Metallothionein expression in tissues of rotenone-treated rats

Abstract

Mitochondrial NADH:ubiquinone oxidoreductase (complex I) carries out a number of well defined functions required for cell physiology. Deficiencies of complex I lead to multi-system disorders that include several well-known phenotypes such as type 2 diabetes mellitus, Alzheimer's disease as well as less known phenotypes such as MELAS, Leigh syndrome and MERRF. It was recently identified that ROS sensitive proteins known as metallothioneins (MTs), are over-expressed in complex I deficient cell lines and that these proteins have a protective effect against ROS related pathologies. It is still not clear if isoform-specific MT expression occurs in this disease and if it plays a significant role in vivo. This study investigated the expression of different MT isoforms in rotenone-treated Sprague Dawley rats, an in vivo model that has been used to study cellular biological responses of mitochondrial complex I deficiency. The hypothesis of this study states that a rotenone-induced complex I deficiency would lead to an increase of MT mRNA expression in vivo. The specific aim was to determine the relative mRNA expression levels of the three main MT isoforms in rotenone-treated rat tissues. Real-time PCR was used to achieve this aim. In this dissertation the differential expression of MT-1, MT-2 and the brain specific isoform, MT-3 in brain, liver, heart- and skeletal muscle tissues of rotenone-treated Sprague Dawley rats is described. The results indicate that MT-1 expression is significantly increased in the liver as well as, but to a lesser extent, in the brain and heart muscle. MT-1 expression in skeletal muscle was not detected. In contrast, significant increases in expression were observed for MT-2 in all the tissue types with an approximate two-fold increase at the highest rotenone dosage in liver, brain and heart muscle. Skeletal muscle had the smallest increase. For MT-3, no detectable levels of expression could be observed in skeletal and heart muscle. Surprisingly, levels of expression occurred in the liver which slightly (43%), but significantly increased at the highest rotenone dose. As expected, much higher relative levels of MT-3 expression were observed in brain tissue with a more pronounced increase (almost two-fold) at the highest rotenone dose. As the hypothesis of this study proposed, the in vivo data generated from this study supports the published in vitro data which showed that a rotenone-induced complex I deficiency results in MT expression. This over expression may contribute to a protected effect on the pathology of this disease although this still needs to be established. Furthermore, the results of this study show that the expression of the various MT isoforms in rotenone-treated rat tissues is not expressed in a similar way to the induced deficiency which may point to a differential regulation and response of the three MT isoforms to such a deficiency.