A requirement for Krüppel Like Factor‐4 in the maintenance of endothelial cell quiescence

Abstract

Rationale and Goal: Endothelial cells (ECs) are quiescent and critical for maintaining homeostatic functions of the mature vascular system, while disruption of quiescence is at the heart of endothelial to mesenchymal transition (EndMT) and tumor angiogenesis. Here, we addressed the hypothesis that KLF4 maintains the EC quiescence.Methods and Results: In ECs, KLF4 bound to KLF2, and the KLF4-transctivation domain (TAD) interacted directly with KLF2. KLF4-depletion increased KLF2 expression, accompanied by phosphorylation of SMAD3, increased expression of alpha-smooth muscle actin (αSMA), VCAM-1, TGF-β1, and ACE2, but decreased VE-cadherin expression. In the absence of Klf4, Klf2 bound to the Klf2-promoter/enhancer region and autoregulated its own expression. Loss of EC-Klf4 in RosamT/mG::Klf4fl/fl::Cdh5CreERT2 engineered mice, increased Klf2 levels and these cells underwent EndMT. Importantly, these mice harboring EndMT was also accompanied by lung inflammation, disruption of lung alveolar architecture, and pulmonary fibrosis.Conclusion: In quiescent ECs, KLF2 and KLF4 partnered to regulate a combinatorial mechanism. The loss of KLF4 disrupted this combinatorial mechanism, thereby upregulating KLF2 as an adaptive response. However, increased KLF2 expression overdrives for the loss of KLF4, giving rise to an EndMT phenotype.

A Single-Short Partial Reprogramming of the Endothelial Cells decreases Blood Pressure via attenuation of EndMT in Hypertensive Mice

“…referred to as platelet endothelial cell adhesion molecule 1 (PECAM1), increased in both LV-treated ECs compared to the cells treated with phosphate-buffered saline (PBS) (Fig.1 G). The monomeric form of Klf-4 (Fig.2A; yellow arrow; ~75 kDa, as described by Mastej et al[16]) was upregulated only in LV-OSK-treated cells. Along with Klf-4 modulation, we observed the presence of histone H3 proteins (Fig.2 A; native H3, 15 kDa and 17-20 kDa).…”

N6-methyladenosine modification of KLF2 may contribute to endothelial-to-mesenchymal transition in pulmonary hypertension

“…Research has demonstrated that KLF proteins exert strict regulatory control over the expression of mesenchymal markers. Specifically, the loss of KLF4 elevates the expression of collagens, VCAM-1, SMA, and SM22 in human lung ECs [ 47 ]. Moreover, KLF4 represses SM22 transcription during the phenotypic transition of smooth muscle cells via cooperatively binding with pELK-1 to the SM22 promoter [ 48 ].…”

Endocardial primary cilia and blood flow are required for regulation of EndoMT during endocardial cushion development

“…Taken together, our data puts forward a model by which primary cilia spatially control cushion growth through selective regulation of mechanosensitive factors. In this model, cilia dependent KLF4 expression is used to maintain endocardial quiescence, as has been seen previously 41 , thus providing an endocardial pool for replenishing differentiated luminal cells. Ciliated endocardium becomes Klf4 positive following the onset of blood flow, and then selectively deciliates in the high shear stress center of the AVC leading to reduced KLF4 (Fig.…”

“…EndoMT is required for ECC development, and KLF4 has been shown to inhibit or activate EndoMT 22,[40][41][42][43] . To decouple KLF4's role in EndoMT, we examined the expression patterns of Vimentin (Vim, mesenchymal marker) and Kinase Insert Domain Receptor (Kdr, endothelial marker) to test whether KLF4-low cells in the center of the AVC were more or less likely to undergo EndoMT.…”

“…Whether KLF4 activates or inhibits cushion EndoMT is still up for debate 40,41 . Given these inconsistencies, it is important to not only understand how KLF4 is regulated during cushion formation, but also how it impacts EndoMT progression.…”