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

The clinical standard for describing intervertebral disc degeneration is the Pfirrmann grading system, a five-level scale originally devised for lumbar discs and later adapted for the cervical spine. A reader looks at the disc on a T2-weighted image and assigns a grade from I to V based on the loss of the bright nuclear signal, the blurring of the boundary between nucleus and annulus, and the collapse of disc height. The system is widely used and reasonably reproducible when performed by experienced readers, but it is ordinal rather than continuous, which means it cannot capture subtle progression, and it compresses a rich spectrum of tissue change into five coarse bins. Two discs with visibly different appearances can receive the same grade, and the same disc can receive different grades from different readers at different times.

The Suzhou team’s answer was to build a pipeline that begins with a single human decision: an experienced radiologist selects the midsagittal slice, the midline image through the spine where the cervical discs are best profiled. From that point onward, everything is automated. A two-dimensional Swin-UNETR, a transformer-based deep learning architecture, segments four structures on the chosen slice: the vertebral bodies, the intervertebral discs, the cerebrospinal fluid, and the spinal cord. Once these masks exist, the software extracts quantitative indices from each disc, including the relative signal intensity of the disc compared with a reference, a disc height index derived from a Euclidean distance transform, and a height-to-diameter ratio that captures disc shape independently of absolute scale.

The choice of a Swin-UNETR reflects broader trends in medical image analysis. Transformer architectures, which process images through attention mechanisms rather than purely local convolutional filters, have proven adept at capturing long-range context, which matters when the task is to distinguish a disc from the adjacent bone marrow and cerebrospinal fluid on a single grayscale slice. The model was trained and tested entirely within a single institution, and its performance was evaluated on an internal test cohort of 54 patients. The Dice coefficients, a standard overlap metric where 1.0 indicates perfect agreement between automated and reference masks, came in at 0.912 for vertebral bodies, 0.900 for intervertebral discs, and 0.821 for cerebrospinal fluid. For the discs, the structure that matters most for the downstream measurements, that level of agreement is respectable, though the lower score for cerebrospinal fluid hints at the difficulty of segmenting thin, low-contrast fluid spaces.

Reliability of the measurements themselves was assessed in a spectrum-enriched nested subset of 34 patients comprising 170 cervical discs, where automated outputs were compared against reference measurements. When the same distance-transform definition was applied to both automated and reference masks on the physical scale, the disc height index showed a correlation of r = 0.894 and an intraclass correlation coefficient of 0.863, indicating strong agreement. The picture was more complicated for measurements taken from the stored historical image series: the intraclass correlation coefficients were 0.770 for relative signal intensity, 0.635 for the disc height index, and just 0.381 for the height-to-diameter ratio. That last figure is a sobering reminder that signal intensity and geometry measured from routine clinical archives carry variability that can erode reproducibility, a problem that any clinical deployment would need to confront through standardized acquisition protocols.

To establish that the quantitative indices actually track the degenerative process, the researchers turned to a separate spectrum-enriched subset of 30 patients in which two readers independently annotated the discs and assigned Pfirrmann grades. Inter-reader agreement was strong, with a Dice of 0.873 for disc segmentation and a linearly weighted kappa of 0.901 for the Pfirrmann grades, a level of concordance that lends credibility to the grades used as the reference construct. The team then examined how the three quantitative indices related to those grades using patient-clustered statistical analyses adjusted for age, sex, and cervical level, an important step because discs at different cervical levels and in patients of different ages have systematically different baseline appearances.

The associations were consistent in direction. All three indices declined as Pfirrmann grade increased: relative signal intensity showed a Spearman correlation of −0.445 with grade, the stored disc height index −0.384, and the stored height-to-diameter ratio −0.635. After adjustment for age, sex, and level, the overall effect of grade remained statistically significant for all three indices, with P values of 0.00164 for relative signal intensity, 0.0185 for the disc height index, and less than 0.001 for the height-to-diameter ratio. But when the researchers applied the Holm correction for multiple comparisons to the pairwise differences between adjacent grades, only the height-to-diameter ratio retained significant discrimination, and only between grades III and IV and between grades IV and V. In other words, the shape-based index was the most robust at telling neighboring grades apart, while the others captured the overall trend without cleanly separating each step.

The team also tested whether the quantitative features could classify discs into Pfirrmann grades automatically, an exploratory exercise with instructive results. Among the classifiers evaluated, a Random Forest performed best numerically, achieving an accuracy of 0.488 on the five-class task and 0.665 on a simplified three-class version. A Decision Tree model was retained for its interpretability and reached 0.435 and 0.635 respectively. These numbers make clear that five-way grading from a handful of image-derived features remains a hard problem; a continuous degeneration score, rather than a categorical grade, may ultimately be the more natural output for quantitative imaging. The authors are careful to frame the entire classification analysis as exploratory and internally evaluated only.

Indeed, the study’s most admirable quality may be its restraint. The authors state explicitly that the observed associations represent correspondence with an imaging construct rather than independent biological or clinical validation, that all analyses were internal with no external scanner or institutional cohort evaluated, and that further multicenter and multi-scanner validation is required before the framework could be considered for clinical use. This matters because the gap between a promising internal evaluation and a deployable clinical tool is wide. Scanners from different manufacturers, coils, field strengths, and sequence parameters all alter signal intensities and apparent geometry, and a model trained on one center’s archive may not transfer gracefully to another’s. The modest reproducibility of the height-to-diameter ratio on stored historical series is a concrete example of exactly the kind of vulnerability that external validation would expose.

Still, the direction of travel is clear and, for patients with neck pain, potentially consequential. Degenerative cervical myelopathy, the most common cause of spinal cord dysfunction in adults worldwide, often develops silently as discs degenerate, narrow, and impinge on the cord, and earlier, more sensitive detection of disc deterioration could shift diagnosis toward a stage where intervention is simpler and more effective. A framework that turns each disc into a set of continuous, trackable numbers could allow clinicians to follow progression over time with far more sensitivity than a five-point grade allows, and could give researchers the measurement precision needed to test whether new therapies actually slow degeneration. The Suzhou study does not prove that vision, and it is honest enough to say so. What it does provide is a carefully documented demonstration that AI-assisted segmentation can extract physically meaningful, grade-correlated measurements from the images that hospitals already acquire every day, which is precisely the foundation on which the necessary multicenter trials can now be built.

Subject of Research: AI-based quantitative MRI assessment of cervical intervertebral disc degeneration

Article Title: Segmentation-based quantitative characterization of cervical disc degeneration on midsagittal T2-weighted MRI: a retrospective internal evaluation

Article References: Li, X., Gong, C., Tang, Z., Li, Z., Xu, K., Chang, W., Ma, Z., Liu, J., Dai, Y., Li, Y., & Yu, P. (2026). Segmentation-based quantitative characterization of cervical disc degeneration on midsagittal T2-weighted MRI: a retrospective internal evaluation. BMC Medical Imaging. https://doi.org/10.1186/s12880-026-02871-6

Image Credits: AI Generated

DOI: 10.1186/s12880-026-02871-6

Keywords: cervical spine, disc degeneration, MRI, deep learning, Swin-UNETR, Pfirrmann grading, image segmentation, quantitative imaging, radiology, spine, machine learning, medical imaging