Tuberous sclerosis complex–associated CNS abnormalities depend on hyperactivation of mTORC1 and Akt
Paola Zordan, … , Pietro L. Poliani, Rossella Galli
Paola Zordan, … , Pietro L. Poliani, Rossella Galli
Published February 1, 2018
Citation Information: J Clin Invest. 2018;128(4):1688-1706. https://doi.org/10.1172/JCI96342.
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Tuberous sclerosis complex–associated CNS abnormalities depend on hyperactivation of mTORC1 and Akt

Abstract

Tuberous sclerosis complex (TSC) is a dominantly inherited disease caused by hyperactivation of the mTORC1 pathway and characterized by the development of hamartomas and benign tumors, including in the brain. Among the neurological manifestations associated with TSC, the tumor progression of static subependymal nodules (SENs) into subependymal giant cell astrocytomas (SEGAs) is one of the major causes of morbidity and shortened life expectancy. To date, mouse modeling has failed in reproducing these 2 lesions. Here we report that simultaneous hyperactivation of mTORC1 and Akt pathways by codeletion of Tsc1 and Pten, selectively in postnatal neural stem cells (pNSCs), is required for the formation of bona fide SENs and SEGAs. Notably, both lesions closely recapitulate the pathognomonic morphological and molecular features of the corresponding human abnormalities. The establishment of long-term expanding pNSC lines from mouse SENs and SEGAs made possible the identification of mTORC2 as one of the mediators conferring tumorigenic potential to SEGA pNSCs. Notably, in spite of concurrent Akt hyperactivation in mouse brain lesions, single mTOR inhibition by rapamycin was sufficient to strongly impair mouse SEGA growth. This study provides evidence that, concomitant with mTORC1 hyperactivation, sustained activation of Akt and mTORC2 in pNSCs is a mandatory step for the induction of SENs and SEGAs, and, at the same time, makes available an unprecedented NSC-based in vivo/in vitro model to be exploited for identifying actionable targets in TSC.

Authors

Paola Zordan, Manuela Cominelli, Federica Cascino, Elisa Tratta, Pietro L. Poliani, Rossella Galli

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Figure 4

Targeted inactivation of Tsc1 and Pten in late-postnatal SVZ NSCs induces SEGA-like lesions.

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Targeted inactivation of Tsc1 and Pten in late-postnatal SVZ NSCs induce...
(A) An aberrant expansion of the lateral ventricles was observed in TPN mice activated at P15–17, which were characterized by the presence of small (H&E, arrowheads) and large cells (H&E, thick arrows) intermixed within a lax fibrillary matrix (H&E; original magnification, ×40, ×400, and ×800). These structures, which were never observed in control brains (H&E; ×40), contained many pS6-IR cells (×100 and ×400). GFAP immunoreactivity was found mostly in reactive glial cells (IHC; ×200 and ×400; IF, pS6 in green, GFAP in red, and DAPI in light blue; ×400, panel with single asterisk), and less frequently in clusters of pS6-IR cells (IF, pS6 in green, GFAP in red, and DAPI in light blue; ×400, panel with double asterisk). Ectopic NeuN-IR neuronal cells were scattered throughout the lesions, some of which were pS6-IR (×200 and ×400). As opposed to SENs, only rare DCX-IR cells were found, which never colabeled with GFAP (×200 and ×400; controls, ×40, ×100, and ×400 for inset and DCX/GFAP staining). (B) Expression of Pax6 and Sox2 was restricted to large cells within the lesions, whereas Tuj1 expression was detected in most cells (mutants, ×40 and ×400; controls, ×40 and ×100). As opposed to SENs, several MBP-IR cells were found in the SEGA-like lesions. (C) S100β-IR cells were found in the intact ependymal layer (arrow), as in controls (×40 and ×100), as well as within the lesions (×40 and ×400). High frequency of Iba1-IR microglial cells and vimentin-IR reactive glial cells was observed in the lesions as compared with SENs (×40, ×200, and ×400; controls, ×40 and ×100). The mitotic index of the lesions as measured by Ki67 was still very low (×40, ×200, and ×400).