BETA-ADRENERGIC BLOCKADE OF THE SYMPATHETIC NERVOUS SYSTEM DECELERATES PERIPORTAL FIBROSIS IN ABCB4 KNOCKOUT MICE

BACKGROUND AND AIM: Hepatic Stellate Cells (HSC) express α- and β-adrenoceptors and adrenergic inhibition results in reduced collagen I and α-smooth muscle actin (SMA) expression. Therefore, HSC were suggested to be the main cellular targets of sympathetic inhibition by β-blockers in experimental sinusoidal fibrosis. In order to study the role of the sympathetic nervous system in liver fibrogenesis we used the Abcb4 knock-out model developing non-HSC based, periportal fibrosis, which mimics primary sclerosing cholangitis (PSC).

Methods: Liver tissues of Abcb4 (-/-) mice untreated or treated with the β-adrenoceptor antagonist propranolol for 6, 12, 20 and 32 weeks were taken to analyse inflammation and fibrosis progression. Each group consists of more than 15 mice. Chloracetate esterase and immunochemical stainings for SMA, F4/80 and CD45 were performed and hydroxyproline contents were analysed. RNA was extracted and transcript levels of angiotensinogen, endothelin–1, TGF-β, TNF-α, CTGF and collagen1A1 were determined. In addition, ten portal fields and parenchymal areas (acinar zone II-III), each of 200µm in diameter, were laser-microdissected from liver tissues of the three months treated and untreated mice and used for transcriptional analyses.

Results: After three months periportal fibrosis has developed in Abcb4 (-/-) mice, but SMA-immunostaining revealed no sinusoidal and only minor periportal contribution of myofibroblasts. Propranolol treatment of the Abcb4 (-/-) mice resulted in inhibited fibrosis and diminished hydroxyproline levels. After three months of treatment the effect of the β-blockade was most prominent. The transcription levels of collagen I, TNF-α, TGF-β, CTGF and endothelin–1 were significantly reduced in the portal areas of the treated mice compared to the untreated Abcb4 (-/-) controls. In contrast, expression pattern of acinar zone II, III was not or only slightly affected by β-adrenergic inhibition.

Conclusion: In Abcb4 (-/-) mice, which undergo primary sclerosing cholangitis, β-blockade of the sympathicus leads to deceleration of periportal fibrogenesis. Periportally limited downregulation of fibrotic mediators by β-adrenergic inhibition indicates that myofibroblastic-activated HSC are not the only cellular targets of the sympathetic nervous system and that additional mechanisms of the sympathetic impact on fibrogenesis might exist.

abcb4 - fibrosis - laser microdissection - propranolol - sympathetic nervous system