Deletion of OSBPL2 in auditory cells increases cholesterol biosynthesis and drives reactive oxygen species production by inhibiting AMPK activity

Hongshun Wang,Jun Yao,Guangqian Xing,Xin Cao,Yajie Lu,Zhibin Chen,Hairong Shi,Cui Zhang,Qinjun Wei,Changsong Lin

doi:10.1038/s41419-019-1858-9

Abstract

Oxysterol-binding protein like 2 (OSBPL2) was identified as a novel causal gene for autosomal dominant nonsyndromic hearing loss. However, the pathogenesis of OSBPL2 deficits in ADNSHL was still unclear. The function of OSBPL2 as a lipid-sensing regulator in multiple cellular processes suggested that OSBPL2 might play an important role in the regulation of cholesterol-homeostasis, which was essential for inner ear. In this study the potential roles of OSBPL2 in cholesterol biosynthesis and ROS production were investigated in Osbpl2-KO OC1 cells and osbpl2b-KO zebrafish. RNA-seq-based analysis suggested that OSBPL2 was implicated in cholesterol biosynthesis and AMPK signaling pathway. Furthermore, Osbpl2/osbpl2b-KO resulted in a reduction of AMPK activity and up-regulation of Srebp2/srebp2, Hmgcr/hmgcr and Hmgcs1/hmgcs1, key genes in the sterol biosynthetic pathway and associated with AMPK signaling. In addition, OSBPL2 was also found to interact with ATIC, key activator of AMPK. The levels of total cholesterol and ROS in OC1 cells or zebrafish inner ear were both increased in Osbpl2/osbpl2b-KO mutants and the mitochondrial damage was detected in Osbpl2-KO OC1 cells. This study uncovered the regulatory roles of OSBPL2 in cellular cholesterol biosynthesis and ROS production. These founds might contribute to the deep understanding of the pathogenesis of OSBPL2 mutation in ADNSHL.

Highlights

Cholesterol is an essential constituent of organelle membranes in eukaryotic cells, where it is implicated in various cellular processes, including the regulation of membrane permeability, membrane trafficking, signal transduction, and endocytosis[1,2,3,4,5]
Our findings showed that Osbpl2/ osbpl2b-KO led to excessive cholesterol biosynthesis by inhibiting AMPK signaling pathway and induced the production of intracellular reactive oxygen species (ROS), which might be the causative factor of mitochondrial damage in Osbpl2-KO OC1 cells
Since Oxysterol-binding protein like 2 (OSBPL2) was identified as the autosomal dominant non-syndromic hearing loss (ADNSHL)-causative gene[21,22], it has drawn much attention to the molecular function of OSBPL2 implicated in multiple biological processes

Summary

Introduction

Cholesterol is an essential constituent of organelle membranes in eukaryotic cells, where it is implicated in various cellular processes, including the regulation of membrane permeability, membrane trafficking, signal transduction, and endocytosis[1,2,3,4,5]. Wang et al Cell Death and Disease (2019)10:627 characteristic features in atherosclerosis and some genetic syndromes that affect intracellular cholesterol synthesis or transport[14,15]. Oxysterol-binding protein like 2 (OSBPL2, OMIM: 606731), a member of the oxysterol-binding proteins (OSBP) related proteins (ORPs) family, is known as a sterol sensor and transporter that modulates lipid/cholesterol metabolism, steroid hormone synthesis, cell signaling, vesicular trafficking and cytoskeleton formation[16,17,18,19,20]. The cellular function of OSBPL2 has been reported to be associated with cholesterol and triacylglycerol homeostasis in distinct cell lines[25,26]. It was suggested that the OSBPL2 deficits might result in the loss of tightly-regulated cholesterol-homeostasis response in inner ear and lead to the auditory dysfunction. Considering the ubiquitous expression of OSBPL2 in diverse cell types and multiple cellular functions of this sterol sensor, the potential pathogenesis of OSBPL2 deficits in ADNSHL still needed to be further investigated in the functional or dysfunctional context of specific cell types in vitro and in vivo

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Conclusion