A Program Investigating New Concepts ofMacrophage Biology in Atherosclerosis and Atherosclerosis-MASH Cardiometabolic Disease - We propose a comprehensive, long-term program that addresses major gaps in our understanding of athero- sclerotic cardiovascular disease (CVD) and cardiometabolic disease. We explore new, disruptive concepts re- lated to the roles of the macrophage (Mφ) efferocytosis-resolution cycle in promoting a key feature of stable human atheroma, notably fibrous cap thickening. We will then integrate these concepts with an area of great interest to NHLBI, namely, the exacerbation of CVD by metabolic dysfunction-associated steatohepatitis (MASH, formerly NASH), with a focus on common mechanisms and therapeutic targets in atherosclerosis and MASH, particularly MASH with liver fibrosis. Major gaps that will be addressed include (1) What are the earliest upstream signaling events in effero-Mφs that activate athero-relevant resolution pathways, particularly fibrous cap for- mation? (2) What is the role of effero-Mφ crosstalk with adaptive immune cells in atherosclerosis? (3) How are lesional Mφs protected from the cellular stresses of efferocytosis? (4) Do atherosclerosis and MASH share com- mon mechanisms that are amenable to integrated therapy? (5) How does MASH fibrosis drive atherosclerosis? Based on exciting new data, our atherosclerosis studies will investigate: (1) a surprising pathway that serves as the initial trigger of resolution signaling in effero-Mφs; (2) a new mechanism of crosstalk between effero-Mφs and regulatory T cells; and (3) effero-induced repair of oxidatively damaged DNA, which is relevant to clonal hema- topoiesis, a risk factor for age-related CVD. Using both hypothesis-driven and unbiased 'omic' approaches, we will carry out mechanistic studies in human Mφs; causation studies in genetically altered mice; single-cell RNA- seq and cell-tracing studies to elucidate links between Mφ effero-resolution and fibrous cap formation; and anal- yses of human atheroma. We will then apply these concepts to the integrated topic of athero-MASH, with the hypothesis that impaired effero-induced reprogramming of Mφs to a repair phenotype is a common, therapeu- tically targetable mechanism of both of these linked diseases. This idea links the lab's work on Mφ effero- resolution in atherosclerosis with exciting new work showing that efferocytosis by liver Mφs is defective in MASH and promotes MASH fibrosis. Using a unique athero-MASH model with human-relevant features, in which spe- cific blockage of liver fibrosis promotes cap thickening in athero-lesions, we will elucidate which effero-resolution programs are relevant to both atherosclerosis and MASH and explore how MASH fibrosis exacerbates athero- sclerosis. We will then test the hypothesis that restoring efferocytosis to Mφs in the athero-MASH model through genetic engineering and, by way of translation, cutting-edge designer Mφ and RNA therapies, will have an additive or synergistic benefit for both diseases. In summary, by focusing on a key root cause of atherosclerosis, i.e., failed Mφ-mediated effero-resolution, and by studying atherosclerosis in the context of MASH, the R35 ad- dresses major gaps relevant to CVD and cardiometabolic disease. Moreover, a major goal is to train young scientists and continue our service to the cardiovascular community, which should amplify the benefit of the R35.
