ATF4 is a novel regulator of MCP-1 in microvascular endothelial cells.

Huibin Huang,Nader Sheibani,Sarah X Zhang,Guangjun Jing,Joshua J Wang

doi:10.1186/s12950-015-0076-1

Abstract

BackgroundMonocyte chemoattractant protein-1 (MCP-1) is a major chemokine that recruits monocyte/macrophage to the site of tissue injury and plays a critical role in microvascular complications of diabetes. However, the mechanisms underlying the regulation of MCP-1 are not fully understood. The present study aims to explore the role of activating transcription factor 4 (ATF4), an ER stress-inducible transcription factor, in regulation of MCP-1 expression and production in brain and retinal microvascular endothelial cells.MethodsFor in vitro study, primary brain microvascular endothelial cells isolated from ATF4 knockout mice or mouse retinal endothelial cells were treated with lipopolysaccharide (LPS) to induce MCP-1 expression. ATF4 expression/function was manipulated by adenoviruses expressing wild type ATF4 (Ad-ATF4) or a dominant negative mutant of the protein (Ad-ATF4DN). For in vivo study, MCP-1 expression was induced by intravitreal injection of LPS or Ad-ATF4 in heterozygous ATF4 knockout or wild type mice.ResultsLPS treatment induced a dose- and time-dependent increase in ATF4 expression, ER stress and MCP-1 production in brain and retinal microvascular endothelial cells. Overexpression of ATF4 in endothelial cells significantly increased the secretion of MCP-1 and promoted THP-1 monocyte-endothelial cell adhesion. Conditioned medium from ATF4-overexpressiing endothelial cells significantly enhanced THP-1 cell migration. Consistently, intravitreal injection of Ad-ATF4 remarkably enhanced retinal levels of MCP-1 and promoted inflammatory cell infiltration into the vitreous and retina. In contrast, LPS-induced MCP-1 upregulation was markedly attenuated in ATF4-deficient endothelial cells and in retinas of ATF4 knockout mice, suggesting that ATF4 is essential for LPS-induced MCP-1 production in endothelial cells and in the retina. Mechanistically, overexpression of ATF4 enhanced, while inhibition of ATF4, attenuated the basal and LPS-stimulated phosphorylation of NF-κB, P38, and JNK. Furthermore, pharmacological inhibition of NF-κB, P38, or JNK significantly reduced ATF4-stimulated MCP-1 secretion from endothelial cells.ConclusionsTaken together, our results suggest a critical role of ATF4 in the regulation of MCP-1 production in retinal and brain microvascular endothelial cells, which may contribute to inflammation-related endothelial injury in diseases such as diabetic retinopathy.

Highlights

Monocyte chemoattractant protein-1 (MCP-1) is a major chemokine that recruits monocyte/macrophage to the site of tissue injury and plays a critical role in microvascular complications of diabetes
LPS increases endoplasmic reticulum (ER) stress and activating transcription factor 4 (ATF4) expression in microvascular endothelial cells We first examined whether activation of the TLR4 signaling by LPS induces ER stress and ATF4 expression in mouse brain and retina microvascular endothelial cells
In line with these changes, 24 h of LPS treatment significantly increased the levels of ATF4-related ER stress markers, including eIF2α phosphorylation and C/EBP homologous protein (CHOP) in both retinal (Figure 1B) and brain (Figure 1C) endothelial cells, and the inductions appeared to be more profound in brain endothelial cells than retinal endothelial cells

Summary

Introduction

Monocyte chemoattractant protein-1 (MCP-1) is a major chemokine that recruits monocyte/macrophage to the site of tissue injury and plays a critical role in microvascular complications of diabetes. The mechanisms underlying the regulation of MCP-1 are not fully understood. The present study aims to explore the role of activating transcription factor 4 (ATF4), an ER stress-inducible transcription factor, in regulation of MCP-1 expression and production in brain and retinal microvascular endothelial cells. A delicate balance between protein synthesis and folding is vital for cell survival and function. Our recent studies have shown that ER stress and the PERK/eIF2α/ ATF4/CHOP pathway are involved in regulation of immune response and retinal vascular injury in diabetic retinopathy, a common complication of diabetes [4,5]. The mechanisms underlying ER stress-related inflammatory signaling are not fully understood

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