Acetylation of c-Myc at Lysine 148 Protects Neurons After Ischemia.

This study focuses on understanding the role of c-Myc, a cancer-associated transcription factor, in the penumbra following ischemic stroke. While its involvement in cell death and survival is recognized, its post-translational modifications, particularly acetylation, remain understudied in ischemia models. Investigating these modifications could have significant clinical implications for controlling c-Myc activity in the central nervous system. Although previous studies on c-Myc acetylation have been limited to non-neuronal cells, our research examines its expression in perifocal cells during stroke recovery to explore regulatory mechanisms via acetylation. We found that in peri-infarct neurons, c-Myc is upregulated with acetylation at K148 but not K323 during the acute phase of stroke, with SIRT2 deacetylase primarily affecting K148 acetylation. Molecular dynamics simulations suggest that lysine 148 plays a crucial role in stabilizing c-Myc spatial structure. Increased acetylation at K148 reduces c-Myc compaction, potentially limiting its nuclear penetration, promoting calpain-mediated cleavage, and decreasing nuclear localization. Additionally, cytoplasmic acetylation at K148 may alter c-Myc's interaction with unidentified proteins, potentially influencing its pro-apoptotic effects and promoting cytoplasmic accumulation. Targeting SIRT2 with selective inhibitors could be a promising avenue for future stroke therapy strategies.

Acetylation of p53 in the Cerebral Cortex after Photothrombotic Stroke.

p53 expression and acetylation are crucial for the survival and death of neurons in penumbra. At the same time, the outcome of ischemia for penumbra cells depends largely on the histone acetylation status, but the effect of histone acetyltransferases and deacetylases on non-histone proteins like p53 is largely understudied. With combined in silico and in vitro approach, we have identified enzymes capable of acetylation/deacetylation, distribution, stability, and pro-apoptotic activity of p53 in ischemic penumbra in the course of post-stroke recovery, and also detected involved loci of acetylation in p53. The dynamic regulation of the acetylation of p53 at lysine 320 is controlled by acetyltransferase PCAF and histone deacetylases HDAC1 and HDAC6. The in silico simulation have made it possible to suggest the acetylation of p53 at lysine 320 acetylation may facilitate the shuttling of p53 between the nucleus and cytoplasm in penumbra neurons. Acetylation of p53 at lysine 320 is more preferable than acetylation at lysine 373 and probably promotes survival and repair of penumbra neurons after stroke. Strategies to increase p53 acetylation at lysine 320 via increasing PCAF activity, inhibiting HDAC1 or HDAC6, inhibiting p53, or a combination of these interventions may have therapeutic benefits for stroke recovery and would be promising for neuroprotective therapy of stroke.

HDAC1 Expression, Histone Deacetylation, and Protective Role of Sodium Valproate in the Rat Dorsal Root Ganglia After Sciatic Nerve Transection.

Nerve injury is an important reason of human disability and death. We studied the role of histone deacetylation in the response of the dorsal root ganglion (DRG) cells to sciatic nerve transection. Sciatic nerve transection in the rat thigh induced overexpression of histone deacetylase 1 (HDAC1) in the ipsilateral DRG at 1-4 h after axotomy. In the DRG neurons, HDAC1 initially upregulated at 1 h but then redistributed from the nuclei to the cytoplasm at 4 h after axotomy. Histone H3 was deacetylated at 24 h after axotomy. Deacetylation of histone H4, accumulation of amyloid precursor protein, a nerve injury marker, and GAP-43, an axon regeneration marker, were observed in the axotomized DRG on day 7. Neuronal injury occurred on day 7 after axotomy along with apoptosis of DRG cells, which were mostly the satellite glial cells remote from the site of sciatic nerve transection. Administration of sodium valproate significantly reduced apoptosis not only in the injured ipsilateral DRG but also in the contralateral ganglion. It also reduced the deacetylation of histones H3 and H4, prevented axotomy-induced accumulation of amyloid precursor protein, which indicated nerve injury, and overexpressed GAP-43, a nerve regeneration marker, in the axotomized DRG. Therefore, HDAC1 was involved in the axotomy-induced injury of DRG neurons and glial cells. HDAC inhibitor sodium valproate demonstrated the neuroprotective activity in the axotomized DRG.

The Expression and Localization of Histone Acetyltransferases HAT1 and PCAF in Neurons and Astrocytes of the Photothrombotic Stroke-Induced Penumbra in the Rat Brain Cortex.

Stroke is one of the leading reasons of human death. Ischemic penumbra that surrounds the stroke-induced infarction core is potentially salvageable, but molecular mechanisms of its formation are poorly known. Histone acetylation induces chromatin decondensation and stimulates gene expression. We studied the changes in the levels and localization of histone acetyltransferases HAT1 and PCAF in penumbra after photothrombotic stroke (PTS, a stroke model). In PTS, laser irradiation induces local occlusion of cerebral vessels after photosensitization by Rose Bengal. HAT1 and PCAF are poorly expressed in normal cortical neurons and astrocytes, but they are overexpressed 4-24 h after PTS. Their predominant localization in neuronal nuclei did not change after PTS, but their levels in the astrocyte nuclei significantly increased. Western blotting showed the increase of HAT1 and PCAF levels in the cytoplasmic fraction of the PTS-induced penumbra. In the nuclear fraction, PCAF level did not change, and HAT1 was overexpressed only at 24 h post-PTS. PTS-induced upregulation of HAT1 and PCAF in the penumbra was mainly associated with overexpression in the cytoplasm of neurons and especially astrocytes. HAT1 and PCAF did not co-localize with TUNEL-positive cells that indicated their nonparticipation in PTS-induced apoptosis.

Overexpression of HDAC6, but not HDAC3 and HDAC4 in the penumbra after photothrombotic stroke in the rat cerebral cortex and the neuroprotective effects of α-phenyl tropolone, HPOB, and sodium valproate.

Epigenetic processes play important roles in brain responses to ischemic injury. We studied effects of photothrombotic stroke (PTS, a model of ischemic stroke) on the intracellular level and cellular localization of histone deacetylases HDAC3, HDAC4 and HDAC6 in the rat brain cortex, and tested the potential neuroprotector ability of their inhibitors. The background level of HDAC3, HDAC4 and HDAC6 in the rat cerebral cortex was relatively low. HDAC3 localized in the nuclei of some neurons and few astrocytes. HDAC4 was found in the neuronal cytoplasm. After PTS, their levels in penumbra did not change, but HDAC4 appeared in the nuclei of some cells. Its level in the cytoplasmic, but not nuclear fraction of penumbra decreased at 24, but not 4 h after PTS. HDAC6 was upregulated in neurons and astrocytes in the PTS-induced penumbra, especially in the nuclear fraction. Unlike HDAC3 and HDAC4, HDAC6 co-localized with TUNEL-positive apoptotic cells. Inhibitory analysis confirmed the involvement of HDAC6, but not HDAC3 and HDAC4 in neurodegeneration. HDAC6 inhibitor HPOB, HDAC2/8 inhibitor α-phenyl tropolone, and non-specific histone deacetylase inhibitor sodium valproate, but not HDAC3 inhibitor BRD3308, or HDAC4 inhibitor LMK235, decreased PTS-induced infarction volume in the mouse brain, reduced apoptosis, and recovered the motor behavior. HPOB also restored PTS-impaired acetylation of α-tubulin. α-phenyl tropolone restored acetylation of histone H4 in penumbra cells. These results suggest that histone deacetylases HDAC6 and HDAC2 are the possible molecular targets for anti-ischemic therapy, and their inhibitors α-phenyl tropolone, HBOP and sodium valproate can be considered as promising neuroprotectors.

Expression of Histone Deacetylases HDAC1 and HDAC2 and Their Role in Apoptosis in the Penumbra Induced by Photothrombotic Stroke.

In ischemic stroke, vascular occlusion rapidly induces tissue infarct. Over the ensuing hours, damage spreads to adjacent tissue and forms transition zone (penumbra), which is potentially salvageable. Epigenetic regulation of chromatin structure controls gene expression and protein synthesis. We studied the expression of histone deacetylases HDAC1 and HDAC2 in the penumbra at 4 or 24 h after photothrombotic stroke (PTS) in the rat brain cortex. PTS increased the expression of HDAC1 and HDAC2 in penumbra and caused the redistribution of HDAC1 but not HDAC2 from the neuronal nuclei to cytoplasm. In astrocytes, HDAC1 expression and localization did not change. In neurons, HDAC2 localized exclusively in nuclei, but in astrocytes, it was also observed in processes. PTS induced neuronal apoptosis in the penumbra. TUNEL-stained apoptotic neurons co-localized with HDAC2 but not HDAC1. These data suggest that HDAC2 may represent the potential target for anti-stroke therapy and its selective inhibition may be a promising strategy for the protection of the penumbra tissue after ischemic stroke.