PLEKHM1/DEF8/RAB7 complex regulates lysosome positioning and bone homeostasis
Toshifumi Fujiwara, … , Stavros C. Manolagas, Haibo Zhao
Toshifumi Fujiwara, … , Stavros C. Manolagas, Haibo Zhao
Published October 20, 2016
Citation Information: JCI Insight. 2016;1(17):e86330. https://doi.org/10.1172/jci.insight.86330.
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Research Article Bone biology

PLEKHM1/DEF8/RAB7 complex regulates lysosome positioning and bone homeostasis

Abstract

Mutations of the Plekhm1 gene in humans and rats cause osteopetrosis, an inherited bone disease characterized by diminished bone resorption by osteoclasts. PLEKHM1 binds to RAB7 and is critical for lysosome trafficking. However, the molecular mechanisms by which PLEKHM1 regulates lysosomal pathways remain unknown. Here, we generated germline and conditional Plekhm1-deficient mice. These mice displayed no overt abnormalities in major organs, except for an increase in trabecular bone mass. Furthermore, loss of PLEKHM1 abrogated the peripheral distribution of lysosomes and bone resorption in osteoclasts. Mechanistically, we indicated that DEF8 interacts with PLEKHM1 and promotes its binding to RAB7, whereas the binding of FAM98A and NDEL1 with PLEKHM1 connects lysosomes to microtubules. Importantly, suppression of these proteins results in lysosome positioning and bone resorption defects similar to those of Plekhm1-null osteoclasts. Thus, PLHKEM1, DEF8, FAM98A, and NDEL1 constitute a molecular complex that regulates lysosome positioning and secretion through RAB7.

Authors

Toshifumi Fujiwara, Shiqiao Ye, Thiago Castro-Gomes, Caylin G. Winchell, Norma W. Andrews, Daniel E. Voth, Kottayil I. Varughese, Samuel G. Mackintosh, Yunfeng Feng, Nathan Pavlos, Takashi Nakamura, Stavros C. Manolagas, Haibo Zhao

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Figure 10

Decreased expression of FAM98A and NDEL1 inhibits the peripheral distribution of lysosomes and their targeting to the ruffled border in osteoclasts.

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Decreased expression of FAM98A and NDEL1 inhibits the peripheral distrib...
Immunofluorescent staining of LAMP-2 (A) and cathepsin K (CTSK) (B) in control (Luc-sh), Fam98a- (Fam98a-sh1 and Fam98a-sh2), and Ndel1- (Ndel1-sh1 and Ndel1-sh2) knocked down osteoclasts cultured on glass coverslips and cortical bovine bone slices. White arrows in the top rows point out the peripheral distribution of LAMP-2 and CTSK in control cells cultured on glass coverslips. White arrowheads in the bottom rows point out the ruffled border localization of LAMP-2 and the secretion of CTSK into the resorption lacuna in control cells cultured on bone slices. Each image is a representative of 6 bone slices/group/culture from at least 3 independent cultures from different mice. Scale bar: 20 μm.