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Cysteine String Protein Controls Two Routes of Export for Misfolded Huntingtin.

ABSTRACT: Extracellular vesicles (EVs) are secreted vesicles of diverse size and cargo that are implicated in the cell-to-cell transmission of disease-causing-proteins in several neurodegenerative diseases. Mutant huntingtin, the disease-causing entity in Huntington's disease, has an expanded polyglutamine track at the N terminus that causes the protein to misfold and form toxic intracellular aggregates. In Huntington's disease, mutant huntingtin aggregates are transferred between cells by several routes. We have previously identified a cellular pathway that is responsible for the export of mutant huntingtin via extracellular vesicles. Identifying the EV sub-populations that carry misfolded huntingtin cargo is critical to understanding disease progression. In this work we expressed a form of polyglutamine expanded huntingtin (GFP-tagged 72Qhuntingtin^exon1) in cells to assess the EVs involved in cellular export. We demonstrate that the molecular chaperone, cysteine string protein (CSPα; DnaJC5), facilitates export of disease-causing-polyglutamine-expanded huntingtin cargo in 180-240 nm vesicles as well as larger 10-30 μm vesicles.

SUBMITTER: Pink D

PROVIDER: S-EPMC8766765 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Neurons Export Extracellular Vesicles Enriched in Cysteine String Protein and Misfolded Protein Cargo.

Project description:The fidelity of synaptic transmission depends on the integrity of the protein machinery at the synapse. Unfolded synaptic proteins undergo refolding or degradation in order to maintain synaptic proteostasis and preserve synaptic function, and buildup of unfolded/toxic proteins leads to neuronal dysfunction. Many molecular chaperones contribute to proteostasis, but one in particular, cysteine string protein (CSPα), is critical for proteostasis at the synapse. In this study we report that exported vesicles from neurons contain CSPα. Extracellular vesicles (EV's) have been implicated in a wide range of functions. However, the functional significance of neural EV's remains to be established. Here we demonstrate that co-expression of CSPα with the disease-associated proteins, polyglutamine expanded protein 72Q huntingtinex°n1 or superoxide dismutase-1 (SOD-1G93A) leads to the cellular export of both 72Q huntingtinex°n1 and SOD-1G93A via EV's. In contrast, the inactive CSPαHPD-AAA mutant does not facilitate elimination of misfolded proteins. Furthermore, CSPα-mediated export of 72Q huntingtinex°n1 is reduced by the polyphenol, resveratrol. Our results indicate that by assisting local lysosome/proteasome processes, CSPα-mediated removal of toxic proteins via EVs plays a central role in synaptic proteostasis and CSPα thus represents a potential therapeutic target for neurodegenerative diseases.

| S-EPMC5430488 | biostudies-literature

Decoding transcriptomic signatures of Cysteine String Protein alpha-mediated synapse maintenance

Project description:Cysteine string protein α (CSPα), encoded by the Dnajc5 gene, is a synaptic vesicle chaperone that is linked to synapse maintenance and neurodegeneration. To investigate the transcriptional changes associated with synapse maintenance, we performed single nucleus transcriptomics on the cortex of CSPα knockout (KO) mice and littermate controls.

2023-10-13 | GSE245339 | GEO

The cysteine-string domain of the secretory vesicle cysteine-string protein is required for membrane targeting.

Project description:The post-translational addition of palmitic acid residues to cysteine-string protein (Csp) was originally thought to form the basis for membrane association of this secretory-vesicle protein. However, subsequent work showed that chemical depalmitoylation of Csp does not result in its release from membranes. We have confirmed these findings and employed [3H]palmitate labelling of PC12 cells to demonstrate that Csp1 remains associated with membranes following the complete removal of palmitic acid residues. Although palmitoylation is not essential for the stable membrane association of Csp, its role in membrane targeting has not been assessed. To examine this, we constructed a Csp mutant protein with seven cysteines replaced by serines in the cysteine-string domain. In contrast to wild-type Csps, this mutant protein was not targeted to membranes when expressed in PC12 or HeLa cells. We conclude that although a palmitoylated cysteine-string domain is not required for stable membrane association of Csp, it is essential for initial membrane targeting.

| S-EPMC1219770 | biostudies-other

Cysteine string protein (CSP) and its role in preventing neurodegeneration.

Project description:Cysteine string protein (CSP) is a member of the DnaJ/Hsp40 family of co-chaperones that localises to neuronal synaptic vesicles. Its name derives from the possession of a string of 12-15 cysteine residues, palmitoylation of which is required for targeting to post-Golgi membranes. The DnaJ domain of CSP enables it to bind client proteins and recruit Hsc70 chaperones, thereby contributing to the maintenance of protein folding in the presynaptic compartment. Mutation of CSP in flies, worms and mice reduces lifespan and causes synaptic dysfunction and neurodegeneration. Furthermore, recent studies have revealed that the neurodegenerative disease, adult onset neuronal ceroid lipofuscinosis, is caused by mutations in the human CSP?-encoding DNAJC5 gene. Accumulating evidence suggests that the major mechanism by which CSP prevents neurodegeneration is by maintaining the conformation of SNAP-25, thereby facilitating its entry into the membrane-fusing SNARE complex. In this review, we focus on the role of CSP in preventing neurodegeneration and discuss how recent studies of this universal neuroprotective chaperone are being translated into potential novel therapeutics for neurodegenerative diseases.

| S-EPMC4447612 | biostudies-literature

Phosphorylation of Cysteine String Protein Triggers a Major Conformational Switch.

Project description:Cysteine string protein (CSP) is a member of the DnaJ/Hsp40 chaperone family that localizes to neuronal synaptic vesicles. Impaired CSP function leads to neurodegeneration in humans and model organisms as a result of misfolding of client proteins involved in neurotransmission. Mammalian CSP is phosphorylated in vivo on Ser10, and this modulates its protein interactions and effects on neurotransmitter release. However, there are no data on the structural consequences of CSP phosphorylation to explain these functional effects. We show that Ser10 phosphorylation causes an order-to-disorder transition that disrupts CSP's extreme N-terminal ? helix. This triggers the concomitant formation of a hairpin loop stabilized by ionic interactions between phosphoSer10 and the highly conserved J-domain residue, Lys58. These phosphorylation-induced effects result in significant changes to CSP conformation and surface charge distribution. The phospho-switch revealed here provides structural insight into how Ser10 phosphorylation modulates CSP function and also has potential implications for other DnaJ phosphoproteins.

| S-EPMC4975591 | biostudies-literature

Palmitoylation and membrane interactions of the neuroprotective chaperone cysteine-string protein.

Project description:Cysteine-string protein (CSP) is an extensively palmitoylated DnaJ-family chaperone, which exerts an important neuroprotective function. Palmitoylation is required for the intracellular sorting and function of CSP, and thus it is important to understand how this essential modification of CSP is regulated. Recent work identified 23 putative palmitoyl transferases containing a conserved DHHC domain in mammalian cells, and here we show that palmitoylation of CSP is enhanced specifically by co-expression of the Golgi-localized palmitoyl transferases DHHC3, DHHC7, DHHC15, or DHHC17. Indeed, these DHHC proteins promote stable membrane attachment of CSP, which is otherwise cytosolic. An inverse correlation was identified between membrane affinity of unpalmitoylated CSP mutants and subsequent palmitoylation: mutants with an increased membrane affinity localize to the endoplasmic reticulum (ER) and are physically separated from the Golgi-localized DHHC proteins. Palmitoylation of an ER-localized mutant could be rescued by brefeldin A treatment, which promotes the mixing of ER and Golgi membranes. Interestingly though, the palmitoylated mutant remained at the ER following brefeldin A washout and did not traffic to more distal membrane compartments. We propose that CSP has a weak membrane affinity that allows the protein to locate its partner Golgi-localized DHHC proteins directly by membrane "sampling." Mutations that enhance membrane association prevent sampling and lead to accumulation of CSP on cellular membranes such as the ER. The coupling of CSP palmitoylation to Golgi membranes may thus be an important requirement for subsequent sorting.

| S-EPMC2882233 | biostudies-literature

Rheb controls misfolded protein metabolism by inhibiting aggresome formation and autophagy.

Project description:Perinuclear aggresome formation is a key mechanism to dispose of misfolded proteins that exceed the degradative capacity of ubiquitin-proteasome and autophagy-lysosome systems. Functional blockade of either degradative system leads to an enhanced aggresome formation. The tuberous sclerosis complex-Ras homologue enriched in brain-mammalian target of rapamycin (TSC-Rheb-mTOR) pathway is known to play a central role in modulating protein synthesis and autophagy. However, in spite of the constitutive activation of mTOR and the abrogated autophagy activity in TSC1- or TSC2-deficient cells, the TSC mutant cells are defective in aggresome formation and undergo apoptosis upon misfolded protein accumulation both in vitro and in vivo. High Rheb activity in TSC mutant cells inhibits aggresome formation and sensitizes cell death in response to misfolded proteins. Surprisingly, this previously unrecognized function of Rheb is independent of TOR complex 1. Active Rheb disrupts the interaction between dynein and misfolded protein cargos, and therefore blocks aggresome formation by inhibiting dynein-dependent transportation of misfolded proteins. This study reveals a function of Rheb in controlling misfolded protein metabolism by modulating aggresome formation.

| S-EPMC2690031 | biostudies-literature

Correction: Cysteine String Protein Limits Expression of the Large Conductance, Calcium-Activated K+ (BK) Channel.

Project description: Not available

| S-EPMC4591990 | biostudies-literature

Oligomerization of Cysteine String Protein alpha mutants causing adult neuronal ceroid lipofuscinosis.

Project description:Cysteine String Protein alpha (CSP?) is a palmitoylated, synaptic vesicle co-chaperone that is essential for neuroprotection. Two mutations in CSP? - L115R and L116? - cause adult neuronal ceroid lipofuscinosis (ANCL), a dominantly-inherited neurodegenerative disease. To elucidate the pathogenesis of ANCL, the intrinsic biochemical properties of human wildtype (WT) and disease mutant CSP? were examined. Mutant proteins purified from Escherichia coli exhibited high potency to oligomerize in a concentration, temperature, and time dependent manner, with L115R possessing the greatest potency. When freshly purified, ANCL mutant proteins displayed normal co-chaperone activity and substrate recognition similar to WT. However, co-chaperone activity was impaired for both CSP? mutants upon oligomerization. When WT and mutant CSP? were mixed together they co-oligomerized leading to an overall decrease of co-chaperone activity. The oligomerization properties of ANCL mutants were faithfully replicated in HEK 293T cells. Interestingly, the oligomers were covalently tagged by ubiquitination instead of palmitoylation. Taken together, ANCL mutations result in both a gain and partial loss-of-function.

| S-EPMC4188699 | biostudies-other

Aggregation of mutant cysteine string protein-? via Fe-S cluster binding is mitigated by iron chelators.

Project description:Point mutations in cysteine string protein-? (CSP?) cause dominantly inherited adult-onset neuronal ceroid lipofuscinosis (ANCL), a rapidly progressing and lethal neurodegenerative disease with no treatment. ANCL mutations are proposed to trigger CSP? aggregation/oligomerization, but the mechanism of oligomer formation remains unclear. Here we use purified proteins, mouse primary neurons and patient-derived induced neurons to show that the normally palmitoylated cysteine string region of CSP? loses palmitoylation in ANCL mutants. This allows oligomerization of mutant CSP? via ectopic binding of iron-sulfur (Fe-S) clusters. The resulting oligomerization of mutant CSP? causes its mislocalization and consequent loss of its synaptic SNARE-chaperoning function. We then find that pharmacological iron chelation mitigates the oligomerization of mutant CSP?, accompanied by partial rescue of the downstream SNARE defects and the pathological hallmark of lipofuscin accumulation. Thus, the iron chelators deferiprone (L1) and deferoxamine (Dfx), which are already used to treat iron overload in humans, offer a new approach for treating ANCL.

| S-EPMC7021000 | biostudies-literature

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