Intestinal Epithelial Serum Amyloid A Modulates Bacterial Growth In Vitro and Pro-Inflammatory Responses in Mouse Experimental Colitis

Abstract

BackgroundSerum Amyloid A (SAA) is a major acute phase protein of unknown function. SAA is mostly expressed in the liver, but also in other tissues including the intestinal epithelium. SAA reportedly has anti-bacterial effects, and because inflammatory bowel diseases (IBD) result from a breakdown in homeostatic interactions between intestinal epithelia and bacteria, we hypothesized that SAA is protective during experimental colitis.MethodsIntestinal SAA expression was measured in mouse and human samples. Dextran sodium sulfate (DSS) colitis was induced in SAA 1/2 double knockout (DKO) mice and in wildtype controls. Anti-bacterial effects of SAA1/2 were tested in intestinal epithelial cell lines transduced with adenoviral vectors encoding the CE/J SAA isoform or control vectors prior to exposure to live Escherichia coli.ResultsSignificant levels of SAA1/SAA2 RNA and SAA protein were detected by in situ hybridization and immunohistochemistry in mouse colonic epithelium. SAA3 expression was weaker, but similarly distributed. SAA1/2 RNA was present in the ileum and colon of conventional mice and in the colon of germfree mice. Expression of SAA3 was strongly regulated by bacterial lipopolysaccharides in cultured epithelial cell lines, whereas SAA1/2 expression was constitutive and not LPS inducible. Overexpression of SAA1/2 in cultured epithelial cell lines reduced the viability of co-cultured E. coli. This might partially explain the observed increase in susceptibility of DKO mice to DSS colitis. SAA1/2 expression was increased in colon samples obtained from Crohn's Disease patients compared to controls.ConclusionsIntestinal epithelial SAA displays bactericidal properties in vitro and could play a protective role in experimental mouse colitis. Altered expression of SAA in intestinal biopsies from Crohn's Disease patients suggests that SAA is involved in the disease process..

A single-cell survey of the small intestinal epithelium

“…9f); 40 genes induced in enterocytes, mostly (65%) in a Salmonella -specific manner (Extended Data Fig. 9d, Methods ) including the pattern-recognition receptor Nlrp6 ; and induction in distal enterocytes of the pro-inflammatory apolipoproteins Serum Amyloid A1 and 2 ( Saa1 and Saa2 ) 40 (Extended Data Fig. 9a,e).…”

Serum Amyloid A Stimulates PKR Expression and HMGB1 Release Possibly through TLR4/RAGE Receptors

“…For instance, despite the well-established pathogenic role of HMGB1 in infection-and injuryelicited inflammatory diseases (60,61), the disruption of HMGB1 expression adversely renders animals more susceptible to infectious (62) or injurious insults (63,64), reinforcing the dramatically distinct roles of HMGB1 in health and disease (65). Similarly, in an animal model of dextran sodium sulfate (DSS)-induced colitis, SAA1/2 knockout mice appeared to be more susceptible to colitis, possibly because the intestinal epithelia-derived SAAs are still critically needed for bactericidal activities (34). Thus, we used pharmacological approaches to evaluate the role of SAA in animal models of lethal systemic inflammation.…”

“…TLR2, TLR4 and RAGE KO mice and TLR2/RAGE and TLR4/RAGEdouble KO mice on a C57BL/6 genetic background were maintained at The Feinstein Institute for Medical Research as previously described (33). SAA1/2 knockout mice were generated by targeted deletion of the exon 2 of both Saa1 and Saa2 genes as previously described (34), and the knockout mice were backcrossed into a C57BL/6 genetic background. Because the KO mice were derived from C57BL/6 mice, small colonies of wild-type C57BL/6 (The Jackson Laboratory) were maintained under the same conditions.…”

Innate Immune Responses and Modified Extracellular Matrix Regulation Characterize Bacterial Infection and Cellular/Connective Tissue Changes in Scarring Trachoma

“…Serum amyloid A, of which SAA1 is a main isoform, is an acutephase protein which is raised in inflammatory diseases and has been shown to have antibacterial effects (19,39). The upregulation of these various proinflammatory, chemotactic, and antimicrobial mediators suggests an important role for the innate immune response in trachomatous scarring.…”