Epigenetic regulation of phenylethanolamine N‐methyltransferase: implications for adrenaline biosynthesis

Abstract

Adrenaline, a neurohormone and neurotransmitter, plays an extensive role in the physiological response to stress, and the sympathetic regulation of blood pressure. Phenylethanolamine N‐methyltransferase (PNMT), the terminal enzyme in the catecholamine biosynthetic pathway, directly responsible for adrenaline synthesis, is elevated in hypertensive animals; genetic linkage studies have associated the PNMT gene to the development of hypertension. Epigenetic changes are heritable changes in gene expression that are a consequence of the modification of the DNA (methylation at CpG sites) or histones (e.g. by methylation, acetylation) that facilitate packaging the DNA into nucleosomes. Changes in the epigenome have been associated with incidences of cancer, metabolic disorders and cardiovascular pathologies. In this study, alteration in PNMT expression modifiable by epigenetic regulation was examined using the rat adrenal pheochromocytoma derived PC12 cells. In vitromethylation of a PNMT promoter driven luciferase construct, using CpG methylases, consequently lead to a radical decrease in promoter activation, even in presence of dexamethasone (Dex) or Forskolin (Fsk), otherwise potent activators of PNMT expression. Further, the influence of a DNA methylation inhibitor 5‐aza‐2′‐deoxycytidine (5aza2DC), and histone deacetylase inhibitor valproic acid (VPA) was examined. Transcript analysis of endogenous PNMT, and PNMT promoter driven luciferase assays, both revealed that PNMT transcription is elevated in presence of these epigenetic modifiers, and these compounds can interact with the activation by Dex or Fsk to modulate PNMT expression. The extent of CpG methylation at the promoter of PNMT using bisulphite‐sequencing, and transcription factor binding sites that are sensitive to epigenetic modification using site directed mutagenesis, are currently being examined. The data suggests that PNMT regulation is sensitive to epigenetic modification which can have repercussions for adrenaline biosynthesis, and consequently on its role as a neurotransmitter.Support or Funding InformationCIHR