Progressive atrophy of cerebellar Purkinje cell dendrites during aging of the heterozygous staggerer mouse (Rora(+/sg))

Epidermal Loss of RORα Enhances Skin Inflammation in a MC903-Induced Mouse Model of Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease featuring skin barrier dysfunction and immune dysregulation. Previously, we reported that the retinoid-related orphan nuclear receptor RORα was highly expressed in the epidermis of normal skin. We also found that it positively regulated the expression of differentiation markers and skin barrier-related genes in human keratinocytes. In contrast, epidermal RORα expression was downregulated in the skin lesions of several inflammatory skin diseases, including AD. In this study, we generated mouse strains with epidermis-specific Rora ablation to understand the roles of epidermal RORα in regulating AD pathogenesis. Although Rora deficiency did not cause overt macroscopic skin abnormalities at the steady state, it greatly amplified MC903-elicited AD-like symptoms by intensifying skin scaliness, increasing epidermal hyperproliferation and barrier impairment, and elevating dermal immune infiltrates, proinflammatory cytokines, and chemokines. Despite the normal appearance at the steady state, Rora-deficient skin showed microscopic abnormalities, including mild epidermal hyperplasia, increased TEWL, and elevated mRNA expression of Krt16, Sprr2a, and Tslp genes, indicating subclinical impairment of epidermal barrier functions. Our results substantiate the importance of epidermal RORα in partially suppressing AD development by maintaining normal keratinocyte differentiation and skin barrier function.

The effect of aging and chronic microglia activation on the morphology and numbers of the cerebellar Purkinje cells

Reduced cerebellar volume and motor dysfunction have previously been observed in the GFAP-IL6 murine model of chronic neuroinflammation. This study aims to extend these findings by investigating the effect of microglial activation and ageing on the total number of Purkinje cells and the morphology of their dendritic arborization. Through comparison of transgenic GFAP-IL6 mice and their wild-type counterparts at the ages of 12 and 24-months, we were able to investigate the effects of ageing and chronic microglial activation on Purkinje cells. Unbiased stereology was used to estimate the number of microglia in Iba1⁺ stained tissue and Purkinje cells in calbindin stained tissue. Morphological analyses were made using 3D reconstructions of images acquired from the Golgi-stained cerebellar tissue. We found that the total number of microglia increased by approximately 5 times in the cerebellum of GFAP-IL6 mice compared to their WT littermates. The number of Purkinje cells decreased by as much as 50 % in aged wild type mice and 83 % in aged GFAP-IL6 mice. The remaining Purkinje cells in these cohorts were found to have significant reductions in their total dendritic length and number of branching points, indicating how the complexity of the Purkinje cell dendritic arbor reduces through age and inflammation. GFAP-IL6 mice, when compared to WT mice, had higher levels of microglial activation and more profound neurodegenerative changes in the cerebellum. The presence of constitutive IL6 production, driving chronic neuroinflammation, may account for these neurodegenerative changes in GFAP-IL6 mice.

Plastic changes to dendritic spines in the cerebellar and prefrontal cortices underlie the decline in motor coordination and working memory during successful aging

Old age is the last stage of life and by taking a multidimensional view of aging, Neuroscientists have been able to characterize pathological or successful aging. Psychomotor and cognitive performance are recognized as two major domains of successful aging, with a loss of motor coordination and working memory deficits two of the most characteristic features of elderly people. Dendritic spines in both the cerebellar and prefrontal cortices diminish in aging, yet the plastic changes in dendritic spines have not been related to behavioral performance neither the changes in the cerebellar or prefrontal cortices. As such, motor coordination and visuospatial working memory (vsWM) was evaluated here in aged, 22-month-old rats, calculating the density of spines and the proportion of the different types of spines. These animals performed erratically and slowly in a motor coordination-related paradigm, and the vsWM was resolved deficiently. Spine density was reduced in aged animals, and the proportional density of each of the spine types studied diminished in both the brain regions studied. The loss of dendritic spines and particularly, the changes in the proportional density of the different spine types could underlie, at least in part, the behavioral deficits observed during aging. To our knowledge, this is the first study of the plastic changes in different dendritic spine types that might underlie the behavioral alterations in motor and cognitive abilities associated with aging. Further neurochemical and molecular studies will help better understand the functional significance of the plastic changes to dendritic spines in both successful and pathological aging.

Implication of JAK1/STAT3/SOCS3 Pathway in Aging of Cerebellum of Male Rat: Histological and Molecular study

Aging causes morphological and functional changes in the cerebellum. This work aimed to demonstrate the implication of JAK1/STAT3/SOCS3 on aging-induced changes of rat cerebellum. Thirty male rats were divided into: adult (12 months), early senile (24 months) and late senile (32 months) groups. Immunohistochemical reaction of the cerebellum to GFAP and caspase-3 was assessed and the expression of JAK1, STAT3, SOCS3 proteins was also evaluated. TNFα as well as the activities of malondialdehyde (MDA) and reduced glutathione (GSH) in cerebellar tissue were also measured. The cerebellum of late senile rats revealed more degenerative changes than early senile rats in the form of increase in GFAP and caspase-3 immunoreaction. Additionally, there was decrease in JAK1and STAT3 expression in early and late senile rats and increase in SOCS3 when compare early and late senile groups with adult one. Enhancement of TNFα was noticed with aging as well as significant decrease in GSH and increase in MDA in early senile group. Moreover, late senile group revealed significant decrease in GSH and increase in MDA. It could be concluded that aging resulting in variable changes of the cerebellum as detected by morphological changes, immunohistochemical reactions of caspase-3 and GFAP and expression of JAK1/STAT3/SOCS3 proteins. Additionally, inflammatory marker TNFα and the activity of oxidative/antioxidative stress markers; malondialdehyde (MDA) and reduced glutathione (GSH) were also affected with aging.

Loss of RAR-related orphan receptor alpha (RORα) selectively lowers docosahexaenoic acid in developing cerebellum

Deficiency in retinoid acid receptor-related orphan receptor alpha (RORα) of staggerer mice results in extensive granule and Purkinje cell loss in the cerebellum as well as in learned motor deficits, cognition impairments and perseverative tendencies that are commonly observed in autistic spectrum disorder (ASD). The effects of RORα on brain lipid metabolism associated with cerebellar atrophy remain unexplored. The aim of this study is to examine the effects of RORα deficiency on brain phospholipid fatty acid concentrations and compositions. Staggerer mice (Rora^sg/sg) and wildtype littermates (Rora^+/+) were fed n-3 polyunsaturated fatty acids (PUFA) containing diets ad libitum. At 2 months and 7 or more months old, brain total phospholipid fatty acids were quantified by gas chromatography-flame ionization detection. In the cerebellum, all fatty acid concentrations were reduced in 2 months old mice. Since total fatty acid concentrations were significantly different at 2-month-old, we examined changes in fatty acid composition. The composition of ARA was not significantly different between genotypes; though DHA composition remained significantly lowered. Despite cerebellar atrophy at >7-months-old, cerebellar fatty acid concentrations had recovered comparably to wildtype control. Therefore, RORα may be necessary for fatty acid accretions during neurodevelopment. Specifically, the effects of RORα on PUFA metabolisms are region-specific and age-dependent.

Role of Nuclear Receptors in Central Nervous System Development and Associated Diseases

The nuclear hormone receptor (NHR) superfamily is composed of a wide range of receptors involved in a myriad of important biological processes, including development, growth, metabolism, and maintenance. Regulation of such wide variety of functions requires a complex system of gene regulation that includes interaction with transcription factors, chromatin-modifying complex, and the proper recognition of ligands. NHRs are able to coordinate the expression of genes in numerous pathways simultaneously. This review focuses on the role of nuclear receptors in the central nervous system and, in particular, their role in regulating the proper development and function of the brain and the eye. In addition, the review highlights the impact of mutations in NHRs on a spectrum of human diseases from autism to retinal degeneration.

Therapeutic Effect of a Synthetic RORα/γ Agonist in an Animal Model of Autism

Autism is a developmental disorder of the nervous system associated with impaired social communication and interactions as well excessive repetitive behaviors. There are no drug therapies that directly target the pathology of this disease. The retinoic acid receptor-related orphan receptor α (RORα) is a nuclear receptor that has been demonstrated to have reduced expression in many individuals with autism spectrum disorder (ASD). Several genes that have been shown to be downregulated in individuals with ASD have also been identified as putative RORα target genes. Utilizing a synthetic RORα/γ agonist, SR1078, that we identified previously, we demonstrate that treatment of BTBR mice (a model of autism) with SR1078 results in reduced repetitive behavior. Furthermore, these mice display increased expression of ASD-associated RORα target genes in both the brains of the BTBR mice and in a human neuroblastoma cell line treated with SR1078. These data suggest that pharmacological activation of RORα may be a method for treatment of autism.

Toll-Like Receptor 4 Deficiency Impairs Motor Coordination

The cerebellum plays an essential role in balance and motor coordination. Purkinje cells (PCs) are the sole output neurons of the cerebellar cortex and are critical for the execution of its functions, including motor coordination. Toll-like receptor (TLR) 4 is involved in the innate immune response and is abundantly expressed in the central nervous system; however, little is known about its role in cerebellum-related motor functions. To address this question, we evaluated motor behavior in TLR4 deficient mice. We found that TLR4(-∕-) mice showed impaired motor coordination. Morphological analyses revealed that TLR4 deficiency was associated with a reduction in the thickness of the molecular layer of the cerebellum. TLR4 was highly expressed in PCs but not in Bergmann glia or cerebellar granule cells; however, loss of TLR4 decreased the number of PCs. These findings suggest a novel role for TLR4 in cerebellum-related motor coordination through maintenance of the PC population.

Differential recruitment of coregulators to the RORA promoter adds another layer of complexity to gene (dys) regulation by sex hormones in autism

BACKGROUND

Our independent cohort studies have consistently shown the reduction of the nuclear receptor RORA (retinoic acid-related orphan receptor-alpha) in lymphoblasts as well as in brain tissues from individuals with autism spectrum disorder (ASD). Moreover, we have found that RORA regulates the gene for aromatase, which converts androgen to estrogen, and that male and female hormones regulate RORA in opposite directions, with androgen suppressing RORA, suggesting that the sexually dimorphic regulation of RORA may contribute to the male bias in ASD. However, the molecular mechanisms through which androgen and estrogen differentially regulate RORA are still unknown.

METHODS

Here we use functional knockdown of hormone receptors and coregulators with small interfering RNA (siRNA) to investigate their involvement in sex hormone regulation of RORA in human neuronal cells. Luciferase assays using a vector containing various RORA promoter constructs were first performed to identify the promoter regions required for inverse regulation of RORA by male and female hormones. Sequential chromatin immunoprecipitation methods followed by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) analyses of RORA expression in hormone-treated SH-SY5Y cells were then utilized to identify coregulators that associate with hormone receptors on the RORA promoter. siRNA-mediated knockdown of interacting coregulators was performed followed by qRT-PCR analyses to confirm the functional requirement of each coregulator in hormone-regulated RORA expression.

RESULTS

Our studies demonstrate the direct involvement of androgen receptor (AR) and estrogen receptor (ER) in the regulation of RORA by male and female hormones, respectively, and that the promoter region between -10055 bp and -2344 bp from the transcription start site of RORA is required for the inverse hormonal regulation. We further show that AR interacts with SUMO1, a reported suppressor of AR transcriptional activity, whereas ERα interacts with the coactivator NCOA5 on the RORA promoter. siRNA-mediated knockdown of SUMO1 and NCOA5 attenuate the sex hormone effects on RORA expression.

CONCLUSIONS

AR and SUMO1 are involved in the suppression RORA expression by androgen, while ERα and NCOA5 collaborate in the up-regulation of RORA by estrogen. While this study offers a better understanding of molecular mechanisms involved in sex hormone regulation of RORA, it also reveals another layer of complexity with regard to gene regulation in ASD. Inasmuch as coregulators are capable of interacting with a multitude of transcription factors, aberrant expression of coregulator proteins, as we have seen previously in lymphoblasts from individuals with ASD, may contribute to the polygenic nature of gene dysregulation in ASD.

Mature Purkinje cells require the retinoic acid-related orphan receptor-α (RORα) to maintain climbing fiber mono-innervation and other adult characteristics

Neuronal maturation during development is a multistep process regulated by transcription factors. The transcription factor RORα (retinoic acid-related orphan receptor α) is necessary for early Purkinje cell (PC) maturation but is also expressed throughout adulthood. To identify the role of RORα in mature PCs, we used Cre-lox mouse genetic tools in vivo that delete it specifically from PCs between postnatal days 10-21. Up to 14 d of age, differences between mutant and control PCs were not detectable: both were mono-innervated by climbing fibers (CFs) extending along their well-developed dendrites with spiny branchlets. By week 4, mutant mice were ataxic, some PCs had died, and remaining PC soma and dendrites were atrophic, with almost complete disappearance of spiny branchlets. The innervation pattern of surviving RORα-deleted PCs was abnormal with several immature characteristics. Notably, multiple functional CF innervation was reestablished on these mature PCs, simultaneously with the relocation of CF contacts to the PC soma and their stem dendrite. This morphological modification of CF contacts could be induced even later, using lentivirus-mediated depletion of rora from adult PCs. These data show that the late postnatal expression of RORα cell-autonomously regulates the maintenance of PC dendritic complexity, and the CF innervation status of the PC (dendritic vs somatic contacts, and mono-innervation vs multi-innervation). Thus, the differentiation state of adult neurons is under the control of transcription factors; and in their absence, adult neurons lose their mature characteristics and acquire some characteristics of an earlier developmental stage.

Genome-wide identification of transcriptional targets of RORA reveals direct regulation of multiple genes associated with autism spectrum disorder

BACKGROUND

We have recently identified the nuclear hormone receptor RORA (retinoic acid-related orphan receptor-alpha) as a novel candidate gene for autism spectrum disorder (ASD). Our independent cohort studies have consistently demonstrated the reduction of RORA transcript and/or protein levels in blood-derived lymphoblasts as well as in the postmortem prefrontal cortex and cerebellum of individuals with ASD. Moreover, we have also shown that RORA has the potential to be under negative and positive regulation by androgen and estrogen, respectively, suggesting the possibility that RORA may contribute to the male bias of ASD. However, little is known about transcriptional targets of this nuclear receptor, particularly in humans.

METHODS

Here we identify transcriptional targets of RORA in human neuronal cells on a genome-wide level using chromatin immunoprecipitation (ChIP) with an anti-RORA antibody followed by whole-genome promoter array (chip) analysis. Selected potential targets of RORA were then validated by an independent ChIP followed by quantitative PCR analysis. To further demonstrate that reduced RORA expression results in reduced transcription of RORA targets, we determined the expression levels of the selected transcriptional targets in RORA-deficient human neuronal cells, as well as in postmortem brain tissues from individuals with ASD who exhibit reduced RORA expression.

RESULTS

The ChIP-on-chip analysis reveals that RORA1, a major isoform of RORA protein in human brain, can be recruited to as many as 2,764 genomic locations corresponding to promoter regions of 2,544 genes across the human genome. Gene ontology analysis of this dataset of genes that are potentially directly regulated by RORA1 reveals statistically significant enrichment in biological functions negatively impacted in individuals with ASD, including neuronal differentiation, adhesion and survival, synaptogenesis, synaptic transmission and plasticity, and axonogenesis, as well as higher level functions such as development of the cortex and cerebellum, cognition, memory, and spatial learning. Independent ChIP-quantitative PCR analyses confirm binding of RORA1 to promoter regions of selected ASD-associated genes, including A2BP1, CYP19A1, ITPR1, NLGN1, and NTRK2, whose expression levels (in addition to HSD17B10) are also decreased in RORA1-repressed human neuronal cells and in prefrontal cortex tissues from individuals with ASD.

CONCLUSIONS

Findings from this study indicate that RORA transcriptionally regulates A2BP1, CYP19A1, HSD17B10, ITPR1, NLGN1, and NTRK2, and strongly suggest that reduction of this sex hormone-sensitive nuclear receptor in the brain causes dysregulated expression of these ASD-relevant genes as well as their associated pathways and functions which, in turn, may contribute to the underlying pathobiology of ASD.

Silencing mutant ataxin-3 rescues motor deficits and neuropathology in Machado-Joseph disease transgenic mice

Machado-Joseph disease (MJD) or spinocerebellar ataxia type 3 (SCA3) is an autosomal dominantly-inherited neurodegenerative disorder caused by the over-repetition of a CAG codon in the MJD1 gene. This expansion translates into a polyglutamine tract that confers a toxic gain-of-function to the mutant protein – ataxin-3, leading to neurodegeneration in specific brain regions, with particular severity in the cerebellum. No treatment able to modify the disease progression is available. However, gene silencing by RNA interference has shown promising results. Therefore, in this study we investigated whether lentiviral-mediated allele-specific silencing of the mutant ataxin-3 gene, after disease onset, would rescue the motor behavior deficits and neuropathological features in a severely impaired transgenic mouse model of MJD. For this purpose, we injected lentiviral vectors encoding allele-specific silencing-sequences (shAtx3) into the cerebellum of diseased transgenic mice expressing the targeted C-variant of mutant ataxin-3 present in 70% of MJD patients. This variation permits to discriminate between the wild-type and mutant forms, maintaining the normal function of the wild-type allele and silencing only the mutant form. Quantitative analysis of rotarod performance, footprint and activity patterns revealed significant and robust alleviation of gait, balance (average 3-fold increase of rotarod test time), locomotor and exploratory activity impairments in shAtx3-injected mice, as compared to control ones injected with shGFP. An important improvement of neuropathology was also observed, regarding the number of intranuclear inclusions, calbindin and DARPP-32 immunoreactivity, fluorojade B and Golgi staining and molecular and granular layers thickness. These data demonstrate for the first time the efficacy of gene silencing in blocking the MJD-associated motor-behavior and neuropathological abnormalities after the onset of the disease, supporting the use of this strategy for therapy of MJD.

The expanding genomic landscape of autism: discovering the 'forest' beyond the 'trees'

Autism spectrum disorders are neurodevelopmental disorders characterized by significant deficits in reciprocal social interactions, impaired communication and restricted, repetitive behaviors. As autism spectrum disorders are among the most heritable of neuropsychiatric disorders, much of autism research has focused on the search for genetic variants in protein-coding genes (i.e., the 'trees'). However, no single gene can account for more than 1% of the cases of autism spectrum disorders. Yet, genome-wide association studies have often identified statistically significant associations of genetic variations in regions of DNA that do not code for proteins (i.e., intergenic regions). There is increasing evidence that such noncoding regions are actively transcribed and may participate in the regulation of genes, including genes on different chromosomes. This article summarizes evidence that suggests that the research spotlight needs to be expanded to encompass far-reaching gene-regulatory mechanisms that include a variety of epigenetic modifications, as well as noncoding RNA (i.e., the 'forest'). Given that noncoding RNA represents over 90% of the transcripts in most cells, we may be observing just the 'tip of the iceberg' or the 'edge of the forest' in the genomic landscape of autism.

Piperine and curcumin exhibit synergism in attenuating D-galactose induced senescence in rats

Aging is associated with progressive decline in mental abilities and functional capacities. Postmitotic tissues are most vulnerable to alteration due to oxidative damage leading to behavioral and biochemical changes. We hypothesized that the anatomical and functional facets of the brain could be protected with powerful antioxidants such as piperine and curcumin by examining their effects individually and in combination in delaying senescence induced by d-galactose. Young adult male Wistar rats were treated with piperine (12 mg/kg) alone, and curcumin (40 mg/kg) alone; and in combination for a period of 49 days by the oral route with treatment being initiated a week prior to d-galactose (60 mg/kg, i.p.). A control group, d-galactose alone and naturally aged control were also evaluated. Behavioral tests, hippocampal volume, CA1 neuron number, oxidative parameters, formation of lipofuscin like autofluorescent substances, neurochemical estimation, and histopathological changes in CA1 region of hippocampus were established. Our results suggest that the combination exerted a superior response compared to monotherapy as evidenced by improved spatial memory, reduced oxidative burden, reduced accumulation of lipofuscin; improvement in signaling, increase in hippocampal volume and protection of hippocampal neurons. We speculate that the powerful antioxidant nature of both, augmented response of curcumin in the presence of piperine and enhanced serotoninergic signaling was responsible for improved cognition and prevention in senescence.

Is retinoic acid-related orphan receptor-alpha (RORA) a target for gene-environment interactions contributing to autism?

It is becoming increasingly clear that gene-environment interactions are risk factors for autism. However, there is limited information regarding the susceptibility of specific autism candidate genes to dysregulation by environmental factors, and even less information on the types of environmental agents that may lead to increased risk for autism. Based on our published studies, I propose that the demonstrated responsiveness of RORA to sex hormones makes it a prime target for disruption by endocrine disrupting compounds.

Chronic treadmill exercise in rats delicately alters the Purkinje cell structure to improve motor performance and toxin resistance in the cerebellum

Although exercise usually improves motor performance, the underlying cellular changes in the cerebellum remain to be elucidated. This study aimed to investigate whether and how chronic treadmill exercise in young rats induced Purkinje cell changes to improve motor performance and rendered the cerebellum less vulnerable to toxin insults. After 1-wk familiarization of treadmill running, 6-wk-old male Wistar rats were divided into exercise and sedentary groups. The exercise group was then subjected to 8 wk of exercise training at moderate intensity. The rotarod test was carried out to evaluate motor performance. Purkinje cells in cerebellar slices were visualized by lucifer yellow labeling in single neurons and by calbindin immunostaining in groups of neurons. Compared with sedentary control rats, exercised rats not only performed better in the rotarod task, but also showed finer Purkinje cell structure (higher dendritic volume and spine density with the same dendritic field). The exercise-improved cerebellar functions were further evaluated by monitoring the long-lasting effects of intraventricular application of OX7-saporin. In the sedentary group, OX7-saporin treatment retarded the rotarod performance and induced ∼60% Purkinje cell loss in 3 wk. As a comparison, the exercise group showed much milder injuries in the cerebellum by the same toxin treatment. In conclusion, exercise training in young rats increased the dendritic density of Purkinje cells, which might play an important role in improving the motor performance. Furthermore, as Purkinje cells in the exercise group were relatively toxin resistant, the exercised rats showed good motor performance, even under toxin-treated conditions.

From genes to environment: using integrative genomics to build a "systems-level" understanding of autism spectrum disorders

Autism spectrum disorders (ASD) are pervasive neurodevelopmental disorders that affect an estimated 1 in 110 individuals. Although there is a strong genetic component associated with these disorders, this review focuses on the multifactorial nature of ASD and how different genome-wide (genomic) approaches contribute to our understanding of autism. Emphasis is placed on the need to study defined ASD phenotypes as well as to integrate large-scale "omics" data in order to develop a "systems-level" perspective of ASD, which in turn is necessary to allow predictions regarding responses to specific perturbations and interventions.

Age-related Purkinje cell death is steroid dependent: RORα haplo-insufficiency impairs plasma and cerebellar steroids and Purkinje cell survival

A major problem of ageing is progressive impairment of neuronal function and ultimately cell death. Since sex steroids are neuroprotective, their decrease with age may underlie age-related neuronal degeneration. To test this, we examined Purkinje cell numbers, plasma sex steroids and cerebellar neurosteroid concentrations during normal ageing (wild-type mice, WT), in our model of precocious ageing (Rora(+/sg), heterozygous staggerer mice in which expression of the neuroprotective factor RORα is disrupted) and after long-term hormone insufficiency (WT post-gonadectomy). During normal ageing (WT), circulating sex steroids declined prior to or in parallel with Purkinje cell loss, which began at 18 months of age. Although Purkinje cell death was advanced in WT long-term steroid deficiency, this premature neuronal loss did not begin until 9 months, indicating that vulnerability to sex steroid deficiency is a phenomenon of ageing Purkinje neurons. In precocious ageing (Rora(+/sg)), circulating sex steroids decreased prematurely, in conjunction with marked Purkinje cell death from 9 months. Although Rora(+/sg) Purkinje cells are vulnerable through their RORα haplo-insufficiency, it is only as they age (after 9 months) that sex steroid failure becomes critical. Finally, cerebellar neurosteroids did not decrease with age in either genotype or gender; but were profoundly reduced by 3 months in male Rora(+/sg) cerebella, which may contribute to the fragility of their Purkinje neurons. These data suggest that ageing Purkinje cells are maintained by circulating sex steroids, rather than local neurosteroids, and that in Rora(+/sg) their age-related death is advanced by premature sex steroid loss induced by RORα haplo-insufficiency.

Sex hormones in autism: androgens and estrogens differentially and reciprocally regulate RORA, a novel candidate gene for autism

Autism, a pervasive neurodevelopmental disorder manifested by deficits in social behavior and interpersonal communication, and by stereotyped, repetitive behaviors, is inexplicably biased towards males by a ratio of ∼4∶1, with no clear understanding of whether or how the sex hormones may play a role in autism susceptibility. Here, we show that male and female hormones differentially regulate the expression of a novel autism candidate gene, retinoic acid-related orphan receptor-alpha (RORA) in a neuronal cell line, SH-SY5Y. In addition, we demonstrate that RORA transcriptionally regulates aromatase, an enzyme that converts testosterone to estrogen. We further show that aromatase protein is significantly reduced in the frontal cortex of autistic subjects relative to sex- and age-matched controls, and is strongly correlated with RORA protein levels in the brain. These results indicate that RORA has the potential to be under both negative and positive feedback regulation by male and female hormones, respectively, through one of its transcriptional targets, aromatase, and further suggest a mechanism for introducing sex bias in autism.

Aging of cerebellar Purkinje cells

Cerebellar Purkinje cells (PCs), the sole output neurons in the cerebellar cortex, play an important role in the cerebellar circuit. PCs appear to be rather sensitive to aging, exhibiting significant changes in both morphology and function during senescence. This article reviews such changes during the normal aging process, including a decrease in the quantity of cells, atrophy in the soma, retraction in the dendritic arborizations, degeneration in the subcellular organelles, a decline in synapse density, disorder in the neurotransmitter system, and alterations in electrophysiological properties. Although these deteriorative changes occur during aging, compensatory mechanisms exist to counteract the impairments in the aging PCs. The possible neural mechanisms underlying these changes and potential preventive treatments are discussed.

Global methylation profiling of lymphoblastoid cell lines reveals epigenetic contributions to autism spectrum disorders and a novel autism candidate gene, RORA, whose protein product is reduced in autistic brain

Autism is currently considered a multigene disorder with epigenetic influences. To investigate the contribution of DNA methylation to autism spectrum disorders, we have recently completed large-scale methylation profiling by CpG island microarray analysis of lymphoblastoid cell lines derived from monozygotic twins discordant for diagnosis of autism and their nonautistic siblings. Methylation profiling revealed many candidate genes differentially methylated between discordant MZ twins as well as between both twins and nonautistic siblings. Bioinformatics analysis of the differentially methylated genes demonstrated enrichment for high-level functions including gene transcription, nervous system development, cell death/survival, and other biological processes implicated in autism. The methylation status of 2 of these candidate genes, BCL-2 and retinoic acid-related orphan receptor alpha (RORA), was further confirmed by bisulfite sequencing and methylation-specific PCR, respectively. Immunohistochemical analyses of tissue arrays containing slices of the cerebellum and frontal cortex of autistic and age- and sex-matched control subjects revealed decreased expression of RORA and BCL-2 proteins in the autistic brain. Our data thus confirm the role of epigenetic regulation of gene expression via differential DNA methylation in idiopathic autism, and furthermore link molecular changes in a peripheral cell model with brain pathobiology in autism.

Differential effects and rates of normal aging in cerebellum and hippocampus

Cognitive functions show many alternative outcomes and great individual variation during normal aging. We examined learning over the adult life span in CBA mice, along with morphological and electrophysiological substrates. Our aim was to compare cerebellum-dependent delay eyeblink classical conditioning and hippocampus-dependent contextual fear conditioning in the same animals using the same conditioned and unconditioned stimuli for eyeblink and fear conditioning. In a subset of the behaviorally tested mice, we used unbiased stereology to estimate the total number of Purkinje neurons in cerebellar cortex and pyramidal neurons in the hippocampus. Several forms of synaptic plasticity were assessed at different ages in CBA mice: long-term depression (LTD) in both cerebellum and hippocampus and NMDA-mediated long-term potentiation (LTP) and voltage-dependent calcium channel LTP in hippocampus. Forty-four CBA mice tested at one of five ages (4, 8, 12, 18, or 24 months) demonstrated statistically significant age differences in cerebellum-dependent delay eyeblink conditioning, with 24-month mice showing impairment in comparison with younger mice. These same CBA mice showed no significant differences in contextual or cued fear conditioning. Stereology indicated significant loss of Purkinje neurons in the 18- and 24-month groups, whereas pyramidal neuron numbers were stable across age. Slice electrophysiology recorded from an additional 48 CBA mice indicated significant deficits in LTD appearing in cerebellum between 4 and 8 months, whereas 4- to 12-month mice demonstrated similar hippocampal LTD and LTP values. Our results demonstrate that processes of aging impact brain structures and associated behaviors differentially, with cerebellum showing earlier senescence than hippocampus.

Retinoid-related orphan receptors (RORs): critical roles in development, immunity, circadian rhythm, and cellular metabolism

The last few years have witnessed a rapid increase in our knowledge of the retinoid-related orphan receptors RORα, -β, and -γ (NR1F1-3), their mechanism of action, physiological functions, and their potential role in several pathologies. The characterization of ROR-deficient mice and gene expression profiling in particular have provided great insights into the critical functions of RORs in the regulation of a variety of physiological processes. These studies revealed that RORα plays a critical role in the development of the cerebellum, that both RORα and RORβ are required for the maturation of photoreceptors in the retina, and that RORγ is essential for the development of several secondary lymphoid tissues, including lymph nodes. RORs have been further implicated in the regulation of various metabolic pathways, energy homeostasis, and thymopoiesis. Recent studies identified a critical role for RORγ in lineage specification of uncommitted CD4⁺ T helper cells into Th17 cells. In addition, RORs regulate the expression of several components of the circadian clock and may play a role in integrating the circadian clock and the rhythmic pattern of expression of downstream (metabolic) genes. Study of ROR target genes has provided insights into the mechanisms by which RORs control these processes. Moreover, several reports have presented evidence for a potential role of RORs in several pathologies, including osteoporosis, several autoimmune diseases, asthma, cancer, and obesity, and raised the possibility that RORs may serve as potential targets for chemotherapeutic intervention. This prospect was strengthened by recent evidence showing that RORs can function as ligand-dependent transcription factors.

Pathogenic mechanisms of a polyglutamine-mediated neurodegenerative disease, spinocerebellar ataxia type 1

Spinocerebellar ataxia type 1 (SCA1) is one of nine inherited neurodegenerative diseases caused by the expansion of a CAG trinucleotide repeat encoding a polyglutamine tract. SCA1 patients lose motor coordination and develop slurred speech, spasticity, and cognitive impairments. Difficulty with coordinating swallowing and breathing eventually causes death. Genetic evidence indicates that the disease mutation induces a toxic gain of function in the SCA1 encoded protein ATXN1. The discovery that residues in ATXN1 outside of the polyglutamine tract are crucial for pathogenesis hinted that alterations in the normal function of this protein are linked to its toxicity. Biochemical and genetic studies provide evidence that the polyglutamine expansion enhances interactions that are normally regulated by phosphorylation at Ser(776) and a subsequent alteration in its interaction with other cellular proteins. Moreover, the finding that other ATXN1 interactions are decreased in disease suggests that the polyglutamine expansion contributes to disease by both a gain-of-function mechanism and partial loss of function.

Favorable effects of a prolonged treatment with melatonin on the level of oxidative damage and neurodegeneration in senescence-accelerated mice

Senescence-accelerated mice (SAMP8) and senescence-accelerated resistant mice (SAMR1) were studied at 5 and 10 months of age, respectively. In the animals, neurodegenerative processes and how they were influenced by melatonin were examined. Melatonin (10 mg/kg) or vehicle (ethanol at 0.066%) treatments were administrated from the age of 1 to 9 months in the drinking water. Differences in the neurodegenerative markers examined were found between the two strains with a more damaged protein, phosphorylated Tau at Ser392, increased neurofibrillary tangles (NT) and higher alpha-synuclein expression in SAMP8 versus SAMR1 mice overall, when the mice were 10 months of age. Changes in density of receptors and oxidative stress-related signaling with age were found in the brains of SAM strains at 10 months as shown by a marked decrease in the level of MT-1 melatonin receptor and retinoic acid receptor-related orphan receptor (ROR)-alpha1. This diminution was earlier and more pronounced in SAMP8 mice. Likewise, the levels of nuclear factor-kappa B (NF-kB) transcriptional factor were higher in SAMP8 mice compared with SAMR1 mice regardless of age confirming the direct role of oxidative stress in the aging process. Treatment with melatonin in SAMP8 and SAMR1 mice reduced the neurodegenerative changes with an increase of ROR-alpha1 levels without an apparent influence in the levels of MT-1 receptor. However, different melatonin effects on NF-kB signaling were observed suggesting that NF-kB could trigger inflammatory processes in a different way, being SAM strain-dependent and associated with age-related oxidative stress levels. The effectiveness of melatonin in improving age-related neural impairments is corroborated.

Serial analysis of gene expression profiles of adult and aged mouse cerebellum

Changes in specific cerebellar molecules contribute to impaired balance and motor coordination frequently observed in aged individuals. Serial analysis of gene expression (SAGE) was used to construct six libraries from adult and aged mouse cerebella. Combined unique tags for each group revealed 325 genes that were differentially expressed (p-chance</=0.05). Four additional tests (mixed effect model, t-test, Wilcoxon rank-sum and z-test) were used to reduce the likelihood of false positives. The first two tests accounted for intra-group variation, the third for outliers and the fourth was a probability test similar to p-chance. Twenty-nine genes were identified by at least two of the four tests as being differentially expressed in the aged cerebellum. Three of these genes are, as yet, unidentified and likely to represent novel genes involved in the cerebellar aging process. The largest group of genes revealed by the combined tests was related to glycerophospholipid metabolism, and included phosphoethanolamine, phosphatidic acid and diacylglycerol synthetic enzymes, suggesting that alterations in lipid biosynthesis may, at least in part, underlie changes in conductivity in the aged cerebellum.

RORalpha-mediated Purkinje cell development determines disease severity in adult SCA1 mice

Spinocerebellar ataxia type 1 (SCA1) is one of nine inherited, typically adult onset, polyglutamine neurodegenerative diseases. To examine whether development impacts SCA1, we used a conditional transgenic mouse model of SCA1 to delay the postnatal expression of mutant ATXN1 until after completion of cerebellar development. Delayed postnatal expression of mutant ATXN1 led to a substantial reduction in severity of disease in adults in comparison with early postnatal gene expression. This was linked to a destabilization of RORalpha, a transcription factor critical for cerebellar development. In SCA1 mice, there was a depletion of RORalpha and a reduction in expression of genes controlled by RORalpha. Partial loss of RORalpha enhanced mutant ATXN1 pathogenicity. Additionally, evidence points to the existence of a complex containing ATXN1, RORalpha, and the RORalpha coactivator Tip60. These studies indicate RORalpha and Tip60 have a role in SCA1 and suggest a mechanism by which compromising cerebellar development contributes to severity of neurodegeneration in an adult.

RORalpha, a pivotal nuclear receptor for Purkinje neuron survival and differentiation: from development to ageing

RORalpha (Retinoid-related Orphan Receptor) is a transcription factor belonging to the superfamily of nuclear receptors. The spontaneous staggerer (sg) mutation, which consists of a deletion in the Rora gene, has been shown to cause the loss of function of the RORalpha protein. The total loss of RORalpha expression leads to cerebellar developmental defects, particularly to a dramatic decreased survival of Purkinje cells and an early block in the differentiation process. This review focuses on recent studies which position RORalpha as a pivotal factor controlling Purkinje cell survival and differentiation, from development to ageing.

Human retinoic acid receptor-related orphan receptor alpha1 overexpression protects neurones against oxidative stress-induced apoptosis

Retinoic acid receptor-related orphan receptor alpha (RORalpha) is a transcription factor belonging to the superfamily of nuclear receptors. Disruption of the Rora gene in the mouse results in a defect in the development of Purkinje cells leading to a cerebellar atrophy, which suggests a neuroprotective role for RORalpha. To test this hypothesis, the survival rate of lentiviral-mediated human RORalpha1-overexpressing neurones has been evaluated in response to different stressors disturbing the redox homeostasis, such as beta-amyloid peptide, c(2)-ceramide and H(2)O(2). We show that overexpression of human RORalpha1 provides neuroprotection by increasing the expression of the antioxidant proteins glutathione peroxidase 1 and peroxiredoxin 6, leading to a reduction in the accumulation of stress-induced reactive oxygen species. We further demonstrate that the neuroprotective effect of RORalpha is predominantly mediated by glutathione peroxidase 1 and peroxiredoxin 6. These results suggest a new role for RORalpha in the control of the neuronal oxidative stress and thus represents a new transcription factor of interest in the regulation of reactive oxygen species-induced neurodegenerative processes during ageing.

Retinoid-related orphan receptor alpha controls the early steps of Purkinje cell dendritic differentiation

Dendritic differentiation involves both regressive and growth events. The mechanisms controlling the regressive events are poorly understood. This study is aimed at determining the role of the nuclear receptor retinoid-related orphan receptor alpha (RORalpha) in Purkinje cell (PC) dendritic differentiation in organotypic cultures. As observed in vivo, in these cultures, fusiform PCs with embryonic bipolar shape undergo regression before the outgrowth of the ultimate dendritic tree. We show that lentiviral-mediated hRORalpha1 overexpression in fusiform PCs leads to a cell-autonomous accelerated progression of dendritic differentiation. In addition, RORalpha is necessary for the PC regressive events: whereas staggerer RORalpha-deficient PCs remain in the embryonic fusiform stage, replacement of hRORalpha1 restores normal dendritogenesis. These results demonstrate that RORalpha expression in fusiform PCs is crucial for the dendritic regression and progression of the following step of extension of dendritic processes. However, it does not seem to participate to the last stage of dendritic growth. This study identifies RORalpha as a nuclear receptor crucial for the control of dendritic remodeling during development.

Age-related changes of structures in cerebellar cortex of cat

We studied the structures of the cerebellar cortex of young adult and old cats for age-related changes, which were statistically analysed. Nissl staining was used to visualize the cortical neurons. The immunohistochemical method was used to display glial fibrillary acidic protein (GFAP)-immunoreactive (IR) astrocytes and neurofilament-immunoreactive (NF-IR) neurons. Under the microscope, the thickness of the cerebellar cortex was measured; and the density of neurons in all the layers as well as that of GFAP-IR cells in the granular layer was analysed. Compared with young adult cats, the thickness of the molecular layer and total cerebellar cortex was significantly decreased in old cats, and that of the granular layer increased. The density of neurons in each layer was significantly lower in old cats than in young adult ones. Astrocytes in old cats were significantly denser than in young adult ones, and accom-panied by evident hypertrophy of the cell bodies and enhanced immunoreaction of GFAP substance. Purkinje cells (PCs) in old cats showed much fewer NF-IR dendrites than those in young adults. The above findings indicate a loss of neurons and decrease in the number of dendrites of the PCs in the aged cerebellar cortex, which might underlie the functional decline of afferent efficacy and information integration in the senescent cerebellum. An age-dependent enhancement of activity of the astrocytes may exert a protective effect on neurons in the aged cerebellum.

Stereological estimation of Purkinje neuron number in C57BL/6 mice and its relation to associative learning

Cerebellar Purkinje neurons are among the most vulnerable neurons in the CNS. Impairment in Purkinje neurons has consequences for cerebellar cortical-dependent forms of behavior. The primary aim of this study was to evaluate Purkinje neuron number over the lifespan of C57BL/6 mice. Stereological estimates of the total number of Purkinje neurons in cerebellar cortex were made in 25 C57BL/6 mice aged 4, 8, 12, 18, and 24 months. Delay eyeblink classical conditioning to a white noise conditioned stimulus was also assessed for 10 daily sessions. Statistically significant age differences in Purkinje neuron number were observed beginning at 18 months. Delay eyeblink conditioning also showed significant age-related impairment, at least some of which resulted from age-related deficits in hearing. Eliminating the hearing-impaired 18- and 24-month-old mice from the analysis, the correlation between Purkinje neuron number and rate of conditioning was -0.435 (P=0.053) in 15 younger mice aged 4-12 months. Purkinje neurons are one of the few types of neurons showing significant age-associated loss. Results indicate that individual variation in Purkinje neuron number is related to eyeblink conditioning in young organisms suggesting that reserves of neuron numbers against which individuals draw are defined early in life.

Retinoid-related Orphan Receptors (RORs): Roles in Cellular Differentiation and Development

Retinoid-related orphan receptors RORalpha, -beta, and -gamma are transcription factors belonging to the steroid hormone receptor superfamily. During embryonic development RORs are expressed in a spatial and temporal manner and are critical in the regulation of cellular differentiation and the development of several tissues. RORalpha plays a key role in the development of the cerebellum particularly in the regulation of the maturation and survival of Purkinje cells. In RORalpha-deficient mice, the reduced production of sonic hedgehog by these cells appears to be the major cause of the decreased proliferation of granule cell precursors and the observed cerebellar atrophy. RORalpha has been implicated in the regulation of a number of other physiological processes, including bone formation. RORbeta expression is largely restricted to several regions of the brain, the retina, and pineal gland. Mice deficient in RORbeta develop retinal degeneration that results in blindness. RORgamma is essential for lymph node organogenesis. In the intestine RORgamma is required for the formation of several other lymphoid tissues: Peyer's patches, cryptopatches, and isolated lymphoid follicles. RORgamma plays a key role in the generation of lymphoid tissue inducer (LTi) cells that are essential for the development of these lymphoid tissues. In addition, RORgamma is a critical regulator of thymopoiesis. It controls the differentiation of immature single-positive thymocytes into double-positive thymocytes and promotes the survival of double-positive thymocytes by inducing the expression of the anti-apoptotic gene Bcl-X(L). Interestingly, all three ROR receptors appear to play a role in the control of circadian rhythms. RORalpha positively regulates the expression of Bmal1, a transcription factor that is critical in the control of the circadian clock. This review intends to provide an overview of the current status of the functions RORs have in these biological processes.

A role for both wild-type and expanded ataxin-7 in transcriptional regulation

Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disease primarily affecting the brainstem, retina and Purkinje cells of the cerebellum. The disease is caused by a polyglutamine expansion in ataxin-7, a protein found in two complexes TFTC and STAGA, involved in transcriptional regulation. Transcriptional dysregulation has been implicated in the pathology of several polyglutamine diseases. In this paper, we analyzed the effect of both wild-type and expanded ataxin-7 on transcription driven by the co-activator CBP and the Purkinje cell expressed nuclear receptor RORalpha1. We could show that transcription mediated by both CBP and RORalpha1 was repressed by expanded ataxin-7. Interestingly, repression of transcription could also be observed with wild-type full-length ataxin-7, not only on CBP- and RORalpha1-mediated transcription, but also on basal transcription. The repression could be counteracted by inhibition of deacetylation, suggesting that ataxin-7 may act as a repressor of transcription by inhibiting the acetylation activity of TFTC and STAGA.

Dynamics and pathology of dendritic spines

Dendritic spines are key players in information processing in the brain. Changes in spine shape and wholesale spine turnover provide mechanisms for modifying existing synaptic connections and altering neuronal connectivity. Although neuronal cell death in acute and chronic neurodegenerative diseases is clearly an important factor in decline of cognitive or motor function, loss of dendritic spines, in the absence of cell death, may also contribute to impaired brain function in these diseases, as well as in psychiatric disorders and aging. Because spines can function in neuroprotection in vitro, advances toward a molecular understanding of spine maintenance might one day aid in the design of therapies to minimize neurological damage following excitotoxic injury. In addition, progress in defining the biochemical basis of spine development and stabilization may yield insights into mental retardation and psychiatric disorders.

Digital Transcriptome Analysis in the Aging Cerebellum

Serial analysis of gene expression (SAGE) was used to identify and quantify all expressed cerebellar genes in the adult (P92) and aged (P810) C57BL/6J mouse cerebellum. A "closest-neighbor" algorithm was used to differentiate low abundance tags from possible sequencing errors in both libraries. Unique tags were categorized into four groups: (1) novel genes; (2) ESTs; (3) RIKEN, KIA, and hypothetical genes; and (4) known genes. Known genes were further subdivided into functional categories based on the gene ontology classification, using a web-based program developed in this laboratory (MmSAGEClass). Comparison of adult and aged cerebellar libraries revealed several genes that were differentially expressed, including growth hormone and prolactin, both of which were markedly decreased in the aged cerebellum. In addition, several tags showing differential expression were not identified in the Unigene database and are likely to represent novel genes. The present SAGE data on the aged cerebellar transcriptome may reveal candidate genes involved in the aging process.

The “CholesteROR” Protective Pathway in the Vascular System

Retinoic acid receptor-related Orphan Receptor α (RORα) is a member of the nuclear hormone receptor superfamily. RORα has long been considered as a constitutive activator of transcription in the absence of exogenous ligand; however, cholesterol has recently been identified as a natural ligand of RORα. The spontaneous staggerer (sg/sg) mutation is a deletion in the Rora gene that prevents the translation of the ligand-binding domain (LBD), leading to the loss of RORα activity. The homozygous Rora sg/sg mutant mouse, of which the most obvious phenotype is ataxia associated with cerebellar degeneration, also displays a variety of other phenotypes, including several vascular ones; in particular, dysfunction of smooth muscle cells and enhanced susceptibility to atherosclerosis. Moreover, RORα appears to participate in the regulation of plasma cholesterol levels, and has been shown to positively regulate apolipoprotein (apo)A-I and apoC-III gene expression. Yet its activity is regulated by cholesterol itself, making RORα an intracellular cholesterol target.

Immunohistochemical characterization of the orphan nuclear receptor ROR alpha in the mouse nervous system

ROR alpha is an orphan nuclear receptor. A deletion mutation in the ROR alpha gene leads to severe cerebellar defects, known as the staggerer mutant mouse. Although previous in situ hybridization (ISH) studies have shown that ROR alpha is highly expressed in the cerebellum, especially in Purkinje cells, and in the thalamus, sufficient immunohistochemical (IHC) study has not yet been presented. I demonstrate here the IHC analysis of ROR alpha using a specific anti-ROR alpha antibody, in adult and developing mouse nervous system. ROR alpha immunoreactivity was observed in the Purkinje cell and molecular layers of the cerebellum. The co-localization of ROR alpha with calbindin D(28K) (CaBP) and parvalbumin indicates that ROR alpha-positive cells were Purkinje cells, stellate cells, and basket cells. In addition to the cerebellum, strong to medium ROR alpha immunoreactivity was found in the thalamus, cerebral cortex (mainly in the layer IV), dorsal cochlear nucleus (DCN), suprachiasmatic nucleus (SCN), superior colliculus, spinal trigeminal nucleus, and retina. The immunostaining was restricted in nuclei of neurons. Developmentally, ROR alpha immunoreactivity was observed in the cerebellum and thalamus from embryonal day 16 (E16). The distribution of ROR alpha immunoreactivity and ROR alpha mRNA hybridization signal was almost coincident. However, the intensity of hybridization signal was not always parallel to that of immunoreactivity.

Effect of training on motor abilities of heterozygous staggerer mutant (Rora(+)/Rora(sg)) mice during aging

Heterozygous cerebellar mutant (Rora(+)/Rora(sg)) mice and control (Rora(+)/Rora(+)) mice of the same C57Bl6/J strain, 3-24 months old, were subjected to motor training on a rotorod for 10 days. Falling latency and percentage of time spent walking were measured. A good correlation was found between falling latency and walking time: the mice which maintained equilibrium for a long time were those which were walking, and the mice which fell early were those which were gripping suggesting that walking is obviously the most adapted strategy to keep balance on the rotorod. In Rora(+)/Rora(+) mice, scores before training were altered very precociously (from 6 months of age). Moreover, scores of Rora(+)/Rora(sg) mice were lower than those of Rora(+)/Rora(+) mice from the age of 3 months, while neuronal number in the cerebellar cortex of these mutants was quite normal and similar to that of Rora(+)/Rora(+) mice. This suggests that the motor skill disability would be due to fine structural and/or biochemical changes preceding neuronal death. Such subtle changes would begin several months earlier in Rora(+)/Rora(sg) than in Rora(+)/Rora(+) mice. Training on the rotorod resulted in increased scores in both genotypes at all ages. Motor learning abilities were therefore preserved in animals with a moderate neuronal loss in the cerebellum. It may be that motor learning is partly compensated by the striatum, which is known to play a major role in learning of motor skills.

Age-related phenotypes in the staggerer mouse expand the RORalpha nuclear receptor's role beyond the cerebellum

The homozygous mutant mouse staggerer (RORa(sg)/RORa(sg)), was initially described as ataxic, due to the presence of massive neurodegeneration in the cerebellum [Science 136 (1962) 610]. The identification of the widely expressed Retinoic acid receptor-related Orphan Receptor, NR1F1 (RORalpha) gene as the site of mutation in the staggerer mouse has led to great progress in understanding the molecular basis of its phenotype in recent years [Nature 379 (1996) 736]. RORalpha is a transcription factor, belonging to the nuclear receptor superfamily, for which no natural ligand has yet been identified. Mice engineered for the disruption of the gene encoding RORalpha display the same cerebellar atrophic phenotype as the staggerer mouse [Proc. Natl. Acad. Sci. USA 95 (1998) 3960]. More recently, it has been shown that the mutation is semi-dominant, as heterozygous animals display an increased loss of Purkinje cells with age. Furthermore, a number of additional phenotypes outside the nervous system have recently been identified. These include a greater susceptibility to atherosclerosis [Circulation 15 (1998) 2738], immunodeficiencies linked to the overexpression of inflammatory cytokines [J. Neurochem. 58 (1992) 192], abnormalities in the formation and maintenance of bone tissue [Proc. Natl. Acad. Sci. USA 97 (2000) 9197] and changes in muscle differentiation [Nucleic Acids Res. 27 (1999) 411]. Thus, RORalpha has been directly linked to a number of age-related pathologies of great medical interest.