Post-injury inhibition of miR-181a promotes restoration of hippocampal CA1 neurons after transient forebrain ischemia in rats

Abstract

The cellular and molecular mechanisms regulating post-injury neurogenesis in the adult hippocampus remain undefined. We have previously demonstrated that pre-injury treatment with anti-microRNA-181a preserved neurons and prevented astrocyte dysfunction in the hippocampal CA1 following transient forebrain ischemia. In the present study we assessed post-injury treatment with anti-miR-181a on recovery of CA1 neurons following transient forebrain ischemia in rats. Stereotactic CA1 injection of miR-181a antagomir at either 2h or 7d post-injury resulted in improved restoration of CA1 measured at 28d post-injury. Treatment with antagomir was associated with overexpression of the mir-181a target cell-adhesion associated/related oncogene (CDON) protein and enhanced expression of the neuroprogenitor cell marker doublecortin (DCX) in the CA1. Assessment of GFAP+ cell fate by Cre/Lox-mediated deletion demonstrated that some GFAP+ cells in CA1 exhibited de novo DCX expression in response to injury. In vitro experiments using primary neuronal stem cells confirmed that miR-181a inhibition augmented expression of DCX and directed cellular differentiation towards a neuronal fate. These results suggest that miR-181a inhibition plays a central role in restoration of CA1 neurons via augmentation of early latent neurogenic gene activation in neuralprogenitor cells, including some reactive astrocytes. Therapeutic interventions targeting this restorative process may represent a novel post-injury approach to improve clinical outcomes in survivors of forebrain ischemia.

Significance Statement Persistent cognitive impairment is a major source of decreased quality of life for survivors of cardiac arrest, with impaired memory cited as the most severe long-term deficit (Moulaert et al., 2009). Interruptions in cerebral blood flow result in delayed death of hippocampal CA1 neurons (Horn and Schlote, 1992). Pharmaceutical therapies given during this two-week therapeutic window could drastically reduce the cognitive deficits experienced by survivors of forebrain ischemia. However, interventions that have attempted to directly target neurons after forebrain ischemia have so far failed to translate to effective therapies. Therefore, there is an urgent need for novel treatments that either provide protection against loss or hasten functional recovery of CA1 neurons.