Biology subjects

Saidi, L.

Publications and source records attributed to Saidi, L..

5 recordsLinked to original sources

bioRxiv2026

CRISPR/CAS9-MEDIATED LOSS OF VESICULAR GLUTAMATE TRANSPORTER IN SEROTONIN NEURONS OF THE DORSAL RAPHE NUCLEUS LEADS TO SYNAPTIC CHANGES AND ANXIETY-LIKE BEHAVIORS

Vesicular glutamate transporter 3 (VGluT3) is expressed in a large subset of serotonin (5-HT) neurons of the dorsal raphe nucleus (DRN), suggesting a potential for glutamate co-transmission. Although VGluT3 has been implicated in the physiology of several non-glutamatergic neuronal populations, its specific role in the organization and function of 5-HT axons remains unclear. Here, we used CRISPR-Cas9 mediated knockdown and viral overexpression of VGluT3 in DRN 5-HT neurons of adult mice to assess its contribution to synaptic architecture in the lateral hypothalamus (LHA) and to 5-HT-related behaviors. VGluT3 depletion did not significantly alter synaptic incidence or organization of 5-HT DRN terminals in the LHA. In contrast, VGluT3 overexpression increased the proportion of asymmetric synapses without changing the overall synaptic incidence. In behavioral assays, VGluT3 depletion impaired motor coordination and increased anxiety-like, repetitive, and social behavior, whereas VGluT3 overexpression selectively reduced repetitive behavior. Basal locomotion and depressive-like behaviors were unchanged by either manipulation. Together, these findings indicate that VGluT3 modulates both the structural organization and behavioral output of DRN 5-HT neurons, supporting a modulatory role for VGluT3-dependent signaling within 5-HT circuits.

neuroscience↗

bioRxiv2025

CHIP protects lysosomes from CLN4 mutant-induced membrane damages

Understanding how cells mitigate lysosomal damage is critical for unraveling pathogenic mechanisms of lysosome-related diseases. Here we use organelle-specific proteomics in iPSC-derived neurons (i3Neuron) and an in vitro lysosome-damaging assay to demonstrate that lysosome damage, caused by the aggregation of Ceroid Lipofuscinosis Neuronal 4 (CLN4)-linked DNAJC5 mutants on lysosomal membranes, serves as a critical pathogenic linchpin in CLN4-associated neurodegeneration. Intriguingly, in non-neuronal cells, a ubiquitin-dependent microautophagy mechanism downregulates CLN4 aggregates to counteract CLN4-associated lysotoxicity. Genome-wide CRISPR screens identify the ubiquitin ligase CHIP as a central microautophagy regulator that confers ubiquitin-dependent lysosome protection. Importantly, CHIPs lysosome protection function is transferrable, as ectopic CHIP improves lysosomal function in CLN4 i3Neurons, and effectively alleviates lipofuscin accumulation and neurodegeneration in a Drosophila CLN4 disease model. Our study establishes CHIP-mediated microautophagy as a key organelle damage guardian that preserves lysosome integrity, offering new insights into therapeutic development for CLN4 and other lysosome-related neurodegenerative diseases.

cell biology↗

bioRxiv2024

NEMF-mediated CAT-tailing defines distinct branches of translocation-associated quality control

Ribosome stalling during co-translational translocation at the endoplasmic reticulum (ER) causes translocon clogging and impairs ER protein biogenesis. Mammalian cells resolve translocon clogging vial a poorly characterized translocation-associated quality control (TAQC) process. Here, we combine genome-wide CRISPR screen with live cell imaging to dissect the molecular linchpin of TAQC. We show that substrates translated from mRNAs bearing a ribosome stalling poly(A) sequence are degraded by lysosomes and the proteasome, while substrates encoded by non-stop mRNAs are degraded by an unconventional ER-associated degradation (ERAD) mechanism involving ER-to-Golgi trafficking and KDEL-dependent substrate retrieval. The triaging diversity appears to result from the heterogeneity of NEMF-mediated CATylation, because a systematic characterization of representative CAT-tail mimetics establishes an AT-rich tail as a "degron" for ERAD, whereas an AG-rich tail can direct a secretory protein to the lysosome. Our study reveals an unexpected protein sorting function for CAT-tailing that safeguards ER protein biogenesis.

cell biology↗

bioRxiv2021

Abnormal triaging of misfolded proteins by adult neuronal ceroid lipofuscinosis-associated CSPα mutants causes lipofuscin accumulation

Mutations in DNAJC5 (encoding the J domain-containing HSP70 co-chaperone CSP) are associated with adult neuronal ceroid lipofuscinosis (ANCL), a dominant-inherited neurodegenerative disease featuring lysosome-derived autofluorescent storage material (AFSM) termed lipofuscin. Functionally, CSP has been implicated in chaperoning synaptic proteins and in misfolding-associated protein secretion (MAPS), but how CSP dysfunction causes lipofuscinosis and neurodegeneration is unclear. Here we report two distinct protein quality control functions of CSP at endolysosomes and perinuclear vesicles, respectively. We show that the endolysosome-associated CSP promotes microautophagy of misfolded clients, but is dispensable for MAPS. By contrast, the perinuclear-localized CSP, regulated by a previously unknown CSP interactor named CD98hc, is critical for MAPS but unneeded for microautophagy. Importantly, these processes are coupled by CSP in a J-domain regulated manner. Uncoupling these two processes, as seen in cells lacking CD98hc or expressing ANCL-associated CSP mutants, generates CSP-containing AFSMs resembling NCL patient-derived lipofuscin, and also induces neurodegeneration in a Drosophila ANCL model. These findings suggest that blocking MAPS while allowing CSP-mediated microautophagy disrupts lysosome homeostasis, causing CSP-associated lipofuscinosis and neurodegeneration.

cell biology↗

bioRxiv2019

Huntington phosphorylation governs BDNF homeostasis and improves the phenotype of Mecp2 knockout mice

Mutations in the X-linked MECP2 gene are responsible for Rett syndrome (RTT), a severe neurological disorder for which there is no treatment. Several studies have linked the loss of MeCP2 function to alterations of brain-derived neurotrophic factor (BDNF) levels, but non-specific overexpression of BDNF only partially improves the phenotype of Mecp2-deficient mice. We and others have previously shown that huntingtin (HTT) scaffolds molecular motor complexes, transports BDNF-containing vesicles, and is under-expressed in Mecp2 knock-out brains. Here we demonstrate that promoting HTT phosphorylation at Ser421, either by a phospho-mimetic mutation or inhibition of the phosphatase calcineurin, restores endogenous BDNF axonal transport in vitro in the corticostriatal pathway, increases striatal BDNF availability and synaptic connectivity in vivo, and improves the phenotype and the survival of Mecp2 knockout mice--even though treatments were initiated only after the mice had already developed symptoms. Stimulation of endogenous cellular pathways may thus be a promising approach for the treatment of RTT patients.

neuroscience↗