Alan Seth Lewis - US grants

DESCRIPTION (provided by applicant): Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels (h channels) mediate the hyperpolarization-activated current (Ih) and are important for regulating excitability in CA1 pyramidal neurons of the hippocampus. Because localization governs h channel function in the homeostasis of neuronal excitability, and h channel dysfunction has been implicated in temporal lobe epilepsy, our longterm goal is to understand the unknown trafficking and targeting mechanism of h channels in the hippocampus, h channels of CA1 pyramidal neurons as well as neocortical layer V neurons exhibit a striking distal dendritic enrichment (DDE), shown to be critical for control of cellular excitability and synchrony. One molecular candidate implicated in h channel trafficking is the tetratricopeptide repeat-containing (TPR) Rab8b interacting protein (TRIPSb). TRIPSb is the only known interactor of h channels to demonstrate pyramidal neuron DDE in both the hippocampus and cortex mimicking that of HCN1 and 2. Additionally, TRIPSb has been shown to regulate Ih density in oocytes. TRIPSb interacts with h channels via its conserved C-terminal TPR domains in a manner homologous to the peroxisomal import receptor proteins. However, the N-terminal region of TRIPSb shares no homology with any known protein and its function is unknown. Our preliminary data indicate the N-terminus is highly alternatively spliced in a developmentally regulated manner, whereby specific isoforms are upregulated concurrent with DDE onset. Notably, alternative splicing alters the presence of cellular sorting signals thought to be important in trafficking. Because of this considerable but indirect evidence associating TRIPSb with h channel trafficking, we reason that TRIPSb plays an important role in the establishment and/or maintenance of h channel DDE in the hippocampus. To determine TRIPSb's role in hippocampal DDE, we propose the following specific aims: 1) Determine whether TRIPSb in general, and the N-terminus of TRIPSb in particular, are required for h channel DDE in CA1 pyramidal neurons. We will use lentiviral delivery of shRNA and dominant negative TRIPSb constructs in both slice culture and the living animal to determine the effect on h channel DDE in the hippocampus in vivo. 2) Determine the role of TRIPSb N-terminal alternative splicing in h channel trafficking and DDE. We will use single-cell RT-PCR, biotinylation, and viral delivery of TRIPSb splice isoforms to determine how TRIPSb splicing impacts h channel surface trafficking and DDE. PUBLIC HEALTH RELEVANCE: epilepsy remains a major lifelong burden. By understanding how the brain regulates excitability, we will gain insight into the causes of epilepsy and mechanisms for targeted treatment.

PROJECT SUMMARY/ABSTRACT There are few treatments for persistent impulsive aggression in individuals with severe neuropsychiatric disorders, and existing treatments are of limited efficacy yet confer the potential for significant side effects. Aggression contributes to repeat institutionalization and significant costs to healthcare and criminal justice systems. As a neuroscientist and board-certified psychiatrist, this mentored patient-oriented research career development award (K23) will provide training to support Dr. Lewis's goal of becoming an independent translational investigator focused on the development of novel therapeutic approaches informed by the neural circuitry regulating impulsive aggression. To accomplish his career and research goals, Dr. Lewis will receive training in translational neuroscience by acquiring new skills to manipulate neural circuitry in mice and humans, identify effects on behaviors related to impulsive aggression, and rigorously analyze resulting data. Training will be guided by a team of mentors and contributors who are leaders in the basic and translational science of neural circuits underlying behavior relevant to neuropsychiatric disorders as well as in statistical analysis. The research plan is supplemented by coursework at Yale in translational neuroscience and statistical modeling, as well as participation in relevant seminars and national scientific meetings. The proposed experiments build upon preliminary data in mouse models demonstrating that activation of ?7 nicotinic receptors in the dentate gyrus (DG) reduces aggressive behavior, while reduction of ?7 receptors increases aggressive behavior. Because ?7 receptors are highly enriched on local inhibitory interneurons of the DG and their activation enhances DG and hippocampal inhibition, the hypothesis will be tested that hippocampal excitatory-inhibitory (E/I) balance governs the expression of aggressive behavior in mice and humans. In Aim 1, activity of excitatory or inhibitory neurons in the mouse DG will be recorded using fiber photometry and manipulated using optogenetics to determine how DG E/I balance influences aggression onset in real time during resident- intruder tests. In Aim 2, this circuit mechanism will be translated to human subjects with schizophrenia using a pharmacological probe. The ?7 partial agonist GTS-21 will be orally administered to enhance hippocampal inhibition, and an Emotional Go/NoGo Task used to determine effects on impulsive responding to negative and neutral valence stimuli. This behavioral task is mediated by prefrontal-temporolimbic circuitry, including the hippocampus, and performance correlates with a history of impulsive aggression in schizophrenia patients. These focused experiments take an innovative translational approach in mice and humans to understand how hippocampal activity influences behavioral measures related to impulsive aggression in neuropsychiatric disorders. Training in contemporary techniques of translational neuroscience, deliberate integration of animal and human paradigms, and data analysis will serve as a critical foundation to support Dr. Lewis's independent translational research career focused on identifying novel therapeutic options for impulsive aggression.