We have discovered a role for the mevalonate (MA) pathway lipid metabolites known as isoprenoids in mediating type 2 inflammation in asthma disease models. This finding is novel and emerges from work previously accomplished in my K08 award, and establishes the MA pathway as integral to allergic eosinophilic inflammation in asthma. Our preliminary data show that excess pools of the isoprenoid molecules known as farnesylpyrophosphate (FPP) and geranylgeranyl-PP (GGPP) markedly augment interleukin-13-induced STAT6 activation and eotaxin-2 and -3 production in human airway epithelial cells in vitro, key molecular pathways in Th2/type 2 inflammation in asthma. Further, inhibition of FPP and GGPP synthesis with HMG-CoA reductase inhibitors (?statins?), the enzyme that synthesizes MA upstream of the isoprenoids, inhibits IL-13-induced eotaxin production and extracellular secretion. The eotaxins being a major chemokine for eosinophil recruitment into airway tissues, our results suggest that high levels of airway isoprenoids mediate and promote type 2 eosinophilic airway inflammation. Furthermore, our in vivo data using mouse models of asthma, confirm the critical role of the MA pathway in mediating allergic eosinophilic inflammation. Depleting MA pharmacologically, and therefore the downstream metabolites FPP and GGPP, significantly inhibits lung and airway eosinophilia. While these data are suggestive of their role in disease pathogenesis, they are limited to human airway epithelial cell culture and mouse models of asthma. Via this R03 proposal, we wish to establish the role of isoprenoids in human disease and ultimately determine if excess levels of airway mucosal isoprenoids correlate with degree of persistent airway eosinophilic inflammation in asthma. Therefore to address this gap in knowledge, we hypothesize that excess levels of airway epithelial isoprenoids enhance type 2 eosinophilic inflammation in vivo by further inducing epithelial JAK/STAT6 phosphorylation. We will address this hypothesis via two specific aims: (1) To determine if high levels of exogenous airway isoprenoids augment eosinophilic airway inflammation in vivo. (2) To validate a quantitative method of measuring airway and lung isoprenoids using specialized mass spectrometry in pre- existing animal and human tissues. Accomplishing these goals will establish the proof-of-principle that excess isoprenoids in vivo play a role in disease pathogenesis, and most importantly, provide the tools necessary to apply this technology to human asthmatics in future grant R01 grant applications.
We have discovered a role for the isoprenoid metabolites in amplifying airway mucosal eosinophilic responses relevant to human asthma. We will conduct proof-of-principle mouse experiments to address our main hypothesis and develop a novel specialized mass spectrometry method to measure the isoprenoids in human airways.
