Functional role of kallikrein 5 and proteinase-activated receptor 2 in eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is a chronic, food antigen-driven, inflammatory disease of the esophagus and is associated with impaired barrier function. Evidence is emerging that loss of esophageal expression of the serine peptidase inhibitor, kazal type 7 (SPINK7), is an upstream event in EoE pathogenesis. Here, we provide evidence that loss of SPINK7 mediates its pro-EoE effects via kallikrein 5 (KLK5) and its substrate, protease-activated receptor 2 (PAR2). Overexpression of KLK5 in differentiated esophageal epithelial cells recapitulated the effect of SPINK7 gene silencing, including barrier impairment and loss of desmoglein-1 expression. Conversely, KLK5 deficiency attenuated allergen-induced esophageal protease activity, modified commensal microbiome composition, and attenuated eosinophilia in a murine model of EoE. Inhibition of PAR2 blunted the cytokine production associated with loss of SPINK7 in epithelial cells and attenuated the allergen-induced esophageal eosinophilia in vivo. Clinical samples substantiated dysregulated PAR2 expression in the esophagus of patients with EoE, and delivery of the clinically approved drug α1 antitrypsin (A1AT, a protease inhibitor) inhibited experimental EoE. These findings demonstrate a role for the balance between KLK5 and protease inhibitors in the esophagus and highlight EoE as a protease-mediated disease. We suggest that antagonizing KLK5 and/or PAR2 has potential to be therapeutic for EoE.

The antiprotease SPINK7 serves as an inhibitory checkpoint for esophageal epithelial inflammatory responses

Loss of barrier integrity has an important role in eliciting type 2 immune responses, yet the molecular events that initiate and connect this with allergic inflammation remain unclear. We reveal an endogenous, homeostatic mechanism that controls barrier function and inflammatory responses in esophageal allergic inflammation. We show that a serine protease inhibitor, SPINK7 (serine peptidase inhibitor, kazal type 7), is part of the differentiation program of human esophageal epithelium and that SPINK7 depletion occurs in a human allergic, esophageal condition termed eosinophilic esophagitis. Experimental manipulation strategies reducing SPINK7 in an esophageal epithelial progenitor cell line and primary esophageal epithelial cells were sufficient to induce barrier dysfunction and transcriptional changes characterized by loss of cellular differentiation and altered gene expression known to stimulate allergic responses (for example, FLG and SPINK5). Epithelial silencing of SPINK7 promoted production of proinflammatory cytokines including thymic stromal lymphopoietin (TSLP). Loss of SPINK7 increased the activity of urokinase plasminogen-type activator (uPA), which in turn had the capacity to promote uPA receptor-dependent eosinophil activation. Treatment of epithelial cells with the broad-spectrum antiserine protease, α1 antitrypsin, reversed the pathologic features associated with SPINK7 silencing. The relevance of this pathway in vivo was supported by finding genetic epistasis between variants in TSLP and the uPA-encoding gene, PLAU We propose that the endogenous balance between SPINK7 and its target proteases is a key checkpoint in regulating mucosal differentiation, barrier function, and inflammatory responses and that protein replacement with antiproteases may be therapeutic for select allergic diseases.