Transforming Growth Factor - Beta Superfamily Signaling in Diabetes and Obesity

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Activated TGF-beta family factors signal via dual Type II (TbetaRII) and dual Type I (TbetaRI/Activin-like kinase 5/ALK5) transmembrane serine/threonine kinases receptors and effector Smad transcription factors. While TGF-beta signaling is critical during endocrine pancreas development, whether TGF-beta plays a role in maintaining adult beta-cell function is unclear. Interestingly, TGF-beta levels are elevated in diabetes, diabetes-associated complications, and obesity. Using primary islets and established beta-cell lines, we are examining the role of various TGF-beta isoforms and their respective receptors on the regulation of key pancreatic specific genes. Smad proteins are the established intracellular effectors of TGF-beta signaling and upon TGF-beta ligand binding, the activated TbetaRI/ALK-5 receptors recruit and phosphorylate receptor-Smads, i.e., Smad2 and Smad3. We are examining the roles of various Smad proteins, in the regulation of gene expression specific to the pancreas. TGF-beta signalling is known to suppress proliferation and promote growth arrest, differentiation/apoptosis of cells of the epithelial lineage. However, the role of this pathway in the growth, proliferation, differentiation and death of constituent pancreatic epithelial cells is unknowm. Using primary islets and established pancreatic ductal and beta cell lines, we are examining the role of TGF-beta signaling in these processes. Of particular interest will be the contribution of TGF-beta signaling in regulation of beta cell mass amd beta cell function. We are using primary islets, and established beta cell lines to examine the effects of TGF-beta isoforms, its receptor activation/inactivation, on beta cell mass and beta cell function. In addition the role of downstream Smad proteins is also being investigated. Several parallel approaches will be taken to explore this issue, which will hopefully lead to an improved understanding of the role of this complex signaling pathway in pancreatic development and specifically in regulation of beta cell mass and function. The information gained will be useful to delineate the role of this pathway in diseases of the pancreas.