Cell-type-specific ER-Mitochondria contact sites in the Progression and Regression of NAFLD – CEMPR

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease affecting one third of the global adult population, yet its complex pathophysiology is partly understood. Insulin resistance, steatosis and inflammation contribute to onset of steatohepatitis (NASH). In NAFLD, the liver’s cellular composition undergoes extensive remodeling, from predominance of parenchymal cells to massive increase in non-parenchymal cells (NPC) at later disease stages, reducing the hepatocyte fraction to less than 50%. Liver NPCs encompass endothelial, immune, and mesodermal lineages, namely liver sinusoidal endothelial cells (LSEC), Kupffer cells (KC) and hepatic stellate cells (HSC), respectively. NPCs respond to hepatocellular stress by activating, proliferating, and recruiting circulating immune cells. Adaptive or maladaptive lineage-dependent responses strongly influencing NAFLD progression and potential reversal. Hence NPCs are valuable candidates to mitigate progression and influence the recovery of NAFLD.
The coordinator’s team showed that steatosis and insulin resistance result from miscommunication between the endoplasmic reticulum (ER) and mitochondria at mitochondria-associated membranes (MAM) in hepatocytes. Defective ER-mitochondria calcium coupling is an early, causal, and reversible trigger of hepatic steatosis and insulin resistance. Partner laboratories elucidated key mechanisms of mitochondrial adaptation, the role of mitochondria in regulating immune reactivity in insulin resistance, and restorative KC-LSEC interactions in NAFLD. Nonetheless, the role of MAMs in controlling mitochondrial function and cell fate in the different NPC lineages remains unknown. Promising preliminary data indicate that MAMs influence responses of the liver’s immune niche, regulating potentially the inflammation. MAM dynamics also vary in LSECs and HSCs that respectively promote sinusoidal capillarization and deposition of extracellular matrix. However, whether MAM-mediated mechanisms can control successful adaptation of NPCs in NAFLD remains unknown.
Given our preliminary data and previous reports, we hypothesize that cell-type-specific ER-mitochondria miscommunication regulates NAFLD progression and the liver’s restorative capacity. We address the hypothesis by 1) investigating MAM dynamics and mitochondrial function in NPCs and hepatocytes in NAFLD development and reversal in vivo; 2) targeting MAMs in the different NPC lineages, and hepatocytes, to alter responses to metabolic stress; and, 3) evaluating MAM dynamics and MAM-associated molecular signatures in human liver biopsies and in circulation.
We will first apply dietary models of NAFLD development and reversal to wild-type mice and mice carrying a lineage-restricted mitochondrial reporter. Next, organelle-targeted molecular spacers and linkers will be applied to primary culture models of NPCs to experimentally disrupt or reinforce MAMs. MAM dynamics will be analyzed by in situ proximity ligation assay and structural imaging; cellular, mitochondrial and molecular adaptations will be mapped. MAM alteration across NAFLD stages will be assessed in a cross-sectional analyses from biobanked human liver biopsies. Finally, we will conduct a prospective pilot study assessing MAM dynamics and associated molecular signatures, in tissue and in circulation, in a model of NAFLD improvement: before and after bariatric surgery.
The consortium brings together established and promising leaders in the fields of mitochondrial biology and liver disease. We will develop a valuable knowledgebase deciphering functional diversity of MAMs and mitochondria across liver NPC lineages in NAFLD development and reversal. Specific NPC functions may be targeted by interfering with MAM formation in specific cells and timepoints in the natural history disease. Project CEMPR promises to widen the repertoire of actionable therapeutic targets with potential to modify NAFLD disease course.