Hyperglycaemia up-regulates placental growth factor (PlGF) expression and secretion in endothelial cells via suppression of PI3 kinase-Akt signalling and activation of FOXO1

Samir Sissaoui,Asif Ahmed,Stuart Egginton,Ling Ting,Peter W Hewett

doi:10.1038/s41598-021-95511-8

Abstract

Placenta growth factor (PlGF) is a pro-inflammatory angiogenic mediator that promotes many pathologies including diabetic complications and atherosclerosis. Widespread endothelial dysfunction precedes the onset of these conditions. As very little is known of the mechanism(s) controlling PlGF expression in pathology we investigated the role of hyperglycaemia in the regulation of PlGF production in endothelial cells. Hyperglycaemia stimulated PlGF secretion in cultured primary endothelial cells, which was suppressed by IGF-1-mediated PI3K/Akt activation. Inhibition of PI3K activity resulted in significant PlGF mRNA up-regulation and protein secretion. Similarly, loss or inhibition of Akt activity significantly increased basal PlGF expression and prevented any further PlGF secretion in hyperglycaemia. Conversely, constitutive Akt activation blocked PlGF secretion irrespective of upstream PI3K activity demonstrating that Akt is a central regulator of PlGF expression. Knock-down of the Forkhead box O-1 (FOXO1) transcription factor, which is negatively regulated by Akt, suppressed both basal and hyperglycaemia-induced PlGF secretion, whilst FOXO1 gain-of-function up-regulated PlGF in vitro and in vivo. FOXO1 association to a FOXO binding sequence identified in the PlGF promoter also increased in hyperglycaemia. This study identifies the PI3K/Akt/FOXO1 signalling axis as a key regulator of PlGF expression and unifying pathway by which PlGF may contribute to common disorders characterised by endothelial dysfunction, providing a target for therapy.

Highlights

Diabetes mellitus is associated with both central and peripheral vasculopathies, notably diabetic retinopathy[1]
As hyperglycaemia is reported to suppress PI3K signalling in many cell types, including endothelial cells[26] we examined the effect of the established PI3K activators, IGF-1 and insulin on Placenta growth factor (PlGF) expression
The basal level of PlGF produced by endothelial cells was reduced in a concentration-dependent manner by IGF-1 (Fig. 1B) and insulin (1 mM) led to a 31% decrease in PlGF secretion, indicating that PlGF release is negatively regulated by PI3K pathway activity in endothelium

Summary

Introduction

Diabetes mellitus is associated with both central and peripheral vasculopathies, notably diabetic retinopathy[1]. The intravitreous or systemic delivery of PlGF in rodents disrupts retinal barrier function and increases vascular leakage in a VEGFR-1-dependent manner, mimicking diabetic retinopathy[15,16]. Elevated circulating PlGF levels are associated with vascular inflammation and adverse outcome in patients with acute coronary syndrome[19], severity of metabolic syndrome[20], development of type-2 diabetes[21] and childhood obesity[22]. In this study we show that manipulation of glucose concentration, PI3K or Akt activity leads to consistent changes in endothelial cell PlGF expression and release, which are dependent on FOXO1 transcription factor activity. The identification of the involvement of the PI3K/Akt/FOXO1 pathway in the control of PlGF expression may have important implications for endothelial homeostasis and dysfunction, and represent a target for therapy in vascular disorders

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Conclusion