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.
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
(A and C) μ-CT images and analyses of the trabecular bone compartment of the distal femurs of 2-month-old male wild-type and germline deletion (KO) mice (n = 17). (B and D) μ-CT images and analyses of the trabecular bone compartment of the distal femurs of 2-month-old male control (con) and Plekhm1 conditional deletion (cKO) mice (con, n = 15; cKO, n = 12). (E and F) μ-CT analyses of the trabecular bone compartment of the distal femurs of 5-month-old male mice (WT, n = 11; KO, n = 10; con, n = 10; cKO, n = 11). BV/TV, percentage of trabecular bone volume to tissue volume; Tb. N, trabecular number; Tb. Th, trabecular thickness; Tb.Sp, trabecular separation. Data in C–F are presented as scatter dot plots. The mean and SD of each group are overlaid to each column of dots. **P < 0.01 versus WT or con by Student’s t test.