Osteoporosis and Alzheimer's disease (AD) are the two common diseases mostly affecting persons aged over 60. Epidemiological findings revealed that osteoporosis and AD have a very high comorbidity. However, the mechanisms underlying their association are poorly understood. The Wnt signaling pathway plays a crucial role in the proper development and maintenance of brain and bone structure and function. Dickkopf-related protein 1 (Dkk1), a vital antagonist of the Wnt signaling, was reported to be closely associated with bone homeostasis and osteoporosis. Interestingly, high level of Dkk1 in the brain increases the risk of AD. It is suggested that Dkk1 may be a common potent risk factor involved in osteoporosis and AD. Therefore, we hypothesize that Dkk1 may play a role in both osteoporosis and AD. Our hypothesis will shed new light on the understanding of the relationship between these two diseases and help to explain some common characters of osteoporosis and AD.
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