Myopathic Tissue Research Articles

Activated IL-22 pathway occurs in the muscle tissues of patients with polymyositis or dermatomyositis and is correlated with disease activity

The aim of this study was to assess the expression of IL-22, IL-22 receptor 1 (IL-22R1), IL-22 binding protein (IL-22BP) and p-STAT3 in muscle tissue from patients with PM and DM. Levels of IL-22, IL-22R1, IL-22BP and STAT3 mRNA were quantified by RT-PCR. The expression of IL-22, IL-22R1, IL-22BP and p-STAT3 was also analysed using immunohistochemistry. Significant modulation of the IL-22 pathway was observed in inflammatory myopathic tissues. In particular, a significant overexpression of IL-22 at the protein but not the mRNA level was observed in PM/DM tissues and was correlated with myositis activity. IL-22R1 aberrant expression was also observed among infiltrating mononuclear cells and necrotic muscle cells. IL-22BP, which inhibits IL-22 signalling, was expressed only in some muscle fibres in PM/DM patients. Our findings indicate that the IL-22 pathway is activated in inflammatory myopathic tissues and may be involved in the induction of muscle inflammatory processes and muscle necrosis.

A computational method for developing hierarchical large deformation viscoelastic models of the contracting heart

In this study, a new computational method for modelling the contracting heart is described. Using this method, the cardiac wall is constructed from basic, repeating contractile units that represent individual myocardial units and collagen, each with its own set of parameters, including orientation, passive and active behaviour and stimulation propagation. The method allows individual control of each structural unit (e.g. at the level of a single myocardial unit). Feasibility of modelling dynamic heart contraction using this method is demonstrated using 2D cross-sections and simplified 3D geometries. Effects of non-contractile scar and myopathic tissue were also tested in these geometrical configurations. Results from the 2D and 3D simulations were, overall, in agreement with well-established physiological data. The present method holds promise for modelling complex heart pathologies, abnormal mechanical properties (e.g. myocardial infarcts) and electrical conduction properties (branch blocks), and their spatial distributions across the myocardial tissues.

Expression of toll‐like receptor 3 and toll‐like receptor 7 in muscle is characteristic of inflammatory myopathy and is differentially regulated by Th1 and Th17 cytokines

To assess the expression of Toll-like receptor 3 (TLR-3) and TLR-7 in muscle tissue from patients with polymyositis (PM) and dermatomyositis (DM) and to investigate the function and regulation of TLR-3 in cultured muscle cells. The expression of TLR-3, TLR-7, HLA class I, and CD56, a marker of immature myoblast precursors, was analyzed using immunohistochemistry. TLR-3 regulation and signaling were assessed in myoblasts and in differentiated myotubes with the TLR-3 agonist poly(I-C), necrotic myoblasts, and Th1 and Th17 cytokines, in the presence or absence of neutralizing anti-TLR-3 antibody. Levels of TLR-3 messenger RNA (mRNA) were quantified by reverse transcription-polymerase chain reaction. Levels of interleukin-6 (IL-6), CCL20, and IL-8 were determined by enzyme-linked immunosorbent assay. TLR-3 and TLR-7 were expressed in PM/DM tissues, but not in noninflammatory muscle tissues, and were primarily detected in inflammatory infiltrates, although a few muscle cells were also positive. These TLR-3- and TLR-7-positive fibers expressed high levels of CD56 and HLA class I antigens. A synergy between poly(I-C) and IL-17 was observed for the production of IL-6 and CCL20. Similarly, stimulation with necrotic myoblasts increased IL-6 production, and stimulation with necrotic myoblasts in combination with IL-17 further increased the induction of IL-6. TLR-3 blockade decreased the inducing effect of necrotic myoblasts and IL-17 on IL-6 production. Stimulation with interferon-gamma (IFNgamma) increased TLR-3 mRNA levels, but IL-17 down-regulated the inducing effect of IFNgamma. Our findings indicate that TLR-3 and TLR-7 are expressed in inflammatory myopathic tissues, particularly in immature myoblast precursors. Necrotic muscle cells activate cytokine production, in part, through the TLR-3 pathway, with a differential regulatory effect of Th1 and Th17 cytokines.

Relation between steady-state force and intracellular [Ca2+] in intact human myocardium. Index of myofibrillar responsiveness to Ca2+.

A novel approach was developed allowing the measurement of steady-state force and intracellular calcium concentration ([Ca2+]i) in tetanized human ventricular trabeculae carneae without pharmacological intervention. We compared and contrasted three methods of assessing calcium sensitivity of the myofilaments: 1) force-[Ca2+] relations in skinned fiber preparations, 2) peak twitch force-peak [Ca2+]i relations, and 3) steady-state force-[Ca2+]i relations in intact muscles. Steady-state contractile activation was achieved rapidly by tetanizing intact human trabeculae, loaded with aequorin, a Ca2(+)-sensitive bioluminescent protein, at a stimulation frequency of 15-20 Hz. Steady-state force and [Ca2+]i were measured during tetani, and the force versus [Ca2+]i relation was obtained by varying the extracellular calcium concentration ([Ca2+]o). Force-[Ca2+]i relations obtained from control and myopathic hearts were fitted to the Hill equation: %Force = [Ca2+]inh/([Ca2+]inh50% + [Ca2+]inh), where nh is the Hill coefficient, and [Ca2+]50% is the [Ca2+] required for 50% activation. The curves of tetani had Hill coefficients of 5.21 +/- 0.20 (n = 6) and 5.61 +/- 0.60 (n = 10) and [Ca2+]50% of 0.56 +/- 0.05 microM (n = 6) and 0.54 +/- 0.09 microM (n = 10) in control and myopathic muscles, respectively. We also constructed peak force-peak [Ca2+]i relations using isometric twitches from the same muscles. These curves were shifted toward higher [Ca2+]i compared with the steady-state force-[Ca2+]i curve derived from tetani. Ryanodine (1 microM), which increased the time course of the Ca2+ and force transients, shifted the peak force-peak [Ca2+]i relation to the left, without affecting the steady-state force-[Ca2+]i relation. Exposure to 10 mM caffeine shifted the steady-state force-[Ca2+]i relation to the left, whereas exposure to 3 microM isoproterenol shifted this relation to the right. Experiments using skinned fiber preparations were performed in parallel with experiments on intact muscles from the same hearts. The force-pCa (-log[Ca2+]) relations in saponin-skinned trabeculae from control and myopathic tissue were superimposable. Ryanodine (1 microM) had no effect on the force-pCa relation in skinned fibers. Maximal tension was evoked by the posttetanic twitch, which was larger than the tetanus. This potentiation was abolished in the presence of ryanodine, a sarcoplasmic reticulum inhibitor. We propose that the changes in the steady-state force-[Ca2+]i relations are correlated with alterations in the sensitivity of the myofilaments to Ca2+, whereas changes in the peak force-peak [Ca2+]i relations represent temporal changes in the twitch transient.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential effect of DPI 201-106 on the sensitivity of the myofilaments to Ca2+ in intact and skinned trabeculae from control and myopathic human hearts.

The effects of DPI, a new inotropic agent, were compared in trabeculae carneae from control and myopathic human hearts loaded with aequorin, a bioluminescent calcium indicator that emits light when it combines with calcium, and in saponin-skinned trabeculae carneae from the same hearts. The force-pCa curves in saponin-skinned fibers and the peak force-peak Ca2+ curves in aequorin-loaded preparations were not significantly different between the control and myopathic tissues. The force-pCa curve in the skinned and aequorin-loaded preparations from the same control hearts displayed no significant shifts with the addition of DPI. In contrast, a leftward shift was present in the force-calcium relationship in the presence of DPI in aequorin-loaded and skinned muscles from myopathic hearts, indicating an increase in the sensitivity of the myofilaments to calcium. These differences in the modulation of calcium activation between myopathic and control tissues indicate that pharmacological agents may produce differential effects in normal and diseased hearts.

Comparison of soft tissue calcium levels throughout the life spans of normal and myopathic hamsters

1. 1. Comparisons of calcium levels in heart, skeletal muscle, brain, liver and plasma were made throughout the life spans of normal and genetically myopathic hamsters. 2. 2. A large calcium accumulation occurred in, and was restricted to, myopathic tissues (heart and skeletal muscle). 3. 3. Calcium elevation in myopathic tissues corresponded to documented lesion appearance, and persisted throughout the remainder of the life span. 4. 4. Calcium buildup in heart and skeletal muscle, as a central feature of the myopathic process, does not reflect a general failure of calcium homeostasis; nonmyopathic tissues are unaffected. 5. 5. Calcium increased moderately in some normal tissues late in life.

Myocardial subcellular fractionation studies on cardiomyopathic Syrian hamsters

Myocardial homogenates from control animals and from hamsters with hereditary cardiomyopathy were subjected to analytical subcellular fractionation and enzymic microanalysis. Animals without ventricular hypertrophy or overt heart failure were used in this study. The principal subcellular organelles were characterised by density gradient centrifugation. Apart from evidence of enhanced lysosomal and peroxisomal fragility, probably secondary to the intracellular oedema, the intracellular organelles investigated in this study were unaffected by the myopathic process. Highly significant increases in 5'-nucleotidase activity, a marker for the sarcolemma, and an increased equilibrium density of this organelle were found in the myopathic tissue. Ultrastructural studies revealed patchy myocytolysis associated with lysosomes and with more extensive invaginations of the sarcolemma. It is suggested that a primary defect in membrane composition, leading to increased cation permeability, is the underlying abnormality in the myopathic hamster.