Escherichia coli Braun Lipoprotein (BLP) exhibits endotoxemia – like pathology in Swiss albino mice

Chikkamenahalli Lakshminarayana Lakshmikanth,Adriana R Silva,Sandeep Kumble Prabhu,Shancy Petsel Jacob,Cassiano F Goncalves-De-Albuquerque,Gopal Kedihithlu Marathe,Calivarathan Latchoumycandane,Hugo C Castro-Faria-Neto,Mosale Seetharam Sumanth,Thomas M Mcintyre,Avinash Kundadka Kudva,Puttaraju Srikanta Murthy Yashaswini,Sridevi Annapurna Singh

doi:10.1038/srep34666

Abstract

The endotoxin lipopolysaccharide (LPS) promotes sepsis, but bacterial peptides also promote inflammation leading to sepsis. We found, intraperitoneal administration of live or heat inactivated E. coli JE5505 lacking the abundant outer membrane protein, Braun lipoprotein (BLP), was less toxic than E. coli DH5α possessing BLP in Swiss albino mice. Injection of BLP free of LPS purified from E. coli DH5α induced massive infiltration of leukocytes in lungs and liver. BLP activated human polymorphonuclear cells (PMNs) ex vivo to adhere to denatured collagen in serum and polymyxin B independent fashion, a property distinct from LPS. Both LPS and BLP stimulated the synthesis of platelet activating factor (PAF), a potent lipid mediator, in human PMNs. In mouse macrophage cell line, RAW264.7, while both BLP and LPS similarly upregulated TNF-α and IL-1β mRNA; BLP was more potent in inducing cyclooxygenase-2 (COX-2) mRNA and protein expression. Peritoneal macrophages from TLR2−/− mice significantly reduced the production of TNF-α in response to BLP in contrast to macrophages from wild type mice. We conclude, BLP acting through TLR2, is a potent inducer of inflammation with a response profile both common and distinct from LPS. Hence, BLP mediated pathway may also be considered as an effective target against sepsis.

Highlights

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection[1]
100% of animals injected with 1 × 109 colony forming units (CFU) of live E. coli (DH5α) died within 48 hours while, 33.33% animals administered with 1 × 109 CFU of heat inactivated E. coli (DH5α) survived at the end of the experiment (Fig. 1A)
50% of animals injected with 1 × 109 CFU of live E. coli that lack Braun lipoprotein (BLP) (JE5505) survived at the end of the experiment while, only 16.66% mortality was observed in animals injected with heat inactivated E. coli (JE5505) (Fig. 1B)

Summary

Introduction

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection[1] It annually accounts for 19 million cases worldwide[2] and 1,400 deaths per day[3]. Attempts to abolish the inflammatory insult using monoclonal antibodies against LPS21,22, its receptor[23,24], and downstream signaling molecules[25,26,27], have been unsuccessful. This suggests LPS may not be the sole endotoxin of Gram negative bacteria. Each E. coli contains 105 molecules of BLP31, and so is the most abundant structural component of the bacterial membrane. BLP is more potent on a molar basis than its synthetic structural analogue Pam3CysSK4, a commercially available TLR2 agonist[30], so other components of the protein contribute to TLR2 activation

Methods

Results

Conclusion