Fibronectin regulates calvarial osteoblast differentiation

Abstract

The secretion of fibronectin by differentiating osteoblasts and its accumulation at sites of osteogenesis suggest that fibronectin participates in bone formation. To test this directly, we determined whether fibronectin-cell interactions regulate progressive differentiation of cultured fetal rat calvarial osteoblasts. Spatial distributions of alpha 5 integrin subunit, fibronectin, osteopontin (bone sialoprotein I) and osteocalcin (bone Gla-protein) were similar in fetal rat calvaria and mineralized, bone-like nodules formed by cultured osteoblasts. Addition of anti-fibronectin antibodies to cultures at confluence reduced subsequent formation of nodules to less than 10% of control values, showing that fibronectin is required for normal nodule morphogenesis. Anti-fibronectin antibodies selectively inhibited steady-state expression of mRNA for genes associated with osteoblast differentiation; mRNA levels for alkaline phosphatase and osteocalcin were suppressed, whereas fibronectin, type I collagen and osteopontin were unaffected. To identify functionally relevant domains of fibronectin, we treated cells with soluble fibronectin fragments and peptides. Cell-binding fibronectin fragments (type III repeats 6–10) containing the Arg-Gly-Asp (RGD) sequence blocked both nodule initiation and maturation, whether or not they contained a functional synergy site. In contrast, addition of the RGD-containing peptide GRGDSPK alone did not inhibit nodule initiation, although it did block nodule maturation. Thus, in addition to the RGD sequence, other features of the large cell-binding fragments contribute to the full osteogenic effects of fibronectin. Nodule formation and osteoblast differentiation resumed after anti-fibronectin antibodies or GRGDSPK peptides were omitted from the media, showing that the inhibition was reversible and the treatments were not cytotoxic. Outside the central cell-binding domain, peptides from the IIICS region and antibodies to the N terminus did not inhibit nodule formation. We conclude that osteoblasts interact with the central cell-binding domain of endogenously produced fibronectin during early stages of differentiation, and that these interactions regulate both normal morphogenesis and gene expression.

Freeze-Dried Secretome (Lyosecretome) from Mesenchymal Stem/Stromal Cells Promotes the Osteoinductive and Osteoconductive Properties of Titanium Cages

“…These results collectively confirm the role of MSC-secretome in inducing bone regen eration, according to previously published research studies [43][44][45][46][47][48]. This effect mainly de pends on the osteogenic factors revealed in Lyosecretome by proteomic characterization [21], such as fibronectin [49], alpha-2-macroglobulin [50], apolipoprotein A [51], and TGF β [52]. Of note, the MSC-secretome employed in this work was formulated as a ready-to use, freeze-dried pharmaceutical dosage form, which can be easily adapted by the clinica community.…”

The synergistic effect of a hybrid graphene oxide–chitosan system and biomimetic mineralization on osteoblast functions

“…Fibronectin plays an important role in osteoblast morphogenesis, differentiation, and mineralization. 33 The distribution pattern of FN is indicative of osteoblast's ability to synthesize, mineralize, and organize the extracellular matrix, irrespective of the nature of the system (GO, HAP-GO, HAP-CS-GO) (Fig. 6).…”

Heparin-induced conformational changes of fibronectin within the extracellular matrix promote hMSC osteogenic differentiation

“…13,14 In addition, Fn has been localized in the periosteum of rat calvaria 15 and in the osteoid surrounding implants. 16 These studies raise the question whether Fn could guide early stages of osteogenic differentiation. In vitro studies have revealed that the effects of Fn on hMSC physiology are complex: Fn-coated biomaterials promoted hMSC attachment 17,18 and culture of hMSCs on Fn-coated surfaces promoted their migration, adhesion and proliferation, however, it did not affect their osteogenic differentiation.…”