Particulate β-glucan activates early and delayed phagosomal maturation and autophagy within macrophage in a NOX-2 dependent manner

Abstract

AimsMacrophage is known to readily engulf any particulate material they encounter, including invading microbes and nano- or micro-particles. While recent studies show that some microparticles (MP) are immunogenic even without drug-cargo, the mechanism underlying this phenomenon is yet unclear. Phagocytosis induces NADPH oxidase-2 (NOX-2) mediated ROS generation that is reported to regulate antibacterial autophagy. We therefore, investigated the role of NOX-2 derived ROS in phagosomal maturation and autophagy induction in response to phagocytic uptake of two kinds of polymeric biodegradable and biocompatible microparticles: yeast-derived β-glucan particles (YDGP) and poly-(D, L-Lactic Acid) microparticles (PMP). Main methodsJ774A.1 macrophage wereas exposed to polymeric particles and the immune responses: ROS, phagosomal maturation and autophagy induction, were examined by assays including NBT, DCFH-DA, NADPH-Oxidase activity, Lysotracker and Acridine Orange. Further, the LC3 and NOX-2 expression were validated by RT-PCR, immunofluorescence assay and Western blotting. Antimicrobial activity of both MP was examined by CFU counting after administration to Mycobacterium tuberculosis and Salmonella typhimurium infected macrophage. Key findingsYDGP induces phagosomal maturation and acidic vesicle accumulation at 30 min and 24 h post-exposure, much more proficiently than that by PMP. YDGP exposure also induced NOX-2 dependent expression of light chain 3 (LC3-II), further confirmed as autophagy activation via autophagic flux assay with autophagolysosome inhibitor bafilomycin A1. Additionally, YDGP displayed superior anti-microbial activity than that by PMP. SignificanceThe induction of NOX-2-dependent autophagy and antimicrobial activity exhibited by particulate glucans has significant implications in harnessing these drug delivery vehicles as potential ‘value-added’ autophagy-mediated therapeutics in future.