Abstract

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common cause of chronic liver disease around the globe; however, the mechanisms that lead to the progression of metabolic liver disease are poorly understood. Liver-resident macrophages, known as Kupffer cells (KCs), are the largest population of macrophage in the human body, playing a critical role in immune sensing and tissue homeostasis. In the context of MASLD, KCs undergo cell death through an unclear mechanism, and monocytes enter the liver where they differentiate into macrophages. Next-generation sequencing and spatial-omics studies have revealed significant, heterogeneity in the recruited macrophage populations in both human and mouse models of MASLD. It is now known that macrophage subpopulations have distinct gene expression profiles and reside in specific niches within the liver. However, the functional role of these macrophage subsets during disease remains to be elucidated. This thesis aims to examine various facets of macrophage biology during MASLD in humans and mice to identify potential diagnostic and therapeutic targets. I first investigated how the early stages of human MASLD influence resident and recruited macrophages (MdMs) using several cellular and molecular approaches on patient tissues. I discovered that human and murine liver macrophages share similar cellular markers. Moreover, the number of human liver macrophages directly correlates with the level of steatosis. Further exploration using mouse models revealed that MdMs can engage in crosstalk with lipid-laden hepatocytes to alleviate hepatic lipid load. Next, I leveraged our understanding of the distinct markers expressed by KCs and MdMs by conducting non-invasive imaging with novel PET tracers target to resident or recruited macrophages. Using these radiotracers in a pre-clinical model of MASLD, I was able to assess the dynamic changes in macrophage populations using PET. The KC-specific probe used for in vivo imaging was further validated with human tissue, supporting the potential for this molecular imaging approach in clinical diagnosis and evaluation. This work has progressed into a clinical study of humans with MASLD which is actively enrolling patients. To further examine the biology of different macrophage subsets in mouse models of MASH, I explored the interaction between liver stromal cells and macrophages. Specifically, we found that hepatic stellate cells (HSCs), which mediate collagen production, closely interact with MdMs and promote their ability to degrade collagen. Additionally, I utilized a novel Trem2-driven Cre system and discovered that Trem2 is expressed as monocytes develop into macrophages. This finding may explain the widespread presence of TREM2+ monocyte-derived macrophages that occurs in response to injury in various tissues. Lastly, I investigated the impact of activating TFEB, a key regulator of lysosomal function and lipid metabolism, on KC fitness and liver pathology during MASLD. We demonstrated that activation of the TFEB pathway makes KCs resistant to oxidative stress and cell death by increasing NADPH levels via a reduction in de novo lipogenesis. These TFEB-induced KCs subsequently improve liver filtration and reduce steatosis during MASLD. Collectively, this thesis leverages patient samples, in vivo animal models, and in vitro mechanistic interrogation to explore several aspects of macrophage biology in MASLD. I confirmed the relevance of the murine model for studying human MASLD pathogenesis by demonstrating that hepatic macrophages have conserved features across species. Based on our understanding of macrophage heterogeneity, I validated novel molecular imaging probes designed to track macrophage subsets during disease. To dissect the cellular interaction in pathogenesis, I further explored how hepatic stromal cells can program macrophage function. Furthermore, I engaged a cell-intrinsic pathway in KCs that promoted their lipid metabolic function, survival, and resistance against oxidative stress, thereby reducing pathology. The data presented in this thesis represents a significant advance in our understanding of macrophage biology in the continuum of MASLD. These findings have the potential to drive the development of novel diagnostic tests and therapeutic targets that will impact the lives of patients with metabolic liver disease.

Committee Chair

Joel Schilling

Committee Members

Babak Razani; Brian Finck; Gwendalyn Randolph; Kory Lavine

Degree

Doctor of Philosophy (PhD)

Author's Department

Biology & Biomedical Sciences (Immunology)

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

7-30-2025

Language

English (en)

Author's ORCID

https://orcid.org/0000-0001-6511-0962

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