The knockout of latent transforming growth factor-β binding protein–1 (LTBP–1) affects the fibrogenic potential in mice liver

Aims: Latent transforming growth factor-β binding proteins (LTBP–1, –2, 3-, –4) are glycosylated proteins of the extracellular matrix involved in the secretion and controlling the bioavailability of active transforming growth factor-β (TGF-β). LTBP–1 and TGF-β are key factors in the pathophysiology of liver fibrogenesis. During this process, hepatic stellate cells (HSC) become activated and transdifferentiate into myofibroblasts. Because the knowledge of LTBP functionality in controlling and regulation the concentration of biological active TGF-β is crucial for the understanding of fibrogenesis in the liver we generated a knockout mice for LTBP–1. Here we present data derived from induced liver fibrosis by bile duct ligation in respective animals.

Methods: Wildtype and knockout mice were bile duct ligated for four weeks. The impact of this induction of fibrosis was traced by blood parameters (bilirubin, AST and ALT) measured by routine methods. The deposition of matrix components was quantified by Western blot against collagen–1. Also the grading of fibrosis was performed by histological Sirius Red stainings. In parallel the in vitro transdifferentiation of HSC was compared between wildtype and knockout mice using the PIQOR^TM microarray chips.

Results: The serum parameters indicated a massive fibrosis in all treated animals which could be analysed after four weeks of bile duct ligation. Both the histological stainings with Sirius Red as well as the semiquantitative analysis of collagen deposition display a stronger progress of fibrogenesis in wildtype than in knockout livers. The differences were around 20 percent. Also the expression analysis of more than 1.000 genes by microarray displayed, that HSC from knockout mice differentiate slower than respective wildtype HSCs.

Conclusions: The reduced speed of fibrogenesis in LTBP–1 knockout mice correlates directly with the absence of LTBP–1. Consequently, the level of bioavailable TGF-β must be obviously reduced and contribute less to the fibrotic occurrence. Nevertheless, also knockout mice show a matrix deposition which could come from internal or LTBP–1 independent TGF-β stores. Microarray analysis illustrate, that the knockout of LTBP–1 affects the expression of several further genes.

LTBP - TGF-beta signalling - bile duct ligation - fibrogenesis - knock out animal model - microarray analysis