PPARγ Controls Dectin-1 Expression Required for Host Antifungal Defense against Candida albicans

Abstract

We recently showed that IL-13 or peroxisome proliferator activated receptor γ (PPARγ) ligands attenuate Candida albicans colonization of the gastrointestinal tract. Here, using a macrophage-specific Dectin-1 deficient mice model, we demonstrate that Dectin-1 is essential to control fungal gastrointestinal infection by PPARγ ligands. We also show that the phagocytosis of yeast and the release of reactive oxygen intermediates in response to Candida albicans challenge are impaired in macrophages from Dectin-1 deficient mice treated with PPARγ ligands or IL-13. Although the Mannose Receptor is not sufficient to trigger antifungal functions during the alternative activation of macrophages, our data establish the involvement of the Mannose Receptor in the initial recognition of non-opsonized Candida albicans by macrophages. We also demonstrate for the first time that the modulation of Dectin-1 expression by IL-13 involves the PPARγ signaling pathway. These findings are consistent with a crucial role for PPARγ in the alternative activation of macrophages by Th2 cytokines. Altogether these data suggest that PPARγ ligands may be of therapeutic value in esophageal and gastrointestinal candidiasis in patients severely immunocompromised or with metabolic diseases in whom the prevalence of candidiasis is considerable. Since the early 1980s, Candida albicans has emerged as major cause of human disease, especially among immunocompromised individuals and those with metabolic dysfunction. The main host defense mechanisms against this yeast are engulfment and the production of reactive oxygen molecules by macrophages through Dectin-1 and the Mannose Receptor, two macrophage receptors for Candida albicans cell wall sugars. However, the contribution of these two receptors remains unclear. In our animal experiments, the lack of Dectin-1 in macrophages renders the animals more susceptible to gastrointestinal infection with Candida albicans, demonstrating the essential role of Dectin-1 in antifungal defense. In addition, our experiments established that the interaction between Dectin-1 and Mannose Receptor is important to orchestrate the host antifungal defense. Thus, Candida albicans clearance would be improved by Dectin-1 and Mannose Receptor up-regulation. Interestingly, we had established that the expression of these two receptors was increased by IL-13 through the activation of the nuclear receptor PPARγ, suggesting that PPARγ could be a therapeutic target to eliminate fungal infection. This paper, which highlights a new area of application of PPARγ ligands in infectious diseases, hence heralds the emergence of a new therapeutic strategy against fungal infection in severely immunocompromised patients or those with metabolic diseases.