Signaling pathways associated with bone loss in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract characterized in many patients by extraintestinal manifestations. One of the most common comorbidities seen in IBD patients is a significant reduction in their bone mass. The pathogenesis of IBD is mainly attributed to the disrupted immune responses in the gastrointestinal mucosa and putative disruptions in the gut microbiomes. The excessive inflammation of the gastrointestinal tract activates different systems, such as the RANKL/RANK/OPG and the Wnt pathways linked with bone alterations in IBD patients, thereby suggesting a multifactorial etiology. The mechanism responsible for the reduced bone mineral density in IBD patients is thought to be multifactorial, and, so far, the principal pathophysiological pathway has not been well established. However, in recent years, many investigations have increased our understanding of the effect of gut inflammation on the systemic immune response and bone metabolism. Here, we review the main signaling pathways associated with altered bone metabolism in IBD.