Tnfaip8 and Tipe2 Gene Deletion Ameliorates Immediate Proteoglycan Loss and Inflammatory Responses in the Injured Mouse Intervertebral Disc.

OBJECTIVE: TNFAIP8 and TIPE2 belong to TNFa-induced protein 8 (TNFAIP8/TIPE) family. They control apoptosis and direct leukocyte migration. Nucleus pulposus (NP) cell loss is a hallmark of intervertebral disc (IVD) degeneration in response to injury, and inflammation may cause pain. Here, we examined the effects of TNFAIP8/TIPE2 deficiency on the IVDs in mice with these genes deleted. DESIGN: Tail IVDs in Tnfaip8 or Tipe2 single and double knockout mice (Tnfaip8-/-, Tipe2-/-, and Tnfaip8/Tipe2 dko), and wild type (WT) controls were injured. The spine motion segments were stained with Safranin O to reveal proteoglycans. Macrophages were identified by immunostaining, and selected inflammatory marker and collagen gene expression was examined by Real Time PCR. RESULTS: The injured tail IVDs of Tnfaip-/-, Tipe2-/-, and Tnfaip8/Tipe2 dko mice all displayed higher levels of proteoglycans than WT controls. Fewer macrophages were found in the injured IVDs of Tipe2-/- and Tnfaip8/Tipe2 dko mice than WT. Il6, Adam8 and Col1 gene expression was downregulated in the injured IVDs of Tnfip8/Tipe2 dko mice. CONCLUSIONS: TNFAIP8 and TIPE2 loss of function ameliorated proteoglycan loss and inflammation in the injured IVDs. They may serve as molecular targets to preserve disc structure and reduce inflammation.

Synovium and infrapatellar fat pad share common mesenchymal progenitors and undergo coordinated changes in osteoarthritis.

Osteoarthritis (OA) affects multiple tissues in the knee joint, including the synovium and intra-articular adipose tissue (IAAT) that are attached to each other. However, whether these two tissues share the same progenitor cells and hence function as a single unit in joint homeostasis and diseases is largely unknown. Single-cell transcriptomic profiling of synovium and infrapatellar fat pad (IFP), the largest IAAT, from control and OA mice revealed five mesenchymal clusters and predicted mesenchymal progenitor cells (MPCs) as the common progenitors for other cells: synovial lining fibroblasts (SLFs), myofibroblasts (MFs), and preadipocytes 1 and 2. Histologic examination of joints in reporter mice having Dpp4-CreER and Prg4-CreER that label MPCs and SLFs, respectively, demonstrated that Dpp4+ MPCs reside in the synovial sublining layer and give rise to Prg4+ SLFs and Perilipin+ adipocytes during growth and OA progression. After OA injury, both MPCs and SLFs gave rise to MFs, which remained in the thickened synovium at later stages of OA. In culture, Dpp4+ MPCs possessed mesenchymal progenitor properties, such as proliferation and multilineage differentiation. In contrast, Prg4+ SLFs did not contribute to adipocytes in IFP and Prg4+ cells barely grew in vitro. Taken together, we demonstrate that the synovium and joint fat pad are one integrated functional tissue sharing common mesenchymal progenitors and undergoing coordinated changes during OA progression.

Both synovium and intra-articular adipose tissue (IAAT) in knee joint play a critical role in joint health and osteoarthritis (OA) progression. Recent single-cell RNA-sequencing studies have been performed on the mouse and human synovium. However, IAATs residing in close proximity to the synovium have not been studied yet. Our study reveals mesenchymal cell heterogeneity of synovium/infrapatellar fat pad (Syn/IFP) tissue and their OA responses. We identify Dpp4+ multipotent progenitors as a source that give rise to Prg4+ lining layer fibroblasts in the synovium, adipocytes in the IFP, and myofibroblasts in the OA Syn/IFP tissue. Our work demonstrates that Syn/IFP is a functionally connected tissue that shares common mesenchymal progenitors and undergoes coordinated OA changes. This novel insight advances our knowledge of previously understudied joint tissues and provides new directions for drug discovery to treat joint disorders.

Persistent Radiculopathy Subsequent to Selective Nerve Root Block.

Transforaminal selective nerve root blocks are commonly performed for low back pain but are not without risk. This case report describes a 55-year-old man who underwent transforaminal selective nerve root block at the left lumbar (L) 4, L5, and sacral (S) 1 levels for radiating low back pain in the setting of moderate narrowing of the left L4-L5 foramen with impingement on the exiting left L4 nerve roots seen on magnetic resonance imaging (MRI). He developed left foot drop immediately after the procedure and presented to the acupuncture clinic two weeks later with persistent pain, left foot drop, and paresthesia of the left lateral shin. A repeat MRI of the lumbar spine showed mild enhancement of the left cauda equina, including the L5 and possibly L4 nerve roots. The large volume of injection into an area with neuroforaminal narrowing as well as the cytotoxicity of the contrast and anesthetic agents may have contributed to axon damage and left foot drop.

Recombinant outer membrane vesicles delivering eukaryotic expression plasmid of cytokines act as enhanced adjuvants against Helicobacter pylori infection in mice.

The widespread prevalence of Helicobacter pylori (H. pylori) infection remains a great challenge to human health. The existing vaccines are not ideal for preventing H. pylori infection; thus, exploring highly effective adjuvants may improve the immunoprotective efficacy of H. pylori vaccines. In a previous study, we found that the outer membrane vesicles (OMVs), a type of nanoscale particle spontaneously produced by Gram-negative bacteria, could act as adjuvants to boost the immune responses to vaccine antigens. In this study, we explored the potential application of OMVs as delivery vectors for adjuvant development. We constructed recombinant OMVs containing eukaryotic expression plasmid of cytokines, including interleukin 17A or interferon-γ, and evaluated their function as adjuvants in combination with inactivated whole-cell vaccine (WCV) or UreB as vaccine antigens. Our results showed that recombinant OMVs as adjuvants could induce stronger humoral and mucosal immune responses in mice than wild-type H. pylori OMVs and the cholera toxin (CT) adjuvant. Additionally, the recombinant OMVs significantly promoted Th1/Th2/Th17-type immune responses. Furthermore, the recombinant OMV adjuvant induced more potent clearance of H. pylori than CT and wild-type OMVs. Our findings suggest that the recombinant OMVs coupled with cytokines may become potent adjuvants for the development of novel and effective vaccines against H. pylori infection.

Embryonic cranial cartilage defects in the Fgfr3Y367C /+ mouse model of achondroplasia.

Achondroplasia, the most common chondrodysplasia in humans, is caused by one of two gain of function mutations localized in the transmembrane domain of fibroblast growth factor receptor 3 (FGFR3) leading to constitutive activation of FGFR3 and subsequent growth plate cartilage and bone defects. Phenotypic features of achondroplasia include macrocephaly with frontal bossing, midface hypoplasia, disproportionate shortening of the extremities, brachydactyly with trident configuration of the hand, and bowed legs. The condition is defined primarily on postnatal effects on bone and cartilage, and embryonic development of tissues in affected individuals is not well studied. Using the Fgfr3Y367C/+ mouse model of achondroplasia, we investigated the developing chondrocranium and Meckel's cartilage (MC) at embryonic days (E)14.5 and E16.5. Sparse hand annotations of chondrocranial and MC cartilages visualized in phosphotungstic acid enhanced three-dimensional (3D) micro-computed tomography (microCT) images were used to train our automatic deep learning-based 3D segmentation model and produce 3D isosurfaces of the chondrocranium and MC. Using 3D coordinates of landmarks measured on the 3D isosurfaces, we quantified differences in the chondrocranium and MC of Fgfr3Y367C/+ mice relative to those of their unaffected littermates. Statistically significant differences in morphology and growth of the chondrocranium and MC were found, indicating direct effects of this Fgfr3 mutation on embryonic cranial and pharyngeal cartilages, which in turn can secondarily affect cranial dermal bone development. Our results support the suggestion that early therapeutic intervention during cartilage formation may lessen the effects of this condition.

Tnfa , Il6 , Cxcl1 , and Adam8 Genes Are the Early Markers After Mouse Tail Intervertebral Disc Injury.

OBJECTIVES: The early molecular events after intervertebral disc injury remain unclear. In this study, we aimed to compare inflammatory markers from 1 day to 4 wks after injury to have a comprehensive understanding of the intervertebral disc response to injury. DESIGN: Mouse tail intervertebral disc injury was induced by a needle puncture. Inflammatory marker gene expression and morphological changes were recorded at 1 day, 1 wk, and 4 wks after injury. RESULTS: Tnfa , Il6 , and Cxcl1 gene expression peaked at day 1 post-needle puncture of the mouse intervertebral disc, Adam8 gene expression peaked at 1-wk time point, while Tipe2 gene expression was upregulated at week 4 postinjury. F4/80 positive cells, likely to be macrophages, are present as early as day 1 in the injured intervertebral discs and consistently present at week 4 postinjury. Loss of Safranin O staining and increased histological scores of the injured intervertebral discs are consistent with progressive degeneration after injury. CONCLUSIONS: Inflammatory cytokines including Tnfa precede Tipe2 , suggesting that Tipe2 is likely induced by Tnfa . Upregulation of Adam8 and Cxcl1 gene expression persisted at week 4, suggesting that they play a role in the transition to chronic phase of intervertebral disc degeneration.

Lactiplantibacillus plantarum attenuates Coxsackievirus B3-induced pancreatitis through the BAX/BCL2/CASP3 signaling pathway.

Lactiplantibacillus plantarum is a lactic acid bacterium widely used in food production. Coxsackievirus B3 (CVB3) is an important human pathogen associated with acute pancreatitis development, and no antiviral therapeutics or vaccines are approved to treat or prevent its infection. However, whether L. plantarum could inhibit CVB3 infection remains unclear. Here, L. plantarum FLPL05 showed antiviral activity against CVB3 infection in vivo and in vitro. Pretreatment with L. plantarum FLPL05 reduced serum amylase levels, CVB3 viral load in the pancreas, serum pro-inflammatory cytokine levels, and macrophage infiltration in CVB3-infected mice. In mice, L. plantarum FLPL05 inhibited CVB3-induced pancreas apoptosis via the B cell leukemia/lymphoma 2 (BCL2)/BCL2-associated X protein (BAX)/caspase-3 (CASP3) signaling pathway. Furthermore, L. plantarum FLPL05 reduced CVB3 replication, protected cells from the cytopathic effect of CVB3 infection, and inhibited cell apoptosis. Moreover, L. plantarum FLPL05's exopolysaccharide (EPS) had activity against CVB3 in vitro, reducing the CVB3 titer and improving cell activity. Therefore, L. plantarum FLPL05 pretreatment improved CVB3-induced pancreatitis by partially reversing pancreatitis, which might be associated with EPS. Consequently, L. plantarum FLPL05 could be a potential probiotic with antiviral activity against CVB3.

Upregulation of ß-catenin signaling represents a single common pathway leading to the various phenotypes of spinal degeneration and pain.

Spine degeneration is an aging-related disease, but its molecular mechanisms remain unknown, although elevated ß-catenin signaling has been reported to be involved in intervertebral disc degeneration. Here, we determined the role of ß-catenin signaling in spinal degeneration and in the homeostasis of the functional spinal unit (FSU), which includes the intervertebral disc, vertebra and facet joint and is the smallest physiological motion unit of the spine. We showed that pain sensitivity in patients with spinal degeneration is highly correlated with ß-catenin protein levels. We then generated a mouse model of spinal degeneration by transgenic expression of constitutively active ß-catenin in Col2+ cells. We found that ß-catenin-TCF7 activated the transcription of CCL2, a known critical factor in osteoarthritic pain. Using a lumbar spine instability model, we showed that a ß-catenin inhibitor relieved low back pain. Our study indicates that ß-catenin plays a critical role in maintaining spine tissue homeostasis, its abnormal upregulation leads to severe spinal degeneration, and its targeting could be an avenue to treat this condition.

Coxsackievirus Group B3 Has Oncolytic Activity against Colon Cancer through Gasdermin E-Mediated Pyroptosis.

Colon cancer is the second leading cause of cancer-related death, and there are few effective therapies for colon cancer. This study explored the use of coxsackievirus group B3 (CVB3) as an oncolytic virus for the treatment of colon cancer. In this study, we verified that CVB3 induces death of colon cancer cell lines by directly observing cell morphology and Western blot results, and observed the oncolytic effects of CVB3 by constructing an immunodeficient nude mice model. Our data show that CVB3 induces pyroptosis in colon cancer cell lines. Mechanistically, we demonstrated that CVB3 causes cleavage of gasdermin E (GSDME), but not gasdermin D (GSDMD), by activating caspase-3. This leads to production of GSDME N-termini and the development of pores in the plasma membrane, inducing pyroptosis of colon cancer cell lines. We also demonstrate that CVB3-induced pyroptosis is promoted by reactive oxygen species (ROS). Finally, in vivo studies using immunodeficient nude mice revealed that intratumoral injection of CVB3 led to significant tumor regression. Our findings indicate that CVB3 has oncolytic activity in colon cancer cell lines via GSDME-mediated pyroptosis.

Interactions among microorganisms open up a new world for anti-infectious therapy.

The human microbiome, containing bacteria, fungi, and viruses, is a community that coexists peacefully with humans most of the time, but with the potential to cause disease under certain conditions. When the environment changes or certain stimuli are received, microbes may interact with each other, causing or increasing the severity of disease in a host. With the appropriate methods, we can make these microbiota work for us, creating new applications for human health. This review discusses the wide range of interactions between microorganisms that result in an increase in susceptibility to, severity of, and mortality of diseases, and also briefly introduces how microorganisms interact with each other directly or indirectly. The study of microbial interactions and their mechanisms has revealed a new world of treatments for infectious disease. The regulation of the balance between intestinal flora, the correct application of probiotics, and the development of effective drugs by symbiosis all demonstrate the great contributions of the microbiota to human health and its powerful potential value. Consequently, the study of interactions between microorganisms plays an essential role in identifying the causes of diseases and the development of treatments.

Renal Mass Found on Imaging of Spine for Back Pain: An Incidental Finding.

A middle-aged female patient who presented with back pain was found incidentally to have a renal mass by magnetic resonance imaging (MRI). Further imaging, including computerized tomography (CT) with contrast, suggested a high likelihood of malignancy. Following surgical resection, the tumor was found to be a rare benign lesion on subsequent pathological examination. The patient had conservative treatment for her presenting spine issues and is doing very well. Prompt work-up and treatment of incidental findings by the team of primary care, physical medicine and rehabilitation physicians, radiologists, pathologists, and surgeons helped to ensure a good outcome. Residents had a learning opportunity about the disease and on timely management of incidental findings.

Extracellular vesicles, a novel model linking bacteria to ferroptosis in the future?

Ferroptosis is a recently discovered modulated cell death mechanism caused by the accumulation of iron-dependent lipid peroxides to toxic levels and plays an important role in tumor immunology and neurology. Recent studies have shown that ferroptosis may play a crucial role in bacterial infection pathogenesis, which may be useful in anti-infection therapies. However, how bacteria enter cells to induce ferroptosis after invading the host immune system remains largely unknown. In addition, the current studies only focus on the relationship between a single bacterial species or genus and host cell ferroptosis, and there is no systematic summary of its regulatory mechanism. Therefore, our review firstly sums up the role of ferroptosis in bacterial infection and its regulatory mechanism, and innovatively speculates on the function and potential mechanism of extracellular vesicles (EVs) in bacterial-induced ferroptosis, in order to provide possible novel directions and ideas for future anti-infection research. KEY POINTS: • Ferroptosis presents a novel mechanism for bacterial host interaction • EVs provide the potential mechanism for bacterial-induced ferroptosis • The relationship of EVs with ferroptosis provides possible directions for future treatment of bacterial infection.

Expression of Human Interleukin 8 in Mice Alters Their Natural Behaviors.

Objective: To examine the effects of human interleukin (IL) 8 expression on mouse behavior. Methods: A mouse line expressing human IL8 in the intervertebral discs (IVD) and cartilaginous tissues (hIL8+ ) was generated. Mouse spontaneous behaviors, including locomotion, climbing, rearing, grooming, eating, drinking, and immobility were recorded with a fully automatic, non-invasive platform. Results: Distance traveled by the hIL8+ mice declined with age compared with control littermates, and male hIL8+ mice traveled a shorter distance than male controls and females of either genotype (p <0.05). The hIL8+ mice also spent less time in locomotion than control mice (p <0.01), and male hIL8+ mice spent the least amount of time and had lowest count in locomotion compared with the other 3 groups at 12 weeks of age or greater (p <0.05). The hIL8+ mice spent less time climbing than controls, and male mice spent less time climbing than female mice of the same genotype (p <0.01). The hIL8+ mice spent more time eating and less time drinking than controls, and all mice spent less time eating and more time drinking with increasing age. Finally, hIL8+ mice spent more time immobile than controls, and male hIL8+ mice spent more time immobile than any other group (p <0.05). Conclusion: The hIL8+ mice, especially hIL8+ males, showed reduced ambulation and climbing. Mice showed age-related decrease in eating and increase in drinking and grooming time that was also influenced by expression of hIL8. These changes in natural behaviors in control mice are consistent with functional decline with age. Effects of hIL8 superimposed on the natural aging process could involve systemic (e.g., on the brain) and local (e.g., in the spine and joint tissues) mechanisms. Future exploration of these mechanisms might be productive.

Biomarkers in the Degenerative Human Intervertebral Disc Tissue and Blood.

ABSTRACT: Patients with back pain comprise a large proportion of the outpatient practice among physiatrists. Diagnostic tools are limited to clinical history, physical examinations, and imaging. Nonsurgical treatments are largely empirical, encompassing medications, physical therapy, manual treatments, and interventional spinal procedures. A body of literature is emerging confirming elevated levels of biomarkers including inflammatory cytokines in patients with back pain and/or radiculopathy, largely because the protein assay sensitivity has increased. These biomarkers may serve as tools to assist diagnosis and assess outcomes.The presence of inflammatory mediators in the intervertebral disc tissues and blood helped to confirm the inflammatory underpinnings of back pain related to intervertebral disc degeneration. Literature reviewed here suggests that biomarkers could assist clinical diagnosis and monitor physiological outcomes during and after treatments for spine-related pain. Biomarkers must be measured in a large and diverse asymptomatic population, in the context of age and comorbidities to prevent false-positive tests. These levels can then be rationally compared with those in patients with back disorders including discogenic back pain, radiculopathy, and spinal stenosis. While studies reviewed here used "candidate marker" approaches, future nonbiased approaches in clearly defined patient populations could uncover novel biomarkers in clinical management of patients.

A microwell-based impedance sensor on an insertable microneedle for real-time in vivo cytokine detection.

Impedance-based protein detection sensors for point-of-care diagnostics require quantitative specificity, as well as rapid or real-time operation. Furthermore, microfabrication of these sensors can lead to the formation of factors suitable for in vivo operation. Herein, we present microfabricated needle-shaped microwell impedance sensors for rapid-sample-to-answer, label-free detection of cytokines, and other biomarkers. The microneedle form factor allows sensors to be utilized in transcutaneous or transvascular sensing applications. In vitro, experimental characterization confirmed sensor specificity and sensitivity to multiple proteins of interest. Mechanical characterization demonstrated sufficient microneedle robustness for transcutaneous insertion, as well as preserved sensor function postinsertion. We further utilized these sensors to carry out real-time in vivo quantification of human interleukin 8 (hIL8) concentration levels in the blood of transgenic mice that endogenously express hIL8. To assess sensor functionality, hIL8 concentration levels in serum samples from the same mice were quantified by ELISA. Excellent agreement between real-time in vivo sensor readings in blood and subsequent ELISA serum assays was observed over multiple transgenic mice expressing hIL8 concentrations from 62 pg/mL to 539 ng/mL.

Development of a standardized histopathology scoring system for intervertebral disc degeneration and regeneration in rabbit models-An initiative of the ORSspine section.

BACKGROUND: The rabbit lumbar spine is a commonly utilized model for studying intervertebral disc degeneration and for the pre-clinical evaluation of regenerative therapies. Histopathology is the foundation for which alterations to disc morphology and cellularity with degeneration, or following repair or treatment are assessed. Despite this, no standardized histology grading scale has yet been established for the spine field for any of the frequently utilized animal models. AIMS: The purpose of this study was to establish a new standardized scoring system to assess disc degeneration and regeneration in the rabbit model. MATERIALS AND METHODS: The scoring system was formulated following a review of the literature and a survey of spine researchers. Validation of the scoring system was carried out using images provided by 4 independent laboratories, which were graded by 12 independent graders of varying experience levels. Reliability testing was performed via the computation of intra-class correlation coefficients (ICC) for each category and the total score. The scoring system was then further refined based on the results of the ICC analysis and discussions amongst the authors. RESULTS: The final general scoring system involves scoring 7 features (nucleus pulposus shape, area, cellularity and matrix condensation, annulus fibrosus/nucleus pulposus border appearance, annulus fibrosus morphology, and endplate sclerosis/thickening) on a 0 (healthy) to 2 (severe degeneration) scale. ICCs demonstrated overall moderate to good agreement across graders. An addendum to the main scoring system is also included for use in studies evaluating regenerative therapeutics, which involves scoring cell cloning and morphology within the nucleus pulposus and inner annulus fibrosus. DISCUSSION: Overall, this new scoring system provides an avenue to improve standardization, allow a more accurate comparison between labs and more robust evaluation of pathophysiology and regenerative treatments across the field. CONCLUSION: This study developed a histopathology scoring system for degeneration and regeneration in the rabbit model based on reported practice in the literature, a survey of spine researchers, and validation testing.

Development of a standardized histopathology scoring system for intervertebral disc degeneration in rat models: An initiative of the ORS spine section.

BACKGROUND: Rats are a widely accepted preclinical model for evaluating intervertebral disc (IVD) degeneration and regeneration. IVD morphology is commonly assessed using histology, which forms the foundation for quantifying the state of IVD degeneration. IVD degeneration severity is evaluated using different grading systems that focus on distinct degenerative features. A standard grading system would facilitate more accurate comparison across laboratories and more robust comparisons of different models and interventions. AIMS: This study aimed to develop a histology grading system to quantify IVD degeneration for different rat models. MATERIALS & METHODS: This study involved a literature review, a survey of experts in the field, and a validation study using 25 slides that were scored by 15 graders from different international institutes to determine inter- and intra-rater reliability. RESULTS: A new IVD degeneration grading system was established and it consists of eight significant degenerative features, including nucleus pulposus (NP) shape, NP area, NP cell number, NP cell morphology, annulus fibrosus (AF) lamellar organization, AF tears/fissures/disruptions, NP-AF border appearance, as well as endplate disruptions/microfractures and osteophyte/ossification. The validation study indicated this system was easily adopted, and able to discern different severities of degenerative changes from different rat IVD degeneration models with high reproducibility for both experienced and inexperienced graders. In addition, a widely-accepted protocol for histological preparation of rat IVD samples based on the survey findings include paraffin embedding, sagittal orientation, section thickness < 10 µm, and staining using H&E and/or SO/FG to facilitate comparison across laboratories. CONCLUSION: The proposed histological preparation protocol and grading system provide a platform for more precise comparisons and more robust evaluation of rat IVD degeneration models and interventions across laboratories.

Development of a standardized histopathology scoring system using machine learning algorithms for intervertebral disc degeneration in the mouse model-An ORS spine section initiative.

Mice have been increasingly used as preclinical model to elucidate mechanisms and test therapeutics for treating intervertebral disc degeneration (IDD). Several intervertebral disc (IVD) histological scoring systems have been proposed, but none exists that reliably quantitate mouse disc pathologies. Here, we report a new robust quantitative mouse IVD histopathological scoring system developed by building consensus from the spine community analyses of previous scoring systems and features noted on different mouse models of IDD. The new scoring system analyzes 14 key histopathological features from nucleus pulposus (NP), annulus fibrosus (AF), endplate (EP), and AF/NP/EP interface regions. Each feature is categorized and scored; hence, the weight for quantifying the disc histopathology is equally distributed and not driven by only a few features. We tested the new histopathological scoring criteria using images of lumbar and coccygeal discs from different IDD models of both sexes, including genetic, needle-punctured, static compressive models, and natural aging mice spanning neonatal to old age stages. Moreover, disc sections from common histological preparation techniques and stains including H&E, SafraninO/Fast green, and FAST were analyzed to enable better cross-study comparisons. Fleiss's multi-rater agreement test shows significant agreement by both experienced and novice multiple raters for all 14 features on several mouse models and sections prepared using various histological techniques. The sensitivity and specificity of the new scoring system was validated using artificial intelligence and supervised and unsupervised machine learning algorithms, including artificial neural networks, k-means clustering, and principal component analysis. Finally, we applied the new scoring system on established disc degeneration models and demonstrated high sensitivity and specificity of histopathological scoring changes. Overall, the new histopathological scoring system offers the ability to quantify histological changes in mouse models of disc degeneration and regeneration with high sensitivity and specificity.

The critical role of Hedgehog-responsive mesenchymal progenitors in meniscus development and injury repair.

Meniscal tears are associated with a high risk of osteoarthritis but currently have no disease-modifying therapies. Using a Gli1 reporter line, we found that Gli1+ cells contribute to the development of meniscus horns from 2 weeks of age. In adult mice, Gli1+ cells resided at the superficial layer of meniscus and expressed known mesenchymal progenitor markers. In culture, meniscal Gli1+ cells possessed high progenitor activities under the control of Hh signal. Meniscus injury at the anterior horn induced a quick expansion of Gli1-lineage cells. Normally, meniscal tissue healed slowly, leading to cartilage degeneration. Ablation of Gli1+ cells further hindered this repair process. Strikingly, intra-articular injection of Gli1+ meniscal cells or an Hh agonist right after injury accelerated the bridging of the interrupted ends and attenuated signs of osteoarthritis. Taken together, our work identified a novel progenitor population in meniscus and proposes a new treatment for repairing injured meniscus and preventing osteoarthritis.