Effect of trehalose on the properties of mutant {gamma}PKC, which causes spinocerebellar ataxia type 14, in neuronal cell lines and cultured Purkinje cells

Identification of a novel aromatic-turmerone analog that activates chaperone-mediated autophagy through the persistent activation of p38

Introduction: Aromatic (Ar)-turmerone is a bioactive component of turmeric oil obtained from Curcuma longa. We recently identified a novel analog (A2) of ar-turmerone that protects dopaminergic neurons from toxic stimuli by activating nuclear factor erythroid 2-related factor 2 (Nrf2). D-cysteine increases Nrf2, leading to the activation of chaperone-mediated autophagy (CMA), a pathway in the autophagy-lysosome protein degradation system, in primary cultured cerebellar Purkinje cells. In this study, we attempted to identify novel analogs of ar-turmerone that activate Nrf2 more potently and investigated whether these analogs activate CMA. Methods: Four novel analogs (A4-A7) from A2 were synthesized. We investigated the effects of A2 and novel 4 analogs on Nrf2 expression via immunoblotting and CMA activity via fluorescence observation. Results: Although all analogs, including A2, increased Nrf2 expression, only A4 activated CMA in SH-SY5Y cells. Additionally, A4-mediated CMA activation was not reversed by Nrf2 inhibition, indicating that A4 activated CMA via mechanisms other than Nrf2 activation. We focused on p38, which participates in CMA activation. Inhibition of p38 significantly prevented A4-mediated activation of CMA. Although all novel analogs significantly increased the phosphorylation of p38 6 h after drug treatment, only A4 significantly increased phosphorylation 24 h after treatment. Finally, we revealed that A4 protected SH-SY5Y cells from the cytotoxicity of rotenone, and that this protection was reversed by inhibiting p38. Conclusion: These findings suggest that the novel ar-turmerone analog, A4, activates CMA and protects SH-SY5Y cells through the persistent activation of p38.

LRRK2 G2019S kinase activity triggers neurotoxic NSF aggregation

Parkinson's disease is characterized by the progressive degeneration of dopaminergic neurons within the substantia nigra pars compacta and the presence of protein aggregates in surviving neurons. The LRRK2 G2019S mutation is one of the major determinants of familial Parkinson's disease cases and leads to late-onset Parkinson's disease with pleomorphic pathology, including α-synuclein accumulation and deposition of protein inclusions. We demonstrated that LRRK2 phosphorylates N-ethylmaleimide sensitive factor (NSF). We observed aggregates containing NSF in basal ganglia specimens from patients with Parkinson's disease carrying the G2019S variant, and in cellular and animal models expressing the LRRK2 G2019S variant. We found that LRRK2 G2019S kinase activity induces the accumulation of NSF in toxic aggregates. Of note, the induction of autophagy cleared NSF aggregation and rescued motor and cognitive impairment observed in aged hG2019S bacterial artificial chromosome (BAC) mice. We suggest that LRRK2 G2019S pathological phosphorylation impacts on NSF biochemical properties, thus causing the formation of cytotoxic protein inclusions.

Trehalose alleviates the phenotype of Machado-Joseph disease mouse models

Background

Machado–Joseph disease (MJD), also known as spinocerebellar ataxia type 3, is the most common of the dominantly inherited ataxias worldwide and is characterized by mutant ataxin-3 aggregation and neuronal degeneration. There is no treatment available to block or delay disease progression. In this work we investigated whether trehalose, a natural occurring disaccharide widely used in food and cosmetic industry, would rescue biochemical, behavioral and neuropathological features of an in vitro and of a severe MJD transgenic mouse model.

Methods

Two MJD animal models, a lentiviral based and a transgenic model, were orally treated with 2% trehalose solution for a period of 4 and 30 weeks, respectively. Motor behavior (rotarod, grip strength and footprint patterns) was evaluated at different time points and neuropathological features were evaluated upon in-life phase termination.

Results

Trehalose-treated MJD mice equilibrated for a longer time in the rotarod apparatus and exhibited an improvement of ataxic gait in footprint analysis. Trehalose-mediated improvements in motor behaviour were associated with a reduction of the MJD-associated neuropathology, as MJD transgenic mice treated with trehalose presented preservation of cerebellar layers thickness and a decrease in the size of ataxin-3 aggregates in Purkinje cells. In agreement, an improvement of neuropathological features was also observed in the full length lentiviral-based mouse model of MJD submitted to 2% trehalose treatment.

Conclusions

The present study suggests trehalose as a safety pharmacological strategy to counteract MJD-associated behavioural and neuropathological impairments.

Testosterone promotes GPX5 expression of goat epididymal epithelial cells cultured in vitro

Androgens are involved in maintaining epididymal structure and function. In the present study, primary culture of goat EECs and effect of testosterone on expression of glutathione peroxidase-5 (GPX5) in goat epididymal epithelial cells (EECs) were investigated. The EECs isolated from 12-mo-old goat caput epididymis were cultured with testosterone in vitro, and expression of glutathione peroxidase-5 (GPX5) and androgen receptors (ARs) was analyzed. Our results showed that testosterone effectively increased EEC proliferation activity, and EECs cultured with testosterone could maintain molecular markers for up to 12 passages. Compared with the control group, 100 nM testosterone significantly increased the mRNA and protein expression of GPX5 (P < 0.05) and ARs (P < 0.01 and P < 0.05, respectively) in EECs, and this effect was blocked by the AR blocker enzalutamide. In conclusion, testosterone can promote the expression of GPX5 in EECs by up-regulating AR expression. We established an effective culture system for goat EECs which can be for further investigation on the regulation of epithelial function.

Pharmacological induction of heat shock proteins ameliorates toxicity of mutant PKCγ in spinocerebellar ataxia type 14

Amyloid and amyloid-like protein aggregations are hallmarks of multiple, varied neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. We previously reported that spinocerebellar ataxia type 14 (SCA14), a dominant-inherited neurodegenerative disease that affects cerebellar Purkinje cells, is characterized by the intracellular formation of neurotoxic amyloid-like aggregates of genetic variants of protein kinase Cγ (PKCγ). A number of protein chaperones, including heat shock protein 70 (Hsp70), promote the degradation and/or refolding of misfolded proteins and thereby prevent their aggregation. Here, we report that, in various SCA14-associated, aggregating PKCγ variants, endogenous Hsp70 is incorporated into aggregates and that expression of these PKCγ mutants up-regulates Hsp70 expression. We observed that PKCγ binds Hsp70 and that this interaction is enhanced in the SCA14-associated variants, mediated by the kinase domain that is involved in amyloid-like fibril formation as well as the C2 domain of PKCγ. Pharmacological up-regulation of Hsp70 by the Hsp90 inhibitors celastrol and herbimycin A attenuated the aggregation of mutant PKCγ in primary cultured Purkinje cells. Up-regulation of Hsp70 diminished net PKCγ aggregation by preventing aggregate formation, resulting in decreased levels of apoptotic cell death among primary cultured Purkinje cells expressing the PKCγ variant. Of note, herbimycin A also ameliorated abnormal dendritic development. Extending our in vitro observations, administration of celastrol to mice up-regulated cerebellar Hsp70. Our findings identify heat shock proteins as important endogenous regulators of pathophysiological PKCγ aggregation and point to Hsp90 inhibition as a potential therapeutic strategy in the treatment of SCA14.

Trehalose reduces retinal degeneration, neuroinflammation and storage burden caused by a lysosomal hydrolase deficiency

The accumulation of undegraded molecular material leads to progressive neurodegeneration in a number of lysosomal storage disorders (LSDs) that are caused by functional deficiencies of lysosomal hydrolases. To determine whether inducing macroautophagy/autophagy via small-molecule therapy would be effective for neuropathic LSDs due to enzyme deficiency, we treated a mouse model of mucopolysaccharidosis IIIB (MPS IIIB), a storage disorder caused by deficiency of the enzyme NAGLU (alpha-N-acetylglucosaminidase [Sanfilippo disease IIIB]), with the autophagy-inducing compound trehalose. Treated naglu^{–/ –} mice lived longer, displayed less hyperactivity and anxiety, retained their vision (and retinal photoreceptors), and showed reduced inflammation in the brain and retina. Treated mice also showed improved clearance of autophagic vacuoles in neuronal and glial cells, accompanied by activation of the TFEB transcriptional network that controls lysosomal biogenesis and autophagic flux. Therefore, small-molecule-induced autophagy enhancement can improve the neurological symptoms associated with a lysosomal enzyme deficiency and could provide a viable therapeutic approach to neuropathic LSDs.

Abbreviations: ANOVA: analysis of variance; Atg7: autophagy related 7; AV: autophagic vacuoles; CD68: cd68 antigen; ERG: electroretinogram; ERT: enzyme replacement therapy; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFAP: glial fibrillary acidic protein; GNAT2: guanine nucleotide binding protein, alpha transducing 2; HSCT: hematopoietic stem cell transplantation; INL: inner nuclear layer; LC3: microtubule-associated protein 1 light chain 3 alpha; MPS: mucopolysaccharidoses; NAGLU: alpha-N-acetylglucosaminidase (Sanfilippo disease IIIB); ONL: outer nuclear layer; PBS: phosphate-buffered saline; PRKCA/PKCα: protein kinase C, alpha; S1BF: somatosensory cortex; SQSTM1: sequestosome 1; TEM: transmission electron microscopy; TFEB: transcription factor EB; VMP/VPL: ventral posterior nuclei of the thalamus

Fluorescent-based evaluation of chaperone-mediated autophagy and microautophagy activities in cultured cells

The autophagy-lysosome protein degradation is further classified into macroautophagy (MA), microautophagy (mA), and chaperone-mediated autophagy (CMA). While MA is involved in various functions and disease pathogenesis, little is known about CMA and mA because of the absence of easy methods to assess their activities. We have recently established a method to assess CMA activity using glyceraldehyde 3-phosphate dehydrogenase (GAPDH), a CMA substrate, and HaloTag (HT) system. Another group has recently identified a mammalian mA pathway, in which substrates are delivered to late endosomes in an heat shock cognate protein (Hsc)70-dependent manner. Because Hsc70 is also involved in CMA, our method would detect both CMA and mA activities. In this study, we attempted to assess CMA and mA activities separately through the siRNA-mediated knockdown of CMA- and mA-related proteins. Knockdown of LAMP2A, a CMA-related protein, and TSG101, an mA-related protein, significantly but only partially decreased the punctate accumulation of GAPDH-HT in AD293 cells and primary cultured rat cortical neurons. Compounds that activate CMA significantly increased GAPDH-HT puncta in TSG101-knockdown cells, but not in LAMP2A-knockdown cells, suggesting that punctate accumulation of GAPDH-HT under LAMP2A- and TSG101-knockdown represents mA and CMA activities, respectively. We succeeded in establishing the method to separately evaluate CMA and mA activities by fluorescence observation.

Potential applications of stress solutes from extremophiles in protein folding diseases and healthcare

Protein misfolding, aggregation and deposition in the brain, in the form of amyloid, are implicated in the etiology of several neurodegenerative disorders, such as Alzheimer's, Parkinson's and prion diseases. Drugs available on the market reduce the symptoms, but they are not a cure. Therefore, it is urgent to identify promising targets and develop effective drugs. Preservation of protein native conformation and/or inhibition of protein aggregation seem pertinent targets for drug development. Several studies have shown that organic solutes, produced by extremophilic microorganisms in response to osmotic and/or heat stress, prevent denaturation and aggregation of model proteins. Among these stress solutes, mannosylglycerate, mannosylglyceramide, di-myo-inositol phosphate, diglycerol phosphate and ectoine are effective in preventing amyloid formation by Alzheimer's Aβ peptide and/or α-synuclein in vitro. Moreover, mannosylglycerate is a potent inhibitor of Aβ and α-synuclein aggregation in living cells, and mannosylglyceramide and ectoine inhibit aggregation and reduce prion peptide-induced toxicity in human cells. This review focuses on the efficacy of stress solutes from hyper/thermophiles and ectoines to prevent amyloid formation in vitro and in vivo and their potential application in drug development against protein misfolding diseases. Current and envisaged applications of these extremolytes in neurodegenerative diseases and healthcare will also be addressed.

FRET sensor-based quantification of intracellular trehalose in mammalian cells

Trehalose acts as a stress protectant and an autophagy inducer in mammalian cells. The molecular mechanisms of action remain obscure because intracellular trehalose at micromolar level is difficult to quantitate. Here, we show a novel trehalose monitoring technology based on FRET. FLIPsuc90μ∆1Venus sensor expressed in mammalian cells enables to quickly and non-destructively detect an infinitesimal amount of intracellular trehalose.

Trehalose attenuates the gait ataxia and gliosis of spinocerebellar ataxia type 17 mice

Spinocerebellar ataxia type 17 (SCA17) is caused by CAG/CAA repeat expansion on the gene encoding a general transcription factor, TATA-box-binding protein (TBP). The CAG repeat expansion leads to the reduced solubility of polyglutamine TBP and induces aggregate formation. The TBP aggregation, mostly present in the cell nuclei, is distinct from that in most other neurodegenerative diseases, in which the aggregation is formed in cytosol or extracellular compartments. Trehalose is a disaccharide issued by the Food and Drug Administration with a Generally Recognized As Safe status. Lines of evidence suggest trehalose could prevent protein aggregate formation in several neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Huntington's disease. In this study, we evaluated the therapeutic potential of trehalose on SCA17 using cerebellar primary and organotypic culture systems and a mouse model. Our results showed that TBP nuclear aggregation was significantly decreased in both the primary and slice cultures. Trehalose (4 %) was further supplied in the drinking water of SCA17 transgenic mice. We found both the gait behavior in the footprint analysis and motor coordination in the rotarod task were significantly improved in the trehalose-treated SCA17 mice. The cerebellar weight was increased and the astrocyte gliosis was reduced in SCA17 mice after trehalose treatment. These data suggest that trehalose could be a potential nontoxic treatment for SCA17.

Paraneoplastic CDR2 and CDR2L antibodies affect Purkinje cell calcium homeostasis

Paraneoplastic cerebellar degeneration (PCD) is characterized by loss of Purkinje cells (PCs) associated with progressive pancerebellar dysfunction in the presence of onconeural Yo antibodies. These antibodies recognize the cerebellar degeneration-related antigens CDR2 and CDR2L. Response to PCD therapy is disappointing due to limited understanding of the neuropathological mechanisms. Here, we report the pathological role of CDR antibodies on the calcium homeostasis in PCs. We developed an antibody-mediated PCD model based on co-incubation of cerebellar organotypic slice culture with human patient serum or rabbit CDR2 and CDR2L antibodies. The CDR antibody-induced pathology was investigated by high-resolution multiphoton imaging and biochemical analysis. Both human and rabbit CDR antibodies were rapidly internalized by PCs and led to reduced immunoreactivity of calbindin D_28K (CB) and L7/Pcp-2 as well as reduced dendritic arborizations in the remaining PCs. Washout of the CDR antibodies partially recovered CB immunoreactivity, suggesting a transient structural change in CB calcium-binding site. We discovered that CDR2 and CB co-immunoprecipitate. Furthermore, the expression levels of voltage-gated calcium channel Cav2.1, protein kinase C gamma and calcium-dependent protease, calpain-2, were increased after CDR antibody internalization. Inhibition of these signaling pathways prevented or attenuated CDR antibody-induced CB and L7/Pcp-2 immunoreactivity loss, morphological changes and increased protein expression. These results signify that CDR antibody internalization causes dysregulation of cell calcium homeostasis. Hence, drugs that modulate these events may represent novel neuroprotective therapies that limit the damaging effects of CDR antibodies and prevent PC neurodegeneration.

Increased protein kinase C gamma activity induces Purkinje cell pathology in a mouse model of spinocerebellar ataxia 14

Spinocerebellar ataxias (SCAs) are hereditary diseases leading to Purkinje cell degeneration and cerebellar dysfunction. Most forms of SCA are caused by expansion of CAG repeats similar to other polyglutamine disorders such as Huntington's disease. In contrast, in the autosomal dominant SCA-14 the disease is caused by mutations in the protein kinase C gamma (PKCγ) gene which is a well characterized signaling molecule in cerebellar Purkinje cells. The study of SCA-14, therefore, offers the unique opportunity to reveal the molecular and pathological mechanism eventually leading to Purkinje cell dysfunction and degeneration. We have created a mouse model of SCA-14 in which PKCγ protein with a mutation found in SCA-14 is specifically expressed in cerebellar Purkinje cells. We find that in mice expressing the mutated PKCγ protein the morphology of Purkinje cells in cerebellar slice cultures is drastically altered and mimics closely the morphology seen after pharmacological PKC activation. Similar morphological abnormalities were seen in localized areas of the cerebellum of juvenile transgenic mice in vivo. In adult transgenic mice there is evidence for some localized loss of Purkinje cells but there is no overall cerebellar atrophy. Transgenic mice show a mild cerebellar ataxia revealed by testing on the rotarod and on the walking beam. Our findings provide evidence for both an increased PKCγ activity in Purkinje cells in vivo and for pathological changes typical for cerebellar disease thus linking the increased and dysregulated activity of PKCγ tightly to the development of cerebellar disease in SCA-14 and possibly also in other forms of SCA.

Trehalose maintains vitality of mouse epididymal epithelial cells and mediates gene transfer

In the present study, trehalose was utilized to improve primary culture of mouse epididymal epithelial cells in vitro, and to enhance naked DNA delivery in epididymis in vivo. During the six-day culture, the proliferation activity of the cells in the medium with addition of trehalose was higher than that of those cells cultured in absence of trehalose (p<0.01). To determine the optimal concentration for cell proliferation, a series of trehalose concentrations (0, 60, 120, 180 mM) were tested, and the result indicated that the cell in the medium with 120 mM trehalose showed the highest proliferation potential. The epididymis epithelial cells were cultured in the medium containing 120 mM trehalose upon 16^th passage, and they continued expressing markers of epididymal epithelial cell, such as rE-RABP, AR and ER-beta. Our study also indicated that trehalose concentrations of 120–240 mM, especially 180 mM, could effectively enhance DNA delivery into the mouse epididymis epithelial cell in vitro. Moreover, trehalose could induce in vivo expression of exogenous DNA in epididymal epithelial cells and help to internalize plasmid into sperm,which did not influence motility of sperm when the mixture of trehalose (180 mM) and DNA was injected into epididymal lumen through efferent tubule. This study suggested that trehalose, as an effective and safer reagent, could be employed potentially to maintain vitality of mouse epididymal epthetial cells during long-term culture in vitro and to mediate in vitro and in vivo gene transfer.

Mutant γPKC that causes spinocerebellar ataxia type 14 upregulates Hsp70, which protects cells from the mutant's cytotoxicity

Several missense mutations in the protein kinase Cγ (γPKC) gene have been found to cause spinocerebellar ataxia type 14 (SCA14), an autosomal dominant neurodegenerative disease. We previously demonstrated that the mutant γPKC found in SCA14 is misfolded, susceptible to aggregation and cytotoxic. Molecular chaperones assist the refolding and degradation of misfolded proteins and prevention of the proteins' aggregation. In the present study, we found that the expression of mutant γPKC-GFP increased the levels of heat-shock protein 70 (Hsp70) in SH-SY5Y cells. To elucidate the role of this elevation, we investigated the effect of siRNA-mediated knockdown of Hsp70 on the aggregation and cytotoxicity of mutant γPKC. Knockdown of Hsp70 exacerbated the aggregation and cytotoxicity of mutant γPKC-GFP by inhibiting this mutant's degradation. These findings suggest that mutant γPKC increases the level of Hsp70, which protects cells from the mutant's cytotoxicity by enhancing its degradation.

Mutant PKCγ in spinocerebellar ataxia type 14 disrupts synapse elimination and long-term depression in Purkinje cells in vivo

Cerebellar Purkinje cells (PCs) express a large amount of the γ isoform of protein kinase C (PKCγ) and a modest level of PKCα. The PKCγ is involved in the pruning of climbing fiber (CF) synapses from developing PCs, and PKCα plays a critical role in long-term depression (LTD) at parallel fiber (PF)-PC synapses. Moreover, the PKC signaling in PCs negatively modulates the nonselective transient receptor potential cation channel type 3 (TRPC3), the opening of which elicits slow EPSCs at PF-PC synapses. Autosomal dominant spinocerebellar ataxia type 14 (SCA14) is caused by mutations in PKCγ. To clarify the pathology of this disorder, mutant (S119P) PKCγ tagged with GFP was lentivirally expressed in developing and mature mouse PCs in vivo, and the effects were assessed 3 weeks after the injection. Mutant PKCγ-GFP aggregated in PCs without signs of degeneration. Electrophysiology results showed impaired pruning of CF synapses from developing PCs, failure of LTD expression, and increases in slow EPSC amplitude. We also found that mutant PKCγ colocalized with wild-type PKCγ, which suggests that mutant PKCγ acts in a dominant-negative manner on wild-type PKCγ. In contrast, PKCα did not colocalize with mutant PKCγ. The membrane residence time of PKCα after depolarization-induced translocation, however, was significantly decreased when it was present with the mutant PKCγ construct. These results suggest that mutant PKCγ in PCs of SCA14 patients could differentially impair the membrane translocation kinetics of wild-type γ and α PKCs, which would disrupt synapse pruning, synaptic plasticity, and synaptic transmission.

Molecular pathophysiology of neurodegenerative disease caused by γPKC mutations

OBJECTIVE

Spinocerebellar ataxia type 14 (SCA14) is an autosomal dominant neurodegenerative disorder, which is caused by missense mutations of PRKCG gene encoding γ type protein kinase C (γPKC). To elucidate the pathophysiology of SCA14, we have analyzed the character of mutant γPKC causing SCA14, expressed in cultured cells.

RESULTS

We found that most of mutant γPKCs were susceptible to cytoplasmic aggregation, suggesting that this aggregate-prone is involved in the etiology of SCA14. When expressed in cultured Purkinje cells, mutant γPKC inhibited the development of dendrites in a manner independent of its aggregate-prone, suggesting that other mechanism is implicated in the pathogenesis of SCA14. FRAP (fluorescence recovery after photobleaching) analysis demonstrated that mobility of mutant γPKC was slower than that of wild type in Purkinje cells. Furthermore, translocation of mutant PKC was attenuated when the cells was treated with high potassium solution. These results suggest that mutant γPKC forms oligomers in Purkinje cells. In addition, enzymological studies revealed that most of mutant γPKC had higher basal activity than wild one. However, the imaging analysis of γPKC demonstrated that mutations slowed the translocation of γPKC, which may explain the low accessibility of mutant γPKC to the plasma membrane.

CONCLUSION

We propose that variety of mutant γPKC characters integrally and complicatedly participate in the pathophysiology of SCA 14.

Hypertonic stress induces rapid and widespread protein damage in C. elegans

Proteostasis is defined as the homeostatic mechanisms that maintain the function of all cytoplasmic proteins. We recently demonstrated that the capacity of the proteostasis network is a critical factor that defines the limits of cellular and organismal survival in hypertonic environments. The current studies were performed to determine the extent of protein damage induced by cellular water loss. Using worm strains expressing fluorescently tagged foreign and endogenous proteins and proteins with temperature-sensitive point mutations, we demonstrate that hypertonic stress causes aggregation and misfolding of diverse proteins in multiple cell types. Protein damage is rapid. Aggregation of a polyglutamine yellow fluorescent protein reporter is observable with <1 h of hypertonic stress, and aggregate volume doubles approximately every 10 min. Aggregate formation is irreversible and occurs after as little as 10 min of exposure to hypertonic conditions. To determine whether endogenous proteins are aggregated by hypertonic stress, we quantified the relative amount of total cellular protein present in detergent-insoluble extracts. Exposure for 4 h to 400 mM or 500 mM NaCl induced a 55-120% increase in endogenous protein aggregation. Inhibition of insulin signaling or acclimation to mild hypertonic stress increased survival under extreme hypertonic conditions and prevented aggregation of endogenous proteins. Our results demonstrate that hypertonic stress causes widespread and dramatic protein damage and that cells have a significant capacity to remodel the network of proteins that function to maintain proteostasis. These findings have important implications for understanding how cells cope with hypertonic stress and other protein-damaging stressors.

Elucidation of the molecular mechanism and exploration of novel therapeutics for spinocerebellar ataxia caused by mutant protein kinase Cγ

Spinocerebellar ataxia (SCA) is an inherited neurodegenerative disorder that is characterized by cerebellar atrophy and progressive ataxia and is classified into 31 types by the genetic locus. Recently, missense mutations of PRKCG genes that code protein kinase Cγ (γPKC) have been identified as a causal gene of SCA14. To explore the molecular mechanism of SCA14 pathogenesis, we investigated how mutant γPKC causes the neurodegeneration of cerebellar Purkinje cells (PCs) by expressing mutant γPKC-GFP in cell lines and primary cultured PCs. Mutant γPKC was susceptible to aggregation in the cytoplasm, which led to an impairment of the ubiquitin-proteasome system and apoptosis. Furthermore, mutant γPKC induced improper dendritic development of cultured PCs in an aggregation-independent manner. Stimulation-induced translocation of mutant γPKC in PC dendrites was prominently attenuated by the reduced mobility of oligomerized mutant γPKC, which resulted in attenuated signal transduction and the improper morphology of PC dendrites. These findings suggested that the oligomerization and aggregation of mutant γPKC caused improper dendritic development and apoptosis of PCs, which led to cerebellar dysfunction and SCA14 pathogenesis. We screened the chemicals that improved these cellular dysfunctions and identified several compounds, including trehalose and Congo red, which could be novel therapeutics for SCA14.