Scientists prove that reducing the expression of a protein in the liver might attenuate liver fibrosis
CONICET/DICYT Guillermo Mazzolini Rizzo, hepatologist and CONICET independent researcher at the Gene Therapy Laboratory of the School of Biomedical Sciences of the Austral University in Buenos Aires, has been studying for ten years the role of the osteonectin protein, or SPARC, in the hepatic fibrosis, a process that progressively replaces the hepatic tissue with fibrous tissue, caused by different pathologies, and thus it could lead to cirrhosis.
According to Mazzolini, among the liver diseases that might lead to liver fibrosis, we can find chronic hepatitis B and C virus, the excessive alcohol consumption, autoimmune diseases, and non-alcoholic esteatohepatitis, an inflammatory process of the liver associated not related to alcohol intake.
All these pathogenic agents could produce damage in hepatocytes – parenchymatous cells – and an inflammatory chronic process. This process is characterized by the activation of other cells’ population: the hepatic stellate cells. They are transformed into myofibroblasts, the major contributors to the production of the scar or fibrous tissue.
“This process takes lots of years, even decades, but if it is not interrupted, the origin of the damage could lead to progressive degrees of fibrosis that at the same time could result in liver cirrhosis. This has several related complications such as the hypertension of the portal venous system, blood clotting disorders that predispose to bleedings and the presence of hepatocellular carcinoma”, the researcher explains.
Together with his team and in collaboration with other Argentine scientists, Mazzolini studied the role of SPARC in the process that leads to hepatic fibrosis either in animal and human models with cirrhosis. For this reason, they analysed cases of the Austral University hospital and worked with the team of the researcher Ramón Bataller of the University of North Carolina in the United States. The results were published in PLOS One magazine.
“We managed to identify a potential future therapy, something very relevant if we take into account the fact that currently there is no variety of tools that allow reversing the cirrhosis”, Mazzolini comments.
There were two studies conducted with mice. In the first case, advanced fibrosis was induced through different mechanisms – among them, the supply of a toxic that produces hepatic inflammation and destruction of the hepatocytes and, after eight weeks, advanced fibrosis. In the second case, the researchers performed a bile duct ligation – blocking the excretory pathway of the bile produced in the liver -, what causes secondary bile cirrhosis.
“In all the experimental models, we observed a strong increase of the SPARC expression. This allowed us to move to a later stage where we seek to manipulate the protein’s expression to check the importance of its role during the liver fibrogenesis process”, Mazzonili remarks.
Two strategies were implemented. A more direct one, which consisted on the use of knock-out mice for SPARC – that is to say that they do not express the protein – to experimentally induce fibrosis with the administration of the same toxic or the bile duct ligation.
The other strategy was developed in experimental models of fibrogenesis, which means that they studied the progeny of mice, where they observed that the animals with lack of SPARC protein significantly decrease the fibrogenic process, though it is not inhibited completely.
“This indicates that possibly, in the cases of not advanced fibrosis stages, the SPARC expression could be impacted and the course of the disease might be detained or delayed”, Mazzolini concludes.
According to the researcher, one of the possible clinical applications would be based on the generation of a viral vector that could be attracted to the liver and express a DNA sequence to inhibit a SPARC in a sustained way.
“It is essential that the expression or the action of this vector last for an extended period of time because in the case of a chronic disease, such as the advanced hepatic fibrosis, a transitory or short term blockage would not have any substantial impact”, he adds.
Throughout the investigation, Osvaldo Podhajcer, CONICET senior researcher at the Biochemistry Research Institute of Buenos Aires (IIBBA, CONICET- Instituto Leloir) collaborated with Mazzolini’s research team.
“We have been working with SPARC for several years and with these studies we generated a range of tools to regulate the expression of the protein. They are genetic engineering constructions that allow overexpressing or blocking SPARC, that is to say, it prevents it from expressing itself. On the basis of that, we analyse its role in different experimental models”, Podhajcer explains.
The IIBBA team developed the genetic engineering tools needed for Maizzolini’s study. First, they provided the animals with the gene that encodes for ‘blocked’ SPARC and then they contributed to the subsequent analysis of the genomic data of the experimental phase.
Thanks to this collaboration, Mazzolini could observe how SPARC inhibition leads to fibrogenesis inhibition in vivo animal models.