Leptin Receptor q223r Polymorphism Influences Clostridioides difficile Infection-Induced Neutrophil CXCR2 Expression in an Interleukin-1β Dependent Manner.

Olivia Horrigan,Alexander Huber,Shinsmon Jose,Divya Sharma,Rajat Madan,Anindita Mukherjee

doi:10.3389/fcimb.2021.619192

Abstract

Neutrophils are key first-responders in the innate immune response to C. difficile infection (CDI) and play a central role in disease pathogenesis. Studies have clearly shown that tissue neutrophil numbers need to be tightly regulated for optimal CDI outcomes: while excessive colonic neutrophilia is associated with severe CDI, neutrophil depletion also results in worse outcomes. However, the biological mechanisms that control CDI-induced neutrophilia remain poorly defined. C-X-C chemokine receptor 2 (CXCR2) is a chemotactic receptor that is critical in neutrophil mobilization from bone marrow to blood and tissue sites. We have previously reported that a single nucleotide polymorphism (SNP) in leptin receptor (LEPR), present in up to 50% of people, influenced CDI-induced neutrophil CXCR2 expression and tissue neutrophilia. Homozygosity for mutant LEPR (i.e. RR genotype) was associated with higher CXCR2 expression and more tissue neutrophils. Here, we investigated the biological mechanisms that regulate neutrophil CXCR2 expression after CDI, and the influence of host genetics on this process. Our data reveal that: a) CXCR2 plays a key role in CDI-induced neutrophil extravasation from blood to colonic tissue; b) plasma from C. difficile-infected mice upregulated CXCR2 on bone marrow neutrophils; c) plasma from C. difficile-infected RR mice induced a higher magnitude of CXCR2 upregulation and had more IL-1β; and d) IL-1β neutralization reduced CXCR2 expression on bone marrow and blood neutrophils and their subsequent accrual to colonic tissue. In sum, our data indicate that IL-1β is a key molecular mediator that communicates between gastro-intestinal tract (i.e. site of CDI) and bone marrow (i.e. primary neutrophil reservoir) and regulates the intensity of CDI-induced tissue neutrophilia by modulating CXCR2 expression. Further, our studies highlight the importance of host genetics in affecting these innate immune responses and provide novel insights into the mechanisms by which a common SNP influences CDI-induced neutrophilia.

Highlights

Clostridioides difficile infection (CDI) affects more than 500,000 people in the United States annually and is classified as one of the top 5 “urgent” public-health threats (CDC, 2019)
We have previously demonstrated that host genetic make-up impacts CDI-induced tissue neutrophilia: homozygosity for a common single nucleotide polymorphism (SNP) in leptin receptor (LEPR), rs1137101, that results in a change of amino acid at position 223 of LEPR from Glutamine [Q] to Arginine [R] (Duggal et al, 2011), is associated with an over-exuberant neutrophil response (Jose et al, 2018a)
We report that: (i) plasma from C. difficile-infected mice was sufficient to upregulate neutrophil CXC chemokine receptor 2 (CXCR2) expression; (ii) CDIinduced CXCR2 was upregulated only on a sub-population of neutrophils: CD11bhi neutrophils; and (iii) Interleukin (IL)-1b was a key driver of CDI-induced neutrophil CXCR2 expression and subsequent colonic neutrophil accumulation

Summary

Introduction

Clostridioides difficile infection (CDI) affects more than 500,000 people in the United States annually and is classified as one of the top 5 “urgent” public-health threats (CDC, 2019). C. difficile causes colonic tissue damage and elicits an intense systemic and tissue immune response that is pre-dominated by neutrophils (Keel and Songer, 2006; Jose and Madan, 2016; Smits et al, 2016). In animal models of CDI, too many colonic neutrophils are associated with severe tissue damage and high mortality (Keel and Songer, 2006), whereas neutrophil depletion is associated with higher mortality due to increased translocation of gut commensals into deeper tissues (Hasegawa et al, 2011; Jarchum et al, 2011; Jarchum et al, 2012). Neutrophil numbers need to be tightly regulated for optimal CDI outcomes. Despite a key role for neutrophils in disease pathogenesis, the underlying biological mechanisms that regulate systemic and tissue neutrophil numbers after CDI remain poorly defined

Methods

Results

Conclusion