Department of Orthopedics, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China.
Department of Orthopedics, Peking University Third Hospital, Beijing, China.
Exp Mol Med. 2024 Feb;56(2):408-421. doi: 10.1038/s12276-024-01168-4. Epub 2024 Feb 5.
Lower back pain (LBP), which is a primary cause of disability, is largely attributed to intervertebral disc degeneration (IDD). Macrophages (MΦs) in degenerated intervertebral discs (IVDs) form a chronic inflammatory microenvironment, but how MΦs are recruited to degenerative segments and transform into a proinflammatory phenotype remains unclear. We evaluated chemokine expression in degenerated nucleus pulposus cells (NPCs) to clarify the role of NPCs in the establishment of an inflammatory microenvironment in IDD and explored the mechanisms. We found that the production of C-C motif chemokine ligand 2 (CCL2) and C-C motif chemokine ligand 7 (CCL7) was significantly increased in NPCs under inflammatory conditions, and blocking CCL2/7 and their receptor, C-C chemokine receptor type 2(CCR2), inhibited the inductive effects of NPCs on MΦ infiltration and proinflammatory polarization. Moreover, activation of the integrated stress response (ISR) was obvious in IDD, and ISR inhibition reduced the production of CCL2/7 in NPCs. Further investigation revealed that activating Transcription Factor 3 (ATF3) responded to ISR activation, and ChIP-qPCR verified the DNA-binding activity of ATF3 on CCL2/7 promoters. In addition, we found that Toll-like receptor 4 (TLR4) inhibition modulated ISR activation, and TLR4 regulated the accumulation of mitochondrial reactive oxygen species (mtROS) and double-stranded RNA (dsRNA). Downregulating the level of mtROS reduced the amount of dsRNA and ISR activation. Deactivating the ISR or blocking CCL2/7 release alleviated inflammation and the progression of IDD in vivo. Moreover, MΦ infiltration and IDD were inhibited in CCR2-knockout mice. In conclusion, this study highlights the critical role of TLR4/mtROS/dsRNA axis-mediated ISR activation in the production of CCL2/7 and the progression of IDD, which provides promising therapeutic strategies for discogenic LBP.
下腰痛(LBP)是导致残疾的主要原因,主要归因于椎间盘退行性变(IDD)。退变椎间盘(IVD)中的巨噬细胞(MΦ)形成慢性炎症微环境,但 MΦ如何募集到退行性节段并转化为促炎表型尚不清楚。我们评估了退变髓核细胞(NPC)中趋化因子的表达,以阐明 NPC 在 IDD 炎症微环境建立中的作用,并探讨其机制。我们发现,在炎症条件下,NPC 中 C-C 基序趋化因子配体 2(CCL2)和 C-C 基序趋化因子配体 7(CCL7)的产生显著增加,阻断 CCL2/7 及其受体 C-C 趋化因子受体 2(CCR2)抑制 NPC 对 MΦ浸润和促炎极化的诱导作用。此外,在 IDD 中整合应激反应(ISR)的激活是明显的,ISR 抑制减少 NPC 中 CCL2/7 的产生。进一步研究表明,激活转录因子 3(ATF3)对 ISR 激活作出反应,ChIP-qPCR 验证了 ATF3 在 CCL2/7 启动子上的 DNA 结合活性。此外,我们发现 Toll 样受体 4(TLR4)抑制调节 ISR 激活,TLR4 调节线粒体活性氧(mtROS)和双链 RNA(dsRNA)的积累。下调 mtROS 水平可减少 dsRNA 的量并抑制 ISR 激活。失活 ISR 或阻断 CCL2/7 释放可减轻体内炎症和 IDD 的进展。此外,在 CCR2 敲除小鼠中,MΦ浸润和 IDD 受到抑制。总之,本研究强调了 TLR4/mtROS/dsRNA 轴介导的 ISR 激活在 CCL2/7 产生和 IDD 进展中的关键作用,为椎间盘源性 LBP 提供了有前景的治疗策略。