Differential expression of genes involved in phase two biotransformation in an NDUFS4 deficient mouse model

Abstract

Mitochondria are involved in a plethora of cellular processes, the most prominent being the production of energy as adenosine triphosphate (ATP) through the oxidative phosphorylation (OXPHOS) system. Dysfunction of the OXPHOS system, especially complex I (CI) is one of the most common groups of inborn errors of metabolism that results in heterogeneous diseases like Leigh Syndrome, which are difficult to treat. To study mitochondrial disease in vivo a whole body Ndufs4 knockout mouse model has been developed and is now commonly used in research. Although mitochondrial disorders have been extensively studied, there are still a lot of gaps in the literature, for example, its effect on biotransformation. The limited ATP of individuals with mitochondrial disorders could affect the activity and capacity of the biotransformation pathway by dysregulating any of the factors that influence metabolism including gene expression through retrograde signalling, allosteric regulation, and the availability of cofactors. The aim of this study was to investigate differential expression of genes involved in phase two biotransformation in an Ndufs4 knockout mouse model. This was achieved by first investigating differential gene expression of glycine conjugation as a primary pathway of phase two biotransformation between Ndufs4 knockout (KO) and wild-type (WT) mice. This investigation was then expanded to explore if the changes observed in glycine conjugation were reflected in the gene expression of seven remaining phase two biotransformation pathways. Significant downregulation of the glycine conjugation pathway in KO mice compared to WT mice was indicated by gene expression analysis of Acsm2 and Glyat. These genes had fold changes of ~-3.6 and ~-1.6, respectively. Gene expression data was validated through enzyme activity analysis of GLYAT, which confirmed the downregulation in KO mice, by exhibiting ~50% residual GLYAT activity compared to WT mice. Significant differential expression was also revealed for 50 of the remaining phase two biotransformation pathway genes. Expression of most of these genes were significantly downregulated. As the exception, gene expression of sulfotransferases was significantly increased. Downstream effects of decreased ATP production and redox imbalance that contribute to retrograde signalling, is hypothesised to be the main contributors to the downregulation of genes investigated. Overall, the data strongly suggests that phase two biotransformation pathways are highly affected by mitochondrial dysfunction.