Ferroportin-Dependent Iron Homeostasis Protects against Oxidative Stress-Induced Nucleus Pulposus Cell Ferroptosis and Ameliorates Intervertebral Disc Degeneration In Vivo

Saideng Lu,Li Ling,Yu Song,Cao Yang,Rongjin Luo,Kun Wang,Shuai Li,Yukun Zhang,Chao Chen,Zhiwei Liao,Wencan Ke,Xinghuo Wu,Qian Xiang,Gaocai Li,Bingjin Wang,Sidong Yang

doi:10.1155/2021/6670497

Abstract

Ferroptosis is a specialized form of regulated cell death that is charactered by iron-dependent lethal lipid peroxidation, a process associated with multiple diseases. However, its role in the pathogenesis of intervertebral disc degeneration (IVDD) is rarely investigated. This study is aimed at investigating the role of ferroptosis in oxidative stress- (OS-) induced nucleus pulposus cell (NPC) decline and the pathogenesis of IVDD and determine the underlying regulatory mechanisms. We used tert-butyl hydroperoxide (TBHP) to simulate OS conditions around human NPCs. Flow cytometry and transmission electron microscopy were used to identify ferroptosis, while iron assay kit, Perl's staining, and western blotting were performed to assay the intracellular iron levels. A ferroportin- (FPN-) lentivirus and FPN-siRNA were constructed and used to explore the relationship between FPN, intracellular iron homeostasis, and ferroptosis. Furthermore, hinokitiol, a bioactive compound known to specifically resist OS and restore FPN function, was evaluated for its therapeutic role in IVDD both in vitro and in vivo. The results indicated that intercellular iron overload plays an essential role in TBHP-induced ferroptosis of human NPCs. Mechanistically, FPN dysregulation is responsible for intercellular iron overload under OS. The increase in nuclear translocation of metal-regulatory transcription factor 1 (MTF1) restored the function of FPN, abolished the intercellular iron overload, and protected cells against ferroptosis. Additionally, hinokitiol enhanced the nuclear translocation of MTF1 by suppressing the JNK pathway and ameliorated the progression of IVDD in vivo. Taken together, our results demonstrate that ferroptosis and FPN dysfunction are involved in the NPC depletion and the pathogenesis of IVDD under OS. To the best of our knowledge, this is the first study to demonstrate the protective role of FPN in ferroptosis of NPCs, suggesting its potential used as a novel therapeutic target against IVDD.

Highlights

Intervertebral disc degeneration (IVDD) is a leading cause of low back pain [1], which approximately 80–90% of the global population suffer from, causing immense health and economic burdens [2]
transmission electron microscopy (TEM) observations indicated that tert-butyl hydroperoxide (TBHP)-treated human nucleus pulposus cell (NPC) contained smaller mitochondria with increased membrane density compared to the control group, a morphological characteristic of ferroptosis that is distinct from necrosis, apoptosis, and autophagy [12] (Figure 1(i))
These results suggested that ferroptosis was involved in TBHP-induced cell death in human NPCs, which was significantly alleviated by treatment with ferroptosis inhibitors and iron chelators

Summary

Introduction

Intervertebral disc degeneration (IVDD) is a leading cause of low back pain [1], which approximately 80–90% of the global population suffer from, causing immense health and economic burdens [2]. Located in the inner disc, NP cells (NPCs) constitute the largest proportion of the cell types found in the NP and are responsible for the synthesis and secretion of the extracellular matrix (ECM) which, in turn, maintains the multiple biological functions of the spine. Reactive oxygen species (ROS) are reportedly involved in the apoptosis, autophagy, and senescence of NPCs, which alter cellular phenotypes and contribute to disc degeneration [2, 8,9,10,11]. These mechanisms do not fully explain the decline of NPCs or the unsatisfactory performance of current IVDD treatment strategies

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