Development of in vivo probes to study the function of TRIP8b in cognition

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Abstract Cognitive dysfunction is a common feature of neuropsychiatric diseases related to chronic stress. These symptoms can be debilitating, and despite the high prevalence of illnesses like Major Depressive Disorder, there are relatively few treatment options. To better address these symptoms, novel molecular targets are needed. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels play a critical role in regulating excitability in the hippocampus, a brain region critically involved in cognition. To avoid cardiac side effects associated with antagonizing HCN channels (which are also expressed in the heart), our group has focused on TRIP8b, a neuron-specific subunit of HCN channels. In our recently published report (Lyman et al, in press at Science Translational Medicine), we established that chemogenetically disrupting the interaction between TRIP8b and HCN in the dorsal hippocampus is sufficient to rescue impairments in cognition after chronic stress. Combined, these results are consistent with the hypothesis that a small molecule that disrupts the TRIP8b-HCN interaction could rescue the cognitive dysfunction seen after chronic stress. In order to capitalize on this discovery, our group recently executed a high throughput screen to identify small molecule inhibitors of the TRIP8b-HCN interaction. We identified one candidate scaffold which shows promising activity as a TRIP8b inhibitor. This compound series serves as the basis for our current submission in which we propose further medicinal chemistry optimization to develop TRIP8b inhibitors for use as chemical probes in order to study TRIP8b in vivo. In our enclosed preliminary data, we show that our inhibitor potently disrupts the interaction between TRIP8b and HCN in cells with negligible toxicity. This inhibition produces robust effects on Ih, the current mediated by HCN channels both in vivo and in vitro. To expand upon this work, we propose three aims. In Aim 1, we will perform iterative medicinal chemistry optimization to develop compounds with improved potency and pharmaceutical characteristics. Compounds that perform well in our biochemical and biophysical assays will be advanced to cellular assays in Aim 2 in order to determine if they are capable of disrupting the TRIP8b-HCN interaction. In Aim 3 we will utilize our compounds in vivo to study their effect on hippocampal function. Promising compounds will be investigated for their ability to rescue cognitive deficits that result from chronic social defeat, an animal model of chronic stress. These experiments will enable us to develop TRIP8b inhibitors that can be used as chemical probes to study the role of HCN channels in regulating cognitive dysfunction after chronic stress.