HO-1 induced autophagy protects against IL-1 β-mediated apoptosis in human nucleus pulposus cells by inhibiting NF-κB.

Luetao Zou,Zhenming Hu,Jie Hao,Longxi Wu,Jieliang Shen,Xulin Liu,Wei Jiang,Hongyan Lei,Xiang Zhang

doi:10.18632/aging.102753

Abstract

In this study, we investigated the role of heme oxygenase-1 (HO-1) in intervertebral disc degeneration (IDD) by assessing the effects of HO-1 overexpression on IL-1β-induced apoptosis in nucleus pulposus cells (NPCs). Immunohistochemical staining showed HO-1 expression to be lower in NPCs from IDD patients than from patients with lumbar vertebral fractures (LVF). Western blot analysis showed HO-1 and LC3-II/I levels to be lower in NP tissues from IDD patients than from LVF patients, suggesting suppression of autophagy in degenerative intervertebral disc. Consistent with that idea, autophagy was increased in HO-1-overexpressing NPCs while IL-1β-induced apoptosis was reduced. These effects were reversed by treatment with the early autophagy inhibitor 3-methyl adenine, which suggests HO-1-induced autophagy suppresses IL-1β-induced apoptosis in NPCs. HO-1 overexpression promoted autophagy by increasing levels of Beclin-1/PI3KC3 complex. Phospho-P65 levels were lower in HO-1-overexpressing NPCs, suggesting inhibition of NF-κB-mediated apoptosis. Our study thus demonstrates that HO-1 promotes autophagy by enhancing formation of Beclin-1/PI3KC3 complex and suppresses IL-1β-induced apoptosis by inhibiting NF-κB. We suggest that HO-1 is a potential therapeutic target to alleviate IDD.

Highlights

Intervertebral disc degeneration (IDD) is a major reason for low back pain (LBP) that affects most people at some point in their lifetime [1,2,3]
Immunohistochemical (IHC) analysis of Nucleus pulposus (NP) tissues showed that heme oxygenase-1 (HO-1) and collagen II positive cells were significantly reduced in the IDD group compared the lumbar vertebral fractures (LVF) group (Figure 1A–1B)
Western blot analysis showed that HO-1 and LC3-II/I protein levels were significantly lower in the IDD group than in the LVF group (Figure 1C)

Summary

Introduction

Intervertebral disc degeneration (IDD) is a major reason for low back pain (LBP) that affects most people at some point in their lifetime [1,2,3]. High levels of pro-inflammatory cytokines such as IL-1β activate signaling pathways that induce apoptosis of the nucleus pulposus cells (NPCs) in the degenerative intervertebral disc [5, 6]. Autophagy is a highly conserved process through which eukaryotic cells recycle cellular components, including organelles and proteins [7]. Macroautophagy is the best studied form of autophagy, which involves formation of autophagosomes that capture and degrade long lived, damaged, aggregated, and misfolded proteins or organelles [8, 9]. Studies have reported increased as well as decreased levels of autophagy in the cellular components of the degenerative intervertebral disc [10, 11]. SIRT1 promotes autophagy in degenerative NPC’s and protects against apoptosis [12]. TGF-β1 protects against apoptosis in serum-starved annulus fibrosus cells by downregulating excessive autophagy [13]

Methods

Results

Conclusion