Abstract
Pyramidal neurons in hippocampal area CA2 are distinct from neighboring CA1 in that they resist synaptic long-term potentiation (LTP) at CA3 Schaffer Collateral synapses. Regulator of G Protein Signaling 14 (RGS14) is a complex scaffolding protein enriched in CA2 dendritic spines that naturally blocks CA2 synaptic plasticity and hippocampus-dependent learning, but the cellular mechanisms by which RGS14 gates LTP are largely unexplored. A previous study has attributed the lack of plasticity to higher rates of calcium (Ca2+) buffering and extrusion in CA2 spines. Additionally, a recent proteomics study revealed that RGS14 interacts with two key Ca2+-activated proteins in CA2 neurons: calcium/calmodulin, and CaMKII. Here, we investigate whether RGS14 regulates Ca2+ signaling in its host CA2 neurons. We find the nascent LTP of CA2 synapses due to genetic knockout (KO) of RGS14 in mice requires Ca2+-dependent postsynaptic signaling through NMDA receptors, CaMK, and PKA, revealing similar mechanisms to those in CA1. We report RGS14 negatively regulates the long-term structural plasticity of dendritic spines of CA2 neurons. We further show that wild-type (WT) CA2 neurons display significantly attenuated spine Ca2+ transients during structural plasticity induction compared with the Ca2+ transients from CA2 spines of RGS14 KO mice and CA1 controls. Finally, we demonstrate that acute overexpression of RGS14 is sufficient to block spine plasticity, and elevating extracellular Ca2+ levels restores plasticity to RGS14-expressing neurons. Together, these results demonstrate for the first time that RGS14 regulates plasticity in hippocampal area CA2 by restricting Ca2+ elevations in CA2 spines and downstream signaling pathways.
Significance Statement Recent studies of hippocampal area CA2 have provided strong evidence in support of a clear role for this apparently plasticity-resistant subregion of the hippocampus in social, spatial, and temporal aspects of memory. Regulator of G Protein Signaling 14 (RGS14) is a critical factor that inhibits synaptic plasticity in CA2, but the molecular mechanisms by which RGS14 limits LTP remained unknown. Here we provide new evidence that RGS14 restricts spine calcium (Ca2+) in CA2 neurons and that key downstream Ca2+-activated signaling pathways are required for CA2 plasticity in mice lacking RGS14. These results define a previously unrecognized role for RGS14 as a natural inhibitor of postsynaptic Ca2+ signaling in hippocampal area CA2.
Author Contributions: PE, PP, and DL performed research; PE, PP, and MS analyzed data; PE, SD, JH, and RY designed research; PE wrote and PE, SD, JH and RY edited the paper.
Footnotes
Conflict of Interest: The authors declare no competing financial interests.
Funding Sources: P.R.E. was supported by a predoctoral fellowship from NINDS (1F31NS086174). J.R.H. was supported by NINDS grants 5R01NS37112 and 1R21NS074975. S.M.D. was supported by the Intramural Research Program of NIEHS (Z01ES100221). R.Y. was supported by NIMH grants R01MH080047 and DP1NS096787.