No abstract

Loss of functional β-cells is a primary mechanism of type 2 diabetes creating an acute need for understanding how β-cell number and function are regulated in adults under normal physiological conditions. Recent studies suggest a role for TGFβ family ligands in regulating β-cell function and glucose homeostasis. These ligands might influence β-cell proliferation and/or incorporation of new β-cells from progenitors in adults. Soluble antagonists of these ligands also appear to have important roles in regulating ligand activity to maintain homeostasis. These studies suggest that the coordinated activity of several TGFβ ligands might have important regulatory actions in adult β-cells and raise the possibility of developing new therapies for diabetes based on using agonists or antagonists of these ligands. TGFβ family, β-cells and diabetesThe recent obesity epidemic in the US and other developed countries has contributed to an increased incidence of insulin resistance and diabetes, resulting in a more urgent search for novel therapeutic approaches. Loss of β-cell number and/or function results in reduced ability to control blood glucose concentrations, hyperglycemia, and diabetes -a process often exacerbated by peripheral insulin resistance that requires ever increasing insulin output from remaining β-cells. Indeed, recent GWAS studies have identified a number of genetic polymorphisms associated with increased diabetes risk, the majority of which implicate genes important for proper β-cell function. [1][2][3]. The critical nature of functional β-cells to glucose control has focused research on finding new sources for β-cells for transplantation or on factors that can lead to enhanced β-cell function and/or mass. Recent studies suggest that several members of the TGFβ family of growth factors might fill this role under normal physiological conditions and thus, might also be exploited to develop new therapies for diabetes. Although these growth factors are most widely known for their critical roles in development and tissue specification [4], more recent evidence suggests they also mediate numerous actions in adults involving homeostatic control of normal physiological processes, as well as roles in pathology, such as cancer [5]. Although potential actions of some TGFβ family members in glucose regulation were suggested more than 20 years ago, a specific role for a subset of these ligands has been only recently described, including regulation of glucose homeostasis in peripheral tissues and modulation of β-cell function (Table 1).In this review, we examine data from both in vitro and in vivo approaches supporting a role for TGFβ family ligands in glucose homeostasis in adults. These actions of TGFβ family © 2010 Elsevier Ltd. All rights reserved.Corresponding Author: Schneyer, A. (alan.schneyer@bhs.org). This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting,...

TGFβ superfamily ligands, including activin and myostatin, modulate body composition, islet function, and glucose homeostasis. Their bioactivity is controlled by the antagonists follistatin (FST) and follistatin like-3 (FSTL3). The hypothesis tested was that FST and FSTL3 have distinct roles in regulating body composition, glucose homeostasis and islet function through regulation of activin and myostatin bioactivity. Three genetic mutant mouse lines were created. FSTL3 knockout (FSTL3 KO), a mouse line producing only the FST288 isoform (FST288-only) and a double mutant (2xM) in which the lines were crossed. FST288-only males were lighter that WT littermates while FSTL3 KO and 2xM males had reduced perigonadal fat pad weights. However, only 2xM mice had increased whole body fat mass and decreased lean mass by qNMR. Fasting glucose levels in FSTL3 WT and KO mice were lower than FST mice in younger animals but were higher in older mice. Serum insulin and pancreatic insulin content in 2xM mice was significantly elevated over other genotypes. Nevertheless, 2xM mice were relatively insulin resistant and glucose intolerant compared to FST288-only and WT mice. Fractional islet area and proportion of β-cells/islet were increased in FSTL3 KO and 2xM, but not FST288-only mice. Despite their larger size, islets from FSTL3 KO and 2xM mice were not functionally enhanced compared to WT mice. These results demonstrate that body composition and glucose homeostasis are differentially regulated by FST and FSTL3 and that their combined loss is associated with increased fat mass and insulin resistance despite elevated insulin production.