Purpose: Phagocytes fight fungi using canonical and noncanonical, also called LC3-associated phagocytosis (LAP), autophagy pathways. By allowing efficient pathogen clearance and/or degradation of inflammatory mediators, autophagy play a broad role in cellular and immune homeostasis during fungal infections. Recently, several studies have demonstrated that LAP but not canonical autophagy participates in the degradation of engulfed Aspergillus conidia. We have described an IFN-γ/DAPK1 signaling that mediates LAP, critical for dampening Aspergillus-triggered immunopathology. Accordingly, mice defective for LAP exhibit increased fungal burden, pathological inflammation and pro-inflammatory cytokine levels. Moving forward we focused our attention in murine and human chronic granulomatous disease (CGD), in which defective LAP, increased inflammation and infectious susceptibility have been described.
Methods: We assessed the contribution of canonical vs noncanonical autophagy in the host response to A. fumigatus in vitro and in vivo. We subjected C57BL/6 and p47phox-/- mice (CGD) to treatment with rapamycin, a known inducer of canonical autophagy, and IFN-γ, known to activate LAP. We also resorted to Indo–/– mice to assess the possible regulatory activity between canonical autophagy and LAP, given the defective tryptophan-starvation autophagy in these mice.
Results: The results show that: a) DAPK1-dependent LAP was defective in p47phox−/−infected mice and in vitro in both p47phox−/− lung macrophages and monocytes from CGD patients. b) Treatment with IFN-γ restored DAPK1-dependent LAP, reduced the fungal growth, and decreased IL-1β production in infection. Similarly, IFN-γ restored DAPK1 expression in vitro and decreased inflammation in murine and human CGD mononuclear cells, a finding suggesting the drugability of DAPK1 in CGD by IFN-γ therapy. c) Canonical autophagy but not LAP was defective in Indo–/– macrophages in vitro. Blocking DAPK1 greatly increased the fungal burden and the inflammatory response in infected Indo–/– mice. d) Rapamycin failed to increase resistance to infection when administered in conventional C57BL/6 and CGD mice with pulmonary aspergillosis. Actually, treatment with rapamycin reduced survival, impeded fungal clearance and greatly promoted inflammation.
Conclusion: Our results clearly indicate that LAP, and not canonical autophagy, pivotally contributes to the control of infection and inflammation at the fungus/host interface. Moreover, they suggest a possible cross-regulatory activity between canonical autophagy and LAP during infection. The ability of LAP to execute pathogen clearance while simultaneously attenuating inflammation, points to DAPK1-dependent LAP as an ideal drugable pathway in immune homeostasis during infections and demands for a better understanding on molecular mechanisms behind the relationship between the different forms of autophagy.
Full conference title:
- AAA 8th (2018)