Endothelial Krüppel-Like Factor 4 Modulates Pulmonary Arterial Hypertension

Abstract

Krüppel-like factor 4 (KLF4) is a transcription factor expressed in the vascular endothelium, where it promotes anti-inflammatory and anticoagulant states, and increases endothelial nitric oxide synthase expression. We examined the role of endothelial KLF4 in pulmonary arterial (PA) hypertension (PAH). Mice with endothelial KLF4 knockdown were exposed to hypoxia for 3 weeks, followed by measurement of right ventricular and PA pressures, pulmonary vascular muscularization, and right ventricular hypertrophy. The effect of KLF4 on target gene expression was assessed in lungs from these mice, verified in vitro by small interfering RNA (siRNA) knockdown of KLF4, and further studied at the promoter level with cotransfection experiments. KLF4 expression was measured in lung tissue from patients with PAH and normal control subjects. We found that, after hypoxia, right ventricular and PA pressures were significantly higher in KLF4 knockdown animals than controls. Knockdown animals also had more severe pulmonary vascular muscularization and right ventricular hypertrophy. KLF4 knockdown resulted in increased pulmonary expression of endothelin-1 and decreased expression of endothelial nitric oxide synthase, endothelin receptor subtype B, and prostacyclin synthase. Concordant findings were observed in vitro, both with siRNA knockdown of KLF4 and promoter activity assays. Finally, KLF4 expression was reduced in lungs from patients with PAH. In conclusion, endothelial KLF4 regulates the transcription of genes involved in key pathways implicated in PAH, and its loss exacerbates pulmonary hypertension in response to chronic hypoxia in mice. These results introduce a novel transcriptional modulator of PAH, with the potential of becoming a new therapeutic target.

Endothelial Krüppel-like Factor 4 Regulates Angiogenesis and the Notch Signaling Pathway

“…In this article we show that KLF4 regulates expression of other angiogenically active factors in addition to Notch and Notch target genes, including VEGFA, VEGFR1, and VEGFR2. Although the multifactorial transcriptional effects of KLF4 can make it difficult to attribute its function to a singular target, these results are consistent with those we have found in other physiologically relevant contexts such as the development of atherosclerosis (12) and pulmonary artery hypertension (27). In fact, diverse activating or inhibitory transcriptional modulation is likely integral to the homeostatic role EC KLF4 appears to play.…”

“…Over the past several years evidence has accrued that suggests the transcription factor KLF4 plays a significant role in the first four of these five essential functions (11,12,27,28). This study completes the description of KLF4 as a mediator of each of these fundamental processes; herein we show that sustained endothelial-specific overexpression of KLF4 causes a profound dysregulation of tumor sprouting angiogenesis, leading to marked reduction in tumor size.…”

PDGF-BB/KLF4/VEGF Signaling Axis in Pulmonary Artery Endothelial Cell Angiogenesis

“…However, studies have confirmed that after hypoxia, right ventricular and PA pressures were significantly higher in KLF4 knockdown animals than in controls. KLF knockdown animals also displayed more-severe pulmonary vascular muscularization and right ventricular hypertrophy [48]. These results suggest that the role of KLF4 in pulmonary arterial hypertension is not consistent.…”

Role of Krüppel-Like Factor 4 and its Binding Proteins in Vascular Disease

“…EC-selective Klf4 knockdown also results in the increased expression of endothelin-1 and decreased expression of endothelial nitric-oxide synthase, endothelin receptor subtype B and prostacyclin synthase in the lungs. Importantly, the KLF4 expression is reduced in the lungs of patients with pulmonary artery hypertension 76) . As such, KLF4 is likely to be a novel transcriptional modulator of pulmonary artery hypertension.…”

“…Most recently, endothelial KLF4 has been shown to modulate pulmonary arterial hypertension 76) . Indeed, Cdh5 promoter-dependent Klf4 knockout mice exhibit elevation of the right ventricular and pulmonary arterial pressures as well as right ventricular hypertrophy following hypoxia.…”