Multiple sclerosis (MS) is a complex disease of the CNS thought to require an environmental trigger. Gut dysbiosis is common in MS, but specific causative species are unknown. To address this knowledge gap, we used sensitive and quantitative PCR detection to show that people with MS were more likely to harbor and show a greater abundance of epsilon toxin–producing (ETX-producing) strains of C. perfringens within their gut microbiomes compared with individuals who are healthy controls (HCs). Isolates derived from patients with MS produced functional ETX and had a genetic architecture typical of highly conjugative plasmids. In the active immunization model of experimental autoimmune encephalomyelitis (EAE), where pertussis toxin (PTX) is used to overcome CNS immune privilege, ETX can substitute for PTX. In contrast to PTX-induced EAE, where inflammatory demyelination is largely restricted to the spinal cord, ETX-induced EAE caused demyelination in the corpus callosum, thalamus, cerebellum, brainstem, and spinal cord, more akin to the neuroanatomical lesion distribution seen in MS. CNS endothelial cell transcriptional profiles revealed ETX-induced genes that are known to play a role in overcoming CNS immune privilege. Together, these findings suggest that ETX-producing C. perfringens strains are biologically plausible pathogens in MS that trigger inflammatory demyelination in the context of circulating myelin autoreactive lymphocytes.

Clostridium perfringens epsilon toxin (ETX) is the third most lethal bacterial toxin and has been suggested to be an environmental trigger of multiple sclerosis, an immune-mediated disease of the human central nervous system. However, ETX cytotoxicity on primary human cells has not been investigated. In this article, we demonstrate that ETX preferentially binds to and kills human lymphocytes expressing increased levels of the myelin and lymphocyte protein MAL. Using flow cytometry, ETX binding was determined to be time and dose dependent and was highest for CD4+ cells, followed by CD8+ and then CD19+ cells. Similar results were seen with ETX-induced cytotoxicity. To determine if ETX preference for CD4+ cells was related to MAL expression, MAL gene expression was determined by RT-qPCR. CD4+ cells had the highest amount of Mal gene expression followed by CD8+ and CD19+ cells. These data indicate that primary human cells are susceptible to ETX and support the hypothesis that MAL is a main receptor for ETX. Interestingly, ETX bindings to human lymphocytes suggest that ETX may influence immune response in multiple sclerosis.

Background/Objectives: Sagittal spinal alignment goals for adult spinal deformity (ASD) surgery are predominantly derived from standing radiographs, despite the biomechanical relevance of sitting posture. Existing studies on sitting alignment involve young, healthy cohorts, which poorly represent ASD patients. This study assessed posture-dependent changes in spinopelvic parameters, including pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and lumbar lordosis (LL), and examined how age, BMI, and gender influence these changes. Methods: In this retrospective cohort study, sitting and standing lateral radiographs of 1447 patients were evaluated. Spinopelvic parameters were measured, and changes (ΔPI, ΔPT, ΔSS, and ΔLL) were calculated. Multiple regression analysis was used to determine associations between these changes and age, BMI, and gender. Results: All parameters differed significantly between positions (p < 0.001); PT and PI increased in sitting (ΔPT = −19.20°; ΔPI = −4.52°), while SS and LL increased in standing (ΔSS = 14.67°; ΔLL = 18.44°). Older age correlated with increased ΔPT (p < 0.001) and ΔPI (p = 0.049) but reduced ΔLL and ΔSS (p < 0.001). Higher BMI was associated with decreased ΔPI, ΔPT, and ΔLL (p < 0.001, 0.003, and 0.025). Females showed greater ΔPT (p = 0.013) but smaller ΔPI, ΔSS, and ΔLL (p = 0.043, <0.001, and 0.001). Conclusions: Spinopelvic parameters vary significantly between sitting and standing positions, affected by age, BMI, and gender. The observed PI change suggests SIJ involvement, highlighting the need for posture-specific and demographic-adjusted alignment goals in ASD surgery to optimize outcomes.

Objectives: To identify synovial transcriptional clusters in human knee osteoarthritis (OA) and determine how these relate to synovial histologic features, cell-type-associated gene expression, and cartilage degeneration severity. Methods: Bulk RNA sequencing (RNA-seq) of synovial tissue from n = 135 patients with knee OA was analyzed using consensus clustering. Clusters were compared by clinical and histologic features, including cartilage degeneration severity (OARSI score). Single-cell RNA-seq (n = 18) and spatial transcriptomics were used to relate cartilage degeneration-associated gene expression patterns to synovial cell populations. Results: Four synovial transcriptional clusters that differed in synovial histologic features and cartilage degeneration severity were identified. Greater cartilage degeneration was associated with enrichment of lining fibroblast- and inflammatory myeloid-associated gene expression, whereas lesser cartilage degeneration was associated with enrichment of sublining fibroblast, endothelial, mural cell, and adipocyte-associated gene expression. Conclusions: Human knee OA synovium segregates into transcriptional clusters associated with cartilage degeneration severity. Synovial transcriptional heterogeneity corresponds to cell-type-associated gene expression.

Objective: Pain in osteoarthritis (OA) is often discordant with structural joint damage, particularly in obesity-associated OA, where adipose-derived signals may drive nociception independently of cartilage pathology. Leptin has been demonstrated to be necessary, but not sufficient, to drive obesity-associated OA. Here, we tested the hypothesis that leptin mediates OA-associated pain through sensory neuron reprogramming rather than chondrocyte-intrinsic signaling, suggesting a fat-sensory nerve axis. Design: Male and female constitutive leptin-deficient (Ob/Ob), heterozygous (Ob/+), and wild-type (WT) mice, as well as chondrocyte-specific leptin receptor knockout mice (Aggrecan-CreERT2;LepRfl/fl), were challenged with destabilization of the medial meniscus (DMM) surgery to induce OA. Pain-related behaviors, joint pathology, serum cytokines, and lumbar dorsal root ganglia (DRG) transcriptomes were assessed. Human DRG cultures treated with leptin underwent transcriptomic profiling. Secondary analyses of human infrapatellar fat pad and synovium single-cell datasets evaluated leptin and leptin receptor expression patterns. Results: Chondrocyte-specific deletion of the leptin receptor did not mitigate OA pathology or pain. Global leptin-deficient (Ob/Ob) mice exhibited worse structural joint outcomes than WT and Ob/+ animals following DMM yet were robustly protected from OA-associated hyperalgesia – directly dissociating pain from structural pathology and demonstrating that leptin is involved in nociceptive sensitization. Serum cytokine profiles were sex-dependent and did not align with pain outcomes, separating systemic inflammation from nociceptive differences. Transcriptomic analysis of DRGs revealed that leptin drives enrichment of lipid metabolism, eicosanoid, and inflammatory programs, whereas leptin deficiency shifts sensory neurons toward a cytoskeletal remodeling state that does not sustain pain signaling. In human DRG cultures, leptin treatment produced a transcriptomic shift to enrich for neuronal excitability while vehicle treated cells were enriched for inflammatory signaling. Human infrapatellar fat pad and synovium transcriptomic data demonstrated adipocyte-enriched leptin expression and broad distribution of the leptin receptor across stromal, vascular, immune, and adipocyte populations. Conclusions: Leptin contributes to OA pain through neuro-immune crosstalk between adipose tissue and sensory neurons rather than through direct cartilage signaling. These findings identify leptin-associated neuronal programs linked to nociceptor sensitization and support targeting leptin-modulated neuro-immune pathways as a strategy to alleviate OA pain independently of structural disease progression.

Purpose: To evaluate the literature regarding the efficacy of various repair and reconstruction surgical techniques for chronic quadriceps tendon ruptures (QTRs) in native knees and to assess their associated outcomes. Methods: A comprehensive literature search of the EMBASE, PubMed/MEDLINE, and Cochrane databases was conducted from October 2023 to November 2024 in accordance with Preferred Reporting Items for Systematic Reviews and Meta‐Analyses guidelines. Clinical studies that analyzed outcomes following surgical intervention of chronic QTRs with Level IV or greater evidence were included. We excluded case reports and QTRs in the setting of total knee arthroplasty. Quality assessment was conducted using Methodological Index for Non‐Randomized Studies criteria. Results: Ten studies published between 1981 and 2022 were included. Described techniques included direct tendon repair, lengthening procedures, and various graft and mesh augmentations. Reported failure rates ranged from 0 to 33%. Extensor lag remained a common reported complication (5 of 10 studies). Conclusions: The current body of literature on the surgical management of chronic QTRs is characterized by significant heterogeneity in surgical technique and a predominantly low quality of evidence. The various surgical techniques described suffer from limited follow‐up and inconsistently reported outcome measures. Level of Evidence: Level IV, systematic review of Level III and IV studies.