Low back pain patients with Modic type 1 changes exhibit distinct bacterial and non-bacterial subtypes

Objectives

Modic type 1 changes (MC1) are vertebral endplate bone marrow (BM) lesions observed on magnetic resonance images in sub-populations of chronic low back pain (CLBP) patients. The etiopathogenesis remains unknown and treatments that modify the underlying pathomechanisms do not exist. We hypothesized that two biological MC1 subtypes exist: a bacterial and a non-bacterial. This would have important implications for developing treatments targeting the underlying pathomechanisms.

Methods

Intervertebral disc (IVD) samples adjacent to MC1 (n ​= ​34) and control (n ​= ​11) vertebrae were collected from patients undergoing spinal fusion. Cutibacterium acnes (C.acnes) genome copy numbers (GCNs) were quantified in IVD tissues with 16S qPCR, transcriptomic signatures and cytokine profiles were determined in MC1 and control BM by RNA sequencing and immunoassay. Finally, we assessed if C.acnes GCNs are associated with blood plasma cytokines.

Results

IVD tissues from control levels had <870 ​C.acnes GCNs/gram IVD. MC1-adjacent IVDs had either "low" (<870) or "high" (>870) C.acnes GCNs. MC1 patients with "high" C.acnes GCNs had upregulated innate immune cell signatures (neutrophil, macrophage/monocyte) and pro-inflammatory cytokines related to neutrophil and macrophage/monocyte function in the BM, consistent with a host defense against bacterium. MC1 patients with "low" C.acnes GCNs had increased adaptive immune cell signatures (T-and B-cell) in the BM and elevated IL-13 blood plasma levels.

Conclusion

Our study provides the first evidence for the existence of bacterial (C.acnes "high") and non-bacterial (C.acnes "low") subtypes in MC1 patients with CLBP. This supports the need for different treatment strategies.

FGF2 overrides key pro-fibrotic features of bone marrow stromal cells isolated from Modic type 1 change patients

Extensive extracellular matrix production and increased cell-matrix adhesion by bone marrow stromal cells (BMSCs) are hallmarks of fibrotic alterations in the vertebral bone marrow known as Modic type 1 changes (MC1). MC1 are associated with non-specific chronic low-back pain. To identify treatment targets for MC1, in vitro studies using patient BMSCs are important to reveal pathological mechanisms. For the culture of BMSCs, fibroblast growth factor 2 (FGF2) is widely used. However, FGF2 has been shown to suppress matrix synthesis in various stromal cell populations. The aim of the present study was to investigate whether FGF2 affected the in vitro study of the fibrotic pathomechanisms of MC1-derived BMSCs. Transcriptomic changes and changes in cell-matrix adhesion of MC1-derived BMSCs were compared to intra-patient control BMSCs in response to FGF2. RNA sequencing and quantitative real-time polymerase chain reaction revealed that pro-fibrotic genes and pathways were not detectable in MC1-derived BMSCs when cultured in the presence of FGF2. In addition, significantly increased cell-matrix adhesion of MC1-derived BMSCs was abolished in the presence of FGF2. In conclusion, the data demonstrated that FGF2 overrides key pro-fibrotic features of MC1 BMSCs in vitro. Usage of FGF2-supplemented media in studies of fibrotic mechanisms should be critically evaluated as it could override normally dominant biological and biophysical cues.

Pro-fibrotic phenotype of bone marrow stromal cells in Modic type 1 changes

Modic type 1 changes (MC1) are painful vertebral bone marrow lesions frequently found in patients suffering from chronic low-back pain. Marrow fibrosis is a hallmark of MC1. Bone marrow stromal cells (BMSCs) are key players in other fibrotic bone marrow pathologies, yet their role in MC1 is unknown. The present study aimed to characterise MC1 BMSCs and hypothesised a pro-fibrotic role of BMSCs in MC1. BMSCs were isolated from patients undergoing lumbar spinal fusion from MC1 and adjacent control vertebrae. Frequency of colony-forming unit fibroblast (CFU-F), expression of stem cell surface markers, differentiation capacity, transcriptome, matrix adhesion, cell contractility as well as expression of pro-collagen type I alpha 1, α-smooth muscle actin, integrins and focal adhesion kinase (FAK) were compared. More CFU-F and increased expression of C-X-C-motif-chemokine 12 were found in MC1 BMSCs, possibly indicating overrepresentation of a perisinusoidal BMSC population. RNA sequencing analysis showed enrichment in extracellular matrix proteins and fibrosis-related signalling genes. Increases in pro-collagen type I alpha 1 expression, cell adhesion, cell contractility and phosphorylation of FAK provided further evidence for their pro-fibrotic phenotype. Moreover, a leptin receptor high expressing (LEPRhigh) BMSC population was identified that differentiated under transforming growth factor beta 1 stimulation into myofibroblasts in MC1 but not in control BMSCs. In conclusion, pro-fibrotic changes in MC1 BMSCs and a LEPRhigh MC1 BMSC subpopulation susceptible to myofibroblast differentiation were found. Fibrosis is a hallmark of MC1 and a potential therapeutic target. A causal link between the pro-fibrotic phenotype and clinical characteristics needs to be demonstrated.

OP0083 INFECTIOUS AND AUTOINFLAMMATORY MODIC TYPE 1 CHANGES HAVE DIFFERENT PATHOMECHANISMS

Background:

Modic type 1 changes (MC1) are vertebral bone marrow (BM) edema that associate with non-specific low back pain (LBP). Two etiologies have been described. In the infectious etiology the anaerobic aerotolerant Cutibacterium acnes (C. acnes) invades damaged intervertebral discs (IVDs) resulting in disc infection and endplate damage, which leads to the evocation of an immune response. In the autoinflammatory etiology disc and endplate damage lead to the exposure of immune privileged disc cells and matrix to leukocytes, thereby evoking an immune response in the BM. Different etiologies require different treatment strategies. However, it is unknown if etiology-specific pathological mechanisms exist.

Objectives:

The aim of this study was to identify etiology-specific dysregulated pathways of MC1 and to perform in-depth analysis of immune cell populations of the autoinflammatory etiology.

Methods:

BM aspirates and biopsies were obtained from LBP patients with MC1 undergoing spinal fusion. Aspirates/biopsies were taken prior screw insertion through the pedicle screw trajectory. From each patient, a MC1 and an intra-patient control aspiration/biopsy from the adjacent vertebral level was taken. If C. acnes in IVDs adjacent to MC1 were detected by anaerobic bacterial culture, patients were assigned to the infectious, otherwise to the autoinflammatory etiology.

Total RNA was isolated from aspirates and sequenced (Novaseq) (infectious n=3 + 3, autoinflammatory n=5 + 5). Genes were considered as differentially expressed (DEG) if p-value < 0.01 and log2fc > ± 0.5. Gene ontology (GO) enrichment was performed in R (GOseq), gene set enrichment analysis (GSEA) with GSEA software.

Changes in cell populations of the autoinflammatory etiology were analyzed with single cell RNA sequencing (scRNAseq): Control and MC1 biopsies (n=1 + 1) were digested, CD45+CD66b- mononuclear cells isolated with fluorescence activated cell sorting (FACS), and 10000 cells were sequenced (10x Genomics). Seurat R toolkit was used for quality-control, clustering, and differential expression analysis.

Transcriptomic changes (n=5 + 5) of CD45+CD66b+ neutrophils isolated with flow cytometry from aspirates were analyzed as for total bulk RNAseq. Neutrophil activation (n=3 + 3) was measured as CD66b+ expression with flow cytometry. CD66bhigh and CD66blow fractions in MC1 and control neutrophils were compared with paired t-test.

Results:

Comparing MC1 to control in total bulk RNAseq, 204 DEG in the autoinflammatory and 444 DEG in the infectious etiology were identified with only 67 shared genes (Fig. 1a). GO enrichment revealed “T-cell activation” (p = 2.50E-03) in the autoinflammatory and “complement activation, classical pathway” (p=1.1E-25) in the infectious etiology as top enriched upregulated biological processes (BP) (Fig 1b). ScRNAseq of autoinflammatory MC1 showed an overrepresentation of T-cells (p= 1.00E-34, OR=1.54) and myelocytes (neutrophil progenitor cells) (p=4.00E-05, OR=2.27) indicating an increased demand of these cells (Fig. 1c). Bulk RNAseq analysis of neutrophils from the autoinflammatory etiology revealed an activated, pro-inflammatory phenotype (Fig 1d), which was confirmed with more CD66bhigh neutrophils in MC1 (+11.13 ± 2.71%, p=0.02) (Fig. 1e).

Figure 1.

(a) Venn diagram of DEG from total bulk RNAseq (b) Top enriched upregulated BP of autoinflammatory (left) and infectious (right) etiology (c) Cell clustering of autoinflammatory MC1 BM (d) Enrichment of “inflammatory response” gene set in autoinflammatory MC1 neutrophils (e) Representative histogram of CD66b+ expression in MC1 and control neutrophils.

Conclusion:

Autoinflammatory and infectious etiologies of MC1 have different pathological mechanisms. T-cell and neutrophil activation seem to be important in the autoinflammatory etiology. This has clinical implication as it could be explored for diagnostic approaches to distinguish the two MC1 etiologies and supports developing targeted treatments for both etiologies.

Disclosure of Interests:

None declared

OP0085 ALTERED EXPRESSION OF NEUROTROPHINS AND THEIR RECEPTORS IN THE SKIN OF PATIENT WITH COMPLEX REGIONAL PAIN SYNDROME (CRPS)

Background:

Complex regional pain syndrome (CRPS) is a rare painful condition that usually appears after trauma or surgery of the extremities. Symptoms include pain, sensory, sudomotor and vasomotor disturbances, trophic changes and impaired motor function. The course varies from mild to chronic disease with a high impact on daily functioning and quality of life. In skin tissue, sustained inflammatory, fibrotic processes together with reduced epidermal nerve fibers are reported. Neurotrophins and their receptors are mediators in cell-to-cell communication and key mediators of pain signaling

Objectives:

The aim of this study was to identify differential expression of neurotrophins and their receptors in the skin and skin fibroblasts of patients with CRPS

Methods:

Healthy controls (HC) and patients with acute CRPS with symptoms for less than 6 months fulfilling the Budapest criteria were recruited. Pain scores were evaluated by numeric rating scale (0=no pain, 100=maximal) and body perception was assessed using the Bath Body Perception Disturbance Scale (BBPDS) (0=no perception disturbance, 57=maximal perception disturbance).

Skin biopsies of the affected and/or non-affected side were taken. Immunohistochemistry on formalin-fixed, paraffin-embedded skin tissue slides was used to show NT3 expression in skin tissues. Blinded analysis was done by an experienced dermato-pathologist determined staining graduated by 0= none, 1= sparse, 2=moderate, 3= dense.

Skin fibroblast were isolated from skin biopsies by outgrowth cultures (CRPS, affected side, n=6 and HC, n=5). Cells (passage 3-6) were starved and subsequently stimulated with TNFα (10 ng/ml) or TGFβ (10 ng/ml) for 24 h to mimic active disease and total RNA was isolated by miRNeasy kit. Gene expression of neurotrophins (NGF, BDNF, and NT3) and neurotrophin receptors (NGFR, TrkA, TrkB and TrkC) was measured by quantitative real time PCR and quantified using the ΔΔCq method with GAPDH as a reference gene. ELISA was used to analyze NT3 protein expression in cell culture supernatants.

Results:

In 5 of 9 patients with CRPS immunohistological staining of NT3 showed an higher expression (from low to moderate) in the affected side versus the non-affected side. In 4 of 9 patients the expression of NT3 was high in the non-affected side (moderate/dense) and stayed high in the affected side.

Of interest, the patients with increasing expression of NT3 in the affected side showed increased pain scores (max pain 80+/-10.95, n=5 versus 48.16+/-18.16, n=4, p=0.059 and changed body perception 26.8+/-8.68 n=5 versus 6.5+/-3.91, n=4, p=0.016).

Isolated skin fibroblasts from the affected side of patients with CRPS compared to healthy skin fibroblasts showed higher basal gene expression of NT3 (log2 fold-change= 1.9 +/- 0.4, p= 0.005) and NGFR (log2 fold-change= 3.6 +/- 2.1, p=0.014). TNFα stimulated CRPS skin fibroblasts showed higher expression for NT3 (log2 fold-change= 2.1 +/- 1.2, p=0.002) compared to HC. TGFb stimulated skin fibroblasts of patients with CRPS showed higher expression of NT3 (log2 fold-change= 1.4+/-0.8, p=0.019), NGFR (log2 fold-change= 2.6 +/- 1.8, p=0.036) and TrkC (log2 fold-change= 2.3 +/- 1.8, p=0.032) compared to HC.

On protein level, NT3 showed a tendency of upregulation in unstimulated fibroblasts from CRPS patients comparing to HC (CRPS mean= 8.0 +/- 2.2 pg/ml, HC mean= 6.3 +/- 1.8 pg/ml, p=0.25). After TNFα stimulation, protein level of NT3 was significantly higher in CRPS skin fibroblasts (CRPS mean= 10.6 +/- 2.4 pg/ml, HC mean= 4.8 +/- 1.3 pg/ml, p=0.004).

Conclusion:

These data indicate a new role of skin fibroblasts in CRPS. Differential basal and stimulated expression of NT3, the receptor for NT3 (TrkC) and NGFR, the common receptor for all neurotrophins, indicates deregulated communication of fibroblasts with the sensory nerve fibers in CRPS. This might contribute to the dysregulated healing process and sustained pain.

Disclosure of Interests:

Sanne Stroeve: None declared, Stefan Dudli: None declared, Isabel Kolm: None declared, Irina Heggli: None declared, Nick Herger: None declared, Sabrina Catanzaro: None declared, Andreas Schweizer: None declared, Maurizio Calcagni Speakers bureau: Arthrex, Consultant of: Medartis, Arthrex, SilkBiomaterials, Grant/research support from: Medartis, Oliver Distler: None declared, Florian Brunner: None declared, Astrid Juengel: None declared

THU0451 CELL-MATRIX ADHESION OF BONE MARROW STROMAL CELLS IN MODIC TYPE 1 CHANGES IS INCREASED AND RELATES TO INCREASED EXPRESSION OF INTEGRIN Β1

Background:

Modic type 1 changes (MC1) are vertebral bone marrow lesions associated with non-specific low back pain (LBP). The pathophysiology of MC1 includes inflammation, fibrosis, and high bone turnover. Bone marrow stromal cells (BMSCs) are key regulators of these processes: BMSCs contribute to inflammation by regulating myelopoiesis/osteoclastogenesis; BMSCs can differentiate into osteoblasts contributing to high bone turnover, and BMSCs can differentiate into pro-fibrotic myofibroblasts.

Objectives:

To identify dysregulated biological processes in MC1 BMSCs contributing to the pathobiology of MC1.

Methods:

Bone marrow aspirates were obtained from LBP patients with MC1 undergoing lumbar spinal fusion. Aspirates were taken prior to screw insertion. From each patient, a MC1 and a healthy control (HC) aspirate from the adjacent vertebral body was collected. BMSCs were isolated by plastic adherence and expanded. RNA from BMSCs passage 3 was sequenced (n=3 + 3) (Illumina Novaseq) and gene ontology of significantly dysregulated genes (p-value < 0.05) was analyzed. Specificity and rate of BMSC matrix adhesion were quantified: BMSCs (n=8 + 8) were seeded on fibronectin-coated, collagen-I-coated, and non-coated plastic dishes. BMSC adhesion was evaluated from 15min to 30min (Δ 30min - 15min). Percentage of adherent cells of MC1 and HC BMSC was compared with paired t-test. In order to identify integrins responsible for dysregulated cell-matrix adhesion, gene expression of 15 relevant integrins was measured by quantitative real-time PCR (qPCR). Normalized expressions were compared between MC1 and HC BMSC with paired t-test. Integrin β1 protein level was semi quantitatively analyzed by Western Blot (n = 5 + 5) and normalized to β-Actin expression.

Results:

By RNA sequencing, 154 genes were differentially expressed between MC1 and HC BMSCs (p-value ≤ 0.01; log2-ratio ≥ 0.5). Gene ontology enrichment analysis revealed an overrepresentation of the biological process “cell-matrix adhesion” among all significantly regulated genes (p-value < 9.3e-13). A change in cell adhesion was corroborated with adhesion assay. Binding (Δ 30min - 15min) to collagen I (MC1 + 16%, HC +10%, p-value = 0.10), fibronectin (MC1 + 17%, HC +6%, p-value = 0.03), and non-coated surface (MC1 + 46%, HC +35%, p-value = 0.05) was increased in MC1 (Figure 1). Integrin gene expression analysis revealed significant upregulation of integrin beta-1 gene (ITGB1) in MC1 vs. HC (fold change = 1.24, p-value = 0.047), whereas there was no significant difference between the other integrins tested. On protein level, integrin β1 was upregulated in MC1 in four out of five patients (Figure 2).

Figure 1.

Adhesion assay.

Figure 2.

Western Blot analysis.

Conclusion:

Adhesion of BMSCs to matrix and integrin β1 expression are increased in MC1. Integrin β1 is essential for cell-matrix adhesion and an important contributor to the initiation and progression of tissue fibrosis, a hallmark of MC1. Therefore, BMSCs and integrin β1 might be relevant novel targets for the treatment of MC1.

Disclosure of Interests: :

Irina Heggli: None declared, Susanne Epprecht: None declared, Tamara Mengis: None declared, Astrid Juengel: None declared, Michael Betz: None declared, Jose Spirig: None declared, Florian Wanivenhaus: None declared, Florian Brunner: None declared, Mazda Farshad: None declared, Oliver Distler Grant/research support from: Grants/Research support from Actelion, Bayer, Boehringer Ingelheim, Competitive Drug Development International Ltd. and Mitsubishi Tanabe; he also holds the issued Patent on mir-29 for the treatment of systemic sclerosis (US8247389, EP2331143)., Consultant of: Consultancy fees from Actelion, Acceleron Pharma, AnaMar, Bayer, Baecon Discovery, Blade Therapeutics, Boehringer, CSL Behring, Catenion, ChemomAb, Curzion Pharmaceuticals, Ergonex, Galapagos NV, GSK, Glenmark Pharmaceuticals, Inventiva, Italfarmaco, iQvia, medac, Medscape, Mitsubishi Tanabe Pharma, MSD, Roche, Sanofi and UCB, Speakers bureau: Speaker fees from Actelion, Bayer, Boehringer Ingelheim, Medscape, Pfizer and Roche, Stefan Dudli: None declared