Sympathetic Nervous System Catecholamines and Neuropeptide Y Neurotransmitters Are Upregulated in Human NAFLD and Modulate the Fibrogenic Function of Hepatic Stellate Cells

Background: Sympathetic nervous system (SNS) signalling regulates murine hepatic fibrogenesis through effects on hepatic stellate cells (HSC), and obesity-related hypertension with SNS activation accelerates progression of non-alcoholic fatty liver disease (NAFLD), the commonest cause of chronic liver disease. NAFLD may lead to cirrhosis. The effects of the SNS neurotransmitters norepinephrine (NE), epinephrine (EPI) and neuropeptide Y (NPY) on human primary HSC (hHSC) function and in NAFLD pathogenesis are poorly understood. Aims: to determine the mechanistic effects of NE/EPI/NPY on phenotypic changes in cultured hHSC, and to study SNS signalling in human NAFLD livers. Methods: Freshly isolated hHSC were assessed for expression of cathecholamine/neuropeptide Y receptors and for the synthesis of NE/EPI. The effects of NE/EPI/NPY and adrenoceptor antagonists prazosin (PRZ)/propranolol (PRL) on hHSC fibrogenic functions and the involved kinases and interleukin pathways were examined. Human livers with proven NAFLD were then assessed for upregulation of SNS signalling components. Results: Activated hHSC express functional alpha/beta-adrenoceptors and NPY receptors, which are upregulated in the livers of patients with cirrhotic NAFLD. hHSC in culture synthesize and release NE/EPI, required for their optimal basal growth and survival. Exogenous NE/EPI and NPY dose-dependently induced hHSC proliferation, mediated via p38 MAP, PI3K and MEK signalling. NE and EPI but not NPY increased expression of collagen-1 alpha 2 via TGF-beta without involvement of the pro-fibrogenic cytokines leptin, IL-4 and IL-13 or the anti-fibrotic cytokine IL-10. Conclusions: hHSC synthesize and require cathecholamines for optimal survival and fibrogenic functionality. Activated hHSC express directly fibrogenic alpha/beta-adrenoceptors and NPY receptors, upregulated in human cirrhotic NAFLD. Adrenoceptor and NPY antagonists may be novel anti-fibrotic agents in human NAFLD.