Glucocorticoids increase myoblast proliferation rates by inhibiting death of cycling cells

Glucocorticoid effects on the skeletal muscle differentiation program: analysis of clonal proliferation, morphological differentiation and the expression of muscle-specific and regulatory genes

We examined the effect of glucocorticoids on the proliferation and differentiation of skeletal muscle cells using the C2C12 cell line. We found that treatment with glucocorticoids enhanced muscle cell differentiation but had only minor effects on the clonal growth rate of C2C12 cells. The stimulatory effect of glucocorticoids on myogenic differentiation was reflected in the increased expression of muscle-specific genes, creatine kinase (CK) and acetylcholine receptor gamma subunit (AChR). Dexamethasone had no effect on CK and AChR mRNA stability and enhanced transcription from a CAT reporter genes containing the 3.3kb 5' flanking region of the murine CK gene (-3300MCK-CAT). Since dexamethasone did not affect the expression levels of the myogenic regulatory genes such as myoD and myogenin, the enhancement of muscle-specific transcription might reflect an increase in the functional activity of the regulatory proteins. Other possible mechanisms involved in the differentiation-enhancing effect of glucocorticoids are discussed.

Neuropathy of metachromatic leukodystrophy: improvement with immunomodulation

A 4-year-old child with metachromatic leukodystrophy was initially diagnosed with chronic immune demyelinating polyneuropathy and treated with immunosuppressive therapy. Physical examination revealed diffuse, distal > proximal weakness and areflexia. Electro-diagnostic studies revealed nerve conduction velocities that were slowed to variable degrees in different nerves. In the 18 months after institution of immunomodulating therapy, she had functionally significant improvement and a quantitative increase in her strength. Treatment was discontinued at age 6 years when the patient developed urinary incontinence, followed by loss of motor and cognitive skills. We conclude that immunomodulation early in the course of metachromatic leukodystrophy presenting as a neuropathy may result in temporary functional improvement. Whether the immunomodulation altered the disease progression or had direct effects on the function of the dysmyelinated axons is not known.

Clinical and neurophysiologic response of myopathy and neuropathy in long-chain L-3-hydroxyacyl-CoA dehydrogenase deficiency to oral prednisone

The purpose of this study was to evaluate the clinical and neurophysiologic responses to oral prednisone therapy in a boy with enzymatically confirmed long-chain L-3-hydroxyacyl-CoA dehydrogenase deficiency in biopsied muscle and cultured skin fibroblasts. This boy presented with progressive limb girdle myopathy, recurrent myoglobinuria, peripheral sensorimotor axonopathy, and intraventricular conduction delays. Prior to prednisone therapy, at age 8 years, he exhibited marked distal weakness greater than proximal weakness with a waddling and high-steppage gait, Gowers' maneuver (10 s to rise from the floor), fatigue after 3-20 yards of walking and the ability to climb only 2 stairs. Serum levels of creatine kinase rose from 34 to 4,124 U/L following mild exertion. Nerve conduction studies revealed progressive axonopathy with secondary demyelination. Four weeks after initiation of oral prednisone (0.75 mg/kg/day) therapy, there was approximately a 100% increase in power and endurance. He was able to walk at least 100 yards before tiring, could rise from sitting on the floor in 3-4 s, and was able to climb 20 steps in 30 s. There was concurrent improvement in nerve conduction studies. Prednisone was gradually withdrawn over the next 4 months to 0.19 mg/kg/day; lower doses of 0.08 mg/kg/day resulted in a marked deterioration in power to the prior state. Although 0.19 mg/kg/day did not maintain the peak power achieved at 0.75 mg/kg/day, it provided adequate baseline power and endurance. It is concluded that there was a significant clinical and neurophysiologic response to prednisone at a dosage > or = 0.16 mg/kg/day. Prednisone may stabilize muscle and neuronal plasma membranes, as well as the fatty acid oxidation enzyme complex in the mitochondrial membrane.

alpha-Methylprednisolone promotes skeletal myogenesis in dystrophin-deficient and control mouse cultures

We have examined the influence of the glucocorticoid alpha-methylprednisolone (PDN) on the morphological differentiation of skeletal muscle cells derived from dystrophin-deficient C57BL/10 mdx, congenic C57BL/10 and allogenic Balb/c newborn mice. We show that PDN enhances myogenic cell numbers in dystrophin-deficient cultures as well as in matched controls. A parallel increase in the fusion rate of myoblasts into myotubes occurs while the size of myotubes, as determined by nuclei per myotube, is slightly increased. This promoting effect of PDN on myogenesis could be related to the enhanced muscular function observed in PDN-treated Duchenne's muscular dystrophy-affected boys.