Biology subjects

Enrich, C.

Publications and source records attributed to Enrich, C..

6 recordsLinked to original sources

bioRxiv2026

Gαq-mediated contact release is required for efficient mitochondrial quality control

Lysosomes and mitochondria are highly dynamic organelles whose coordinated interactions are essential for cellular homeostasis, while their dysfunction contributes to numerous human diseases. Here, we identify the mitochondrial outer membrane protein Fis1 and the RabGAPs TBC1D15 and TBC1D17 as novel interacting partners of the heterotrimeric G protein -subunit Gq. Using mitochondrial proteomics, co-immunoprecipitation, proximity ligation assays, and in vitro binding studies with purified proteins, we demonstrate that Gq forms a complex with Fis1 and TBC1D15/TBC1D17 through a non-canonical interaction interface. Gq localizes to mitochondria-lysosome contact sites, where it regulates the dynamic balance between contact formation and dissociation. Loss of Gq resulted in enlarged and clustered lysosomes and increased the extent and duration of mitochondria-lysosome contacts. Live-cell imaging revealed prolonged organelle tethering in Gq-deficient cells, while proximity ligation and three-dimensional reconstruction analyses localized Gq and TBC1D15 to mitochondrial tips closely associated with lysosomes. This localization, together with increased mitochondrial fission and altered mitophagic turnover following Gq loss, links the regulation of contacts at mitochondrial tips to mitochondrial fragmentation and quality control. Re-expression of Gq, but not the non-canonical interaction-deficient mutant, restored normal lysosomal morphology, contact-site dynamics, mitochondrial fragmentation, and mitophagy. Together, these findings identify a Gq as a dynamic regulator of mitochondria-lysosome untethering and connect contact site turnover with mitochondria fragmentation and mitophagy. Our work uncovers a novel link between G protein signaling, organelle communication, and mitochondrial quality control.

cell biology↗

bioRxiv2025

Fasting-induced hepatic gluconeogenesis is compromised in Anxa6-/- mice

Maintaining constant blood glucose levels is essential for energizing glucose-dependent tissues. During the fed state, insulin lowers elevated blood glucose, while in the fasted state, glucagon maintains blood glucose levels through hepatic stimulation of fatty acid oxidation, glycogenolysis, and gluconeogenesis (GNG). The liver plays a crucial role in these metabolic adaptations. Deregulation of GNG is a hallmark of type 2 diabetes mellitus (T2DM), driven by hepatic insulin resistance, elevated glucagon levels, and excess circulating free fatty acids. Despite normal insulin-sensitive control of glucose levels and effective glycogen mobilization, Anxa6 knockout (Anxa6-/-) mice display rapid hypoglycaemia during fasting. This metabolic disarrangement, in particular during the early stages of fasting is characterized by a low respiratory exchange ratio (RER) and increased lipid oxidation during the diurnal period, indicating a reliance on lipid oxidation due to hypoglycaemia. Elevated glucagon levels during fasting suggest deficiencies in GNG. Further analysis reveals that Anxa6-/- mice are unable to utilize alanine for hepatic GNG, highlighting a specific impairment in the glucose-alanine cycle in fasted Anxa6-/- mice, underscoring the critical role of ANXA6 in maintaining glucose homeostasis under metabolic stress. During fasting, slightly reduced expression levels of alanine aminotransferase 2 (Gpt2) and lactate dehydrogenase (Ldha2), enzymes converting alanine to pyruvate, and the hepatic alanine transporter SNAT4 might contribute to these observations in the Anxa6-/- mice. These findings identify that ANXA6 deficiency causes an inability to maintain glycolytic metabolism under fasting conditions due to impaired alanine-dependent GNG.

physiology↗

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↗

bioRxiv2022

Proteostatic regulation of caveolins avoids premature oligomerisation and preserves ER homeostasis

Caveolin-1 (CAV1) and CAV3 are membrane sculpting proteins driving formation of plasma membrane caveolae. Caveola formation is unique as it requires oligomerisation of newly synthesised caveolins through the biosynthetic-secretory pathway. Here, we combine structural, biochemical, and microscopy analyses to examine the early proteostasis of caveolin family members and mutants. We describe striking trafficking differences between newly synthesised caveolins, with CAV1 rapidly exported to the Golgi but CAV3 showing ER retention and targeting to lipid droplets. Only monomeric/low oligomeric caveolins are efficiently exported from the ER, with oligomers assembling beyond the cis-Golgi and disease-causing mutations leading to detrimental non-functional complexes. Caveolins in the ER are maintained at low levels by active proteasomal degradation, avoiding premature oligomerisation and ER stress. Increasing lipid availability, cholesterol for CAV1 and fatty acids for CAV3, enhances trafficking and reduces proteasomal degradation. In conclusion, we identify proteostatic mechanisms that modulate stability and trafficking of newly synthesised caveolins, protecting cells against ER stress but perturbed in caveolin-related disease. SummaryUnderstanding the unique proteostasis of caveolins has important implications for cell biology and physiopathology. Combining structural, microscopy, and biochemical analyses, we uncover new insights into the mechanisms that differentiate the early biosynthetic steps of caveolin family members, isoforms, and pathogenic mutants.

cell biology↗

bioRxiv2021

Direct reprogramming of human fibroblasts into insulin-producing cells by transcription factors

Direct lineage reprogramming of one somatic cell into another bypassing an intermediate pluripotent state has emerged as an alternative to embryonic or induced pluripotent stem cell differentiation to generate clinically relevant cell types. One cell type of clinical interest is the pancreatic {beta} cell that secretes insulin and whose loss and/or dysfunction leads to diabetes. Generation of functional {beta}-like cells from developmentally related somatic cell types (pancreas, liver, gut) has been achieved via enforced expression of defined sets of transcription factors. However, clinical applicability of these findings is challenging because the starting cell types are not easily obtainable. Skin fibroblasts are accessible and easily manipulated cells that could be a better option, but available studies indicate that their competence to give rise to {beta} cells through similar direct reprogramming approaches is limited. Here, using human skin fibroblasts and a protocol that ensures high and consistent expression of adenovirus-encoded reprogramming factors, we show that the transcription factor cocktail consisting of Pdx1, Ngn3, MafA, Pax4 and Nkx2-2 activates key {beta} cell genes and down-regulates the fibroblast transcriptional program. The converted cells produce insulin and exhibit intracellular calcium responses to glucose and/or membrane depolarization. Furthermore, they secrete insulin in response to glucose in vitro and after transplantation in vivo. These findings demonstrate that transcription factor-mediated direct reprogramming of human fibroblasts is a feasible strategy to generate insulin-producing cells.

developmental biology↗

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↗