Neuronal Primary Cilia Dysfunction in Tuberous Sclerosis Complex

Boston Children'S Hospital, Boston MA

Investigators

Abstract

Tuberous sclerosis complex (TSC) is a genetic disorder caused by heterozygous inactivating variants in TSC1 or TSC2. TSC is characterized by the growth of benign tumors in multiple organs, as well as neurological manifestations such as refractory epilepsy, autism spectrum disorder, and intellectual disability. TSC1 and TSC2 form a protein complex with TBC1D7 that acts as a key upstream negative regulator of the mechanistic target of rapamycin complex 1 (mTORC1), and mTORC1 hyperactivation is thought to be a key pathogenic driver of TSC. Treatments that inhibit mTORC1 cause arrest or regression of tumors in TSC but have shown limited efficacy in treating epilepsy and no efficacy in treating the neurocognitive symptoms of TSC. Consequently, there is a substantial unmet need for the development of new therapeutics, which will require further understanding of the molecular mechanisms of neurological symptoms in TSC. Among the several downstream consequences of mTORC1 dysregulation, disruption of primary cilia has emerged as one potential candidate for mediating neuronal dysfunction in TSC. The primary cilium is an immotile organelle that extends from the plasma membrane and contains a distinct composition of transmembrane receptors, rendering it a signaling hub. Our work has shown that in TSC, neurons are less often ciliated, and the remaining cilia are significantly lengthened. Accordingly, in the proposed research the applicant aims to investigate the molecular mechanisms underlying these alterations. Preliminary data suggests that upregulation of HSP27 in astrocytes may be a non-cell autonomous modulator of neuronal cilia in TSC. Therefore, in Aim 1 we propose to determine whether astrocytic expression of Hsp27 is necessary and/or sufficient to modulate cilia in Tsc1- deficient neurons. To enhance the translational relevance of this work, in Aim 2, we will evaluate neuronal primary cilia and astrocytic HSP27 expression in human cells. Our finding of altered neuronal cilia morphology in TSC also raises the question of whether cilia are functionally impaired. Our preliminary data suggests that ciliary calcium channels are differentially expressed in neurons in TSC, so in Aim 3 we will characterize ciliary calcium signaling in Tsc1-deficient neurons. mTOR dysregulation and cilia dysfunction are common observations across several disorders that display high rates of epilepsy and/or autism, making the proposal an excellent project to introduce the applicant to neurodevelopmental disorders and to broaden the impact of this research. The proposal contains a comprehensive training plan for the applicant to become a productive independent investigator, including plans to obtain key technical skills in stem cell culture and calcium imaging, and to increase presentation and publication opportunities. The research outlined in this proposal will take place at Boston Children’s Hospital (BCH) in the lab of Dr. Mustafa Sahin, an expert in the neurobiology of TSC. The institutional environment at BCH, including talented scientists and abundant resources and equipment, together with the mentorship of Dr. Sahin, will support the evolving needs of this project.