Biology subjects

Larsen, S. B.

Publications and source records attributed to Larsen, S. B..

7 recordsLinked to original sources

bioRxiv2024

The Role of Alpha Synuclein in Synucleinopathy: Impact on Lipid Regulation at Mitochondria ER Membranes

The protein alpha-synuclein (Syn) plays a critical role in the pathogenesis of synucleinopathy, which includes Parkinsons disease and multiple system atrophy, and mounting evidence suggests that lipid dyshomeostasis is a critical phenotype in these neurodegenerative conditions. Previously, we identified that Syn localizes to mitochondria-associated endoplasmic reticulum membranes (MAMs), temporary functional domains containing proteins that regulate lipid metabolism, including the de novo synthesis of phosphatidylserine. In the present study, we have analyzed the lipid composition of postmortem human samples, focusing on the substantia nigra pars compacta of Parkinsons disease and controls, as well as three less affected brain regions of Parkinsons donors. To further assess synucleinopathy-related lipidome alterations, similar analyses were performed on the striatum of multiple system atrophy cases. Our data show region-and disease-specific changes in the levels of lipid species. Specifically, our data revealed alterations in the levels of specific phosphatidylserine species in brain areas most affected in Parkinsons disease. Some of these alterations, albeit to a lesser degree, are also observed multiples system atrophy. Using induced pluripotent stem cell-derived neurons, we show that Syn contributes to regulating phosphatidylserine metabolism at MAM domains, and that Syn dosage parallels the perturbation in phosphatidylserine levels. Our results support the notion that Syn pathophysiology is linked to the dysregulation of lipid homeostasis, which may contribute to the vulnerability of specific brain regions in synucleinopathy. These findings have significant therapeutic implications. Significance StatementSynucleinopathy is a complex group of neurodegenerative disorders whose causes and underlying mechanisms remain unknown. In this work, we examined synucleinopathy postmortem brain samples and patient-derived neuron models and identified the functional impairment of the mitochondrial-associated endoplasmic reticulum membrane (MAM) domain, which facilitates lipid regulation. The protein alpha-synuclein is associated with synucleinopathy and increasing levels result in the mislocalization of this protein and the disruption of MAM domains, which, in turn, results in lipid and membrane composition alterations. Specifically, we report that increased alpha-synuclein expression impairs the regulation of phosphatidylserine synthase 2 and the levels of phosphatidylserine in cellular membranes from affected cells. Our study offers mechanistic insight tying alpha-synuclein pathology and lipid dysregulation as seminal factors in synucleinopathy, which may have pathogenic and therapeutic implications.

neuroscience↗

bioRxiv2023

A reproducible enteric phage community improves blood glucose regulation in an obesity mouse model

Metabolic syndrome encompasses amongst other conditions like obesity, type-2 diabetes, and metabolic dysfunction associated fatty liver disease (MAFLD), which are all associated with gut microbiome (GM) dysbiosis. Fecal microbiota transplantation (FMT) has been explored to treat metabolic syndrome by restoring the GM. FMT is generally safe, but motivated by case reports, accidental transfer of pathogenic bacteria remains a concern. As a safer alternative, fecal virome transplantation (FVT, sterile-filtrated feces) has the advantage over FMT in that mainly bacteriophages are transferred and FVT from lean male donors has shown promise in alleviating the metabolic effects of a high-fat diet in a preclinical mouse study. However, FVT still carries the risk of eukaryotic viral infections. To address this, we here apply recently developed modification methodologies to inactivate or remove the eukaryotic viral component of FVT while maintaining an active enteric bacteriophage community. Modified FVTs were compared with unmodified FVT and saline in an animal model of diet-induced obesity using male C57BL/6N mice. In contrast to the obese control group, mice administered a modified FVT, nearly depleted from eukaryotic viruses (0.1%), exhibited enhanced blood glucose clearance, although without a concurrent reduction in weight gain. The unmodified FVT improved liver pathology and reduced the proportions of immune cells in the adipose tissue with a non-uniform response. GM analysis suggested that bacteriophage-mediated GM modulation had influenced these outcomes. When optimized, this may pave the way for developing safe bacteriophage-based therapies targeting metabolic syndrome through GM restoration.

microbiology↗

bioRxiv2023

Development of safe and effective bacteriophage-mediated therapies against C. difficile infections a proof-of-concept preclinical study

BackgroundFecal microbiota transplantation (FMT) and fecal virome transplantation (FVT, sterile filtrated donor feces) have been effective in treating recurrent Clostridioides difficile infections, possibly through bacteriophage-mediated modulation of the gut microbiome. However, challenges like donor variability, costly screening, coupled with concerns over pathogen transfer (incl. eukaryotic viruses) with FMT or FVT hinders their wider clinical application in treating less acute diseases. MethodsTo overcome these challenges, we developed methods to broaden FVTs clinical application while maintaining efficacy and increasing safety. Specifically, we employed the following approaches: 1) Chemostat-fermentation to reproduce the bacteriophage FVT donor component and remove eukaryotic viruses (FVT-ChP), 2) solvent-detergent treatment to inactivate enveloped viruses (FVT-SDT), and 3) pyronin-Y treatment to inhibit RNA-virus replication (FVT-PyT). We assessed the efficacy of these processed FVTs in a C. difficile infection mouse model and compared them with untreated FVT (FVT-UnT), FMT, and saline. ResultsFVT-SDT, FVT-UnT, and FVT-ChP reduced the incidence of mice reaching the humane endpoint (0/8, 2/7, and 3/8, respectively) compared to the FMT, FVT-PyT, and saline control (5/8, 7/8, and 5/7, respectively) and significantly reduced the load of colonizing C. difficile cells and toxin A/B levels. There was a potential elimination of C. difficile colonization, with 7 out of 8 mice treated with FVT-SDT testing negative with qPCR. In contrast, all other treatments exhibited the continued presence of C. difficile. Moreover, the results were supported by changes in the gut microbiome profiles, cecal cytokine levels and histopathological findings. Assessment of viral engraftment following FMT/FVT treatment and host-phage correlations analysis suggested that transfer of phages likely were an important contributing factor associated with treatment efficacy. ConclusionsThis proof-of-concept study show that specific modifications to FVT hold promise in addressing challenges related to donor variability and infection risks. Two strategies lead to treatments significantly limiting C. difficile colonization in mice, with solvent/detergent treatment and chemostat-propagation emerging as promising approaches.

microbiology↗

bioRxiv2023

Reproducible chemostat cultures to eliminate eukaryotic viruses from fecal transplant material

The effect of fecal microbiota transplantation (FMT) on various gut-related diseases is intensively investigated in clinical trials. In addition to bacteria, the gut microbiome also contains eukaryotic, archaeal, and bacterial viruses (bacteriophages, in short phages), which collectively is referred to as the gut virome. Application of FMT in clinical settings is associated with a potential risk for the recipient of transferring infectious eukaryotic viruses or bacteria, despite strict screening procedures for the donor material. A safer and more targeted method to modulate the gut microbiota is therefore needed to extend the application width of FMT. Emerging evidence suggests that gut phages play a key role in maintaining a balanced gut microbiome as well as in FMT efficacy. Thus, a phageome from a cultured fecal donor microbiome may be a more efficient alternative to modulate the gut bacteriome than FMT. Here, we analyzed the dynamic changes of the viromes of mice cecal and human fecal matter inoculated chemostat cultures. Sequencing results showed that the relative abundance of eukaryotic viruses remarkably decreased during continuous cultivation, likely due to the lack of eukaryotic hosts. The corresponding phageome profiles showed dilution rate dependency, a reproducibility between biological replicates, and maintained high diversity of phages although being different from the inoculum phageome. This proof-of-concept study may constitute the first step of developing therapeutic tools to target a broad spectrum of gut-related diseases and thereby replacing FMT with a safer phage-mediated therapy.

microbiology↗

bioRxiv2022

Brief synaptic inhibition persistently interrupts firing of fast-spiking interneurons

Neurons perform input-output operations that integrate synaptic inputs with intrinsic electrical properties, operations generally constrained by the brevity of synaptic events. Here we report that sustained firing of CA1 hippocampal fast-spiking parvalbumin-expressing interneurons (PV-INs) can be persistently interrupted for up to several hundred milliseconds following brief GABAAR-mediated inhibition in vitro and in vivo. A single presynaptic neuron could interrupt PV-INs firing, occasionally with a single action potential (AP), and reliably with AP bursts. Experiments and computational modeling revealed that the persistent interruption of firing maintains neurons in a depolarized, quiescent state through a cell-autonomous mechanism. Strikingly, interrupted PV-INs are highly responsive to Schaffer collateral inputs. The persistent interruption of firing provides a disinhibitory circuit mechanism favoring spike generation in CA1 pyramidal cells. Overall, our results demonstrate that neuronal silencing can far outlast brief synaptic inhibition owing to well-tuned interplay between neurotransmitter release and postsynaptic membrane dynamics, a phenomenon impacting microcircuit function.

neuroscience↗

bioRxiv2020

IPSC-derived midbrain astrocytes from Parkinson's disease patients carrying pathogenic SNCA mutations exhibit alpha-synuclein aggregation, mitochondrial fragmentation and excess calcium release

Parkinsons disease (PD) is characterized by the loss of A9 midbrain dopaminergic neurons and the accumulation of alpha-synuclein aggregates in remaining neurons. Many studies of the molecular and cellular basis of neurodegeneration in PD have made use of iPSC-derived neurons from patients with familial PD mutations. However, approximately half of the cells in the brain are glia, and their role facilitating neurodegeneration is unclear. We developed a novel serum-free protocol to generate midbrain astrocytes from patient-derived iPSCs harbouring the pathogenic p.A30P, p.A53T mutations in SNCA, as well as duplication and triplication of the SNCA locus. In our cellular model, aggregates of alpha-synuclein occurred only within the GFAP+ astrocytes carrying the pathogenic SNCA mutations. Assessment of spontaneous cytosolic calcium (Ca2+) release using Fluo4 revealed that SNCA mutant astrocytes released excess Ca2+ compared to controls. Unbiased evaluation of 3D mitochondrial morphometric parameters showed that these SNCA mutant astrocytes had increased mitochondrial fragmentation and decreased mitochondrial connectivity compared to controls, and reduced mitochondrial bioenergetic function. This comprehensive assessment of different pathogenic SNCA mutations derived from PD patients using the same cellular model enabled assessment of the mutation effect, showing that p.A53T and triplication astrocytes were the most severely affected. Together, our results indicate that astrocytes harbouring the familial PD mutations in SNCA are dysfunctional, suggesting a contributory role for dysfunctional astrocytes in the disease mechanism and pathogenesis of PD. Table of Contents Image O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=89 SRC="FIGDIR/small/053470v1_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@974d72org.highwire.dtl.DTLVardef@15d9da0org.highwire.dtl.DTLVardef@1177d4eorg.highwire.dtl.DTLVardef@123c0c2_HPS_FORMAT_FIGEXP M_FIG C_FIG Main PointsO_LIWe used a novel serum-free protocol to generate midbrain-specific functional astrocytes from Parkinsons disease patients carrying pathological mutations in SNCA C_LIO_LIPatient-derived astrocytes show morphological and functional impairments C_LI

neuroscience↗

bioRxiv2020

Mitochondria-mitochondria interaction networks show altered topological patterns in Parkinson's disease

Mitochondrial dysfunction is linked to pathogenesis of Parkinsons disease (PD). However, individual-mitochondria-based analyses do not show a uniform feature in PD patients. Since mitochondria interact with each other, we hypothesize that PD-related features might exist in topological patterns of mitochondria-mitochondria interaction networks (MINs). Here we showed that MINs form non-classical scale-free supernetworks in colonic ganglia both from healthy controls and PD patients, however, altered topological patterns are observed in PD patients. These patterns highly correlate with PD clinical scores and a machine-learning approach based on the MIN features accurately distinguish between patients and controls with an area-under-curve value of 0.989. The MINs of midbrain dopaminergic neurons (mDANs) derived from several genetic PD patients also display specific changes. CRISPR/CAS9-based genome correction of alpha-synuclein point mutations reverses the changes in MINs of mDANs. Our MIN network analysis opens a new dimension for a deeper characterization of various complex diseases with mitochondrial dysregulation.

neuroscience↗