Cytoskeleton organization and lysosome secretion are critical for osteoclast activation and function. However, the molecular mechanisms regulating these processes are poorly understood. The goal of this grant application is to elucidate the mechanisms by which the cytoskeletal and lysosomal proteins regulate osteoclasts. PLEKHM1, a newly identified protein mutated in human and rat osteopetrosis, is critically involved in osteoclast lysosome trafficking and secretion. Furthermore, Plekhm1 was found to bind to LIS1, a key regulator of microtubule dynamic in eukaryotic cells. LIS1 interacts with dynein/dynactin, a motor complex that regulates microtubule dynamic and transportation. LIS1 also binds to the catalytic 1-subunit of PAF-AH (platelet-activating factor (PAF) acetylhydrolase) 1b complex, which inactivates PAF, a lipid messenger functional important for osteoclast survival and activities. LIS1 has also been shown to regulate cdc42, a small GTPase that is required for bone homeostasis in mice by modulating M-CSF and RANKL signaling. More importantly, LIS1-flox;LysM-Cre mice, in which LIS1 is specifically deleted in myeloid cells, have increased bone mass and impaired osteoclast formation and bone resorption. These data led to the hypothesis that Plekhm1 is essential for skeleton homeostasis and Plekhm1/LIS1 interaction is critical for lysosome secretion and bone resorption. LIS1 regulates osteoclast formation and function through its modulation of dynein function and M-CSF/RANKL signaling pathways via PAF and/or cdc42. To test these hypotheses, genetically modified mice and osteoclasts derived from these mice will be used to: a) determine the role of Plekhm1 in osteoclast function and identify the mechanisms mediating Plekhm1/LIS1 interaction (Aim 1). b) determine whether LIS1 regulates osteoclast function and dissect the mechanisms by which LIS1 regulates microtubule organization and Cathepsin K secretion in osteoclasts (Aim 2). c) determine whether LIS1 regulates osteoclastogenesis and define the molecular mechanisms by which LIS1 modulates M-CSF and RANKL signaling pathways (Aim 3).

Public Health Relevance

Enhanced osteoclast activity causes bone loss, leading to major public health problems. We have identified novel proteins in osteoclasts which contribute to their activity. We plan to determine how these proteins regulate the osteoclast, raising the possibility that we will be able to provide new therapeutic targets for the treatment of metabolic bone diseases.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Research Project (R01)
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Skeletal Biology Development and Disease Study Section (SBDD)
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Chen, Faye H
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University of Arkansas for Medical Sciences
Internal Medicine/Medicine
Schools of Medicine
Little Rock
United States
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Wang, Lei; Fang, Bin; Fujiwara, Toshifumi et al. (2018) Deletion of ferroportin in murine myeloid cells increases iron accumulation and stimulates osteoclastogenesis in vitro and in vivo. J Biol Chem 293:9248-9264
Fujiwara, Toshifumi; Ye, Shiqiao; Castro-Gomes, Thiago et al. (2016) PLEKHM1/DEF8/RAB7 complex regulates lysosome positioning and bone homeostasis. JCI Insight 1:e86330
Fujiwara, T; Zhou, J; Ye, S et al. (2016) RNA-binding protein Musashi2 induced by RANKL is critical for osteoclast survival. Cell Death Dis 7:e2300
Ye, Shiqiao; Fujiwara, Toshifumi; Zhou, Jian et al. (2016) LIS1 Regulates Osteoclastogenesis through Modulation of M-SCF and RANKL Signaling Pathways and CDC42. Int J Biol Sci 12:1488-1499
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