Cytokine-like 1 knock-out mice (Cytl1-/-) show normal cartilage and bone development but exhibit augmented osteoarthritic cartilage destruction

A cytokine-like factor 1 homolog acts as a macrophage chemoattractant in grass carp

Cytokine-like factor 1 (CYTL1) is a small cytokine and has diverse biological functions in mammals. However, whether CYTL1 exists in lower vertebrates is not clear. In this study, we identified cytl homologs in fish and characterized the immune functions in a teleost species, grass carp (Ctenopharyngodon idella). Fish CYTL1 homologs share conserved molecular features with their mammalian counterparts, including 6 cysteine residues in the mature peptide, genomic organization and synteny. Gene expression analysis revealed that cytl1 was constitutively expressed in tissues of grass carp, with the highest expression detected in the heart. Upon infection with Aeromonas hydrophila (A. hydrophila), cytl1 was downregulated in the hindgut, head kidney, skin, and spleen. In the primary head kidney leukocytes (HKLs), stimulation with inactivated A. hydrophila, LPS, poly(I:C), IL-22, IFN-a or IFN-γrel resulted in downregulation of cytl1 expression. Recombinant grass carp CYTL1 protein produced in the HEK293-F cells was potent to induce il-10 expression, but had little effect on the expression of il-1β and il-6. In vivo experiments revealed that CYTL1 was effective to recruit macrophages to the muscle injected with cytl expression plasmids. Taken together, our results indicate that CYTL1 is a potent chemokine for recruitment of macrophages in fish.

Porcine nasal septum cartilage-derived decellularized matrix promotes chondrogenic differentiation of human umbilical mesenchymal stem cells without exogenous growth factors

BACKGROUND

In the domain of plastic surgery, nasal cartilage regeneration is of significant importance. The extracellular matrix (ECM) from porcine nasal septum cartilage has shown potential for promoting human cartilage regeneration. Nonetheless, the specific biological inductive factors and their pathways in cartilage tissue engineering remain undefined.

METHODS

The decellularized matrix derived from porcine nasal septum cartilage (PN-DCM) was prepared using a grinding method. Human umbilical cord mesenchymal stem cells (HuMSCs) were cultured on these PN-DCM scaffolds for 4 weeks without exogenous growth factors to evaluate their chondroinductive potential. Subsequently, proteomic analysis was employed to identify potential biological inductive factors within the PN-DCM scaffolds.

RESULTS

Compared to the TGF-β3-cultured pellet model serving as a positive control, the PN-DCM scaffolds promoted significant deposition of a Safranin-O positive matrix and Type II collagen by HuMSCs. Gene expression profiling revealed upregulation of ACAN, COL2A1, and SOX9. Proteomic analysis identified potential chondroinductive factors in the PN-DCM scaffolds, including CYTL1, CTGF, MGP, ITGB1, BMP7, and GDF5, which influence HuMSC differentiation.

CONCLUSION

Our findings have demonstrated that the PN-DCM scaffolds promoted HuMSC differentiation towards a nasal chondrocyte phenotype without the supplementation of exogenous growth factors. This outcome is associated with the chondroinductive factors present within the PN-DCM scaffolds.

Proteomic profiling of human menisci from mild joint degeneration and end-stage osteoarthritis versus healthy controls

Objective

To gain new insight into the molecular changes of the meniscus by comparing the proteome profiles of healthy controls with mild degeneration and end-stage osteoarthritis (OA).

Method

We obtained tissue plugs from lateral and medial menisci of 37 individuals (central part of the posterior horn) classified as healthy (n ​= ​12), mild signs of joint damage (n ​= ​13) and end-stage OA (n ​= ​12). The protein profile was analysed by nano-liquid chromatography-mass spectrometry using data-independent acquisition and quantified by Spectronaut. Linear-mixed effects modelling was applied to extract the between-group comparisons.

Results

A similar protein profile was observed for the mild group as compared to healthy controls while the most different group was end-stage OA mainly for the medial compartment. When a pattern of gradual change in protein levels from healthy to end-stage OA was required, a 42-proteins panel was identified, suggesting a potential role in OA development. The levels of QSOX1 were lower and G6PD higher in the mild group following the proposed protein abundance pattern. Qualitative protein changes suggest lower levels of CYTL1 as a potential biomarker of early joint degradation.

Conclusion

For future targeted proteomic approaches, we propose a candidate panel of 42 proteins based on gradually altered meniscal posterior horn protein abundance patterns associated with joint degradation.

Single-cell RNA sequencing in osteoarthritis

Osteoarthritis is a progressive and heterogeneous joint disease with complex pathogenesis. The various phenotypes associated with each patient suggest that better subgrouping of tissues associated with genotypes in different phases of osteoarthritis may provide new insights into the onset and progression of the disease. Recently, single-cell RNA sequencing was used to describe osteoarthritis pathogenesis on a high-resolution view surpassing traditional technologies. Herein, this review summarizes the microstructural changes in articular cartilage, meniscus, synovium and subchondral bone that are mainly due to crosstalk amongst chondrocytes, osteoblasts, fibroblasts and endothelial cells during osteoarthritis progression. Next, we focus on the promising targets discovered by single-cell RNA sequencing and its potential applications in target drugs and tissue engineering. Additionally, the limited amount of research on the evaluation of bone-related biomaterials is reviewed. Based on the pre-clinical findings, we elaborate on the potential clinical values of single-cell RNA sequencing for the therapeutic strategies of osteoarthritis. Finally, a perspective on the future development of patient-centred medicine for osteoarthritis therapy combining other single-cell multi-omics technologies is discussed. This review will provide new insights into osteoarthritis pathogenesis on a cellular level and the field of applications of single-cell RNA sequencing in personalized therapeutics for osteoarthritis in the future.

Cytokine-Like Protein 1 (CYTL1) as a Key Target of M-Stage Immune Infiltration in Stomach Adenocarcinoma

Background

Stomach adenocarcinoma (STAD) has an extremely high fatality rate worldwide, and survival after metastasis is extremely poor. Cytokine-like protein 1 (CYTL1) has prognostic significance in various tumors. We aimed to explore the impact and underlying molecular mechanisms of CYTL1 in STAD through bioinformatics analysis.

Methods

We used R software to analyze CYTL1 expression in STAD samples (n = 375) and normal samples (n = 32) in The Cancer Genome Atlas database. Kaplan-Meier analysis was used to verify the relationship between CYTL1 expression and overall survival (OS) and disease-specific survival (DSS) based on the clinical characteristics and subgroups of patients with STAD. Furthermore, univariate and multivariate Cox regression analyses were used to verify the outcome variables of OS and DSS in patients with STAD. Receiver operating characteristic curves were used to test the predictive power of CYTL1. The biological functions and signaling pathways of CYTL1 were determined using gene set enrichment analysis (GSEA), and the immune infiltration patterns of CYTL1 and correlation of immune-related markers were analyzed using single-sample GSEA (ssGSEA) and an estimate algorithm.

Results

In our research, low CYTL1 expression (tumor vs. normal) was noted in patients with STAD. High CYTL1 expression was detrimental to OS and DSS and had good diagnostic performance (AUC = 0.731). In the subtype analysis of STAD, T3 and T4 stages, N0 and N1 stages, M0 stage, gender (female), and age (≤65 years) showed different performances between OS and DSS. Univariate and multivariate Cox analyses identified CYTL1 as an independent factor, and logistic regression analysis indicated that CYTL1 was associated with M stage (OR = 3.406) and sex (OR = 1.535). GSEA of the differential genes of CYTL1 showed the possible involvement of immunity. ssGSEA and estimation algorithms were used to further evaluate whether immune cells were closely related to CYTL1 expression, and many markers of immune cells also had statistical significance with the expression of CYTL1.

Conclusion

CYTL1 may, thus, act as an independent prognostic factor for STAD and regulate STAD progression by affecting the immune microenvironment.

Deciphering postnatal limb development at single-cell resolution

The early postnatal limb developmental progression bridges embryonic and mature stages and mirrors the pathological remodeling of articular cartilage. However, compared with multitudinous research on embryonic limb development, the early postnatal stage seems relatively unnoticed. Here, a systematic work to portray the postnatal limb developmental landscape was carried out by characterization of 19,952 single cells from murine hindlimbs at 4 postnatal stages using single-cell RNA sequencing technique. By delineation of cell heterogeneity, the candidate progenitor sub-clusters marked by Cd34 and Ly6e were discovered in articular cartilage and enthesis, and three cellular developmental branches marked by Col10a1, Spp1, and Tnni2 were reflected in growth plate. The representative transcriptomes and developmental patterns were intensively explored, and the key regulation mechanisms as well as evolvement in osteoarthritis were discussed. Above all, these results expand horizons of postnatal limb developmental biology and reach the interconnections between limb development, remodeling, and regeneration.

Single-cell RNA sequencing reveals resident progenitor and vascularization-associated cell subpopulations in rat annulus fibrosus

Background

One of the main causes of low back pain is intervertebral disc degeneration (IDD). Annulus fibrosus (AF) is important for the integrity and functions of the intervertebral disc (IVD). However, the resident functional cell components such as progenitors and vascularization-associated cells in AF are yet to be fully identified.

Purpose

Identification of functional AF cell subpopulations including resident progenitors and vascularization-associated cells.

Methods

In this study, the single-cell RNA sequencing data of rat IVDs from a public database were analyzed using Seurat for cell clustering, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) for functional analysis, StemID for stem cell identification, Monocle and RNA velocity for pseudotime differentiation trajectory validation, single-cell regulatory network inference and clustering (SCENIC) for gene regulatory network (GRN) analysis, and CellChat for cell-cell interaction analysis. Immunostaining on normal and degenerated rat IVDs, as well as human AF, was used for validations.

Results

From the data analysis, seven AF cell clusters were identified, including two newly discovered functional clusters, the Grem1 ⁺ subpopulation and the Lum ⁺ ​subpopulation. The Grem1 ⁺ subpopulation had progenitor characteristics, while the Lum ⁺ ​subpopulation was associated with vascularization during IDD. The GRN analysis showed that Sox9 and Id1 were among the key regulators in the Grem1 ⁺ subpopulation, and Nr2f2 and Creb5 could be responsible for the vascularization function in the Lum ⁺ ​subpopulation. Cell-cell interaction analysis revealed highly regulated cellular communications between these cells, and multiple signaling networks including PDGF and MIF signaling pathways were involved in the interactions.

Conclusions

Our results revealed two new functional AF cell subpopulations, with stemness and vascularization induction potential, respectively.

The Translational potential of this article

These findings complement our knowledge about IVDs, especially the AF, and in return provide potential cell source and regulation targets for IDD treatment and tissue repair. The existence of the cell subpopulations was also validated in human AF, which strengthen the clinical relevance of the findings.

Cellular responses in the FGF10-mediated improvement of hindlimb regenerative capacity in Xenopus laevis revealed by single-cell transcriptomics

Xenopus laevis tadpoles possess regenerative capacity in their hindlimb buds at early developmental stages (stages ~52-54); they can regenerate complete hindlimbs with digits after limb bud amputation. However, they gradually lose their regenerative capacity as metamorphosis proceeds. Tadpoles in late developmental stages regenerate fewer digits (stage ~56), or only form cartilaginous spike without digits or joints (stage ~58 or later) after amputation. Previous studies have shown that administration of fibroblast growth factor 10 (FGF10) in late-stage (stage 56) tadpole hindlimb buds after amputation can improve their regenerative capacity, which means that the cells responding to FGF10 signaling play an important role in limb bud regeneration. In this study, we performed single-cell RNA sequencing (scRNA-seq) of hindlimb buds that were amputated and administered FGF10 by implanting FGF10-soaked beads at a late stage (stage 56), and explored cell clusters exhibiting a differential gene expression pattern compared with that in controls treated with phosphate-buffered saline. The scRNA-seq data showed expansion of fgf8-expressing cells in the cluster of the apical epidermal cap of FGF10-treated hindlimb buds, which was reported previously, indicating that the administration of FGF10 was successful. On analysis, in addition to the epidermal cluster, a subset of myeloid cells and a newly identified cluster of steap4-expressing cells showed remarkable differences in their gene expression profiles between the FGF10- or phosphate-buffered saline-treatment conditions, suggesting a possible role of these clusters in improving the regenerative capacity of hindlimbs via FGF10 administration.

The Clinical Significance of Changes in Serum New Cytokine CYTL1 in Patients with Knee Osteoarthritis

Objective

The present study aims to investigate the clinical significance of changes in the expression of new cytokine-like 1 (CYTL1) in the serum of patients with knee osteoarthritis (KOA).

Methods

A total of 182 patients with KOA, including 84 males and 98 females aged 39–86 with an average age of 66.4 ± 9.7 and an average body mass index (BMI) of 24.9 ± 2.4 kg/m², were enrolled in the study. The patients were divided into three subgroups: the grade II subgroup (n = 23), grade III subgroup (n = 63), and grade IV subgroup (n = 96) based on severity, as calculated by the Kellgren and Lawrence (K&L) classification system. In addition, 152 volunteers from our health center who came in for physical examination were selected as the control group, including 70 males and 82 females aged 37–82 with an average age of 63.4 ± 9.5 and an average BMI of 24.8 ± 2.2 kg/m². An enzyme-linked immunosorbent assay was adopted to detect the serum CYTL1 levels, and the correlation between CYTL1 and the severity of KOA was analyzed.

Results

The serum level of CYTL1 was significantly lower in the KOA group than in the control group (P < 0.05). In the KOA group, the difference in the serum level of CYTL1 was statistically significant between the subgroups and decreased significantly with an increase in the severity of the disease (F = 54.826, P < 0.001). Therefore, the serum level of CYTL1 was correlated with the severity of the disease, as determined by the K&L classification system (r = −0.613, P < 0.001).

Conclusion

The serum levels of CYTL1 are strongly correlated with the severity of the disease in patients with KOA and could be a new therapeutic target for KOA.

Proteomics analysis of hip articular cartilage identifies differentially expressed proteins associated with osteonecrosis of the femoral head

OBJECTIVE

The cartilage degeneration that accompanies subchondral bone necrosis plays an important role in the development of osteonecrosis of femoral head (ONFH). To better understand the molecular basis of cartilage degradation in ONFH, we compared the proteomic profiles of ONFH cartilage with that of fracture control.

DESIGN

Hip cartilage samples were collected from 16 ONFH patients and 16 matched controls with femoral neck fracture. Proteomics analysis was conducted using tandem mass tag-based quantitation technique. Gene ontology (GO) analysis, KEGG pathway and protein-protein interaction analysis were used to investigate the functions of the altered proteins and biological pathways. Differentially expressed proteins including alpha-2-HS-glycoprotein (AHSG) and Cytokine-like protein 1 (Cytl1) were validated by Western blot (WB) and immunohistochemistry (IHC).

RESULTS

303 differentially expressed proteins were identified in ONFH cartilage with 72 up-regulated and 231 down-regulated. Collagen turnover, glycosaminoglycan biosynthesis, metabolic pathways, and complement and coagulation cascades were significantly modified in ONFH cartilage. WB and IHC confirmed the increased expression of AHSG and decreased expression of Cytl1 in ONFH cartilage.

CONCLUSIONS

Our results reveal the implication of altered protein expression in the development of ONFH, and provide novel clues for pathogenesis studies of cartilage degradation in ONFH.

CYTL1 Promotes the Activation of Neutrophils in a Sepsis Model

As a novel cytokine, cytokine-like 1 (CYTL1) is a classical secretory protein, and its potential biological function remains to be determined. In this study, we found that expression of CYTL1 was upregulated in neutrophils upon inflammatory stimuli. We demonstrated that CYTL1 enhanced phagocytosis of Escherichia coli by activated neutrophils both in vivo and in vitro through phosphorylation of protein kinase B (Akt). CYTL1-induced chemotactic activity in lipopolysaccharide (LPS) stimulated neutrophils, and the mechanism may be related to CC chemokine receptor 2 (CCR2) mediated action. CYTL1 also increased the release of reactive oxygen species (ROS) in LPS-stimulated neutrophils. These data indicate that upon inflammatory stimulation, neutrophil-derived CYTL1 may play a crucial role in the activation of neutrophils during pathogenic infections.

LPS-Induced Inflammation Prior to Injury Exacerbates the Development of Post-Traumatic Osteoarthritis in Mice

Osteoarthritis (OA) is a debilitating and painful disease characterized by the progressive loss of articular cartilage. Post-traumatic osteoarthritis (PTOA) is an injury-induced type of OA that persists in an asymptomatic phase for years before it becomes diagnosed in ~50% of injured individuals. Although PTOA is not classified as an inflammatory disease, it has been suggested that inflammation could be a major driver of PTOA development. Here we examined whether a state of systemic inflammation induced by lipopolysaccharide (LPS) administration 5-days before injury would modulate PTOA outcomes. RNA-seq analysis at 1-day post-injury followed by micro-computed tomography (μCT) and histology characterization at 6 weeks post-injury revealed that LPS administration causes more severe PTOA phenotypes. These phenotypes included significantly higher loss of cartilage and subchondral bone volume. Gene expression analysis showed that LPS alone induced a large cohort of inflammatory genes previously shown to be elevated in synovial M1 macrophages of rheumatoid arthritis (RA) patients, suggesting that systemic LPS produces synovitis. This synovitis was sufficient to promote PTOA in MRL/MpJ mice, a strain previously shown to be resistant to PTOA. The synovium of LPS-treated injured joints displayed an increase in cellularity, and immunohistological examination confirmed that this increase was in part attributable to an elevation in type 1 macrophages. LPS induced the expression of Tlr7 and Tlr8 in both injured and uninjured joints, genes known to be elevated in RA. We conclude that inflammation before injury is an important risk factor for the development of PTOA and that correlating patient serum endotoxin levels or their state of systemic inflammation with PTOA progression may help develop new, effective treatments to lower the rate of PTOA in injured individuals. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

The involvement of cytokine-like 1 (Cytl1) in chondrogenesis and cartilage metabolism

The Cytokine-like 1 (Cytl1) is first identified in bone marrow cells and preferentially expressed in cartilaginous tissue, and showed chondrogenic effects in mesenchymal cells, not essential for cartilage or bone development as in Cytl1 knock-out mice but associated with cartilage inflammatory and destruction. Here, we show the involvement of Cytl1 in chondrogenesis. Using specified chondrogenic embryonic skeleton and adult cartilage, the Cytl1 gene expression was investigated with associated chondrogenic factors by quantitative RT-PCR. The effect of Cytl1 protein (rCytl1) on cultured chondrocytes to regulate expression of key factors and phenotypic markers was studied. The results revealed that Cytl1 was highly expressed in chondrogenic process in embryos and adult cartilage. The rCytl1 increased the expression of Sox9 and Col2α1 with stabilized Col1α1 in cultured chondrocytes (redifferentiation). The Cytl1 was expressed and involved at all stages of cartilage development. Furthermore, Cytl1 expression shared similar patterns as other chondrogenic factors, implying interactions with other factors in chondrogenic process. Cytl1 is involved in cartilage development and matrix homeostasis, which defines the dedifferentiation phenotype of chondrocytes, essential to forming of functional cartilage in both physiologic remodeling and pathologic regeneration.

Global Gene Expression Analysis Identifies Age-Related Differences in Knee Joint Transcriptome during the Development of Post-Traumatic Osteoarthritis in Mice

Aging and injury are two major risk factors for osteoarthritis (OA). Yet, very little is known about how aging and injury interact and contribute to OA pathogenesis. In the present study, we examined age- and injury-related molecular changes in mouse knee joints that could contribute to OA. Using RNA-seq, first we profiled the knee joint transcriptome of 10-week-old, 62-week-old, and 95-week-old mice and found that the expression of several inflammatory-response related genes increased as a result of aging, whereas the expression of several genes involved in cartilage metabolism decreased with age. To determine how aging impacts post-traumatic arthritis (PTOA) development, the right knee joints of 10-week-old and 62-week-old mice were injured using a non-invasive tibial compression injury model and injury-induced structural and molecular changes were assessed. At six-week post-injury, 62-week-old mice displayed significantly more cartilage degeneration and osteophyte formation compared with young mice. Although both age groups elicited similar transcriptional responses to injury, 62-week-old mice had higher activation of inflammatory cytokines than 10-week-old mice, whereas cartilage/bone metabolism genes had higher expression in 10-week-old mice, suggesting that the differential expression of these genes might contribute to the differences in PTOA severity observed between these age groups.

Cytokine-Like 1 Is a Novel Proangiogenic Factor Secreted by and Mediating Functions of Endothelial Progenitor Cells

RATIONALE

Endothelial colony forming cells (ECFCs) or late blood outgrowth endothelial cells can be isolated from human cord or peripheral blood, display properties of endothelial progenitors, home into ischemic tissues and support neovascularization in ischemic disease models.

OBJECTIVE

To assess the functions of CYTL1 (cytokine-like 1), a factor we found preferentially produced by ECFCs, in regard of vessel formation.

METHODS AND RESULTS

We show by transcriptomic analysis that ECFCs are distinguished from endothelial cells of the vessel wall by production of high amounts of CYTL1. Modulation of expression demonstrates that the factor confers increased angiogenic sprouting capabilities to ECFCs and can also trigger sprouting of mature endothelial cells. The data further display that CYTL1 can be induced by hypoxia and that it functions largely independent of VEGF-A (vascular endothelial growth factor-A). By recombinant production of CYTL1 we confirm that the peptide is indeed a strong proangiogenic factor and induces sprouting in cellular assays and functional vessel formation in animal models comparable to VEGF-A. Mass spectroscopy corroborates that CYTL1 is specifically O-glycosylated on 2 neighboring threonines in the C-terminal part and this modification is important for its proangiogenic bioactivity. Further analyses show that the factor does not upregulate proinflammatory genes and strongly induces several metallothionein genes encoding anti-inflammatory and antiapoptotic proteins.

CONCLUSIONS

We conclude that CYTL1 can mediate proangiogenic functions ascribed to endothelial progenitors such as ECFCs in vivo and may be a candidate to support vessel formation and tissue regeneration in ischemic pathologies.

Protein Cytl1: its role in chondrogenesis, cartilage homeostasis, and disease

Cytokine-like protein 1 (Cytl1), also named Protein C17 or C4orf4 is located on human chromosome 4p15-p16 and encodes a polypeptide of 126 amino acid residues that displays characteristics of a secretory protein. Cytl1 is expressed by a sub-population of CD34+ human mononuclear cells from bone marrow and cord blood, and by chondrocytes (cartilage-forming cells). In this review, we explore evidence suggesting that Cytl1 may be involved in the regulation of chondrogenesis, cartilage homeostasis and osteoarthritis progression, accompanied by the modulation of Sox9 and insulin-like growth factor 1 expression. In addition, Cytl1 exhibits chemotactic and pro-angiogenic biological effects. Interestingly, CCR2 (C-C chemokine receptor type 2) has been identified as a likely receptor for Cytl1, which mediates the ERK signalling pathway. Cytl1 also appears to mediate the TGF-beta-Smad signalling pathway, which is hypothetically independent of the CCR2 receptor. More recently, studies have also potentially linked Cytl1 with a variety of conditions including cardiac fibrosis, smoking, alcohol dependence risk, and tumours such as benign prostatic hypertrophy, lung squamous cell carcinoma, neuroblastoma and familial colorectal cancer. Defining the molecular structure of Cytl1 and its role in disease pathogenesis will help us to design therapeutic approaches for Cytl1-associated pathological conditions.

Endocytosing Escherichia coli as a Whole-Cell Biocatalyst of Fatty Acids

Whole cell biocatalysts can be used to convert fatty acids into various value-added products. However, fatty acid transport across cellular membranes into the cytosol of microbial cells limits substrate availability and impairs membrane integrity, which in turn decreases cell viability and bioconversion activity. Because these problems are associated with the mechanism of fatty acid transport through membranes, a whole-cell biocatalyst that can form caveolae-like structures was generated to promote substrate endocytosis. Caveolin-1 ( CAV1) expression in Escherichia coli increased both the fatty acid transport rate and intracellular fatty acid concentrations via endocytosis of the supplemented substrate. Furthermore, fatty-acid endocytosis alleviated substrate cytotoxicity in E. coli. These traits attributed to bacterial endocytosis resulted in dramatically elevated biotransformation efficiencies in fed-batch and cell-recycle reaction systems when caveolae-forming E. coli was used for the bioconversion of ricinoleic acid (12-hydroxyoctadec-9-enoic acid) to ( Z)-11-(heptanoyloxy) undec-9-enoic acid. We propose that CAV1-mediated endocytosing E. coli represents a versatile tool for the biotransformation of hydrophobic substrates.

Articular cartilage and sternal fibrocartilage respond differently to extended microgravity

The effects of spaceflight on cartilaginous structure are largely unknown. To address this deficiency, articular cartilage (AC) and sternal cartilage (SC) from mice exposed to 30 days of microgravity on the BION-M1 craft were investigated for pathological changes. The flight AC showed some evidence of degradation at the tissue level with loss of proteoglycan staining and a reduction in mRNA expression of mechano-responsive and structural cartilage matrix proteins compared to non-flight controls. These data suggest that degradative changes are underway in the AC extracellular matrix exposed to microgravity. In contrast, there was no evidence of cartilage breakdown in SC flight samples and the gene expression profile was distinct from that of AC with a reduction in metalloproteinase gene transcription. Since the two cartilages respond differently to microgravity we propose that each is tuned to the biomechanical environments in which they are normally maintained. That is, the differences between magnitude of normal terrestrial loading and the unloading of microgravity dictates the tissue response. Weight-bearing articular cartilage, but not minimally loaded sternal fibrocartilage, is negatively affected by the unloading of microgravity. We speculate that the maintenance of physiological loading on AC during spaceflight will minimize AC damage.

CYTL1 inhibits tumor metastasis with decreasing STAT3 phosphorylation

CYTL1 is a novel cytokine that was first identified in CD34⁺ hematopoietic cells. We previously prepared recombinant CYTL1 and verified that it chemoattracted human monocytes via the CCR2/ERK pathway. It has been reported that CYTL1 plays contradictory roles in neuroblastoma and lung cancer. We found that the expression level of CYTL1 was notably decreased and it was hypermethylated in various tumors, including breast and lung cancer, by bioinformatics analyses. After validating the expression of CYTL1 in lung cancer, we identified that CYTL1 exerted no obvious effect on tumor cell proliferation but inhibited their migration and invasion, and these effects were accompanied by decreasing STAT3 phosphorylation, using recombinant CYTL1 and CYTL1-overexpressing tumor cell lines. Furthermore, we constructed experimental and spontaneous metastasis models of breast cancer in BALB/c mice and found that CYTL1 significantly inhibited tumor metastasis in vivo. In summary, CYTL1 is a cytokine with tumor-suppressing characteristics that inhibits tumor metastasis and STAT3 phosphorylation in multiple types of tumors.

CYTL1 regulates bone homeostasis in mice by modulating osteogenesis of mesenchymal stem cells and osteoclastogenesis of bone marrow-derived macrophages

We previously showed that mice with knockout of Cytl1, a functionally uncharacterized cytokine candidate, exhibit normal endochondral ossification and long-bone development. Here, we investigated the potential functions of CYTL1 in bone homeostasis. We found that Cytl1^−/− mice exhibited higher bone mass than wild-type littermates and resisted ovariectomy-induced bone resorption. This led us to investigate the functions of CYTL1 in the osteogenesis and osteoclastogenesis of bone marrow-derived stem cells. CYTL1 was down-regulated during the osteogenesis of human mesenchymal stem cells (hMSCs). The osteogenesis of hMSCs was inhibited by overexpression or exogenous treatment of CYTL1, but enhanced by CYTL1 knockdown. CYTL1 decreased osteogenesis by inhibiting RUNX2 and promoted proliferation among undifferentiated hMSCs, but stimulated apoptosis among osteogenically differentiating cells. Finally, Cytl1^−/− mice exhibited inhibition of osteoclast activity and the osteoclastogenesis of bone marrow-derived macrophages. Our results collectively suggest that CYTL1 negatively regulates the osteogenesis of MSCs and positively regulates osteoclastogenesis to modulate bone mass in mice.

Smad4 deficiency impairs chondrocyte hypertrophy via the Runx2 transcription factor in mouse skeletal development

Chondrocyte hypertrophy is the terminal step in chondrocyte differentiation and is crucial for endochondral bone formation. How signaling pathways regulate chondrocyte hypertrophic differentiation remains incompletely understood. In this study, using a Tbx18:Cre (Tbx18^Cre/+) gene-deletion approach, we selectively deleted the gene for the signaling protein SMAD family member 4 (Smad4^f/f ) in the limbs of mice. We found that the Smad4-deficient mice develop a prominent shortened limb, with decreased expression of chondrocyte differentiation markers, including Col2a1 and Acan, in the humerus at mid-to-late gestation. The most striking defects in these mice were the absence of stylopod elements and failure of chondrocyte hypertrophy in the humerus. Moreover, expression levels of the chondrocyte hypertrophy-related markers Col10a1 and Panx3 were significantly decreased. Of note, we also observed that the expression of runt-related transcription factor 2 (Runx2), a critical mediator of chondrocyte hypertrophy, was also down-regulated in Smad4-deficient limbs. To determine how the skeletal defects arose in the mouse mutants, we performed RNA-Seq with ChIP-Seq analyses and found that Smad4 directly binds to regulatory elements in the Runx2 promoter. Our results suggest a new mechanism whereby Smad4 controls chondrocyte hypertrophy by up-regulating Runx2 expression during skeletal development. The regulatory mechanism involving Smad4-mediated Runx2 activation uncovered here provides critical insights into bone development and pathogenesis of chondrodysplasia.

High hydrostatic pressure induces pro-osteoarthritic changes in cartilage precursor cells: A transcriptome analysis

Due to the high water content of cartilage, hydrostatic pressure is likely one of the main physical stimuli sensed by chondrocytes. Whereas, in the physiological range (0 to around 10 MPa), hydrostatic pressure exerts mostly pro-chondrogenic effects in chondrocyte models, excessive pressures have been reported to induce detrimental effects on cartilage, such as increased apoptosis and inflammation, and decreased cartilage marker expression. Though some genes modulated by high pressure have been identified, the effects of high pressure on the global gene expression pattern have still not been investigated. In this study, using microarray technology and real-time PCR validation, we analyzed the transcriptome of ATDC5 chondrocyte progenitors submitted to a continuous pressure of 25 MPa for up to 24 h. Several hundreds of genes were found to be modulated by pressure, including some not previously known to be mechano-sensitive. High pressure markedly increased the expression of stress-related genes, apoptosis-related genes and decreased that of cartilage matrix genes. Furthermore, a large set of genes involved in the progression of osteoarthritis were also induced by high pressure, suggesting that hydrostatic pressure could partly mimic in vitro some of the genetic alterations occurring in osteoarthritis.

Biochemical and biophysical characterization of cytokine-like protein 1 (CYTL1)

Cytokine-like protein 1 (CYTL1) is a small widely expressed secreted protein lacking significant primary sequence homology to any other known protein. CYTL1 expression appears to be highest in the hematopoietic system and in chondrocytes; however, maintenance of cartilage in mouse models of arthritis is its only reported function in vivo. Despite lacking sequence homology to chemokines, CYTL1 is predicted by computational methods to fold like a chemokine, and has been reported to function as a chemotactic agonist at the chemokine receptor CCR2 in mouse monocyte/macrophages. Nevertheless, since chemokines are defined by structure and chemokine receptors are able to bind many non-chemokine ligands, direct determination of the CYTL1 tertiary structure will ultimately be required to know whether it actually folds as a chemokine and therefore is a chemokine. Towards this goal, we have developed a method for producing functional recombinant human CYTL1 in bacteria, and we provide new evidence about the biophysical and biochemical properties of recombinant CYTL1. Circular dichroism analysis showed that, like chemokines, CYTL1has a higher content of beta-sheet than alpha-helix secondary structure. Furthermore, recombinant CYTL1 promoted calcium flux in chondrocytes. Nevertheless, unlike chemokines, CYTL1 had limited affinity to proteoglycans. Together, these properties further support cytokine-like properties for CYTL1 with some overlap with the chemokines.

Salvianolic acid B regulates gene expression and promotes cell viability in chondrocytes

Articular chondrocytes reside in lacunae distributed in cartilage responsible for the remodelling of the tissue with limited ability of damage repairing. The in vitro expanded chondrocytes enhanced by factors/agents to obtain large numbers of cells with strengthened phenotype are essential for successful repair of cartilage lesions by clinical cell implantation therapies. Because the salvianolic acid B (Sal B), a major hydrophilic therapeutic agent isolated from Salvia miltiorrhiza, has been widely used to treat diseases and able to stimulate activity of cells, this study examines the effects of Sal B on passaged chondrocytes. Chondrocytes were treated with various concentrations of Sal B in monolayer culture, their morphological properties and changes, and mitochondrial membrane potential were analysed using microscopic analyses, including cellular biochemical staining and confocal laser scanning microscopy. The proteins were quantified by BCA and Western blotting, and the transcription of genes was detected by qRT‐PCR. The passaged chondrocytes treated with Sal B showed strengthened cellular synthesis and stabilized mitochondrial membrane potential with upregulated expression of the marker genes for chondrocyte phenotype, Col2‐α1, Acan and Sox9, the key Wnt signalling molecule β‐catenin and paracrine cytokine Cytl‐1. The treatments using CYTL‐1 protein significantly increased expression of Col2‐α1 and Acan with no effect on Sox9, indicating the paracrine cytokine acts on chondrocytes independent of SOX9. Sal B has ultimately promoted cell growth and enhanced chondrocyte phenotype. The chondrocytes treated with pharmaceutical agent and cytokine in the formulated medium for generating large number of differentiated chondrocytes would facilitate the cell‐based therapies for cartilage repair.

Nanoindentation modulus of murine cartilage: a sensitive indicator of the initiation and progression of post-traumatic osteoarthritis

OBJECTIVE

This study aims to demonstrate that cartilage nanoindentation modulus is a highly sensitive indicator of the onset and spatiotemporal progression of post-traumatic osteoarthritis (PTOA) in murine models.

DESIGN

Destabilization of the medial meniscus (DMM) surgery was performed on the right knees of 12-week old male, wild-type C57BL/6 mice, with Sham control on contralateral left knees. Atomic force microscopy (AFM)-based nanoindentation was applied to quantify the nanoindentation modulus, Eind, of femoral condyle cartilage at 3 days to 12 weeks after surgery. The modulus changes were compared against the timeline of histological OA signs. Meanwhile, at 8 weeks after surgery, changes in meniscus, synovium and subchondral bone were evaluated to reveal the spatial progression of PTOA.

RESULTS

The modulus of medial condyle cartilage was significantly reduced at 1 week after DMM, preceding the histological OA signs, which only became detectable at 4-8 weeks after. This reduction is likely due to concomitantly elevated proteolytic activities, as blocking enzymatic activities in mice can attenuate this modulus reduction. In later OA, lateral condyle cartilage and medial meniscus also started to be weakened, illustrating the whole-organ nature of PTOA.

CONCLUSIONS

This study underscores the high sensitivity of nanoindentation in examining the initiation, attenuation and progression of PTOA in murine models. Meanwhile, modulus changes highlight concomitant changes in lateral cartilage and meniscus during the advancement of OA.

Identification of marker genes for pars tuberalis morphogenesis in chick embryo: expression of Cytokine-like 1 and Gap junction protein alpha 5 in pars tuberalis

The adenohypophysis is formed from the oral ectoderm and consists of the pars distalis (PD), pars intermedia, and pars tuberalis (PT). The mechanisms of PD development have been extensively studied, and the cellular differentiation of the PD is well understood. However, the morphogenesis and differentiation of the PT are still unclear, and the genes expressed during PT development remain largely unknown. We have explored genes specifically expressed in the PT during embryonic development and analyzed their spatiotemporal expression patterns. Microarray analysis of laser-captured PT and PD tissues obtained from chick embryos on embryonic day 10 (E10.0) has shown high expression of Cytokine-like 1 (CYTL1) and Gap junction protein alpha 5 (GJA5) genes in the PT. Detailed analysis of these spatiotemporal expression patterns during chick embryo development by in situ hybridization has revealed that CYTL1 mRNA first appears in the lateral head ectoderm and ventral head ectoderm at E1.5. The expression of CYTL1 moves into Rathke's pouch at E2.5 and is then localized in the PT primordium where it is continuously expressed until E12.0. GJA5 mRNA is transiently detected in the PT primordium from E6.0 to E12.0, whereas its expression is not detected in the PD during development. Thus, these genes might be involved in the regulation mechanisms of PT development and could be useful markers for PT development.

Cytokine-Like 1 Regulates Cardiac Fibrosis via Modulation of TGF-β Signaling

Cytokine-like 1 (Cytl1) is a secreted protein that is involved in diverse biological processes. A comparative modeling study indicated that Cytl1 is structurally and functionally similar to monocyte chemoattractant protein 1 (MCP-1). As MCP-1 plays an important role in cardiac fibrosis (CF) and heart failure (HF), we investigated the role of Cytl1 in a mouse model of CF and HF. Cytl1 was upregulated in the failing mouse heart. Pressure overload-induced CF was significantly attenuated in cytl1 knock-out (KO) mice compared to that from wild-type (WT) mice. By contrast, adeno-associated virus (AAV)-mediated overexpression of cytl1 alone led to the development of CF in vivo. The endothelial-mesenchymal transition (EndMT) and the transdifferentiation of fibroblasts (FBs) to myofibroblasts (MFBs) have been suggested to contribute considerably to CF. Adenovirus-mediated overexpression of cytl1 was sufficient to induce these two critical CF-related processes in vitro, which were completely abrogated by co-treatment with SB-431542, an antagonist of TGF-β receptor 1. Cytl1 induced the expression of TGF-β2 both in vivo and in vitro. Antagonizing the receptor for MCP-1, C-C chemokine receptor type 2 (CCR2), with CAS 445479-97-0 did not block the pro-fibrotic activity of Cytl1 in vitro. Collectively, our data suggest that Cytl1 plays an essential role in CF likely through activating the TGF-β-SMAD signaling pathway. Although the receptor for Cyt1l remains to be identified, Cytl1 provides a novel platform for the development of anti-CF therapies.

Cytokine-Like Protein 1(Cytl1): A Potential Molecular Mediator in Embryo Implantation

Cytokine-like protein 1 (Cytl1), originally described as a protein expressed in CD34+ cells, was recently identified as a functional secreted protein involved in chondrogenesis and cartilage development. However, our knowledge of Cytl1 is still limited. Here, we determined the Cytl1 expression pattern regulated by ovarian hormones at both the mRNA and protein levels. We found that the endometrial expression of Cytl1 in mice was low before or on the first day of gestation, significantly increased during embryo implantation, and then decreased at the end of implantation. We investigated the effects of Cytl1 on endometrial cell proliferation, and the effects on the secretion of leukemia inhibitory factor (LIF) and heparin-binding epidermal growth factor (HB-EGF). We also explored the effect of Cytl1 on endometrial adhesion properties in cell-cell adhesion assays. Our findings demonstrated that Cytl1 is an ovarian hormone-dependent protein expressed in the endometrium that enhances the proliferation of HEC-1-A and RL95-2 cells, stimulates endometrial secretion of LIF and HB-EGF, and enhances the adhesion of HEC-1-A and RL95-2 cells to JAR spheroids. This study suggests that Cytl1 plays an active role in the regulation of embryo implantation.

Distinct differences in global gene expression profiles in non-implanted blastocysts and blastocysts resulting in live birth

Results from animal models points towards the existence of a gene expression profile that is distinguishably different in viable embryos compared with non-viable embryos. Knowledge of human embryo transcripts is however limited, in particular with regard to how gene expression is related to clinical outcome. The purpose of the present study was therefore to determine the global gene expression profiles of human blastocysts. Next Generation Sequencing was used to identify genes that were differentially expressed in non-implanted embryos and embryos resulting in live birth. Three trophectoderm biopsies were obtained from morphologically high quality blastocysts resulting in live birth and three biopsies were obtained from non-implanting blastocysts of a comparable morphology. Total RNA was extracted from all samples followed by complete transcriptome sequencing. Using a set of filtering criteria, we obtained a list of 181 genes that were differentially expressed between trophectoderm biopsies from embryos resulting in either live birth or no implantation (negative hCG), respectively. We found that 37 of the 181 genes displayed significantly differential expression (p<0.05), e.g. EFNB1, CYTL1 and TEX26 and TESK1, MSL1 and EVI5 in trophectoderm biopsies associated with live birth and non-implanting, respectively. Out of the 181 genes, almost 80% (145 genes) were up-regulated in biopsies from un-implanted embryos, whereas only 20% (36 genes) showed an up-regulation in the samples from embryos resulting in live birth. Our findings suggest the presence of molecular differences visually undetectable between implanted and non-implanted embryos, and represent a proof of principle study.

Cord blood gene expression supports that prenatal exposure to perfluoroalkyl substances causes depressed immune functionality in early childhood

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a class of synthetic compounds that have widespread use in consumer and industrial applications. PFAS are considered environmental pollutants that have various toxic properties, including effects on the immune system. Recent human studies indicate that prenatal exposure to PFAS leads to suppressed immune responses in early childhood. In this study, data from the Norwegian BraMat cohort was used to investigate transcriptomics profiles in neonatal cord blood and their association with maternal PFAS exposure, anti-rubella antibody levels at 3 years of age and the number of common cold episodes until 3 years. Genes associated with PFAS exposure showed enrichment for immunological and developmental functions. The analyses identified a toxicogenomics profile of 52 PFAS exposure-associated genes that were in common with genes associated with rubella titers and/or common cold episodes. This gene set contains several immunomodulatory genes (CYTL1, IL27) as well as other immune-associated genes (e.g. EMR4P, SHC4, ADORA2A). In addition, this study identified PPARD as a PFAS toxicogenomics marker. These markers can serve as the basis for further mechanistic or epidemiological studies. This study provides a transcriptomics connection between prenatal PFAS exposure and impaired immune function in early childhood and supports current views on PPAR- and NF-κB-mediated modes of action. The findings add to the available evidence that PFAS exposure is immunotoxic in humans and support regulatory policies to phase out these substances.

High-throughput screening of mouse gene knockouts identifies established and novel skeletal phenotypes

Screening gene function in vivo is a powerful approach to discover novel drug targets. We present high-throughput screening (HTS) data for 3 762 distinct global gene knockout (KO) mouse lines with viable adult homozygous mice generated using either gene-trap or homologous recombination technologies. Bone mass was determined from DEXA scans of male and female mice at 14 weeks of age and by microCT analyses of bones from male mice at 16 weeks of age. Wild-type (WT) cagemates/littermates were examined for each gene KO. Lethality was observed in an additional 850 KO lines. Since primary HTS are susceptible to false positive findings, additional cohorts of mice from KO lines with intriguing HTS bone data were examined. Aging, ovariectomy, histomorphometry and bone strength studies were performed and possible non-skeletal phenotypes were explored. Together, these screens identified multiple genes affecting bone mass: 23 previously reported genes (Calcr, Cebpb, Crtap, Dcstamp, Dkk1, Duoxa2, Enpp1, Fgf23, Kiss1/Kiss1r, Kl (Klotho), Lrp5, Mstn, Neo1, Npr2, Ostm1, Postn, Sfrp4, Slc30a5, Slc39a13, Sost, Sumf1, Src, Wnt10b), five novel genes extensively characterized (Cldn18, Fam20c, Lrrk1, Sgpl1, Wnt16), five novel genes with preliminary characterization (Agpat2, Rassf5, Slc10a7, Slc26a7, Slc30a10) and three novel undisclosed genes coding for potential osteoporosis drug targets.

Doublecortin may play a role in defining chondrocyte phenotype

Embryonic development of articular cartilage has not been well understood and the role of doublecortin (DCX) in determination of chondrocyte phenotype is unknown. Here, we use a DCX promoter-driven eGFP reporter mouse model to study the dynamic gene expression profiles in mouse embryonic handplates at E12.5 to E13.5 when the condensed mesenchymal cells differentiate into either endochondral chondrocytes or joint interzone cells. Illumina microarray analysis identified a variety of genes that were expressed differentially in the different regions of mouse handplate. The unique expression patterns of many genes were revealed. Cytl1 and 3110032G18RIK were highly expressed in the proximal region of E12.5 handplate and the carpal region of E13.5 handplate, whereas Olfr538, Kctd15, and Cited1 were highly expressed in the distal region of E12.5 and the metacarpal region of E13.5 handplates. There was an increasing gradient of Hrc expression in the proximal to distal direction in E13.5 handplate. Furthermore, when human DCX protein was expressed in human adipose stem cells, collagen II was decreased while aggrecan, matrilin 2, and GDF5 were increased during the 14-day pellet culture. These findings suggest that DCX may play a role in defining chondrocyte phenotype.

Quantitative proteomics reveals regulatory differences in the chondrocyte secretome from human medial and lateral femoral condyles in osteoarthritic patients

Background

Osteoarthritis (OA) is a destructive joint disease and there are no known biomarkers available for an early diagnosis. To identify potential disease biomarkers and gain further insight into the disease mechanisms of OA we applied quantitative proteomics with SILAC technology on the secretomes from chondrocytes of OA knees, designated as high Mankin (HM) scored secretome. A quantitative comparison was made between the secretomes of the medial and lateral femur condyle chondrocytes in the same knee since the medial femur condyle is usually more affected in OA than the lateral condyle, which was confirmed by Mankin scoring. The medial/lateral comparison was also made on the secretomes from chondrocytes taken from one individual with no clinically apparent joint-disease, designated as low Mankin (LM) scored secretome.

Results

We identified 825 proteins in the HM secretome and 69 of these showed differential expression when comparing the medial and lateral femoral compartment. The LM scored femoral condyle showed early signs of OA in the medial compartment as assessed by Mankin score. We here report the identification and relative quantification of several proteins of interest for the OA disease mechanism e.g. CYTL1, DMD and STAB1 together with putative early disease markers e.g. TIMP1, PPP2CA and B2M.

Conclusions

The present study reveals differences in protein abundance between medial/lateral femur condyles in OA patients. These regulatory differences expand the knowledge regarding OA disease markers and mechanisms.

Post-traumatic osteoarthritis: from mouse models to clinical trials

Osteoarthritis (OA), the most common of all arthropathies, is a leading cause of disability and has a large (and growing) worldwide socioeconomic cost. Despite its burgeoning importance, translation of disease-modifying OA therapies from the laboratory into clinical practice has slowed. Differences between the OA models studied preclinically and the disease evaluated in human clinical trials contribute to this failure. Most animal models of OA induce disease through surgical or mechanical disruption of joint biomechanics in young individuals rather than the spontaneous development of age-associated disease. This instability-induced joint disease in animals best models the arthritis that develops in humans after an injurious event, known as post-traumatic OA (PTOA). Studies in genetically modified mice suggest that PTOA has a distinct molecular pathophysiology compared with that of spontaneous OA, which might explain the poor translation from preclinical to clinical OA therapeutic trials. This Review summarizes the latest data on potential molecular targets for PTOA prevention and modification derived from studies in genetically modified mice, and describes their validation in preclinical therapeutic trials. This article focuses on how these findings might best be translated to humans, and identifies the potential challenges to successful implementation of clinical trials of disease-modifying drugs for PTOA.

Dkk-1 expression in chondrocytes inhibits experimental osteoarthritic cartilage destruction in mice

OBJECTIVE

Dkk is a family of canonical Wnt antagonists with 4 members (Dkk-1, Dkk-2, Dkk-3, and Dkk-4). We undertook this study to explore the roles of Dkk-1 and Dkk-2 in osteoarthritic (OA) cartilage destruction in mice.

METHODS

Expression of Dkk and other catabolic factors was determined at the messenger RNA and protein levels in human and mouse OA cartilage. Experimental OA in mice was induced by destabilization of the medial meniscus (DMM) or by intraarticular injection of Epas1 adenovirus (AdEPAS-1). The role of Dkk in OA pathogenesis was examined by intraarticular injection of AdDkk-1 or by using chondrocyte-specific Dkk1 (Col2a1-Dkk1)-transgenic mice and Dkk2 (Col2a1-Dkk2)-transgenic mice. Primary culture mouse chondrocytes were also treated with recombinant Dkk proteins.

RESULTS

We found opposite patterns of Dkk1 and Dkk2 expression in human and mouse experimental OA cartilage: Dkk1 was up-regulated and Dkk2 was down-regulated. Overexpression of Dkk1 by intraarticular injection of AdDkk-1 significantly inhibited DMM-induced experimental OA. DMM-induced OA was also significantly inhibited in Col2a1-Dkk1-transgenic mice compared with their wild-type littermates. However, Col2a1-Dkk2-transgenic mice showed no significant difference in OA pathogenesis. Wnt-3a, which activates the canonical Wnt pathway, induced Mmp13 and Adamts4 expression in primary culture chondrocytes, an effect that was significantly inhibited by Dkk-1 pretreatment or Dkk1 overexpression.

CONCLUSION

Our findings indicate that expression of Dkk1, but not Dkk2, in chondrocytes inhibits OA cartilage destruction. The protective effect of Dkk-1 appears to be associated with its capacity to inhibit Wnt-mediated expression of catabolic factors, such as Mmp13, providing evidence that Dkk-1 might serve as a therapeutic target for OA treatment.

BMP2 is superior to BMP4 for promoting human muscle-derived stem cell-mediated bone regeneration in a critical-sized calvarial defect model

Muscle-derived cells have been successfully isolated using a variety of different methods and have been shown to possess multilineage differentiation capacities, including an ability to differentiate into articular cartilage and bone in vivo; however, the characterization of human muscle-derived stem cells (hMDSCs) and their bone regenerative capacities have not been fully investigated. Genetic modification of these cells may enhance their osteogenic capacity, which could potentially be applied to bone regenerative therapies. We found that hMDSCs, isolated by the preplate technique, consistently expressed the myogenic marker CD56, the pericyte/endothelial cell marker CD146, and the mesenchymal stem cell markers CD73, CD90, CD105, and CD44 but did not express the hematopoietic stem cell marker CD45, and they could undergo osteogenic, chondrogenic, adipogenic, and myogenic differentiation in vitro. In order to investigate the osteoinductive potential of hMDSCs, we constructed a retroviral vector expressing BMP4 and GFP and a lentiviral vector expressing BMP2. The BMP4-expressing hMDSCs were able to undergo osteogenic differentiation in vitro and exhibited enhanced mineralization compared to nontransduced cells; however, when transplanted into a calvarial defect, they failed to regenerate bone. Local administration of BMP4 protein and cell pretreatment with N-acetylcysteine (NAC), which improves cell survival, did not enhance the osteogenic capacity of the retro-BMP4-transduced cells. In contrast, lenti-BMP2-transduced hMDSCs not only exhibited enhanced in vitro osteogenic differentiation but also induced robust bone formation and nearly completely healed a critical-sized calvarial defect in CD-1 nude mice 6 weeks following transplantation. Herovici's staining of the regenerated bone demonstrated that the bone matrix contained a large amount of type I collagen. Our findings indicated that the hMDSCs are likely mesenchymal stem cells of muscle origin and that BMP2 is more efficient than BMP4 in promoting the bone regenerative capacity of the hMDSCs in vivo.

Misexpression of Dickkopf-1 in endothelial cells, but not in chondrocytes or hypertrophic chondrocytes, causes defects in endochondral ossification

Developing cartilage serves as a template for long-bone development during endochondral ossification. Although the coupling of cartilage and bone development with angiogenesis is an important regulatory step for endochondral ossification, the molecular mechanisms are poorly understood. One possible mechanism involves the action of Dickkopf (DKK), which is a family of soluble canonical Wnt antagonists with four members (DKK1-4). We initially observed opposite expression patterns of Dkk1 and Dkk2 during angiogenesis and chondrocyte differentiation: downregulation of Dkk1 and upregulation of Dkk2. We examined the in vivo role of Dkk1 and Dkk2 in linking cartilage/bone development and angiogenesis by generating transgenic (TG) mice that specifically express Dkk1 or Dkk2 in chondrocytes, hypertrophic chondrocytes, or endothelial cells. Despite specific expression pattern during cartilage development, chondrocyte- and hypertrophic chondrocyte-specific Dkk1 and Dkk2 TG mice showed normal developmental phenotypes. However, Dkk1 misexpression in endothelial cells resulted in defects of endochondral ossification and reduced skeletal size. The defects are caused by the inhibition of angiogenesis in developing bone and subsequent inhibition of apoptosis of hypertrophic chondrocytes and cartilage resorption.