Signal detection of endothelin receptor subtypes in human cirrhotic liver by a new in situ hybridization method

Endothelin (ET) has been implicated in the regulation of hepatic microcirculation and development of portal hypertension, but the role of ET in cirrhosis of the liver has not yet been elucidated. We present here the application of peptide nucleic acid (PNA) probes in a fast and sensitive in situ hybridization (ISH) method for localizing the mRNA of endothelin receptor subtypes in formalin-fixed, paraffin-embedded sections of normal and cirrhotic human liver. The results of ISH using synthetic FITC-labeled PNA probes combined with the catalyzed signal amplification (CSA) system were compared with those using the standard detection system. It was indicated that the CSA-ISH protocol is more sensitive for the detection of mRNA target than the standard ISH protocol. Our results with CSA-ISH showed that the expression of mRNA for the endothelin B receptor was significantly upregulated in hepatic sinusoidal lining cells in cirrhotic human liver tissues compared to control normal liver tissue. Therefore, the CSA detection system may facilitate and enhance the use of in situ hybridization protocols, and CSA-ISH will be used as an important diagnostic technique in the future.