Modulation of airway epithelial syndecan-1 in a preclinical model of steroid-resistant asthma - PROJECT SUMMARY Syndecans are transmembrane cell surface proteoglycans that bind to cytokines and growth factors, and assist in the formation of scaffolds that support signaling of other cell surface receptors. Importantly, syndecan-1 (SDC1) is implicated in the control of IL-17A signaling. Transmembrane SDC1 (tmSDC1) is cleaved from the cell surface to generate soluble bioactive molecules that can become PAMPs/DAMPs, function as decoy receptors, and create chemokine gradients that augment inflammation. tmSDC1 is highly expressed on airway epithelial cells and its loss occurs concomitantly with E-cadherin and is considered a sign of epithelial-to-mesenchymal transition (EMT) and impaired airway epithelial barrier function. Soluble SDC1 is a biomarker in numerous fibrotic, oncogenic, and inflammatory diseases. tmSDC1 cleavage is caused predominantly by the enzyme heparanase (Hpse), which is secreted by inflammatory myeloid cells and lymphocytes. Specific Hpse inhibitors are being studied in early-phase clinical trials. We and others have reported on the anti-inflammatory effects of capsaicin, the active compound found in chili peppers and a potent TRPV1 agonist, which can inhibit IL-6 and TNFα secretion from macrophages, and can also inhibit NLRP3 inflammasome activation to suppress IL-1β secretion. Our lab has established a model of mixed-granulocytic, T2/T17, steroid-resistant severe allergic asthma, which has revealed the key role of IL-17A in driving airway neutrophilia and glucocorticoid resistance, while also establishing the importance of IL-6 and IL-1β in the development of T17 disease. sSDC1 levels are augmented in this severe allergic asthma model and capsaicin treatment reduces the release of sSDC1 from airway epithelial club cells. We hypothesize that cleavage of airway epithelial syndecan-1 (SDC1) by leukocyte-derived heparanases augments inflammation, barrier dysfunction, and steroid resistance in a mixed-granulocytic model of severe allergic asthma, and that this activity and its pathological consequences are inhibited by capsaicin. In SA1, we will evaluate the consequences of HDM-induced heparanase activity from mouse macrophages on mouse airway epithelial cell SDC1 cleavage. We will determine whether this upregulation of gene expression translates into increased enzyme activity, whether these effects can be abrogated by capsaicin in vitro, and whether macrophage Hpse activity induces airway epithelial cell tmSDC1 shedding. In SA2, we will determine the anti-heparanase effects of capsaicin on airway epithelial cells in vitro and lungs in vivo. We will determine whether the direct effects of Hpse on airway epithelial cells can be alleviated by capsaicin treatment. We will also determine in vivo if oral capsaicin can alleviate the inflammatory and steroid-resistant outcomes of our mixed-granulocytic model of severe allergic asthma and restore corticosteroid insensitivity. Identifying plant-derived dietary compounds that function as therapeutics to combat heparanase activity and altered proteoglycan homeostasis may provide a valuable alternative to pharmacological interventions in severe, treatment-resistant allergic airway disease. Fig. 1. Overall schematic of the central function of heparanase-modulated SDC1 and the steps of inhibition by capsaicin in vitro and in an in vivo model of mixed granulocytic severe allergic asthma.
