Autophagy Induced by Palmitic Acid: a Brake in NAFLD Neutrophils

Abstract

Innate immune suppression and high blood fatty acid levels are the pathological basis of multiple metabolic diseases. Neutrophil vacuolation is an indicator of the immune status of patients, which is associated with autophagy-dependent granule degradation. Vacuolated neutrophils are observed in ethanol toxicity and septicemia patients due to the changes in their blood constituents, but how about the neutrophils in nonalcoholic fatty liver disease (NAFLD) patient is unknown. Here, we confirmed that an adhesion deficiency and an increased autophagy level existed in NAFLD neutrophils, and the three neutrophil granule subunits, namely, the azurophil granules, specific granules and gelatinase granules, could be engulfed by autophagosomes for degradation, and these autophagy-triggered granule degradation events were associated with vacuolation in palmitic acid (PA)-treated and NAFLD neutrophils. Concordantly, the adhesion-associated molecules CD11a, CD11b, CD18 and Rap1 on the three granule subunits were degraded during PA induced autophagy. Moreover, the cytosolic CD11a, CD11b, CD18 and Rap1 were targeted by Hsc70 and then delivered to lysosomal-like granules for degradation. Notably, in vitro and ex vivo, PA induced autophagy by inhibiting the p-PKC/PKD2 pathway. Overall, we showed that high blood PA level inhibited the p-PKC/PKD2 pathway to induce NAFLD neutrophil autophagy, which promoted the degradation of CD11a, CD11b, CD18 and Rap1 and further decreased the adhesion of neutrophils, thereby impairing the neutrophil function of NAFLD patients. This theory provides a new therapeutic strategy to improve the immune deficiency in NAFLD patients. Visual Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/438261v1_ufig1.gif" ALT="Figure 1"> View larger version (61K): org.highwire.dtl.DTLVardef@454a53org.highwire.dtl.DTLVardef@112a7e7org.highwire.dtl.DTLVardef@1cd397forg.highwire.dtl.DTLVardef@7a0058_HPS_FORMAT_FIGEXP M_FIG C_FIG Key PointsO_LIVacuolation and adhesion deficiency of NAFLD neutrophils are associated with autophagy-dependent granule degradation C_LIO_LIPA inhibits p-PKC/PKD2 to induce autophagy, which induces the degradation of CD11a, CD11b, CD18 and Rap1 and decreases neutrophil adhesion C_LI