TSC the Cerebellum and ASD
Approximately 30% of patients with TSC have cerebellar lesions, though little is known about their pathophysiology. Imaging and pathologic studies have suggested an important role of the cerebellum in autistic patients. Both TSC and autism spectrum disorders are highly associated, and may be linked through cerebellar pathology. In an effort to learn more about the importance of the Tsc2 gene in cerebellar pathology and function, we have generated a mouse model with complete loss of function of Tsc2 in Purkinje cells, the main cellular output of the cerebellum. These Tsc2f/-Cre mice demonstrate progressive Purkinje cell degeneration, which suggests a crucial role for tuberin, the product of the Tsc2 gene, in Purkinje cell survival. One consequence of loss of Tsc2, was increased oxidative stress. In collaboration with Jack Arbiser, MD, PhD we are testing if an inhibitor of NADPH oxidase, an enzyme required for the generation of reactive oxygen species, can prevent Purkinje cell degeneration.
Behavioral testing of Tsc2f/fCre mice revealed social deficits and repetitive behavior, features of human ASD. It is unclear how loss of PC efferents leads to ASD-like behavior. One hypothesis is that loss of inhibitory PC input to the deep cerebellar nuclei leads to abnormal cerebellar-cortical signaling. This suggests that abnormal signaling from the deep cerebellar nuclei might also lead to ASD-like behavior. We are using a tamoxifen inducible Cre system to delete Tsc2 from the deep cerebellar nuclei to test this hypothesis. We are using other in vivo cell labeling systems to examine abnormalities in cerebellar cortical projections caused by abnormal Tsc2 signaling.
TSC and Cilia
(Left:Primary cilia (red) along the third ventricle of the mouse brain; Right: Confluent MEF's showing developing cilia(red))
Primary cilia, the slender, microtubule-based projections found on the eukaryotic cell surface, are linked to a number of signaling pathways. Primary cilia are built and maintained by intraflagellar transport (IFT), whereby the two IFT complexes, IFTA and IFTB, carry cargo via kinesin and dynein motors for anterograde and retrograde transport, respectively. Many signaling pathways, including Sonic hedgehog (Shh), PDGF, and mTORC1, are linked to primary cilia since mutations in IFTA, IFTB, kinesins, or dyneins alter the signaling response. Loss of cilia can result in increased mTORC1 signaling. As TSC is well established for its role in regulating mTORC1, we are using cell-based and in vivo animal models to explore the connection between cilia, the TSC complex and the phenotypes exhibited by TSC patients.
N-Glycanase Neurodevelopmental and Movement Disorder
N-glycanase 1 deficiency is a newly discovered autosomal recessive disorder associated with severe intellectual disability, movement abnormalities, and abnormal tear production. NGLY1 is important for endoplasmic reticulum-associated protein degradation. How loss of NGLY1 causes this severe neurogenetic disorder is completely unknown. To study NGLY1 deficiency, we have engineered mice harboring an Ngly1 deletion using the NIH Mouse Knockout Project (KOMP) Resources. We are generating homozygous mice to study the neuropathology of this new disease. We also have cells lines from human patients and plan to profile the abnormal glycoproteins associated with this disease.