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We report that KLF2 substantially enhances antioxidant activity of Nrf2 by increasing its nuclear localization and activation. The synergistic activity of these two transcription factors forms a major contribution to the shear stress-elicited transcriptome in endothelial cells.

In an in-situ approach towards tissue engineered cardiovascular replacement grafts, cell-free scaffolds are implanted that engage in endogenous tissue formation. Bioactive molecules can be incorporated into such grafts to facilitate cellular recruitment. Stromal cell derived factor 1α (SDF1α) is a powerful chemoattractant of lymphocytes, monocytes and progenitor cells and plays an important role in cellular signaling and tissue repair. Short SDF1α-peptides derived from its receptor-activating domain are capable of activating the SDF1α-specific receptor CXCR4. Here, we show that SDF1α-derived peptides can be chemically modified with a supramolecular four-fold hydrogen bonding ureido-pyrimidinone (UPy) moiety, that allows for the convenient incorporation of the UPy-SDF1α-derived peptides into a UPy-modified polymer scaffold. We hypothesized that a UPy-modified material bioactivated with these UPy-SDF1α-derived peptides can retain and stimulate circulating cells in an anti-inflammatory, pro-tissue formation signaling environment. First, the early recruitment of human peripheral blood mononuclear cells to the scaffolds was analyzed in vitro in a custom-made mesofluidic device applying physiological pulsatile fluid flow. Preferential adhesion of lymphocytes with reduced expression of inflammatory factors TNFα, MCP1 and lymphocyte activation marker CD25 was found in the bioactivated scaffolds, indicating a reduction in inflammatory signaling. As a proof of concept, in-vivo implantation of the bioactivated scaffolds as rat abdominal aorta interposition grafts showed increased cellularity by CD68+ cells after 7 days. These results indicate that a completely synthetic, cell-free biomaterial can attract and stimulate specific leukocyte populations through supramolecular incorporation of short bioactive SDF1α derived peptides.

The stabilization of KLF2 steady-state levels, as induced by prolonged shear stress but not by statins, may be essential for sustaining the quiescent, atheroprotective status of the vascular endothelium under inflammatory conditions.

BackgroundTechniques to treat urethral stricture and hypospadias are restricted, as substitution of the unhealthy urethra with tissue from other origins (skin, bladder or buccal mucosa) has some limitations. Therefore, alternative sources of tissue for use in urethral reconstructions are considered, such as ex vivo engineered constructs.PurposeTo review recent literature on tissue engineering for human urethral reconstruction.MethodsA search was made in the PubMed and Embase databases restricted to the last 25 years and the English language.ResultsA total of 45 articles were selected describing the use of tissue engineering in urethral reconstruction. The results are discussed in four groups: autologous cell cultures, matrices/scaffolds, cell-seeded scaffolds, and clinical results of urethral reconstructions using these materials. Different progenitor cells were used, isolated from either urine or adipose tissue, but slightly better results were obtained with in vitro expansion of urothelial cells from bladder washings, tissue biopsies from the bladder (urothelium) or the oral cavity (buccal mucosa). Compared with a synthetic scaffold, a biological scaffold has the advantage of bioactive extracellular matrix proteins on its surface. When applied clinically, a non-seeded matrix only seems suited for use as an onlay graft. When a tubularized substitution is the aim, a cell-seeded construct seems more beneficial.ConclusionsConsiderable experience is available with tissue engineering of urethral tissue in vitro, produced with cells of different origin. Clinical and in vivo experiments show promising results.

Objective-The flow-responsive Kruppel-like factor 2 (KLF2) is crucial for maintaining endothelial cell quiescence. Here, we describe its detailed effects on transforming growth factor-␤ (TGF-␤) signaling, which normally has proatherogenic effects on endothelium. Methods and Results-In-depth analysis of genome-wide expression data shows that prolonged lentiviral-mediated overexpression of KLF2 in human umbilical vein endothelial cells (HUVECs) diminishes the expression of a large panel of established TGF-␤-inducible genes. Both baseline and TGF-␤-induced expression levels of plasminogen activator inhibitor 1 (PAI-1) and thrombospondin-1 are greatly diminished by KLF2. Using a combination of ectopic expression, small interfering RNA-mediated knockdown, and promoter activity assays, we show that KLF2 partly inhibits the phosphorylation and subsequent nuclear accumulation of Smad2, thereby suppressing the TGF-␤-induced Smad4-mediated transcriptional activity. This is achieved through TGF-␤-independent induction of inhibitory Smad7. Additionally, a full inhibition of TGF-␤ signaling is functionally achieved through a simultaneous suppression of activator protein 1 (AP-1), which is an essential cofactor for TGF-␤-dependent transcription of many genes. Conclusions-The concerted mechanism by which KLF2 inhibits TGF-␤ signaling through induction of inhibitory Smad7 and attenuation of AP-1 activity provides a novel mechanism by which KLF2 contributes to sustaining a quiescent, atheroprotective status of vascular endothelium. (Arterioscler Thromb Vasc Biol. 2007;27:532-539.)

The shear stress-induced transcription factor Krü ppel-like factor 2 (KLF2) confers antiinflammatory properties to endothelial cells through the inhibition of activator protein 1, presumably by interfering with mitogen-activated protein kinase (MAPK) cascades. To gain insight into the regulation of these cascades by KLF2, we used antibody arrays in combination with time-course mRNA microarray analysis. No gross changes in MAPKs were detected; rather, phosphorylation of actin cytoskeleton-associated proteins, including focal adhesion kinase, was markedly repressed by KLF2. Furthermore, we demonstrate that KLF2-mediated inhibition of Jun NH 2 -terminal kinase (JNK) and its downstream targets ATF2/c-Jun is dependent on the cytoskeleton. Specifically, KLF2 directs the formation of typical short basal actin filaments, termed shear fibers by us, which are distinct from thrombinor tumor necrosis factor-␣-induced stress fibers. KLF2 is shown to be essential for shear stress-induced cell alignment, concomitant shear fiber assembly, and inhibition of JNK signaling. These findings link the specific effects of shear-induced KLF2 on endothelial morphology to the suppression of JNK MAPK signaling in vascular homeostasis via novel actin shear fibers. (Blood. 2010;115:2533-2542)