ABSTRACT
Title
Targeting NF-kappaB and epigenetic chromatin remodelling in the therapy of post-ischemic brain injury
Authors
A. Lanzillotta(1), I. Sarnico (1), M. Benarese (1), C. Branca (1), G. Pignataro (2), O. Cuomo (2), L. Annunziato (2), G. Faraco (3), F.Blasi (3), A. Chiarugi (3), PF. Spano (1), M. Pizzi (1).
(1) Department of Biomedical Sciences & Biotechnologies, School of Medicine, University of Brescia, 25123 Brescia, Italy; (2) Department of Neuroscience, School of Medicine, Federico II University of Naples, Italy; (3) Department of Preclinical and Clinical Pharmacology, University of Florence, Italy.
(1) Department of Biomedical Sciences & Biotechnologies, School of Medicine, University of Brescia, 25123 Brescia, Italy; (2) Department of Neuroscience, School of Medicine, Federico II University of Naples, Italy; (3) Department of Preclinical and Clinical Pharmacology, University of Florence, Italy.
Abstract
Diverse nuclear factor-kappaB (NF-kappaB) subunits can be responsible for opposite effects on neuronal survivaland they are highly implicated in the pathophysiology of post-ischemic brain injury. NF-kappaB is a dimeric transcription factor that can be formed by the assembly of five diverse proteins, p50, p52, RelA (p65), RelB and c-Rel which dimerize to form the active complexes. We demonstrated that within the same neuronal cell the balance between activation of p50/RelA and c-Rel-containing complexes fine-tunes the threshold of neuron vulnerability to the ischemic insult. Both in vivo and in vitro experimental models of brain ischemia demonstrate that while p50/p65 dimer promotes the expression of proapoptotic genes Bim and Noxa and neuronal cell death, c-Rel-containing dimers can rescue neuronal cells by activating transcription of antiapoptotic Bcl-xL gene.
The neurotoxic effects of p50/RelA during ischemia is associated with epigenetic regulation of the NF-kappaB protein, i.e. site specific acetylation of RelA. RelA can be acetylated on five different lysines (Lys122, Lys123, Lys218, Lys221, and Lys310) and each lysine can differently regulate the activity of NF-kappaB. The acetylation status of RelA is modulated by a family of histone acetyl transferase (HAT) and by histone deacetylase (HDAC) belonging to class I and class II. A Class III HDAC, sirtuin 1 (SIRT1), activated by resveratrol, selectively deacetylates RelA at Lys310 residue. In neurons exposed to oxygen glucose deprivation, as well as in cortices of mice exposed to middle cerebral artery occlusion, the acetylation of RelA at the Lys310 residue increases, while the acetylation at the other lysine residues falls down. On the contrary, after a preconditioning ischemia able to limit the injury produced by lethal ischemia, total acetylation of RelA is predominant and acetylation at the Lys 310 is negligible. It can be inferred that during lethal ischemia the activation of p50/RelA is associated with unbalanced Lys310 RelA acetylation versus the total acetylation of RelA. Treatments able to restore the normal acetylation of RelA produce neuroprotection as well as treatment targeting RelA activation. Thus, administration of resveratrol, by deacetylating RelA on Lys310, can reproduce the protective effects of preconditioning. Likewise, treatment withthe HDAC inhibitor MS-275 or SAHA, by increasing total acetylation of RelA, induce neuroprotection. These results suggest that acetylation status of p50/RelA has a key role in the epigenetic regulation of transcription and can represent a neuroprotective target in brain ischemia.
The neurotoxic effects of p50/RelA during ischemia is associated with epigenetic regulation of the NF-kappaB protein, i.e. site specific acetylation of RelA. RelA can be acetylated on five different lysines (Lys122, Lys123, Lys218, Lys221, and Lys310) and each lysine can differently regulate the activity of NF-kappaB. The acetylation status of RelA is modulated by a family of histone acetyl transferase (HAT) and by histone deacetylase (HDAC) belonging to class I and class II. A Class III HDAC, sirtuin 1 (SIRT1), activated by resveratrol, selectively deacetylates RelA at Lys310 residue. In neurons exposed to oxygen glucose deprivation, as well as in cortices of mice exposed to middle cerebral artery occlusion, the acetylation of RelA at the Lys310 residue increases, while the acetylation at the other lysine residues falls down. On the contrary, after a preconditioning ischemia able to limit the injury produced by lethal ischemia, total acetylation of RelA is predominant and acetylation at the Lys 310 is negligible. It can be inferred that during lethal ischemia the activation of p50/RelA is associated with unbalanced Lys310 RelA acetylation versus the total acetylation of RelA. Treatments able to restore the normal acetylation of RelA produce neuroprotection as well as treatment targeting RelA activation. Thus, administration of resveratrol, by deacetylating RelA on Lys310, can reproduce the protective effects of preconditioning. Likewise, treatment withthe HDAC inhibitor MS-275 or SAHA, by increasing total acetylation of RelA, induce neuroprotection. These results suggest that acetylation status of p50/RelA has a key role in the epigenetic regulation of transcription and can represent a neuroprotective target in brain ischemia.