Cartducin, a paralog of Acrp30/adiponectin, is induced during chondrogenic differentiation and promotes proliferation of chondrogenic precursors and chondrocytes

Relation between serum sclerostin and CTRP3 levels and bone mineral density in diabetic postmenopausal women

BACKGROUND

Osteoporosis (OP) is a common finding in diabetic patients especially high-risk populations such as postmenopausal women. Sclerostin is a glycoprotein chiefly secreted by mature osteocytes and is considered a main regulator of bone formation. The C1q/TNF-Related Protein 3 (CTRP3) was found to be significantly associated with OP in postmenopausal women. The effect of type 2 diabetes mellitus (T2DM) on sclerostin and CTRP3 levels in postmenopausal women is rarely investigated. The present study aimed to assess the impact of T2DM on sclerostin and CTRP3 levels and their relation to OP in postmenopausal women.

METHODS

The study included 60 postmenopausal women with T2DM and 60 age-matched postmenopausal non-diabetic women. Bone mineral density (BMD) was assessed using dual energy X-ray absorptiometry (DEXA). Serum levels of sclerostin and CTRP3 were assessed using enzyme-linked immunosorbent assay (ELISA) technique.

RESULTS

Diabetic group expressed significantly higher serum levels of sclerostin when compared with non-diabetic group (110.0 ± 29.0 versus 51.5 ± 23.2 ng; p < 0.001). Oppositely, CTRP3 were significantly lower in the diabetic group (3.5 ± 3.5 versus 9.9 ± 3.7 ng/ml, p < 0.001). Multivariate logistic regression analysis identified HbA1c levels [OR (95% CI): 0.49 (0.26-0.93), p = 0.028], sclerotin levels [OR (95% CI): 1.06 (1.0-1.012), p = 0.041] and CTRP3 levels [OR (95%) CI: 1.64 (1.0-2.68), p = 0.047] as significant predictors of OP in diabetic patients.

CONCLUSIONS

Sclerostin and CTRP3 levels are involved in OP in postmenopausal diabetic patients.

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

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

FOXQ1 inhibits the progression of osteoarthritis by regulating pyroptosis

BACKGROUND

Osteoarthritis (OA) is the most common age-related joint disease, and the NLRP3-induced pyroptosis has been demonstrated in its progression. The upstream molecules or specific mechanisms controlling NLRP3 and pyroptosis in OA remain unclear.

METHODS

Transcriptome sequencing was performed in the OA mice model, and the expression levels of differentially expressed genes were assessed by qRT-PCR. The cell model was constructed by IL-1β-induced ATDC5 cells. The cell proliferation was examined using CCK-8 assay, and apoptosis was tested using flow cytometry. Western blot was used in protein inspection, and ELISA was used in inflammatory response evaluation.

RESULTS

Compared with the control group, there were 229 up-regulated and 32 down-regulated genes in model group. We detected that FOXQ1 was down-regulated in the OA mice model, improved proliferation, and restrained apoptosis of chondrocytes. Over-expression of FOXQ1 could inhibit pyroptosis-related proteins and inflammatory cytokines, containing NLRP3, Caspase-1, GSDMD, IL-6, IL-18, and TNF-α, and in contrast, FOXQ1 silencing exerted the opposite trend.

CONCLUSIONS

FOXQ1 may inhibit OA progression via down-regulating NLRP3-induced pyroptosis in the present study.

African swine fever virus infection activates inflammatory responses through downregulation of the anti-inflammatory molecule C1QTNF3

African swine fever (ASF) is the most dangerous pig disease, and causes enormous economic losses in the global pig industry. However, the mechanisms of ASF virus (ASFV) infection remains largely unclear. Hence, this study investigated the host response mechanisms to ASFV infection. We analyzed the differentially expressed proteins (DEPs) between serum samples from ASFV-infected and uninfected pigs using quantitative proteomics. Setting the p-value &lt; 0.05 and |log2 (fold change)| &gt; 1.5, we identified 173 DEPs, comprising 57 upregulated and 116 downregulated proteins, which belonged to various biological processes and pathways based on the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses. The enriched pathways include immune responses, metabolism, and inflammation signaling pathways. Western blot analysis validated the DEPs identified using quantitative proteomics. Furthermore, our proteomics data showed that C1QTNF3 regulated the inflammatory signaling pathway. C1QTNF3 knockdown led to the upregulation of pro-inflammatory factors IL-1β, IL-8, and IL-6, thus inhibiting ASFV replication. These results indicated that C1QTNF3 was critical for ASFV infection. In conclusion, this study revealed the molecular mechanisms underlying the host-ASFV interaction, which may contribute to the development of novel antiviral strategies against ASFV infection in the future.

Adipocyte-Derived CTRP3 Exhibits Anti-Inflammatory Effects via LAMP1-STAT3 Axis in Psoriasis

Psoriasis is a systemic disease that is associated with metabolic disorders, which may contribute to abnormal adipokine levels. However, the underlying mechanism is largely unknown. Here, we investigated the role of the adipokine CTRP3 in the pathogenesis of psoriasis and comorbidities. The circulating CTRP3 level in patients with psoriasis was significantly lower than that in healthy controls and negatively correlated with metabolic risk factors. Rescuing CTRP3 levels with the GLP-1 receptor agonist exendin-4 in diet-induced obese mice could alleviate its more severe psoriatic symptoms in an imiquimod-induced mouse model. Topical application of CTRP3 also exerted a protective effect on imiquimod-induced normal diet mice. Moreover, CTRP3 could directly inhibit the inflammatory responses of psoriatic keratinocytes by blocking phosphorylation of signal transducer and activator of transcription 3 via LAMP1 in vitro. We identified the critical psoriatic cytokines, including IL-17A and TNF-α, that impaired adipocyte differentiation and sufficient CTRP3 secretion. In sum, our study reveals that adipocyte dysfunction and low level of CTRP3 caused by IL-17A exacerbates psoriasis progression and related metabolic syndrome, implying a mechanism underlying the vicious cycle between psoriasis and metabolic disorders. Pharmacological agents that improve CTRP3 level in obese patients with psoriasis may be considered as a potential strategy for psoriasis treatment.

CTRP3 exacerbates tendinopathy by dysregulating tendon stem cell differentiation and altering extracellular matrix composition

Tendinopathy, the most common disorder affecting tendons, is characterized by chronic disorganization of the tendon matrix, which leads to tendon tear and rupture. The goal was to identify a rational molecular target whose blockade can serve as a potential therapeutic intervention for tendinopathy. We identified C1q/TNF-related protein-3 (CTRP3) as a markedly up-regulated cytokine in human and rodent tendinopathy. Overexpression of CTRP3 enhanced the progression of tendinopathy by accumulating cartilaginous proteoglycans and degenerating collagenous fibers in the mouse tendon, whereas CTRP3 knockdown suppressed the tendinopathy pathogenesis. Functional blockade of CTRP3 using a neutralizing antibody ameliorated overuse-induced tendinopathy of the Achilles and rotator cuff tendons. Mechanistically, CTRP3 elicited a transcriptomic pattern that stimulates abnormal differentiation of tendon stem/progenitor cells and ectopic chondrification as an effect linked to activation of Akt signaling. Collectively, we reveal an essential role for CTRP3 in tendinopathy and propose a potential therapeutic strategy for the treatment of tendinopathy.

Role of the CTRP family in tumor development and progression

C1q tumor necrosis factor-related proteins (CTRPs), which are members of the adipokine superfamily, have gained significant interest in the recent years. CTRPs are homologs of adiponectin with numerous functions and are closely associated with metabolic diseases, such as abnormal glucose and lipid metabolism and diabetes. Previous studies have demonstrated that CTRPs are highly involved in the regulation of numerous physiological and pathological processes, including glycolipid metabolism, protein kinase pathways, cell proliferation, cell apoptosis and inflammation. CTRPs also play important roles in the development and progression of numerous types of tumor, including liver, colon and lung cancers. This observation can be attributed to the fact that diabetes, obesity and insulin resistance are independent risk factors for tumorigenesis. Numerous CTRPs, including CTRP3, CTRP4, CTRP6 and CTRP8, have been reported to be associated with tumor progression by activating multiple signal pathways. CTRPs could therefore be considered as diagnostic markers and therapeutic targets in some cancers. However, the underlying mechanisms of CTRPs in tumorigenesis remain unknown. The present review aimed to determine the roles and underlying mechanisms of CTRPs in tumorigenesis, which may help the development of novel cancer treatments in the future.

New Insights Into Implications of CTRP3 in Obesity, Metabolic Dysfunction, and Cardiovascular Diseases: Potential of Therapeutic Interventions

Adipose tissue, as the largest endocrine organ, secretes many biologically active molecules circulating in the bloodstream, collectively termed adipocytokines, which not only regulate the metabolism but also play a role in pathophysiological processes. C1q tumor necrosis factor (TNF)-related protein 3 (CTRP3) is a member of C1q tumor necrosis factor-related proteins (CTRPs), which is a paralog of adiponectin. CTRP3 has a wide range of effects on glucose/lipid metabolism, inflammation, and contributes to cardiovascular protection. In this review, we comprehensively discussed the latest research on CTRP3 in obesity, diabetes, metabolic syndrome, and cardiovascular diseases.

Adipokines: New Potential Therapeutic Target for Obesity and Metabolic, Rheumatic, and Cardiovascular Diseases

Besides its role as an energy storage organ, adipose tissue can be viewed as a dynamic and complex endocrine organ, which produces and secretes several adipokines, including hormones, cytokines, extracellular matrix (ECM) proteins, and growth and vasoactive factors. A wide body of evidence showed that adipokines play a critical role in various biological and physiological functions, among which feeding modulation, inflammatory and immune function, glucose and lipid metabolism, and blood pressure control. The aim of this review is to summarize the effects of several adipokines, including leptin, diponectin, resistin, chemerin, lipocalin-2 (LCN2), vaspin, omentin, follistatin-like 1 (FSTL1), secreted protein acidic and rich in cysteine (SPARC), secreted frizzled-related protein 5 (SFRP5), C1q/TNF-related proteins (CTRPs), family with sequence similarity to 19 member A5 (FAM19A5), wingless-type inducible signaling pathway protein-1 (WISP1), progranulin (PGRN), nesfatin-1 (nesfatin), visfatin/PBEF/NAMPT, apelin, retinol binding protein 4 (RPB4), and plasminogen activator inhibitor-1 (PAI-1) in the regulation of insulin resistance and vascular function, as well as many aspects of inflammation and immunity and their potential role in managing obesity-associated diseases, including metabolic, osteoarticular, and cardiovascular diseases.

CTRP3 Regulates Endochondral Ossification and Bone Remodeling During Fracture Healing

C1q/TNF-related protein 3 (CTRP3) is a cytokine known to regulate a variety of metabolic processes. Though previously undescribed in the context of bone regeneration, high throughput gene expression experiments in mice identified CTRP3 as one of the most highly upregulated genes in fracture callus tissue. Hypothesizing a positive regulatory role for CTRP3 in bone regeneration, we phenotyped skeletal development and fracture healing in CTRP3 knockout (KO) and CTRP3 overexpressing transgenic (TG) mice relative to wild-type (WT) control animals. CTRP3 KO mice experienced delayed endochondral fracture healing, resulting in abnormal mineral distribution, the presence of periosteal marrow compartments, and a nonunion-like state. Decreased osteoclast number was also observed in CTRP3 KO mice, whereas CTRP3 TG mice underwent accelerated callus remodeling. Gene expression profiling revealed a broad impact on osteoblast/osteoclast lineage commitment and metabolism, including arrested progression toward mature skeletal lineages in the KO group. A single systemic injection of CTRP3 protein at the time of fracture was insufficient to phenocopy the chronic TG healing response in WT mice. By associating CTRP3 levels with fracture healing progression, these data identify a novel protein family with potential therapeutic and diagnostic value. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:00-19966, 2020.

High molecular weight, but not total, CTRP3 levels are associated with serum triglyceride levels

C1q/TNF-related protein 3 (CTRP3) is a relatively novel adipose tissue-derived cytokine (adipokine) which has been linked to improved glucose regulation and insulin sensitivity. However, the relationship between circulating CTRP3 levels and diabetes is controversial. CTRP3 can circulate in different oligomeric complexes: trimeric, hexameric, and high molecular weight (HMW) oligomeric complexes. However, the concentration of the different oligomeric complexes in human disease states has not been previously investigated. Therefore, the purpose of this study was to compare the levels of different oligomeric complexes of CTRP3 between type 2 diabetic and nondiabetic individuals. Additionally, the association between the oligomeric complexes and other serum factors was examined. CTRP3 primarily circulates in the HMW complex (>50%) and the hexametric multimer, with no CTRP3 detected in the trimeric complex or as a monomer. Further, no differences were observed in total, hexameric, or HMW CTRP3 levels regardless of diabetic status. Surprisingly, HMW CTRP3 was found to be positively correlated with circulating triglyceride levels. Combined, these data suggest that CTRP3 is associated with triglyceride regulation, not diabetic status. These data may explain some of the discrepancies in the literature as elevated triglyceride levels are often detected in patients with obesity and type 2 diabetes.

C1q/TNF-related protein-3 and glucose homeostasis

Adipokines are cytokines produced by adipocytes that may mediate inflammatory processes, whilst adipocyte-derived proteins may have the converse effect. C1q/TNF-related protein-3 or CTRP3 is a novel adipokine that is expressed and released by most types of human tissues including adipose tissue. This adipokine, considered as an adiponectin, can normalize blood glucose by several mechanisms. In addition, it can modulate the expression/secretion of other cytokine and adipokines leading to lower insulin resistance in peripheral tissues. Beneficial effects of CTRP3 against hyperglycemia-induced complications in the kidney and eye have been reported. In this review, we have presented the latest findings on the in vitro and in vivo hypoglycemic effects of CTRP3, followed by the findings on the preventive/therapeutic effects of CTRP3 adipokines against diabetes related complications.

C1QTNF3 in the murine ovary and its function in folliculogenesis

C1q/tumor necrosis factor-related protein 3 (C1QTNF3) is a novel adipokine with modulating effects on metabolism, inflammation and the cardiovascular system. C1QTNF3 expression levels in the sera and omental adipose tissues of women with PCOS are low compared to control subjects. However, the expression and function of C1QTNF3 in the ovary has not previously been examined. Here, we assessed the expression patterns of C1qtnf3 in the ovary and explored its role in folliculogenesis. The C1qtnf3 transcript abundance was higher in large follicles than in small follicles and was under the influence of gonadotropin. C1QTNF3 was detected mainly in the granulosa cells and oocytes of growing follicles and modestly in the granulosa cells of atretic follicles and in luteal cells. Excess androgen significantly decreased C1QTNF3 expression in the ovaries in vivo and in granulosa cells in vitro. Recombinant C1QTNF3 protein accelerated the weight gain of ovarian explants and the growth of preantral follicles induced by follicle stimulating hormone (FSH) in vitro. The stimulatory effect of C1QTNF3 on ovarian growth was accompanied by the initiation of AKT, mTOR, p70S6K and 4EBP1 phosphorylation, an increase in CCND2 expression and a reduction in cleaved CASP3 levels. Moreover, the addition of C1QTNF3 accelerated proliferation and reduced activated CASP3/7 activity in granulosa cells. In vivo, the ovarian intrabursal administration of the C1QTNF3 antibody delayed gonadotropin-induced antral follicle development. Taken together, our data demonstrate that C1QTNF3 is an intraovarian factor that promotes follicle growth by accelerating proliferation, decelerating apoptosis and promoting AKT/mTOR phosphorylation.

C1q/TNF-Related Protein 3 (CTRP3) Function and Regulation

As the largest endocrine organ, adipose tissue secretes many bioactive molecules that circulate in blood, collectively termed adipokines. Efforts to identify such metabolic regulators have led to the discovery of a family of secreted proteins, designated as C1q tumor necrosis factor (TNF)-related proteins (CTRPs). The CTRP proteins, adiponectin, TNF-alpha, as well as other proteins with the distinct C1q domain are collectively grouped together as the C1q/TNF superfamily. Reflecting profound biological potency, the initial characterization of these adipose tissue-derived CTRP factors finds wide-ranging effects upon metabolism, inflammation, and survival-signaling in multiple tissue types. CTRP3 (also known as CORS26, cartducin, or cartonectin) is a unique member of this adipokine family. In this review we provide a comprehensive overview of the research concerning the expression, regulation, and physiological function of CTRP3. © 2017 American Physiological Society. Compr Physiol 7:863-878, 2017.

Cartilage rings contribute to the proper embryonic tracheal epithelial differentiation, metabolism, and expression of inflammatory genes

The signaling cross talk between the tracheal mesenchyme and epithelium has not been researched extensively, leaving a substantial gap of knowledge in the mechanisms dictating embryonic development of the proximal airways by the adjacent mesenchyme. Recently, we reported that embryos lacking mesenchymal expression of Sox9 did not develop tracheal cartilage rings and showed aberrant differentiation of the tracheal epithelium. Here, we propose that tracheal cartilage provides local inductive signals responsible for the proper differentiation, metabolism, and inflammatory status regulation of the tracheal epithelium. The tracheal epithelium of mesenchyme-specific Sox9^Δ/Δ mutant embryos showed altered mRNA expression of various epithelial markers such as Pb1fa1, surfactant protein B (Sftpb), secretoglobulin, family 1A, member 1 (Scgb1a1), and trefoil factor 1 (Tff1). In vitro tracheal epithelial cell cultures confirmed that tracheal chondrocytes secrete factors that inhibit club cell differentiation. Whole gene expression profiling and ingenuity pathway analysis showed that the tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), and transforming growth factor-β (TGF-β) signaling pathways were significantly altered in the Sox9 mutant trachea. TNF-α and IFN-γ interfered with the differentiation of tracheal epithelial progenitor cells into mature epithelial cell types in vitro. Mesenchymal knockout of Tgf-β1 in vivo resulted in altered differentiation of the tracheal epithelium. Finally, mitochondrial enzymes involved in fat and glycogen metabolism, cytochrome c oxidase subunit VIIIb (Cox8b) and cytochrome c oxidase subunit VIIa polypeptide 1 (Cox7a1), were strongly upregulated in the Sox9 mutant trachea, resulting in increases in the number and size of glycogen storage vacuoles. Our results support a role for tracheal cartilage in modulation of the differentiation and metabolism and the expression of inflammatory-related genes in the tracheal epithelium by feeding into the TNF-α, IFN-γ, and TGF-β signaling pathways.

Identification of Putative Receptors for the Novel Adipokine CTRP3 Using Ligand-Receptor Capture Technology

C1q TNF Related Protein 3 (CTRP3) is a member of a family of secreted proteins that exert a multitude of biological effects. Our initial work identified CTRP3’s promise as an effective treatment for Nonalcoholic fatty liver disease (NAFLD). Specifically, we demonstrated that mice fed a high fat diet failed to develop NAFLD when treated with CTRP3. The purpose of this current project is to identify putative receptors which mediate the hepatic actions of CTRP3.

CTRP3 acts as a negative regulator of osteoclastogenesis through AMPK-c-Fos-NFATc1 signaling in vitro and RANKL-induced calvarial bone destruction in vivo

Adipokines derived from adipocytes are important factors that act as circulating regulators of bone metabolism. C1q/tumor necrosis factor (TNF)-related Protein-3 (CTRP3) is a novel adipokine with multiple effects such as lowering glucose levels, inhibiting gluconeogenesis in the liver, and increasing angiogenesis and anti-inflammation. However, the effects and the mechanisms of CTRP3 on bone metabolism, which is regulated by osteoblasts and osteoclasts, have not been investigated. Here, we found that CTRP3 inhibited osteoclast differentiation induced by osteoclastogenic factors in bone marrow cell-osteoblast co-cultures, but did not affect the ratio of receptor activator of nuclear factor κB (NF-κB) ligand (RANKL) to osteoprotegerin (OPG) induced by osteoclastogenic factors in osteoblasts. We also found that CTRP3 inhibited osteoclast differentiation from mouse bone marrow macrophages (BMMs) induced by RANKL in a dose-dependent manner without cytotoxicity. Functionally, CTRP3 inhibited the F-actin formation and bone resorbing activity of mature osteoclasts. Pretreatment with CTRP3 significantly inhibited RANKL-induced expression of c-Fos and nuclear factor of activated T-cells (NFATc1), essential transcription factors for osteoclast development. Surprisingly, the activation of AMP-activated protein kinase (AMPK) was considerably increased by pretreatment with CTRP3 for 1h. The CTRP3-stimulated AMPK activation was also maintained during RANKL-induced osteoclastogenesis. CTRP3 did not affect RANKL-induced p38, ERK, JNK, Akt, IκB, CREB, and calcium signaling (Btk and PLCγ2). These results suggest that CTRP3 plays an important role as a negative regulator of RANKL-mediated osteoclast differentiation by acting as an inhibitor of NFATc1 activation through the AMPK signaling pathway. Furthermore, CTRP3 treatment reduced RANKL-induced osteoclast formation and bone destruction in mouse calvarial bone in vivo based on micro-CT and histologic analysis. In conclusion, these findings strongly suggest that CTRP3 deserves new evaluation as a potential treatment target in various bone diseases associated with excessive osteoclast differentiation and bone destruction.

CTRP3 Stimulates Proliferation and Anti-Apoptosis of Prostate Cells through PKC Signaling Pathways

C1q/TNF-related protein-3 (CTRP3) is a novel adipokine with roles in multiple cellular processes. However, little is known about its function in prostate cells. This study investigated the effects and mechanisms of CTRP3 in prostate cells. We first generated and purified CTRP3 protein in HEK 293T cells. Proliferation of RWPE-1 prostate cells was evaluated by MTT analyses under treatment with different concentrations of CTRP3 for various exposure times. The results revealed maximum enhancement of proliferation with 10 μg/mL CTRP3 for 72 h. Cell apoptosis and cell cycle were determined by TUNEL staining and flow cytometry analysis. TUNEL assay showed decreased TUNEL-positive cells in RWPE-1 prostate cells treated with CTRP3, and flow cytometry showed significantly decreased apoptotic cells upon CTRP3 treatment (treated cells, 8.34±1.175 vs. controls, 20.163±0.35) (P < 0.01). Moreover, flow cytometry analysis also showed a significant decrease of cells in the G1 phase and an increase of cells in the S and G2 phase upon CTRP3 treatment (treated cells, 42.85±1.40 vs. control, 52.77±0.90; 28.41±0.57 vs. 23.49±1.13; 27.08±1.97 vs. 22.20±1.32, respectively) (all P < 0.05). Two-dimensional gel electrophoresis and mass spectrometry identified differentially expressed proteins, including cytokeratin-19, GLRX3 and DDAH1, which were upregulated in CTRP3 treated cells, and cytokeratin-17 and 14-3-3 sigma, which were downregulated. GLRX3, DDAH1 and 14-3-3 sigma were confirmed using western blot analysis. A PKC inhibitor, staurosporine, was used to inhibit PKC activity in CTRP3 treated RWPE-1 cells. Staurosporine completely abolished the CTRP3-induced increased phosphorylation of intracellular PKC substrates and CTRP3-stimulated effect by RWPE-1 cells. Our results provide the first evidence for a physiological role of the novel adipokine, CTRP3, in prostate cells. Our findings suggest that CTRP3 could improve proliferation and anti-apoptosis of prostate cells through protein kinase C signaling pathways.

RXFP1 is Targeted by Complement C1q Tumor Necrosis Factor-Related Factor 8 in Brain Cancer

The relaxin-like RXFP1 ligand-receptor system has important functions in tumor growth and tissue invasion. Recently, we have identified the secreted protein, CTRP8, a member of the C1q/tumor necrosis factor-related protein (CTRP) family, as a novel ligand of the relaxin receptor, RXFP1, with functions in brain cancer. Here, we review the role of CTRP members in cancers cells with particular emphasis on CTRP8 in glioblastoma.

C1q/TNF-related protein-3 (CTRP-3) attenuates lipopolysaccharide (LPS)-induced systemic inflammation and adipose tissue Erk-1/-2 phosphorylation in mice in vivo

BACKGROUND

The C1q/TNF-related proteins comprise a growing family of adiponectin paralogous proteins. CTRP-3 represents a novel adipokine with strong expression in adipose tissue and was shown to inhibit chemokine and cytokine release in adipocytes and monocytes in vitro. The aim of the study was to gain the proof of principle that CTRP-3 is a potent anti-inflammatory adipokine in vivo.

METHODS

C57BL/6N mice were treated intraperitoneally (i.p.) with bacterial lipopolysaccharide (LPS) for 2h. The effects of a 30 min pre-treatment with CTRP-3 i.p. or intravenously (i.v.) on systemic and on epididymal, perirenal and subcutaneous adipose tissue inflammation was analyzed via real-time RT-PCR, ELISA and Western blot analysis.

RESULTS

LPS (1 μg i.p.) significantly increased serum IL-6 and MIP-2 levels as well as epididymal adipose tissue expression of IL-6 and MIP-2 in mice, whereas CTRP-3 (10 μg i.p.) alone or PBS (i.p.) had no effect. Pre-treatment of mice by CTRP-3 i.p. prior to LPS application significantly attenuated LPS-induced cytokine levels but had no effect on adipose tissue cytokine mRNA expression. In contrast to i.p. application of CTRP-3, systemic i.v. application was not sufficient to inhibit LPS-induced cytokine levels or mRNA tissue expression. CTRP-3 given i.p. significantly attenuated LPS-induced phosphorylation of Erk-1/-2 in inguinal adipose tissue.

CONCLUSION

The present study shows the proof of principle that the novel adipokine CTRP-3 is a potent inhibitor of LPS-induced systemic inflammation and LPS-induced signaling in adipose tissue in vivo.

High-level expression, purification and characterization of active human C1q and tumour necrosis factor-related protein-1 in Escherichia coli

C1q and tumour necrosis factor-related proteins (CTRPs) are a family of adiponectin paralogues. CTRP1 plays important biological functions in diabetes, obesity and hypertension. To further explore the physiological roles of human CTRP1 and its mechanisms of action, hCTRP1 gene was expressed in Escherichia coli. In the E. coli expression system, a large amount of soluble thioredoxin (Trx)-hCTRP1 fusion protein could be produced using the expression plasmid pET32a (+) and induction with IPTG at 18°C, which accounts about 20% of the total soluble bacterial proteins. The recombinant Trx-hCTRP1 fusion protein was purified to an approx. 95% purity using Ni-NTA affinity chromatography and Superdex G-75 column with a yield of about 28-mg protein from 1-l bacterial cultures. The purified recombinant Trx-hCTRP1 was shown to be active under in vivo and in vitro assay conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

CTRP1 plays important biological functions and warrants further investigation. However, large-scale production of recombinant CTRP1 has been technically challenging, which becomes a major obstacle in the structural and functional analysis of this important family of proteins. To explore the possible clinical applications and mechanisms of its action, an efficient method to produce large amounts of active recombinant human CTRP1 is necessary. This study should facilitate basic functional and pharmacological studies of this important protein family.

Metabolic function of the CTRP family of hormones

Maintaining proper energy balance in mammals entails intimate crosstalk between various tissues and organs. These inter-organ communications are mediated, to a great extent, by secreted hormones that circulate in blood. Regulation of the complex metabolic networks by secreted hormones (e.g., insulin, glucagon, leptin, adiponectin, FGF21) constitutes an important mechanism governing the integrated control of whole-body metabolism. Disruption of hormone-mediated metabolic circuits frequently results in dysregulated energy metabolism and pathology. As part of an effort to identify novel metabolic hormones, we recently characterized a highly conserved family of 15 secreted proteins, the C1q/TNF-related proteins (CTRP1-15). While related to adiponectin in sequence and structural organization, each CTRP has its own unique tissue expression profile and non-redundant function in regulating sugar and/or fat metabolism. Here, we summarize the current understanding of the physiological functions of CTRPs, emphasizing their metabolic roles. Future studies using gain-of-function and loss-of-function mouse models will provide greater mechanistic insights into the critical role CTRPs play in regulating systemic energy homeostasis.

Overexpression of C1q/Tumor Necrosis Factor–Related Protein-3 Promotes Phosphate-Induced Vascular Smooth Muscle Cell Calcification Both In Vivo and In Vitro

Objective—

Vascular calcification is highly correlated with increased cardiovascular morbidity and mortality. C1q/tumor necrosis factor–related protein-3 (CTRP3) is a newly identified adipokine that plays important roles in cardiovascular system. Here, we investigated the role of CTRP3 in vascular calcification and its underlying mechanism.

Approach and Results—

Adenine-induced chronic renal failure rat model was used to mimic the process of arterial medial calcification. The level of CTRP3 was elevated in serum and abdominal aorta of chronic renal failure rats. Periadventitial gene delivery of CTRP3 significantly accelerated the calcification of abdominal aorta and arterial ring. In cultured vascular smooth muscle cells (VSMCs), CTRP3 increased β-glycerophosphate–induced calcium deposition and alkaline phosphatase activity. Although CTRP3 alone was not sufficient to induce calcification in VSMCs, it upregulated the expression of osteogenic marker genes including runt-related transcription factor 2 ( Runx2 ), bone morphogenetic protein 2, and osteopontin. CTRP3 further enhanced β-glycerophosphate–induced downregulation of smooth muscle α-actin and smooth muscle 22α, while augmenting osteogenic marker expression in VSMCs induced by β-glycerophosphate. In contrast, knockdown of CTRP3 in VSMCs potently suppressed β-glycerophosphate–induced calcification. Mechanistically, knockdown of Runx2 inhibited CTRP3-promoted VSMC calcification. CTRP3 increased extracellular signal–regulated kinase 1/2 phosphorylation and reactive oxygen species production. Preincubation with U0126, an extracellular signal–regulated kinase 1/2 upstream kinase inhibitor, had no effect on CTRP3-induced reactive oxygen species production. However, pretreatment with N-acetyl- l -cysteine, a reactive oxygen species scavenger, suppressed CTRP3-induced extracellular signal–regulated kinase 1/2 phosphorylation. Both N-acetyl- l -cysteine and U0126 significantly inhibited CTRP3-induced upregulation of Runx2 and calcified nodule formation.

Conclusions—

CTRP3 promotes vascular calcification by enhancing phosphate-induced osteogenic transition of VSMC through reactive oxygen species–extracellular signal–regulated kinase 1/2–Runx2 pathway.

CTRP3 plays an important role in the development of collagen-induced arthritis in mice

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease exhibited most commonly in joints. We found that the expression of C1qtnf3, which encodes C1q/TNF-related protein 3 (CTRP3), was highly increased in two mouse RA models with different etiology. To elucidate the pathogenic roles of CTRP3 in the development of arthritis, we generated C1qtnf3(-/-) mice and examined the development of collagen-induced arthritis in these mice. We found that the incidence and severity score was higher in C1qtnf3(-/-) mice compared with wild-type (WT) mice. Histopathology of the joints was also more severe in C1qtnf3(-/-) mice. The levels of antibodies against type II collagen and pro-inflammatory cytokine mRNAs in C1qtnf3(-/-) mice were higher than WT mice. These observations indicate that CTRP3 plays an important role in the development of autoimmune arthritis, suggesting CTRP3 as a possible medicine to treat RA.

CTRP3 attenuates diet-induced hepatic steatosis by regulating triglyceride metabolism

CTRP3 is a secreted plasma protein of the C1q family that helps regulate hepatic gluconeogenesis and is downregulated in a diet-induced obese state. However, the role of CTRP3 in regulating lipid metabolism has not been established. Here, we used a transgenic mouse model to address the potential function of CTRP3 in ameliorating high-fat diet-induced metabolic stress. Both transgenic and wild-type mice fed a high-fat diet showed similar body weight gain, food intake, and energy expenditure. Despite similar adiposity to wild-type mice upon diet-induced obesity (DIO), CTRP3 transgenic mice were strikingly resistant to the development of hepatic steatosis, had reduced serum TNF-α levels, and demonstrated a modest improvement in systemic insulin sensitivity. Additionally, reduced hepatic triglyceride levels were due to decreased expression of enzymes (GPAT, AGPAT, and DGAT) involved in triglyceride synthesis. Importantly, short-term daily administration of recombinant CTRP3 to DIO mice for 5 days was sufficient to improve the fatty liver phenotype, evident as reduced hepatic triglyceride content and expression of triglyceride synthesis genes. Consistent with a direct effect on liver cells, recombinant CTRP3 treatment reduced fatty acid synthesis and neutral lipid accumulation in cultured rat H4IIE hepatocytes. Together, these results establish a novel role for CTRP3 hormone in regulating hepatic lipid metabolism and highlight its protective function and therapeutic potential in attenuating hepatic steatosis.

A novel adipokine C1q/TNF-related protein 1 (CTRP1) regulates chondrocyte proliferation and maturation through the ERK1/2 signaling pathway

Adipose tissue-derived adipokines play important roles as regulators of skeletal growth and development. CTRP1, a paralog of adiponectin, is a member of the C1q and tumor necrosis factor (TNF)-related protein (CTRP) superfamily. It is expressed at high levels in adipose tissue and has recently emerged as a novel adipokine. In the present study, we provide the first evidence for a physiological role of the CTRP1 in chondrocyte proliferation and maturation using a mouse chondrocytic cell line, N1511. The CTRP1 protein was strongly expressed and predominantly distributed in the reserve and proliferative chondrocytes in the fetal growth plate and its mRNA decreased during the maturation of N1511 chondrocytes. Recombinant CTRP1 promoted proliferation of immature proliferating N1511 chondrocytes in a dose-dependent manner, whereas it inhibited maturation of maturing N1511 chondrocytes. The stimulatory effect of CTRP1 on chondrocyte proliferation was associated with activation of the extracellular signal-regulated kinases 1/2 (ERK1/2) signaling pathway. On the other hand, the inhibitory effect of CTRP1 on chondrocyte maturation is associated with suppression of the ERK1/2 pathway. These results suggest a novel physiological role for CTRP1 in endochondral ossification.

Gene expression profiling in human craniosynostoses: a tool to investigate the molecular basis of suture ossification

INTRODUCTION

Non-syndromic craniosynostoses (NSC) occur as isolated skull malformations due to the premature ossification of one (single-suture forms) or more (complex forms) calvarial sutures and represent the most frequent form of craniosynostosis worldwide. The etiology of NSC is still largely unknown as a genetic basis can be rarely demonstrated especially in single-suture forms. In these cases, during the prenatal/perinatal development of affected patients, only one suture undergoes a premature direct ossification within an otherwise physiologically grown skull. This could suggest that definite somatic alterations, possibly due to unclear environmental agents, occur locally at the site of premature suture fusion during skull development. A promising tool to investigate the molecular mechanisms that may orchestrate this event is the comparative analysis of suture- and synostosis-derived tissues and cells.

PURPOSE

This review focuses on the different studies that attempted to clarify this issue using genome-wide microarray-based technologies for the comparative analysis of gene expression profiles. All relevant results have been comprehensively reviewed, possibly compared, and critically discussed.

CONCLUSION

Due to the heterogeneity of the dataset available in the literature, a univocal CRS-associated molecular profile could not be deciphered. Most differentially expressed genes are found in different studies to be involved in extracellular matrix remodeling.

Endopeptidase cleavage generates a functionally distinct isoform of C1q/tumor necrosis factor-related protein-12 (CTRP12) with an altered oligomeric state and signaling specificity

Adipose tissue-derived adipokines are an important class of secreted metabolic regulators that mediate tissue cross-talk to control systemic energy balance. We recently described C1q/TNF-related protein-12 (CTRP12), a novel insulin-sensitizing adipokine that regulates glucose metabolism in liver and adipose tissue. However, the biochemical properties of CTRP12 and its naturally occurring cleaved isoform have not been characterized. Here, we show that CTRP12 is a secreted hormone subjected to multiple functionally relevant posttranslational modifications at highly conserved residues. For example, Asn(39) is glycosylated, whereas Cys(85) mediates the assembly of higher order oligomeric structure. Endopeptidase cleavage at Lys(91) generates a cleaved globular gCTRP12 isoform, the expression of which is increased by insulin. PCSK3/furin was identified as the major proprotein convertase expressed by adipocytes that mediates the endogenous cleavage of CTRP12. Cleavage at Lys(91) is context-dependent: mutation of the charged Arg(93) to Ala on the P2' position enhanced cleavage, and triple mutations (K90A/K91A/R93A) abolished cleavage. Importantly, the two isoforms of CTRP12 differ in oligomeric structures and are functionally distinct. The full-length protein forms trimers and larger complexes, and the cleaved isoform consisted of predominantly dimers. Whereas full-length fCTRP12 strongly activated Akt signaling in H4IIE hepatocytes and 3T3-L1 adipocytes, gCTRP12 preferentially activated MAP kinase (ERK1/2 and p38 MAPK) signaling. Further, only fCTRP12 improved insulin-stimulated glucose uptake in adipocytes. These results reveal a novel mechanism controlling signaling specificity and function of a hormone via cleavage-dependent alteration in oligomeric state.

Involvement of SIK3 in glucose and lipid homeostasis in mice

Salt-inducible kinase 3 (SIK3), an AMP-activated protein kinase-related kinase, is induced in the murine liver after the consumption of a diet rich in fat, sucrose, and cholesterol. To examine whether SIK3 can modulate glucose and lipid metabolism in the liver, we analyzed phenotypes of SIK3-deficent mice. Sik3(-/-) mice have a malnourished the phenotype (i.e., lipodystrophy, hypolipidemia, hypoglycemia, and hyper-insulin sensitivity) accompanied by cholestasis and cholelithiasis. The hypoglycemic and hyper-insulin-sensitive phenotypes may be due to reduced energy storage, which is represented by the low expression levels of mRNA for components of the fatty acid synthesis pathways in the liver. The biliary disorders in Sik3(-/-) mice are associated with the dysregulation of gene expression programs that respond to nutritional stresses and are probably regulated by nuclear receptors. Retinoic acid plays a role in cholesterol and bile acid homeostasis, wheras ALDH1a which produces retinoic acid, is expressed at low levels in Sik3(-/-) mice. Lipid metabolism disorders in Sik3(-/-) mice are ameliorated by the treatment with 9-cis-retinoic acid. In conclusion, SIK3 is a novel energy regulator that modulates cholesterol and bile acid metabolism by coupling with retinoid metabolism, and may alter the size of energy storage in mice.

CTRP family: linking immunity to metabolism

It is well known that infectious and inflammatory diseases such as sepsis and severe inflammatory response syndrome are accompanied by metabolic alterations such as insulin resistance. Conversely, metabolic diseases such as visceral obesity and type 2 diabetes are characterized by high levels of proinflammatory cytokines. Metabolism and immunity are linked by proteins of dual function. Adiponectin, a member of the C1q/TNF-related protein (CTRP) family, has attracted much interest because of its anti-inflammatory and insulin-sensitizing effects. To date, 15 additional CTRP family members have been identified that might also play a role in metabolism and immunity. This review focuses on the biochemistry and pleiotropic physiological functions of CTRPs as new molecular mediators connecting inflammatory and metabolic diseases.

The adiponectin paralog C1q/TNF-related protein 3 (CTRP3) stimulates testosterone production through the cAMP/PKA signaling pathway

CTRP3, a paralog of adiponectin, is a member of the C1q and tumor necrosis factor (TNF)-related protein (CTRP) superfamily. It is expressed at high levels in adipose tissue and has recently emerged as a novel adipokine. In the present study, we provide the first evidence for a physiological role of the new adipokine, CTRP3, in the reproductive system. CTRP3 was specifically expressed in interstitial Leydig cells, where testosterone is produced, in the adult mouse testis. CTRP3 increased testosterone production by TM3 mouse Leydig cells in a dose-dependent manner. The increased testosterone production was linked to upregulation of steroidogenic proteins expression, such as steroidogenic acute regulatory (StAR) protein and cholesterol side-chain cleavage cytochrome P450 (P450scc). Moreover, increases in intracellular cyclic AMP (cAMP) concentrations and the phosphorylation of cAMP-response element binding protein (CREB) in CTRP3-stimulated TM3 Leydig cells were observed. Inhibition of this signaling pathway by a specific protein kinase A (PKA) inhibitor, H89, blocked testosterone production in CTRP3-stimulated Leydig cells, suggesting that the stimulatory effect of CTRP3 on testosterone production is associated with activation of the cAMP/PKA signaling pathway. Thus, our results demonstrate a physiological role for CTRP3 in testicular steroidogenesis and provide novel insights in the intracellular mechanisms activated by this protein.

C1q/TNF-related protein-12 (CTRP12), a novel adipokine that improves insulin sensitivity and glycemic control in mouse models of obesity and diabetes

Despite the prevalence of insulin resistance and type 2 diabetes mellitus, their underlying mechanisms remain incompletely understood. Many secreted endocrine factors and the intertissue cross-talk they mediate are known to be dysregulated in type 2 diabetes mellitus. Here, we describe CTRP12, a novel adipokine with anti-diabetic actions. The mRNA and circulating levels of CTRP12 were decreased in a mouse model of obesity, but its expression in adipocytes was increased by the anti-diabetic drug rosiglitazone. A modest rise in circulating levels of CTRP12 by recombinant protein administration was sufficient to lower blood glucose in wild-type, leptin-deficient ob/ob, and diet-induced obese mice. A short term elevation of serum CTRP12 by adenovirus-mediated expression improved glucose tolerance and insulin sensitivity, normalized hyperglycemia and hyperinsulinemia, and lowered postprandial insulin resistance in obese and diabetic mice. CTRP12 improves insulin sensitivity in part by enhancing insulin signaling in the liver and adipose tissue. Further, CTRP12 also acts in an insulin-independent manner; in cultured hepatocytes and adipocytes, CTRP12 directly activated the PI3K-Akt signaling pathway to suppress gluconeogenesis and promote glucose uptake, respectively. Collectively, these data establish CTRP12 as a novel metabolic regulator linking adipose tissue to whole body glucose homeostasis through insulin-dependent and independent mechanisms.

C1q/TNF-related protein-3 (CTRP-3) is secreted by visceral adipose tissue and exerts antiinflammatory and antifibrotic effects in primary human colonic fibroblasts

BACKGROUND

The adipokine CTRP-3 (C1q/TNF-related protein-3) belongs to the C1q/TNF-related protein family which antagonizes the effects of lipopolysaccharide (LPS). The aim was to investigate the antiinflammatory and antifibrotic role of CTRP-3 in Crohn's disease (CD).

METHODS

Mesenteric adipose tissue (MAT) of patients with CD or colonic cancer (CC) was resected. Human primary colonic lamina propria fibroblasts (CLPF) were isolated from controls and CD patients. Concentrations of chemokines and cytokines in the supernatants were measured by enzyme-linked immunosorbent assay (ELISA). Expression of connective tissue growth factor (CTGF), collagen I, and collagen III was analyzed by real-time polymerase chain reaction (PCR). Recombinant CTRP-3 expressed in insect cells was used for stimulation experiments.

RESULTS

CTRP-3 is synthesized and secreted by MAT resected from patients with CD, ulcerative colitis (UC), CC, and sigma diverticulitis as well as by murine and human mature adipocytes. CTRP-3 had no effect on the basal secretion of MCSF, MIF, or RANTES in MAT of CD and control patients. LPS-stimulation (10 ng/mL) significantly increased IL-8 release in CLPF of CD patients and, to a lesser extent, in cells of controls and of fibrotic CD tissue. CTRP-3 significantly and dose-dependently reduced LPS-induced IL-8 secretion in CLPF within 8 hours after LPS exposure, whereas LPS-induced IL-6 and TNF release was not affected. CTRP-3 inhibited TGF-β production and the expression of CTGF and collagen I in CLPF, whereas collagen III expression remained unchanged.

CONCLUSIONS

CTRP-3 exerts potent antiinflammatory and antifibrotic effects in CLPF by antagonizing the LPS pathway and by targeting the TGF-β-CTGF-collagen I pathway.

Systems genetics analysis of mouse chondrocyte differentiation

One of the goals of systems genetics is the reconstruction of gene networks that underlie key processes in development and disease. To identify cartilage gene networks that play an important role in bone development, we used a systems genetics approach that integrated microarray gene expression profiles from cartilage and bone phenotypic data from two sets of recombinant inbred strains. Microarray profiles generated from isolated chondrocytes were used to generate weighted gene coexpression networks. This analysis resulted in the identification of subnetworks (modules) of coexpressed genes that then were examined for relationships with bone geometry and density. One module exhibited significant correlation with femur length (r = 0.416), anteroposterior diameter (r = 0.418), mediolateral diameter (r = 0.576), and bone mineral density (r = 0.475). Highly connected genes (n = 28) from this and other modules were tested in vitro using prechondrocyte ATDC5 cells and RNA interference. Five of the 28 genes were found to play a role in chondrocyte differentiation. Two of these, Hspd1 and Cdkn1a, were known previously to function in chondrocyte development, whereas the other three, Bhlhb9, Cugbp1, and Spcs3, are novel genes. Our integrative analysis provided a systems-level view of cartilage development and identified genes that may be involved in bone development.

Functional analysis of CTRP3/cartducin in Meckel's cartilage and developing condylar cartilage in the fetal mouse mandible

CTRP3/cartducin, a novel C1q family protein, is expressed in proliferating chondrocytes in the growth plate and has an important role in regulating the growth of both chondrogenic precursors and chondrocytes in vitro. We examined the expression of CTRP3/cartducin mRNA in Meckel's cartilage and in condylar cartilage of the fetal mouse mandible. Based on in situ hybridization studies, CTRP3/cartducin mRNA was not expressed in the anlagen of Meckel's cartilage at embryonic day (E)11.5, but it was strongly expressed in Meckel's cartilage at E14.0, and then reduced in the hypertrophic chondrocytes at E16.0. CTRP3/cartducin mRNA was not expressed in the condylar anlagen at E14.0, but was expressed in the upper part of newly formed condylar cartilage at E15.0. At E16.0, CTRP3/cartducin mRNA was expressed from the polymorphic cell zone to the upper part of the hypertrophic cell zone, but was reduced in the lower part of the hypertrophic cell zone. CTRP3/cartducin-antisense oligodeoxynucleotide (AS-ODN) treatment of Meckel's cartilage and condylar anlagen from E14.0 using an organ culture system indicated that, after 4-day culture, CTRP3/cartducin abrogation induced curvature deformation of Meckel's cartilage with loss of the perichondrium and new cartilage formation. Aggrecan, type I collagen, and tenascin-C were simultaneously immunostained in this newly formed cartilage, indicating possible transformation from the perichondrium into cartilage. Further, addition of recombinant mouse CTRP3/cartducin protein to the organ culture medium with AS-ODN tended to reverse the deformation. These results suggest a novel function for CTRP3/cartducin in maintaining the perichondrium. Moreover, AS-ODN induced a deformation of the shape, loss of the perichondrium/fibrous cell zone, and disorder of the distinct architecture of zones in the mandibular condylar cartilage. Additionally, AS-ODN-treated condylar cartilage showed reduced levels of mRNA expression of aggrecan, collagen types I and X, and reduced BrdU-incorporation. These results suggest that CTRP3/cartducin is not only involved in the proliferation and differentiation of chondrocytes, but also contributes to the regulation of mandibular condylar cartilage.

C1q/TNF-related protein-3 represents a novel and endogenous lipopolysaccharide antagonist of the adipose tissue

Proteins secreted by adipocytes (adipokines) play an important role in the pathophysiology of type 2 diabetes mellitus and the associated chronic and low-grade state of inflammation. It was the aim to characterize the antiinflammatory potential of the new adipocytokine, C1q/TNF-related protein-3 (CTRP-3), which shows structural homologies to the pleiotropic adipocytokine adiponectin. mRNA and protein expression of CTRP-3 was analyzed by RT-PCR and Western blot. Recombinant CTRP-3 and small interfering RNA-based strategies were used to investigate the effect of CTRP-3 on toll-like receptor (TLR) ligand, lipopolysaccharide (LPS)-, and lauric acid-induced chemokine release of monocytes and adipocytes. Together with complex ELISA-based techniques, a designed TLR4/myeloid differentiation protein-2 fusion molecule shown to bind LPS was used to prove the ability of CTRP-3 to act as endogenous LPS antagonist. CTRP-3 is synthesized in monocytes and adipocytes. The recombinant protein dose-dependently inhibits the release of chemokines in monocytes and adipocytes that were induced by lauric acid, LPS, and other TLR ligands in vitro and ex vivo. CTRP-3 inhibits monocyte chemoattractant protein-1 release in adipocytes, whereas small interfering RNA-mediated knockdown of CTRP-3 up-regulates monocyte chemoattractant protein-1 release, reduces lipid droplet size, and decreases intracellular triglyceride concentration in adipocytes, causing a dedifferentiation into a more proinflammatory and immature phenotype. By using a designed TLR4/MD-2 fusion molecule, it is shown by different techniques that CTRP-3 specifically and effectively inhibits the binding of LPS to its receptor, TLR4/MD-2. CTRP-3 inhibits three basic and common proinflammatory pathways involved in obesity and type 2 diabetes mellitus (adipo-inflammation) by acting as an endogenous LPS antagonist of the adipose tissue.

Effect of adiponectin on ATDC5 proliferation, differentiation and signaling pathways

Adiponectin, an adipose-secreted adipocytokine, exhibits various metabolic functions but has no known effect on bone development through the growth plate and specifically, in chondrocytes. Using the mouse ATDC5 cell line, a widely used in vitro model of chondrogenesis, we demonstrated the expression of adiponectin and its receptors during chondrogenic differentiation. Adiponectin at 0.5mug/ml increased chondrocyte proliferation, proteoglycan synthesis and matrix mineralization, as reflected by upregulation of the expression of type II collagen, aggrecan, Runx2 and type X collagen, and of alkaline phosphatase activity. Quantitative RT-PCR and gelatin zymography showed a significant increase in the matrix metalloproteinase MMP9's expression and activity following adiponectin treatment. We therefore concluded that adiponectin can directly stimulate chondrocyte proliferation and differentiation. To evaluate the underlying mechanisms, we examined the effect of adiponectin on the expression of chondrogenic signaling molecules: Ihh, PTHrP, Ptc1, FGF18, BMP7, IGF1 and p21 were all upregulated while FGF9 was downregulated. This study reveals novel and direct activity of adiponectin in chondrocytes, suggesting its positive effects on bone development.

C1qTNF-related protein-6 increases the expression of interleukin-10 in macrophages

C1qTNF-Related proteins (CTRPs), a new highly conserved family of adiponectin paralogs, were recently identified as being involved in diverse processes including metabolism, host defense, apoptosis, cell differentiation, and organogenesis. However, the functional role of CTRP6 remains poorly identified. Here we provide evidence that CTRP6 induces the expression of interleukin-10 (IL-10) in macrophages. Conditioned medium from CTRP6-expressing HEK293 cells increased IL-10 expression in Raw264.7 cells. The globular domain of CTRP6 (gCTRP6) also dose-dependently increased both IL-10 mRNA and protein expression levels, with transcript levels increasing within 2 h. Furthermore, the globular domain of CTRP6 rapidly induced phosphorylation of ERK1/2 in Raw264.7 cells. Treatment with U0126, a selective inhibitor, abolished CTRP6-stimulated IL-10 induction. Taken together, there results demonstrate that CTRP6 induces expression of IL-10 via ERK1/2 activation. Considering that IL-10 is a potent anti-inflammatory cytokine that modulates inflammatory signaling pathways, CTRP6 may be a novel target for pharmacological drugs in inflammatory diseases.

C1q tumor necrosis factor alpha-related protein isoform 5 is increased in mitochondrial DNA-depleted myocytes and activates AMP-activated protein kinase

Depletion of mtDNA in myocytes causes insulin resistance and alters nuclear gene expression that may be involved in rescuing processes against cellular stress. Here we show that the expression of C1q tumor necrosis factor alpha-related protein isoform 5 (C1QTNF5) is drastically increased following depletion of mtDNA in myocytes. C1QTNF5 is homologous to adiponectin in respect to domain structure, and its expression and secretion from myocytes correlated negatively with the cellular mtDNA content. Similar to adiponectin, C1QTNF5 induced the phosphorylation of AMP-activated protein kinase (AMPK), leading to increased cell surface recruitment of GLUT4 and increased glucose uptake. Treatment of cells with purified recombinant C1QTNF5 increased the phosphorylation of acetyl-CoA carboxylase and stimulated fatty acid oxidation. C1QTNF5-mediated phosphorylation of AMPK or acetyl-CoA carboxylase was unaffected by depletion of adiponectin receptors such as AdipoR1 or AdipoR2, which indicated that adiponectin receptors do not participate in C1QTNF5-induced activation of AMPK. Serum C1QTNF5 levels were significantly higher in obese/diabetic animals (OLETF rats, ob/ob mice, and db/db mice). These results highlight C1QTNF5 as a putative biomarker for mitochondrial dysfunction and a potent activator of AMPK.

A novel adipokine CTRP1 stimulates aldosterone production

Complement-C1q TNF-related protein 1 (CTRP1), a member of the CTRP superfamily, is expressed at high levels in adipose tissues of obese Zucker diabetic fatty (fa/fa) rats, and CTRP1 expression is induced by proinflammatory cytokines, including TNF-alpha and IL-1beta. In the present study, we investigated stimulation of aldosterone production by CTRP1, since it was observed that CTRP1 was specifically expressed in the zona glomerulosa of the adrenal cortex, where aldosterone is produced. Increased aldosterone production by CTRP1 in cells of the human adrenal cortical cell line H295R was dose-dependent. Expression levels of aldosterone synthase CYP11B2 were examined to investigate the molecular mechanisms by which CTRP1 enhances the production of aldosterone. The expression of CYP11B2 was greatly increased by treatment with CTRP1, as was the expression of the transcription factors NGFIB and NURR1, which play critical roles in stimulation of CYP11B2 gene expression. It was also revealed that angiotensin II-induced aldosterone production is, at least in part, mediated by the stimulation of CTRP1 secretion, not by the increase of CTRP1 mRNA transcription. In addition, the levels of CTRP1 were significantly up-regulated in hypertensive patients' serum. As CTRP1 was highly expressed in obese subjects as well as up-regulated in hypertensive patients, CTRP1 may be a newly identified molecular link between obesity and hypertension.

Unravelling the molecular control of calvarial suture fusion in children with craniosynostosis

BACKGROUND

Craniosynostosis, the premature fusion of calvarial sutures, is a common craniofacial abnormality. Causative mutations in more than 10 genes have been identified, involving fibroblast growth factor, transforming growth factor beta, and Eph/ephrin signalling pathways. Mutations affect each human calvarial suture (coronal, sagittal, metopic, and lambdoid) differently, suggesting different gene expression patterns exist in each human suture. To better understand the molecular control of human suture morphogenesis we used microarray analysis to identify genes differentially expressed during suture fusion in children with craniosynostosis. Expression differences were also analysed between each unfused suture type, between sutures from syndromic and non-syndromic craniosynostosis patients, and between unfused sutures from individuals with and without craniosynostosis.

RESULTS

We identified genes with increased expression in unfused sutures compared to fusing/fused sutures that may be pivotal to the maintenance of suture patency or in controlling early osteoblast differentiation (i.e. RBP4, GPC3, C1QTNF3, IL11RA, PTN, POSTN). In addition, we have identified genes with increased expression in fusing/fused suture tissue that we suggest could have a role in premature suture fusion (i.e. WIF1, ANXA3, CYFIP2). Proteins of two of these genes, glypican 3 and retinol binding protein 4, were investigated by immunohistochemistry and localised to the suture mesenchyme and osteogenic fronts of developing human calvaria, respectively, suggesting novel roles for these proteins in the maintenance of suture patency or in controlling early osteoblast differentiation. We show that there is limited difference in whole genome expression between sutures isolated from patients with syndromic and non-syndromic craniosynostosis and confirmed this by quantitative RT-PCR. Furthermore, distinct expression profiles for each unfused suture type were noted, with the metopic suture being most disparate. Finally, although calvarial bones are generally thought to grow without a cartilage precursor, we show histologically and by identification of cartilage-specific gene expression that cartilage may be involved in the morphogenesis of lambdoid and posterior sagittal sutures.

CONCLUSION

This study has provided further insight into the complex signalling network which controls human calvarial suture morphogenesis and craniosynostosis. Identified genes are candidates for targeted therapeutic development and to screen for craniosynostosis-causing mutations.

Adipose tissue as an immunological organ: Toll-like receptors, C1q/TNFs and CTRPs

Adipose tissue has long been regarded as a mostly resting tissue that is dedicated solely to energy storage and release. However, in recent years, this view has changed dramatically following new insights into the metabolic and immunological functions of preadipocytes and adipocytes. There are several lines of evidence for the involvement of adipose tissue in innate and acquired immune responses. First, adipocytes are potent producers of proinflammatory cytokines, such as interleukin-6 and tumor necrosis factor (TNF), and chemokines. Furthermore, adipocytes secrete high amounts of adipokines, such as leptin, adiponectin and resistin, that regulate monocyte/macrophage function, and also secrete molecules associated with the innate immune system, such as the C1qTNF-related protein superfamily. Finally, preadipocytes and adipocytes express a broad spectrum of functional Toll-like receptors and the former can convert into macrophage-like cells. Collectively, these data clearly establish the role of adipose tissue as a new member of the immune system.

CTRP3/cartducin promotes proliferation and migration of endothelial cells

CTRP3/cartducin, a novel secretory protein, is a member of the C1q and tumor necrosis factor (TNF)-related protein (CTRP) superfamily. CTRP3/cartducin gene is transiently up-regulated in a balloon-injured rat carotid artery tissue. In this study, we report a new function of CTRP3/cartducin as a regulator of angiogenic processes. CTRP3/cartducin promoted proliferation and migration of mouse endothelial MSS31 cells in a dose-dependent manner. Further, stimulation of MSS31 by CTRP3/cartducin led to activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK). MAPK/ERK kinase 1/2 (MEK1/2) inhibitor, U0126, and p38 MAPK inhibitor, SB203580, blocked the CTRP3/cartducin-induced cell proliferation, and migration was blocked by U0126, but not the SB203580. Taken together, these results suggest that CTRP3/cartducin may be involved as a novel angiogenic factor in the formation of neointima following angioplasty.

Plasma levels of leptin, omentin, collagenous repeat-containing sequence of 26-kDa protein (CORS-26) and adiponectin before and after oral glucose uptake in slim adults

BACKGROUND

Adipose tissue secreted proteins are collectively named adipocytokines and include leptin, adiponectin, resistin, collagenous repeat-containing sequence of 26-kDa protein (CORS-26) and omentin. Several of these adipocytokines influence insulin sensitivity and glucose metabolism and therefore systemic levels may be affected by oral glucose uptake. Whereas contradictory results have been published for leptin and adiponectin, resistin has not been extensively investigated and no reports on omentin and CORS-26 do exist.

METHODS

Therefore the plasma levels of these proteins before and 120 min after an oral glucose load were analyzed in 20 highly-insulin sensitive, young adults by ELISA or immunoblot.

RESULTS

Circulating leptin was reduced 2 h after glucose uptake whereas adiponectin and resistin levels are not changed. Distribution of adiponectin and CORS-26 isoforms were similar before and after glucose ingestion. Omentin is highly abundant in plasma and immunoblot analysis revealed no alterations when plasma levels before and 2 h after glucose intake were compared.

CONCLUSION

Taken together our data indicate that only leptin is reduced by glucose uptake in insulin-sensitive probands whereas adiponectin and resistin are not altered. CORS-26 was demonstrated for the first time to circulate as high molecular weight form in plasma and like omentin was not influenced by oral glucose load. Omentin was shown to enhance insulin-stimulated glucose uptake but systemic levels are not correlated to postprandial blood glucose.