Key Roles of CACNA1C/Cav1.2 and CALB1/Calbindin in Prefrontal Neurons Altered in Cognitive Disorders

Abstract

ImportanceThe risk of mental disorders is consistently associated with variants in CACNA1C (L-type calcium channel Cav1.2) but it is not known why these channels are critical to cognition, and whether they affect the layer III pyramidal cells in the dorsolateral prefrontal cortex that are especially vulnerable in cognitive disorders.ObjectiveTo examine the molecular mechanisms expressed in layer III pyramidal cells in primate dorsolateral prefrontal cortices.Design, Setting, and ParticipantsThe design included transcriptomic analyses from human and macaque dorsolateral prefrontal cortex, and connectivity, protein expression, physiology, and cognitive behavior in macaques. The research was performed in academic laboratories at Yale, Harvard, Princeton, and the University of Pittsburgh. As dorsolateral prefrontal cortex only exists in primates, the work evaluated humans and macaques.Main Outcomes and MeasuresOutcome measures included transcriptomic signatures of human and macaque pyramidal cells, protein expression and interactions in layer III macaque pyramidal cells using light and electron microscopy, changes in neuronal firing during spatial working memory, and working memory performance following pharmacological treatments.ResultsLayer III pyramidal cells in dorsolateral prefrontal cortex coexpress a constellation of calcium-related proteins, delineated by CALB1 (calbindin), and high levels of CACNA1C (Cav1.2), GRIN2B (NMDA receptor GluN2B), and KCNN3 (SK3 potassium channel), concentrated in dendritic spines near the calcium-storing smooth endoplasmic reticulum. L-type calcium channels influenced neuronal firing needed for working memory, where either blockade or increased drive by β1-adrenoceptors, reduced neuronal firing by a mean (SD) 37.3% (5.5%) or 40% (6.3%), respectively, the latter via SK potassium channel opening. An L-type calcium channel blocker or β1-adrenoceptor antagonist protected working memory from stress.Conclusions and RelevanceThe layer III pyramidal cells in the dorsolateral prefrontal cortex especially vulnerable in cognitive disorders differentially express calbindin and a constellation of calcium-related proteins including L-type calcium channels Cav1.2 (CACNA1C), GluN2B-NMDA receptors (GRIN2B), and SK3 potassium channels (KCNN3), which influence memory-related neuronal firing. The finding that either inadequate or excessive L-type calcium channel activation reduced neuronal firing explains why either loss- or gain-of-function variants in CACNA1C were associated with increased risk of cognitive disorders. The selective expression of calbindin in these pyramidal cells highlights the importance of regulatory mechanisms in neurons with high calcium signaling, consistent with Alzheimer tau pathology emerging when calbindin is lost with age and/or inflammation.

Kynurenic acid inflammatory signaling expands in primates and impairs prefrontal cortical cognition

“…We analyzed single cell RNA sequencing data from mouse frontal cortex 50 , and single nucleus data from the dlPFC of macaque 51 and human 52 to investigate the expression of AADAT, encoding the KAT II enzyme that synthesizes KYNA, showed marked species differences between mouse mPFC and primate dlPFC. In mouse, there was very low-to-undetectable expression of AADAT across all cell types, and it was further concentrated in glia, with limited expression in neurons (Fig.…”

“… AADAT encodes KAT II, the enzyme that metabolizes kynurenine into kynurenic acid. Single cell/nucleus RNA expression data are from frontal cortex in mouse 50 (a) , and from dlPFC in macaque 51 (b) and human 52 (c) . Note the large differences in scale between mouse and primates, where normalized levels in mouse are much lower, and more focused in glia than in primates.…”

“…We obtained AADAT expression from the following previously published single cell/nucleus RNA sequencing datasets: mouse frontal cortex 50 ; dlPFC (BA46) of neurotypical postmortem human donors 52 ; and dlPFC (BA46) of macaque monkeys 51 . For each dataset, preprocessing and clustering assignments were retained as in the original publications.…”