Topic: Trafficking

EMBO Workshop: Proteostasis shaping health span: from protein folding to failure

This EMBO Workshop examines how protein synthesis, folding, trafficking, and degradation shape health across the lifespan, connecting fundamental proteostasis mechanisms with ageing and degenerative disease.

EMBO Workshop: Organelle dynamics in health and disease: bridging molecules to organisms

This EMBO Workshop connects organelle contact sites and cytoskeletal interactions with metabolism, signalling, and trafficking, and examines their relevance to neurodegeneration, cancer, and other diseases.

LRRK2 – a master regulator of neurodegeneration: acting on multiple systems including neuroinflammatory signaling, vesicular trafficking, and cell death pathways

mRNA transport, trafficking, localization

In the second of this year’s Brain Prize webinars, Rob Singer (Einstein Medical College, USA), Florence Besse (Institut de Biologie Valrose, France) and Jennifer Lippincott-Schwartz (Janelia Farm Research Campus, USA) will present their work on mRNA transport, trafficking, and localization. Each speaker will present for 25 minutes, and the webinar will conclude with an open discussion. The webinar will be moderated by the winners of the 2023 Brain Prize, Michael Greenberg, Erin Schuman and Christine Holt.

Numbing intraneuronal Tau levels to prevent neurodegeneration in tauopathies

Intraneuronal accumulation of the microtubule associated protein Tau is largely recognized as an important toxic factor linked to neuronal cell death in Alzheimer’s disease and tauopathies. While there has been progress uncovering mechanisms leading to the formation of toxic Tau tangles, less is known about how intraneuronal Tau levels are regulated in health and disease. Here, I will discuss our recent work showing that the intracellular trafficking adaptor protein Numb is critical to control intraneuronal Tau levels. Inactivation of Numb in retinal ganglion cells increases monomeric and oligomeric Tau levels and leads to axonal blebbing in optic nerves, followed by significant neuronal cell loss in old mice. Interestingly, overexpression of the long isoform of Numb (Numb-72) decreases intracellular Tau levels by promoting exocytosis of monomeric Tau. In TauP301S and triple transgenic AD mouse models, expression of Numb-72 in RGCs reduces the number of axonal blebs and prevents neurodegeneration. Finally, inactivation of Numb in TauP301S mice accelerates neurodegeneration in both the retina and spinal cord and leads to precocious paralysis. Taken together, these results uncover Numb as a essential regulator of Tau homeostasis in neurons and as a potential therapeutic agent for AD and tauopathies.

Translational upregulation of STXBP1 by non-coding RNAs as an innovative treatment for STXBP1 encephalopathy

Developmental and epileptic encephalopathies (DEEs) are a broad spectrum of genetic epilepsies associated with impaired neurological development as a direct consequence of a genetic mutation, in addition to the effect of the frequent epileptic activity on brain. Compelling genetic studies indicate that heterozygous de novo mutations represent the most common underlying genetic mechanism, in accordance with the sporadic presentation of DEE. De novo mutations may exert a loss-of-function (LOF) on the protein by decrementing expression level and/or activity, leading to functional haploinsufficiency. These diseases share several features: severe and frequent refractory seizures, diffusely abnormal background activity on EEG, intellectual disability often profound, and severe consequences on global development. One of major causes of early onset DEE are de novo heterozygous mutations in syntaxin-binding-protein-1 gene STXBP1, which encodes a membrane trafficking protein playing critical role in vesicular docking and fusion. LOF STXBP1 mutations lead to a failure of neurotransmitter secretion from synaptic vesicles. Core clinical features of STXBP1 encephalopathy include early-onset epilepsy with hypsarrhythmic EEG, or burst-suppression pattern, or multifocal epileptiform activity. Seizures are often resistant to standard treatments and patients typically show intellectual disability, mostly severe to profound. Additional neurologic features may include autistic traits, movement disorders (dyskinesia, dystonia, tremor), axial hypotonia, and ataxia, indicating a broader neurologic impairment. Patients with severe neuro-cognitive features but without epilepsy have been reported. Recently, a new class of natural and synthetic non-coding RNAs have been identified, enabling upregulation of protein translation in a gene-specific way (SINEUPs), without any increase in mRNA of the target gene. SINEUPs are translational activators composed by a Binding Domain (BD) that overlaps, in antisense orientation, to the sense protein-coding mRNA, and determines target selection; and an Effector Domain (ED), that is essential for protein synthesis up regulation. SINEUPs have been shown to restore the physiological expression of a protein in case of haploinsufficiency, without driving excessive overexpression out of the physiological range. This technology brings many advantages, as it mainly acts on endogenous target mRNAs produced in situ by the wild-type allele; this action is limited to mRNA under physiological regulation, therefore no off-site effects can be expected in cells and tissues that do not express the target transcript; by acting only on a posttranscriptional level, SINEUPs do not trigger hereditable genome editing. After bioinformatic analysis of the promoter region of interest, we designed SINEUPs with 3 different BD for STXBP1. Human neurons from iPSCs were treated and STXBP1 levels showed a 1.5-fold increase compared to the Negative control. RNA levels of STXBP1 after the administration of SINEUPs remained stable as expected. These preliminary results proved the SINEUPs potential to specifically increase the protein levels without impacting on the genome. This is an extremely flexible approach to target many developmental and epileptic encephalopathies caused by haploinsufficiency, and therefore to address these diseases in a more tailored and radical way.

Non-equilibrium molecular assembly in reshaping and cutting cells

A key challenge in modern soft matter is to identify the principles that govern the organisation and functionality in non-equilibrium systems. Current research efforts largely focus on non-equilibrium processes that occur either at the single-molecule scale (e.g. protein and DNA conformations under driving forces), or at the scale of whole tissues, organisms, and active colloidal and microscopic objects. However, the range of the scales in-between — from molecules to large-scaled molecular assemblies that consume energy and perform work — remains under-explored. This is, nevertheless, the scale that is crucial for the function of a living cell, where molecular self-assembly driven far from equilibrium produces mechanical work needed for cell reshaping, transport, motility, division, and healing. Today I will discuss physical modelling of active elastic filaments, called ESCRT-III filaments, that dynamically assemble and disassemble on cell membranes. This dynamic assembly changes the filaments’ shape and mechanical properties and leads to the remodelling and cutting of cells. I will present a range of experimental comparisons of our simulation results: from ESCRT-III-driven trafficking in eukaryotes to division of evolutionary simple archaeal cells.

“Understanding the Function and Dynamics of Organelles through Imaging”

Powerful new ways to image the internal structures and complex dynamics of cells are revolutionizing cell biology and bio-medical research. In this talk, I will focus on how emerging fluorescent technologies are increasing spatio-temporal resolution dramatically, permitting simultaneous multispectral imaging of multiple cellular components. In addition, results will be discussed from whole cell milling using Focused Ion Beam Electron Microscopy (FIB-SEM), which reconstructs the entire cell volume at 4 voxel resolution. Using these tools, it is now possible to begin constructing an “organelle interactome”, describing the interrelationships of different cellular organelles as they carry out critical functions. The same tools are also revealing new properties of organelles and their trafficking pathways, and how disruptions of their normal functions due to genetic mutations may contribute to important diseases.

Keynote talk: Imaging Interacting Organelles to Understand Metabolic Homeostasis

Powerful new ways to image the internal structures and complex dynamics of cells are revolutionizing cell biology and bio-medical research. In this talk, I will focus on how emerging fluorescent technologies are increasing spatio-temporal resolution dramatically, permitting simultaneous multispectral imaging of multiple cellular components. In addition, results will be discussed from whole cell milling using Focused Ion Beam Electron Microscopy (FIB-SEM), which reconstructs the entire cell volume at 4 voxel resolution. Using these tools, it is now possible to begin constructing an “organelle interactome”, describing the interrelationships of different cellular organelles as they carry out critical functions. The same tools are also revealing new properties of organelles and their trafficking pathways, and how disruptions of their normal functions due to genetic mutations may contribute to important diseases.

Neuronal morphology imposes a tradeoff between stability, accuracy and efficiency of synaptic scaling

Synaptic scaling is a homeostatic normalization mechanism that preserves relative synaptic strengths by adjusting them with a common factor. This multiplicative change is believed to be critical, since synaptic strengths are involved in learning and memory retention. Further, this homeostatic process is thought to be crucial for neuronal stability, playing a stabilizing role in otherwise runaway Hebbian plasticity [1-3]. Synaptic scaling requires a mechanism to sense total neuron activity and globally adjust synapses to achieve some activity set-point [4]. This process is relatively slow, which places limits on its ability to stabilize network activity [5]. Here we show that this slow response is inevitable in realistic neuronal morphologies. Furthermore, we reveal that global scaling can in fact be a source of instability unless responsiveness or scaling accuracy are sacrificed." "A neuron with tens of thousands of synapses must regulate its own excitability to compensate for changes in input. The time requirement for global feedback can introduce critical phase lags in a neuron’s response to perturbation. The severity of phase lag increases with neuron size. Further, a more expansive morphology worsens cell responsiveness and scaling accuracy, especially in distal regions of the neuron. Local pools of reserve receptors improve efficiency, potentiation, and scaling, but this comes at a cost. Trafficking large quantities of receptors requires time, exacerbating the phase lag and instability. Local homeostatic feedback mitigates instability, but this too comes at the cost of reducing scaling accuracy." "Realization of the phase lag instability requires a unified model of synaptic scaling, regulation, and transport. We present such a model with global and local feedback in realistic neuron morphologies (Fig. 1). This combined model shows that neurons face a tradeoff between stability, accuracy, and efficiency. Global feedback is required for synaptic scaling but favors either system stability or efficiency. Large receptor pools improve scaling accuracy in large morphologies but worsen both stability and efficiency. Local feedback improves the stability-efficiency tradeoff at the cost of scaling accuracy. This project introduces unexplored constraints on neuron size, morphology, and synaptic scaling that are weakened by an interplay between global and local feedback.