Prominent contribution of portal mesenchymal cells to liver fibrosis in ischemic and obstructive cholestatic injuries

Abstract

Liver fibrosis is produced by myofibroblasts of different origins. In culture models, rat myofibroblasts derived from hepatic stellate cells (HSCs) and from periductal portal mesenchymal cells, show distinct proliferative and immunophenotypic evolutive profiles, in particular regarding desmin microfilament (overexpressed vs shut-down, respectively). Here, we examined the contributions of both cell types, in two rat models of cholestatic injury, arterial liver ischemia and bile duct ligation (BDL). Serum and (immuno)histochemical hepatic analyses were performed at different time points (2 days, 1, 2 and 6 weeks) after injury induction. Cholestatic liver injury, as attested by serum biochemical tests, was moderate/ resolutive in ischemia vs severe and sustained in BDL. Spatio-temporal and morphometric analyses of cytokeratin-19 and Sirius red stainings showed that in both models, fibrosis accumulated around reactive bile ductules, with a significant correlation between the progression rates of fibrosis and of the ductular reaction (both higher in BDL). After 6 weeks, fibrosis was stabilized and did not exceed F2 (METAVIR) in arterial ischemia, whereas micronodular cirrhosis (F4) was established in BDL. Immuno-analyses of a-smooth muscle actin and desmin expression profiles showed that intralobular HSCs underwent early phenotypic changes marked by desmin overexpression in both models and that the accumulation of fibrosis coincided with that of a-SMA-labeled myofibroblasts around portal/septal ductular structures. With the exception of desmin-positive myofibroblasts located at the portal/septal-lobular interface at early stages, and of myofibroblastic HSCs detected together with fine lobular septa in BDL cirrhotic liver, the vast majority of myofibroblasts were desmin-negative. These findings suggest that both in resolutive and sustained cholestatic injury, fibrosis is produced by myofibroblasts that derive predominantly from portal/periportal mesenchymal cells. While HSCs massively undergo phenotypic changes marked by desmin overexpression, a minority fully converts into matrix-producing myofibroblasts, at sites, which however may be important in the healing process that circumscribes wounded hepatocytes.

Transforming growth factor-β and substrate stiffness regulate portal fibroblast activation in culture

“…10 These cells have been studied in culture, although generally after outgrowth from fragments of the biliary tree or late after isolation 16,17 ; the characteristics of PF myofibroblastic differentiation have not been studied. We suggest that myofibroblastic PFs are fibrogenic and that PFs in culture can be studied in much the same way as HSCs.…”

“…Although in chronic liver injury hepatic stellate cells (HSCs) differentiate into myofibroblasts (also termed activation) and produce ECM, 2 the myofibroblast population of the diseased liver is heterogeneous, and fibrogenic myofibroblasts also arise from other cells, including portal fibroblasts (PFs). [3][4][5][6][7][8][9][10] PFs are fibroblasts surrounding the biliary tree; their differentiation into myofibroblasts in bile duct ligation (BDL) models of fibrosis precedes HSC activation, and they may function as first responders after biliary injury. [11][12][13][14] Isolation of rat liver myofibroblast precursor cells distinct from HSCs was first reported in 1984.…”

Thy-1 Is Expressed in Hepatic Myofibroblasts and Not Oval Cells in Stem Cell-Mediated Liver Regeneration

“…This would imply that the SMA-positive cells would be myofibroblasts, derived from the periportal fibroblasts, as proposed by Ramadori and Saile 32 and Beaussier and colleagues. 33 As far as we know, co-staining for SMA and desmin has not been published in oval cell proliferation experiments. Considering the above data, the Thy-1-positive cells in the zone of the oval cells show the closest association with the myofibroblasts.…”

Ezrin-Radixin-Moesin-Binding Phosphoprotein (EBP50), an Estrogen-Inducible Scaffold Protein, Contributes to Biliary Epithelial Cell Proliferation

“…21 Sham operation consisted in laparotomy and bile duct exposure without ligation. To assess the impact of estrogens, female rats were ovariectomized 3 to 5 weeks before BDL was performed, as previously described.…”