The Essential Role of Selenoproteins on Macrophage phenotype switching in Helminth clearance
Open Access
- Author:
- Nelson, Shakira Melissa
- Graduate Program:
- Pathobiology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 22, 2013
- Committee Members:
- Kumble Sandeep Prabhu, Dissertation Advisor/Co-Advisor
Kumble Sandeep Prabhu, Committee Chair/Co-Chair
Margherita Teresa Anna Cantorna, Committee Member
Connie Jo Rogers, Committee Member
Pamela Hankey Giblin, Committee Member - Keywords:
- Selenium
macrophages
helminths
PPARgamma
NSAIDS
small intestines
Nippostrongylus brasiliensis - Abstract:
- Selenium (Se) is an essential micronutrient with anti-inflammatory properties that are fundamental to human health. A vital component of many metabolic pathways, an inverse causal relationship of Se with inflammatory diseases, including cancers, and infections has been suggested. While deficiency is frequently the center of discussion, some studies have emphasized the importance of different Se levels in disease regulation, establishing the true physiological significance of this element. The metabolic action of Se is seen through selenoproteins, which are synthesized by a complex mechanism. With over 25 identified selenoproteins, the health implications of these proteins are seen in their ability to decrease oxidative stress and inflammation. The study presented here aims to understand the anti-inflammatory effects of Se. Using a combination of ex-vivo and in-vitro macrophage models, the anti-inflammatory benefits of Se were investigated using a bacterial endotoxin, LPS, and Th-2 cytokine, IL-4, treated murine bone marrow derived macrophages (BMDM). Previous studies have shown that Se supplementation of macrophages led to a decrease in LPS-induced expression of inducible nitric oxide synthase (iNOS), a prototypical marker of classical (M1) macrophage activation. In the current study, IL-4 treated macrophages supplemented with 100 nM Se significantly increased the expression of alternatively activated macrophage (M2) markers, Arg-I, Ym1, and Fizz1. Se treatment also increased the enzymatic activity of Arg-I. Conversely, expression of classically activated macrophage (M1) markers, TNFα, iNOS, and IL1β, were significantly decreased in LPS treated macrophages cultured in 100 nM Se and IL-4, suggesting a synergistic effect of Se and IL-4. Interestingly, studies utilizing Trspfl/flCreLysM KO mice macrophages, characterized by a total loss of selenoprotein expression, or those lacking GPX1, a highly expressed selenoprotein, showed a complete abrogation of Arg-I activity, even under high Se (250nM) conditions, demonstrating the importance of selenoproteins for alternative macrophage activation, leading to attenuated inflammation. To effectively translate these findings into an in-vivo model, a gastrointestinal helminthic parasite model was used. The helminthic parasite Nippostrongylus brasiliensis (Nb) is a short-lived murine parasite that migrates from the skin via the lungs to the small intestines, before clearance 14 days after infection. Mice infected with Nb and supplemented with Se significantly increased the expression of the M2 markers Arg-I, Ym1, and Fizz1 in the small intestines, while decreasing the presence of intestinal worms and fecal eggs. To implicate macrophage-specific selenoproteins in resolution of the infection, Se supplemented Trspfl/flCreWT and Trspfl/flCreLysM mice were infected and compared. Results showed a complete abrogation of M2 marker expression with a significant increase in intestinal worms and fecal eggs in the Trsp KO mice, even in the presence of Se supplementation. Moreover, inhibition of the COX pathway using indomethacin, a non-specific COX inhibitor, stunted the expression of M2 markers despite high Se levels. Intriguingly, treatment of Nb-infected Se deficient mice with 15d-PGJ2, an anti-inflammatory prostaglandin metabolite of the COX pathway enhanced by dietary Se, partially recapitulated the effect of Se deficiency. Taken together, the experiments conducted in this dissertation suggest that optimal Se status, in the form of selenoproteins, is critical to shunt macrophage activation towards an M2 phenotype that promotes enhanced clearance of gastrointestinal parasites.