Lazaroids enhance skeletal myogenesis in primary cultures of dystrophin-deficient mdx mice

The difficult-to-cultivate coxsackieviruses A can productively multiply in primary culture of mouse skeletal muscle

Coxsackieviruses A (CVA) are associated with several clinical manifestations such as aseptic meningitis and paralytic syndromes in humans. Most CVA are difficult-to-cultivate, which impedes their propagation and isolation from clinical material. Here, we tested the ability of cultivable (CVA-13, CVA-14), and difficult-to-cultivate (CVA-6, CVA-22) strains to infect primary cultures of skeletal muscle cells established from newborn mice. We found that such cultures sustained the multiplication of these CVA, as evidenced by the development of a cytopathic effect, already in the initial preparation or after passaging once. Cultures established for no more than 24h were sensitive to infection whereas older preparations were resistant. Using confocal microscopy after double-immunolabeling of the VP1 capsid protein and the muscle cell marker myosin, we demonstrated that only the myoblasts were infected, resulting in VP1 expression throughout their cytoplasm. Inoculation of infected cultures to suckling mice resulted in paralysis indicating that infection was productive. The nature of candidate receptors for virus entry in such cultures and the influence of cell culture conditions on the expression of these putative receptors are discussed. This work suggests that primary cultures of skeletal muscle cells could be used to propagate and isolate any CVA strain.

Cellular basis of steroid neuroprotection in the wobbler mouse, a genetic model of motoneuron disease

1. The Wobbler mouse suffers an autosomal recessive mutation producing severe motoneuron degeneration and astrogliosis in the spinal cord. It has been considered a suitable model of human motoneuron disease, including the sporadic form of amyotrophic lateral sclerosis (ALS). 2. Evidences exist demonstrating increased oxidative stress in the spinal cord of Wobbler mice, whereas antioxidant therapy delayed neurodegeneration and improved muscle trophism. 21-Aminosteroids are glucocorticoid-derived hydrophobic compounds with antioxidant potency 3 times higher than vitamin E and 100 times higher than methylprednisolone. They do not bind to intracellular receptors, and prevent lipid peroxidation by insertion into membrane lipid bilayers. 3. In common with the spinal cord of ALS patients, Wobbler mice present astrocytosis with hyperexpression of glial fibrillary acidic protein (GFAP), and increased expression of nitric oxide synthase (NOS) and growth-associated protein (GAP-43) in motoneurons. Here, we review our studies on the effects of a 21-aminosteroid on GFAP, NOS, and GAP-43. 4. First, we showed that 21-aminosteroid treatment further increased GFAP-expressing astrocytes in gray matter of the Wobbler spinal cord. This effect may provide neuroprotection if one considers a trophic and beneficial function of astrocytes during the course of degeneration. Other neuroprotectans used in Wobbler mice (T-588) also increased pre-existing astrocytosis. 5. Second, histochemical determination of NADPH-diaphorase, a parameter indicative of neuronal NOS activity, showed that the 21-aminosteroid down-regulated the high activity of this enzyme in ventral horn motoneurons. Therefore, suppression of nitric oxide by decreasing NADPH-diaphorase (NOS) activity may provide neuroprotection considering that excess NO is highly toxic to motoneurons. 6. Finally, 21-aminosteroid treatment significantly attenuated the aberrant expression of both GAP-43 protein and mRNA in Wobbler motoneurons. Hyperexpression of GAP-43 possibly indicated abnormal synaptogenesis, denervation, and muscle atrophy, parameters which may return to normal following antioxidant steroid treatment. 7. Besides 21-aminosteroids, other steroids also behave as neuroprotectans. In this regard, degenerative diseases may constitute potential targets of these hormones, based on the fact that the spinal cord expresses in a regional and cell-specific fashion, receptors for androgens. progesterone, adrenal steroids, and estrogens.

The 21-aminosteroid U-74389F attenuates hyperexpression of GAP-43 and NADPH-diaphorase in the spinal cord of wobbler mouse, a model for amyotrophic lateral sclerosis

The wobbler mouse suffers an autosomal recessive mutation producing severe neurodegeneration and astrogliosis in spinal cord. It has been considered a model for amyotrophic lateral sclerosis. We have studied in these animals the expression of two proteins, the growth-associated protein (GAP-43) and the NADPH-diaphorase, the nitric oxide synthesizing enzyme, employing immunocytochemistry and histochemistry. We found higher expression of GAP-43 immunoreactivity in dorsal horn, Lamina X, corticospinal tract and ventral horn motoneurons in wobbler mice compared to controls. Weak NADPH-diaphorase activity was present in control motoneurons, in contrast to intense labeling of the wobbler group. No differences in diaphorase activity was measured in the rest of the spinal cord between control and mutant mice. A group of animals received subcutaneously for 4 days a 50 mg pellet of U-74389F, a glucocorticoid-derived 21-aminosteroid with antioxidant properties but without glucocorticoid activity. U-74389F slightly attenuated GAP-43 immunostaining in dorsal regions of the spinal cord from wobblers but not in controls. However, in motoneurons of wobbler mice number of GAP-43 immunopositive neurons, cell processes and reaction intensity were reduced by U-74389F. The aminosteroid reduced by 50% motoneuron NADPH-diaphorase activity. Hyperexpression of GAP-43 immunoreactivity in wobbler mice may represent an exaggerated neuronal response to advancing degeneration or muscle denervation. It may also be linked to increased nitric oxide levels. U-74389F may stop neurodegeneration and/or increase muscle trophism and stop oxidative stress, consequently GAP-43 hyperexpression was attenuated. Wobbler mice may be important models to evaluate the use of antioxidant steroid therapy with a view to its use in human motoneuron disease.

Calcium influx inhibition by steroids and analogs in C2C12 skeletal muscle cells

Glucocorticoids, namely alpha-methylprednisolone (PDN) and deflazacort, are the only drugs reported to have a beneficial effect on the degenerative course of Duchenne muscular dystrophy (DMD). Increased cytosolic calcium concentrations ([Ca2+]c) have been implicated as one of the pathological events responsible for the degeneration of dystrophic skeletal muscles. In previous studies, we have demonstrated that PDN treatment of both normal and dystrophic murine skeletal muscle cells was able to normalize elevated [Ca2+]c and improved myogenesis. Here we have investigated the mechanism underlying the effects of glucocorticoids on cellular Ca2+ influx into C2C12 skeletal muscle cells. Long-term incubation of C2C12 myocytes with PDN was necessary to observe a reduction of 45Ca2+ influx. PDN was most effective in inhibiting 45Ca2+ uptake when added for 4 days (at the time of fusion of myoblasts into myotubes) and to a lesser extent, when added after fusion. It was ineffective when added to C2C12 cells at the myoblast stage. Short PDN incubation times, at the time of fusion were insufficient to elicit a response. Several steroids were tested for their ability to inhibit 45Ca2+ influx in C2C12 myocytes. All four glucocorticoids examined were able to reduce Ca2+ influx, dexamethasone being the most potent (IC50 3.14+/-0.34 x 10(-8) M). Mineralocorticoids (aldosterone and 11-deoxycorticosterone) were also able to reduce Ca2+ influx. The vitamin E-derived lazaroid U-83836E and the glucocorticoid-derived lazaroid U-74389G also elicited a decrease in Ca2+ influx, but higher concentrations were necessary. Because both glucocorticoids and lazaroids display antioxidant properties, but U-83836E is devoid of glucocorticoid activity, the reduction in Ca2+ influx was suspected to be triggered via an antioxidant mechanism. To test this hypothesis, we assessed the action of several antioxidants, such as vitamin E, vitamin C, 2-tert.-butyl-4-methoxyphenol (BHA), 2,6-di-tert.-butyl-4-methyl-phenol (BHT) and nordihydroguaiaretic acid (NDGA), on 45Ca2+ influx. None of these agents had an effect on 45Ca2+ influx. In addition, several oxidants were tested (either acutely or chronically) for their ability to elicit 45Ca2+ influx in C2C12 myocytes and were found to be inactive. The involvement of the glucocorticoid receptor on the modulation of Ca2+ influx was investigated. The glucocorticoid receptor antagonist mifepristone (code name RU38486, 10(-6) M) caused a shift of two orders of magnitude of the PDN response. However, neither actinomycin D nor cycloheximide affected the response to PDN. Results with the phospholipase A2 inhibitor, manoalide, suggest that glucocorticoid-induced protein synthesis (e.g. enhanced stimulation of lipocortin) does not play a role in the reduction of calcium influx. Our results suggest that steroids elicit a decrease in calcium influx in C2C12 skeletal muscle cells. This decrease is not due to an antioxidant mechanism or to a mechanism which requires gene expression. Since mineralocorticoids and U-83836E also had similar effects, the mechanism could belong to the non-genomic effects of corticoids (e.g. membrane stabilization). The beneficial effect of glucocorticoids in DMD could be attributed to a reduction of the pathological increase in Ca2+ influx via an effect on the sarcolemma.

Commentary: extraocular muscle sparing in muscular dystrophy: a critical evaluation of potential protective mechanisms

Muscles or muscle groups exhibiting responses to neuromuscular disease that are unlike those of other skeletal muscles may provide novel information about pathogenesis leading to improved treatment strategies. The author's laboratory studies the relationship between the unique phenotype of the extraocular muscles and their selective sparing or targeting in neuromuscular disease. This commentary evaluates the evidence for and against four hypotheses for the selective protection of extraocular muscle in Duchenne muscular dystrophy (DMD) and merosin-deficient congenital muscular dystrophy (CMD).

Deflazacort but not prednisone improves both muscle repair and fiber growth in diaphragm and limb muscle in vivo in the mdx dystrophic mouse

The effects of the glucocorticoids deflazacort and prednisone on mdx mouse dystrophy and muscle regeneration were evaluated in a 4.5-week double-blind study to test whether they would decrease dystrophy by anti-inflammatory effects [in intact diaphragm and left tibialis anterior (TA) muscle] and increase new muscle formation (after crush injury). In the left TA, fiber diameter was greater after deflazacort and prednisone compared to placebo. However, only deflazacort increased the centronucleation index of accumulated damage and repair, and myotube growth over the long term. In crush-injured TA, the fusion of proliferative muscle precursors to myotubes (by autoradiography) was increased only after deflazacort. Diaphragm muscle was much less inflamed, and fiber diameter was greater after deflazacort. Results suggest that glucocorticoids decreased the severe phenotype of dystrophy in the mdx diaphragm. Moreover, deflazacort uniquely promoted myogenic repair over short and longer terms, in addition to stimulating fiber growth. These first clues to the targets of deflazacort action on muscle repair have important positive implications for treating Duchenne dystrophy.

Regulation of cytosolic calcium in skeletal muscle cells of the mdx mouse under conditions of stress

1. In Duchenne muscular dystrophy (DMD) dysregulation of cytosolic calcium appears to be involved in the degeneration of skeletal muscle fibres. Therefore, we have studied the regulation of the free cytosolic calcium concentration ([Ca2+]c) under specific stress conditions in cultured myotubes isolated from the hind limbs of wild-type (C57BL10) and dystrophin-deficient mutant mdx mice. [Ca2+]c in the myotubes was estimated by the use of the Ca(2+)-sensitive fluorescent dye, fura-2. 2. Resting [Ca2+]c was similar in mdx and normal myotubes (35 +/- 9 nM and 38 +/- 11 nM, respectively). However, when mdx myotubes were exposed to a high extracellular calcium concentration ([Ca2+]c) of 40 mM, the [Ca2+]c was elevated to 84 +/- 29 nM, compared to 49 +/- 7 nM in normal myotubes. 3. Lowering the osmolarity of the superfusion solution from 300 mOsm to 100 mOsm resulted also in a rise in [Ca2+]c which was about two times higher for mdx (243 +/- 65 nM) than for C57BL10 (135 +/- 37 nM). Replacing extracellular Ca2+ by EGTA (0.2 mM) prevented the rise in [Ca2+]c in both mdx and normal myotubes when exposed to the low osmolarity solution. 4. Gadolinium ion (50 microM), an inhibitor of Ca2+ entry, antagonized the rise in [Ca2+]c of myotubes superfused with 40 mM [Ca2+]c by 20-40% for both mdx and C57BL10 cells, but did not significantly reduce the rise in [Ca2+]c when the cells were exposed to the hypo-osmotic buffer (100 mOsm). 5. Incubation of the cell culture for 3-5 days from the onset of induction of myotube formation with the membrane permeable protease inhibitor, calpeptin (50 microM) abolished the rise in [Ca2+]c in mdx myotubes upon exposure to hypo-osmotic shock. 6. Treatment of the cell culture for 3-5 days with alpha-methylprednisolone (PDN, 10 microM) attenuated the rise in [Ca2+]c following hypo-osmotic stress for both normal and mdx myotubes by about 50%. 7. The results described here suggest an increased permeability of mdx myotubes to Ca2+ under specific stress conditions. The ameliorating effect of PDN on [Ca2+]c could explain, at least partly, the beneficial effect of this drug on DMD patients.

Modulation by prednisolone of calcium handling in skeletal muscle cells

1. Increased calcium (Ca2+) influx has been incriminated as a potential pathological mechanism in the chronic skeletal muscle degeneration exhibited by Duchenne muscular dystrophy (DMD) patients. We have studied the influence of the glucocorticoid alpha-methylprednisolone (PDN), the only drug known to have a beneficial effect on the degenerative course of DMD, on Ca2+ handling in the C2 skeletal muscle cell line. 2. PDN, when added 3 days (when myoblasts start to fuse into myotubes) after cell seeding, led to a 2 to 4 fold decrease in cellular Ca2+ uptake. This decrease was independent of the extracellular Ca2+ concentration applied to cells. The effect took at least 24 h in order to become established (PDN of 10(-5) M) and took longer for lower PDN concentrations (EC50 of ca. 10(-6) M at day 5, 10(-6.5) M at day 7 and 10(-7.5) M at day 9 in culture). 3. Cellular calcium accumulation was also decreased in PDN-treated myotubes exposed to 45Ca(2+)-containing medium for 1 to 6 days. 4. No effect of PDN was seen on 45Ca2+ efflux; a decrease in the amount of 45Ca2+ released was observed due to the reduction of cellular 45Ca2+ loading. 5. PDN treatment led to an approximately 2 fold decrease in basal cytosolic Ca2+ concentration. 6. Three antioxidant drugs (lazaroids), previously shown to enhance in vitro skeletal muscle cell differentiation to the same extent as PDN, induced a similar decrease in Ca2+ influx. 7. Our results suggest that long-term incubation of C2 cells with PDN leads to a decrease of the size of the cellular Ca2+ pools and to reduced resting cytosolic Ca2+ levels. Part of the beneficial effect of PDN in DMD patients could be attributed to a reduction of Ca2+ influx and of the size of Ca2+ pools in dystrophic muscle fibres.

Antioxidant lazaroids enhance differentiation of C2 skeletal muscle cells

We have examined the incidence of new antioxidant compounds, so-called lazaroids, on the morphological and biochemical aspects of differentiation of C2 mouse skeletal muscle cells. We show that three lazaroids (U-74006F, U-74389F and U-83836E) enhance fusion of myogenic cells when added at the day of fusion. A parallel increase in nicotinic acetylcholine receptor expression and skeletal muscle alpha-actin content was observed. This promoting effect of lazaroids on myogenesis could be related to inhibition of free radical-mediated muscle damage. Therefore, one could expect that lazaroids might be useful in the treatment of degenerating muscle diseases such as Duchenne muscular dystrophy.