To date, manipulating hypothalamic function mostly relies on the use of conditional knockout mice or transgenic overexpression. The major limitation to these approaches is that they do not take into account the complexities in the development of neuroendocrine neurons and their projections, and the compensatory adaptations that occur when these neurons are manipulated during early life. Alternatively, microinjections of adeno-associated viruses (AAV) delivering siRNAs have been used to modify hypothalamic function in adulthood. The greatest limitation of this technique is the invasiveness and relative inefficiency of the procedure. The present application intends to circumvent these limitations by developing a novel, minimally invasive method to manipulate hypothalamic neuronal function in a temporally defined and cell-specific manner. Among the hypothalamic systems that can be used as a prototype for these studies, the melanocortin system of the arcuate nucleus (ARC) stands out as an ideal candidate. It has been extensively studied and shown to play a critical role in regulating energy balance through modulation of food intake, body weight and glucose homeostasis. It is composed of two major populations of neurons with opposite functions;neurons containing pro-opiomelanocortin (POMC) inhibit the drive to eat and stimulate energy expenditure, neurons containing neuropeptide Y/Agouti-related peptide (NPY/AgRP) stimulate feeding behavior and inhibit energy expenditure. The consequences of altering the functions of either neuronal subset can be reliably assessed non-invasively, by measuring food intake and body weight. From the human health standpoint, developing new tools to study this system has an enormous value;the dramatic increase in childhood and adult obesity resulting from nutritional alterations during early life makes it urgent to develop novel methods to better understand the central mechanisms underlying the control of feeding behavior and energy homeostasis. This is a particularly important issue because energy balance can be permanently affected by nutritional challenges taking place during the critical period of "developmental programming" that in humans occurs during late gestation and in rodents, during the early postnatal period. A major advantage of the technology we propose to develop is that it can be used to modify ARC function after the developmental programming of energy balance is complete. We propose to silence the POMC and AgRP genes by delivering RNA interference (RNAi) to the ARC via the intravascular administration of modified AAV2 particles engineered to transduce hypothalamic cells. We anticipate that the successful execution of these studies will pave the way to the eventual application of similar approaches to treat disorders of the neuroendocrine brain. We also anticipate that these studies will provide the basis for new delivery strategies to the brain for basic research purposes and emerging therapies.
This application proposes to develop a novel approach to manipulate gene expression in the neuroendocrine brain. This approach is based on the intravascular delivery of RNAi via modified viruses engineered to display tropism for the hypothalamus. It is anticipated that this strategy will provide an invaluable tool to generate animal models of neuroendocrine disorders and to attempt therapeutic intervention of hypothalamic disease.