The small proteoglycans of cartilage matrix

Mutant Presenilin 1 Dysregulates Exosomal Proteome Cargo Produced by Human-Induced Pluripotent Stem Cell Neurons

The accumulation and propagation of hyperphosphorylated tau (p-Tau) is a neuropathological hallmark occurring with neurodegeneration of Alzheimer's disease (AD). Extracellular vesicles, exosomes, have been shown to initiate tau propagation in the brain. Notably, exosomes from human-induced pluripotent stem cell (iPSC) neurons expressing the AD familial A246E mutant form of presenilin 1 (mPS1) are capable of inducing tau deposits in the mouse brain after in vivo injection. To gain insights into the exosome proteome cargo that participates in propagating tau pathology, this study conducted proteomic analysis of exosomes produced by human iPSC neurons expressing A246E mPS1. Significantly, mPS1 altered the profile of exosome cargo proteins to result in (1) proteins present only in mPS1 exosomes and not in controls, (2) the absence of proteins in the mPS1 exosomes which were present only in controls, and (3) shared proteins which were upregulated or downregulated in the mPS1 exosomes compared to controls. These results show that mPS1 dysregulates the proteome cargo of exosomes to result in the acquisition of proteins involved in the extracellular matrix and protease functions, deletion of proteins involved in RNA and protein translation systems along with proteasome and related functions, combined with the upregulation and downregulation of shared proteins, including the upregulation of amyloid precursor protein. Notably, mPS1 neuron-derived exosomes displayed altered profiles of protein phosphatases and kinases involved in regulating the status of p-tau. The dysregulation of exosome cargo proteins by mPS1 may be associated with the ability of mPS1 neuron-derived exosomes to propagate tau pathology.

Collagen Type IV and Laminin Expressions during Cartilage Repair and in Late Clinically Failed Repair Tissues from Human Subjects

OBJECTIVE

To identify the collagen type IV (Col4) isoform in articular cartilage and to evaluate the expressions of Col4 and laminin in the pericellular matrix (PCM) in damaged cartilage and during cartilage repair.

DESIGN

The Col4 isoform was determined in chondrocytes isolated from 6 patients cultured up to 6 days and in 21% O2 or 1% O2, and the gene expression of Col4 α-chains was investigated. The distribution of Col4 and laminin in traumatically damaged cartilage (n = 7) and clinically failed cartilage repair (microfracture, TruFit, autologous chondrocyte implantation; n = 11) were investigated using immunohistochemistry. Normal human cartilage was used as control (n = 8). The distribution during clinical cartilage repair procedures was investigated in a minipig model with 6-month follow-up (untreated chondral, untreated osteochondral, microfracture, autologous chondrocyte implantation; n = 10).

RESULTS

The Col4 isoform in articular cartilage was characterized as α1α1α2, which is an isoform containing antiangiogenic domains in the NC1-terminals (arresten and canstatin). In normal cartilage, laminin and Col4 was exclusively found in the PCM. High amounts (>50%) of Col4 in the PCM significantly decreased in damaged cartilage (P = 0.004) and clinically failed repair tissue (P < 0.001). Laminin was only found with high expression (>50%) in 4/8 of the normal samples, which was not statistically significantly different from damaged cartilage (P = 0.15) or failed cartilage repair (P = 0.054).

CONCLUSIONS

Col4 in cartilage contain antiangiogenic domains and may play a role in the hypoxic environment in articular cartilage. Col4 and laminin was not found in the PCM of damaged and clinically failed repair.

The proteoglycan biglycan enhances antigen-specific T cell activation potentially via MyD88 and TRIF pathways and triggers autoimmune perimyocarditis

Biglycan is a proteoglycan ubiquitously present in extracellular matrix of a variety of organs, including heart, and it was reported to be overexpressed in myocardial infarction. Myocardial infarction may be complicated by perimyocarditis through unknown mechanisms. Our aim was to investigate the capacity of TLR2/TLR4 ligand biglycan to enhance the presentation of specific Ags released upon cardiomyocyte necrosis. In vitro, OVA-pulsed bone marrow-derived dendritic cells from wild-type (WT; C57BL/6) and TLR2-, TLR4-, MyD88-, or TRIF-deficient mice were cotreated with LPS, biglycan, or vehicle and incubated with OVA-recognizing MHC I- or MHC II-restricted T cells. Biglycan enhanced OVA-specific cross-priming by >80% to MHC I-restricted T cells in both TLR2- and TLR4-pathway-dependent manners. Accordingly, biglycan-induced cross-priming by both MyD88- and TRIF-deficient dendritic cells (DCs) was strongly diminished. OVA-specific activation of MHC II-restricted T cells was predominantly TLR4 dependent. Our first in vivo correlate was a model of experimental autoimmune perimyocarditis triggered by injection of cardiac Ag-pulsed DCs (BALB/c). Biglycan-treated DCs triggered perimyocarditis to a comparable extent and intensity as LPS-treated DCs (mean scores 1.3 ± 0.3 and 1.5 ± 0.4, respectively). Substitution with TLR4-deficient DCs abolished this effect. In a second in vivo approach, WT and biglycan-deficient mice were followed 2 wk after induction of myocardial infarction. WT mice demonstrated significantly greater myocardial T lymphocyte infiltration in comparison with biglycan-deficient animals. We concluded that the TLR2/4 ligand biglycan, a component of the myocardial matrix, may enhance Ag-specific T cell priming, potentially via MyD88 and TRIF, and stimulate autoimmune perimyocarditis.

Expression of small leucine-rich proteoglycans in the developing retina and kainic acid-induced retinopathy in ICR mice

The aim of this study was to determine the developmental changes of small leucine-rich proteoglycans (PGs), decorin, biglycan and fibromodulin, in ICR mouse retinas and to elucidate their role in the adult retina using kainic acid (KA)-induced retinal degeneration model. Retinas of prenatal, postnatal and adult mice were collected for histological and immunohistochemical staining to investigate the changes in distribution of these PGs. Decorin-and fibromodulin-immunostainings were diffusely distributed at prenatal and early postnatal stages and were stronger in the adult retina. However, biglycan was moderately distributed in the prenatal and early postnatal stages and was faint in the adult retina. Retinas were collected at 1, 3 and 7 days after intravitreal injection of KA. Retinas of KA injected eyes underwent shrinkage accompanied by serious damage in the inner layers. Decorin and fibromodulin were upregulated in the inner retinal layers of KA-injected eyes compared to the normal ones. Our results suggest that decorin and fibromodulin play key roles in retinal differentiation, and contribute to the retinal damage and repair process. However, biglycan may have no or only a limited role in the mouse retinal development or repair process.

The Factor H Variant Associated with Age-related Macular Degeneration (His-384) and the Non-disease-associated Form Bind Differentially to C-reactive Protein, Fibromodulin, DNA, and Necrotic Cells

Recently, a polymorphism in the complement regulator factor H (FH) gene has been associated with age-related macular degeneration. When histidine instead of tyrosine is present at position 384 in the seventh complement control protein (CCP) domain of FH, the risk for age-related macular degeneration is increased. It was recently shown that these allotypic variants of FH, in the context of a recombinant construct corresponding to CCPs 6-8, recognize polyanionic structures differently, which may lead to altered regulation of the alternative pathway of complement. We show now that His-384, corresponding to the risk allele, binds C-reactive protein (CRP) poorly compared with the Tyr-384 form. We also found that C1q and phosphorylcholine do not compete with FH for binding to C-reactive protein. The interaction with extracellular matrix protein fibromodulin, which we now show to be mediated, at least in part, by CCP6-8 of FH, occurs via the polypeptide of fibromodulin and not through its glycosaminoglycan modifications. The Tyr-384 variant of FH bound fibromodulin better than the His-384 form. Furthermore, we find that CCP6-8 is able to interact with DNA and necrotic cells, but in contrast the His-384 allotype binds these ligands more strongly than the Tyr-384 variant. The variations in binding affinity of the two alleles indicate that complement activation and local inflammation in response to different targets will differ between His/His and Tyr/Tyr homozygotes.

Cartilage elasticity resides in shape module decoran and aggrecan sumps of damping fluid: implications in osteoarthrosis

Cartilage ultrastructure is based on collagen fibrils tied together by proteoglycans (PGs). Interfibrillar orthogonal PG bridges ('shape modules') were located by electron histochemistry using Cupromeronic blue methodology. Their frequency and size, similar to those in tendon, cornea, etc., were compatible with biochemical estimates of tissue decoran (formerly decorin), the PG component of shape module bridges. Digestion by hyaluronanase and chondroitinase AC helped to identify aggrecan and decoran and exemplified the destruction of shape modular organization by glycan-splitting agents. The anionic glycosaminoglycan (AGAG) of decoran, dermochondan sulphate (DS, formerly dermatan sulphate), contains L-iduronate, an elastic sugar unit. Chondroitan, keratan (present in aggrecan) and hyaluronan are not similarly elastic but can participate in sliding-filament reversible deformability. Mechanical properties predicted for the interfibrillar bridges accord with anisotropic stress/strain responses of articular cartilage to compressive or tensile stresses. We propose that fluid from pericellular aggrecan-rich domains moves under pressure into the interterritorial fibrillar arrays against the elastic resistance of the shape modules, which return the fluid, post-compression, to its original position. Cartilage is tendon-like, with the addition of expansile aggrecan-rich reservoirs of aqueous shock absorber fluid. Rupture or loss of interfibrillar ties would allow expansile PG to force the collagenous matrix apart, imbibing water, increasing swelling and fissuring--characteristic manifestations of osteoarthrosis (OA), a joint disease of major economic importance. Decoran may be a primary target of the OA disease process.

A history of the understanding of cartilage

OBJECTIVE

To review the historic development of the understanding of articular cartilage from the earliest comment in the fourth century BCE until about 2000.

DESIGN

The history up to 1900 is told chronologically, divided into (1) recognition of the tissue, (2) structure, and (3) chemistry. The twentieth century is sketched with a timeline of discoveries that at the time were important and a bibliography of journal review articles.

RESULTS

By 1900 the avascular, aneural state and fibrillar composition have been accepted. The nutrition of articular cartilage remained in dispute. The composition of the binding substance and its relation to collagen remained unknown. Research in the first half of the twentieth century continued to be impeded by lack of technology. The advent of electron microscopy, isotopic tracer technics and enzymology rapidly accelerated the understanding of hyaline cartilage beginning in the 1950s.

CONCLUSIONS

The history of research on hyaline cartilage illustrates the dependence of scientific progress on technologic innovation.

Microarray-based identification of VegT targets in Xenopus

The Xenopus T box family member VegT is expressed maternally in the vegetal hemisphere of the embryo. Mis-expression of VegT in prospective ectodermal tissue causes ectopic activation of mesodermal and endodermal markers, and ablation of VegT transcripts prevents proper formation of the mesendoderm, with the entire embryo developing as epidermis. These observations define VegT as a key initiator of mesendodermal development in the Xenopus embryo, and in an effort to understand how it exerts its effects we have used microarray analysis to compare gene expression in control animal caps with that in ectodermal tissue expressing an activated form of VegT. This procedure allowed the identification of 99 potential VegT targets, and we went on to study the expression patterns of these genes and then to ask, for those that are expressed in mesoderm or endoderm, which are direct targets of VegT. The putative regulatory regions of the resulting 14 genes were examined for T domain binding sites, and we also asked whether their expression is down-regulated in embryos in which VegT RNA is ablated. Finally, the functions of these genes were assayed by both over-expression and by use of antisense morpholino oligonucleotides. Our results provide new insights into the function of VegT during early Xenopus development.

In vitro demonstration of cell-to-cell interaction in growth plate cartilage using chondrocytes established from p53-/- mice

Three clonal cell lines (MMR14, MMR17, and MMR32) were established from the costal cartilage derived from p53-/- mice. Expression profiles of cartilage-related molecules in MMR14 and MMR17 were compatible with those in cells of the hypertrophic zone. Prolonged in vitro culture induced the expression of calcification-related genes in both cell lines, but calcified nodules were observed only in MMR14. The expression profile of cartilage-related molecules in MMR32 was compatible with that of cells in the perichondrium, with high expression levels of decorin, bone morphogenetic protein-3, and parathyroid hormone-related peptide (PTHrP). When MMR14 was co-cultured with an equal amount of MMR32 without direct contact, the nodule formation was completely inhibited, whereas no such inhibition was observed when MMR14 was co-cultured with MMR17, indicating that soluble factors produced by MMR32 were responsible for the inhibition. Blocking the effects of PTHrP by either antagonizing peptide or neutralizing antibody against PTHrP failed to rescue the inhibitory effects of MMR32, and no increase of the cyclic adenosine monophosphate production in MMR14 was observed when co-cultured with MMR32, suggesting that soluble factors other than PTHrP produced by MMR32 were responsible for the inhibition of terminal differentiation of hypertrophic chondrocytes. This report is the first to show cell-to-cell interaction in the growth plate using cell lines, which will be useful material to investigate the regulatory mechanism of chondrocyte differentiation.

The interactions of cartilage proteoglycans with collagens are determined by their structures

In the present work, the interaction of aggrecan, decorin and biglycan isolated from pig laryngeal cartilage and of the three squid cartilage proteoglycans with collagen type I and II was studied. The interaction was examined under conditions allowing the formation of collagen fibrils. It was found that biglycan interacted strongly with collagen type II and not with type I and the interaction seemed to proceed exclusively through its core proteins. Decorin interacted with collagen type I but not with type II. Aggrecan interacted very poorly with both collagen types. The two squid proteoglycans of large size, D1D1A and D1D2, interacted only with collagen type I through both glycosaminoglycans and core proteins. The third squid proteoglycan of small size, D1D1B, interacted poorly only with collagen type I. The results suggested that the interactions of cartilage proteoglycans with collagen were mainly due to the primary structure of both molecules, and would contribute to the maintenance of the integrity of the tissue. The biochemical significance of these interactions might be more critical in aged vertebrate cartilage, where loss of aggrecan and increase of the small proteoglycans was observed, a large proportion of which is found in the extracellular matrix free of glycosaminoglycan chains.

Effects of intraoral splint wear on proteoglycans in the temporomandibular joint disc

Intraoral splints are a common dental treatment for dysfunctions of the temporomandibular joint (TMJ), but their effects on the structures of the joint, specifically the disc, have not been well investigated. This study examined proteoglycans (PGs) of the TMJ disc of the miniature pig and tested for alterations resulting from intraoral splint wear. Sixteen female pigs were divided into three groups: control (C), control splint (CS), and protrusive splint (PS). Splinted groups received chrome-cobalt ramp splints which were worn continuously for 2 months. PG content within various disc locations was determined by colorimeteric assay. PG synthesis and type were examined by labeling with (35)S-sulfate and SDS-PAGE analysis. Average water content of the disc was 77.1%, which places it at the high end of the normal range for collagenous biomaterials (60-80%). PGs migrating to the positions typical of aggrecan, biglycan, and decorin on SDS-PAGE were present in all locations of all groups. The highest content and synthesis of PGs were always found in the intermediate band of the disc regardless of group (P < 0.05), supporting the notion that this band encounters heavy compressive loading during function. The joints of animals from both splinted groups showed a high frequency of gross pathology. Biglycan synthesis was increased in both splinted groups (P < 0.05). Newly synthesized biglycan had a shorter migration distance in the intermediate bands of the CS group, suggesting increased hydrodynamic size. These findings suggest that intraoral splint wear may cause disc damage or remodeling.

The small proteoglycan fibromodulin is expressed in mitotic, but not in postmitotic fibroblasts

The small proteoglycan fibromodulin is involved in a variety of adhesion processes of connective tissue, binds to collagen and seems to influence fibrillogenesis by regulating collagen fibril spacing and thickness. Using subtractive hybridisation and Northern blotting, we found expression of the fibromodulin gene only in mitotic but not in mitomycinC-induced postmitotic fibroblasts. Furthermore, we could show that in skin only fibroblasts but not endothelial cells and keratinocytes express fibromodulin. With age the thickness of collagen fibrils increases as well as the occurrence of postmitotic fibroblasts. We could show with different chemotaxis and similar collagen gel contraction experiments further physiological differences between mitotic and postmitotic fibroblasts. This is the first report showing the switch of mitotic to postmitotic fibroblasts at the molecular level. Therefore, fibromodulin provides a specific marker for mitotic versus postmitotic fibroblasts and could indicate cell ageing. Mitomycin C is therapeutically used in bladder carcinoma and could thus induce premature ageing of fibroblasts.

Inhibition of human fibroblast adhesion by cartilage surface proteoglycans

OBJECTIVE

Recent studies from our laboratory have identified the nonaggregating, collagen-binding proteoglycans, fibromodulin (FM) and decorin, and fibronectin (Fn) and albumin, noncovalently bound at the articular surface of cartilage. The present studies were designed to investigate the interactions between these cartilage macromolecules and the underlying collagen matrix and their role as a barrier to cell adhesion in intact articular cartilage.

METHODS

Cell adhesion studies were carried out with human skin fibroblasts incubated on the articular surface of bovine cartilage explants and on collagen-coated and/or Fn-coated plastic surfaces. Interactions of collagen and Fn with either FM or decorin were studied by radioimmunoassay of the same surfaces, using specific antibodies.

RESULTS

The present studies show that 1) Fn is immunologically detectable at the intact articular surface of cartilage; 2) fibroblast adhesion to Fn is inhibited by cartilage surface extract proteins and by purified FM, but not by purified decorin; 3) FM has binding affinity for Fn; 4) FM interferes with the binding of a monoclonal antibody specific for the cell-binding domain of Fn; and 5) FM and decorin inhibit collagen-dependent fibroblast adhesion.

CONCLUSION

These results indicate that the small proteoglycans at the normal articular surface may act as a barrier to cell adhesion. Since protective cartilage surface proteins break down readily after the induction of acute arthritis in experimental animals, and in rheumatoid cartilage specimens, it is postulated that proteolytic degradation of the surface proteoglycans may be responsible for increasing cell adhesion to, and subsequent pannus invasion of, articular cartilage in inflammatory arthritis.

Mechanism of longitudinal bone growth and its regulation by growth plate chondrocytes

Growth plate chondrocytes play a pivotal role in promoting longitudinal bone growth. The current review represents a brief survey of the phenomena involved in this process at the cellular level; it delineates the contributions made by various activities during the course of the chondrocyte life cycle, notably proliferation and hypertrophy, and illustrates how the relative contributions may be modulated according to the particular needs of an organism at critical phases of growth. The cellular mechanisms by which a few well characterized growth-promoting substances exert their influences are discussed in the light of recent findings pertaining to epiphyseal plate chondrocytes in vivo.

The effects of orally administered calcium pentosan polysulfate on inflammation and cartilage degradation produced in rabbit joints by intraarticular injection of a hyaluronate-polylysine complex

OBJECTIVE

To determine the antiinflammatory and cartilage-protecting activities of orally administered calcium pentosan polysulfate (CaPPS) in a rabbit model of inflammatory arthritis.

METHODS

A single intraarticular injection of a preformed polycation complex (PC) of poly-D-lysine and hyaluronan was used to induce joint inflammation; saline was injected into the contralateral joint as a control. Animals were killed 1, 4, 7, or 10 days post-PC injection. CaPPS, at 5 mg/kg, 10 mg/kg, or 75 mg/kg, was given every 48 hours commencing 7 days prior to PC injection. Serum interleukin-6 (IL-6), synovial fluid (SF) prostaglandin E2, cell numbers, and cartilage proteoglycan (PG) content, composition, and biosynthesis were determined for PC- and saline-injected joints.

RESULTS

In PC-injected, non-drug-treated animals, serum IL-6 activity, SF leukocyte numbers, and prostaglandin E2 levels were elevated, while cartilage PG content and biosynthesis were reduced. CaPPS at 10 mg/kg, but not at 5 mg/kg, decreased serum IL-6 levels but maintained cartilage PG concentration and biosynthesis. However, SF leukocyte counts and prostaglandin E2 levels (except on day 1) were not reduced.

CONCLUSION

The ability of CaPPS to attenuate serum IL-6 levels and preserve cartilage PGs in inflamed rabbit joints suggests that this substance could be of value as an effective orally administered chondroprotective, antiarthritic drug.

Proteoglycan heterogeneity in the normal adult ovine intervertebral disc

Proteoglycans (PGs) were isolated from 4 M GuHCl extracts of young adult ovine Intervertebral disc (IVD) tissues using sequential CsCl density gradient centrifugation, and a combination of gel-permeation and hydrophobic chromatography. A total of six PG sub-populations were identified in both the Annulus fibrosus (AF) and Nucleus pulposus (NP), i.e. two high buoyant density aggregatable PGs, two high buoyant density non-aggregatable PGs and two small, low-intermediate buoyant density, non-aggregatable, DS-rich PG species. These latter PGs were identified as biglycan and decorin on the basis of analyses of their core protein native size, and glycosaminoglycan composition. Additional low-intermediate buoyant density PG species were also evident in the non-aggregatable PG pool, particularly in extracts of NP tissues. These PGs did not bind to the octyl affinity matrix under the experimental conditions employed and thus were readily separated from the DS-PGs by hydrophobic chromatography, their constituent glycosaminoglycans (CS and KS) also differed and were of a smaller size to the CS and KS chains isolated from the large high buoyant density PGs, the small PGs which did not bind to octyl-sepharose may therefore represent distinct PG species in their own right. Differences were evident in the absolute size, and in the distribution of individual PG species in the respective IVD tissues but the NP always contained a larger proportion of high buoyant density non-aggregatable PGs of somewhat smaller size than those isolated from the AF. Decorin and biglycan, however, were generally more abundant in AF tissues.

Identification and characterization of glycanated and non-glycanated forms of biglycan and decorin in the human intervertebral disc

Immunological studies revealed the presence of several different forms of biglycan and decorin in human intervertebral-disc tissues (annulus fibrosus, nucleus pulposus and cartilage end-plate). In the young intervertebral disc, glycosaminoglycan-containing (glycanated) forms of both biglycan and decorin represented a greater proportion of the total proteoglycan population present in extracts of annulus fibrosus and cartilage end-plate compared with extracts of nucleus pulposus, in which they were barely detectable. In older discs the glycanated forms of biglycan and decorin represented only a small proportion of the total proteoglycan present. Immunochemical analyses with an antibody to chondroitin/dermatan sulphate isomers indicated differences in the glycosaminoglycans substituted on glycanated forms of small proteoglycans found in different disc tissues. Dermatan sulphate was the predominant glycosaminoglycan present on biglycan and decorin in annulus fibrosus extracts, whereas chondroitin 4-sulphate was present in both small proteoglycans isolated from cartilage end-plate. In addition, immunochemical analyses with antibodies against core protein epitopes identified two non-glycanated forms of both biglycan and decorin. These non-glycanated forms of the small proteoglycans were found in all three regions of the disc. The two nonglycanated forms of biglycan had estimated molecular masses of 37 and 41 kDa and those of decorin were 43 and 45 kDa, respectively. These non-glycanated forms of biglycan and decorin increased in proportion with aging. N-terminal sequence analysis indicated that the larger non-glycanated form of decorin was a degradation product of its glycanated precursor. However, no N-terminal sequence information was obtainable from the other non-glycanated form of decorin or the two non-glycanated forms of biglycan. These data are consistent with the hypothesis that some of the non-glycanated forms of decorin and biglycan are degradation products of native precursors. However, the possibility remains that several different post-translationally modified forms of decorin and biglycan are synthesized by intervertebral-disc tissues.

Effects of intraarticular hyaluronan on matrix changes induced in the lateral meniscus by total medial meniscectomy and exercise

Total medial meniscectomy was performed in 12 adult merino sheep. Immediately after surgery, 8 animals received high-molecular-weight hyaluronan (HA) (1 mL, 10 mg/mL) and 4 were given sterile saline (1 mL) intraarticularly. Injections were given for 5 more weeks. In week 3 an exercise program, consisting of walking 24 km/wk, was initiated. This program was continued until the animals were killed at week 26 postmeniscectomy. At necropsy the lateral menisci were removed and divided into three concentric zones--inner, middle, and outer. Powdered aliquots of tissues from each zone were analyzed for collagen and hexuronate contents using colormetric methods. The glycosaminoglycans (GAGs)--chondroitin-O-sulfate (C-O-S), chondroitin-4-sulfate (C-4-S), chondroitin-6-sulfate (C-6-S), and dermatan sulfate (DS)--were determined using a high-performance liquid chromatography method. The lateral menisci from the joints of animals injected with HA showed higher hexuronate and GAG levels than those of controls. This increase was mainly due to C-6-S, which had highest levels in the inner and middle meniscal zones. In addition, dermatan sulfate levels increased significantly in the middle and outer zones of the lateral menisci compared with the same zones of the meniscus from the saline-treated group. Collagen and C-O-S levels were not statistically different from those of controls. These data suggest that intraarticular administration of high-molecular-weight HA immediately after open total medial meniscectomy may help preserve the proteoglycans in the lateral meniscus remaining in the joint.