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Enhancing neurogenesis may be a powerful stroke therapy. Here, we tested in a rat model of ischemic stroke the beneficial effects of NSI‐189, an orally active, new molecular entity (mol. wt. 366) with enhanced neurogenic activity, and indicated as an anti‐depressant drug in a clinical trial (Fava et al., 2015, Molecular Psychiatry, DOI: 10.1038/mp.2015.178) and being tested in a Phase 2 efficacy trial (ClinicalTrials.gov, 2016, ClinicalTrials.gov Identifier: NCT02695472) for treatment of major depression. Oral administration of NSI‐189 in adult Sprague–Dawley rats starting at 6 hr after middle cerebral artery occlusion, and daily thereafter over the next 12 weeks resulted in significant amelioration of stroke‐induced motor and neurological deficits, which was maintained up to 24 weeks post‐stroke. Histopathological assessment of stroke brains from NSI‐189‐treated animals revealed significant increments in neurite outgrowth as evidenced by MAP2 immunoreactivity that was prominently detected in the hippocampus and partially in the cortex. These results suggest NSI‐189 actively stimulated remodeling of the stroke brain. Parallel in vitro studies further probed this remodeling process and demonstrated that oxygen glucose deprivation and reperfusion (OGD/R) initiated typical cell death processes, which were reversed by NSI‐189 treatment characterized by significant attenuation of OGD/R‐mediated hippocampal cell death and increased Ki67 and MAP2 expression, coupled with upregulation of neurogenic factors such as BDNF and SCF. These findings support the use of oral NSI‐189 as a therapeutic agent well beyond the initial 6‐hr time window to accelerate and enhance the overall functional improvement in the initial 6 months post stroke.

SummaryClass-switch DNA recombination (CSR) is central to the antibody response, in that it changes the immunoglobulin heavy chain (IgH) constant region, thereby diversifying biological effector functions of antibodies. The activation-induced cytidine deaminase (AID)-centered CSR machinery excises and rejoins DNA between an upstream (donor) and a downstream (acceptor) S region, which precede the respective constant region DNA. AID is stabilized on S regions by 14-3-3 adaptors. These adaptors display a high affinity for 5′-AGCT-3′ repeats, which recur in all S regions. However, how 14-3-3, AID, and the CSR machinery target exclusively the donor and acceptor S regions is poorly understood. Here, we show that histone methyltransferases and acetyltransferases are induced by CD40 or Toll-like receptor signaling and catalyze H3K4me3 and H3K9ac/K14ac histone modifications, which are enriched in S regions but do not specify the S region targets of CSR. By contrast, the combinatorial H3K9acS10ph modification specifically marks the S regions set to recombine and directly recruits 14-3-3 adaptors for AID stabilization there. Inhibition of the enzymatic activity of GCN5 and PCAF histone acetyltransferases reduces H3K9acS10ph in S regions, 14-3-3 and AID stabilization, and CSR. Thus, H3K9acS10ph is a histone code that is “written” specifically in S regions and is “read” by 14-3-3 adaptors to target AID for CSR as an important biological outcome.