mTORC1 Inhibition Corrects Neurodevelopmental and Synaptic Alterations in a Human Stem Cell Model of Tuberous Sclerosis

Abstract

Hyperfunction of the mTORC1 pathway has been associated with idiopathic and syndromic forms of autism spectrum disorder (ASD), including tuberous sclerosis, caused by loss of either TSC1 or TSC2. It remains largely unknown how developmental processes and biochemical signaling affected by mTORC1 dysregulation contribute to human neuronal dysfunction. Here, we have characterized multiple stages of neurogenesis and synapse formation in human neurons derived from TSC2-deleted pluripotent stem cells. Homozygous TSC2 deletion causes severe developmental abnormalities that recapitulate pathological hallmarks of cortical malformations in patients. Both TSC2(+/-) and TSC2(-/-) neurons display altered synaptic transmission paralleled by molecular changes in pathways associated with autism, suggesting the convergence of pathological mechanisms in ASD. Pharmacological inhibition of mTORC1 corrects developmental abnormalities and synaptic dysfunction during independent developmental stages. Our results uncouple stage-specific roles of mTORC1 in human neuronal development and contribute to a better understanding of the onset of neuronal pathophysiology in tuberous sclerosis.

Impaired Mitochondrial Dynamics and Mitophagy in Neuronal Models of Tuberous Sclerosis Complex

“…Notably, we detected mTORC1 activation in TSC2 +/− iPSC-derived neurons (M-J.H. and M.S., unpublished), similar to recently published observations of mTORC1 hyperfunction in TSC2 +/− human embryonic stem cell-derived neurons (Costa et al, 2016). …”

Cellular Phenotypes in Human iPSC-Derived Neurons from a Genetic Model of Autism Spectrum Disorder

“…In line with previous studies, patch clamp recordings from 16pdel neurons showed intrinsic electrical properties consistent with their larger size, i.e., increased C m , decreased R inp and reduced excitability(Costa et al, 2016; Williams et al, 2015). Based on increased dendrite length of 16pdel neurons, we would predict increased number of synapses on the dendrites.…”

“…Similarly, loss of TSC2, which inhibits mTOR, an effector of the PI3K/AKT pathway, often results in macrocephaly associated with ASD, ID and seizures. Loss of TSC2 in human iPSC-derived neurons results in increased soma size, dendritic arborization and total dendrite length (similar to our observations in 16pdel) mediated by a hyperactive PI3K/AKT pathway(Costa et al, 2016). The 16p11.2 region harbors genes encoding proteins that are known to interact with the PI3K/AKT or Ras/MAPK pathway, hence it may affect cellular phenotypes in a dosage-dependent manner via this interaction.…”

“…Reduced synaptic density, predominantly excitatory, has been demonstrated in several iPSC studies modeling NDDs(Russo et al, 2015) such as Rett syndrome and tuberous sclerosis. In fact, the TSC2 deficient iPSC-derived neurons show neuronal and synaptic alterations(Costa et al, 2016) that closely resemble those we found in 16pdel neurons. This suggests that 16p11.2 genes may regulate (or dysregulate) the same synaptic pathways that are impaired in other NDDs, implying shared pathophysiological mechanisms.…”

Abnormal Neural Progenitor Cells Differentiated from Induced Pluripotent Stem Cells Partially Mimicked Development of TSC2 Neurological Abnormalities

“…First, we did not investigate further the link between mTOR hyperactivation and synaptic transmission and plasticity, which might influence neuronal excitability and trigger epileptogenesis. However, a recent study on neurons derived from TSC2 -deleted pluripotent stem cells demonstrated that heterozygous and homozygous loss of TSC2 led to altered synaptogenesis and transmission and that pharmacological inhibition of mTORC1 could ameliorate synaptic dysfunction (Costa et al., 2016). Second, only the proband who was carrying TSC2 gene mutation was compared with the normal control subject in our study.…”