Biology subjects

Kaila, K.

Publications and source records attributed to Kaila, K..

5 recordsLinked to original sources

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↗

bioRxiv2020

Dependence of behavioral and neocortical seizures on brain pH and oxygen levels in a rat model of term birth asphyxia

Birth asphyxia (BA) is often associated with seizures which emerge during the recovery and may exacerbate the ensuing hypoxic-ischemic encephalopathy. In rodent models of BA, exposure to hypoxia is used to evoke seizures, which commence already during the insult. Here, we introduce a term-equivalent model of BA, in which seizures are triggered after, not during, brain hypoxia. Postnatal day 11-12 rat pups were exposed either to steady asphyxia (15 min; 5 % O2 + 20 % CO2) or to intermittent asphyxia (30 min; three 5+5 min cycles of 9 % and 5 % O2 at constant 20 % CO2). Cortical activity and seizures were recorded in freely-behaving animals. Simultaneous electrode measurements of cortical local field potentials (LFP) and intracortical pH and Po2 were made under urethane-anesthesia. Both protocols decreased blood pH to <7.0 and base excess by 20 mmol/l, and evoked an increase in plasma copeptin (0.2 to 5 nM). Clonic and tonic convulsions were triggered after intermittent but not steady asphyxia, and they were tightly associated with electrographic seizures. During intermittent asphyxia LFP activity was suppressed as brain pH decreased from 7.3 to 6.7. Brain Po2 fell below detection level in 5 % ambient O2 but returned to the baseline level during steps to 9 % O2. Neuronal hyperexcitability and seizures were suppressed in all types of experiments when the post-asphyxia brain pH recovery was slowed down by 5 % CO2. Our data suggest that the recurring hypoxic episodes during intermittent asphyxia promote neuronal excitability, which becomes established as hyperexcitability and seizures only after the suppressing effect of the hypercapnic acidosis is relieved. The present rodent model of BA is to our knowledge the first one in which, consistent with clinical BA, robust behavioral and electrographic seizures are triggered after and not during the BA-mimicking insult.

developmental biology↗

bioRxiv2019

Endogenous responses in brain pH and PO2 in a rodent model of birth asphyxia

AimTo study brain-sparing physiological responses in a rodent model of birth asphyxia which reproduces the asphyxia-defining systemic hypoxia and hypercapnia. MethodsSteady or intermittent asphyxia was induced for 15-45 min in anesthetized 6 and 11 days old rats and neonatal guinea pigs using gases containing 5% or 9% O2 plus 20% CO2 (in N2). Hypoxia and hypercapnia were induced with low O2 and high CO2, respectively. Oxygen partial pressure (PO2) and pH were measured with microsensors within the brain and subcutaneous ("body") tissue. Blood lactate was measured after asphyxia. ResultsBrain and body PO2 fell to apparent zero with little recovery during 5% O2 asphyxia and 5% or 9% O2 hypoxia, and increased more than twofold during 20% CO2 hypercapnia. Unlike body PO2, brain PO2 recovered rapidly to control after a transient fall (rat), or was slightly higher than control (guinea pig) during 9% O2 asphyxia. Asphyxia (5% O2) induced a respiratory acidosis paralleled by a progressive metabolic (lact)acidosis that was much smaller within than outside the brain. Hypoxia (5% O2) produced brain-confined alkalosis. Hypercapnia outlasting asphyxia suppressed pH recovery and prolonged the post-asphyxia PO2 overshoot. All pH changes were accompanied by consistent shifts in the blood-brain barrier potential. ConclusionRegardless of brain maturation stage, hypercapnia can restore brain PO2 and protect the brain against metabolic acidosis despite compromised oxygen availability during asphyxia. This effect extends to recovery phase if normocapnia is restored slowly, and it is absent during hypoxia, demonstrating that exposure to hypoxia does not mimic asphyxia.

neuroscience↗

bioRxiv2019

Carbonic anhydrase VII regulates dendritic spine morphology and density via actin filament bundling

Intracellular pH is a potent modulator of neuronal functions. By catalyzing (de)hydration of CO2, intracellular carbonic anhydrase (CAi) isoforms CAII and CAVII contribute to neuronal pH buffering and dynamics. The presence of two highly active isoforms suggests that they form spatially distinct CAi pools enabling subcellular modulation of pH. Here we show that CAVII, unlike CAII, is localized to the filamentous actin network, and its overexpression induces formation of thick actin bundles and membrane protrusions in fibroblasts. In neurons, CAVII is enriched in dendritic spines, and its over-expression causes aberrant spine morphology. We identified amino acids unique to CAVII that are required for direct actin interactions, promoting actin filament bundling and spine targeting. Lack of CAVII in neocortical neurons leads to reduced spine density and increased proportion of small spines. Thus, our work demonstrates highly distinct subcellular expression patterns of CAII and CAVII, and a novel, structural role of CAVII.

cell biology↗

bioRxiv2017

RhoGEF9 splice isoforms influence neuronal maturation and synapse formation downstream of a2 GABAA receptors

In developing brain neuronal migration, dendrite outgrowth and dendritic spine outgrowth are controlled by Cdc42, a small GTPase of the Rho family, and its activators. Cdc42 function in promoting actin polymerization is crucial for glutamatergic synapse regulation. Here, we focus on GABAergic synapse-specific activator of Cdc42, collybistin (CB) and examine functional differences between its splice isoforms CB1 and CB2. We report that CB1 and CB2 differentially regulate GABAergic synapse formation in vitro along proximal-distal axis and adult-born neuron maturation in vivo. The functional specialization between CB1 and CB2 isoforms arises from their differential protein half-life, in turn regulated by ubiquitin conjugation of the unique CB1 C-terminus. We report that CB1 and CB2 negatively regulate Cdc42; however, Cdc42 activation is dependent on CB interaction with gephyrin. During hippocampal adult neurogenesis CB1 regulates neuronal migration, while CB2 is essential for dendrite outgrowth. Finally, using mice lacking Gabra2 subunit, we show that CB1 function is downstream of GABAARs, and we can rescue adult neurogenesis deficit observed in Gabra2 KO. Overall, our results uncover previously unexpected role for CB isoforms downstream of 2-containing GABAARs during neuron maturation in a Cdc42 dependent mechanism.\n\nAuthor SummaryGABAergic inhibition regulates distinct stages of brain development; however, cellular mechanisms downstream of GABAA receptors (GABAARs) that influence neuronal migration, maturation and synaptogenesis are less clear. ArfGEF9 encodes for RhoGEF with Cdc42 and TC10 GTPase as its substrates. Interestingly, ArhGEF9 is the only known RhoGEF essential for GABAergic synapse formation and maintenance. We report that during brain development ArfGEF9 mRNA splicing regulation generates different ratios of CB1 and CB2 splice isoforms. CB1 mRNA splicing is enhanced during early brain developmental, while CB2 levels remains constant throughout brain development. We also show that CB1 protein has shorter half-life and ubiquitin proteasome system restricts CB1 abundance within developing neuron to modulate neuron migration and distributing GABAergic synapse along the proximal-distal axis. On the other hand, CB2 isoform although expressed abundantly throughout brain development is essential for neuron dendrite maturation. Together, our data identifies specific post-transcriptional and post-translational mechanisms downstream of GABAARs influencing ArhGEF9 function to regulate distinct aspects of neuronal maturation process.

neuroscience↗