Perspectives on the Activities of ANGPTL8/Betatrophin

Figure 1. Hydrodynamic Tail Vein Injection of Mouse ANGPTL8/Betatrophin Plasmid DNA Induces Pancreatic Beta Cell Proliferation with Significant Variability, and hBetatrophin Exists in a Large Protein Complex in Serum (A) Pancreatic beta cell proliferation rate (% Ki67/insulin) after hydrodynamic tail vein injection of GFP (n = 14mice) ormBetatrophin (n = 38mice) plasmids (p = 0.016). This figure combines data from 5 separate experiments. (B) The data from our original report (Yi et al., 2013, Figure S3F) is replotted in the same format. (C) Human serum fractionated in a nondenaturing gel stained with anti-hBetatrophin antibody. hBetatrophin migrates as a high molecular weight (480–1,000 kDa) complex compared to recombinant hBetatrophin protein (60–100 kDa. Phoenix Pharmaceuticals). In this issue of Cell, Gusarova et al. (2014) show that deletion of ANGPTL8 in mice does not affect the compensatory proliferation of pancreatic beta cells in response to insulin resistance induced by a high-fat diet or treatment with the insulin antagonist S961. They also show that overexpression of human ANGPTL8 in mouse liver leads to elevated serum triglyceride levels but not significant pancreatic beta cell proliferation. They conclude that ANGPTL8 (also called betatrophin [Yi et al., 2013]/RIFL [Ren et al., 2012]/lipasin [Zhang, 2012]) does not control pancreatic beta cell expansion. Their experimental design and data are clearly presented and straightforward, and we agree with their conclusions. Our own follow-up experiments using an independent knockout of ANGPTL8 produced the same result. Taken together, these new data contradict our previous conclusion (Yi et al., 2013) that betatrophin is the sole agent responsible for beta cell proliferation following S961 treatment. Furthermore, these new results cast doubt on the finding that beta cell proliferation can be induced by overexpression of ANGPTL8/ betatrophin. The work presented in Yi et al. (2013) hadat its foundation the finding that the insulin antagonist S961 causes a specific and robust increase in beta cell proliferation and subsequently beta cell mass. This finding has now been reproduced by Kaestner’s group (Jiao et al., 2014) and Gusarova et al. However, additional experiments by our lab (Figure 1A) and those by Gusarova et al. (Gusarova et al., 2014; Figures 2F and S1) using tail vein injection to overexpress ANGPTL8/ betatrophin show a significant and unsatisfactory variation, perhaps as a result of liver inflammation, which makes it difficult to draw a secure conclusion about beta cell replication. InYi et al.we reported an average beta cell replication rate of 4% in betatrophin-injected mice (n = 7); with five additional experiments (n = 52 mice in total), the averagebeta cell replication rate in betatrophin-injected mice drops to 1.2%. While still significantly above control levels (p = 0.016 for all experiments) of beta cell replication (0.6%), the conclusion from Yi et al. must be corrected and modified with respect to the magnitude of the effect. A confounding issue is that these injection experiments show a ‘‘jackpot’’ effect on beta cell replication (Figures 1A and 1B); some mice respond strongly to ANGPTL8/betatrophin expression but many do not. When all mice are taken into account (three experiments in Yi et al. [Yi et al., 2013], five new experiments here in Figure 1A, and Gusarova et al. [Gusarova et al. 2014]), and compared to control injected animals, the results show a modest average increase in beta cell replication.