Assessment of CSF biomarkers and microRNA-mediated disease mechanisms in SMA

ObjectiveCerebral spinal fluid (CSF) is a promising biospecimen for the detection of central nervous system (CNS) biomarkers to monitor therapeutic efficacy at the cellular level in neurological diseases. Spinal muscular atrophy (SMA) patients receiving intrathecal antisense oligonucleotide (nusinersen) therapy tend to show improved motor function, but the treatment effect on cellular function remains unknown. The objective of this study was to assess the potential of extracellular RNAs and microRNAs in SMA patient CSF as indicators of neuron and glial health following nusinersen treatment. MethodsCSF samples from SMA Type 1-3 patients were screened using quantitative RT-PCR to assess expression of extracellular RNAs associated with inflammation and cellular stress, and microRNAs previously implicated in SMA pathogenesis. We also used mRNA sequencing and multi-electrode array approaches to assess the transcriptional and functional effects of astrocyte-associated miR-146a on healthy and SMA induced pluripotent stem cell (iPSC)-derived motor neurons. ResultsExtracellular RNA analysis is suggestive of ongoing cellular stress, even in nusinersen treated samples. microRNAs previously associated with SMA pathology tended to show improvement in expression levels in nusinersen treated samples, with the exception of the astrocyte-secreted miR-146a. miR-146a treated iPSC-derived motor neurons showed a downregulation of extracellular matrix genes found in the synaptic perineuronal net and decreased spontaneous activity. InterpretationExtracellular RNAs and microRNAs can be detected in SMA patient CSF samples, potentially serving as useful biomarkers to monitor cellular health during nusinersen treatment. Astrocyte health and response to nusinersen are important aspects to address in SMA pathogenesis and treatment strategies.