Introduction: The vertebral cartilage endplate (CEP), crucial for intervertebral disc health, is prone to degeneration linked to chronic low back pain, disc degeneration, and Modic changes (MC). While it is known that disc cells express toll-like receptors (TLRs) that recognize pathogen- and damage-associated molecular patterns (PAMPs and DAMPs), it is unclear if CEP cells (CEPCs) share this trait. The CEP has a higher cell density than the disc, making CEPCs an important contributor. This study aimed to identify TLRs on CEPCs and their role in pro-inflammatory and catabolic gene expression. Methods: Gene expression of TLR1–10 was measured in human CEPs and expanded CEPCs using quantitative polymerase chain reaction. Additionally, surface TLR expression was measured in CEPs grouped into non-MC and MC. CEPCs were stimulated with tumor necrosis factor alpha, interleukin 1 beta, small-molecule TLR agonists, or the 30 kDa N-terminal fibronectin fragment. TLR2 signaling was inhibited with TL2-C29, and TLR2 protein expression was measured with flow cytometry. Results: Ex vivo analysis found all 10 TLRs expressed, while cultured CEPCs lost TLR8 and TLR9 expression. TLR2 expression was significantly increased in MC1 CEPCs, and its expression increased significantly after pro-inflammatory stimulation. Stimulation of the TLR2/6 heterodimer upregulated TLR2 protein expression. The TLR2/1 and TLR2/6 ligands upregulated pro-inflammatory genes and matrix metalloproteases (MMP1, MMP3, and MMP13), and TLR2 inhibition inhibited their upregulation. Endplate resorptive capacity of TLR2 activation was confirmed in a CEP explant model. Conclusions: The expression of TLR1–10 in CEPCs suggests that the CEP is susceptible to PAMP and DAMP stimulation. Enhanced TLR2 expression in MC1, and generally in CEPCs under inflammatory conditions, has pro-inflammatory and pro-catabolic effects, suggesting a potential role in disc degeneration and MC.

Purpose: Evaluate how variations in hydrogels viscoelasticity for nucleus pulposus (NP) replacement affect biomechanical function and re-herniation resistance when combined with a mechanically competent annulus fibrosus (AF) repair technique in an intervertebral disc explant model. Methods: Bovine caudal discs (n = 48) were divided into three repair groups (each n = 12) and one no-repair group (n = 12). Repair groups were treated with hyaluronic acid-tyramine hydrogel (HA-Tyr) of varying viscosities (low, medium, high), and AF was repaired using a mechanically interlocked patch (iPatch) made of polyethylene terephthalate fibers. Disc biomechanics were assessed under rotational and compressive-tensile cycles for each specimen (A) in intact state, (B) after experimental herniation/discectomy, and (C) after treatment. Afterwards, load capacity until NP herniation or hydrogel extrusion was determined. Results: Discectomy significantly altered axial and torsional parameters compared to intact discs. Combined iPatch/hydrogel treatment improved axial parameters by reducing range of motion (ROM), neutral zone length, and restoring compressive stiffness, whereas tensile stiffness remained unaffected. Significant differences in ROM were found between unrepaired discs and medium or high viscoelasticity hydrogels. Torsional parameters improved likewise. Low viscoelasticity hydrogel showed the highest load resistance (8.5 MPa) and lowest herniation probability. Under physiological load, only medium viscoelasticity hydrogels did not herniate. Conclusion: Higher viscoelastic hydrogels enhance compressive ROM and axial compressive stiffness after discectomy but increase herniation risk. Medium viscoelastic hydrogels resist physiological loads without herniating while still enhancing ROM. This study highlights the need to optimize NP replacement and suggests a combination that opens promising therapeutic avenues for future applications.

Objectives: Modic changes (MC) are vertebral endplate bone marrow lesions frequently observed in patients with chronic low back pain (CLBP), but their immunogenetic underpinnings remain unknown. We investigated HLA allele associations to uncover immune-mediated mechanisms and potential biomarkers for patient stratification. Methods: We analysed the blood transcriptome from 257 patients with CLBP aged ≥40 years, consisting of 187 patients with MC (types 1–3) and 70 without MC. Bootstrapped LASSO regression identified candidate HLA alleles, which were correlated with MC status using multivariate logistic regression adjusted for demographic covariates. Key findings were validated against US population allele frequencies from 8830 subjects stratified by race and ethnicity. Results: HLA-A*26:01 was strongly associated with MC in CLBP patients (OR = 18.9; FDR = 0.041), and enrichment was independently confirmed by comparison with external population data (OR = 2.15; FDR = 0.008). HLA-DQA1*03:03 was associated with reduced risk of MC (OR = 0.09; FDR = 0.0038). A trend toward positive association was noted for HLA-DRB1*11:01 (OR = 6.0; FDR = 0.069). Conclusions: This is the first study to identify significant associations between HLA and MC. The link to HLA-A*26:01 highlights the significance of CD8 ⁺ T-cell–mediated immune responses in MC pathobiology. These findings suggest HLA typing may enable personalised treatment strategies in chronic low back pain patients with MC. Key messages: What is already known: MC are inflammatory spinal lesions common in CLBP, but their immunogenetic basis is undefined. What this study adds: We identify HLA-A*26:01 as a novel risk allele for MC, validated across external population datasets. How this may affect research, practice or policy: HLA typing may help stratify patients with MC for targeted therapy or inclusion in immunomodulatory trials.

This study aimed to develop a method allowing high-dimensional and technically uniform screening of surface markers on cells of hematopoietic origin. High-dimensional screening of cell phenotypes is primarily the domain of single-cell RNA sequencing (RNAseq), which allows simultaneous analysis of the expression of thousands of genes in several thousands of cells. However, rare cell populations can often substantially impact tissue homeostasis or disease pathogenesis, and dysregulation of rare populations can easily be missed when only a few thousand cells are analyzed. With the presented methodological approach, it is possible to screen hundreds of markers on millions of cells in a technically uniform manner and thus identify and characterize changes in rare populations. We utilize the highly expressed markers CD45 on immune cells and CD71 on erythroid progenitors to create unique fluorescent barcodes on each of the 25 samples. Double-barcoded samples are co-stained with a broad immunophenotyping panel. The panel is designed in such a way that allows the addition of PE-labelled antibody, which was used for screening purposes. Multiplexed samples are divided into hundreds of aliquots and costained, each aliquot with a different PE-labelled antibody. Utilizing a broad immunophenotyping panel and machine-learning algorithms, we can predict the co-expression of hundreds of screened markers with a high degree of precision. This technique is suitable for screening immune cells in bone marrow from different locations, blood specimens, or any tissue with a substantial presence of immune cells, such as tumors or inflamed tissue areas in autoimmune conditions. It represents an approach that can significantly improve our ability to recognize dysregulated immune cell populations and, if needed, precisely target subsequent experiments covering lower cell counts such as RNAseq.

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterised by persistent joint inflammation and systemic immune dysregulation. While bone marrow activation has been linked to RA pathogenesis, direct access to bone marrow tissue for progenitor analysis remains limited by ethical and technical constraints. Analysis of progenitor cells in peripheral blood can serve as a surrogate reflecting bone marrow activation. In this study, we analysed peripheral blood cells from 12 RA patients and 9 healthy controls using high-dimensional spectral flow cytometry with a nine-marker panel (CD45, CD31, CD235, CD133, CD34, CD105, CD271, CD90, PDPN). Flow Self-Organizing Map (FlowSOM) clustering identified 20 distinct cell populations. Additionally, a complementary flow cytometry panel was used to assess CD31 expression on immune subsets in peripheral mononuclear cells (PBMCs) from 9 RA and 9 healthy donors of this cohort. RA patients showed increased CD45⁺CD31⁻ immune cells, but not their putative progenitors. Conversely, putative CD45⁺CD31^int progenitors and CD45⁺CD31^int mature cells were reduced, along with CD31 expression on T cells. Levels of CD235a⁺ putative erythroid precursors and CD45⁺CD31⁺ progenitors were significantly increased in RA patients. Three putative stromal cell populations were detected in circulation. Together, these findings reveal expanded erythroid precursor populations and reduced CD31 expression on T cells in RA. Our data underscore broad systemic alterations in cellular homeostasis in RA patients. In conclusion, our results suggest that the loss of CD31 expression on immune cell precursors plays a role in age-associated immune remodelling and immune activation in RA and provides the rationale for further studies on erythroblast differentiation and the functional role of erythroblasts in chronic inflammation.