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 6

NDR2 KO promoted mitophagy via ULK1.

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NDR2 KO promoted mitophagy via ULK1. (A) Representative image of the tra...
(A) Representative image of the transmission electron microscope (TEM), with purple arrows indicating mitochondria and yellow arrows indicating autophagosomes. (B) Western blot was used to detect the classical regulatory signaling pathway of mitophagy. Tom, mitochondrial outer membrane protein. (C) Immunofluorescence staining images of Lysm+NDR2fl/fl BMMs were obtained to visualize the expression of PINK and PARKIN. The staining was performed using antibodies against PINK/PARKIN (green) and DAPI for nuclear counterstaining (blue). (D and E) Quantitative analysis was conducted to determine the fluorescence intensities of PINK and PARKIN (n = 6). (F and G) BMMs derived from Lysm+NDR2fl/fl mice were transfected with ULK1 siRNA (F) or treated with ULK1 inhibitor (G), and the classical mitophagy signaling pathway was analyzed by Western blot. (H) PINK and PARKIN immunofluorescence staining images of BMMs derived from Lysm+NDR2fl/fl mice treated with ULK1 inhibitor. PINK/PARKIN (green) and DAPI (blue). (I) Statistical analysis of PINK and PARKIN fluorescence intensity (n = 6). Statistical analyses were determined by 1-way ANOVA (I) and 2-way ANOVA (D and E). *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001. Data were presented as mean ± SD.