NDR2 is critical for osteoclastogenesis by regulating ULK1-mediated mitophagy
Xiangxi Kong, Zhi Shan, Yihao Zhao, Siyue Tao, Jingyun Chen, Zhongyin Ji, Jiayan Jin, Junhui Liu, Wenlong Lin, Xiao-jian Wang, Jian Wang, Fengdong Zhao, Bao Huang, Jian Chen
Xiangxi Kong, Zhi Shan, Yihao Zhao, Siyue Tao, Jingyun Chen, Zhongyin Ji, Jiayan Jin, Junhui Liu, Wenlong Lin, Xiao-jian Wang, Jian Wang, Fengdong Zhao, Bao Huang, Jian Chen
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Research Article Development Metabolism

NDR2 is critical for osteoclastogenesis by regulating ULK1-mediated mitophagy

Abstract

Bone homeostasis primarily stems from the balance between osteoblasts and osteoclasts, wherein an augmented number or heightened activity of osteoclasts is a prevalent etiological factor in the development of bone loss. Nuclear Dbf2-related kinase (NDR2), also known as STK38L, is a member of the Hippo family with serine/threonine kinase activity. We unveiled an upregulation of NDR2 expression during osteoclast differentiation. Manipulation of NDR2 levels through knockdown or overexpression facilitated or hindered osteoclast differentiation, respectively, indicating a negative feedback role for NDR2 in the osteoclastogenesis. Myeloid NDR2-dificient mice (Lysm+NDR2fl/fl) showed lower bone mass and further exacerbated ovariectomy-induced or aging-related bone loss. Mechanically, NDR2 enhanced autophagy and mitophagy through mediating ULK1 instability. In addition, ULK1 inhibitor (ULK1-IN2) ameliorated NDR2 conditional KO–induced bone loss. Finally, we clarified a significant inverse association between NDR2 expression and the occurrence of osteoporosis in patients. The NDR2/ULK1/mitophagy axis is a potential innovative therapeutic target for the prevention and management of bone loss.

Authors

Xiangxi Kong, Zhi Shan, Yihao Zhao, Siyue Tao, Jingyun Chen, Zhongyin Ji, Jiayan Jin, Junhui Liu, Wenlong Lin, Xiao-jian Wang, Jian Wang, Fengdong Zhao, Bao Huang, Jian Chen

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Figure 2

Lysm+NDR2fl/fl mice exhibited decreased bone mass and enhanced osteoclastogenesis.

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Lysm+NDR2fl/fl mice exhibited decreased bone mass and enhanced osteocla...
(A) Femurs from 2-month-old Lysm–NDR2fl/fl and Lysm+NDR2fl/fl littermates were imaged using μCT techniques. (B) Parameters related to trabecular bone in the proximal femur (n = 6) were analyzed, including bone volume to tissue volume (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), and trabecular separation (Tb.Sp). (C) Representative 2D images of cortical bone were captured. (D) Statistical analysis was performed on cortical bone thickness (Ct.Th). (E) H&E staining and TRAP staining were conducted on sections of the femur. (F and G) Histomorphological analysis was carried out on TRAP staining, specifically osteoclast number per unit of bone surface area (N.Oc/BS) and osteoclast surface area per unit of bone surface area (Oc.S/BS; n = 6 per group). (H) Bone marrow–derived macrophages (BMMs) extracted from Lysm–NDR2fl/fl and Lysm+NDR2fl/fl littermates were induced for osteoclast differentiation at different concentrations of RANKL. After 5 days, TRAP staining was performed. (I) Western blotting was used to detect differences in expression levels of osteoclast-related proteins between the 2 groups after RANKL stimulation. (J) The activity of osteoclasts was assessed using hydroxyapatite-coated plates. (K) Statistical analysis was conducted to assess the extent of bone erosion area (n = 3). Statistical analyses were determined by 2-tailed Student’s t test (B, D, F, G, and K). **P < 0.01, ***P < 0.001, and ****P < 0.0001. Data were presented as mean ± SD.