Megalin and cubilin in the human gallbladder epithelium

Although the role of cholesterol absorption by the gallbladder epithelium in gallstone formation is well established, the exact process is poorly understood. Potential candidates for regulation of transepithelial cholesterol transport are suggested to be two large membrane multiple ligand receptors, megalin and cubilin. We studied the expression of these two proteins in both acalculous and calculous human gallbladder epithelia. Adult human gallbladder tissues were received from 21 patients (9 men, 12 women) who had undergone cholecystectomy. The patients were divided into two groups: group A (calculous gallbladder group; 5 men, 6 women; mean age 64.4 +/- 11.1 years) with cholelithiasis, and group B (acalculous gallbladder group; 4 men, 6 women; mean age 55.3 +/- 16.1 years). In the gallbladder tissues megalin and cubilin expression was studied by immunohistochemistry and conventional RT-PCR, and gene expression levels were estimated by real-time RT-PCR. Both megalin and cubilin gene transcripts were found in total RNA preparations from acalculous gallbladder. In contrast, in preparations from calculous gallbladder, none or only one of the proteins was detected. Immunoreactive proteins were detected in the simple columnar acalculous gallbladder epithelium but not in the calculous gallbladder epithelium. Our results show different expression patterns of the two proteins in calculous gallbladders and acalculous gallbladders. In the latter both proteins are expressed, suggesting an association with gallstone formation and implying a putative role of the two proteins in cholesterol endocytosis. In other words, the presence of both proteins may be essential for the prevention of stone formation.