Studying Macrophages in the Murine Steatotic Liver Using Flow Cytometry and Confocal Microscopy

The study of macrophage functions in the context of metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction associated steatohepatitis (MASH) has been hampered by the fact that until recently all macrophages in the liver were thought to be Kupffer cells, the resident macrophages of the liver. With the advent of single-cell technologies, it is now clear that the steatotic liver harbors many distinct populations of macrophages, likely each with their own unique functions as well as subsets of monocytes and dendritic cells which can be difficult to discriminate from one another. Here, we detail the protocols we utilize to (i) induce MASLD/MASH in mice, (ii) isolate cells from the steatotic liver, and (iii) describe reliable gating strategies, which can be used to identify the different subsets of myeloid cells. Finally, we also discuss the issue of increased autofluorescence in the steatotic liver and the techniques we use to minimize this both for flow cytometry and confocal microscopy analyses.

Lipid-associated macrophages transition to an inflammatory state in human atherosclerosis increasing the risk of cerebrovascular complications

The immune system is integral to cardiovascular health and disease. Targeting inflammation ameliorates adverse cardiovascular outcomes. Atherosclerosis, a major underlying cause of cardiovascular disease (CVD), is conceptualised as a lipid-driven inflammation where macrophages play a non-redundant role. However, evidence emerging so far from single cell atlases suggests a dichotomy between lipid associated and inflammatory macrophage states. Here, we present an inclusive reference atlas of human intraplaque immune cell communities. Combining scRNASeq of human surgical carotid endarterectomies in a discovery cohort with bulk RNASeq and immunohistochemistry in a validation cohort (the Carotid Plaque Imaging Project-CPIP), we reveal the existence of PLIN2hi/TREM1hi macrophages as a toll-like receptor-dependent inflammatory lipid-associated macrophage state linked to cerebrovascular events. Our study shifts the current paradigm of lipid-driven inflammation by providing biological evidence for a pathogenic macrophage transition to an inflammatory lipid-associated phenotype and for its targeting as a new treatment strategy for CVD.