Alicia Roldán

Insulin-like growth factor-1 increases the mitogenic response of human peripheral blood lymphocytes to phytohemagglutinin

Receptors for insulin and insulin-like growth factor-1 (IGF-1) have been demonstrated on activated T-lymphocytes. The question is whether receptors for insulin or IGF-1 have any function in these cells. In this study we demonstrate that the concentration of IGF-1 in commercial samples of fetal calf serum is about 70 times that of insulin. Moreover, antibodies binding IGF-1 reduce responses of human peripheral blood mononuclear cells to PHA by about 50%, whereas antibodies to insulin have no demonstrable effect. These observations suggest that binding of IGF-1 to specific receptors contributes to the proliferative responses of activated T-lymphocytes.

Early effects of insulin-like growth factor-1 in activated human T lymphocytes

This study evaluates the effects of insulin‐like growth factor (IGF)‐1 receptor (IGF‐1R) down‐regulation in stimulated T lymphocytes by investigating the expression of early activation proteins CD69, CD25, and interleukin (IL)‐2. We found that IGF‐1 does not modify CD69 expression but increases transcription and protein synthesis of CD25 and IL‐2. The lowest level of IGF‐1R detected after 15 min of activation suggested that the effects of IGF‐1 occur at the initiation of cell activation. The activation of IGF‐1R was confirmed by IGF‐1R phosphorylation and increased phosphorylation of microtubule‐associated protein kinase. We also detected the alternative IGF‐1 transcripts Ea, with paracrine/autocrine regulation, and Eb, with endocrine regulation, in Jurkat cells and in quiescent T lymphocytes, and we detected IGF‐1 protein in the culture medium after stimulation. These data suggest that the proliferative effects of IGF‐1 on T lymphocytes include both autocrine/paracrine and endocrine processes.

In Vitro Differences Between Astrocytes of Control and Wobbler Mice Spinal Cord

The Wobbler mouse, a model of amyotrophic lateral sclerosis (ALS), presents motorneuron degeneration and pronounced astrogliosis in the spinal cord. We have studied factors controlling astrocyte proliferation in cultures derived from Wobbler and control mice spinal cord. Basal rate of [3H]thymidine incorporation was 15 times lower in Wobbler astrocytes. While in control cultured cells interleukin-1α (IL-1) and corticosterone (CORT) significantly increased proliferation, both agents were inactive in Wobbler astrocytes. The lack of response to CORT was not due to the absence of glucocorticoid receptors, because similar receptor amounts were found in Wobbler and control astrocytes. In contrast to IL-1 and CORT, transforming growth factor-β1 (TGF-β1) substantially increased proliferation of Wobbler astrocytes but not of control cells. Differences in response to TGF-β1 were also obtained by measuring glial fibrillary acidic protein (GFAP) immunoreaction intensity, which was substantially higher in Wobbler astrocytes. Thus, abnormal responses to different mitogens characterized Wobbler astrocytes in culture. We suggest that TGF-β1 may play a role in the reactive gliosis and GFAP hyperexpression found in the degenerating spinal cord of this model of ALS.

Insulin-Like Growth Factor-1 Receptor Regulation in Activated Human T Lymphocytes

Objective: To investigate the kinetics of insulin-like growth factor-1 receptor (IGF-1R) expression in PHA-stimulated T lymphocytes. Methods: IGF-1R protein and mRNA were detected by flow cytometry and RT-PCR respectively, between 0 and 48 h after cell activation. Results: Few minutes after T lymphocytes were activated, internalization of the IGF-1R from the cell membrane was observed, achieving the lower level between 1 and 6 h and was accompanied by a reduction in its mRNA. This was followed by re-expression of IGF-1R on the cell surface and an increase in IGF-1R mRNA levels in the cytoplasm, reaching levels higher than those recorded initially after 48 h activation. Conclusion: This down- and up-regulation suggests that restoration of IGF-1R would be the result of receptor recycling and de novo synthesis and highlights its importance for T lymphocyte proliferation.

Role of insulin-like growth factor-1 on the kinetics of human lymphocytes stimulation in serum-free culture medium

In a serum‐free medium addition of insulin‐like growth factor‐1 (IGF‐1) consistently enhanced lymphocyte proliferation response to PHA in a dose‐dependent fashion. This effect was produced by an acceleration in the expression of clone expansion and not in the number of proliferating cells. This was documented by kinetics data obtained from the first proliferation round of PHA‐stimulated lymphocytes, in which addition of IGE‐1 reduced G1‐phase length, without changing Go‐phase, S‐phase or cloned size. The data were confirmed in 10‐day culture of stimulated lymphocytes where IGF‐1 only accelerated cell proliferation without modifying the area enclosed by the proliferation curve. As IGF‐1 is under the control of growth hormone, our results suggest that some of the immunoregulation effects ascribed to growth hormone in vivo could be produced by IGF‐1.

Inhibitory effect of 11β‐hydroxypregna‐l,4‐diene‐3,20‐dione (ΔHOP) on lymphocyte proliferation

We have compared the immunosuppressive effect of ΔHOP and glucocorticoids on lymphocyte proliferation and IL‐1 secretion. The new synthetic steroid only inhibited proliferation of phytohaemagglutinin (PHA)‐stimulated human lymphocyte at high concentrations and the effect did not persist after washing out the steroid‐ In contrast, glucocorticoids produced the classical dose‐response inhibition and the effect persisted when they were removed from the cultured medium. Although both steroids decreased IL‐1 secretion from human monocytes stimulated with lipopolysaccharide (LPS), they exert the same effect through a different mechanism. The experiments we report suggest that the decrease of IL‐1 synthesis produced by ΔHOP could be caused by inhibition of LPS phagocytosis. These results support our hypothesis that ΔHOP exerts its immunosuppressive and anti‐inflammatory effect by a non‐genomic mechanism.

Co‐operative effect between insulin‐like growth factor‐1 and interleukin‐2 on DNA synthesis and interleukin‐2 receptor‐α chain expression in human lymphocytes

Recently we demonstrated that IGF‐1 has the same effect on DNA synthesis and G1‐phase length during human lymphocyte proliferation as IL‐2. In order to determine the link between IGF‐1 and IL‐2 on lymphocyte proliferation, we tested the ability of these cytokines, alone or in combination, to induce DNA synthesis and increase the number of cells expressing IL‐2‐α chain receptors. Our results showed that the increase in DNA synthesis produced by the addition of IGF‐1 to cells cultured with saturable concentrations of IL‐2, correlated well with an increase in the number of cells expressing IL‐2‐α chain receptor. The effect on both DNA synthesis and IL‐2‐α chain receptor expression was greater at lower concentrations of PHA. This study suggests that the proliferative effect of IGF‐1 might be due to separate stimulation of different cell populations and/or by activation of a tyrosine‐kinase signal transduction pathway complementary to the IL‐2 activation signal.