17Beta-estradiol attenuates programmed cell death in cortical pericontusional zone following traumatic brain injury via upregulation of ERalpha and inhibition of caspase-3 activation
Research highlights
▶ 17Beta-estradiol prevents the cortical pericontusional zone (PCZ) from programmed cell death. ▶ 17Beta-estradiol treatment enhances mRNA induction and protein expression of estrogen receptor alpha in PCZ. ▶ The protective role of 17beta-estradiol in PCZ is via estragon receptor alpha. ▶ 17Beta-estradiol treatment inhibits the activation of caspase-3 in PCZ. ▶ ERalpha specific antagonist reverses the inhibition of caspase-3 activation by 17beta-estradiol in PCZ.
Introduction
Traumatic cerebral contusion is well recognized following severe head injury and important to neurosurgeons since the treatment strategies are still widely debated. More than half of parenchymal lesions in patients with fatal head injuries demonstrated focal contusions at the frontal or temporal lobes (Becker et al., 1977). In the acute phase, traumatic cerebral contusion is characterized by a central necrotic core surrounded by a rim of edematic nonnecrotic tissue, pericontusional zone (PCZ) (Schröder et al., 1995). This PCZ has the potential to lead to prolonged neurological and neuropsychological deterioration. Therefore, PCZ becomes a target for pharmacological manipulation.
An increasing body of studies has demonstrated the contribution of programmed cell death to neuronal and glial cell loss in traumatic cerebral contusion (Ng et al., 2000, Raghupathi et al., 2000) and in PCZ (Miñambres et al., 2008) following traumatic brain injuries. Programmed cell death can be explored through terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL) staining, an indicator of DNA fragmentation (Willingham, 1999), and by observing caspase-3 activation (Davoli et al., 2002, Namura et al., 1998).
Estrogens are now well recognized to affect numerous regions of the brain besides hypothalamus to regulate mood and cognitive function. In addition, a growing body of studies supports that estrogens are effective at protecting against cellular dysfunction and/or damage (Goodman et al., 1996, Green and Simpkins, 2000). The neuroprotective effects of estrogens have been demonstrated in acute cerebral ischemia (Dubal et al., 1998, Simpkins et al., 1997). Therefore, estrogens are valuable candidates for brain protection in the ischemic injury models. In the case of traumatic brain injury, although several studies indicate that estrogens therapy can prevent brain damage after traumatic brain injury (Chen et al., 2009, Soustiel et al., 2005), some published contradictory findings also exist (Bruce-Keller et al., 2007, Lebesgue et al., 2006). Therefore, estrogens therapy deserves further research.
Among three major forms of estrogens in humans and rodents including 17beta-estradiol, estrone and estriol, 17beta-estradiol has the most biological prevalence and potency. Estrogen binding to their receptors, estrogen receptor-α (ERalpha) and estrogen receptor-β (ERbeta) promotes receptor dimerization and translocates to the nucleus to interact with specific DNA sequences in the promoter region of target genes, leading to the regulation of transcription (Landers and Spelsberg, 1992). ERalpha is upregulated in ischemic brain injury upon the estrogen treatment (Dubal et al., 2001, Dubal et al., 2006), but the regulation of ERalpha and ERbeta following traumatic brain injury, especially in PCZ, is still not well understood.
Our results in this study indicated that 17beta-estradiol protects cortical pericontusional zone from programmed cell death via upregulation of ERalpha and this effect is mediated by reverting caspase-3 activation.
Section snippets
Animal, hormone replacement and operation
Adult three-months-old female Sprague–Dawley rats (225–275 g), maintained in a 14/10 light/dark cycle with ad libitum access to food and water, were bilaterally ovariectomized to eliminate endogenous estrogens production and then implanted with a Silastic capsule (0.062 in./0.125 in., inner/outer diameter; Dow Corning, Midland, MI) containing sesame oil or 17beta-estradiol (180 μg/ml; Sigma, St. Louis, MO) under methoxyflurane anesthesia (Dubal et al., 1999, Dubal et al., 2006). One week after
17Beta-estradiol attenuates programmed cell death in the cortical pericontusional zone (PCZ) after traumatic cerebral contusion
Since TUNEL assay is widely used to evaluate programmed cell death, here we made use of it to investigate the effect of 17beta-estradiol on programmed cell death in the cortical pericontusional zone after brain injury. The rats were treated as schematics in Fig. 1. TUNEL assay was performed and showed that programmed cell death occurs in PCZ and it decreases in the estradiol-implanted rats after traumatic brain injury (P < 0.01, the 17beta-estradiol-treated rats compared with the oil-treated
Discussion
Pericontusional zone around traumatic brain contusion is a potential target of treatment since the enlargement and swelling of pericontusional zone enhance intracranial pressure, increase the brain damage and lead to delayed neurological and neuropsychological impairment. Microvascular disturbance and profound hypoperfusion accompanied by edema due to compression and/or occlusion occurs in PCZ after traumatic brain injury (Kushi et al., 2003, Schröder et al., 1995). Programmed cell death is a
Conflict of interest
The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Acknowledgment
This study was supported by Grant from Natural Science Foundation of Liaoning Provincial Science and Technology Commission, Liaoning, China (No. 20071051).
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