Protective role of OPN-High macrophages in NASH - Non-alcoholic steatohepatitis (NASH) is emerging as a major worldwide cause of liver disease in children and adults. Recent studies demonstrate substantial heterogeneity in the phenotype of macrophages (MFs) infiltrating the liver during NASH. Recruited MFs exist as two subsets, with distinct activation states: (1) those closely resembling homeostatic Kupffer cells (KCs), or (2) lipid-associated MFs (LAMs). In 2020, a cluster of LAMs with high expression of osteopontin (OPN) was identified in livers with NASH. Notably, LAMs are differentially activated, compared to resident- and monocyte-derived KCs, and with a distinct ability to metabolize lipids. However, whether they also crosstalk with neighboring cells, to prevent steatosis and fibrosis in NASH, remains unknown. While recruitment of MFs into the liver, and subsequent activation, are considered proinflammatory and profibrotic events, currently a significant knowledge gap is a lack of understanding of whether OPNHigh MFs, are detrimental or protective in NASH. Preliminary data demonstrates that Spp1KI Mye are protected, whereas Spp1ΔMye have worse NASH activity scores than WT mice. Thus, our results suggest a paradigm shift, in that OPNHigh MFs may protect from NASH. Yet, the intercellular communication, and preventive and therapeutic potential of OPNHigh MFs, remain to be determined. Our overarching hypothesis is that OPNHigh MFs, by signaling to hepatocytes (HEPs) and hepatic stellate cells (HSCs), reduce liver steatosis and fibrosis, and protect from NASH. Aim 1 is to identify how OPNHigh MFs protect from steatosis. We hypothesize that OPNHigh MFs signal HEPs to upregulate arginase-2 (ARG2), which increases mitochondrial bioenergetics and fatty acid oxidation (FAO), reduces nitrosative stress, and protects from steatosis. To test this, first, we will identify the OPNHigh MF ‘secretome’ proteins that signal HEPs to upregulate ARG2; second, we will determine how the identified OPNHigh MF secretome proteins transactivate the ARG2 promoter, in HEPs; and third, we will elucidate how ARG2 increases mitochondrial bioenergetics and FAO, and reduces nitrosative stress, in HEPs. Aim 2 is to dissect how OPNHigh MFs protect from fibrosis. We hypothesize that OPNHigh MFs signal through secretome proteins to lower collagen-I, and/or modify the ‘matrisome’ landscape, to prevent fibrosis, and regulate cell behavior, in NASH. To prove this, first, we will identify the OPNHigh MF secretome proteins that signal HSCs to lower collagen-I deposition and/or increase its degradation; second, we will analyze whether OPNHigh MFs modify the matrisome landscape, and establish the OPNHigh MF-ECM correlation network; and third, we will perform liver scRNA-seq, and computationally identify how the OPNHigh MF-ECM network regulates cell behavior in NASH.
