Is the Vitamin D Receptor Found in Muscle?

The function of vitamin D on muscle is either indirect or does not involve the known receptor. The active form of vitamin D, 1α,25-dihydroxyvitamin D3, is critical for the regulation of serum calcium and phosphorus levels that in turn support bone mineralization and neuromuscular activity. It is well known that vitamin D deficiency causes rachitic/osteomalacic myopathy and cardiac disorder and the provision of vitamin D can reverse the symptoms. However, the underlying mechanisms remain unclear. The question of whether the vitamin D receptor is found in muscle has been debated but not settled. We recently studied all available antibodies against the vitamin D receptor and found that most antibodies used detect proteins other than the vitamin D receptor, and therefore, the utility of these antibodies may generate the false-positive results. Using antibodies that do not detect proteins in tissues from vitamin D receptor null mice, we have developed a specific and sensitive immunohistochemical assay. The results from this investigation show that the vitamin D receptor is undetectable in skeletal, cardiac, and smooth muscle, suggesting that the function of vitamin D on muscle is either of an indirect nature or does not involve the known receptor.