Chronic administration of a HDAC inhibitor boosts microglial differentiation and treats neurological disease in a mouse model of intellectual disability.

Histone deacetylase inhibitors (HDACi) control chromatin states through histone acetylation and are of interest to treat neurological disorders. Defect in lysine-specific methyltransferase 2D (KMT2D) decreases the open chromatin mark H3K4me3 in brains of a mouse model of Kabuki Syndrome (KS), a rare intellectual disability disorder. We utilized single-cell RNA sequencing to explore the molecular landscape of microglia from the mouse hippocampus under different treatment conditions. untreated, PEG [dimethyl sulfoxide, 5% (DMSO) and polyethylene glycol, 45% (PEG)], HPBCD [DMSO (5%), PEG (45%), Hydroxypropyl-ß-cyclodextrin, 0.2 gm/ml (HPBCD)], and TCF [DMSO (5%), PEG (45%), HPBCD (0.2 gm/ml), Vorinostat (5 mg/ml, Vo)]. Administration of a brain-permeant triple combination formulation (TCF) of 2-hydroxypropyl-b-cyclodextrin (HPBCD), polyethylene glycol-400 (PEG) and the FDA-approved histone deacetylase inhibitor (HDACi), vorinostat, weekly over 3 months, increased microglial levels (but failed to stimulate hippocampal neurogenesis). The differential gene expression analysis in combination with ingenuity pathway analysis predicted the specific effect of TCF on microglial histone 3, whose acetylation restored H3K4me3 independent of Kmt2D.This study examines the impact of the histone deacetylase inhibitor (Vo as a brain permeant formulation) on microglia in a Kabuki syndrome model. Overall design: To investigate the molecular response to various treatment regimens, we performed single-cell RNA sequencing. Hippocampi were extracted from all mice, and single cells were isolated from each hippocampus. The single cells were hash-tagged to distinguish between WT and Kbk individual samples. Due to the large sample size, the experiment was conducted across eight batches. A total of 60 mice were used, balanced for sex and genotype. Hash-tagged single cells from each batch were pooled and subsequently processed for single-cell capture, library preparation, RNA sequencing, and analysis using Cell Ranger and Seurat. The 3–4-month-old group, comprising both male and female mice, was divided into four treatment categories: untreated, PEG (dimethyl sulfoxide, 5% [DMSO] and polyethylene glycol, 45% [PEG]), HPBCD (DMSO 5%, PEG 45%, and hydroxypropyl-ß-cyclodextrin, 0.2 g/mL), and TCF (DMSO 5%, PEG 45%, HPBCD 0.2 g/mL, and Vorinostat 5 mg/mL [Vo]). This cohort consisted of 48 mice (2 genotypes [WT and Kbk] × 2 sexes [male and female] × 4 treatments × 3 mice per sex per treatment). The one-month-old cohort consisted of 12 mice (2 genotypes × 2 sexes × 3 mice per sex).