ESTROGENIC REGULATION OF GENE EXPRESSION DURING NEURONAL

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Recently, estrogen receptors (ER) have been discovered in primary sensory neurons of the rat dorsal root ganglion (DRG), suggesting that specific properties of these neurons are subject to regulation by gonadal steroid hormones. Preliminary findings indicate that several major cytoskeletal protein mRNAs as well as neurotrophin receptor mRNAs are targets of estrogenic regulation in DRG neurons. This suggests that estrogen and ER may have an important role in regulating the neurite growth properties of DRG neurons. The long-term objectives of this project are to define the molecular programs affected by estrogen in sensory neurons and to understand how gonadal steroids influence the growth and regeneration of these neurons. The specific aims of this proposal are to test the following 3 hypotheses. The first hypothesis is that ER expression in the DRG is regulated by circulating gonadal steroid hormones. In situ hybridization, RNA blotting; immunocytochemistry will be used to evaluate the effects of estrogen treatment on the distribution and levels of ER and its encoding mRNA in the DRG of ovariectomized female rats, and to determine if sex differences in ER/ER mRNA expression in the DRG exist. Reverse transcription-polymerase chain reaction (RT-PCR) will be used to evaluate alternative splicing of ER mRNA as a function of hormone state and gender. The second hypothesis is that estrogenic regulation of specific cytoskeletal and neurotrophin receptor genes can modulate the axotomy response of DRG neurons. In situ hybridization, RNase protection assays and RNA blotting methods will be used to study the effects of estrogen on the steady-state levels of mRNAs encoding specific cytoskeletal proteins (BetaII, BetaIII and alpha1-tubulin, peripherin and tau) and those encoding neurotrophin receptors (p75, trkA, trkB) in normal as well as in regenerating DRG neurons. The third hypothesis is that estrogen influences the regenerative properties of DRG neurons. We will determine if estrogen alters the regeneration rate of either the fastest growing DRG axons or the growth properties of the more slowly regenerating axons in the sciatic nerve of ovariectomized female rats after a peripheral nerve crush using the fast axonal transport paradigm. Gender differences in regeneration parameters will be assessed in those studies. The health-relatedness of this proposal is in the potential identification of gender differences in neuronal injury and in the new information that will be gained concerning the potentially therapeutic role of estrogen in neuronal injury.