Periodic Reporting for period 4 - MyeFattyLiver (Unravelling the heterogeneity and functions of hepatic myeloid cells in Non-Alcoholic Fatty Liver Disease)
Periodo di rendicontazione: 2024-06-01 al 2025-05-31
Non-alcoholic fatty liver disease (NAFLD) recently renamed metabolic dysfunction associated steatotic liver disease (MASLD) represents a spectrum of disease states ranging from simple steatosis (a build-up of lipid in the liver) to the more end stage of the disease characterised by fibrosis, cirrhosis and potentially even cancer (termed HCC). Due to the ongoing obesity epidemic, MASLD has become the disease of the Western world. It is already the biggest cause of HCC in the Western world and by 2030 it is predicted to be the main cause of liver transplantation. Despite this, we still do not have any therapeutic options for patients and while weight loss can be effective early, this is not sufficient at the end stages of the disease spectrum. Immune cells such as macrophages and dendritic cells have been proposed to play crucial roles in driving the progression of MASLD, but we still do not fully understand what roles they play. This is because in recent years it has become clear that there are many different subsets of these cells in the liver, likely performing different functions. In the past, these cells have been studied collectively, however now it's clear that we need to split these up and study them individually to fully understand their unique contributions to MASLD progression. This was the goal of this project. In MyeFattyLiver, we aimed to investigate the different subsets of these cells in both MASLD mouse models and patient liver samples. We wanted to understand which subsets are there and most importantly what each subset does. Using a range of state-of-the-art techniques including single cell and spatial transcriptomics with MyeFattyLiver we have been able to unravel the heterogeneity of myeloid cells in MASLD. We have shown that MASLD results in both the activation and loss of the resident liver macrophages, called Kupffer cells (KCs) and the recruitment of monocytes from the bone marrow which differentiate in the liver towards distinct types of macrophages namely monocyte-derived KCs (moKCs) or lipid associated macrophages (LAMs). Importantly these subsets are highly conserved in human MASLD and we were able to define key conserved gene signatures allowing the different populations to be identified across species and studies. We have also demonstrated a role for efferocytosis of injured/dying cells in driving the LAM phenotype, hinting at how we could generate these cells in vitro. Functionally, we have shown that LAMs and activated KCs (called LAM-like KCs) are critical for tissue repair and preventing fibrosis. This highlights the potential of these cells for future exploitation for therapeutic approaches which could be used to slow and prevent or possibly even reverse MASLD progression.
We utilised state-of-the-art technologies including single cell and spatial transcriptomic approaches to investigate the different subsets of myeloid cells present in the liver in murine MASLD models and in patients with MASLD. Moreover, these technologies allow us to study where in the liver these cells are and with which other cells they interact. This analysis has allowed us to, for the first time, accurately identify the different macrophage and dendritic cell subsets in the healthy and obese human liver. We have identified markers for these different populations so that any lab can now study the different subsets specifically. Utilising different genetic mouse models, we have also been able to determine the functions of these different macrophage populations at different stages of MASLD progression. This has led to three publications to date, 1 in Cell and 2 in Immunity. There are an additional 3 papers currently being prepared for submission. Moreover, these results have been disseminated at multiple conferences and shared with the public at different outreach events. These data are currently being further interrogated to determine how they can be exploited for therapeutic gain, for example through the generation of the different subsets in vitro from patient monocytes or iPSCs to utilise as a cell therapy.
This research has shown that, contrary to what was previously assumed, there are numerous distinct populations of myeloid cells in the MASLD liver that contribute in different ways to disease progression and tissue repair. The high similarity between mouse and human further highlights the relevance of the mouse models for this research, enabling meaningful functional and pre-clinical studies to be performed. All data are available for further interrogation of download at www.livercellatlas.org ensuring the results from this ERC are as useful to the larger community as possible. Taken together our results open the door for novel therapeutic approaches, and this is something we are currently investigating and will continue to research moving forward.