The hepatic vagus nerve stimulates hepatic stellate cell proliferation in rat acute hepatitis via muscarinic receptor type 2

Abstract

Background & aims: We have previously shown that the hepatic vagus nerve stimulates the activation of hepatic progenitor cells (HPC), via muscarinic acetylcholine receptor type 3. Given the coproliferation of HPC and hepatic stellate cells (HSC) in acute hepatitis, we determined whether HSC proliferation is also modulated by vagal activity. Methods: We induced acute hepatitis in Wistar rats by injection of galactosamine and lipopolysaccharides. Hepatitis was preceded by hepatic branch vagotomy or sham vagotomy, by electrical stimulation or sham stimulation and by muscarinic receptor antagonist atropine, nicotinic receptor antagonist mecamylamine or saline injection. Rats were sacrificed after 12 and 48 h and HSC numbers were quantified on immunohistochemical stainings. Furthermore, we performed reverse transcriptase-polymerase chain reaction with receptor-specific primers on total RNA from isolated HSC and determined the in vitro proliferation of HSC in response to acetylcholine, atropine and mecamylamine. Results: HSC numbers were significantly lower after vagotomy than after sham vagotomy. Conversely, more HSC were seen after electrical stimulation than after sham stimulation. Atropine resulted in less HSC than saline at both time points, while mecamylamine treatment only diminished HSC after 12 h, suggesting a predominant involvement of muscarinic receptors. Moreover, HSC express muscarinic receptor type 2 mRNA and protein, as well as nicotinic receptor α1, α5, β1 and vasoactive intestinal peptide receptor 1 mRNA. Furthermore, acetylcholine enhanced the in vitro proliferation of HSC, which was inhibited by atropine, but not by mecamylamine. Conclusions: We show here that the hepatic vagus nerve stimulates HSC proliferation, most likely through binding of acetylcholine on muscarinic receptor type 2.