Role Of Insulin-like Growth factor-I Research Articles

IGF-I protects porcine granulosa cells from hypoxia-induced apoptosis by promoting homologous recombination repair through the PI3K/AKT/E2F8/RAD51 pathway.

Severe hypoxia induced by vascular compromise (ovarian torsion, surgery), obliteration of vessels (aging, chemotherapy, particularly platinum drugs) can cause massive follicle atresia. On the other hand, hypoxia increases the occurrence of DNA double-strand breaks (DSBs) and triggers cellular damage repair mechanisms; however, if the damage is not promptly repaired, it can also induce the apoptosis program. Insulin-like growth factor-I (IGF-I) is a polypeptide hormone that plays essential roles in stimulating mammalian follicular development. Here, we report a novel role for IGF-I in protecting hypoxic GCs from apoptosis by promoting DNA repair through the homologous recombination (HR) process. Indeed, the hypoxic environment within follicles significantly inhibited the efficiency of HR-directed DNA repair. The presence of IGF-I-induced HR pathway to alleviate hypoxia-induced DNA damage and apoptosis primarily through upregulating the expression of the RAD51 recombinase. Importantly, we identified a new transcriptional regulator of RAD51, namely E2F8, which mediates the protective effects of IGF-I on hypoxic GCs by facilitating the transcriptional activation of RAD51. Furthermore, we demonstrated that the PI3K/AKT pathway is crucial for IGF-I-induced E2F8 expression, resulting in increased RAD51 expression and enhanced HR activity, which mitigates hypoxia-induced DNA damage and thereby protects against GCs apoptosis. Together, these findings define a novel mechanism of IGF-I-mediated GCs protection by activating the HR repair through the PI3K/AKT/E2F8/RAD51 pathway under hypoxia.

​Effects of Time Specific Supplementation of Insulin Like Growth Factor-I (IGF-I) on in vitro Development of Sheep Preantral Follicles

Background: In in vitro culture systems IGF-I was known to promote follicular maturation, granulosa cell proliferation and increase overall cellular function. The expression patterns of developmentally important markers for IGF-I are expressed differentially during the transition of preantral follicles to the ovulatory stage. Therefore, we aimed to investigate the influence of time specific addition of Insulin like growth factor-I (IGF-I) on in vitro development of sheep preantral follicles (PFs’). Methods: Mechanically isolated sheep preantral follicles were cultured for six days either in TCM 199B or standard medium supplemented with IGF-I at different points during the culture period and were subsequently subjected to in vitro maturation (IVM) for additional 24hrs to evaluate different follicular development parameters. Conclusion: Based on the results, it is concluded that: 1) IGF-I supplementation was needed during early rather than later stages of culture period, therefore, role of IGF-I in time/stage specific manner in cultured preantral follicles is confirmed. 2) Supplementation of TCM 199B with IGF-I simultaneously for the first two days followed by TCM 199B alone without any growth factor (s) in later days (Treatment 1) supported better development of PFs’ in vitro.

IGF-1 Induces GHRH Neuronal Axon Elongation during Early Postnatal Life in Mice.

Nutrition during the perinatal period programs body growth. Growth hormone (GH) secretion from the pituitary regulates body growth and is controlled by Growth Hormone Releasing Hormone (GHRH) neurons located in the arcuate nucleus of the hypothalamus. We observed that dietary restriction during the early postnatal period (i.e. lactation) in mice influences postnatal growth by permanently altering the development of the somatotropic axis in the pituitary gland. This alteration may be due to a lack of GHRH signaling during this critical developmental period. Indeed, underfed pups showed decreased insulin-like growth factor I (IGF-I) plasma levels, which are associated with lower innervation of the median eminence by GHRH axons at 10 days of age relative to normally fed pups. IGF-I preferentially stimulated axon elongation of GHRH neurons in in vitro arcuate explant cultures from 7 day-old normally fed pups. This IGF-I stimulating effect was selective since other arcuate neurons visualized concomitantly by neurofilament labeling, or AgRP immunochemistry, did not significantly respond to IGF-I stimulation. Moreover, GHRH neurons in explants from age-matched underfed pups lost the capacity to respond to IGF-I stimulation. Molecular analyses indicated that nutritional restriction was associated with impaired activation of AKT. These results highlight a role for IGF-I in axon elongation that appears to be cell selective and participates in the complex cellular mechanisms that link underfeeding during the early postnatal period with programming of the growth trajectory.

The Supportive Role of Insulin-Like Growth Factor-I in the Differentiation of Murine Mesenchymal Stem Cells into Corneal-Like Cells.

This study was focused on characterizing the differentiation of bone marrow-derived mesenchymal stem cells (MSCs) into corneal-like cells. Mouse MSCs were isolated from the bone marrow, grown in cell culture for 3 weeks, and purified using a magnetic activated cell sorter. Purified MSCs were cultured with an extract prepared from excised corneas and in the presence or absence of insulin-like growth factor-I (IGF-I). Analysis by quantitative real-time polymerase chain reaction showed that the expression of corneal specific markers, such as cytokeratin 12 (K12), keratocan, and lumican, was already induced after a 3-day cultivation and gradually increased during the 10-day incubation of MSCs with the extract. The presence of IGF-I significantly increased differentiation. Immunofluorescence analysis of differentiated MSCs showed positive results for the K12 protein. The morphology of the differentiated cells and the expression of cell surface markers CD45, CD11b, CD73, CD44, and CD105 were comparable in the control and differentiated MSCs. Proliferative activity was even higher in differentiated cells than in untreated MSCs. Both untreated and differentiated MSCs inhibited the production of interleukin-2 and interferon-γ in spleen cells stimulated with Concanavalin A. The results thus show that MSCs cultured in the presence of corneal extract and IGF-I efficiently differentiate into corneal-like cells. The differentiated cells possess characteristics of corneal epithelial cells and keratocytes, while at the same time maintaining MSC properties.

Enteral Nutrition in the Management of Pediatric Intestinal Failure

Intestinal failure is an uncommon but devastating condition whose natural history has dramatically improved over the past two decades (1). Infants with intestinal failure due to severe short bowel syndrome or other diagnoses previously considered incompatible with life are now routinely being saved and cared for in cutting edge, multidisciplinary programs. Enteral nutrition plays a central role in the management of children with intestinal failure. This review provides an overview of enteral nutrition in pediatric intestinal failure, with specific emphasis on recent advances in clinical management, patient outcomes, and emerging therapies.

IGF-I and NEFA concentrations in fetal fluids of term pregnancy dogs

Insulin-like growth factor-I (IGF-I) and non-esterified fatty acids (NEFA) play an essential role in fetal growth and development. To date, fetal fluids IGF-I and NEFA levels at term canine pregnancy are unknown and could be related to the neonatal development and breed size. For these reasons, the aims of the present study were as follows: (1) to evaluate IGF-I and NEFA concentrations in fetal fluids collected from normally developed and viable newborn puppies born at term of normal pregnancies; (2) to assess possible differences between IGF-I and NEFA levels in amniotic compared with allantoic fluid; (3) to detect possible relationship between breed body size and IGF-I and NEFA amniotic and allantoic concentrations; (4) to evaluate possible differences in IGF-I fetal fluids levels between male and female puppies; and (5) to assess possible correlations between the two hormones in each type of fluid. The study enrolled 25 pure breed bitches submitted to elective Cesarean section at term because of the high risk of dystocia or previous troubles at parturition. At surgery, amniotic and allantoic fluids were collected and assayed for IGF-I and NEFA. IGF-I and NEFA amounts in both amniotic and allantoic fluids of different breed size bitches (small: ≤10 kg; medium: 11–25 kg; large: 26–40 kg) were detected, as well as the effect of gender on IGF-I levels. On a total of 73 amniotic and 76 allantoic samples collected by normal, viable, and mature newborns, the mean IGF-I concentration was significantly higher in amniotic than in allantoic fluid in all three groups, but the amniotic IGF-I levels were significantly lower in small and medium size bitches when compared with large ones. No significant differences were found in allantoic IGF-I concentrations among size groups. A significant effect of the puppy gender on IGF-I content in both fetal fluids was not reported. Regarding NEFA, in all the three groups, the mean NEFA concentration did not significantly differ between amnion and allantois, but in both fetal fluids, higher NEFA levels were detected in samples belonging to small breeds when compared with medium and large. These data strongly indicated that, also in the dog, a relation between fetal fluids IGF-I and NEFA concentrations and breed size exists. Further research is needed to elucidate the possible role of IGF-I and NEFA in the pathologic conditions related to canine fetal growth.

Gender differences and lateralization in the distribution pattern of insulin-like growth factor-1 receptor in developing rat hippocampus: an immunohistochemical study.

Numerous investigators have provided data supporting essential roles for insulin-like growth factor-I (IGF-I) in development of the brain. The aim of this study was to immunohistochemically determine the distinct regional distribution pattern of IGF-1 receptor (IGF-IR) expression in various portions of newborn rat hippocampus on postnatal days 0 (P0), 7 (P7), and 14 (P14), with comparison between male/female and right/left hippocampi. We found an overall significant increase in distribution of IGF-IR-positive (IGF-IR+) cells in CA1 from P0 until P14. Although, no marked changes in distribution of IGF-IR+ cells in areas CA2 and CA3 were observed; IGF-IR+ cells in DG decreased until P14. The smallest number of immunoreactive cells was present in CA2 and the highest number in DG at P0. Moreover, in CA1, CA3, and DG, the number of IGF-IR+ cells was markedly higher in both sides of the hippocampus in females. Our data also showed a higher mean number of IGF-IR+ cells in the left hippocampus of female at P7. By contrast, male pups showed a significantly higher number of IGF-IR+ cells in the DG of the right hippocampus. At P14, the mean number of immunoreactive cells in CA1, CA3, and DG areas found to be significantly increased in left side of hippocampus of males, compared to females. These results indicate the existence of a differential distribution pattern of IGF-IR between left-right and male-female hippocampi. Together with other mechanisms, these differences may underlie sexual dimorphism and left-right asymmetry in the hippocampus.

Dietary Energy Balance Modulation of Kras- and Ink4a/Arf+/−-Driven Pancreatic Cancer: The Role of Insulin-like Growth Factor-I

New molecular targets and intervention strategies for breaking the obesity-pancreatic cancer link are urgently needed. Using relevant spontaneous and orthotopically transplanted murine models of pancreatic cancer, we tested the hypothesis that dietary energy balance modulation impacts pancreatic cancer development and progression through an insulin-like growth factor (IGF)-I-dependent mechanism. In LSL-Kras(G12D)/Pdx-1-Cre/Ink4a/Arf(lox/+) mice, calorie restriction versus overweight- or obesity-inducing diet regimens decreased serum IGF-I, tumoral Akt/mTOR signaling, pancreatic desmoplasia, and progression to pancreatic ductal adenocarcinoma (PDAC), and increased pancreatic tumor-free survival. Serum IGF-I, Akt/mTOR signaling, and orthotopically transplanted PDAC growth were decreased in liver-specific IGF-I-deficient mice (vs. wild-type mice), and rescued with IGF-I infusion. Thus, dietary energy balance modulation impacts spontaneous pancreatic tumorigenesis induced by mutant Kras and Ink4a deficiency, the most common genetic alterations in human pancreatic cancer. Furthermore, IGF-I and components of its downstream signaling pathway are promising mechanistic targets for breaking the obesity-pancreatic cancer link.

Observations on the effects of Suppressor of Cytokine Signaling 7 (SOCS7) knockdown in breast cancer cells: their in vitro response to Insulin Like Growth Factor I (IGF-I)

Suppressor of cytokine signaling 7 (SOCS7) is a member of the SOCS family and is known to interact with phospholipase Cγ-1 (PLCγ-1), one of the insulin-like growth factor-I (IGF-I) receptor downstream molecules. In this study, we sought to observe the effect of knocking down SOCS7 gene on breast cancer cells in vitro growth and migration and to elucidate whether this involves IGF-I-PLCγ1 route using the PLCγ-1 blocker U73122. Suitable breast cancer cells (MCF7 and MDA-MB-231) were transfected with anti-SOCS7 ribozymal transgene, to create sub-lines with SOCS7 knockdown verified by RT-PCR. The growth and migration of the cells were evaluated in the presence or absence of IGF-I and PLCγ-1 inhibitor using growth assay, scratch-wound and electrical cell impedance sensing (ECIS) migration assays. IGF-I treatment produced more pronounced influence on MCF7 growth and migration and on MDA-MB-231 migration when SOCS7 gene was knocked down in both lines (p < 0.05). The absence of IGF-I-induced growth response in MDA-MB-231 could be due to the intrinsic characteristics of these cells. PLCγ-1 pharmacological inhibition during their in vitro migration seemed to only occur when SOCS7 gene was knocked down. To the best of our knowledge, this is the first report of the SOCS7 regulatory role in IGF-I induced in vitro functions in ER-positive and ER-negative breast cancer cells. IGF-I treatment and SOCS7 loss have synergistically resulted in increased growth and migration of MCF7 and in increased migration of MDA-MB-231 cells. The migratory effects could be due to a precise anti-PLCγ-1 role.

Circulating endothelial progenitor cells in acromegaly.

Endothelial progenitor cells (EPCs), involved in the repairing mechanisms of vascular damage, are positively correlated to insulin-like growth factor I (IGF-I) concentrations in healthy adults. However, the levels of EPCs and their role in acromegalic patients have never been investigated. We conducted a cross-sectional study in order to assess the levels of the different phenotypes of circulating EPC in acromegalic patients. The study was performed at the Endocrinology Unit of Federico II University and at the Unit of Metabolic Diseases and Endocrinology of the Second University of Naples. Fifty-five acromegalic patients and 65 healthy controls were studied. EPCs were assessed by flow cytometry and IGF-I by immunoradiometric assay. Compared with subjects of the control group, acromegalic patients showed significantly higher levels of EPCs phenotypes expressing KDR antigen [KDR+, cells per 106 events, median and interquartile range, 44 (28-67) vs 23 (13-40), p=0.006; CD34+KDR+ 25 (18-38) vs 12 (8-17), p<0.001; CD133+KDR+ 17 (13-30) vs 8 (6-12), p<0.001; CD34+KDR+CD133+ 16 (12-25) vs 8 (6-10), p<0.001]. There was a positive correlations between CD34+KDR+CD133+ cells count and IGF-I in acromegaly group (r=0.79, p<0.001). Acromegalic patients show higher circulating EPCs levels expressing KDR, positively correlated with IGF-I, suggesting a role for IGF-I in regulating the expression of this surface marker in the early phase of EPCs differentiation.

Role of insulin-like growth factor-I and follicular fluid from ovarian follicles with different diameters on porcine oocyte maturation and fertilization in vitro

The objective of this study was to determine the effects of insulin-like growth factor-I (IGF-I) (0, 60, 120, 180, and 240 ng/mL) and follicular fluid (FF) derived from 2 to 5 and 6 to 10 mm diameter follicles (SpFFs and LpFFs, respectively) added during in vitro maturation (IVM) of porcine oocytes on nuclear maturation and IVF. Cumulus-oocyte complexes (COCs) were matured in NCSU-37 medium supplemented with SpFFs or LpFFs and various IGF-I concentrations. The COCs were cultured for 44 hours, and then fertilized in vitro. Maturation and IVF results were recorded 18 hours after insemination. The IVM (%) was higher (P < 0.05) in the COCs matured in LpFFs than with SpFFs when 0 (90.0 ± 6.9 vs. 76.3 ± 10.7) or 60 ng/mL IGF-I (92.0 ± 8.1 vs. 81.8 ± 10.2) was added. In SpFFs media, there was a quadratic relationship (P < 0.01) between IGF-I concentration and IVM (peak results at IGF-I = 129 ng/mL). However, when the COCs were matured with LpFFs, there was a decreasing linear effect between IGF-I concentration and IVM. At all concentrations of IGF-I, the percentage of degenerated oocytes was higher in COCs matured in SpFFs than in LpFFs. Penetration (%) did not differ (P > 0.05) between COCs matured with SpFFs or LpFFs when 60 (66.8 ± 9.4 vs. 72.7 ± 11.3) or 180 ng/mL of IGF-I (75.7 ± 10.4 vs. 73.8 ± 13.2) were used. Monospermy (%) was similar between SpFFs and LpFFs only with addition of 120 ng/mL IGF-I. The IVF performance (%) did not differ between COCs matured with SpFFs or LpFFs when IGF-I concentrations of 120 (28.5 ± 8.8 vs. 38.5 ± 8.3) and 180 ng/mL (24.3 ± 10.2 vs. 30.12 ± 8.2) were used. There was no effect of IGF-I concentration or of FF type on the number of penetrated sperm per oocyte and on male pronuclear formation. For COCs matured with SpFFs, there was a quadratic relationship between IGF-I concentration and penetration, monospermy, and IVF performance (peak results at IGF-I = 179, 122, and 135 ng/mL, respectively). Thus, on the basis of the observed quadratic relationships, we inferred that when using SpFFs, the addition of IGF-I (122–179 ng/mL) to the IVM medium produced results similar to those obtained with LpFFs without adding IGF-I. In conclusion, the addition of IGF-I to the IVM medium supplemented with SpFFs increased maturation and improved IVF results. Alternatively, IGF-I had no effect on IVM or IVF when used with LpFFs.

Early nutrition impact on the insulin-like growth factor axis and later health consequences

There is increasing interest in the role of insulin-like growth factor-I (IGF-I) in the relation between early growth and later risk of noncommunicable diseases (NCDs). This review presents and discusses a selection of recent publications on this topic. Nutrition during pregnancy and in preterm infants has an influence on IGF-I. Breastfeeding is associated with lower IGF-I values and the effect of early protein intake was confirmed in a large intervention study. IGF-I levels are associated with early obesity, but the relation is complex and differs with age. Further studies and reviews support that there is a programming of the IGF axis, with higher levels during early life being associated with lower levels in adulthood, which is likely to influence the risk of NCDs later in life. Recent studies support that IGF-I plays an important role in the complex association between early diet, growth and later health, but more studies are needed to better understand the role of IGF-I, especially in the early development of obesity. Studies with data on how IGF-I is influenced by early diet in studies of preterm infants and young children with undernutrition from low-income countries will be helpful in recommending optimal diets.

The role of insulin-like growth factor-I and polyamines in developing rat small intestine

IGF-I, Insulin like growth factor-I is a multi-functional polypeptide which organizes the proliferation and differentiation of various cell types and has a metabolic activity similar to insulin. We know that IGF-I receptors localize in the gastrointestinal tract. Polyamines play an important role in the gastrointestinal growth which connect with IGF-I. DFMO, I±-difluoromethylornithine is an irreversible inhibitor of ODC, ornithine decarboxylase, the rate-limiting enzyme in the synthesis of polyamines. In the IGF-I-promoted growth the role of polyamines mainly investigate in vitro systems, however, in vivo studies are necessary to clarify the subject. Our aim in this study is to examine the in vivo role of IGF-I as a stimulant in the growth of developing rat's small intestine, and to clarify the role of polyamines in the period of growth promoted by IGF-I. In this study, animals were divided into 2 groups. DFMO (500 mg/kg/day) was administered for 10 days to 9 rats forming the experimental group. Sterile 0.9% NaCl was injected at the same volume as for the experimental animals into 8 rats forming the control group. Tissue samples were taken from the rats for histological, immunohistochemical and biochemical analyses on the 10th day. In the group given DFMO, the expansion and compression of the villi, as well as a decrease in the PAS-positive reaction intensity of brush border and in the number of goblet cells were observed. mmunohistochemical assessments showed that the number of PCNA, ODC and IGF-I positive cells in the DFMO-treated group decreased significantly, compared with the control group. Biochemical investigations showed that DNA values in the small intestinal tissue decreased insignificantly in the DFMO treated group as compared to the control one. We concluded that application of DFMO in the developing rat small intestine inhibited polyamine synthesis and IGF-I synthesis and partially prevented growth of the intestine. Keywords: Polyamine, I±-difluoromethylornithine, insulin-like growth factor-I, ornithine decarboxylase

The Role of Insulin-Like Growth Factor-I on Developmental Competence of Bovine Oocytes Exposed to Heat Shock.

The Role of Insulin-Like Growth Factor-I on Developmental Competence of Bovine Oocytes Exposed to Heat Shock.

Involvement of Insulin-Like Growth Factor-I Secretion and All-Trans-Retinoic Acid-Induced Decrement in Viability in MCF-7 Cells

Background/Aim: Insulin-like growth factor-I (IGF-I) is associated with survival, apoptosis and proliferation in MCF-7 cells. All-trans-retinoic acid (RA) is used as a cancer therapeutic, but the use of RA in cancer therapy is limited by the unpredictable resistance of cancer cells to drug action. Furthermore, the relationship of IGF-I with RA-induced decrement in cell viability has yet to be elucidated. Materials and Methods: MCF-7 cells were grown as confluent monolayers. To demonstrate the signaling pathways and roles of IGF-I, we suppressed endogenous target IGF-I with specific small interfering RNA treatment. Protein kinase C-δ and insulin receptor substrate 1 (IRS-1) protein levels were analyzed by Western blot. Radioimmunoassays were used to assess the concentration of endogenous IGF-I, and RT-PCR was used to assess IGF-I mRNA expression. Cell viability was analyzed with the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay. Results: We showed that RA treatment resulted in a dose- and time-dependent decrease in the secretion and synthesis of IGF-I. Subsequently, we found that suppression of IGF-I and IRS-1 protein decreased cell viability. In contrast, suppression of protein kinase C-δ and stimulation of IGF-I protected cells from RA-induced decrement in cell viability. The combination of RA treatment with IGF-I or IRS-1 small interfering RNA resulted in an additive decrease in cell viability. Conclusion: These results indicate that IGF-I plays an important role in the effect of RA and that suppression of IGF-I is implicated in the RA-induced inhibition of cell viability in MCF-7 cells.

The Role of Insulin-Like Growth Factor-I in the Physiopathology of Hearing

Insulin-like growth factor-I (IGF-I) belongs to the family of polypeptides of insulin, which play a central role in embryonic development and adult nervous system homeostasis by endocrine, autocrine, and paracrine mechanisms. IGF-I is fundamental for the regulation of cochlear development, growth, and differentiation, and its mutations are associated with hearing loss in mice and men. Low levels of IGF-I have been shown to correlate with different human syndromes showing hearing loss and with presbyacusis. Animal models are fundamental to understand the genetic, epigenetic, and environmental factors that contribute to human hearing loss. In the mouse, IGF-I serum levels decrease with aging and there is a concomitant hearing loss and retinal degeneration. In the Igf1−/− null mouse, hearing loss is due to neuronal loss, poor innervation of the sensory hair cells, and age-related stria vascularis alterations. In the inner ear, IGF-I actions are mediated by intracellular signaling networks, RAF, AKT, and p38 MAPK protein kinases modulate the expression and activity of transcription factors, as AP1, MEF2, FoxM1, and FoxP3, leading to the regulation of cell cycle and metabolism. Therapy with rhIGF-I has been approved in humans for the treatment of poor linear growth and certain neurodegenerative diseases. This review will discuss these findings and their implications in new IGF-I-based treatments for the protection or repair of hearing loss.

Involvement of insulin-like growth factor-I for the regulation of prolactin synthesis by estrogen and postnatal proliferation of lactotrophs in the mouse anterior pituitary

Estradiol (E2) stimulates not only secretion of prolactin (PRL) and proliferation of PRL-producing cells (PRL cells) in the anterior pituitary, but also the expression of growth factors. In insulin-like growth factor-I (IGF-I) knockout (KO) mice, the number of PRL cells is decreased and administration of IGF-I does not increase either the number of PRL cells or plasma PRL levels, indicating that IGF-I plays a pivotal role in PRL cells. The effect of E2 on PRL cells in KO mice was investigated by immunohistochemistry and real-time RT-PCR. The number of PRL cells in KO mice was significantly lower than in the wild-type (WT) control mice. E2 increased the PRL mRNA in WT and KO mice; however, an increase of PRL mRNA in KO was less than that in WT. In addition, no vasoactive intestinal peptide (VIP)-immunoreactive cells were found in KO mice, therefore IGF-I is essential for VIP expression. To investigate the roles of IGF-I on PRL cells in the postnatal development, double-immunostaining with PRL and BrdU was performed in WT and KO mice from days 5-20. The percentages of PRL cells and BrdU-labeled cells in the anterior pituitary of KO mice were lower than in WT mice. Thus, IGF-I may be responsible for proliferation and differentiation of PRL cells in this postnatal period. Differentiation and the proliferation of PRL cells are controlled by IGF-I during the postnatal development, and IGF may be a mediator of E2 action through VIP induction in PRL cells of adults.

Structural organization of binding determinants in the molecule of insulin-like growth factor-I (IGF-I)

Insulin-like growth factor I (IGF-I) is a peptide related to insulin and IGF-II. These three related peptides produce similar biological effects, but each of them has its irreplaceable physiological significance in the organism. Multisided functional role of IGF-I in the organism is due to its unique binding properties. Specifically, but with different degree of affinity, it is able to interact with three receptors (IGF-I-receptor, insulin receptor, and IGF-II-receptor) and six binding proteins (IGFBP 1–6). To interact with each of the above objects, the IGF-I molecule contains individual structural determinants—binding domains (BD) providing strict specificity of interaction with them. Responsible for the IGF-I biological effects and binding with IGF-I-receptor is α-domain, for binding with insulin receptor—β-, EGF-II—γ-, while with all BP—δ-BD, respectively. Results of experimental study of binding domains not always can be estimated unanimously. The proposed by the author system of criteria for evaluation of changes in affinity of the IGF-I analogies allows unraveling the structural organization of each of the domains and tracing dependence on it of the peptide affinity to the particular object. This work considers composition, organization, and principle of formation of affinity of three binding IGF-I domains (α-, γ-, and δ-BD). The α-domain includes three tyrosines from three different molecule sites (B-24, C-31, and A-60) disposed spatially in the direct vicinity on its one surface. The β-domain also is considered as the domain participating in the high-affinity interaction; by composition and location in molecule it principally differs from α-BD, with the structural organization that so far has not been deciphered. Analyzed in detail is the key significance of the N-terminal site of the B-chain—the linear site of the domain—for binding of IGF-I with BP, functional heterogeneity of its constituent residues, and the characteristic principle of formation of affinity to BP. Analysis indicates a probability of the second δ-BD, quite possibly not the only one, and a high sensitivity of the domain to configuration of the IGH-I molecule surface. Structural organization and peculiarities of formation of affinity in the γ-domain are studied the best in three related peptides; it consists of two linearly exposed sites of A-chain. Composition of the site S-1 A (Phen8, Arg9, Ser10) provides a possibility of binding the ligand with IGF-I-receptor, while the level of affinity to it depends on the composition of S-2. The S-2 A composition (Arg14, Arg15) determines the low affinity of IGF-I to the IGF-II-receptor. The clear functioning of IGF-I and elimination of mixture of functions at the level of the binding activity depend on the spatial autonomy of BD of different nature, difference in structural organization of each of the domains, and a peculiarity of principles of formation of affinity in each case. The spatial coordination of several BD sites is the condition for transmission of the “structural signal“ by regulatory peptide. The performed analysis provides the direct notion of dependence of the binding ability of the IGF-I molecule that has BD of different nature on their structural peculiarities and allows using the revealed regularities at searching for BD in the newly discovered insulinlike peptides.

Coordinated increase in skeletal muscle fiber area and expression of IGF-I with resistance exercise in elderly post-operative patients

Hypertrophy of developing skeletal muscle involves stimulation by insulin-like growth factor-I (IGF-I), however, the role of IGF-I in adult muscle is less clarified. In the present study, the mRNA splice variants of IGF-I (IGF-IEa and MGF) and the changes in muscle fiber cross sectional area after 12 weeks of training were studied in elderly post-operative patients. About 28 subjects, 14 men and 14 women (age 69, range 60–86 years) were randomized to unilateral resistance training (RT: 3/week), electrical stimulation (ES: 1 h/day) or functional exercises (FE: 1 h/day). The non-operated-side served as a within subject control. Muscle biopsies were obtained from the vastus lateralis of both limbs at +2d post-operative (baseline), at 5 weeks and 12 weeks post-surgery to analyze for changes in type 1 and type 2 muscle fiber area. Changes in expression levels of IGF-I mRNA isoforms were determined using real-time RT-PCR, normalized to the ribosomal protein large protein 0 (RPLP0) mRNA and presented relative to the control-side. At baseline there was no difference between the three groups in muscle fiber area or resting levels of IGF-IEa and MGF. RT resulted in a significant increase in muscle fiber area of type 1 (+17%, p < 0.05) and type 2 (+36%, p < 0.05) parallel to an increase in the expression of IGF-IEa and MGF, in contrast to ES and FE. The present study demonstrates that resistance training initiated in the acute post-operative phase is highly effective in increasing mean fiber area and in addition induces marked increases in the expression of IGF-I splice variants, supporting the idea that IGF-I is involved in regulating muscle hypertrophy.

Endogenous IGF-I and αVβ3 Integrin Ligands Regulate Increased Smooth Muscle Hyperplasia in Stricturing Crohn's Disease

Insulin-like growth factor-I (IGF-I) regulates human intestinal smooth muscle growth by stimulating proliferation and inhibiting apoptosis. IGF-I-stimulated growth is augmented when alphaVbeta3 integrin is occupied by its ligands, fibronectin and vitronectin. Increased IGF-I expression and muscle cell hyperplasia are features of stricturing Crohn's disease (CD); however, the role of IGF-I in stricture formation is unknown. The aim was to identify the functional role of endogenous IGF-I and alphaVbeta3 integrin ligands in regulating muscle cell hyperplasia in stricturing CD. Smooth muscle cells were isolated from muscularis propria of stricturing CD or normal margins. Quantitative polymerase chain reaction, immunoblot analysis, and enzyme-linked immunosorbent assay were used to measure fibronectin, vitronectin, alphaVbeta3 integrin, and IGF-I levels. Activation of the IGF-I receptor, Erk1/2, p70S6 kinase, and GSK-3beta was measured by immunoblot. Proliferation was quantified by Ki67 immunostaining and [(3)H]thymidine incorporation. Apoptosis was measured from caspase-3 cleavage and nucleosome accumulation. IGF-I, vitronectin, and fibronectin RNA and protein levels were increased 1.8- to 3.4-fold in muscle cells from strictures over normal margins. Basal IGF-I receptor phosphorylation was increased 320% in strictured over normal muscle, and basal Erk1/2, p70S6 kinase, and GSK-3beta phosphorylation were increased 205%-292% in strictures. In muscle cells from strictures, Ki67 immunoreactivity and [(3)H]thymidine incorporation were increased and apoptosis was decreased compared with normal margins. Antagonists of the IGF-I receptor or alphaVbeta3 integrin reversed these changes. Smooth muscle cell hyperplasia in stricturing CD is regulated by increased endogenous IGF-I and alphaVbeta3 integrin ligands that regulate augmented proliferation and diminished apoptosis.