Expression of the protein clusterin (green) in human liver cirrhosis is closely associated with collagen deposits (magenta) in the extracellular matrix in scar tissue. Cell nuclei are labeled in blue. Image credit: Jirouskova et al. (CC BY 4.0)
Alcoholism or chronic conditions like hepatitis damage the liver. Over time, scar tissue builds up in the liver, causing cirrhosis. The scaring results from the liver’s repeated attempts to repair itself by creating more structural proteins called extracellular matrix proteins. A buildup of these scaffolding proteins leads to tissue stiffening or fibrosis. Fibrosis may heal in some cases but in others, it may progress to cirrhosis, liver cancer or liver failure.
Learning more about these processes may help scientists and clinicians understand why fibrosis is reversible in some cases but not others. It may also allow them to develop treatments that can treat or reverse fibrosis and prevent cirrhosis, liver cancer, or liver failure. The first step is studying how fibrosis occurs in mouse models that mimic different types of liver disease. For example, repetitive ingestion of a toxic substance, such as alcohol, can cause one type of liver disease. However, slowing or stalling bile flow through the biliary system (the liver, gallbladder, and bile ducts), leads to a different type of chronic liver injury.
Jirouskova et al. identify an extracellular protein called clusterin that may help heal fibrosis. The experiments used mouse models of two different types of liver disease. One mimicked liver disease caused by repetitive toxin injury, and the other modelled liver disease caused by chronic stalling of the bile flow in the liver (cholestasis). In the experiments, Jirouskova et al. looked at all the proteins made in each type of liver disease as the animals developed fibrosis or their fibrosis resolved. They also studied extracellular matrix proteins and how they affected molecular signaling in the liver tissue. The experiments revealed different patterns of protein production and healing in the different types of liver disease. The animals with liver diseases caused by chronic cholestatic injury were less likely to heal their livers and showed potential to progress to liver cancer. Production of the clusterin protein was connected with better liver recovery from toxic injuries.
Jirouskova et al. provide a comprehensive map of all the proteins produced over the course of liver fibrosis progression and healing in two different animal models of liver disease. Scientists and clinicians may use this information to study liver disease types. It may also one day help them personalize patient's therapies. The experiments show that extracellular matrix proteins are essential contributors to fibrosis and key signaling agents in liver disease. This may make them good targets for new therapies. Boosting clusterin production may be one approach to promoting liver recovery. More studies are needed to confirm this before such therapies can be developed and tested in humans.
