Transcriptional profiling of articular cartilage in a porcine model of early post-traumatic osteoarthritis

A synoptic literature review of animal models for investigating the biomechanics of knee osteoarthritis

Osteoarthritis (OA) is a common chronic disease largely driven by mechanical factors, causing significant health and economic burdens worldwide. Early detection is challenging, making animal models a key tool for studying its onset and mechanically-relevant pathogenesis. This review evaluate current use of preclinical in vivo models and progressive measurement techniques for analysing biomechanical factors in the specific context of the clinical OA phenotypes. It categorizes preclinical in vivo models into naturally occurring, genetically modified, chemically-induced, surgically-induced, and non-invasive types, linking each to clinical phenotypes like chronic pain, inflammation, and mechanical overload. Specifically, we discriminate between mechanical and biological factors, give a new explanation of the mechanical overload OA phenotype and propose that it should be further subcategorized into two subtypes, post-traumatic and chronic overloading OA. This review then summarises the representative models and tools in biomechanical studies of OA. We highlight and identify how to develop a mechanical model without inflammatory sequelae and how to induce OA without significant experimental trauma and so enable the detection of changes indicative of early-stage OA in the absence of such sequelae. We propose that the most popular post-traumatic OA biomechanical models are not representative of all types of mechanical overloading OA and, in particular, identify a deficiency of current rodent models to represent the chronic overloading OA phenotype without requiring intraarticular surgery. We therefore pinpoint well standardized and reproducible chronic overloading models that are being developed to enable the study of early OA changes in non-trauma related, slowly-progressive OA. In particular, non-invasive models (repetitive small compression loading model and exercise model) and an extra-articular surgical model (osteotomy) are attractive ways to present the chronic natural course of primary OA. Use of these models and quantitative mechanical behaviour tools such as gait analysis and non-invasive imaging techniques show great promise in understanding the mechanical aspects of the onset and progression of OA in the context of chronic knee joint overloading. Further development of these models and the advanced characterisation tools will enable better replication of the human chronic overloading OA phenotype and thus facilitate mechanically-driven clinical questions to be answered.

Mechanical loading and orthobiologic therapies in the treatment of post-traumatic osteoarthritis (PTOA): a comprehensive review

The importance of mechanical loading and its relationship to orthobiologic therapies in the treatment of post-traumatic osteoarthritis (PTOA) is beginning to receive attention. This review explores the current efficacy of orthobiologic interventions, notably platelet-rich plasma (PRP), bone marrow aspirate (BMA), and mesenchymal stem/stromal cells (MSCs), in combating PTOA drawing from a comprehensive review of both preclinical animal models and human clinical studies. This review suggests why mechanical joint loading, such as running, might improve outcomes in PTOA management in conjunction with orthiobiologic administration. Accumulating evidence underscores the influence of mechanical loading on chondrocyte behavior and its pivotal role in PTOA pathogenesis. Dynamic loading has been identified as a key factor for optimal articular cartilage (AC) health and function, offering the potential to slow down or even reverse PTOA progression. We hypothesize that integrating the activation of mechanotransduction pathways with orthobiologic treatment strategies may hold a key to mitigating or even preventing PTOA development. Specific loading patterns incorporating exercise and physical activity for optimal joint health remain to be defined, particularly in the clinical setting following joint trauma.

microRNA-105-5p protects against chondrocyte injury, extracellular matrix degradation, and osteoarthritis progression by targeting SPARCL1

OBJECTIVE

Both microRNA (miR)-105-5p and SPARCL1 were discovered to be differentially expressed in osteoarthritis (OA), but their roles and exact mechanisms have not been entirely elaborated. This paper sets out to probe the impact of miR-105-5p/SPARCL1 on chondrocyte injury, extracellular matrix degradation, and osteoarthritis progression.

METHODS

C28/I2 cells were stimulated with IL-1β to construct an in vitro OA model. C28/I2 cells were transfected with sh-SPARCL1, oe-SPARCL1, or miR-105-5p mimic before IL-1β induction. CCK-8 assay, flow cytometry, and ELISA were adopted to assess cell viability, apoptosis, and inflammatory factor expression, respectively. The binding relationship of miR-105-5p to SPARCL1 was assessed using dual-luciferase reporter assay. After an OA rat model was established, rats underwent intra-articular injection with ago-miR-105-5p. TUNEL was applied to determine cell apoptosis in vivo. mRNA and protein levels were measured by qRT-PCR and western blot, respectively, in vitro and in vivo.

RESULTS

IL-1β treatment diminished miR-105-5p expression and augmented SPARCL1 expression in C28/I2 cells. miR-105-5p decreased SPARCL1 expression by targeting SPARCL1. miR-105-5p overexpression or SPARCL1 silencing prominently reversed the decrease in viability and the promotion of inflammatory factor production, cartilage matrix degradation, and apoptosis in IL-1β-stimulated C28/I2 cells. Furthermore, upregulation of SPARCL1 nullified the influence of miR-105-5p overexpression on viability, apoptosis, inflammation, and cartilage matrix degradation in IL-1β-stimulated C28/I2 cells. miR-105-5p overexpression ameliorated knee cartilage tissue injury in OA rats.

CONCLUSION

Conclusively, miR-105-5p exerted suppressive effects on chondrocyte injury, extracellular matrix degradation, and OA progression by targeting SPARCL1.

Proteomic profiling of human menisci from mild joint degeneration and end-stage osteoarthritis versus healthy controls

Objective

To gain new insight into the molecular changes of the meniscus by comparing the proteome profiles of healthy controls with mild degeneration and end-stage osteoarthritis (OA).

Method

We obtained tissue plugs from lateral and medial menisci of 37 individuals (central part of the posterior horn) classified as healthy (n ​= ​12), mild signs of joint damage (n ​= ​13) and end-stage OA (n ​= ​12). The protein profile was analysed by nano-liquid chromatography-mass spectrometry using data-independent acquisition and quantified by Spectronaut. Linear-mixed effects modelling was applied to extract the between-group comparisons.

Results

A similar protein profile was observed for the mild group as compared to healthy controls while the most different group was end-stage OA mainly for the medial compartment. When a pattern of gradual change in protein levels from healthy to end-stage OA was required, a 42-proteins panel was identified, suggesting a potential role in OA development. The levels of QSOX1 were lower and G6PD higher in the mild group following the proposed protein abundance pattern. Qualitative protein changes suggest lower levels of CYTL1 as a potential biomarker of early joint degradation.

Conclusion

For future targeted proteomic approaches, we propose a candidate panel of 42 proteins based on gradually altered meniscal posterior horn protein abundance patterns associated with joint degradation.

A novel large animal model of posttraumatic osteoarthritis induced by inflammation with mechanical stability

OBJECTIVES

Animal models are needed to reliably separate the effects of mechanical joint instability and inflammation on posttraumatic osteoarthritis (PTOA) pathogenesis. We hypothesized that our modified intra-articular drilling (mIAD) procedure induces cartilage damage and synovial changes through increased inflammation without causing changes in gait.

METHODS

Twenty-four Yucatan minipigs were randomized into the mIAD (n=12) or sham control group (n=12). mIAD animals had two osseous tunnels drilled into each of the tibia and femur adjacent to the anterior cruciate ligament (ACL) attachment sites on the left hind knee. Surgical and contralateral limbs were harvested 15 weeks post-surgery. Cartilage degeneration was evaluated macroscopically and histologically. Synovial changes were evaluated histologically. Interleukin-1 beta (IL-1β), nuclear factor kappa B (NF-κB), and tumor necrosis factor alpha (TNF-α) mRNA expression levels in the synovial membrane were measured using quantitative real-time polymerase chain reaction. IL-1β and NF-κB levels in chondrocytes were assessed using immunohistochemistry. Load asymmetry during gait was recorded by a pressure-sensing walkway system before and after surgery.

RESULTS

The mIAD surgical knees demonstrated greater gross and histological cartilage damage than contralateral (P<.01) and sham knees (P<.05). Synovitis was present only in the mIAD surgical knee. Synovial inflammatory marker (IL-1β, NF-κB, and TNF-α) expression was three times higher in the mIAD surgical knee than the contralateral (P<.05). Chondrocyte IL-1β and NF-κB levels were highest in the mIAD surgical knee. In general, there were no significant changes in gait.

CONCLUSIONS

The mIAD model induced PTOA through inflammation without affecting gait mechanics. This large animal model has significant applications for evaluating the role of inflammation in PTOA and for developing therapies aimed at reducing inflammation following joint injury.

Wheatgrass extract has chondroprotective and anti-inflammatory effects on porcine cartilage

Lameness is a commonly observed disorder in sows and negatively impacts both animal welfare and the profitability of the pig sector. The purpose of this study was to determine anti-inflammatory and/or chondroprotective effects of wheatgrass (WG) on porcine cartilage explants stimulated with lipopolysaccharide (LPS). Explants were aseptically prepared from the intercarpal joints of nine market-weight pigs and placed in culture at 37°C for a total of 120 hours. For the final 96 hours, explants were conditioned with an aqueous extract of WG (0, 5 or 15 μg/mL), and for the final 48 hours explants were stimulated with LPS (0 or 10 µg/mL). Media was removed and replaced every 24 hours. Samples from the final 48 hours were analyzed for biomarkers of cartilage inflammation [prostaglandin E2 (PGE2) and nitric oxide (NO)] and cartilage structure [glycosaminoglycan (GAG)], and cartilage explants were stained for an estimate of cell viability. Stimulation of explants with LPS significantly increased media concentrations of PGE2, GAG and NO compared with that from unstimulated explants. LPS stimulation did not significantly affect cell viability. Conditioning of explants with WG (5 μg/mL) significantly reduced LPS-stimulated cartilage release of PGE2, NO, and GAG (5 and 15 μg/mL), without impairing chondrocyte viability. These data provide evidence for a non-cytotoxic chondroprotective and anti-inflammatory effect of WG extract in cartilage and suggest a role of WG in protection against cartilage breakdown, inflammation, and pain associated with osteoarthritis.

Articular cartilage and synovium may be important sources of post-surgical synovial fluid inflammatory mediators

The primary source of synovial fluid inflammatory mediators is currently unknown and may include different tissues comprising the joint, including the synovium and articular cartilage. Prior work in a porcine model has demonstrated that anterior cruciate ligament (ACL) surgery leads to significant changes in early gene expression in the synovium and articular cartilage, which are the same whether concomitant ligament restoration is performed or not. In this study, 36 Yucatan minipigs underwent ACL surgery, and a custom multiplex assay was used to measure synovial fluid protein levels of MMP-1, MMP-2, MMP-3, MMP-7, MMP-9, MMP-12, MMP-13, IL-1α, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-18, GM-CSF, and TNFα in 18 animals at 1 and 4 weeks after surgery. Linear regressions were used to evaluate the relationships between synovial fluid protein levels and the previously reported gene expression levels in the articular cartilage and synovium from the same animal cohort. Synovial fluid levels of MMP-13 and IL-6 were significantly correlated with synovial gene expression (P=.003 and P<.001 respectively), while IL-1α levels were significantly correlated with articular cartilage gene expression (P=.037). The synovium may be an important source of MMP-13 and IL-6, and the articular cartilage may be an important source of IL-1α in post-surgical inflammation. In developing treatments for post-surgical inflammation, the synovium may therefore be a promising target for modulating inflammatory mediators such as MMP-13 and IL-6 in the synovial fluid.

Terminal sterilization influences the efficacy of an extracellular matrix-blood composite for treating posttraumatic osteoarthritis in the rat model

The objective was to determine if an intra-articular injection of an extracellular matrix (ECM) powder and blood composite (ECM-B) after anterior cruciate ligament (ACL) injury would have a mitigating effect on posttraumatic osteoarthritis and if that effect would be different with terminal sterilization of the ECM powder before use. Eighty Lewis rats underwent ACL transection and were divided into four groups: (1) intra-articular injection with phosphate-buffered saline (PBS; n = 20), (2) intra-articular injection of ECM-B using aseptically processed ECM (ASEPTIC; n = 20), (3) intra-articular injection of the ECM-busing ECM powder sterilized with 15 kGy electron beam irradiation (EBEAM; n = 20), and (4) intra-articular injection of the ECM-B using ECM powder sterilized with ethylene oxide (EO; n = 20). Twenty additional animals received capsulotomy only (SHAM). The animals were followed for 6 weeks and evaluations of gait, radiographs, and joint cartilage histology were performed. At 6 weeks, when compared to the SHAM group, the group treated with PBS had significantly worse gait and histologic changes, while the ASEPTIC group was not different from SHAM for either of these outcomes. When compared to the SHAM group, the EO group had similar gait outcomes, but greater histologic damage, and the EBEAM group had significantly worse gait and histological outcomes. The ECM-B composite produced using aseptically processed ECM powder mitigated the gait and histologic changes associated with osteoarthritis after ACL transection in the rat; however, care must be taken when selecting a terminal sterilization method as this may affect the effectiveness of treatment.

Gene expression analysis of subchondral bone, cartilage, and synovium in naturally occurring equine palmar/plantar osteochondral disease

Osteoarthritis (OA) is a disease of the entire joint but the relationship between pathological events in various joint tissues is poorly understood. We examined concurrent changes in bone, cartilage, and synovium in a naturally occurring equine model of joint degeneration. Joints (n = 64) were grossly assessed for palmar/plantar osteochondral disease (POD) in racehorses that required euthanasia for unrelated reasons and assigned a grade of 0 (n = 34), 1 (n = 17), 2 or 3 (n = 13) using a recognized grading scheme. Synovium, cartilage, and subchondral bone were collected for histological and gene expression analysis. Relations between POD grade, cartilage histological score, and gene expression levels were examined using one-way analysis of variance or Kruskal-Wallis test and Spearman's correlation coefficient with corrections for multiple comparisons. Cartilage histological score increased in joints with POD grade 1 (p = 0.002) and 2 or 3 (p < 0.001) compared to 0. At grade 1, expression of COL1A1, COL2A1, and MMP1 increased and BGN decreased in subchondral bone while expression of BGN and ACAN decreased in cartilage. These changes further progressed at grades 2 and 3. POD grades 2 and 3 were associated with decreased expression of osteoclast inhibitor OPG and increased markers of cartilage degeneration (MMP13, COL1A1). Expression of the vascular endothelial growth factor decreased with POD grade and negatively correlated with cartilage histological score. Synovium showed no histological or transcriptomic changes related to pathology grade. Cartilage degeneration in POD is likely to be secondary to remodeling of the subchondral bone. Limited activation of proinflammatory and catabolic genes and moderate synovial pathology suggests distinct molecular phenotype of POD compared with OA.

The Clinical Significance of Changes in Serum New Cytokine CYTL1 in Patients with Knee Osteoarthritis

Objective

The present study aims to investigate the clinical significance of changes in the expression of new cytokine-like 1 (CYTL1) in the serum of patients with knee osteoarthritis (KOA).

Methods

A total of 182 patients with KOA, including 84 males and 98 females aged 39–86 with an average age of 66.4 ± 9.7 and an average body mass index (BMI) of 24.9 ± 2.4 kg/m², were enrolled in the study. The patients were divided into three subgroups: the grade II subgroup (n = 23), grade III subgroup (n = 63), and grade IV subgroup (n = 96) based on severity, as calculated by the Kellgren and Lawrence (K&L) classification system. In addition, 152 volunteers from our health center who came in for physical examination were selected as the control group, including 70 males and 82 females aged 37–82 with an average age of 63.4 ± 9.5 and an average BMI of 24.8 ± 2.2 kg/m². An enzyme-linked immunosorbent assay was adopted to detect the serum CYTL1 levels, and the correlation between CYTL1 and the severity of KOA was analyzed.

Results

The serum level of CYTL1 was significantly lower in the KOA group than in the control group (P < 0.05). In the KOA group, the difference in the serum level of CYTL1 was statistically significant between the subgroups and decreased significantly with an increase in the severity of the disease (F = 54.826, P < 0.001). Therefore, the serum level of CYTL1 was correlated with the severity of the disease, as determined by the K&L classification system (r = −0.613, P < 0.001).

Conclusion

The serum levels of CYTL1 are strongly correlated with the severity of the disease in patients with KOA and could be a new therapeutic target for KOA.

Peripheral shift in the viable chondrocyte population of the medial femoral condyle after anterior cruciate ligament injury in the porcine knee

Anterior cruciate ligament injuries result in posttraumatic osteoarthritis in the medial compartment of the knee, even after surgical treatment. How the chondrocyte distribution within the articular cartilage changes early in this process is currently unknown. The study objective was to investigate the chondrocyte distribution within the medial femoral condyle after an anterior cruciate ligament transection in a preclinical model. Forty-two adolescent Yucatan minipigs were allocated to receive unilateral anterior cruciate ligament surgery (n = 36) or no surgery (n = 6). Central coronal sections of the medial femoral condyle were obtained at 1- and 4 weeks after surgery, and the chondrocyte distribution was measured via whole slide imaging and a cell counting batch processing tool utilized in ImageJ. Ki-67 immunohistochemistry was performed to identify proliferating cells. Empty lacunae, karyolysis, karyorrhexis, and pyknosis were used to identify areas of irreversible cell injury. The mean area of irreversible cell injury was 0% in the intact controls, 13.4% (95% confidence interval: 6.4, 20.3) at 1-week post-injury and 19.3% (9.7, 28.9) at 4 weeks post-injury (p < .015). These areas occurred closest to the femoral intra-articular notch. The remaining areas containing viable chondrocytes had Ki-67-positive cells (p < .02) and increased cell density in the middle (p < .03) and deep zones (p = .001). For the entire section, the total chondrocyte number did not change significantly post-operatively; however, the density of cells in the peripheral regions of the medial femoral condyle increased significantly at 1- and 4 weeks post-injury relative to the intact control groups (p = .032 and .004, respectively). These data demonstrate a peripheral shift in the viable chondrocyte population of the medial femoral condyle after anterior cruciate ligament injury and further suggest that chondrocytes with the capacity to proliferate are not confined to one particular cartilage layer.

Bridge-Enhanced Anterior Cruciate Ligament Repair Leads to Greater Limb Asymmetry and Less Cartilage Damage Than Untreated ACL Transection or ACL Reconstruction in the Porcine Model

BACKGROUND

The extent of posttraumatic osteoarthritis (PTOA) in the porcine anterior cruciate ligament (ACL) transection model is dependent on the surgical treatment selected. In a previous study, animals treated with bridge-enhanced ACL repair using a tissue-engineered implant developed less PTOA than those treated with ACL reconstruction (ACLR). Alterations in gait, including asymmetric weightbearing and shorter stance times, have been noted in clinical studies of subjects with osteoarthritis.

HYPOTHESIS

Animals receiving a surgical treatment that results in less PTOA (ie, bridge-enhanced ACL repair) would exhibit fewer longitudinal postoperative gait asymmetries over a 1-year period when compared with treatments that result in greater PTOA (ie, ACLR and ACL transection).

STUDY DESIGN

Controlled laboratory study.

METHODS

Thirty-six Yucatan minipigs underwent ACL transection and were randomized to receive (1) no further treatment, (2) ACLR, or (3) bridge-enhanced ACL repair. Gait analyses were performed preoperatively, and at 4, 12, 26, and 52 weeks postoperatively. Macroscopic cartilage assessments were performed at 52 weeks.

RESULTS

Knees treated with bridge-enhanced ACL repair had less macroscopic damage in the medial tibial plateau than those treated with ACLR or ACL transection (adjusted P = .03 for both comparisons). The knees treated with bridge-enhanced ACL repair had greater asymmetry in hindlimb maximum force and impulse loading at 52 weeks than the knees treated with ACL transection (adjusted P < .05 for both comparisons). Although not significant, there was a trend that knees treated with bridge-enhanced ACL repair had greater asymmetry in hindlimb maximum force and impulse loading (adjusted P < .10 for both comparisons) compared with ACLR.

CONCLUSION

Contrary to our hypothesis, the surgical treatment resulting in less macroscopic cartilage damage (ie, bridge-enhanced ACL repair) exhibited greater asymmetry in load-related gait parameters than the other surgical groups. This finding suggests that increased offloading of the surgical knee may be associated with a slower rate of PTOA development.

CLINICAL RELEVANCE

Less cartilage damage at 52 weeks was found in the surgical group that continued to protect the limb from full body weight during gait. This finding suggests that protection of the knee from maximum stresses may be important in minimizing the development of PTOA in the ACL-injured knee within 1 year.

A Translational Porcine Model for Human Cell-Based Therapies in the Treatment of Posttraumatic Osteoarthritis After Anterior Cruciate Ligament Injury

BACKGROUND

There is a high incidence of posttraumatic osteoarthritis (PTOA) after anterior cruciate ligament (ACL) injury, and these injuries represent an enormous health care economic burden. In an effort to address this unmet clinical need, there has been increasing interest in cell-based therapies.

PURPOSE

To establish a translational large animal model of PTOA and demonstrate the feasibility of intra-articular human cell-based interventions.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Nine Yucatan mini-pigs underwent unilateral ACL transection and were monitored for up to 12 weeks after injury. Interleukin 1 beta (IL-1β) levels and collagen breakdown were evaluated longitudinally using enzyme-linked immunosorbent assays of synovial fluid, serum, and urine. Animals were euthanized at 4 weeks (n = 3) or 12 weeks (n = 3) after injury, and injured and uninjured limbs underwent magnetic resonance imaging (MRI) and histologic analysis. At 2 days after ACL injury, an additional 3 animals received an intra-articular injection of 10⁷ human bone marrow-derived mesenchymal stem cells (hBM-MSCs) combined with a fibrin carrier. These cells were labeled with the luciferase reporter gene (hBM-MSCs-Luc) as well as fluorescent markers and intracellular iron nanoparticles. These animals were euthanized on day 0 (n = 1) or day 14 (n = 2) after injection. hBM-MSC-Luc viability and localization were assessed using ex vivo bioluminescence imaging, fluorescence imaging, and MRI.

RESULTS

PTOA was detected as early as 4 weeks after injury. At 12 weeks after injury, osteoarthritis could be detected grossly as well as on histologic analysis. Synovial fluid analysis showed elevation of IL-1β shortly after ACL injury, with subsequent resolution by 2 weeks after injury. Collagen type II protein fragments were elevated in the synovial fluid and serum after injury. hBM-MSCs-Luc were detected immediately after injection and at 2 weeks after injection using fluorescence imaging, MRI, and bioluminescence imaging.

CONCLUSION

This study demonstrates the feasibility of reproducing the chondral changes, intra-articular cytokine alterations, and body fluid biomarker findings consistent with PTOA after ACL injury in a large animal model. Furthermore, we have demonstrated the ability of hBM-MSCs to survive and express transgene within the knee joint of porcine hosts without immunosuppression for at least 2 weeks.

CLINICAL RELEVANCE

This model holds great potential to significantly contribute to investigations focused on the development of cell-based therapies for human ACL injury-associated PTOA in the future (see Appendix Figure A1, available online).

Proteolysis and cartilage development are activated in the synovium after surgical induction of post traumatic osteoarthritis

Anterior cruciate ligament (ACL) transection surgery in the minipig induces post-traumatic osteoarthritis (PTOA) in a pattern similar to that seen in human patients after ACL injury. Prior studies have reported the presence of cartilage matrix-degrading proteases, such as Matrix metalloproteinase-1 (MMP-1) and A disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS-4), in the synovial fluid of injured or arthritic joints; however, the tissue origin of these proteases is unknown. The objective of this study was to identify transcriptional processes activated in the synovium after surgical induction of PTOA with ACL transection, and to determine if processes associated with proteolysis were enriched in the synovium after ACL transection. Unilateral ACL transection was performed in adolescent Yucatan minipigs and synovium samples were collected at 1, 5, 9, and 14 days post-injury. Transcriptome-wide gene expression levels were determined using bulk RNA-Sequencing in the surgical animals and control animals with healthy knees. The greatest number of transcripts with significant changes was observed 1 day after injury. These changes were primarily associated with cellular proliferation, consistent with measurements of increased cellularity of the synovium at the two-week time point. At five to 14 days, the expression of transcripts relating to proteolysis and cartilage development was significantly enriched. While protease inhibitor-encoding transcripts (TIMP2, TIMP3) represented the largest fraction of protease-associated transcripts in the uninjured synovium, protease-encoding transcripts (including MMP1, MMP2, ADAMTS4) predominated after surgery. Cartilage development-associated transcripts that are typically not expressed by synovial cells, such as ACAN and COMP, were enriched in the synovium following ACL-transection. The upregulation in both catabolic processes (proteolysis) and anabolic processes (cartilage development) suggests that the synovium plays a complex, balancing role in the early response to PTOA induction.

Cartilage Damage Is Related to ACL Stiffness in a Porcine Model of ACL Repair

Inferior anterior cruciate ligament (ACL) structural properties may inadequately restrain tibiofemoral joint motion following surgery, contributing to the increased risk of post-traumatic osteoarthritis. Using both a direct measure of ACL linear stiffness and an in vivo magnetic resonance imaging (MRI) T₂ *-based prediction model, we hypothesized that cartilage damage and ACL stiffness would increase over time, and that an inverse relationship between cartilage damage and ACL stiffness would emerge at a later stage of healing. After either 6, 12, or 24 weeks (w) of healing after ACL repair, ACL linear stiffness was determined from the force-displacement relationship during tensile testing ex vivo and predicted in vivo from the MRI T₂ *-based multiple linear regression model in 24 Yucatan minipigs. Tibiofemoral cartilage was graded postmortem. There was no relationship between cartilage damage and ACL stiffness at 6 w (R²  = 0.04; p = 0.65), 12 w (R²  = 0.02; p = 0.77), or when the data from all animals were pooled (R²  = 0.02; p = 0.47). A significant inverse relationship between cartilage damage and ACL stiffness based on both ex vivo measurement (R²  = 0.90; p < 0.001) and in vivo MRI prediction (R²  = 0.78; p = 0.004) of ACL stiffness emerged at 24 w. This result suggests that 90% of the variability in gross cartilage changes is associated with the repaired ACL linear stiffness at 6 months of healing. Clinical Significance: Techniques that provide a higher stiffness to the repaired ACL may be required to mitigate the post-traumatic osteoarthritis commonly seen after ACL injury, and MRI T₂ * can be used as a noninvasive estimation of ligament stiffness. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2249-2257, 2019.

Protein Cytl1: its role in chondrogenesis, cartilage homeostasis, and disease

Cytokine-like protein 1 (Cytl1), also named Protein C17 or C4orf4 is located on human chromosome 4p15-p16 and encodes a polypeptide of 126 amino acid residues that displays characteristics of a secretory protein. Cytl1 is expressed by a sub-population of CD34+ human mononuclear cells from bone marrow and cord blood, and by chondrocytes (cartilage-forming cells). In this review, we explore evidence suggesting that Cytl1 may be involved in the regulation of chondrogenesis, cartilage homeostasis and osteoarthritis progression, accompanied by the modulation of Sox9 and insulin-like growth factor 1 expression. In addition, Cytl1 exhibits chemotactic and pro-angiogenic biological effects. Interestingly, CCR2 (C-C chemokine receptor type 2) has been identified as a likely receptor for Cytl1, which mediates the ERK signalling pathway. Cytl1 also appears to mediate the TGF-beta-Smad signalling pathway, which is hypothetically independent of the CCR2 receptor. More recently, studies have also potentially linked Cytl1 with a variety of conditions including cardiac fibrosis, smoking, alcohol dependence risk, and tumours such as benign prostatic hypertrophy, lung squamous cell carcinoma, neuroblastoma and familial colorectal cancer. Defining the molecular structure of Cytl1 and its role in disease pathogenesis will help us to design therapeutic approaches for Cytl1-associated pathological conditions.

RNA-seq in Skeletal Biology

PURPOSE OF REVIEW

The goal of this paper is to review state-of-the-art transcriptome profiling methods and their recent applications in the field of skeletal biology.

RECENT FINDINGS

Next-generation sequencing of mRNA (RNA-seq) methods have been established and routinely used in skeletal biology research. RNA-seq has led to the identification of novel genes and transcription factors involved in skeletal development and disease, through its application in small and large animal models, as well as human tissue and cells. With the availability of advanced techniques such as single-cell RNA-seq, novel cell types in skeletal tissues are being identified. As the sequencing technologies are rapidly evolving, the exciting discoveries supported by transcriptomics will continue to emerge and improve our understanding of the biology of the skeleton.

Multi-pathway Protective Effects of MicroRNAs on Human Chondrocytes in an In Vitro Model of Osteoarthritis

Osteoarthritis (OA) is the most common degenerative joint disease. One of the main pathogenic factors of OA is thought to be inflammation. Other factors associated with OA are dysregulation of microRNAs, reduced autophagic activity, oxidative stress, and altered metabolism. microRNAs are small non-coding RNAs that are powerful regulators of gene expression. miR-140-5p is considered a cartilage-specific microRNA, is necessary for in vitro chondrogenesis, has anti-inflammatory properties, and is downregulated in osteoarthritic cartilage. Its passenger strand, miR-140-3p, is the most highly expressed microRNA in healthy cartilage and increases during in vitro chondrogenesis. miR-146a is a well-known anti-inflammatory microRNA. Several studies have illustrated its role in OA and autoimmune diseases. We show that, when human chondrocytes were transfected individually with miR-140-5p, miR-140-3p, or miR-146a prior to stimulation with interleukin-1 beta and tumor factor necrosis-alpha as an inflammatory model of OA, each of these microRNAs exhibited similar protective effects. Mass spectrometry analysis provided an insight to the altered proteome. All three microRNAs downregulated important inflammatory mediators. In addition, they affected different proteins belonging to the same biological processes, suggesting an overall inhibition of inflammation and oxidative stress, enhancement of autophagy, and restoration of other homeostatic cellular mechanisms, including metabolism.

RIPK1 suppresses apoptosis mediated by TNF and caspase-3 in intervertebral discs

BACKGROUND

Low back pain has become a serious social and economic burden and the leading cause of disability worldwide. Among a variety of pathophysiological triggers, intervertebral disc (IVD) degeneration plays a primary underlying role in causing such pain. Specifically, multiple independent endplate changes have been implicated in the initiation and progression of IVD degeneration.

METHODS

In this study, we built a signaling network comprising both well-characterized IVD pathology-associated proteins as well as some potentially correlated proteins that have been associated with one or more of the currently known pathology-associated proteins. We then screened for the potential IVD degeneration-associated proteins using patients' normal and degenerative endplate specimens. Short hairpin RNAs for receptor interacting serine/threonine kinase 1 (RIPK1) were constructed to examine the effects of RIPK1 knockdown in primary chondrocyte cells and in animal models of caudal vertebra intervertebral disc degeneration in vivo.

RESULTS

RIPK1 was identified as a potential IVD degeneration-associated protein based on IVD pathology-associated signaling networks and the patients' degenerated endplate specimens. Construction of the short hairpin RNAs was successful, with short-term RIPK1 knockdown triggering inflammation in the primary chondrocytes, while long-term knockdown triggered apoptosis through cleavage of the caspase 3 pathway, down-regulated NF-κB and mitogen-activating protein kinase (MAPK)s cascades, and decreased cell survival and inflammation. Animal models of caudal vertebra intervertebral disc degeneration further demonstrated that apoptosis was induced by up-regulation of tumor necrosis factor (TNF) accompanied by down-regulation of NF-κB and MAPKs cascades that are dependent on caspase and RIPK1.

CONCLUSIONS

These results provide proof-of-concept for developing novel therapies to combat IVD degeneration through interfering with RIPK1-mediated apoptosis signaling pathways especially in patients with RIPK1 abnormality.

Synovial fluid proteome changes in ACL injury-induced posttraumatic osteoarthritis: Proteomics analysis of porcine knee synovial fluid

Surgical transection of the anterior cruciate ligament (ACL) in the porcine model leads to posttraumatic osteoarthritis if left untreated. However, a recently developed surgical treatment, bridge-enhanced ACL repair, prevents further cartilage damage. Since the synovial fluid bathes all the intrinsic structures of knee, we reasoned that a comparative analysis of synovial fluid protein contents could help to better understand the observed chondroprotective effects of the bridge-enhanced ACL repair. We hypothesized that post-surgical changes in the synovial fluid proteome would be different in the untreated and repaired knees, and those changes would correlate with the degree of cartilage damage. Thirty adolescent Yucatan mini-pigs underwent unilateral ACL transection and were randomly assigned to either no further treatment (ACLT, n = 14) or bridge-enhanced ACL repair (BEAR, n = 16). We used an isotopically labeled high resolution LC MS/MS-based proteomics approach to analyze the protein profile of synovial fluid at 6 and 12 months after ACL transection in untreated and repaired porcine knees. A linear mixed effect model was used to compare the normalized protein abundance levels between the groups at each time point. Bivariate linear regression analyses were used to assess the correlations between the macroscopic cartilage damage (total lesion area) and normalized abundance levels of each of the identified secreted proteins. There were no significant differences in cartilage lesion area or quantitative abundance levels of the secreted proteins between the ACLT and BEAR groups at 6 months. However, by 12 months, greater cartilage damage was seen in the ACLT group compared to the BEAR group (p = 0.005). This damage was accompanied by differences in the abundance levels of secreted proteins, with higher levels of Vitamin K-dependent protein C (p = 0.001), and lower levels of Apolipoprotein A4 (p = 0.021) and Cartilage intermediate layer protein 1 (p = 0.049) in the ACLT group compared to the BEAR group. There were also group differences in the secreted proteins that significantly changed in abundance between 6 and 12 months in ACLT and BEAR knees. Increased concentration of Ig lambda-1 chain C regions and decreased concentration of Hemopexin, Clusterin, Coagulation factor 12 and Cartilage intermediate layer protein 1 were associated with greater cartilage lesion area. In general, ACLT knees had higher concentrations of pro-inflammatory proteins and lower concentrations of anti-inflammatory proteins than BEAR group. In addition, the ACLT group had a lower and declining synovial concentrations of CILP, in contrast to a consistently high abundance of CILP in repaired knees. These differences suggest that the knees treated with bridge-enhanced ACL repair may be maintaining an environment that is more protective of the extracellular matrix, a function which is not seen in the ACLT knees.

Articular cartilage gene expression patterns in the tissue surrounding the impact site following applications of shear and axial loads

BACKGROUND

Osteoarthritis is a degradative joint disease found in humans and commercial swine which can develop from a number of factors, including prior joint trauma. An impact injury model was developed to deliver in vitro loads to disease-free porcine patellae in a model of OA.

METHODS

Axial impactions (2000 N normal) and shear impactions (500 N normal with induced shear forces) were delivered to 48 randomly assigned patellae. The patellae were then cultured for 0, 3, 7, or 14 days following the impact. Specimens in the tissue surrounding the loading site were harvested and expression of 18 OA related genes was studied via quantitative PCR. The selected genes were previously identified from published work and fell into four categories: cartilage matrix, degradative enzymes, inflammatory response, and apoptosis.

RESULTS

Type II collagen (Col2a1) showed significantly lower expression in shear vs. axial adjacent tissue at day 0 and 7 (fold changes of 0.40 & 0.19, respectively). In addition, higher expression of degradative enzymes and Fas, an apoptosis gene, was observed in the shear specimens.

CONCLUSIONS

The results suggest that a more physiologically valid shear load may induce more damage to surrounding articular cartilage than a normal load alone.

Identification of transcription factors responsible for dysregulated networks in human osteoarthritis cartilage by global gene expression analysis

OBJECTIVE

Osteoarthritis (OA) is the most prevalent joint disease. As disease-modifying therapies are not available, novel therapeutic targets need to be discovered and prioritized for their importance in mediating the abnormal phenotype of cells in OA-affected joints. Here, we generated a genome-wide molecular profile of OA to elucidate regulatory mechanisms of OA pathogenesis and to identify possible therapeutic targets using integrative analysis of mRNA-sequencing data obtained from human knee cartilage.

DESIGN

RNA-sequencing (RNA-seq) was performed on 18 normal and 20 OA human knee cartilage tissues. RNA-seq datasets were analysed to identify genes, pathways and regulatory networks that were dysregulated in OA.

RESULTS

RNA-seq data analysis revealed 1332 differentially expressed (DE) genes between OA and non-OA samples, including known and novel transcription factors (TFs). Pathway analysis identified 15 significantly perturbed pathways in OA with ECM-related, PI3K-Akt, HIF-1, FoxO and circadian rhythm pathways being the most significantly dysregulated. We selected DE TFs that are enriched for regulating DE genes in OA and prioritized these TFs by creating a cartilage-specific interaction subnetwork. This analysis revealed eight TFs, including JUN, Early growth response (EGR)1, JUND, FOSL2, MYC, KLF4, RELA, and FOS that both target large numbers of dysregulated genes in OA and are themselves suppressed in OA.

CONCLUSIONS

We identified a novel subnetwork of dysregulated TFs that represent new mediators of abnormal gene expression and promising therapeutic targets in OA.

Transcriptional profiling of synovium in a porcine model of early post-traumatic osteoarthritis

To determine the transcriptional profile of synovium during the molecular phase of post-traumatic osteoarthritis, anterior cruciate ligament transections (ACL) were performed in 36 Yucatan minipigs. Equal numbers were randomly assigned to no further treatment, ACL reconstruction or repair. Perimeniscal synovium for histopathology and RNA-sequencing was harvested at 1 and 4 weeks post-operatively and from six healthy control animals. Microscopic synovitis scores significantly worsened at 1 (p < 0.001) and 4 weeks (p = 0.003) post-surgery relative to controls, and were driven by intimal hyperplasia and increased stromal cellularity without inflammatory infiltrates. Synovitis scores were similar between no treatment, reconstruction, and repair groups (p ≥ 0.668). Relative to no treatment at 1 week, 88 and 367 genes were differentially expressed in the reconstruction and repair groups, respectively (227 and 277 at 4 weeks). Relative to controls and with the treatment groups pooled, 1,683 transcripts were concordantly differentially expressed throughout the post-surgery time-course. Affected pathways included, proteolysis_connective tissue degradation (including upregulations of protease-encoding MMP1, MMP13, and ADAMTS4), and development_cartilage development (including upregulations of ACAN, SOX9, and RUNX2), among others. Using linear regression, significant associations of post-surgery synovial expression levels of 20 genes with the articular cartilage glycosaminoglycan loss were identified. These genes were predominantly related to embryonic skeletal system development and included RUNX2. In conclusion, this study confirmed an increased synovial expression of genes that may serve as targets to prevent cartilage degradation, including MMP1, MMP13, and ADAMTS4, in knees with microscopic synovitis and cartilage proteoglycan loss. Attractive novel targets include regulators of embryonic developmental processes in synovium. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.