Ras signaling regulates osteoprogenitor cell proliferation and bone formation

During endochondral bone development, osteoblasts are continuously differentiated from locally residing progenitor cells. However, the regulation of such endogenous osteoprogenitor cells is still poorly understood mainly due to the difficulty in identifying such cells in vivo. In this paper, we genetically labeled different cell populations of the osteoblast linage using stage-specific, tamoxifen-inducible Cre transgenic mice to investigate their responses to a proliferative stimulus. We have found that overactivation of Kras signaling in type II collagen-positive, immature osteoprogenitor cells, but not in mature osteoblasts, substantially increases the number of their descendant stromal cells and mature osteoblasts, and subsequently increases bone mass. This effect was mediated by both, the extracellular signal-regulated kinase (ERK) and phosphoinositide 3 kinase (PI3K), pathways. Thus we demonstrate that Ras signaling stimulates proliferation of immature osteoprogenitor cells to increase the number of their osteoblastic descendants in a cell-autonomous fashion

miRNAs in Bone Development

Skeletal development is a multistage process during which mesenchymal progenitor cells undergo proliferation and differentiation and subsequently give rise to bone and cartilage forming cells. Each step is regulated by various transcription factors and signaling molecules. microRNAs are small non-coding RNAs that post-transcriptionally regulate gene expression. Several in vivo and in vitro studies have shown that miRNAs play significant roles in skeletal development. Identifying their functions may give insights into the treatment of developmental disorders of the skeleton. This review summarizes miRNAs that have been shown to participate in various stages of skeletal development by targeting crucial factors

Polymorphisms in the promoters of cytokines and CRP genes in the pathogenesis of heart failure in diabetes mellitus

Introduction: Diabetes mellitus (DM) is very often associated with theoccurence of heart failure (HF). The inflammation appears to be thecommon underlying pathophysiological mechanism connecting DM toHF. The serum levels of C-reactive protein (CRP), interleukin-6 (IL-6)and tumor necrosis factor-alpha (TNF-α) are elevated in diabetes and inchronic HF (CHF). Polymorphisms in the genes of these factors havebeen identified as risk factors for the occurence of inflammation andcardiovascular disease. These polymorphisms have not beeninvestigated extensively in CHF.Aim: To investigate the possible involvement of single nucleotidepolymorphisms in the promoter region of CRP, IL-6 and TNF-α inpatients with DM who developed heart failure (group +CHF) and toassess their relation to the severity of heart failure.Material and Methods: In 249 patients with DM the SNPs in thepromoters of TNF-α (-308), IL-6 (-174) and CRP (from -300 to -1 bases)were examined. Moreover, the concentrations in the peripheral blood ofCRP, IL-6 and TNF-α were measured. Sixty-six patients had signs andsymptoms of HF whereas 183 showed no symptoms or signs ofcardiovascular disease. In all patients the cardiac function wasassessed. The genotype was determined by molecular biology technicsand the serum levels of the inflammatory factors were measured byspecific methods.Results: The genotype TNF-A2 (-308/G→A) had the greatest predictivevalue for the prediction of heart failure in diabetes. The CRP, IL-6 andTNF-α serum levels were negatively correlated with the ejection fractionof the left ventricle. The patients with the TNF A2 genotype were at2fold higher risk of developing CHF in relation to the patients with TNFA1genotype (-308/G→G, OR=2.1 vs OR=0.33 respectively). Thepolymorphisms in IL-6 and CRP had not any predictive value.Conclusions: The elevated serum levels of CRP, IL-6 and TNF-α aswell as the genotype TNFA2 are related to a large extent with CHF indiabetes 1 and 2. Additional factors may have greater predictive value.Εισαγωγή: Ο σακχαρώδης διαβήτης (ΣΔ) πολύ συχνά συνδέεται με τηνεμφάνιση καρδιακής ανεπάρκειας (ΚΑ). Η φλεγμονή φαίνεται νααποτελεί τον κοινό υποκείμενο παθοφυσιολογικό μηχανισμό πουσυνδέει τον ΣΔ με την ΚΑ. Τα επίπεδα της C-αντιδρώσας πρωτεΐνης(CRP), της ιντερλευκίνης (IL-6) και του παράγοντα νέκρωσης όγκου-άλφα (TNF-α) είναι αυξημένα στο ΣΔ και στη χρόνια ΚΑ (ΧΚΑ).Πολυμορφισμοί στα γονίδια των παραγόντων αυτών έχουναναγνωριστεί ως παράγοντες κινδύνου για την εμφάνιση φλεγμονής καικαρδιαγγειακής νόσου. Για τη ΧΚΑ ο γονότυπος αυτών δεν έχειδιερευνηθεί εκτενώς.Σκοπός: Να διερευνηθεί η τυχόν συμμετοχή σημειακώνπολυμορφισμών στους προεκκινητές των CRP, IL-6 και TNF-α σεασθενείς με ΣΔ που ανέπτυξαν ΧΚΑ, (ομάδα +ΧΚΑ), σε σχέση με τουςδιαβητικούς χωρίς ΧΚΑ, (ομάδα -ΧΚΑ) και να αξιολογηθούν σε σχέσημε τη βαρύτητα της καρδιακής ανεπάρκειας.Υλικό και Μέθοδοι: Σε 249 ασθενείς με ΣΔ διερευνήθηκαν οι σημειακοίπολυμορφισμοί στους προεκκινητές των γονιδίων του TNF-α (-308), τηςIL-6 (-174) και της CRP (από -300 εως -1 βάσεις). Επίσηςπροσδιορίστηκαν οι συγκεντρώσεις στο περιφερικό αίμα των TNF-α, IL-6 και CRP. Εξήντα έξη ασθενείς εμφάνιζαν σημεία και συμπτώματα ΚΑ,ενώ οι υπόλοιποι δεν εμφάνιζαν συμπτώματα ή σημεία καρδιαγγειακήςνόσου. Σε όλους τους ασθενείς εκτιμήθηκε η καρδιακή λειτουργία. Μετεχνικές μοριακής βιολογίας προσδιορίστηκε ο γονότυπος, ενώ για ταεπίπεδα των φλεγμονωδών παραγόντων χρησιμοποιήθηκαν ειδικέςτεχνικές ανάλυσης συγκεντρώσεων ουσιών στον ορό.Αποτελέσματα: Ο γονότυπος TNF-A2 (-308/G→A) είχε τη μεγαλύτερηπρογνωστική αξία για τη πρόβλεψη της ΧΚΑ στο ΣΔ. Οι συγκεντρώσειςτων CRP, IL-6 και TNF-α στο περιφερικό αίμα συσχετίζονταν αρνητικάμε το κλάσμα εξώθησης της αριστερής κοιλίας. Οι ασθενείς με τογονότυπο TNF-A2 είχαν 2πλάσιο κίνδυνο για την εμφάνιση ΧΚΑ σεσχέση με τους ασθενείς με το γονότυπο TNF-A1 (-308/G→G, OR=2,1έναντι OR=0,33 αντίστοιχα). Οι πολυμορφισμοί στην IL-6 και στη CRPδεν είχαν ιδιαίτερη διακριτική ικανότητα.Συμπεράσματα: Τα αυξημένα επίπεδα των CRP, IL-6 και TNF-ακαθώς και ο γονότυπος TNFA2 σχετίζονται σε μεγάλο βαθμό με τη ΧΚΑστο ΣΔ τύπου 1 και 2. Πιθανώς και άλλοι παράγοντες να έχουνμεγαλύτερη προγνωστική αξία

Phosphate-induced activation of VEGFR2 leads to caspase-9-mediated apoptosis of hypertrophic chondrocytes

Summary: Low circulating phosphate (Pi) leads to rickets, characterized by expansion of the hypertrophic chondrocytes (HCs) in the growth plate due to impaired HC apoptosis. Studies in HCs demonstrate that Pi activates the Raf/MEK/ERK1/2 and mitochondrial apoptotic pathways. To determine how Pi activates these pathways, a small-molecule screen was undertaken to identify inhibitors of Pi-induced ERK1/2 phosphorylation in HCs. Vascular endothelial growth factor receptor 2 (VEGFR2) was identified as a target. In vitro studies in HCs demonstrate that VEGFR2 inhibitors block Pi-induced pERK1/2 and caspase-9 cleavage. Like Pi, rhVEGF activates ERK1/2 and caspase-9 in HCs and induces phosphorylation of VEGFR2, confirming that Pi activates this signaling pathway in HCs. Chondrocyte-specific depletion of VEGFR2 leads to an increase in HCs, impaired vascular invasion, and a decrease in HC apoptosis. Thus, these studies define a role for VEGFR2 in transducing Pi signals and mediating its effects on growth plate maturation

Distinct molecular pathways mediate Mycn and Myc-regulated miR-17-92 microRNA action in Feingold syndrome mouse models

Feingold syndrome is a skeletal dysplasia caused by loss-of-function mutations of either MYCN (type 1) or MIR17HG that encodes miR-17-92 microRNAs (type 2). Since miR-17-92 expression is transcriptionally regulated by MYC transcription factors, it has been postulated that Feingold syndrome type 1 and 2 may be caused by a common molecular mechanism. Here we show that Mir17-92 deficiency upregulates TGF-β signaling, whereas Mycn-deficiency downregulates PI3K signaling in limb mesenchymal cells. Genetic or pharmacological inhibition of TGF-β signaling efficiently rescues the skeletal defects caused by Mir17-92 deficiency, suggesting that upregulation of TGF-β signaling is responsible for the skeletal defect of Feingold syndrome type 2. By contrast, the skeletal phenotype of Mycn-deficiency is partially rescued by Pten heterozygosity, but not by TGF-β inhibition. These results strongly suggest that despite the phenotypical similarity, distinct molecular mechanisms underlie the pathoetiology for Feingold syndrome type 1 and 2

Polycomb repressive complex 2 regulates skeletal growth by suppressing Wnt and TGF-β signalling

Polycomb repressive complex 2 (PRC2) controls maintenance and lineage determination of stem cells by suppressing genes that regulate cellular differentiation and tissue development. However, the role of PRC2 in lineage-committed somatic cells is mostly unknown. Here we show that Eed deficiency in chondrocytes causes severe kyphosis and a growth defect with decreased chondrocyte proliferation, accelerated hypertrophic differentiation and cell death with reduced Hif1a expression. Eed deficiency also causes induction of multiple signalling pathways in chondrocytes. Wnt signalling overactivation is responsible for the accelerated hypertrophic differentiation and kyphosis, whereas the overactivation of TGF-β signalling is responsible for the reduced proliferation and growth defect. Thus, our study demonstrates that PRC2 has an important regulatory role in lineage-committed tissue cells by suppressing overactivation of multiple signalling pathways