TISSUE-SPECIFICITY OF RAT MITOCHONDRIAL DIMETHYLGLYCINE DEHYDROGENASE EXPRESSION

Expression of mitochondrial dimethylglycine dehydrogenase (Me(2)GlyDH) was analysed in various tissues, liver cell types and developmental stages of the rat. Total RNA extracted from liver, spleen, brain, kidney, lung and heart was reverse-transcribed into cDNA and amplified with Me(2)GlyDH cDNA-specific oligonucleotides by PCR. Expression of the enzyme was observed mainly in liver and kidney. In addition, Me(2)GlyDH mRNA could be demonstrated in total RNA samples of lung, heart and brain but was barely detectable in spleen total RNA. In RNA prepared from 14-day rat embryos, Me(2)GlyDH-specific mRNA was clearly present. Among various liver cell types, besides hepatocytes, endothelial cells showed a high level of Me(2)GlyDH mRNA expression. There was no amplification product detectable in liver macrophages (Kupffer cells) and only a very faint one in fat-storing cells (Ito cells). Western blots confirmed at the protein level the predominant expression of the enzyme in liver and kidney, but Me(2)GlyDH protein was also present in the protein extract of lung, heart, spleen and brain. Immunohistochemical staining of liver slices with Me(2)GlyDH-specific antiserum revealed that expression of this enzyme is evenly distributed throughout the liver tissue. In the kidney, expression of the enzyme was located in the proximal tubule cells. Our results demonstrate that, contrary to the previously assumed liver-restricted expression, this enzyme is specifically expressed predominantly in the liver and kidney, but, in addition, it is detectable in many other tissues of the rat.