Activins A and B Regulate Fate-Determining Gene Expression in Islet Cell Lines and Islet Cells From Male Mice

Abstract

TGFβ superfamily ligands, receptors, and second messengers, including activins A and B, have been identified in pancreatic islets and proposed to have important roles regulating development, proliferation, and function. We previously demonstrated that Fstl3 (an antagonist of activin activity) null mice have larger islets with β-cell hyperplasia and improved glucose tolerance and insulin sensitivity in the absence of altered β-cell proliferation. This suggested the hypothesis that increased activin signaling influences β-cell expansion by destabilizing the α-cell phenotype and promoting transdifferentiation to β-cells. We tested the first part of this hypothesis by treating α- and β-cell lines and sorted mouse islet cells with activin and related ligands. Treatment of the αTC1-6 α cell line with activins A or B suppressed critical α-cell gene expression, including Arx, glucagon, and MafB while also enhancing β-cell gene expression. In INS-1E β-cells, activin A treatment induced a significant increase in Pax4 (a fate determining β-cell gene) and insulin expression. In sorted primary islet cells, α-cell gene expression was again suppressed by activin treatment in α-cells, whereas Pax4 was enhanced in β-cells. Activin treatment in both cell lines and primary cells resulted in phosphorylated mothers against decapentaplegic-2 phosphorylation. Finally, treatment of αTC1-6 cells with activins A or B significantly inhibited proliferation. These results support the hypothesis that activin signaling destabilized the α-cell phenotype while promoting a β-cell fate. Moreover, these results support a model in which the β-cell expansion observed in Fstl3 null mice may be due, at least in part, to enhanced α- to β-cell transdifferentiation.

Growth Hormone Reprograms Macrophages toward an Anti-Inflammatory and Reparative Profile in an MAFB-Dependent Manner

“…In the current study, GH reduced activin A secretion and promoted MAFB upregulation, and thus supporting the role of GH in GM-Mf reprogramming. In accord with these results, activin A was shown to suppress MAFB expression in a pancreatic islet cell line (68). MAFB stabilization is controlled by GSK3b (48), an inhibitory serine/threonine kinase that is inactivated by phosphorylation at serine-9 (49).…”

Visualizing subcellular rearrangements in intact β cells using soft x-ray tomography

“…Before purchasing, all cell lines were authenticated by each supplier. INS-1E cells were analyzed using COI Assay by the supplier (Addex Bio) to ensure no interspecies contamination (40,41). In addition, we performed RNA sequencing to confirm the presence of insulin, observed the cells under microscopy to identify changes in morphology and attachment properties, and maintained growth curves to monitor cell doubling time, growth trends, and passage number.…”

TGF-β Family Signaling in Ductal Differentiation and Branching Morphogenesis

“…However, other, yet similar, experiments with pancreatic explants showed that activin A or activin B (activin-b B dimer) did not affect pancreatic cell differentiation; instead, activin A caused a transdifferentiation of the embryonic pancreatic tissue to intestinal tissue (van Eyll et al 2004). Independent transdifferentiation and signaling experiments confirmed that activin A or activin B suppress exocrine a-cell differentiation and promote endocrine b-cell differentiation, enabling insulin secretion (Andrzejewski et al 2015). The activins repress the expression of a-cell transcription factors and induce b-cell transcription factor expression, and their actions explain the phenotype of mice with a deletion of the Fstl3 gene, encoding follistatin-like 3, which show hyperplasia of their b-islets (Andrzejewski et al 2015).…”

“…Independent transdifferentiation and signaling experiments confirmed that activin A or activin B suppress exocrine a-cell differentiation and promote endocrine b-cell differentiation, enabling insulin secretion (Andrzejewski et al 2015). The activins repress the expression of a-cell transcription factors and induce b-cell transcription factor expression, and their actions explain the phenotype of mice with a deletion of the Fstl3 gene, encoding follistatin-like 3, which show hyperplasia of their b-islets (Andrzejewski et al 2015). Despite these observations, normal pancreatic tissue expresses activin-b A and activin-b B in the epithelium, and follistatin and activin receptors in the mesenchyme (Ritvos et al 1995;Maldonado et al 2000).…”