Estradiol is a known neurotrophic and neuroprotective factor. Our previous work demonstrated that replacement with physiological concentrations of
estradiol protects the cortex against
middle cerebral artery occlusion (MCAO)-induced cell death. The cerebral cortex exhibits
caspase-dependent programmed cell death (PCD) in many models of focal
cerebral ischemia. We hypothesized that
estradiol attenuates PCD during
stroke injury. The current study explored the temporospatial pattern of markers of PCD, their relationship to the evolution of injury, and their modulation by
estradiol. Rats were ovariectomized and treated with either
estradiol or vehicle. One week later, rats underwent MCAO, and brains were collected at 1, 4, 8, 16, and 24 hr. We assessed the temporospatial evolution of
infarction volume, DNA fragmentation, and levels of
spectrin cleavage products in ischemic cortex.
Estradiol led to a delay and attenuation of injury-mediated DNA fragmentation as early
as 8 hr after MCAO.
Estradiol also dramatically reduced the level of the 120 kDa
caspase-mediated
spectrin breakdown product (SBDP120) at 4 hr but not at 8 or 16 hr. The SBDP150, produced by
caspase and
calpain, showed peak levels at 16 hr but was not altered by
estradiol. These results strongly suggest that
estradiol protects the ischemic cortex by attenuating PCD, thereby reducing
caspase activity, DNA fragmentation, and subsequently, overall cell death. These studies deepen our understanding of the mechanisms underlying
estrogen-mediated neuroprotection.