Exploring the dimorphism during fibrosis development and regression in a murine model of toxin-induced chronic liver injury

Liver fibrosis represents a crucial biological process, being the final common pathway of chronic or iterative liver damage. It is consequent to repeated wounds which are known to heal not in a timely manner. The contribution of gender-biased hepatic responses to liver injury represents a lively research topic to be investigated. With this PhD research the crosstalk between fibrosis, the drivers and targets of matrix remodelling and the hepatic immune microenvironment was ascertained and characterized. A murine model of chronic hepatic damage established by repeated administrations of the toxin CCl4 was developed and the injured liver was analysed in a timeframe of 12 weeks, including in addition also a period of washout of 8 weeks which allowed the liver to self-heal. Fibrosis, HSCs activation, analysis of matrix remodelling players in the liver along with immune infiltrating cellular components and circulating sexual hormones and cytokines were deeply investigated. An impaired capability for injured females to resorb excessive hepatic ECM during the self-healing was demonstrated, associated both with a decrease in estradiol concentrations and a delayed MMP9 activity in the onset of chronic hepatic damage. The characterization of the fibrotic milieu demonstrated an imbalance in the axis MMP-TIMP associated with a more inflammatory prone immune profile in female mice. The differences in the immune profile between injured males and females were also confirmed by analysing an array of circulating cytokines. The investigations in liver single cell suspensions of the immune cellular components present accordingly to different stages of severity of the disease, unveiled a residual population of Kupffer cells in females and a restorative macrophages component in males, after the self-healing, which could be responsible for the gender-biased effective fibrosis resolution. Further investigations are needed to ascertain if an angiocrine altered signalling is also part of this imbalance, considering data obtained on VEGFA mRNAs and protein modulations. Moreover, the possibility to translate into other models of hepatic injury data evidenced by this PhD thesis and, above all, to study in humans the biological processes below the liver dimorphism in fibrosis dynamics represents a mandatory condition to augment the knowledge in this lively field of research.