Fibrinogen modulates gene expression in wounded fibroblasts

Impaired Contracture of 3D Collagen Constructs by Fibronectin-Deficient Murine Fibroblasts

Fibronectin (FN) is an extracellular matrix glycoprotein that is abundantly expressed by fibroblasts in contracting wounds, where it mediates cell adhesion, migration and proliferation. FN also efficiently binds to collagen. Therefore, we and others hypothesized that FN and its cellular receptor integrin α₅β₁ might be involved in collagen matrix contracture by acting as linkers. However, there are conflicting reports on this issue. Moreover, several publications suggest an important role of collagen-binding integrin receptors α₂β₁ and α₁₁β₁ in collagen matrix contracture. Therefore, the aim of the present study was to determine the contributions of FN-integrin α₅β₁ interactions relative to those of collagen receptors α₂β₁ and α₁₁β₁ in this process. To assess the role of cellular FN directly, we employed FN-deficient mouse fibroblasts, subjected them to a collagen gel contracture assay in vitro, and compared them to their wildtype counterparts. Exogenous FN was removed from serum-containing medium. For dissecting the role of major collagen receptors, we used two FN-deficient mouse fibroblast lines that both possess integrin α₅β₁ but differ in their collagen-binding integrins. Embryo-derived FN-null fibroblasts, which express α₁₁- but no α₂-integrin, barely spread and tended to cluster on collagen gels. Moreover, FN-null fibroblasts required exogenously added FN to assemble α₅β₁-integrin in fibrillar adhesion contacts, and to contract collagen matrices. In contrast, postnatal kidney fibroblasts were found to express α₂- but barely α₁₁-integrin. When FN expression was suppressed in these cells by shRNA transfection, they were able to spread on and partially contract collagen gels in the absence of exogenous FN. Also in this case, however, collagen contracture was stimulated by adding FN to the medium. Antibody to integrin α₅β₁ or RGD peptide completely abolished collagen contracture by FN-deficient fibroblasts stimulated by FN addition. We conclude that although collagen-binding integrins (especially α₂β₁) can mediate contracture of fibrillar collagen gels by murine fibroblasts to some extent, full activity is causally linked to the presence of pericellular FN and its receptor integrin α₅β₁.

Identification of novel serum peptide biomarkers for high-altitude adaptation: a comparative approach

We aimed to identify serum biomarkers for screening individuals who could adapt to high-altitude hypoxia at sea level. HHA (high-altitude hypoxia acclimated; n = 48) and HHI (high-altitude hypoxia illness; n = 48) groups were distinguished at high altitude, routine blood tests were performed for both groups at high altitude and at sea level. Serum biomarkers were identified by comparing serum peptidome profiling between HHI and HHA groups collected at sea level. Routine blood tests revealed the concentration of hemoglobin and red blood cells were significantly higher in HHI than in HHA at high altitude. Serum peptidome profiling showed that ten significantly differentially expressed peaks between HHA and HHI at sea level. Three potential serum peptide peaks (m/z values: 1061.91, 1088.33, 4057.63) were further sequence identified as regions of the inter-α trypsin inhibitor heavy chain H4 fragment (ITIH4 347–356), regions of the inter-α trypsin inhibitor heavy chain H1 fragment (ITIH1 205–214), and isoform 1 of fibrinogen α chain precursor (FGA 588–624). Expression of their full proteins was also tested by ELISA in HHA and HHI samples collected at sea level. Our study provided a novel approach for identifying potential biomarkers for screening people at sea level who can adapt to high altitudes.

Dermal templates and the wound-healing paradigm: the promise of tissue regeneration

Dermal regeneration templates arguably represent the first and most clinically successful 'tissue engineering' solution designed for organ reconstruction. Wound healing in the skin normally occurs on a continuum. At one extreme of the continuum lies the promise of tissue regeneration and the complete restoration of normal structure and function. Unfortunately, in the adult, all too often, wound healing occurs at the other extreme of the continuum and the dermis is reconstituted as scar tissue. Dermal regeneration templates are designed to manage the wound-healing process and tip the scales toward regeneration. This review discusses the architecture and molecular composition of the skin and the events that mediate wound healing and scar formation. The development, evolution and commercialization of dermal templates are examined and the clinical and business considerations that drive the product-development cycle are discussed. In the near term, dermal templates cannot be expected to dramatically change in overall composition. Product development will be dominated by continued refinements of existing templates and the field of use will continue to expand as manufacturers seek to increase revenue and capture market share. Continued exploration of novel processing strategies, such as electrospinning, that can be used to fabricate nanoscale biomaterials, may provide a gateway to the next generation of dermal templates.

Optical imaging of fibrin deposition to elucidate participation of mast cells in foreign body responses

Mast cell activation has been shown to be an initiator and a key determinant of foreign body reactions. However, there is no non-invasive method that can quantify the degree of implant-associated mast cell activation. Taking advantage of the fact that fibrin deposition is a hallmark of mast cell activation around biomaterial implants, a near infrared probe was fabricated to have high affinity to fibrin. Subsequent in vitro testing confirmed that this probe has high affinity to fibrin. Using a subcutaneous particle implantation model, we found significant accumulation of fibrin-affinity probes at the implant sites as early as 15 min following particle implantation. The accumulation of fibrin-affinity probes at the implantation sites could also be substantially reduced if anti-coagulant - heparin was administered at the implant sites. Further studies have shown that subcutaneous administration of mast cell activator - compound 48/80 - prompted the accumulation of fibrin-affinity probes. However, implant-associated fibrin-affinity probe accumulation was substantially reduced in mice with mast cell deficiency. The results show that our fibrin-affinity probes may serve as a powerful tool to monitor and measure the extent of biomaterial-mediated fibrin deposition and mast cell activation in vivo.

Induced expression of humanCCND1 alternative transcripts in mouseCyl-1 knockout fibroblasts highlights functional differences

Splicing of human cyclin D1 (CCND1) mRNA producing transcripts a and b is modulated by a common polymorphism (A --> G) located in a conserved splice donor region at nucleotide 870. CCND1 A/G(870) genotype is associated with tumour progression and clinical outcome in a variety of cancers. Although in vitro expression of cyclin D1 transcript a (CCND1(tra)) has been widely investigated, few studies have examined the expression of CCND1 transcript b (CCND1(trb)). We have studied the effects of inducible expression of human CCND1(trb) in comparison with human CCND1(tra) in a mouse fibroblast knock-out for cyclin D1 (MEF(Cyl-1-/-)). Inducible expression was in stable clones isolated from MEF(Cyl-1-/-) transfectants. Induction of CCND1(tra) produced a 36-kDa protein, which led to a significant increase in the proportion of cells in S-phase, as detected by BrdU incorporation after 32 hr, compared to non-induced cells (p = 0.012). Clones induced to express CCND1(tra) exhibited a significantly increased ability to grow in serum depleted (2% FCS) medium compared to non-induced clones (p = 0.0004). Induced expression of CCND1(trb) in MEF(Cyl-1-/-) transfectants produced a 31-kDa protein and resulted in no significant difference in DNA synthesis, neither did the cells acquire the ability to grow in serum-depleted conditions compared to non-induced cells. Induction of CCND1(trb) significantly enhanced the ability of MEF(Cyl-1-/-) transfectants to form colonies in soft agar, (average 30-fold increase) compared to non-induced clones or those induced to express CCND1(tra). Our data supports the emerging view that CCND1 alternate transcripts encode proteins with differing independent biological functions. We suggest that CCND1(tra) encodes a protein involved in regulating mitogen responsive, anchorage-dependent G(1) progression, whereas CCND1(trb) modulates the ability of the cell to grow in an anchorage-independent manner.

The incorporation of fibrinogen into extracellular matrix is dependent on active assembly of a fibronectin matrix

Fibrinogen is a soluble protein produced by hepatocytes and secreted into plasma, where it functions in hemostasis. During inflammation, the hepatic synthesis of fibrinogen is induced 2-10 fold. Recent studies demonstrate that after an inflammatory stimulus, fibrinogen gene expression and protein production is upregulated in lung epithelial cells, where it is secreted basolaterally and consequently deposited into the extracellular matrix in fibrils that extensively colocalize with fibronectin fibrils. In this study, we show that the deposition of fibrinogen into the matrix of fibroblasts occurred rapidly and in a Rho-dependent manner in response to serum or lysophosphatidic acid; RhoA GTPase signaling is also required for fibronectin matrix assembly. Using mouse embryonic fibronectin-null cells, we show that incorporation of exogenous fibrinogen into matrix fibrils occurred only in the presence of exogenous fibronectin, which is also assembled into matrix fibrils. Furthermore, treatment of fibroblasts and fibronectin-null cells with an antibody that inhibits fibronectin matrix assembly impaired incorporation of fibrinogen into matrix fibrils. Collectively, these data suggest that incorporation of fibrinogen into the extracellular matrix requires active fibronectin polymer elongation into matrix fibrils. From these data, we hypothesize that fibrinogen deposition rapidly changes the topology of the extracellular matrix to provide a surface for cell migration and matrix remodeling during tissue repair.