Resveratrol attenuates experimental allergic asthma in mice by restoring inositol polyphosphate 4 phosphatase (INPP4A)

Abstract

Asthma is a chronic airway inflammatory disorder which is characterized by reversible airway obstruction, airway hyperresponsiveness and airway inflammation. Oxidative stress has been shown to be strongly associated with most of the features of asthma and leads to accumulation of phosphatidyl inositol (3,4) bis-phosphate {PtdIns(3,4)P2} which is the major substrate for inositol polyphosphate 4 phosphatase (INPP4A). PtdIns(3,4)P2 in turn activates PI3K pathway and contributes to oxidative stress. Thus, there exists a vicious loop between oxidative stress and lipid phosphatase signaling. In this context, we have recently shown that INPP4A, a crucial molecular checkpoint in controlling PI3K-Akt signaling pathway, is downregulated in allergic airway inflammation. Resveratrol, a potent antioxidant found in red wines, has been shown to attenuate asthma features in murine model of allergic airway inflammation (AAI), however the underlying mode of its action was not completely understood. In this study, the effect of resveratrol on mitochondrial dysfunction, PI3K-Akt signaling and inositol polyphosphate 4 phosphatase was studied in murine model of allergic airway inflammation. We observed that resveratrol treatment of allergic mice was found to significantly downregulate oxidative stress and restore mitochondrial function. It also decreased calpain activity and restored the expression of INPP4A in lungs which in turn reduced Akt kinase activity and Akt phosphorylation. These results suggest a novel mechanism of action of resveratrol in attenuating asthma phenotype by downregulating PI3K-Akt pathway via upregulating INPP4A.

Introduction

Asthma, a chronic airway inflammatory disorder, is characterized by reversible airway obstruction, airway hyperresponsiveness (AHR), allergic airway inflammation (AAI) including mucus hypersecretion, increased IgE synthesis and airway eosinophilia [1]. The ever-increasing prevalence and mortality of asthma indicate the necessity to explore novel pathways for better understanding and efficient management [2]. Most of the asthma features are mediated by Th2 dominant response which leads to the release of various proinflammatory mediators in local microenvironment in lung. Importantly, lipid mediators, such as 5-lipoxygenase, cysteinyl leukotrienes and phosphoinositide 3-kinase (PI3K) play crucial roles in asthma pathogenesis [3], [4], [5]. PI3K has various proinflammatory and deleterious effects in asthma pathogenesis due to its property of causing airway smooth muscle proliferation [5], platelet activation [6], mast cell degranulation [7], and corticosteroid insensitivity in chronic respiratory diseases [8]. Inositol polyphosphate 4 phosphatase A (INPP4A) catalyzes the dephosphorylation of PtdIns(3,4)P2 to PtdIns(3)P [9]. Earlier, we identified INPP4A as a novel asthma candidate gene and showed that its genotype variants affect the stability of INPP4A protein due to the alteration in the PEST sequence motif which affects the susceptibility to calpain proteases [10]. There are evidences demonstrating that oxidative stress leads to accumulation of PtdIns(3,4)P2 [11], [12]. On the other hand, activation of PI3K pathway contributes to oxidative stress which indicates the existence of vicious loop between oxidative stress and INPP4A activity [13]. Hence, INPP4A enzyme is not only a vulnerable target for oxidative stress but also counteracts oxidative stress by conversion of PtdIns(3,4)P2 to PtdIns(3)P. Recruited inflammatory cells release reactive oxygen species (ROS) in the asthmatic airways which causes elevation of lipid peroxidation leading to aggravated inflammatory response in asthma [14].

Resveratrol (3,4′,5 tri-hydroxystilbene) is a natural dietary polyphenol found in red wine, grape skins, peanut seeds, berries and various other foods [15]. Besides being an antioxidant, resveratrol is also known to have anti-inflammatory and anti-mutagenic activities due to its property of inhibiting cyclooxygenase-1 and 2 (COX-1 and COX-2) and 5 lipoxygenase [16], [17]. However, the mechanism of action of resveratrol is yet to be elucidated using novel targets. Therefore, we investigated the effect of resveratrol on mitochondrial dysfunction, oxidative stress and INPP4A in a murine model of AAI. We report in this study for the first time that administration of resveratrol in murine model of AAI is associated with restoration of mitochondrial function. It also potently upregulates INPP4A expression leading to the downregulation of Akt phosphorylation, and thus it could be involved in attenuation of allergic airway inflammation.