Phenotypic characterization of epiphycan-deficient and epiphycan/biglycan double-deficient mice

Apolipoprotein E is a novel marker for chondrocytes in the growth plate resting zone

The resting zone (RZ) in mammalian growth plates is critical for maintaining and regulating chondrocyte turnover during longitudinal bone growth as a control tower and stem cell reservoir. Although recent lineage tracing studies have identified several markers for stem cells in the RZ, these markers only partially label chondrocytes in the RZ, suggesting that the resting chondrocytes (RCs) are a heterogeneous population with different types of stem cells. Since a comprehensive marker for RCs is still lacking, the RZ is generally determined based on ambiguous histological criteria, such as small and round chondrocytes without columnar formation, which may lead to inconsistencies among researchers. Therefore, in this study, we used single-cell RNA sequencing (scRNAseq) of growth plate chondrocytes followed by validation by fluorescence in situ hybridization (FISH) to precisely annotate cell clusters in scRNAseq and search for a marker of RCs. The scRNAseq analysis revealed that apolipoprotein E (Apoe) was the top-hit gene, which was ubiquitously expressed in the RC cluster. FISH confirmed that Apoe was exclusively localized to the histologically defined RZ. In newly generated Apoe-mCherry knock-in mice, we further confirmed that mCherry expression mirrored the distribution of Apoe-expressing chondrocytes in the RZ particularly after the formation of the secondary ossification center. These mCherry+ RCs were slow cycling in vivo and exhibited stem cell properties both in vitro and in vivo. Moreover, APOE was detected in human growth plate RCs. These findings suggest that Apoe is a novel pan-RC marker in both mouse and human growth plates.

Cartilage decellularized matrix hydrogel loaded with protocatechualdehyde for targeted epiphycan treatment of osteoarthritis

Osteoarthritis (OA) is a prevalent chronic disease, characterized by chronic inflammation and cartilage degradation. This study aims to deepen the understanding of OA's pathophysiology and to develop novel therapeutic strategies. Our study underscores the pivotal role of Epiphycan (EPYC) and the IL-17 signaling pathway in OA. EPYC, an essential extracellular matrix constituent, has been found to exhibit a positive correlation with the severity of OA. We have discovered that EPYC modulates the activation of the IL-17 signaling pathway within chondrocytes by regulating the interaction between IL-17A and its receptor, IL-17RA. This regulatory mechanism underscores the intricate interplay between the extracellular matrix and immune signaling in the pathogenesis of OA Another finding of our study is the therapeutic effectiveness of protocatechualdehyde (PAH) in OA. PAH significantly reduces chondrocyte hypertrophy and supports cartilage tissue recovery.by targets EPYC. To reduce the side effects of orally administered PAH and maintain its effective drug concentration, we have developed a decellularized matrix hydrogel loaded with PAH for intra-articular injection. This novel drug delivery system is advantageous in minimizing drug-related side effects and ensuring sustained release PAH within the joint cavity.

Effects of immediate loading directionality on the mechanical sensing protein PIEZO1 expression and early-stage healing process of peri-implant bone

BACKGROUND

The reduced treatment time of dental implants with immediate loading protocol is an appealing solution for dentists and patients. However, there remains a significant risk of early peri-implant bone response following the placement of immediately loaded implants, and limited information is available regarding loading directions and the associated in vivo characteristics of peri-implant bone during the early stages. This study aimed to investigate the effects of immediate loading directionality on the expression of mechanical sensing protein PIEZO1 and the healing process of peri-implant bone in the early stage.

METHODS

Thirty-two implants were inserted into the goat iliac crest models with 10 N static lateral immediate loading applied, followed by histological, histomorphological, immunohistochemical, X-ray microscopy and energy dispersive X-ray spectroscopy evaluations conducted after 10 days.

RESULTS

From evaluations at the cellular, tissue, and organ levels, it was observed that the expression of mechanical sensing protein PIEZO1 in peri-implant bone was significantly higher in the compressive side compared to the tensile side. This finding coincided with trends observed in interfacial bone extracellular matrix (ECM) contact percentage, bone mass, and new bone formation.

CONCLUSIONS

This study provides a novel insight into the immediate loading directionality as a potential influence factor for dental implant treatments by demonstrating differential effects on the mechanical sensing protein PIEZO1 expression and related early-stage healing processes of peri-implant bone. Immediate loading directions serve as potential therapeutic influence factors for peri-implant bone during its early healing stage.

Osteomodulin downregulation is associated with osteoarthritis development

Abnormal subchondral bone remodeling leading to sclerosis is a main feature of osteoarthritis (OA), and osteomodulin (OMD), a proteoglycan involved in extracellular matrix mineralization, is associated with the sclerotic phenotype. However, the functions of OMD remain poorly understood, specifically in vivo. We used Omd knockout and overexpressing male mice and mutant zebrafish to study its roles in bone and cartilage metabolism and in the development of OA. The expression of Omd is deeply correlated with bone and cartilage microarchitectures affecting the bone volume and the onset of subchondral bone sclerosis and spontaneous cartilage lesions. Mechanistically, OMD binds to RANKL and inhibits osteoclastogenesis, thus controlling the balance of bone remodeling. In conclusion, OMD is a key factor in subchondral bone sclerosis associated with OA. It participates in bone and cartilage homeostasis by acting on the regulation of osteoclastogenesis. Targeting OMD may be a promising new and personalized approach for OA.

Unravelling the limb regeneration mechanisms of Polypedates maculatus, a sub-tropical frog, by transcriptomics

BACKGROUND

Regeneration studies help to understand the strategies that replace a lost or damaged organ and provide insights into approaches followed in regenerative medicine and engineering. Amphibians regenerate their limbs effortlessly and are indispensable models to study limb regeneration. Xenopus and axolotl are the key models for studying limb regeneration but recent studies on non-model amphibians have revealed species specific differences in regeneration mechanisms.

RESULTS

The present study describes the de novo transcriptome of intact limbs and three-day post-amputation blastemas of tadpoles and froglets of the Asian tree frog Polypedates maculatus, a non-model amphibian species commonly found in India. Differential gene expression analysis between early tadpole and froglet limb blastemas discovered species-specific novel regulators of limb regeneration. The present study reports upregulation of proteoglycans, such as epiphycan, chondroadherin, hyaluronan and proteoglycan link protein 1, collagens 2,5,6, 9 and 11, several tumour suppressors and methyltransferases in the P. maculatus tadpole blastemas. Differential gene expression analysis between tadpole and froglet limbs revealed that in addition to the expression of larval-specific haemoglobin and glycoproteins, an upregulation of cysteine and serine protease inhibitors and downregulation of serine proteases, antioxidants, collagenases and inflammatory genes in the tadpole limbs were essential for creating an environment that would support regeneration. Dermal myeloid cells were GAG+, EPYC+, INMT+, LEF1+ and SALL4+ and seemed to migrate from the unamputated regions of the tadpole limb to the blastema. On the other hand, the myeloid cells of the froglet limb blastemas were few and probably contributed to sustained inflammation resulting in healing.

CONCLUSIONS

Studies on non-model amphibians give insights into alternate tactics for limb regeneration which can help devise a plethora of methods in regenerative medicine and engineering.

Unusual Suspects: Bone and Cartilage ECM Proteins as Carcinoma Facilitators

The extracellular matrix (ECM) is the complex three-dimensional network of fibrous proteins and proteoglycans that constitutes an essential part of every tissue to provide support for normal tissue homeostasis. Tissue specificity of the ECM in its topology and structure supports unique biochemical and mechanical properties of each organ. Cancers, like normal tissues, require the ECM to maintain multiple processes governing tumor development, progression and spread. A large body of experimental and clinical evidence has now accumulated to demonstrate essential roles of numerous ECM components in all cancer types. Latest findings also suggest that multiple tumor types express, and use to their advantage, atypical ECM components that are not found in the cancer tissue of origin. However, the understanding of cancer-specific expression patterns of these ECM proteins and their exact roles in selected tumor types is still sketchy. In this review, we summarize the latest data on the aberrant expression of bone and cartilage ECM proteins in epithelial cancers and their specific functions in the pathogenesis of carcinomas and discuss future directions in exploring the utility of this selective group of ECM components as future drug targets.

Benefits of lumican on human bone health: clinical evidence using bone marrow aspirates

BACKGROUND/AIMS

Lumican, a small leucine-rich proteoglycan, has shown osteoprotective effects by synchronously stimulating bone formation and suppressing bone resorption. To clarify the role of lumican in human bone metabolism, the association between lumican concentrations and osteoporosis-related phenotypes was evaluated using bone marrow (BM) samples directly reflecting local microenvironments.

METHODS

BM aspirates were obtained from 77 patients during hip surgery for either fragility hip fractures (HF) (n = 29) or osteoarthritis (n = 48) and centrifuged. Concentrations of lumican and biochemical bone markers in BM supernatants were measured using enzyme linked immunosorbent assays.

RESULTS

After considering confounders, lumican concentrations in BM supernatants were 16.9% lower in patients with HF than in controls, with each increase in the standard deviation of lumican concentration being associated with a 61% lower likelihood of HF. The odds ratios for HF decreased linearly with increasing lumican tertiles in BM, with the odds of having fragility HF markedly lower in participants in the highest than in the lowest lumican tertile. Higher lumican level correlated significantly with higher femur neck bone mineral density and higher bone-specific alkaline phosphatase levels, but not with tartrate-resistant acid phosphatase 5b concentrations, in BM supernatants.

CONCLUSION

These data clinically validate previous in vitro and animal experiments showing the beneficial roles of lumican for bone homeostasis and suggest that lumican may contribute to a reduction in fracture risk in humans mainly through its stimulation of bone formation.

Local depletion of proteoglycans mediates cartilage tissue repair in an ex vivo integration model

Successfully replacing damaged cartilage with tissue-engineered constructs requires integration with the host tissue and could benefit from leveraging the native tissue's intrinsic healing capacity; however, efforts are limited by a poor understanding of how cartilage repairs minor defects. Here, we investigated the conditions that foster natural cartilage tissue repair to identify strategies that might be exploited to enhance the integration of engineered/grafted cartilage with host tissue. We damaged porcine articular cartilage explants and using a combination of pulsed SILAC-based proteomics, ultrastructural imaging, and catabolic enzyme blocking strategies reveal that integration of damaged cartilage surfaces is not driven by neo-matrix synthesis, but rather local depletion of proteoglycans. ADAMTS4 expression and activity are upregulated in injured cartilage explants, but integration could be reduced by inhibiting metalloproteinase activity with TIMP3. These observations suggest that catabolic enzyme-mediated proteoglycan depletion likely allows existing collagen fibrils to undergo cross-linking, fibrillogenesis, or entanglement, driving integration. Catabolic enzymes are often considered pathophysiological markers of osteoarthritis. Our findings suggest that damage-induced upregulation of metalloproteinase activity may be a part of a healing response that tips towards tissue destruction under pathological conditions and in osteoarthritis, but could also be harnessed in tissue engineering strategies to mediate repair. STATEMENT OF SIGNIFICANCE: Cartilage tissue engineering strategies require graft integration with the surrounding tissue; however, how the native tissue repairs minor injuries is poorly understood. We applied pulsed SILAC-based proteomics, ultrastructural imaging, and catabolic enzyme blocking strategies to a porcine cartilage explant model and found that integration of damaged cartilage surfaces is driven by catabolic enzyme-mediated local depletion of proteoglycans. Although catabolic enzymes have been implicated in cartilage destruction in osteoarthritis, our findings suggest that damage-induced upregulation of metalloproteinase activity may be a part of a healing response that tips towards tissue destruction under pathological conditions. They also suggest that this natural cartilage tissue repair process could be harnessed in tissue engineering strategies to enhance the integration of engineered cartilage with host tissue.

Nanoscale Imaging and Analysis of Bone Pathologies

Understanding the properties of bone is of both fundamental and clinical relevance. The basis of bone’s quality and mechanical resilience lies in its nanoscale building blocks (i.e., mineral, collagen, non-collagenous proteins, and water) and their complex interactions across length scales. Although the structure–mechanical property relationship in healthy bone tissue is relatively well characterized, not much is known about the molecular-level origin of impaired mechanics and higher fracture risks in skeletal disorders such as osteoporosis or Paget’s disease. Alterations in the ultrastructure, chemistry, and nano-/micromechanics of bone tissue in such a diverse group of diseased states have only been briefly explored. Recent research is uncovering the effects of several non-collagenous bone matrix proteins, whose deficiencies or mutations are, to some extent, implicated in bone diseases, on bone matrix quality and mechanics. Herein, we review existing studies on ultrastructural imaging—with a focus on electron microscopy—and chemical, mechanical analysis of pathological bone tissues. The nanometric details offered by these reports, from studying knockout mice models to characterizing exact disease phenotypes, can provide key insights into various bone pathologies and facilitate the development of new treatments.

Epiphycan Predicts Poor Outcomes and Promotes Metastasis in Ovarian Cancer

The small leucine-rich proteoglycan (SLRP) family is widely expressed in extracellular matrix and aggravates tumor progression. However, epiphycan (EPYC), as a member of the SLRPs family, its biological function in cancer has not been confirmed. Thus, we aimed to clarify the role of EPYC in progression of ovarian cancer (OC), and further analyze the molecular mechanisms implicated in tumorigenesis. Here, we analyzed the differential expression genes of GSE38734, including 4 matched primary OC and metastatic tissues. We obtained OC RNAseqs data from the Cancer Genome Atlas (TCGA) and analyzed the correlation between EPYC expression and OC staging, pathological grading, etc. The expression of EPYC in OC and normal ovarian tissues was compared in Oncomine website. We used siRNAs to interfere the expression of EPYC in ovarian cancer cell line SKOV3. Scratch test, transwell-matrigel chamber, CCK8 assay were used to detect the changes of SKOV3 migration, invasion and proliferation ability after EPYC was interfered. We used R software to make GO and KEGG analysis of related genes of EPYC. We used the Hitpredict website to predict interacting proteins. The results showed that the expression of EPYC in metastatic ovarian cancer was higher than primary ovarian cancer, and that in primary cancer was higher than normal ovaries. After siRNA interferes with EPYC expression, the migration, invasion and proliferation of SKOV3 cells were weakened. EPYC mainly played a role in ECM organization, and involved in PI3K/Akt, focal adhesion signaling pathways. EPYC might interact with PLCG2 and CRK, and be involved in signal transduction.

Differentiated activities of decorin and biglycan in the progression of post-traumatic osteoarthritis

OBJECTIVE

To delineate the activities of decorin and biglycan in the progression of post-traumatic osteoarthritis (PTOA).

DESIGN

Three-month-old inducible biglycan (BgniKO) and decorin/biglycan compound (Dcn/BgniKO) knockout mice were subjected to the destabilization of the medial meniscus (DMM) surgery to induce PTOA. The OA phenotype was evaluated by assessing joint structure and sulfated glycosaminoglycan (sGAG) staining via histology, surface collagen fibril nanostructure and calcium content via scanning electron microscopy, tissue modulus via atomic force microscopy-nanoindentation, as well as subchondral bone structure and meniscus ossification via micro-computed tomography. Outcomes were compared with previous findings in the inducible decorin (DcniKO) knockout mice.

RESULTS

In the DMM model, BgniKO mice developed similar degree of OA as the control (0.44 [-0.18 1.05] difference in modified Mankin score), different from the more severe OA phenotype observed in DcniKO mice (1.38 [0.91 1.85] difference). Dcn/BgniKO mice exhibited similar histological OA phenotype as DcniKO mice (1.51 [0.97 2.04] difference vs control), including aggravated loss of sGAGs, salient surface fibrillation and formation of osteophyte. Meanwhile, Dcn/BgniKO mice showed further cartilage thinning than DcniKO mice, resulting in the exposure of underlying calcified tissues and aberrantly high surface modulus. BgniKO and Dcn/BgniKO mice developed altered subchondral trabecular bone structure in both Sham and DMM groups, while DcniKO and control mice did not.

CONCLUSION

In PTOA, decorin plays a more crucial role than biglycan in regulating cartilage degeneration, while biglycan is more important in regulating subchondral bone structure. The two have distinct activities and modest synergy in the pathogenesis of PTOA.

Males and Females Have Distinct Molecular Events in the Articular Cartilage during Knee Osteoarthritis

Osteoarthritis (OA) is a major public health challenge that imposes a remarkable burden on the affected individuals and the healthcare system. Based on the clinical observation, males and females have different prevalence rates and severity levels of OA. Thus, sex-based differences may play essential roles in OA’s prognosis and treatment outcomes. To date, the comprehensive understanding of the relationship between sex and OA is still largely lacking. In the current study, we analyzed a published transcriptome dataset of knee articular cartilage (GSE114007) from 18 healthy (five females, 13 males) and 20 OA (11 females, nine males) donors to provide a slight insight into this important but complex issue. First, comparing female healthy cartilage samples with those of males revealed 36 differential expression genes (DEGs), indicating the fundamental sex-related differences at the molecular level. Meanwhile, 923 DEGs were distinguished between OA and healthy female cartilage, which can be enriched to 15 Reactome pathways. On the other hand, when comparing OA and healthy male cartilage, there are only 419 DEGs were identified, and only six pathways were enriched against the Reactome database. The different signaling response to OA in the male and female cartilage was further enforced by recognizing 50 genes with significantly different OA-responsive expression fold changes in males and females. Particularly, 14 Reactome pathways, such as “Extracellular matrix organization”, “Collagen biosynthesis and modifying enzymes”, “Dissolution of fibrin clot”, and “Platelet Aggregation (Plug formation)”, can be noted from these 50 sex-dependent OA-responsive genes. Overall, the current study explores the Sex as a Biological Variable (SABV) at the transcriptomic level in the knee articular cartilage in both healthy status and OA event, which could help predict the differential OA prognosis and treatment outcome of males and female patients.

Lumican Inhibits Osteoclastogenesis and Bone Resorption by Suppressing Akt Activity

Lumican, a ubiquitously expressed small leucine-rich proteoglycan, has been utilized in diverse biological functions. Recent experiments demonstrated that lumican stimulates preosteoblast viability and differentiation, leading to bone formation. To further understand the role of lumican in bone metabolism, we investigated its effects on osteoclast biology. Lumican inhibited both osteoclast differentiation and in vitro bone resorption in a dose-dependent manner. Consistent with this, lumican markedly decreased the expression of osteoclastogenesis markers. Moreover, the migration and fusion of preosteoclasts and the resorptive activity per osteoclast were significantly reduced in the presence of lumican, indicating that this protein affects most stages of osteoclastogenesis. Among RANKL-dependent pathways, lumican inhibited Akt but not MAP kinases such as JNK, p38, and ERK. Importantly, co-treatment with an Akt activator almost completely reversed the effect of lumican on osteoclast differentiation. Taken together, our findings revealed that lumican inhibits osteoclastogenesis by suppressing Akt activity. Thus, lumican plays an osteoprotective role by simultaneously increasing bone formation and decreasing bone resorption, suggesting that it represents a dual-action therapeutic target for osteoporosis.

Mouse Models of Osteoarthritis: Surgical Model of Post-traumatic Osteoarthritis Induced by Destabilization of the Medial Meniscus

The surgical model of destabilization of the medial meniscus (DMM) has become a gold standard for studying the onset and progression of post-traumatic osteoarthritis (OA). The DMM model mimics clinical meniscal injury, a known predisposing factor for the development of human OA, and permits the study of structural and biological changes over the course of the disease. In addition, when applied to genetically modified or engineered mouse models, this surgical procedure permits dissection of the relative contribution of a given gene to OA initiation and/or progression. This chapter describes the requirements for the surgical induction of OA in mouse models, and provides guidelines and tools for the subsequent histological, immunohistochemical, and molecular analyses. Methods for the assessment of the contributions of selected genes in genetically modified strains are also provided.

Decorin regulates cartilage pericellular matrix micromechanobiology

In cartilage tissue engineering, one key challenge is for regenerative tissue to recapitulate the biomechanical functions of native cartilage while maintaining normal mechanosensitive activities of chondrocytes. Thus, it is imperative to discern the micromechanobiological functions of the pericellular matrix, the ~ 2-4 µm-thick domain that is in immediate contact with chondrocytes. In this study, we discovered that decorin, a small leucine-rich proteoglycan, is a key determinant of cartilage pericellular matrix micromechanics and chondrocyte mechanotransduction in vivo. The pericellular matrix of decorin-null murine cartilage developed reduced content of aggrecan, the major chondroitin sulfate proteoglycan of cartilage and a mild increase in collagen II fibril diameter vis-à-vis wild-type controls. As a result, decorin-null pericellular matrix showed a significant reduction in micromodulus, which became progressively more pronounced with maturation. In alignment with the defects of pericellular matrix, decorin-null chondrocytes exhibited decreased intracellular calcium activities, [Ca²⁺]_i, in both physiologic and osmotically evoked fluidic environments in situ, illustrating impaired chondrocyte mechanotransduction. Next, we compared [Ca²⁺]_i activities of wild-type and decorin-null chondrocytes following enzymatic removal of chondroitin sulfate glycosaminoglycans. The results showed that decorin mediates chondrocyte mechanotransduction primarily through regulating the integrity of aggrecan network, and thus, aggrecan-endowed negative charge microenvironment in the pericellular matrix. Collectively, our results provide robust genetic and biomechanical evidence that decorin is an essential constituent of the native cartilage matrix, and suggest that modulating decorin activities could improve cartilage regeneration.

Palaeoproteomic identification of breast milk protein residues from the archaeological skeletal remains of a neonatal dog

Accurate postmortem estimation of breastfeeding status for archaeological or forensic neonatal remains is difficult. Confident identification of milk-specific proteins associated with these remains would provide direct evidence of breast milk consumption. We used liquid chromatography coupled to tandem mass spectrometry (MS) to confidently identify beta-lactoglobulin-1 (LGB1) and whey acidic protein (WAP), major whey proteins associated with a neonatal dog (Canis lupus familiaris) skeleton (430–960 cal AD), from an archaeological site in Hokkaido, Japan. The age at death of the individual was estimated to be approximately two weeks after birth. Protein residues extracted from rib and vertebra fragments were analyzed and identified by matching tandem MS spectra against the dog reference proteome. A total of 200 dog protein groups were detected and at least one peptide from canine LGB1 and two peptides from canine WAP were confidently identified. These milk proteins most probably originated from the mother’s breast milk, ingested by the neonate just before it died. We suggest the milk diffused outside the digestive apparatus during decomposition, and, by being absorbed into the bones, it partially preserved. The result of this study suggests that proteomic analysis can be used for postmortem reconstruction of the breastfeeding status at the time of death of neonatal mammalian, by analyzing their skeletal archaeological remains. This method is also applicable to forensic and wildlife studies.

Human mesenchymal stem cells induced to differentiate as chondrocytes follow a biphasic pattern of extracellular matrix production

Regenerative medicine and tissue engineering studies are actively developing novel means to repair adult articular cartilage defects using biological approaches. One such approach is the harnessing of adult human therapeutic cells such as those referred to as mesenchymal stem cells. Upon exposure to chondrogenic signals, these cells differentiate and initiate the production of a complex and voluminous cartilaginous matrix that is crucial to both the structure and function of cartilage. Furthermore, this complexity requires the time-sensitive activation of a large number of genes to produce the components of this matrix. The current study analyzed the kinetics of matrix production in an aggregate culture model where adult human mesenchymal stem cells were induced to differentiate as chondrocytes. The results indicate the existence of a biphasic mode of differentiation and maturation during which matrix genes and molecules are differentially activated and secreted. These results have important implications for developing novel approaches for the creation of tissue engineered articular cartilage. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1757-1766, 2018.

In vivo effect of opticin deficiency in cartilage in a surgically induced mouse model of osteoarthritis

The SLRP opticin (OPTC) has been demonstrated to be produced and degraded in osteoarthritic (OA) human cartilage. Here, we investigated the in vivo effect of OPTC deficiency in OA cartilage. OA was induced in 10-week-old Optc^−/− and Optc^+/+ mice. Ten weeks post-surgery, cartilage was processed for histology and immunohistochemistry. SLRP expression was determined in non-operated mouse cartilage. OA Optc^−/− demonstrated significant protection against cartilage degradation. Data revealed that in non-operated Optc^−/− cartilage, expression of SLRPs lumican and epiphycan was up-regulated at day 3 and in 10-week-olds (p ≤ 0.039), and fibromodulin down-regulated in 10-week-olds (p = 0.001). Immunohistochemistry of OA mice showed a similar pattern. In OA Optc^−/− cartilage, markers of degradation and complement factors were all down-regulated (p ≤ 0.038). In OA Optc^−/− cartilage, collagen fibers were thinner and better organized (p = 0.038) than in OA Optc^+/+ cartilage. The protective effect of OPTC deficiency during OA results from an overexpression of lumican and epiphycan, known to bind and protect collagen fibers, and a decrease in fibromodulin, contributing to a reduction in the complement activation/inflammatory process. This work suggests that the evaluation of the composition of the different SLRPs in OA cartilage could be applied as a new tool for OA prognosis classification.

Irx3 and Bmp2 regulate mouse mesenchymal cell chondrogenic differentiation in both a Sox9-dependent and -independent manner

Sox9, a master regulator of cartilage development, controls the cell fate decision to differentiate from mesenchymal to chondrogenic cells. In addition, Sox9 regulates the proliferation and differentiation of chondrocytes, as well as the production of cartilage-specific proteoglycans. The existence of Sox9-independent mechanisms in cartilage development remains to be determined. Here, we attempted to identify genes involved in such putative mechanisms via microarray analysis using a mouse chondrogenic cell line, N1511. We first focused on transcription factors that exhibited upregulated expression following Bmp2 treatment, which was not altered by subsequent treatment with Sox9 siRNA. Among these, we selected positive regulators for chondrogenesis and identified Iroquois-related homeobox 3 (Irx3) as one of the candidate genes. Irx3 expression gradually increased with chondrocyte terminal differentiation in a reciprocal manner to Sox9 expression, and promoted the chondrogenic differentiation of mesenchymal cells upon Bmp2 treatment. Furthermore, Irx3 partially rescued impaired chondrogenesis by upregulating the expression of epiphycan and lumican under reduced Sox9 expression. Finally, Irx3 was shown to act in concert with Bmp2 signaling to activate the p38 MAPK pathway, which in turn stimulated Sox9 expression, as well as the expression of epiphycan and lumican in a Sox9-independent manner. These results indicate that Irx3 represents a novel chondrogenic factor of mesenchymal cells, acts synergistically with Bmp2-mediated signaling, and regulates chondrogenesis independent of the transcriptional machinery associated with Sox9-mediated regulation.

Different responses of articular cartilage to strenuous running and joint immobilization

OBJECTIVE

To compare the pathological changes in cartilage derived from rats that developed osteoarthritis either by joint immobilization or by strenuous treadmill running in order to better understand their respective pathomechanism.

METHOD

A total of 24 male Wistar rats were randomly assigned to three groups: sedentary control (CON), immobilization (IM), and strenuous running (SR). For rats in the IM group, unilateral knee joint was immobilized in flexion. Rats in the SR group underwent treadmill running with high intensity. Eight weeks later, all animals were sacrificed. Femoral condyles were collected to take histological observation for cartilage characteristic and immunohistochemistry for collagen type II. In addition, cartilage samples were obtained to assess gene expression of aggrecan, collagen type II, biglycan, and fibromodulin by quantitative RT-PCR.

RESULTS

Gross and histological observation showed osteoarthritic changes in groups SR and IM; however, more severe cartilage degradation was revealed in the latter. Proteoglycan and collagen II content decreased in groups SR and IM in comparison to group CON, with more loss in group IM. In group SR, mRNA levels in femoral cartilage were found to be unaltered for all the molecules measured. On the contrary, these molecules were significantly downregulated in group IM.

CONCLUSION

Differences in gross observation, histological characteristics, and gene expression of proteoglycans and collagen II suggest that both knee immobilization and strenuous running would lead to degenerative change of cartilage, but at different stages of the degenerative process.

Proteoglycan form and function: A comprehensive nomenclature of proteoglycans

We provide a comprehensive classification of the proteoglycan gene families and respective protein cores. This updated nomenclature is based on three criteria: Cellular and subcellular location, overall gene/protein homology, and the utilization of specific protein modules within their respective protein cores. These three signatures were utilized to design four major classes of proteoglycans with distinct forms and functions: the intracellular, cell-surface, pericellular and extracellular proteoglycans. The proposed nomenclature encompasses forty-three distinct proteoglycan-encoding genes and many alternatively-spliced variants. The biological functions of these four proteoglycan families are critically assessed in development, cancer and angiogenesis, and in various acquired and genetic diseases where their expression is aberrant.

Mouse models of osteoarthritis: surgical model of posttraumatic osteoarthritis induced by destabilization of the medial meniscus

The surgical model of destabilization of the medial meniscus (DMM) has become a gold standard for studying the onset and progression of posttraumatic osteoarthritis (OA). The DMM model mimics clinical meniscal injury, a known predisposing factor for the development of human OA, and permits the study of structural and biological changes over the course of the disease. In addition, when applied to genetically modified or engineered mouse models, this surgical procedure permits dissection of the relative contribution of a given gene to OA initiation and/or progression. This chapter describes the requirements for the surgical induction of OA in mouse models, and provides guidelines and tools for the subsequent histological, immunohistochemical, and molecular analyses. Methods for the assessment of the contributions of selected genes in genetically modified strains are also provided.

CRISPR/Cas9 mediated generation of stable chondrocyte cell lines with targeted gene knockouts; analysis of an aggrecan knockout cell line

The Swarm rat chondrosarcoma (RCS) cell lines derived from a spontaneous neoplasm in a rat spine several decades ago have provided excellent models of chondrosarcoma tumor development. In addition the robust chondrocyte phenotype (expression of a large panel of genes identical to that seen in normal rat cartilage) and the ability to generate cell clones have facilitated their extensive use in the identification of chondrocyte proteins and genes. The clustered regularly interspersed short palindromic repeat (CRISPR) technology employing the RNA-guided nuclease Cas9 has rapidly dominated the genome engineering field as a unique and powerful gene editing tool. We have generated a stable RCS cell line (RCS Cas9) expressing the nuclease Cas9 that enables the editing of any target gene or non-coding RNA by simple transfection with a guide RNA. As proof of principle, stable cell lines with targeted ablation of aggrecan expression (Acan KO) were generated and characterized. The studies show that stable chondrocyte cell lines with targeted genome editing can be quickly generated from RCS Cas9 cells using this system. The Acan KO cell lines also provided a tool for characterizing the response of chondrocytes to aggrecan loss and the role of aggrecan in chondrosarcoma development. Loss of aggrecan expression while not affecting the chondrocyte phenotype resulted in a much firmer attachment of cells to their substrate in culture. Large changes in the expression of several genes were observed in response to the absence of the proteoglycan matrix, including those for several small leucine rich proteoglycans (SLRPs), transcription factors and membrane transporters. Acan KO cells failed to form a substantial chondrosarcoma when injected subcutaneously in nude mice consistent with previous suggestions that the glycosaminoglycan-rich matrix surrounding the chondrosarcoma protects it from destruction by the host immune system. The studies provide new understanding of aggrecan function and the RCS Cas9 cell line is expected to provide a very valuable tool for the study gene function in chondrocytes.

The role of small leucine-rich proteoglycans in osteoarthritis pathogenesis

OBJECTIVE

To give an overview of the literature on the role of small leucine-rich proteoglycans (SLRPs) in osteoarthritis (OA) pathogenesis.

METHOD

A literature search was performed and reviewed using the narrative approach.

RESULTS

(1) OA is an organ disease with many tissue types and specific roles for each in the pathogenic process. (2) Key biological functions of SLRPs include interacting with collagens to modulate fibril formation, and binding various cell surface receptors and growth factors to influence cellular functions; (3) Accumulating evidence has demonstrated the involvement of SLRPs in OA pathogenesis, most of which came from SLRP-deficient mice models; (4) Possible mechanisms for SLRPs being involved in OA pathogenic process include their roles in the extracellular collagen network, TGF-β signaling pathways, subchondral bone, muscle weakness, and the innate immune inflammation; (5) SLRP-deficient mice offer a potential to understand the molecular mechanisms of OA initiation and progression. (6) Targeting SLRPs may offer a new therapeutic modality for OA through controlling and modifying the TGF-β-ECM system. (7) Monitoring SLRP fragmentation may be a promising biomarker strategy to evaluate OA status.

CONCLUSIONS

Recent literature has shown that SLRPs may play an important role in OA pathogenesis. Possible mechanisms by which SLRPs are involved in this process have also been proposed. However, further investigations are needed in this field to better understand its mechanisms, develop treatments to slow down the degenerative process, and explore new approaches for effective and timely diagnosis of OA.

Posterior amorphous corneal dystrophy is associated with a deletion of small leucine-rich proteoglycans on chromosome 12

Posterior amorphous corneal dystrophy (PACD) is a rare, autosomal dominant disorder affecting the cornea and iris. Next-generation sequencing of the previously identified PACD linkage interval on chromosome 12q21.33 failed to yield a pathogenic mutation. However, array-based copy number analysis and qPCR were used to detect a hemizygous deletion in the PACD linkage interval containing 4 genes encoding small leucine-rich proteoglycans (SLRPs): KERA, LUM, DCN, and EPYC. Two other unrelated families with PACD also demonstrated deletion of these SLRPs, which play important roles in collagen fibrillogenesis and matrix assembly. Given that these genes are essential to the maintenance of corneal clarity and the observation that knockout murine models display corneal phenotypic similarities to PACD, we provide convincing evidence that PACD is associated with haploinsufficiency of these SLRPs.

Key roles for the small leucine-rich proteoglycans in renal and pulmonary pathophysiology

BACKGROUND

Small leucine-rich proteoglycans (SLRPs) are molecules that have signaling roles in a multitude of biological processes. In this respect, SLRPs play key roles in the evolution of a variety of diseases throughout the human body.

SCOPE OF REVIEW

We will critically review current developments in the roles of SLRPs in several types of disease of the kidney and lungs. Particular emphasis will be given to the roles of decorin and biglycan, the best characterized members of the SLRP gene family.

MAJOR CONCLUSIONS

In both renal and pulmonary disorders, SLRPs are essential elements that regulate several pathophysiological processes including fibrosis, inflammation and tumor progression. Decorin has remarkable antifibrotic and antitumorigenic properties and is considered a valuable potential treatment of these diseases. Biglycan can modulate inflammatory processes in lung and renal inflammation and is a potential target in the treatment of inflammatory conditions.

GENERAL SIGNIFICANCE

SLRPs can serve as either treatment targets or as potential treatment in renal or lung disease. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Small leucine-rich proteoglycans in the vertebrae of Atlantic salmon Salmo salar

We analysed the distribution and expression of the small leucine-rich proteoglycans (SLRPs) decorin, biglycan and lumican in vertebral columns of Atlantic salmon Salmo salar L. with and without radiographically detectable deformities. Vertebral deformities are a reoccurring problem in salmon and other intensively farmed species, and an understanding of the components involved in the pathologic development of the vertebrae is important in order to find adequate solutions to this problem. Using immunohistology and light microscopy, we found that in non-deformed vertebrae biglycan, lumican and decorin were all expressed in osteoblasts at the vertebral growth zones and at the ossification front of the chondrocytic arches. Hence, the SLRPs are expressed in regions where intramembranous and endochondral ossification take place. In addition, mRNA expression of biglycan, decorin and lumican was demonstrated in a primary osteoblast culture established from Atlantic salmon, supporting the in vivo findings. Transcription of the SLRPs increased during differentiation of the osteoblasts in vitro and where lumican mRNA expression increased later in the differentiation compared with decorin and biglycan. Intriguingly, in vertebral fusions, biglycan, decorin and lumican protein expression was extended to trans-differentiating cells at the border between arch centra and osteoblast growth zones. In addition, mRNA expression of biglycan, decorin and lumican differed between non-deformed and fused vertebrae, as shown by quantitative PCR (qPCR). Western blotting revealed an additional band of biglycan in fused vertebrae which had a higher molecular weight than in non-deformed vertebrae. Fourier-transform infrared (FTIR) spectroscopy revealed more spectral focality in the endplates of vertebral fusions and significantly more non-reducible collagen crosslinks compared with non-deformed vertebrae, thus identifying differences in bone structure.

Dermatan 4-O-sulfotransferase1 ablation accelerates peripheral nerve regeneration

Chondroitin sulfate (CS) and dermatan sulfate (DS) proteoglycans are major components of the extracellular matrix implicated in neural development, plasticity and regeneration. While it is accepted that CS are major inhibitors of neural regeneration, the contributions of DS to regeneration have not been assessed. To enable a novel approach in studies on DS versus CS roles during development and regeneration, we generated a mouse deficient in the dermatan 4-O-sulfotransferase1 (Chst14(-/-)), a key enzyme in the synthesis of iduronic acid-containing modules found in DS but not CS. In wild-type mice, Chst14 is expressed at high levels in the skin and in the nervous system, and is enriched in astrocytes and Schwann cells. Ablation of Chst14, and the assumed failure to produce DS, resulted in smaller body mass, reduced fertility, kinked tail and increased skin fragility compared with wild-type (Chst14(+/+)) littermates, but brain weight and gross anatomy were unaffected. Neurons and Schwann cells from Chst14(-/-) mice formed longer processes in vitro, and Chst14(-/-) Schwann cells proliferated more than Chst14(+/+) Schwann cells. After femoral nerve transection/suture, functional recovery and axonal regrowth in Chst14(-/-) mice were initially accelerated but the final outcome 3months after injury was not better than that in Chst14(+/+) littermates. These results suggest that while Chst14 and its enzymatic products might be of limited importance for neural development, they may contribute to the regeneration-restricting environment in the adult mammalian nervous system.

Comparative proteomic analysis of normal and collagen IX null mouse cartilage reveals altered extracellular matrix composition and novel components of the collagen IX interactome

BACKGROUND

Collagen IX is an integral cartilage extracellular matrix component important in skeletal development and joint function.

RESULTS

Proteomic analysis and validation studies revealed novel alterations in collagen IX null cartilage.

CONCLUSION

Matrilin-4, collagen XII, thrombospondin-4, fibronectin, βig-h3, and epiphycan are components of the in vivo collagen IX interactome.

SIGNIFICANCE

We applied a proteomics approach to advance our understanding of collagen IX ablation in cartilage. The cartilage extracellular matrix is essential for endochondral bone development and joint function. In addition to the major aggrecan/collagen II framework, the interacting complex of collagen IX, matrilin-3, and cartilage oligomeric matrix protein (COMP) is essential for cartilage matrix stability, as mutations in Col9a1, Col9a2, Col9a3, Comp, and Matn3 genes cause multiple epiphyseal dysplasia, in which patients develop early onset osteoarthritis. In mice, collagen IX ablation results in severely disturbed growth plate organization, hypocellular regions, and abnormal chondrocyte shape. This abnormal differentiation is likely to involve altered cell-matrix interactions but the mechanism is not known. To investigate the molecular basis of the collagen IX null phenotype we analyzed global differences in protein abundance between wild-type and knock-out femoral head cartilage by capillary HPLC tandem mass spectrometry. We identified 297 proteins in 3-day cartilage and 397 proteins in 21-day cartilage. Components that were differentially abundant between wild-type and collagen IX-deficient cartilage included 15 extracellular matrix proteins. Collagen IX ablation was associated with dramatically reduced COMP and matrilin-3, consistent with known interactions. Matrilin-1, matrilin-4, epiphycan, and thrombospondin-4 levels were reduced in collagen IX null cartilage, providing the first in vivo evidence for these proteins belonging to the collagen IX interactome. Thrombospondin-4 expression was reduced at the mRNA level, whereas matrilin-4 was verified as a novel collagen IX-binding protein. Furthermore, changes in TGFβ-induced protein βig-h3 and fibronectin abundance were found in the collagen IX knock-out but not associated with COMP ablation, indicating specific involvement in the abnormal collagen IX null cartilage. In addition, the more widespread expression of collagen XII in the collagen IX-deficient cartilage suggests an attempted compensatory response to the absence of collagen IX. Our differential proteomic analysis of cartilage is a novel approach to identify candidate matrix protein interactions in vivo, underpinning further analysis of mutant cartilage lacking other matrix components or harboring disease-causing mutations.

Large-scale mouse knockouts and phenotypes

Standardized phenotypic analysis of mutant forms of every gene in the mouse genome will provide fundamental insights into mammalian gene function and advance human and animal health. The availability of the human and mouse genome sequences, the development of embryonic stem cell mutagenesis technology, the standardization of phenotypic analysis pipelines, and the paradigm-shifting industrialization of these processes have made this a realistic and achievable goal. The size of this enterprise will require global coordination to ensure economies of scale in both the generation and primary phenotypic analysis of the mutant strains, and to minimize unnecessary duplication of effort. To provide more depth to the functional annotation of the genome, effective mechanisms will also need to be developed to disseminate the information and resources produced to the wider community. Better models of disease, potential new drug targets with novel mechanisms of action, and completely unsuspected genotype-phenotype relationships covering broad aspects of biology will become apparent. To reach these goals, solutions to challenges in mouse production and distribution, as well as development of novel, ever more powerful phenotypic analysis modalities will be necessary. It is a challenging and exciting time to work in mouse genetics.

The biology of small leucine-rich proteoglycans in bone pathophysiology

The class of small leucine-rich proteoglycans (SLRPs) is a family of homologous proteoglycans harboring relatively small (36-42 kDa) protein cores compared with the larger cartilage and mesenchymal proteoglycans. SLRPs have been localized to most skeletal regions, with specific roles designated during all phases of bone formation, including periods relating to cell proliferation, organic matrix deposition, remodeling, and mineral deposition. This is mediated by key signaling pathways regulating the osteogenic program, including the activities of TGF-β, bone morphogenetic protein, Wnt, and NF-κB, which influence both the number of available osteogenic precursors and their subsequent development, differentiation, and function. On the other hand, SLRP depletion is correlated with degenerative diseases such as osteoporosis and ectopic bone formation. This minireview will focus on the SLRP roles in bone physiology and pathology.

Quantitative proteomic analysis of eight cartilaginous tissues reveals characteristic differences as well as similarities between subgroups

Human synovial joints display a characteristic anatomic distribution of arthritis, e.g. rheumatoid arthritis primarily affects the metacarpophalangeal and proximal finger joints, but rarely the distal finger joints, whereas osteoarthritis occurs in the distal and proximal finger joints. Pelvospondylitis has a selective localization to the spine and sacroiliac joints. Is this tropism due to differences between the cartilages at the molecular level? To substantiate this concept the present study provides a background detailed compositional analysis by relative quantification of extracellular matrix proteins in articular cartilages, meniscus, intervertebral disc, rib, and tracheal cartilages on samples from 5-6 different individuals using an optimized approach for proteomics. Tissue extraction followed by trypsin digestion and two-dimensional LC separations coupled to tandem mass spectrometry, relative quantification with isobaric labeling, iTRAQ(TM), was used to compare the relative abundance of about 150 proteins. There were clear differences in protein patterns between different kinds of cartilages. Matrilin-1 and epiphycan were specific for rib and trachea, whereas asporin was particularly abundant in the meniscus. Interestingly, lubricin was prominent in the intervertebral disc, especially in the nucleus pulposus. Fibromodulin and lumican showed distributions that were mirror images of one other. Analyses of the insoluble residues from guanidine extraction revealed that a fraction of several proteins remained unextracted, e.g. asporin, CILP, and COMP, indicating cross-linking. Distinct differences in protein patterns may relate to different tissue mechanical properties, and to the intriguing tropism in different patterns of joint pathology.

Transcriptional regulation of proteoglycans and glycosaminoglycan chain-synthesizing glycosyltransferases by UV irradiation in cultured human dermal fibroblasts

Various kinds of glycosaminoglycans (GAGs) and proteoglycans (PGs) have been known to be involved in structural and space-filling functions, as well as many physiological regulations in skin. To investigate ultraviolet (UV) radiation-mediated regulation of GAGs and PGs in cultured human dermal fibroblasts, transcriptional changes of many types of PGs and GAG chain-synthesizing enzymes at 18 hr after 75 mJ/cm(2) of UV irradiation were examined using quantitative real-time polymerase chain reaction methods. Hyaluronic acid synthase (HAS)-1, -2, and -3 and hyaluronidase-2 mRNA expressions were significantly increased by UV irradiation. Expressions of lumican, fibromodulin, osteoglycin, syndecan-2, perlecan, agrin, versican, decorin, and biglycan were significantly decreased by UV irradiation, while syndecan-1 was increased. Expressions of GAG chain-synthesizing glycosyltransferases, xylosyltransferase-1, β1,3-glucuronyltransferase-1, β1,4-galactosyltransferase-2, -4, exostosin-1, chondroitin polymerizing factor, and chondroitin sulfate synthase-3 were significantly reduced, whereas those of β1,3-galactosyltransferase-6, β1,4-galactosyltransferase-3, -7, β-1,3-N-acetylglucosaminyltran sferase-2, and -7 were increased by UV irradiation. Heparanase-1 mRNA expression was increased, but that of heparanase-2 was reduced by UV irradiation. Time-course investigation of representative genes showed consistent results. In conclusion, UV irradiation may increase hyaluronic acid production through HAS induction, and decrease other GAG productions through downregulation of PG core proteins and GAG chain-synthesizing glycosyltransferases in cultured human dermal fibroblasts.