JAG2/Notch2 inhibits intervertebral disc degeneration by modulating cell proliferation, apoptosis, and extracellular matrix

Abstract

Background Intervertebral disc degeneration (IVDD)-related disorders are the major causes of low back pain. A previous study suggested that Notch activation serves as a protective mechanism and is a part of the compensatory response that maintains the necessary resident nucleus pulposus (NP) cell proliferation to replace lost or non-functional cells. However, the exact mechanism remains to be determined. In this study, we aimed to investigate the role of JAG2/Notch2 in NP cell proliferation and apoptosis. Methods Recombinant JAG2 or Notch2, Hes1, and Hey2 siRNAs were used to activate or inhibit Notch signaling. Cell proliferation, apoptosis, cell cycle regulatory factors, and pathways associated with Notch-mediated proliferation were examined. In vivo experiments involving an intradiscal injection of Sprague-Dawley rats were performed. Results Recombinant JAG2 induced Notch2 and Hes1/Hey2 expression together with NP cell proliferation. Downregulation of Notch2/Hes1/Hey2 induced G0/G1 phase cell cycle arrest in NP cells. Moreover, Notch2 mediated NP cell proliferation by regulating cyclin D1 and by activating PI3K/Akt and Wnt/β-catenin signaling. Furthermore, Notch signaling inhibited TNF-α-promoted NP cell apoptosis by suppressing the formation of the RIP1-FADD-caspase-8 complex. Finally, we found that intradiscal injection of JAG2 alleviated IVDD and that sh-Notch2 aggravated IVDD in a rat model. These results indicated that JAG2/Notch2 inhibited IVDD by modulating cell proliferation, apoptosis, and extracellular matrix. The JAG2/Notch2 axis regulated NP cell proliferation via PI3K/Akt and Wnt/β-catenin signaling and inhibited TNF-α-induced apoptosis by suppressing the formation of the RIP1-FADD-caspase-8 complex. Conclusions The current and previous results shed light on the therapeutic implications of targeting the JAG2/Notch2 axis to inhibit or reverse IVDD.

Multiscale Regulation of the Intervertebral Disc: Achievements in Experimental, In Silico, and Regenerative Research

“…As transmembrane receptors with a direct route from the membrane to the nucleus, Notch 1-4 can only exhibit such diverse functionality by a range of regulatory mechanisms such as tissue topology, ligand expression patterns, expression of certain enzymes, or the extent of cell–cell contact [ 234 ]. In IVD cells, the expression of Notch 2 is increased during DD [ 235 ], whereas intradiscal injection of JAG2 (which induces Notch 2) reduced DD processes in rats [ 236 ]. Notch signaling in the IVD was activated by hypoxia [ 237 ] and pro-inflammatory cytokine exposure [ 235 ], thereby activating NP and AF cell proliferation [ 236 , 237 ], inhibiting NP cell apoptosis promoted by TNF-α [ 236 ] and modulating the expression of anabolic and catabolic genes [ 238 ].…”

“…In IVD cells, the expression of Notch 2 is increased during DD [ 235 ], whereas intradiscal injection of JAG2 (which induces Notch 2) reduced DD processes in rats [ 236 ]. Notch signaling in the IVD was activated by hypoxia [ 237 ] and pro-inflammatory cytokine exposure [ 235 ], thereby activating NP and AF cell proliferation [ 236 , 237 ], inhibiting NP cell apoptosis promoted by TNF-α [ 236 ] and modulating the expression of anabolic and catabolic genes [ 238 ]. Yet, these effects seem to be zone-dependent, with Notch activation causing catabolic and anabolic responses in AF and NP cells, respectively [ 238 ].…”

“…Yet, these effects seem to be zone-dependent, with Notch activation causing catabolic and anabolic responses in AF and NP cells, respectively [ 238 ]. Importantly, cross talk between the Notch signaling pathway and MAPK, NF-kB, PI3K/Akt, and Wnt/β-catenin ( Section 4.1 ) seems to exist [ 235 , 236 ]. Despite these fascinating findings, relatively little research has thus far been conducted on the Notch pathway in the IVD.…”

<p>Knockdown of hsa_circ_0059955 Induces Apoptosis and Cell Cycle Arrest in Nucleus Pulposus Cells via Inhibiting <em>Itchy E3 Ubiquitin Protein Ligase</em></p>

“…Low back pain (LBP) is one of the most common health problems, influencing the quality of people's life, and leading to huge global economic burden. 1,2 Evidence has been shown that intervertebral disc degeneration (IVDD) is a primary mechanical cause of LBP. 3 In addition, IVDD is characterized by decreased extracellular matrix (ECM), increased cell death and fibrosis.…”

“…7,8 Additionally, it has been shown that multiple factors can induce the apoptosis of NP cells including infection, genetics, inflammatory cytokines, and signaling networks. 1,9 Recently, cell, growth factor, and gene therapy are the main therapies for the treatment of IVDD; 10 however, current strategies for the treatment of IVDD remains unsatisfying. Therefore, development of effective strategies for the patients with IVDD is extremely required.…”