Biology subjects

Michaluk, P.

Publications and source records attributed to Michaluk, P..

3 recordsLinked to original sources

bioRxiv2022

Blood cells communicate remotely via an NMDA receptor-mediated glutamatergic chain-reaction

Neutrophils are white blood cells that are critical to the acute inflammatory and adaptive immune responses. Their swarming-pattern behaviour is controlled by multiple cellular cascades involving calcium-dependent release of various signalling molecules. Previous studies have reported that neutrophils express glutamate receptors and can release glutamate but evidence of direct neutrophil-neutrophil communication has been elusive. Here, we hold semi-suspended cultured human neutrophils in patch-clamp whole-cell mode to find that calcium mobilisation induced by stimulating one neutrophil can trigger an NMDA receptor-driven membrane current and calcium signal in neighbouring neutrophils. We employ an enzymatic-based imaging assay to image, in real time, glutamate release from neutrophils induced by glutamate released from their neighbours. These observations provide direct evidence for a positive-feedback inter-neutrophil communication that could contribute to mechanisms regulating communal neutrophil behaviour.

cell biology↗

bioRxiv2020

Serum response factor is essential for synaptic maturation in the hippocampus

Disturbances of gene expression patterns that occur during brain development can severely affect signal transmission, connectivity, and plasticity--key features that underlie memory formation and storage in neurons. Abnormalities at the molecular level can manifest as changes in the structural and functional plasticity of dendritic spines that harbor excitatory synapses. This can lead to such developmental neuropsychiatric conditions as Autism spectrum disorders, intellectual disabilities, and schizophrenia. The present study investigated the role of the major transcriptional regulator serum response factor (SRF) in synapse maturation and its impact on behavioral phenotypes. Using in vitro and in vivo models of early postnatal SRF deletion, we studied its influence on key morphological and physiological hallmarks of spine development. The elimination of SRF in developing neurons resulted in a phenotype of immature dendritic spines and impairments in excitatory transmission. Moreover, using a combination of molecular and imaging techniques, we showed that SRF-depleted neurons exhibited a lower level of specific glutamate receptor mRNAs and a decrease in their surface expression. Additionally, the early postnatal elimination of SRF in hippocampal CA1 excitatory neurons caused spine immaturity and a specific social deficit that is frequently observed in autism patients. Altogether, our data suggest that the regulation of structural and functional dendritic spine maturation begins at the stage of gene transcription, which underpins the crucial role of such transcription factors as SRF. Moreover, disturbances of the postnatal expression of SRF translate to behavioral changes in adult animals.

neuroscience↗

bioRxiv2020

Rapid recycling of glutamate transporters on the astroglial surface

Glutamate uptake by high-affinity astroglial transporters confines excitatory transmission to the synaptic cleft. The efficiency of this mechanism depends on the transporter dynamics in the astrocyte membrane, which remains poorly understood. Here, we visualise the main glial glutamate transporter GLT1 by generating its functional pH-sensitive fluorescent analogue, GLT1-SEP. Combining FRAP-based methods with molecular dissection shows that 70-75% of GLT1-SEP are expressed on the astroglial surface, recycling with a lifetime of only ~22 s. Genetic deletion of the C-terminus accelerates GLT1-SEP membrane turnover by ~60% while disrupting its molecule-resolution surface pattern as revealed by dSTORM. Excitatory activity boosts surface mobility of GLT1-SEP, involving its C-terminus, metabotropic glutamate receptor activation, intracellular Ca2+ signalling and calcineurin-phosphatase activity, but not the broad-range kinase activity. The results suggest that membrane turnover, rather than than lateral diffusion, is the main redeployment route for the immobile fraction (20-30%) of surface-expressed GLT1. This reveals a novel mechanism by which the brain controls extrasynaptic glutamate escape, in health and disease.

neuroscience↗