Lipid droplets are intracellular mechanical stressors that promote hepatocyte dedifferentiation

Abstract

Matrix stiffening and associated mechanical stress have been linked to disease and cancer development in multiple tissues. In the liver, cirrhosis, characterized by architectural rearrangements and an up to ten times increase in liver stiffness, is the most significant risk factor for hepatocellular carcinoma development. Patients with non-alcoholic fatty liver disease, typified by lipid-droplet-filled hepatocytes, can, however, develop cancer in non-cirrhotic, and relatively soft tissue. Here, we used primary human hepatocytes to show that lipid droplets are intracellular mechanical stressors with similar effects to tissue stiffening, including hepatocyte dedifferentiation. Specifically, we demonstrate that lipid droplets deform the nucleus, that expression of the hepatocyte transcription factor hepatocyte nuclear factor 4α decreases in proportion to the magnitude of lipid-droplet mediated nuclear deformation, that lipid droplets disrupt the cytoskeleton and resist contractility, preventing cells from properly adapting to stiffer environments, and that modulating contractility rescues hepatocyte differentiation. Mathematical modelling of lipid droplets as spherical inclusions that can have mechanical interactions with other cellular components generated results consistent with our experiments, further supporting the idea that these changes are due to mechanical stress. Taken as a whole, our data show that lipid droplets, and potentially other cytoplasmic inclusions, are intracellular sources of mechanical stress and that nuclear membrane tension may serve to integrate cell responses to combined internal and external stresses.

Mechanisms of Lipid Droplet Accumulation in Steatotic Liver Diseases

“…In humans with MASLD, sinusoidal portal hypertension is related to steatosis grade [76]. In vitro, large LDs can also distort hepatocyte nuclei and chromatin structure [77]. In pre-clinical rodent models, LD-laden hepatocytes compress the space of Disse, the subendothelial space that lies between the liver sinusoidal endothelial cells and hepatocytes.…”

“…75 In vitro, large LDs can also distort hepatocyte nuclei and chromatin structure. 76 In preclinical rodent models, LD-laden hepatocytes compress the space of Disse, the subendothelial space that lies between the liver sinusoidal endothelial cells and hepatocytes. Under normal conditions, this region regulates blood flow (70% portal vein and 30% hepatic artery).…”

Lipid droplets in steatotic liver disease

“…Emerging evidence also indicates that the presence of large lipid droplets within hepatocytes disrupts mechanosensing and acts as intracellular mechanical stressors that may exacerbate hepatocyte dysfunction and the progression of SLD [24,25]. Lipid-laden hepatocytes were observed to have disrupted stress fibres and focal adhesion and cultured hepatocytes with large lipid droplets from patients with SLD were found to have deformed nuclei [24].…”

“…Emerging evidence also indicates that the presence of large lipid droplets within hepatocytes disrupts mechanosensing and acts as intracellular mechanical stressors that may exacerbate hepatocyte dysfunction and the progression of SLD [24,25]. Lipid-laden hepatocytes were observed to have disrupted stress fibres and focal adhesion and cultured hepatocytes with large lipid droplets from patients with SLD were found to have deformed nuclei [24]. Additionally, the presence of large lipid droplets was associated with increased nuclear localisation of mechano-sensor Yes-associated protein, which is thought to have a pathological role in SLD-associated fibrosis development [24,26].…”

“…Lipid-laden hepatocytes were observed to have disrupted stress fibres and focal adhesion and cultured hepatocytes with large lipid droplets from patients with SLD were found to have deformed nuclei [24]. Additionally, the presence of large lipid droplets was associated with increased nuclear localisation of mechano-sensor Yes-associated protein, which is thought to have a pathological role in SLD-associated fibrosis development [24,26]. Increased lipid droplet number and size in hepatocytes cause liver anatomical changes, engendering the compression of sinusoidal cells and the reduction of blood flow, ultimately leading to hypoxia and increased portal pressure.…”