In situ nucleic acid detection of PDC-E2, BCOADC-E2, OGDC-E2, PDC-E1 alpha, BCOADC-E1 alpha, OGDC-E1, and the E3 binding protein (protein X) in primary biliary cirrhosis

The characteristic serological feature of primary biliary cirrhosis (PBC) i s the presence of antimitochondrial antibodies (AMAs), and the major protei ns recognized by AMAs are subunits of the 2-oxo acid dehydrogenase complexe s (2-OADC), including the E2 components of the pyruvate dehydrogenase compl ex (PDC), the 2-oxo-glutarate dehydrogenase complex (OGDC), the branched-ch ain 2-oxoacid dehydrogenase complex (BCOADC), the E3 binding protein (E3BP or protein X) and the E1a component of mammalian PDC, Previous work has pos tulated that either E3BP, or a molecule cross-reactive with the PDC-E2 mole cule, is uniquely expressed on the surface of biliary epithelial cells in P BC, To address this issue, we performed ill situ hybridization for all of t he major 2-OADC components at the mRNA level, including PDC-E2, BCOADC-E2, OGDCE2, PDC-E1a, BCOADC-E1a, OGDC-E1, and E3BP using 13 PBC and 9 control l ivers using 7 mitochondrial antisense probes. In both PBC and controls, the expression of all 2-OADC component mRNA studied herein were found in hepat ocytes and infiltrating mononuclear cells, without significant differences. Interestingly, however, despite published data on immunohistochemical stai ning, interlobular bile ducts including the injured bile ducts in PBC were generally negative or only faintly positive, with the exception of 1 bile d uct in 1 of 13 cases of PBC and 1 of 9 control liver specimens. Moreover, c onfocal microscopic examination and image analysis revealed that the mRNA s ignal intensity of each of the 2-OADC components in the bile ducts of PBC w as relatively lower in comparison with control liver diseases. These data s uggest that continuous enhanced synthesis of the 2-OADC components is not l ikely to be occurring in the biliary epithelial cells in PBC, and that an i ncrease of PDC-E2 or E3BP immunoreactivity in PBC is caused by exogenous im ported or cross-reactive molecules.