Decreased cAMP Response Element-mediated Transcription

Protein kinase A regulates molecular chaperone transcription and protein aggregation

Heat shock factor 1 (HSF1) regulates one of the major pathways of protein quality control and is essential for deterrence of protein-folding disorders, particularly in neuronal cells. However, HSF1 activity declines with age, a change that may open the door to progression of neurodegenerative disorders such as Huntington's disease. We have investigated mechanisms of HSF1 regulation that may become compromised with age. HSF1 binds stably to the catalytic domain of protein kinase A (PKAcα) and becomes phosphorylated on at least one regulatory serine residue (S320). We show here that PKA is essential for effective transcription of HSP genes by HSF1. PKA triggers a cascade involving HSF1 binding to the histone acetylase p300 and positive translation elongation factor 1 (p-TEFb) and phosphorylation of the c-terminal domain of RNA polymerase II, a key mechanism in the downstream steps of HSF1-mediated transcription. This cascade appears to play a key role in protein quality control in neuronal cells expressing aggregation-prone proteins with long poly-glutamine (poly-Q) tracts. Such proteins formed inclusion bodies that could be resolved by HSF1 activation during heat shock. Resolution of the inclusions was inhibited by knockdown of HSF1, PKAcα, or the pTEFb component CDK9, indicating a key role for the HSF1-PKA cascade in protein quality control.

PGC-1α at the intersection of bioenergetics regulation and neuron function: from Huntington's disease to Parkinson's disease and beyond

Neurons are specialized cells with unique features, including a constant high demand for energy. Mitochondria satisfy this constant demand, and are emerging as a central target for dysfunction in neurodegenerative disorders, such as Huntington's disease (HD) and Parkinson's disease. PPARγ co-activator-1α (PGC-1α) is a transcription co-activator for nuclear receptors such as the PPARs, and thereby coordinates a number of gene expression programs to promote mitochondrial biogenesis and oxidative phosphorylation. Studies of PGC-1α knock-out mice have yielded important insights into the role of PGC-1α in normal nervous system function and potentially neurological disease. HD is caused by a polyglutamine repeat expansion in the huntingtin protein, and decades of work have established mitochondrial dysfunction as a key feature of HD pathogenesis. However, after the discovery of the HD gene, numerous reports produced strong evidence for altered transcription in HD. In 2006, a series of studies revealed that PGC-1α transcription interference contributes to HD neurodegeneration, linking the nuclear transcriptionopathy with the mitochondrial dysfunction. Subsequent work has strengthened this view, and further extended the role of PGC-1α within the CNS. Within the last year, studies of Parkinson's disease, another involuntary movement disorder long associated with mitochondrial dysfunction, have shown that PGC-1α dysregulation is contributing to its pathogenesis. As PGC-1α is likely also important for aging, a process with considerable relevance to neuron function, translational studies aimed at developing therapies based upon the PGC-1α pathway as a high priority target are underway.

Neuronal store-operated calcium entry pathway as a novel therapeutic target for Huntington's disease treatment

Huntington's disease (HD) is a neurodegenerative disorder caused by a polyglutamine expansion within Huntingtin (Htt) protein. In the phenotypic screen we identified a class of quinazoline-derived compounds that delayed a progression of a motor phenotype in transgenic Drosophila HD flies. We found that the store-operated calcium (Ca(2+)) entry (SOC) pathway activity is enhanced in neuronal cells expressing mutant Htt and that the identified compounds inhibit SOC pathway in HD neurons. The same compounds exerted neuroprotective effects in glutamate-toxicity assays with YAC128 medium spiny neurons primary cultures. We demonstrated a key role of TRPC1 channels in supporting SOC pathway in HD neurons. We concluded that the TRPC1-mediated neuronal SOC pathway constitutes a novel target for HD treatment and that the identified compounds represent a novel class of therapeutic agents for treatment of HD and possibly other neurodegenerative disorders.

Truncated peroxisome proliferator-activated receptor-γ coactivator 1α splice variant is severely altered in Huntington's disease

BACKGROUND

Reduced peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) gene expression has been observed in striatal cell lines, transgenic mouse models of Huntington's disease (HD), and brain tissue from HD patients. As this protein is a key transcription regulator of the expression of many mitochondrial proteins, these observations strongly support the role of aberrant mitochondrial function in the pathogenesis of HD. The PGC1α protein undergoes posttranslational modifications that affect its transcriptional activity. The N-truncated splice variant of PGC1α (NT-PGC1α) is produced in tissues, but the role of truncated splice variants of PGC1α in HD and in the regulation of mitochondrial gene expression has not been elucidated.

OBJECTIVE

To examine the expression and modulation of expression of NT-PGC1α levels in HD.

METHODS AND RESULTS

We found that the NT-PGC1α protein, a splice variant of ∼38 kDa, but not full-length PGC1α is severely and consistently altered in human HD brain, human HD myoblasts, mouse HD models, and HD striatal cells. NT-PGC1α levels were significantly upregulated in HD cells and mouse brown fat by physiologically relevant stimuli that are known to upregulate PGC1α gene expression. This resulted in an increase in mitochondrial gene expression and cytochrome c content.

CONCLUSION

Our data suggest that NT-PGC1α is an important component of the PGC1α transcriptional network, which plays a significant role in the pathogenesis of HD.

Decreased striatal RGS2 expression is neuroprotective in Huntington's disease (HD) and exemplifies a compensatory aspect of HD-induced gene regulation

Background

The molecular phenotype of Huntington's disease (HD) is known to comprise highly reproducible changes in gene expression involving striatal signaling genes. Here we test whether individual changes in striatal gene expression are capable of mitigating HD-related neurotoxicity.

Methodology/Principal Findings

We used protein-encoding and shRNA-expressing lentiviral vectors to evaluate the effects of RGS2, RASD2, STEP and NNAT downregulation in HD. Of these four genes, only RGS2 and RASD2 modified mutant htt fragment toxicity in cultured rat primary striatal neurons. In both cases, disease modulation was in the opposite of the predicted direction: whereas decreased expression of RGS2 and RASD2 was associated with the HD condition, restoring expression enhanced degeneration of striatal cells. Conversely, silencing of RGS2 or RASD2 enhanced disease-related changes in gene expression and resulted in significant neuroprotection. These results indicate that RGS2 and RASD2 downregulation comprises a compensatory response that allows neurons to better tolerate huntingtin toxicity. Assessment of the possible mechanism of RGS2-mediated neuroprotection showed that RGS2 downregulation enhanced ERK activation. These results establish a novel link between the inhibition of RGS2 and neuroprotective modulation of ERK activity.

Conclusions

Our findings both identify RGS2 downregulation as a novel compensatory response in HD neurons and suggest that RGS2 inhibition might be considered as an innovative target for neuroprotective drug development.

Does Huntingtin play a role in selective macroautophagy?

The accumulation of protein aggregates in neurons appears to be a basic feature of neurodegenerative disease. In Huntington's Disease (HD), a progressive and ultimately fatal neurodegenerative disorder caused by an expansion of the polyglutamine repeat within the protein Huntingtin (Htt), the immediate proximal cause of disease is well understood. However, the cellular mechanisms which modulate the rate at which fragments of Htt containing polyglutamine accumulate in neurons is a central issue in the development of approaches to modulate the rate and extent of neuronal loss in this disease. We have recently found that Htt is phosphorylated by the kinase IKK on serine (S) 13, activating its phosphorylation on S16 and its acetylation and poly-SUMOylation, modifications that modulate its clearance by the proteasome and lysosome in cells. In the discussion here I suggest that Htt may have a normal function in the lysosomal mechanism of selective macroautophagy involved in its own degradation which may share some similarity with the yeast cytoplasm to vacuole targeting (Cvt) pathway. Pharmacologic activation of this pathway may be useful early in disease progression to treat HD and other neurodegenerative diseases characterized by the accumulation of disease proteins.

Molecular biology of Huntington's disease

It has been more than 17 years since the causative mutation for Huntington's disease was discovered as the expansion of the triplet repeat in the N-terminal portion of the Huntingtin (HTT) gene. In the intervening time, researchers have discovered a great deal about Huntingtin's involvement in a number of cellular processes. However, the role of Huntingtin in the key pathogenic mechanism leading to neurodegeneration in the disease process has yet to be discovered. Here, we review the body of knowledge that has been uncovered since gene discovery and include discussions of the HTT gene, CAG triplet repeat expansion, HTT expression, protein features, posttranslational modifications, and many of its known protein functions and interactions. We also highlight potential pathogenic mechanisms that have come to light in recent years.

Longitudinal behavioral, cross-sectional transcriptional and histopathological characterization of a knock-in mouse model of Huntington's disease with 140 CAG repeats

The discovery of the gene mutation responsible for Huntington's disease (HD), huntingtin, in 1993 allowed for a better understanding of the pathology of and enabled the development of animal models. HD is caused by the expansion of a polyglutamine repeat region in the N-terminal of the huntingtin protein. Here we examine the behavioral, transcriptional, histopathological and anatomical characteristics of a knock-in HD mouse model with a 140 polyglutamine expansion in the huntingtin protein. This CAG 140 model contains a portion of the human exon 1 with 140 CAG repeats knocked into the mouse huntingtin gene. We have longitudinally examined the rearing behavior, accelerating rotarod, constant speed rotarod and gait for age-matched heterozygote, homozygote and non-transgenic mice and have found a significant difference in the afflicted mice. However, while there were significant differences between the non-transgenic and the knock-in mice, these behaviors were not progressive. As in HD, we show that the CAG 140 mice also have a significant decrease in striatally enriched mRNA transcripts. In addition, striatal neuronal intranuclear inclusion density increases with age. Lastly these CAG 140 mice show slight cortical thinning compared to non-transgenic mice, similarly to the cortical thinning recently reported in HD.

Inhibition of the striatal specific phosphodiesterase PDE10A ameliorates striatal and cortical pathology in R6/2 mouse model of Huntington's disease

BACKGROUND

Huntington's disease is a devastating neurodegenerative condition for which there is no therapy to slow disease progression. The particular vulnerability of striatal medium spiny neurons to Huntington's pathology is hypothesized to result from transcriptional dysregulation within the cAMP and CREB signaling cascades in these neurons. To test this hypothesis, and a potential therapeutic approach, we investigated whether inhibition of the striatal-specific cyclic nucleotide phosphodiesterase PDE10A would alleviate neurological deficits and brain pathology in a highly utilized model system, the R6/2 mouse.

METHODOLOGY/PRINCIPAL FINDINGS

R6/2 mice were treated with the highly selective PDE10A inhibitor TP-10 from 4 weeks of age until euthanasia. TP-10 treatment significantly reduced and delayed the development of the hind paw clasping response during tail suspension, deficits in rotarod performance, and decrease in locomotor activity in an open field. Treatment prolonged time to loss of righting reflex. These effects of PDE10A inhibition on neurological function were reflected in a significant amelioration in brain pathology, including reduction in striatal and cortical cell loss, the formation of striatal neuronal intranuclear inclusions, and the degree of microglial activation that occurs in response to the mutant huntingtin-induced brain damage. Striatal and cortical levels of phosphorylated CREB and BDNF were significantly elevated.

CONCLUSIONS/SIGNIFICANCE

Our findings provide experimental support for targeting the cAMP and CREB signaling pathways and more broadly transcriptional dysregulation as a therapeutic approach to Huntington's disease. It is noteworthy that PDE10A inhibition in the R6/2 mice reduces striatal pathology, consistent with the localization of the enzyme in medium spiny neurons, and also cortical pathology and the formation of neuronal nuclear inclusions. These latter findings suggest that striatal pathology may be a primary driver of these secondary pathological events. More significantly, our studies point directly to an accessible new therapeutic approach to slow Huntington's disease progression, namely, PDE10A inhibition. There is considerable activity throughout the pharmaceutical industry to develop PDE10A inhibitors for the treatment of basal ganglia disorders. The present results strongly support the investigation of PDE10A inhibitors as a much needed new treatment approach to Huntington's disease.

The therapeutic potential of G-protein coupled receptors in Huntington's disease

Huntington's disease is a late-onset autosomal dominant inherited neurodegenerative disease characterised by increased symptom severity over time and ultimately premature death. An expanded CAG repeat sequence in the huntingtin gene leads to a polyglutamine expansion in the expressed protein, resulting in complex dysfunctions including cellular excitotoxicity and transcriptional dysregulation. Symptoms include cognitive deficits, psychiatric changes and a movement disorder often referred to as Huntington's chorea, which involves characteristic involuntary dance-like writhing movements. Neuropathologically Huntington's disease is characterised by neuronal dysfunction and death in the striatum and cortex with an overall decrease in cerebral volume (Ho et al., 2001). Neuronal dysfunction begins prior to symptom presentation, and cells of particular vulnerability include the striatal medium spiny neurons. Huntington's is a devastating disease for patients and their families and there is currently no cure, or even an effective therapy for disease symptoms. G-protein coupled receptors are the most abundant receptor type in the central nervous system and are linked to complex downstream pathways, manipulation of which may have therapeutic application in many neurological diseases. This review will highlight the potential of G-protein coupled receptor drug targets as emerging therapies for Huntington's disease.

Ultrastructural and transcriptional profiling of neuropathological misregulation of CREB function

We compare here the neurodegenerative processes observed in the hippocampus of bitransgenic mice with chronically altered levels of cAMP-response element-binding protein (CREB) function. The combination of genome-wide transcriptional profiling of degenerating hippocampal tissue with microscopy analyses reveals that the sustained inhibition of CREB function in A-CREB mice is associated with dark neuron degeneration, whereas its strong chronic activation in VP16-CREB mice primarily causes excitotoxic cell death and inflammation. Furthermore, the meta-analysis with gene expression profiles available in public databases identifies relevant common markers to other neurodegenerative processes and highlights the importance of the immune response in neurodegeneration. Overall, these analyses define the ultrastructural and transcriptional signatures associated with these two forms of hippocampal neurodegeneration, confirm the importance of fine-tuned regulation of CREB-dependent gene expression for CA1 neuron survival and function, and provide novel insight into the function of CREB in the etiology of neurodegenerative processes.

CREB is a key regulator of striatal vulnerability in chemical and genetic models of Huntington's disease

Evidence of dysregulation of the CREB/CRE transcriptional pathway in animal models of Huntington's disease (HD) suggests that strategies designed to augment CRE-mediated transcription may be of therapeutic value. Here, we investigated the consequences of CREB activation and repression in chemical and transgenic mouse models of HD. In the 3-nitropropionic acid (3-NP) model, CREB phospho-activation in the striatum was potently repressed within the neurotoxic "core" region prior to cell death. Conversely, marked expression of phospho-CREB, as well the CREB-regulated cytoprotective gene Bcl-2, was detected in the "penumbral" region. To examine potential contributory roles for the CREB/CRE transcriptional pathway in striatal degeneration, we used both CREB loss- (A-CREB) and gain- (VP16-CREB) of-function transgenic mouse strains. 3-NP-induced striatal lesion size and motor dysfunction were significantly increased in A-CREB mice compared to controls. Conversely, striatal damage and motor deficits were diminished in VP16-CREB mice. Furthermore, transgenic A-CREB significantly accelerated motor impairment in the YAC128 mouse model of HD. Together, these results indicate that CREB functionality is lost during the early stages of striatal cell stress and that the repression of CREB-mediated transcription contributes to the pathogenic process.

Epigenetic dysregulation in cognitive disorders

Epigenetic mechanisms are not only essential for biological functions requiring stable molecular changes such as the establishment of cell identity and tissue formation, they also constitute dynamic intracellular processes for translating environmental stimuli into modifications in gene expression. Over the past decade it has become increasingly clear that both aspects of epigenetic mechanisms play a pivotal role in complex brain functions. Evidence from patients with neurodegenerative and neurodevelopmental disorders such as Alzheimer's disease and Rett syndrome indicated that epigenetic mechanisms and chromatin remodeling need to be tightly controlled for proper cognitive functions, and their dysregulation can have devastating consequences. However, because they are dynamic, epigenetic mechanisms are also potentially reversible and may provide powerful means for pharmacological intervention. This review outlines major cognitive disorders known to be associated with epigenetic dysregulation, and discusses the potential of 'epigenetic medicine' as a promising cure.

Phosphodiesterase type IV inhibition prevents sequestration of CREB binding protein, protects striatal parvalbumin interneurons and rescues motor deficits in the R6/2 mouse model of Huntington's disease

The phosphodiesterase type IV inhibitor rolipram increases cAMP response element-binding protein (CREB) phosphorylation and exerts neuroprotective effects in both the quinolinic acid rat model of Huntington's disease (DeMarch et al., 2007) and the R6/2 mouse including sparing of striatal neurons, prevention of neuronal intranuclear inclusion formation and attenuation of microglial reaction (DeMarch et al., 2008). In this study, we sought to determine if rolipram has a beneficial role in the altered distribution of CREB binding protein in striatal spiny neurons and in the motor impairments shown by R6/2 mutants. Moreover, we investigated whether rolipram treatment altered the degeneration of parvalbuminergic interneurons typical of Huntington's disease (Fusco et al., 1999). Transgenic mice and their wild-type controls from a stable colony maintained in our laboratory were treated with rolipram (1.5 mg/kg) or saline daily starting from 4 weeks of age. The cellular distribution of CREB binding protein in striatal spiny neurons was assessed by immunofluorescence, whereas parvalbuminergic neuron degeneration was evaluated by cell counts of immunohistochemically labeled tissue. Motor coordination and motor activity were also examined. We found that rolipram was effective in preventing CREB binding protein sequestration into striatal neuronal intranuclear inclusions, sparing parvalbuminergic interneurons of R6/2 mice, and rescuing their motor coordination and motor activity deficits. Our findings demonstrate the possibility of reversing pharmacologically the behavioral and neuropathological abnormalities of symptomatic R6/2 mice and underline the potential therapeutic value of phosphodiesterase type IV inhibitors in Huntington's disease.

Inhibition of cAMP response element-binding protein reduces neuronal excitability and plasticity, and triggers neurodegeneration

The cAMP-responsive element-binding protein (CREB) pathway has been involved in 2 major cascades of gene expression regulating neuronal function. The first one presents CREB as a critical component of the molecular switch that controls long-lasting forms of neuronal plasticity and learning. The second one relates CREB to neuronal survival and protection. To investigate the role of CREB-dependent gene expression in neuronal plasticity and survival in vivo, we generated bitransgenic mice expressing A-CREB, an artificial peptide with strong and broad inhibitory effect on the CREB family, in forebrain neurons in a regulatable manner. The expression of A-CREB in hippocampal neurons impaired L-LTP, reduced intrinsic excitability and the susceptibility to induced seizures, and altered both basal and activity-driven gene expression. In the long-term, the chronic inhibition of CREB function caused severe loss of neurons in the CA1 subfield as well as in other brain regions. Our experiments confirmed previous findings in CREB-deficient mutants and revealed new aspects of CREB-dependent gene expression in the hippocampus supporting a dual role for CREB-dependent gene expression regulating intrinsic and synaptic plasticity and promoting neuronal survival.

Mitochondrial approaches for neuroprotection

A large body of evidence from postmortem brain tissue and genetic analysis in humans and biochemical and pathological studies in animal models (transgenic and toxin) of neurodegeneration suggest that mitochondrial dysfunction is a common pathological mechanism. Mitochondrial dysfunction from oxidative stress, mitochondrial DNA deletions, pathological mutations, altered mitochondrial morphology, and interaction of pathogenic proteins with mitochondria leads to neuronal demise. Therefore, therapeutic approaches targeting mitochondrial dysfunction and oxidative damage hold great promise in neurodegenerative diseases. This review discusses the potential therapeutic efficacy of creatine, coenzyme Q10, idebenone, synthetic triterpenoids, and mitochondrial targeted antioxidants (MitoQ) and peptides (SS-31) in in vitro studies and in animal models of Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and Alzheimer's disease. We have also reviewed the current status of clinical trials of creatine, coenzyme Q10, idebenone, and MitoQ in neurodegenerative disorders. Further, we discuss newly identified therapeutic targets, including peroxisome proliferator-activated receptor-gamma-coactivator and sirtuins, which provide promise for future therapeutic developments in neurodegenerative disorders.

N-terminal polyglutamine-containing fragments inhibit androgen receptor transactivation function

Several neurodegenerative diseases, including Kennedy's disease (KD), are associated with misfolding and aggregation of polyglutamine (polyQ)-expansion proteins. KD is caused by a polyQ-expansion in the androgen receptor (AR), a key player in male sexual differentiation. Interestingly, KD patients often show signs of mild-to-moderate androgen insensitivity syndrome (AIS) resulting from AR dysfunction. Here, we used the yeastSaccharomyces cerevisiaeto investigate the molecular mechanism behind AIS in KD. Upon expression in yeast, polyQ-expanded N-terminal fragments of AR lacking the hormone binding domain caused a polyQ length-dependent growth defect. Interestingly, while AR fragments with 67 Q formed large, SDS-resistant inclusions, the most pronounced toxicity was observed upon expression of 102 Q fragments which accumulated exclusively as soluble oligomers in the 100–600 kDa range. Analysis using a hormone-dependent luciferase reporter revealed that full-length polyQ-expanded AR is fully functional in transactivation, but becomes inactivated in the presence of the corresponding polyQ-expanded N-terminal fragment. Furthermore, the greatest impairment of AR activity was observed upon interaction of full-length AR with soluble AR fragments. Taken together, our results suggest that soluble polyQ-containing fragments bind to full-length AR and inactivate it, thus providing insight into the mechanism behind AIS in KD and possibly other polyglutamine diseases, such as Huntington's disease.

Huntingtin modulates transcription, occupies gene promoters in vivo, and binds directly to DNA in a polyglutamine-dependent manner

Transcriptional dysregulation is a central pathogenic mechanism in Huntington's disease, a fatal neurodegenerative disorder associated with polyglutamine (polyQ) expansion in the huntingtin (Htt) protein. In this study, we show that mutant Htt alters the normal expression of specific mRNA species at least partly by disrupting the binding activities of many transcription factors which govern the expression of the dysregulated mRNA species. Chromatin immunoprecipitation (ChIP) demonstrates Htt occupation of gene promoters in vivo in a polyQ-dependent manner, and furthermore, ChIP-on-chip and ChIP subcloning reveal that wild-type and mutant Htt exhibit differential genomic distributions. Exon 1 Htt binds DNA directly in the absence of other proteins and alters DNA conformation. PolyQ expansion increases Htt-DNA interactions, with binding to recognition elements of transcription factors whose function is altered in HD. Together, these findings suggest mutant Htt modulates gene expression through abnormal interactions with genomic DNA, altering DNA conformation and transcription factor binding.

Phosphatidylinositide 3-kinase and protein kinase C zeta mediate retinoic acid induction of DARPP-32 in medium size spiny neurons in vitro

Mature striatal medium size spiny neurons express the dopamine and cAMP-regulated phosphoprotein, 32 kDa (DARPP-32), but little is known about the mechanisms regulating its levels, or the specification of fully differentiated neuronal subtypes. Cell extrinsic molecules that increase DARPP-32 mRNA and/or protein levels include retinoic acid (RA), brain-derived neurotrophic factor, and estrogen (E(2)). We now demonstrate that RA regulates DARPP-32 mRNA and protein in primary striatal neuronal cultures. Furthermore, DARPP-32 induction by RA in vitro requires phosphatidylinositide 3-kinase, but is independent of tropomyosin-related kinase B, cyclin-dependent kinase 5, and protein kinase B. Using pharmacologic inhibitors of various isoforms of protein kinase C (PKC), we also demonstrate that DARPP-32 induction by RA in vitro is dependent on PKC zeta (PKCzeta). Thus, the signal transduction pathways mediated by RA are very different than those mediating DARPP-32 induction by brain-derived neurotrophic factor. These data support the presence of multiple signal transduction pathways mediating expression of DARPP-32 in vitro, including a novel, important pathway via which phosphatidylinositide 3-kinase regulates the contribution of PKCzeta.

Activation of p38MAPK contributes to expanded polyglutamine-induced cytotoxicity

Background

The signaling pathways that may modulate the pathogenesis of diseases induced by expanded polyglutamine proteins are not well understood.

Methodologies/Principal Findings

Herein we demonstrate that expanded polyglutamine protein cytotoxicity is mediated primarily through activation of p38MAPK and that the atypical PKC iota (PKCι) enzyme antagonizes polyglutamine-induced cell death through induction of the ERK signaling pathway. We show that pharmacological blockade of p38MAPK rescues cells from polyglutamine-induced cell death whereas inhibition of ERK recapitulates the sensitivity observed in cells depleted of PKCι by RNA interference. We provide evidence that two unrelated proteins with expanded polyglutamine repeats induce p38MAPK in cultured cells, and demonstrate induction of p38MAPK in an in vivo model of neurodegeneration (spinocerebellar ataxia 1, or SCA-1).

Conclusions/Significance

Taken together, our data implicate activated p38MAPK in disease progression and suggest that its inhibition may represent a rational strategy for therapeutic intervention in the polyglutamine disorders.

Ca2+-Operated Transcriptional Networks: Molecular Mechanisms and In Vivo Models

Calcium is the most universal signal used by living organisms to convey information to many different cellular processes. In this review we present well-known and recently identified proteins that sense and decode the calcium signal and are key elements in the nucleus to regulate the activity of various transcriptional networks. When possible, the review also presents in vivo models in which the genes encoding these calcium sensors-transducers have been modified, to emphasize the critical role of these Ca2+-operated mechanisms in many physiological functions.

Beneficial effects of rolipram in the R6/2 mouse model of Huntington's disease

We have previously showed that rolipram, a phosphodiesterase type IV inhibitor, displays a neuroprotective effect in a rat quinolinic acid model of HD [DeMarch Z., Giampa C., Patassini S., Martorana A., Bernardi G. and Fusco F.R., (2007) Beneficial effects of rolipram in a quinolinic acid model of striatal excitotoxicity. Neurobiol. Dis. 25:266-273.]. In this study, we sought to determine if rolipram exerts a neuroprotective effect in R6/2 mutant mice, which recapitulates, in many aspects, human HD [Mangiarini L., Sathasivam K., Seller M., Cozens B., Harper A., Hetherington C., Lawton M., Trottier Y., Lehrach H., Davies S.W. and Bates G.P. (1996) Exon 1 of the HD gene with an expanded CAG repeat is sufficient to cause a progressive neurological phenotype in transgenic mice. Cell. 87:493-506]. Transgenic mice were treated with rolipram 1.5 mg/kg daily starting from 4 weeks of age. After transcardial perfusion, histological and immunohistochemical studies were performed. We found that rolipram-treated R6/2 mice survived longer and displayed less severe signs of neurological dysfunction than the vehicle treated ones. Primary outcome measures such as brain volume, striatal atrophy, size and morphology of striatal neurons, neuronal intranuclear inclusions and microglial reaction confirmed a neuroprotective effect of the compound. Rolipram was effective in increasing significantly the levels of activated CREB and of BDNF the striatal spiny neurons, which might account for the beneficial effects observed in this model. Our findings show that rolipram could be considered as a valid therapeutic approach for HD.

Can directed activity improve mobility in Huntington's disease?

Huntington's disease is an inherited disorder of the CNS that results in progressive deterioration of mobility and cognition and also affects behaviour. There are no disease-modifying interventions available to date, although there has been considerable progress in research directed at understanding the pathological basis of the disease with a view to identifying potential treatments. It is however important not to overlook currently available treatment strategies, including rehabilitation approaches. There has been little work to date to explore the potential of such approaches and here we highlight the need for more systematic studies in this area as well as the need for good objective assessment tools and the potential role that rehabilitation and training may have in the application of novel treatment options.

Transcriptional signatures in Huntington's disease

While selective neuronal death has been an influential theme in Huntington's disease (HD), there is now a preponderance of evidence that significant neuronal dysfunction precedes frank neuronal death. The best evidence for neuronal dysfunction is the observation that gene expression is altered in HD brain, suggesting that transcriptional dysregulation is a central mechanism. Studies of altered gene expression began with careful observations of postmortem human HD brain and subsequently were accelerated by the development of transgenic mouse models. The application of DNA microarray technology has spurred tremendous progress with respect to the altered transcriptional processes that occur in HD, through gene expression studies of both transgenic mouse models as well as cellular models of HD. Gene expression profiles are remarkably comparable across these models, bolstering the idea that transcriptional signatures reflect an essential feature of disease pathogenesis. Finally, gene expression studies have been applied to human HD, thus not only validating the approach of using model systems, but also solidifying the idea that altered transcription is a key mechanism in HD pathogenesis. In the future, gene expression profiling will be used as a readout in clinical trials aimed at correcting transcriptional dysregulation in Huntington's disease.

Oxidative stress and mitochondrial dysfunction in neurodegenerative diseases

In recent years, it has become increasingly clear that mitochondrial dysfunction and oxidative damage are major contributors to neuronal loss. Free radicals, typically generated from mitochondrial respiration, cause oxidative damage of nucleic acids, lipids, carbohydrates and proteins. Despite enormous amount of effort, however, the mechanism by which oxidative damage causes neuronal death is not well understood. Emerging data from a number of neurodegenerative diseases suggest that there may be common features of toxicity that are related to oxidative damage. In this review, while focusing on Huntington's disease (HD), we discuss similarities among HD, Friedreich ataxia and xeroderma pigmentosum, which provide insight into shared mechanisms of neuronal death.

Beneficial effects of rolipram in a quinolinic acid model of striatal excitotoxicity

Activity of c-AMP responsive element-binding protein (CREB) is decreased in Huntington's disease (HD). Such decrease was also described by our group in the quinolinic acid lesion model of striatal excitotoxicity. The phosphodiesterase type IV inhibitor rolipram increases CREB phosphorylation. Such drug has a protective effect in global ischaemia and embolism in rats. In this study, we sought to determine whether rolipram displays a neuroprotective effect in our rat model of HD. Animals were surgically administered QA and subsequently treated with rolipram daily up to 2 and 8 weeks respectively. After these time points, rats were sacrificed and immunohistochemical studies were performed in the striata. In the rolipram-treated animals, striatal lesion size was about 62% smaller that in the vehicle-treated ones at 2 weeks time point. Moreover, the surviving cell number was several times higher in the rolipram-treated animals than in the vehicle group at both time points. Rolipram also showed to be effective in increasing significantly the levels of activated CREB in the striatal spiny neurons, which accounts mostly for its beneficial effect in our rodent model of excitotoxicity. Our findings show that rolipram could be considered as a valid therapeutic approach for HD.

Reduced expression of PSA-NCAM in the hippocampus and piriform cortex of the R6/1 and R6/2 mouse models of Huntington's disease

Cognitive deficits and impaired olfactory function are observed in early stages of Huntington's disease (HD). The polysialylated form of the neural cell adhesion molecule (PSA-NCAM) is strongly associated with plastic events in the brain. During adulthood, it is most abundantly expressed in the hippocampus and the piriform cortex, which are involved in cognition and olfaction, respectively. We show that the numbers of PSA-NCAM-positive cells in the hippocampus and piriform cortex are dramatically reduced in the R6/1 and the R6/2 mouse models of HD. We hypothesize that the decrease in NCAM polysialylation reflects an impaired plasticity and might underlie some of the early symptoms in HD.

ESET/SETDB1 gene expression and histone H3 (K9) trimethylation in Huntington's disease

Chromatin remodeling and transcription regulation are tightly controlled under physiological conditions. It has been suggested that altered chromatin modulation and transcription dysfunction may play a role in the pathogenesis of Huntington's disease (HD). Increased histone methylation, a well established mechanism of gene silencing, results in transcriptional repression. ERG-associated protein with SET domain (ESET), a histone H3 (K9) methyltransferase, mediates histone methylation. We show that ESET expression is markedly increased in HD patients and in transgenic R6/2 HD mice. Similarly, the protein level of trimethylated histone H3 (K9) was also elevated in HD patients and in R6/2 mice. We further demonstrate that both specificity protein 1 (Sp1) and specificity protein 3 (Sp3) act as transcriptional activators of the ESET promoter in neurons and that mithramycin, a clinically approved guanosine-cytosine-rich DNA binding antitumor antibiotic, interferes with the DNA binding of these Sp family transcription factors, suppressing basal ESET promoter activity in a dose dependent manner. The combined pharmacological treatment with mithramycin and cystamine down-regulates ESET gene expression and reduces hypertrimethylation of histone H3 (K9). This polytherapy significantly ameliorated the behavioral and neuropathological phenotype in the R6/2 mice and extended survival over 40%, well beyond any existing reported treatment in HD mice. Our data suggest that modulation of gene silencing mechanisms, through regulation of the ESET gene is important to neuronal survival and, as such, may be a promising treatment in HD patients.

Ubiquitin crosstalk connecting cellular processes

The polypeptide ubiquitin is used in many processes as different as endocytosis, multivesicular body formation, and regulation of gene transcription. Conjugation of a single ubiquitin moiety is typically used in these processes. A polymer of ubiquitin moieties is required for tagging proteins for proteasomal degradation. Besides its role in protein degradation, ubiquitin is also engaged as mono- or polymer in intracellular signalling and DNA repair. Since free ubiquitin is present in limiting amounts in cells, changes in the demands for ubiquitin in any of these processes is likely to indirectly affect other ubiquitin modifications. For example, proteotoxic stress strongly increases poly-ubiquitylated proteins at the cost of mono-ubiquitylated histones resulting in chromatin remodelling and altered transcription. Here we discuss the interconnection between ubiquitin-dependent processes and speculate on the functional significance of the ubiquitin equilibrium as a signalling route translating cellular stress into molecular responses.

Expression and Characterization of Full-length Human Huntingtin, an Elongated HEAT Repeat Protein

Huntington disease is an inherited neurodegenerative disorder that is caused by expanded CAG trinucleotide repeats, resulting in a polyglutamine stretch of >37 on the N terminus of the protein huntingtin (htt). htt is a large (347 kDa), ubiquitously expressed protein. The precise functions of htt are not clear, but its importance is underscored by the embryonic lethal phenotype in htt knock-out mice. Despite the fact that the htt gene was cloned 13 years ago, little is known about the properties of the full-length protein. Here we report the expression and preliminary characterization of recombinant full-length wild-type human htt. Our results support a model of htt composed entirely of HEAT repeats that stack to form an elongated superhelix.

Reduced expression of the TrkB receptor in Huntington's disease mouse models and in human brain

Deficits of neurotrophic support caused by reduced levels of brain-derived neurotrophic factor (BDNF) have been implicated in the selective vulnerability of striatal neurones in Huntington's disease (HD). Therapeutic strategies based on BDNF administration have been proposed to slow or prevent the disease progression. However, the effectiveness of BDNF may depend on the proper expression of its receptor TrkB. In this study, we analysed the expression of TrkB in several HD models and in postmortem HD brains. We found a specific reduction of TrkB receptors in transgenic exon-1 and full-length knock-in HD mouse models and also in the motor cortex and caudate nucleus of HD brains. Our findings also demonstrated that continuous expression of mutant huntingtin is required to down-regulate TrkB levels. This was shown by findings in an inducible HD mouse model showing rescue of TrkB by turning off mutant huntingtin expression. Interestingly, the length of the polyglutamine tract in huntingtin appears to modulate the reduction of TrkB. Finally, to analyse the effect of BDNF in TrkB we compared TrkB expression in mutant huntingtin R6/1 and double mutant (R6/1 : BDNF+/-) mice. Similar TrkB expression was found in both transgenic mice suggesting that reduced TrkB is not a direct consequence of decreased BDNF. Therefore, taken together our findings identify TrkB as an additional component that potentially might contribute to the altered neurotrophic support in HD.

Brain-specific factors in combination with mutant huntingtin induce gene-specific transcriptional dysregulation

Mutant huntingtin lowered steady-state levels of DARPP-32 mRNA in the brain but not kidney of R6 transgenic HD mice by repressing transcription from one of two promoters. The activity of DARPP-32 promoter deletion constructs were lower in the presence of mutant huntingtin in immortalized striatal cell lines but no difference in transcription factor binding to the promoter was detected. The activity of CMV, TK and HPRT promoters was also affected by mutant huntingtin in these cell lines. Transient transfection experiments demonstrated that short-term expression of mutant huntingtin exerted a cell- and promoter-specific transcriptional repression. In in vitro experiments, transcription of the CMV promoter was reduced in the presence of striatal proteins and mutant huntingtin. It is likely that select combinations of trans-acting factors, co-activators and components of the Pol II holoenzyme acting in concert provide the basis for both the gene- and tissue-specific effects of mutant huntingtin.

Striatal modulation of cAMP-response-element-binding protein (CREB) after excitotoxic lesions: implications with neuronal vulnerability in Huntington's disease

Recent evidence has shown that the activity of cAMP responsive element-binding protein (CREB) and of CREB-binding protein (CBP) is decreased in Huntington's disease (HD) [Steffan et al. (2000)Proc. Natl Acad. Sci. USA, 97, 6763-6768; Gines et al. (2003)Hum. Mol. Genet., 12, 497-508; Rouaux et al. (2004) Biochem. Pharmacol., 68, 1157-1164; Sugars et al. (2004)J. Biol. Chem., 279, 4988-4999]. Such decrease is thought to reflect the impaired energy metabolism observed in a HD mouse model, where a decline in striatum cAMP levels has been observed [Gines et al. (2003)Hum. Mol. Genet., 12, 497-508]. Increased levels of CREB have also been demonstrated to exert neuroprotective functions [Lonze & Ginty (2002)Neuron, 35, 605-623; Lonze et al. (2002)Neuron, 34, 371-385]. Our study aimed to investigate the distribution of CREB in the neuronal subpopulations of the striatum in normal rats compared to the HD model of quinolinic acid lesion. Twenty-five Wistar rats were administered quinolinic acid 100 mm into the right striatum, and killed after 24 h, 48 h, 1 week, 2 weeks, and six weeks, respectively. The contralateral striata were used as controls. Dual-label immunofluorescence was employed using antibodies against phosphorylated CREB and each of the different neuronal subpopulations markers. Our results show that activated CREB levels decrease progressively in projection neurons and parvalbumin (PARV) and calretinin (CALR) interneurons, whereas such levels remain stable in cholinergic and somatostatin interneurons. Thus, we speculate that the ability of cholinergic interneurons to maintain their levels of CREB after excitotoxic lesions is one of the factors determining their protection in Huntington's disease.

Selective neuronal degeneration in Huntington's disease

Huntington's disease (HD) is a progressive neurodegenerative disorder that generally begins in middle age with abnormalities of movement, cognition, personality, and mood. Neuronal loss is most marked among the medium-sized projection neurons of the dorsal striatum. HD is an autosomal dominant genetic disorder caused by a CAG expansion in exon 1 of the HD gene, encoding an expanded polyglutamine (polyQ) tract near the N-terminus of the protein huntingtin. Despite identification of the gene mutation more than a decade ago, the normal function of this ubiquitously expressed protein is still under investigation and the mechanisms underlying selective neurodegeneration in HD remain poorly understood. Detailed postmortem analyses of brains of HD patients have provided important clues, and HD transgenic and knock-in mouse models have facilitated investigations into potential pathogenic mechanisms. Subcellular fractionation and immunolocalization studies suggest a role for huntingtin in organelle transport, protein trafficking, and regulation of energy metabolism. Consistent with this, evidence from vertebrate and invertebrate models of HD indicates that expression of the polyQ-expanded form of huntingtin results in early impairment of axonal transport and mitochondrial function. As well, alteration in activity of the N-methyl-d-aspartate (NMDA) type glutamate receptor, which has been implicated as a main mediator of excitotoxic neuronal death, especially in the striatum, is an early effect of mutant huntingtin. Proteolysis and nuclear localization of huntingtin also occur relatively early, while formation of ubiquitinated aggregates of huntingtin and transcriptional dysregulation occur as late effects of the gene mutation. Although each of these processes may contribute to neuronal loss in HD, here we review the data to support a strong role for NMDA receptor (NMDAR)-mediated excitotoxicity and mitochondrial dysfunction in conferring selective neuronal vulnerability in HD.

Differential role for CBP and p300 CREB-binding domain in motor skill learning

Cyclic adenosine monophosphate response element binding protein (CREB) binding protein (CBP) and E1A binding protein (p300) are highly homologous transcriptional coactivators with histone acetyltransferase activity. Although CBP and p300 have unique functions in vivo during embryogenesis and hematopoiesis, their functions within the nervous system remain poorly understood. The authors demonstrate that these coactivators have differential roles in motor skill learning. Mice with a mutation in the CREB-binding (KIX) domain of CBP exhibited motor learning deficits. However, mice with the analogous mutation in the KIX domain of p300 showed normal motor learning. Further, CREB knock-out mice exhibited a motor learning deficit similar to that of CBP-KIX mutant mice. These results suggest that the CREB-CBP interaction is more limiting or critical than the CREB-p300 interaction for motor skill learning. Thus, CBP and p300 are genetically distinct at the behavioral level.

Regulation of CRE-dependent transcription by presenilins: prospects for therapy of Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder and is characterized by memory loss and other cognitive disabilities. Mutations in the presenilin genes are the major cause of familial AD. Analysis of conditional knockout mice has shown that inactivation of presenilins results in progressive memory impairment and age-dependent neurodegeneration, suggesting that reduced presenilin activity might represent an important pathogenic mechanism. Presenilins positively regulate the transcription of cAMP response element (CRE)-containing genes, some of which are known to be important for memory formation and neuronal survival. Phosphodiesterase 4 and histone deacetylase inhibitors, which can enhance CRE-dependent gene expression, have been shown to ameliorate memory deficits and neurodegeneration in animal models. Thus, modulation of CRE-dependent transcription might be beneficial for the treatment of dementia in AD.

Mutant huntingtin represses CBP, but not p300, by binding and protein degradation

Huntington's disease can be used as a model to study neurodegenerative disorders caused by aggregation-prone proteins. It has been proposed that the entrapment of transcription factors in aggregates plays an important role in pathogenesis. We now report that the transcriptional activity of CBP is already repressed in the early time points by soluble mutant huntingtin, whereas the histone acetylase activity of CBP/p300 is gradually diminished over time. Mutant huntingtin bound much stronger to CBP than normal huntingtin, possibly contributing to repression. Especially at the later time points, CBP protein level was gradually reduced via the proteasome pathway. In sharp contrast, p300 was unaffected by mutant huntingtin. This selective degradation of CBP was absent in spinocerebellar ataxia 3. Thus, mutant huntingtin specifically affects CBP and not p300 both at the early and later time points, via multiple mechanisms. In addition to the reduction of CBP, also the altered ratio of these closely related histone acetyltransferases may affect chromatin structure and transcription and thus contribute to neurodegeneration.

Intrastriatal rAAV-mediated delivery of anti-huntingtin shRNAs induces partial reversal of disease progression in R6/1 Huntington's disease transgenic mice

Huntington's disease (HD) is a fatal neurodegenerative disorder caused by the presence of an abnormally expanded polyglutamine domain in the N-terminus of huntingtin. We developed a recombinant adeno-associated viral serotype 5 (rAAV5) gene transfer strategy to posttranscriptionally suppress the levels of striatal mutant huntingtin (mHtt) in the R6/1 HD transgenic mouse via RNA interference. Transient cotransfection of HEK293 cells with plasmids expressing a portion of human mHtt derived from R6/1 transgenic HD mice and a short-hairpin RNA directed against the 5' UTR of the mHtt mRNA (siHUNT-1) resulted in reduction in the levels of mHtt mRNA (-75%) and protein (-60%). Long-term in vivo rAAV5-mediated expression of siHUNT-1 in the striatum of R6/1 mice reduced the levels of mHtt mRNA (-78%) and protein (-28%) as determined by quantitative RT-PCR and Western blot analysis, respectively. The reduction in mHtt was concomitant with a reduction in the size and number of neuronal intranuclear inclusions and a small but significant normalization of the steady-state levels of preproenkephalin and dopamine- and cAMP-responsive phosphoprotein 32 kDa mRNA. Finally, bilateral expression of rAAV5-siHUNT-1 resulted in delayed onset of the rear paw clasping phenotype exhibited by the R6/1 mice. These results suggest that a reduction in the levels of striatal mHtt can ameliorate the HD phenotype of R6/1 mice.

Progressive phenotype and nuclear accumulation of an amino-terminal cleavage fragment in a transgenic mouse model with inducible expression of full-length mutant huntingtin

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized behaviorally by chorea, incoordination, and shortened lifespan and neuropathologically by huntingtin inclusions and neuronal degeneration. In order to facilitate studies of pathogenesis and therapeutics, we have generated a new inducible mouse model of HD expressing full-length huntingtin (Htt) using a tetracycline-regulated promoter. In double transgenic mice Htt was expressed widely in the brain under the control of the tet-transactivator (tTA) driven by the prion promoter PrP (in the absence of doxycycline). Mice expressing full-length mutant Htt, but not full-length normal Htt, displayed a progressive behavioral phenotype, consisting of slowed and irregular voluntary movements, gait ataxia, tremor and jerky movements, incoordination, and weight loss, with a shortened lifespan. Neuropathology included prominent intranuclear inclusions in cortex and striatum as well as cytoplasmic aggregates. This phenotype is very similar to the phenotypes of previous transgenic mice expressing N-terminal fragments of mutant Htt. The current HD-transgenic mice had nuclear accumulation of Htt, particularly an approximately 60-kDa fragment, which appears to represent an N-terminal cleavage product. This fragment is smaller than calpain or caspase-derived cleavage products of Htt, but it is comparable to a product, termed cp-A, which accumulates in nuclei of cells in a previously described cell model. This new mouse model may be useful in the future for pathogenic and preclinical therapeutic studies related to HD. The data suggest that proteolytic processing could be a part of the pathogenesis of HD, potentially representing an attractive therapeutic target.

Clinico-pathological rescue of a model mouse of Huntington's disease by siRNA

Huntington's disease (HD) is an autosomal dominant inheritable neurodegenerative disorder currently without effective treatment. It is caused by an expanded polyglutamine (poly Q) tract in the corresponding protein, huntingtin (htt), and therefore suppressing the huntingtin expression in brain neurons is expected to delay the onset and mitigate the severity of the disease. Here, we have used small interfering RNAs (siRNAs) directed against the huntingtin gene to repress the transgenic mutant huntingtin expression in an HD mouse model, R6/2. Results showed that intraventricular injection of siRNAs at an early postnatal period inhibited transgenic huntingtin expression in brain neurons and induced a decrease in the numbers and sizes of intranuclear inclusions in striatal neurons. Treatments using this siRNA significantly prolonged model mice longevity, improved motor function and slowed down the loss of body weight. This work suggests that siRNA-based therapy is promising as a future treatment for HD.

Cdk5 phosphorylation of huntingtin reduces its cleavage by caspases: implications for mutant huntingtin toxicity

Huntington's disease (HD) is a neurodegenerative disorder caused by an expanded polyglutamine (polyQ) tract in the huntingtin (htt) protein. Mutant htt toxicity is exposed after htt cleavage by caspases and other proteases release NH(2)-terminal fragments containing the polyQ expansion. Here, we show htt interacts and colocalizes with cdk5 in cellular membrane fractions. Cdk5 phosphorylates htt at Ser434, and this phosphorylation reduces caspase-mediated htt cleavage at residue 513. Reduced mutant htt cleavage resulting from cdk5 phosphorylation attenuated aggregate formation and toxicity in cells expressing the NH(2)-terminal 588 amino acids (htt588) of mutant htt. Cdk5 activity is reduced in the brains of HD transgenic mice compared with controls. This result can be accounted for by the polyQ-expanded htt fragments reducing the interaction between cdk5 and its activator p35. These data predict that the ability of cdk5 phosphorylation to protect against htt cleavage, aggregation, and toxicity is compromised in cells expressing toxic fragments of htt.

Novel therapeutic targets for Huntington’s disease

Huntington's disease (HD) is a fatal autosomal-dominant disorder involving progressive motor, cognitive and psychiatric symptoms. HD is one of a large family of neurodegenerative diseases caused by a trinucleotide (CAG) repeat mutation, encoding an expanded tract of glutamines in the disease protein. HD was one of the first neurological disorders for which accurate transgenic models were created, allowing mechanisms of pathogenesis to be explored at molecular, cellular and behavioural levels. In the last decade, the understanding of molecular and cellular changes which occur in HD prior to onset of symptoms, and at early and late stages of disease progression, has been greatly expanded. A wide range of potential molecular targets for therapeutic intervention have been identified, associated with a variety of cellular processes including gene transcription, protein trafficking, protein degradation, protein-protein interactions, glutamatergic synaptic transmission, presynaptic signalling, postsynaptic signalling, synaptic plasticity, dopaminergic and neurotrophic modulation of synaptic function, experience-dependent neurogenesis, mitochondrial function and oxidative metabolism. Presymptomatic testing for the HD gene mutation necessitates future development of novel therapeutics aimed at delaying onset of symptoms, as well as slowing or reversing disease progression.

cAMP-response element-binding protein and heat-shock protein 70 additively suppress polyglutamine-mediated toxicity in Drosophila

Gene-specific expansion of polyglutamine-encoding CAG repeats can cause neurodegenerative disorders, including Huntington's disease. It is believed that part of the pathological effect of the expanded protein is due to transcriptional dysregulation. Using Drosophila as a model, we show that cAMP-response element-binding protein (CREB) is involved in expanded polyglutamine-induced toxicity. A mutation in the Drosophila homolog of CREB, dCREB2, enhances lethality due to polyglutamine peptides (polyQ), and an additional copy of dCREB2 partially rescues this lethality. Neuronal expression of expanded polyQ attenuates in vivo CRE-mediated transcription of a reporter gene. As reported previously, overexpression of heat-shock protein 70 (Hsp70) rescues polyglutamine-dependent lethality. However, it does not rescue CREB-mediated transcription. The protective effects of CREB and heat-shock protein 70 against polyQ are additive, suggesting that targeting multiple pathways may be effective for treatment of polyglutamine diseases.