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Biomedical subjects

P Ye

Publications and source records attributed to P Ye.

At least 19 recordsLinked to original sources
PubMed1999

Increased insulin-like growth factor-I (IGF-I) expression during early postnatal development differentially increases neuron number and growth in medullary nuclei of the mouse.

Morphometric analyses of the medulla were performed in transgenic mice that overexpress insulin-like growth factor-I (IGF-I) postnatally and in non-transgenic littermates. The total volume of the medulla was increased in transgenic mice at all postnatal ages studied: 14 days (18%), 21 days (23%), 28 days (23%), and 35 days (27%). By 35 days of age, the volumes of individual medullary nuclei were also increased: nucleus of the tractus solitarius (NTS, 59%), dorsal motor nucleus of the vagus (DMV, 84%), hypoglossal nucleus (HN, 29%) and facial nucleus (FN, 21%). Neuron number in transgenic mice was significantly greater in NTS (50%) and DMV (53%), but not in the HN or the FN. Motor neurons in DMV, HN and FN of transgenic mice exhibited increases in mean profile areas of the soma and decreased numerical densities, suggesting increases in neuritic outgrowth. These results point to IGF-I actions in promoting neuron survival and growth, and suggest that IGF-I has differential effects on distinct neuron populations, possibly depending upon its time of expression.

Animals↗
PubMed1999

IFN-gamma and CD8+ T cells restore host defenses against Pneumocystis carinii in mice depleted of CD4+ T cells.

Host defenses against infection are profoundly compromised in HIV-infected hosts due to progressive depletion of CD4+ T lymphocytes and defective cell-mediated immunity. Although recent advances in antiretroviral therapy can dramatically lower HIV viral load, blood CD4+ T lymphocytes are not restored to normal levels. Therefore, we investigated mechanisms of host defense other than those involving CD4+ T lymphocytes against a common HIV-related opportunistic infection, Pneumocystis carinii (PC) pneumonia. Using CD4-depleted mice, which are permissive for chronic PC infection, we show that up-regulation of murine IFN-gamma by gene transfer into the lung tissue results in clearance of PC from the lungs in the absence of CD4+ lymphocytes. This resolution of infection was associated with a >4-fold increase in recruited CD8+ T lymphocytes and NK cells into the lungs. The role of CD8+ T cells as effector cells in this model was further confirmed by a lack of an effect of IFN-gamma gene transfer in scid mice or mice depleted of both CD4+ and CD8+ T cells. Cytokine mRNA analysis revealed that recruited, lung-derived CD8+ T cells had greater expression of IFN-gamma message in animals treated with the IFN-gamma gene. These results indicate that CD8+ T cells are capable of clearing PC pneumonia in the absence of CD4+ T cells and that this host defense function of CD8+ T cells, as well as their cytokine repertoire, can be up-regulated through cytokine gene transfer.

Adenoviridae↗
PubMed1999

Insulin-like growth factor-I (IGF-I) ameliorates and IGF binding protein-1 (IGFBP-1) exacerbates the effects of undernutrition on brain growth during early postnatal life: studies in IGF-I and IGFBP-1 transgenic mice.

Insulin-like growth factor-I (IGF-I) plays an important role in the stimulation of postnatal brain growth. In transgenic (Tg) mice, IGF-I overexpression stimulates postnatal brain growth, whereas decreased IGF-I availability caused by ectopic brain expression of IGF binding protein-1 [(IGFBP-1), an inhibitor of IGF-I action] retards postnatal brain growth. Because undernutrition during early postnatal development profoundly retards growth and maturation of the brain in rodents, we sought to determine the influence of IGF-I on undernutrition-induced brain growth retardation. Caloric restriction was imposed on IGF-I Tg mice, IGFBP-1 Tg mice, and their non-Tg littermates by separating half of each litter from their dams during the suckling period, postnatal d 1 to 21. Undernutrition reduced the brain growth of each group of mice, but the growth of undernourished IGF-I Tg mice was comparable to that of well-fed control mice (increased 4.13- and 4.22-fold, respectively) and greater than that of undernourished control mice (increased 3.45-fold), whereas undernourished IGFBP-1 Tg mice exhibited less growth (increased 3.15-fold) than undernourished control mice. When the effects of undernutrition were examined in specific brain regions of each group, the same pattern was observed, and IGF-I was found to be more effective in preserving the growth of the regions with the highest transgene expression (cerebral cortex, hippocampus, and diencephalon). Despite undernutrition, IGF-I transgene expression stimulated overgrowth of these regions as well as that of the posterior medial barrel subfield, a somatosensory area of the cerebral cortex in which IGF-I may be especially important in development. These data indicate that IGF-I can ameliorate the brain growth retardation caused by undernutrition imposed during development, although it is unclear whether IGF-I directly opposes the impact of undernutrition or acts independently of nutritional status. Nonetheless, these findings raise the possibility that the relatively high IGF-I expression during early postnatal life may be responsible for sparing the brain from the full impact of undernutrition during this time in development.

Animal Nutritional Physiological Phenomena↗
PubMed1999

Androgen receptor up-regulates insulin-like growth factor binding protein-5 (IGFBP-5) expression in a human prostate cancer xenograft.

The insulin-like growth factor (IGF) binding proteins (IGFBPs) are important modulators of IGF action in many tissues including human prostate. IGFBPs and the androgen receptor (AR) are expressed in CWR22, an androgen-dependent epithelial cell human CaP xenograft that retains biological characteristics of human CaPs, including regression following androgen withdrawal and recurrent growth of AR-containing cells in the absence of testicular androgens beginning several months after castration. Northern blot and in situ hybridization analyses demonstrated that IGFBP-5 is androgen-regulated in CWR22. IGFBP-5 messenger RNA (mRNA) decreased by 90% following castration of tumor-bearing mice compared with noncastrate androgen-stimulated mice. Testosterone treatment of CWR22 tumor-bearing mice 6 or 12 days after castration increased IGFBP-5 mRNA 10- to 12-fold. Levels of other IGFBP mRNAs did not change following androgen withdrawal and replacement. IGFBP-5 protein in tumor extracts bound 125I-labeled IGF-I in ligand blot assays and the amounts of IGFBP-5 measured by immunoblotting paralleled the levels of IGFBP-5 mRNA. Androgen-induced expression of IGFBP-5 was at a maximum level within 24 h after testosterone replacement, whereas the major increase in cell proliferation as measured by Ki-67 immunostaining occurred between 24-48 h. This time course suggested IGFBP-5 may be a mediator of androgen-induced growth of CWR22. In tumors that recurred several months following castration, IGFBP-5 mRNA and protein increased to levels that approached those in androgen-stimulated CWR22 tumors from noncastrate mice. IGFBP-5 immunohistochemical staining of prostate tissue specimens from patients was stronger in androgen-dependent and androgen-independent CaP than in areas of intraepithelial neoplasia (PIN) or benign prostatic hyperplasia (BPH). IGFBP-5 mRNA in these specimens was localized predominantly to stromal cells and IGFBP-5 protein to epithelial cell membranes.

Animals↗
PubMed1999

Insulin-like growth factor I protects oligodendrocytes from tumor necrosis factor-alpha-induced injury.

Tumor necrosis factor-alpha (TNF-alpha) has been causally implicated in several demyelinating disorders, including multiple sclerosis. Because insulin-like growth factor I (IGF-I) is a potent stimulator of myelination, we investigated whether it can protect oligodendrocytes and myelination from TNF-alpha-induced damage using mouse glial cultures as a model. Compared with controls, TNF-alpha decreased oligodendrocyte number by approximately 40% and doubled the number of apoptotic oligodendrocytes and their precursors. Addition of Boc-aspartyl(Ome)-fluoromethyl ketone (BAF), an inhibitor of interleukin-1beta converting enzyme (ICE)/caspase proteases, blocked TNF-alpha-induced reductions in oligodendrocytes, indicating that the TNF-alpha-induced reduction in oligodendrocytes is, at least in part, due to apoptosis, and that ICE/caspases are one of TNF-alpha action mediators. Simultaneous addition of IGF-I to TNF-alpha-treated cultures negated these TNF-alpha effects nearly completely. Furthermore, IGF-I promoted oligodendrocyte precursor proliferation and/or differentiation in TNF-alpha-treated cultures. To analyze TNF-alpha and IGF-I actions on oligodendrocyte function, we measured the abundance of messenger RNAs (mRNAs) for two major myelin-specific proteins, myelin basic protein (MBP) and proteolipid protein (PLP). While TNF-alpha decreased MBP and PLP mRNA abundance by 5- to 6-fold, IGF-I abrogated TNF-alpha-induced reductions in a dose- and time-dependent manner. The changes in MBP and PLP mRNA abundance could not be completely explained by the changes in oligodendrocyte number, indicating that myelin protein gene expression is regulated by both TNF-alpha and IGF-I. These data support the hypothesis that TNF-alpha can mediate oligodendrocyte and myelin damage, and indicate that IGF-I protects oligodendrocytes from TNF-alpha insults by blocking TNF-alpha-induced apoptosis, and by promoting oligodendrocyte and precursor proliferation/differentiation and myelin protein gene expression.

Amino Acid Chloromethyl Ketones↗
PubMed1998

IL-17 stimulates granulopoiesis in mice: use of an alternate, novel gene therapy-derived method for in vivo evaluation of cytokines.

IL-17 is a novel cytokine secreted principally by CD4+ T cells. It has been shown to support the growth of hemopoietic progenitors in vitro; however, its in vivo effects are presently unknown. Adenovirus-mediated gene transfer of the murine IL-17 cDNA targeted to the liver (5 x 10(9) plaque-forming units (PFU) intravenous) resulted in a transiently transgenic phenotype, with dramatic effects on in vivo granulopoiesis. Initially, there was a significant increase (fivefold) in the peripheral white blood count (WBC), including a 10-fold rise in the absolute neutrophil count. This was associated with a doubling in the spleen size over 7-14 days after gene transfer, which returned to near baseline by day 21, although the white blood cell count remained elevated. There was a profound stimulation of splenic hemopoiesis as demonstrated by an increase in total cellularity by 50% 7 days after gene transfer and an increase in hemopoietic colony formation. A maximal increase in frequency of high proliferative potential colonies (HPPC) (11-fold) and CFU-granulocyte-macrophage (GM) and CFU-granulocyte-erythrocyte-megakaryocyte-monocyte (GEMM) (CFU) (6-fold) was seen on day 3 after IL-17 gene transfer. Both CFU and HPPC remained significantly elevated in the spleen throughout day 21, but at reduced levels compared with day 3. Bone marrow CFU and HPPC were elevated on day 3 only by 75% and 25%, respectively, without changes in total cellularity. Thus, murine IL-17 is a cytokine that can stimulate granulopoiesis in vivo. Since IL-17 is principally produced by CD4+ T cells, this cytokine could have therapeutic implications in AIDS-related bone marrow failure and opportunistic infections.

3T3 Cells↗
PubMed1998

The domain structure of human receptor-associated protein. Protease sensitivity and guanidine HCl denaturation.

The 39-kDa receptor-associated protein (RAP), a specialized chaperone for endocytic receptors of the low density lipoprotein receptor gene family, is a triplicate repeat sequence (residues 1-100, 101-200, and 201-323, respectively), with the three repeats having different functional roles. The goal of the present study was to use a combination of protease sensitivity and guanidine denaturation analyses to investigate whether human RAP correspondingly contained multiple structural domains. Protease sensitivity analysis using six proteolytic enzymes of varying specificity showed that RAP has two protease-resistant regions contained within repeat 1 (residues 15-94) and repeat 3 (residues 223-323). Guanidine denaturation analysis showed that RAP has two phases in its denaturation, an early denaturation transition at 0.6 M guanidine HCl, and a broad second transition between 1.0 and 3.0 M guanidine HCl. Analysis of the denaturation of the individual repeats showed that, despite the similarity in sequence and protease sensitivity between repeats 1 and 3, repeat 1 was a stable structure, with a sharp transition midpoint at 2.4 M guanidine HCl, while repeat 3 was relatively unstable, with a transition midpoint at 0.6 M guanidine HCl. Repeat 2 had a denaturation profile almost identical to that of repeat 3. Denaturation analysis of the contiguous repeats 1 and 2 (residues 1-210) indicated that repeats 1 and 2 probably interact to form one structural domain represented by the broad transition, while repeat 3 constitutes a separate domain represented by the early transition. A two-domain model of RAP three-dimensional structure is proposed that integrates both structural and functional information, in which a helical segment from repeat 2 interacts with the known three-helix bundle of repeat 1 to form a four-helix bundle structural domain, while repeat 3 forms the other structural domain.

Amino Acid Sequence↗
PubMed1998

Production and testing of Schistosoma japonicum candidate vaccine antigens in the natural ovine host.

The objectives of this work were to clone and express Chinese strain Schistosoma japonicum antigens and evaluate their immunogenicity and protective efficacy in the natural ovine host in China. Recombinant antigens selected for testing were: isoforms of glutathione S-transferase Sj28GST and Sj26GST; the large hydrophilic domain of Sj23, the homologue of the protective S. mansoni membrane antigen Sm23; and a 3' fragment of S. japonicum paramyosin. In addition, Chinese strain S. japonicum native paramyosin and GST were purified and used for vaccination. Antigens were co-administered with Freund's adjuvants or BCG. We also examined the effects of co-administration of native unfractionated GSTs with keyhole limpet haemocyanin (KLH), which shares a cross-reactive protective epitope with schistosomes. These are the first side-by-side comparisons of candidate defined-antigen schistosomiasis vaccines in a natural host. Significant partial protection was obtained with each of the antigens tested. Less protection was obtained with a recombinant fragment of S. japonicum paramyosin compared with native paramyosin. Co-administration of native GST and KLH was no more effective than vaccination with either antigen alone. Although encouraging levels of protection against S. japonicum were demonstrated using each of these antigens, further work is needed to optimise vaccine delivery and vaccination schedules.

Adjuvants, Immunologic↗
PubMed1998

Antitumor activity with the HSV-tk-gene-modified cell line PA-1-STK in malignant mesothelioma.

Malignant mesothelioma (MM) is a thoracic malignancy that is increasing in incidence. Since it is uniformly fatal and kills by local spread, investigators have proposed that MM is a good target for novel treatment approaches, such as gene therapy. We hypothesized that delivery of the HSV-tk gene, using gene-modified tumor cells (PA-1-STK cells), would result in an antitumor effect after treatment with ganciclovir. In in vitro mixing experiments, we found that PA-1-STK cells killed both mouse and human mesothelioma cells in a dose-dependent manner. Moreover, we found that PA-1-STK cells also prolonged survival of mice with MM when the percentage of total tumor cells was high (70%), but observed no survival benefit when the percentage of PA-1-STK cells was low (30%). These data support the rationale for a cell-based gene therapy approach to MM.

Animals↗
PubMed1998

Insulin-like growth factor I (IGF-I) regulates IGF binding protein-5 gene expression in the brain.

Insulin-like growth factor (IGF-I) plays an important role during brain development. IGF binding protein-5 (IGFBP-5) is known to be capable of modulating IGF-I actions and is expressed in brain during development. To begin to investigate the interaction between IGF-I and IGFBP-5 in brain, we asked whether IGF-I influences the brain expression of IGFBP-5. We quantified IGFBP-5 expression in multiple brain regions of two lines of IGF-I transgenic (Tg) mice that exhibit distinctive patterns of brain transgene expression. MT-I/IGF-I Tg mice carry a transgene driven by metallothionein-I (MT-I) promoter and exhibit highest levels of transgene expression in cerebral cortex, whereas in IGF-II/IGF-I Tg mice the mouse IGF-II promoter drives the transgene and the expression is highest in the cerebellum. In normal adult mice, IGFBP-5 messenger RNA (mRNA) was detected in all brain regions examined, and the highest levels of the mRNA were found in cerebellum, followed by brainstem, diencephalon, hippocampus, and cerebral cortex. Compared to these littermate controls, IGFBP-5 mRNA abundance was increased in both lines of Tg mice. In MT-I/IGF-I Tg mice, cerebral cortex had the greatest increase (approximately 200%), whereas cerebella of IGF-II/IGF-I Tg mice had the greatest increase in IGFBP-5 mRNA (approximately 350%). The increase in IGFBP-5 mRNA correlated with the regional expression of the transgene during development. The abundance of IGFBP-5 protein was also found to be increased in both IGF-I Tg mouse lines. The influence of IGF-I on IGFBP-5 expression was specific because we found no evidence of changes in IGFBP-2, IGFBP-4, or cyclophilin expression. Furthermore, as judged by in situ hybridization histochemistry, IGF-I appeared to increase both the number of IGFBP-5-expressing cells and the magnitude of their expression, an observation that was especially marked in the molecular layer and white matter of the cerebellum. These data indicate that IGF-I regulates IGFBP-5 expression in vivo and is consistent with the in situ hybridization data of others showing that IGFBP-5 expression is temporally and spatially related to that of IGF-I.

Animals↗
PubMed1998

Adenoviral-mediated interferon-gamma gene therapy augments pulmonary host defense of ethanol-treated rats.

Alcohol has long been recognized as an immunosuppressive drug and a risk factor for a spectrum of infectious diseases. Among these infections, bacterial pneumonias are most closely correlated with alcohol abuse. One potential mechanism of ethanol-induced immunosuppression is through its ability to suppress alveolar macrophage production of tumor necrosis factor (TNF-alpha). This defect can be reversed by priming macrophages with interferon-gamma (IFN-gamma). We hypothesized that macrophage priming in vivo in a model of acute ethanol intoxication could augment pulmonary host defenses. To test this hypothesis, we used adenoviral-mediated gene transfer of the IFN-gamma gene. This strategy resulted in prolonged expression of IFN-gamma in vivo. Moreover, in a model of acute ethanol intoxication, this vector significantly enhanced lipopolysaccharide-induced TNF-alpha responses and lung polymorphonuclear leukocyte recruitment. Furthermore, pulmonary host defenses against Klebsiella pneumoniae were significantly augmented. These enhanced host defenses were not reversed with pretreatment with a polyclonal anti-TNF-alpha antibody, suggesting that IFN-gamma's effect was through a non-TNF-alpha-dependent mechanism. These data demonstrate that ethanol-induced suppression of pulmonary host defenses can be reversed with IFN-gamma gene therapy.

Adenoviridae↗
PubMed1998

Gene therapy for malignant mesothelioma: a novel approach for an incurable cancer with increased incidence in Louisiana.

Malignant mesothelioma (MM) is a tumor of the pleura for which there is no satisfactory treatment. It is an almost universally fatal disease, regardless of the stage of the tumor at the time of diagnosis. Current treatment modalities include surgery, chemotherapy, and radiation therapy, although in some series none of these modalities is superior to no treatment at all. Because of the dismal prognosis for patients with MM, new modes of treatment are desperately needed. A promising area of research into the treatment of various malignancies is gene therapy. Recent studies have demonstrated the utility of exposing tumor cells to cells transduced to express the Herpes simplex virus gene for thymidine kinase (HSV-TK). By virtue of their expression of HSV-TK, the transduced cells are rendered susceptible to the antiviral drug, ganciclovir (GCV). Nearby untransduced tumor cells are killed by a so-called bystander effect. We are describing a Phase I clinical gene therapy trial for MM, which we are presently conducting at the Louisiana State University Medical Center of New Orleans. The purpose is to study the safety and to determine the maximal tolerated dose of an HSV-TK-transduced ovarian cancer cell line (PA1-STK cells) that is infused into the pleural cavities of patients. This infusion is followed by systemic administration of GCV. The hope is that administration of GCV will result in killing of both the transduced ovarian cancer cells as well as the nearby malignant cells.

Ganciclovir↗
PubMed1997

Regulation of insulin-like growth factor I (IGF-I) gene expression in brain of transgenic mice expressing an IGF-I-luciferase fusion gene.

Insulin-like growth factor I (IGF-I) plays an important role in the development and function of the central nervous system (CNS). Little is known, however, about the factors and mechanisms involved in regulation of CNS IGF-I gene expression. To facilitate our goal to define mechanisms of IGF-I gene regulation in the CNS, we generated several lines of transgenic (Tg) mice that express firefly luciferase (LUC) under control of a 11.3-kb fragment from the 5' region of the rat IGF-I gene. Consistent with expression of the native IGF-I gene in murine brain, expression of the transgene predominated in neurons and astrocytes and used promoter 1, the major IGF-I promoter in the CNS and in most tissues. Transgene messenger RNA and protein expression rapidly increased after birth and peaked at postnatal (P) day 4 in all brain regions studied. LUC activities in all regions then gradually decreased to 0.5-4% of their peak values at P31, except for the olfactory bulb, which maintained about one third of its maximal activity. Compared with littermate controls, administration of dexamethasone decreased LUC activity and transgenic IGF-I messenger RNA abundance, whereas GH significantly increased the expression of the transgene. Addition of GH to cultured fetal brain cells from Tg mice for 12 h also increased LUC activity in a dose-dependent manner (77-388%). These results show that this IGF-I promoter transgene is expressed in a fashion similar to the endogenous IGF-I gene, and thus indicates that the transgene contains cis-elements essential for developmental, GH, and glucocorticoid regulation of IGF-I gene expression in the CNS. These Tg mice should serve as an useful model to study mechanisms of IGF-I gene regulation in the brain.

Aging↗
PubMed1997

[Accumulation and excretion of fluorine and effect of selenium on them in rats with chronic fluorosis].

2 groups of Wistar rats with chronic fluorosis were duplicated with 30 and 50 mg/L fluorine (F) in drinking water. 2. 0 mg/kg selenium (Se) in fodder was supplemented in the other 2 groups of rats with fluorosis. The amount of drinking water and diet, the excretion of urine and the contents of urine F were tendentiously surveyed every month in one year and then, intake and excretion of F were calculated per day. The contents of Se in urine, liver and serum and F in bone, liver, kidney and serum were measured in the 4th, 8th, and 14th month. The results showed that F absorption increased and F excretion/F absorption rate decreased in 2 groups of rats with fluorosis compared with control group and there were positive correlations between concentration of urine F and water F, as well as concentration of F urine and time of drinking F water. The accumulation of F in bone and liver occurred in the middle period of fluorosis and then, the increase of serum F was observed in the late period of fluorosis in 2 groups of rats with fluorosis. After supplement of Se, urine, liver and serum Se ascended. At the same time, state of eating and drinking improved, the weight rose and the amount of urine excretion heightened, as well as there was an increase of urine F and excretion F/absorption F rate and there was a decrease of bone, live, kidney and serum F in rat of Se supplementation with fluorosis compared with non-Se groups.

Animals↗
PubMed1997

Repair of incomplete simple syndactyly by a web flap on a subcutaneous tissue pedicle.

A new web flap on a subcutaneous tissue pedicle was developed to repair incomplete simple syndactyly. It was isolated from the top skin in syndactyly and transferred down into the depth of the web space to create a web commissure. With use of this technique, aesthetic appearance of the web and well-functioning fingers were gained. Moreover, this technique made full use of the original skin of the syndactyly, and a skin graft was not needed. We report here the operative technique, which presents another alternative for repair of incomplete simple syndactyly.

Adolescent↗
PubMed1996

In vivo actions of insulin-like growth factor-I (IGF-I) on cerebellum development in transgenic mice: evidence that IGF-I increases proliferation of granule cell progenitors.

The in vivo actions of insulin-like growth factor-I (IGF-I) on cerebellum development have been investigated in transgenic (Tg) mice (IGF-II/I Tg mice) in whom an IGF-II promoter-driven IGF-I transgene is highly expressed in cerebellum. Compared to normal littermates, the brains of IGF-II/I Tg mice exhibited overgrowth beginning from the second week of postnatal life. Among the brain regions examined, cerebellum exhibited the greatest increase in size, such that by 50 days of age cerebellar weight and DNA content were increased by 90% and 143%, respectively, compared to littermate controls. Morphological studies of adult IGF-II/I Tg mice showed that the total number of granule and Purkinje cells was increased by 82% and 20%, respectively, findings consistent with the increased cerebellar DNA content and indicating that the increased cerebellar weight was due in part to an increase in cell number. The thickness of the molecular layer also was increased in IGF-II/I Tg mice. During early postnatal development the number of external granular layer cells, as well as the number of BrdU labeled external granular cells, was increased. These data strongly indicate that IGF-I increases granule cell number by a mechanism that involves the stimulation of granule cell progenitor proliferation. Our findings also indicate that IGF-I influences the growth of Purkinje cells and possibly of other cell types in the cerebellum.

Animals↗
PubMed1996

The role of the insulin-like growth factors in the central nervous system.

Increasing evidence strongly supports a role for insulin-like growth factor-I (IGF-I) in central nervous system (CNS) development. IGF-I, IGF-II, the type IIGF receptor (the cell surface tyrosine kinase receptor that mediates IGF signals), and some IGF binding proteins (IGFBPs; secreted proteins that modulate IGF actions) are expressed in many regions of the CNS beginning in utero. The expression pattern of IGF system proteins during brain growth suggests highly regulated and developmentally timed IGF actions on specific neural cell populations. IGF-I expression is predominantly in neurons and, in many brain regions, peaks in a fashion temporally coincident with periods in development when neuron progenitor proliferation and/or neuritic outgrowth occurs. In contrast, IGF-II expression is confined mainly to cells of mesenchymal and neural crest origin. While expression of type I IGF receptors appears ubiquitous, that of IGFBPs is characterized by regional and developmental specificity, and often occurs coordinately with peaks of IGF expression. In vitro IGF-I has been shown to stimulate the proliferation of neuron progenitors and/or the survival of neurons and oligodendrocytes, and in some cultured neurons, to stimulate function. Transgenic (Tg) mice that overexpress IGF-I in the brain exhibit postnatal brain overgrowth without anatomic abnormality (20-85% increases in weight, depending on the magnitude of expression). In contrast, Tg mice that exhibit ectopic brain expression of IGFBP-1, an inhibitor of IGF action when present in molar excess, manifest postnatal brain growth retardation, and mice with ablated IGF-I gene expression, accomplished by homologous recombination, have brains that are 60% of normal size as adults. Taken together, these in vivo studies indicate that IGF-I can influence the development of most, if not all, brain regions, and suggest that the cerebral cortex and cerebellum are especially sensitive to IGF-I actions. IGF-I's growth-promoting in vivo actions result from its capacity to increase neuron number, at least in certain populations, and from its potent stimulation of myelination. These IGF-I actions, taken together with its neuroprotective effects following CNS and peripheral nerve injury, suggest that it may be of therapeutic benefit in a wide variety of disorders affecting the nervous system.

Animals↗