Control of mitochondrial function in neurons by microRNAs during inflammation-induced neurodegeneration

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Multiple sclerosis (MS) is the most frequent inflammatory disease of the central nervous system (CNS). Inflammatory insults lead to progressive degeneration of axons and neurons that are key for the development of permanent neurological disability. While it is clear that inflammation contributes to neuronal stress responses resulting in mitochondrial dysfunction and energy depletion, it remains ill defined which factors stabilise these response networks. Regulation by microRNAs (miRNAs) is an important mechanism of regulating translational activity and stability of mRNAs during stress responses. Therefore, we aim at understanding how the changes of neuronal gene expression during inflammation are regulated by miRNAs and whether this regulation impacts on protein expression that are critical for mitochondrial function thereby reinforcing or ameliorating neurodegeneration. Accordingly, the first necessary step in the characterisation of the role of miRNAs in inflammation-induced regulation of expression networks in neurons is a comprehensive characterisation of matched mRNA and miRNA expression profiles by excluding other cell types. Hence, we acquired mRNA and miRNA profiles at the level of distinct neurons in healthy mice and compared them to mice with experimental autoimmune encephalomyelitis (EAE), the animal model of MS. By taking advantage of novel genetic methods allowed us to directly isolate neuronal mRNAs and miRNAs from inflamed and healthy CNS homogenates. Using next generation sequencing on these neuron-specific mRNA and miRNA isolates gave us a never before acquired quantification of transcript compositions in neurons during CNS inflammation. Notably, the mRNA profiles showed a significant underrepresentation of mitochondrial transcripts in neurons during the EAE model. At the same time these transcripts where predicted to be targets of newly identified inflammation-induced neuronal miRNAs. Therefore, we now propose to further narrow our results by UV crosslinking and immunoprecipitation of mRNA targets together with their miRNAs specifically from neurons to reveal direct interaction sites. In order to functionally characterise the impact of an altered composition of miRNAs, we will use in vitro and in vivo studies of the most significantly regulated miRNAs, deciphering their contribution to mitochondrial metabolic function and neuronal preservation or degeneration. Together, this will offer a new approach of understanding miRNA control of mRNA networks that govern mitochondrial function and contribute to neurodegeneration or -protection during CNS inflammation. Understanding the role of miRNAs in the pathophysiologic mechanisms may offer a new therapeutic modality for disease modification.