Biology subjects

Havlicek, S.

Publications and source records attributed to Havlicek, S..

3 recordsLinked to original sources

bioRxiv2024

Human stem cell-derived GABAergic interneuron development reveals early emergence of subtype diversity followed by gradual electrochemical maturation

Medial ganglionic eminence-derived inhibitory GABAergic pallial interneurons (MGE-pINs) are essential regulators of cortical circuits; their dysfunction is associated with numerous neurological disorders. We developed human (h) MGE-pINs from pluripotent stem cells for the treatment of drug-resistant epilepsy. Here, we analyzed xenografted hMGE-pINs over the lifespan of host mice using single nuclei RNA sequencing. Comparative transcriptomics against endogenous human brain datasets revealed that 97% of grafted cells developed into somatostatin (SST) and parvalbumin (PVALB) subtypes, including populations that exhibit selective vulnerability in Alzheimers disease. Transplanted hMGE-pINs demonstrated rapid emergence of subclass features, progressing through distinct transcriptional states sequentially involving neuronal migration, synapse organization, and membrane maturation. We present molecular, electrophysiological, and morphological data that collectively confirm the derivation of diverse bona-fide human SST and PVALB subtypes, providing a high-fidelity model to study human MGE-pIN development and functional maturation as well as a compositional atlas for regenerative cell therapy applications.

neuroscience↗

bioRxiv2020

Constitutively active TrkB kinase signalling reduces actin filopodia dynamics and cell migration

Trk receptors and gene fusions of NTRK are targets in precision oncology. Classical Trk signalling concepts fail to explain ligand-independent signalling of intracellular TrkB or NTRK fusion proteins. Here, we show that abundance of the intracellular domain of TrkB is sufficient for ligand-independent autophosphorylation. This constitutive TrkB signalling reduced actin filopodia dynamics, could phosphorylate FAK, and changed cell morphology. Mutating Y705 in the kinase domain of TrkB alone specifically blocked these pathways. Engineered intracellular kinase domain proteins and a cancer-related intracellular NTRK2-fusion protein (SQSTM1-NTRK2) also underwent constitutive activation. In migrating glioblastoma-like U87MG cells, self-active TrkB kinase reduced cell migration. Moreover, we found evidences for constitutively active, intracellular TrkB in tissue of human grade IV glioblastoma. Structural modelling of the kinase domain let us postulate that release from cis-autoinhibition by abundance is sufficient for TrkB/FAK/Actin signalling via Y705. These constitutive signalling pathways could be fully blocked within minutes by clinically approved, anti-tumorigenic Trk inhibitors. In conclusion, our data provide an explanation and biological function for TrkB kinase domain signalling in the absence of a ligand.

neuroscience↗

bioRxiv2020

Patient-specific Alzheimer-like pathology in trisomy 21 cerebral organoids reveals BACE2 as a gene-dose-sensitive AD-suppressor in human brain

A population of >6 million people worldwide at high risk of Alzheimers disease (AD) are those with Down Syndrome (DS, caused by trisomy 21 (T21)), 70% of whom develop dementia during lifetime, caused by an extra copy of {beta}-amyloid-(A{beta})-precursor-protein gene. We report AD-like pathology in cerebral organoids grown in vitro from non-invasively sampled strands of hair from 71% of DS donors. The pathology consisted of extracellular diffuse and fibrillar A{beta} deposits, hyperphosphorylated/pathologically conformed Tau, and premature neuronal loss. Presence/absence of AD-like pathology was donor-specific (reproducible between individual organoids/iPSC lines/experiments). Pathology could be triggered in pathology-negative T21 organoids by CRISPR/Cas9-mediated elimination of the third copy of chromosome-21-gene BACE2, but prevented by combined chemical {beta} and {gamma}-secretase inhibition. We found that T21-organoids secrete increased proportions of A{beta}-preventing (A{beta}1-19) and A{beta}-degradation products (A{beta}1-20 and A{beta}1-34). We show these profiles mirror in cerebrospinal fluid of people with DS. We demonstrate that this protective mechanism is mediated by BACE2-trisomy and cross-inhibited by clinically trialled BACE1-inhibitors. Combined, our data prove the physiological role of BACE2 as a dose-sensitive AD-suppressor gene, potentially explaining the dementia delay in [~]30% of people with DS. We also show that DS cerebral organoids could be explored as pre-morbid AD-risk population detector and a system for hypothesis-free drug screens as well as identification of natural suppressor genes for neurodegenerative diseases.

neuroscience↗