Paget's disease of bone (PDB) is an age-related metabolic bone disorder, characterised by focally increased and disorganised bone remodelling initiated by abnormal and hyperactive osteoclasts. The germline P392L mutation of SQSTM1 (encoding p62) is a strong genetic risk factor for PDB in humans, and the equivalent mutation in mice (P394L) causes a PDB-like disorder. However, it is unclear why pagetic lesions become more common with age. Here, we assessed the effect of the p62 P394L mutation on osteoclastogenesis and bone morphometry in relation to ageing, the natural history of lesion progression in p62^P394L mice and the effect of zoledronic acid (ZA) on lesion development. p62^P394L+/+ osteoclast precursors had increased sensitivity to RANKL (also known as TNFSF11) compared with wild-type (WT) cells, and the sensitivity further increased in both genotypes with ageing. Osteoclastogenesis from 12-month-old p62^P394L+/+ mice was twofold greater than that from 3-month-old p62^P394L+/+ mice (P<0.001) and three-fold greater than that from age-matched WT littermates. The p62^P394L+/+ mice lost 33% more trabecular bone volume in the long bones by 12 months compared with WT mice (P<0.01), and developed pagetic-like lesions in the long bones which progressed with ageing. ZA prevented the development of pagetic-like lesions, and increased trabecular bone volume tenfold compared with vehicle by 12 months of age (P<0.01). This demonstrates that ageing has a pro-osteoclastogenic effect, which is further enhanced by the p62 P394L mutation, providing an explanation for the increased penetrance of bone lesions with age in this model. Lesions are prevented by ZA, providing a rationale for early intervention in humans.

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