ABSTRACT
Transcription factor expression fluctuates during ß-cell ontogeny, and disruptions in this pattern can affect the development or function of those cells. Here we uncovered that murine endocrine pancreatic progenitors express high levels of the homeodomain transcription factor Prox1, whereas both immature and mature ß-cells scarcely express this protein. We also investigated if sustained Prox1 expression is incompatible with ß-cell development or maintenance using transgenic mouse approaches. We discovered that Prox1 upregulation in mature ß-cells has no functional consequences; in contrast, Prox1 overexpression in immature ß-cells promotes acute fasting hyperglycemia. Using a combination of immunostaining and quantitative and comparative gene expression analyses, we determined that Prox1 upregulation reduces proliferation, impairs maturation, and enables apoptosis in postnatal ß-cells. Also, we uncovered substantial deficiency in ß-cells that overexpress Prox1 of the key regulator of ß-cell maturation MafA, several MafA downstream targets required for glucose-stimulated insulin secretion, and genes encoding important components of FGF signaling. Moreover, knocking down PROX1 in human EndoC-ßH1 ß-cells caused increased expression of many of these same gene products. These and other results in our study indicate that reducing the expression of Prox1 is beneficial for the expansion and maturation of postnatal ß-cells.
Subject(s)
Cell Differentiation/genetics , Cell Proliferation/genetics , Homeodomain Proteins/genetics , Hyperglycemia/genetics , Insulin-Secreting Cells/metabolism , Insulin/metabolism , Maf Transcription Factors, Large/genetics , RNA, Messenger/metabolism , Tumor Suppressor Proteins/genetics , Animals , Animals, Newborn , Cell Line , Chromatin Immunoprecipitation , Computer Simulation , Down-Regulation , Enzyme-Linked Immunosorbent Assay , Gene Expression Profiling , Gene Knockdown Techniques , Glucose Tolerance Test , Humans , Insulin-Secreting Cells/cytology , Maf Transcription Factors, Large/metabolism , Mice , Mice, Transgenic , Real-Time Polymerase Chain ReactionABSTRACT
Islet cell growth and function are affected by ligands from the epidermal growth factor (EGF) family. We describe here the expression, regional distribution, and effect on growth and secretion of insulin of a subset of these, the neuregulin (NRG) family. The expression of NRG1α, NRG1ß, NRG2α, NRG2ß, NRG3, and NRG4 in rat islets was determined using immunohistochemical and double immunofluorescent staining. We also report the expression of the 4 receptors and the remaining 7 ligands using immunohistochemistry. The NRG1α splice variant was expressed in ß-cells and the NRG1ß variant mainly in α-cells. NRG3 was also predominantly present in α-cells. Most of the members of the EGF family of ligands were also expressed, with Epigen being present at the highest levels. The rat islet-derived cell line CRI-G1 was used to study the effect of addition of EGF, NRG1ß, NRG3, and NRG4 on cell growth and insulin secretion. Synthetic refolded NRG3 strongly stimulated the growth of the CRI-G1 cells, and NRG4 gave the greatest stimulation of insulin release. Different members of the NRG family are therefore potentially potent stimuli for islet cell growth and insulin release and differ in expression in α- and ß-cells.
