Christine Carlsson-Skwirut

IGF-I has a direct proliferative effect in adult hippocampal progenitor cells

The aim of the present study was to investigate the potential direct effects of insulin-like growth factor-I (IGF-I) on adult rat hippocampal stem/progenitor cells (AHPs). IGF-I-treated cultures showed a dose-dependent increase in thymidine incorporation, total number of cells, and number of cells entering the mitosis phase. Pretreatment with fibroblast growth factor-2 (FGF-2) increased the IGF-I receptor (IGF-IR) expression, and both FGF-2 and IGF-I were required for maximal proliferation. Time-lapse recordings showed that IGF-I at 100 ng/ml decreased differentiation and increased proliferation of single AHPs. Specific inhibition of mitogen-activated protein kinase kinase (MAPKK), phosphatidylinositol 3-kinase (PI3-K), or the downstream effector of the PI3-K pathway, serine/threonine p70 S6 kinase (p70(S6K)), showed that both the MAPK and the PI3-K pathways participate in IGF-I-induced proliferation but that the MAPK activation is obligatory. These results were confirmed with dominant-negative constructs for these pathways. Stimulation of differentiation was found at a low dose (1 ng/ml) of IGF-I, clonal analysis indicating an instructive component of IGF-I signaling.

Identification of Gly-Pro-Glu (GPE), the aminoterminal tripeptide of insulin-like growth factor 1 which is truncated in brain, as a novel neuroactive peptide

A truncated form of IGF-1 which lacks the aminoterminal tripeptide Gly-Pro-Glu (GPE) is found in human brain. It was proposed that GPE may result from neural specific processing and also have a function within the CNS. GPE was synthesized and shown to inhibit glutamate binding to the N-methyl-D-aspartate (NMDA) receptor. Whilst the carboxyterminal glutamate was necessary for NMDA receptor binding, the aminoterminal glycine potentiated receptor crossreaction. Furthermore, GPE had a potent stimulatory effect on the potassium induced release of acetylcholine from rat cortical slices. A less potent stimulation of dopamine release from striatum was also observed. The specific competitive NMDA receptor antagonist, (+/-)2-amino-7-phosphonoheptanoate (AP7), inhibited the action of GPE on dopamine but not on acetylcholine release. These studies have identified GPE as a novel neuroactive peptide with a potent action on acetylcholine release and support the general concept that the proteolytic products of the IGF-1 precursor play a role in the regulation of brain function.

A comparison of the biological activity of the recombinant intact and truncated insulin-like growth factor 1 (IGF-1)

A truncated form of insulin-like growth factor 1 (IGF-1), which lacked the aminoterminal tripeptide Gly-Pro-Glu has been isolated from human fetal and adult brain. This truncated IGF-1 displayed more potent cross-reactivity and biological action on brain cells than IGF-1 isolated from human serum. We now present data on a recombinant DNA-derived truncated IGF-1 lacking the aminoterminal tripeptide. Recombinant truncated IGF-1 was 1.4-5-times more potent than recombinant and natural IGF-1 in displacing [125 I]IGF-1 from human fetal and adult brain and placenta membranes. These differences were slightly enhanced when truncated IGF-1 was used as radioligand. The relative potencies compared to insulin-like growth factor 2 (IGF-2) in displacing [125I]IGF-2 from rat liver membranes were recombinant truncated IGF-1, 0.3% and recombinant IGF-1, 0.2%. Recombinant truncated IGF-1 displayed 100-fold reduced affinity for the low molecular weight binding protein (IGF-BP) isolated from human amniotic fluid when compared to recombinant IGF-1. Likewise, the IGF-BP was 100-fold less potent in inhibiting the receptor binding of recombinant truncated IGF-1 than that of recombinant IGF-1. Recombinant truncated IGF-1 was 4-times more potent than recombinant and natural IGF-1 in stimulating DNA synthesis in fetal rat brain cells. This biological activity of recombinant truncated IGF-1 was not affected by the IGF-BP at concentrations which abolished the biological activity of recombinant IGF-1. The hypothesis that IGF-BP bound intact IGF-1 represents the endocrine form of IGF-1, whereas truncated IGF-1 represents the paracrine or autocrine form of IGF-1, is proposed.

Isolation and characterization of variant IGF-1 as well as IGF-2 from adult human brain

The forms of somatomedin present in the adult human brain have been characterized in this study. Two peptides were purified by acidification, size exclusion chromatography, affinity chromatography, FPLC and HPLC. structural analysis identified these peptides as the variant form of IGF‐1 with a truncated N‐terminal region earlier isolated from human fetal brain and IGF‐2. The presence of the truncated IGF‐1 variant and IGF‐2 in the human CNS suggests their role as neuropeptides.

The role of the insulin-like growth factors in the regulation of brain development

Publisher Summary This chapter discusses the role of the somatomedins or insulin-like growth factors (IGFs) in the regulation of brain development. These growth promoting peptide hormones are recently characterized in the brain, where they are produced as paracrine hormones and regulate cell proliferation and hypertrophic growth. The IGFs were first implicated in the regulation of brain growth with the hypothesis of a brain growth factor whose production could be stimulated by growth hormone. In simple terms, cellular growth occurs initially as the rapid proliferation of undifferentiated cells. In all species, the critical period of brain growth occurs during the early stages of development. The hormones that regulate the growth of the brain are gradually being identified. The IGFs are paracrine hormones produced in the nervous system throughout life. The IGFs have a potent growth-promoting action on neural tissues and are proposed to be major growth-regulating hormones for the central nervous system.

Insulin‐like growth factor‐I increases astrocyte intercellular gap junctional communication and connexin43 expression in vitro

Connexin43 (cx43) forms gap junctions in astrocytes, and these gap junctions mediate intercellular communication by providing transport of low‐molecular‐weight metabolites and ions. We have recently shown that systemic growth hormone increases cx43 in the brain. One possibility was that local brain insulin‐like growth factor‐I (IGF‐I) could mediate the effect by acting directly on astrocytes. In the present study, we examined the effects of direct application of recombinant human IGF‐I (rhIGF‐I) on astrocytes in primary culture concerning cx43 protein expression and gap junctional communication (GJC). After 24 hr of stimulation with rhIGF‐I under serum‐free conditions, the GJC and cx43 protein were analyzed. Administration of 30 ng/ml rhIGF‐I increased the GJC and the abundance of cx43 protein. Cell proliferation of the astrocytes was not significantly increased by rhIGF‐I at this concentration. However, a higher concentration of rhIGF‐I (150 ng/ml) had no effect on GJC/cx43 but increased cell proliferation. Because of the important modulatory role of IGF binding proteins (IGFBPs) on IGF‐I action, we analyzed IGFBPs in conditioned media. In cultures with a low abundance of IGFBPs (especially IGFBP‐2), the GJC response to 30 ng/ml rhIGF‐I was 81%, compared with the average of 25%. Finally, as a control, insulin was given in equimolar concentrations. However, GJC was not affected, which suggests that rhIGF‐I acted via IGF‐I receptors. In summary, the data show that rhIGF‐I may increase GJC/cx43, whereas a higher concentration of rhIGF‐I—at which stimulation of proliferation occurred—did not affect GJC/cx43. Furthermore, IGFBP‐2 appeared to modulate the action of rhIGF‐I on GJC in astrocytes by a paracrine mechanism.

Interstitial IGF-I in exercising skeletal muscle in women

OBJECTIVE To study interstitial IGF-I concentrations in resting and exercising skeletal muscle in relation to the circulating components of the IGF-IGF binding protein (IGFBP) system. DESIGN AND METHODS Seven women performed endurance exercise with 1 leg (Ex-leg) for 1 h. The resting leg (Rest-leg) served as a control. IGF-I was determined in microdialysate (MD) and was compared with veno-arterial (v-a) concentrations of circulating IGF-IGFBP components. RESULTS Median (range) basal MD-IGF-I was 0.87 (0.4-1.5) microg/l or 0.4 (0.2)% of total-IGF-I (t-IGF-I) determined in arterial serum and in the same concentration range as free dissociable IGF-I (f-IGF-I). Rest-leg MD-IGF-I decreased, reaching significance after exercise. Ex-leg MD-IGF-I was unchanged during exercise and declined after exercise at the level of significance (P = 0.05). There was a release of f-IGF-I from the Ex-leg into the circulation at the end of and shortly after exercise. A small but significant increase in circulating IGFBP-1 was detected at the end of exercise and IGFBP-1 increased further after exercise. Although interleukin-6 (IL-6) has been associated with IGFBP-3 proteolysis, the circulating molecular forms of IGFBP-3 remained unchanged in spite of an IL-6 release from the muscle compartment. CONCLUSIONS Circulating IGFBP-1 is related to interstitial IGF-I in resting muscle although the temporal relationship may not be simple. Further studies should explore the role of local release of IGF-I and its impact on IGF-I activity during contraction.

Ribosomal Protein S19 Interacts with Macrophage Migration Inhibitory Factor and Attenuates Its Pro-inflammatory Function

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that has been implicated in the pathogenesis of inflammatory disorders such as infection, sepsis, and autoimmune disease. MIF exists preformed in cytoplasmic pools and exhibits an intrinsic tautomerase and oxidoreductase activity. MIF levels are elevated in the serum of animals and patients with infection or different inflammatory disorders. To elucidate how MIF actions are controlled, we searched for endogenous MIF-interacting proteins with the potential to interfere with key MIF functions. Using in vivo biotin-tagging and endogenous co-immunoprecipitation, the ribosomal protein S19 (RPS19) was identified as a novel MIF binding partner. Surface plasmon resonance and pulldown experiments with wild type and mutant MIF revealed a direct physical interaction of the two proteins (KD = 1.3 × 10-6 m). As RPS19 is released in inflammatory lesions by apoptotic cells, we explored whether it affects MIF function and inhibits its binding to receptors CD74 and CXCR2. Low doses of RPS19 were found to strongly inhibit MIF-CD74 interaction. Furthermore, RPS19 significantly compromised CXCR2-dependent MIF-triggered adhesion of monocytes to endothelial cells under flow conditions. We, therefore, propose that RPS19 acts as an extracellular negative regulator of MIF.

Anti-apoptotic factor humanin is expressed in the testis and prevents cell-death in leydig cells during the first wave of spermatogenesis

Humanin (HN) is a 24 amino acids peptide with potent neuro‐survival properties that protects against damage associated with Alzheimers disease. In the present report, we have demonstrated by immunohistochemical analysis and Western blotting the pattern of expression of rat humanin (HNr) in the testis of 10‐ to 60‐day‐old rats. The Leydig cells of 10‐ and 40‐ day‐old rats expressed this peptide at high levels; and in the testis of 60‐day‐old rats the expression of HNr expanded to include Leydig, endothelial, peritubular and germ cells. As monitored by Western blotting, HNr was released into the medium of cultures of Leydig cells isolated from 10‐, 40‐, and 60‐days‐old rats. HNr stimulated the incorporation of [3H]TdR into DNA of Leydig cells from 10‐days‐old rats, in a manner that indicated promotion of cell survival rather than an increase in the rate of cell multiplication. This peptide also enhanced steroidogenesis by cultured Leydig cells from 10‐ to 40‐day‐old rats both alone and synergistically with IGF‐I. The expression of HNr in cultured Leydig cells increased in response to GH and IGF‐I. In summary, we demonstrated here that HNr was expressed at all stages of maturation in the rat testis. This peptide promoted the survival of Leydig cells in culture and interacted with IGF‐I to stimulate DNA synthesis and steroidogenesis. We propose that HNr is a novel testicular anti‐apoptotic factor. J. Cell. Physiol. 208: 373–385, 2006.

Free Insulin-Like Growth Factor I: Are We Hunting a Ghost?

During the last decade, there has been an increasing number of publications reporting concentrations of free dissociable insulin-like growth factor I (IGF-I) in serum or plasma. The goal for attempting to measure free IGF-I in a serum sample in vitro has been to obtain information about the bioactivity of IGF-I in target tissues, and thus relate a measurable parameter to biological responses such as longitudinal growth or glucose disappearance rate. In this review, the serum free IGF-I approach is placed into a physiological perspective. In addition, methodological aspects are discussed and suggestions for the validation of free IGF-I assays are presented.