Histone deacetylase 3 regulates microglial function through histone deacetylation.

As the primary innate immune cells of the brain, microglia respond to damage and disease through pro-inflammatory release of cytokines and neuroinflammatory molecules. Histone acetylation is an activating transcriptional mark that regulates inflammatory gene expression. Inhibition of histone deacetylase 3 (Hdac3) has been utilized in pre-clinical models of depression, stroke, and spinal cord injury to improve recovery following injury, but the molecular mechanisms underlying Hdac3's regulation of inflammatory gene expression in microglia is not well understood. To address this lack of knowledge, we examined how pharmacological inhibition of Hdac3 in an immortalized microglial cell line (BV2) impacted histone acetylation and gene expression of pro- and anti-inflammatory genes in response to immune challenge with lipopolysaccharide (LPS). Flow cytometry and cleavage under tags & release using nuclease (CUT & RUN) revealed that Hdac3 inhibition increases global and promoter-specific histone acetylation, resulting in the release of gene repression at baseline and enhanced responses to LPS. Hdac3 inhibition enhanced neuroprotective functions of microglia in response to LPS through reduced nitric oxide release and increased phagocytosis. The findings suggest Hdac3 serves as a regulator of microglial inflammation, and that inhibition of Hdac3 facilitates the microglial response to inflammation and its subsequent clearing of debris or damaged cells. Together, this work provides new mechanistic insights into therapeutic applications of Hdac3 inhibition which mediate reduced neuroinflammatory insults through microglial response.

Gap junctions mediate discrete regulatory steps during fly spermatogenesis.

Gametogenesis requires coordinated signaling between germ cells and somatic cells. We previously showed that Gap junction (GJ)-mediated soma-germline communication is essential for fly spermatogenesis. Specifically, the GJ protein Innexin4/Zero population growth (Zpg) is necessary for somatic and germline stem cell maintenance and differentiation. It remains unknown how GJ-mediated signals regulate spermatogenesis or whether the function of these signals is restricted to the earliest stages of spermatogenesis. Here we carried out comprehensive structure/function analysis of Zpg using insights obtained from the protein structure of innexins to design mutations aimed at selectively perturbing different regulatory regions as well as the channel pore of Zpg. We identify the roles of various regulatory sites in Zpg in the assembly and maintenance of GJs at the plasma membrane. Moreover, mutations designed to selectively disrupt, based on size and charge, the passage of cargos through the Zpg channel pore, blocked different stages of spermatogenesis. Mutations were identified that progressed through early germline and soma development, but exhibited defects in entry to meiosis or sperm individualisation, resulting in reduced fertility or sterility. Our work shows that specific signals that pass through GJs regulate the transition between different stages of gametogenesis.