The dimorphic fungus, Histoplasma capsulatum (Hc), is endemic to the Midwestern and Southeastern US and is the most frequent cause of fungal respiratory infection. Yeast cells thrive in the intracellular environment of macrophages (M?) until these phagocytes are activated by cytokines such as interferon-? or granulocyte M? colony-stimulating factor. The transcriptional elements that license M? to promote clearance of the fungus are largely unknown. We have discovered that the transcription factors hypoxia inducing factors (HIF)-1? and -2? calibrate the behavior of M? infected with Hc. In a recent publication, we reported that the lack of HIF-1? in M? exacerbates infection with Hc by promoting the generation of interleukin (IL)-10. The absence of both HIF-1? and -2? further exaggerates IL-10 production by M?. Excessive IL-10 dampens the ability of activating cytokines to arm the anti-Hc function of M?. We demonstrate that Hc induces HIFs and that pharmacologically inflating HIF accrual enhances the anti-Hc activity of mouse and human M?. These data triggered two hypotheses: 1) HIFs in M? are required to temper IL-10 generation, and 2) pharmacologically amplifying expression of HIFs arms M? to exert anti-Hc activity. To test these hypotheses, we propose three Specific Aims.
Aim 1 will examine the interplay between HIFs and metabolism. Specifically, we will determine if a glycolytic metabolite initiates and tumor necrosis factor-? sustains expression of HIFs. We will determine if overproduction of a specific metabolite by infected HIF-deficient cells promotes IL-10 release.
Specific Aim 2 will examine how HIFs regulate IL-10. We will determine if miRNA-27a is involved in the generation of IL-10 and if IL-10 modifies the metabolism of HIF- deficient cells. We will test the possibility that a metabolic product regulates the expression of an miRNA that controls the decay of IL-10 transcription. We will ascertain if IL-1receptor antagonist is a downstream effector of IL-10-mediated inhibition of M? function.
Specific Aim 3 will investigate how pharmacological activation of HIFs promotes the anti-Hc activity of M???We will identify a mechanism and the in vivo effect of these agents. We expect these studies to provide a greater understanding of the regulation of M? function in response to Hc.
Macrophages are a principal effector cell in combating histoplasmosis and require exogenous signals to limit intracellular growth. The transcription factors hypoxia-inducing factors-1? and -2? are needed for proper functioning of these cells. We will explore how these factors regulate the antifungal properties of macrophages.
