Augmenter of Liver Regeneration (alr) Promotes Liver Outgrowth during Zebrafish Hepatogenesis

Abstract

Augmenter of Liver Regeneration (ALR) is a sulfhydryl oxidase carrying out fundamental functions facilitating protein disulfide bond formation. In mammals, it also functions as a hepatotrophic growth factor that specifically stimulates hepatocyte proliferation and promotes liver regeneration after liver damage or partial hepatectomy. Whether ALR also plays a role during vertebrate hepatogenesis is unknown. In this work, we investigated the function of alr in liver organogenesis in zebrafish model. We showed that alr is expressed in liver throughout hepatogenesis. Knockdown of alr through morpholino antisense oligonucleotide (MO) leads to suppression of liver outgrowth while overexpression of alr promotes liver growth. The small-liver phenotype in alr morphants results from a reduction of hepatocyte proliferation without affecting apoptosis. When expressed in cultured cells, zebrafish Alr exists as dimer and is localized in mitochondria as well as cytosol but not in nucleus or secreted outside of the cell. Similar to mammalian ALR, zebrafish Alr is a flavin-linked sulfhydryl oxidase and mutation of the conserved cysteine in the CxxC motif abolishes its enzymatic activity. Interestingly, overexpression of either wild type Alr or enzyme-inactive AlrC131S mutant promoted liver growth and rescued the liver growth defect of alr morphants. Nevertheless, alr C131S is less efficacious in both functions. Meantime, high doses of alr MOs lead to widespread developmental defects and early embryonic death in an alr sequence-dependent manner. These results suggest that alr promotes zebrafish liver outgrowth using mechanisms that are dependent as well as independent of its sulfhydryl oxidase activity. This is the first demonstration of a developmental role of alr in vertebrate. It exemplifies that a low-level sulfhydryl oxidase activity of Alr is essential for embryonic development and cellular survival. The dose-dependent and partial suppression of alr expression through MO-mediated knockdown allows the identification of its late developmental role in vertebrate liver organogenesis.

Effects of copper oxide nanoparticles on developing zebrafish embryos and larvae

“…cp is a specific molecular marker that detects early hepatic cells and is expressed in the liver bud from 32 to 34 hpf onward. 43,44 In embryos and larvae from the 12.5 and 50 mg/L exposed groups, the cellular localization of cp-expressing cells was similar to that of unexposed embryos or larvae. However, the exposed embryos or larvae exhibited livers of reduced size ( Figure 4B, C, E, F, H, and I).…”

The lure of zebrafish in liver research: regulation of hepatic growth in development and regeneration

“…Several genes that are highly enriched in the developing liver such as matrix metalloproteinase mmp23b [56], as well as the secretory pathway components leg1 [57,58] and sec13 [59] are required for hepatocyte proliferation. Other genes including augmenter of liver regeneration ( alr )[60], zfyve9a [61] and klf6 [62] seem to be specifically requires for proliferation during the outgrowth phase of liver development. Together, these studies begin to identify factors that are required for the survival and proliferation during liver development.…”

Hepassocin is required for hepatic outgrowth during zebrafish hepatogenesis

“…For example, the fibroblast growth factor (FGF) signaling pathway regulates liver homeostasis in zebrafish, and augmenter of liver regeneration (ALR) promotes liver growth during zebrafish hepatogenesis [17,18]. Importantly, the structure of HPS is similar to angiopoietinlike factors (Angptls).…”