IAPP modulates cellular autophagy, apoptosis, and extracellular matrix metabolism in human intervertebral disc cells

Xinghuo Wu,Zhenfeng Duan,Shuhua Yang,Yu Song,Shuai Li,Kun Wang,Yong Gao,Cao Yang,Zengwu Shao,Wei Liu

doi:10.1038/cddiscovery.2016.107

Abstract

The pathogenic process of intervertebral disc degeneration (IDD) is characterized by imbalance in the extracellular matrix (ECM) metabolism. Nucleus pulposus (NP) cells have important roles in maintaining the proper structure and tissue homeostasis of disc ECM. These cells need adequate supply of glucose and oxygen. Islet amyloid polypeptide (IAPP) exerts its biological effects by regulating glucose metabolism. The purpose of this study was to investigate the expression of IAPP in degenerated IVD tissue, and IAPP modulation of ECM metabolism in human NP cells, especially the crosstalk mechanism between apoptosis and autophagy in these cells. We found that the expression of IAPP and Calcr-RAMP decreased considerably during IDD progression, along with the decrease in the expression of AG, BG, and Col2A1. Induction of IAPP in NP cells by transfection with pLV-IAPP enhanced the synthesis of aggrecan and Col2A1 and attenuated the expression of pro-inflammatory factors, tumor necrosis factor (TNF)-α, and interleukin (IL)-1. Upregulation of IAPP also affected the expression of the catabolic markers—matrix metalloproteinases (MMPs) 3, 9 and 13 and ADAMTS 4 and 5. Downregulation of IAPP by siRNA inhibited the expression of anabolic genes but increased the expression of catabolic genes and inflammatory factors. The expressions of autophagic and apoptotic markers in NP cells transfected with pLV-IAPP were upregulated, including BECLIN1, ATG5, ATG7, LC3 II/I and Bcl-2, while significantly increase in the expression of Bax and Caspase-3 in NP cells transfected with pLV-siIAPP. Mechanistically, PI3K/AKT-mTOR and p38/JNK MAPK signal pathways were involved. We propose that IAPP might play a pivotal role in the development of IDD, by regulating ECM metabolism and controlling the crosstalk between apoptosis and autophagy in NP, thus potentially offering a novel therapeutic approach to the treatment of IDD.

Highlights

Intervertebral disc degeneration (IDD) is a common cause of low back pain
Activation of Phosphoinositide-3 kinase (PI3K)/Akt-mTOR and P38/JNK Mitogenactivated protein kinases (MAPK) signaling by Islet amyloid polypeptide (IAPP) induction The results showed that the activation of PI3K/Akt-mTOR was significantly enhanced in Nucleus pulposus (NP) cells transfected with pLV-IAPP and IAPP siRNA administration could remarkably weaken the effects (Figure 8)
Progression of the degeneration in the late stages impacts collagen synthesis and degradation mCMV-IAPP, PLVX-ShRNA2-Puro, pLVX-ShRNA2-Puro-IAPP, or treated with pramlintide. (a) Protein expressions of matrix metalloproteinases (MMPs)-3, MMP-9, MMP-13, ADAMTS-4, and ADAMTS-5 were determined by western blotting. (b–h) Statistical analysis showing the relative expression of MMP-3 (b), MMP-9 (c), MMP-13 (d), ADAMTS-4 (e), ADAMTS-5 (f), Aggrecan (g), and Col[2] (h) proteins

Summary

Introduction

Intervertebral disc degeneration (IDD) is a common cause of low back pain. The pathogenic processes of IDD include biochemical, cellular, and structural disorders of inter vertebral discs (IVD) that exacerbate metabolic imbalance of the extracellular matrix (ECM).[1,2,3] Increased cell death in the disc has been demonstrated to contribute to the process of IDD.[4,5] It is known that impairedIVD cells can cause an imbalance in these processes, leading to disc degenerative changes.[6,7] Disc cells require essential nutrients such as glucose and oxygen for optimal cellular activity and function. Intervertebral disc degeneration (IDD) is a common cause of low back pain. The pathogenic processes of IDD include biochemical, cellular, and structural disorders of inter vertebral discs (IVD) that exacerbate metabolic imbalance of the extracellular matrix (ECM).[1,2,3] Increased cell death in the disc has been demonstrated to contribute to the process of IDD.[4,5] It is known that impaired. IVD cells can cause an imbalance in these processes, leading to disc degenerative changes.[6,7] Disc cells require essential nutrients such as glucose and oxygen for optimal cellular activity and function. Any change in the nutrient balance in the disc affects cellular activity and cell survival significantly.[8,9]

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