3-Nitropropionic acid: a mitochondrial toxin to uncover physiopathological mechanisms underlying striatal degeneration in Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder caused by a mutation in the gene encoding Huntingtin. The mechanisms underlying the preferential degeneration of the striatum, the most striking neuropathological change in HD, are unknown. Of those probably involved, mitochondrial defects might play an important role. The behavioural and anatomical similarities found between HD and models using the mitochondrial toxin 3-nitropropionic acid (3NP) in rats and primates support this hypothesis. Here, we discuss the recently identified mechanisms of 3NP-induced striatal degeneration. Two types of important factor have been identified. The first are the 'executioner' components that have direct roles in cell death, such as c-Jun N-terminal kinase and Ca2+-activated protease calpains. The second are 'environmental' factors, such as glutamate, dopamine and adenosine, which modulate the striatal degeneration induced by 3NP. Interestingly, these recent studies support the hypothesis that 3NP and mutated Huntingtin have certain mechanisms of toxicity in common, suggesting that the use of 3NP might give new insights into the pathogenesis of HD. Research on 3NP provides additional proof that the neurochemical environment of a given neurone can determine its preferential vulnerability in neurodegenerative diseases.     

Cellular and molecular mechanisms implicated in pathogenesis of selective neurodegeneration in Huntington’s disease

Huntington??s disease (HD) is one of the most common dominantly-inherited neurodegenerative disorders and is caused by a CAG repeat expansion in the huntingtin gene. HD is characterized by selective degeneration of subpopulations of neurons in the brain, however the precise underlying mechanisms how a ubiquitously expressed disease protein could target specific types of neurons for degeneration remains a critical, yet unanswered question for HD and other major neurodegenerative disorders. In this review, we describe the expanding view of selective neuronal vulnerability in HD, based on recent neuropathological and neuroimaging studies. We will also summarize the systematic effort to define the cell types in which mutant Huntingtin expression is critical for pathogenesis of vulnerable neurons in the striatum and cortex. Finally, we will describe selected, emerging molecular mechanisms that are implicated in selective disease processes in HD. Together, the field has begun to appreciate the distinct molecular pathogenic roles of mutant huntingtin in different cell types that may contribute to the selective neuronal vulnerability, with dissection of such mechanisms likely to yield novel molecular targets for HD therapy.     

The effect of Ginkgo biloba extract on 3-nitropropionic acid-induced neurotoxicity in rats

3-Nitropropionic acid (3-NP), an irreversible inhibitor of succinate dehydrogenase enzyme (SDH), induces neurodegeneration similar to that observed in Huntington’s disease (HD). Reduction of prepulse inhibition (PPI) of acoustic startle response, locomotor hypoactivity, bilateral striatal lesions as well as brain oxidative stress are major features of HD. The present study was designed to investigate neuroprotective effect of Ginkgo biloba extract (EGb 761) on 3-NP induced neurobehavioral changes and striatal lesions.Rats administered 3-NP (20 mg/kg, s.c.) for five consecutive days exhibited PPI deficits and locomotor hypoactivity whereas, pretreatment of animals with EGb 761 (100 mg/kg, i.p. for 15 days) ahead of and during the induction of HD by 3-NP (20 mg/kg for 5 days starting at day 8) ameliorated 3-NP-induced neurobehavioral deficits. Administration of 3-NP increased the level of striatal malondialdehyde (MDA). This effect was prevented in animals pre-treated with EGb 761. Changes in the level of apoptotic regulatory gene expressions, following 3-NP treatment, were demonstrated as both an up-regulation and a down-regulation of the expression levels of striatal Bax and Bcl-xl genes, respectively. In addition, an up-regulation of the expression level of striatal glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was also observed. Pre-treatment with EGb 761 caused a down-regulation in striatal GAPDH and Bax together with an up-regulation of striatal Bcl-xl expression level as compared to the 3-NP treated group. Histochemical examination of striatal tissue showed that EGb 761 significantly prevented 3-NP induced inhibition of SDH activity. Histopathological examination further affirmed the neuroprotective effect of EGb 761 against 3-NP toxicity.Taken together, these results suggest that EGb 761 has a neuroprotective role in the current HD paradigm, which may be related to improvement of energy metabolism, antioxidant properties and antiapoptotic effects.     

N-terminal Huntingtin Knock-In Mice: Implications of Removing the N-terminal Region of Huntingtin for Therapy

The Huntington’s disease (HD) protein, huntingtin (HTT), is a large protein consisting of 3144 amino acids and has conserved N-terminal sequences that are followed by a polyglutamine (polyQ) repeat. Loss of Htt is known to cause embryonic lethality in mice, whereas polyQ expansion leads to adult neuronal degeneration. Whether N-terminal HTT is essential for neuronal development or contributes only to late-onset neurodegeneration remains unknown. We established HTT knock-in mice (N160Q-KI) expressing the first 208 amino acids of HTT with 160Q, and they show age-dependent HTT aggregates in the brain and neurological phenotypes. Importantly, the N-terminal mutant HTT also preferentially accumulates in the striatum, the brain region most affected in HD, indicating the importance of N-terminal HTT in selective neuropathology. That said, homozygous N160Q-KI mice are also embryonic lethal, suggesting that N-terminal HTT alone is unable to support embryonic development. Using Htt knockout neurons, we found that loss of Htt selectively affects the survival of developing neuronal cells, but not astrocytes, in culture. This neuronal degeneration could be rescued by a truncated HTT lacking the first 237 amino acids, but not by N-terminal HTT (1–208 amino acids). Also, the rescue effect depends on the region in HTT known to be involved in intracellular trafficking. Thus, the N-terminal HTT region may not be essential for the survival of developing neurons, but when carrying a large polyQ repeat, can cause selective neuropathology. These findings imply a possible therapeutic benefit of removing the N-terminal region of HTT containing the polyQ repeat to treat the neurodegeneration in HD.     

Reduction in Subventricular Zone-Derived Olfactory Bulb Neurogenesis in a Rat Model of Huntington’s Disease Is Accompanied by Striatal Invasion of Neuroblasts

Huntington’s disease (HD) is an inherited progressive neurodegenerative disorder caused by an expanded CAG repeat in exon 1 of the huntingtin gene (HTT). The primary neuropathology of HD has been attributed to the preferential degeneration of medium spiny neurons (MSN) in the striatum. Reports on striatal neurogenesis have been a subject of debate; nevertheless, it should be considered as an endogenous attempt to repair the brain. The subventricular zone (SVZ) might offer a close-by region to supply the degenerated striatum with new cells. Previously, we have demonstrated that R6/2 mice, a widely used preclinical model representing an early onset HD, showed reduced olfactory bulb (OB) neurogenesis but induced striatal migration of neuroblasts without affecting the proliferation of neural progenitor cell (NPCs) in the SVZ. The present study revisits these findings, using a clinically more relevant transgenic rat model of late onset HD (tgHD rats) carrying the human HTT gene with 51 CAG repeats and mimicking many of the neuropathological features of HD seen in patients. We demonstrate that cell proliferation is reduced in the SVZ and OB of tgHD rats compared to WT rats. In the OB of tgHD rats, although cell survival was reduced, the frequency of neuronal differentiation was not altered in the granule cell layer (GCL) compared to the WT rats. However, an increased frequency of dopamenergic neuronal differentiation was noticed in the glomerular layer (GLOM) of tgHD rats. Besides this, we observed a selective proliferation of neuroblasts in the adjacent striatum of tgHD rats. There was no evidence for neuronal maturation and survival of these striatal neuroblasts. Therefore, the functional role of these invading neuroblasts still needs to be determined, but they might offer an endogenous alternative for stem or neuronal cell transplantation strategies.     

Upregulation of guanylyl cyclase expression and activity in striatum of MPTP-induced parkinsonism in mice

The aim of our study was to investigate the expression and the activity of soluble guanylyl cyclase (GC) and phosphodiesterase (PDE) activities that regulate cGMP level in the striatum, hippocampus, and brain cortex in an animal model of PD, induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We observed the increase of total activity and protein level of GC in striatum after MPTP injection. It was accompanied by an enhancement of both mRNA expression and protein level of GCbeta1 subunit. MPTP induces mRNA expression and elevates protein concentration of GCbeta1 in striatum up to 14 days after its injection, which in turn causes a marked enhancement of cGMP formation. Furthermore, the activation of GC occurs through change of maximal enzyme activity (V(max)). Simultaneously, no change in PDE activity has been detected in all investigated regions of the brain after MPTP. MPTP injection caused the elevation of GCbeta1 protein level in both the membrane and cytosol fractions being significantly higher in cytosol. Western blot analysis demonstrated about 45-67% decrease of tyrosine hydroxylase protein content in striatum. These data suggest that NO/cGMP signaling pathway may at least partially contribute to dopaminergic fiber degeneration in the striatum, the damage attributed to PD.     

小鼠脑内NO/NOS-cGMP信号系统与吗啡依赖形成的机制

本文观察了吗啡依赖小鼠脑组织ｃＧＭＰ含量,钙依赖性及非钙依赖性ＮＯＳ活性的变化,蛋白激酶Ａ对ＮＯＳ活性的磷酸化调节以及一氧化氮合酶（ＮＯＳ）抑制剂对吗啡依赖形成的影响。结果发现：（１）小脑,纹状体,海马及大脑皮质ｃＧＭＰ含量明显下降;（２）纹状体及大脑皮质钙依赖性ＮＯＳ活性明显升高,而ＩＰ２０（ＰＫＡ抑制剂）可抑制比变化,小脑及海马依赖性ＮＯＳ活性及以上各脑区非钙依赖性ＮＯＳ活性无明显变化;（３）     

Effect of acute and chronic cholinesterase inhibition with diisopropylfluorophosphate on muscarinic, dopamine, and GABA receptors of the rat striatum

The effects of acute and chronic administration of diisopropylfluorophosphate (DFP) to rats on acetylcholinesterase (AChE) activity (in striatum, medulla, diencephalon, cortex, and medulla) and muscarinic, dopamine (DA), and gamma-aminobutyric acid (GABA) receptor characteristics (in striatum) were investigated. After a single injection of (acute exposure to) DFP, striatal region was found to have the highest degree of AChE inhibition. After daily DFP injections (chronic treatment), all brain regions had the same degree of AChE inhibition, which remained at a steady level despite the regression of the DFP-induced cholinergic overactivity. Acute administration of DFP increased the number of DA and GABA receptors without affecting the muscarinic receptor characteristics. Whereas chronic administration of DFP for either 4 or 14 days reduced the number of muscarinic sites without affecting their affinity, the DFP treatment caused increase in the number of DA and GABA receptors only after 14 days of treatment; however, the increase was considerably lower than that observed after the acute treatment. The in vitro addition of DFP to striatal membranes did not affect DA, GABA, or muscarinic receptors. The results indicate an involvement of GABAergic and dopaminergic systems in the actions of DFP. It is suggested that the GABAergic and dopaminergic involvement may be a part of a compensatory inhibitory process to counteract the excessive cholinergic activity produced by DFP.     

Huntington's disease and its animal model: alterations in kainic acid binding.

The density of ³H-kainic acid (KA) binding was determined in several regions of Huntington's Diseased (HD) and control human brains. ³H-Kainic acid binding was significantly reduced by 55% in the caudate nucleus and by 53% in the putamen of HD brains. In addition, ³H-KA binding was determined in rat striatum at various intervals following lesion with KA, a procedure which produces an animal model of HD. After KA lesion, ³H-KA binding in the rat striatum underwent a slow reduction, reaching 25% of control after 6 weeks. Several properties of ³H-KA binding to rat brain membranes were also investigated, including inhibition by ions, regional distribution and displacement by various compounds. The findings confirm the validity of the KA-lesioned model for HD and suggest a post-synaptic location for kainic acid receptors in the striatum.     

AAV-Dominant Negative Tumor Necrosis Factor (DN-TNF) Gene Transfer to the Striatum Does Not Rescue Medium Spiny Neurons in the YAC128 Mouse Model of Huntington's Disease

CNS inflammation is a hallmark of neurodegenerative disease, and recent studies suggest that the inflammatory response may contribute to neuronal demise. In particular, increased tumor necrosis factor (TNF) signaling is implicated in the pathology of both Parkinson''s disease (PD) and Alzheimer''s disease (AD). We have previously shown that localized gene delivery of dominant negative TNF to the degenerating brain region can limit pathology in animal models of PD and AD. TNF is upregulated in Huntington''s disease (HD), like in PD and AD, but it is unknown whether TNF signaling contributes to neuronal degeneration in HD. We used in vivo gene delivery to test whether selective reduction of soluble TNF signaling could attenuate medium spiny neuron (MSN) degeneration in the YAC128 transgenic (TG) mouse model of Huntington''s disease (HD). AAV vectors encoding cDNA for dominant-negative tumor necrosis factor (DN-TNF) or GFP (control) were injected into the striatum of young adult wild type WT and YAC128 TG mice and achieved 30–50% target coverage. Expression of dominant negative TNF protein was confirmed immunohistologically and biochemically and was maintained as mice aged to one year, but declined significantly over time. However, the extent of striatal DN-TNF gene transfer achieved in our studies was not sufficient to achieve robust effects on neuroinflammation, rescue degenerating MSNs or improve motor function in treated mice. Our findings suggest that alternative drug delivery strategies should be explored to determine whether greater target coverage by DN-TNF protein might afford some level of neuroprotection against HD-like pathology and/or that soluble TNF signaling may not be the primary driver of striatal neuroinflammation and MSN loss in YAC128 TG mice.     

Brain-derived neurotrophic factor over-expression in the forebrain ameliorates Huntington's disease phenotypes in mice

Huntington's disease (HD), a dominantly inherited neurodegenerative disorder characterized by relatively selective degeneration of striatal neurons, is caused by an expanded polyglutamine tract of the huntingtin (htt) protein. The htt mutation reduces levels of brain-derived neurotrophic factor (BDNF) in the striatum, likely by inhibiting cortical BDNF gene expression and anterograde transport of BDNF from cortex to striatum. However, roles of the BDNF reduction in HD pathogenesis have not been established conclusively. We reasoned that increasing striatal BDNF through over-expression would slow progression of the disease if BDNF reduction plays a pivotal role in HD pathogenesis. We employed a Bdnf transgene driven by the promoter for the alpha subunit of Ca²⁺/calmodulin-dependent kinase II to over-express BDNF in the forebrain of R6/1 mice which express a fragment of mutant htt with a 116-glutamine tract. The Bdnf transgene increased BDNF levels and TrkB signaling activity in the striatum, ameliorated motor dysfunction, and reversed brain weight loss in R6/1 mice. Furthermore, it normalized DARPP-32 expression of the 32 kDa dopamine and cAMP-regulated phosphoprotein, increased the number of enkephalin-containing boutons, and reduced formation of neuronal intranuclear inclusions in the striatum of R6/1 mice. These results demonstrate crucial roles of reduced striatal BDNF in HD pathogenesis and suggest potential therapeutic values of BDNF to HD.     

Metabonomic Characterization of the 3-Nitropropionic Acid Rat Model of Huntington’s Disease

3-Nitropropionic acid (3-NP)-induced neurotoxicity can be used as a model for the genetic neurodegenerative disorder Huntington’s disease (HD). A metabolic profiling strategy was adopted to explore the biochemical consequences of 3-NP administered to rats in specific brain regions. ¹H NMR spectroscopy was used to characterize the metabolite composition of several brain regions following 3-NP-intoxication. Dose-dependent increases in succinate levels were observed in all neuroanatomical regions, resulting from the 3-NP-induced inhibition of succinate dehydrogenase. Global decreases in taurine and GABA were observed in the majority of brain regions, whereas altered lipid profiles were observed only in the globus pallidus and dorsal striatum. Depleted phosphatidylcholine and elevated glycerol levels, which are indicative of apoptosis, were also observed in the frontal cortex of the 3-NP model. Many of the metabolic anomalies are consistent with those reported in HD. The 3-NP-induced model of HD provides a means of monitoring potential mechanisms of pathology and therapeutic response for drug interventions, which can be efficiently assessed using metabolic profiling strategies.     

Increased sensitivity to N-methyl-D-aspartate receptor-mediated excitotoxicity in a mouse model of Huntington's disease

Previous work suggests N-methyl-D-aspartate receptor (NMDAR) activation may be involved in degeneration of medium-sized spiny striatal neurons in Huntington's disease (HD). Here we show that these neurons are more vulnerable to NMDAR-mediated death in a YAC transgenic FVB/N mouse model of HD expressing full-length mutant huntingtin, compared with wild-type FVB/N mice. Excitotoxic death of these neurons was increased after intrastriatal injection of quinolinate in vivo, and after NMDA but not AMPA exposure in culture. NMDA-induced cell death was abolished by an NR2B subtype-specific antagonist. In contrast, NMDAR-mediated death of cerebellar granule neurons was not enhanced, consistent with cell-type and NMDAR subtype specificity. Moreover, increased NMDA-evoked current amplitude and caspase-3 activity were observed in transgenic striatal neurons. Our data support a role for NR2B-subtype NMDAR activation as a trigger for selective neuronal degeneration in HD.     

Attenuation of MPTP-induced dopaminergic neurotoxicity by TV3326, a cholinesterase-monoamine oxidase inhibitor

(R)-[(N-propargyl-(3R) aminoindan-5-yl) ethyl methyl carbamate] (TV3326) is a novel cholinesterase and brain-selective monoamine oxidase (MAO)-A/-B inhibitor. It was developed for the treatment of dementia co-morbid with extra pyramidal disorders (parkinsonism), and depression. On chronic treatment in mice it attenuated striatal dopamine depletion induced by MPTP and prevented the reduction in striatal tyrosine hydroxylase activity, like selective B and non-selective MAO inhibitors. TV3326 preferentially inhibits MAO-B in the striatum and hippocampus, and the degree of MAO-B inhibition correlates with the prevention of MPTP-induced dopamine depletion. Complete inhibition of MAO-B is not necessary for full protection from MPTP neurotoxicity. Unlike that seen after treatment with other MAO-A and -B inhibitors, recovery of striatal and hippocampal MAO-A and -B activities from inhibition by TV3326 did not show first-order kinetics. This has been attributed to the generation of a number of metabolites by TV3326 that cause differential inhibition of these enzymes. Inhibition of brain MAO-A and -B by TV3326 resulted in significant elevations of dopamine, noradrenaline and serotonin in the striatum and hippocampus. This may explain its antidepressant-like activity, resembling that of moclobemide in the forced-swim test in rats.     

Inhibition of Monoamine Oxidase Within Monoaminergic Neurons in the Rat Brain by (E)-β-Fluoromethylene-m-Tyrosine (MDL 72394)

The irreversible inhibition of the monoamine oxidase (MAO) activity within monoaminergic neurons in the rat brain 24 h after single or repeated administration of (E)-beta-fluoromethylene-m-tyrosine (FMMT, MDL 72394) was examined. The enzyme activity was determined by incubating synaptosome-rich homogenates of hypothalamus or striatum with low concentrations of 5-[14C]hydroxytryptamine (5-HT), [14C]noradrenaline (NA), or [14C]dopamine (DA) in the absence and presence of the selective amine uptake inhibitors citalopram (5-HT), maprotiline (NA), and GBR 12909 (DA). After a single subcutaneous injection of FMMT, the inhibition of MAO within the noradrenergic and dopaminergic neurons was significant but only slightly greater than that outside these neurons. The opposite relationship was observed for the serotonergic neurons. After 7 days' treatment of rats with carbidopa, 20 mg/kg p.o., + FMMT once daily, the preference for the inhibition of MAO within the noradrenergic and dopaminergic neurons was accentuated further. The inhibition outside the serotonergic neurons was still greater than within these neurons. The NA uptake inhibitor CPP 199 antagonized the selective inhibition of MAO within the noradrenergic neurons, which indicates that this preference is due to the accumulation of the active metabolite (E)-beta-fluoromethylene-m-tyramine by the NA transporter.     

Selective deficits in the expression of striatal-enriched mRNAs in Huntington's disease

We have identified and cataloged 54 genes that exhibit predominant expression in the striatum. Our hypothesis is that such mRNA molecules are likely to encode proteins that are preferentially associated with particular physiological processes intrinsic to striatal neurons, and therefore might contribute to the regional specificity of neurodegeneration observed in striatal disorders such as Huntington's disease (HD). Expression of these genes was measured simultaneously in the striatum of HD R6/1 transgenic mice using Affymetrix oligonucleotide arrays. We found a decrease in expression of 81% of striatum-enriched genes in HD transgenic mice. Changes in expression of genes associated with G-protein signaling and calcium homeostasis were highlighted. The most striking decrement was observed for a newly identified subunit of the sodium channel, beta 4, with dramatic decreases in expression beginning at 8 weeks of age. A subset of striatal genes was tested by real-time PCR in caudate samples from human HD patients. Similar alterations in expression were observed in human HD and the R6/1 model for the striatal genes tested. Expression of 15 of the striatum-enriched genes was measured in 6-hydroxydopamine-lesioned rats to determine their dependence on dopamine innervation. No changes in expression were observed for any of these genes. These findings demonstrate that mutant huntingtin protein causes selective deficits in the expression of mRNAs responsible for striatum-specific physiology and these may contribute to the regional specificity of degeneration observed in HD.     

CAG trinucleotide RNA repeats interact with RNA-binding proteins.

Genes associated with several neurological diseases are characterized by the presence of an abnormally long trinucleotide repeat sequence. By way of example, Huntington's disease (HD), is characterized by selective neuronal degeneration associated with the expansion of a polyglutamine-encoding CAG tract. Normally, this CAG tract is comprised of 11-34 repeats, but in HD it is expanded to > 37 repeats in affected individuals. The mechanism by which CAG repeats cause neuronal degeneration is unknown, but it has been speculated that the expansion primarily causes abnormal protein functioning, which in turn causes HD pathology. Other mechanisms, however, have not been ruled out. Interactions between RNA and RNA-binding proteins have previously been shown to play a role in the expression of several eukaryotic genes. Herein, we report the association of cytoplasmic proteins with normal length and extended CAG repeats, using gel shift and UV crosslinking assays. Cytoplasmic protein extracts from several rat brain regions, including the striatum and cortex, sites of neuronal degeneration in HD, contain a 63-kD RNA-binding protein that specifically interacts with these CAG-repeat sequences. These protein-RNA interactions are dependent on the length of the CAG repeat, with longer repeats binding substantially more protein. Two CAG repeat-binding proteins are present in human cortex and striatum; one comigrates with the rat protein at 63 kD, while the other migrates at 49 kD. These data suggest mechanisms by which RNA-binding proteins may be involved in the pathological course of trinucleotide repeat-associated neurological diseases.     

Acute and Chronic Treatments with Citalopram Lower Somatostatin Levels in Rat Brain Striatum Through Different Mechanisms

Abstract: The suggestion that somatostatin is involved in the pathophysiology of obsessive-compulsive disorder and the evidence that selective serotonin reuptake inhibitors show significant antiobsessional effect prompted us to examine the effect of citalopram, a selective and potent serotonin reuptake inhibitor, on the somatostatinergic system in different brain regions of the rat. A single intraperitoneal injection of 10 mg/kg citalopram significantly reduced somatostatin levels in the striatum and nucleus accumbens after 4 but not 1, 8, or 24 h. No changes were found in hippocampus. In addition, we found that the K⁺-evoked overflow of somatostatin-like immunoreactivity from striatal slices was significantly increased 1 h after a single injection of citalopram and was still higher, although not significantly, 4 h after the drug injection. Levels of preprosomatostatin mRNA were unchanged in striatum and accumbens 1 and 4 h after a single drug administration. In rats treated with citalopram (10 mg/kg i.p.) twice daily for 14 days, the levels of somatostatin and its mRNA were significantly decreased in the striatum but not in other brain regions 24 h after the last dose. No change was found in the basal or K⁺-evoked overflow of somatostatin-like immunoreactivity at 1, 4, and 24 h after the last drug injection. These results suggest that acute and chronic treatment with citalopram reduces somatostatin levels in striatum by different mechanisms. Whereas a single dose of the drug reduces somatostatin levels by increasing the release of the peptide, repeated drug treatment reduces the biosynthesis of somatostatin.     

Atg4b-Dependent Autophagic Flux Alleviates Huntington’s Disease Progression

The accumulation of aggregated mutant huntingtin (mHtt) inclusion bodies is involved in Huntigton’s disease (HD) progression. Medium sized-spiny neurons (MSNs) in the corpus striatum are highly vulnerable to mHtt aggregate accumulation and degeneration, but the mechanisms and pathways involved remain elusive. Here we have developed a new model to study MSNs degeneration in the context of HD. We produced organotypic cortico-striatal slice cultures (CStS) from HD transgenic mice mimicking specific features of HD progression. We then show that induction of autophagy using catalytic inhibitors of mTOR prevents MSNs degeneration in HD CStS. Furthermore, disrupting autophagic flux by overexpressing Atg4b in neurons and slice cultures, accelerated mHtt aggregation and neuronal death, suggesting that Atg4b-dependent autophagic flux influences HD progression. Under these circumstances induction of autophagy using catalytic inhibitors of mTOR was inefficient and did not affect mHtt aggregate accumulation and toxicity, indicating that mTOR inhibition alleviates HD progression by inducing Atg4b-dependent autophagic flux. These results establish modulators of Atg4b-dependent autophagic flux as new potential targets in the treatment of HD.