Emerging incretin hormones actions: focus on bone metabolism

Incretin hormones, namely glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are gastro-intestinal hormones released from different enteroendocrine cells after nutrient intake. Incretins exert their actions though binding to and activation of specific GIP and GLP-1 receptors which are present in several target tissues. Incretin receptor activation in the pancreas leads to the incretin effect and other significant non-insulinotropic effects. Extra-pancreatic effects of incretin hormones in several other target tissues, such as their role in the pathophysiology of obesity and their potential relation with cardiovascular function, cognitive function, triglyceride storage in adipose tissue and bone metabolism, have attracted scientific interest. In the current review we intend to summarize existing knowledge on specific effects of GIP and GLP-1 in bone cells and bone metabolism. Starting from the identification of GIP receptor and GLP-1 receptor in animal and human bone cells, continuing with the skeletal effects of incretin deficiency or overexpression in animals, ending to the latest data on incretin and incretin agonists administration in cells, animals and humans, incretins play a significant yet complex role in the pathophysiology of bone metabolism affecting both formation and resorption. Although existing evidence seem strong and concrete, there is still a long way to go until their possible therapeutic or adjuvant use as bone modulating drugs can be considered.