Extracellular Acidification Impairs Macrophage Lipophagy Through ASIC1/RIP1 Pathway / 生物化学与生物物理进展

ABSTRACT

ObjectiveOur recent study has demonstrated that extracellular acidification promotes lipid accumulation in macrophages via the activation of acid sensing ion channel 1 (ASIC1), but the underlying mechanism remains unclear. This study aims to explore the effect of extracellular acidification on macrophage lipophagy and the underlying mechanism. MethodsRAW264.7 macrophages were incubated with 25 mg/Lox-LDL in a pH 6.5 culture medium for 24 h to build macrophage-derived foam cell models induced by extracellular acidification. Then, RAW264.7 macrophages were cultured in the acidic medium of pH 6.5 with or without PcTx-1 (ASIC1 specific blocker, 10 μg/L) or Nec-1 (RIP1 specific inhibitor, 20 μmol/L) for 24 h, intracellular lipid accumulation was observed by oil red O staining. The expressions of total ASIC1, plasma membrane ASIC1, RIP1, p-RIP1 Ser166, TFEB, p-TFEB Ser142, LC3 and p62 were measured by Western blot. The co-localization of lipids (indicated by Bodipy) with LC3II (autophagosomes) and LAMP1 (lysosomes) was analyzed by a confocal laser scanning microscopy, respectively. Morphological changes of lipophagy in the cells were observed by using transmission electron microscopy. ABCA1-mediated cholesterol efflux was determined by cholesterol fluorescence kits. ResultsCompared with pH 7.4+ox-LDL group, the intracellular lipid accumulation in the pH 6.5+ox-LDL group was significantly increased. Meanwhile, the expressions of plasma membrane ASIC1, p-RIP1 Ser166, p-TFEB Ser142, and p62 proteins were elevated significantly, while LC3II protein level and LC3II/LC3I ratio were decreased. Accordingly, compared with pH 7.4+ox-LDL group, the macrophage lipophagy of the pH 6.5+ox-LDL group was inhibited as indicated by the decreased localization of lipid droplets with LC3 and LAMP1, a decrease in the number of lipophagosomes as well as an increase in lipid droplets. Furthermore, ATP binding cassette transporter A1 (ABCA1)-dependent cholesterol efflux from the macrophages of pH 6.5+ox-LDL group reduced dramatically. However, these above effects of extracellular acidification on RAW264.7 macrophages were abolished by PcTx-1 and Nec-1, respectively. ConclusionThese findings suggest extracellular acidification promotes the phosphorylation of TFEB at Ser142 via activating ASIC1/RIP1 pathway, thereby impeding lipophagy in RAW 264.7 macrophages, and that ASIC1 may be a new potential target for preventing aberrant lipid accumulation diseases including atherosclerosis.