Biology subjects

Pitsch, J.

Publications and source records attributed to Pitsch, J..

6 recordsLinked to original sources

bioRxiv2026

Single-cell profiling reveals tumor grade-dependent immune remodeling in BRAFV600E-driven glioneuronal tumors

BRAFV600E is the key driver variant in epilepsy-associated glioneuronal tumors (GNTs). These tumors often share MAPK/PI3K hyperactivation, a generally benign biological course and rare occurrence of malignant variants. We aimed to characterize the poorly defined immune cell milieu of GNTs with distinct biological behavior. We mapped cellular heterogeneity of the tumor microenvironment (TME) using single-cell transcriptomics on murine models of low-grade (LG-GNT; BRAFV600E/AKTA) and high-grade (HG-GNT; BRAFV600E/AKTA/Trp53KO) tumors, generated via intraventricular in utero electroporation (IUE). Furthermore, ex vivo functional assays with CSF1R-mediated myeloid depletion were utilized to assess the role of identified signaling molecules on tumor viability. We observed a striking, grade-dependent immunological dichotomy: LG-GNT exhibited a permissive niche with prominent surveillance by T cells and pro-inflammatory microglia. In contrast, HG-GNT TME was characterized by a restricted T cell infiltration, massively dominated by myeloid cell infiltrates. Differential gene expression analysis identified Spp1 (osteopontin) as a key mediator of this immunosuppressive HG-GNT TME, exclusively expressed in microglia and border-associated macrophages (BAMs). Crucially, ex vivo functional assays demonstrated that recombinant SPP1 enhances tumor viability through a paracrine mechanism. These findings suggest fundamentally distinct immune activation (a) stimulated by aberrant MAPK/PI3K signaling in LG-GNT, versus (b) malignant tumor feature-driven, e.g. through necrosis in HG-GNT. In the latter, SPP1 signaling creates the immunosuppressive niche. Consequently, while modulating the pro-inflammatory niche may mitigate tumor-related epileptogenicity in LG-GNTs, targeting the SPP1-myeloid axis may restore anti-tumor immunity in HG-GNTs.

neuroscience↗

bioRxiv2025

Hippocampal network activity changes during early epileptogenesis predict subsequent epilepsy

The circuit mechanisms underlying focal epileptogenesis are, despite of decades of epilepsy research, still incompletely understood. In this study, we aimed to characterize the changes in hippocampal network activity induced by a potentially epileptogenic insult. In rats, long-lasting electrical perforant pathway stimulation leads in a high percentage of animals to the development of temporal lobe epilepsy. However, a subset of animals remains resilient against the stimulation. We monitored alterations of neuronal activity by chronically recording the local field potential (LFP) from the hippocampal dentate gyrus before, during and after the potentially epileptogenic insult. Intriguingly, epilepsy animals identified by subsequent spontaneous epileptic seizures were characterized by a transient increase in the aperiodic exponent suggesting a shift towards a reduced local excitation-to-inhibition (E/I) ratio during the first days after the perforant path stimulation. Furthermore, these animals developed a strong impairment of theta oscillation prevalence and regularity during early epileptogenesis. In contrast, resilient non-epilepsy animals without spontaneous seizures neither showed this modulation in E/I ratio nor a corruption of hippocampal theta activity. In fact, the increase in the aperiodic exponent on the first day after completion of the electrical stimulation paradigm could predict epileptogenesis with very high fidelity (AUC 0.92) and correlated significantly with later seizure rate. This finding opens the opportunity to dissect mechanisms of epileptogenesis and to test the effectiveness of anti-epileptogenesis treatment in very early disease stages by allowing identification of individuals at high risk. Furthermore, it might offer a potential explanation for the frequently observed failure of anti-epileptogenesis drugs boosting GABAergic inhibition.

neuroscience↗

bioRxiv2024

Region-specific spreading depolarization drives aberrant post-ictal behavior

Confusion, aphasia, and unaware wandering are prominent post-ictal symptoms regularly observed in temporal lobe epilepsy (TLE)1. Despite the potentially life-threatening nature of the immediate post-ictal state2, its neurobiological underpinnings remain understudied3. We provide evidence in mice and humans that seizure-associated focal spreading depolarization (sSD) is a pathoclinical key factor in epilepsy. Using two-photon or widefield imaging (hippocampus, neocortex), field potential and single unit recordings, and behavioral assessment in mice, we first studied seizures during viral encephalitis, and subsequently established an optogenetic approach to dissociate hippocampal seizures and SD. We find region-specific occurrence of sSD that displays distinct spatial trajectories to preceding seizures, and show that seizure-related and isolated hippocampal SD prompt post-ictal wandering. This clinically relevant locomotor phenotype occurred in the absence of hippocampal SD progression to the neocortex. Finally, we confirm sSD existence in human epilepsy, in a patient cohort with refractory focal epilepsy, via Behnke-Fried electrode recordings. In this cohort, sSD displayed a similar temporomesial propensity as in mice. This work uncovers sSD as a previously underrecognized pathoclinical entity underlying postictal behavioral abnormalities in epilepsy. Our results carry wide-reaching ramifications for epilepsy research and neurology, and challenge current EEG-standards.

neuroscience↗

bioRxiv2021

Heterogeneity and excitability of BRAFV600E-induced tumors is determined by PI3K/mTOR-signaling state and Trp53-loss

BackgroundDevelopmental brain tumors harboring BRAFV600E somatic mutation are diverse. Here, we describe molecular factors that determine BRAFV600E-induced tumor biology and function. MethodsIntraventricular in utero electroporation in combination with the piggyBac transposon system is employed as a tool to generate developmental brain neoplasms. In vivo tumor growth is monitored by using the infrared fluorescent protein (iRFP). Lineage inference is carried out by using the Brainbow transgene. Neural activity from tumor slices is assessed by multielectrode array. RNA sequencing is exploited to analyze the induced neoplasms at the transcriptomic level. ResultsBRAFV600E in murine neural progenitors only in concert with active PI3K/mTOR-signaling through constitutively phosphorylated Akt-kinase (pAkt) elicits benign neoplasms composed of enlarged dysmorphic neurons and neoplastic astroglia recapitulating ganglioglioma (GG). Purely glial tumors partially resembling polymorphous low-grade neuroepithelial tumors of the young (PLNTYs) emerge from BRAFV600E alone. Additional somatic Trp53-loss is sufficient to induce anaplastic GGs (aGGs) with glioneuronal clonality. Functionally, only BRAFV600E/pAkt tumors intrinsically generate substantial neuronal activity and show enhanced relay to adjacent tissue conferring high epilepsy propensity. In contrast, PLNTY- and aGG-models lack significant spike activity, which appears in line with the glial differentiation of the former and a dysfunctional tissue structure combined with reduced neuronal transcript signatures in the latter. ConclusionmTOR-signaling and Trp53-loss critically determine the biological diversity and electrical activity of BRAFV600E-induced tumors. Key pointsO_LIIUE of BRAFV600E and activation of mTOR leads to ganglioglioma (GG)-like tumors, while BRAFV600E alone give rise to PLNTY-like neoplasms. C_LIO_LIAnaplastic GGs depend on the Trp53 deletion in combination to BRAFV600E and PI3K-mTOR signaling cascade. C_LI Importance of the StudyGlioneuronal tumors are challenging with respect to biological behavior and seizure emergence. While BRAFV600E in murine neural precursors induces oligoid tumors, it requires an overactivation of PI3K/mTOR-signaling for the development of hyperexcitable gangliogliomas and additional Trp53-loss for anaplastic transformation.

neuroscience↗

bioRxiv2021

Leaky wiring of the brain: local cluster of coupled synapses and extracellular signal integration

The wiring scheme of neurons is key to the function of the brain. Neurons are structurally wired by synapses and it is a long-held view that most synapses in the CNS are sufficiently isolated to avoid cross-talk to AMPA receptors of neighboring synapses. Here we report in hippocampal brain slices that quantal glutamate release activated optical reporter proteins >1.5 {micro}m distant to the releasing synapse. 2P-glutamate uncaging was used to quantitatively probe glutamate spread in the neuropil. Releasing [~]35000 molecules of glutamate ([~]5 vesicles) at a distance of 500 nm to a spine generated an uncaging EPSC reaching [~]30% of the quantal amplitude at synaptic AMPA-Rs. The same stimulus activated [~]70% of the quantal amplitude at NMDA-Rs and still generated clear current and calcium responses when applied at >= 2 {micro}m remote to the spine. Extracellular spread of glutamate on the sub-micrometer scale appeared cooperative and caused supra-additive activation of AMPA-Rs in a spine. These observations are not predicted by previously used models of glutamate diffusion in the neuropil. An extracellular glutamate scavenger system weakly reduced field potential responses but not the quantal amplitude, indicating that a cross-talk component regularly contributes to synaptic transmission. Our data suggest that slight synaptic crosstalk responses at AMPA receptors of [~]2-4 adjacent synapses may be common (>70 synapses for NMDA receptors). Such broadcasting of synaptic signals to very local neighborhoods could stabilize network learning performance and allow for integration of synaptic activity within the extracellular space.

neuroscience↗

bioRxiv2020

Ste20-like kinase is critical for inhibitory synapse maintenance and its deficiency confers a developmental dendritopathy

The size and structure of the dendritic arbor play important roles in determining how synaptic inputs of neurons are converted to action potential output. The regulatory mechanisms governing the development of dendrites, however, are insufficiently understood. The evolutionary conserved Ste20/Hippo kinase pathway has been proposed to play an important role in regulating the formation and maintenance of dendritic architecture. A key element of this pathway, Ste20-like kinase (SLK), regulates cytoskeletal dynamics in non-neuronal cells and is strongly expressed throughout neuronal development. However, its function in neurons is unknown. We show that during development of mouse cortical neurons, SLK has a surprisingly specific role for proper elaboration of higher, [≥] 3rd, order dendrites. Moreover, we demonstrate that SLK is required to maintain excitation-inhibition balance. Specifically, SLK knockdown caused a selective loss of inhibitory synapses and functional inhibition after postnatal day 15, while excitatory neurotransmission was unaffected. Finally, we show that this mechanism may be relevant for human disease, as dysmorphic neurons within human cortical malformations revealed significant loss of SLK expression. Overall, the present data identify SLK as a key regulator of both dendritic complexity during development and of inhibitory synapse maintenance.

neuroscience↗