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 TGFβ/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.

Mocetinostat activates Krüppel-like factor 4 and protects against tissue destruction and inflammation in osteoarthritis

Osteoarthritis (OA) is the most common joint disorder, and disease-modifying OA drugs (DMOADs) represent a major need in OA management. Krüppel-like factor 4 (KLF4) is a central transcription factor upregulating regenerative and protective functions in joint tissues. This study was aimed to identify small molecules activating KLF4 expression and to determine functions and mechanisms of the hit compounds. High-throughput screening (HTS) with 11,948 clinical-stage compounds was performed using a reporter cell line detecting endogenous KLF4 activation. Eighteen compounds were identified through the HTS and confirmed in a secondary screen. After testing in SW1353 chondrosarcoma cells and human chondrocytes, mocetinostat - a class I selective histone deacetylase (HDAC) inhibitor - had the best profile of biological activities. Mocetinostat upregulated cartilage signature genes in human chondrocytes, meniscal cells, and BM-derived mesenchymal stem cells, and it downregulated hypertrophic, inflammatory, and catabolic genes in those cells and synoviocytes. I.p. administration of mocetinostat into mice reduced severity of OA-associated changes and improved pain behaviors. Global gene expression and proteomics analyses revealed that regenerative and protective effects of mocetinostat were dependent on peroxisome proliferator-activated receptor γ coactivator 1-α. These findings show therapeutic and protective activities of mocetinostat against OA, qualifying it as a candidate to be used as a DMOAD.

RNA-binding proteins that are highly expressed and enriched in healthy cartilage but suppressed in osteoarthritis

Objectives: RNA-binding proteins (RBPs) have diverse and essential biological functions, but their role in cartilage health and disease is largely unknown. The objectives of this study were (i) map the global landscape of RBPs expressed and enriched in healthy cartilage and dysregulated in osteoarthritis (OA); (ii) prioritize RBPs for their potential role in cartilage and in OA pathogenesis and as therapeutic targets. Methods: Our published bulk RNA-sequencing (RNA-seq) data of healthy and OA human cartilage, and a census of 1,542 RBPs were utilized to identify RBPs that are expressed in healthy cartilage and differentially expressed (DE) in OA. Next, our comparison of healthy cartilage RNA-seq data to 37 transcriptomes in the Genotype-Tissue Expression (GTEx) database was used to determine RBPs that are enriched in cartilage. Finally, expression of RBPs was analyzed in our single cell RNA-sequencing (scRNA-seq) data from healthy and OA human cartilage. Results: Expression of RBPs was higher than nonRBPs in healthy cartilage. In OA cartilage, 188 RBPs were differentially expressed, with a greater proportion downregulated. Ribosome biogenesis was enriched in the upregulated RBPs, while splicing and transport were enriched in the downregulated. To further prioritize RBPs, we selected the top 10% expressed RBPs in healthy cartilage and those that were cartilage-enriched according to GTEx. Intersecting these criteria, we identified Tetrachlorodibenzodioxin (TCDD) Inducible Poly (ADP-Ribose) Polymerase (TIPARP) as a candidate RBP. TIPARP was downregulated in OA. scRNA-seq data revealed TIPARP was most significantly downregulated in the "pathogenic cluster". Conclusion: Our global analyses reveal expression patterns of RBPs in healthy and OA cartilage. We also identified TIPARP and other RBPs as novel mediators in OA pathogenesis and as potential therapeutic targets.

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-1β. 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.

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 TGFβ 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.

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-1β 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-1β. 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.

Suppression of Autoimmune Rheumatoid Arthritis with Hybrid Nanoparticles That Induce B and T Cell Tolerance to Self-Antigen

Autoimmune diseases affect over 4% of the world's population. Treatments are generally palliative or use broad spectrum immunosuppressants to reduce symptoms and disease progression. In some diseases, antibodies generated to a single autoantigen are the major cause of pathogenic inflammation, suggesting that treatments to induce tolerance to the autoantigen could be therapeutic. Here we report the development of hybrid nanoparticles (NPs) that induce tolerance in both T cells and B cells. The NPs comprise a lipid monolayer encapsulating a PLGA core loaded with rapamycin that promotes development of regulatory T cells (Tregs). The lipid monolayer displays the protein antigen and a ligand of the B cell inhibitory co-receptor CD22 (CD22L) that act together to suppress activation of B cells recognizing the antigen. We demonstrate that the hybrid NPs decorated with ovalbumin (OVA) elicit tolerance to OVA in naı̈ve mice, as judged by low OVA-specific antibody titers after the challenge. In the K/BxN mouse model of rheumatoid arthritis caused by B and T cell-dependent responses to the self-antigen glucose-6-phosphate-isomerase (GPI), we show that GPI hybrid NPs delay development of disease, with some treated mice remaining arthritis-free for 300 days. We provide evidence that the mechanism of rheumatoid arthritis suppression involves induction of B cell tolerance, as measured by low anti-GPI antibodies and decreased plasma cell populations, and T cell tolerance, as measured by increased Tregs. The results show the potential of this versatile NP platform for inducing immune tolerance to a self-antigen and suppressing autoimmune disease.

Urolithin A improves mitochondrial health, reduces cartilage degeneration, and alleviates pain in osteoarthritis

Osteoarthritis (OA) is the most common age‐related joint disorder with no effective therapy. According to the World Health Organization, OA affects over 500 million people and is characterized by degradation of cartilage and other joint tissues, severe pain, and impaired mobility. Mitochondrial dysfunction contributes to OA pathology. However, interventions to rescue mitochondrial defects in human OA are not available. Urolithin A (Mitopure) is a natural postbiotic compound that promotes mitophagy and mitochondrial function and beneficially impacts muscle health in preclinical models of aging and in elderly and middle‐aged humans. Here, we showed that Urolithin A improved mitophagy and mitochondrial respiration in primary chondrocytes from joints of both healthy donors and OA patients. Furthermore, Urolithin A reduced disease progression in a mouse model of OA, decreasing cartilage degeneration, synovial inflammation, and pain. These improvements were associated with increased mitophagy and mitochondrial content, in joints of OA mice. These findings indicate that UA promotes joint mitochondrial health, alleviates OA pathology, and supports Urolithin A's potential to improve mobility with beneficial effects on structural damage in joints.

The mechanosensitive ion channel PIEZO1 is expressed in tendons and regulates physical performance

How mechanical stress affects physical performance via tendons is not fully understood. Piezo1 is a mechanosensitive ion channel, and E756del PIEZO1 was recently found as a gain-of-function variant that is common in individuals of African descent. We generated tendon-specific knock-in mice using R2482H Piezo1, a mouse gain-of-function variant, and found that they had higher jumping abilities and faster running speeds than wild-type or muscle-specific knock-in mice. These phenotypes were associated with enhanced tendon anabolism via an increase in tendon-specific transcription factors, Mohawk and Scleraxis, but there was no evidence of changes in muscle. Biomechanical analysis showed that the tendons of R2482H Piezo1 mice were more compliant and stored more elastic energy, consistent with the enhancement of jumping ability. These phenotypes were replicated in mice with tendon-specific R2482H Piezo1 replacement after tendon maturation, indicating that PIEZO1 could be a target for promoting physical performance by enhancing function in mature tendon. The frequency of E756del PIEZO1 was higher in sprinters than in population-matched nonathletic controls in a small Jamaican cohort, suggesting a similar function in humans. Together, this human and mouse genetic and physiological evidence revealed a critical function of tendons in physical performance, which is tightly and robustly regulated by PIEZO1 in tenocytes.

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.

Mohawk is a transcription factor that promotes meniscus cell phenotype and tissue repair and reduces osteoarthritis severity

Meniscus tears are common knee injuries and a major osteoarthritis (OA) risk factor. Knowledge gaps that limit the development of therapies for meniscus injury and degeneration concern transcription factors that control the meniscus cell phenotype. Analysis of RNA sequencing data from 37 human tissues in the Genotype-Tissue Expression database and RNA sequencing data from meniscus and articular cartilage showed that transcription factor Mohawk (MKX) is highly enriched in meniscus. In human meniscus cells, MKX regulates the expression of meniscus marker genes, OA-related genes, and other transcription factors, including Scleraxis (SCX), SRY Box 5 (SOX5), and Runt domain-related transcription factor 2 (RUNX2). In mesenchymal stem cells (MSCs), the combination of adenoviral MKX (Ad-MKX) and transforming growth factor-β3 (TGF-β3) induced a meniscus cell phenotype. When Ad-MKX-transduced MSCs were seeded on TGF-β3-conjugated decellularized meniscus scaffold (DMS) and inserted into experimental tears in meniscus explants, they increased glycosaminoglycan content, extracellular matrix interconnectivity, cell infiltration into the DMS, and improved biomechanical properties. Ad-MKX injection into mouse knee joints with experimental OA induced by surgical destabilization of the meniscus suppressed meniscus and cartilage damage, reducing OA severity. Ad-MKX injection into human OA meniscus tissue explants corrected pathogenic gene expression. These results identify MKX as a previously unidentified key transcription factor that regulates the meniscus cell phenotype. The combination of Ad-MKX with TGF-β3 is effective for differentiation of MSCs to a meniscus cell phenotype and useful for meniscus repair. MKX is a promising therapeutic target for meniscus tissue engineering, repair, and prevention of OA.

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.

TAFI deficiency causes maladaptive vascular remodeling after hemophilic joint bleeding

Excessive vascular remodeling is characteristic of hemophilic arthropathy (HA) and may contribute to joint bleeding and the progression of HA. Mechanisms for pathological vascular remodeling after hemophilic joint bleeding are unknown. In hemophilia, activation of thrombin-activatable fibrinolysis inhibitor (TAFI) is impaired, which contributes to joint bleeding and may also underlie the aberrant vascular remodeling. Here, hemophilia A (factor VIII-deficient; FVIII-deficient) mice or TAFI-deficient mice with transient (antibody-induced) hemophilia A were used to determine the role of FVIII and TAFI in vascular remodeling after joint bleeding. Excessive vascular remodeling and vessel enlargement persisted in FVIII-deficient and TAFI-deficient mice, but not in transient hemophilia WT mice, after similar joint bleeding. TAFI-overexpression in FVIII-deficient mice prevented abnormal vessel enlargement and vascular leakage. Age-related vascular changes were observed with FVIII or TAFI deficiency and correlated positively with bleeding severity after injury, supporting increased vascularity as a major contributor to joint bleeding. Antibody-mediated inhibition of uPA also prevented abnormal vascular remodeling, suggesting that TAFI's protective effects include inhibition of uPA-mediated plasminogen activation. In conclusion, the functional TAFI deficiency in hemophilia drives maladaptive vascular remodeling in the joints after bleeding. These mechanistic insights allow targeted development of potentially new strategies to normalize vascularity and control rebleeding in HA.

FoxO transcription factors modulate autophagy and proteoglycan 4 in cartilage homeostasis and osteoarthritis

Aging is a main risk factor for osteoarthritis (OA). FoxO transcription factors protect against cellular and organismal aging, and FoxO expression in cartilage is reduced with aging and in OA. To investigate the role of FoxO in cartilage, Col2Cre-FoxO1, 3, and 4 single knockout (KO) and triple KO mice (Col2Cre-TKO) were analyzed. Articular cartilage in Col2Cre-TKO and Col2Cre-FoxO1 KO mice was thicker than in control mice at 1 or 2 months of age. This was associated with increased proliferation of chondrocytes of Col2Cre-TKO mice in vivo and in vitro. OA-like changes developed in cartilage, synovium, and subchondral bone between 4 and 6 months of age in Col2Cre-TKO and Col2Cre-FoxO1 KO mice. Col2Cre-FoxO3 and FoxO4 KO mice showed no cartilage abnormalities until 18 months of age when Col2Cre-FoxO3 KO mice had more severe OA than control mice. Autophagy and antioxidant defense genes were reduced in Col2Cre-TKO mice. Deletion of FoxO1/3/4 in mature mice using Aggrecan(Acan)-CreERT2 (AcanCreERT-TKO) also led to spontaneous cartilage degradation and increased OA severity in a surgical model or treadmill running. The superficial zone of knee articular cartilage of Col2Cre-TKO and AcanCreERT-TKO mice exhibited reduced cell density and markedly decreased Prg4 In vitro, ectopic FoxO1 expression increased Prg4 and synergized with transforming growth factor-β stimulation. In OA chondrocytes, overexpression of FoxO1 reduced inflammatory mediators and cartilage-degrading enzymes, increased protective genes, and antagonized interleukin-1β effects. Our observations suggest that FoxO play a key role in postnatal cartilage development, maturation, and homeostasis and protect against OA-associated cartilage damage.

Characterization of synovial fluid metabolomic phenotypes of cartilage morphological changes associated with osteoarthritis

OBJECTIVE

Osteoarthritis (OA) is a multifactorial disease with etiological heterogeneity. The objective of this study was to classify OA subgroups by generating metabolomic phenotypes from human synovial fluid.

DESIGN

Post mortem synovial fluids (n = 75) were analyzed by high performance-liquid chromatography mass spectrometry (LC-MS) to measure changes in the global metabolome. Comparisons of healthy (grade 0), early OA (grades I-II), and late OA (grades III-IV) donor populations were considered to reveal phenotypes throughout disease progression.

RESULTS

Global metabolomic profiles in synovial fluid were distinct between healthy, early OA, and late OA donors. Pathways differentially activated among these groups included structural deterioration, glycerophospholipid metabolism, inflammation, central energy metabolism, oxidative stress, and vitamin metabolism. Within disease states (early and late OA), subgroups of donors revealed distinct phenotypes. Synovial fluid metabolomic phenotypes exhibited increased inflammation (early and late OA), oxidative stress (late OA), or structural deterioration (early and late OA) in the synovial fluid.

CONCLUSION

These results revealed distinct metabolic phenotypes in human synovial fluid, provide insight into pathogenesis, represent novel biomarkers, and can move toward developing personalized interventions for subgroups of OA patients.

Wwp2 maintains cartilage homeostasis through regulation of Adamts5

The WW domain-containing protein 2 (Wwp2) gene, the host gene of miR-140, codes for the Wwp2 protein, which is an HECT-type E3 ubiquitin ligases abundantly expressed in articular cartilage. However, its function remains unclear. Here, we show that mice lacking Wwp2 and mice in which the Wwp2 E3 enzyme is inactivated (Wwp2-C838A) exhibit aggravated spontaneous and surgically induced osteoarthritis (OA). Consistent with this phenotype, WWP2 expression level is downregulated in human OA cartilage. We also identify Runx2 as a Wwp2 substrate and Adamts5 as a target gene, as similar as miR-140. Analysis of Wwp2-C838A mice shows that loss of Wwp2 E3 ligase activity results in upregulation of Runx2-Adamts5 signaling in articular cartilage. Furthermore, in vitro transcribed Wwp2 mRNA injection into mouse joints reduces the severity of experimental OA. We propose that Wwp2 has a role in protecting cartilage from OA by suppressing Runx2-induced Adamts5 via Runx2 poly-ubiquitination and degradation.

FOXO are required for intervertebral disk homeostasis during aging and their deficiency promotes disk degeneration

Intervertebral disk (IVD) degeneration is a prevalent age-associated musculoskeletal disorder and a major cause of chronic low back pain. Aging is the main risk factor for the disease, but the molecular mechanisms regulating IVD homeostasis during aging are unknown. The aim of this study was to investigate the function of FOXO, a family of transcription factors linked to aging and longevity, in IVD aging and age-related degeneration. Conditional deletion of all FOXO isoforms (FOXO1, 3, and 4) in IVD using the Col2a1Cre and AcanCreER mouse resulted in spontaneous development of IVD degeneration that was driven by severe cell loss in the nucleus pulposus (NP) and cartilaginous endplates (EP). Conditional deletion of individual FOXO in mature mice showed that FOXO1 and FOXO3 are the dominant isoforms and have redundant functions in promoting IVD homeostasis. Gene expression analyses indicated impaired autophagy and reduced antioxidant defenses in the NP of FOXO-deficient IVD. In primary human NP cells, FOXO directly regulated autophagy and adaptation to hypoxia and promoted resistance to oxidative and inflammatory stress. Our findings demonstrate that FOXO are critical regulators of IVD homeostasis during aging and suggest that maintaining or restoring FOXO expression can be a therapeutic strategy to promote healthy IVD aging and delay the onset of IVD degeneration.

Platelet-derived growth factor-coated decellularized meniscus scaffold for integrative healing of meniscus tears

The aim of this study was to examine the potential of platelet-derived growth factor (PDGF)-coated decellularized meniscus scaffold in mediating integrative healing of meniscus tears by inducing endogenous cell migration. Fresh bovine meniscus was chemically decellularized and covalently conjugated with heparin and PDGF-BB. In vitro PDGF release kinetics was measured. The scaffold was transplanted into experimental tears in avascular bovine meniscus explants and cultured for 2 and 4 weeks. The number migrating and proliferating cells at the borderline between the scaffold and injured explant and PDGF receptor-β (PDGFRβ) expressing cells were counted. The alignment of the newly produced ECM and collagen was analyzed by Safranin-O, picrosirius red staining, and differential interference contrast (DIC). Tensile testing of the explants was performed after culture for 2 and 4 weeks. Heparin conjugated scaffold showed immobilization of high levels of PDGF-BB, with sustained release over 2 weeks. Insertion of the PDGF-BB treated scaffold in defects in avascular meniscus led to increased PDGFRβ expression, cell migration and proliferation into the defect zone. Safranin-O, picrosirius red staining and DIC showed tissue integration between the scaffold and injured explants. Tensile properties of injured explants treated with PDGF-BB coated scaffold were significantly higher than in the scaffold without PDGF. In conclusion, PDGF-BB-coated scaffold increased PDGFRβ expression and promoted migration of endogenous meniscus cells to the defect area. New matrix was formed that bridged the space between the native meniscus and the scaffold and this was associated with improved biomechanical properties. The PDGF-BB-coated scaffold will be promising for clinical translation to healing of meniscus tears.

STATEMENT OF SIGNIFICANCE

Meniscus tears are the most common injury of the knee joint. The most prevalent forms that occur in the inner third typically do not spontaneously heal and represent a major risk factor for the development of knee osteoarthritis. The goal of this project was to develop an approach that is readily applicable for clinical use. We selected a natural and readily available decellularized meniscus scaffold and conjugated it with PDGF, which we had previously found to have strong chemotactic activity for chondrocytes and progenitor cells. The present results show that insertion of the PDGF-conjugated scaffold in defects in avascular meniscus led to endogenous cell migration and proliferation into the defect zone with tissue integration between the scaffold and injured explants and improved tensile properties. This PDGF-conjugated scaffold will be promising for a translational approach to healing of meniscus tears.

Using Ultrapure Water in Hemodialysis Delays Carpal Tunnel Syndrome

Since 1977, our patients have undergone chronic HD with ultra-pure dialysate (UPD), defined as having endotoxin levels below 0.008 ng/ml and less than 1 bacteria/ml of dialysate. We evaluated the incidence of carpal tunnel syndrome (CTS) in three groups of patients. Group I (GI), 84 patients, dialysed for 6.1 ± 3.2 years (mean ± SD) with UPD only; Group II (GII), 39 patients, first dialysed for 3.7 ± 2.3 years with non-UPD and afterwards for 8.4 ± 2.1 years with UPD; Group III (G III), 103 patients treated for 6 ± 5.9 years exclusively with non-UPD. All patients were dialysed with cuprophan or cellulose acetate membranes.

Results, expressed by Kaplan-Meier actuarial survival curves as the percent of patients without CTS, show that CTS occurred significantly less in GI than in GIII. This may be due to less stimulation of monocytes resulting from the absence of bacteria, endotoxins and pyrogens in the dialysate which would reduce the stimulation of cytokines release, interleukin 1 and 6, and tumor necrosis factor, known to stimulate β2 microglobulin synthesis.

Age-related reduction in the expression of FOXO transcription factors and correlations with intervertebral disc degeneration

Aging is a main risk factor for intervertebral disc (IVD) degeneration, the main cause of low back pain. FOXO transcription factors are important regulators of tissue homeostasis and longevity. Here, we determined the expression pattern of FOXO in healthy and degenerated human IVD and the associations with IVD degeneration during mouse aging. FOXO expression was assessed by immunohistochemistry in normal and degenerated human IVD samples and in cervical and lumbar IVD from 6-, 12-, 24-, and 36-month-old C57BL/6J mice. Mouse spines were graded for key histological features of disc degeneration in all the time points and expression of two key FOXO downstream targets, sestrin 3 (SESN3) and superoxide dismutase (SOD2), was assessed by immunohistochemistry. Histological analysis revealed that FOXO proteins are expressed in all compartments of human and mouse IVD. Expression of FOXO1 and FOXO3, but not FOXO4, was significantly deceased in human degenerated discs. In mice, degenerative changes in the lumbar spine were seen at 24 and 36 months of age whereas cervical IVD showed increased histopathological scores at 36 months. FOXO expression was significantly reduced in lumbar IVD at 12-, 24-, and 36-month-old mice and in cervical IVD at 36-month-old mice when compared with the 6-month-old group. The reduction of FOXO expression in lumbar IVD was concomitant with a decrease in the expression of SESN3 and SOD2. These findings suggest that reduced FOXO expression occurs in lumbar IVD during aging and precedes the major histopathological changes associated with lumbar IVD degeneration. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2682-2691, 2017.

Transthyretin deposition promotes progression of osteoarthritis

Deposition of amyloid is a common aging-associated phenomenon in several aging-related diseases. Osteoarthritis (OA) is the most prevalent joint disease, and aging is its major risk factor. Transthyretin (TTR) is an amyloidogenic protein that is deposited in aging and OA-affected human cartilage and promotes inflammatory and catabolic responses in cultured chondrocytes. Here, we investigated the role of TTR in vivo using transgenic mice overexpressing wild-type human TTR (hTTR-TG). Although TTR protein was detected in cartilage in hTTR-TG mice, the TTR transgene was highly overexpressed in liver, but not in chondrocytes. OA was surgically induced by destabilizing the medial meniscus (DMM) in hTTR-TG mice, wild-type mice of the same strain (WT), and mice lacking endogenous Ttr genes. In the DMM model, both cartilage and synovitis histological scores were significantly increased in hTTR-TG mice. Further, spontaneous degradation and OA-like changes in cartilage and synovium developed in 18-month-old hTTR mice. Expression of cartilage catabolic (Adamts4, Mmp13) and inflammatory genes (Nos2, Il6) was significantly elevated in cartilage from 6-month-old hTTR-TG mice compared with WT mice as was the level of phospho-NF-κB p65. Intra-articular injection of aggregated TTR in WT mice increased synovitis and significantly increased expression of inflammatory genes in synovium. These findings are the first to show that TTR deposition increases disease severity in the murine DMM and aging model of OA.

Compromised autophagy precedes meniscus degeneration and cartilage damage in mice

OBJECTIVE

Autophagy is a cellular homeostasis mechanism that facilitates normal cell function and survival. Objectives of this study were to determine associations between autophagic responses with meniscus injury, joint aging, and osteoarthritis (OA), and to establish the temporal relationship with structural changes in menisci and cartilage.

METHODS

Constitutive activation of autophagy during aging was measured in GFP-LC3 transgenic reporter mice between 6 and 30 months. Meniscus injury was created by surgically destabilizing the medial meniscus (DMM) to induce posttraumatic OA in C57BL/6J mice. Levels of autophagy proteins and activation were analyzed by confocal microscopy and immunohistochemistry. Associated histopathological changes, such as cellularity, matrix staining, and structural damage, were graded in the meniscus and compared to changes in articular cartilage.

RESULTS

In C57BL/6J mice, basal autophagy was lower in the meniscus than in articular cartilage. With increasing age, expression of the autophagy proteins ATG5 and LC3 was significantly reduced by 24 months. Age-related changes included abnormal Safranin-O staining and reduced cellularity, which preceded structural damage in the meniscus and articular cartilage. In mice with DMM, autophagy was induced in the meniscus while it was suppressed in cartilage. Articular cartilage exhibited the most profound changes in autophagy and structure that preceded meniscus degeneration. Systemic administration of rapamycin to mice with DMM induced autophagy activation in cartilage and reduced degenerative changes in both meniscus and cartilage.

CONCLUSION

Autophagy is significantly affected in the meniscus during aging and injury and precedes structural damage. Maintenance of autophagic activity appears critical for meniscus and cartilage integrity.

Expression of Noggin and Gremlin1 and its implications in fine-tuning BMP activities in mouse cartilage tissues

Increasing evidence supports the idea that bone morphogenetic proteins (BMPs) regulate cartilage maintenance in the adult skeleton. The aim of this study is to obtain insight into the regulation of BMP activities in the adult skeletal system. We analyzed expression of Noggin and Gremlin1, BMP antagonists that are known to regulate embryonic skeletal development, in the adult skeletal system by Noggin-LacZ and Gremlin1-LacZ knockin reporter mouse lines. Both reporters are expressed in the adult skeleton in a largely overlapping manner with some distinct patterns. Both are detected in the articular cartilage, pubic symphysis, facet joint in the vertebrae, and intervertebral disk, suggesting that they regulate BMP activities in these tissues. In a surgically induced knee osteoarthritis model in mice, expression of Noggin mRNA was lost from the articular cartilage, which correlated with loss of BMP2/4 and pSMAD1/5/8, an indicator of active BMP signaling. Both reporters are also expressed in the sterna and rib cartilage, suggesting an extensive role of BMP antagonism in adult cartilage tissue. Moreover, Noggin-LacZ was detected in sutures in the skull and broadly in the nasal cartilage, while Gremlin1-LacZ exhibits a weaker and more restricted expression domain in the nasal cartilage. These results suggest broad regulation of BMP activities by Noggin and Gremlin1 in cartilage tissues in the adult skeleton, and that BMP signaling and its antagonism by NOGGIN play a role in osteoarthritis development. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1671-1682, 2017.

Regulated in Development and DNA Damage Response 1 Deficiency Impairs Autophagy and Mitochondrial Biogenesis in Articular Cartilage and Increases the Severity of Experimental Osteoarthritis

OBJECTIVE

Regulated in development and DNA damage response 1 (REDD1) is an endogenous inhibitor of mechanistic target of rapamycin (mTOR) that regulates cellular stress responses. REDD1 expression is decreased in aged and osteoarthritic (OA) cartilage, and it regulates mTOR signaling and autophagy in articular chondrocytes in vitro. This study was undertaken to investigate the effects of REDD1 deletion in vivo using a mouse model of experimental OA.

METHODS

OA severity was histologically assessed in 4-month-old wild-type and REDD1^-/- mice subjected to surgical destabilization of the medial meniscus (DMM). Chondrocyte autophagy, apoptosis, mitochondrial content, and expression of mitochondrial biogenesis markers were determined in cartilage and cultured chondrocytes from wild-type and REDD1^-/- mice.

RESULTS

REDD1 deficiency increased the severity of changes in cartilage, menisci, subchondral bone, and synovium in the DMM model of OA. Chondrocyte death was increased in the cartilage of REDD1^-/- mice and in cultured REDD1^-/- mouse chondrocytes under oxidative stress conditions. Expression of key autophagy markers (microtubule-associated protein 1A/1B light chain 3 and autophagy protein 5) was markedly reduced in cartilage from REDD1^-/- mice and in cultured human and mouse chondrocytes with REDD1 depletion. Mitochondrial content, ATP levels, and expression of the mitochondrial biogenesis markers peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) and transcription factor A, mitochondrial (TFAM) were also decreased in REDD1-deficient chondrocytes. REDD1 was required for AMP-activated protein kinase-induced PGC-1α in chondrocytes.

CONCLUSION

Our findings suggest that REDD1 is a key mediator of cartilage homeostasis through regulation of autophagy and mitochondrial biogenesis and that REDD1 deficiency exacerbates the severity of injury-induced OA.

Regulated in Development and DNA Damage Response 1 Deficiency Impairs Autophagy and Mitochondrial Biogenesis in Articular Cartilage and Increases the Severity of Experimental Osteoarthritis

OBJECTIVE

Regulated in development and DNA damage response 1 (REDD1) is an endogenous inhibitor of mechanistic target of rapamycin (mTOR) that regulates cellular stress responses. REDD1 expression is decreased in aged and osteoarthritic (OA) cartilage, and it regulates mTOR signaling and autophagy in articular chondrocytes in vitro. This study was undertaken to investigate the effects of REDD1 deletion in vivo using a mouse model of experimental OA.

METHODS

OA severity was histologically assessed in 4-month-old wild-type and REDD1^-/- mice subjected to surgical destabilization of the medial meniscus (DMM). Chondrocyte autophagy, apoptosis, mitochondrial content, and expression of mitochondrial biogenesis markers were determined in cartilage and cultured chondrocytes from wild-type and REDD1^-/- mice.

RESULTS

REDD1 deficiency increased the severity of changes in cartilage, menisci, subchondral bone, and synovium in the DMM model of OA. Chondrocyte death was increased in the cartilage of REDD1^-/- mice and in cultured REDD1^-/- mouse chondrocytes under oxidative stress conditions. Expression of key autophagy markers (microtubule-associated protein 1A/1B light chain 3 and autophagy protein 5) was markedly reduced in cartilage from REDD1^-/- mice and in cultured human and mouse chondrocytes with REDD1 depletion. Mitochondrial content, ATP levels, and expression of the mitochondrial biogenesis markers peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) and transcription factor A, mitochondrial (TFAM) were also decreased in REDD1-deficient chondrocytes. REDD1 was required for AMP-activated protein kinase-induced PGC-1α in chondrocytes.

CONCLUSION

Our findings suggest that REDD1 is a key mediator of cartilage homeostasis through regulation of autophagy and mitochondrial biogenesis and that REDD1 deficiency exacerbates the severity of injury-induced OA.

Suppression of Sestrins in aging and osteoarthritic cartilage: dysfunction of an important stress defense mechanism

OBJECTIVES

Aging is an important osteoarthritis (OA) risk factor and compromised stress defense responses may mediate this risk. The Sestrins (Sesn) promote cell survival under stress conditions and regulate AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) signaling. This study examined Sesn expression in normal and OA cartilage and functions of Sesn in chondrocytes.

METHODS

Sesn expression in human and mouse normal and OA cartilage was analyzed by quantitative polymerase chain reaction (PCR) and immunohistochemistry. Sesn function was investigated by using small interfering RNA (siRNA) mediated Sesn knockdown and overexpression with analysis of cell survival, gene expression, autophagy, and AMPK and mTOR activation.

RESULTS

Sesn mRNA levels were significantly reduced in human OA cartilage and immunohistochemistry of human and mouse OA cartilage also showed a corresponding reduction in protein levels. In cultured human chondrocytes Sesn1, 2 and 3 were expressed and increased by tunicamycin, an endoplasmic reticulum (ER) stress response inducer and 2-deoxyglucose (2DG), a metabolic stress inducer. Sesn1 and 2 were increased by tBHP, an oxidative stress inducer. Sesn knockdown by siRNA reduced chondrocyte viability under basal culture conditions and in the presence of 2DG. Sesn overexpression enhanced LC3-II formation and autophagic flux, and this was related to changes in mTOR but not AMPK activation.

CONCLUSION

These findings are the first to show that Sesn expression is suppressed in OA affected cartilage. Sesn support chondrocyte survival under stress conditions and promote autophagy activation through modulating mTOR activity. Suppression of Sesn in OA cartilage contributes to deficiency in an important cellular homeostasis mechanism.

Increased autophagy in CD4+ T cells of rheumatoid arthritis patients results in T-cell hyperactivation and apoptosis resistance

Rheumatoid arthritis (RA) is an autoimmune disease hallmarked by aberrant cellular homeostasis, resulting in hyperactive CD4⁺ T cells that are more resistant to apoptosis. Both hyperactivation and resistance to apoptosis may contribute to the pathogenicity of CD4⁺ T cells in the autoimmune process. A better knowledge of the mechanisms determining such impaired homeostasis could contribute significantly to both the understanding and the treatment of the disease. Here we investigated whether autophagy, is dysregulated in CD4⁺ T cells of RA patients, resulting in disturbed T-cell homeostasis. We demonstrate that the rate of autophagy is significantly increased in CD4⁺ T cells from RA patients, and that increased autophagy is also a feature of in vitro activated CD4⁺ T cells. The increased apoptosis resistance observed in CD4⁺ T cells from RA patients was significantly reversed upon autophagy inhibition. These mechanisms may contribute to RA pathogenesis, as autophagy inhibition reduced both arthritis incidence and disease severity in a mouse collagen induced arthritis mouse model. Conversely, in Atg5^flox/flox -CD4-Cre⁺ mice, in which all T cells are autophagy deficient, T cells showed impaired activation and proliferation. These data provide novel insight into the pathogenesis of RA and underscore the relevance of autophagy as a promising therapeutic target.

Suppression of REDD1 in osteoarthritis cartilage, a novel mechanism for dysregulated mTOR signaling and defective autophagy

OBJECTIVE

Aging is a main risk factor for the development of osteoarthritis (OA) and the molecular mechanisms underlying the aging-related changes in articular cartilage include increased mammalian target of rapamycin (mTOR) signaling and defective autophagy. REDD1 is an endogenous inhibitor of mTOR that regulates cellular stress responses. In this study we measured REDD1 expression in normal, aged and OA cartilage and assessed REDD1 function in human and mouse articular chondrocytes.

METHODS

REDD1 expression was analyzed in human and mouse articular cartilage by qPCR, western blotting, and immunohistochemistry. For functional studies, REDD1 and TXNIP knockdown or overexpression was performed in chondrocytes in the presence or absence of rapamycin and chloroquine, and mTOR signaling and autophagy were measured by western blotting. REDD1/TXNIP protein interaction was assessed by co-immunoprecipitation experiments.

RESULTS

Human and mouse cartilage from normal knee joints expressed high levels of REDD1. REDD1 expression was significantly reduced in aged and OA cartilage. In cultured chondrocytes, REDD1 knockdown increased whereas REDD1 overexpression decreased mTOR signaling. In addition, REDD1 activated autophagy by an mTOR independent mechanism that involved protein/protein interaction with TXNIP. The REDD1/TXNIP complex was required for autophagy activation in chondrocytes.

CONCLUSION

The present study shows that REDD1 is highly expressed in normal human articular cartilage and reduced during aging and OA. REDD1 in human chondrocytes negatively regulates mTOR activity and is essential for autophagy activation. Reduced REDD1 expression thus represents a novel mechanism for the increased mTOR activation and defective autophagy observed in OA.

Histopathological analyses of murine menisci: implications for joint aging and osteoarthritis

OBJECTIVE

To establish a standardized protocol for histopathological assessment of murine menisci that can be applied to evaluate transgenic, knock-out/in, and surgically induced OA models.

METHODS

Knee joints from C57BL/6J mice (6-36 months) as well as from mice with surgically-induced OA were processed and cut into sagittal sections. All sections included the anterior and posterior horns of the menisci and were graded for (1) surface integrity, (2) cellularity, (3) Safranin-O staining distribution and intensity. Articular cartilage in the knee joints was also scored.

RESULTS

The new histopathological grading system showed good inter- and intra-class correlation coefficients. The major age-related changes in murine menisci in the absence of OA included decreased Safranin O staining intensity, abnormal cell distribution and the appearance of acellular areas. Menisci from mice with surgically-induced OA showed severe fibrillations, partial/total loss of tissue, and calcifications. Abnormal cell arrangements included both regional hypercellularity and hypocellularity along with hypertrophy and cell clusters. In general, the posterior horns were less affected by age and OA.

CONCLUSION

A new standardized protocol and histopathological grading system has been developed and validated to allow for a comprehensive, systematic evaluation of changes in aging and OA-affected murine menisci. This system was developed to serve as a standardized technique and tool for further studies in murine meniscal pathophysiology models.

Vascular remodeling underlies rebleeding in hemophilic arthropathy

Hemophilic arthropathy is a debilitating condition that can develop as a consequence of frequent joint bleeding despite adequate clotting factor replacement. The mechanisms leading to repeated spontaneous bleeding are unknown. We investigated synovial, vascular, stromal, and cartilage changes in response to a single induced hemarthrosis in the FVIII-deficient mouse. We found soft-tissue hyperproliferation with marked induction of neoangiogenesis and evolving abnormal vascular architecture. While soft-tissue changes were rapidly reversible, abnormal vascularity persisted for months and, surprisingly, was also seen in uninjured joints. Vascular changes in FVIII-deficient mice involved pronounced remodeling with expression of α-Smooth Muscle Actin (SMA), Endoglin (CD105), and vascular endothelial growth factor, as well as alterations of joint perfusion as determined by in vivo imaging. Vascular architecture changes and pronounced expression of α-SMA appeared unique to hemophilia, as these were not found in joint tissue obtained from mouse models of rheumatoid arthritis and osteoarthritis and from patients with the same conditions. Evidence that vascular changes in hemophilia were significantly associated with bleeding and joint deterioration was obtained prospectively by dynamic in vivo imaging with musculoskeletal ultrasound and power Doppler of 156 joints (elbows, knees, and ankles) in a cohort of 26 patients with hemophilia at baseline and during painful episodes. These observations support the hypothesis that vascular remodeling contributes significantly to bleed propagation and development of hemophilic arthropathy. Based on these findings, the development of molecular targets for angiogenesis inhibition may be considered in this disease.

Transthyretin deposition in articular cartilage: a novel mechanism in the pathogenesis of osteoarthritis

OBJECTIVE

Amyloid deposits are prevalent in osteoarthritic (OA) joints. We undertook this study to define the dominant precursor and to determine whether the deposits affect chondrocyte functions.

METHODS

Amyloid deposition in human normal and OA knee cartilage was determined by Congo red staining. Transthyretin (TTR) in cartilage and synovial fluid was analyzed by immunohistochemistry and Western blotting. The effects of recombinant amyloidogenic and nonamyloidogenic TTR variants were tested in human chondrocyte cultures.

RESULTS

Normal cartilage from young donors did not contain detectable amyloid deposits, but 7 of 12 aged normal cartilage samples (58%) and 12 of 12 OA cartilage samples (100%) had Congo red staining with green birefringence under polarized light. TTR, which is located predominantly at the cartilage surfaces, was detected in all OA cartilage samples and in a majority of aged normal cartilage samples, but not in normal cartilage samples from young donors. Chondrocytes and synoviocytes did not contain significant amounts of TTR messenger RNA. Synovial fluid TTR levels were similar in normal and OA knees. In cultured chondrocytes, only an amyloidogenic TTR variant induced cell death as well as the expression of proinflammatory cytokines and extracellular matrix-degrading enzymes. The effects of amyloidogenic TTR on gene expression were mediated in part by Toll-like receptor 4, receptor for advanced glycation end products, and p38 MAPK. TTR-induced cytotoxicity was inhibited by resveratrol, a plant polyphenol that stabilizes the native tetrameric structure of TTR.

CONCLUSION

These findings are the first to suggest that TTR amyloid deposition contributes to cell and extracellular matrix damage in articular cartilage in human OA and that therapies designed to reduce TTR amyloid formation might be useful.

The relationship of autophagy defects to cartilage damage during joint aging in a mouse model

OBJECTIVE

Aging is a main risk factor for osteo arthritis (OA), the most prevalent musculoskeletal disorder. Defects in autophagy, an essential cellular homeostasis mechanism, have recently been observed in OA articular cartilage. The objectives of this study were to establish the constitutive level of autophagy activation in normal cartilage and to monitor the temporal relationship between changes in autophagy and aging-related degradation of cartilage in a mouse model.

METHODS

In GFP-LC3-transgenic mice, green fluorescent protein (GFP)-light chain 3 (LC3) is ubiquitously expressed, and the accumulation of GFP puncta, representing autophagosomes, was quantified by confocal microscopy as a measure of autophagy activation. Expression of the autophagy proteins autophagy-related protein 5 (ATG-5) and microtubule-associated protein 1 light chain 3 (LC3) was analyzed by immunohistochemistry. Cartilage cellularity, apoptotic cell death, and cartilage structural damage and changes in synovium and bone were examined by histology and immunohistochemistry.

RESULTS

Basal autophagy activation was detected in liver and knee articular cartilage from young (6-month-old) mice, with higher levels in cartilage than in liver in the same animals. In 28-month-old mice, there was a statistically significant reduction in the total number of autophagic vesicles per cell (P < 0.01) and in the total area of vesicles per cell (P < 0.01) in the articular cartilage as compared to that from young 6-month-old mice. With increasing age, the expression of ATG-5 and LC3 decreased, and this was followed by a reduction in cartilage cellularity and an increase in the apoptosis marker poly(ADP-ribose) polymerase p85. Cartilage structural damage progressed in an age-dependent manner subsequent to the autophagy changes.

CONCLUSION

Autophagy is constitutively activated in normal cartilage. This is compromised with aging and precedes cartilage cell death and structural damage.

Induction versus noninduction in renal transplant recipients with tacrolimus-based immunosuppression

BACKGROUND

The aim of this study was to compare the efficacy and safety of induction treatment with antithymocyte globulins (ATG) followed by tacrolimus therapy with immediate tacrolimus therapy in renal transplant recipients.

METHODS

This 12-month, open, prospective study was conducted in 15 centers in France and 1 center in Belgium; 309 patients were randomized to receive either induction therapy with ATG (n=151) followed by initiation of tacrolimus on day 9 or immediate tacrolimus-based triple therapy (n=158). In both study arms, the initial daily tacrolimus dose was 0.2 mg/kg. Steroid boluses were given in the first 2 days and tapered thereafter from 20 mg/day to 5 mg/day. Azathioprine was administered at 1-2 mg/kg per day.

RESULTS

At month 12, biopsy-confirmed acute rejections were reported for 15.2% (induction) and 30.4% (noninduction) of patients (P=0.001). The incidence of steroid-sensitive acute rejections was 7.9% (induction) and 22.2% (noninduction)(P=0.001). Steroid-resistant acute rejections were reported for 8.6% (induction) and 8.9% (noninduction) of patients. A total of nine patients died. Patient survival and graft survival at month 12 was similar in both treatment groups (97.4% vs. 96.8% and 92.1% vs. 91.1%, respectively). Statistically significant differences in the incidence of adverse events were found for cytomegalovirus (CMV) infection (induction, 32.5% vs. noninduction, 19.0%, P=0.009), leukopenia (37.3% vs. 9.5%, P<0.001), fever (25.2% vs. 10.1%, P=0.001), herpes simplex (17.9% vs. 5.7%, P=0.001), and thrombocytopenia (11.3% vs. 3.2%, P=0.007). In the induction group, serum sickness was observed in 10.6% of patients. The incidence of new onset diabetes mellitus was 3.4% (induction) and 4.5% (noninduction).

CONCLUSION

Low incidences of acute rejection were found in both treatment arms. Induction treatment with ATG has the advantage of a lower incidence of acute rejection, but it significantly increases adverse events, particularly CMV infection.

TT virus infection in French hemodialysis patients: study of prevalence and risk factors

The TT virus (TTV) is a recently discovered DNA virus which was first identified in patients with non-A to -G hepatitis following blood transfusion. In this study, we tested 150 attendees of two hemodialysis (HD) units of the public hospitals of Marseilles, France, for the presence of TTV genome by using a PCR-based methodology. The overall prevalence of TTV viremia was 28% (compared to 5.3% in blood donors from the same region). We demonstrated the existence of chronic infections and superinfections by strains belonging to different genotypes. The prevalence of infection was higher in patients originating from Africa, in patients with previous blood transfusion or organ transplantation, in patients with antibody to hepatitis B core antigen, and in those with diabetes mellitus. A high prevalence of TTV infection (50%) was also observed in a population of patients with diabetes mellitus but without renal disease. No significant relationship was found between TTV viremia and hepatitis C virus or GB virus C, transaminases, age, sex, and duration of HD treatment. The PCR amplification products (located in open reading frame 1 of the TTV genome) were sequenced. These genomic sequences were submitted to phylogenetic analysis by using the Jukes-Cantor algorithm for distance determination and the neighbor-joining method for tree building. In several instances, sequences from viruses isolated in a HD unit were grouped in the same phylogenetic cluster. These results together with the different distribution of cases in the two HD units suggest there is viral transmission within each.

Long-term nonprogressive human immunodeficiency virus-1 infection in a kidney allograft recipient

We report a unique case of a renal transplant patient with a long-term nonprogressive human immunodeficiency virus type-1 (HIV-1) infection and who is asymptomatic despite sustained immunosuppression. Renal function is normal, and HIV infection was probably acquired through blood transfusion before the transplant. Nonprogression may be due either to an effective immune control of HIV replication or to particular genetic aspects of the virus. Several virological investigations were carried out to verify if she is infected with an attenuated virus strain. Results show an unusual combination of high and stable CD4 count, ongoing viral replication and elevated viral loads. Attempts to isolate the virus from plasma were unsuccessful, but isolation was possible from peripheral blood mononuclear cells, and the virus was shown to be non-syncytium-inducing. Sequence analysis of the nef gene revealed no mutation. This exceptional lack of progression of HIV infection under immunosuppressive therapy requires further investigation.

A new approach to evaluate vascular access in hemodialysis patients

We evaluated the importance of vascular access in hemodialysis patients using noninvasive methods with the Transonic Systems monitor in 108 patients. Most of these patients (84%) had native vein fistulas. We found that a blood flow rate of below 500 ml/min suggested the occurrence of vascular stenosis and justified confirmation by angiography. Increased recirculation could be evaluated readily and was detected in only 10% of patients. Finally, employing the evaluation of the Kt/V index, we found a good correlation between low flux through the fistula and a low Kt/V value.

Preliminary evidence for a role of apolipoprotein E alleles in identifying haemodialysis patients at high vascular risk

Conventional risk factors have very low predictive power in identifying haemodialysis patients at high risk of vascular accidents. A role for apolipoprotein E isotypes was looked for in a small, but rigorously defined, cohort of longterm haemodialysis patients. In individuals with high vascular risk, as identified by higher common carotid intima/media thickness, we found an excess of apolipoprotein E4 alleles. This preliminary result requires confirmation in large patient cohorts.

Transmission of the hepatitis C virus in an hemodialysis unit: evidence for nosocomial infection

Hepatitis C virus (HCV) infection is a frequent feature in hemodialysis (HD) patients. The way of viral transmission is difficult to establish, but in previous studies the role of blood transfusions and of HD treatment duration, and the possibility of nosocomial transmission of the virus have been suggested. We present here the results of a virological follow-up of HCV infection in our HD unit in 1993-1994, and a molecular study of viral strains that led to a possible reconstruction of viral spreading. All patients in our unit were regularly tested for alanine aminotransferase, HCV antibodies and HCV RNA in serum. Seven seroconversions were detected during follow-up, and a high proportion of type 1b HCV strains was found in infected patients. Nucleotide sequences located in the envelope 1 (E1) viral coding region of type 1b strains were compared in our patients and numerous controls infected with the same HCV genotype. A high proportion of patients with antibodies to HCV were detected in our unit (32.5%). Blood transfusions and duration of HD treatment were risk factors for HCV infection. Seroconversions in patients never transfused and predominance of type 1b HCV strains suggested that infection had occurred via the nosocomial pathway in our unit. Similar sequences in the E1 region were found in four patients treated, forming a distinct cluster in a phylogenetic tree. Of these four patients, two had been infected before 1991, and the others made a seroconversion for HCV at the same period in 1994. In all other patients, including a nurse who had been in charge of some infected patients, distinct strains were found. Duration of HD treatment seems to be a major factor of risk for HCF infection in HD units. Contamination could occur during blood transfusion or via the nosocomial pathway through a crossinfection mechanism from patients already infected. The latter mechanism was formally demonstrated in this study.

Monocyte production of transforming growth factor beta in long-term hemodialysis: modulation by hemodialysis membranes

Cytokines are likely involved in hemodialysis-associated complications such as immunodeficiency and beta 2 microglobulin amyloidosis. Because transforming growth factors beta (TGF beta) exert immunosuppressive effects on lymphocytes, down-modulate monocyte functions, and promote fibrosis, we hypothesize that they participate in the deleterious effects of hemodialysis. We investigated the production of TGF beta 1 and TGF beta 2 by monocytes from controls and patients dialyzed with high-flux cellulose triacetate (CT) and polyacrylonitrile (PAN) membranes. The detection of both TGF beta s required an acidification step, suggesting that they are secreted as latent complexes. The spontaneous production of TGF beta 1 and TGF beta 2 was significantly higher in patients dialyzed with CT or PAN than in controls, but the oversecretion of TGF beta 1 was more sustained in CT-treated patients than in PAN-dialyzed patients. The production of interleukin-6 (IL-6) was increased in both patient groups as compared with controls. In contrast to TGF beta 1, the increase was greater in PAN-treated patients than in CT-treated patients, and the release of tumor necrosis factor alpha (TNF alpha) was increased only in PAN-treated patients. Taken together, our results show that hemodialysis is associated with the oversecretion of monocyte cytokines. Moreover, the type of dialysis membrane specifically affects the balance between the secretion of suppressive cytokines such as TGF beta and that of inflammatory cytokines such as IL-6 and TNF alpha.

Nosocomial transmission of hepatitis C virus in haemodialysis patients

A systematic virological follow-up of 114 haemodialysis patients treated in the same unit showed that 37, including 17 PCR positive patients, were seropositive for hepatitis C virus (HCV). Type 1b HCV was detected in 10 patients and was much more frequent in this population than in the whole population of patients treated in the hepatogastroenterology departments in southeastern France. The E1/E2 genomic region of seven type 1b HCV strains was sequenced. In four patients, a similar strain was detected in both the E1 variable region and the E2 hypervariable region (HVR1). In addition, two of these four patients were seronegative and PCR negative at the beginning of the study and had not been transfused or transplanted during this period. A phylogenetic tree was drawn which confirmed that these strains were very similar and showed that HCV was transmitted via the nosocomial pathway in this haemodialysis unit.

Transplantation of a horseshoe kidney into 2 recipients

We report the case of a transplantation of a horseshoe kidney to 2 recipients after isthmic section of the kidney. A review of the literature since 1975 mentions only 14 cases of transplantation of a horseshoe kidney. In the absence of a significant urological clinical history of the donor, the presence of a horseshoe kidney, in the case of multiorgan harvesting, does not represent a contraindication for transplantation.