Biology subjects

Heller, J. P.

Publications and source records attributed to Heller, J. P..

4 recordsLinked to original sources

bioRxiv2024

A stolen future: aberrant hippocampal neurogenesis produces glial cells in epilepsy

Adult hippocampal neurogenesis is disturbed in epilepsy. The increased neuronal activity in the epileptic brain leads to an increased production of newborn cells, increased mossy fibre sprouting and altered integration of new neurons within the hippocampus. Here, we set out to investigate increased astrocyte numbers following status epilepticus. We used immunolabelling of brain sections from the mouse intra-amygdala kainic acid model of epilepsy and publicly available single cell RNA sequencing datasets to assess newborn cells in the dentate gyrus. Similar to published series we found on increased number of reactive astrocytes present in the epileptic hippocampus. Additionally, we identified a cell population that expressed neurogenesis (doublecortin) and astrocyte (glial fibrillary acidic protein) markers in the epileptic brain, both in mouse and in human tissue. We further evaluated the expression profile of these cells. Immunolabelling showed expression of mature astrocyte markers aquaporin 4 and glutamate transporter-1. The single cell RNA sequencing data highlighted expression of neurogenesis and astrocyte markers in the doublecortin/glial fibrillary acidic protein-expressing cells. In conclusion, epilepsy pushes early neuroblasts to fate-switch to an astrocyte lineage as seen in the kainic acid-induced mouse model and in human resected brain tissue. Further understanding how neurogenesis is altered in epilepsy and whether the neuroblast fate-switch can be reverted will help in finding novel therapy strategies for epilepsy and other neurological diseases associated with aberrant adult hippocampal neurogenesis. Key MessagesFollowing kainic acid-induced status epilepticus early neuroblasts appear to undergo a fate-switch to an astrocyte lineage. We were able to confirm the presence of cells positive for early neurogenesis and astrocyte markers in human epileptic tissue using scRNAseq data.

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↗

bioRxiv2020

Immunochemical analysis of the integrin expression in retinal pigment epithelial cells

Retinal pigment epithelial (RPE) cells have been used in disease modelling and transplantation studies in retinal diseases. Several types of RPE cells have been trialed, ranging from primary cells and immortalized cell lines to stem cell-derived RPE cells. During aging and in disease, the extracellular environment of the RPE cells changes, interfering with RPE cell adhesion. We hypothesize that this could be a key problem in transplantation studies that have reported lack of adhesion and survival of the transplanted RPE cells. Integrins are essential for the proper function of the RPE, mediating adhesion to Bruchs membrane, and the binding and subsequent phagocytosis of photoreceptor outer segments. Variability that has been found in clinical trials might be due to the variability of cell types used and their expression profiles of surface molecules. Here, we set out to analyze integrin expression in primary rat RPE cells and in the human cell line ARPE-19 using immunochemistry. We found that both cell types express integrins to varying degrees. After long-term culturing, ARPE-19 cells resemble mature RPE cells, and increase integrin expression. We hence argue that it is important to test the properties of these cells prior to transplantation to avoid failure of adhesion and to facilitate correct function.

neuroscience↗

bioRxiv2019

Loss of Bardet-Biedl syndrome proteins causes synaptic aberrations in principal neurons

Bardet-Biedl syndrome (BBS), a ciliopathy, is a rare genetic condition characterised by retina degeneration, obesity, kidney failure and cognitive impairment. In spite of a progress made in general understanding of BBS aetiology, the molecular mechanism of cognitive impairment remains elusive. Here we report that loss of Bardet-Biedl syndrome proteins causes synaptic dysfunction in principal neurons providing possible explanation for cognitive impairment phenotype in BBS patients. Using synaptosomal proteomics and immunocytochemistry we demonstrate the presence of Bbs in postsynaptic density of hippocampal neurons. Loss of Bbs results in the significant reduction of dendritic spines in principal neurons of Bbs mice models. Furthermore, we demonstrate that spine deficiency correlates with events that destabilize spine architecture, such as, impaired spine membrane receptors signalling known to be involved in the maintenance of dendritic spines. Finally, we show that voluntary exercise rescues spine deficiency in the neurons. Based on our data, we propose a model in which Bbs proteins, similar to their function in primary cilia, regulate trafficking of signalling receptors into and out of the membrane of dendritic spines, thus providing the basis for synaptic plasticity.

cell biology↗