Biology subjects

Mari, M.

Publications and source records attributed to Mari, M..

7 recordsLinked to original sources

bioRxiv2025

The expression level of CACNA1C-encoded CaV1.2 is a tipping point between promotion and inhibition of dendritic growth in neurons

The CACNA1C gene encodes the CaV1.2 L-type voltage-gated calcium channel, which plays a crucial role in neuronal signaling. CACNA1C is a risk gene for psychiatric conditions involving disruption of neuronal connectivity such as schizophrenia, autism, and bipolar disorders. While genomic studies are consistently reinforcing the notion of CACNA1C as an important locus related to these diseases, the role of CaV1.2 channels in determining neuronal architecture is incompletely understood. Several studies pinpoint the L-type current (ICaL) as regulator of dendritic arborization development. ICaL lays upstream of competing cellular mechanisms leading to both inhibition and promotion of dendritic growth. How signal selectivity is achieved remains an open question. Here, we report that ICaL-dependent dendritic development of murine cultured hippocampal neurons relies on CaV1.2 and is determined by an equilibrium between the level of CaV1.2 protein expression and ICaL activity. Indeed, increasing ICaL enhances dendritic complexity only when CaV1.2 expression level is reduced. In contrast, when channel levels are at baseline, the CaV1.2-dependent growing signal is overcome by the elevation of the dendritic growth inhibiting CaMKII signaling beyond basal conditions. These findings suggest that CaV1.2 expression level acts as a molecular switch between dendritic growing and inhibiting signals. Consequently, altered CaV1.2 expression during early development may alter neuronal structure, potentially impairing neural network formation and increasing susceptibility to psychiatric disorders. SIGNIFICANCE STATEMENTL-type voltage-gated calcium channels (L-VGCCs) allow calcium influx upon membrane depolarization. In neurons, L-VGCCs play a crucial role in regulating gene transcription, synaptic plasticity, and membrane excitability. Our data demonstrate that the L-VGCCs CaV1.2 isoform is a key regulator of early dendritic development. Calcium influx via CaV1.2 is necessary for proper dendritic growth under basal conditions. However, enhanced calcium currents boost dendritic growth only when channel expression levels are reduced. When the amount of CaV1.2 is at baseline, current stimulation antagonizes the growing process by upregulating the CaMKII signaling. Our findings suggest that the number of CaV1.2 available determines whether channel activity leads to aberrant dendritic arborization by sizing the recruitment of growth inhibiting CaMKII cascade.

neuroscience↗

bioRxiv2023

The endosomal sorting complex Retromer has a central role insystemic cholesterol homeostasis by controlling endo-lysosomal cholesterol transport in hepatocytes

BackgroundDisturbed hepatic cholesterol homeostasis is associated with multiple diseases, including atherosclerotic cardiovascular disease and metabolic dysfunction- associated steatotic liver disease. The endo-lysosomal system is essential for cholesterol uptake and intracellular distribution, yet the mechanisms governing these processes remain incompletely understood. Here, we investigated the impact of hepatic VPS35, a subunit of the endosomal sorting complex retromer, on hepatocellular and whole-body cholesterol homeostasis. MethodsWe generated a liver-specific Vps35 knockout mouse model (Vps35HepKO) and applied biochemical analyses, proteomics, and stable-isotope-labeled tracers to quantify critical processes of cholesterol metabolism. Human iPSC-derived liver organoids and CRISPR technology were used to translate our findings to humans. Mechanistic studies were performed in precision-cut liver slices from WT and Vps35HepKO mice. ResultsHepatic VPS35 deficiency led to an increase in endo-lysosomal degradative compartments and a marked reduction in specific lysosomal proteins, including lysosomal acid lipase (LAL), Scavenger Receptor Class B Member 2 (SCARB2), and Niemann-Pick type C1 (NPC1). Using pathway-specific inhibitors, we showed that VPS35 loss impairs the translation of SCABR2 and NPC1. Consistently, human iPSC-derived liver organoids lacking VPS35 also exhibited reduced expression of NPC1 and SCARB2 proteins. The decrease in these lysosomal proteins correlated with increased cholesterol levels in the plasma and liver of Vps35HepKO mice. This was likely explained by the disrupted cholesterol trafficking through the endo-lysosomal system, delayed plasma cholesterol turnover, and upregulated cholesterol biosynthesis. ConclusionThese findings uncover a previously unknown role for the hepatic retromer complex in maintaining systemic cholesterol homeostasis. Beyond its established function in endosomal cargo transport, we now demonstrate that retromer is also essential for lysosomal cholesterol handling. This role is mediated by regulating key lysosomal proteins involved in cholesterol metabolism, including LAL, NPC1, and SCARB2.

molecular biology↗

bioRxiv2021

The molecular chaperone DNAJB6 provides surveillance of FG-Nups and is required for interphase nuclear pore complex biogenesis

Biogenesis of nuclear pore complexes (NPCs) includes the formation of the permeability barrier composed of phenylalanine-glycine-rich nucleoporins (FG-Nups) that regulate the selective passage/crossing of biomolecules. The FG-Nups are intrinsically disordered and prone to liquid-liquid phase separate1,2 and aggregate when isolated3. It has remained largely unclear how FG-Nups are protected from making inappropriate interactions during NPC biogenesis. We found that DNAJB6, a molecular chaperone of the heat shock protein network, formed foci next to NPCs. The number of these foci decreases upon removal of proteins involved in the early steps of interphase NPC biogenesis. Reversely, when this process is stalled in the last steps, the number of DNAJB6-containing foci increases and they could be identified as herniations at the nuclear envelope (NE). Immunoelectron tomography showed that DNAJB6 localizes inside the lumen of the herniations arising at NPC biogenesis intermediates. Interestingly, loss of DNAJB6 results in annulate lamellae, which are structures containing partly assembled NPCs associated with disturbances in NPC biogenesis. We find that DNAJB6 binds to FG-Nups and can prevent the aggregation of the FG-region of several FG-Nups in cells and in vitro. Together, our data show that DNAJB6 provides quality control during NPC biogenesis and is the first molecular chaperone that is involved in the surveillance of native intrinsically disordered proteins, including FG-Nups.

molecular biology↗

bioRxiv2021

Acyl chain shortening induced by inhibition of acetyl-CoA carboxylase renders phosphatidylcholine redundant

Phosphatidylcholine (PC) is an abundant membrane lipid component in most eukaryotes including yeast. PC has been assigned a multitude of functions in addition to that of building block of the lipid bilayer. Here we show that PC is evolvable essential in yeast by isolating suppressor mutants devoid of PC that exhibit robust growth. The requirement for PC is suppressed by monosomy of chromosome XV, or by a point mutation in the ACC1 gene encoding acetyl-CoA carboxylase. Although these two genetic adaptations rewire lipid biosynthesis differently, both decrease Acc1 activity thereby reducing the average acyl chain length. Accordingly, soraphen A, a specific inhibitor of Acc1, rescues a yeast mutant with deficient PC synthesis. In the aneuploid suppressor, up-regulation of lipid synthesis is instrumental to accomplish feed-back inhibition of Acc1 by acyl-CoA produced by the fatty acid synthase (FAS). The results show that yeast regulates acyl chain length by fine-tuning the activities of Acc1 and FAS, and indicate that PC evolved by benefitting the maintenance of membrane fluidity.

biochemistry↗

bioRxiv2020

Targeting of integral membrane proteins to the surface of lipid droplets

Lipid droplets (LDs) are globular subcellular structures that mainly serve to store energy in form of neutral lipids, particularly triacylglycerols and steryl esters. LDs are closely associated with the membrane of the endoplasmic reticulum (ER), and are limited by a monolayer membrane of phospholipids harboring a specific set of proteins. Most of these proteins associate with LDs through either an amphipathic helix or a membrane-embedded hairpin motif. Here we address the question whether integral membrane spanning proteins could localize to the surface of LDs. To test this, we fused perilipin 3 (PLIN3), a mammalian LD-targeted protein, to ER resident proteins, such as Wbp1 (a N-glycosyl transferase complex subunit), Sec61 (a translocon subunit), and Pmt1 (a protein O-mannosyltransferase). The resulting fusion proteins localize to the periphery of LDs in both yeast and mammalian cells. This peripheral LD localization of the fusion proteins, however, is due to redistribution of the ER around LDs, as revealed by bimolecular fluorescence complementation between ER- and LD-localized partners in cells coexpressing the membrane-anchored perilipin. A LD-tethering function of PLIN3-containing membrane proteins was confirmed by fusing PLIN3 to the cytoplasmic domain of OM14, an outer mitochondrial membrane protein. Expression of OM14-PLIN3 resulted in close apposition of mitochondria and LDs. Taken together, these data indicate that the LD surface constitutes a barrier for ER-localized integral membrane spanning proteins.

cell biology↗

bioRxiv2019

Pseudomonas aeruginosa lectin LecB impairs keratinocyte fitness by abrogating growth factor signalling

Lectins are glycan-binding proteins with no catalytic activity and ubiquitously expressed in nature. Numerous bacteria employ lectins to efficiently bind to epithelia, thus facilitating tissue colonisation. Wounded skin is one of the preferred niches for Pseudomonas aeruginosa, which has developed diverse strategies to impair tissue repair processes and promote infection.\n\nHere, we analyse the effect of the P. aeruginosa fucose-binding lectin LecB on human keratinocytes and demonstrate that it triggers events in the host, upon binding to fucosylated residues on cell membrane receptors, that extend beyond its role as an adhesion molecule. We found that LecB associates with several growth factor receptors and dampens their signalling pathways, leading to the arrest of cell cycle. Additionally, we describe a novel LecB-triggered mechanism to downregulate host cell receptors by showing that LecB leads to insulin-like growth factor receptor 1 internalisation, without receptor activation, and subsequent missorting towards intracellular endosomal compartments.\n\nOverall, these data highlight that LecB is a multitask virulence factor that, through subversion of several host pathways, has a profound impact on keratinocyte proliferation and survival.

cell biology↗

bioRxiv2017

SRGAP2 And The Gradual Evolution Of The Modern Human Language Faculty

In this paper we examine a new source of evidence that draws on data from archaic human genomes to support the hypothesis that vocal learning in Homo preceded the emergence of Anatomically Modern Humans. We build our claim on the evolutionary history of the SLITROBO GTPase 2 gene (SRGAP2). The SLIT-ROBO molecular pathway has been shown to have an important role in the context of vocal learning. Though the relevance of the SRGAP2 gene duplication in the emergence of some aspect of language has not gone completely unnoticed, recent results now allow us to articulate a mechanistic hypothesis of its role in the context of axon guidance. Specifically, SRGAP2C, a duplication of SRGAP2 crucially also found in Neanderthals and Denisovans, but not in extant mammals, inhibits the ancestral SRGAP2A, which in turn modulates the axon guidance function of the SLIT-ROBO molecular pathway. This, we claim, could have contributed to the establishment of the critical cortico-laryngeal connection of the vocal learning circuit. Our conclusions support the idea that complex vocal learning could already have been part of the arsenal of some of our extinct ancestors.

genetics↗