Notch‐1 signaling through MCL‐1 modulates macrophage polarization and immune defense against Mycobacterium avium paratuberculosis infection in autoimmune disease

Abstract

We previously reported that IL‐6 plays a major role in the survival of Mycobacterium avium paratuberculosis (MAP) in infected macrophages. MAP has been associated with Crohn’s disease (CD) and Rheumatoid Arthritis (RA) pathogenesis. The role of Notch‐1 signaling in macrophages during intracellular infection such as MAP is not clearly understood. We hypothesis that IL‐6 expression in macrophages is induced by Notch‐1 signaling which inhibits apoptosis through Myeloid cell leukemia sequence‐1 (MCL‐1), which ultimately induce persistence of chronic infection. In this study, we measured the in vitro effect of MAP infection on Notch‐1 signaling and downstream influence on IL‐6 and MCL‐1. Specifically, we evaluated the role of Notch‐1 signaling in apoptosis and consequent MAP viability in infected macrophages and its effect on macrophage polarization and inflammatory response. Overall, the data showed that MAP infection upregulated Notch‐1, IL‐6, and MCL‐1 by (1.2, 1.8 and 4.2 fold expression, respectively) in activated THP‐1 compared to uninfected macrophages. Interestingly, treatment of MAP‐infected macrophages with IL‐6 showed upregulation of Notch‐1 and MCL‐1, which suggest a role for Notch‐1 and IL‐6 in the upregulation of MCL‐1 and possibly regulation of apoptosis in MAP infected macrophages. Targeting Notch signaling by a gamma‐secretase inhibitor resulted in decreased expression of IL‐6 and MCL‐1 (1.38 ± 0.32 and 0.63 ± 0.034, respectively) in infected macrophages compared to untreated macrophages (2.7 ± 0.25 and 2.0 ± 0.21, respectively). Moreover, gamma‐secretase inhibitor decreased MAP viability by 1.3 log CFU/ml. On the other hand, MAP modulates the macrophage polarization toward M1 macrophage polarization (M1/M2=2.20) compared uninfected macrophages (M1/M2=1.27), whereas the Notch inhibitor promotes M2 and diminish M1 macrophage polarization (M1/M2=0.76). Collectively, targeting Notch‐1 signaling will regulates the inflammatory response and enhances bacterial clearance in MAP infected macrophages. The study provides significant data that support the mechanistic role of Notch‐1 signaling in chronic infection in autoimmune disease.Support or Funding InformationThis work was funded, in part, by the Florida Legislative Grant.