New approach to testing treatments for osteoarthritis: FastOA.

Animal models of post traumatic osteoarthritis have shown many promising treatments for disease, but human trials have mostly failed to identify effective treatments. This viewpoint suggests that the frequent failure of drug and treatment development in osteoarthritis is due, in part, to the advanced stage of disease of patients in trials and suggests that mirroring the animal model approach might be more successful. It suggests a path forward by enriching trial enrollees with those likely to develop post traumatic OA quickly.

Senescent cell population with ZEB1 transcription factor as its main regulator promotes osteoarthritis in cartilage and meniscus.

OBJECTIVES: Single-cell level analysis of articular cartilage and meniscus tissues from human healthy and osteoarthritis (OA) knees. METHODS: Single-cell RNA sequencing (scRNA-seq) analyses were performed on articular cartilage and meniscus tissues from healthy (n=6, n=7) and OA (n=6, n=6) knees. Expression of genes of interest was validated using immunohistochemistry and RNA-seq and function was analysed by gene overexpression and depletion. RESULTS: scRNA-seq analyses of human knee articular cartilage (70 972 cells) and meniscus (78 017 cells) identified a pathogenic subset that is shared between both tissues. This cell population is expanded in OA and has strong OA and senescence gene signatures. Further, this subset has critical roles in extracellular matrix (ECM) and tenascin signalling and is the dominant sender of signals to all other cartilage and meniscus clusters and a receiver of TGFß signalling. Fibroblast activating protein (FAP) is also a dysregulated gene in this cluster and promotes ECM degradation. Regulons that are controlled by transcription factor ZEB1 are shared between the pathogenic subset in articular cartilage and meniscus. In meniscus and cartilage cells, FAP and ZEB1 promote expression of genes that contribute to OA pathogenesis, including senescence. CONCLUSIONS: These single-cell studies identified a senescent pathogenic cell cluster that is present in cartilage and meniscus and has FAP and ZEB1 as main regulators which are novel and promising therapeutic targets for OA-associated pathways in both tissues.

Human-specific duplicate CHRFAM7A gene is associated with more severe osteoarthritis and amplifies pain behaviours.

OBJECTIVES: CHRFAM7A is a uniquely human fusion gene that functions as a dominant negative regulator of alpha 7 acetylcholine nicotinic receptor (α7nAChR) in vitro. This study determined the impact of CHRFAM7A on α7nAChR agonist responses, osteoarthritis (OA) severity and pain behaviours and investigated mechanisms. METHODS: Transgenic CHRFAM7A (TgCHRFAM7A) mice were used to determine the impact of CHRFAM7A on knee OA histology, pain severity in OA and other pain models, response to nAchR agonist and IL-1ß. Mouse and human cells were used for mechanistic studies. RESULTS: Transgenic (Tg) TgCHRFAM7A mice developed more severe structural damage and increased mechanical allodynia than wild type (WT) mice in the destabilisation of medial meniscus model of OA. This was associated with a decreased suppression of inflammation by α7nAchR agonist. TgCHRFAM7A mice displayed a higher basal sensitivity to pain stimuli and increased pain behaviour in the monoiodoacetate and formalin models. Dorsal root ganglia of TgCHRFAM7A mice showed increased macrophage infiltration and expression of the chemokine fractalkine and also had a compromised antinociceptive response to the α7nAchR agonist nicotine. Both native CHRNA7 and CHRFAM7A subunits were expressed in human joint tissues and the CHRFAM7A/CHRNA7 ratio was increased in OA cartilage. Human chondrocytes with two copies of CHRFAM7A had reduced anti-inflammatory responses to nicotine. CONCLUSION: CHRFAM7A is an aggravating factor for OA-associated inflammation and tissue damage and a novel genetic risk factor and therapeutic target for pain.

Targeting FoxO transcription factors with HDAC inhibitors for the treatment of osteoarthritis.

OBJECTIVES: Osteoarthritis (OA) features ageing-related defects in cellular homeostasis mechanisms in articular cartilage. These defects are associated with suppression of forkhead box O (FoxO) transcription factors. FoxO1 or FoxO3 deficient mice show early onset OA while FoxO1 protects against oxidative stress in chondrocytes and promotes expression of autophagy genes and the essential joint lubricant proteoglycan 4 (PRG4). The objective of this study was to identify small molecules that can increase FoxO1 expression. METHODS: We constructed a reporter cell line with FoxO1 promoter sequences and performed high-throughput screening (HTS) of the Repurposing, Focused Rescue and Accelerated Medchem (ReFRAME) library . Hits from the HTS were validated and function was assessed in human chondrocytes, meniscus cells and synoviocytes and following administration to mice. The most promising hit, the histone deacetylase inhibitor (HDACI) panobinostat was tested in a murine OA model. RESULTS: Among the top hits were HDACI and testing in human chondrocytes, meniscus cells and synoviocytes showed that panobinostat was the most promising compound as it increased the expression of autophagy genes and PRG4 while suppressing the basal and IL-1ß induced expression of inflammatory mediators and extracellular matrix degrading enzymes. Intraperitoneal administration of panobinostat also suppressed the expression of mediators of OA pathogenesis induced by intra-articular injection of IL-1ß. In a murine OA model, panobinostat reduced the severity of histological changes in cartilage, synovium and subchondral bone and improved pain behaviours. CONCLUSION: Panobinostat has a clinically relevant activity profile and is a candidate for OA symptom and structure modification.

FOXO1 and FOXO3 transcription factors have unique functions in meniscus development and homeostasis during aging and osteoarthritis.

The objective of this study was to examine FoxO expression and FoxO function in meniscus. In menisci from human knee joints with osteoarthritis (OA), FoxO1 and 3 expression were significantly reduced compared with normal menisci from young and old normal donors. The expression of FoxO1 and 3 was also significantly reduced in mouse menisci during aging and OA induced by surgical meniscus destabilization or mechanical overuse. Deletion of FoxO1 and combined FoxO1, 3, and 4 deletions induced abnormal postnatal meniscus development in mice and these mutant mice spontaneously displayed meniscus pathology at 6 mo. Mice with Col2Cre-mediated deletion of FoxO3 or FoxO4 had normal meniscus development but had more severe aging-related damage. In mature AcanCreERT2 mice, the deletion of FoxO1, 3, and 4 aggravated meniscus lesions in all experimental OA models. FoxO deletion suppressed autophagy and antioxidant defense genes and altered several meniscus-specific genes. Expression of these genes was modulated by adenoviral FoxO1 in cultured human meniscus cells. These results suggest that FoxO1 plays a key role in meniscus development and maturation, and both FoxO1 and 3 support homeostasis and protect against meniscus damage in response to mechanical overuse and during aging and OA.

Krüppel-like factor-4 and Krüppel-like factor-2 are important regulators of joint tissue cells and protect against tissue destruction and inflammation in osteoarthritis.

OBJECTIVES: Analysing expression patterns of Krüppel-like factor (KLF) transcription factors in normal and osteoarthritis (OA) human cartilage, and determining functions and mechanisms of KLF4 and KLF2 in joint homoeostasis and OA pathogenesis. METHODS: Experimental approaches included human joint tissues cells, transgenic mice and mouse OA model with viral KLF4 gene delivery to demonstrate therapeutic benefit in structure and pain improvement. Mechanistic studies applied global gene expression analysis and chromatin immunoprecipitation sequencing (ChIP-seq). RESULTS: Several KLF genes were significantly decreased in OA cartilage. Among them, KLF4 and KLF2 were strong inducers of cartilage collagen genes and Proteoglycan-4. Cartilage-specific deletion of Klf2 in mature mice aggravated severity of experimental OA. Transduction of human chondrocytes with Adenovirus (Ad) expressing KLF4 or KLF2 enhanced expression of major cartilage extracellular matrix (ECM) genes and SRY-box transcription factor-9, and suppressed mediators of inflammation and ECM-degrading enzymes. Ad-KLF4 and Ad-KLF2 enhanced similar protective functions in meniscus cells and synoviocytes, and promoted chondrocytic differentiation of human mesenchymal stem cells. Viral KLF4 delivery into mouse knees reduced severity of OA-associated changes in cartilage, meniscus and synovium, and improved pain behaviours. ChIP-seq analysis suggested that KLF4 directly bound cartilage signature genes. Ras-related protein-1 signalling was the most enriched pathway in KLF4-transduced cells, and its signalling axis was involved in upregulating cartilage ECM genes by KLF4 and KLF2. CONCLUSIONS: KLF4 and KLF2 may be central transcription factors that increase protective and regenerative functions in joint tissue cells, suggesting that KLF gene transfer or molecules upregulating KLFs are therapeutic candidates for OA.

FOXO1 transcription factor regulates chondrogenic differentiation through transforming growth factor ß1 signaling.

The forkhead box O (FOXO) proteins are transcription factors involved in the differentiation of many cell types. Type II collagen (Col2) Cre-Foxo1-knockout and Col2-Cre-Foxo1,3,4 triple-knockout mice exhibit growth plate malformation. Moreover, recent studies have reported that in some cells, the expressions and activities of FOXOs are promoted by transforming growth factor ß1 (TGFß1), a growth factor playing a key role in chondrogenic differentiation. Here, using a murine chondrogenic cell line (ATDC5), mouse embryos, and human mesenchymal stem cells, we report the mechanisms by which FOXOs affect chondrogenic differentiation. FOXO1 expression increased along with chondrogenic differentiation, and FOXO1 inhibition suppressed chondrogenic differentiation. TGFß1/SMAD signaling promoted expression and activity of FOXO1. In ATDC5, FOXO1 knockdown suppressed expression of sex-determining region Y box 9 (Sox9), a master regulator of chondrogenic differentiation, resulting in decreased collagen type II α1 (Col2a1) and aggrecan (Acan) expression after TGFß1 treatment. On the other hand, chemical FOXO1 inhibition suppressed Col2a1 and Acan expression without suppressing Sox9 To investigate the effects of FOXO1 on chondrogenic differentiation independently of SOX9, we examined FOXO1's effects on the cell cycle. FOXO1 inhibition suppressed expression of p21 and cell-cycle arrest in G0/G1 phase. Conversely, FOXO1 overexpression promoted expression of p21 and cell-cycle arrest. FOXO1 inhibition suppressed expression of nascent p21 RNA by TGFß1, and FOXO1 bound the p21 promoter. p21 inhibition suppressed expression of Col2a1 and Acan during chondrogenic differentiation. These results suggest that FOXO1 is necessary for not only SOX9 expression, but also cell-cycle arrest during chondrogenic differentiation via TGFß1 signaling.

Bioactive proteins delivery through core-shell nanofibers for meniscal tissue regeneration.

Mimicking the ultrastructural morphology of the meniscus with nanofiber scaffolds, coupled with controlled growth-factor delivery to the appropriate cells, can help engineer tissue with the potential to grow, mature, and regenerate after in vivo implantation. We electrospun nanofibers encapsulating platelet-derived growth factor (PDGF-BB), which is a potent mitogen and chemoattractant in a core of serum albumin contained within a shell of polylactic acid. We controlled the local PDGF-BB release by adding water-soluble polyethylene glycol to the polylactic acid shell to serve as a porogen. The novel core-shell nanofibers generated 3D scaffolds with an interconnected macroporous structure, with appropriate mechanical properties and with high cell compatibility. Incorporating PDGF-BB increased cell viability, proliferation, and infiltration, and upregulated key genes involved in meniscal extracellular matrix synthesis in human meniscal and synovial cells. Our results support proof of concept that these core-shell nanofibers can create a cell-favorable nanoenvironment and can serve as a system for sustained release of bioactive factors.

Gene targeting of the transcription factor Mohawk in rats causes heterotopic ossification of Achilles tendon via failed tenogenesis.

Cell-based or pharmacological approaches for promoting tendon repair are currently not available because the molecular mechanisms of tendon development and healing are not well understood. Although analysis of knockout mice provides many critical insights, small animals such as mice have some limitations. In particular, precise physiological examination for mechanical load and the ability to obtain a sufficient number of primary tendon cells for molecular biology studies are challenging using mice. Here, we generated Mohawk (Mkx)(-/-) rats by using CRISPR/Cas9, which showed not only systemic hypoplasia of tendons similar to Mkx(-/-) mice, but also earlier heterotopic ossification of the Achilles tendon compared with Mkx(-/-) mice. Analysis of tendon-derived cells (TDCs) revealed that Mkx deficiency accelerated chondrogenic and osteogenic differentiation, whereas Mkx overexpression suppressed chondrogenic, osteogenic, and adipogenic differentiation. Furthermore, mechanical stretch stimulation of Mkx(-/-) TDCs led to chondrogenic differentiation, whereas the same stimulation in Mkx(+/+) TDCs led to formation of tenocytes. ChIP-seq of Mkx overexpressing TDCs revealed significant peaks in tenogenic-related genes, such as collagen type (Col)1a1 and Col3a1, and chondrogenic differentiation-related genes, such as SRY-box (Sox)5, Sox6, and Sox9 Our results demonstrate that Mkx has a dual role, including accelerating tendon differentiation and preventing chondrogenic/osteogenic differentiation. This molecular network of Mkx provides a basis for tendon physiology and tissue engineering.

Extracellular vesicles in cartilage homeostasis and osteoarthritis.

PURPOSE OF REVIEW: Extracellular vesicles carry bioactive molecules that can be transferred between cells and tissues. The purpose of this review is to describe how extracellular vesicles regulate functions of cells in cartilage and other joint tissues. The potential application of extracellular vesicles in the treatment of osteoarthritis and as biomarkers will also be discussed. RECENT FINDINGS: Extracellular vesicles are found in synovial fluid, in articular cartilage and in the supernatants of synoviocytes and chondrocytes. Extracellular vesicles in cartilage have been proposed to be involved in cross talk between cells in joint tissues and to affect extracellular matrix turnover and inflammation. Extracellular vesicles from arthritic joints can promote abnormal gene expression and changes in cartilage extracellular matrix, including abnormal mineralization. Promising results were obtained in the therapeutic application of mesenchymal stem cell-derived extracellular vesicles for cartilage repair and experimental osteoarthritis. SUMMARY: Extracellular vesicles have emerged as vehicles for the exchange of bioactive signaling molecules within cartilage and between joint tissues to promote joint homeostasis and arthritis pathogenesis. As the molecular content of extracellular vesicles can be customized, they offer utility in therapeutic applications.

MicroRNA-140 plays dual roles in both cartilage development and homeostasis.

Osteoarthritis (OA), the most prevalent aging-related joint disease, is characterized by insufficient extracellular matrix synthesis and articular cartilage degradation, mediated by several proteinases, including Adamts-5. miR-140 is one of a very limited number of noncoding microRNAs (miRNAs) specifically expressed in cartilage; however, its role in development and/or tissue maintenance is largely uncharacterized. To examine miR-140 function in tissue development and homeostasis, we generated a mouse line through a targeted deletion of miR-140. miR-140(-/-) mice manifested a mild skeletal phenotype with a short stature, although the structure of the articular joint cartilage appeared grossly normal in 1-mo-old miR-140(-/-) mice. Interestingly, miR-140(-/-) mice showed age-related OA-like changes characterized by proteoglycan loss and fibrillation of articular cartilage. Conversely, transgenic (TG) mice overexpressing miR-140 in cartilage were resistant to antigen-induced arthritis. OA-like changes in miR-140-deficient mice can be attributed, in part, to elevated Adamts-5 expression, regulated directly by miR-140. We show that miR-140 regulates cartilage development and homeostasis, and its loss contributes to the development of age-related OA-like changes.

Relevance of meniscal cell regional phenotype to tissue engineering.

PURPOSE: Meniscus contains heterogeneous populations of cells that have not been fully characterized. Cell phenotype is often lost during culture; however, culture expansion is typically required for tissue engineering. We examined and compared cell-surface molecule expression levels on human meniscus cells from the vascular and avascular regions and articular chondrocytes while documenting changes during culture-induced dedifferentiation. MATERIALS AND METHODS: Expressions of 16 different surface molecules were examined by flow cytometry after monolayer culture for 24 h, 1 week, and 2 weeks. Menisci were also immunostained to document the spatial distributions of selected surface molecules. RESULTS: Meniscus cells and chondrocytes exhibited several similarities in surface molecule profiles with dynamic changes during culture. A greater percentage of meniscal cells were positive for CD14, CD26, CD49c, and CD49f compared to articular chondrocytes. Initially, more meniscal cells from the vascular region were positive for CD90 compared to cells from the avascular region or chondrocytes. Cells from the vascular region also expressed higher levels of CD166 and CD271 compared to cells from the avascular region. CD90, CD166, and CD271-positive cells were predominately perivascular in location. However, CD166-positive cells were also located in the superficial layer and in the adjacent synovial and adipose tissue. CONCLUSIONS: These surface marker profiles provide a target phenotype for differentiation of progenitors in tissue engineering. The spatial location of progenitor cells in meniscus is consistent with higher regenerative capacity of the vascular region, while the surface progenitor subpopulations have potential to be utilized in tears created in the avascular region.

Glucosamine activates autophagy in vitro and in vivo.

OBJECTIVE: Aging-associated changes in articular cartilage represent a main risk factor for osteoarthritis (OA). Autophagy is an essential cellular homeostasis mechanism. Aging-associated or experimentally induced defects in autophagy contribute to organismal- and tissue-specific aging, while enhancement of autophagy may protect against certain aging-related pathologies such as OA. The objective of this study was to determine whether glucosamine can activate autophagy. METHODS: Chondrocytes from normal human articular cartilage were treated with glucosamine (0.1- 10 mM). Autophagy activation and phosphorylation levels of Akt, FoxO3, and ribosomal protein S6 were determined by Western blotting. Autophagosome formation was analyzed by confocal microscopy. Reporter mice systemically expressing green fluorescent protein (GFP) fused to light chain 3 (LC3) (GFP-LC3-transgenic mice) were used to assess changes in autophagy in response to starvation and glucosamine treatment. RESULTS: Glucosamine treatment of chondrocytes activated autophagy, as indicated by increased LC3-II levels, formation of LC3 puncta, and increased LC3 turnover. This was associated with glucosamine-mediated inhibition of the Akt/FoxO3/mammalian target of rapamycin pathway. Administration of glucosamine to GFP-LC3-transgenic mice markedly activated autophagy in articular cartilage. CONCLUSION: Glucosamine modulates molecular targets of the autophagy pathway in vitro and in vivo, and the enhancement of autophagy is mainly dependent on the Akt/FoxO/mTOR pathway. These findings suggest that glucosamine is an effective autophagy activator and should motivate future studies on the efficacy of glucosamine in modifying aging-related cellular changes and supporting joint health.

Transcription factor Mohawk and the pathogenesis of human anterior cruciate ligament degradation.

OBJECTIVE: To investigate the expression and function of Mohawk (MKX) in human adult anterior cruciate ligament (ACL) tissue and ligament cells from normal and osteoarthritis (OA)-affected knees. METHODS: Knee joints were obtained at autopsy (within 24-48 hours postmortem) from 13 donors with normal knees (mean ± SD age 36.9 ± 11.0 years), 16 donors with knee OA (age 79.7 ± 11.4 years), and 8 aging donors without knee OA (age 76.9 ± 12.9 years). All cartilage surfaces were graded macroscopically. MKX expression was analyzed by immunohistochemistry and quantitative polymerase chain reaction. ACL-derived cells were used to study regulation of MKX expression by interleukin-1ß (IL-1ß). MKX was knocked down with small interfering RNA (siRNA) to analyze the function of MKX in extracellular matrix (ECM) production and differentiation in ACL-derived cells. RESULTS: The expression of MKX was significantly decreased in ACL-derived cells from OA knees compared with normal knees. Consistent with this finding, immunohistochemistry analysis showed that MKX-positive cells were significantly reduced in ACL tissue from OA donors, in particular in cells located in disorientated fibers. In ACL-derived cells, IL-1ß strongly suppressed MKX expression and reduced expression of the ligament ECM genes COL1A1 and TNXB. In contrast, SOX9, a chondrocyte master transcription factor, was up-regulated by IL-1ß treatment. Importantly, knockdown of MKX expression with siRNA up-regulated SOX9 expression in ACL-derived cells, whereas the expression of COL1A1 and TNXB was reduced. CONCLUSION: Reduced expression of MKX is a feature of degenerated ACL in OA-affected joints, and this may be mediated in part by IL-1ß. MKX appears necessary to maintain the tissue-specific cellular differentiation status and ECM production in adult human tendons and ligaments.

Zone-specific gene expression patterns in articular cartilage.

OBJECTIVE: To identify novel genes and pathways specific to the superficial zone (SZ), middle zone (MZ), and deep zone (DZ) of normal articular cartilage. METHODS: Articular cartilage was obtained from the knees of 4 normal human donors. The cartilage zones were dissected on a microtome. RNA was analyzed on human genome arrays. The zone-specific DNA array data obtained from human tissue were compared to array data obtained from bovine cartilage. Genes differentially expressed between zones were evaluated using direct annotation for structural or functional features, and by enrichment analysis for integrated pathways or functions. RESULTS: The greatest differences in genome-wide RNA expression data were between the SZ and DZ in both human and bovine cartilage. The MZ, being a transitional zone between the SZ and DZ, thereby shared some of the same pathways as well as structural/functional features of the adjacent zones. Cellular functions and biologic processes that were enriched in the SZ relative to the DZ included, most prominently, extracellular matrix-receptor interactions, cell adhesion molecule functions, regulation of actin cytoskeleton, ribosome-related functions, and signaling aspects such as the IFN, IL4, Cdc42/Rac, and JAK/STAT signaling pathways. Two pathways were enriched in the DZ relative to the SZ, including PPARG and EGFR/SMRTE. CONCLUSION: These differences in cartilage zonal gene expression identify new markers and pathways that govern the unique differentiation status of chondrocyte subpopulations.

Shared and Compartment-Specific Processes in Nucleus Pulposus and Annulus Fibrosus During Intervertebral Disc Degeneration.

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) is 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, depletion of cell subsets involved in maintenance of healthy IVD is observed, specifically the immature cell subsets - fibroblast progenitors and stem cells - indicative of an impairment of normal tissue self-renewal. Tissue-specific changes are also identified. In NP, several fibrotic populations are increased in degenerated IVD, indicating tissue-remodeling. In degenerated AF, a novel disease-associated subset is identified, which expresses disease-promoting genes. It is associated with pathogenic biological processes and the main gene regulatory networks include thrombospondin signaling and FOXO1 transcription factor. In NP and AF cells thrombospondin protein promoted expression of genes associated with TGFß/fibrosis signaling, angiogenesis, and nervous system development. The 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.

vSPACE: Exploring Virtual Spatial Representation of Articular Chondrocytes at the Single-Cell Level.

Single cell RNA sequencing technology has been dramatically changing how gene expression studies are performed. However, its use has been limited to identifying subtypes of cells by comparing cells' gene expression levels in an unbiased manner to produce a 2D plot (e.g., UMAP/tSNE). We developed a new method of placing cells in 2D space. This system, called vSPACE, shows a virtual spatial representation of scRNAseq data obtained from human articular cartilage by emulating the concept of spatial transcriptomics technology, but virtually. This virtual 2D plot presentation of human articular cartage cells generates several zonal distribution patterns, in one or multiple genes at a time, reveling patterns that scientists can appreciate as imputed spatial distribution patterns along the zonal axis. The discovered patterns are explainable and remarkably consistent across all six healthy doners despite their respectively different clinical variables (age and sex), suggesting the confidence of the discovered patterns.

Histopathological changes in the human posterior cruciate ligament during aging and osteoarthritis: correlations with anterior cruciate ligament and cartilage changes.

OBJECTIVES: To determine the histological patterns of posterior cruciate ligament (PCL) degeneration during aging and in relation to changes in articular cartilage and anterior cruciate ligament (ACL) across the entire adult age spectrum. METHODS: Human knee joints (n=120 from 65 donors) were processed within 72 h of postmortem. Articular cartilage surfaces were graded macroscopically. Each PCL was histologically evaluated for inflammation, mucinous changes, chondroid metaplasia, cystic changes and orientation of collagen fibres. The severity of PCL degeneration was classified as normal, mild, moderate or severe. PCL scores were compared to ACL and cartilage scores from the same knees. RESULTS: All knees had intact PCL. Histologically, 6% were normal, 76% showed mild, 12% moderate and 9% severe degeneration. Fibre disorientation was the most prevalent and severe change. Histological grades of PCL and ACL correlated, but significantly fewer PCL than ACL showed severe changes. There was a weaker correlation between aging and total histological PCL scores (R=0.26) compared to aging and ACL scores (R=0.42). ACL scores correlated with cartilage scores (R=0.54) while PCL scores increased with the severity of osteoarthritis from grades 0 to III but not between osteoarthritis grades III-IV (R=0.32). In knees with ruptured ACL, the PCL scores correlated with cartilage scores of the lateral compartment. CONCLUSIONS: PCL histopathological changes were less severe than in the ACL. PCL degeneration was associated with ACL and cartilage damage. The lack of correlation with age indicates independent pathways for PCL versus ACL degeneration.

Anterior cruciate ligament changes in the human knee joint in aging and osteoarthritis.

OBJECTIVE: The development and patterns of spontaneous age-related changes in the anterior cruciate ligament (ACL) and their relationship to articular cartilage degeneration are not well characterized. This study was undertaken to investigate the types and temporal sequence of age-related ACL changes and to determine their correlation with cartilage lesion patterns at all stages of osteoarthritis (OA) development in human knee joints without prior joint trauma. METHODS: Human knee joints (n = 120 from 65 donors ages 23-92) were obtained at autopsy, and ACLs and cartilage were graded macroscopically and histologically. Inflammation surrounding the ACL was assessed separately. RESULTS: Histologic ACL substance scores and ligament sheath inflammation scores increased with age. Collagen fiber disorganization was the earliest and most prevalent change. The severity of mucoid degeneration and chondroid metaplasia in the ACL increased with the development of cartilage lesions. A correlation between ACL degeneration and cartilage degeneration was observed, especially in the medial compartment of the knee joint. CONCLUSION: Our findings indicate that ACL degeneration is highly prevalent in knees with cartilage defects and may even precede cartilage changes. Hence, ACL deficiencies may not only be important in posttraumatic OA, but may also be a feature associated with knee OA pathogenesis in general.

Extracellular sulfatases support cartilage homeostasis by regulating BMP and FGF signaling pathways.

The balance between anabolic and catabolic signaling pathways is critical in maintaining cartilage homeostasis and its disturbance contributes to joint diseases such as osteoarthritis (OA). A unique mechanism that modulates the activity of cell signaling pathways is controlled by extracellular heparan endosulfatases Sulf-1 and Sulf-2 (Sulfs) that are overexpressed in OA cartilage. This study addressed the role of Sulfs in cartilage homeostasis and in regulating bone morphogenetic protein (BMP)/Smad and fibroblast growth factor (FGF)/Erk signaling in articular cartilage. Spontaneous cartilage degeneration and surgically induced OA were significantly more severe in Sulf-1(-/-) and Sulf-2(-/-) mice compared with wild-type mice. MMP-13, ADAMTS-5, and the BMP antagonist noggin were elevated whereas col2a1 and aggrecan were reduced in cartilage and chondrocytes from Sulf(-/-) mice. Articular cartilage and cultured chondrocytes from Sulf(-/-) mice showed reduced Smad1 protein expression and Smad1/5 phosphorylation, whereas Erk1/2 phosphorylation was increased. In human chondrocytes, Sulfs siRNA reduced Smad phosphorylation but enhanced FGF-2-induced Erk1/2 signaling. These findings suggest that Sulfs simultaneously enhance BMP but inhibit FGF signaling in chondrocytes and maintain cartilage homeostasis. Approaches to correct abnormal Sulf expression have the potential to protect against cartilage degradation and promote cartilage repair in OA.