Single cell RNA sequencing reveals a shift in cell function and maturation of endogenous and infiltrating cell types in response to acute intervertebral disc injury
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ABSTRACT: The intervertebral disc (IVD) is a spinal joint that accumulates damage with age but has limited tissue repair capabilities. IVD damage progresses into degeneration, and IVD degeneration is a leading cause of lower back pain. There are no effective therapies to treat IVD degeneration, but understanding the cell populations that change and respond to injury will uncover targets to restore IVD function. Mesenchymal stem cells (MSCs) are cells within the IVD that can potentially replenish the cells lost after IVD damage. To identify the cell populations of the IVD and how they change with injury, we performed single cell RNA sequencing of IVD tissue 7 days post injury and analyzed the differences in gene regulation. We identified diverse cells populations such as IVD specific tissues, immune cells, vascular cells, and MSCs. We discovered the presence of Saa2 and Grem1 expressing MSCs that become less stem cell-like and express higher levels of IVD gene markers after injury. We also determined that Saa2 and Grem1 have slightly different expression patterns in IVD tissues, and this expression becomes reduced after injury. These MSCs could be used in future stem cell therapies to prevent IVD degeneration.
Project description:Elucidating how cell populations promote onset and progression of intervertebral disc degeneration (IDD) has the potential to enable more precise therapeutic targeting of cells and mechanisms. Single cell RNA-sequencing (scRNA-seq) was performed on surgically separated annulus fibrosus (AF) (19,978; 26,983 cells) and nucleus pulposus (NP) (20,884; 24,489 cells) from healthy and diseased human intervertebral discs (IVD). In both tissue types, we observed depletion of cell subsets involved in maintenance of healthy IVD, specifically the immature cell subsets – fibroblast progenitors and stem cells – indicative of an impairment of normal tissue self-renewal. We also identified tissue-specific changes. In NP, several fibrotic populations were increased in degenerated IVD, indicating tissue-remodeling. In degenerated AF, we identified a novel disease-associated subset, which is a stem cell-derived abnormally differentiated chondrocytic population and expresses disease-promoting genes. It was associated with pathogenic biological processes and the main gene regulatory networks includedthrombospondinsignaling and FOXO1 transcription factor. Our data reveal new insights of both shared and tissue-specific changes in specific cell populations in AF and NP during IVD degeneration. These identified mechanisms and molecules are novel and more precise targets for IDD prevention and treatment.
Project description:The gene expression of bone marrow cells of mice enriched for Gremlin1 vs control was measured (n=3). It is not known if endogenous adult mesenchymal stem cells (MSCs) exist.Following culture,perisinusoidal mesenchymal cells can clonally recapitulate the skeletal microenvironment, but this fails to confirm their endogenous lineage repertoire. Multipotential MSCs in vitro may be fate-restricted in vivo and specific perisinusoidal recombination does not trace bone or cartilage Reconciling in vitro MSCs with their in vivo potential has been challenging and remains untested outside of the bone. We prove that expression of the bone morphogenetic protein (BMP)-antagonist gremlin 1 (Grem1) identifies a population of self-renewing, multipotent bone, cartilage and stromal-primed MSCs in both health and healing that are completely distinct from the established Nes-GFP niche-supporting mesenchymal cells. Grem1 recombination also identifies small intestinal MSCs (siMSCs) that can be transplanted and clonally trace the self-renewing, multilineage periepithelial mesenchymal sheath. Our findings prove the existence of adult MSCs that are regionally and functionally distinct from perisinusoidal Nes-GFP cells. We also established that the mesenchyme undergoes ordered turnover outside of the bone and may help to preserve regional niches. Grem1 MSCs provide a new focus for investigating mesenchymal renewal and repair. a.Adult (6-8 weeks) Grem1;TdTomato mice were induced by oral tamoxifen and their bone marrow harvested by digestion sorted for Non-recombined CD45/CD31/Ter-119 triple negative bone marrow cells (n=3). b.Adult (6-8 weeks) Grem1;TdTomato mice were induced by oral tamoxifen and their bone marrow harvested by digestion sorted for Grem1 (n=3). Same mice as in a so that samples are matched.
Project description:Failure of the nucleus pulposus (NP) causes intervertebral disc (IVD) disease and associated low-back pain, which are highly prevalent among the aged populations. Molecular and cellular changes underpinning the structural failures in age-associated IVD diseases (IDDs) remain poorly elucidated. Here, we first identified that TAGLN, which encodes the cytoskeleton regulator transgelin, was transcribed in healthy NPs of both human and mouse, but diminished with ageing. Immunostaining showed that TAGLN were expressed on the peripheral of mouse NP (periNP). Lineage analyses in Tagln-CreERT2 mice showed that NP cells were derived from Tagln+ cells in the periNP. The PeriNP cells were proliferative and can differentiate into the inner NP (innerNP). These Tagln+ cells and their descendants diminish with ageing or puncture-induced degeneration. Single-cell transcriptomics from neonatal and adult Tagln-CreERT2 IVDs confirmed that Tagln descendants uniquely populate the NP, wherein four sub-populations were identified: chondrocyte-like, Cd228+, Tagln+ and Car3+. Immunostaining confirmed Car3 expressed in innerNP. Computational analysis indicated the lineage trajectory from Tagln+ to Car3+ sub-population, along with the involvement of Fos/Jun/TGFβ cascades and partial epithelial-to-mesenchymal transition process. Removal of TGFβ mediator Smad4 by notochord specific Foxa2mNE-Cre resulted in decreased Tagln+ cells and abnormal disc morphology, resembling disc degeneration. Our study generates a single-cell transcriptomic atlas for healthy IVD, identifies Tagln+ PeriNP cells as a progenitor pool crucial for the IVD homeostasis, and provides potential targets for regenerative cell therapy against IVD degeneration.
Project description:Osteoarthritis (OA), which carries an enormous disease burden across the world, is characterised by irreversible degeneration of articular cartilage (AC), and subsequently of bone. The cellular cause of OA is unknown. Here, using lineage tracing in mice, we show that the BMP-antagonist Gremlin 1 (Grem1) marks a novel chondrogenic stem/progenitor (CSP) cell population in the articular surface that generates joint cartilage and subchondral bone during development and adulthood. Notably, this CSP population is depleted when OA-inducing injury is created in two independent models, and with age. OA is also induced by toxin mediated ablation of Grem1 CSP cells in young mice. Transcriptomic analysis and functional modelling in mice revealed articular surface Grem1 CSP cells are dependent on Foxo1; ablation of Foxo1 in Grem1 cells also led to early OA. This analysis identified FGFR3 signalling as a therapeutic target, and injection of its activator, FGF18, caused proliferation of Grem1 CSP cells (but not hypertrophic AC), increased cartilage thickness, and reduced OA pathology. We propose that OA arises from the loss of CSP cells at the articular surface secondary to an imbalance in stem/progenitor cell homeostasis and present a new stem cell progenitor population as a locus for OA therapy.
Project description:Osteoarthritis (OA) is characterised by an irreversible degeneration of articular cartilage. Here we show that the BMP-antagonist Gremlin 1 (Grem1) marks a bipotent chondrogenic and osteogenic progenitor cell population within the articular surface. Notably, these progenitors are depleted by injury-induced OA and increasing age. OA is also caused by ablation of Grem1 cells in mice. Transcriptomic and functional analysis in mice found that articular surface Grem1-lineage cells are dependent on Foxo1 and ablation of Foxo1 in Grem1-lineage cells caused OA. FGFR3 signalling was confirmed as a promising therapeutic pathway by administration of pathway activator, FGF18, resulting in Grem1-lineage chondrocyte progenitor cell proliferation, increased cartilage thickness and reduced OA. These findings suggest that OA, in part, is caused by mechanical, developmental or age-related attrition of Grem1 expressing articular cartilage progenitor cells. These cells, and the FGFR3 signalling pathway that sustains them, may be effective future targets for biological management of OA.
Project description:The gene expression of bone marrow cells of mice enriched for Gremlin1 vs control was measured (n=3). It is not known if endogenous adult mesenchymal stem cells (MSCs) exist.Following culture,perisinusoidal mesenchymal cells can clonally recapitulate the skeletal microenvironment, but this fails to confirm their endogenous lineage repertoire. Multipotential MSCs in vitro may be fate-restricted in vivo and specific perisinusoidal recombination does not trace bone or cartilage Reconciling in vitro MSCs with their in vivo potential has been challenging and remains untested outside of the bone. We prove that expression of the bone morphogenetic protein (BMP)-antagonist gremlin 1 (Grem1) identifies a population of self-renewing, multipotent bone, cartilage and stromal-primed MSCs in both health and healing that are completely distinct from the established Nes-GFP niche-supporting mesenchymal cells. Grem1 recombination also identifies small intestinal MSCs (siMSCs) that can be transplanted and clonally trace the self-renewing, multilineage periepithelial mesenchymal sheath. Our findings prove the existence of adult MSCs that are regionally and functionally distinct from perisinusoidal Nes-GFP cells. We also established that the mesenchyme undergoes ordered turnover outside of the bone and may help to preserve regional niches. Grem1 MSCs provide a new focus for investigating mesenchymal renewal and repair.
Project description:Description: The intervertebral disc (IVD) is a joint in the spine that is comprised of three major structures, the nucleus pulposus (NP), annulus fibrosus (AF) and cartilaginous endplate (EP). The NP is a proteoglycan-rich structure which contains a heterogenous population including the presence of progenitors such as the notochordal-like cells (NLCs) and NP cells, which are responsible for the synthesis and turnover of extracellular matrix in the NP. During aging and degeneration, there is a loss of cells, hydration, and changes in the ECM, that leads to the alterations in the biomechanical function of the IVD. The replenishment of cells, in particular, the progenitors are a potential therapy for IVD degeneration. However, a major challenge lies in obtaining sufficient numbers of healthy cells for treatment. This study used a 3 part protocol to differentiate pluripotent stem cells into NLCs in vitro.
Project description:Purpose: We used single-cell RNA-sequencing analysis of degenerating tissues of the rat IVD following lumbar disc puncture Methods: Two control, uninjured IVDs (L2-3, L3-4) and two degenerated, injured IVDs (L4-5, L5-6) from each animal were examined either at the two- or eight-week post-operative time points. The cells from these IVDs were extracted and transcriptionally profiled at the single-cell resolution Results: Unsupervised cluster analysis revealed the presence of four known cell types in both non-degenerative and degenerated IVDs based on previously established gene markers: IVD cells, endothelial cells, myeloid cells, and lymphoid cells. As a majority of cells were associated with the IVD cell cluster, sub-clustering was used to further identify the cell populations of the nucleus pulposus, inner and outer annulus fibrosus Conclusions: . Differential gene expression analysis revealed multiple distinct cell types from the myeloid and lymphoid lineages, most notably macrophages and B lymphocytes, and demonstrated a high degree of immune specificity during degeneration. In addition to the heterogenous infiltrating immune cell populations in the degenerating IVD, the increased number of cells in the AF sub-cluster expressing Ngf and Ngfr, encoding for p75NTR, suggest that NGF signaling may be one of the key mediators of the IVD crosstalk between immune and neuronal cell populations
Project description:The pathophysiology of intervertebral disc (IVD) degeneration is not entirely understood; however, environmental and endogenous factors under genetic predisposition are considered to initiate the degenerative changes of human IVDs. Aberrant epigenetic alterations play a pivotal role in several diseases, including osteoarthritis. However, epigenetic alternations, including DNA methylation, in IVD degeneration have not been evaluated. The purpose of this study was to comprehensively compare the genome-wide DNA methylation profiles of human IVD tissues, specifically nucleus pulpous (NP) tissues, with early and advanced stages of disc degeneration. We conducted, for the first time, a genome-wide DNA methylation profile comparative study and observed significant differences in DNA methylation profiles between early and advanced stages of human IVD degeneration. The overview of the DNA methylation profile in the current study revealed that differentially methylated loci were identified in many genes associated with known molecules that have been reported to be relevant to IVD degeneration. Importantly, changes in DNA methylation profiles were also found in genes that regulate the major signaling pathways, such as NF-κB, MAPK, and Wnt signaling, that are well known to be responsible for the pathogenesis of human disc degeneration.
Project description:To characterize the dysregulated MSCs in the murine MDS models, we performed a single-cell RNA sequence (scRNA-seq) analysis of FACS-sorted MSCs. The proportions of subclusters comprising MSCs were discrete between controls and MDS, and Osteolineage population was reduced in MDS compared with the control. In addition, Lepr+ mesenchymal population in MDS mice exhibited the remarkable reduction of skeletal stem marker Grem1 and MSC marker genes. This transcriptome analysis suggested that the osteolineage differentiation of MSCs is suppressed in vivo in the presence of MDS cells.