Denervated mouse CA1 pyramidal neurons express homeostatic synaptic plasticity following entorhinal cortex lesion

Abstract

Structural, functional, and molecular reorganization of denervated neural networks is often observed in neurological conditions. The loss of input is accompanied by homeostatic synaptic adaptations, which can affect the reorganization process. A major challenge of denervation-induced homeostatic plasticity operating in complex neural networks is the specialization of neuronal inputs. It remains unclear whether neurons respond similarly to the loss of distinct inputs. Here, we used in vitro entorhinal cortex lesion (ECL) and Schaffer collateral lesion (SCL) in mouse organotypic entorhino-hippocampal tissue cultures to study denervation-induced plasticity of CA1 pyramidal neurons. We observed microglia accumulation, presynaptic bouton degeneration, and a reduction in dendritic spine numbers in the denervated layers 3 days after SCL and ECL. Transcriptome analysis of the CA1 region revealed complex changes in differential gene expression following SCL and ECL compared to non-lesioned controls with a specific enrichment of differentially expressed synapse-related genes observed after ECL. Consistent with this finding, denervation-induced homeostatic plasticity of excitatory synapses was observed 3 days after ECL but not after SCL. Chemogenetic silencing of the EC but not CA3 confirmed the pathway-specific induction of homeostatic synaptic plasticity in CA1. Additionally, increased RNA oxidation was observed after SCL and ECL. These results reveal important commonalities and differences between distinct pathway lesions and demonstrate a pathway-specific induction of denervation-induced homeostatic synaptic plasticity.

Regional Microglial Response in Entorhino–Hippocampal Slice Cultures to Schaffer Collateral Lesion and Metalloproteinases Modulation

“…The biological significance of these alterations is yet to be determined. Earlier research has shown denervation-induced spine density changes in CA1, but no significant functional alterations in CA1 neurons post-SCL after 3 days [22]. The transcriptomic analysis in this previous study also revealed higher MMP16 mRNA levels post-SCL [22], a membrane-bound MMP expressed by microglia, potentially involved in synaptic rewiring and hippocampal spine density regulation [22,60,61].…”

“…Entorhinohippocampal slice cultures are particularly valuable in this context as they allow for in vitro investigation while preserving the complex cyto-and fiber architecture of the neuroglial network. This makes them an effective experimental model for studying the morphological, molecular, and functional dynamics of glial cells [22,37,38].…”

“…However, the impact of MMPs on hippocampal synaptic plasticity has presented inconsistent findings [18,19]. To understand the cellular and molecular mechanisms involving glial cell plasticity, various functional and mechanical lesion models have been established [20][21][22][23][24]. Despite these advancements, the precise links and underlying mechanisms connecting reactive gliosis, MMPs modulation, and the progression of neurological disorder remain to be fully elucidated.…”

Regional Microglial Response in Enthorino-hippocampal Slice Cultures to Schaffer Collateral Lesion and Metalloproteinases Modulation

“…Earlier research showed denervation-induced spine density changes in CA1, but no significant functional alterations in CA1 neurons post-SCL at 3 days [18]. Transcriptomic analysis in this previous study also revealed higher MMP16 mRNA levels post-SCL [18], a membrane-bound MMP expressed by microglia, potentially involved in synaptic rewiring and hippocampal spine density regulation [18,46,47]. Regardless of these considerations, the results of the present study clearly show distinct responses in glial cells following SCL and with GM6001, a broad-spectrum MMP inhibitor.…”

“…Mechanical pathway transection was performed with a sterile scalpel in mature tissue cultures (≥ 18 days in vitro) as described in [18]. SCL was applied between the CA3 and the CA1 region of the hippocampus, without affecting the perforant path projections to CA3 (Fig.1a).…”