Marie Demay, M.D.

Physician Investigator (Cl)
Endocrine Division, Mass General Research Institute
Professor of Medicine
Harvard Medical School
Medicine-Endocrinology, Massachusetts General Hospital
MD University of Saskatchewan 1980
bone development; chondrocytes; chondrogenesis; endochondral bone formation; growth plate; keratinocytes; osteoblasts; osteocalcin; osteomalacia; phosphates; receptors calcitriol; rickets; vitamin d; vitamin d therapy; x-linked hypophosphatemia Studies into the effects of the vitamin D signaling pathway in the skeleton have demonstrated that its effects are largely indirect. It is through its actions on maintaining normal calcium and phosphate levels that it prevents the development of rickets and osteomalacia.

Low phosphate causes rickets by preventing normal maturation of the growth plate. Interestingly, the active form of vitamin D is able to compensate for the effects of low phosphate, promoting normal growth-plate development and maturation. 

Investigations in other hypophosphatemic models of rickets, including X-linked hypophosphatemia, are directed at comparing the effectiveness of vitamin D therapy versus other treatments at normalizing growth and preventing rickets in this disorder.

Intriguingly, the effects of the vitamin D signaling pathway that maintain normal regeneration of hair do not require vitamin D but do require the vitamin D receptor (VDR). Studies are underway to identify actions of this receptor that are required to prevent hair loss and maintain skin homeostasis.

The laboratory uses genetically manipulated mice, as well as cells and tissues isolated from these mice, to study the role of the VDR and the biological consequences of hypophosphatemia. 

These studies led to the identification of the VDR as a key factor in maintenance of keratinocyte stem cell homeostasis and revealed that the mechanism by which VDR inactivation leads to rickets is due to the development of hypophosphatemia.

These latter studies have led to an additional line of investigation examining the role of phosphate in endochondral bone formation. These studies are being performed in the animal model of X-linked hypophosphatemia.