Periodic Reporting for period 1 - ForgettingNAFLD (Unravelling the pathogenic cell-cell circuits underlying the tissue memory of non-alcoholic fatty liver disease)
Reporting period: 2022-10-01 to 2024-09-30
Non-alcoholic fatty liver disease (NAFLD) refers to a spectrum of disease states in which the liver undergoes profound changes ranging from non-symptomatic simple steatosis (build-up of fat in the liver) to the more end stages of the disease including non-alcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC). With the ongoing obesity epidemic, NAFLD has a global prevalence of 25% and approximately a fifth of those patients will progress to NASH. For these last disease stages there are currently no treatment options other than liver transplant.
During early stages of NAFLD a change in lifestyle and weight loss can alleviate symptoms in patients. However, it remains unclear to what degree the liver can fully recover. Recent work pioneered the idea that tissue develops a ‘memory’ of previous inflammatory events. If so, patients recovered from NAFLD following weight loss might also carry such a memory in their liver with potentially long-lasting effects. This memory can be carried by individual long-lived cells in the form of changed to the DNA structure (so called epigenetic changes). In the liver the various structural cells (hepatocytes, stellate cells and endothelial cells) are closely interlinked with a specific population of immune cells, the macrophages. Macrophages are found in all tissues and perform unique functions that are essential to maintain homeostasis in their respective organ. In the liver a large population of long-lived macrophages exists referred to as Kupffer cells (KCs). As these various cells in the liver form a close-knit circuit a ‘memory ‘in one population has the capacity to alter the complete liver circuitry. During NAFLD all the cells in the liver are heavily affected and could potentially carry such a memory. Hence the overall objective of this project is to investigate to what degree the various cells in the liver carry a memory following recovery of NAFLD.
During early stages of NAFLD a change in lifestyle and weight loss can alleviate symptoms in patients. However, it remains unclear to what degree the liver can fully recover. Recent work pioneered the idea that tissue develops a ‘memory’ of previous inflammatory events. If so, patients recovered from NAFLD following weight loss might also carry such a memory in their liver with potentially long-lasting effects. This memory can be carried by individual long-lived cells in the form of changed to the DNA structure (so called epigenetic changes). In the liver the various structural cells (hepatocytes, stellate cells and endothelial cells) are closely interlinked with a specific population of immune cells, the macrophages. Macrophages are found in all tissues and perform unique functions that are essential to maintain homeostasis in their respective organ. In the liver a large population of long-lived macrophages exists referred to as Kupffer cells (KCs). As these various cells in the liver form a close-knit circuit a ‘memory ‘in one population has the capacity to alter the complete liver circuitry. During NAFLD all the cells in the liver are heavily affected and could potentially carry such a memory. Hence the overall objective of this project is to investigate to what degree the various cells in the liver carry a memory following recovery of NAFLD.
The first stages of the project sought to investigate to what degree the liver can recover from NAFLD. Using microscopy and by measuring the levels of circulating ALT/AST (a measure of liver damage) it was observed that the liver has the capacity to near-completely recover from NAFLD relatively quickly. These data are consistent with anecdotal data suggesting a similar recovery in humans. However, during NAFLD unique granuloma-like structures appeared in the liver. These structures comprised of their own unique F4/80 macrophage population and were encapsulated by Desmin+ fibroblast (See figure). Importantly, these structures persisted during the recovery and thus constituted a long-lasting change to liver following NAFLD recovery. The macrophages that inhabited these structures relied on the survival factors CSF1 and Il34, derived from the adjacent fibroblast. Consequently, in the absence of local fibroblast-derived CSF1 and Il34 these structures failed to form. These structures underpin a heightened sensitivty of the recovered liver to subsequent acute liver injury.
Taken together these data indicated that following NAFLD recovery the composition of the liver remains altered long-term. These compositional changes have a profound impact on the liver functionality. In addition, there are epigenetic changes to the resident KCs in the liver suggesting much more profound long-lasting changes.
Taken together these data indicated that following NAFLD recovery the composition of the liver remains altered long-term. These compositional changes have a profound impact on the liver functionality. In addition, there are epigenetic changes to the resident KCs in the liver suggesting much more profound long-lasting changes.
This MSCA accomodated the development of a cutting-edge pipeline to investigate the persistent transcriptional and epigenetic changes to macrophages in the liver following NAFLD-recovery. Using these techniques the existence of an epigenetic memory carried by long-lived KCs in the liver was definitively shown. Conceptually this is an important finding because if resident macrophages in the liver are capable to carry such memory it is likely that other tissue macrophages can do so as well. Given the importance of macrophages across organs and diseases, epigenetic memory is likely to be important in various pathological settings.
Perhaps more importantly the work carried out during this fellowship led to to the identification of NAFLD unique cell-cell circuits develop that persist during recovery (Image attached). These structures are largely self-maintaining and seem to have a striking effect on the liver to respond to subsequent inflammatory events. To our knowledge such structures have not been observed in the liver or any other organs to date. As such they represent an interesting avenue to explore further and are likely to develop during other liver pathologies and potentially in other organs.
Hence, the data generated during this fellowship suggest a long-lasting compositional alteration to the liver following recovery in the form of these unique structures. Hence, in addition to the more traditional epigenetic memory these data support a model of ‘compositional memory’ that persist following an inflammatory
Perhaps more importantly the work carried out during this fellowship led to to the identification of NAFLD unique cell-cell circuits develop that persist during recovery (Image attached). These structures are largely self-maintaining and seem to have a striking effect on the liver to respond to subsequent inflammatory events. To our knowledge such structures have not been observed in the liver or any other organs to date. As such they represent an interesting avenue to explore further and are likely to develop during other liver pathologies and potentially in other organs.
Hence, the data generated during this fellowship suggest a long-lasting compositional alteration to the liver following recovery in the form of these unique structures. Hence, in addition to the more traditional epigenetic memory these data support a model of ‘compositional memory’ that persist following an inflammatory