Manfred Reinecke

Increased Number of Islet-Associated Macrophages in Type 2 Diabetes

Activation of the innate immune system in obesity is a risk factor for the development of type 2 diabetes. The aim of the current study was to investigate the notion that increased numbers of macrophages exist in the islets of type 2 diabetes patients and that this may be explained by a dysregulation of islet-derived inflammatory factors. Increased islet-associated immune cells were observed in human type 2 diabetic patients, high-fat–fed C57BL/6J mice, the GK rat, and the db/db mouse. When cultured islets were exposed to a type 2 diabetic milieu or when islets were isolated from high-fat–fed mice, increased islet-derived inflammatory factors were produced and released, including interleukin (IL)-6, IL-8, chemokine KC, granulocyte colony-stimulating factor, and macrophage inflammatory protein 1α. The specificity of this response was investigated by direct comparison to nonislet pancreatic tissue and β-cell lines and was not mimicked by the induction of islet cell death. Further, this inflammatory response was found to be biologically functional, as conditioned medium from human islets exposed to a type 2 diabetic milieu could induce increased migration of monocytes and neutrophils. This migration was blocked by IL-8 neutralization, and IL-8 was localized to the human pancreatic α-cell. Therefore, islet-derived inflammatory factors are regulated by a type 2 diabetic milieu and may contribute to the macrophage infiltration of pancreatic islets that we observe in type 2 diabetes.

Interleukin-6 enhances insulin secretion by increasing glucagon-like peptide-1 secretion from L cells and alpha cells

Exercise, obesity and type 2 diabetes are associated with elevated plasma concentrations of interleukin-6 (IL-6). Glucagon-like peptide-1 (GLP-1) is a hormone that induces insulin secretion. Here we show that administration of IL-6 or elevated IL-6 concentrations in response to exercise stimulate GLP-1 secretion from intestinal L cells and pancreatic alpha cells, improving insulin secretion and glycemia. IL-6 increased GLP-1 production from alpha cells through increased proglucagon (which is encoded by GCG) and prohormone convertase 1/3 expression. In models of type 2 diabetes, the beneficial effects of IL-6 were maintained, and IL-6 neutralization resulted in further elevation of glycemia and reduced pancreatic GLP-1. Hence, IL-6 mediates crosstalk between insulin-sensitive tissues, intestinal L cells and pancreatic islets to adapt to changes in insulin demand. This previously unidentified endocrine loop implicates IL-6 in the regulation of insulin secretion and suggests that drugs modulating this loop may be useful in type 2 diabetes.

The development of functional digestive and metabolic organs in turbot, Scophthalmus maximus

The functional status of organ systems involved into the processing of exogenous food is critical for the survival and growth of fish early life stages. The present study on laboratory-reared larval turbot, Scophthalmus maximus, provides an overview on the ontogeny of structure and functions involved in digestion, absorption and metabolism of nutrients. At start of exogenous feeding the intestine of larval turbot is anatomically differentiated, with enterocytes displaying an adult-type ultrastructure and being able to process lipids. At the microvillous border of the enterocytes, enzymes of contact digestion such as aminopeptidase are found. The ultrastructure of the exocrine pancreatic cells is fully differentiated from hatching onwards. Likewise, substantial activities of trypsin-type proteases are present. A stomach anlage exists in first-feeding larvae; however, the stomach becomes functional (appearance of gastric glands and pepsin secretion) only during metamorphosis. Liver parenchymal cells already display a functional ultrastructure during the endotrophic phase; with onset of exogenous feeding they develop pronounced diet-related changes of their energy stores. Larval respiration is not executed by the gills since respiratory surface of these structures develops only towards metamorphosis. The energy generation of larval muscle tissue depends on aerobic metabolism, whereas glycolytic activities start to increase at metamorphosis. In conclusion, two important patterns can be recognized in the development of turbot larvae: (1) The structure/function is differentiated at hatching or at the onset of exogenous feeding (afterwards it experiences mainly quantitative but not qualitative growth, i.e., intestine, exocrine pancreas, liver); or (2) the structure/function is absent in larvae and develops only during metamorphosis (i.e., gills, glycolytic muscle metabolism, stomach).

THE PHYLOGENY OF THE INSULIN-LIKE GROWTH FACTORS

The insulin-like growth factors are major regulators of growth and development in mammals and their presence in lower vertebrates suggests that they played a similarly fundamental role throughout vertebrate evolution. While originally perceived simply as mediators of growth hormone, on-going research in mammals has revealed several hierarchical layers of complexity in the regulation of ligand bioavailability and signal transduction. Our understanding of the biological role and mechanisms of action of these important growth factors in mammals patently requires further elucidation of the IGF hormone system in the simple model systems that can be found in lower vertebrates and protochordates. This review contrasts our knowledge of the IGF hormone system in mammalian and nonmammalian models through comparison of tissue and developmental distributions and gene structures of IGF system components in different taxa. We also discuss the evolutionary origins of the system components and their possible evolutionary pathways.

Effect of Growth Hormone and Insulin-Like Growth Factor I (IGF-I) on the Expression of IGF-I Messenger Ribonucleic Acid and Peptide in Rat Tibial Growth Plate and Articular Chondrocytes in Vivo*

Conflicting data exist as to whether insulin-like growth factor I (IGF-I) messenger RNA (mRNA) and peptide are expressed within chondrocytes. This question is pertinent to the mode of GH action on longitudinal bone growth. We have, therefore, investigated this issue in normal rats and in hypophysectomized rats treated for 24 h with GH or IGF-I using in situ hybridization and immunohistochemistry. Serum IGF-I, body weight, and tibial growth plate, but not articular cartilage, height increased with both treatments. Both IGF-I mRNA and IGF-I immunoreactivity occurred in all chondrocyte layers of growth plate and articular cartilage. The percentage of cells with IGF-I mRNA correlated well with IGF-I immunoreactivity under all experimental conditions. In normal rats, IGF-I expression was highest in the upper hypertrophic zone in growth plate (68–71%) and articular cartilage (32–34%). Hypophysectomy, GH, or IGF-I did not significantly affect this percentage. In the stem cell and proliferative and lower hypertro...

Insulin-like Growth Factors and Fish Reproduction

Knowledge of fish reproduction is of high relevance to basic fish biology and comparative evolution. Furthermore, fish are excellent biomedical models, and the impact of aquaculture on worldwide food production is steadily increasing. Consequently, research on fish reproduction and the potential modes of its manipulation has become more and more important. Reproduction in fish is regulated by the integration of endogenous neuroendocrine (gonadotropins), endocrine, and autocrine/paracrine signals with exogenous (environmental) factors. The main endocrine regulators of gonadal sex differentiation and function are steroid hormones. However, recent studies suggest that other hormones are also involved. Most prominent among these hormones are the insulin-like growth factors (Igfs), i.e., Igf1, Igf2, and, most recently, Igf3. Thus, the present review deals with the expression patterns and potential physiological functions of Igf1 and Igf2 in male and female gonads. It further considers the potential involvement of growth hormone (Gh) and balances the reasons for endocrine vs. autocrine/paracrine action of the Igfs on the gonads of fish. Finally, this review discusses the early and late development of gonadal Igf1 and Igf2 and whether they are targets of endocrine-disrupting compounds. Future topics for novel research investigation on Igfs and fish reproduction are presented.

An immunohistochemical analysis of the ontogeny, distribution and coexistence of 12 regulatory peptides and serotonin in endocrine cells and nerve fibers of the digestive tract of the turbot, Scophthalmus maximus (Teleostei).

Abstract The ontogeny of endocrine cells and nerve fibers containing immunoreactivities for 12 regulatory peptides and serotonin was studied in the digestive tract of a flatfish, the turbot (Scophthalmus maximus), using antisera specific for mammalian and teleostean hormones. Transient insulin-immunoreactive (-IR) endocrine cells were detected from day 5 to day 10 in stomach and intestine I. Somatostatin (SOM)-IR cells appeared at day 8 in the stomach anlage and intestine I. In contrast to the islet cells, they reacted with antisera against mammalian (m) SOM-14 and salmon (s) SOM-25. Infrequent nerve fibers reacting only with anti-mSOM-14 appeared around day 24. Thus, different forms of SOM seem to be present in the gastro-entero-pancreatic system and the enteric nervous system. Neuropeptide Y (NPY)-, salmon pancreatic polypeptide (sPP)- and mPP-immunoreactivities coexisted thoughout development. In entero-endocrine cells, NPY/PP-immunoreactivity was first observed at day 8 and around day 24 in enteric nerve fibers. Glucagon (GLUC)-IR entero-endocrine cells appeared at day 5. No coexistence of NPY/PP- and GLUC-immunoreactivities was observed. The first insulin-like growth factor I (IGF-I)-IR cells were identified around day 8. They seemed to contain none of the other peptides. Their number and distribution exhibited great interindividual differences. Vasoactive intestinal polypeptide (VIP)-IR entero-endocrine cells appeared as late as around day 24. The first VIP-IR nerve fibers, however, were identified at day 5. Infrequent neurotensin (NT)-IR cells appeared along the intestine around day 10 and NT-IR nerve fibers at day 17. The first serotonin (SER)-IR cells were observed in the stomach anlage around day 10 and SER-IR nerve fibers at day 15 thoughout the gastro-intestinal tract. Gastrin (GAS)/cholecystokinin (CCK)-IR cells appeared around day 11 in stomach and intestine I. The first substance P (SP)-IR enteric nerve fibers were detected around day 8 and SP-IR endocrine cells at day 11. Pancreastatin (PST)-IR cells were identified in the stomach anlage and intestine I around day 8 and contained NT-, GAS/CCK- and SER-immunoreactivities in coexistence. Thus, several developmental phases can be distinguished: (1) at the onset of exogenous feeding only transient INS-IR cells and VIP-IR nerve fibers are present; (2) a differentiated entero-endocrine system establishes during the early phase of exogenous feeding; (3) before the final differentiation of stomach and gut GAS/CCK-IR cells appear; (4) after metamorphosis most of the different types of regulatory peptide-containing nerve fibers develop, probably setting up the fine regulation of gastro-intestinal blood flow and motility.

Insulin-like growth factor-I and -II in the ovary of a bony fish, Oreochromis mossambicus, the tilapia: in situ hybridisation, immunohistochemical localisation, Northern blot and cDNA sequences.

There is accumulating evidence that insulin-like growth factor (IGF)-I and IGF-II are present in the mammalian ovary but comparable studies on bony fish remain scarce. Thus, the present study aims to analyse several parameters of the IGFs in the ovary of a bony fish, the tilapia, (Oreochromis mossambicus). Molecular biological and morphological techniques were applied. The IGF-I and IGF-II cDNA sequences established from the ovary indicate that the same molecules are present in ovary and liver. Northern blot analysis revealed four IGF-I mRNA transcripts (6.0, 3.9, 1.9, 0.5 kb) and three IGF-II mRNA transcripts (5.0, 4.0, 2.0 kb) in ovary and liver. The amounts of IGF-I and IGF-II mRNA in the ovary were considerably high when compared to those in liver (IGF-I: 80.7%; IGF-II: 63.7%). The expression of IGF-I mRNA and IGF-II mRNA in the ovary were studied by in situ hybridisation and the peptides located by immunohistochemistry. The expression of IGF-I varied between the different developmental stages. Both IGF-I mRNA and IGF-I immunoreactivity were present in small oocytes. Moderate IGF-I expression and immunoreactivity occurred in granulosa cells of follicles at the lipid stage. A high IGF-I expression was observed in the granulosa and theca cells surrounding oocytes at the yolk globule stages and mature oocytes but neither IGF-I mRNA nor IGF-I immunoreactivity occurred in oocytes of the later stages. Thus, the IGF-I production seems to change from the young oocyte to the surrounding follicle cells at the later stages. In contrast, IGF-II mRNA and IGF-II-immunoreactivity occurred only in granulosa cells of the late follicle stages. The results suggest that both IGF-I and IGF-II are involved in the maturation of bony fish oocytes and in follicle development in a paracrine/autocrine manner. IGF-I and IGF-II may exert their effects at different stages of development. Furthermore, the intraovarian IGF-I and IGF-II systems seem to have a long phylogenetic history indicating the importance of the IGFs in reproductive biology.

Immunohistochemical localization of insulin-like growth factor 1 and 2 in the endocrine pancreas of rat, dog, and man, and their coexistence with classical islet hormones.

Immunohistochemical techniques were used to study the occurrence and distribution of insulin-like growth factor 1 (IGF-1) and IGF-2 in the pancreas of man, dog, and rat and their possible coexistence with insulin (INS), glucagon (GLUC), somatostatin (SOM) and pancreatic polypeptide (PP). All control experiments, including pre-absorption of the antisera with synthetic peptide hormones, indicated the specificity of the immunoreactions obtained. In all species investigated, IGF-2-immunoreactivity occurred exclusively in INS-immunoreactive cells as was found by the use of consecutive sections and double immunofluorescence on identical sections. In contrast, IGF-1-immunoreactivity co-existed with GLUC-immunoreactivity. In man, singular SOM-immunoreactive cells also contained IGF-1-immunoreactivity. Thus, IGF-1 and IGF-2 can be localized by means of immunohistochemistry in the mammalian pancreas, and can be shown to occur in different islet cell populations. It is presumed that IGF-1 derived from A-cells and/or D-cells acts on the B-cells in a paracrine manner. The co-existence of IGF-2-immunoreactivity and INS-immunoreactivity in the human, rat, and dog endocrine pancreas indicates that mammalian IGF-2 and INS genes are regulated simultaneously.

Environmentally Relevant Concentrations of 17α-Ethinylestradiol (EE2) Interfere With the Growth Hormone (GH)/Insulin-Like Growth Factor (IGF)-I System in Developing Bony Fish

The aim of this study was to evaluate whether effects of environmental estrogens on fish growth and reproduction may be mediated via modulating the growth hormone (GH)/insulin-like growth factor I (IGF-I) system. To this end, developing male and female monosex populations of tilapia were exposed to 17alpha-ethinylestradiol (EE2) at 5 and 25 ng EE2/l water from 10-day postfertilization (DPF) until 100 DPF. Under exposure to both EE2 concentrations, sex ratio shifted toward more females and body length, and weight were significantly reduced in males. The growth-reducing effect was associated with significant changes in hepatic IGF-I expression, both in males and females and with significant alterations of IGF-I mRNA and GH mRNA in the brain. The changes in IGF-I and GH mRNA were accompanied by altered estrogen receptor alpha (ERalpha) expression in brain and liver. These findings point to an influence of estrogenic exposure on the endocrine GH/IGF-I axis. In addition, the EE2 treatment resulted in significant changes of ERalpha and IGF-I expression in ovaries and testis, suggesting that the estrogens interact not only with the endocrine but also with the autocrine/paracrine part of the IGF-I system. Overall, our results provide evidence that EE2 at environmentally relevant concentrations is able to interfere with the GH/IGF-I system in bony fish and that the impairing effects of estrogens reported on fish growth and reproductive functions may rather result from a cross talk between the sex steroid and the IGF-I system than be toxicological.