Noncanonical autophagy inhibits the autoinflammatory, lupus-like response to dying cells

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Abstract

Defects in clearance of dying cells have been proposed to underlie the pathogenesis of systemic lupus erythematosus (SLE)1. Mice lacking molecules associated with dying cell clearance develop SLE-like disease2, and phagocytes from patients with SLE often display defective clearance and increased inflammatory cytokine production when exposed to dying cellsin vitro. Previously, we3,4,5,6and others7described a form of noncanonical autophagy known as LC3-associated phagocytosis (LAP), in which phagosomes containing engulfed particles, including dying cells3,4,7, recruit elements of the autophagy pathway to facilitate maturation of phagosomes and digestion of their contents. Genome-wide association studies have identified polymorphisms in theAtg5(ref.8) and possiblyAtg7(ref.9) genes, involved in both canonical autophagy and LAP3,4,5,6,7, as markers of a predisposition for SLE. Here we describe the consequences of defective LAPin vivo. Mice lacking any of several components of the LAP pathway show increased serum levels of inflammatory cytokines and autoantibodies, glomerular immune complex deposition, and evidence of kidney damage. When dying cells are injected into LAP-deficient mice, they are engulfed but not efficiently degraded and trigger acute elevation of pro-inflammatory cytokines but not anti-inflammatory interleukin (IL)-10. Repeated injection of dying cells into LAP-deficient, but not LAP-sufficient, mice accelerated the development of SLE-like disease, including increased serum levels of autoantibodies. By contrast, mice deficient in genes required for canonical autophagy but not LAP do not display defective dying cell clearance, inflammatory cytokine production, or SLE-like disease, and, like wild-type mice, produce IL-10 in response to dying cells. Therefore, defects in LAP, rather than canonical autophagy, can cause SLE-like phenomena, and may contribute to the pathogenesis of SLE.

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