Biology subjects

Müller, S. A.

Publications and source records attributed to Müller, S. A..

6 recordsLinked to original sources

bioRxiv2025

BACE1 regulates sleep-wake cycle through both enzymatic and non-enzymatic actions.

The {beta}-secretase BACE1 has become a prime target in Alzheimers disease (AD) therapy, because it drives the production of pathogenic amyloid {beta} peptides. However, clinical trials with BACE1-targeting drugs were halted due to adverse effects on cognitive performance. We propose here that cognitive impairment by BACE1 inhibitors may be a corollary of a higher function of BACE1 related to proper sleep regulation. To address non-enzymatic effects of BACE1 on ion channels likely involved in the sleep-wake cycle, we analyzed sleep patterns in both BACE1-KO mice and a newly generated transgenic line expressing a proteolysis-deficient BACE1 variant (BACE1-KI). We found that BACE1-KI and BACE1-KO mice displayed common and distinct sleep-wake disturbances. Compared to their respective wild-type littermates, both mutant lines slept less during the light phase (when they preferentially rest). Furthermore, transition rates between wake and sleep states were altered, as were sleep spindles and EEG power spectra mainly in the gamma range. Thus, a better understanding of how BACE1 interferes with sleep-modulated behaviors is needed if clinical trials with BACE1-targeted inhibitors are to resume.

animal behavior and cognition↗

bioRxiv2024

The late onset Alzheimer's disease risk factor iRhom2/RHBDF2 is a modifier of microglial TREM2 proteolysis

The cell surface receptor TREM2 is a key genetic risk factor and drug target in Alzheimers disease (AD). In the brain, TREM2 is expressed in microglia, where it undergoes proteolytic cleavage, linked to AD risk, but the responsible protease in microglia is still unknown. Another microglia-expressed AD risk factor is catalytically inactive rhomboid 2 (iRhom2, RHBDF2), which binds to and acts as a non-catalytic subunit of the metalloprotease ADAM17. A potential role in TREM2 proteolysis is not yet known. Using microglial-like BV2 cells, bone marrow-derived macrophages and primary murine microglia, we identify iRhom2 as a modifier of ADAM17-mediated TREM2 shedding. Loss of iRhom2 increased TREM2 in cell lysates and at the cell surface and enhanced TREM2 signaling and microglial phagocytosis of the amyloid {beta}-peptide (A{beta}). This study establishes ADAM17 as a physiological TREM2 protease in microglia, and suggests iRhom2 as a potential drug target for modulating TREM2 proteolysis in AD.

biochemistry↗

bioRxiv2022

LncRNA RUS shapes the gene expression program towards neurogenesis

The evolution of brain complexity correlates with an increased expression of long, non- coding (lnc) RNAs in neural tissues. Although prominent examples illustrate the potential of lncRNAs to scaffold and target epigenetic regulators to chromatin loci, only few cases have been described to function during brain development. We present a first functional characterization of the lncRNA LINC01322, which we term RUS for RNA upstream of Slitrk3. The RUS gene is well conserved in mammals by sequence and synteny next to the neurodevelopmental gene Slitrk3. RUS is exclusively expressed in neural cells and its expression increases along with neuronal markers during neuronal differentiation of mouse embryonic cortical neural stem cells. Depletion of RUS locks neuronal precursors in an intermediate state towards neuronal differentiation resulting in arrested cell cycle and increased apoptosis. RUS associates with chromatin in the vicinity of genes involved in neurogenesis, most of which change their expression upon RUS depletion. The identification of a range of epigenetic regulators as specific RUS interactors suggests that the lncRNA may mediate gene activation and repression in a highly context-dependent manner.

molecular biology↗

bioRxiv2020

Quantitative secretome analysis establishes the cell type-resolved mouse brain secretome

To understand how cells communicate in the nervous system, it is essential to define their secretome, which is challenging for primary cells because of large cell numbers being required. Here, we miniaturized secretome analysis by developing the high-performance secretome-protein-enrichment-with-click-sugars method (hiSPECS). To demonstrate its broad utility, hiSPECS was used to identify the secretory response of brain slices upon LPS-induced neuroinflammation and to establish the cell type-resolved mouse brain secretome resource using primary astrocytes, microglia, neurons and oligodendrocytes. This resource allowed mapping the cellular origin of CSF proteins and revealed that an unexpectedly high number of secreted proteins in vitro and in vivo are proteolytically-cleaved membrane protein ectodomains. Two examples are neuronally secreted ADAM22 and CD200, which we identified as substrates of the Alzheimer-linked protease BACE1. hiSPECS and the brain secretome resource can be widely exploited to systematically study protein secretion, brain function and to identify cell type-specific biomarkers for CNS diseases.

neuroscience↗

bioRxiv2019

Loss of NPC1 enhances phagocytic uptake and impairs lipid trafficking in microglia

Niemann-Pick type C disease is a rare neurodegenerative disorder mainly caused by mutations in Npc1, resulting in abnormal late endosomal/lysosomal lipid storage. Although microgliosis is a prominent pathological feature, consequences of NPC1 loss on microglial function remain uncharacterized. Here, we provide an in-depth characterization of microglial proteomic signatures and phenotypes in a NPC1-deficient (Npc1-/-) murine model and patient blood-derived macrophages. We demonstrate enhanced phagocytic uptake and impaired lipid trafficking in Npc1-/- microglia that precede neuronal death. Loss of NPC1 compromises microglial developmental functions as revealed by increased synaptic pruning and deficient myelin turnover. Undigested myelin accumulates within multi-vesicular bodies of Npc1-/- microglia while lysosomal degradation remains preserved. To translate our findings to human disease, we generated novel ex vivo assays using patient macrophages that displayed similar proteomic disease signatures and lipid trafficking defects as murine Npc1-/- microglia. Thus, peripheral macrophages provide a novel promising clinical tool for monitoring disease progression and therapeutic efficacy in NPC patients. Our study underscores an essential role for NPC1 in immune cells and implies microglial therapeutic potential.

neuroscience↗

bioRxiv2018

Profound functional and molecular diversity of mitochondria revealed by cell type-specific profiling in vivo

Mitochondria vary in morphology and function in different tissues, however little is known about their molecular diversity among cell types. To investigate mitochondrial diversity in vivo, we developed an efficient protocol to isolate cell type-specific mitochondria based on a new MitoTag mouse. We profiled the mitochondrial proteome of three major neural cell types in cerebellum and identified a substantial number of differential mitochondrial markers for these cell types in mice and humans. Based on predictions from these proteomes, we demonstrate that astrocytic mitochondria metabolize long-chain fatty acids more efficiently than neurons. Moreover, we identified Rmdn3 as a major determinant of ER-mitochondria proximity in Purkinje cells. Our novel approach enables exploring mitochondrial diversity on the functional and molecular level in many in vivo contexts.

cell biology↗