The formation of cardiac valves depends on mechanical forces exerted by blood flow. Endocardial cells lining the interior of the heart are sensitive to these stimuli and respond by rearranging into luminal cells subjected to shear stress and abluminal cells not exposed to it. The mechanisms by which endocardial cells sense these dynamic biomechanical stimuli and how they evoke different cellular responses are largely unknown. Here, we show that blood flow activates two parallel mechanosensitive pathways, one mediated by Notch and the other by Klf2a. Both pathways negatively regulate the angiogenesis receptor Vegfr3/Flt4, which becomes restricted to abluminal endocardial cells. Its loss disrupts valve morphogenesis and results in the occurrence of Notch signaling within abluminal endocardial cells. Our work explains how antagonistic activities by Vegfr3/Flt4 on the abluminal side and by Notch on the luminal side shape cardiac valve leaflets by triggering unique differences in the fates of endocardial cells.

Bone is a remarkable dynamic structure, which integrates mechanical and biochemical signaling inputs. Interstitial fluid in the intramedullary space transmits signals derived from compression‐induced fluid shear stress (FSS) to stimulate osteoblasts for bone formation. Using a flow system and human osteoblasts, this study demonstrates how BMP/TGF‐β signaling integrates stimuli derived from FSS and YAP/TAZ and confirms these findings by transcriptome analyses. Here, FSS positively affects the phosphorylation of both SMAD1/5 and SMAD2/3, the respective BMP‐ and TGFβ‐R‐SMADs. Increase in phosphorylated SMAD1/5 levels affects distinct target genes, which are susceptible to low levels of phosphorylated SMADs (such as ID1–3) or dependent on high levels of phosphorylated SMAD1/5 (NOG, noggin). Thus, FSS lowers the threshold for genes dependent on high levels of phosphorylated SMAD1/5 when less BMP is available. While the impact of FSS on direct BMP target genes is independent of YAP/TAZ, FSS acts cooperatively with YAP/TAZ on TGF‐β target genes, which are shared by both pathways (such as CTGF). As mechanical stimuli are key in bone regeneration, their crosstalk to biochemical signaling pathways such as BMP and TGF‐β and YAP/TAZ acts on different levels, which allows now to think about new and more specified intervention strategies for age‐related bone loss.

Background: Fluid shear stress enhances endothelial SMAD1/5 signaling via the BMP9-bound ALK1 receptor complex supported by the co-receptor Endoglin. While moderate SMAD1/5 activation is required to maintain endothelial quiescence, excessive SMAD1/5 signaling promotes endothelial dysfunction. Increased BMP signaling participates in endothelial-to-mesenchymal transition and inflammation culminating in vascular diseases such as atherosclerosis. While the function of Endoglin has so far been described under picomolar concentrations of BMP9 and short-term shear application, we investigated Endoglin under physiological BMP9 and long-term pathophysiological shear conditions. Results: We report here that knock-down of Endoglin leads to exacerbated SMAD1/5 phosphorylation and atheroprone gene expression profile in HUVECs sheared for 24 h. Making use of the ligand-trap ALK1-Fc, we furthermore show that this increase is dependent on BMP9/10. Mechanistically, we reveal that long-term exposure of ECs to low laminar shear stress leads to enhanced Endoglin expression and endocytosis of Endoglin in Caveolin-1-positive early endosomes. In these endosomes, we could localize the ALK1-Endoglin complex, labeled BMP9 as well as SMAD1, highlighting Caveolin-1 vesicles as a SMAD signaling compartment in cells exposed to low atheroprone laminar shear stress. Conclusions: We identified Endoglin to be essential in preventing excessive activation of SMAD1/5 under physiological flow conditions and Caveolin-1-positive early endosomes as a new flow-regulated signaling compartment for BMP9-ALK1-Endoglin signaling axis in atheroprone flow conditions.

Immediate pigment darkening, the first response of skin to solar exposure leading to undesired irregular pigmentation and dark spots, is the rapid onset of melanin pigmentation resulting from oxidation of the melanogenic indoles, namely 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) available in epidermal melanocytes. The search for effective sunscreen formulations is nowadays focused on UVA/B filters and additional ingredients that may scavenge the reactive oxygen species generated in these processes. In this work the effects of phenolic cosmetic ingredients (CIs), paradol-6, a ginger CO₂ extract, and phenylethyl resorcinol on photosensitized DHI and DHICA oxidation were investigated showing a decrease of their consumption and melanin formation (25–30% decrease with phenylethyl resorcinol). The photoprotective role of CIs was also evaluated in model systems. Paradol-6 and ginger CO₂ extract can halve linoleic acid peroxidation in the riboflavin-sensitized reaction, while dienes generation reduction (30% of control) was observed in the Rose-Bengal-sensitized photooxidation with paradol-6. The presence of DHI/DHICA melanin exerted a synergistic effect. The decay of thymine free or as a DNA base was almost completely inhibited by CIs. These results open new perspectives in the design of skin care formulations for ameliorating skin spots and contrasting ageing processes associated with sun exposure.

The human dermal skin is permanently exposed to mechanical stress, for instance during facial expression, which might cause wrinkles with age. Cyclic mechanical stretching of cells results in cellular and cytoskeleton alignment perpendicular to the stretch direction regulating cellular response. With gene expression profiling it was aimed to identify the differentially expressed genes associated with the regulation of the cytoskeleton to investigate the stretch-induced cell alignment mechanism. Here, the transcription activity of the genome in response to cyclic mechanical stress was measured using DNA microarray technology with Agilent SurePrint G3 Human GE 8x60k Microarrays, based on the overall measurement of the mRNA. Gene expression was measured at the beginning of the alignment process showing first reoriented cells after 5 h stretching and at the end after 24 h, where nearly all cells are aligned. Gene expression data of control vs. stretched primary human dermal fibroblasts after 5 h and 24 h demonstrated the regulation of differentially expressed genes associated with metabolism, differentiation and morphology and were deposited at http://www.ncbi.nlm.nih.gov/geo with the accession number GSE58389.