Developmental brain abnormalities in tuberous sclerosis complex: A comparative tissue analysis of cortical tubers and perituberal cortex

Abstract

SUMMARYObjective: Genetic loss of Tsc1/Tsc2 function in tuberous sclerosis complex (TSC) results in altered mammalian target of rapamycin (mTOR) signaling and abnormal brain development. Although earlier studies have focused on characterization of cortical tubers, in this study we sought to examine the unique cellular and molecular features of the perituberal cortex in order to better understand its contribution to epileptogenesis, cognitive dysfunction, and autism. Methods: Standard histologic and immunohistochemical labeling was used to assess structural abnormalities and cell-specific pattern of mTORC1 activation in surgically resected cortical tubers and perituberal cortex. Western blotting was performed to quantify the expression of the mTORC1 and mTORC2 biomarkers phospho-S6 (Ser235/236), phospho-S6 (Ser240/244), and phospho-Akt (Ser473), in addition to evaluating the differential expression levels of several neuronal and glial-specific proteins in tubers and peritubers, as compared to non-TSC epilepsy specimens. Results: Tubers demonstrated mild to severe disruption of cortical lamination, the presence of pS6-positive dysplastic neurons and giant cells, an overall increase in mTORC1 and a decrease in mTORC2 activity, increased axonal connectivity and growth, and hypomyelination. Perituberal cortex presented similar histologic, immunohistochemical, and molecular features; however, they were overall milder. Axonal growth was specific for TSC and was negatively correlated with deficient myelination. Significance: Our results show an extension of cellular dysplasia and dysregulated mTOR signaling in the perituberal tissue, and demonstrate for the first time aberrant connectivity in human TSC brain. This study provides new insights into the pathophysiology of neurologic dysfunction associated with TSC and supports the intrinsic epileptogenicity of normal-appearing perituberal cortex.

Reduction in retinal nerve fiber layer thickness in tuberous sclerosis complex

“…Furthermore, several studies using MRI diffusion techniques revealed diffuse alterations in the so-called normally appearing WM [3,4], but the relation between WM alterations and neurologic phenotype remains to be clarified. WM alterations seen by MRI studies are in good agreement with diffuse microstructural WM abnormalities found in neuropathological studies in individuals with TSC, reflecting axonal disorganization, reduced/altered myelination, or gliosis [5][6][7]. WM alterations might result from the dysregulation of the mTOR pathway, which is responsible for abnormal connectivity as well as for altered axonal growth [8][9][10].…”

DTI of tuber and perituberal tissue can predict epileptogenicity in tuberous sclerosis complex

“…7 AD changes are caused by axonal and functional changes, 7 suggesting that our observed increases in AD within epileptogenic perituberal tissue may result from increased axonal connectivity and growth. 3 The coexistence of both AD and RD changes have resulted in no substantial anisotropy changes, as indicated by our findings of no FA difference between epileptogenic and nonepileptogenic tubers. This result conflicts with previous studies reporting significantly lower FA values in epileptogenic tubers or in normal-appearing white matter adjacent to epileptogenic tubers compared with nonepileptogenic areas.…”

“…Histopathologically, tubers show the presence of dysplastic neurons and giant cells, increased axonal connectivity, and hypomyelination. 3 Perituberal cortex also demonstrates similar histologic features. 3 Our results are therefore consistent with these histopathologic changes since dysplastic neurons and astrogliosis may result in increased ADC.…”

“…3 Perituberal cortex also demonstrates similar histologic features. 3 Our results are therefore consistent with these histopathologic changes since dysplastic neurons and astrogliosis may result in increased ADC. Cystic degeneration of tubers also causes increased ADC, which is consistent with the notion that tubers with cystic degeneration correlate with epileptogenicity.…”

“…2,3 We hypothesized that microstructural changes in perituberal tissue may be measurable using diffusion tensor imaging (DTI), an MRI technique sensitive to subvoxel microstructural orientation and density. To test this hypothesis, we measured DTI characteristics, including apparent diffusion coefficient (ADC), fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD), in both tubers and perituberal tissue in a group of pediatric patients with TSC, and then correlated these findings with epileptogenicity.…”