Glucocorticoid receptor concentrations in muscle biopsies from patients with neuromuscular diseases

Distribution of glucocorticoid receptor alpha and beta subtypes in the idiopathic inflammatory myopathies

In contrast with dermatomyositis and polymyositis, inclusion body myositis is unresponsive to glucocorticoid treatment. Glucocorticoid action is mediated through an active glucocorticoid receptor-alpha and negatively regulated by another glucocorticoid receptor isoform. In several autoimmune diseases glucocorticoid receptor-beta up-regulation is involved in glucocorticoid resistance. We studied glucocorticoid receptor distribution in normal and inflammatory myopathy muscle and investigated whether differences in glucocorticoid receptor-alpha and glucocorticoid receptor-beta protein expression are involved in the differential glucocorticoid sensitivity in inclusion body myositis versus polymyositis. Multistep immunofluorescence and Western blotting on fractionated cytoplasmic or nuclear muscle samples were used. Glucocorticoid receptor-alpha was the predominant receptor subtype in muscle and occurred abundantly in myonuclei of control and diseased muscle alike. Glucocorticoid receptor-beta was constitutively expressed on a subset of endothelial cells. No differences between dermatomyositis and the other idiopathic inflammatory myopathies were observed. Increased nuclear glucocorticoid receptor that has dissociated from heat shock protein 90 was found in glucocorticoid treated subjects. Glucocorticoid receptor-alpha and -beta isoform levels were unaltered in muscle tissues from control subjects that had received glucocorticoid treatment prior to biopsy. No differences in relative glucocorticoid receptor-alpha and glucocorticoid receptor-beta protein expression were seen in inclusion body myositis versus polymyositis specimens. Our study indicates that the different glucocorticoid sensitivity in the idiopathic inflammatory myopathies is not related to up- or down-regulation of a given glucocorticoid receptor isoform at the protein level.

Expression of glucocorticoid receptor alpha- and beta-isoforms in human cells and tissues

Alternative splicing of the human glucocorticoid receptor (GR) primary transcript generates two protein isoforms: GR-alpha and GR-beta. We investigated the expression of both GR isoforms in healthy human cells and tissues. GR-alpha mRNA abundance (x10(6) cDNA copies/microg total RNA) was as follows: brain (3.83 +/- 0.80) > skeletal muscle > macrophages > lung > kidney > liver > heart > eosinophils > peripheral blood mononuclear cells (PBMCs) > nasal mucosa > neutrophils > colon (0.33 +/- 0.04). GR-beta mRNA was much less expressed than GR-alpha mRNA. Its abundance (x10(3) cDNA copies/microg total RNA) was as follows: eosinophils (1.55 +/- 0.58) > PBMCs > liver > or = skeletal muscle > kidney > macrophages > lung > neutrophils > brain > or = nasal mucosa > heart (0.15 +/- 0.08). GR-beta mRNA was not found in colon. While GR-alpha protein was detected in all cells and tissues, GR-beta was not detected in any specimen. Our results suggest that, in physiological conditions, the default splicing pathway is the one leading to GR-alpha. The alternative splicing event leading to GR-beta is minimally activated.

Influence of age on metabolism of testosterone, dihydrotestosterone, and 3-α-androstanediol in muscle biopsies from patients with neuromuscular diseases

We investigated the possible effect of age on the metabolism of androgens in muscle biopsies from patients with neuromuscular diseases. The conversion of testosterone, dihydrotestosterone (DHT) and 5-alpha-androstane-3-alpha-17-beta-diol (3-alpha-androstanediol) was measured in muscle biopsies from 24 patients with neuromuscular diseases and seven controls. The reductive metabolism of 3-alpha-HSDH was significantly higher than the oxidative metabolism. Significant metabolism of testosterone to DHT was not found. Only the age of the patients emerged as a significant negative predictor in a stepwise multiple linear regression model for V(max) and K(m) (Lineweaver-Burke plots) of the reductive metabolism of 3-alpha-HSDH. Therefore, altered metabolism of anabolic androgens in skeletal muscles could be demonstrated. We conclude that this could alter the androgenic catabolic/anabolic balance in the (androgenic target organ) skeletal muscle.