Authors: Tyrone DeSpenza; Stephanie Getz; Sheng Chih Jin; Jinhui Zhang; Wei Wang; Murat Gunel; Bryan Luikart; Duy Phan; August Allocco; Carol Nelson-Williams; Richard Lifton; Kristopher Kahle (New Haven, CT)

Introduction: Congenital hydrocephalus (CH) is a morbid, heterogeneous disorder treated mainly with surgical shunting. A personalized medical approach could enhance therapeutic options for patients. We have found loss-of-function de novo mutations in PTEN , which over-activate downstream mTOR signaling, to cause multiple cases of sporadic CH. We hypothesized that drug inhibition of mTOR signaling in PTEN -mutated hydrocephalus could represent a feasible non-surgical treatment strategy for CH. Methods: We conditionally knocked out PTEN in C57BL/6J mice using Cre-LoxP recombination in fluorescently labeled neural progenitor cells. Kaplan-Meier survival curves were constructed for PTEN KO and their WT, control littermates. Rapamycin was injected intraperitoneally in PTEN KO and WT mice daily from postnatal (P) day 10-22. PTEN KO and WT mice brains were sectioned, immunostained, and imaged with confocal microscopy to assess for ventricular size. Results: PTEN KO resulted in fully penetrant, fatal hydrocephalus with a median survival of P17.5. The Kaplan Meier survival analysis showed that WT animals (n=41) survived significantly longer than PTEN animals (n=10) (p<.0001). Rapamycin was able to fully rescue the fatal hydrocephalus phenotype (n=8) by inhibition of mTOR (p<.0001). Conclusion: Conditional PTEN KO in neural progenitor cells in mice caused fatal hydrocephalus that was rescued by pharmacological inhibition of the mTOR pathway with Rapamycin. These results show that dysregulated neural progenitor cell fate is involved in the pathogenesis of CH, and suggest a novel treatment paradigm that may be adopted into clinical trials in a subset of CH patients that harbor PTEN mutations.