Evidence From Human and Zebrafish That GPC1 Is a Biliary Atresia Susceptibility Gene

Abstract

BACKGROUND & AIMS Biliary atresia (BA) is a progressive fibroinflammatory disorder of infants involving the extrahepatic and intrahepatic biliary tree. Its etiology is unclear but is believed to involve exposure of a genetically susceptible individual to certain environmental factors. BA occurs exclusively in the neonatal liver, so variants of genes expressed during hepatobiliary development could affect susceptibility. Genome-wide association studies previously identified a potential region of interest at 2q37. We continued these studies to narrow the region and identify BA susceptibility genes. METHODS We searched for copy number variants that were increased among patients with BA (n = 61) compared with healthy individuals (controls; n = 5088). After identifying a candidate gene, we investigated expression patterns of orthologues in zebrafish liver and the effects of reducing expression, with morpholino antisense oligonucleotides, on biliary development, gene expression, and signal transduction. RESULTS We observed a statistically significant increase in deletions at 2q37.3 in patients with BA that resulted in deletion of one copy of GPC1, which encodes glypican 1, a heparan sulfate proteoglycan that regulates Hedgehog signaling and inflammation. Knockdown of gpc1 in zebrafish led to developmental biliary defects. Exposure of the gpc1 morphants to cyclopamine, a Hedgehog antagonist, partially rescued the gpc1-knockdown phenotype. Injection of zebrafish with recombinant Sonic Hedgehog led to biliary defects similar to those of the gpc1 morphants. Liver samples from patients with BA had reduced levels of apical GPC1 in cholangiocytes compared with samples from controls. CONCLUSIONS Based on genetic analysis of patients with BA and zebrafish, GPC1 appears to be a BA susceptibility gene. These findings also support a role for Hedgehog signaling in the pathogenesis of BA.

Embryonic cholecystitis and defective gallbladder contraction in the Sox17-haploinsufficient mouse model of biliary atresia

“…For example, Jung et al (2015) reported that SHH pathway activation was observed, especially in the cholangiocytes of the peribiliary glands, in human patients with biliary atresia. In pathological studies, some have reported that Hh expression is considerably increased in fibrotic damaged biliary diseases in response to injury (Omenetti et al, 2008;Omenetti and Diehl, 2011;Cui et al, 2013;Hu et al, 2015). It has also been speculated that the SHH signaling pathway regulates the epithelial-mesenchymal transition of cholangiocytes (Omenetti et al, 2008;Jung et al, 2015).…”

“…It has also been speculated that the SHH signaling pathway regulates the epithelial-mesenchymal transition of cholangiocytes (Omenetti et al, 2008;Jung et al, 2015). The effects of excess SHH signaling encompass defective hepatobiliary ducts in a zebrafish model (Cui et al, 2013;Tang et al, 2016), suggesting that excess SHH signaling can have detrimental effects on the proper development and maintenance of the biliary duct. The current phenotype of reduced SHH signaling in the defective gallbladder might be explained by the distinct roles of SHH signaling during developmental and early pathogenic stages (i.e.…”

Management of Biliary Atresia: A Review

“…19 A possible association with the gene GPC1 which encodes a glypican 1-a heparan sulfate proteoglycan has been reported. 20 This gene is located on the long arm of chromosome 2 (2q37). This gene is involved in the regulation of the gene Hedgehog and also of inflammation.…”

Genetic Contributors and Modifiers of Biliary Atresia

“…Another potential causative gene, glypican 1 (GPC1), has garnered attention through genome-wide association studies of DNA copy number variation that identified a potential region of susceptibility to biliary atresia on chromosome 2q37.3, which was replicated in an independent cohort of patients demonstrating heterozygous deletion of GPC1 as the sole gene in this region [66]. Glypican family members are involved in various signaling and developmental pathways in hepatocytes and cholangiocytes, though GPC1 had not been previously associated with liver development or function.…”