Postnatal expression of the lysine methyltransferase SETD1B is essential for learning and the regulation of neuron-enriched genes

Epigenetic Mechanism of SETD1B-mediated Histone Methylation in Cognitive Impairment Induced by Sevoflurane Anesthesia in Neonatal Mice

Sevoflurane (Sev) anesthesia is associated with cognitive deficits and neurotoxicity. This study explores the epigenetic mechanism of SET domain containing 1B (SETD1B) in Sev-induced cognitive impairment in neonatal mice. Neonatal mice (C57BL/6, n = 72) were exposed to 3% Sev for 2 h per day at P6, 7, and 8, and the control neonatal mice were only separated from the mother for 2 h. The mice were divided into groups of 12 individuals, with an equal number of male and female mice in each group. Mice were intraperitoneally injected with adenovirus-packaged SETD1B overexpression vector. Behavioral tests (Morris water maze, open field test, T-maze, novel object recognition, etc.) were performed at P30. Mouse hippocampal neuronal cells were cultured in vitro. SETD1B, C-X-C motif chemokine receptor 4 (CXCR4), NLR family pyrin domain containing 1 (NLRP1), Cleaved Caspase1, and GSDMD-N expressions in hippocampal tissues or cells were determined by quantitative real-time polymerase chain reaction and Western blot. SETD1B and histone H3 lysine 4 methylation (H3K4me1, H3K4me2, and H3K4me3) enrichment on the CXCR4 promoter was analyzed by ChIP. Sev insulted cognitive impairment and diminished SETD1B expression in mouse hippocampal tissues. SETD1B overexpression mitigated cognitive impairment, enhanced H3K4me3 levels in hippocampal tissues, and restrained hippocampal neuronal pyroptosis. SETD1B increased CXCR4 expression by elevating the H3K4me3 level on the CXCR4 promoter, thereby curbing NLRP1/Caspase1-mediated hippocampal neuronal pyroptosis. To conclude, SETD1B enhances CXCR4 expression by elevating the H3K4me3 level on the CXCR4 promoter, thereby suppressing NLRP1/Caspase1-triggered hippocampal neuronal pyroptosis and alleviating Sev-induced cognitive impairment in neonatal mice.

KMT2 Family of H3K4 Methyltransferases: Enzymatic Activity-dependent and -independent Functions

Histone-lysine N-methyltransferase 2 (KMT2) methyltransferases are critical for gene regulation, cell differentiation, animal development, and human diseases. KMT2 biological roles are often attributed to their methyltransferase activities on lysine 4 of histone H3 (H3K4). However, recent data indicate that KMT2 proteins also possess non-enzymatic functions. In this review, we discuss the current understanding of KMT2 family, with a focus on their enzymatic activity-dependent and -independent functions. Six mammalian KMT2 proteins of three subgroups, KMT2A/B (MLL1/2), KMT2C/D (MLL3/4), and KMT2F/G (SETD1A/B or SET1A/B), have shared and distinct protein domains, catalytic substrates, genomic localizations, and associated complex subunits. Recent studies have revealed the importance of KMT2C/D in enhancer regulation, differentiation, development, tumor suppression and highlighted KMT2C/D enzymatic activity-dependent and -independent roles in mouse embryonic development and cell differentiation. Catalytic dependent and independent functions for KMT2A/B and KMT2F/G in gene regulation, differentiation, and development are less understood. Finally, we provide our perspectives and lay out future research directions that may help advance the investigation on enzymatic activity-dependent and -independent biological roles and working mechanisms of KMT2 methyltransferases.

Conserved reduction of m6A RNA modifications during aging and neurodegeneration is linked to changes in synaptic transcripts

N⁶-methyladenosine (m⁶A) regulates mRNA metabolism. While it has been implicated in the development of the mammalian brain and in cognition, the role of m⁶A in synaptic plasticity, especially during cognitive decline, is not fully understood. In this study, we employed methylated RNA immunoprecipitation sequencing to obtain the m⁶A epitranscriptome of the hippocampal subregions CA1, CA3, and the dentate gyrus and the anterior cingulate cortex (ACC) in young and aged mice. We observed a decrease in m⁶A levels in aged animals. Comparative analysis of cingulate cortex (CC) brain tissue from cognitively intact human subjects and Alzheimer's disease (AD) patients showed decreased m⁶A RNA methylation in AD patients. m⁶A changes common to brains of aged mice and AD patients were found in transcripts linked to synaptic function including calcium/calmodulin-dependent protein kinase 2 (CAMKII) and AMPA-selective glutamate receptor 1 (Glua1). We used proximity ligation assays to show that reduced m⁶A levels result in decreased synaptic protein synthesis as exemplified by CAMKII and GLUA1. Moreover, reduced m⁶A levels impaired synaptic function. Our results suggest that m⁶A RNA methylation controls synaptic protein synthesis and may play a role in cognitive decline associated with aging and AD.

The role of histone methyltransferases in neurocognitive disorders associated with brain size abnormalities

Brain size is controlled by several factors during neuronal development, including neural progenitor proliferation, neuronal arborization, gliogenesis, cell death, and synaptogenesis. Multiple neurodevelopmental disorders have co-morbid brain size abnormalities, such as microcephaly and macrocephaly. Mutations in histone methyltransferases that modify histone H3 on Lysine 36 and Lysine 4 (H3K36 and H3K4) have been identified in neurodevelopmental disorders involving both microcephaly and macrocephaly. H3K36 and H3K4 methylation are both associated with transcriptional activation and are proposed to sterically hinder the repressive activity of the Polycomb Repressor Complex 2 (PRC2). During neuronal development, tri-methylation of H3K27 (H3K27me3) by PRC2 leads to genome wide transcriptional repression of genes that regulate cell fate transitions and neuronal arborization. Here we provide a review of neurodevelopmental processes and disorders associated with H3K36 and H3K4 histone methyltransferases, with emphasis on processes that contribute to brain size abnormalities. Additionally, we discuss how the counteracting activities of H3K36 and H3K4 modifying enzymes vs. PRC2 could contribute to brain size abnormalities which is an underexplored mechanism in relation to brain size control.

Histone lysine methyltransferase-related neurodevelopmental disorders: current knowledge and saRNA future therapies

Neurodevelopmental disorders encompass a group of debilitating diseases presenting with motor and cognitive dysfunction, with variable age of onset and disease severity. Advances in genetic diagnostic tools have facilitated the identification of several monogenic chromatin remodeling diseases that cause Neurodevelopmental disorders. Chromatin remodelers play a key role in the neuro-epigenetic landscape and regulation of brain development; it is therefore not surprising that mutations, leading to loss of protein function, result in aberrant neurodevelopment. Heterozygous, usually de novo mutations in histone lysine methyltransferases have been described in patients leading to haploinsufficiency, dysregulated protein levels and impaired protein function. Studies in animal models and patient-derived cell lines, have highlighted the role of histone lysine methyltransferases in the regulation of cell self-renewal, cell fate specification and apoptosis. To date, in depth studies of histone lysine methyltransferases in oncology have provided strong evidence of histone lysine methyltransferase dysregulation as a determinant of cancer progression and drug resistance. As a result, histone lysine methyltransferases have become an important therapeutic target for the treatment of different cancer forms. Despite recent advances, we still lack knowledge about the role of histone lysine methyltransferases in neuronal development. This has hampered both the study and development of precision therapies for histone lysine methyltransferases-related Neurodevelopmental disorders. In this review, we will discuss the current knowledge of the role of histone lysine methyltransferases in neuronal development and disease progression. We will also discuss how RNA-based technologies using small-activating RNAs could potentially provide a novel therapeutic approach for the future treatment of histone lysine methyltransferase haploinsufficiency in these Neurodevelopmental disorders, and how they could be first tested in state-of-the-art patient-derived neuronal models.