Interindividual glucocorticoid sensitivity in young healthy subjects: the role of glucocorticoid receptor alpha and beta isoforms ratio.

Only few studies have addressed the interindividual variation and tissue specificity of glucocorticoid (GC) sensitivity in healthy individuals, a phenomenon observed in pathological conditions. Alternative splicing of the glucocorticoid receptor (GR) produces alpha and beta isoforms. GRbeta has dominant-negative effects on hormone-induced GRalpha effects, and an increased expression of the GRbeta has been associated with glucocorticoid resistance. We determined, using a simple, rapid, and accurate Real-Time PCR assay, the individual mRNAs expression of GRalpha and GRbeta in 26 normal subjects (mean+/-SE, age 30+/-6 years; 12 males and 14 females), in order to evaluate the role of these isoforms in glucocorticoid sensitivity in health. Glyceraldehydes-3-phosphate dehydrogenase (GAPDH) was used as a housekeeper gene. GRalpha/GAPDH, GRbeta/GAPDH and GRalpha/GRbeta ratios showed a normal distribution. We observed a higher expression of GRalpha compared to GRbeta and an interindividual variability in the GRalpha, GRbeta, and GAPDH gene expressions in the young healthy population. In addition, no correlation was observed between GRalpha/GRbeta ratio and the dexamethasone (DEX) doses needed to suppress plasma cortisol, GRalpha/GRbeta ratio and the concentration of DEX that caused inhibition of Con-A stimulated cell proliferation, and GRalpha/GRbeta ratio and the affinity of GR (Kd) of each subject. Therefore, the variability of GC sensitivity observed in normal subjects can not be ascribed to the variation in the GRalpha and GRbeta expression.     

Expression of glucocorticoid receptors in the regenerating human skeletal muscle

Many stress conditions are accompanied by skeletal muscle dysfunction and regeneration, which is essentially a recapitulation of the embryonic development. However, regeneration usually occurs under conditions of hypothalamus-pituitary-adrenal gland axis activation and therefore increased glucocorticoid (GC) levels. Glucocorticoid receptor (GR), the main determinant of cellular responsiveness to GCs, exists in two isoforms (GRalpha and GRbeta) in humans. While the role of GRalpha is well characterized, GRbeta remains an elusive player in GC signalling. To elucidate basic characteristics of GC signalling in the regenerating human skeletal muscle we assessed GRalpha and GRbeta expression pattern in cultured human myoblasts and myotubes and their response to 24-hour dexamethasone (DEX) treatment. There was no difference in GRalpha mRNA and protein expression or DEX-mediated GRalpha down-regulation in myoblasts and myotubes. GRbeta mRNA level was very low in myoblasts and remained unaffected by differentiation and/or DEX. GRbeta protein could not be detected. These results indicate that response to GCs is established very early during human skeletal muscle regeneration and that it remains practically unchanged before innervation is established. Very low GRbeta mRNA expression and inability to detect GRbeta protein suggests that GRbeta is not a major player in the early stages of human skeletal muscle regeneration.