Development of an AAV-based model of tauopathy targeting retinal ganglion cells and the mouse visual pathway to study the role of microglia in Tau pathology.

Tauopathy is a typical feature of Alzheimer's disease of major importance because it strongly correlates with the severity of cognitive deficits experienced by patients. During the pathology, it follows a characteristic spatiotemporal course which takes its origin in the transentorhinal cortex, and then gradually invades the entire forebrain. To study the mechanisms of tauopathy, and test new therapeutic strategies, it is necessary to set-up relevant and versatile in vivo models allowing to recapitulate tauopathy. With this in mind, we have developed a model of tauopathy by overexpression of the human wild-type Tau protein in retinal ganglion cells in mice (RGCs). This overexpression led to the presence of hyperphosphorylated forms of the protein in the transduced cells as well as to their progressive degeneration. The application of this model to mice deficient in TREM2 (Triggering Receptor Expressed on Myeloid cells-2, an important genetic risk factor for AD) as well as to 15-month-old mice showed that microglia actively participate in the degeneration of RGCs. Surprisingly, although we were able to detect the transgenic Tau protein up to the terminal arborization of RGCs at the level of the superior colliculi, spreading of the transgenic Tau protein to post-synaptic neurons was detected only in aged animals. This suggests that there may be neuron-intrinsic- or microenvironment mediators facilitating this spreading that appear with aging.

Time-Course of Alterations in the Endocannabinoid System after Viral-Mediated Overexpression of α-Synuclein in the Rat Brain.

Since the discovery of α-synuclein as the major component in Lewy bodies, research into this protein in the context of Parkinson's disease pathology has been exponential. Cannabinoids are being investigated as potential therapies for Parkinson's disease from numerous aspects, but still little is known about the links between the cannabinoid system and the pathogenic α-synuclein protein; understanding these links will be necessary if cannabinoid therapies are to reach the clinic in the future. Therefore, the aim of this study was to investigate the time-course of alterations in components of the endocannabinoid system after viral-mediated α-synuclein overexpression in the rat brain. Rats were given unilateral intranigral injections of AAV-GFP or AAV-α-synuclein and sacrificed 4, 8 and 12 weeks later for qRT-PCR and liquid chromatography-mass spectrometry analyses of the endocannabinoid system, in addition to histological visualization of α-synuclein expression along the nigrostriatal pathway. As anticipated, intranigral delivery of AAV-α-synuclein induced widespread overexpression of human α-synuclein in the nigrostriatal pathway, both at the mRNA level and the protein level. However, despite this profound α-synuclein overexpression, we detected no differences in CB1 or CB2 receptor expression in the nigrostriatal pathway; however, interestingly, there was a reduction in the expression of neuroinflammatory markers. Furthermore, there was a reduction in the levels of the endocannabinoid 2-AG and the related lipid immune mediator OEA at week 12 post-surgery, indicating that α-synuclein overexpression triggers dysregulation of the endocannabinoid system. Although this research does show that the endocannabinoid system is impacted by α-synuclein, further research is necessary to more comprehensively understand the link between the cannabinoid system and the α-synuclein aspect of Parkinson's disease pathology in order for cannabinoid-based therapies to be feasible for the treatment of this disease in the coming years.

The Small Molecule Alpha-Synuclein Aggregator, FN075, Enhances Alpha-Synuclein Pathology in Subclinical AAV Rat Models.

Animal models of Parkinson's disease, in which the human α-synuclein transgene is overexpressed in the nigrostriatal pathway using viral vectors, are widely considered to be the most relevant models of the human condition. However, although highly valid, these models have major limitations related to reliability and variability, with many animals exhibiting pronounced α-synuclein expression failing to demonstrate nigrostriatal neurodegeneration or motor dysfunction. Therefore, the aim of this study was to determine if sequential intra-nigral administration of AAV-α-synuclein followed by the small α-synuclein aggregating molecule, FN075, would enhance or precipitate the associated α-synucleinopathy, nigrostriatal pathology and motor dysfunction in subclinical models. Rats were given unilateral intra-nigral injections of AAV-α-synuclein (either wild-type or A53T mutant) followed four weeks later by a unilateral intra-nigral injection of FN075, after which they underwent behavioral testing for lateralized motor functionality until they were sacrificed for immunohistological assessment at 20 weeks after AAV administration. In line with expectations, both of the AAV vectors induced widespread overexpression of human α-synuclein in the substantia nigra and striatum. Sequential administration of FN075 significantly enhanced the α-synuclein pathology with increased density and accumulation of the pathological form of the protein phosphorylated at serine 129 (pS129-α-synuclein). However, despite this enhanced α-synuclein pathology, FN075 did not precipitate nigrostriatal degeneration or motor dysfunction in these subclinical AAV models. In conclusion, FN075 holds significant promise as an approach to enhancing the α-synuclein pathology in viral overexpression models, but further studies are required to determine if alternative administration regimes for this molecule could improve the reliability and variability in these models.

Neuronal tau species transfer to astrocytes and induce their loss according to tau aggregation state.

Deposits of different abnormal forms of tau in neurons and astrocytes represent key anatomo-pathological features of tauopathies. Although tau protein is highly enriched in neurons and poorly expressed by astrocytes, the origin of astrocytic tau is still elusive. Here, we used innovative gene transfer tools to model tauopathies in adult mouse brains and to investigate the origin of astrocytic tau. We showed in our adeno-associated virus (AAV)-based models and in Thy-Tau22 transgenic mice that astrocytic tau pathology can emerge secondarily to neuronal pathology. By designing an in vivo reporter system, we further demonstrated bidirectional exchanges of tau species between neurons and astrocytes. We then determined the consequences of tau accumulation in astrocytes on their survival in models displaying various status of tau aggregation. Using stereological counting of astrocytes, we report that, as for neurons, soluble tau species are highly toxic to some subpopulations of astrocytes in the hippocampus, whereas the accumulation of tau aggregates does not affect their survival. Thus, astrocytes are not mere bystanders of neuronal pathology. Our results strongly suggest that tau pathology in astrocytes may significantly contribute to clinical symptoms.

The striatal kinase DCLK3 produces neuroprotection against mutant huntingtin.

The neurobiological functions of a number of kinases expressed in the brain are unknown. Here, we report new findings on DCLK3 (doublecortin like kinase 3), which is preferentially expressed in neurons in the striatum and dentate gyrus. Its function has never been investigated. DCLK3 expression is markedly reduced in Huntington's disease. Recent data obtained in studies related to cancer suggest DCLK3 could have an anti-apoptotic effect. Thus, we hypothesized that early loss of DCLK3 in Huntington's disease may render striatal neurons more susceptible to mutant huntingtin (mHtt). We discovered that DCLK3 silencing in the striatum of mice exacerbated the toxicity of an N-terminal fragment of mHtt. Conversely, overexpression of DCLK3 reduced neurodegeneration produced by mHtt. DCLK3 also produced beneficial effects on motor symptoms in a knock-in mouse model of Huntington's disease. Using different mutants of DCLK3, we found that the kinase activity of the protein plays a key role in neuroprotection. To investigate the potential mechanisms underlying DCLK3 effects, we studied the transcriptional changes produced by the kinase domain in human striatal neurons in culture. Results show that DCLK3 regulates in a kinase-dependent manner the expression of many genes involved in transcription regulation and nucleosome/chromatin remodelling. Consistent with this, histological evaluation showed DCLK3 is present in the nucleus of striatal neurons and, protein-protein interaction experiments suggested that the kinase domain interacts with zinc finger proteins, including the transcriptional activator adaptor TADA3, a core component of the Spt-ada-Gcn5 acetyltransferase (SAGA) complex which links histone acetylation to the transcription machinery. Our novel findings suggest that the presence of DCLK3 in striatal neurons may play a key role in transcription regulation and chromatin remodelling in these brain cells, and show that reduced expression of the kinase in Huntington's disease could render the striatum highly vulnerable to neurodegeneration.

Potentiating tangle formation reduces acute toxicity of soluble tau species in the rat.

Tauopathies are neurodegenerative diseases characterized by the aggregation of tau protein. These pathologies exhibit a wide variety of clinical and anatomo-pathological presentations, which may result from different pathological mechanisms. Although tau inclusions are a common feature in all these diseases, recent evidence instead implicates small oligomeric aggregates as drivers of tau-induced toxicity. Hence in vivo model systems displaying either soluble or fibrillary forms of wild-type or mutant tau are needed to better identify their respective pathological pathways. Here we used adeno-associated viruses to mediate gene transfer of human tau to the rat brain to develop models of pure tauopathies. Two different constructs were used, each giving rise to a specific phenotype developing in less than 3 months. First, hTAUWT overexpression led to a strong hyperphosphorylation of the protein, which was associated with neurotoxicity in the absence of any significant aggregation. In sharp contrast, its co-expression with the pro-aggregation peptide TauRD-ΔK280 in the hTAUProAggr group strongly promoted its aggregation into Gallyas-positive neurofibrillary tangles, while preserving neuronal survival. Our results support the hypothesis that soluble tau species are key players of tau-induced neurodegeneration.

Energy defects in Huntington's disease: Why "in vivo" evidence matters.

Huntington's disease (HD) is an inherited progressive neurodegenerative disorder associated with involuntary abnormal movements (chorea), cognitive deficits and psychiatric disturbances. The most striking neuropathological change in HD is the early atrophy of the striatum. While the disease progresses, other brain structures also degenerate, including the cerebral cortex. Changes are also seen outside the brain, in particular weight loss/cachexia despite high dietary intake. The disease is caused by an abnormal expansion of a CAG repeat in the gene encoding the huntingtin protein (Htt). This mutation leads to the expression of a poly-glutamine stretch that changes the biological functions of mutant Htt (mHtt). The mechanisms underlying neurodegeneration in HD are not totally elucidated. Here, we discuss recent results obtained in patients, animal and cellular models suggesting that early disturbance in energy metabolism at least in part associated with mitochondrial defects may play a central role, even though all data are not congruent, possibly because most findings were obtained in cell culture systems or using biochemical analyses of post mortem tissues from rodent models. Thus, we put a particular focus on brain imaging studies that could identify biomarkers of energy defects in vivo and would be of prime interest in preclinical and clinical trials testing the efficacy of new therapies targeting energy metabolism in HD.

Evidence for a "metabolically inactive" inorganic phosphate pool in adenosine triphosphate synthase reaction using localized 31P saturation transfer magnetic resonance spectroscopy in the rat brain at 11.7 T.

With the increased spectral resolution made possible at high fields, a second, smaller inorganic phosphate resonance can be resolved on (31)P magnetic resonance spectra in the rat brain. Saturation transfer was used to estimate de novo adenosine triphosphate synthesis reaction rate. While the main inorganic phosphate pool is used by adenosine triphosphate synthase, the second pool is inactive for this reaction. Accounting for this new pool may not only help us understand (31)P magnetic resonance spectroscopy metabolic profiles better but also better quantify adenosine triphosphate synthesis.

Early alterations of brain cellular energy homeostasis in Huntington disease models.

Brain energy deficit has been a suggested cause of Huntington disease (HD), but ATP depletion has not reliably been shown in preclinical models, possibly because of the immediate post-mortem changes in cellular energy metabolism. To examine a potential role of a low energy state in HD, we measured, for the first time in a neurodegenerative model, brain levels of high energy phosphates using microwave fixation, which instantaneously inactivates brain enzymatic activities and preserves in vivo levels of analytes. We studied HD transgenic R6/2 mice at ages 4, 8, and 12 weeks. We found significantly increased creatine and phosphocreatine, present as early as 4 weeks for phosphocreatine, preceding motor system deficits and decreased ATP levels in striatum, hippocampus, and frontal cortex of R6/2 mice. ATP and phosphocreatine concentrations were inversely correlated with the number of CAG repeats. Conversely, in mice injected with 3-nitroproprionic acid, an acute model of brain energy deficit, both ATP and phosphocreatine were significantly reduced. Increased creatine and phosphocreatine in R6/2 mice was associated with decreased guanidinoacetate N-methyltransferase and creatine kinase, both at the protein and RNA levels, and increased phosphorylated AMP-dependent protein kinase (pAMPK) over AMPK ratio. In addition, in 4-month-old knock-in Hdh(Q111/+) mice, the earliest metabolic alterations consisted of increased phosphocreatine in the frontal cortex and increased the pAMPK/AMPK ratio. Altogether, this study provides the first direct evidence of chronic alteration in homeostasis of high energy phosphates in HD models in the earliest stages of the disease, indicating possible reduced utilization of the brain phosphocreatine pool.

Chronic systemic treatment with a high-dose proteasome inhibitor in mice produces akinesia unrelated to nigrostriatal degeneration.

Supporting the hypothesis that proteasome dysfunction is involved in Parkinson's disease (PD), McNaught et al. (2004) reported that the systemic administration of the proteasome inhibitor Z-Ile-Glu(OtBu)-Ala-Leu-aldehyde (PSI) in rats led to the degeneration of the nigrostriatal pathway. However, several groups could not reproduce this finding. We herein attempted to improve the reliability of the PSI model by chronically delivering the inhibitor using osmotic minipumps in aged mice. We also tested whether PSI co-administered with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) could act synergistically to induce toxicity. We found that PSI produced a significant reduction in locomotor activity that was mildly exacerbated by MPTP. However, PSI alone produced no sign of degeneration of the nigrostriatal dopaminergic pathway and did not exacerbate MPTP toxicity. To conclude, PSI administration does not provide a reliable phenotypic model of PD.

In vivo expression of polyglutamine-expanded huntingtin by mouse striatal astrocytes impairs glutamate transport: a correlation with Huntington's disease subjects.

Huntington's disease (HD) is a neurodegenerative disorder previously thought to be of primary neuronal origin, despite ubiquitous expression of mutant huntingtin (mHtt). We tested the hypothesis that mHtt expressed in astrocytes may contribute to the pathogenesis of HD. To better understand the contribution of astrocytes in HD in vivo, we developed a novel mouse model using lentiviral vectors that results in selective expression of mHtt into striatal astrocytes. Astrocytes expressing mHtt developed a progressive phenotype of reactive astrocytes that was characterized by a marked decreased expression of both glutamate transporters, GLAST and GLT-1, and of glutamate uptake. These effects were associated with neuronal dysfunction, as observed by a reduction in DARPP-32 and NR2B expression. Parallel studies in brain samples from HD subjects revealed early glial fibrillary acidic protein expression in striatal astrocytes from Grade 0 HD cases. Astrogliosis was associated with morphological changes that increased with severity of disease, from Grades 0 through 4 and was more prominent in the putamen. Combined immunofluorescence showed co-localization of mHtt in astrocytes in all striatal HD specimens, inclusive of Grade 0 HD. Consistent with the findings from experimental mice, there was a significant grade-dependent decrease in striatal GLT-1 expression from HD subjects. These findings suggest that the presence of mHtt in astrocytes alters glial glutamate transport capacity early in the disease process and may contribute to HD pathogenesis.

Sustained effects of nonallele-specific Huntingtin silencing.

OBJECTIVE: Huntington's disease (HD) is a fatal autosomal dominant neurodegenerative disorder caused by a polyglutamine expansion in the huntingtin (htt) protein. No cure is available to date to alleviate neurodegeneration. Recent studies have demonstrated that RNA interference represents a promising approach for the treatment of autosomal dominant disorders. But whether an allele-specific silencing of mutant htt or a nonallele-specific silencing should be considered has not been addressed. METHODS: We developed small hairpin RNA targeting mutant or wild-type htt transcripts, or both. RESULTS: We confirmed the therapeutic potential of sihtt administered with lentiviral vectors in rodent models of HD and showed that initiation of small interfering RNA treatment after the onset of HD symptoms is still efficacious and reduces the HD-like pathology. We then addressed the question of the impact of nonallele-specific silencing and demonstrated that silencing of endogenous htt to 25 to 35% in vivo is altering several pathways associated with known htt functions but is not inducing overt toxicity or increasing striatal vulnerability up to 9 months after treatment. INTERPRETATION: These data indicate that the coincident silencing of the wild-type and mutant htt may be considered as a therapeutic tool for HD.

Multimodal neuroimaging provides a highly consistent picture of energy metabolism, validating 31P MRS for measuring brain ATP synthesis.

Neuroimaging methods have considerably developed over the last decades and offer various noninvasive approaches for measuring cerebral metabolic fluxes connected to energy metabolism, including PET and magnetic resonance spectroscopy (MRS). Among these methods, (31)P MRS has the particularity and advantage to directly measure cerebral ATP synthesis without injection of labeled precursor. However, this approach is methodologically challenging, and further validation studies are required to establish (31)P MRS as a robust method to measure brain energy synthesis. In the present study, we performed a multimodal imaging study based on the combination of 3 neuroimaging techniques, which allowed us to obtain an integrated picture of brain energy metabolism and, at the same time, to validate the saturation transfer (31)P MRS method as a quantitative measurement of brain ATP synthesis. A total of 29 imaging sessions were conducted to measure glucose consumption (CMRglc), TCA cycle flux (V(TCA)), and the rate of ATP synthesis (V(ATP)) in primate monkeys by using (18)F-FDG PET scan, indirect (13)C MRS, and saturation transfer (31)P MRS, respectively. These 3 complementary measurements were performed within the exact same area of the brain under identical physiological conditions, leading to: CMRglc = 0.27 +/- 0.07 micromol x g(-1) x min(-1), V(TCA) = 0.63 +/- 0.12 micromol x g(-1) x min(-1), and V(ATP) = 7.8 +/- 2.3 micromol x g(-1) x min(-1). The consistency of these 3 fluxes with literature and, more interestingly, one with each other, demonstrates the robustness of saturation transfer (31)P MRS for directly evaluating ATP synthesis in the living brain.

Normal aging modulates the neurotoxicity of mutant huntingtin.

Aging likely plays a role in neurodegenerative disorders. In Huntington's disease (HD), a disorder caused by an abnormal expansion of a polyglutamine tract in the protein huntingtin (Htt), the role of aging is unclear. For a given tract length, the probability of disease onset increases with age. There are mainly two hypotheses that could explain adult onset in HD: Either mutant Htt progressively produces cumulative defects over time or "normal" aging renders neurons more vulnerable to mutant Htt toxicity. In the present study, we directly explored whether aging affected the toxicity of mutant Htt in vivo. We studied the impact of aging on the effects produced by overexpression of an N-terminal fragment of mutant Htt, of wild-type Htt or of a beta-Galactosidase (beta-Gal) reporter gene in the rat striatum. Stereotaxic injections of lentiviral vectors were performed simultaneously in young (3 week) and old (15 month) rats. Histological evaluation at different time points after infection demonstrated that the expression of mutant Htt led to pathological changes that were more severe in old rats, including an increase in the number of small Htt-containing aggregates in the neuropil, a greater loss of DARPP-32 immunoreactivity and striatal neurons as assessed by unbiased stereological counts.The present results support the hypothesis that "normal" aging is involved in HD pathogenesis, and suggest that age-related cellular defects might constitute potential therapeutic targets for HD.

Cannabinoid CB2 receptor agonists protect the striatum against malonate toxicity: relevance for Huntington's disease.

Cannabinoid agonists might serve as neuroprotective agents in neurodegenerative disorders. Here, we examined this hypothesis in a rat model of Huntington's disease (HD) generated by intrastriatal injection of the mitochondrial complex II inhibitor malonate. Our results showed that only compounds able to activate CB2 receptors were capable of protecting striatal projection neurons from malonate-induced death. That CB2 receptor agonists are neuroprotective was confirmed by using the selective CB2 receptor antagonist, SR144528, and by the observation that mice deficient in CB2 receptor were more sensitive to malonate than wild-type animals. CB2 receptors are scarce in the striatum in healthy conditions, but they are markedly upregulated after the lesion with malonate. Studies of double immunostaining revealed a significant presence of CB2 receptors in cells labeled with the marker of reactive microglia OX-42, and also in cells labeled with GFAP (a marker of astrocytes). We further showed that the activation of CB2 receptors significantly reduced the levels of tumor necrosis factor-alpha (TNF-alpha) that had been increased by the lesion with malonate. In summary, our results demonstrate that stimulation of CB2 receptors protect the striatum against malonate toxicity, likely through a mechanism involving glial cells, in particular reactive microglial cells in which CB2 receptors would be upregulated in response to the lesion. Activation of these receptors would reduce the generation of proinflammatory molecules like TNF-alpha. Altogether, our results support the hypothesis that CB2 receptors could constitute a therapeutic target to slowdown neurodegeneration in HD.

Stem cell factor and mesenchymal and neural stem cell transplantation in a rat model of Huntington's disease.

Neural and mesenchymal stem cells have been proposed as alternative sources of cells for transplantation into the brain in neurodegenerative disorders. However, the endogenous factors controlling their engraftment within the injured parenchyma remain ill-defined. Here, we demonstrate significant engraftment of undifferentiated exogenous mesenchymal or neural stem cells throughout the lesioned area in a rat model for Huntington's disease, as late as 8 weeks post-transplantation. We show that stem cell factor (SCF), strongly up-regulated within host cells in the damaged striatum, is able to activate the SCF receptor c-kit and its signaling pathway and to promote the migration and proliferation of mesenchymal and neural stem cells in vitro. Furthermore, c-kit receptor blockade alters neural stem cell distribution within the lesioned striatum. Host SCF expression is observed in atypical cells expressing glial fibrillary acidic protein and doublecortin in the lesioned striatum and in migrating doublecortin-positive progenitors. Taken together, these data demonstrate that SCF produced in situ in the lesioned striatum is an important factor in promoting the engraftment of stem cells within the lesioned brain.

Haloperidol protects striatal neurons from dysfunction induced by mutated huntingtin in vivo.

Huntington's disease (HD) results from an abnormal polyglutamine extension in the N-terminal region of the huntingtin protein. This mutation causes preferential degeneration of striatal projection neurons. We previously demonstrated, in vitro, that dopaminergic D2 receptor stimulation acted synergistically with mutated huntingtin (expHtt) to increase aggregate formation and striatal death. In the present work, we extend these observations to an in vivo system based on lentiviral-mediated expression of expHtt in the rat striatum. The early and chronic treatment with the D2 antagonist haloperidol decanoate protects striatal neurons from expHtt-induced dysfunction, as analyzed by DARPP-32 and NeuN stainings. Haloperidol treatment also reduces aggregates formation, an effect that is maintained over time. These findings indicate that D2 receptors activation contributes to the deleterious effects of expHtt on striatal function and may represent an interesting early target to alter the subsequent course of neuropathology in HD.

BH3-only proteins Bid and Bim(EL) are differentially involved in neuronal dysfunction in mouse models of Huntington's disease.

Apoptosis, a cell death mechanism regulated by Bcl-2 family members, has been proposed as one of the mechanisms leading to neuronal loss in Huntington's disease (HD). Here we examined the regulation of Bcl-2 family proteins in three different mouse models of HD with exon 1 mutant huntingtin: the R6/1, the R6/1:BDNF+/-, and the Tet/HD94 in which the huntingtin transgene is controlled by the tetracycline-inducible system. Our results disclosed an increase in the levels of the BH3-only proteins Bid and Bim(EL) in the striatum of HD mouse models that was different depending on the stage of the disease. At 16 weeks of age, Bid was similarly enhanced in the striatum of R6/1 and R6/1:BDNF+/- mice, whereas Bim(EL) protein levels were enhanced only in R6/1:BDNF+/- mice. In contrast, at later stages of the disease, both genotypes displayed increased levels of Bid and Bim(EL) proteins. Furthermore, Bax, Bak, Bad, Bcl-2, and Bcl-x(L) proteins were not modified in any of the points analyzed. We next explored the potential reversibility of this phenomenon by analyzing conditional Tet/HD94 mice. Constitutive expression of the transgene resulted in increased levels of Bid and Bim(EL) proteins, and only the Bid protein returned to wild-type levels 5 months after mutant huntingtin shutdown. In conclusion, our results show that enhanced Bid protein levels represent an early mechanism linked to the continuous expression of mutant huntingtin that, together with enhanced Bim(EL), may be a reporter of the progress and severity of neuronal dysfunction.

Neuroprotection by Hsp104 and Hsp27 in lentiviral-based rat models of Huntington's disease.

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by an expansion of glutamine repeats in the huntingtin (htt) protein. Abnormal protein folding and the accumulation of mutated htt are hallmarks of HD neuropathology. Heat-shock proteins (hsps), which refold denatured proteins, might therefore mitigate HD. We show here that hsp104 and hsp27 rescue striatal dysfunction in primary neuronal cultures and HD rat models based on lentiviral-mediated overexpression of a mutated htt fragment. In primary rat striatal cultures, production of hsp104 or hsp27 with htt171-82Q restored neuronal nuclei (NeuN)-positive cell density to that measured after infection with vector expressing the wild-type htt fragment (htt171-19Q). In vivo, both chaperones significantly reduced mutated-htt-related loss of DARPP-32 expression. Furthermore, hsps affected the distribution and size of htt inclusions, with the density of neuritic aggregates being remarkably increased in striatal neurons overexpressing hsps. We also found that htt171-82Q induced the up-regulation of endogenous hsp70 that was co-localized with htt inclusions, and that the overexpression of hsp104 and hsp27 modified the subcellular localization of hsp70 that became cytoplasmic. Finally, hsp104 induced the production of endogenous hsp27. These data demonstrate the protective effects of chaperones in mammalian models of HD.

Cystamine and cysteamine increase brain levels of BDNF in Huntington disease via HSJ1b and transglutaminase.

There is no treatment for the neurodegenerative disorder Huntington disease (HD). Cystamine is a candidate drug; however, the mechanisms by which it operates remain unclear. We show here that cystamine increases levels of the heat shock DnaJ-containing protein 1b (HSJ1b) that are low in HD patients. HSJ1b inhibits polyQ-huntingtin-induced death of striatal neurons and neuronal dysfunction in Caenorhabditis elegans. This neuroprotective effect involves stimulation of the secretory pathway through formation of clathrin-coated vesicles containing brain-derived neurotrophic factor (BDNF). Cystamine increases BDNF secretion from the Golgi region that is blocked by reducing HSJ1b levels or by overexpressing transglutaminase. We demonstrate that cysteamine, the FDA-approved reduced form of cystamine, is neuroprotective in HD mice by increasing BDNF levels in brain. Finally, cysteamine increases serum levels of BDNF in mouse and primate models of HD. Therefore, cysteamine is a potential treatment for HD, and serum BDNF levels can be used as a biomarker for drug efficacy.