mTOR-related neuropathology in mutant tsc2 zebrafish: Phenotypic, transcriptomic and pharmacological analysis

- tsc2−/− larvae show abnormal brain activity with reduced locomotor response.
- Rapamycin, a well-known mTOR inhibitor rescues the phenotype.
- Transcriptomics revealed 1414 differentially expressed genes between WT and tsc2−/−.
- Genes related to inflammation and immune response were up-regulated in tsc2−/−.
- The tsc2−/− zebrafish model is useful to identify new treatment targets for TSC.

Tuberous sclerosis complex (TSC) is a rare, genetic disease caused by loss-of-function mutations in either TSC1 or TSC2. Patients with TSC are neurologically characterized by the presence of abnormal brain structure, intractable epilepsy and TSC-associated neuropsychiatric disorders. Given the lack of effective long-term treatments for TSC, there is a need to gain greater insight into TSC-related pathophysiology and to identify and develop new treatments.In this work we show that homozygous tsc2−/− mutant zebrafish larvae, but not tsc2+/− and WT larvae, display enlarged brains, reduced locomotor behavior and epileptiform discharges at 7 dpf. In addition, we pharmacologically validated the TSC model by demonstrating the dramatic rescue effect of pericardially injected rapamycin, a well-known mTOR inhibitor, on selected behavioral read-outs and at the molecular level.By means of trancriptome profiling we also acquired more insight into the neuropathology of TSC, and as a result were able to highlight possible new treatment targets. The gene expression profiles of WT and tsc2+/− larvae revealed 117 differentially expressed genes (DEGs), while between WT and tsc2−/− larvae and tsc2+/− and tsc2−/− larvae there were 1414 and 1079 DEGs, respectively. Pathway enrichment analysis from the WT and tsc2−/− DEGs, identified 14 enriched pathways from the up-regulated genes and 6 enriched pathways from the down-regulated genes. Moreover, genes related to inflammation and immune response were up-regulated in the heads of tsc2−/− larvae, in line with the findings in human brain tissue where inflammatory and immune responses appear to be major hallmarks of TSC.Taken together, our phenotypic, transcriptomic and pharmacological analysis identified the tsc2−/− zebrafish as a preclinical model that mirrors well aspects of the human condition and delineated relevant TSC-related biological pathways. The model may be of value for future TSC-related drug discovery and development programs.