The Potential Influence of Bone-Derived Modulators on the Progression of Alzheimer’s Disease

Osteoporosis is a common disease characterised by a systemic impairment of bone mass and microarchitecture that results in fragility fractures. With an ageing population, the medical and socioeconomic effect of osteoporosis, particularly postmenopausal osteoporosis, will increase further. A detailed knowledge of bone biology with molecular insights into the communication between bone-forming osteoblasts and bone-resorbing osteoclasts and the orchestrating signalling network has led to the identification of novel therapeutic targets. Novel treatment strategies have been developed that aim to inhibit excessive bone resorption and increase bone formation. The most promising novel treatments include: denosumab, a monoclonal antibody for receptor activator of NF-κB ligand, a key osteoclast cytokine; odanacatib, a specific inhibitor of the osteoclast protease cathepsin K; and antibodies against the proteins sclerostin and dickkopf-1, two endogenous inhibitors of bone formation. This overview discusses these novel therapies and explains their underlying physiology. Copyright © 2011 Elsevier Ltd. All rights reserved.

Low bone mass and strength lead to fragility fractures, for example, in elderly individuals affected by osteoporosis or children with osteogenesis imperfecta. A decade ago, rare human mutations affecting bone negatively (osteoporosis-pseudoglioma syndrome) or positively (high-bone mass phenotype, sclerosteosis and Van Buchem disease) have been identified and found to all reside in components of the canonical WNT signaling machinery. Mouse genetics confirmed the importance of canonical Wnt signaling in the regulation of bone homeostasis, with activation of the pathway leading to increased, and inhibition leading to decreased, bone mass and strength. The importance of WNT signaling for bone has also been highlighted since then in the general population in numerous genome-wide association studies. The pathway is now the target for therapeutic intervention to restore bone strength in millions of patients at risk for fracture. This paper reviews our current understanding of the mechanisms by which WNT signalng regulates bone homeostasis.