The study combined deCODE cis-pQTL summary data with the FinnGen R12 M13_INTERVERTEB endpoint, labelled “other intervertebral disc disorders.” After harmonization, 5,820 usable SNP rows supported screening across 1,723 genes. Investigators calculated single-SNP Wald ratios, inverse-variance weighted random-effects estimates when multiple variants were available, weighted-median estimates, MR-Egger slopes, heterogeneity statistics, Egger intercepts and leave-one-out estimates. Benjamini–Hochberg correction was applied to the 1,723 primary gene-level tests. The four multi-SNP signals that passed this threshold were MST1, with an odds ratio of 1.057, 95% confidence interval 1.038–1.077 and q = 4.15 × 10⁻⁶; DLK1, with an odds ratio of 0.933, 95% CI 0.903–0.964 and q = 0.016; ITIH1, with an odds ratio of 0.926, 95% CI 0.893–0.961 and q = 0.016; and SAA1, with an odds ratio of 0.927, 95% CI 0.892–0.962 and q = 0.023. These estimates describe associations between genetically proxied protein abundance and the recorded disc-disorder outcome, not direct effects on disc tissue.

Directional agreement was seen across several analytical methods for the four correction-positive genes: the weighted-median and MR-Egger estimates pointed in the same direction as inverse-variance weighting. Leave-one-out analyses also preserved the sign of each estimate when individual variants were omitted, and MST1 and SAA1 remained nominally significant after every displayed omission. Those checks provide internal consistency but cannot replace validation of instrument independence, particularly because the supplied pQTL table did not include a reference linkage-disequilibrium panel or an auditable record of variant clumping. The authors consequently described the results as local MR screening signals. TP53I3 and BPI were also examined because they were directionally concordant and present in the single-cell matrix, but their q values of 0.13 and 0.17 placed them only in an exploratory tier.

Human nucleus pulposus tissue supplied a cell-level view of the genetic candidates. The researchers analyzed GEO dataset GSE153066, which contains eight relatively normal libraries and eight libraries from degenerated discs. Quality control filtered the original 85,205 barcodes to 70,622 cells, retaining cells with more than 200 and fewer than 5,000 detected genes and less than 20% mitochondrial counts. Marker-informed annotation resolved eight broad populations: B cells, erythroid-like cells, fibroblasts, macrophages, natural killer cells, nucleus-pulposus chondrocyte-like cells, T cells and a deliberately unresolved stress population. Low-specificity clusters were not assigned forced identities, and the cell maps were treated as descriptive because individual cells from the same donor or library are not independent patient-level replicates.

Condition comparisons were instead anchored to the 16 libraries, with eight controls and eight degenerated samples treated as unpaired observations. Counts were summed within each library and transformed into log2 counts per million plus one for pseudobulk analysis. This design exposed substantial between-library heterogeneity and prevented the much larger number of cells from being mistaken for independent clinical evidence. The control group had a median age of 34.5 years, compared with 43 years in the degenerated group, but no age-adjusted or paired estimate was substituted for the unpaired screen. The dataset is cross-sectional, so its cell states cannot establish trajectories of degeneration or reveal whether a particular population caused a change over time.

Macrophages supplied the largest positive nominal difference in cell composition between degenerated and control libraries, amounting to 20.58 percentage points, with P = 0.031 and q = 0.250. The result did not survive correction within the composition panel and was therefore treated as exploratory rather than as an FDR-supported shift. Among 12 displayed follow-up genes, BPI had the largest positive library-level expression effect, with log2 fold change 2.932, P = 0.035 and q = 0.27. GCLM was also nominally positive, with log2 fold change 0.812, P = 0.044 and q = 0.27, but neither estimate met the within-panel false-discovery threshold. These findings indicate that some molecular differences may accompany degeneration while emphasizing that sample variability and multiple testing limit the strength of the conclusions.

A prespecified six-gene ferroptosis-related pQTL panel was analyzed separately from the four correction-positive multi-SNP genes. It included TFRC, FTL, AKR1C3, GCLM, HMOX1 and HSPB1, with a broader marker program that added GPX4, SLC7A11, ACSL4, FTH1, NFE2L2 and PTGS2 for expression context. TFRC was the only member supported in the genetic screen: a single-SNP analysis produced an odds ratio of 1.471, 95% CI 1.212–1.785, P = 9.42 × 10⁻⁵ and q = 0.023. Because this result rested on one SNP rather than a multi-SNP instrument, it supports follow-up but does not demonstrate that circulating transferrin receptor 1 is a causal driver of intervertebral disc disorders. The other panel members entered the tissue analysis as expression markers, independently of genetic significance.

The researchers also sought experimental support for selected findings in a human monocytic cell line. They differentiated THP-1 cells with 100 nM phorbol 12-myristate 13-acetate for 24 hours, allowed a 24-hour recovery, and then exposed the macrophage-like cells to 10 ng/mL each of interleukin-1 beta and tumor necrosis factor alpha for 24 hours. Relative to controls, the inflammatory condition produced higher MST1 expression, measured at 1.34 ± 0.07, higher BPI at 3.46 ± 0.28 and higher GCLM at 1.70 ± 0.12, while SAA1 expression was lower at 0.31 ± 0.03. Each comparison used four independent biological replicates per group and produced a two-sided Welch P value below 0.001. The directions were consistent with the corresponding library-level single-cell results, providing cross-platform concordance for four selected genes.

That laboratory agreement nevertheless has clear boundaries. THP-1 cells are a macrophage-like in vitro model, not primary nucleus-pulposus cells, and the PMA differentiation and recovery conditions can shape inflammatory responsiveness. The experiment therefore supports the plausibility of the measured expression directions in this selected system, not a mechanism of disc degeneration or a clinical effect in patients. Replication would require primary or disc-relevant models, prespecified stimulation conditions, independent biological replication and fuller qPCR reporting, including raw Ct values, primer details and verified amplification efficiency. The genetic analysis likewise needs independent instruments with documented linkage disequilibrium, broader outcome phenotypes, ancestry-diverse data and separate single-cell cohorts. Taken together, the study offers a layered candidate map linking circulating protein signals, cellular context and an inflammatory cell model, but it does not yet establish causal pathways, therapeutic targets or clinical interventions.

Subject of Research: Genetic and single-cell evidence for protein signals and ferroptosis-related states in human intervertebral disc degeneration

Article Title: Genetically supported protein signals and ferroptosis-related cell states in human intervertebral disc degeneration: local pQTL–FinnGen screening integrated with nucleus pulposus single-cell RNA sequencing

Article References: Tang, G., Wu, X., Lin, Y., Tang, Z., & Liang, H. (2026). Genetically supported protein signals and ferroptosis-related cell states in human intervertebral disc degeneration: local pQTL–FinnGen screening integrated with nucleus pulposus single-cell RNA sequencing. Frontiers in Cell and Developmental Biology, 14, Article 1944218. https://doi.org/10.3389/fcell.2026.1944218

Image Credits: AI Generated

DOI: 10.3389/fcell.2026.1944218

Keywords: intervertebral disc degeneration, Mendelian randomization, protein quantitative trait loci, nucleus pulposus, single-cell RNA sequencing, ferroptosis, TFRC, MST1, SAA1, THP-1 cells, FinnGen, Genetically

The pathway in question is Wnt signaling, a master regulator of cell identity, proliferation, and repair that operates in nearly every tissue of the body. Its central messenger, a protein called β-catenin, shuttles from the cell’s cytoplasm into the nucleus when the pathway is active, where it teams up with transcription factors known as TCF and LEF to switch on target genes. In the intervertebral disc, Wnt signaling helps maintain the youthful, gel-filled nucleus pulposus cells that produce the disc’s abundant extracellular matrix. Previous work from the same group showed that deleting β-catenin from disc cells weakens the disc’s compressive stiffness, while stabilizing β-catenin makes discs stiffer and more resistant to deformation. Aging, meanwhile, is known to strip Wnt signaling from disc cells, pushing them toward a more mature, cartilage-like state that produces less matrix.

What remained unclear was whether this age-related loss of Wnt signaling changes how disc cells behave during injury, specifically whether it alters their ability to recruit immune cells to the damaged tissue. To find out, the researchers engineered mice in which β-catenin could be deleted from disc cells in adulthood, using a tamoxifen-activated Cre system targeted to aggrecan-producing cells throughout the disc, or more selectively to nucleus pulposus cells using a Sonic hedgehog-driven driver. Because the deletion was induced at four months of age, well after spinal development was complete, the researchers could isolate the effect of losing Wnt signaling without the confounding systemic inflammation that accompanies natural aging. They then injured the discs mechanically using a tail compression device that applies a precisely calibrated load, roughly equivalent to the change in pressure a human disc experiences when standing up from a chair.

The first surprise came from the genetic confirmation itself. Deleting β-catenin reduced Wnt reporter activity in the annulus fibrosus of male mice by 62 percent, and the deletion cut β-catenin gene expression by 65 percent in male discs and a striking 90 percent in female discs. But the most consequential change was in a single chemokine: Ccl2, also known as MCP-1, the monocyte chemoattractant protein that acts as a beacon guiding monocytes and macrophages toward inflamed tissue. Its expression plummeted by 58 percent in male discs and 79 percent in female discs after β-catenin deletion. Intriguingly, other inflammatory genes responded differently by sex: male discs upregulated the pro-inflammatory cytokine Il1b nearly fivefold and the activated-neutrophil marker S100a9 threefold, while female discs showed no such changes.

To track immune cell recruitment in living animals rather than inferring it from gene expression alone, the team deployed an elegant imaging strategy. They injected mice with PERFECTA-HDL nanoparticles, high-density lipoprotein-like particles that are preferentially taken up by myeloid cells, radiolabeled with zirconium-89, and then scanned the animals with PET/CT before and after disc injury. The results were dramatic. In wild-type mice, disc injury increased tracer signal in the injured region by more than 800 to 1000 percent, reflecting a massive influx of myeloid cells. In mice lacking β-catenin in their disc cells, baseline myeloid accumulation was already reduced by roughly 76 to 79 percent, and the injury-induced surge was blunted by about half. Immunohistochemical staining for the pan-myeloid marker CD11b corroborated the imaging, showing that β-catenin deletion attenuated injury-induced myeloid infiltration by 30 percent in males and 42 percent in females.

Bulk RNA sequencing of injured discs revealed just how profoundly β-catenin shapes the transcriptional response to damage. In wild-type discs, injury upregulated nearly 3,000 gene ontology pathways, and 60 percent of the top twenty were immune-related, including the positive regulation of MCP-1 production itself. Genes like saa3, nos2, il1b, and the neutrophil chemotactic pair cxcl2-cxcr2 were strongly induced, painting a picture of an aggressive early innate immune response dominated by neutrophils and inflammatory macrophages. In β-catenin-deficient discs, that immune signature was largely absent. Instead, injury pushed the transcriptome toward pathways of cell cycle progression, reverse transcription, and developmental biology, with upregulation of genes like twist2, pole, and myog that hint at progenitor-like differentiation programs rather than inflammatory mobilization.

Among the most striking findings was what happened to two anti-inflammatory regulators. In β-catenin-deficient injured discs, five of the seven most downregulated genes relative to wild-type injured discs were inflammation-related, including the serpinA1 family, which encodes alpha-1 antitrypsin, a potent inhibitor of neutrophil elastase that normally restrains tissue degradation and modulates cytokine production. The enzyme ephx2, which metabolizes anti-inflammatory eicosanoids called EETs, was also suppressed. The researchers suggest that losing these brakes on inflammation may paradoxically impair proper inflammatory resolution, allowing neutrophil elastase to chew up the extracellular matrix while the disc fails to mount the coordinated immune response needed for genuine repair.

To connect the engineered deletion back to real aging, the team compressed the tail discs of mice at five, twelve, and twenty-four months of age and measured inflammatory gene expression. Aging reproduced the pattern seen in β-catenin-deficient discs: the injury-induced upregulation of Il6 was attenuated in old female mice, and the regulation of serpinA1a shifted with age in ways that mirrored the knockout phenotype. This corroboration strengthens the central claim that the Wnt-deficient young disc is a legitimate model of the aged disc’s impaired chemotactic signaling, and that the immune recruitment failure observed in the knockouts reflects what actually happens in aging tissue.

The study also surfaced a notable sex difference. Male mice showed a far larger myeloid cell influx after disc injury than females, and β-catenin deletion suppressed that response more dramatically in males. The authors note this may relate to the higher incidence of chronic low back pain among young-adult men compared with young-adult women, while the elevated prevalence in older women may have different, menopause-related origins. It is a reminder that inflammatory biology in the spine, as in so many tissues, is not one-size-fits-all.

The implications reach beyond basic biology. If aged, Wnt-deficient disc cells under-recruit immune cells after injury, they may fail to trigger the acute neutrophil response that recent human pain research has linked to protection against chronic pain, potentially explaining why some degenerating discs become persistently painful while others do not. At the same time, the loss of anti-inflammatory regulators like alpha-1 antitrypsin suggests that simply damping inflammation with NSAIDs, the current mainstay of treatment, may be precisely the wrong approach for aged discs. The authors argue that effective therapies for age-related discogenic pain will need to strike a careful balance, restoring enough chemotactic signaling to permit proper immune-mediated healing without amplifying the chronic, excessive inflammation that drives tissue destruction. It is a subtle prescription, but one that this study, for the first time, grounds in a concrete molecular mechanism.

Subject of Research: The role of Wnt/β-catenin signaling in intervertebral disc cells in regulating chemotactic gene expression and myeloid cell recruitment during disc injury and aging

Article Title: β‐Catenin‐Deficient Intervertebral Disc Cells Reduce Chemotactic Transcription and Myeloid Cell Recruitment to Injured Discs of Mice

Article References: Kroon, T. M., Munitz, J., Ranzenigo, A., Umali, M., Wang, W., Huang, J. J., Teunissen, A. J. P., & Holguin, N. (2026). β‐Catenin ‐Deficient Intervertebral Disc Cells Reduce Chemotactic Transcription and Myeloid Cell Recruitment to Injured Discs of Mice. Aging Cell, 25(10), Article e70740. https://doi.org/10.1111/acel.70740

Image Credits: AI Generated

DOI: 10.1111/acel.70740

Keywords: intervertebral disc, Wnt signaling, beta-catenin, chronic low back pain, disc degeneration, myeloid cells, inflammation, chemokines, Ccl2, PET imaging, aging, nucleus pulposus