LC3-associated phagocytosis in macrophage responses to Paracoccidioides spp

TL;DR

This study shows that LC3-associated phagocytosis helps macrophages fight Paracoccidioides fungi, a cause of a Latin American disease, and suggests it could be a target for new treatments.

Contribution

The study reveals that LAP is involved in macrophage defense against Paracoccidioides spp. with distinct activation mechanisms compared to other fungi.

Findings

LC3 recruitment to phagosomes was observed in macrophages infected with Paracoccidioides spp.

ATG5 RNA interference reduced antifungal activity in J774.16 cells, showing LAP's importance.

Syk and NADPH inhibition did not affect LAP against P. brasiliensis, indicating unique activation pathways.

Abstract

Paracoccidioidomycosis (PCM) is a systemic infection that is endemic to Latin America, caused by thermodimorphic fungi from the Paracoccidioides genus. These fungi are facultative intracellular parasites of macrophages. LC3-associated phagocytosis (LAP), a non-canonical form of autophagy, plays a critical role in the response of these phagocytes to similar pathogens.

In this study, we investigated the role of LAP in the macrophage responses to Paracoccidioides spp.

We detected LAP in macrophages infected with Paracoccidioides spp by immunofluorescence microscopy with antibodies to LC3. Piceatannol and diphenyleneiodonium chloride (DPI), respectively Syk and nicotinamide adenine dinucleotide phosphate oxidase (NADPH) inhibitors, were used to understand the role their pathways played. To determine the function of LAP, we targeted ATG5, a key autophagy gene, by RNA interference.

We observed LC3 recruitment to phagosomes containing Paracoccidioides spp. in RAW264.7 and J774.16 cell lines and in bone marrow-derived macrophages. ATG5 RNA interference reduced the antifungal activity of J774.16 cells, highlighting the importance of LC3 recruitment for effective fungal control. Interestingly, pharmacological inhibition of Syk kinase and NADPH oxidase pathways, essential for LAP against Aspergillus fumigatus and Candida albicans, did not impair LAP against P. brasiliensis.

This suggests distinct triggering mechanisms, possibly due to differences in the fungal cell surface composition. These findings suggest that LAP plays a significant role in the host defense against Paracoccidioides spp. and may represent a promising target for host-directed PCM therapies.

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