Biology subjects

Klaassen, R. V.

Publications and source records attributed to Klaassen, R. V..

3 recordsLinked to original sources

bioRxiv2025

A Tiered Approach to Human Synapse Proteomics: Optimized LC-MS/MS Analysis of Whole-Tissue and Synaptosome Preparations from Frozen Post-mortem Brain Samples

Recent advancements in neuroproteomics have enabled detailed analysis of protein expression and function in the human brain. Post-mortem human brain studies have significantly advanced our understanding of the relationship between genetics, cell biology of neurological and psychiatric disorders and their clinical diagnosis. Synaptic dysfunction often has a central role in these disorders. Therefore, we specifically evaluated the sensitivity of liquid chromatography-tandem mass spectrometry (LC-MS/MS) to detect synaptic proteins in whole-tissue lysates versus synaptosome preparations. First, we optimized sample preparation protocols for frozen human gray matter (GM), refining the suspension TRAPping (sTRAP) digestion method to improve protein solubilization and Cysteine reduction and alkylation using thin human tissue sections, and to accomplish low technical variation by minimizing sample handling. We achieved a highly reproducible sample preparation workflow by rigorously applying standardization and randomization across dissection, processing, and LC-MS/MS runs. Second, comparative LC-MS/MS analysis showed that cortical whole-tissue lysates are a practical solution for large-scale studies and broadly detected synaptic proteins focusing on excitatory neurons. However, enrichment by synaptosome isolation offered improved resolution of synapse-specific proteins. Because synapse-proteomics enables insight into spatial regulation--i.e., alterations at the synapse that are not reflected in the soma-we recommend a tiered approach: initial whole-tissue analysis for broad disease-associated changes, followed by targeted synaptosome proteomics to deepen insight into synaptic alterations. This strategy optimally balances throughput, reproducibility, and biological relevance, and enhances the study of brain disorders through proteomics. Moreover, analyzing synaptic proteins first at the tissue level improves insight into overall regulation of synaptic proteins induced by synapse loss or gain.

neuroscience↗

bioRxiv2021

β-amyloid-driven synaptic depression requires PDZ protein interaction at AMPA-receptor subunit GluA3

Soluble oligomeric amyloid-{beta} (A{beta}) is a prime suspect to cause cognitive deficits in Alzheimers disease and weakens synapses by removing AMPA-type glutamate receptors (AMPARs). We show that synapses of CA1 pyramidal neurons become vulnerable to A{beta} when they express AMPAR subunit GluA3. We found that A{beta}-oligomers reduce the levels of GluA3 immobilized at spines, indicating they deplete GluA3-containing AMPARs from synapses. These A{beta}-driven effects critically depended on the PDZ-binding motif of GluA3. When GluA3 was expressed with a single amino acid mutation in its PDZ-binding motif that prevents GRIP binding, it did not end up at spines and A{beta} failed to trigger synaptic depression. GluA3 with a different point mutation in the PDZ-motif that leaves GRIP-binding intact but prevents its endocytosis, was present at spines in normal amounts but was fully resistant to effects of A{beta}. Our data indicate that A{beta}-mediated synaptic depression requires the removal of GluA3 from synapses. We propose that GRIP-detachment from GluA3 is a critical early step in the cascade of events through which A{beta} accumulation causes a loss of synapse.

neuroscience↗

bioRxiv2019

Specific nanoscale synaptic reshuffling and control of short-term plasticity following NMDAR- and P2XR-dependent Long-Term Depression

Long-Term Potentiation (LTP) and Long-Term Depression (LTD) of excitatory synaptic transmission are considered as cellular basis of learning and memory. These two forms of synaptic plasticity have been mainly attributed to global changes in the number of synaptic AMPA-type glutamate receptor (AMPAR) through a regulation of the diffusion/trapping balance at the PSD, exocytosis and endocytosis. While the precise molecular mechanisms at the base of LTP have been intensively investigated, the ones involved in LTD remains elusive. Here we combined super-resolution imaging technique, electrophysiology and modeling to describe the various modifications of AMPAR nanoscale organization and their effect on synaptic transmission in response to two different LTD protocols, based on the activation of either NMDA receptors or P2X receptors. While both type of LTD are associated with a decrease in synaptic AMPAR clustering, only NMDAR-dependent LTD is associated with a reorganization of PSD-95 at the nanoscale. This change increases the pool of diffusive AMPAR improving synaptic short-term facilitation through a post-synaptic mechanism. These results demonstrate that specific dynamic reorganization of synapses at the nanoscale during specific LTD paradigm allows to improve the responsiveness of depressed synapses.

neuroscience↗