Acetylcholine regulates melanogenesis of retinal pigment epithelia (RPE) cells : a non-neuronal function of cholinergic system in retina

Abstract

Human retinal pigment epithelium is a polarized layer of pigmented epithelium located in vertebrate eyes, which is specifically localized at between photoreceptors and choroidal blood supply. The main functions of this pigmented epithelium are to absorb scattering light entering the eyes. The epithelial cell contains melanin, a pigmented chemical, and which is able to phagocytize the sheds deriving from photoreceptors outer segments, as well as to serve as an antioxidant to the super oxides being produced during the trespassing of light. Today, very limited research works have been done in examining the role of cholinergic system in functionality of retinal pigment epithelium. The melanin production, i.e., melanogenesis, in adult retinal pigment epithelium was reported to be in minimum, as compared to foetal retinal pigment epithelial cells. Hence, ARPE-19 cell, a human retinal pigment epithelia cell line, was used to determine the role of cholinergic molecules in the process of melanogenesis. In cultured ARPE-19 cells, acetylcholinesterase (AChE) was expressed mainly as G4 form. The enzymatic activities of AChE and tyrosinase (TYR) were measured during the culture of ARPE-19 cells. The expression of AChE protein was upregulated and peaked on day 4 (~2.8-fold) after the culture. Applied acetylcholine upregulated the melanogenesis of cultured ARPE-19 cells in dose-and time-dependent manners. Moreover, the activation of M2 and M4 muscarinic acetylcholine receptors (mAChRs) by bethanechol (a selective mAChR agonist), upregulated the melanogenesis in ARPE-19 cells via cAMP-dependent pathway. In addition, the treatments of ultraviolet (UV) B and blue light promoted the rate of melanogenesis in ARPE-19 cells through the activation of M2/M4 mAChR in a time-dependent manner. Besides, the rate of phagocytosis in UVB-treated ARPE-19 cells was upregulated in a time-dependent manner and through the activation of ɑ7 nicotinic AChR. Thus, the cholinergic system plays a regulatory role in the process of melanogenesis in human retinal pigment epithelia cells

Date of Award	2023
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Karl Wah Keung TSIM (Supervisor)