Progesterone Differentially Regulates Pro- and Anti-Apoptotic Gene Expression in Cerebral Cortex Following Traumatic Brain Injury in Rats

Although the administration of progesterone has been shown to be neuroprotective in experimental models of traumatic brain injury (TBI), the mechanisms for this beneficial effect are still poorly understood. The present study examined the effects of progesterone on mRNA and protein levels of the Bcl-2 apoptosis regulatory genes, bax, bad, bcl-2, and bcl-x_L, in cerebral cortex after TBI. Male Sprague-Dawley rats were subjected to either sham surgery or lateral fluid percussion brain injury of moderate severity (2.4–2.6 atm). Within 1 h post-surgery, progesterone (4 mg/kg) or vehicle (corn oil) administration was initiated for 1–7 days postoperatively. Our results indicate that bax and bad mRNA levels and Bax and Bad protein expression in the ipsilateral, injured cerebral cortex were significantly elevated post-TBI, while mRNA levels of bcl-2 and bcl-x_L or Bcl-2 and Bcl-x_L protein expression were not changed. Under the sham-treated condition, progesterone significantly increased mRNA levels of the anti-apoptotic gene, bcl-2, but down-regulated pro-apoptotic gene expression(bax and bad) in cerebral cortex. After TBI, progesterone treatment reduced bax and bad mRNA levels in the ipsilateral cerebral cortex of TBI rats, and decreased Bax and Bad protein levels. In addition, bcl-2 and bcl-x_L mRNA levels, as well as Bcl-2 and Bcl-x_L protein expression, were increased by progesterone in TBI injured cortex. These data indicate that one of the neuroprotective mechanisms of progesterone may be related to its differential regulation of apoptotic signals.