Schizophrenia is a debilitating psychiatric disorder of unknown etiology, affecting approximately 1% of the population. Recently, the glutamate system has become an exciting new focus in the study and treatment of schizophrenia. In particular, genetic and pharmacological evidence reveal that the metabotropic glutamate receptor 3 (mGluR3) is a promising drug target for anti-schizophrenia therapies. Moreover, astrocyte dysfunction is linked with schizophrenia, and astrocytes express high levels of mGluR3. Taken together, experiments in primary astrocytes can be used to selectively study mGluR3 physiology, potentially facilitating the development of more specific anti-schizophrenia drug therapies. One useful approach to study astrocytic mGluR3 is the identification of mGluR3-specific interacting partners, such as scaffold proteins. Scaffolds link proteins together, forming signaling complexes and coordinating the trafficking of proteins. However, nothing is currently known about astrocytic scaffold regulation of mGluR3. By screening a large proteomic array, we have found a novel interacting partner for mGluR3, known as the scaffold protein Na+/H+ exchanger regulatory factor 2 (NHERF-2). Interestingly, NHERF-2 is highly expressed in astrocytes, although little is known about its function. The goal of this project is to test if NHERF-2 is a central regulator of the activity and localization of mGluR3 in astrocytes.
In Specific Aim 1, we seek to elucidate the effects of NHERF-2 on mGluR3 signaling. Our preliminary data suggest that association with NHERF-2 may switch the G protein-coupling specificity of mGluR3;thus, we propose to directly study mGluR3 G protein-coupling in cultured astrocytes, as well as downstream mGluR3 signaling outputs in the presence/absence of NHERF-2. A more thorough characterization of mGluR3 signaling in astrocytes will facilitate our understanding of mGluR3 physiology.
In Specific Aim 2, we will examine the role of NHERF-2 in the regulation of mGluR3 agonist-dependent internalization and recycling, using cell surface expression assays. Understanding how NHERF-2 coordinates the trafficking of mGluR3 will provide important insight into the regulation of mGluR3 activity. Finally, in Specific Aim 3, we will determine how NHERF-2 regulates astrocytic mGluR3 localization in vivo. NHERF-2 knockout mice and electron microscopy will be used to visualize mGluR3 localization in astrocytes.
Given the emerging evidence for dysregulation of glutamate signaling in schizophrenia and links between mGluR3 and astrocyte dysfunction in the disease, this research proposal is designed to more fully characterize the physiological function of mGluR3 in the context of its interaction with the astrocytic scaffold NHERF-2. A more clear understanding of the function and regulation of mGluR3 may facilitate the development of more efficacious mGluR3-specific drugs for schizophrenia.