive cells compared with mice transplanted with CXCR4-negative fractions. Our data suggest that CXCR4 expression by muscle progenitor cells increases their extravasation into skeletal muscle shortly after transplantation. Furthermore, this enhanced extravasation likely promotes higher donor cell engraftment rates over time.
    Muscle & Nerve 10/2009; 40(4):562-72. · 2.31 Impact Factor
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    ABSTRACT: Duchenne muscular dystrophy (DMD) involves a complex pathophysiology that is not easily explained by the loss of the protein dystrophin, the primary defect in DMD. Instead, many features of the pathology are attributable to the secondary loss of neuronal nitric oxide synthase (nNOS) from dystrophin-deficient muscle. In this investigation, we tested whether the loss of nNOS contributes to the increased fatigability of mdx mice, a model of DMD. Our findings show that the expression of a muscle-specific, nNOS transgene increases the endurance of mdx mice and enhances glycogen metabolism during treadmill-running, but did not affect vascular perfusion of muscles. We also find that the specific activity of phosphofructokinase (PFK; the rate limiting enzyme in glycolysis) is positively affected by nNOS in muscle; PFK-specific activity is significantly reduced in mdx muscles and the muscles of nNOS null mutants, but significantly increased in nNOS transgenic muscles and muscles from mdx mice that express the nNOS transgene. PFK activity measured under allosteric conditions was significantly increased by nNOS, but unaffected by endothelial NOS or inducible NOS. The specific domain of nNOS that positively regulates PFK activity was assayed by cloning and expressing different domains of nNOS and assaying their effects on PFK activity. This approach yielded a polypeptide that included the flavin adenine dinucleotide (FAD)-binding domain of nNOS as the region of the molecule that promotes PFK activity. Smaller peptides in this domain were then synthesized and used in activity assays that showed a 36-amino acid peptide in the FAD-binding domain in which most of the positive allosteric activity of nNOS for PFK resides. Mapping this peptide onto the structure of nNOS shows that the peptide is exposed on the surface, readily available for binding. Collectively, these findings indicate that defects in glycolytic metabolism and increased fatigability in dystrophic muscle may be caused in part by the loss of positive allosteric interactions between nNOS and PFK.
    Human Molecular Genetics 07/2009; 18(18):3439-51. · 7.69 Impact Factor
  • James G Tidball, S Armando Villalta
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    ABSTRACT: A remote, downstream event in the pathology of muscular dystrophy may have a key role in the disease (pages 325–330). It seems that induction of nitric oxide synthase causes calcium to leak inside the cell through ryanodine receptors. The findings provide new options for therapeutic interventions.
    Nature medicine 04/2009; 15(3):243-4. · 27.14 Impact Factor
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    Bo Deng, David Glanzman, James G Tidball
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    ABSTRACT: Duchenne muscular dystrophy (DMD) results from null mutation of dystrophin, a membrane-associated structural protein that is expressed in skeletal muscle. Dystrophin deficiency causes muscle membrane lesions, muscle degeneration and eventually death in afflicted individuals. However, dystrophin deficiency also causes cognitive defects that are difficult to relate to the loss of dystrophin. We assayed neurogenesis in the dentate gyrus (DG) in the mdx mouse model of DMD, using bromodeoxyuridine incorporation as a marker of proliferation and NeuN expression as a marker of differentiation. Our findings show that dystrophin mutation disrupts adult neurogenesis by promoting cell proliferation in the DG and suppressing neuronal differentiation. Because loss of dystrophin from muscle results in the secondary loss of neuronal nitric oxide synthase (nNOS), and NO is able to modulate neurogenesis, we assayed whether the genetic restoration of nNOS to mdx muscles corrected defects in adult, hippocampal neurogenesis. Assays of NO in the sera of active mice showed significant reductions in NO caused by the dystrophin mutation. However, over-expression of nNOS in the muscles of mdx mice increased serum NO and normalized cell proliferation and neuronal differentiation in the DG. These findings indicate that muscle-derived NO regulates adult neurogenesis in the brain and loss of muscle nNOS may underlie defects in the central nervous system in DMD.
    The Journal of Physiology 03/2009; 587(Pt 8):1769-78. · 4.38 Impact Factor
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    ABSTRACT: Duchenne muscular dystrophy (DMD) is the most common, lethal, muscle-wasting disease of childhood. Previous investigations have shown that muscle macrophages may play an important role in promoting the pathology in the mdx mouse model of DMD. In the present study, we investigate the mechanism through which macrophages promote mdx dystrophy and assess whether the phenotype of the macrophages changes between the stage of peak muscle necrosis (4 weeks of age) and muscle regeneration (12 weeks). We find that 4-week-old mdx muscles contain a population of pro-inflammatory, classically activated M1 macrophages that lyse muscle in vitro by NO-mediated mechanisms. Genetic ablation of the iNOS gene in mdx mice also significantly reduces muscle membrane lysis in 4-week-old mdx mice in vivo. However, 4-week mdx muscles also contain a population of alternatively activated, M2a macrophages that express arginase. In vitro assays show that M2a macrophages reduce lysis of muscle cells by M1 macrophages through the competition of arginase in M2a cells with iNOS in M1 cells for their common, enzymatic substrate, arginine. During the transition from the acute peak of mdx pathology to the regenerative stage, expression of IL-4 and IL-10 increases, either of which can deactivate the M1 phenotype and promote activation of a CD163+, M2c phenotype that can increase tissue repair. Our findings further show that IL-10 stimulation of macrophages activates their ability to promote satellite cell proliferation. Deactivation of the M1 phenotype is also associated with a reduced expression of iNOS, IL-6, MCP-1 and IP-10. Thus, these results show that distinct subpopulations of macrophages can promote muscle injury or repair in muscular dystrophy, and that therapeutic interventions that affect the balance between M1 and M2 macrophage populations may influence the course of muscular dystrophy.
    Human Molecular Genetics 12/2008; 18(3):482-96. · 7.69 Impact Factor
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    ABSTRACT: The immune response to dystrophin-deficient muscle promotes the pathology of Duchenne muscular dystrophy (DMD) and the mdx mouse model of DMD. In this investigation, we find that the release of major basic protein (MBP) by eosinophils is a prominent feature of DMD and mdx dystrophy and that eosinophils lyse muscle cells in vitro by the release of MBP-1. We also show that eosinophil depletions of mdx mice by injections of anti-chemokine receptor-3 reduce muscle cell lysis, although lysis of mdx muscle membranes is not reduced by null mutation of MBP-1 in vivo. However, ablation of MBP-1 expression in mdx mice produces other effects on muscular dystrophy. First, fibrosis of muscle and hearts, a major cause of mortality in DMD, is greatly reduced by null mutation of MBP-1 in mdx mice. Furthermore, either ablation of MBP-1 or eosinophil depletion causes large increases in cytotoxic T-lymphocytes (CTLs) in mdx muscles. The increase in CTLs in MBP-1-null mice does not reflect a general shift toward a Th1 inflammatory response, because the mutation had no significant effect on the expression of interferon-gamma, inducible nitric oxide synthase or tumor necrosis factor. Rather, MBP-1 reduces the activation and proliferation of splenocytes in vitro, indicating that MBP-1 acts in a more specific immunomodulatory role to affect the inflammatory response in muscular dystrophy. Together, these findings show that eosinophil-derived MBP-1 plays a significant role in regulating muscular dystrophy by attenuating the cellular immune response and promoting tissue fibrosis that can eventually contribute to increased mortality.
    Human Molecular Genetics 09/2008; 17(15):2280-92. · 7.69 Impact Factor
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    ABSTRACT: Myotonic dystrophy (DM), the most common adult-onset muscular dystrophy, is caused by CTG or CCTG microsatellite repeat expansions. Expanded DM mRNA microsatellite repeats are thought to accumulate in the nucleus, sequester Muscleblind proteins, and interfere with alternative mRNA splicing. Muscleblind2 (Mbnl2) is a member of the family of Muscleblind RNA binding proteins (that also include Mbnl1 and Mbnl3) that are known to bind CTG/CCTG RNA repeats. Recently, it was demonstrated that Mbnl1-deficient mice have characteristic features of human DM, including myotonia and defective chloride channel expression. Here, we demonstrate that Mbnl2-deficient mice also develop myotonia and have skeletal muscle pathology consistent with human DM. We also find defective expression and mRNA splicing of the chloride channel (Clcn1) in skeletal muscle that likely contributes to the myotonia phenotype. Our results support the hypothesis that Muscleblind proteins and specifically MBNL2 contribute to the pathogenesis of human DM.
    Developmental Dynamics 03/2008; 237(2):403-10. · 2.59 Impact Factor

Publication Stats

5k Citations
525.03 Total Impact Points

Institutions

  • 1989–2014
    • University of California, Los Angeles
      • • Department of Integrative Biology and Physiology
      • • School of Nursing
      Los Angeles, California, United States
  • 1992–2011
    • University of Southern California
      • Department of Biological Sciences
      Los Angeles, California, United States
  • 2000–2008
    • CSU Mentor
      Long Beach, California, United States
  • 2001
    • Baylor College of Medicine
      • Department of Medicine
      Houston, TX, United States
  • 1986–1988
    • University of California, Riverside
      • Division of Biomedical Sciences
      Riverside, CA, United States
  • 1983
    • Duke University
      Durham, North Carolina, United States