Biology subjects

Hübner, C. A.

Publications and source records attributed to Hübner, C. A..

5 recordsLinked to original sources

bioRxiv2026

Ncbe is the main basolateral Na+ loading mechanism of the choroid plexus epithelium

Cerebrospinal fluid (CSF) provides a specialized extracellular environment for the central nervous system, which is predominantly produced by the choroid plexus, a highly vascularized epithelial structure whose ion transport processes are fundamental to CSF secretion, composition, and homeostasis. The mechanisms of Na+ entry into choroid plexus epithelial cells (CPECs) from the interstitial side remain disputed. The slc4a10 gene product encoding the Na+-dependent Cl-/HCO3- exchanger, Ncbe, was suggested as a key transport mechanism based on its impact on the cell's Na+-dependent regulation of intracellular pH and its basolateral membrane expression. The current study was undertaken to directly assess the contribution of Ncbe to the Na+ uptake into CPECs. Intracellular Na+ was recorded by fluorometry using the Na+ probe Sodium Binding Fluorescent Indicator in clusters of CPECs with access to both the luminal and basolateral membranes. Removal of extracellular Na+ reduced the apparent ex vivo intracellular [Na+] to ~5 mM from a baseline of ~43 mM in the absence of CO2/HCO3- and ~54 mM in the presence of CO2/HCO3-. Flame photometry estimated the intracellular [Na+] ex vivo to ~28 mM. The CO2/HCO3--dependent rate of [Na+] recovery amounted to ~53% of the total recovery rate upon re-addition of Na+. Experiments with access to only the luminal membrane show a [Na+] recovery of a similar rate as observed in the absence of CO2/HCO3- in the clusters. The CO2/HCO3--independent [Na+] recovery was inhibited to ~50% by the NKCC1 inhibitor bumetanide and to ~30% by the TRPv4 inhibitor RN1734. NHE contributed to a minor extent to the CO2/HCO3--independent transport. The HCO3- transport inhibitor DIDS, however, inhibited the total [Na+] recovery rate to ~50%, indicating a role for Ncbe rather than NBCn1 in the cellular [Na+] recovery. Indeed, docking of DIDS into Ncbe and NBCn1 indicated that both proteins can accommodate the binding of DIDS. However, the orientation of the DIDS poses in Ncbe suggests a binding mode more similar to that found in the Anion Exchangers (SLC4A1-3), which seems to accommodate the covalent-type docking more than NBCn1. The Ncbe inhibition by DIDS was supported by the rate of [Na+] recovery that was significantly higher in CPECs from Ncbe-wt than Ncbe-ko mice in the presence of CO2/HCO3-. As both NKCC1 and TRPv4 are localized to the luminal membrane, the findings collectively suggest that Ncbe is the most prominent mechanism for Na+ entry into CPECs expressed at the basolateral side. We suggest Ncbe as the rate-limiting mechanism in the vectorial Na+ transport driving CSF secretion.

physiology↗

bioRxiv2024

Disease-associated microglia and activation of CD8+ T cells precede neuronal cell loss in a model of hereditary spastic paraplegia

In central nervous system (CNS) diseases characterized by late-onset neurodegeneration, the interplay between innate and adaptive immune responses remains poorly understood. This knowledge gap is amplified by the prolonged nature of these diseases, complicating the delineation of brain-resident and infiltrating cells. Here, we conducted a comprehensive profiling of innate and adaptive immune cells across various CNS regions in a murine model of spastic paraplegia 15 (SPG15), a complicated form of hereditary spastic paraplegia (HSP). Using fate-mapping of bone marrow-derived cells via genetic labeling, we identified microgliosis and microglial MHC-II upregulation accompanied by infiltration and local expansion of T cells in the CNS of Spg15-/- mice. Single-cell analysis revealed an increase of disease-associated microglia (DAM) and clonal expansion of effector CD8+ T cells across CNS regions occurring prior to neuronal loss. Analysis of potential cell-cell communication pathways suggested bidirectional interactions between DAM and effector CD8+ T cells potentially contributing to disease progression in Spg15-/- mice. In summary, we identified a shift in microglial phenotypes associated with recruitment and clonal expansion of T cells as a new characteristic of Spg15-driven neuropathology. Targeting activated microglia, CD8+ T cells and their communication represent promising avenues to prevent the loss of neuronal function in HSP.

immunology↗

bioRxiv2021

The Cl- channel TMEM16A controls the generation of cochlear Ca2+ waves and promotes the refinement of auditory brainstem networks

Before hearing onset (postnatal day 12 in mice), inner hair cells (IHC) spontaneously fire action potentials thereby driving pre-sensory activity in the ascending auditory pathway. The rate of IHC action potential bursts is modulated by inner supporting cells (ISC) of Kollikers organ through the activity of the Ca2+ activated Cl- channel TMEM16A. Here we show that conditional deletion of Tmem16a in mice disrupts the generation of Ca2+ waves within Kollikers organ, reduces the burst firing activity and the frequency-selectivity of auditory brainstem neurons in the medial nucleus of the trapezoid body (MNTB), and also impairs the refinement of MNTB projections to the lateral superior olive (LSO). These results reveal the importance of the activity of Kollikers organ for the refinement of central auditory connectivity. In addition, our study suggests a mechanism for the generation of Ca2+ waves, which may also apply to other tissues expressing TMEM16A.

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↗

bioRxiv2020

Intraneuronal chloride accumulation via NKCC1 is not essential for hippocampal network development in vivo

NKCC1 is the primary transporter mediating chloride uptake in immature principal neurons, but its role in the development of in vivo network dynamics and cognitive abilities remains unknown. Here, we address the function of NKCC1 in developing mice using electrophysiological, optical and behavioral approaches. We report that NKCC1 deletion from telencephalic glutamatergic neurons decreases in-vitro excitatory GABA actions and impairs neuronal synchrony in neonatal hippocampal brain slices. In vivo, it has a minor impact on correlated spontaneous activity in the hippocampus and does not affect network activity in the intact visual cortex. Moreover, long-term effects of the developmental NKCC1 deletion on synaptic maturation, network dynamics and behavioral performance are subtle. Our data reveal a neural network function of depolarizing GABA in the hippocampus in vivo, but challenge the hypothesis that NKCC1 is essential for major aspects of hippocampal development.

neuroscience↗