# Microglial histone deacetylase-3 conditional deletion attenuates neurological deficits after intracerebral hemorrhage

## TL;DR

Deleting HDAC3 in microglia reduces brain inflammation and improves recovery after intracerebral hemorrhage in mice.

## Contribution

This study reveals a novel role of microglial HDAC3 in regulating neurological outcomes after ICH.

## Key findings

- Conditional deletion of HDAC3 in microglia improves acute and long-term neurological outcomes after ICH.
- HDAC3 deletion reduces proinflammatory mediators and increases anti-inflammatory mediators in the brain after ICH.
- The effects of HDAC3 deletion are independent of hematoma size.

## Abstract

Stimulation of the innate immune system after intracerebral hemorrhage (ICH), characterized by microglial activation, contributes to ICH-induced neuroinflammation and brain damage. Despite the efficacy of broad-spectrum histone deacetylase (HDAC) inhibitors in improving acute neurological outcomes after ICH, the isoform- or cell-specific roles of histone deacetylases (HDACs) after ICH remain largely understudied. Given the emerging role of HDAC3 in various neuropathological conditions, we herein evaluate the functional role of microglial HDAC3 after ICH using newly developed microglia-specific HDAC3 conditional knockout mice (cKO). The microglia-specific conditional deletion of HDAC3 in male and female mice improved acute and long-term neurobehavioral outcomes following ICH. Furthermore, conditional deletion of HDAC3 in microglia significantly attenuated the expression of proinflammatory mediators, such as Nos2, S100A9, TNF-α, and IL-6, and augmented the expression of anti-inflammatory mediators, such as Arg-1, in the ipsilateral brain region following ICH. This observation was found to be concomitant with a reduction in the number of Iba1-positive cells, further implicating attenuation of neuroinflammatory response after ICH. Moreover, conditional deletion of HDAC3 in microglia did not alter hematoma volume after ICH, suggesting that the observed effects are independent of hematoma size. Overall, the data implicate a novel role of microglial HDAC3 in regulating neurological deficits after ICH in male and female subjects.