In vivo optical imaging of early-stage apoptosis in mouse brain after transient cerebral ischemia

Apoptosis is one of the mechanisms contributing to neuronal degeneration in ischemic stroke. In vivo imaging of annexin V (A5) was performed at 12 hr, 24 hr, 48 hr, and 4 days after 90-min transient middle cerebral artery occlusion (tMCAO) in mice with a fluorescent protein Cy5.5. Immunohistochemistry for heat shock protein 70 (HSP70), A5, and TUNEL were also performed with brain sections after the tMCAO. In vivo fluorescence was strongly observed at 48 hr over the head, especially with removal of both head skin and skull bone. Zonal ex vivo fluorescent signals were surrounding the ischemic core, and double-positive cells with Cy5.5/exogenous A5 antibody were found in this area. HSP70 was observed at the peak time of 24 hr; A5 became detectable at 12 hr, with increasing numbers until 48 hr. The number of TUNEL-positive cells increased at 24 hr and retained the high level until 4 days, showing a dissociating temporal pattern with A5. Double-positive cells for A5/TUNEL reached their peak at 48 hr. All the data suggest that some cells still have a chance to be rescued for a long period after acute cerebral ischemia. The in vivo Cy5.5 fluorescence representing A5 signal spatially surrounding the ischemic core temporally detects an early-stage apoptosis after cerebral ischemia.