The Regulatory Role of GBF1 on Osteoclast Activation Through EIF2a Mediated ER Stress and Novel Marker FAM129A Induction.

Cailing Wen,Chun Zhou,Yuheng Zhou,Tian Qin,Kaifei Liu,Caixia Pang,Linlin Wei,Huijing Tan,Chonghua He,Hui Luo,Haiqian Liu,Yanting Xu,Cuiling Liu

doi:10.3389/fcell.2021.706768

Abstract

Bone-resorbing activities of osteoclasts (OCs) are highly dependent on actin cytoskeleton remodeling, plasma membrane reorganization, and vesicle trafficking pathways, which are partially regulated by ARF-GTPases. In the present study, the functional roles of Golgi brefeldin A resistance factor 1 (GBF1) are proposed. GBF1 is responsible for the activation of the ARFs family and vesicular transport at the endoplasmic reticulum–Golgi interface in different stages of OCs differentiation. In the early stage, GBF1 deficiency impaired OCs differentiation and was accompanied with OCs swelling and reduced formation of mature OCs, indicating that GBF1 participates in osteoclastogenesis. Using siRNA and the specific inhibitor GCA for GBF1 knockdown upregulated endoplasmic reticulum stress-associated signaling molecules, including BiP, p-PERK, p-EIF2α, and FAM129A, and promoted autophagic Beclin1, Atg7, p62, and LC3 axis, leading to apoptosis of OCs. The present data suggest that, by blocking COPI-mediated vesicular trafficking, GBF1 inhibition caused intense stress to the endoplasmic reticulum and excessive autophagy, eventually resulting in the apoptosis of mature OCs and impaired bone resorption function.

Highlights

Bone homeostasis is finely regulated through spatial and temporal control of the bone remodeling process, which is a repetitive cycle of osteoblastic bone formation and osteoclastic bone resorption (Kim et al, 2020)
Through RANKL, c-Fos regulates the induction of NFATc1 expression, and the cooperation between c-Fos and NFATc1 induces the expression of downstream factors including tartrate-resistant acid phosphatase (TRAP), cathepsin K (CtsK), matrix metalloproteinase (MMP2/9), and αvβ3-Integrin, and eventually damages the bone structure (Quan et al, 2015)
The proton pumps localized on the ruffled border secrete acids, degrade organic bone matrix with releasing hydrolase, and form resorption lacunae on the bone surface (Boyle et al, 2003). siRNA sequence targeting Golgi brefeldin A resistance factor 1 (GBF1) and the specific inhibitor Golgicide A (GCA) thereof in RAW 264.7 cells was used to knock down the expression of GBF1, so as to explore the role of GBF1 on OC differentiation and activation

Summary

Introduction

Bone homeostasis is finely regulated through spatial and temporal control of the bone remodeling process, which is a repetitive cycle of osteoblastic bone formation and osteoclastic bone resorption (Kim et al, 2020). RANKL stimulation activates components of the NF-κB and MAPK signaling pathways and various transcription factors, including c-Fos and T cell nuclear factor 1 (NFATc1) (Takayanagi et al, 2002; Ihn et al, 2015). Through replacing GDP with GTP for subsequent recruitment of different vesicle coating proteins in different compartments, the conversion of activated ARFs is facilitated by GBF1 being preferentially concentrated at vesicular and tubular structures apposed to the cis-Golgi network, endoplasmic reticulum–Golgi intermediate compartment (ERGIC), and minor fractions to the Golgi stacks (Zhao et al, 2006). Emerging evidence has revealed that GBF1 regulated different cycles of RNA replication in several virus families (Martínez and Arias, 2020), participated in mitochondrial migration and localization (Ackema et al, 2014), and affected the occurrence and development of neurodegenerative diseases (Mendoza-Ferreira et al, 2020)

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