Abstract
Paget's disease of bone (PDB) is characterized by focal areas of aberrant and excessive bone turnover, specifically increased bone resorption and disorganized bone formation. Germline mutations in the sequestosome 1/p62 (SQSTM1/p62) gene are common in PDB patients, with most mutations affecting the ubiquitin-associated domain of the protein. In vitro, osteoclast precursor cells expressing PDB-mutant SQSTM1/p62 protein are associated with increases in nuclear factor kappa B activation, osteoclast differentiation, and bone resorption. Although the precise mechanisms by which SQSTM1/p62 mutations contribute to disease pathogenesis and progression are not well defined, it is apparent that as well as affecting nuclear factor kappa B signaling, SQSTM1/p62 is a master regulator of ubiquitinated protein turnover via autophagy and the ubiquitin-proteasome system. Additional roles for SQSTM1/p62 in the oxidative stress-induced Keap1/Nrf2 pathway and in caspase-mediated apoptosis that were recently reported are potentially relevant to the pathogenesis of PDB. Thus, SQSTM1/p62 may serve as a molecular link or switch between autophagy, apoptosis, and cell survival signaling. The purpose of this review is to outline recent advances in understanding of the multiple pathophysiological roles of SQSTM1/p62 protein, with particular emphasis on their relationship to PDB, including challenges associated with translating SQSTM1/p62 research into clinical diagnosis and treatment.
