Adekunle T. Bademosi

Summary Paragraph: Many cellular processes rely on accumulating highly diffusive cytoplasmic proteins to a specific location within the cell. This spatial enrichment is generally thought to rely on locally immobilizing proteins or slowing diffusion through binding and molecular crowding. Paradoxically, cytoplasmic proteins that are enriched within nerve terminals remain highly diffusive ¹ , raising questions about the mechanisms that govern presynaptic enrichment. Here, using in vivo single-molecule microscopy, we tracked the diffusion of a model cytoplasmic protein, α-Synuclein (α-Syn), and synaptic vesicles (SVs), in motor neuron presynapses of live Drosophila larvae. We demonstrate that α-Syn undergoes rapid and frequent ‘bouncing’ events at a presynaptic interface, locally impeding escape from the presynapse. We measured escape probabilities at the interface, and show that impeding escape, without dramatically slowing diffusion, is sufficient to govern presynaptic enrichment. The interface is liquid-like and coincides with the boundary of the SV cluster, which is a necessary scaffold for the presynaptic enrichment of α-Syn. Our results provide direct evidence of interfacial reflectivity at the interface of liquid-like compartments, and that this phenomenon can govern the subcellular enrichment of proteins and small organelles at the level of individual particles.

α-Synuclein (α-syn) transfer between neurons is increasingly implicated in the spread of synucleinopathies, yet its functional impact on recipient neurons remains poorly defined. Here, using microfluidic chamber technology, we show that conditioned medium from α-syn ^WT -GFP-expressing donor hippocampal neurons, but not Parkinson’s disease mutant α-syn ^A30P or EGFP controls, selectively reduced the flux of retrogradely transported cholera toxin B-positive carriers in recipient axons. A similar reduction was observed with conditioned medium from neurosecretory PC12 cells co-expressing α-syn ^WT -GFP and the chaperone HSP90 ^WT , but not the HSP90 ^MD7 mutant that disrupts multivesicular body fusion. This effect was prevented by inhibiting dynamin-dependent endocytosis, but not by immunodepletion of soluble α-syn, consistent with uptake of extracellular vesicle (EV)-associated α-syn. Accordingly, isolated EVs from α-syn ^WT -GFP-expressing PC12 cells contained α-syn. Single-molecule imaging further detected EV-transmitted α-syn ^WT in recipient axons, where it exhibited reduced mobility and periodic nanoscale clustering relative to α-syn ^A30P . Together, these findings identify EV-associated α-syn ^WT as a modulator of retrograde axonal trafficking.

Extra-motor symptoms are increasingly recognised in amyotrophic lateral sclerosis (ALS), encompassing cognitive, social, and behavioural deficits that can substantially impact quality of life. TAR DNA binding protein 43 (TDP-43) pathology is the central disease marker of almost all cases of ALS and approximately half of all frontotemporal dementia (FTD). However, the mechanisms linking TDP-43 pathology with extra-motor symptoms in TDP-43-associated neurodegenerative diseases remain unresolved. In this study, we used the rNLS8 mouse model, which expresses human TDP-43 with an ablated nuclear localisation sequence (hTDP-43 ^ΔNLS ) in a doxycycline-regulatable manner causing progressive motor decline reminiscent of ALS, to delineate the molecular changes associated with disease-relevant phenotypes. We found that in addition to previously reported dramatic motor decline, rNLS8 mice also develop extra-motor phenotypes consistent with FTD, including disinhibition-like and anxiety-like behaviours, and social interaction impairments. These changes began in the earliest disease stages and remained readily detectable even when rNLS8 mice became severely motor impaired. Notably, extra-motor deficits persisted in rNLS8 mice that had recovered motor function upon hTDP-43 ^ΔNLS transgene suppression, regardless of whether recovery was initiated at timepoints prior to or after overt neurodegeneration begins. Transcriptomic analysis of rNLS8 mouse cortex tissues revealed early alterations in expression of 321 genes, most notably involving neuroinflammatory-related pathway activation, and all but 2 of these genes returned to control levels upon suppression of hTDP-43 ^ΔNLS expression. Further, 814 genes showed differential exon usage, indicating changes in alternative splicing, in rNLS8 mouse cortex. Of these, differential exon usage of 10 neuronal genes persisted after hTDP-43 ^ΔNLS transgene suppression, including synapse component genes Nrxn1 , Unc13a , and Gls . Similarly, proteomics analysis of the cortex of rNLS8 mice revealed depletion of synaptic proteins, particularly those involved in glutamatergic signalling pathways, which also persisted following hTDP-43 ^ΔNLS transgene suppression. Similar glutamatergic pathway changes were detected in human ALS and FTD post-mortem cortex tissues. Our findings indicate that extra-motor phenotypes emerge early in disease in rNLS8 mice and remain evident despite progressive motor impairments. Further, extra-motor phenotypes persist even upon motor recovery, correlating with specific synaptic gene expression and splicing changes. Overall, this study suggests the potential utility of an expanded suite of behavioural paradigms in preclinical testing using rNLS8 mice, with enhanced relevance to the diversity of TDP-43 proteinopathies including FTD. Our findings further suggest that targeting glutamatergic synaptic components may be an avenue to correct extra-motor deficits associated with TDP-43 pathology.

The classical diagnosis of Parkinsonism is based on motor symptoms that are the consequence of nigrostriatal pathway dysfunction and reduced dopaminergic output. However, a decade prior to the emergence of motor issues, patients frequently experience non-motor symptoms, such as a reduced sense of smell (hyposmia). The cellular and molecular bases for these early defects remain enigmatic. To explore this, we developed a new collection of five fruit fly models of familial Parkinsonism and conducted single-cell RNA sequencing on young brains of these models. Interestingly, cholinergic projection neurons are the most vulnerable cells and genes associated with presynaptic function are the most deregulated. Additional single nucleus sequencing of three specific brain regions of Parkinson’s disease patients confirms these findings. Indeed, the disturbances lead to early synaptic dysfunction, notably affecting cholinergic olfactory projection neurons crucial for olfactory function in flies. Correcting these defects specifically in olfactory cholinergic interneurons in flies or inducing cholinergic signaling in Parkinson mutant human induced dopaminergic neurons in vitro using nicotine, both rescue age-dependent dopaminergic neuron decline. Hence, our research uncovers that one of the earliest indicators of disease in 5 different models of familial Parkinsonism is synaptic dysfunction in higher-order cholinergic projection neurons and this contributes to the development of hyposmia. Furthermore, the shared pathways of synaptic failure in these cholinergic neurons ultimately contribute to dopaminergic dysfunction later in life.

Understanding the mechanisms that drive TDP-43 pathology is integral to combating amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD) and other neurodegenerative diseases. Here we generated a longitudinal quantitative proteomic map of the cortex from the cytoplasmic TDP-43 rNLS8 mouse model of ALS and FTLD, and developed a complementary open-access webtool, TDP-map (https://shiny.rcc.uq.edu.au/TDP-map/). We identified distinct protein subsets enriched for diverse biological pathways with temporal alterations in protein abundance, including increases in protein folding factors prior to disease onset. This included increased levels of DnaJ homolog subfamily B member 5, DNAJB5, which also co-localized with TDP-43 pathology in diseased human motor cortex. DNAJB5 over-expression decreased TDP-43 aggregation in cell and cortical neuron cultures, and knockout of Dnajb5 exacerbated motor impairments caused by AAV-mediated cytoplasmic TDP-43 expression in mice. Together, these findings reveal molecular mechanisms at distinct stages of ALS and FTLD progression and suggest that protein folding factors could be protective in neurodegenerative diseases.

Background: The hallmark of motor neuron disease (MND) pathology is the abnormal accumulation of insoluble proteins that form inclusions in motor neurons within the spinal cord and primary motor cortex. How, why, and when these proteins begin to aggregate has not been fully elucidated. In up to 97% of all MND cases, TAR DNA‐binding protein‐43 (TDP‐43) is a key protein that is mislocalised from its native nuclear presence into cytoplasmic inclusions. Furthermore, genetic mutations in TDP‐43 are implicated in familial MND, further linking the function of this protein to this neurodegenerative disease. The precise mechanism that drives the aggregation of TDP‐43 in MND is unknown, however identifying the changes in the dynamics of the protein within the nucleus could shed light on how the different mutations contribute to its altered function in MND.Method: We applied nanoscale single‐molecule imaging to identify the changes in the dynamics and localisation of TDP‐43 caused by well characterised pathogenic‐causing mutation. This was done by tagging the proteins with the photoconvertible fluorescent protien ‐ mEOS3.2. Single molecule imaging was subsequently carried out in cells and neurons expressing the proteins.Result: We observe that the different pathogenic mutations uniquely influence the mobility of TDP‐43. Most of the MND‐linked mutations inhibit the movement of TDP‐43 similar to how oxidative stressors such as arsenite induce inclusions of TDP‐43 thereby immobilising the molecules. Furthermore, our data indicates that post‐translational modifications in TDP‐43 such as acetylation similarly restricts its dynamics within the nucleus.Conclusion: Together, our data suggests that the confinement of mobility of TDP‐43 is a key step in the formation of toxic aggregates in disease.

Long noncoding RNAs (lncRNAs) represent a multidimensional class of regulatory molecules that are involved in many aspects of brain function. Emerging evidence indicates that lncRNAs are localized to the synapse; however, a direct role for their activity in this subcellular compartment in memory formation has yet to be demonstrated. Using lncRNA capture-seq, we identified a specific set of lncRNAs that accumulate in the synaptic compartment within the infralimbic prefrontal cortex of adult male C57/Bl6 mice. Among these was a splice variant related to the stress-associated lncRNA, Gas5. RNA immunoprecipitation followed by mass spectrometry and single-molecule imaging revealed that this Gas5 isoform, in association with the RNA binding proteins G3BP2 and CAPRIN1, regulates the activity-dependent trafficking and clustering of RNA granules. In addition, we found that cell-type-specific, activity-dependent, and synapse-specific knockdown of the Gas5 variant led to impaired fear extinction memory. These findings identify a new mechanism of fear extinction that involves the dynamic interaction between local lncRNA activity and RNA condensates in the synaptic compartment.

Duplication of PMP22 causes Charcot-Marie-Tooth disease type 1A (CMT1A) and is known to disrupt the lipid metabolism in myelinating Schwann cells by unknown mechanisms. By using two CMT1A mouse models overexpressing human PMP22 , we discovered that PMP22 dose-dependently downregulates genes that are involved in lipid and cholesterol metabolism. Lipidomic analysis on CMT1A mouse sciatic nerves confirmed lipid metabolic abnormalities primarily associated with cholesterol and sphingolipids. We observed similar lipidomic profiles and downregulation of genes associated with lipid metabolism in human CMT1A patient induced pluripotent stem cell-derived Schwann cell precursors (iPSC-SCPs). We confirmed these findings by demonstrating altered lipid raft dynamics and plasma membrane fluidity in CMT1A iPSC-SCPs. Additionally, we identified impaired cholesterol incorporation in the plasma membrane due to altered lipid storage homeostasis in CMT1A iPSC-SCPs, which could be modulated by changing the lipid composition of the cell culture medium. These findings suggest that PMP22 plays a role in regulating the lipid composition of the plasma membrane and lipid storage homeostasis. Targeting lipid metabolism may hold promise as a potential treatment for CMT1A patients. Graphical Highlights: PMP22 copy number causes a dose-dependent suppression of cholesterol and lipid biosynthesis in peripheral nerves of CMT1A mice Lipid composition is altered in the sciatic nerves of CMT1A mice and in the membranes of patient derived iPSC-SCPs, with a significant reduction in sphingolipids CMT1A iPSC-SCPs show decreased plasma membrane lipids required for regulating lipid raft dynamics, membrane fluidity, and membrane order Lipid storage misregulation is key in the pathogenesis of CMT1A

The classical diagnosis of Parkinsonism is based on motor symptoms that are the consequence of nigrostriatal pathway dysfunction and reduced dopaminergic output. However, a decade prior to the emergence of motor issues, patients frequently experience non-motor symptoms, such as a reduced sense of smell (hyposmia). The cellular and molecular bases for these early defects remain enigmatic. To explore this, we developed a new collection of five fruit fly models of familial Parkinsonism and conducted single-cell RNA sequencing on young brains of these models. Interestingly, cholinergic projection neurons are the most vulnerable cells and genes associated with presynaptic function are the most deregulated. Additional single nucleus sequencing of three specific brain regions of Parkinson’s disease patients confirms these findings. Indeed, the disturbances lead to early synaptic dysfunction, notably affecting cholinergic olfactory projection neurons crucial for olfactory function in flies. Correcting these defects specifically in olfactory cholinergic interneurons in flies or inducing cholinergic signaling in Parkinson mutant human induced dopaminergic neurons in vitro using nicotine, both rescue age-dependent dopaminergic neuron decline. Hence, our research uncovers that one of the earliest indicators of disease in 5 different models of familial Parkinsonism is synaptic dysfunction in higher-order cholinergic projection neurons and this contributes to the development of hyposmia. Furthermore, the shared pathways of synaptic failure in these cholinergic neurons ultimately contribute to dopaminergic dysfunction later in life.

Summary: General anesthetics disrupt brain network dynamics through multiple pathways, predominately through post-synaptic potentiation of GABA _A R and pre-synaptic inhibition of neuroexocytosis. Common clinical general anesthetic drugs, such as propofol and isoflurane, have been shown to interact and interfere with a core component of the exocytic release machinery, Syntaxin1A, to cause impaired neurotransmitter release. Recent in vitro studies however suggest that these drugs to not affect all synapse subtypes equally. We investigated the role of Syntaxin1A in multiple neurotransmitter systems under isoflurane general anesthesia in the adult Drosophila brain using live-cell super resolution microscopy and optogenetic readouts of exocytosis. We found that effects of isoflurane anesthesia were neuron specific and only impaired Syntaxin1A activity in excitatory neurons at cholinergic synapses, but not inhibitory GABAergic or glutamatergic neurons. These results indicate that general anesthetics could work by producing successive bouts of inhibition across the brain, by reducing neuroexocytosis from excitatory neurons specifically as well as silencing arousal systems through GABA _A R potentiation.