Reciprocal regulation of bone and energy metabolism.

BACKGROUND: The primary relationship affecting skeletal tissue involves the association between fat mass and bone mass. However, there is some complexity in this relationship that may be explained by endocrine and neural pathways representing direct, reciprocal signalling between fat and bone tissue. For example, leptin signalling can directly stimulate osteoblastic differentiation and osteoblast proliferation and mineralization, but it also has central signalling actions in that it decreases cancellous bone volume. A novel regulatory loop between bone and adipose tissue suggests that uncarboxylated osteocalcin may affect energy homeostasis and afford a pathway by which fat mass can be regulated by bone mass.
CONCLUSIONS: The multilayered and complex signals between fat and bone tissue involve both direct and indirect pathways. The endocrinologic nature of these signals highlights an emerging trend in medicine: identification of organ-based endocrine signals.