Intracerebral hemorrhage (ICH) activates thrombin, a potent mitogen. Thrombin triggers mitosis by modulating several intracellular mitogenic molecules including Src family kinases. These molecules regulate mitogen-activated protein kinases (MAPKs) and cell cycle proteins such as cyclin-dependent kinases (Cdks); and play critical roles in mitogenic signaling pathways and cell cycle progression. Since aberrant cell cycle reentry results in death of mature neurons, cell cycle inhibition appears to be a candidate strategy for the treatment of neurological diseases including ICH. However, this can also block cell cycle (proliferation) of neural progenitor cells (NPCs) and thus impair brain neurogenesis leading to cognitive deficits. We hypothesized that inhibition of cell cycle by blocking mitogenic signaling molecules (i.e., Src family kinase members) blocks cell cycle reentry of mature neurons without injuring NPCs, which will avoid cognitive side effects during cell cycle inhibition treatment for ICH. Our data shows: (1) Thrombin 30U/ml results in apoptosis of mature neurons via neuronal cell cycle reentry
in vitro
; (2) PP2 (Src family kinase inhibitor) 0.3 µM attenuates the thrombin-induced neuronal apoptosis via blocking neuronal cell cycle reentry, but does not affect the viability of NPCs at the same doses
in vitro
; (3) Intracerebral ventricular thrombin injection (20U, i.c.v.) results in neuron loss in hippocampus and cognitive deficits 5 weeks after thrombin injection
in vivo
; (4) PP2 (1mg/kg, i.p.), given immediately after thrombin injection (i.c.v.), blocks the thrombin-induced neuron loss in hippocampus and cognitive deficits, whereas PP2 on its own at the same doses does not affect normal cognition
in vivo
. These suggest that Src kinase inhibition prevents hippocampal neuron death via blocking neuronal cell cycle reentry after ICH, but does not affect survival of NPCs.
The effect of ATM knockdown on ionizing radiation-induced neuronal cell cycle reentry in Drosophila
