Project description:Glycosylation is central to the localization and function of biomolecules1. We recently discovered that small RNAs undergo N-glycosylation2 at the modified RNA base 3-(3-amino-3-carboxypropyl) uridine (acp3U)3. However, the functional significance of N-glycosylation of RNAs is unknown. Here we show that the N-glycans on glycoRNAs prevent innate immune sensing of endogenous small RNAs. We found that de-N-glycosylation of cell culture-derived and circulating human and mouse glycoRNA elicited potent inflammatory responses including the production of type I interferons in a TLR3- and TLR7-dependent manner. Further, we show that N-glycans of cell surface RNAs prevent apoptotic cells from triggering endosomal RNA sensors in efferocytes, thus facilitating the non-inflammatory clearance of dead cells. Mechanistically, N-glycans conceal the hypermodified uracil base acp3U, which we identified as immunostimulatory when exposed in RNA. Consistent with this, genetic deletion of an enzyme (DTWD2) that synthesizes acp3U abrogated innate immune activation by de-N-glycosylated of small RNAs and apoptotic cells. Additionally, synthetic acp3U-containing RNAs are sufficient to trigger innate immune responses. Thus, our study has uncovered a natural mechanism by which N-glycans block RNAs from inducing acp3U-driven innate immune activation, demonstrating how glycoRNAs exist on the cell surface and in the endosomal network without inducing autoinflammatory responses.
Project description:The phagocytic clearance of apoptotic cells, termed efferocytosis, is essential for both tissue homeostasis and tissue health during cell death-inducing treatments. Failure to efficiently clear apoptotic cells augment the risk of pathological inflammation and has been linked to a myriad of autoimmune and inflammatory diseases. Although past studies have elucidated local molecular signals that regulate homeostatic efferocytosis in a tissue, whether signals arising distally also regulate homeostatic efferocytosis remains elusive. Interestingly, clinical evidence suggests that prolonged use of broad-spectrum antibiotics is associated with an increased risk of autoimmune and inflammatory disease development. We therefore hypothesized that intestinal microbes produce molecular signals that regulate efferocytotic ability in tissue phagocytes beyond the intestines. Here, we find that macrophages, the body’s professional phagocyte, display impaired efferocytosis in the peritoneum of broad-spectrum antibiotics (ABX)-treated, vancomycin-treated, and germ-free mice in vivo, the latter of which could be rescued by fecal microbiota transplantation. Mechanistically, the microbiota-derived short-chain fatty acid butyrate directly boosted efferocytosis efficiency and capacity in mouse and human macrophages, with both intestinal and local delivery of butyrate capable of rescuing ABX-induced large peritoneal macrophage (LPM) efferocytosis defects. Bulk mRNA sequencing of butyrate-treated primary macrophages in vitro and single cell mRNA sequencing of LPMs isolated from ABX-treated and butyrate-rescued mice revealed specific regulation of efferocytosis-supportive transcriptional programs. Specifically, we found that the efferocytosis receptor T-cell immunoglobulin and mucin domain containing 4 (TIM-4, Timd4) was downregulated in LPMs of ABX-treated mice which was rescued by oral butyrate and that TIM-4 was required for the butyrate-induced enhancement of LPM efferocytosis capacity in vivo. Strikingly, LPM efferocytosis was impaired well-beyond withdrawal of ABX and, importantly, ABX-treated mice exhibited significantly worse disease in a mouse model of system lupus erythematosus. Collectively, our results demonstrate that homeostatic efferocytosis relies on distal molecular signals and suggest that a defect in homeostatic efferocytosis may contribute to the clinically observed link between broad-spectrum antibiotics use and inflammatory disease.
Project description:The clearance of apoptotic cells, termed efferocytosis, is essential for tissue homeostasis and prevention of autoimmunity. Although past studies have elucidated local molecular signals that regulate homeostatic efferocytosis1 in a tissue, whether signals arising distally also regulate homeostatic efferocytosis remains elusive. Here, we find that large peritoneal macrophages (LPMs) display impaired efferocytosis in broad-spectrum antibiotics (ABX)-treated, vancomycin-treated, and germ-free mice in vivo. Mechanistically, the microbiota-derived short-chain fatty acid butyrate directly boosted efferocytosis efficiency/capacity in mouse and human macrophages, and rescued ABX-induced LPM efferocytosis defects in vivo. Bulk mRNA sequencing of butyrate-treated macrophages in vitro and single cell mRNA sequencing of LPMs isolated from ABX-treated and butyrate-rescued mice revealed regulation of efferocytosis-supportive transcriptional programs. Specifically, we found that the efferocytosis receptor T-cell immunoglobulin and mucin domain containing 4 (TIM-4, Timd4) was downregulated in LPMs of ABX-treated mice but rescued by oral butyrate and TIM-4 was required for the butyrate-induced enhancement of LPM efferocytosis capacity. LPM efferocytosis was impaired beyond withdrawal of ABX and ABX-treated mice exhibited significantly worse disease in a mouse model of lupus. Our results demonstrate that homeostatic efferocytosis relies on distal metabolic signals and suggest that defective homeostatic efferocytosis may explain link between ABX use and inflammatory disease.
Project description:The clearance of apoptotic cells, termed efferocytosis, is essential for tissue homeostasis and prevention of autoimmunity. Although past studies have elucidated local molecular signals that regulate homeostatic efferocytosis1 in a tissue, whether signals arising distally also regulate homeostatic efferocytosis remains elusive. Here, we find that large peritoneal macrophages (LPMs) display impaired efferocytosis in broad-spectrum antibiotics (ABX)-treated, vancomycin-treated, and germ-free mice in vivo. Mechanistically, the microbiota-derived short-chain fatty acid butyrate directly boosted efferocytosis efficiency/capacity in mouse and human macrophages, and rescued ABX-induced LPM efferocytosis defects in vivo. Bulk mRNA sequencing of butyrate-treated macrophages in vitro and single cell mRNA sequencing of LPMs isolated from ABX-treated and butyrate-rescued mice revealed regulation of efferocytosis-supportive transcriptional programs. Specifically, we found that the efferocytosis receptor T-cell immunoglobulin and mucin domain containing 4 (TIM-4, Timd4) was downregulated in LPMs of ABX-treated mice but rescued by oral butyrate and TIM-4 was required for the butyrate-induced enhancement of LPM efferocytosis capacity. LPM efferocytosis was impaired beyond withdrawal of ABX and ABX-treated mice exhibited significantly worse disease in a mouse model of lupus. Our results demonstrate that homeostatic efferocytosis relies on distal metabolic signals and suggest that defective homeostatic efferocytosis may explain link between ABX use and inflammatory disease.