Efficient and innocuous delivery of small interfering RNA to microglia using an amphiphilic dendrimer nanovector

International audienceAim: Alterations of microglia, the brain-resident macrophages, are associated with numerous brain pathologies. Genetic manipulation of microglia in diseases using small interfering RNA (siRNA) is hampered by the lack of safe and efficient siRNA delivery methods. We assessed the amphiphilic dendrimer (AD) for functional siRNA delivery and gene knockdown in primary microglia. Materials & methods: We characterized the ability of AD to form nanoparticles with siRNA, and studied their size, surface potential , cell uptake and gene silencing in rodent microglia. Results: AD effectively delivered siRNA to primary microglia and decreased target gene and protein expression, leading to transcriptomic changes without affecting basal microglial functions. Conclusion: The dendrimer AD promises to be an innocuous carrier for siRNA delivery into microglia. Keywords: amphiphilic dendrimer • basal microglial responses • dendrimer nanovector • gene silencing • glioma-initiated response • inhibitor of differentiation Id1 • microglial function • nonviral vector • primary microglia • siRNA delivery Microglia are the resident macrophages of the central nervous system (CNS). They participate in brain development , regulation of homeostasis and synaptic plasticity, as well as protecting the brain from infections, metabolic disturbances or misfolded proteins [1-3]. However, aberrant or chronic microglial activation leads to neuroinflamma-tory brain damage linked to the pathogenesis of stroke and many neurodegenerative and psychiatric disorders [4-9]. Moreover, microglia contribute to the progression of brain tumors, including the most common and deadliest glioblastoma multiforme (GBM) [10]. Microglia and peripheral macrophages massively infiltrate GBM tumors [11], where they become polarized to promote glioma invasion, immunosuppression and angiogenesis [12,13]. Due to their critical role as instigators of inflammatory or pro-tumorigenic events, microglia are considered to be a potentially promising therapeutic target [14]. Therefore, further molecular insights into microglial functions are of paramount importance for our understanding of neurological disorders and for fostering the development of effective treatments for the related diseases. Genetic manipulation using small interfering RNA (siRNA) is frequently used for studying genotype-phenotype relationships and identifying potential drug targets and candidates [15-17]. RNA interference (RNAi) is a biological process in which siRNA molecules specifically inhibit gene translation by neutralizing targeted mRNA molecules via Watson-Crick base-pairing. However, siRNA delivery to microglia has been difficult due to the high immune-reactivity of microglia to transfection agents and the characteristic high charge and enzyme sensitivity of siRN