Liver macrophage changes during early adaptation to alcohol exposure

Liver macrophages consist of both Kupffer cells (KCs) and infiltrating macrophages (IM), and both populations change during alcohol associated liver disease. It has been suggested that KCs undergo a pro-inflammatory change after alcohol exposure, but the extent to which a pro-inflammatory shift results from IMs rather than KC activation is unclear. The purpose of this study was to examine the early effects of alcohol exposure on KCs and IMs in a murine model and compare these effects to observations in human liver. Mice were fed the Lieber-Decarli ethanol diet and total liver macrophage, and KC specific phenotypes were examined by flow cytometry, ex vivo cell culture and KC single cell RNAseq. Liver tissues from autopsy and transplant patients with different alcohol phenotypes were assessed. Early alcohol exposure caused a shift in the properties of total liver macrophages with an initial pro-inflammatory effect that partially resolved by 10 days. KCs became steadily less inflammatory over the first 10 days of alcohol exposure. Alcohol exposure in the absence of liver disease also shifted macrophage phenotypes in human livers. These results show that early alcohol exposure is sufficient to cause KC adaptation in a way that maintains liver homeostasis and limits inflammation. Understanding the mechanisms of these changes and how to sustain them may help prevent the development of long-term liver injury. Overall design: We performed scRNAseq of liver Kupffer cells from chow fed mice and mice fed the Lieber-DeCarli liquid diet with 5% ethanol for either 3 or 10 days (n=1 mouse for each condition. Total nonparenchymal cells (NPCs) were isolated by liver perfusion, and FACS sorted F4/80-high, CD11b-intermediate cells were sequenced. Sequencing yield averaged 3,000-5,000 cells per sample and results from all 3 animals were combined for initial clustering.