| Popis: |
Background Background: Spinocerebellar ataxia type 7 (SCA7) is primarily characterized by progressive cerebellar degeneration with major alteration of Purkinje cells (PC) due to polyglutamine expansion in ATXN7, a subunit of SAGA transcriptional co-regulator complex. Additional neural tissues are affected and contribute to diverse symptoms. Current animal models were insufficient to recapitulate the broad spectrum of SCA7 pathology and the mechanisms of PC degeneration remain poorly explored. Methods: To delineate spatio-temporal features of SCA7, we performed a longitudinal characterization of a new knock-in mice line expressing ATXN7 with 140 glutamines (SCA7 140Q/5Q ) using a battery of analyses including motor tests, brain and retina imaging, morphometry, electrophysiology, electron microscopy and immunohistochemistry of disease tissues. We also determined the cerebellar transcriptome and cell-type specific gene deregulation. Results: Here we describe the first SCA7 knock-in mice that combine most cardinal features of SCA7, including retinal, cerebellar, cerebral and peripheral nerves pathologies, which account for progressive impairment of behavior, motor and vision functions. MRI and brain morphometry reveal atrophy of grey and white matter of specific cerebral regions, while peripheral nerves and photoreceptors show functional and morphological alterations. We show that cerebellar pathology is characterized by gene deregulation in all cerebellar cell types and alterations of SAGA-dependent epigenetic marks. Intranuclear accumulation of mutant ATXN7 and gene downregulation precede the onset of PC pacemaker dysfunction. Interestingly, PC show loss of expression of 83 PC-specific genes coding for ion channels, receptors and signaling proteins involved in pacemaker function and long-term depression, which are causal factors of many type of ataxias. Comparison of cerebellar transcriptome with other SCAs reveals a subset of 67 PC-specific genes downregulated in SCA1, SCA2 and SCA7, providing a common signature of early PC dysfunction. Conclusions: The SCA7 140Q/5Q mice represent a promising model for the investigation of different aspects of SCA7 pathogenesis, and offers opportunities for translational development of therapeutic strategies by targeting the brain, retina, peripheral nerve or whole body. Our results also provide insight into converging mechanisms of PC degeneration in polyglutamine SCAs and point out molecular targets for therapeutic development w hich may prove beneficial for several SCAs. |
