Effects of exercise and pharmacological inhibition of histone deacetylases (HDACs) on epigenetic regulations and gene expressions crucial for neuronal plasticity in the motor cortex

Highlights

• HDAC inhibition decreased total HDAC activity in the motor cortex.

• HDAC inhibition increased acetylation level of histone H4 and H3 in the motor cortex.

• Exercise increased acetylation level of histone H4 and H3 in the motor cortex.

• HDAC inhibition enhanced the transcription of crucial genes for neuroplasticity.

• HDAC inhibition presents an enriched platform for neurorehabilitation.

Abstract

The objective of this study was to examine the effect of epigenetic treatment using an histone deacetylases (HDAC) inhibitor in addition to aerobic exercise on the epigenetic markers and neurotrophic gene expressions in the motor cortex, to find a more enriched brain pre-conditioning for motor learning in neurorehabilitation. ICR mice were divided into four groups based on two factors: HDAC inhibition and exercise. Intraperitoneal administration of an HDAC inhibitor (1.2 g/kg sodium butyrate, NaB) and treadmill exercise (approximately at 10 m/min for 60 min) were conducted five days a week for four weeks. NaB administration inhibited total HDAC activity and enhanced acetylation level of histones specifically in histone H4, accompanying the increase of transcription levels of immediate-early genes (IEGs) (c-fos and Arc) and neurotrophins (BDNF and NT-4) crucial for neuroplasticity in the motor cortex. However, exercise enhanced HDAC activity and acetylation level of histone H4 and H3 without the modification of transcription levels. In addition, there were no synergic effects between HDAC inhibition and the exercise regime on the gene expressions. This study showed that HDAC inhibition could present more enriched condition for neuroplasticity to the motor cortex. However, exercise-induced neurotrophic gene expressions could depend on exercise regimen based on the intensity, the term etc. Therefore, this study has a novelty suggesting that pharmacological HDAC inhibition could be an alternative potent approach to present a neuronal platform with enriched neuroplasticity for motor learning and motor recovery, however, an appropriate exercise regimen is expected in this approach.

Introduction

Physical therapy is a primary intervention to rehabilitate the motor impairment of patients with central nervous system (CNS) disorders such as cerebrovascular accident (CVA), Parkinson’s disease, spinocerebellar degeneration, etc. Physical therapy has two distinct physiological targets, focused on by different exercise-types: (1) motor learning exercises targeting inferred movements due to neuronal deficits and (2) aerobic exercises to adjust physical condition and metabolic system. Specifically, in the rehabilitation of a CVA patient with motor deficits, cortical synapses compensate for the inferred neuronal system; however, it is required to enhance the regeneration and plasticity in the modulation of post-synaptic receptors, the expression of pre-synaptic neurotransmitters, and synaptic formation to rebuild or expand neuronal networks (Murphy and Corbett, 2009). An important therapeutic goal of motor recovery is therefore to maximize neuronal plasticity and facilitate motor tasks throughout motor learning.

Neurotrophins play a crucial role in neuroplasticity, neurogenesis, and neuroprotection (neuronal maintenance and survival) in the central nervous system. Of these, brain-derived neurotrophic factor (BDNF) has a high affinity for Tropomyosin receptor kinase B (TrkB), which transduces intracellular signals for neuroplasticity in the brain (Reichardt, 2006, Sandhya et al., 2013). Findings from recent studies have indicated that aerobic exercise increases the expression of neurotrophins in the motor-related cortex, including cerebral and cerebellar cortex, in addition to the hippocampus, and beneficially contributes to motor learning by enhancing neuronal plasticity in the brain to rebuild motor function (Neeper et al., 1996, Rasmussen et al., 2009, Uysal et al., 2015). Thus, it is expected that aerobic exercise would condition a beneficial platform for motor learning exercise through the upregulation of neurotrophins in the motor-related cortex. Similarly, it is expected that combination of aerobic exercise with motor learning exercise could more beneficially upregulate the outcomes of motor learning in physical therapy for patients with motor deficit caused by CNS disorders.

Furthermore, aerobic exercise beneficially modulates the expression of genes related to neuroplasticity in the brain, such as BDNF, under epigenetic regulation. Epigenetic mechanisms regulate gene transcription based on the modifications of DNA promoter regions and histones in the chromatin. Epigenetic mechanisms involve a variety of DNA and histone modifications (i.e., methylation and acetylation of DNA and histones). In particular, acetylation level of specific lysine residues in histones is one of the most potent epigenetic modifications and is essential for transcriptional regulation (Abel and Rissman, 2013, Cosin-Tomas et al., 2014, de Meireles et al., 2016, Ieraci et al., 2015, Lovatel et al., 2013, Zhong et al., 2016). Histone acetylation on lysine residues generally increases DNA transcription and is regulated by histone acetyltransferases (HATs) and histone deacetylases (HDACs) (Elsner et al., 2011). HATs acetylate the histone and increase DNA transcription, whereas HDACs deacetylate the histone and inhibit DNA transcription. Specifically, studies show that aerobic exercise decreases the expression (Ieraci et al., 2015) and the activity of HDACs (Elsner et al., 2011, Spindler et al., 2014a), and increases histone acetylation (Abel and Rissman, 2013, Ieraci et al., 2015, Intlekofer et al., 2013, Zhong et al., 2016), upregulating the expression of crucial genes for neuroplasticity (Ieraci et al., 2015, Intlekofer et al., 2013).

Interestingly, researchers are currently focusing on pharmacological treatment using HDAC inhibitors (HDACis) in order to present more beneficial epigenetic condition for neurological improvement (neuroprotection, neurogeneration, and neuroplasticity) in patients with CNS disorders. Beneficial effects of treatment with HDACis have been recognized in the recovery of ischemic stroke, degenerative diseases with motor and cognitive deficits, and neuropsychiatric diseases, in animal and clinical studies (Fischer et al., 2010, Ganai et al., 2016, Gupta et al., 2020, Ziemka-Nalecz and Zalewska, 2014). It is well recognized that HDACis inhibit HDAC activity and acetylate histones H3 and H4, relax the chromatin machinery, and enhance the binding of transcription factors like Cyclic AMP responsive element binding protein (CREB) with coactivators to gene promotor regions (Kim et al., 2009). Research has also shown that HDACis increased the transcription of crucial genes for neuroplasticity, including BDNF (Bredy et al., 2007, Intlekofer et al., 2013, Zeng et al., 2011).

Altogether, we can expect a novel clinical strategy based on interactive effects between HDAC inhibition and aerobic exercise on further beneficial outcomes of physical therapy for motor learning. Targeting the correct HDACs using HDACis could be a potent intervention presenting an epigenetic platform and lowering the threshold of the expression of neurotrophic genes caused by aerobic exercise, that leads to a more beneficial environment for rehabilitation of motor functions in patients with CNS disorders. Unfortunately, the interactive effects between HDAC inhibition and aerobic exercise on the modification of epigenetic markers and neurotrophic gene expressions in the brain has not been reported. Therefore, the objective of this study was to examine the possibility of synergistic effects of an HDAC inhibitor (sodium butyrate, NaB) and aerobic exercise on epigenetic regulations of HDAC activity, histone acetylation, and crucial gene transcriptions for neuronal improvement in the motor cortex.