Biology subjects

Kuenen, S.

Publications and source records attributed to Kuenen, S..

7 recordsLinked to original sources

bioRxiv2025

BIN1 expression in the presynaptic compartment leads to isoform-specific synaptotoxicity

Alzheimers disease (AD) is characterized by a strong genetic predisposition and by an early loss of synaptic connectivity that strongly correlates with cognitive deficit. Some genetic determinants could contribute to synapse frailty toward AD pathology. However, the role of genetic determinants in AD pathogenesis remains poorly understood at the synaptic level. Here, we show that the expression of an isoform of the major AD susceptibility gene BIN1 in the presynaptic compartment results in synaptic loss. Using electrophysiology, we observed an early loss of synaptic transmission upon BIN1 isoform 1 (BIN1iso1) expression in Drosophila retinal photoreceptor neurons. This was not observed for the other human BIN1 isoforms tested, isoform 8 and isoform 9. Structural analysis of photoreceptor neuron synapses shows a strong accumulation of abnormally large vesicles in the presynaptic compartment, reminiscent of this same isoform-induced endosome defects in cell bodies. In addition, the expression of BIN1iso1 in motoneurons of the Drosophila neuromuscular junction alters the morphology of synaptic boutons, with a greater number and a smaller size of synaptic boutons, and the appearance of satellite boutons. As opposed to endosomal defects in cell body, modulating the Rab11 recycling endosome regulator did not prevent BIN1iso1 synaptotoxicity. To test if synaptic deficits are conserved in a mammalian model and to assert a presynaptic vs postsynaptic role for BIN1, we used rat primary neurons cultured in microfluidic devices that restrict gene expression modulation in particular neuron populations. We found a loss of synaptic connectivity only when expressing BIN1iso1 in the presynaptic compartment, which was confirmed by microelectrode array analysis. Together, our results suggest that BIN1 expression in the presynaptic terminal, but not the postsynaptic terminal leads to an isoform-specific, deleterious effect on synaptic integrity. BIN1 synaptotoxicity could contribute to the synapse loss observed early in AD. This supports the idea that genetic determinants could make synapses prone to failure in AD.

neuroscience↗

bioRxiv2024

Soma-centered control of synaptic autophagy by Rab39-regulated anterograde trafficking of Atg9

Presynaptic terminals can be located far from the neuronal cell body and are thought to independently regulate protein and organelle turnover. In this work, we report a soma-centered mechanism that regulates autophagy-driven protein turnover at distant presynaptic terminals in Drosophila. We show that this system is regulated by Rab39, whose human homolog is mutated in Parkinsons disease. Although Rab39 is localized in the soma, its loss of function causes increased autophagy at presynaptic terminals, resulting in faster synaptic protein turnover and neurodegeneration. Using a large-scale unbiased genetic modifier screen, we identified genes encoding cytoskeletal and axonal organizing proteins, including Shortstop (Shot), as suppressors of synaptic autophagy. We demonstrate that Rab39 controls Shot-and Unc104/KIF1a-mediated transport of autophagy-related Atg9 vesicles to synapses. Under starvation conditions, Rab39 in the soma shifts its localization from endosomes to lysosomes, thereby controlling the availability of Atg9 vesicles for trafficking to synapses. Our findings indicate that Rab39-mediated trafficking in the soma orchestrates a cross-compartmental mechanism that regulates the abundance of autophagy at synapses.

neuroscience↗

bioRxiv2024

Neuronal autophagosomes are transported to astrocytes for degradation

Autophagy is a vital catabolic process responsible for the degradation of cytosolic components, playing a key role in cellular homeostasis and survival. At synapses, autophagy is crucial for regulating neuronal activity and utilizes a specialized machinery. While considerable progress has been made in understanding the initiation of autophagy and autophagosome formation, the mechanisms governing the clearance of autophagosomes from synaptic sites remain poorly understood. Here, we identify a novel pathway in which astrocytes actively participate in the clearance of pre-synaptic autophagosomes. Using neurons derived from human induced pluripotent stem cell (hiPSC) lines expressing fluorescent autophagy markers and chimeric mouse models, we demonstrate that neuronal autophagosomal vesicles are physically transferred to astrocytes, a process that is enhanced when synaptic activity is suppressed. Autophagosome transfer does not require direct physical cellular contact, but it does require Dynamin and cholesterol-dependent endocytosis for the internalized neuronal autophagosomes to ultimately fuse with astrocytic lysosomes. Our findings reveal a previously unrecognized mechanism of neuronal autophagosome clearance that does not require slow axonal retrograde transport but their transfer to nearby astrocytes.

neuroscience↗

bioRxiv2024

Behavioral screening defines three molecular Parkinsonism subgroups in Drosophila

Parkinsonism is defined by motor dysfunction, but the specific upstream molecular causes of these clinical symptoms can vary widely. We hypothesize that these causes converge onto a limited number of core cellular pathways. To investigate this, we created a new collection of 24 genetically very well-controlled animal models of familial forms of parkinsonism. Using unbiased behavioral screening and machine learning we identified three clusters of mutants that converge on (1) mitochondrial function; (2) retromer/vesicle trafficking; and (3) proteostasis/autophagy. Genes within each cluster have a similar genetic interaction profile and compounds that target specific molecular pathways ameliorate dopaminergic neuron dysfunction in a cluster-specific manner. This suggests that familial parkinsonism can be stratified into three broad functional groups and our findings pave the way for targeted biomarker discovery and drug development.

neuroscience↗

bioRxiv2022

Neuronal identity defines a-synuclein and tau toxicity

Pathogenic -synuclein and tau are critical drivers of neurodegeneration and their mutations cause neuronal loss in patients. Whether the underlying preferential neuronal vulnerability is a cell-type intrinsic property or a consequence of increased expression levels is an open question. Here, we explore cell-type specific -synuclein and tau expression in human brain datasets and use deep phenotyping as well as brain-wide single-cell RNA sequencing of >200 live neuron types in fruit flies to ask which cellular environments react most to -synuclein or tau toxicity. We detect phenotypic and transcriptomic evidence of differential neuronal vulnerability independent of -synuclein or tau expression levels. Comparing vulnerable with resilient neurons enabled us to identify molecular signatures associated with these differential responses. We used these to verify, and then predict resilient and vulnerable neuron subtypes in human brains. This confirms substantia nigra dopaminergic neurons to be sensitive to -synuclein, and we predict pathogenic tau vulnerable and protected cortical neuron subtypes. Our work indicates that cellular determinants confer selective vulnerability to specific types of amyloid toxicity, thus paving the way to leverage neuronal identity to uncover modifiers of neurodegeneration-associated toxic proteins.

neuroscience↗

bioRxiv2022

EndophilinA-dependent coupling between activity-dependent calcium influx and synaptic autophagy is disrupted by a Parkinson-risk mutation

Neuronal activity and neurotransmitter release cause use-dependent decline in protein function. However, it is unclear how this is coupled to local protein turnover and quality control mechanisms. Here we show that the endocytic protein Endophilin-A (EndoA/ENDOA1) couples activity-induced calcium influx to synaptic autophagy and neuronal survival. We identify single mutations in the EndoA flexible region that either increases EndoA diffusion and promotes autophagosome formation in the absence of calcium, or immobilizes EndoA and blocks autophagy, even in the presence of calcium. Hence, the EndoA flexible region is a switch that responds to calcium, regulating EndoA nanoscale synaptic organization and association with autophagosomes driving their formation. Interestingly, a pathogenic variant in the human ENDOA1 variable region that confers risk to Parkinsons disease (PD), also confines ENDOA1 to the synaptic plasma membrane and equally blocks autophagy in flies in vivo and in induced human neurons. Thus, our work reveals a mechanism neurons use to connect neuronal activity to local protein turnover by autophagy, which is critical for neuronal survival.

neuroscience↗

bioRxiv2022

Parkinson mutations in DNAJC6 cause lipid defects and neurodegeneration that are rescued by Synj1

Recent evidence links dysfunctional lipid metabolism to the pathogenesis of Parkinsons disease, but the mechanisms are not resolved. Here, we created a new Drosophila knock-in model of DNAJC6/Auxilin and find that the pathogenic mutation causes synaptic dysfunction, neurological defects and neurodegeneration, as well as specific lipid metabolism alterations. In these mutants membrane lipids containing long-chain polyunsaturated fatty acids, including phosphatidylinositol lipid species that are key for synaptic vesicle recycling and organelle function are reduced. Overexpression of another protein mutated in Parkinsons disease, Synaptojanin-1, known to bind and synthesize specific phosphoinositides, strongly rescues the DNAJC6/Auxilin neuronal defects and neurodegeneration. Our work reveals a functional relation between two proteins mutated in Parkinsons disease and implicates deregulated phosphoinositide metabolism in the maintenance of neuronal integrity and neuronal survival in Parkinsonism.

cell biology↗