Trafficking Processes Research Articles

Biomolecular condensates mediate bending and scission of endosome membranes.

Multivesicular bodies are key endosomal compartments implicated in cellular quality control through their degradation of membrane-bound cargo proteins1-3. The ATP-consuming ESCRT protein machinery mediates the capture and engulfment of membrane-bound cargo proteins through invagination and scission of multivesicular-body membranes to form intraluminal vesicles4,5. Here we report that the plant ESCRT component FREE16 forms liquid-like condensates that associate with membranes to drive intraluminal vesicle formation. We use a minimal physical model, reconstitution experiments and in silico simulations to identify the dynamics of this process and describe intermediate morphologies of nascent intraluminal vesicles. Furthermore, we find that condensate-wetting-induced line tension forces and membrane asymmetries are sufficient to mediate scission of the membrane neck without the ESCRT protein machinery or ATP consumption. Genetic manipulation of the ESCRT pathway in several eukaryotes provides additional evidence for condensate-mediated membrane scission in vivo. We find that the interplay between condensate and machinery-mediated scission mechanisms is indispensable for osmotic stress tolerance in plants. We propose that condensate-mediated scission represents a previously undescribed scission mechanism that depends on the physicomolecular properties of the condensate and is involved in a range of trafficking processes. More generally, FREE1 condensate-mediated membrane scission in multivesicular-body biogenesis highlights the fundamental role of wetting in intracellular dynamics and organization.

The metal tolerance protein OsMTP11 facilitates cadmium sequestration in the vacuoles of leaf vascular cells for restricting its translocation into rice grains

Rice (Oryza sativa) provides >20% of the consumed calories in the human diet. However, rice is also a leading source of dietary cadmium (Cd) that poses a serious threat to human health. Deciphering the genetic network that underlies the grain-Cd accumulation will benefit the development of low-Cd rice to mitigate the effects of Cd accumulation in the rice grain. In this study, we identified a QTL-gene, OsCS1, that is allelic to OsMTP11 and encodes a protein sequestering Cd in the leaf during vegetative growth and preventing Cd from being translocated to the grain after heading in rice. OsCS1 is predominantly expressed in leaf vascular parenchyma cells, where it binds to a vacuole sorting receptor protein OsVSR2 and is translocated intracellularly from the trans-Golgi network (TGN) to pre-vacuolar compartments (PVCs) and then to the vacuole. In this trafficking process, OsCS1 actively transports Cd into the endomembrane system and eventually sequesters it in vacuoles. There are natural variations in the promoter of OsCS1 between the indica and japonica rice subspecies. Duplication of a G-box-like motif in the promoter region of the superior allele of OsCS1 from indica rice enhances the binding of the transcription factor OsIRO2 to the OsCS1 promoter, thereby promoting OsCS1 expression. Introgression of this allele into commercial rice varieties could significantly lower grain-Cd levels compared to the inferior allele present in japonica rice. Our findings fill a gap in the genetic control of leaf-to-grain Cd translocation and provide a novel gene and its superior allele for the genetic improvement of low-Cd variety in rice.

The conserved protein adaptors CALM/AP180 and FCHo1/2 cooperatively recruit Eps15 to promote the initiation of clathrin-mediated endocytosis in yeast.

Clathrin-mediated endocytosis (CME) is a critical trafficking process that begins when an elaborate endocytic protein network is established at the plasma membrane. Interaction of early endocytic proteins with anionic phospholipids and/or cargo has been suggested to trigger CME initiation. However, the exact mechanism by which CME sites are initiated has not been fully elucidated. In the budding yeast Saccharomyces cerevisiae, higher levels of anionic phospholipids and cargo molecules exist in the newly formed daughter cell compared to the levels in the mother cell during polarized growth. Taking advantage of this asymmetry, we quantitatively compared CME proteins in S. cerevisiae mother versus daughter cells, observing differences in the dynamics and composition of key endocytic proteins. Our results show that CME site initiation occurs preferentially on regions of the plasma membrane with a relatively higher density of endocytic cargo and/or acidic phospholipids. Furthermore, our combined live cell-imaging and yeast genetics analysis provided evidence for a molecular mechanism in which CME sites are initiated when Yap1801 and Yap1802 (yeast CALM/AP180) and Syp1 (yeast FCHo1/2) coordinate with anionic phospholipids and cargo molecules to trigger Ede1 (yeast Eps15)-centric CME initiation complex assembly at the plasma membrane.

The small GTPase RAB-18 is involved in regulating development/diapause by recruiting the intestinal cholesterol transporter NCR-1 onto the apical side in Caenorhabditis elegans

RAB family proteins, which are small GTPases, are integral to the process of eukaryotic membrane trafficking. In the nematode, Caenorhabditis elegans, 31 RAB proteins have been identified through genome sequencing. Using an RNAi screen specifically targeting C. elegans rab genes, we identified multiple genes that are involved in the regulation of larval development, in particular, the rab-18 gene. Our molecular genetic studies resulted in several findings. First, RAB-18 predominantly functions in the intestine to regulate larval development by modulating steroid hormone signaling. Second, the C. elegans cholesterol transporter NCR-1 is a target of RAB-18 in the intestine. Third, the membrane trafficking of NCR-1 to the apical side in intestinal cells is particularly influenced by RAB-18. Finally, RAB-18 and NCR-1 possibly co-localize on membrane vesicles. Our study is the first to demonstrate the relationship between a RAB protein and a cholesterol transporter, in which the RAB protein probably drives the transporter to the apical membrane in the intestine to regulate cholesterol uptake. This study provides insight into the molecular mechanisms underlying human disease stemming from a transport defect of cholesterol and its derivative.

Botulinum toxin intoxication requires retrograde transport and membrane translocation at the ER in RenVM neurons

Botulinum neurotoxin A (BoNT/A) is a highly potent proteolytic toxin specific for neurons with numerous clinical and cosmetic uses. After uptake at the synapse, the protein is proposed to translocate from synaptic vesicles to the cytosol through a self-formed channel. Surprisingly, we found that after intoxication proteolysis of a fluorescent reporter occurs in the neuron soma first and then centrifugally in neurites. To investigate the molecular mechanisms at play, we use a genome-wide siRNA screen in genetically engineered neurons and identify over three hundred genes. An organelle-specific split-mNG complementation indicates BoNT/A traffic from the synapse to the soma-localized Golgi in a retromer-dependent fashion. The toxin then moves to the ER and appears to require the Sec61 complex for retro-translocation to the cytosol. Our study identifies genes and trafficking processes hijacked by the toxin, revealing a new pathway mediating BoNT/A cellular toxicity.

Botulinum toxin intoxication requires retrograde transport and membrane translocation at the ER in RenVM neurons.

Botulinum neurotoxin A (BoNT/A) is a highly potent proteolytic toxin specific for neurons with numerous clinical and cosmetic uses. After uptake at the synapse, the protein is proposed to translocate from synaptic vesicles to the cytosol through a self-formed channel. Surprisingly, we found that after intoxication proteolysis of a fluorescent reporter occurs in the neuron soma first and then centrifugally in neurites. To investigate the molecular mechanisms at play, we use a genome-wide siRNA screen in genetically engineered neurons and identify over three hundred genes. An organelle-specific split-mNG complementation indicates BoNT/A traffic from the synapse to the soma-localized Golgi in a retromer-dependent fashion. The toxin then moves to the ER and appears to require the Sec61 complex for retro-translocation to the cytosol. Our study identifies genes and trafficking processes hijacked by the toxin, revealing a new pathway mediating BoNT/A cellular toxicity.

Autosomal Recessive Spastic Paraplegia Type 51 Caused by Homozygous Mutation of the AP4E1 Gene: A Case Report of a 17-Years-Old Boy

Autosomal recessive spastic paraplegia-51 (SPG51) is a rare neurodevelopmental disorder caused by a homozygous mutation in the AP4E1 gene, located on chromosome 15q21. Spastic paraplegia-51 (SPG51) is an extremely rare autosomal recessive neurodevelopmental disorder characterized by neonatal hypotonia that progresses to hypertonia and spasticity. Mutations in the AP-4E1 gene on chromosome 15q21.2, which is part of the AP-4 complex, can lead to autosomal recessive spastic paraplegia 51 (SPG51). Different mutations in this gene have been identified in affected individuals, leading to disruption of the AP4 complex and vesicular trafficking processes. The specific characteristics of SPG51 are, due to only few cases, not well understood due to limited reports of affected families. Affected individuals also have global developmental delay with impaired intellectual development and poor or absent speech. Studies linked to an additive symptom of persistent stuttering. Affected individuals typically present with hypotonia in the neonatal period, which progresses to muscular hypertonia, especially in the lower limbs. They may also exhibit contractures, talipes equinovarus, decreased muscle mass, short stature, and microcephaly. Severe mental retardation, absent speech, and dysmorphic facial features are common. Some patients may experience seizures. Neurological examination often reveals spastic paraplegia of the lower limbs, and brain imaging may show atrophy of the cerebellar vermis and cortical atrophy. We present an extremely rare case of a 17 years-old boy with autosomal recessive spastic paraplegia type 51.

Organelle-Targeted Laurdans Measure Heterogeneity in Subcellular Membranes and Their Responses to Saturated Lipid Stress.

Organelles feature characteristic lipid compositions that lead to differences in membrane properties. In cells, membrane ordering and fluidity are commonly measured using the solvatochromic dye Laurdan, whose fluorescence is sensitive to lipid packing. As a general lipophilic dye, Laurdan stains all hydrophobic environments in cells; therefore, it is challenging to characterize membrane properties in specific organelles or assess their responses to pharmacological treatments in intact cells. Here, we describe the synthesis and application of Laurdan-derived probes that read out the membrane packing of individual cellular organelles. The set of organelle-targeted Laurdans (OTL) localizes to the ER, mitochondria, lysosomes, and Golgi compartments with high specificity while retaining the spectral resolution needed to detect biological changes in membrane ordering. We show that ratiometric imaging with OTLs can resolve membrane heterogeneity within organelles as well as changes in lipid packing resulting from inhibition of trafficking or bioenergetic processes. We apply these probes to characterize organelle-specific responses to saturated lipid stress. While the ER and lysosomal membrane fluidity is sensitive to exogenous saturated fatty acids, that of mitochondrial membranes is protected. We then use differences in ER membrane fluidity to sort populations of cells based on their fatty acid diet, highlighting the ability of organelle-localized solvatochromic probes to distinguish between cells based on their metabolic state. These results expand the repertoire of targeted membrane probes and demonstrate their application in interrogating lipid dysregulation.

Paracellular Delivery of Protein Drugs with Smart EnteroPatho Nanoparticles.

A general platform for the safe and effective oral delivery of biologics would revolutionize the administration of protein-based drugs, improving access for patients and lowering the financial burden on the health-care industry. Because of their dimensions and physiochemical properties, nanomaterials stand as promising vehicles for navigating the complex and challenging environment in the gastrointestinal (GI) tract. Recent developments have led to materials that protect protein drugs from degradation and enable controlled release in the small intestine, the site of absorption for most proteins. Yet, once present in the small intestine, the protein must transit through the secreted mucus and epithelial cells of the intestinal mucosa into systemic circulation, a process that remains a bottleneck for nanomaterial-based delivery. One attractive pathway through the intestinal mucosa is the paracellular route, which avoids cell trafficking and other degradative processes in the interior of cells. Direct flux between cells is regulated by epithelial tight junctions (TJs) that seal the paracellular space and prevent protein flux. Here, we describe a smart nanoparticle system that directly and transiently disrupts TJs for improved protein delivery, an unrealized goal to-date. We take inspiration from enteropathogenic bacteria that adhere to intestinal epithelia and secrete inhibitors that block TJ interactions in the local environment. To mimic these natural mechanisms, we engineer nanoparticles (EnteroPatho NPs) that attach to the epithelial glycocalyx and release TJ modulators in response to the intestinal pH. We show that EnteroPatho NPs lead to TJ disruption and paracellular protein delivery, giving rise to a general platform for oral delivery.

A type II phosphatidylinositol-4-kinase coordinates sorting of cargo polarizing by endocytic recycling

Depending on their phosphorylation status, derivatives of phosphatidylinositol play important roles in vesicle identity, recognition and intracellular trafficking processes. In eukaryotic cells, phosphatidylinositol-4 phosphate pools generated by specific kinases are key determinants of the conventional secretion pathways. Earlier work in yeast has classified phosphatidylinositol-4 kinases in two types, Stt4p and Pik1p belonging to type III and Lsb6p to type II, with distinct cellular localizations and functions. Eurotiomycetes appear to lack Pik1p homologues. In Aspergillus nidulans, unlike homologues in other fungi, AnLsb6 is associated to late Golgi membranes and when heterologously overexpressed, it compensates for the thermosensitive phenotype in a Saccharomyces cerevisiae pik1 mutant, whereas its depletion leads to disorganization of Golgi-associated PHOSBP-labelled membranes, that tend to aggregate dependent on functional Rab5 GTPases. Evidence provided herein, indicates that the single type II phosphatidylinositol-4 kinase AnLsb6 is the main contributor for decorating secretory vesicles with relevant phosphatidylinositol-phosphate species, which navigate essential cargoes following the route of apical polarization via endocytic recycling.

Interview with Journal of Cell Science Editor Rob Parton

ABSTRACT Rob Parton is a Group Leader and Australian Research Council Laureate Fellow in the Institute for Molecular Bioscience and Deputy Director of the Centre for Microscopy and Microanalysis at the University of Queensland in Brisbane, Australia. He completed his doctorate at the University of Leicester in the UK. After using electron microscopy (EM) during his PhD to study trafficking of tetanus toxin in neurons, he was inspired to continue using advanced microscopy approaches to further our understanding of the fundamental cellular process of membrane trafficking. After several years fostering international collaborations as a postdoctoral fellow and junior Group Leader at the European Molecular Biology Laboratory in Heidelberg, Germany, his lab moved to the University of Queensland in 1996. In 2023, he was elected an Associate Member of the European Molecular Biology Organization (EMBO). Rob joined Journal of Cell Science as an Editor in March 2024 and brings to the journal his expertise in multiscale analysis of membrane function, membrane microdomains, lipid droplets and advanced microscopy techniques in cell biology. We spoke to Rob over Zoom to hear more about his career journey, the evolution of the membrane trafficking field and his advice for running a highly collaborative lab.

Dynamic links between the cardiac intermediate filaments of the cytoskeleton and nucleoskeleton for proper cardiomyocyte differentiation, maturation and reprogramming

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): 1) ESPA 09SYN-21-966 2) ELIDEK 1594 Accumulating evidence suggests that mechanical forces are integral to the commitment and differentiation of cardiac stem cells. Studies have proposed that the cardiac cytoskeleton and specifically the desmin intermediate filament (IF) network and its association with nuclear lamins through the LINC complex, link the contractile apparatus to both the extracellular and nuclear matrix, thus regulating trafficking processes and mechanotransduction during development and adulthood, governing myocyte homeostasis and survival(1-3). Desmin, in addition to being one of the earliest myogenic markers both in heart and somites(4,5), regulates nuclear shape and positioning(6,7), as well as the expression of myogenic (MyoD, Myogenin)(8) and cardiogenic (MEF2, Nkx2.5) transcription regulators, during embryonic stem cell differentiation(4,5). Consistent with the above findings, desmin deficiency has negative impact in the proper regeneration of skeletal muscle cells by hematopoietic stem cells(9). Despite these overwhelming data linking desmin to the establishment and maintenance of myogenesis and cardiogenesis, the precise underlying mechanisms remain elusive. To dissect the exact mechanism of cardiogenic regulation we took advantage of the fibroblast-to-cardiomyocyte direct reprogramming, where fibroblasts trans-differentiate into functional induced cardiomyocytes (iCM) through ectopic expression of three transcription factors, GATA4, Mef2C and Tbx5 (GMT)(10). We hypothesized that desmin could enhance the reprogramming of fibroblasts into cardiomyocytes. Indeed, we have found that expression of desmin together with the GMT factors increases reprogramming by 40-60%. Involvement of a cytoskeletal protein such as desmin in cell differentiation and potentially regeneration, raises intriguing questions and exciting possibilities. To unravel the mechanism of this enhancement we focused on desmin serving as direct mechanotransducer (through the LINC complex) to chromatin. Toward this goal, we investigate the changes of the genetic profile induced by the GMT cocktail during reprogramming in the presence or absence of desmin. RNA sequence analysis has shown that the Notch developmental pathway is regulated by desmin. With the use of Chromosome Conformation Capture, Hi-C and Chip-sequence analysis, we demonstrated the importance of desmin cytoskeleton on the genome 3D organization. In addition, we show that desmin is expressed in most of the cardiac progenitor cells population declaring its role in proper cardiac formation. Moreover, immunofluorescence, calcium influx and electron microscopy studies establish desmin as a major player for cardiac maturity, a critical subject in cardiac regenerative medicine, since its absence substantial reduces expression and proper localization of cardiac specific proteins, delays myofibril formation and impairs function of the induced cardiomyocytes driving most of them to senescence. All the above data will be presented.

Pseudorabies virus hijacks the Rab6 protein to promote viral assembly and egress

Pseudorabies virus (PRV) is recognized as the aetiological agent responsible for Aujeszky’s disease, or pseudorabies, in swine populations. Rab6, a member of the small GTPase family, is implicated in various membrane trafficking processes, particularly exocytosis regulation. Its involvement in PRV infection, however, has not been documented previously. In our study, we observed a significant increase in the Rab6 mRNA and protein levels in both PK-15 porcine kidney epithelial cells and porcine alveolar macrophages, as well as in the lungs and spleens of mice infected with PRV. The overexpression of wild-type Rab6 and its GTP-bound mutant facilitated PRV proliferation, whereas the GDP-bound mutant form of Rab6 had no effect on viral propagation. These findings indicated that the GTPase activity of Rab6 was crucial for the successful spread of PRV. Further investigations revealed that the reduction in Rab6 levels through knockdown significantly hampered PRV proliferation and disrupted virus assembly and egress. At the molecular level, Rab6 was found to interact with the PRV glycoproteins gB and gE, both of which are essential for viral assembly and egress. Our results collectively suggest that PRV exploits Rab6 to expedite its assembly and egress and identify Rab6 as a promising novel target for therapeutic treatment for PRV infection.

Endophilin A2 controls touch and mechanical allodynia via kinesin-mediated Piezo2 trafficking

BackgroundTactile and mechanical pain are crucial to our interaction with the environment, yet the underpinning molecular mechanism is still elusive. Endophilin A2 (EndoA2) is an evolutionarily conserved protein that is documented in the endocytosis pathway. However, the role of EndoA2 in the regulation of mechanical sensitivity and its underlying mechanisms are currently unclear.MethodsMale and female C57BL/6 mice (8–12 weeks) and male cynomolgus monkeys (7–10 years old) were used in our experiments. Nerve injury-, inflammatory-, and chemotherapy-induced pathological pain models were established for this study. Behavioral tests of touch, mechanical pain, heat pain, and cold pain were performed in mice and nonhuman primates. Western blotting, immunostaining, co-immunoprecipitation, proximity ligation and patch-clamp recordings were performed to gain insight into the mechanisms.ResultsThe results showed that EndoA2 was primarily distributed in neurofilament-200-positive (NF200+) medium-to-large diameter dorsal root ganglion (DRG) neurons of mice and humans. Loss of EndoA2 in mouse NF200+ DRG neurons selectively impaired the tactile and mechanical allodynia. Furthermore, EndoA2 interacted with the mechanically sensitive ion channel Piezo2 and promoted the membrane trafficking of Piezo2 in DRG neurons. Moreover, as an adaptor protein, EndoA2 also bound to kinesin family member 5B (KIF5B), which was involved in the EndoA2-mediated membrane trafficking process of Piezo2. Loss of EndoA2 in mouse DRG neurons damaged Piezo2-mediated rapidly adapting mechanically activated currents, and re-expression of EndoA2 rescued the MA currents. In addition, interference with EndoA2 also suppressed touch sensitivity and mechanical hypersensitivity in nonhuman primates.ConclusionsOur data reveal that the KIF5B/EndoA2/Piezo2 complex is essential for Piezo2 trafficking and for sustaining transmission of touch and mechanical hypersensitivity signals. EndoA2 regulates touch and mechanical allodynia via kinesin-mediated Piezo2 trafficking in sensory neurons. Our findings identify a potential new target for the treatment of mechanical pain.

Trafficking dynamics of VEGFR1, VEGFR2, and NRP1 in human endothelial cells.

The vascular endothelial growth factor (VEGF) family of cytokines are key drivers of blood vessel growth and remodeling. These ligands act via multiple VEGF receptors (VEGFR) and co-receptors such as Neuropilin (NRP) expressed on endothelial cells. These membrane-associated receptors are not solely expressed on the cell surface, they move between the surface and intracellular locations, where they can function differently. The location of the receptor alters its ability to 'see' (access and bind to) its ligands, which regulates receptor activation; location also alters receptor exposure to subcellularly localized phosphatases, which regulates its deactivation. Thus, receptors in different subcellular locations initiate different signaling, both in terms of quantity and quality. Similarly, the local levels of co-expression of other receptors alters competition for ligands. Subcellular localization is controlled by intracellular trafficking processes, which thus control VEGFR activity; therefore, to understand VEGFR activity, we must understand receptor trafficking. Here, for the first time, we simultaneously quantify the trafficking of VEGFR1, VEGFR2, and NRP1 on the same cells-specifically human umbilical vein endothelial cells (HUVECs). We build a computational model describing the expression, interaction, and trafficking of these receptors, and use it to simulate cell culture experiments. We use new quantitative experimental data to parameterize the model, which then provides mechanistic insight into the trafficking and localization of this receptor network. We show that VEGFR2 and NRP1 trafficking is not the same on HUVECs as on non-human ECs; and we show that VEGFR1 trafficking is not the same as VEGFR2 trafficking, but rather is faster in both internalization and recycling. As a consequence, the VEGF receptors are not evenly distributed between the cell surface and intracellular locations, with a very low percentage of VEGFR1 being on the cell surface, and high levels of NRP1 on the cell surface. Our findings have implications both for the sensing of extracellular ligands and for the composition of signaling complexes at the cell surface versus inside the cell.

Endolysosomal trafficking controls yolk granule biogenesis in vitellogenic Drosophila oocytes.

Endocytosis and endolysosomal trafficking are essential for almost all aspects of physiological functions of eukaryotic cells. As our understanding on these membrane trafficking events are mostly from studies in yeast and cultured mammalian cells, one challenge is to systematically evaluate the findings from these cell-based studies in multicellular organisms under physiological settings. One potentially valuable in vivo system to address this challenge is the vitellogenic oocyte in Drosophila, which undergoes extensive endocytosis by Yolkless (Yl), a low-density lipoprotein receptor (LDLR), to uptake extracellular lipoproteins into oocytes and package them into a specialized lysosome, the yolk granule, for storage and usage during later development. However, by now there is still a lack of sufficient understanding on the molecular and cellular processes that control yolk granule biogenesis. Here, by creating genome-tagging lines for Yl receptor and analyzing its distribution in vitellogenic oocytes, we observed a close association of different endosomal structures with distinct phosphoinositides and actin cytoskeleton dynamics. We further showed that Rab5 and Rab11, but surprisingly not Rab4 and Rab7, are essential for yolk granules biogenesis. Instead, we uncovered evidence for a potential role of Rab7 in actin regulation and observed a notable overlap of Rab4 and Rab7, two Rab GTPases that have long been proposed to have distinct spatial distribution and functional roles during endolysosomal trafficking. Through a small-scale RNA interference (RNAi) screen on a set of reported Rab5 effectors, we showed that yolk granule biogenesis largely follows the canonical endolysosomal trafficking and maturation processes. Further, the data suggest that the RAVE/V-ATPase complexes function upstream of or in parallel with Rab7, and are involved in earlier stages of endosomal trafficking events. Together, our study provides s novel insights into endolysosomal pathways and establishes vitellogenic oocyte in Drosophila as an excellent in vivo model for dissecting the highly complex membrane trafficking events in metazoan.

Membrane trafficking in neurodevelopmental disorders – new insight and therapeutic implications

Introduction: Membrane trafficking processes are essential for cell viability and basic functions, as well as for interactions between the cell interior and the surrounding environment.
 Purpose: This article focuses on the review of specific subgroup of inherited neurodevelopmental disorders caused by membrane trafficking dysfunction. The possibility of innovative therapeutic approaches based on selective effects on membrane trafficking processes is also discussed.
 State of knowledge: Most previously published reviews are lists of multi-organ diseases related to membrane trafficking dysfunction that are grouped by damaged genes/proteins or by single dominant clinical symptom. No review that focused exclusively on the subgroup of neurodevelopmental diseases related to membrane trafficking defects and their differential diagnosis useful in clinical practice, could be identified.
 Conclusions: Neurodevelopmental diseases related to membrane trafficking defects constitute a significant still growing group of rare/ultra-rare disorders which, due to the spectrum of symptoms, require differentiation from the more common neurogenetic syndromes with different pathomechanisms of the disease, but also related to intellectual disability, autism, epilepsy or neurodegenerative processes. The design of innovative drugs based on selective effects on membrane trafficking processes creates wide opportunities for precise, targeted therapeutic intervention, with a significantly minimized risk of its ineffectiveness or side effects.

Membrane trafficking in neurodevelopmental disorders – new insight and therapeutic implications

Introduction: Membrane trafficking processes are essential for cell viability and basic functions, as well as for interactions between the cell interior and the surrounding environment.
 Purpose: This article focuses on the review of specific subgroup of inherited neurodevelopmental disorders caused by membrane trafficking dysfunction. The possibility of innovative therapeutic approaches based on selective effects on membrane trafficking processes is also discussed.
 State of knowledge: Most previously published reviews are lists of multi-organ diseases related to membrane trafficking dysfunction that are grouped by damaged genes/proteins or by single dominant clinical symptom. No review that focused exclusively on the subgroup of neurodevelopmental diseases related to membrane trafficking defects and their differential diagnosis useful in clinical practice, could be identified.
 Conclusions: Neurodevelopmental diseases related to membrane trafficking defects constitute a significant still growing group of rare/ultra-rare disorders which, due to the spectrum of symptoms, require differentiation from the more common neurogenetic syndromes with different pathomechanisms of the disease, but also related to intellectual disability, autism, epilepsy or neurodegenerative processes. The design of innovative drugs based on selective effects on membrane trafficking processes creates wide opportunities for precise, targeted therapeutic intervention, with a significantly minimized risk of its ineffectiveness or side effects.

Dipping contacts - a novel type of contact site at the interface between membraneless organelles and membranes.

Liquid-liquid phase separation is a major mechanism for organizing macromolecules, particularly proteins with intrinsically disordered regions, in compartments not limited by a membrane or a scaffold. The cell can therefore be perceived as a complex emulsion containing many of these membraneless organelles, also referred to as biomolecular condensates, together with numerous membrane-bound organelles. It is currently unclear how such a complex concoction operates to allow for intracellular trafficking, signaling and metabolic processes to occur with high spatiotemporal precision. Based on experimental observations of synaptic vesicle condensates - a membraneless organelle that is in fact packed with membranes - we present here the framework of dipping contacts: a novel type of contact site between membraneless organelles and membranes. In this Hypothesis, we propose that our framework of dipping contacts can serve as a foundation to investigate the interface that couples the diffusion and material properties of condensates to biochemical processes occurring in membranes. The identity and regulation of this interface is especially critical in the case of neurodegenerative diseases, where aberrant inclusions of misfolded proteins and damaged organelles underlie cellular pathology.

Cellular Trafficking of Nanotechnology-Mediated mRNA Delivery.

Messenger RNA (mRNA)-based therapy has emerged as a powerful, safe, and rapidly scalable therapeutic approach that involves technologies for both mRNA itself and the delivery vehicle. Although there are some unique challenges for different applications of mRNA therapy, a common challenge for all mRNA therapeutics is the transport of mRNA into the target cell cytoplasm for sufficient protein expression. This review is focused on the behaviors at the cellular level of nanotechnology-mediated mRNA delivery systems, which have not been comprehensively reviewed yet. First, the four main therapeutic applications of mRNA are introduced, including immunotherapy, protein replacement therapy, genome editing, and cellular reprogramming. Second, common types of mRNA cargos and mRNA delivery systems are summarized. Third, strategies to enhance mRNA delivery efficiency during the cellular trafficking process are highlighted, including accumulation to the cell, internalization into the cell, endosomal escape, release of mRNA from the nanocarrier, and translation of mRNA into protein. Finally, the challenges and opportunities for the development of nanotechnology-mediated mRNA delivery systems are presented. This review can provide new insights into the future fabrication of mRNA nanocarriers with desirable cellular trafficking performance.