Loss of homeostatic functions in microglia from a murine model of Friedreich's ataxia
Background Friedreich's ataxia (FRDA) is a rare genetic disorder characterized by motor discoordination and predominant cerebellar involvement. It is caused by mutations leading to decreased transcription of frataxin (FXN), a gene encoding for a mitochondrial protein involved in the biogenesis of iron-sulfur clusters and iron handling. Many advances have been achieved in understanding the pathophysiology of FRDA and the mechanisms whereby FXN deficiency causes cerebellar degeneration. However, the issue concerning the contribution of central nervous system-resident non-neuronal cells to the pathogenesis of FRDA is still poorly explored. In this work, we set out to verify if specific vulnerabilities of cerebellar microglia could be involved in the pathogenesis of FRDA. Methods Primary cerebellar microglia were obtained from the KIKO mouse model of FRDA. We analyzed their phenotype and functions by a multilayer study, encompassing morphological analysis, migration and phagocytosis assays, gene expression by RNA-seq, RT-PCR, western blot, and immunofluorescence. Mitochondria functionality was evaluated by flow cytometry and real-time metabolic analysis. We assessed the effect of FRDA microglia on cell viability and neurite length in primary neurons. We analyzed in vivo microglia phenotype in the cerebellum of KIKO miceduring an early developmental stage by means of morphology analysis, RT-PCR and immunofluorescence. Results We demonstrated that FRDA microglia exhibit traceable morphological, transcriptional and functional changes, particularly regarding inflammatory pathways and mitochondria functionality. In addition, we found that FRDA microglia impair neuron survival and neurite length in vitro. Finally, we showed that cerebellar microglia in vivo exhibit dysregulations at early postnatal age of FRDA mice. Conclusions These results indicate that FRDA microglia display aberrant features and may participate in neuron dysfunction, evidencing a non-cell-autonomous mechanism in FRDA. Therefore, microglia targeting could be a valuable strategy in ameliorating cerebellar degeneration in the disease. Overall design: Gene expression analysis of primary microglia from cerebellum of KIKO (B6.Cg-Fxntm1MknFxntm1Pand/J ) and control WT (C57BL/6) mice. A total of n=8 sample were analysed by RNA seq: n=4 KIKO and n=4 control WT samples.