Insulin-related Growth Factor Research Articles

Insulin-Related Biomarkers in Cerebrospinal Fluid in Mild Cognitive Impairment and Alzheimer’s Disease: A Systematic Review

Glucose metabolism and insulin signaling alterations play an important role in Alzheimer's disease (AD) pathogenesis. Researchers have extensively attempted to characterize the exact pathophysiological mechanisms in the cerebrospinal fluid (CSF), as evidence concerning this fluid biomarkers is expected to enhance AD diagnosis' specificity and accuracy and serve as an early disease detection tool. There is controversy about insulin levels in the CSF relationship with mild cognitive impairment (MCI) and AD. This systematic review provides an overview of the state-of-the-art knowledge about insulin-related CSF biomarkers in AD and MCI. We performed a qualitative systematic literature review of reported data of CSF glucose, insulin, or insulin-related molecules in humans with AD or MCI, consulting the electronic databases Medline, Scopus, Web of Science, Cochrane, and BASE until May 2022. We selected 19 studies, 10 of them reporting data on CSF insulin and 8 on insulin-related molecules like growth factors or their binding proteins. They predominantly found decreased levels of CSF insulin and increased levels of CSF insulin-related growth factors and their binding proteins. Due to the studies' protocols and results heterogeneity, we recommend a larger database of clinical trials with similar characteristics for a better understanding of this relationship.

Insulin-induced changes in metabolism-related proteins during maize germination

Insulin regulates a wide range of metabolic processes in mammals, such as homeostasis and the breakdown of glucose. Recently, the existence of an insulin-related growth factor in maize (ZmIGF) and a possible receptor for this growth factor has been reported. This peptide exerts effects on plant growth and promotes germination by activating the target of rapamycin (TOR) signaling pathways, which is similar to the insulin response in mammals. In this study, we analyzed the insulin response in maize embryos using a proteomic approach. Our results indicated that insulin modulates the expression of proteins involved in processes, such as storage protein degradation, protein processing, redox and desiccation stress, and glucose metabolism. The involvement of TOR signaling pathways was analyzed using the TOR inhibitor, rapamycin. The results showed that the modulation of these proteins by insulin is independent of the TOR pathway. These results indicated that insulin promotes changes in metabolism-related proteins to ensure successful germination in maize.

Enhanced memory consolidation in mice lacking the circadian modulators Sharp1 and -2 caused by elevated Igf2 signaling in the cortex

The bHLH transcription factors SHARP1 and SHARP2 are partially redundant modulators of the circadian system. SHARP1/DEC2 has been shown to control sleep length in humans and sleep architecture is also altered in double mutant mice (S1/2(-/-)). Because of the importance of sleep for memory consolidation, we investigated the role of SHARP1 and SHARP2 in cognitive processing. S1/2(-/-) mice show enhanced cortex (Cx)-dependent remote fear memory formation as well as improved reversal learning, but do not display alterations in hippocampus (Hi)-dependent recent fear memory formation. SHARP1 and SHARP2 single null mutants do not display any cognitive phenotype supporting functional redundancy of both factors. Molecular and biochemical analyses revealed elevated insulin-related growth factor 2 (IGF2) signaling and increased phosphorylation of MAPK and S6 in the Cx but not the Hi of S1/2(-/-) mice. No changes were detected in single mutants. Moreover, adeno-associated virus type 2-mediated IGF2 overexpression in the anterior cingulate cortex enhanced remote fear memory formation and the analysis of forebrain-specific double null mutants of the Insulin and IGF1 receptors revealed their essential function for memory formation. Impaired fear memory formation in aged S1/2(-/-) mice indicates that elevated IGF2 signaling in the long term, however, has a negative impact on cognitive processing. In summary, we conclude that the bHLH transcription factors SHARP1 and SHARP2 are involved in cognitive processing by controlling Igf2 expression and associated signaling cascades. Our analyses provide evidence that the control of sleep and memory consolidation may share common molecular mechanisms.

Aromatic Anchor at an Invariant Hormone-Receptor Interface: FUNCTION OF INSULIN RESIDUE B24 WITH APPLICATION TO PROTEIN DESIGN

Crystallographic studies of insulin bound to fragments of the insulin receptor have recently defined the topography of the primary hormone-receptor interface. Here, we have investigated the role of Phe(B24), an invariant aromatic anchor at this interface and site of a human mutation causing diabetes mellitus. An extensive set of B24 substitutions has been constructed and tested for effects on receptor binding. Although aromaticity has long been considered a key requirement at this position, Met(B24) was found to confer essentially native affinity and bioactivity. Molecular modeling suggests that this linear side chain can serve as an alternative hydrophobic anchor at the hormone-receptor interface. These findings motivated further substitution of Phe(B24) by cyclohexanylalanine (Cha), which contains a nonplanar aliphatic ring. Contrary to expectations, [Cha(B24)]insulin likewise exhibited high activity. Furthermore, its resistance to fibrillation and the rapid rate of hexamer disassembly, properties of potential therapeutic advantage, were enhanced. The crystal structure of the Cha(B24) analog, determined as an R6 zinc-stabilized hexamer at a resolution of 1.5 Å, closely resembles that of wild-type insulin. The nonplanar aliphatic ring exhibits two chair conformations with partial occupancies, each recapitulating the role of Phe(B24) at the dimer interface. Together, these studies have defined structural requirements of an anchor residue within the B24-binding pocket of the insulin receptor; similar molecular principles are likely to pertain to insulin-related growth factors. Our results highlight in particular the utility of nonaromatic side chains as probes of the B24 pocket and suggest that the nonstandard Cha side chain may have therapeutic utility.

Relationships between the transcriptome and physiological indicators of reproduction in female rainbow trout over an annual cycle

Normal transcriptomic patterns along the brain-pituitary-gonad-liver (BPGL) axis should be better characterized if endocrine-disrupting compound-induced changes in gene expression are to be understood. Female rainbow trout were studied over a complete year-long reproductive cycle. Tissue samples from pituitary, ovary, and liver were collected for microarray analysis using the 16K Genomic Research on Atlantic Salmon Project (GRASP) microarray and for quantitative polymerase chain reaction measures of estrogen receptor (ER) isoform messenger RNA (mRNA) levels. Plasma was collected to determine levels of circulating estradiol-17β (E2), follicle-stimulating hormone (FSH), and luteinizing hormone (LH). As an a priori hypothesis, changes in gene expression were correlated to either circulating levels of E2, FSH, and LH, or ER mRNAs quantified by quantitative polymerase chain reaction. In the liver, most transcriptomic patterns correlated to levels of either E2, LH, or ERs. Fewer ovarian transcripts could be correlated to levels of E2, ERα, or FSH. No significant associations were obvious in the pituitary. As a post hoc hypothesis, changes in transcript abundance were compared with microarray features with known roles in gonadal maturation. Many altered transcripts in the ovary correlated to transcript levels of estradiol 17-beta-dehydrogenase 8 or 17 B HSD12, or to glycoprotein alpha chain 1 or 2. In the pituitary, genes involved with the growth axis (e.g., growth hormone, insulin-related growth factor binding protein) correlated with the most transcripts. These results suggest that transcriptional networks along the BPGL axis may be regulated by factors other than circulating steroid hormones.

Dietary Glycemic Index and Glycemic Load and Risk of Pancreatic Cancer: A Case-Control Study

Carbohydrates and dietary glycemic index (GI) influence the secretion of insulin and insulin-related growth factors and may play a role in the development of diabetes and obesity, both of which have been related to pancreatic cancer risk. We examined the association between dietary GI and glycemic load (GL) and pancreatic cancer by conducting a hospital-based case-control study in Italy in 1991-2008 of 326 cases of pancreatic cancer and 652 control patients. Dietary data were obtained with the use of a validated food-frequency questionnaire. Odds ratios (ORs) and corresponding 95% confidence intervals (95% CIs) were computed with the use of multiple logistic regression. GI was positively associated with pancreatic cancer, with ORs of 1.56 (95% CI, 1.06-2.30) and 1.78 (95% CI, 1.20-2.62) for the second and third tertiles, respectively, compared with the lowest. No significant association was observed between GL and pancreatic cancer. Consumption of sugar, candy, honey, and jam was positively associated with pancreatic cancer, whereas consumption of fruit was inversely associated. In conclusion, the positive association with high GI, in the absence of an association with dietary GL, fruit, or total carbohydrates, likely reflects the positive association between sweets or refined carbohydrates and pancreatic cancer in this study population.

Contribution of Residue B5 to the Folding and Function of Insulin and IGF-I: CONSTRAINTS AND FINE-TUNING IN THE EVOLUTION OF A PROTEIN FAMILY

Proinsulin exhibits a single structure, whereas insulin-like growth factors refold as two disulfide isomers in equilibrium. Native insulin-related growth factor (IGF)-I has canonical cystines (A6-A11, A7-B7, and A20-B19) maintained by IGF-binding proteins; IGF-swap has alternative pairing (A7-A11, A6-B7, and A20-B19) and impaired activity. Studies of mini-domain models suggest that residue B5 (His in insulin and Thr in IGFs) governs the ambiguity or uniqueness of disulfide pairing. Residue B5, a site of mutation in proinsulin causing neonatal diabetes, is thus of broad biophysical interest. Here, we characterize reciprocal B5 substitutions in the two proteins. In insulin, His(B5) --> Thr markedly destabilizes the hormone (DeltaDeltaG(u) 2.0 +/- 0.2 kcal/mol), impairs chain combination, and blocks cellular secretion of proinsulin. The reciprocal IGF-I substitution Thr(B5) --> His (residue 4) specifies a unique structure with native (1)H NMR signature. Chemical shifts and nuclear Overhauser effects are similar to those of native IGF-I. Whereas wild-type IGF-I undergoes thiol-catalyzed disulfide exchange to yield IGF-swap, His(B5)-IGF-I retains canonical pairing. Chemical denaturation studies indicate that His(B5) does not significantly enhance thermodynamic stability (DeltaDeltaG(u) 0.2 +/- 0.2 kcal/mol), implying that the substitution favors canonical pairing by destabilizing competing folds. Whereas the activity of Thr(B5)-insulin is decreased 5-fold, His(B5)-IGF-I exhibits 2-fold increased affinity for the IGF receptor and augmented post-receptor signaling. We propose that conservation of Thr(B5) in IGF-I, rescued from structural ambiguity by IGF-binding proteins, reflects fine-tuning of signal transduction. In contrast, the conservation of His(B5) in insulin highlights its critical role in insulin biosynthesis.

Identification of the insulin-responsive tyrosine phosphorylation sites on IRSp53

The 53-kDa insulin receptor substrate protein (IRSp53) is part of a regulatory network that organises the actin cytoskeleton in response to stimulation by small GTPases, promoting formation of actin-rich cell protrusions such as filopodia and lamellipodia. It had been established earlier that IRSp53 is tyrosine phosphorylated in response to stimulation of the insulin and insulin-related growth factor receptors, but the consequences of tyrosine phosphorylation for IRSp53 function are unknown. Here, we have used a variety of IRSp53 truncation and point mutants to identify insulin-responsive tyrosine phosphorylation sites on IRSp53. We have found that the C-terminal half of IRSp53 (residues 251–521) undergoes tyrosine phosphorylation in response to insulin stimulation of the insulin β receptor or epidermal growth factor stimulation via the epidermal growth factor receptor, and that the key residue for insulin receptor-mediated phosphorylation is tyrosine 310, located in a region between the N-terminal IRSp53/MIM homology domain (IMD, residue 1–250) and the central SH3 domain (residues 374–438) that is predicted to be natively unstructured. Mutation of tyrosine 310 to phenylalanine or glutamic acid abrogates the phosphorylation in response to insulin stimulation, but not in response to stimulation of the epidermal growth factor receptor. The N-terminal IMD, which mediates dimerisation of IRSp53, is required for efficient tyrosine phosphorylation downstream of either the insulin or epidermal growth factor receptor stimulation, yet does not appear to include a tyrosine-phosphorylated site itself. Thus, we have identified tyrosine 310 as a primary site of tyrosine phosphorylation in response to insulin signalling and we have shown that although IRSp53 is tyrosine phosphorylated in response to epidermal growth factor receptor signalling, tyrosine 310 is not crucial. Furthermore, the tyrosine phosphorylation status does not appear to affect the cell morphology and production of filopod-like structures upon expression of IRSp53.

Serum concentrations of IGF-I, IGFBP-3 and c-peptide and risk of hyperplasia and cancer of the breast in postmenopausal women.

Experimental evidence suggests that insulin and insulin-related growth factors may play a role in breast pathology through their mitogenic and anti-apoptotic effects on breast cells. Our objective was to assess the relationship between serum concentrations of insulin-like growth factor-I (IGF-I), its major binding protein (IGFBP-3), the ratio IGF-I:IGFBP-3, c-peptide (a marker of insulin secretion) and the ratio c-peptide:fructosamine (a marker of insulin resistance) and the risk of epithelial hyperplasia (an established breast cancer risk factor) and localized breast cancer among postmenopausal women. Study subjects were patients who provided serum before breast biopsy or mastectomy in 3 hospitals in Grand Rapids, MI between 1977 and 1987. Two case groups, 186 subjects with epithelial hyperplasia of the breast and 185 subjects with localized breast cancer, were compared to 159 subjects with nonproliferative breast changes that have not been associated with increased breast cancer risk. Serum concentrations of IGF-I, IGFBP-3 and the ratio IGF-I:IGFBP-3 were not related to risk of either hyperplasia or breast cancer. For women in the highest quartile of c-peptide or of c-peptide:fructosamine compared to those in the lowest quartile, the odds ratios (ORs) for hyperplasia were 3.0 (95% confidence interval [CI] 1.4-6.5) and 3.3 (95% CI 1.5-7.3), respectively (p trend = 0.02 and 0.02, respectively). The corresponding ORs for breast cancer were 1.5 (95% CI 0.7-3.0) and 1.6 (95% CI 0.8-3.2), respectively (p trend = 0.35 and 0.25, respectively). Our results suggest that insulin and insulin resistance may play a role in breast pathology in postmenopausal women.

Insulin and Insulin-Like Growth Factors (IGFs) promote Vascular Endothelial Growth Factor (VEGF-A) secretion by human luteinizing granulosa cells following Controlled Ovarian Stimulation (COS)

Objective: To investigate the role of insulin-related growth factors and luteinizing hormone (LH) in the physiological regulation of VEGF-A production by luteinized granulosa cells (LGC) from preovulatory follicles in humans. Design: Prospective, comparative, experimental study. Materials and Methods: LGC were obtained from women (n=6), with IRB approval, by follicular aspiration after undergoing COS for in-vitro fertilization. Subjects (33.5 ± 1.2 years, mean age ± SEM) had regular menstrual cycles with no evidence of PCOS or other endocrinopathies. LGC were isolated and plated at 50,000 cells/well on fibronectin in DMEM-Ham’s F-12 medium with 5 μg/ml transferrin, 5 ng/ml selenium, 10 μg/ml aprotinin and 25 μg/ml human LDL. Cells were incubated in the presence and absence of 100 ng/ml recombinant human (r-h) LH (Ares Serono) and 0, 1, 10, 100 ng/ml of r-h IGF-1, IGF-II or insulin (Sigma). Media were collected daily and assayed for free VEGF-A (Quantikine VEGF ELISA, R&D Systems). After 3 days (d), cells were fixed, Crystal Violet stained and analyzed for DNA content to estimate cell numbers. Data were analyzed by two-way repeated ANOVA, using a randomized block design. Results: In the absence of LH or insulin-related growth factors, LGCs secreted low but detectable levels of VEGF-A through d 3 of culture (179–304 pg/ml on d 3). However, exposure to IGF-I or -II resulted in a dose-related increase in VEGF-A levels by d 1 (e.g., 568 vs 183 pg/ml or 453 vs 278 pg/ml,100 ng/ml IGF-I or-II vs controls, respectively; p<0.05), which was sustained through d 3 (1001 vs 179 pg/ml or 701 vs 255 pg/ml, p<0.05). Conversely, the addition of insulin (100 ng/ml) did not increase VEGF-A levels until d 2 (737 vs 436 pg/ml, p<0.05). Although LH alone did not increase VEGF-A levels above controls on d 1–3, the combination of LH and insulin-related growth factors increased VEGF-A levels to a greater extent than IGFs alone at all doses (1181 vs 717 or 800 vs 567 pg/ml, LH + 10 ng/ml IGF-I or -II vs IGF-I or -II alone, respectively, on d 2; p<0.05). The synergistic effect of LH with IGF-I/-II was evident earlier on d 2 and at lower doses (10 ng/ml), compared to insulin and LH, which was not significant until d 3. There was no change in DNA content following incubation for 3 days in the presence of IGF-I, -II, insulin or LH when compared to controls. However, DNA content decreased (p<0.05) in the presence of LH + IGF-II at the maximum dose. Conclusion: Exposure to both insulin-related growth factors and LH is required for optimal VEGF-A secretion by human LGC. Thus, local (IGFs) as well as endocrine (LH, insulin) factors may combine to regulate VEGF-A production, and thus angiogenesis and vascular permeability, in the primate ovulatory follicle and corpus luteum. Evidence of insulin/IGFs, as well as LH, regulation of VEGF-A production supports further studies on their role in regulating angiogenic factors during COS cycles in women with endocrinopathies, such as PCOS. Supported by: NICHD U54 HD18185, RR 00163.

Effects of Oral Dehydroepiandrosterone on Bone Density in Young Women With Anorexia Nervosa: A Randomized Trial

More than half of the patients with anorexia nervosa (AN) have early bone loss and fractures. Despite the usual marked estrogen deficiency in young women with AN, hormone replacement therapy (HRT) has given mixed results at best. Because subnormal dehydroepiandrosterone (DHEA) levels may contribute to bone loss in AN, this study compared a 12-month course of oral DHEA (50 mg daily) with conventional HRT (20 μg ethinyl estradiol plus 0.1 mg levonorgestrel) in 61 females with AN (age range, 14-28 years). Among 51 women completing the study, those in both treatment groups gained significant body weight and had increased lean body and fat mass. Regular bleeding was reported by 58% of those taking DHEA and 80% of the HRT group. Lumbar bone mineral density (BMD) did not change significantly, but BMD at the hip did increase and correlated positively with increasing body weight in both treatment groups (Fig. 1). Increased BMD also correlated with elevations in insulin-related growth factor I and bone-specific alkaline phosphatase, a marker of bone formation, but only in the DHEA group (Fig. 2). No substantial effect on BMD was evident after controlling for weight gain. Daily caloric intake decreased 10% in the HRT group and 15% in patients given DHEA. Psychological ratings, including measures of body image, eating attitudes, and anxiety, indicated improvement in the DHEA group only. It seems that DHEA has both anabolic and antiresorptive effects on bone in young women with AN and that it may be preferable to standard HRT, in part because of favorable psychological effects.

Locally Born Olfactory Bulb Stem Cells Proliferate in Response to Insulin-Related Factors and Require Endogenous Insulin-Like Growth Factor-I for Differentiation into Neurons and Glia

After late embryogenesis, new neurons are continuously added to the olfactory bulb (OB) from stem cells located in the forebrain subventricular zone. Nonetheless, stem cells have not been described within the embryonic olfactory bulb. Here we report the isolation of local olfactory bulb stem cells from the embryonic day 12.5-14.5 mouse embryo. These cells were 99.2% nestin positive and proliferated extensively in culture to at least 150 cell doublings. Clonal analysis demonstrated that neurons (TuJ1(+)), astrocytes (GFAP(+)), and oligodendrocytes (O4(+)) could be generated from single-plated cells, indicating that they are multipotent. At least 90% of proliferating cells expressed insulin-like growth factor-I (IGF-I), (pro)insulin, and their cognate receptors; these growth factors collaborated with fibroblast growth factor-2 plus epidermal growth factor (EGF) to promote stem cell proliferation and sphere formation. Cells from Igf-I(-)/- mice, however, proliferated as extensively as did Igf-I(+/+) cells. Differentiation and survival of stem cell-generated neurons and glia showed strong dependence on exogenous IGF-I, but oligodendrocyte differentiation also required insulin at low concentration. Furthermore, the percentages of stem cell-generated neurons, astrocytes, and oligodendrocytes were markedly lower in the cultures prepared from the Igf-I(-)/- mice compared with those of Igf-I(+/+). Concordantly, lack of IGF-I resulted in abnormal formation of the olfactory bulb mitral cell layer and altered radial glia morphology. These results support the presence within the embryonic mouse olfactory bulb of stem cells with specific requirements for insulin-related growth factors for proliferation or differentiation. They demonstrate that IGF-I is an endogenous factor regulating the differentiation of stem and other precursor cells within the olfactory bulb.

Cell death in the nervous system: lessons from insulin and insulin-like growth factors.

Programmed cell death is an essential process for proper neural development. Cell death, with its similar regulatory and executory mechanisms, also contributes to the origin or progression of many or even all neurodegenerative diseases. An understanding of the mechanisms that regulate cell death during neural development may provide new targets and tools to prevent neurodegeneration. Many studies that have focused mainly on insulin-like growth factor-I (IGF-I), have shown that insulin-related growth factors are widely expressed in the developing and adult nervous system, and positively modulate a number of processes during neural development, as well as in adult neuronal and glial physiology. These factors also show neuroprotective effects following neural damage. Although some specific actions have been demonstrated to be anti-apoptotic, we propose that a broad neuroprotective role is the foundation for many of the observed functions of the insulin-related growth factors, whose therapeutical potential for nervous system disorders may be greater than currently accepted.

RNA travels with ZBP1

On page 77, Farina et al. get a handle on RNA localization machinery by proving that an RNA-binding protein is essential for both mRNA transport and cell motility. Figure Lamella-localized ZBP1 (white) granules do not form if ZBP1 cannot bind actin mRNA (right). The cell motility connection comes about because localization of the β-actin mRNA to the lamellae is required for cell polarity and motility in fibroblasts. The new results show that this localization depends on ZBP1, a protein associated with cytoplasmic granules that contain the actin mRNA. ZBP1 bound to the mRNA through two COOH-terminal KH domains that were required for granule formation and attachment to the actin cytoskeleton. NH2-terminal regions of ZBP1 were necessary for granule localization in the lamellae. Dominant–negative ZBP1 constructs that mislocalized actin RNA inhibited fibroblast motility. Since mRNAs for some actin-associated proteins, such as ARP3, also contain ZBP1-binding sequences, the authors believe that ZBP1 may link several messages involved in motility to a transport complex. But ZBP1 may be more than just a scaffold: a ZBP1 homologue has been linked to translational repression of the insulin-related growth factor. Perhaps ZBP1 also ensures that the actin mRNA is not translated until it reaches its ultimate destination.The group plans to purify ZBP1- associated proteins in the complex to identify the motor responsible for actin-based transport. ZBP1 is also known to be associated with microtubules in neurons, so it may connect to different motors depending on the cell type. ▪

Ethanol-Induced Death of Postnatal Hippocampal Neurons

Fetal alcohol exposure causes severe neuropsychiatric problems, but mechanisms of the ethanol-associated changes in central nervous system development are unclear. In vivo, ethanol's interaction with N-methyl- d-aspartate (NMDA) and γ-aminobutyric acid type A (GABA A) receptors may cause increased apoptosis in the immature forebrain. We examined whether ethanol affects survival of neonatal hippocampal neurons in primary cultures. A 6-day ethanol exposure killed hippocampal neurons with an LD50 of ∼25 mM. Elevated extracellular potassium or insulin-related growth factor 1 inhibited cell loss. Although potentiation of GABA A receptors or complete block of NMDA receptors also kills hippocampal neurons, pharmacological studies suggest that ethanol's interaction with GABA A and NMDA receptors is not sufficient to explain ethanol's effects on neuronal survival. Ca 2+ influx in response to depolarization was depressed >50% by chronic ethanol treatment. We suggest that chronic ethanol may promote neuronal loss through a mechanism affecting Ca 2+ influx in addition to effects on postsynaptic GABA and glutamate receptors.

New trends in the etiopathogenesis of diabetic peripheral neuropathy.

Neuropathy is well recognized as a major complication of insulin-dependent diabetes mellitus in adults, resulting in significant morbidity and possibly an increased mortality. Both the peripheral and autonomic nervous systems can be involved, and adolescents with diabetes can show early evidence of neuropathy. The pathogenesis of diabetic neuropathy remains unclear but is thought to involve various mechanisms. This complication can be traced to the metabolic effects of hyperglycemia and/or other effects of insulin deficiency on the various constituents of the peripheral nerve. The polyol pathway and/or nonenzymatic glycation affecting one or more cell types in the multicellular constituents of the peripheral nerve appear likely to have an inciting role. The role of other factors, such as possible direct neurotrophic effects of insulin and insulin-related growth factors, seems to be relevant.

A role for Akt in mediating the estrogenic functions of epidermal growth factor and insulin-like growth factor I.

This study examines whether the serine/threonine protein kinase, Akt, is involved in the cross-talk between epidermal growth factor (EGF) and insulin-related growth factor I (IGF-I) receptors and ER-alpha. Treatment of MCF-7 cells with either EGF or IGF-I resulted in a rapid phosphorylation of Akt and a 14- to 16-fold increase in Akt activity, respectively. Akt activation was blocked by inhibitors of phosphatidylinositol 3-kinase, but not by an inhibitor of the ribosomal protein kinase p70S6K. Stable transfection of cells with a dominant negative Akt mutant blocked the effects of EGF and IGF-I on ER-alpha expression and activity, whereas stable transfection of cells with a constitutively active Akt mutant mimicked the effects of EGF and IGF-I. In the latter cells, there was a decrease in the amount of ER-alpha protein and messenger RNA (70-80%) and an increase in the amount of progesterone receptor protein, messenger RNA (4- to 9- and by 3.5- to 7-fold, respectively) and pS2 (3- to 5-fold). Coexpression of wild-type ER-alpha and the dominant negative Akt mutant in COS-1 cells also blocked the growth factor-stimulated activation of ER-alpha, but coexpression of the wild-type receptor with the constitutively active Akt mutant increased ER-alpha activity. Receptor activation was blocked by an antiestrogen. Studies using mutants of ER-alpha demonstrated that Akt increased estrogen receptor activity through the amino-terminal activation function-1 (AF-1). Serines S104 S106, S118, and S167 appear to play a role in the activation of ER-alpha by Akt.

Insulin-related growth factors stimulate proliferation of retinal progenitors in the goldfish

The retina of the adult goldfish grows throughout the life of the animal, in part, by the continual addition of new neurons. Further, destruction of extant neurons in this tissue stimulates neuronal regeneration. In an attempt to identify growth factors that regulate both normal and injury-stimulated neurogenesis, we used organ culture techniques and tested nine peptide growth factors for their ability to modulate cell proliferation in both normal retinas and retinas with lesions. Of the growth factors tested, only the insulin-related peptides (insulin and insulin-like growth factors I and II) consistently stimulated proliferation, and this was restricted to the retinal progenitors within the circumferential germinal zone. None of the growth factors tested stimulated proliferation of rod precursors (cells in the mature retina whose progeny are exclusively rod photoreceptors) or the injury-stimulated retinal progenitors. Although the negative data are subject to multiple interpretations, these data suggest that in the retina of the adult goldfish, insulin-related peptides regulate proliferation of retinal progenitors within the circumferential germinal zone, but molecules that modulate the proliferation of the rod precursors or injury-induced retinal progenitors in the retina of the adult goldfish have yet to be identified.

Autocrine/paracrine role of insulin-related growth factors in neurogenesis: local expression and effects on cell proliferation and differentiation in retina.

Early neurogenesis progresses by an initial massive proliferation of neuroepithelial cells followed by a sequential differentiation of the various mature neural cell types. The regulation of these processes by growth factors is poorly understood. We intend to understand, in a well-defined biological system, the embryonic chicken retina, the role of the insulin-related growth factors in neurogenesis. We demonstrate the local presence of signaling elements together with a biological response to the factors. Neuroretina at days 6-8 of embryonic development (E6-E8) expressed proinsulin/insulin and insulin-like growth factor I (IGF-I) mRNAs as well as insulin receptor and IGF type I receptor mRNAs. In parallel with this in vivo gene expression, E5 cultured neuroretinas synthesized and released to the medium a metabolically radiolabeled immunoprecipitable insulin-related peptide. Furthermore, insulin-related immunoreactive material with a HPLC mobility close to that of proinsulin was found in the E6-E8 vitreous humor. Exogenous chicken IGF-I, human insulin, and human proinsulin added to E6 cultured neuroretinas showed relatively close potencies stimulating proliferation, as determined by [methyl-3H]thymidine incorporation, with a plateau reached at 10(-8) M. These factors also stimulated neuronal differentiation, indicated by the expression of the neuron-specific antigen G4. Thus, insulin-related growth factors, interestingly including proinsulin, are present in the developing chicken retina and appear to play an autocrine/paracrine stimulatory role in the progression of neurogenesis.

Insulin-related growth factor binding protein-1 levels in ovum donation pregnancies

The finding that endometrial maturation may be delayed following hormone replacement therapy has suggested that a generalised endometrial dysfunction may exist in ovum recipients. In order to investigate this suggestion further, circulating levels of IGFBP-1 were measured in samples taken throughout pregnancies conceived either spontaneously or following ovum donation. When analysed at two-weekly intervals, the serum levels of IGFBP-1 in ovum donation pregnancies failed to show the expected peak towards the end of the first trimester and were significantly reduced at week ten (U = 364.5, p = 0.0002) and twelve (U = 138.0, p = 0.0047). For the remainder of pregnancy, circulating IGFBP-1 levels were similar in both groups. The birth weight of children born to the ovum donation group was not significantly different from a normal control group, suggesting that circulating levels of IGFBP-1 in early pregnancy do not reflect local function and that IGFBP-1 does not have an essential function (in relation to birth weight) in early pregnancy.