Retinoic acid receptor beta protects striatopallidal medium spiny neurons from mitochondrial dysfunction and neurodegeneration

Retinoic acid is a powerful regulator of brain development, however its postnatal functions only start to be elucidated. We show that retinoic acid receptor beta (RAR beta), is involved in neuroprotection of striatopallidal medium spiny neurons (spMSNs), the cell type affected in different neuropsychiatric disorders and particularly prone to degenerate in Huntington disease (HD). Accordingly, the number of spMSNs was reduced in the striatum of adult Rar beta(-/-) mice, which may result from mitochondrial dysfunction and neurodegeneration. Mitochondria morphology was abnormal in mutant mice whereas in cultured striatal Rar beta(-/-) neurons mitochondria displayed exacerbated depolarization, and fragmentation followed by cell death in response to glutamate or thapsigargininduced calcium increase. In vivo, Rar beta(-/-)spMSNs were also more vulnerable to the mitochondrial toxin 3-nitropropionic acid (3NP), known to induce HD symptoms in human and rodents. In contrary, an RAR beta agonist, AC261066, decreased glutamate-induced toxicity in primary striatal neurons in vitro, and diminished mitochondrial dysfunction, spMSN cell death and motor deficits induced in wild type mice by 3NP. We demonstrate that the striatopallidal pathway is compromised in Rar beta(-/-) mice and associated with HD-like motor abnormalities. Importantly, similar motor abnormalities and selective reduction of spMSNs were induced by striatal or spMSNspecific inactivation of RAR beta, further supporting a neuroprotective role of RAR beta in postnatal striatum

Molecular Targets and Therapeutic Strategies in Spinocerebellar Ataxia Type 7

Spinocerebellar ataxia type 7 (SCA7) is a rare autosomal dominant neurodegenerative disorder characterized by progressive neuronal loss in the cerebellum, brainstem, and retina, leading to cerebellar ataxia and blindness as major symptoms. SCA7 is due to the expansion of a CAG triplet repeat that is translated into a polyglutamine tract in ATXN7. Larger SCA7 expansions are associated with earlier onset of symptoms and more severe and rapid disease progression. Here, we summarize the pathological and genetic aspects of SCA7, compile the current knowledge about ATXN7 functions, and then focus on recent advances in understanding the pathogenesis and in developing biomarkers and therapeutic strategies. ATXN7 is a bona fide subunit of the multiprotein SAGA complex, a transcriptional coactivator harboring chromatin remodeling activities, and plays a role in the differentiation of photoreceptors and Purkinje neurons, two highly vulnerable neuronal cell types in SCA7. Polyglutamine expansion in ATXN7 causes its misfolding and intranuclear accumulation, leading to changes in interactions with native partners and/or partners sequestration in insoluble nuclear inclusions. Studies of cellular and animal models of SCA7 have been crucial to unveil pathomechanistic aspects of the disease, including gene deregulation, mitochondrial and metabolic dysfunctions, cell and non-cell autonomous protein toxicity, loss of neuronal identity, and cell death mechanisms. However, a better understanding of the principal molecular mechanisms by which mutant ATXN7 elicits neurotoxicity, and how interconnected pathogenic cascades lead to neurodegeneration is needed for the development of effective therapies. At present, therapeutic strategies using nucleic acid-based molecules to silence mutant ATXN7 gene expression are under development for SCA7

Longitudinal MRI and 1H-MRS study of SCA7 mouse forebrain reveals progressive multiregional atrophy and early brain metabolite changes indicating early neuronal and glial dysfunction

International audienceSpinoCerebellar Ataxia type 7 (SCA7) is an inherited disorder caused by CAG triplet repeats encoding polyglutamine expansion in the ATXN7 protein, which is part of the transcriptional coactivator complex SAGA. The mutation primarily causes neurodegeneration in the cerebellum and retina, as well as several forebrain structures. The SCA7 140Q/5Q knock-in mouse model recapitulates key disease features, including loss of vision and motor performance. To characterize the temporal progression of brain degeneration of this model, we performed a longitudinal study spanning from early to late symptomatic stages using high-resolution magnetic resonance imaging (MRI) and in vivo 1 H-magnetic resonance spectroscopy ( 1 H-MRS). Compared to wild-type mouse littermates, MRI analysis of SCA7 mice shows progressive atrophy of defined brain structures, with the striatum, thalamus and cortex being the first and most severely affected. The volume loss of these structures coincided with increased motor impairments in SCA7 mice, suggesting an alteration of the sensory-motor network, as observed in SCA7 patients. MRI also reveals atrophy of the hippocampus and anterior commissure at mid-symptomatic stage and the midbrain and brain stem at late stage. 1 H-MRS of hippocampus, a brain region previously shown to be dysfunctional in patients, reveals early and progressive metabolic alterations in SCA7 mice. Interestingly, abnormal glutamine accumulation precedes the hippocampal atrophy and the reduction in myo-inositol and total N-acetyl-aspartate concentrations, two markers of glial and neuronal damage, respectively. Together, our results indicate that non-cerebellar alterations and glial and neuronal metabolic impairments may play a crucial role in the development of SCA7 mouse pathology, particularly at early stages of the disease. Degenerative features of forebrain structures in SCA7 mice correspond to current observations made in patients. Our study thus provides potential biomarkers that could be used for the evaluation of future therapeutic trials using the SCA7 140Q/5Q model

Selective transduction of cerebellar Purkinje and granule neurons using delivery of AAV-PHP.eB and AAVrh10 vectors at axonal terminal locations

Adeno-associated virus (AAV)-based brain gene therapies require precision without off-targeting of unaffected neurons to avoid side effects. The cerebellum and its cell populations, including granule and Purkinje cells, are vulnerable to neurodegeneration; hence, conditions to deliver the therapy to specific cell populations selectively remain challenging. We have investigated a system consisting of the AAV serotypes, targeted injections, and transduction modes (direct or retrograde) for targeted delivery of AAV to cerebellar cell populations. We selected the AAV-PHP.eB and AAVrh10 serotypes valued for their retrograde features, and we thoroughly examined their cerebellar transduction pattern when injected into lobules and deep cerebellar nuclei. We found that AAVrh10 is suitable for the transduction of neurons in the mode highly dependent on placing the virus at axonal terminals. The strategy secures selective transduction for granule cells. The AAV-PHP.eB can transduce Purkinje cells and is very selective for the cell type when injected into the DCN at axonal PC terminals. Therefore, both serotypes can be used in a retrograde mode for selective transduction of major neuronal types in the cerebellum. Moreover, our in vivo transduction strategies are suitable for pre-clinical protocol development for gene delivery to granule cells by AAVrh10 and Purkinje cells by AAV-PHPeB

9-cis-13,14-Dihydroretinoic Acid Is an Endogenous Retinoid Acting as RXR Ligand in Mice

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Molecular evidence for 9CDHRA selective activation of RXRs.

<p>(a) Significant overlap between global transcriptional changes induced by R-9CDHRA (10^{<b><i>-5</i></b>}M), 9CRA (10^{<b><i>-6</i></b>}M) or a synthetic RXR agonist (LG268; 10^{<b><i>-7</i></b>}M) revealed by DNA microarray analyses in differentiating monocyte-derived human dendritic cells. (b) Scatter plot comparison of fold-changes for transcripts altered by 9CRA and R-9CDHRA treatments. (c) S- and R-9CDHRA, similarly to 9CRA and/or LG268 (see “RXR” columns), induced the expression of genes (see rows) identified previously as direct transcriptional targets of LXR-RXR, PPAR-RXR and RAR-RXR. Corresponding transcripts were also induced by agonists of respective RXR-heterodimer partners (see “partners” column and arrowheads): GW3965 (LXRα/β; 10^{<b><i>-6</i></b>}M), RSG (PPARγ; 10^{<b><i>-6</i></b>}M), GW1516 (PPARδ; 10^{<b><i>-6</i></b>}M) and AM580 (RAR; 10^{<b><i>-7</i></b>}M).</p

9CDHRA binds and transactivates RXR <i>in vitro</i>, and displays RXR agonist-like activities <i>in vivo</i>.

<p>(a) ESI mass spectra of hRXRα LBD protein after incubation with a 5-fold molar excess of 9CRA, R-9CDHRA and S-9CDHRA. (b) Distribution plot of the percentage of bound hRXRα. (c) Close-up view showing the ligand-binding pocket of RXRα bound to R-9CDHRA (in grey). Residues in close contacts (<3.5 Å) are labelled. Dashed lines indicate hydrogen bonds and the red sphere a water molecule. (d) Superposition of the RXRalpha ligand-binding pocket bound to R-9CDHRA (grey) and 9CRA (cyan, PDB code: 1XDK). Superposition was made on the protein. Hydrogen bonds with R-9CDHRA or 9CRA are shown by grey and cyan dashed lines, respectively. Water molecules are shown by spheres (red for RXR-R-9CDHRA and cyan for RXR-9CRA). (e) Transcriptional activation of RXRα by R-9CDHRA and S-9CDHRA in comparison to 9CRA (10^{<b><i>–5</i></b>}–10^{<b><i>-9</i></b>}M) in RXR-reporter COS1 cells. (f) 9CRA (10^{<b><i>-7</i></b>}M) and both 9CDHRA enantiomers (10^{<b><i>-5</i></b>}M) induced RXRα-mediated signaling. RXR-antagonist LG101208 (LG; 10^{<b><i>-6</i></b>}M) diminished activity of both 9CDHRA enantiomers (10^{<b><i>-5</i></b>}M). (g) Transcriptional activation of RAR-RXR heterodimers by R- and S-9CDHRA in comparison to ATRA in RARα-RXRα-reporter COS1 cells. (h) Increasing doses of R-9CDHRA reversed working memory deficits in <i>Rbp1</i>^{<b><i>-/-</i></b>} mice and showed pro-mnemonic activity in WT mice (n = 8/group) in DNMTP task when tested at minimal ITI, at which mice performed at chance level (50%) and which was 6min for the <i>Rbp1-/-</i> or 12min for WT mice. ttt: ATRA at concentration 10^{<b><i>–5</i></b>} M was cytotoxic. *, p<0.05. #, p<0.05; ##, p<0.01 as compared to vehicle treatment in the same group; $, p<0.05;$$, p<0.01; one group student t-test for comparison with performance at chance level of 50%. All the error bars represent S.E.M.</p