Gα12 Regulates Interleukin-8 Expression after Epithelial Cell Injury

Alexandra K Kim,Bradley M Denker,Barrett Richard,Wanfeng Yu,Tianqing Kong,Ilene Boucher

doi:10.4236/ojpathology.2016.63018

Abstract

Acute kidney injury (AKI) is common in hospitalized patients and is strongly correlated with increased morbidity, mortality, and prolonged hospitalization. However, signals that determine whether injured tissues following AKI will repair or fibrose and lead to chronic kidney disease (CKD) are not well defined. Numerous cytokines are activated at various times after injury and recruit inflammatory cells. Interleukin-8 (IL-8) is upregulated following activation of Gα12 by H2O2, a reactive oxygen species (ROS). Herein, we study this occurrence in vitro and in vivo. IL-8 was measured by ELISA in Gα12-silenced (si-Gα12) and inducible QLα12 (constitutively active Gα12) Madin-Darby Canine Kidney (QLα12-MDCK) cell lines after H2O2/catalase cell injury. QLα12- and si-Gα12 MDCK cells showed time-, agonist- and Gα12-dependent increases in IL-8 mRNA and protein. Gα12-silenced MDCK cells demonstrated lower IL-8 expression and blunted IL-8 increases. In transgenic mice (QLα12γGTCre+, proximal tubule Qα12 expression) ischemia reperfusion injury led to significant upregulation of CXCL-1 (IL-8 homologue) at 48 hours that was not observed in Gα12 knockout mice. Macrophages in renal cells from these mice were imaged by immunofluorescent microscopy and QLα12γGTCre+ showed increased macrophage infiltration. We demonstrate that IL-8 is a critical link between H2O2 stimulated Gα12 and renal injury. Gα12 activation led to increased IL-8 expression, a potent mediator of inflammation after injury. Future studies targeting Gα12 for inhibition after injury may blunt the IL-8 response and allow for organ recovery.

Highlights

Acute kidney injury (AKI) is common in hospitalized patients, reporting to affect 1% - 25% of intensive care unit (ICU) patients, and is frequently not recognized in the outpatient setting [1]
Based on the importance of IL-8 in inflammation and our recent findings showing that Gα12 knockout mice were protected from injury, we further examined a possible link between Gα12 activation and IL-8 expression
QLα12 expression (−dox) led to >20 fold higher IL-8 levels at day 1 when compared to Gα12 +/−dox or QLα12-MDCK maintained in +dox (Figure 1)

Summary

Introduction

Acute kidney injury (AKI) is common in hospitalized patients, reporting to affect 1% - 25% of intensive care unit (ICU) patients, and is frequently not recognized in the outpatient setting [1]. AKI in hospitalized patients is strongly correlated with prolonged hospitalization and increased morbidity and mortality, with mortality rates ranging from 15% to 60% in ICU patients [2]-[4]. Etiologies of AKI include ischemic and toxic injury (drugs), obstruction, and delayed graft function after renal transplantation. Mechanisms initiated with acute kidney injury can lead to renal tubular fibrosis and progressive chronic kidney disease (CKD) [6]-[8]. Reactive oxygen species (ROS) are increased with tissue injury and contribute to progressive fibrosis, diabetic nephropathy and hypertensive nephrosclerosis [11]-[13]. Oxidative stress through ROS leads to proximal tubule cell detachment, actin cytoskeleton disruption and TJ disruption [15]; all processes are linked to G protein signaling and Gα12 [16]-[18]

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