Roles of Toll-like Receptors in Regulating Fibroblastic Reticular Cells Pathobiology during Sepsis

Abstract

Abstract Fibroblastic reticular cells (FRCs), a subpopulation of stromal cells in lymphoid organs and fat-associated lymphoid clusters (FALCs) in peritoneal fat, play immune-regulatory roles in the host defense. However, the mechanisms underlying the regulation of FRC pathobiology, especially in response to Toll-like receptor (TLR) signaling is unclear. Therefore, we aimed to understand the roles of TLR signaling in FRC pathobiology during sepsis. FALC cells were isolated from mesenteric adipose tissue in wild-type mice before and after cecal ligation and puncture (CLP). The transcriptomic profile of FALC cells were assessed using single cell RNA sequencing. Notably, FRCs were a major population of FALC cells (50 +/− 10.2 % in control, 30 +/− 8.6% in CLP). One population of FRCs were identified in control mice, and two populations of FRCs were identified in CLP mice. According to gene set enrichment analysis, FRCs after CLP are enriched in gene expression associated with inflammatory response and chemotaxis. Interestingly, activation of TLR4 (LPS) and TLR3 (Poly I:C) signaling in mesenteric adipose tissue derived FRCs significantly increased the expression of chemokines known to attract neutrophils (Cxcl2 and Cxcl5), monocytes (Cxcl3), and lymphocytes (Cxcl13 and Ccl20), while activation of TLR9 (ODN1518) significantly decreased these chemokine gene expressions. Importantly, we found similar regulatory effects of TLR3, 4, and 9 on chemokine production in human adipose tissue-derived FRCs. Together, our results indicate that TLRs plays critical roles in regulating chemokine production by FRCs. These data form a knowledge basis upon which to design new therapeutic strategies of FRC-based treatments for sepsis.