Patients with Complex Regional Pain Syndrome (CRPS) present prolonged, debilitating pain and functional impairment. Treatments are not disease-modifying due to the poorly understood underlying pathomechanisms. This study aimed to identify the molecular signatures of potential CRPS type 1 subgroups. Twelve women with CRPS type 1 were included. Demographics and pain questionnaires were recorded. Skin biopsies of the affected and non-affected limbs (n = 6 + 6) and peripheral blood (n = 11) were collected. RNA sequencing was performed on skin and peripheral blood mononuclear cells (PBMCs). Twenty cytokines were quantified in blood plasma (n = 12). Cluster analysis of the affected skin identified two CRPS subgroups (SG). SG1 exhibited increased gene expression related to epidermal development, metabolic processes, and a greater abundance of keratinocytes. SG2 showed enhanced transcriptomic changes in inflammatory, immune, and fibrotic processes, along with higher abundance of fibroblasts, macrophages, and endothelial cells. PBMCs transcriptomics revealed the same SG1/SG2 clusters and highlighted a stronger inflammatory response in the blood of SG1, suggesting distinct tissue-specific immune responses for the subgroups. Interleukin-1 receptor antagonist (IL-1RA) levels were higher in the blood plasma of SG1 (FDR = 0.01), consistent with its encoding gene IL1RN expression in PBMCs (log2 FC = 1.10, P < 0.001) and affected skin (log2 FC = 0.88, P = 0.006). Subgroups did not differ in demographic or clinical parameters but correlations among clinical factors varied between them. This study identified two potential biological subgroups of CRPS type 1 in women through skin and blood transcriptomic profiling, advancing the understanding of this condition. This could facilitate the development of targeted treatments for CRPS type 1.

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 co-stained, 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.

The TCR-mediated activation of T cells expressing the TCR Vγ9Vδ2 relies on an innate-like mechanism involving the butyrophilin 3A1, 3A2 and 2A1 molecules and phospho-antigens, without the participation of classical antigen-presenting molecules. Whether TCR Vγ9Vδ2 cells also recognize complexes composed of antigens and antigen-presenting molecules in an adaptive-like manner is unknown. Here, we identify MR1-autoreactive cells expressing the TCR Vγ9Vδ2. This MR1-restricted response is antigen- and CDR3δ-dependent and butyrophilin-independent. TCR gene transfer reconstitutes MR1-antigen recognition, and engineered TCR Vγ9Vδ2 tetramers interact with soluble MR1-antigen complexes in an antigen-dependent manner. These cells are present in healthy individuals with low frequency and are mostly CD8+ or CD4-CD8 double negative. We also describe a patient with autoimmune symptoms and TCR γδ lymphocytosis in which ~10% of circulating T cells are MR1-self-reactive and express a TCR Vγ9Vδ2. These cells release pro-inflammatory cytokines, suggesting a possible participation in disease pathogenesis. Thus, MR1-self-antigen complexes can interact with some TCRs Vγ9Vδ2, promoting full cell activation and potentially contributing to diseases.

Abstract Metabolic mediators play an important role in regulating inflammation(1). Rheumatoid arthritis and spondyloarthritis are common inflammatory diseases of the joint, aggravated in context of obesity(2). These patients experience systemic bone loss(3,4), which is not sufficiently controlled by disease-modifying therapeutics, despite adequate control of inflammation(5,6). Here we report an unexpected role for GDF15 (Growth Differentiation Factor 15), a central mediator of food intake(7–10), in inflammation-associated bone loss. Serum GDF15 levels were found to be elevated in arthritis patients and inversely correlated with bone density. However, GDF15 itself does not appear to promote arthritis. Rather, GDF15 mediates trabecular bone loss through its receptor GFRAL, which is expressed exclusively in the hindbrain(7–10). GDF15-GFRAL binding results in β-adrenergic activation of bone Marrow Adipogenic Lineage Precursors (MALPs), mesenchymal cells which are known to stimulate osteoclasts and trigger bone loss(11–14). These data demonstrate how a metabolic mediator controls bone loss through a brain-bone axis in inflammatory diseases. These findings may lead to more specific therapeutic interventions to protect bone through targeting GDF15 or MALPs.

Crohn's disease (CD) is a chronic immune-mediated disorder of the gastrointestinal tract. Extensive screening studies have revealed the accumulation of immune cell subsets with unique plasticity and immunoregulatory properties in patients with CD. We performed phenotypic and functional studies on inflamed and non-inflamed bioptic tissue to investigate the presence of distinct T cells in the intestinal mucosa of CD patients. We analysed hundreds of surface molecules expressed on cells isolated from the intestinal tissue of CD patients using anti-CD45 mAbs-based barcoding. A gene ontology enrichment analysis showed that proteins that regulate the activation of T cells were the most enriched group. We, therefore, designed T-cell focused multicolour flow-cytometry panels and performed clustering analysis which revealed an accumulation of activated TEM CD4+CD39+ T cells producing IL-17 and IL-21 and increased frequency of terminally differentiated TCR Vδ1+ cells producing TNF-α and IFN-γ in inflamed tissue of CD patients. The different functional capacities of CD4+ and TCR Vδ1+ cells in CD lesions indicate their non-overlapping contribution to inflammation. The abnormally high number of terminally differentiated TCR Vδ1+ cells suggests that they are continuously activated in inflamed tissue, making them a potential target for novel therapies.

AbstractIntroductionThe emerging field of the disc microbiome challenges traditional views of disc sterility, which opens new avenues for novel clinical insights. However, the lack of methodological consensus in disc microbiome studies introduces discrepancies. The aims of this study were to (1) compare the disc microbiome of non‐Modic (nonMC), Modic type 1 change (MC1), and MC2 discs to findings from prior disc microbiome studies, and (2) investigate if discrepancies to prior studies can be explained with bioinformatic variations.MethodsSequencing of 16S rRNA in 70 discs (24 nonMC, 25 MC1, and 21 MC2) for microbiome profiling. The experimental setup included buffer contamination controls and was performed under aseptic conditions. Methodology and results were contrasted with previous disc microbiome studies. Critical bioinformatic steps that were different in our best‐practice approach and previous disc microbiome studies (taxonomic lineage assignment, prevalence cut‐off) were varied and their effect on results were compared.ResultsThere was limited overlap of results with a previous study on MC disc microbiome. No bacterial genera were shared using the same bioinformatic parameters. Taxonomic lineage assignment using “amplicon sequencing variants” was more sensitive and detected 48 genera compared to 22 with “operational taxonomic units” (previous study). Increasing filter cut‐off from 4% to 50% (previous study) reduced genera from 48 to 4 genera. Despite these differences, both studies observed dysbiosis with an increased abundance of gram‐negative bacteria in MC discs as well as a lower beta‐diversity. Cutibacterium was persistently detected in all groups independent of the bioinformatic approach, emphasizing its prevalence.ConclusionThere is dysbiosis in MC discs. Bioinformatic parameters impact results yet cannot explain the different findings from this and a previous study. Therefore, discrepancies are likely caused by different sample preparations or true biologic differences. Harmonized protocols are required to advance understanding of the disc microbiome and its clinical implications.

Background The multimodal properties of mesenchymal stromal cells (MSCs), particularly their ability to modulate immune responses is of high interest in translational research. Pro-inflammatory, hypoxic, and 3D culture priming are promising and often used strategies to improve the immunosuppressive potency of MSCs, but the underlying mechanisms are not well understood. Therefore, the aims of this study were i) to compare the effects of pro-inflammatory, hypoxic, and 3D culture priming on the in vitro immunosuppressive potential of MSCs, ii) to assess if immunosuppressive priming effects are temporally preserved under standard and translationally relevant culture conditions, and iii) to investigate if the three priming strategies engage the same immunosuppressive mechanisms. Methods Functional in vitro T cell suppressive potency measurements were conducted to assess the impact of pro-inflammatory, hypoxic, and 3D culture priming on the immunosuppressive potential of human bone marrow-derived MSCs. Primed MSCs were either cultured under standard cell culture conditions or translationally relevant culture conditions, and their transcriptomic adaptations were monitored over time. Next-generation sequencing was performed to assess if different priming strategies activate distinct immunosuppressive mechanisms. Results i) Pro-inflammatory, hypoxic, and 3D culture priming induced profound transcriptomic changes in MSCs resulting in a significantly enhanced T cell suppressive potential of pro-inflammatory and 3D culture primed MSCs. ii) Priming effects rapidly faded under standard cell culture conditions but were partially preserved under translationally relevant conditions. Interestingly, continuous 3D culture priming of MSCs maintained the immunosuppressive potency of MSCs. iii) Next-generation sequencing revealed that priming strategy-specific differentially expressed genes are involved in the T cell suppressive capacity of MSCs, indicating that different priming strategies engage distinct immunosuppressive mechanisms. Conclusion Priming can be a useful approach to improve the immunosuppressive potency of MSCs. However, future studies involving primed MSCs should carefully consider the significant impact of translationally relevant conditions on the preservation of priming effects. Continuous 3D culture could act as a functionalized formulation, supporting the administration of MSC spheroids for a sustainably improved immunosuppressive potency.

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.

SUMMARY Metabolic mediators play an important role in regulating chronic inflammation in the body. Here we report an unexpected role for GDF15 (Growth Differentiation Factor 15), a central mediator of food intake, in inflammation-associated bone loss. GDF15 serum levels were found to be elevated in arthritis patients and inversely correlated with bone density. Despite being associated with inflammation, we found that GDF15 itself does not cause, nor contribute to, clinical or histopathological arthritis. Rather, under inflammatory conditions, GDF15 mediates trabecular bone loss through its receptor GFRAL, which is exclusively expressed in the hindbrain. GDF15-GFRAL binding results in β-adrenergic activation of MALPs (Marrow Adipocytic Lineage Precursors) in the bone marrow, which stimulate osteoclasts and trigger bone loss. These data suggest a metabolic mediator-controlled brain-bone axis in inflammation, through which bone loss is induced in a contextual rather than general manner. These findings may lead to more specific therapeutic interventions to protect bone.