AIMS: Tuberous sclerosis complex (TSC) is a genetic disorder associated with dysregulation of the mechanistic target of rapamycin complex 1 (mTORC1) signalling pathway. Neurodevelopmental disorders, frequently present in TSC, are linked to cortical tubers in the brain. We previously reported microRNA-34a (miR-34a) among the most upregulated miRs in tubers. Here, we characterised miR-34a expression in tubers with the focus on the early brain development and assessed the regulation of mTORC1 pathway and corticogenesis by miR-34a. METHODS: We analysed the expression of miR-34a in resected cortical tubers (n = 37) compared with autopsy-derived control tissue (n = 27). The effect of miR-34a overexpression on corticogenesis was assessed in mice at E18. The regulation of the mTORC1 pathway and the expression of the bioinformatically predicted target genes were assessed in primary astrocyte cultures from three patients with TSC and in SH-SY5Y cells following miR-34a transfection. RESULTS: The peak of miR-34a overexpression in tubers was observed during infancy, concomitant with the presence of pathological markers, particularly in giant cells and dysmorphic neurons. miR-34a was also strongly expressed in foetal TSC cortex. Overexpression of miR-34a in mouse embryos decreased the percentage of cells migrated to the cortical plate. The transfection of miR-34a mimic in TSC astrocytes negatively regulated mTORC1 and decreased the expression of the target genes RAS related (RRAS) and NOTCH1. CONCLUSIONS: MicroRNA-34a is most highly overexpressed in tubers during foetal and early postnatal brain development. miR-34a can negatively regulate mTORC1; however, it may also contribute to abnormal corticogenesis in TSC.

Brigham and Women's Hospital Harvard Medical School Boston MA USA

Center for Neuroscience Swammerdam Institute for Life Sciences University of Amsterdam Amsterdam The Netherlands

Chalfont Centre for Epilepsy Chalfont St Peter UK

Child Neurology and Psychiatry Unit Systems Medicine Department Tor Vergata University Rome Italy

Department of Child Neurology Medical University of Warsaw Warsaw Poland

Department of Clinical and Experimental Epilepsy University College London London UK

Department of Development and Regeneration Section Pediatric Neurology University Hospitals KU Leuven Leuven Belgium

Department of Neuroimmunology Netherlands Institute for Neuroscience Amsterdam The Netherlands

Department of Neurology and Epileptology The Children's Memorial Health Institute Warsaw Poland

Department of Neurology University of Maryland School of Medicine Baltimore MD USA

Department of Paediatric Neurology University Medical Center Utrecht Utrecht The Netherlands

Department of Pathology Amsterdam UMC University of Amsterdam Amsterdam Neuroscience Amsterdam The Netherlands

Department of Pathology and Molecular Medicine 2nd Faculty of Medicine and Motol University Hospital Prague Czech Republic

Department of Pathology University Medical Center Utrecht Utrecht The Netherlands

Department of Pediatric Neurology 2nd Faculty of Medicine and Motol University Hospital Prague Czech Republic

Department of Pediatrics Medical University Vienna Vienna Austria

Graduate School of Medical Science and Engineering Korea Advanced Institute of Science and Technology Daejeon Republic of Korea

Institute of Neurology Medical University Vienna Vienna Austria

Pediatric Neurology Unit Universitair Ziekenhuis Brussel Brussels Belgium

SoVarGen Inc Daejeon Republic of Korea

Stichting Epilepsie Instellingen Nederland Heemstede The Netherlands

University Medical Center Brain Centre Rudolf Magnus Institute for Neuroscience Utrecht The Netherlands

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