FN-EDA domain knock-in and knock-out mice, as a model for the study of the hepatic fibronectin (FN) functions

• Main Author: Moretti, Federico Andrea
• Published: Open University 2007
• Subjects: 591.35
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487161

Fibronectin (FN) is a multidomain glycoprotein found in plasma and tissue extracellular matrices (ECM). Plasma FN (pFN) is produced and secreted into the bloodstream by the liver. Liver ECM-FN and pFN are characte,rized by the absence of the EDA domain, one of the three FN exons undergoing alternative splicing. However, in pathological situations such as wound healing, the liver produces and accumulates huge amounts of EDA⁺FN in sinusoidal ECM. In order to study the functions of the FN isoforms produced by the liver, we used two mouse strains devoid of EDA-exon alternative splicing, which constitutively include (EDA^+/+ strain) or exclude (EDA^-/- strain) the EDA domain. The EDA^+/+ strain is characterized by an important decrease of FN levels both in plasma and tissues. Here, we show that the atypycal presence of the EDA domain in hepatocytes affects pFN secretion into the bloodstream and we demonstrate that a high proportion of tissue ECM-FN is supplied by plasma. In fact, removal of the EDA exon only from the liver, by hepatocyt'-specific deletion of the EDA exon, restores normal levels of FN in both plasma and tissues of the EDA^+/+ animals. This finding not only suggests that plasma behaves as a sort of FN reservoir for tissue maintenance but also shows for the first time that the pFN contribution to the ECM of tissues is roughly equal to that produced locally. The EDA^-/- strain was used to study the role of the EDA domain in the onset of liver fibrosis. In two different liver fibrosis models, we observed that EDA^-/- animals develop attenuated fibrosis in comparison to control mice. The important role of the EDA domain in the activation and proliferation of the hepatic stellate cells (HSCs), these are the key cells responsible for the ECM protein overproduction in the fibrotic processes, is demonstrated for the first time <i>in vivo</i>. EDA^-/- livers treated to induce fibrosis, present a striking reduction in the number of myofibroblasts or activated HSCs, suggesting that the EDA domain could be a potential target for the treatment of liver fibrosis.