Uropathogenic Escherichia coli Induces Serum Amyloid A in Mice following Urinary Tract and Systemic Inoculation Andreja Erman1, Katja Lakota2, Katjusa Mrak-Poljsak2, Matthew G. Blango3, Veronika Krizan-Hergouth4, Matthew A. Mulvey3, Snezna Sodin-Semrl2*, Peter Veranic1 1 Faculty of Medicine, Institute of Cell Biology, University of Ljubljana, Ljubljana, Slovenia, 2 Department of Rheumatology, University Medical Centre-Ljubljana, Ljubljana, Slovenia, 3 Division of Microbiology and Immunology, Department of Pathology, University of Utah, Salt Lake City, Utah, United States of America, 4 Faculty of Medicine, Institute of Microbiology and Immunology, University of Ljubljana, Ljubljana, Slovenia Abstract Serum amyloid A (SAA) is an acute phase protein involved in the homeostasis of inflammatory responses and appears to be a vital host defense component with protective anti-infective properties. SAA expression remains poorly defined in many tissues, including the urinary tract which often faces bacterial challenge. Urinary tract infections (UTIs) are usually caused by strains of uropathogenic Escherichia coli (UPEC) and frequently occur among otherwise healthy individuals, many of whom experience bouts of recurrent and relapsing infections despite the use of antibiotics. To date, whether SAA is present in the infected urothelium and whether or not the induction of SAA can protect the host against UPEC is unclear. Here we show, using mouse models coupled with immunofluorescence microscopy and quantitative RT-PCR, that delivery of UPEC either directly into the urinary tract via catheterization or systemically via intraperitoneal injection triggers the expression of SAA. As measured by ELISA, serum levels of SAA1/2 were also transiently elevated in response to UTI, but circulating SAA3 levels were only up-regulated substantially following intraperitoneal inoculation of UPEC. In in vitro assays, physiological relevant levels of SAA1/2 did not affect the growth or viability of UPEC, but were able to block biofilm formation by the uropathogens. We suggest that SAA functions as a critical host defense against UTIs, preventing the formation of biofilms both upon and within the urothelium and possibly providing clinicians with a sensitive serological marker for UTI. Citation: Erman A, Lakota K, Mrak-Poljsak K, Blango MG, Krizan-Hergouth V, et al. (2012) Uropathogenic Escherichia coli Induces Serum Amyloid A in Mice following Urinary Tract and Systemic Inoculation. PLoS ONE 7(3): e32933. doi:10.1371/journal.pone.0032933 Editor: Adam J. Ratner, Columbia University, United States of America Received July 22, 2011; Accepted February 3, 2012; Published March 12, 2012 Copyright: 2012 Erman et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by the Ministry of High Education, Science and Technology of Slovenia and National Institutes of Health (NIH) Public Health Service grants DK068585 and AI095647 (USA). M.G.B. was supported by NIH Microbial Pathogenesis Training Grant T32 AI055434. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: ssodin1@yahoo.com Introduction Upon entering the urinary tract, strains of uropathogenic Escherichia coli (UPEC) face a barage of both constitutive and inducible host defenses. Despite this hostile environment, which often includes the presence of antibiotics, UPEC is frequently able to establish itself within the host, multiply, and persist for many days to months. Persistence of UPEC within the bladder is in part attributable to the ability of these pathogens to invade urothelial cells where they can either multiply, forming large biofilm-like communities, or alternatively establish latent resevoirs which may ultimately lead to episodes of recurrent or relapsing urinary tract infections (UTIs) [1,2]. Persistent and recurring UTIs due to UPEC represent a major clinical and financial burden worldwide [1]. The development of better approaches for the prevention and treatment of UTIs is dependent upon improved understanding of UPEC virulence strategies as well as the make-up and limitations of the host defenses employed against UPEC. Serum amyloid A (SAA) is an acute phase protein thought to be involved in inflammation and homeostasis. SAA is a seemingly critical host defense component and has been reported to have beneficial properties in the protection against fungal, viral, and bacterial infections [3,4,5,6,7,8,9], and may help reduce the incidence of recurrent infections [4]. In planar lipid bilayers, SAA can assemble into hexameric structures, each containing a central channel of about 2.5 nm in diameter, and having the potential to damage bacterial membranes [10,11]. Overexpression of SAA by intestinal epithelial cells in culture can reduce E. coli viability [12], and in in vitro assays SAA can act as an opsonin for various Gram- negative bacteria by binding to the highly expressed outer membrane protein OmpA [9]. Of note, the ability of some E. coli strains to invade host cells and form biofilms is critically dependent upon OmpA [13,14,15,16]. Preferential binding of SAA to OmpA over endogenous host ligands, including high density lipoprotein (HDL) [4], may significantly impact both the host environment and pathogen fitness during the course of an infection. During acute phase responses to infection, SAA secretion by hepatocytes can be greatly increased, leading to highly elevated concentrations of SAA in the circulation. This phenomenon is common among vertebrate species. For example, LPS treatment stimulates SAA expression by salmon hepatocytes [17] and in zebrafish infection models, SAA is often among the most highly upregulated gene products [18,19,20,21]. In reindeer, as well as mice and humans, SAA can be used as a sensitive marker of the acute phase response to bacterial infection [22]. Similarities in SAA as an acute-phase marker in both mice and humans make mice an accessible model for investigating the regulatory and PLoS ONE | www.plosone.org 1 March 2012 | Volume 7 | Issue 3 | e32933