ABSTRACT
Recent human exome-sequencing studies have implicated polymorphic Brg1-associated factor (BAF) complexes (mammalian SWI/SNF chromatin remodeling complexes) in several intellectual disabilities and cognitive disorders, including autism. However, it remains unclear how mutations in BAF complexes result in impaired cognitive function. Post-mitotic neurons express a neuron-specific assembly, nBAF, characterized by the neuron-specific subunit BAF53b. Subdomain 2 of BAF53b is essential for the differentiation of neuronal precursor cells into neurons. We generated transgenic mice lacking subdomain 2 of Baf53b (BAF53bΔSB2). Long-term synaptic potentiation (LTP) and long-term memory, both of which are associated with phosphorylation of the actin severing protein cofilin, were assessed in these animals. A phosphorylation mimic of cofilin was stereotaxically delivered into the hippocampus of BAF53bΔSB2 mice in an effort to rescue LTP and memory. BAF53bΔSB2 mutant mice show impairments in phosphorylation of synaptic cofilin, LTP, and memory. Both the synaptic plasticity and memory deficits are rescued by overexpression of a phosphorylation mimetic of cofilin. Baseline physiology and behavior were not affected by the mutation or the experimental treatment. This study suggests a potential link between nBAF function, actin cytoskeletal remodeling at the dendritic spine, and memory formation. This work shows that a targeted manipulation of synaptic function can rescue adult plasticity and memory deficits caused by manipulations of nBAF, and thereby provides potential novel avenues for therapeutic development for multiple intellectual disability disorders.
Subject(s)
Chromatin Assembly and Disassembly/genetics , Chromosomal Proteins, Non-Histone/metabolism , Memory/physiology , Mutation/genetics , Neuronal Plasticity/genetics , Phosphopyruvate Hydratase/metabolism , Actin Depolymerizing Factors/genetics , Actin Depolymerizing Factors/metabolism , Animals , Calcium-Calmodulin-Dependent Protein Kinase Type 2/genetics , Calcium-Calmodulin-Dependent Protein Kinase Type 2/metabolism , Cell Nucleolus/metabolism , Chromosomal Proteins, Non-Histone/genetics , Hippocampus/cytology , Hippocampus/metabolism , In Vitro Techniques , Long-Term Potentiation/genetics , Mice , Mice, Inbred C57BL , Mice, Transgenic , Nerve Net/physiology , Neurons/ultrastructure , Phosphopyruvate Hydratase/genetics , Phosphorylation/genetics , Sequence Deletion/genetics , Transduction, GeneticABSTRACT
Designer receptors exclusively activated by designer drug (DREADDs) are a novel tool with the potential to bidirectionally drive cellular, circuit, and ultimately, behavioral changes. We used DREADDs to evaluate memory formation in a hippocampus-dependent task in mice and effects on synaptic physiology in the dorsal hippocampus. We expressed neuron-specific (hSyn promoter) DREADDs that were either excitatory (HM3D) or inhibitory (HM4D) in the dorsal hippocampus. As predicted, hSyn-HM3D was able to transform a subthreshold learning event into long-term memory (LTM), and hSyn-HM4D completely impaired LTM formation. Surprisingly, the opposite was observed during experiments examining the effects on hippocampal long-term potentiation (LTP). hSyn-HM3D impaired LTP and hSyn-HM4D facilitated LTP. Follow-up experiments indicated that the hSyn-HM3D-mediated depression of fEPSP appears to be driven by presynaptic activation of inhibitory currents, whereas the hSyn-HM4D-mediated increase of fEPSP is induced by a reduction in GABAA receptor function. To determine whether these observations were promoter specific, we next examined the effects of using the CaMKIIα promoter that limits expression to forebrain excitatory neurons. CaMKIIα-HM3D in the dorsal hippocampus led to the transformation of a subthreshold learning event into LTM, whereas CaMKIIα-HM4D blocked LTM formation. Consistent with these findings, baseline synaptic transmission and LTP was increased in CaMKIIα-HM3D hippocampal slices, whereas slices from CaMKIIα-HM4D mice produced expected decreases in baseline synaptic transmission and LTP. Together, these experiments further demonstrate DREADDs as being a robust and reliable means of modulating neuronal function to manipulate long-term changes in behavior, while providing evidence for specific dissociations between LTM and LTP. SIGNIFICANCE STATEMENT: This study evaluates the efficacy of designer receptors exclusively activated by designer drug (DREADDs) as a means of bidirectionally modulating the hippocampus in not only a hippocampus-dependent task but also in hippocampal synaptic plasticity. This is the first study to evaluate the effects of DREADD-mediated inhibition and excitation in hippocampal long-term potentiation. More specifically, this study evaluates the effect of promoter-specific expression of DREADD viruses in a heterogenic cell population, which revealed surprising effects of different promoters. With chemogenetics becoming a more ubiquitous tool throughout studies investigating circuit-specific function, these data are of broad interest to the neuroscientific community because we have shown that promoter-specific effects can drastically alter synaptic function within a specific region, without parallel changes at the level of behavior.