Interferon Regulatory Factor-1 Regulates the Autophagic Response in LPS-Stimulated Macrophages through Nitric Oxide

Lemeng Zhang,Matthew R. Rosengart,Allan Tsung,Jon S. Cardinal,Runalia Bahar,Pinhua Pan,Gary Nace,John Evankovich,Hai Huang,Timothy R. Billiar

doi:10.2119/molmed.2011.00282

Abstract

The pathogenesis of sepsis is complex and, unfortunately, poorly understood. The cellular process of autophagy is believed to play a protective role in sepsis; however, the mechanisms responsible for its regulation in this setting are ill defined. In the present study, interferon regulatory factor 1 (IRF-1) was found to regulate the autophagic response in lipopolysaccharide (LPS)-stimulated macrophages. In vivo, tissue macrophages obtained from LPS-stimulated IRF-1 knockout (KO) mice demonstrated increased autophagy and decreased apoptosis compared to those isolated from IRF-1 wild-type (WT) mice. In vitro, LPS-stimulated peritoneal macrophages obtained from IRF-1 KO mice experienced increased autophagy and decreased apoptosis. IRF-1 mediates the inhibition of autophagy by modulating the activation of the mammalian target of rapamycin (mTOR). LPS induced the activation of mTOR in WT peritoneal macrophages, but not in IRF-1 KO macrophages. In contrast, overexpression of IRF-1 alone increased the activation of mTOR and consequently decreased autophagic flux. Furthermore, the inhibitory effects of IRF-1 mTOR activity were mediated by nitric oxide (NO). Therefore, we propose a novel role for IRF-1 and NO in the regulation of macrophage autophagy during LPS stimulation in which IRF-1/NO inhibits autophagy through mTOR activation.

Highlights

Sepsis is a leading cause of death in intensive care units and accounts for an estimated 250,000 deaths per year in the United States [1]
Downstream of interferon regulatory factor 1 (IRF-1), we find that inducible nitric oxide synthase-dependent nitric oxide (NO) exerts an inhibitory effect on autophagy through the activation of mammalian target of rapamycin
Adenoviral IRF-1 (AdIRF-1) overexpression, in and of itself, resulted in an increase in the phosphorylation status of both mammalian target of rapamycin (mTOR) and P70S6 and a concomitant decrease in the activity of autophagy as measured by Western blot analysis for LC3B I/II. This effect was reversed by pretreatment with the selective inducible nitric oxide synthase (iNOS) inhibitor L-NIL (Figure 5D). These findings suggest that IRF-1 activation leads to the induction of iNOS, which exerts an inhibitory effect on autophagy by activating the mTOR/P70S6 signaling pathway

Summary

Introduction

Sepsis is a leading cause of death in intensive care units and accounts for an estimated 250,000 deaths per year in the United States [1]. The pathophysiology of the septic response occurs in two distinct phases: the initial hyperdynamic phase which is dominated by innate immune system overactivity and a later, immunosuppressed phase in which adaptive immunity fails to protect the host from opportunistic infections [2,3]. Macrophages are key regulators of both innate and adaptive immune responses during sepsis. They function in eliminating invasive bacteria, producing cytokines and participating in antigen presentation. Autophagy is a process by which cells degrade and recycle nonessential and/or redundant components. Autophagy participates in the clearance of intracellular bacteria, viruses and protozoa from host cells.

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