IGF-1 Gene Therapy as a Potentially Useful Therapy for Spontaneous Prolactinomas in Senile Rats.

BACKGROUND: Insulin-like Growth Factor1 (IGF1) is a powerful neuroprotective molecule. We have previously shown that short-term hypothalamic IGF1 gene therapy restores tuberoinfundibular dopaminergic neuron function in aging female rats. OBJECTIVE: Our aim was to implement long-term IGF-I gene therapy in pituitary prolactinomas in senile female rats. METHODS: Here, we assessed the long-term effect of IGF1 gene therapy in the hypothalamus of young (4 mo.) and aging (24 mo.) female rats carrying spontaneous pituitary prolactinomas. We constructed and injected a Helper-Dependent (HD) adenovector expressing the gene for rat IGF1 or the reporter red fluorescent protein DsRed. Ninety-one days post vector injection, all rats were sacrificed and their brains and pituitaries fixed. Serum prolactin (PRL), Estrogen (E2) and progesterone (P4), as well as hypothalamic IGF1 content, were measured by RIA. Anterior pituitaries were immunostained with an anti-rat PRL antibody and submitted to morphometric analysis. RESULTS: DsRed expression in the Mediobasal Hypothalamus (MBH) was strong after the treatment in the DsRed group while IGF1 content in the MBH was higher in the IGF1 group. The IGF1 treatment affected neither pituitary weight nor PRL, E2 or P4 serum levels in the young rats. In the old rats, IGF1 gene therapy reduced gland weight as compared with intact counterparts and tended to reduce PRL levels as compared with intact counterparts. The treatment significantly rescued the phenotype of the lactotropic cell population in the senile adenomas. CONCLUSION: We conclude that long-term hypothalamic IGF1 gene therapy is effective to rescue spontaneous prolactinomas in aging female rats.

Rejuvenating Effect of Long-Term Insulin-Like Growth Factor-I Gene Therapy in the Hypothalamus of Aged Rats with Dopaminergic Dysfunction.

The aging female rat constitutes an interesting model of spontaneous and progressive age-related dopaminergic dysfunction as it allows assessing new therapeutic strategies for Parkinson's disease. Insulin-like growth factor I (IGF-I) is emerging as a powerful neuroprotective molecule, strongly induced in the central nervous system after different insults. We constructed a helper-dependent recombinant adenoviral vector (HDRAd-IGFI) harboring the gene for rat IGF-I. This was used to implement long-term IGF-I gene therapy in the hypothalamus of aged female rats, which display hypothalamic dopaminergic (DA) dysfunction and, as a consequence, chronic hyperprolactinemia. Rejuvenating long-term IGF-I gene therapy was implemented in young (3 months) and aged (24 months) female rats, which received a single intrahypothalamic injection of 4 × 109 viral particles of either HD-RAd-IGFI or HD-RAd-DsRed (control vector) and were sacrificed 119 days postinjection. In the young animals, neither vector modified serum prolactin (PRL) levels, but in the RAd-IGFI-injected aged rats a nearly full reversion of their hyperprolactinemic status was recorded. Morphometric analysis revealed a significant increase in the total number of tyrosine hydroxylase (TH)-positive cells in the hypothalamus of experimental compared with control aged animals (5874 ± 486 and 3390 ± 498, respectively). Our results indicate that IGF-I gene therapy in aged female rats is highly effective in rejuvenating the hypothalamic DA neuron groups.

Estrogen inhibits tuberoinfundibular dopaminergic neurons but does not cause irreversible damage.

Dopaminergic neurons of the hypothalamic tuberoinfundibular dopaminergic (TIDA) system exert a tonic inhibitory control on prolactin (PRL) secretion whereas estrogen, known to inhibit TIDA neuron function, has been postulated to be toxic to TIDA neurons when it is chronically high. In order to determine whether estrogen in high doses can cause permanent damage to TIDA function, we submitted young female rats to continue high doses of estrogen administered, either centrally (intrahypothalamic estrogen implants) or peripherally (subcutaneous estrogen implants or weekly intramuscular (i.m.) injections for 7 weeks), subsequently withdrawing the steroid and observing the evolution of lactotrophes, serum PRL and TIDA neurons. Serum PRL was measured by radioimmunoassay whereas tyrosine hydroxylase positive (TH+) neurons and PRL cells were morphometrically assessed in sections of fixed hypothalami and pituitaries, respectively. After 30 days, hypothalamic estrogen implants induced a significant increase in serum PRL, whereas TH+ neurons were not detectable in the arcuate-periventricular hypothalamic (ARC) region of estrogen-implanted rats. Removal of implants on day 30 restored TH expression in the ARC and brought serum PRL back to basal levels 30 days after estrogen withdrawal. Subcutaneous or i.m. administration of estrogen for 7 weeks induced a marked hyperprolactinemia. However, 30 weeks after estrogen withdrawal, TH neuron numbers in the ARC were back to normal and serum PRL returned to basal levels. After peripheral but not central estrogen withdrawal, pituitary weight and lactotrophic cell numbers remained slightly increased. Our data suggest that estrogen even at high doses, does not cause permanent damage to TIDA neurons.