Melatonin inhibits hypothalamic gonadotropin-releasing hormone release and reduces biliary hyperplasia and fibrosis in cholestatic rats

Abstract

Melatonin is a hormone produced by the pineal gland with increased circulating levels shown to inhibit biliary hyperplasia and fibrosis during cholestatic liver injury. Melatonin also has the capability to suppress the release of hypothalamic gonadotropin-releasing hormone (GnRH), a hormone that promotes cholangiocyte proliferation when serum levels are elevated. However, the interplay and contribution of neural melatonin and GnRH to cholangiocyte proliferation and fibrosis in bile duct-ligated (BDL) rats have not been investigated. To test this, cranial levels of melatonin were increased by implanting osmotic minipumps that performed an intracerebroventricular (ICV) infusion of melatonin or saline for 7 days starting at the time of BDL. Hypothalamic GnRH mRNA and cholangiocyte secretion of GnRH and melatonin were assessed. Cholangiocyte proliferation and fibrosis were measured. Primary human hepatic stellate cells (HSCs) were treated with cholangiocyte supernatants, GnRH, or the GnRH receptor antagonist cetrorelix acetate, and cell proliferation and fibrosis gene expression were assessed. Melatonin infusion reduced hypothalamic GnRH mRNA expression and led to decreased GnRH and increased melatonin secretion from cholangiocytes. Infusion of melatonin was found to reduce hepatic injury, cholangiocyte proliferation, and fibrosis during BDL-induced liver injury. HSCs supplemented with BDL cholangiocyte supernatant had increased proliferation, and this increase was reversed when HSCs were supplemented with supernatants from melatonin-infused rats. GnRH stimulated fibrosis gene expression in HSCs, and this was reversed by cetrorelix acetate cotreatment. Increasing bioavailability of melatonin in the brain may improve outcomes during cholestatic liver disease. We have previously demonstrated that GnRH is expressed in cholangiocytes and promotes their proliferation during cholestasis. In addition, dark therapy, which increases melatonin, reduced cholangiocyte proliferation and fibrosis during cholestasis. This study expands these findings by investigating neural GnRH regulation by melatonin during BDL-induced cholestasis by infusing melatonin into the brain. Melatonin infusion reduced cholangiocyte proliferation and fibrosis, and these effects are due to GNRH receptor 1-dependent paracrine signaling between cholangiocytes and hepatic stellate cells.

Melatonin and circadian rhythms in liver diseases: Functional roles and potential therapies

“…Overexpression of AANAT inhibits VEGF‐A and VEGF‐C expression as well as cell proliferation in murine cultured cholangiocytes, indicating local melatonin synthesis followed by regulations of cholangiocyte functions during cholestatic liver injury . A previous study has performed melatonin administration (1 mg/kg per day for 7 days) via intracerebroventricular‐implanted cannulas for BDL rats and found that melatonin ameliorated ductular reaction and liver fibrosis by inhibition of gonadotropin‐releasing hormone (GnRH) secretion in vivo . Elevated GnRH secretion activates HSCs leading to robust liver fibrosis .…”

“…59,60 A previous study has performed melatonin administration (1 mg/kg per day for 7 days) via intracerebroventricular-implanted cannulas for BDL rats and found that melatonin ameliorated ductular reaction and liver fibrosis by inhibition of gonadotropin-releasing hormone (GnRH) secretion in vivo. 61 Elevated GnRH secretion activates HSCs leading to robust liver fibrosis. 62 Dark therapy, which maintains animals in complete dark 24 hours for 1 week, facilitates AANAT expression and melatonin secretion form the pineal gland in rats.…”

Recent advances in understanding bile duct remodeling and fibrosis

“…This phenotypic switch is characterized by increases in both secretion and responsiveness to certain neurohormones and neuropeptides. This induces a critical autocrine and paracrine signaling network that contributes to overall bile duct remodeling by tipping the balance between proliferation and bile duct loss as well as increasing fibrosis 25 . Recent research has shown that neuropeptide Y (NPY) plays an important role in this process.…”

“…Another key proliferative player is GnRH, which increases cholangiocyte proliferation 31 . Additionally, melatonin has been shown to attenuate cholangiocyte proliferation and recent research has investigated how these two neurohormones interact to alter the cholangiocyte response 25 , 29 , 32 . Cholangiocytes express GnRH receptors 1 and 2, respectively, and through the action of GnRH, cholangiocyte proliferation has been shown to increase via a cAMP-dependent mechanism.…”

Protective role of melatonin in early‐stage and end‐stage liver cirrhosis

“…63 Fortunately, MT exerts protective effects against BDL-induced injury and inhibits the progression of liver fibrosis ( Table 2) supernatant. 66 BDL not only increased collagen deposition but also improved MDA expression and luminol and lucigenin signal while decreasing GSH levels, whereas MT serves as a powerful physiological scavenger of hydroxyl radicals to reverse the activation of HSCs. 67 BDL increased the prevalence of kidney and brain injury in animal models.…”