Tuberous sclerosis complex (TSC) is a genetic disorder that often causes neurologic pathology such as epilepsy, developmental disability, or neuropsychiatric disease. TSC is caused by heterozygous, inactivating mutations in the TSC1 or TSC2 genes that encode protein binding partners hamartin and tuberin. Dimerized hamartin and tuberin negatively regulate mTORC1, the mechanistic target of rapamycin complex 1. In response to anabolic signals, activated mTORC1 stimulates protein synthesis, cell growth and cell cycle progression. The pathogenesis of TSC is largely due to constitutive mTORC1 activation and consequent cellular anabolism. Despite advances in our knowledge about the molecular basis of TSC, the downstream events causing TSC pathology remain unclear. Using an unbiased, global metabolomic profiling approach, we assayed hippocampal tissue from a well-characterized mouse model of TSC in which the Tsc2 gene is conditionally disrupted in radial glial precursor cells (Tsc2-RG). These and subsequent data revealed an upregulation of the polyamine putrescine and increase in ornithine decarboxylase (ODC) activity, the rate limiting enzyme in polyamine synthesis, in Tsc2-RG mutants. Polyamines are essential for cell proliferation and survival and evidence suggests an interaction between polyamines and mTORC signaling. In this proposal, we will determine if directly reducing ODC activity ameliorates TSC-associated neuropathology and dampens mTORC signaling in mice. We will use complementary genetic and pharmacological approaches to reduce ODC activity and concomitant putrescine levels and polyamine flux. We propose to generate Tsc2-RG; Odc+/- compound mutants and determine if Odc haploinsufficiency affects (1) ODC activity and polyamine levels in brain lysates; (2) markers of neuropathology typical of TSC; and (3) levels of TSC/mTORC1 signaling proteins. Similarly, we will treat Tsc2-RG and control mice from postnatal days 1-21 with the ODC inhibitor difluoromethylornithine (DFMO) and determine its effects on these same phenotypic parameters. This project is expected to expand our understanding of the molecular basis of TSC by establishing a novel function for polyamines in determining TSC pathology. Additionally, these studies may define novel targets for TSC therapeutics.
Tuberous sclerosis complex (TSC) is a genetic disorder that causes epilepsy, developmental disability, autism and neuropsychiatric disease. This proposal examines the importance of the polyamine pathway in TSC neuropathology. We will investigate the phenotypic consequences of genetically and pharmacologically decreasing the activity of ornithine decarboxylase, the rate limiting enzyme in polyamine metabolism, in a well characterized mouse model of TSC.
| McKenna 3rd, James; Kapfhamer, David; Kinchen, Jason M et al. (2018) Metabolomic studies identify changes in transmethylation and polyamine metabolism in a brain-specific mouse model of tuberous sclerosis complex. Hum Mol Genet 27:2113-2124 |
