Recent work has uncovered a role of the microRNA (miRNA) miR-29 in remodeling of the extracellular matrix. Partial bladder outlet obstruction is a prevalent condition in older men with prostate enlargement that leads to matrix synthesis in the lower urinary tract and increases bladder stiffness. Here we tested the hypothesis that miR-29 is repressed in the bladder in outlet obstruction and that this has an impact on protein synthesis and matrix remodeling leading to increased bladder stiffness. c-Myc, NF-κB and SMAD3, all of which repress miR-29, were activated in the rat detrusor following partial bladder outlet obstruction but at different times. c-Myc and NF-κB activation occurred early after obstruction, and SMAD3 phosphorylation increased later, with a significant elevation at 6 weeks. c-Myc, NF-κB and SMAD3 activation, respectively, correlated with repression of miR-29b and miR-29c at 10 days of obstruction and with repression of miR-29c at 6 weeks. An mRNA microarray analysis showed that the reduction of miR-29 following outlet obstruction was associated with increased levels of miR-29 target mRNAs, including mRNAs for tropoelastin, the matricellular protein Sparc and collagen IV. Outlet obstruction increased protein levels of eight out of eight examined miR-29 targets, including tropoelastin and Sparc. Transfection of human bladder smooth muscle cells with antimiR-29c and miR-29c mimic caused reciprocal changes in target protein levels in vitro. Tamoxifen inducible and smooth muscle-specific deletion of Dicer in mice reduced miR-29 expression and increased tropoelastin and the thickness of the basal lamina surrounding smooth muscle cells in the bladder. It also increased detrusor stiffness independent of outlet obstruction. Taken together, our study supports a model where the combined repressive influences of c-Myc, NF-κB and SMAD3 reduce miR-29 in bladder outlet obstruction, and where the resulting drop in miR-29 contributes to matrix remodeling and altered passive mechanical properties of the detrusor.

Shear detection and mechanotransduction by arterial endothelium requires junctional complexes containing PECAM‐1 and VE‐cadherin, as well as firm anchorage to the underlying basement membrane. While considerable information is available for junctional complexes in these processes, gained largely from in vitro studies, little is known about the contribution of the endothelial basement membrane. Using resistance artery explants, we show that the integral endothelial basement membrane component, laminin 511 (laminin α5), is central to shear detection and mechanotransduction and its elimination at this site results in ablation of dilation in response to increased shear stress. Loss of endothelial laminin 511 correlates with reduced cortical stiffness of arterial endothelium in vivo, smaller integrin β1‐positive/vinculin‐positive focal adhesions, and reduced junctional association of actin–myosin II. In vitro assays reveal that β1 integrin‐mediated interaction with laminin 511 results in high strengths of adhesion, which promotes p120 catenin association with VE‐cadherin, stabilizing it at cell junctions and increasing cell–cell adhesion strength. This highlights the importance of endothelial laminin 511 in shear response in the physiologically relevant context of resistance arteries.

Background An individual with a bicuspid aortic valve (BAV) runs a substantially higher risk of developing aneurysm in the ascending aorta compared to the normal population with tricuspid aortic valves (TAV). Aneurysm formation in patients with BAV and TAV is known to be distinct at the molecular level but the underlying mechanisms are undefined. Here, we investigated the still incompletely described role of microRNAs (miRNAs), important post‐transcriptional regulators of gene expression, in such aortic disease of patients with BAV as compared with TAV. Methods and Results Using a system biology approach, based on data obtained from proteomic analysis of non‐dilated aortas from BAV and TAV patients, we constructed a gene‐interaction network of regulatory microRNAs associated with the observed differential protein signature. The miR‐200 family was the highest ranked miRNA, hence potentially having the strongest effect on the signalling network associated with BAV. Further, qRT‐PCR and ChIP analyses showed lower expression of miR‐200c, higher expression of miR‐200 target genes, ZEB1/ZEB2 transcription factors, and higher chromatin occupancy of the miR‐200c promoter by ZEB1/ZEB2 in BAV patients, indicating a miR‐200c/ZEBs negative feedback loop and induction of endothelial/epithelial mesenchymal transition (EndMT/EMT). Conclusion We propose that a miR‐200‐dependent process of EndMT/EMT is a plausible biological mechanism rendering the BAV ascending aorta more prone to aneurysm development. Although initially supported by a miR‐200c/ZEB feedback loop, this process is most probably advanced by cooperation of other miRNAs.

Vascular smooth muscle cells are constantly exposed to mechanical force by the blood pressure, which is thought to regulate smooth muscle growth, differentiation and contractile function. We have previously shown that the expression of microRNAs (miRNAs), small non-coding RNAs, is essential for regulation of smooth muscle phenotype including stretch-dependent contractile differentiation. In this study, we have investigated the effect of mechanical stretch on miRNA expression and the role of stretch-sensitive miRNAs for intracellular signaling in smooth muscle. MiRNA array analysis, comparing miRNA levels in stretched versus non-stretched portal veins, revealed a dramatic decrease in the miR-144/451 cluster level. Because this miRNA cluster is predicted to target AMPK pathway components, we next examined activation of this pathway. Diminished miR-144/451 expression was inversely correlated with increased phosphorylation of AMPKα at Thr172 in stretched portal vein. Similar to the effect of stretch, contractile differentiation could be induced in non-stretched portal veins by the AMPK activator, AICAR. Transfection with miR-144/451 mimics reduced the protein expression level of mediators in the AMPK pathway including MO25α, AMPK and ACC. This effect also decreased AICAR-induced activation of the AMPK signaling pathway. In conclusion, our results suggest that stretch-induced activation of AMPK in vascular smooth muscle is in part regulated by reduced levels of miR-144/451 and that this effect may play a role in promoting contractile differentiation of smooth muscle cells.