Ferroptosis, an iron-dependent form of regulated cell death, has been reported to affect the activity of nucleus pulposus (NP) cells in the intervertebral disc (IVD), thereby contributing to intervertebral disc degeneration (IVDD). Exosomes (EXOs), extracellular nanovesicles that participate in intercellular communication, are potential therapeutic options for IVDD. Interestingly, while EXOs play an important role in inhibiting ferroptosis, whether EXOs from mesenchymal stem cells (MSCs) modulate the progression of IVDD through regulating ferroptosis is unclear. To reveal the role of ferroptosis in IVDD, IVD tissues with varying degrees of degeneration were collected and abnormal expression of ferroptosis markers was detected. Ferroptotic death was observed in TBHP-induced NP cell death in vitro, which can be specifically inhibited by the ferroptosis inhibitors DFO and Fer-1. Interestingly, MSC-derived EXOs alleviated TBHP-induced or RSL3-induced ferroptosis and rescued NP cell degeneration. Mechanistically, either an NRF2 inhibitor or p62 knockdown dampened the inhibitory effects of EXOs on ferroptosis, suggesting that EXOs attenuated oxidative stress-induced ferroptosis in NP cells by regulating the p62/KEAP1/NRF2 axis. Moreover, EXOs effectively alleviated IVDD in an in vivo rat model. The current study revealed that ferroptosis is associated with the development of IVDD. MSC-derived EXOs slowed IVDD progression by inhibiting NP cell ferroptosis through the p62/KEAP1/NRF2 signaling pathway, suggesting that EXOs are a potential therapeutic option for IVDD.

Background: Intervertebral disc degeneration (IDD) naturally occurs during the aging process. Its occurrence is closely related to chronic inflammation; however, the causal relationship between them is controversial. This study aimed to investigate if inflammation would promote IDD incidence and explore the underlying mechanism. Methods: A chronic inflammation mouse model was established by intraperitoneal injection of lipopolysaccharide (LPS). Enzyme-linked immunosorbent assay was performed to determine proinflammatory cytokines in serum. Histological staining was used to evaluate the degeneration of IVDs. Immunoblots and RT-qPCR analyses were performed to measure protein and mRNA expression levels. Immunoprecipitation, mass spectrometry, and co-immunoprecipitation assays were used to determine the assembly of protein complex. Results: We found that an inflammatory microenvironment activated p38 kinase, which phosphorylated the Runx2 transcription factor at the Ser28 site. The phosphorylated Runx2 (pRunx2) then recruited a deubiquitinase, ubiquitin-specific peptidase 24 (USP24), which stabilized pRunx2 and protected it from ubiquitin-dependent proteasomal degradation. The stabilized pRunx2 recruited histone acetyltransferase p300 and nuclear receptor coactivator 3 (NCOA3) to assemble a complex. This NCOA3-p300-pRunx2 complex then transactivated the expression of 13 ADAMTS (a disintegrin and metalloproteinase with thrombospondin motif) genes, thereby promoting the degradation of extracellular matrix (ECM) in intervertebral discs (IVDs) and causing IDD. Administration of either a p38 inhibitor (doramapimod), a NCOA3 inhibitor (bufalin), or a p300 inhibitor (EML425) significantly decreased the expression of the 13 ADAMTS genes and slowed the degeneration of IVDs. Conclusion: In summary, our results demonstrate that USP24 protects pRunx2 from proteasomal degradation under chronic inflammation conditions, enabling pRunx2 to transactivate ADAMTS genes and degrade ECM. Our findings provide direct evidence that chronic inflammation triggers IDD and offer a therapeutic strategy for retarding IDD in patients with chronic inflammation.

Background: N6-methyladenosine (m⁶A) methylation is a prevalent RNA modification implicated in various diseases. However, its role in intervertebral disc degeneration (IDD), a common cause of low back pain, remains unclear. Results: In this investigation, we explored the involvement of m⁶A demethylation in the pathogenesis of IDD. Our findings revealed that ALKBH5 (alkylated DNA repair protein AlkB homolog 5), an m⁶A demethylase, exhibited upregulation in degenerative discs upon mild inflammatory stimulation. ALKBH5 facilitated m⁶A demethylation within the three prime untranslated region (3′-UTR) of Runx2 mRNA, consequently enhancing its mRNA stability in a YTHDF1 (YTH N6-methyladenosine RNA binding protein F1)-dependent manner. The subsequent elevation in Runx2 expression instigated the upregulation of ADAMTSs and MMPs, pivotal proteases implicated in extracellular matrix (ECM) degradation and IDD progression. In murine models, subcutaneous administration of recombinant Runx2 protein proximal to the lumbar disc in mice elicited complete degradation of intervertebral discs (IVDs). Injection of recombinant MMP1a and ADAMTS10 proteins individually induced mild to moderate degeneration of the IVDs, while co-administration of MMP1a and ADAMTS10 resulted in moderate to severe degeneration. Notably, concurrent injection of the Runx2 inhibitor CADD522 with recombinant Runx2 protein did not result in IVD degeneration in mice. Furthermore, genetic knockout of ALKBH5 and overexpression of YTHDF1 in mice, along with lipopolysaccharide (LPS) treatment to induce inflammation, did not alter the expression of Runx2, MMPs, and ADAMTSs, and no degeneration of the IVDs was observed. Conclusion: Our study elucidates the role of ALKBH5-mediated m⁶A demethylation of Runx2 mRNA in activating MMPs and ADAMTSs, thereby facilitating ECM degradation and promoting the occurrence of IDD. Our findings suggest that targeting the ALKBH5/Runx2/MMPs/ADAMTSs axis may represent a promising therapeutic strategy for preventing IDD.

Recombinant human bone morphogenetic proteins (rhBMPs) can stimulate bone formation and growth in the treatment of spinal fusions and nonunions. However, it is still unclear whether rhBMPs function in the prevention of intervertebral disc degeneration (IDD). Here, we discovered that BMP levels were decreased in IDD patients, which impaired the BMP/Smad (Mothers against decapentaplegic homologs) signaling. Conducting a microarray assay in Smad4-knockdown cells, we found that expression of PUMA (p53-upregulated modulator of apoptosis) was significantly induced. The molecular analysis revealed that Smad4 recruited HDAC1 (histone deacetylase 1) and the phosphorylated Smad1/5/8 to dock on the promoter of PUMA to repress its expression. The impairment of BMP/Smad signaling in IDD patients caused the significant induction of Puma-dependent apoptosis and resulted in the pathogenesis of IDD. In vitro knockdown of BMP receptors (BMPR1a and BMPR2) in nucleus pulposus (NP) cells could mimic the molecular changes of BMP/Smad signaling and Puma-dependent apoptotic signaling that were observed in IDD patients. Exposing NP cells to RITA (reactivating p53 and inducing tumor apoptosis) small molecule and rhBMP2 (or rhBMP7), we observed that rhBMP2/7 could significantly decrease protein levels of Puma and its downstream proapoptotic molecules, blocking cell apoptosis. Importantly, administration of rhBMPs in aged rats could inhibit the occurrence of IDD. Our results provide a link between BMP/Smad signaling and Puma-dependent apoptotic signaling, revealing a new mechanism of how BMPs contribute to IDD pathogenesis and providing evidence that rhBMPs may decrease apoptosis and improve the outcome of IDD.

Study design: Systematic review and meta-analysis. Objective: To compare the effectiveness and safety between the anterior and posterior approach, and identify the more effective surgical approach for treating ossification of the posterior longitudinal ligament (OPLL) in the cervical spine. Method: This meta-analysis searched three electronic databases (PubMed, Embase, Cochrane library), including 17 randomized and non-randomized controlled studies published since 2000–2023 that compared the effectiveness and safety of anterior and posterior surgical approaches for the treatment of ossification of the posterior longitudinal ligament. Japanese Orthopaedic Association (JOA) scores, functional recovery rates, excellent and good outcomes of the surgical approaches, Visual Analogue Scale (VAS), C2–C7 angle cobb and complication were analyzed. RevMan 5.3 was utilized for data analysis. Results: This study suggested that there were no statistically differences between the anterior group and posterior group in terms of preoperative JOA score [WMD=0.23, 95% CI, (−0.22, 0.67), P=0.32], preoperative VAS [WMD=0.03, 95% CI, (−0.24, 0.30)], postoperative VAS [WMD=−0.16, 95% CI, (−0.47, 0.15) P=0.97] function recovery rate of patients with canal narrowing ratio less than 50–60% [WMD=−1.54, 95% CI, (−4.46, 1.38), P=0.30]. The anterior group showed higher postoperative JOA score [WMD=0.99, 95% CI, (036,1.63) P<0.05], post C2–C7 angle cobb [WMD=2.62, 95% CI, (0.36, 4.87), P=0.02] as well as function recovery rate (regardless of canal narrowing ratio) [WMD=16.05, 95% CI, (14.08, 18.03), P<0.05], especially a significant higher function recovery rate of patients with canal narrowing ratio greater than 50–60% [WMD=19.32, 95% CI, (17.25, 21.40), P<0.05]. There was a significant difference between anterior group and posterior group in complication. [OR=0.12, 95% CI, (0.01, 0.24), P<0.05]. Conclusion: Based on the study’s finding, The study suggested that when the conservative treatment for OPLL is unsatisfied, the surgical approach of entering through the anterior approach is a better choice. Nevertheless, it is still necessary to consider the specific situation of the patient. One of the next research directions is how to reduce the complications of anterior surgery.