Contribution of apoptosis and apoptosis-related proteins to the malformation of the primitive intrahepatic biliary system in Meckel syndrome

In the developing liver, the complete or partial persistence of the primiti ve double-layered cylinder of biliary-type cells that surrounds the branche s of portal vein and its mesenchyme gives origin to portal tracts with an i ncreased number of bile duct structures. The term "ductal plate malformatio n of the liver" was coined to label the insufficient remodeling of the prim itive intrahepatic biliary system. Meckel syndrome is an autosomal recessiv e inherited disease characterized by occipital encephalocele, postaxial pol ydactyly, diffuse cystic renal dysplasia, and malformation of the ductal pl ate of the liver. We studied 52 fetuses with Meckel syndrome from five Germ an centers (Berlin, Freiburg, Heidelberg, Mainz, and Marburg), Analysis of apoptosis and cell proliferation (Ki-67) was performed by terminal deoxynuc leotide transferase-mediated dUTP nick-end, labeling (TUNEL) and immunohist ochemistry in the liver of 24 normal fetuses of different gestational ages (14-38 weeks of gestation) and in 14 fetuses with Meckel syndrome (17-38 we eks of gestation). The expression of two apoptosis-related proteins, Fas (a transmembrane cell surface protein involved in the apoptosis) and Bcl-2 Ca n anti-apoptotic protein), was studied by immunohistochemistry in the liver of 11 normal fetuses of different gestational ages (14-40 weeks of gestati on) and in 40 fetuses with Meckel syndrome (16-38 weeks of gestation). In c ontrol fetuses, apoptosis rate and cell proliferation were high in the remo deling ductal plate and moderate in the ductal plate and in remodeled bile ducts. During gestation, expression of Fas and Bcl-2 decreased and increase d, respectively. The malformed ductal plates in the fetal livers with Mecke l syndrome showed a marked decrease in the apoptotic rate and Fas expressio n and an increase in proliferative activity and Bcl-2 expression in compari son with control fetuses. Furthermore, by linear regression analysis, we fo und that both proliferation activity and apoptosis rate in the ductal plate malformation of fetuses with Meckel syndrome were practically constant alo ng the gestation. These results, which represent the first systematic study of apoptosis in ductal plate malformation of the liver, indicate that 1) a nimals harboring the gene defect of Meckel syndrome could be a good model f or the study of the abnormal development of the primitive intrahepatic bili ary system, 2) a decreased cell turnover occurs in the ductal plate malform ation of fetuses with Meckel syndrome, and 3) the increase of Bcl-2 express ion contributes to the pathogenesis of the lack of remodeling of ductal pla te of the liver in Meckel syndrome.