Cytoarchitectural alterations are widespread in cerebral cortex in tuberous sclerosis complex

Abstract

Tubers are cerebral cortical developmental malformations associated with epilepsy and autism in tuberous sclerosis complex (TSC). The disparity between tuber number and severity of neurological impairment often observed in TSC led us to hypothesize that microscopic structural abnormalities distinct from tubers may occur in TSC. Serial frontal to occipital lobe sections were prepared from five postmortem TSC brain specimens. Sections were probed with cresyl violet stain or NeuN antibodies to define cytoarchitectural abnormalities and phospho-S6 (Ser235/236) antibodies to define mammalian target of rapamycin complex 1 (mTORC1) pathway activation. Tubers identified in all specimens (mean, 5 tubers per brain specimen) were defined by abnormal cortical lamination, dysmorphic neurons, and giant cells (GCs) and exhibited robust phospho-S6 immunolabeling. Histopathological analysis of non-tuber cortices demonstrated that 32% of the sections exhibited microscopic cytoarchitectural alterations, whereas 68% of the sections did not. Four types of morphological abnormalities were defined including: (1) focal dyslamination, (2) heterotopic neurons, (3) small collections of giant cells (GCs) and neurons we termed "microtubers", (4) isolated GCs we termed "sentinel" cells. When compared with control cortex, phospho-S6 labeling was enhanced in microtubers and sentinel cells and in some but not all areas of dyslamination. There are microscopic cytoarchitectural abnormalities identified in postmortem TSC brain specimens that are distinct from tubers. mTORC1 cascade activation in these areas supports a widespread effect of TSC1 or TSC2 mutations on brain development. Tubers may represent the most dramatic developmental abnormality in TSC; however, more regionally pervasive yet subtle abnormalities may contribute to neurological disability in TSC.

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].…”

Neurophysiological evidence of preserved connectivity in tuber tissue

“…The observed physiologic and imaging phenomena, the presence of robust MEPs from nTMS stimulation and preserved CS tracts identified by DTI tractography, within the tuber tissue in our patient provide functional and structural support of the intermixing of tuber and functional tissue. This is in agreement with current pathological [4], [26] diffusion imaging [27], and with physiological evidence of widespread and variable degrees of pathology in TSC [28], [29], [30], [31].…”

Multi-compartment microscopic diffusion imaging

“…Recent studies with mouse models of TSC (Meikle et al, 2008; Carson et al, 2012, 2013) suggested that global diffuse changes in white matter might give rise to universal cortical dysfunction together with various neuropsychiatric conditions, in addition to the multifocal tuber pathology. Indeed, Marcotte et al (2012) demonstrated widespread microstructural alterations distinct from tubers in human patients via histological analysis of post-mortem brain specimen. This ex-vivo MRI study with conditional knockouts of Rictor and Tsc2 in Olig2-Cre mice has shown that the developed technique is capable of discovering non-tuber white matter abnormalities, e.g.…”