Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a fatal autosomal recessive disease caused by mutations in the TYMP gene encoding thymidine phosphorylase (TP). The disease typically begins in childhood or early adulthood causes ptosis, ophthalmoplegia, severe gastrointestinal dysmotility leading to cachexia, peripheral neuropathy, leukoencephalopathy, and alterations of mitochondrial DNA (mtDNA). Most patients die by age 40. Through genetic linkage studies, we identified the causative gene and demonstrated that TYMP mutations cause TP deficiency, which leads to dramatic elevations of thymidine and deoxyuridine in plasma and tissues of patients. In addition, we identified multiple deletions, depletion, and site-specific point mutations of mtDNA in patients'tissues and cells. Based on these findings, we hypothesize that toxic accumulations of thymidine and deoxyuridine nucleosides cause imbalances of mitochondrial deoxynucleotide pools leading to mtDNA instability. Other investigators have demonstrated that TP-expressing human cells cultured in high concentrations of thymidine have unbalanced mitochondrial nucleotide pools and develop partial depletion or multiple deletions of mtDNA. We have generated a TP and uridine phosphorylase (UP) double-knockout (TP-/-UP-/-) mouse model of MNGIE. The TP-/-UP-/- mice show loss of TP activity, elevated levels of thymidine and deoxyuridine in tissues, mitochondrial nucleotide pool imbalances, and leukoencephalopathy with mtDNA depletion and respiratory chain defect. In this application, we propose to further test our hypotheses that: 1) TP deficiency causes toxic accumulation of thymidine, that, in turn, lead to nucleotide pool imbalances and mtDNA instability and 2) restoration of TP activity by bone marrow transplantation or nanoparticle enzyme replacement will be therapeutic.
Three specific aims are proposed.
Aim 1 : TP-/-UP-/- mice will be administered thymidine to enhance the mitochondrial abnormalities.
Aim 2 : TP-/-UP-/- mice will undergo bone marrow transplantation before and after onset of leukoencephalopathy.
Aim 3 : TP encapulated in nanoparticles will be administered to TP-/-UP-/- mice.
Our studies of a rare and fatal genetic disease called MNGIE have revealed how a particular biochemical defects causes instability of genetic material in people. We propose to study a mouse model to understand and to treat this disorder. Studies of MNGIE may be relevant to a variety of human diseases, aging, comprehending stability of genetic material, and possibly neurodegenerative diseases.
|Balreira, Andrea; Boczonadi, Veronika; Barca, Emanuele et al. (2014) ANO10 mutations cause ataxia and coenzyme Q?? deficiency. J Neurol 261:2192-8|
|Garcia-Diaz, Beatriz; Garone, Caterina; Barca, Emanuele et al. (2014) Deoxynucleoside stress exacerbates the phenotype of a mouse model of mitochondrial neurogastrointestinal encephalopathy. Brain 137:1337-49|
|Garone, Caterina; Garcia-Diaz, Beatriz; Emmanuele, Valentina et al. (2014) Deoxypyrimidine monophosphate bypass therapy for thymidine kinase 2 deficiency. EMBO Mol Med 6:1016-27|
|Quinzii, Catarina M; Garone, Caterina; Emmanuele, Valentina et al. (2013) Tissue-specific oxidative stress and loss of mitochondria in CoQ-deficient Pdss2 mutant mice. FASEB J 27:612-21|
|Melia, Maria J; Kubota, Akatsuki; Ortolano, Saida et al. (2013) Limb-girdle muscular dystrophy 1F is caused by a microdeletion in the transportin 3 gene. Brain 136:1508-17|
|Paradas, Carmen; Camano, Pilar; Otaegui, David et al. (2013) Longitudinal clinical follow-up of a large family with the R357P Twinkle mutation. JAMA Neurol 70:1425-8|
|Marti, Ramon; Lopez, Luis C; Hirano, Michio (2012) Assessment of thymidine phosphorylase function: measurement of plasma thymidine (and deoxyuridine) and thymidine phosphorylase activity. Methods Mol Biol 837:121-33|
|Marti, Ramon; Dorado, Beatriz; Hirano, Michio (2012) Measurement of mitochondrial dNTP pools. Methods Mol Biol 837:135-48|
|Emmanuele, Valentina; Silvers, David S; Sotiriou, Evangelia et al. (2011) MERRF and Kearns-Sayre overlap syndrome due to the mitochondrial DNA m.3291T>C mutation. Muscle Nerve 44:448-51|
|Quinzii, Catarina M; Hirano, Michio (2011) Primary and secondary CoQ(10) deficiencies in humans. Biofactors 37:361-5|
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