Background: Molecular mechanisms underlying stroke-induced neurogenesis have not been fully investigated. The microRNA 17-92 cluster (miR17-92) regulates proliferation and differentiation of adult neural progenitor cells (NPCs). The present study investigated whether the miR17-92 cluster in NPCs is required for stroke-induced neurogenesis.
Methods and Results: Mice with inducible and conditional knockdown of the miR17-92 cluster in nestin lineage NPCs (nestin-CreERT2/miR17-92-/-, 17-92-cKO, n=9) and wild-type litters (WT, n=9) were treated by tamoxifen. Administration of tamoxifen resulted in more than 60% reduction of individual members of the miR-17-92 cluster (miR-17: 1.0 vs 0.4; miR-19a: 1.0 vs 0.3; miR-19b: 1.0 vs 0.2; miR-20a: 1.0 vs 0.4; miR-92a: 1.0 vs 0.4 fold in WT, p<0.05) in NPCs localized to the subventricular zone (SVZ). Two days after termination of tamoxifen treatment, these mice were subjected to permanent right middle cerebral artery occlusion (MCAO) and sacrificed 28 days post-MCAo. Compared to WT mice, 17-92-cKO mice exhibited significant (p<0.05) reduction of proliferation of NPCs measured by the number of Ki67+ cells (226±43 vs 471±100 cells/mm2) and the number of DCX+ neuroblasts (11±2% vs 24±4% ) in the ischemic SVZ. Cultured NPCs harvested from ischemic cKO mice showed significant (p<0.05) reduction of BrdU+ cells (37±2% vs 61±4% WT , n=3/group), Tuj1+ neuroblasts (5±0.2% vs 9±0.4% ), GFAP+ cells (33±3% vs 53±2% ), and NG2+ oligodendrocyte progenitor cells (OPCs, 3±0.1% vs 5±0.5%). These in vivo and in vitro data indicate that reduction of the miR17-92 cluster suppresses stroke-induced neurogenesis and gliogenesis. Western blot analysis showed that miR17-92 cKO significantly (p<0.05) increased and reduced a cytoskeleton-associated protein, Enigma homolog1 (ENH1, 1.6 vs 1.0 fold), and its down-stream transcription factor, inhibitor of differentiation1 (ID1, 1.0 vs 0.6 fold), respectively. ENH1 is a putative target of the miR17-92 cluster.
Conclusion: Our data indicate that the miR17-92 cluster in adult nestin lineage NPCs is required for stroke-induced neurongenesis and gliogenesis, and that the miR17-92 cluster possibly targets ENH1/ID1 signaling.