RGS14 limits postsynaptic calcium to block CA2 synaptic plasticity Open Access

Evans II, Paul (2016)

Permanent URL: https://etd.library.emory.edu/concern/etds/t722h930z?locale=en
Published

Abstract

The regulators of G protein signaling (RGS) proteins are a diverse family of proteins that function as central components of G protein and other signaling pathways. RGS14 is an unusual RGS protein that acts as a multifunctional scaffolding protein to integrate signaling events and pathways essential for synaptic plasticity, including conventional and unconventional G protein signaling and mitogen-activated protein kinase (MAPK). In primate and rodent brain, RGS14 is highly expressed in pyramidal neurons in hippocampal area CA2. However, the protein distribution and spatiotemporal expression patterns of RGS14 in mouse brain during postnatal development have not been described. We find that RGS14 mRNA/protein are upregulated in mouse brain during early postnatal development until reaching highest, sustained levels in adulthood. Our findings also reveal a dynamic localization of RGS14 protein in mouse brain. CA2 pyramidal neurons differ dramatically from neighboring regions CA1/CA3 in that they lack a capacity for long-term potentiation (LTP) of synaptic transmission, which is highly correlated with memory formation. While we previously identified RGS14 as a critical factor limiting CA2 plasticity and hippocampus-dependent learning and memory, the mechanisms by which RGS14 blocks synaptic plasticity in CA2 remained unknown. Independent studies attributed this lack of plasticity to robust calcium (Ca2+) buffering and extrusion in CA2 spines relative to CA1. However, RGS14 has not been implicated in Ca2+ signaling required synaptic potentiation. Here we provide the first evidence that RGS14 natively associates with key members of Ca2+ signaling pathways in mouse brain. Additionally, the nascent LTP found in CA2 neurons of mice lacking RGS14 requires Ca2+-stimulated pathways. Our results further show RGS14 impairs CA2 spine structural plasticity, the activity-dependent enlargement of spines associated with synaptic potentiation. Finally, we find that CA2 neurons lacking RGS14 display robust spine structural plasticity and significantly larger spine Ca2+ transients than WT CA2 or CA1 controls. Our findings define a previously unknown role of RGS14 in the regulation of Ca2+ signaling in neurons. Moreover, we provide strong evidence that RGS14 limits spine Ca2+ levels during synaptic activity to restrict plasticity in area CA2.

Table of Contents

Table of Contents

Page

Chapter 1: Introduction 1

1.1 Overview of G protein/GPCR/RGS signaling 2

1.2 Molecular characterization of Regulator of G protein Signaling 14 (RGS14) 3

1.2.1 RGS14 protein architecture 3

1.2.2 RGS14 bridges conventional, unconventional, and MAPK signaling 5

1.2.3 Cellular regulation of RGS14 10

1.3 RGS14 naturally limits learning and synaptic plasticity in hippocampal CA2 12

1.3.1 RGS14 suppresses LTP and spatial learning 12

1.3.2 LTP as a model of memory formation and typical mechanisms 14

1.3.3 Possible mechanisms by which RGS14 suppresses plasticity in hippocampal CA2 17

1.3.4 Connecting CA2 - redefining anatomical substrates of learning 20

1.4 Overall hypothesis and objective of this dissertation 26

Chapter 2: Postnatal developmental expression of RGS14 in the mouse brain 29

2.1 Introduction 30

2.2 Experimental Procedures 32

2.3 Results 38

2.4 Discussion 55

Chapter 3: RGS14 limits postsynaptic calcium to block CA2 synaptic plasticity 63

3.1 Introduction 64

3.2 Experimental Procedures 64

3.3 Results 76

3.4 Discussion 100

Chapter 4: Discussion 106

4.1 RGS14 expression during early postnatal development: the aging conspiracy 107

against plasticity in CA2

4.2 RGS14 regulation of Ca2+ signaling in CA2 spines 108

4.3 Working model of CA2 plasticity regulation by RGS14 109

4.4 Defining mnemonic functions for CA2 and RGS14 113

4.5 Roles for CA2 in human behavior and disease 117

4.6 RGS14: more than just a suppressor of learning and memory? 121

4.7 Summary and Perspectives 123

References 126

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