WISP3-IGF1 interaction regulates chondrocyte hypertrophy

A spectral framework to map QTLs affecting joint differential networks of gene co-expression

Studying the mechanisms underlying the genotype-phenotype association is crucial in genetics. Gene expression studies have deepened our understanding of the genotype → expression → phenotype mechanisms. However, traditional expression quantitative trait loci (eQTL) methods often overlook the critical role of gene co-expression networks in translating genotype into phenotype. This gap highlights the need for more powerful statistical methods to analyze genotype → network → phenotype mechanism. Here, we develop a network-based method, called snQTL, to map quantitative trait loci affecting gene co-expression networks. Our approach tests the association between genotypes and joint differential networks of gene co-expression via a tensor-based spectral statistics, thereby overcoming the ubiquitous multiple testing challenges in existing methods. We demonstrate the effectiveness of snQTL in the analysis of three-spined stickleback (Gasterosteus aculeatus) data. Compared to conventional methods, our method snQTL uncovers chromosomal regions affecting gene co-expression networks, including one strong candidate gene that would have been missed by traditional eQTL analyses. Our framework suggests the limitation of current approaches and offers a powerful network-based tool for functional loci discoveries.

Directed differentiation of human pluripotent stem cells into articular cartilage reveals effects caused by absence of WISP3, the gene responsible for progressive pseudorheumatoid arthropathy of childhood

OBJECTIVES

Progressive pseudorheumatoid arthropathy of childhood (PPAC), caused by deficiency of WNT1 inducible signalling pathway protein 3 (WISP3), has been challenging to study because no animal model of the disease exists and cartilage recovered from affected patients is indistinguishable from common end-stage osteoarthritis. Therefore, to gain insights into why precocious articular cartilage failure occurs in this disease, we made in vitro derived articular cartilage using isogenic WISP3-deficient and WISP3-sufficient human pluripotent stem cells (hPSCs).

METHODS

We generated articular cartilage-like tissues from induced-(i) PSCs from two patients with PPAC and one wild-type human embryonic stem cell line in which we knocked out WISP3. We compared these tissues to in vitro-derived articular cartilage tissues from two isogenic WISP3-sufficient control lines using histology, bulk RNA sequencing, single cell RNA sequencing and in situ hybridisation.

RESULTS

WISP3-deficient and WISP3-sufficient hPSCs both differentiated into articular cartilage-like tissues that appeared histologically similar. However, the transcriptomes of WISP3-deficient tissues differed significantly from WISP3-sufficient tissues and pointed to increased TGFβ, TNFα/NFκB, and IL-2/STAT5 signalling and decreased oxidative phosphorylation. Single cell sequencing and in situ hybridisation revealed that WISP3-deficient cartilage contained a significantly higher fraction (~4 fold increase, p<0.001) of superficial zone chondrocytes compared with deeper zone chondrocytes than did WISP3-sufficient cartilage.

CONCLUSIONS

WISP3-deficient and WISP3-sufficient hPSCs can be differentiated into articular cartilage-like tissues, but these tissues differ in their transcriptomes and in the relative abundances of chondrocyte subtypes they contain. These findings provide important starting points for in vivo studies when an animal model of PPAC or presymptomatic patient-derived articular cartilage becomes available.

Clinical and molecular characterization in a cohort of patients with progressive pseudorheumatoid dysplasia

Progressive pseudorheumatoid dysplasia (PPRD), a rare autosomal recessive syndrome, is a type of skeletal dysplasia associated with pain, stiffness, swelling of multiple joints, and the absence of destructive changes. PPRD occurs due to loss of function pathogenic variants in WISP3 (CCN6) gene, located on chromosome 6q22. In this study, 23 unrelated Egyptian PPRD patients were clinically diagnosed based on medical history, physical and radiological examinations, and laboratory investigations. Sequencing of the whole WISP3 (CCN6) exons and introns boundaries was carried out for all patients. A total of 11 different sequence variations were identified in the WISP3 (CCN6) gene, five of them were new pathogenic variants: the NM_003880.3: c.80T>A (p.L27*), c.161delG (p.C54fs*12), c.737T>C (p.Leu246Pro), c.347-1G>A (IVS3-1G>A), and c.376C>T (p.Q126*). The results of this study expand the spectrum of WISP3 (CCN6) pathogenic variants associated with PPRD. Clinical and genetic analysis is important for proper genetic counseling to curb this rare disorder in the families.

Directed differentiation of human pluripotent stem cells into articular cartilage reveals effects caused by absence of WISP3 , the gene responsible for Progressive Pseudorheumatoid Arthropathy of Childhood

Objectives

Progressive Pseudorheumatoid Arthropathy of Childhood (PPAC), caused by deficiency of WNT1 inducible signaling pathway protein 3 ( WISP3 ), has been challenging to study because no animal model of the disease exists and cartilage recovered from affected patients is indistinguishable from common end-stage osteoarthritis. Therefore, to gain insights into why precocious articular cartilage failure occurs in this disease, we made in vitro derived articular cartilage using isogenic WISP3 -deficient and WISP3 -sufficient human pluripotent stem cells (hPSCs).

Methods

We generated articular cartilage-like tissues from induced-(i)PSCs from 2 patients with PPAC and 1 wild-type human embryonic stem cell line in which we knocked out WISP3. We compared these tissues to in vitro -derived articular cartilage tissues from 2 isogenic WISP3 -sufficient control lines using histology, bulk RNA sequencing, single cell RNA sequencing, and in situ hybridization.

Results

WISP3 -deficient and WISP3 -sufficient hPSCs both differentiated into articular cartilage-like tissues that appeared histologically similar. However, the transcriptomes of WISP3 -deficient tissues differed significantly from WISP3 -sufficient tissues and pointed to increased TGFβ, TNFα/NFkB, and IL-2/STAT5 signaling and decreased oxidative phosphorylation. Single cell sequencing and in situ hybridization revealed that WISP3 -deficient cartilage contained a significantly higher fraction (∼ 4-fold increase, p < 0.001) of superficial zone chondrocytes compared to deeper zone chondrocytes than did WISP3 -sufficient cartilage. Conclusions WISP3 -deficient and WISP3 -sufficient hPSCs can be differentiated into articular cartilage-like tissues, but these tissues differ in their transcriptomes and in the relative abundances of chondrocyte sub-types they contain. These findings provide important starting points for in vivo studies when an animal model of PPAC or presymptomtic patient-derived articular cartilage becomes available.

KEY MESSAGES

What is already known on this topic: Loss-of-function mutations in WISP3 cause Progressive Pseudorheumatoid Arthropathy of Childhood (PPAC), yet the precise function of WISP3 in cartilage is unknown due to the absence of cartilage disease Wisp3 knockout mice and the lack of available PPAC patient cartilage that is not end-stage. Thus, most functional studies of WISP3 have been performed in vitro using WISP3 over-expressing cell lines (i.e., not wild-type) and WISP3 -deficient chondrocytes. What this study adds: We describe 3 new WISP3 -deficient human pluripotent stem cell (hPSC) lines and show they can be differentiated into articular cartilage-like tissue. We compare in vitro -derived articular cartilage made from WISP3 -deficient and isogenic WISP3 - sufficient hPSCs using bulk RNA sequencing, single cell RNA sequencing, and in situ hybridization. We observe significant differences in the expression of genes previously associated with cartilage formation and homeostasis in the TGFβ, TNFα/NFkB, and IL-2/STAT5 signaling pathways. We also observe that WISP3-deficient cartilage-like tissues contain significantly higher fractions of chondrocytes that express superficial zone transcripts. These data suggest precocious cartilage failure in PPAC is the result of abnormal articular cartilage formation, dysregulated homeostatic signaling, or both.How this study might affect research, practice or policy: This study uses in vitro -derived articular cartilage to generate hypotheses for why cartilage fails in children with PPAC. This work prioritizes downstream studies to be performed when pre-symptomatic patient-derived cartilage samples or animal model of PPAC becomes available. It is essential to know how WISP3 functions in cartilage to develop therapies that benefit patients with PPAC and other degenerative joint diseases.

Cellular communication network factor 3 in cartilage development and maintenance

Cellular communication network factor (CCN) 3 is one of the classical members of the CCN family, which are characterized by common molecular structures and multiple functionalities. Although this protein was discovered as a gene product overexpressed in a truncated form in nephroblastoma, recent studies have revealed its physiological roles in the development and homeostasis of mammalian species, in addition to its pathological association with a number of diseases. Cartilage is a tissue that creates most of the bony parts and cartilaginous tissues that constitute the human skeleton, in which CCN3 is also differentially produced to exert its molecular missions therein. In this review article, after the summary of the molecular structure and function of CCN3, recent findings on the regulation of ccn3 expression and the roles of CCN3 in endochondral ossification, cartilage development, maintenance and disorders are introduced with an emphasis on the metabolic regulation and function of this matricellular multifunctional molecule.

CCN proteins in the musculoskeletal system: current understanding and challenges in physiology and pathology

The acronym for the CCN family was recently revised to represent “cellular communication network”. These six, small, cysteine-enriched and evolutionarily conserved proteins are secreted matricellular proteins, that convey and modulate intercellular communication by interacting with structural proteins, signalling factors and cell surface receptors. Their role in the development and physiology of musculoskeletal system, constituted by connective tissues where cells are interspersed in the cellular matrix, has been broadly studied. Previous research has highlighted a crucial balance of CCN proteins in mesenchymal stem cell commitment and a pivotal role for CCN1, CCN2 and their alter ego CCN3 in chondrogenesis and osteogenesis; CCN4 plays a minor role and the role of CCN5 and CCN6 is still unclear. CCN proteins also participate in osteoclastogenesis and myogenesis. In adult life, CCN proteins serve as mechanosensory proteins in the musculoskeletal system providing a steady response to environmental stimuli and participating in fracture healing. Substantial evidence also supports the involvement of CCN proteins in inflammatory pathologies, such as osteoarthritis and rheumatoid arthritis, as well as in cancers affecting the musculoskeletal system and bone metastasis. These matricellular proteins indeed show involvement in inflammation and cancer, thus representing intriguing therapeutic targets. This review discusses the current understanding of CCN proteins in the musculoskeletal system as well as the controversies and challenges associated with their multiple and complex roles, and it aims to link the dispersed knowledge in an effort to stimulate and guide readers to an area that the writers consider to have significant impact and relevant potentialities.

CCN Family Proteins in Cancer: Insight Into Their Structures and Coordination Role in Tumor Microenvironment

The crosstalk between tumor cells and the tumor microenvironment (TME), triggers a variety of critical signaling pathways and promotes the malignant progression of cancer. The success rate of cancer therapy through targeting single molecule of this crosstalk may be extremely low, whereas co-targeting multiple components could be complicated design and likely to have more side effects. The six members of cellular communication network (CCN) family proteins are scaffolding proteins that may govern the TME, and several studies have shown targeted therapy of CCN family proteins may be effective for the treatment of cancer. CCN protein family shares similar structures, and they mutually reinforce and neutralize each other to serve various roles that are tightly regulated in a spatiotemporal manner by the TME. Here, we review the current knowledge on the structures and roles of CCN proteins in different types of cancer. We also analyze CCN mRNA expression, and reasons for its diverse relationship to prognosis in different cancers. In this review, we conclude that the discrepant functions of CCN proteins in different types of cancer are attributed to diverse TME and CCN truncated isoforms, and speculate that targeting CCN proteins to rebalance the TME could be a potent anti-cancer strategy.

Ccn6 Is Required for Mitochondrial Integrity and Skeletal Muscle Function in Zebrafish

Mutations in the CCN6 (WISP3) gene are linked with a debilitating musculoskeletal disorder, termed progressive pseudorheumatoid dysplasia (PPRD). Yet, the functional significance of CCN6 in the musculoskeletal system remains unclear. Using zebrafish as a model organism, we demonstrated that zebrafish Ccn6 is present partly as a component of mitochondrial respiratory complexes in the skeletal muscle of zebrafish. Morpholino-mediated depletion of Ccn6 in the skeletal muscle leads to a significant reduction in mitochondrial respiratory complex assembly and activity, which correlates with loss of muscle mitochondrial abundance. These mitochondrial deficiencies are associated with notable architectural and functional anomalies in the zebrafish muscle. Taken together, our results indicate that Ccn6-mediated regulation of mitochondrial respiratory complex assembly/activity and mitochondrial integrity is important for the maintenance of skeletal muscle structure and function in zebrafish. Furthermore, this study suggests that defects related to mitochondrial respiratory complex assembly/activity and integrity could be an underlying cause of muscle weakness and a failed musculoskeletal system in PPRD.

Investigating the molecular control of deer antler extract on articular cartilage

BACKGROUND

Deer antler is considered as a precious traditional Chinese medicinal material and has been widely used to reinforce kidney's yang, nourish essence, and strengthen bone function. The most prominent bioactive components in deer antler are water-soluble proteins that play potential roles in bone formation and repair. The aim of this study was to explore the molecular control and therapeutic targets of deer antler extract (DAE) on articular cartilage.

METHODS

DAE was prepared as previously described. All rats were randomly divided into Blank group and DAE group (10 rats per group) after 7-day adaptive feeding. The rats in DAE group were orally administrated with DAE at a dose of 0.2 g/kg per day for 3 weeks, and the rats in Blank group were fed with drinking water. Total RNA was isolated from the articular cartilage of knee joints. RNA sequencing (RNA-seq) experiment combined with quantitative real-time polymerase chain reaction (qRT-PCR) verification assay was carried out to explore the molecular control and therapeutic targets of DAE on articular cartilage.

RESULTS

We demonstrated that DAE significantly increased the expression levels of functional genes involved in cartilage formation, growth, and repair and decreased the expression levels of susceptibility genes involved in the pathophysiology of osteoarthritis.

CONCLUSIONS

DAE might serve as a candidate supplement for maintaining cartilage homeostasis and preventing cartilage degeneration and inflammation. These effects were possibly achieved by accelerating the expression of functional genes involved in chondrocyte commitment, survival, proliferation, and differentiation and suppressing the expression of susceptibility genes involved in the pathophysiology of osteoarthritis. Thus, our findings will contribute towards deepening the knowledge about the molecular control and therapeutic targets of DAE on the treatment of cartilage-related diseases.

CCN6 regulates mitochondrial respiratory complex assembly and activity

Cellular communication network factor 6 (CCN6) mutations are linked with Progressive Pseudo Rheumatoid Dysplasia (PPRD) a debilitating musculoskeletal disorder. The function of CCN6 and the mechanism of PPRD pathogenesis remain unclear. Accordingly, we focused on the functional characterization of CCN6 and CCN6 mutants. Using size exclusion chromatography and native polyacrylamide gel electrophoresis we demonstrated that CCN6 is present as a component of the mitochondrial respiratory complex in human chondrocyte lines. By means of siRNA-mediated transfection and electron microscopy we showed that moderate reduction in CCN6 expression decreases the RER- mitochondria inter-membrane distance. Parallel native PAGE, immunoblotting and Complex I activity assays furthermore revealed increase in both mitochondrial distribution of CCN6 and mitochondrial respiratory complex assembly/activity in CCN6 depleted cells. CCN6 mutants resembling those linked with PPRD, which were generated by CRISPR-Cas9 technology displayed low level of expression of mutant CCN6 protein and inhibited respiratory complex assembly/activity. Electron microscopy and MTT assay of the mutants revealed abnormal mitochondria and poor cell viability. Taken together, our results indicate that CCN6 regulates mitochondrial respiratory complex assembly/activity as part of the mitochondrial respiratory complex by controlling the proximity of RER with the mitochondria, and CCN6 mutations disrupt mitochondrial respiratory complex assembly/activity resulting in mitochondrial defects and poor cell viability.

The Actions of IGF-1 in the Growth Plate and Its Role in Postnatal Bone Elongation

PURPOSE OF REVIEW

Bone elongation is a complex process driven by multiple intrinsic (hormones, growth factors) and extrinsic (nutrition, environment) variables. Bones grow in length by endochondral ossification in cartilaginous growth plates at ends of developing long bones. This review provides an updated overview of the important factors that influence this process.

RECENT FINDINGS

Insulin-like growth factor-1 (IGF-1) is the major hormone required for growth and a drug for treating pediatric skeletal disorders. Temperature is an underrecognized environmental variable that also impacts linear growth. This paper reviews the current state of knowledge regarding the interaction of IGF-1 and environmental factors on bone elongation. Understanding how internal and external variables regulate bone lengthening is essential for developing and improving treatments for an array of bone elongation disorders. Future studies may benefit from understanding how these unique relationships could offer realistic new approaches for increasing bone length in different growth-limiting conditions.

Progressive pseudorheumatoid dysplasia: a rare childhood disease

Progressive pseudorheumatoid dysplasia (PPRD) is a genetic bone disorder characterised by the progressive degeneration of articular cartilage that leads to pain, stiffness and joint enlargement. As PPRD is a rare disease, available literature is mainly represented by single case reports and only a few larger case series. Our aim is to review the literature concerning clinical, laboratory and radiological features of PPRD. PPRD is due to a mutation in Wnt1-inducible signalling protein 3 (WISP3) gene, which encodes a signalling factor involved in cartilage homeostasis. The disease onset in childhood and skeletal changes progresses over time leading to significant disability. PPRD is a rare condition that should be suspected if a child develops symmetrical polyarticular involvement without systemic inflammation, knobbly interphalangeal joints of the hands, and gait abnormalities. A full skeletal survey, or at least a lateral radiograph of the spine, can direct towards a correct diagnosis that can be confirmed molecularly. More than 70 WISP3 mutations have so far been reported. Genetic testing should start with the study of genomic DNA extracted from blood leucocytes, but intronic mutations in WISP3 causing splicing aberrations can only be detected by analysing WISP3 mRNA, which can be extracted from cultured skin fibroblasts. A skin biopsy is, therefore, indicated in patients with typical PPRD findings and negative mutation screening of genomic DNA.

WISP-3/CCN6 inhibits apoptosis by regulating caspase pathway after hyperoxia in lung epithelial cells

Cell death is a normal phenomenon in the course of biological development, moreover, which is also a prominent feature in lung exposed to hyperoxia. Severe hypoxia occurs in ALI/ARDS patients, who generally require high concentration oxygen therapy assisted by mechanical ventilation. Nevertheless, high oxygen can cause excessive reactive oxygen species (ROS), leading to apoptosis in lung epithelial cells, which has been reported in our previous study. Herein, the correlation between increments of ROS and CCN6 expression was negative in CCN6-mediated the mitochondria dependent, intrinsic apoptotic pathway. Our latest research explained that CCN6 can inhibit caspase-8 mediated extrinsic apoptotic pathway to protect cells from hyperoxia-induced apoptosis. As demonstrated by Western Blot Analysis, Caspase 8 cleavage and Caspase 3 cleavage in CCN6-depleted cells exceeded the control group treated with high oxygen (48 h). And deletion of CCN6 enhanced caspase-8 activation after hyperoxia shown by Flow Cytometry. Although, it is unclear how CCN6 participated in the regulation of apoptotic pathways, the future targeted therapy drugs inhibiting CCN6 may be useful in the treatment of ALI/ARDS.

Association analysis on polymorphisms in WISP3 gene and developmental dysplasia of the hip in Han Chinese population: A case-control study

Developmental dysplasia of the hip (DDH) is a common skeletal disorder whereby genetic factors play a role in etiology. Multiple genes have been reported to be associated with the occurrence of DDH. WISP3 gene was found to be a causative gene for progressive pseudorheumatoid dysplasia (PPD). Reports of WISP3 gene in association with DDH are lacking. We conducted a case-control candidate gene association study enrolling three hundred and eighty-six patients with radiology confirmed DDH and 558 healthy controls. Additional haplotype-analysis was conducted to find the significant haplotype for DDH. Five SNPs rs69306665 (upstream of WISP3), rs1022313 (WISP3), rs1230345 (WISP3), rs17073268 (WISP3) and rs10456877 (downstream of WISP3) were identified for association with DDH, showing significant difference of allele frequencies with similar odds ratio ranging from 0.71 to 0.77 (p < 0.01) between cases and controls. Two haplotypes were identified between cases and controls through haplotype analysis: AAAAA with an odds ratio of 0.76 (95% CI: 0.60-0.98, p = 0.032299) and GGCGG with an odds ratio of 1.67 (95% CI: 1.37-2.04, p = 3.67 ∗ 10^-7). The results suggested WISP3 gene was associated with DDH in Chinese Han population. GGCGG haplotype might be a biomarker for DDH.

WISP3 mutation associated with pseudorheumatoid dysplasia

Progressive pseudorheumatoid dysplasia (PPD) is a skeletal dysplasia characterized by predominant involvement of articular cartilage with progressive joint stiffness. Here we report genetic characterization of a consanguineous family segregating an uncharacterized from of skeletal dysplasia. Whole-exome sequencing of four affected siblings and their parents identified a loss-of-function homozygous mutation in the WISP3 gene, leading to diagnosis of PPD in the affected individuals. The identified variant (Chr6: 112382301; WISP3:c.156C>A p.Cys52*) is rare and predicted to cause premature termination of the WISP3 protein.

Ca2+/Mg2+ homeostasis‑related TRPM7 channel mediates chondrocyte hypertrophy via regulation of the PI3K‑Akt signaling pathway

Chondrocytes are specialized cells that form cartilage tissue, and are able to respond to their osmotic environment and exercise important roles in endochondral ossification via undergoing proliferation, hypertrophy and apoptosis. The transient receptor melastatin potential 7 (TRPM7) cation channel can modulate the intracellular and extracellular levels of Ca2+ and Mg2+, and therefore the cellular osmotic environment. However, the molecular pathways involved in TRPM7‑mediated signal transduction have yet to be elucidated. In the present study, the expression and functionality of TRPM7 were investigated during chondrocyte proliferation and hypertrophy. The ATDC5 mouse cell line was employed and cellular viability was evaluated using the MTT assay, whereas hypertrophy was monitored via evaluating the expression of chondrogenic marker genes and the activity of alkaline phosphatase (ALP). Gene expression of TRPM7 appeared slightly upregulated during the proliferative stages of chondrocyte development, and significantly upregulated during the hypertrophic stages, suggesting the importance of Ca2+/Mg2+ homeostasis for chondrocyte growth. Low extracellular Ca2+/Mg2+ levels significantly reduced the expression of type X collagen, Indian hedgehog homolog (Ihh) and matrix metalloproteinase (MMP)‑13 genes, as well as ALP activity; however, cell viability remained unaffected. Conversely, the gene expression levels of TRPM7 appeared upregulated in ATDC5 cells under low extracellular Ca2+ or Mg2+ conditions. Silencing TRPM7 expression during the chondrocyte differentiation period also reduced type X collagen, Ihh and MMP‑13 gene expression, and ALP activity. Furthermore, the phosphatidylinositol‑4,5‑bisphosphate 3‑kinase (PI3K)‑Akt signaling pathway was activated following TRPM7 overexpression, and inhibited following TRPM7 silencing. Notably, the actions of TRPM7 on chondrocyte hypertrophy were abolished through the inhibition of PI3K‑Akt signaling. The present results suggested that TRPM7 may be involved in Ca2+/Mg2+ homeostasis during chondrocyte hypertrophy, and contribute to endochondral ossification via interacting with the PI3K‑Akt signaling pathway.

Pregestational type 2 diabetes mellitus induces cardiac hypertrophy in the murine embryo through cardiac remodeling and fibrosis

BACKGROUND

Cardiac hypertrophy is highly prevalent in patients with type 2 diabetes mellitus. Experimental evidence has implied that pregnant women with type 2 diabetes mellitus and their children are at an increased risk of cardiovascular diseases. Our previous mouse model study revealed that maternal type 2 diabetes mellitus induces structural heart defects in their offspring.

OBJECTIVE

This study aims to determine whether maternal type 2 diabetes mellitus induces embryonic heart hypertrophy in a murine model of diabetic embryopathy.

STUDY DESIGN

The type 2 diabetes mellitus embryopathy model was established by feeding 4-week-old female C57BL/6J mice with a high-fat diet for 15 weeks. Cardiac hypertrophy in embryos at embryonic day 17.5 was characterized by measuring heart size and thickness of the right and left ventricle walls and the interventricular septum, as well as the expression of β-myosin heavy chain, atrial natriuretic peptide, insulin-like growth factor-1, desmin, and adrenomedullin. Cardiac remodeling was determined by collagen synthesis and fibronectin synthesis. Fibrosis was evaluated by Masson staining and determining the expression of connective tissue growth factor, osteopontin, and galectin-3 genes. Cell apoptosis also was measured in the developing heart.

RESULTS

The thicknesses of the left ventricle walls and the interventricular septum of embryonic hearts exposed to maternal diabetes were significantly thicker than those in the nondiabetic group. Maternal diabetes significantly increased β-myosin heavy chain, atrial natriuretic peptide, insulin-like growth factor-1, and desmin expression, but decreased expression of adrenomedullin. Moreover, collagen synthesis was significantly elevated, whereas fibronectin synthesis was suppressed, in embryonic hearts from diabetic dams, suggesting that cardiac remodeling is a contributing factor to cardiac hypertrophy. The cardiac fibrosis marker, galectin-3, was induced by maternal diabetes. Furthermore, maternal type 2 diabetes mellitus activated the proapoptotic c-Jun-N-terminal kinase 1/2 stress signaling and triggered cell apoptosis by increasing the number of terminal deoxynucleotidyl transferase 2'-deoxyuridine 5'-triphosphate nick end labeling-positive cells (10.4 ± 2.2% of the type 2 diabetes mellitus group vs 3.8 ± 0.7% of the nondiabetic group, P < .05).

CONCLUSION

Maternal type 2 diabetes mellitus induces cardiac hypertrophy in embryonic hearts. Adverse cardiac remodeling, including elevated collagen synthesis, suppressed fibronectin synthesis, profibrosis, and apoptosis, is implicated as the etiology of cardiac hypertrophy.

Signaling pathways regulating cartilage growth plate formation and activity

The growth plate is a highly specialized and dynamic cartilage structure that serves many essential functions in skeleton patterning, growth and endochondral ossification in developing vertebrates. Major signaling pathways initiated by classical morphogens and by other systemic and tissue-specific factors are intimately involved in key aspects of growth plate development. As a corollary of these essential functions, disturbances in these pathways due to mutations or environmental factors lead to severe skeleton disorders. Here, we review these pathways and the most recent progress made in understanding their roles in chondrocyte differentiation in growth plate development and activity. Furthermore, we discuss newly uncovered pathways involved in growth plate formation, including mTOR, the circadian clock, and the COP9 signalosome.

CCN6 regulates mitochondrial function

Despite established links of CCN6, or Wnt induced signaling protein-3 (WISP3), with progressive pseudo rheumatoid dysplasia, functional characterization of CCN6 remains incomplete. In light of the documented negative correlation between accumulation of reactive oxygen species (ROS) and CCN6 expression, we investigated whether CCN6 regulates ROS accumulation through its influence on mitochondrial function. We found that CCN6 localizes to mitochondria, and depletion of CCN6 in the chondrocyte cell line C-28/I2 by using siRNA results in altered mitochondrial electron transport and respiration. Enhanced electron transport chain (ETC) activity of CCN6-depleted cells was reflected by increased mitochondrial ROS levels in association with augmented mitochondrial ATP synthesis, mitochondrial membrane potential and Ca(2+) Additionally, CCN6-depleted cells display ROS-dependent PGC1α (also known as PPARGC1A) induction, which correlates with increased mitochondrial mass and volume density, together with altered mitochondrial morphology. Interestingly, transcription factor Nrf2 (also known as NFE2L2) repressed CCN6 expression. Taken together, our results suggest that CCN6 acts as a molecular brake, which is appropriately balanced by Nrf2, in regulating mitochondrial function.

The Regulatory Role of Signaling Crosstalk in Hypertrophy of MSCs and Human Articular Chondrocytes

Hypertrophic differentiation of chondrocytes is a main barrier in application of mesenchymal stem cells (MSCs) for cartilage repair. In addition, hypertrophy occurs occasionally in osteoarthritis (OA). Here we provide a comprehensive review on recent literature describing signal pathways in the hypertrophy of MSCs-derived in vitro differentiated chondrocytes and chondrocytes, with an emphasis on the crosstalk between these pathways. Insight into the exact regulation of hypertrophy by the signaling network is necessary for the efficient application of MSCs for articular cartilage repair and for developing novel strategies for curing OA. We focus on articles describing the role of the main signaling pathways in regulating chondrocyte hypertrophy-like changes. Most studies report hypertrophic differentiation in chondrogenesis of MSCs, in both human OA and experimental OA. Chondrocyte hypertrophy is not under the strict control of a single pathway but appears to be regulated by an intricately regulated network of multiple signaling pathways, such as WNT, Bone morphogenetic protein (BMP)/Transforming growth factor-β (TGFβ), Parathyroid hormone-related peptide (PTHrP), Indian hedgehog (IHH), Fibroblast growth factor (FGF), Insulin like growth factor (IGF) and Hypoxia-inducible factor (HIF). This comprehensive review describes how this intricate signaling network influences tissue-engineering applications of MSCs in articular cartilage (AC) repair, and improves understanding of the disease stages and cellular responses within an OA articular joint.

Expression profiles of human CCN genes in patients with osteoarthritis or rheumatoid arthritis

OBJECTIVE

Osteoarthritis (OA) and rheumatoid arthritis (RA) are widespread disabling joint disorders that are considered to be polygenic in nature. This study investigated the spatial expression patterns of all six known human CCN genes using end-stage OA and RA joint samples.

DESIGN

We performed in situ hybridization and histological analysis to investigate the spatial expression patterns of human CCN genes using joint tissues obtained during total knee and hip joint replacement procedures on patients with advanced OA or RA. Normal joint tissues taken while performing bipolar hip replacement surgeries were used as controls.

RESULTS

All CCN genes were expressed at higher levels in OA and RA synovial samples as compared with normal controls. Whereas CCN3 and CCN6 were undetectable in control, OA, and RA cartilage, CCN1, CCN2, CCN4, and CCN5 were expressed to a greater extent in OA and RA knee cartilage.

CONCLUSIONS

Our results indicate an involvement of several CCN genes in the pathophysiology of OA and RA.

Chondrocytes play a major role in the stimulation of bone growth by thyroid hormone

Thyroid hormone (T3) is required for postnatal skeletal growth. It exerts its effect by binding to nuclear receptors, TRs including TRα1 and TRβ1, which are present in most cell types. These cell types include chondrocytes and osteoblasts, the interactions of which are known to regulate endochondral bone formation. In order to analyze the respective functions of T3 stimulation in chondrocytes and osteoblasts during postnatal growth, we use Cre/loxP recombination to express a dominant-negative TRα1(L400R) mutant receptor in a cell-specific manner. Phenotype analysis revealed that inhibiting T3 response in chondrocytes is sufficient to reproduce the defects observed in hypothyroid mice, not only for cartilage maturation, but also for ossification and mineralization. TRα1(L400R) in chondrocytes also results in skull deformation. In the meantime, TRα1(L400R) expression in mature osteoblasts has no visible effect. Transcriptome analysis identifies a number of changes in gene expression induced by TRα1(L400R) in cartilage. These changes suggest that T3 normally cross talks with several other signaling pathways to promote chondrocytes proliferation, differentiation, and skeletal growth.

Cartilage to bone transitions in health and disease

Aberrant redeployment of the 'transient' events responsible for bone development and postnatal longitudinal growth has been reported in some diseases in what is otherwise inherently 'stable' cartilage. Lessons may be learnt from the molecular mechanisms underpinning transient chondrocyte differentiation and function, and their application may better identify disease aetiology. Here, we review the current evidence supporting this possibility. We firstly outline endochondral ossification and the cellular and physiological mechanisms by which it is controlled in the postnatal growth plate. We then compare the biology of these transient cartilaginous structures to the inherently stable articular cartilage. Finally, we highlight specific scenarios in which the redeployment of these embryonic processes may contribute to disease development, with the foresight that deciphering those mechanisms regulating pathological changes and loss of cartilage stability will aid future research into effective disease-modifying therapies.