The role of TGF-b family members in the regulation of beta cell growth and function
We have recently found that members of the TGF-bfamily of growth and differentiation factors have potent effects on beta cell proliferation and function in vitro. While some factors stimulate beta cell proliferation others are potent inhibitors of both beta cell growth and function. The inhibitory factors are produced in the beta cells and the expression is regulated by cytokines and metabolic factors known to be involved in diabetes development. The mechanism by which these factors regulate beta cell growth and function is being investigated by analysis of global gene expression pattern and signal transduction induced by the factors. An important goal for this project is to understand the possible role of these factors in the development of diabetes and to prevent and/or treat diabetes by neutralizing the inhibitory factors.
Proliferation and differentiation of human beta cell precursor cells
Mitosis of beta cells from rats and mice can be stimulated by several known hormones and growth factors including Growth Hormone (GH) and Glucagon-like Peptide-1 (GLP-1) and may thus represent a possible principle for up-regulation of beta cell mass in diabetes. However, stimulation of proliferation in human beta cells have proven much more difficult. Factors effective in stimulating animal beta cell proliferation show no activity in beta cells of human origin. We have identified a novel cell type in human islets, which proliferates in response to GH and GLP-1 but does not express insulin. This cell type express several markers indicating an endocrine lineage (Pax6 and Isl1), but does not express any of the known islet hormones. This project aims at characterizing this cell types and identify pathways and factors that can stimulate the differentiation and maturation of these cells into functional insulin expressing beta cells. Proliferation and differentiation of cells is being studies both in cultures and after transplantation into animals.
Mechanisms of beta cell expansion in pregnancy
In pregnancy the demand for insulin is increased and normally a compensatory expansion of the beta cell mass takes place. In rodents the increased levels of placental lactogen, prolactin and growth hormone have shown to be involved in beta cell proliferation and insulin production both in vivo and in vitro. We have previously studied the regulation of expression and signal transduction via the JAK/STAT/SOCS pathway of the receptors for growth hormone and prolactin in beta cells. Studies in human pancreatic islets suggest that that other factors present in serum from pregnant women contribute to the beta cell expansion. We are currently working on the identification of these factors using a proteomics approach. In order to identify the signalling parhways we have investigated the effect of serum from pregnant women on expression of mRNA and microRNA in human pancreatic islets using micro array technology. Identification of the factors and their signalling pathways may reveal new insight into the molecular mechanisms involved in beta cell generation.
Molecular mechanisms involved in beta cell formation and maturation around birth
As there is a marked increase in beta cell mass in the period around birth in the rat offsprings we have studied the expression of mRNA and microRNA in pancreas from fetal rats 2 days before birth, newborn rats and 2 days old rats using micro array technology. We have identified several changes in expression of genes involved in lipid metabolism and cell growth that currently are investigated for cellular localization and biological function. By comparing mRNA and microRNA expression pattern we may identify potential targets for some of the microRNAs that may regulate beta cell formation and maturation. As there was an overrepresentation of genes involved in stellate cell function we are investigating the possible role of pancreatic stellate cells in beta cell formation and maturation in vitro using cultures of dispersed fetal rat pancreas. The stellate cells may either be progenitor cells to beta cells or produce factors that promote beta cell differentiation.
Signalling mechanisms involved in beta cell growth, survival, and function
Intestinal hormones like GLP-1 and GIP are known to stimulate both insulin secretion, beta cell proliferation, survival and differentiation. The receptors belong to the G-protein coupled receptor family that act via cAMP that can activate protein kinase A (PKA). The compartmentalization of PKA and other effector molecules is mediated by scaffold proteins including A-kinase anchoring proteins (AKAPs). WE have found that AKAP 7 isoforms have reciprocal effects on cAMP mediated insulin secretion. Other AKAPs may be involved in regulation of the effects of GLP-1 on beta cell proliferation and survival.
The role of CK2 in beta cell function and survival
The protein kinase CK2 (formerly casein kinase 2) is a constitutive active serine-threonine kinase that uses both GTP and ATP as phosphate donor. With more than 300 identified substrates CK2 controls a wide range of processes, including cell cycle, apoptosis and inflammation. The role of CK2 in pancreatic β-cells is, however, not known. We have now demonstrated that CK2 may have a function in β-cell apoptosis in response to inflammatory cytokines, and are currently investigating the role of CK2 in glucose-induced gene expression and exocytosis.
The role of gut bacteria in beta cell function
The bacterial flora in the gut has recently attracted much interest as they may contribute to both metabolic and immunologic diseases including type 1 and type 2 diabetes. Inflammatory reactions have been implicated in both types and we are currently investigating the possible direct and indirect effects of bacterial constituents on beta cell survival and function by exposing isolated islets to bacterial extracts.
Fetal programming of the endocrine pancreas
The association between birth weight and development of obesity and type 2 diabetes has lead to the "thrifty phenotype" hypothesis about 20 years ago, now called the "Developmental Origin of Health and Disease" hypothesis. It implies that the intrauterine environment influences the development and function of several organs including the endocrine pancreas by epigenetic changes that may be maintained throughout adulthood and result in increased risk of metabolic disorders like type 2 diabetes. Both epidemiological studies and animal experiments have supported this hypothesis. We have found a marked difference in gene expression in the perinatal pancreas between the offspring of mothers fed low protein diet and normal chow. We are currently investigating the functional implications of the changes in selected genes as well as the epigenetic mechanisms that may be involved. In the newly established Center for Fetal Programming it is the plan to integrate these studies with gene expression studies in other tissues as well as physiological and metabolic parameters in order to understand the molecular mechanisms and the opportunity to prevent or reverse the consequences of an adverse fetal programming.
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