{'fraction_non_alphanumeric': 0.02330793366203496, 'fraction_numerical': 0.010309278350515464, 'mean_word_length': 5.395415472779369, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Activation of Smad2/3 signaling by low fluid shear stress mediates artery inward remodeling

Significance This paper analyzes the signaling network that regulates the size of artery lumens and thus their ability to transport blood to tissues. Lumen diameter is under close homeostatic regulation to match artery flow to the needs of downstream tissues. However, in atherosclerosis, this regulation is compromised, resulting in restricted blood flow and tissue ischemia. The elucidation of a Smad2/3 pathway that is specifically activated at low flow to trigger inward remodeling and thus restore normal shear stress levels not only reveals a mechanism of physiological regulation but also explains how activation of the same pathway by inflammatory factors in diseased arteries can lead to artery restriction. Endothelial cell (EC) sensing of wall fluid shear stress (FSS) from blood flow governs vessel remodeling to maintain FSS at a specific magnitude or set point in healthy vessels. Low FSS triggers inward remodeling to restore normal FSS but the regulatory mechanisms are unknown. In this paper, we describe the signaling network that governs inward artery remodeling. FSS induces Smad2/3 phosphorylation through the type I transforming growth factor (TGF)-β family receptor Alk5 and the transmembrane protein Neuropilin-1, which together increase sensitivity to circulating bone morphogenetic protein (BMP)-9. Smad2/3 nuclear translocation and target gene expression but not phosphorylation are maximal at low FSS and suppressed at physiological high shear. Reducing flow by carotid ligation in rodents increases Smad2/3 nuclear localization, while the resultant inward remodeling is blocked by the EC-specific deletion of Alk5. The flow-activated MEKK3/Klf2 pathway mediates the suppression of Smad2/3 nuclear translocation at high FSS, mainly through the cyclin-dependent kinase (CDK)-2-dependent phosphosphorylation of the Smad linker region. Thus, low FSS activates Smad2/3, while higher FSS blocks nuclear translocation to induce inward artery remodeling, specifically at low FSS. These results are likely relevant to inward remodeling in atherosclerotic vessels, in which Smad2/3 is activated through TGF-β signaling.