Biology subjects

Posfai, B.

Publications and source records attributed to Posfai, B..

8 recordsLinked to original sources

bioRxiv2023

Infection-induced vascular inflammation in COVID-19 links focal microglial dysfunction with neuropathologies through IL-1/IL-6-related systemic inflammatory states

COVID-19 is associated with diverse neurological abnormalities, which predict poor outcome in patients. However, the mechanisms whereby infection-induced inflammation could affect complex neuropathologies in COVID-19 are unclear. We hypothesized that microglia, the resident immune cells of brain, are centrally involved in this process. To study this, we developed an autopsy platform allowing the integration of molecular anatomy-, protein- and mRNA data sets in post-mortem mirror blocks of brain and peripheral organ samples from COVID-19 cases. Nanoscale microscopy, single-cell RNA sequencing and analysis of inflammatory and metabolic signatures revealed distinct mechanisms of microglial dysfunction associated with cerebral SARS-CoV-2 infection. We observed focal loss of microglial P2Y12R at sites of virus-associated vascular inflammation together with dysregulated microglia-vascular-astrocyte interactions, Cx3Cr1-fractalkine axis deficits and mitochondrial failure in severely affected medullary autonomic nuclei and other brain areas. Microglial dysfunction occurs at sites of excessive synapse- and myelin phagocytosis and loss of glutamatergic terminals. While central and systemic viral load is strongly linked in individual patients, the regionally heterogenous microglial reactivity in the brain correlated with the extent of central and systemic inflammation related to IL-1 / IL-6 via virus-sensing pattern recognition receptors (PRRs) and inflammasome activation pathways. Thus, SARS-CoV-2-induced central and systemic inflammation might lead to a primarily glio-vascular failure in the brain, which could be a common contributor to diverse COVID-19-related neuropathologies.

immunology↗

bioRxiv2022

Rapid microglial phenotype changes modulate neuronal networks and sharp wave-ripple activity in acute slice preparations

Acute brain slices represent a "workhorse" model for studying the central nervous system (CNS) from nanoscale events to complex circuits. While slice preparation inherently involves tissue injury, it is unclear how microglia, the main immune cells and damage sensors of the CNS shape tissue integrity ex vivo. To this end, we have studied the mechanisms of microglial phenotype changes and contribution to neuronal network organisation and functioning in acute brain slices. Using a novel ATP- reporter mouse line and microglia reporter mice, we show that acute slice preparation induces rapid, P2Y12 receptor (P2Y12R) dependent dislocation and migration of microglia, paralleled with marked morphological transformations driven by early ATP surges and subsequent ATP flashes. Gradual depolarization of microglia is associated with the downregulation of purinergic P2Y12R and time-dependent changes of microglia-neuron interactions, paralleled by altered numbers of excitatory and inhibitory synapses. Importantly, functional microglia not only modulate synapse sprouting, but the absence of microglia or microglial P2Y12R markedly diminishes the incidence, amplitude, and frequency of sharp wave-ripple activity in hippocampal slices. Collectively, our data suggest that microglia are inherent modulators of complex neuronal networks, and their specific actions are indispensable to maintain neuronal network integrity and activity ex vivo. These findings could facilitate new lines of research resulting in improved ex vivo methodologies and a better understanding of microglia-neuron interactions both in physiological and pathological conditions.

neuroscience↗

bioRxiv2021

Somatic junctions connect microglia and developing neurons

Microglia are the resident immune cells of the brain with multiple homeostatic and regulatory roles. Emerging evidence also highlights the fundamental transformative role of microglia in brain development. While tightly controlled, bi-directional communication between microglia and neuronal progenitors or immature neurons has been postulated, the main sites of interaction and the underlying mechanisms remain elusive. By using correlated light and electron microscopy together with super-resolution imaging, here we provide evidence that microglial processes form specialized nanoscale contacts with the cell bodies of developing and immature neurons throughout embryonic, early postnatal and adult neurogenesis. These early developmental contacts are highly reminiscent to somatic purinergic junctions that are instrumental for microglia-neuron communication in the adult brain. We propose that early developmental formation of somatic purinergic junctions represents an ideal interface for microglia to monitor the status of developing neurons and to direct prenatal, early postnatal and adult neurogenesis.

neuroscience↗

bioRxiv2021

Microglia control cerebral blood flow and neurovascular coupling via P2Y12R-mediated actions

Microglia, the main immunocompetent cells of the brain regulate neuronal function in health and disease, but their contribution to cerebral blood flow (CBF) remained elusive. Here we identify microglia as important modulators of CBF both under physiological conditions and during hypoperfusion. We show that microglia establish direct purinergic contacts with cells in the neurovascular unit that shape cerebral perfusion in both mice and humans. Surprisingly, the absence of microglia or blockade of microglial P2Y12 receptor (P2Y12R) substantially impairs neurovascular coupling in the barrel cortex after whisker stimulation. We also reveal that hypercapnia, which is associated with acidification, induces microglial adenosine production, while depletion of microglia reduces brain pH and impairs hypercapnia-induced vasodilation. Furthermore, the absence or dysfunction of microglia markedly impairs adaptation to hypoperfusion via P2Y12R after transient unilateral common carotid artery occlusion, which is also influenced by CX3CR1-mediated actions. Thus, our data reveal a previously unrecognized role for microglia in CBF regulation with broad implications for common neurological diseases.

neuroscience↗

bioRxiv2021

Microglial NKCC1 shapes microglial phenotype, cerebral inflammatory responses and brain injury

The NKCC1 ion transporter contributes to the pathophysiology of common neurological disorders, but its function in microglia, the main inflammatory cells of the brain, has remained unclear to date. Therefore, we generated a novel transgenic mouse line in which microglial NKCC1 was deleted. We show that microglial NKCC1 shapes both baseline and reactive microglia morphology, process recruitment to the site of injury, and adaptation to osmotic stress in a cell-autonomous manner via regulating membrane potential and chloride fluxes. In addition, microglial NKCC1 deficiency results in increased expression of the D subunit of volume regulated anion channel (VRAC), NLRP3 inflammasome priming and production of interleukin-1{beta} (IL-1{beta}), rendering microglia prone to exaggerated inflammatory responses. In line with this, central (intracortical) administration of the NKCC1 blocker, bumetanide, potentiated intracortical lipopolysaccharide (LPS)-induced cytokine levels, whereas systemic bumetanide application decreased inflammation in the brain. Microglial NKCC1 KO animals exposed to experimental stroke showed significantly increased brain injury, inflammation, cerebral edema and worse neurological outcome. Thus, NKCC1 emerges as an important player in controlling microglial ion homeostasis and inflammatory responses through which microglia modulate brain injury. The contribution of microglia to central NKCC1 actions is likely to be relevant for common neurological disorders.

neuroscience↗

bioRxiv2019

Microglia monitor and protect neuronal function via specialized somatic purinergic junctions

Microglia are the main immune cells in the brain with emerging roles in brain homeostasis and neurological diseases, while mechanisms underlying microglia-neuron communication remain elusive. Here, we identify a novel site of interaction between neuronal cell bodies and microglial processes in mouse and human brain. Somatic microglia-neuron junctions possess specialized nanoarchitecture optimized for purinergic signaling. Activity of neuronal mitochondria is linked with microglial junction formation, which is rapidly induced in response to neuronal activation and blocked by inhibition of P2Y12-receptors (P2Y12R). Brain injury-induced changes at somatic junctions trigger P2Y12R-dependent microglial neuroprotection, regulating neuronal calcium load and functional connectivity. Collectively, our results suggest that microglial processes at these junctions are in ideal position to monitor and protect neuronal functions in both the healthy and injured brain.\n\nOne-sentence summaryNeuronal cell bodies possess specialized, pre-formed sites, through which microglia monitor their status and exert neuroprotection.

neuroscience↗

bioRxiv2017

Mitochondrial Ultrastructure Is Coupled to Synaptic Performance at Axonal Release Sites

VISUAL ABSTRACT O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY\n\nSIGNIFICANCE STATEMENTNeuronal networks are highly dynamic structures: cellular morphology and synaptic strength is changing as information is processed and stored. This means that the demand for mitochondrial supply is changing in space and time in neurons. Since the architecture ultimately determines the output performance of these organelles, we hypothesized that the ultrastructure of axonal mitochondria could well be a major parameter of adjusting their performance to the actual energetic needs of the synapse. Our results - describing a cell-type independent and synapse-specific correlation between mitochondrial ultrastructure, mitochondrial molecular fingerprints and synaptic performance - highlight the importance of activity-dependent ultrastructural plasticity of these organelles in neurons, and suggest an even more prominent role for mitochondria in neuroplasticity, than it was thought previously.\n\nABSTRACTMitochondrial function in neurons is tightly linked with metabolic and signalling mechanisms that ultimately determine neuronal performance. The subcellular distribution of these organelles is dynamically regulated as they are directed to axonal release sites on demand, but whether mitochondrial internal ultrastructure and molecular properties would reflect the actual performance requirements in a synapse-specific manner, remains to be established. Here, we examined performance-determining ultrastructural features of presynaptic mitochondria in GABAergic and glutamatergic axons of mice and human. Using electron-tomography and super-resolution microscopy we found, that these features were coupled to synaptic strength: mitochondria in boutons with high synaptic activity exhibited an ultrastructure optimized for high rate metabolism and contained higher levels of the respiratory chain protein cytochrome-c than mitochondria in boutons with lower activity. The strong, cell-type independent correlation between mitochondrial ultrastructure, molecular fingerprints and synaptic performance suggests that changes in synaptic activity could trigger ultrastructural plasticity of presynaptic mitochondria, likely to adjust their performance to the actual metabolic demand.

neuroscience↗

bioRxiv2017

Synaptic co-transmission of acetylcholine and GABA regulates hippocampal states

The basal forebrain cholinergic system is widely assumed to control cortical functions via non-synaptic transmission of a single neurotransmitter, acetylcholine. Yet, using immune-electron tomographic, molecular anatomical, optogenetic and physiological techniques, we find that mouse hippocampal cholinergic terminals invariably establish synapses and their vesicles dock at synapses only. We demonstrate that these synapses do not co-release but co-transmit GABA and acetylcholine via different vesicles, whose release is triggered by distinct calcium channels. This co-transmission evokes fast composite postsynaptic potentials, which are mutually cross-regulated by presynaptic auto-receptors and display different short-term plasticity. The GABAergic component alone effectively suppresses hippocampal sharp wave-ripples and epileptiform activity. The synaptic nature of the forebrain cholinergic system with differentially regulated, fast, GABAergic and cholinergic co-transmission suggests a hitherto unrecognized level of synaptic control over cortical states. This novel model of hippocampal cholinergic neurotransmission could form the basis for alternative pharmacotherapies after cholinergic deinnervation seen in neurodegenerative disorders.\n\nSupplementary materials are attached after the main text.

neuroscience↗