Intestinal Toll-like receptor 9 deficiency leads to Paneth cell hyperplasia and exacerbates kidney, intestine, and liver injury after ischemia/reperfusion injury.

Intestinal Paneth cells play a critical role in ischemic acute kidney injury (AKI) by releasing interleukin 17A (IL-17A). Because Toll-like receptor 9 (TLR9) activation degranulates Paneth cells and necrotic tubular epithelial cells release several damage associated molecular patterns that target TLR9, we tested the hypothesis that intestinal TLR9 deficiency would protect against ischemic AKI and associated remote intestinal and hepatic dysfunction by decreasing Paneth cell degranulation. We generated mice lacking TLR9 in intestinal epithelia (TLR9fl/fl Villin Cre mice) and compared them to wild type (TLR9fl/fl) mice following right nephrectomy and left ischemia/reperfusion. To our surprise, mice lacking intestinal TLR9 had exacerbated kidney, liver, and small intestine injury after ischemia/reperfusion compared to wild type mice, characterized by increased kidney and intestinal inflammation, apoptosis, and necrosis as well as increased hepatic inflammation and apoptosis. Mice lacking intestinal TLR9 had larger Paneth cell granule size, pronounced intestinal macrophage infiltration, and higher intestinal crypt IL-17A expression. Administration of IL-17A neutralizing antibody prevented the exacerbation of ischemic AKI in mice lacking intestinal TLR9. These studies suggest that intestinal TLR9 activation protects against ischemic AKI and associated remote multi-organ dysfunction syndrome by regulating Paneth cell IL-17A synthesis.