Pathophysiology of bone remodelling cycle: Role of immune system and lipids

Osteoporosis is the most common skeletal disease worldwide, characterized by low bone mineral density, resulting in weaker bones, and an increased risk of fragility fractures. The maintenance of bone mass relies on the precise balance between bone synthesis and resorption. The close relationship between the immune and skeletal systems, called "osteoimmunology", was coined to identify these overlapping "scientific worlds", and its function resides in the evaluation of the mutual effects of the skeletal and immune systems at the molecular and cellular levels, in both physiological and pathological states. Lipids play an essential role in skeletal metabolism and bone health. Indeed, bone marrow and its skeletal components demand a dramatic amount of daily energy to control hematopoietic turnover, acquire and maintain bone mass, and actively being involved in whole-body metabolism. Statins, the main therapeutic agents in lowering plasma cholesterol levels, are able to promote osteoblastogenesis and inhibit osteoclastogenesis. This review is meant to provide an updated overview of the pathophysiology of bone remodelling cycle, focusing on the interplay between bone, immune system and lipids. Novel therapeutic strategies for the management of osteoporosis are also discussed.