Biology subjects

Fujise, K.

Publications and source records attributed to Fujise, K..

8 recordsLinked to original sources

bioRxiv2026

Dopamine vesicles are specified by mechanisms overriding canonical synaptic vesicle size constraints

Dopaminergic neurons contain distinct synaptic vesicle (SV) populations that segregate dopamine from glutamate, but the molecular basis of this segregation remains unclear. Using an established in vitro SV reconstitution system in fibroblasts, we show that synaptogyrin family proteins--synaptogyrin 1, synaptogyrin 2 and synaptogyrin 3--but not synaptophysin, selectively associate with VMAT2-positive dopamine vesicles in the presence of synapsin. Despite the known role of synaptophysin and synaptogyrin family proteins in generating small SVs (40-50 nm), VMAT2 vesicles retain a larger size (50-80 nm) when co-expressed with synaptogyrins, while remaining segregated from synaptophysin-containing vesicles. SV2 family proteins (SV2A, SV2B, and SV2C) localize to both VMAT2- and synaptophysin-positive vesicle populations, with SV2C preferentially enriched on VMAT2-positive dopamine vesicles. Consistent with the selective dystrophy of SV2C/VMAT2/DAT-positive dopaminergic terminals in parkinsonism-associated SJ1RQKI mice, iPSC-derived dopaminergic neurons carrying the same mutation accumulate small and enlarged SV-like organelles within autophagosomes, indicating defective SV clearance. Together, our findings suggest that dopamine vesicles are regulated by distinct trafficking mechanisms that override canonical SV size control, providing insight into the selective vulnerability of dopaminergic terminals in Parkinsons disease.

neuroscience↗

bioRxiv2025

Fecal microbiota transplantation mitigates cardiac remodeling and functional impairment in mice with chronic colitis

BackgroundInflammatory bowel disease (IBD) is a chronic inflammatory disorder with significant extraintestinal manifestations, including cardiovascular derangements. However, the molecular mechanisms underlying the cardiac remodeling and dysfunction remain unclear. MethodsWe investigated the effects of chronic colitis on the heart using two mouse models: DSS-induced colitis and Il10-/-spontaneous colitis. Echocardiography was employed to assess heart function and molecular characterization was performed using bulk RNA-sequencing, RT-qPCR, and western blot. ResultsBoth models exhibited significant cardiac impairment, including reduced ejection fraction and fractional shortening as well as increased collagen deposition, inflammation, and myofibril reorganization. Molecular analyses revealed upregulation of fibrosis markers (i.e. COL1A1, COL3A1, Fibronectin) and {beta}-catenin reactivation, indicating a pro-fibrotic cardiac environment. Each model yielded common upregulation of eicosanoid-associated and inflammatory genes (Cyp2e1, Map3k6, Pck1, Cfd), and model-specific alterations in pathways regulating cAMP- and cGMP-signaling, arachidonic and linoleic acid metabolism, Cushing syndrome-related genes, and immune cell responses. DSS colitis caused differential regulation of 232 cardiac genes, while Il10-/- colitis yielded 105 dysregulated genes, revealing distinct molecular pathways driving cardiac dysfunction. Importantly, therapeutic fecal microbiota transplantation (FMT) restored heart function in both models, characterized by reduced fibrosis markers and downregulated pro-inflammatory genes (Lbp and Cdkn1a in Il10-/- mice and Fos in DSS mice), while also mitigating intestinal inflammation. Post-FMT cardiac RNA-sequencing revealed significant gene expression changes, with three altered genes in DSS mice and 67 genes in Il10-/- mice. Notably, Il10-/- mice showed relatively less cardiac recovery following FMT, highlighting IL-10s cardioprotective and anti-inflammatory contribution. ConclusionsOur findings elucidate novel insights into colitis-induced cardiac remodeling and dysfunction and suggest that FMT mitigates cardiac dysfunction by attenuating systemic inflammation and correcting gut dysbiosis. This study underscores the need for further evaluation of gut-heart interactions and microbiome-based therapies to improve cardiovascular health in IBD patients. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=119 SRC="FIGDIR/small/643179v1_ufig1.gif" ALT="Figure 1"> View larger version (54K): org.highwire.dtl.DTLVardef@13d79eaorg.highwire.dtl.DTLVardef@10f28a7org.highwire.dtl.DTLVardef@35f4b0org.highwire.dtl.DTLVardef@538d7e_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2025

Multiple interactions mediate the localization of BLTP2 at ER-PM contacts to control plasma membrane dynamics

BLTP2/KIAA0100, a bridge-like lipid transfer protein, was reported to localize at contacts of the endoplasmic reticulum (ER) with either the plasma membrane (PM) or recycling tubular endosomes depending on the cell type. Our findings suggest that mediating bulk lipid transport between the ER and the PM is a key function of this protein as BLTP2 tethers the ER to tubular endosomes only after they become continuous with the PM and that it also tethers the ER to macropinosomes in the process of fusing with the PM. We further identify interactions underlying binding of BLTP2 to the PM, including phosphoinositides, the adaptor proteins FAM102A and FAM102B, and also N-BAR domain proteins at membrane-connected tubules. The absence of BLTP2 results in the accumulation of intracellular vacuoles, many of which are connected to the plasma membrane, pointing to a role of the lipid transport function of BLTP2 in the control of PM dynamics.

cell biology↗

bioRxiv2024

Bridge-like lipid transfer protein 3A (BLTP3A) is associated with membranes of the late endocytic pathway and is an effector of CASM

Recent studies have identified a family of rod-shaped proteins thought to mediate lipid transfer at intracellular membrane contacts by a bridge-like mechanism. We show one such protein, bridge-like lipid transfer protein 3A (BLTP3A)/UHRF1BP1 binds VAMP7 vesicles via its C-terminal region and anchors them to lysosomes via its chorein domain containing N-terminal region to Rab7. Upon lysosome damage, BLTP3A-positive vesicles rapidly (within minutes) dissociate from lysosomes. Lysosome damage is known to activate the CASM (Conjugation of ATG8 to Single Membranes) pathway leading to lipidation and recruitment to lysosomes of mammalian ATG8 (mATG8) proteins. We find that this process drives the reassociation of BLTP3A with damaged lysosomes via an interaction of its LIR motif with mATG8 which coincides with a dissociation from the vesicles. Our findings reveal that BLTP3A is an effector of CASM, potentially as part of a mechanism to help repair or minimize lysosome damage. TeaserBLTP3A is localized on membranes of the late endocytic system and is CASM effector, pointing to a role of this proteins in the response to lysosome damage

cell biology↗

bioRxiv2024

Overlapping role of synaptophysin and synaptogyrin family proteins in determining the small size of synaptic vesicles

Members of the synaptophysin and synaptogyrin family are vesicle proteins with four transmembrane domains. In spite of their abundance in synaptic vesicle (SV) membranes, their role remains elusive and only mild defects at the cellular and organismal level are observed in mice lacking one or more family members. Here, we show that co-expression with synapsin of each of the four brain-enriched members of this family - synaptophysin, synaptoporin, synaptogyrin1 and synaptogyrin3 - in fibroblasts is sufficient to generate clusters of small vesicles in the same size range of SVs. Moreover, mice lacking all these four proteins have larger SVs. We conclude that synaptophysin and synaptogyrin family proteins play an overlapping function in the biogenesis of SVs and in determining their small size.

neuroscience↗

bioRxiv2024

Synaptic vesicle characterization of iPSC-derived dopaminergic neurons provides insight into distinct secretory vesicle pools

The impairment of dopaminergic (DA) neurons plays a central role in the development of Parkinsons disease. Evidence for distinct populations of synaptic vesicles (SVs) differing in neurotransmitter content (glutamate versus dopamine) has been attributed to differences in trafficking pathways and their exocytosis kinetics. However, the molecular and ultrastructural organization of the two types of vesicles remains poorly understood. Here we examined the development of axonal varicosities in human iPSC-derived DA neurons and glutamatergic neurons (i3Neurons). While i3Neurons are comprised of 40-50 nm small clear SVs, DA neurons are predominantly comprised of large pleiomorphic vesicles including empty and dense core vesicles, in addition to the classical SVs. The large vesicles were positive for VMAT2, the monoamine vesicular transporter responsible for loading dopamine, and are distinctly larger in size and spatially segregated from the VGLUT1/2-positive vesicles when expressed in an ectopic SV-like organelle reconstitution system. Moreover, these VMAT2-positive vesicles were also colocalized to known SV markers such as Rab3, SCAMP5, VAMP2, SV2C and can be clustered by the matrix protein synapsin. Our results show that DA neurons display inherent differences in their populations of neurotransmitter-containing secretory vesicles, and iPSC-derived neurons are powerful models for the study of presynaptic structures.

neuroscience↗

bioRxiv2023

Parkinsonism Sac domain mutation in Synaptojanin-1 affects ciliary properties in iPSC-derived dopaminergic neurons

Synaptojanin-1 (SJ1) is a major neuronal-enriched PI(4,5)P2 4- and 5-phosphatase implicated in the shedding of endocytic factors during endocytosis. A mutation (R258Q) that impairs selectively its 4-phosphatase activity causes Parkinsonism in humans and neurological defects in mice (SJ1RQKI mice). Studies of these mice showed, besides an abnormal assembly state of endocytic factors at synapses, the presence of dystrophic nerve terminals selectively in a subset of nigro-striatal dopamine (DA)-ergic axons, suggesting a special lability of DA neurons to the impairment of SJ1 function. Here we have further investigated the impact of SJ1 on DA neurons using iPSC-derived SJ1 KO and SJ1RQKI DA neurons and their isogenic controls. In addition to the expected enhanced clustering of endocytic factors in nerve terminals, we observed in both SJ1 mutant neuronal lines increased cilia length. Further analysis of cilia of SJ1RQDA neurons revealed abnormal accumulation of the Ca2+ channel Cav1.3 and of ubiquitin chains, suggesting an impaired clearing of proteins from cilia which may result from an endocytic defect at the ciliary base, where a focal concentration of SJ1 was observed. We suggest that SJ1 may contribute to the control of ciliary protein dynamics in DA neurons, with implications on cilia-mediated signaling.

neuroscience↗

bioRxiv2021

Imaging-based evaluation of pathogenicity by novel DNM2 variants associated with centronuclear myopathy

Centronuclear myopathy (CNM) is characterized clinically by muscle weakness and pathologically by the presence of centralized nuclei and disarrangement of T-tubules in muscle fibers. DNM2 which encodes a large GTPase dynamin 2 have been identified as a causative gene for CNM. Nevertheless, the identification of DNM2 variants may not always lead to the definitive diagnosis as their pathogenicity is often unknown. In this study, by imaging T-tubule-like structures reconstituted in cellulo, we demonstrated that aberrant membrane remodeling by mutant dynamin 2 is tightly associated with gain-of-function features of DNM2 variants. This simple in cellulo assay provided quantitative data required for accurately evaluating pathogenicity of reported and novel DNM2 variants identified from CNM patients in our cohort. Our approaches combining the in cellulo assay with clinical information of the patients enabled to explain the course of a disease progression by pathogenesis of each variant in DNM2-associated CNM.

cell biology↗