Invited by the Teachers' Assembly, at the suggestion of Professors Hugues de Thé, Philippe Sansonetti and Alain Prochiantz.
Gerard Karsenty, M.D., Ph.D.
Professor and Chairman
Department of Genetics & Development
Columbia University
Invited by the Teachers' Assembly, at the suggestion of Professors Hugues de Thé, Philippe Sansonetti and Alain Prochiantz.
Gerard Karsenty, M.D., Ph.D.
Professor and Chairman
Department of Genetics & Development
Columbia University
A major yet unforeseen consequence of the introduction of genetic approaches in the study of model organism has been to rejuvenate a biological discipline that had been progressively abandoned; whole-organism physiology.
When it comes to bony vertebrates, it can be said that the most unexpected findings of mouse genetics are in the realm of physiology. Along these lines the four conferences that I will present on how an interpretation of bone biology taking into account evolutionary aspects, unique cell biological features and clinical observations led to a working hypothesis linking bone physiology, energy metabolism and reproduction. Every aspects of this hypothesis has been verified experimentally in the mouse and whenever possible in humans. The most provocative inference of this working hypothesis is that bone itself should be an endocrine organ regulating aspects of energy metabolism and reproduction. As will be presented during these conferences, this is indeed the case. Bone cells produce a hormone called osteocalcin that favors glucose homeostasis at rest and during exercise. Osteocalcin also promotes male fertility in mice and in humans.
Osteocalcin has cardinal features of a hormone. It is synthesized in one single cell type, the osteoblast, acts at a distance in pancreatic β cells and Leydig cells of the testes, in these cells it needs to bind to a specific receptor we have identified to trigger a series of signaling events that culminate in the synthesis and secretion of insulin and testosterone respectively. Going beyond the defined boundaries of the initial working hypothesis we subsequently showed that osteocalcin convey the remarkable, even if unexpected, influence of the bone skeleton on brain development and function. As a matter of fact, osteocalcin is not only necessary but sufficient to promote cognitive functions in the mouse and to restore them to levels seen in young mice in older mice. This aspect of osteocalcin biology is mediated by a record receptor we have identified and studied the function.
The demonstration that osteocalcin is such a powerful regulator of brain development and functions represented a breach in the logic of the initial working hypothesis. This forced us to reassess not only the entire biology of osteocalcin but also what were the initial purposes of the classical functions of bone. The last conference of this cycle will present unpublished results that, because of their nature, provides a single conceptual framework that captures classical and endocrine functions of bone. We will end this cycle of conferences by highlighting some salient features of osteocalcin that distinguishes it from other hormones and that suggest that harnessing these pathways may potentially have great therapeutic impact on several age-related diseases ranging from sarcopenia to age-related memory loss.