ORCID

0009-0002-7625-523X

Keywords

IL-6, MAP, MCT4, Crohn’s disease, intestinal epithelial injury, paratuberculosis, IBD

Abstract

Like TNFα, IL-6 is upregulated in Crohn’s disease (CD) associated with Mycobacterium avium paratuberculosis (MAP) infection. Limited therapeutic response to anti-IL-6 therapy may be related to the dual role of IL-6. In this study, we investigated the effects and the signaling mechanism of IL-6 in intestinal epithelial integrity and function during MAP infection using an in vitro model that consists of THP-1, HT-29 and Caco-2 cell lines. Clinically, we determined that plasma samples from MAP-infected CD patients have higher IL-6 levels compared to controls (P-value < 0.001). In CD-like macrophages, MAP infection has significantly upregulated the secretion of IL-6 and the shedding of IL-6 receptor (IL-6R). Moreover, it resulted in significant upregulation of intestinal damage markers including CLDN2, NOX-1 and SERPINE1. Blocking IL-6 signaling exacerbated that damage and enhanced the levels of the damage markers. In HT-29 cells, MAP infection upregulated MUC2 expression, a protective response that was reversed when IL-6R was neutralized. More importantly, blocking IL-6 signaling during MAP infection rescued damaged Caco-2 cells from MAP-induced apoptosis. We also examined the role of monocarboxylate transporter 4 (MCT4), a proton-coupled lactate symporter, that facilitates the inflammatory shift in macrophages, and its impact on intestinal epithelial homeostasis during MAP infection. MAP infection increased lactate export and upregulated the expression of MCT4, TNFα, and IL-6 via TLR2. Inhibition of MCT4 during MAP infection using α-cyano-4-hydroxycinnamic acid (CHCα) significantly reduced TNFα and IL-6 and led to restoring baseline oxidative status, mucin level, and SERPINE1. It also enhanced tight junction protein TJP1 (ZO-1) expression. These findings emphasize the role of IL-6 in MAP-associated CD pathogenesis and explain the ineffective response to IL-6 therapies in CD patients. Moreover, our findings revealed the role of MCT4 in CD pathophysiology during MAP infection and highlighted MCT4 as a potential therapeutic target for effective CD treatment.

Completion Date

2025

Semester

Spring

Committee Chair

Naser, Saleh A.

Degree

Doctor of Philosophy (Ph.D.)

College

College of Medicine

Department

Burnett School of Biomedical Sciences

Identifier

DP0029261

Document Type

Dissertation/Thesis

Campus Location

Orlando (Main) Campus

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