Biology subjects

Hsieh, F.

Publications and source records attributed to Hsieh, F..

7 recordsLinked to original sources

bioRxiv2026

Subtype-specific secretion of extracellular vesicles by LRRK2 and Rab GTPases under lysosomal stress

LRRK2, the Parkinsons disease-associated kinase, phosphorylates a subset of Rab GTPases and regulates membrane dynamics. We previously reported that lysosomal stress activates LRRK2 and thereby induces the exocytic secretion of lysosomal contents, but the detailed secretion mechanism remained unclear. Here we found that, under lysosomal stress, endolysosomal luminal and membrane components were secreted with extracellular vesicles (EVs) via LRRK2. Bis(monoacylglycerol)phosphate, an endolysosomal lipid and a urinary marker of LRRK2 activity, was similarly secreted via LRRK2, whereas CD9-positive EVs were not involved. Further dissection of the secreted EVs revealed that Alix-positive EVs were secreted via Rab8a as well as the ESCRT component VPS4, whereas LAMP1/cathepsin B-positive EVs were secreted via Rab10/Rab35, and SNARE proteins syntaxin 2 and VAMP8 regulated the secretion of both EV subtypes. These findings suggest a distinctive stress-induced secretory mechanism whereby LRRK2 facilitates the secretion of multiple EV subtypes by controlling Rab GTPases involved in each pathway.

cell biology↗

bioRxiv2025

Behavioral Efficacy of AAV FOXG1 Gene Replacement Therapy in a Mouse Model of FOXG1 Syndrome

FOXG1 syndrome is a severe neurodevelopmental disorder characterized by microcephaly, profound intellectual disability with communication deficits including lack of speech, impaired social interaction, increased anxiety, hyperkinetic/dyskinetic movements, seizures and abnormal sleep patterns. Mutations in a single allele of the FOXG1 gene cause disease, likely due to loss-of-function. However, current therapies do not target this root cause of FOXG1 syndrome and have little to modest therapeutic benefit on only a small subset of symptoms. To date, the therapeutic potential of restoring FOXG1 levels in the brain with adeno-associated virus (AAV) FOXG1 gene replacement therapy has only been reported in a Foxg1fl/+;NexCre mouse model that lacks one Foxg1 allele but does not express mutant FOXG1, and with only neuroanatomical endpoints evaluated. Here, in a FOXG1 mouse model that contains a highly prevalent, patient-specific Q84P mutation, we describe the beneficial effects of AAV human FOXG1 gene replacement therapy administered by intracerebroventricular (ICV) injection at postnatal day 6 (P6) on several behavioral deficits that are relevant to key features of human FOXG1 syndrome. Our studies demonstrate that AAV FOXG1 gene replacement therapy is a promising approach for the treatment of a subset of functional deficits in human FOXG1 syndrome.

neuroscience↗

bioRxiv2025

Robust analytical methods for bis(monoacylglycero)phosphate profiling in health and disease

Bis(monoacylglycero)phosphate (BMP), a distinct anionic phospholipid predominantly found in late endosomes and lysosomes, plays a pivotal role in supporting lysosomal functions and maintaining metabolic homeostasis. Its impaired function is associated with an array of disorders, notably neurodegenerative diseases. However, the identification and quantitation of BMP remains difficult due to its structural similarity to isomer phosphatidylglycerol (PG), thus necessitating robust analytical methods for accurate and reliable BMP profiling. In this study, we present comprehensive liquid chromatography - tandem mass spectrometry (MS2) methodologies for the precise and systematic analysis of BMP species in biological samples. We detail LC/MS methods for both an untargeted Orbitrap mass spectrometer and a targeted triple quadrupole (QQQ) mass spectrometer. We utilize differences in polarity and structure to annotate BMPs and PGs based on retention time and positive mode MS2 fragmentation patterns, respectively. Further, we propose a new approach for overcoming common challenges in BMP profiling by leveraging the newly discovered biochemical function of CLN5 as the BMP synthase. Since genetic ablation of CLN5 leads to specific depletion of BMPs but not PGs, we use lipid extracts from CLN5 knockout (KO) and wild-type (WT) cells as biological standards to confidently annotate BMPs as targets with significantly low BMP Identification Index (BMPII), defined as BMPII = CLN5 KO / WT. We additionally propose the BMP enrichment score (BMPES) as a secondary validation metric, defined as lysosomal abundance of BMP / whole-cell abundance. Altogether, this approach constitutes a robust method for BMP profiling and annotation, furthering research into health and disease.

biochemistry↗

bioRxiv2023

The packaging signal of Xanthomonas integrative filamentous phages

Unlike Ff, the packaging signal (PS) and the mechanism of integrative filamentous phage assembly remain largely unknown. Here we revived two Inoviridae prophage sequences, {phi}Lf2 and {phi}Lf-UK, as infectious virions lysogenize black rot pathogen Xanthomonas campestris pv. campestris. {phi}Lf2 and {phi}Lf-UK genomes consist of 6,363 and 6,062 nucleotides and share 85.8% and 98.7% identity with {phi}Lf, respectively. To explore their assembly, we first identified 20-26- nucleotide long PS sequences of 10 Xanthomonas phages. These PS consist of a DNA hairpin with the consensus GGX(A/-)CCG(C/T)G sequence in the stem and C/T nucleotides in the loop, both of which are conserved and essential for PS activity. In contrast to Ff, the 5 to 3 orientation of PS sequence is not conserved or critical for their competence. This is the first report to offer insights into the structure and function of integrative phage PS, revealing the diversity of filamentous phage encapsidation.

molecular biology↗

bioRxiv2023

Exosome-mediated release of bis(monoacylglycerol)phosphate is regulated by LRRK2 and Glucocerebrosidase activity

The endolysosomal phospholipid, bis(monoacylglycerol)phosphate (BMP), is aberrantly elevated in the urine of Parkinsons patients with mutations in genes encoding leucine-rich repeat kinase 2 (LRRK2) and glucocerebrosidase (GCase). Because BMP resides on and regulates the biogenesis of endolysosomal intralumenal membranes that become extracellular vesicles (EVs) upon release, we hypothesized that elevated urinary BMP may be driven by increased exocytosis of BMP-enriched EVs. To test this hypothesis, we analyzed BMP metabolism and EV-associated release of BMP in wild type (WT) and R1441G LRRK2-expressing mouse embryonic fibroblast (MEF) cells. Using immunofluorescence microscopy and transmission electron microscopy we detected structural alterations in endolysosomes and antibody-accessible BMP pool, indicating that mutant LRRK2 affects endolysosomal homeostasis. Biochemical analyses of isolated EV fractions confirmed the effect on endolysosomes by showing an increase in LAMP2-positive EVs in mutant cells, which was partially restored by LRRK2 kinase inhibition but further augmented, albeit to a more variable extent, by GCase inhibition. Using mass spectrometry, we detected an overall increase in total di-22:6-BMP and total di-18:1-BMP in cell lysates from mutant LRRK2 MEFs compared to WT cells. Inhibition of LRRK2 kinase partially restored cellular BMP levels, whereas inhibition of GCase further increased the BMP content. In isolated EVs from LRRK2 mutant cells, LRRK2 inhibition decreased BMP content whereas GCase inhibition tended to increase it. Using metabolic labeling experiments, we demonstrated that the increase in cellular BMP content is not due to an increase in BMP synthesis, even though we observed an increase in BMP synthesizing enzyme, CLN5, in LRRK2 mutant MEFs and patient-derived fibroblasts. Finally, pharmacological modulation of EV release and live total internal reflection fluorescence (TIRF) microscopy of endolysosomal exocytosis in human G2019S LRRK2 fibroblasts, further confirmed that BMP release is associated with EV secretion. Together, these results establish LRRK2 as a regulator of BMP levels in cells and its release through EVs and suggest that GCase activity further modulates this process in LRRK2 mutant cells. Mechanistic insights from these studies have implications for the potential use of BMP-positive EVs as a biomarker for Parkinsons disease and associated treatments.

neuroscience↗

bioRxiv2021

CRISPR screens for lipid regulators reveal a role for ER-bound SNX13 in lysosomal cholesterol export

We report here two genome-wide CRISPR screens carried out to identify genes that when knocked out, alter levels of lysosomal cholesterol or bis(monoacylglycero)phosphate. In addition, these screens were also carried out under conditions of NPC1 inhibition to identify modifiers of NPC1 function in lysosomal cholesterol export. The screens confirm tight co- regulation of cholesterol and bis(monoacylglycero)phosphate levels in cells, and reveal an unexpected role for the ER-localized, SNX13 protein as a negative regulator of lysosomal cholesterol export. In the absence of NPC1 function, SNX13 knockout decreases lysosomal cholesterol, and is accompanied by triacylglycerol-rich lipid droplet accumulation and increased lysosomal bis(monoacylglycero)phosphate. These experiments provide unexpected insight into the regulation of lysosomal lipids and modification of these processes by novel gene products. SUMMARYGenome-wide CRISPR screens carried out with and without NPC1 function identify shared pathways that coordinately control lysosomal cholesterol and bis(monoacylglycero)phosphate. ER-localized SNX13 protein plays an unexpected regulatory role in modifying NPC1 function to regulate cellular cholesterol localization.

cell biology↗

bioRxiv2020

Predictive Markers of LRRK2 Inhibition in Biofluids

Hyper-activated LRRK2 is linked to Parkinson’s disease susceptibility and progression. Quantitative measures of LRRK2 inhibition, especially in the brain, may be critical in the clinical development of successful LRRK2-targeting therapeutics. In this study, three different brain-penetrant and selective LRRK2 small-molecule kinase inhibitors (PFE-360, MLi2, and RA283) were orally administered to groups of cynomolgus macaques at different doses. Biofluid markers with proposed pharmacodynamic properties for assessing LRRK2 inhibition were measured from samples of blood, urine, and cerebral-spinal fluid (CSF). LRRK2 kinase inhibition led to consistent reduced pS935-LRRK2 and pRab10 proteins in blood mononuclear cells, reduced exosome LRRK2 protein and di-docosahexaenoyl (22:6) bis (monoacylglycerol) phosphate in urine, and reduced exosome LRRK2 and autophosphorylated pS1292-LRRK2 protein in CSF. Incomplete LRRK2 kinase inhibition reduced LRRK2 protein secretion in exosomes whereas high drug exposures may reduce both exosome and tissue levels of LRRK2 protein. These orthogonal markers for LRRK2 inhibition in urine and CSF can be used in combination with blood markers to non-invasively monitor the potency of LRRK2-targeting therapeutics in the brain and periphery.Competing Interest StatementThe authors have declared no competing interest.AbbreviationsPDParkinson’s diseaseLRRK2Leucine-rich repeat kinase 2 NHPs: Non-human primatesdi-22:6-BMPdi-docosahexaenoyl (22:6) bis (monoacylglycerol) phosphate CSF: Cerebrospinal fluidATPadenosine-tri phosphateView Full Text

neuroscience↗