Histone acetylation as a new mechanism for bilirubin-induced encephalopathy in the Gunn rat

Eleonora Vianello,Cristina Bottin,Fabrizio Zanconati,Andrea Dardis,Stefania Zampieri,Silvia Gazzin,Thomas Marcuzzo,Fabio Tordini,Claudio Tiribelli

doi:10.1038/s41598-018-32106-w

Abstract

Bilirubin neurotoxicity has been studied for decades and has been shown to affect various mechanisms via significant modulation of gene expression. This suggests that vital regulatory mechanisms of gene expression, such as epigenetic mechanisms, could play a role in bilirubin neurotoxicity. Histone acetylation has recently received attention in the CNS due to its role in gene modulation for numerous biological processes, such as synaptic plasticity, learning, memory, development and differentiation. Aberrant epigenetic regulation of gene expression in psychiatric and neurodegenerative disorders has also been described. In this work, we followed the levels of histone 3 lysine 14 acetylation (H3K14Ac) in the cerebellum (Cll) of the developing (2, 9, 17 days after the birth) and adult Gunn rat, the natural model for neonatal hyperbilirubinemia and kernicterus. We observed an age-specific alteration of the H3K14Ac in the hyperbilirubinemic animals. The GeneOntology analysis of the H3K14Ac linked chromatin revealed that almost 45% of H3K14Ac ChiP-Seq TSS-promoter genes were involved in CNS development including maturation and differentiation, morphogenesis, dendritogenesis, and migration. These data suggest that the hallmark Cll hypoplasia in the Gunn rat occurs also via epigenetically controlled mechanisms during the maturation of this brain structure, unraveling a novel aspect of the bilirubin-induced neurotoxicity.

Highlights

Bilirubin toxicity to the CNS has been extensively studied for decades and has been shown to be linked to the activation of multiple complex signal cascades, and affects potential toxic/adaptation mechanisms in the brain through gene expression modulation
Cll hypoplasia is a hallmark of hyperbilirubinemia in rodents[26,27,28,29], and cerebellar involvement with morphological and behavioral abnormalities has been reported in severely hyperbilirubinemic neonates[30,31,32]
Inflammation and oxidative stress are considered the major mechanisms of bilirubin neurotoxicity, whereas the impact of hyperbilirubinaemia on CNS development has been only marginally envisaged, and evaluated mostly by in vitro experiments[33,34]

Summary

Introduction

Bilirubin toxicity to the CNS has been extensively studied for decades and has been shown to be linked to the activation of multiple complex signal cascades, and affects potential toxic/adaptation mechanisms in the brain through gene expression modulation. Examples include oxidative stress and the antioxidant response, excitotoxicity, inflammation, intracellular trafficking, protein degradation, apoptosis, as well as bilirubin transport and bilirubin oxidization (reviewed in[1]) Epigenetic processes, such as histone acetylation and DNA methylation, regulate the expression of genes through modifications of DNA structure and accessibility. It is reported that temporal changes in gene expression by acetylation/deacetylation of gene promoters induce persistent changes in the cell (e.g. cell fate), changes in the neurological behaviour[8], as well induction of excitotoxicity, calcium overload, oxidative stress, inflammation and apoptosis[13], with the last five described mechanisms in hyperbilirubinemic animals and humans This suggests the possibility of a link between the hyperbilirubinemic phenotype and the epigenetic. Western blot analysis of the level of histone 3 acetylation (H3K14Ac) P: post-natal age in days, Adult: more than

Methods

Results

Conclusion