COQMITMEL · Mouse Model of CoQ deficiency: pathogenesis and treatment

Mouse Model of CoQ deficiency: pathogenesis and treatment

Coenzyme Q (CoQ) is a lipophilic molecule synthesized in a complex biosynthetic pathway not completely characterized in mammals. CoQ is essential for ATP synthesis and for the scavenging of reactive oxygen species. However, controversy exists regarding other functions of CoQ, e.g. its role in the formation of mitochondrial active supercomplexes, its role in the activity of the mitochondrial permeability transition pore and uncoupling proteins, and its participation in the pirimidine metabolism through its involvement in the reaction catalyzed by dihydrooratate dehydrogenase. In humans, deficiencies of CoQ10 cause clinically heterogeneous mitochondrial diseases, but this heterogeneity is not understood. In the last years, mutations in CoQ10 biosynthetic or regulated genes have been identified. Importantly, only 6 of the 30 patients with identified molecular defect improved after oral CoQ10 supplementation. According to previous studies in cell culture, we have hypothesized that the clinical heterogeneity of CoQ10 deficiency and the fail in the treatment may be due to the differences in: 1) molecular defects; 2) tissue-specific CoQ levels and CoQ functions; 3) effects on the stability of the CoQ biosynthetic protein complex; 4) grade of bioenergetics defect and oxidative stress; and 5) poor absorption and bioavailability of the exogenous CoQ10. To evaluate this hypothesis, identify the function and regulation of some functionally-unknown CoQ biosynthetic proteins, clarify the disputed functions of CoQ, and evaluate alternative therapies, we have proposed: 1. To generate a knockin mouse of a CoQ biosynthetic gene in order to produce a mouse model of CoQ deficiency. 2. To study the pathophysiological consequences of CoQ deficiency syndrome in this mouse model of CoQ deficiency, making special attention to the tissue differences. 3. To evaluate the treatment with some CoQ formulations, as well as the antioxidant therapy with melatonin. We have been able to generate a knockin (KI) mouse for a CoQ biosynthetic gene. Our characterization homozygous KI mice (Coq9X/X) has demonstrated that: (i) the reduction in the Coq7 protein levels with the subsequent reduction in CoQ9 and CoQ10 levels (Fig. 2) and accumulation of DMQ in Coq9X/X mice suggest that Coq9 protein specifically regulates Coq7 protein in the CoQ biosyhthetic pathway, (ii) the presence of a dysfunctional Coq9 protein and/or the deficit in CoQ in the brain causes an increase in free complex III, leading to a decrease in mitochondrial respiration and ATP synthesis, (iii) mitochondrial dysfunction in the brain induces oxidative damage and a caspase-independent apoptotic cell death and (iv) the encephalomyopathic form of CoQ deficiency is progressive and takes place with neuronal death, severe reactive astrogliosis and spongiform degeneration. Therefore, the bioenergetics impairment and the increased oxidative stress seem to be key components in the understanding of the encephalopatyc form of CoQ deficiency (Garcia-Corzo, Hum Mol Genet 2013). In this mouse model (Coq9X/X) of mitochondrial encephalopathy due to CoQ deficiency, we have also evaluated oral supplementation with water-soluble formulations of reduced (ubiquinol-10) and oxidized (ubiquinone-10) forms of CoQ10. Our results show that CoQ10 was increased in all tissues after supplementation with ubiquinone-10 or ubiquinol-10, being the tissue levels of CoQ10 higher with ubiquinol-10 than with ubiquinone-10. Moreover, only ubiquinol-10 was able to increase the levels of CoQ10 in mitochondria from cerebrum of Coq9X/X mice. Consequently, ubiquinol-10 was more efficient than ubiquinone-10 in increasing the animal body weight and CoQ-dependent respiratory chain complexes activities, and reducing the vacuolization, astrogliosis and oxidative damage in diencephalon, septum-striatum and, to a lesser extend, in brainstem. These results suggest that water-soluble formulations of ubiquinol-10 may improve the efficacy of CoQ10 therapy in primary and secondary CoQ10 deficiencies, other mitochondrial diseases and neurodegenerative diseases (Garcia-Corzo, Hum Mol Genet, submitted). Our results are contributing to the goals of the International Rare Disease Research Consortium (IRDiRC). Moreover, the project has an economic relevance since pharmaceutical companies have showed interest in our study.

Data: CORDIS, © European Union