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.

In vivo, homozygous staggerer (Rora(sg/sg)) Purkinje cells (PCs) remain in an early stage of development with rudimentary spineless dendrites, associated with a lack of parallel fiber (PF) input and the persistence of multiple climbing fibers (CFs). In this immunocytochemical study we used cerebellar organotypic cultures to monitor the development of Rora(sg/sg) PF-PC synapses in the absence of CF innervation. Ex vivo the vesicular glutamate transporters VGluT1 and VGluT2 reactivity was preferentially localized around the Rora(sg/sg) PC soma and proximal dendrites, which are typically CF domains. The shift from VGluT2 to VGluT1 in PF terminals during development was delayed in Rora(sg/sg) slices. The postsynaptic receptors mGluR1 and GluRdelta2 were differently distributed on Rora(sg/sg) PCs. mGluR1 reactivity was evenly distributed in PC soma and dendrites, whereas GluRdelta2 reactivity, normally restricted at PF synapses, was dense in Rora(sg/sg) PC somata. The presynaptic distribution of VGluT1 and VGluT2 on Rora(sg/sg) PCs matched the postsynaptic distribution of the glutamate receptor GluRdelta2, but not mGluR1.

The staggerer (Rora sg/sg) mutation is a deletion in the retinoid-related orphan receptor (RORalpha) gene that prevents translation of the ligand-binding domain (LBD), leading to the loss of RORalpha activity. RORalpha is a transcription factor that belongs to the nuclear receptor superfamily. In the brain, RORalpha is expressed in specific areas, including the cerebellum and suprachiasmatic nucleus (SCN). The homozygous Rora sg/sg mutant mouse, of which the most obvious phenotype is ataxia associated with cerebellar degeneration, also overproduces inflammatory cytokines. Here we compared the response to novelty stress of staggerer and wild-type mice as well as their diurnal cycles of adrenocorticotropic hormone and corticosterone secretion. We show that the staggerer mouse displays an enhanced endocrine response to novelty stress, which is not due to the enhanced production of interleukin-1 (IL-1), insofar as it is not blocked by pretreatment with IL-1ra and lacks the diurnal shift in corticosterone nonstressed levels; this last feature might be related to the expression of RORalpha in the SCN, a structure that maintains the circadian clock and plays a role in timing rhythmic physiology and behavior.

The staggerer (sg/sg) mutation is a spontaneous deletion in the Rora gene that prevents the translation of the ligand-binding domain (LBD), leading to the loss of ROR\alpha activity. The homozygous Rorasg/sg mutant mouse, whose most obvious phenotype is ataxia associated with cerebellar degeneration, also displays a variety of other phenotypes. The heterozygous Rora+/sg is able to develop a cerebellum which is qualitatively normal but with advancing age suffers a significant loss of cerebellar neuronal cells. A truncated protein synthesized by the mutated allele may play a role, both in Rorasg/sg and Rora+/sg. To determine the effects during life span of true haplo-insufficiency of the ROR\alpha protein, derived from the invalidation of the gene, we compared the evolution of Purkinje cell numbers in heterozygous Rora knock-out males (Rora+/-) and in their wildtype counterparts from 1 to 24 months of age. We also compared the evolution of Purkinje cell numbers in Rora+/- and Rora+/sg males from 1 to 9 months. The main finding is that in Rora+/- mice, when only a half dose of protein is synthesized, the deficit was already established at 1 month and did not change during life span....

RORα (Retinoid-relatedOrphanReceptor) is a transcription factor belonging to the superfamily of nuclear receptors. The spontaneousstaggerer (sg) mutation, which consists of a deletion in theRora gene, has been shown to cause the loss of function of the RORα protein. The total loss of RORα 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 RORα as a pivotal factor controlling Purkinje cell survival and differentiation, from development to ageing