mTOR-dependent abnormalities in autophagy characterize human malformations of cortical development: evidence from focal cortical dysplasia and tuberous sclerosis
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Focal cortical dysplasia (FCD) is a localized malformation of cortical development and is the commonest cause of severe childhood epilepsy in surgical practice. Children with FCD are severely disabled by their epilepsy, presenting with frequent seizures early in life. The commonest form of FCD in children is characterized by the presence of an abnormal population of cells, known as balloon cells. Similar pathological changes are seen in the cortical malformations that characterize patients with tuberous sclerosis complex (TSC). However, the cellular and molecular mechanisms that underlie the malformations of FCD and TSC are not well understood. We provide evidence for a defect in autophagy in FCD and TSC. We have found that balloon cells contain vacuoles that include components of the autophagy pathway. Specifically, we show that balloon cells contain prominent lysosomes by electron microscopy, immunohistochemistry for LAMP1 and LAMP2, LysoTracker labelling and enzyme histochemistry for acid phosphatase. Furthermore, we found that balloon cells contain components of the ATG pathway and that there is cytoplasmic accumulation of the regulator of autophagy, DOR. Most importantly we found that there is abnormal accumulation of the autophagy cargo protein, p62. We show that this defect in autophagy can be, in part, reversed in vitro by inhibition of the mammalian target of rapamycin (mTOR) suggesting that abnormal activation of mTOR may contribute directly to a defect in autophagy in FCD and TSC.
KeywordsAutophagy Epilepsy Balloon cells Focal cortical dysplasia Tuberous sclerosis
TSJ was in receipt of funding from the Great Ormond Street Hospital Children’s Charity and holds a HEFCE Clinical Senior Lecturer Award. This report is independent research supported by the National Institute for Health Research Great Ormond Street Hospital Biomedical Research Centre. The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, the National Institute for Health Research or the Department of Health. We are grateful to Prof. Zorzano, Institute of Research in Biomedicine, Barcelona for the DOR antibody.
Supplementary video 1 LysoTracker™ labelling of cultured balloon cells showed that they contained abundant lysosomes, which were dynamic in culture. Lysosomes were particularly concentrated close to the nucleus and were dynamic in the periphery of cells (MP4 152 kb)
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