Heparan sulfate potentiates leukocyte adhesion on cardiac fibroblast by enhancing Vcam-1 and Icam-1 expression.

Cardiac fibroblasts (CF) act as sentinel cells responding to chemokines, cytokines and growth factors released in cardiac tissue in cardiac injury events, such as myocardial infarction (MI). Cardiac injury involves the release of various damage-associated molecular patterns (DAMPs) including heparan sulfate (HS), a constituent of the extracellular matrix (ECM), through the TLR4 receptor activation triggering a strong inflammatory response, inducing leukocytes recruitment. This latter cells are responsible of clearing cell debris and releasing cytokines that promote CF differentiation to myofibroblast (CMF), thus initiating scar formation. CF were isolated from adult male rats and subsequently stimulated with HS or LPS, in the presence or absence of chemical inhibitors, to evaluate signaling pathways involved in ICAM-1 and VCAM-1 expression. siRNA against ICAM-1 and VCAM-1 were used to evaluate participation of these adhesion molecules on leukocytes recruitment. HS through TLR4, PI3K/AKT and NF-ΚB increased ICAM-1 and VCAM-1 expression, which favored the adhesion of spleen mononuclear cells (SMC) and bone marrow granulocytes (PMN) to CF. These effects were prevented by siRNA against ICAM-1 and VCAM-1. Co-culture of CF with SMC increased α-SMA expression, skewing CF towards a pro-fibrotic phenotype, while CF pretreatment with HS partially reverted this effect. CONCLUSION: These data show the dual role of HS during the initial stages of wound healing. Initially, HS enhance the pro-inflammatory role of CF increasing cytokines secretion; and later, by increasing protein adhesion molecules allows the adhesion of SMC on CF, which trigger CF-to-CMF differentiation.

Lipopolysaccharide Activates Toll-Like Receptor 4 and Prevents Cardiac Fibroblast-to-Myofibroblast Differentiation.

Bacterial lipopolysaccharide (LPS) is a known ligand of Toll-like receptor 4 (TLR4) which is expressed in cardiac fibroblasts (CF). Differentiation of CF to cardiac myofibroblasts (CMF) is induced by transforming growth factor-ß1 (TGF-ß1), increasing alpha-smooth muscle actin (α-SMA) expression. In endothelial cells, an antagonist effect between LPS-induced signaling and canonical TGF-ß1 signaling was described; however, it has not been studied whether in CF and CMF the expression of α-SMA induced by TGF-ß1 is antagonized by LPS and the mechanism involved. In adult rat CF and CMF, α-SMA, ERK1/2, Akt, NF-κß, Smad3, and Smad7 protein levels were determined by western blot, TGF-ß isoforms by ELISA, and α-SMA stress fibers by immunocytochemistry. CF and CMF secrete the three TGF-ß isoforms, and the secretion levels of TGF-ß2 was affected by LPS treatment. In CF, LPS treatment decreased the protein levels of α-SMA, and this effect was prevented by TAK-242 (TLR4 inhibitor) and LY294002 (Akt inhibitor), but not by BAY 11-7082 (NF-κß inhibitor) and PD98059 (ERK1/2 inhibitor). TGF-ß1 increased α-SMA protein levels in CF, and LPS prevented partially this effect. In addition, in CMF α-SMA protein levels were decreased by LPS treatment, which was abolished by TAK-242. Finally, in CF LPS decreased the p-Smad3 phosphorylation and increased the Smad7 protein levels. LPS treatment prevents the CF-to-CMF differentiation and reverses the CMF phenotype induced by TGF-ß1, through decreasing p-Smad3 and increasing Smad7 protein levels.