Turnover of histones and histone variants in postnatal rat brain: effects of alcohol exposure

Nadia Rachdaoui,Belinda Willard,Dipak Sarkar,Stephen Previs,Takhar Kasumov,Ling Li

doi:10.1186/s13148-017-0416-5

Abstract

BackgroundAlcohol consumption during pregnancy is a significant public health problem and can result in a continuum of adverse outcomes to the fetus known as fetal alcohol spectrum disorders (FASD). Subjects with FASD show significant neurological deficits, ranging from microencephaly, neurobehavioral, and mental health problems to poor social adjustment and stress tolerance. Neurons are particularly sensitive to alcohol exposure. The neurotoxic action of alcohol, i.e., through ROS production, induces DNA damage and neuronal cell death by apoptosis. In addition, epigenetics, including DNA methylation, histone posttranslational modifications (PTMs), and non-coding RNA, play an important role in the neuropathology of FASD. However, little is known about the temporal dynamics and kinetics of histones and their PTMs in FASD.ResultsWe examined the effects of postnatal alcohol exposure (PAE), an animal model of human third-trimester equivalent, on the kinetics of various histone proteins in two distinct brain regions, the frontal cortex, and the hypothalamus, using in vivo 2H2O-labeling combined with mass spectrometry-based proteomics. We show that histones have long half-lives that are in the order of days. We also show that H3.3 and H2Az histone variants have faster turnovers than canonical histones and that acetylated histones, in general, have a faster turnover than unmodified and methylated histones. Our work is the first to show that PAE induces a differential reduction in turnover rates of histones in both brain regions studied. These alterations in histone turnover were associated with increased DNA damage and decreased cell proliferation in postnatal rat brain.ConclusionAlterations in histone turnover might interfere with histone deposition and chromatin stability, resulting in deregulated cell-specific gene expression and therefore contribute to the development of the neurological disorders associated with FASD. Using in vivo 2H2O-labeling and mass spectrometry-based proteomics might help in the understanding of histone turnover following alcohol exposure and could be of great importance in enabling researchers to identify novel targets and/or biomarkers for the prevention and management of fetal alcohol spectrum disorders.

Highlights

Alcohol consumption during pregnancy is a significant public health problem and can result in a continuum of adverse outcomes to the fetus known as fetal alcohol spectrum disorders (FASD)
postnatal alcohol exposure (PAE) altered the turnover rates of canonical histones and histone variants To explore the effects of alcohol exposure on histone turnover in postnatal rat brain, we administered a milk diet containing 11.34% of ethanol (2.5 g/kg per day, alcohol-fed, AF) or an isocaloric liquid control diet to 2-day-old Sprague Dawley rat pups for 5 days
Most neuroepigenetic studies have focused on DNA methylation and histone posttranslational modifications (PTM) as the primary mechanisms affecting chromatin structure and gene expression; little is known about the temporal dynamics and turnover of histones

Summary

Introduction

Alcohol consumption during pregnancy is a significant public health problem and can result in a continuum of adverse outcomes to the fetus known as fetal alcohol spectrum disorders (FASD). The neurotoxic action of alcohol, i.e., through ROS production, induces DNA damage and neuronal cell death by apoptosis. Neurons are sensitive to alcohol exposure during critical periods of brain development when neurons form intricate spatial connections and organizations [4]. Mechanisms such as apoptosis, inhibition of proliferation, migration, and differentiation have been implicated in the establishment of alcohol-mediated patterning defects [5, 6]. We showed that alcohol increases βendorphin neuronal death by apoptosis and reduces expression of important neuronal genes such as Pomc gene and brain-derived neurotrophic factors (BDNF), which regulate neurogenesis and cell survival in the hypothalamus [12,13,14,15]. Alcohol metabolism produces reactive oxygen species (ROS) and acetaldehyde, which have been shown to cause oxidative DNA damage [17, 18] and induce the production of 7,8-dihydro-8-oxo-2′-deoxyguanosine (oxo8dG) DNA lesions [19, 20]

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