Biology subjects

Madry, C.

Publications and source records attributed to Madry, C..

5 recordsLinked to original sources

bioRxiv2026

Syncytial coupling of mid-capillary pericytes underlies seizure-associated electro-metabolic signaling

Disturbances of neurovascular coupling (NVC) contribute to metabolic derailment and neurological symptoms associated with epilepsy. While postictal arterial constriction can be alleviated by inhibitors of voltage gated calcium channels (VGCCs), less is knownregarding seizure-associated electrical signals in higher-order capillaries and their role in determining pericyte tone during seizures. Here we investigated electrical signaling within the ex vivo neurovascular unit (NVU) derived from rat and human brain tissue. We focused on electrical signal transduction between pericytes and endothelial cells and the potential role of VGCCs in vasomotion. Using dye coupling and paired patch-clamp recordings, we showed that morphologically heterogeneous groups of mid-capillary pericytes build a functional syncytium with endothelial cells. Coupling was asymmetric, allowing for directed propagation of electrical signals. Regardless of their morphology, mid-capillary pericytes responded with depolarization and constriction to metabotropic receptor (GPCR) activation (by thromboxane, norepinephrine and UDP-glucose). However, depolarization via the patch pipette induced neithe r Ca2+-influx nor constriction, suggesting lack of contribution of VGCCs to vasomotion. On inducing epileptiform activity, A2a adenosine receptors and inwardly rectifying potassium channels hyperpolarized the capillary syncytium, followed by repeated depolarizations due to seizure-associated potassium increase in the parenchyma. Thus, while mid-capillary pericytes are contractile, their tone does not rely on their membrane potential and VGCCs. However, syncytial coupling allows for transmission of seizure-associated hyper- and depolarizing signals to upstream feeding arterioles.

neuroscience↗

bioRxiv2024

CryoEM Structure of the human THIK-1 K2P K+ Channel Reveals a Lower 'Y-gate' Regulated by Lipids and Anaesthetics

THIK-1 (KCNK13) is a halothane-inhibited and anionic lipid-activated Two-Pore Domain (K2P) K+ channel implicated in microglial activation and neuroinflammation, and a current target for the treatment of neurodegenerative disorders such as Alzheimers and Amyothropic Lateral Sclerosis (ALS). However, compared to other K2P channels, little is known about the structural and functional properties of THIK-1. Here we present a 3.16 [A] resolution cryoEM structure of human THIK-1 that reveals several unique features, in particular, a tyrosine in M4 (Y273) which contributes to a lower Y-gate that opens upon activation by physiologically-relevant signalling pathways. We further demonstrate that binding of linoleic acid within a modulatory pocket adjacent to the filter also activates THIK-1, and that halothane inhibition involves a binding site within the inner cavity resulting in changes to the Y-gate. Finally, the extracellular cap domain contains positively-charged residues that line the ion exit pathway and which contribute to the unique biophysical properties of this channel. Overall, our results provide important insights into the structural basis of THIK1 function and identify distinct regulatory sites that expand its potential as a drug target for the modulation of microglial function.

biophysics↗

bioRxiv2023

Microglia shape hippocampal networks but are dispensable for pruning of synapses during development

Microglia, the brain-resident macrophages, are believed to sculpt developing neural circuits by eliminating excess synapses in a process called synaptic pruning, removing apoptotic neurons, and promoting neuronal survival. To elucidate the role of microglia during embryonic and postnatal brain development, we used a mouse model deficient in microglia throughout life as a consequence of deletion of the fms-intronic regulatory element (FIRE) in the Csf1r locus. Surprisingly, young adult Csf1r{Delta}FIRE/{Delta}FIRE mice displayed no changes in excitatory synapse number and spine density of CA1 hippocampal neurons compared to Csf1r+/+ littermates. However, CA1 neurons were less excitable, received less CA3 Schaffer collateral-mediated excitatory input and showed altered synaptic properties, but this did not affect novel object recognition. Cytokine profiling indicated an anti-inflammatory state along with increases in ApoE levels and astrocyte reactivity in brains of Csf1r{Delta}FIRE/{Delta}FIRE mice. Notably, these morphological and functional changes in Csf1r{Delta}FIRE/{Delta}FIRE mice closely resemble the effects of acute microglial depletion in adult mice that had undergone normal development. Thus, our findings challenge the prevailing view that microglia are indispensable for the establishment of neural networks during development.

neuroscience↗

bioRxiv2023

Amyloidosis and ageing have differential effectson microglial Ca2+ activity in the mouse brain

In microglia, changes in intracellular calcium concentration ([Ca2+]i) may regulate process motility, inflammasome activation, and phagocytosis. However, while neurons and astrocytes exhibit frequent spontaneous Ca2+ activity, microglial Ca2+ signals are much rarer and poorly understood. Here, we studied [Ca2+]i changes of microglia in acute brain slices using Fluo-4-loaded cells and mice expressing GCaMP5g in microglia. Spontaneous Ca2+ transients occurred [~]5 times more frequently in individual microglial processes than in their somata. We assessed whether microglial Ca2+ responses change in Alzheimers disease (AD) using AppNL- G-F knock-in mice. Proximity to A{beta} plaques strongly affected microglial Ca2+ activity. Although spontaneous Ca2+ transients were unaffected in microglial processes, they were 5-fold more frequent in microglial somata near A{beta} plaques than in wild-type microglia. Microglia away from A{beta} plaques in AD mice showed intermediate properties for morphology and Ca2+ responses, partly resembling those of wild-type microglia. By contrast, somatic Ca2+ responses evoked by tissue damage were less intense in microglia near A{beta} plaques than in wild-type microglia, suggesting different mechanisms underlying spontaneous vs. damage-evoked Ca2+ signals. Finally, as similar processes occur in neurodegeneration and old age, we studied whether ageing affected microglial [Ca2+]i. Somatic damage-evoked Ca2+ responses were greatly reduced in microglia from old mice, as in the AD mice. In contrast to AD, however, old age did not alter the occurrence of spontaneous Ca2+ signals in microglial somata but reduced the rate of events in processes. Thus, we demonstrate distinct compartmentalised Ca2+ activity in microglia from healthy, aged and AD-like brains.

neuroscience↗

bioRxiv2018

Amyloid β oligomers constrict human capillaries in Alzheimer’s disease via signalling to pericytes

Vascular compromise occurs early in Alzheimers disease (AD) and other dementias1-3. Amyloid {beta} (A{beta}) reduces cerebral blood flow4-6 and, as most of the cerebral vasculature resistance is in capillaries7, A{beta} might mainly act on contractile pericytes on capillary walls8-10. Employing human tissue to establish disease-relevance, and rodent experiments to define mechanism, we now show that A{beta} constricts brain capillaries at pericyte locations in human subjects with cognitive decline. Applying soluble A{beta}1-42 oligomers to live human cortical tissue constricted capillaries. Using rat cortical slices, this was shown to reflect A{beta} evoking capillary pericyte contraction, with an EC50 of 4.7 nM, via the generation of reactive oxygen species and activation of endothelin ET-A receptors. In freshly-fixed diagnostic biopsies from human patients investigated for cognitive decline, mean capillary diameters were less in subjects showing A{beta} deposition than in subjects without A{beta} deposition. For patients with A{beta} deposition, the capillary diameter was 31% less at pericyte somata than away from somata, predicting a halving of blood flow. Constriction of capillaries by A{beta} will contribute to the energy lack1-3 occurring in AD, which promotes further A{beta} generation11,12. This mechanism reconciles the amyloid hypothesis13-15 with the earliest events in AD being vascular1.

neuroscience↗