Periodic Reporting for period 1 - VOLIV (Role of volume-regulated anion channels in liver physiology and metabolism)
Berichtszeitraum: 2019-08-01 bis 2021-07-31
The volume of animal cells needs to be tightly controlled, especially upon osmotic challenges but also during cell growth, migration and death. Cellular volume changes are also believed to have a role in cell signaling, in particular for insulin secretion by pancreatic β-cells and liver metabolism. Indeed, several studies established that anabolic processes (e.g. induced by insulin) are associated with swelling and catabolic processes (e.g. induced by glucagon) with shrinkage of hepatocytes, the main epithelial cells in the liver. However, the causal relationship between changes in hepatocyte volume and liver metabolism is largely obscure. Under physiological conditions, postprandial uptake of nutrients such as amino acids would increase hepatic metabolism after induction of osmotic cell swelling. The question of how hepatocyte swelling is sensed and transduced to regulate metabolism also remains unanswered.
As major player in cell volume regulation, the Volume-Regulated Anion Channel VRAC may influence liver metabolism by controlling hepatocyte volume. In parallel with another group, VRAC has been identified by the host laboratory as LRRC8 heteromers with LRRC8A being the obligatory subunit. With the recent identification of LRRC8 subunits as VRAC components, it is now possible to rigorously assess physiological roles of VRAC in the liver and its metabolic pathways.
Because the liver is a key organ controlling lipid and carbohydrate metabolism, dysregulations of hepatic signaling pathways can lead to metabolic diseases. If some cascades are identified as regulated by VRAC, this channel may therefore represent an interesting therapeutic target for the treatment of metabolic diseases such as the non-alcoholic steatosis hepatitis (NASH).
The overarching aim of this study was thus to (i) investigate the role of VRAC in liver function and in particular, (ii) to determine whether it is involved in the coupling of cell swelling with metabolism in hepatocytes.
As major player in cell volume regulation, the Volume-Regulated Anion Channel VRAC may influence liver metabolism by controlling hepatocyte volume. In parallel with another group, VRAC has been identified by the host laboratory as LRRC8 heteromers with LRRC8A being the obligatory subunit. With the recent identification of LRRC8 subunits as VRAC components, it is now possible to rigorously assess physiological roles of VRAC in the liver and its metabolic pathways.
Because the liver is a key organ controlling lipid and carbohydrate metabolism, dysregulations of hepatic signaling pathways can lead to metabolic diseases. If some cascades are identified as regulated by VRAC, this channel may therefore represent an interesting therapeutic target for the treatment of metabolic diseases such as the non-alcoholic steatosis hepatitis (NASH).
The overarching aim of this study was thus to (i) investigate the role of VRAC in liver function and in particular, (ii) to determine whether it is involved in the coupling of cell swelling with metabolism in hepatocytes.
I started this project by analyzing the native cellular distribution of LRRC8A using sophisticated mouse models. After analysis of liver tissues, I confirmed that LRRC8A is indeed expressed in hepatocytes. In order to investigate the potential role of VRAC in liver physiology, I then generated a mouse line in which Lrrc8a expression is specifically abolished in hepatocytes (KO). Because KO animals didn’t present any liver phenotype, I decided to challenge their liver metabolism by feeding control and KO mice with a high fat diet (HFD), characterized by very high fat contents (60% of total energy) for different durations. Males and females were studied separately and some control and KO animals were fed with a control diet (CD) as a control.
Histological analyses revealed that males fed with HFD presented hepatic abnormalities (hepatocyte swelling) and hepatocyte lipid accumulation, which seemed to be more severe in the KO compared to the control animals. However, no difference in weight gain and in hepatic biomarkers (AST, ALT, alkaline dehydrogenase, …) concentrations in serum were observed. Preliminary results also show no difference in triglycerides concentration in serum and in liver tissue.
Further experiments couldn’t be carried out within the reporting period as coronavirus pandemic restrictions hindered the progress of the project.
Unfortunately, I had no opportunities to disseminate the results of this project due to conference cancellation due to pandemic restrictions. Nonetheless, even if negative, these results will be useful for discussion about the role of VRAC in mouse physiology and will be exploited in future manuscripts.
Histological analyses revealed that males fed with HFD presented hepatic abnormalities (hepatocyte swelling) and hepatocyte lipid accumulation, which seemed to be more severe in the KO compared to the control animals. However, no difference in weight gain and in hepatic biomarkers (AST, ALT, alkaline dehydrogenase, …) concentrations in serum were observed. Preliminary results also show no difference in triglycerides concentration in serum and in liver tissue.
Further experiments couldn’t be carried out within the reporting period as coronavirus pandemic restrictions hindered the progress of the project.
Unfortunately, I had no opportunities to disseminate the results of this project due to conference cancellation due to pandemic restrictions. Nonetheless, even if negative, these results will be useful for discussion about the role of VRAC in mouse physiology and will be exploited in future manuscripts.
Even if negative, the results obtained with the completion of this MSCA project give us better insights of what can be the role(s) of VRAC in physiology: VRAC does not seem to play an important role in liver metabolism.
Furthermore, the mouse lines generated during this reporting period can serve as valuable tools for other projects investigating the role of VRAC in mouse physiology.
Furthermore, the mouse lines generated during this reporting period can serve as valuable tools for other projects investigating the role of VRAC in mouse physiology.