In situ detection of 1,25-dihydroxyvitamin D-3 receptor in human skeletal muscle tissue

Growing evidence suggests that intracellular vitamin D receptors are presen t in skeletal muscle tissue mediating vitamin D hormone response. The aim o f the work reported here was to investigate the in situ expression of 1,25- dihydroxy vitamin D-3 receptor in human skeletal muscle tissue. Intraoperat ive periarticular muscle biopsies were taken from 20 female orthopaedic pat ients (17 middle-aged and elderly patients receiving total hip arthroplasty due to osteoarthritis of the hip or an osteoporotic hip fracture and 3 you ng patients who received back surgery). The immunohistological distribution of the vitamin D-3 receptor was investigated using a monoclonal rat antibo dy to the receptor (Clone Nr. 9A7). The receptor-positive nuclei were quant ified by counting 500 nuclei per biopsy. Strong intranuclear immunostaining of the vitamin D receptor was detected in human muscle cells. Biopsies of hip patients had significantly fewer receptor-positive nuclei compared to t hose of back surgery patients (Mann-Whitney U-test: p = 0.0025). VDR expres sion (number of antigen-positive nuclei) was significantly correlated with age (coefficient of correlation = 0.46; p = 0.005), but not with 25-hydroxy vitamin D or 1,25-dihydroxyvitamin D levels. The data clearly demonstrate p resence of nuclear 1,25-dihydroxyvitamin D-3 receptor in human skeletal mus cle. To our knowledge this is the first in situ detection of the receptor i n human skeletal muscle. The difference in the expression of the receptor b etween hip and spinal muscle biopsies might be explained by age or location . Further research is needed in order to evaluate whether vitamin D-3 recep tor expression in human skeletal muscle is age-dependent and varies between different muscles.