Biology subjects

de Andres, R.

Publications and source records attributed to de Andres, R..

3 recordsLinked to original sources

bioRxiv2026

Neurogranin enhances spontaneous activity and neuronal survival of hippocampal neurons

Neurogranin (Ng) is a postsynaptic protein highly enriched in forebrain neurons and implicated in synaptic plasticity through its ability to bind calmodulin. However, its impact on neuronal development, network dynamics, and cellular homeostasis remains incompletely understood. In this study, we examined the effects of manipulating Ng expression in primary hippocampal neurons using viral gene delivery, with emphasis on structural, functional, and molecular outcomes. Restoring Ng expression to adult physiological levels enhanced dendritic growth, increased synaptic number, and induced a proximal shift of the axon initial segment, consistent with adaptive responses to increased connectivity. Functionally, Ng markedly increased spontaneous neuronal activity and network synchronization, even under culture conditions that normally show minimal baseline activity. Electrophysiological recordings revealed enhanced burst firing and spike synchrony, indicating strengthened functional coupling rather than increased membrane excitability. Ng-dependent activity required action potential firing and glutamatergic transmission. At the molecular level, Ng increased total calmodulin levels in a binding-dependent manner, reduced overall calcium/calmodulin-dependent protein kinase II abundance while enhancing its relative autophosphorylation, and selectively decreased both total and surface levels of ionotropic glutamate receptors. These changes are consistent with a coordinated homeostatic reorganization of calcium-dependent signaling. Despite robust increases in activity, Ng expression improved neuronal viability, reduced cellular stress markers, and increased expression of the anti-apoptotic protein Bcl-2. Active caspase-3 was selectively elevated without triggering apoptosis, suggesting a non-apoptotic role in activity-dependent structural remodeling. Together, these findings identify Ng as a homeostatic regulator that promotes coordinated network activity, adaptive synaptic remodeling, and neuronal survival.

neuroscience↗

bioRxiv2025

CaMK2rep: A Highly Sensitive Genetically Encoded Biosensor for Monitoring CaMKII Activity in Mammalian Cells

Accurately monitoring calcium/calmodulin-dependent protein kinase II (CaMKII) activity in cells remains a significant challenge due to the limited sensitivity and narrow dynamic range of existing genetically encoded sensors. Here, we introduce CaMK2rep, a novel phosphorylation-based biosensor that enables robust, specific, and high-sensitivity detection of CaMKII activity. CaMK2rep is designed with two tandem CaMKII consensus sites embedded within the native sequence context of synapsin, and its phosphorylation is detected via a phospho-specific antibody, allowing both biochemical and morphological analyses. We validated CaMK2rep in HeLa cells and cultured hippocampal neurons, demonstrating a near-linear response to CaMKII expression levels and stimulation intensity, and no detectable cytotoxicity. To complement CaMK2rep measurements, we employed the live-cell CaMKAR1 reporter to monitor CaMKII activity dynamics. Using both tools, we investigated the role of neurogranin (Ng), a major postsynaptic calmodulin (CaM) binding protein, and obtained consistent evidence supporting a CaM-buffering model in which Ng limits basal CaMKII activation by sequestering CaM. These findings establish CaMK2rep as a sensitive, specific, and versatile biosensor for CaMKII signaling, particularly well-suited for immunoblot-based population analyses. They also illustrate the value of combining orthogonal genetically encoded tools to interrogate complex signaling mechanisms in both physiological and pathological contexts.

neuroscience↗

bioRxiv2024

HDAC4 Inhibits NMDA Receptor-Mediated Stimulation of Neurogranin Expression

The coordination of neuronal wiring and activity within the central nervous system (CNS) is crucial for cognitive function, particularly in the context of aging and neurological disorders. Neurogranin (Ng), an abundant forebrain protein, modulates calmodulin (CaM) activity and deeply influences synaptic plasticity and neuronal processing. This study investigates the regulatory mechanisms of Ng expression, a critical but underexplored area for combating cognitive impairment. Utilizing both in vitro and in vivo hippocampal models, we show that Ng expression arises during late developmental stages, coinciding with synaptic maturation and neuronal circuit consolidation of. We observed that Ng expression increases in neuronal networks with heightened synaptic activity and identified GluN2B-containing N-methyl-D-aspartate (NMDA) receptors as key drivers of this expression. Additionally, we discovered that nuclear-localized HDAC4 inhibits Ng expression, establishing a regulatory axis that is counteracted by NMDA receptor stimulation. Analysis of the Ng gene promoter activity revealed regulatory elements between the -2.4 and -0.85 Kbp region, including a binding site for RE1-Silencing Transcription factor (REST), which may mediate HDAC4s repressive effect on Ng expression. Further analysis of the promoter sequence revealed conserved binding sites for the myocyte enhancer factor-2 (MEF2) transcription factor, a target of HDAC4-mediated transcription regulation. Our findings elucidate the interplay between synaptic activity, NMDAR function, and transcriptional regulation in controlling Ng expression, offering insights into synaptic plasticity mechanisms and potential therapeutic strategies to prevent cognitive dysfunction.

neuroscience↗