Serum IGFBP-2 levels are associated with reduced insulin sensitivity in obese children

Insulin-like growth factor binding protein 2 (IGFBP-2) may represent a critical link between body composition and insulin sensitivity. We investigated the relationship between circulating IGFBP-2 levels, body composition, insulin sensitivity, energy intake and physical activity in children with obesity. Children were recruited via the Weight Management Service at the Royal Children's Hospital, Melbourne, as part of the Childhood Overweight BioRepository of Australia (COBRA). Comprehensive anthropometric, biochemical and environmental data were collected and compared to serum IGFBP-2 levels (measured by enzyme-linked immunosorbent assay). Multiple regression modelling was used to assess the influence of circulating IGFBP-2 levels on anthropometric and biochemical measures. One hundred and ninety-four children were included in this study (46% male). Circulating IGFBP-2 negatively correlated with age, anthropometric measures, blood pressure and insulin concentration. Positive associations were observed between insulin sensitivity index-homeostasis model assessment (ISI-HOMA) and serum IGFBP-2. In multiple regression modelling, IGFBP-2 significantly contributes to variance in systolic blood pressure (-19%, P < 0.05), circulating triglycerides (-16%, P < 0.05) and ISI-HOMA (18%, P < 0.05). No associations were observed between dietary energy intake or physical activity and IGFBP-2 levels. Circulating IGFBP-2 levels in children with obesity correlate inversely with body mass and markers of metabolic dysfunction, and positively with insulin sensitivity. These findings suggest that reduced levels of IGFBP-2 may play an important role in the pathogenesis of obesity complications in early life.

Growth and the Growth Hormone-Insulin Like Growth Factor 1 Axis in Children With Chronic Inflammation: Current Evidence, Gaps in Knowledge, and Future Directions

Growth failure is frequently encountered in children with chronic inflammatory conditions like juvenile idiopathic arthritis, inflammatory bowel disease, and cystic fibrosis. Delayed puberty and attenuated pubertal growth spurt are often seen during adolescence. The underlying inflammatory state mediated by proinflammatory cytokines, prolonged use of glucocorticoid, and suboptimal nutrition contribute to growth failure and pubertal abnormalities. These factors can impair growth by their effects on the GH-IGF axis and also directly at the level of the growth plate via alterations in chondrogenesis and local growth factor signaling. Recent studies on the impact of cytokines and glucocorticoid on the growth plate further advanced our understanding of growth failure in chronic disease and provided a biological rationale of growth promotion. Targeting cytokines using biological therapy may lead to improvement of growth in some of these children, but approximately one-third continue to grow slowly. There is increasing evidence that the use of relatively high-dose recombinant human GH may lead to partial catch-up growth in chronic inflammatory conditions, although long-term follow-up data are currently limited. In this review, we comprehensively review the growth abnormalities in children with juvenile idiopathic arthritis, inflammatory bowel disease, and cystic fibrosis, systemic abnormalities of the GH-IGF axis, and growth plate perturbations. We also systematically reviewed all the current published studies of recombinant human GH in these conditions and discussed the role of recombinant human IGF-1.

IGFBP-2 nuclear translocation is mediated by a functional NLS sequence and is essential for its pro-tumorigenic actions in cancer cells

IGFBP-2 is highly expressed in both the serum and tumor tissues of most cancers, and is considered one of the most significant genes in the signature of major cancers. IGFBP-2 mainly modulates IGF actions in the pericellular space; however, there is considerable evidence to suggest that IGFBP-2 may also act independently of the IGFs. These IGF-independent actions of IGFBP-2 are exerted either via interactions at the cell surface or intracellularly, via interaction with cytoplasmic or nuclear-binding partners. The precise mechanism underlying the intracellular/intranuclear localization of IGFBP-2 remains unclear. In this study, we investigated IGFBP-2 nuclear localization in several common cancer cells with the aim of dissecting the mechanism of its nuclear trafficking. IGFBP-2 is detected in the nuclei of common cancer cells, including breast, prostate and several neuroblastoma cell lines, using cell fractionation and confocal microscopy. Via nuclear import assays, we show that nuclear entry of IGFBP-2 is mediated by the classical nuclear import mechanisms, primarily through importin-α, as demonstrated by the use of blocking, competition and co-immunoprecipitation assays. Bioinformatics analysis of the IGFBP-2 protein sequence with PSORT II identified a classical nuclear localization signal (cNLS) sequence at 179PKKLRPP185, within the IGFBP-2 linker domain, mutagenesis of which abolishes IGFBP-2 nuclear import. Accordingly, the NLSmutIGFBP-2 fails to activate the VEGF promoter, which would otherwise occur in the presence of wild-type IGFBP-2. As a consequence, no activation of angiogenic processes were observed in NLSmutIGFBP-2 expressing SHEP cells when implanted onto our in vivo quail chorio-allantoic membrane model. Taken together, these data show for the first time that IGFBP-2 possesses a functional NLS sequence and that IGFBP-2 actively translocates into the nucleus by a classical nuclear import mechanism, involving formation of IGFBP-2 complexes with importin-α. Nuclear IGFBP-2 is required for the activation of VEGF expression and consequent angiogenesis.

Fibroblast growth factor 2 reactivates G1 checkpoint in SK-N-MC cells via regulation of p21, inhibitor of differentiation genes (Id1-3), and epithelium-mesenchyme transition-like events

We have recently demonstrated that fibroblast growth factor (FGF)-2 promotes neuroblastoma cell differentiation and overrides their mitogenic response to IGF-I. However, the mechanisms involved are unknown. SK-N-MC cells were cultured with FGF-2 (50 ng/ml) and/or IGF-I (100 ng/ml) up to 48 h. Fluorescence-activated cell sorting analysis indicated that FGF-2 promotes G1/G0 cell cycle phase arrest. Gene expression by RT2-PCR and cellular localization showed up-regulation of p21. We then investigated whether FGF-2-induced differentiation of SK-N-MC cells (by GAP43 and NeuroD-6 expression) involves epithelium-mesenchyme transition interconversion. Real-time PCR (RT2-PCR) showed modulation of genes involved in maintenance of the epithelial phenotype and cell-matrix interactions (E-cadherin, Snail-1, MMPs). Zymography confirmed FGF-2 up-regulated MMP2 and induced MMP9, known to contribute to neuronal differentiation and neurite extension. Id1-3 expression was determined by RT2-PCR. FGF-2 induced Id2, while down-regulating Id1 and Id3. FGF-2 induced nuclear accumulation of ID2 protein, while ID1 and ID3 remained cytoplasmic. RNA interference demonstrated that Id3 regulates differentiation and cell cycle (increased Neuro-D6 and p21 mRNA), while d Id2 modulates epithelium-mesenchyme transition-like events (increased E-cadherin mRNA). In conclusion, we have shown for the first time that FGF-2 induces differentiation of neuroblastoma cells via activation of a complex gene expression program enabling modulation of cell cycle, transcription factors, and suppression of the cancer phenotype. The use of RNA interference indicated that Id-3 is a key regulator of these events, thus pointing to a novel therapeutic target for this devastating childhood cancer.

Twice-daily variable insulin regimens: proportions of insulin types have little impact on glycaemic control in primary school-aged children

AIM

To ascertain the relationship between glycaemic outcome and proportions and timing of insulin admixture in a cohort of primary school-aged children who were receiving insulin in a twice-daily regimen.

METHODS

Children aged 4-10 years with Type 1 diabetes of > 2 years duration and on twice-daily variable insulin regimens were eligible for inclusion in this study, which took place over a 12-month period. Characteristics of insulin regimen [total daily dose (TDD), proportion of total daily dose given in the morning and proportion of the TDD given as intermediate-acting insulin] were compared with parameters of glycaemia including glycated haemoglobin (HbA(1c)) and continuous glucose monitoring measures (mean glucose, per cent time in various glycaemic ranges, and intra- and inter-day glycaemic variation).

RESULTS

Forty-nine children completed the study. Participants were all prepubertal at the start of the study and representative of the local diabetes population aged 4-10 years (mean age 8.2 years, mean duration of diabetes 3.5 years, mean HbA(1c) 8.1%). The mean TDD was 0.9 units/kg/day (range 0.6-1.3). The TDD, percentage of TDD given as intermediate-acting insulin and the percentage of TDD given as the morning dose were not associated with HbA(1c), mean continuous glucose monitoring system glucose, per cent time in various glycaemic ranges or intra- and inter-day glycaemic variation.

CONCLUSIONS

Insulin proportions in twice-daily, variable insulin regimens are not associated with any short- or medium-term glycaemic outcomes.

Estrogens and growth

Estrogen plays a key role in the regulation of growth in both genders, via its stimulation of the pubertal growth spurt and mediation of epiphyseal fusion. Mouse knockout models suggest a differential effect of oestrogen receptor (ER) alpha and beta on the growth plate, with ER beta possibly being more important in regulating epiphyseal fusion. Epiphyseal fusion may also depend on growth plate senescence, which is regulated by oestrogen. While molecular mechanisms for oestrogen's actions remain unclear, local production of oestrogen may be important for growth. Aromatase inhibitors appear to be effective in improving final height outcome in short stature, however long term safety data is lacking particularly in regards to reproductive function. Future studies are required to further understand the mechanisms by which ER alpha and ER beta affect growth plate function, while longer term studies of aromatase inhibitor usage, preferably utilising animal models, are required to verify the safety of these compounds.

Elevated glucose concentrations during an oral glucose tolerance test are associated with the presence of metabolic syndrome in childhood obesity

AIMS

To investigate whether changes in glucose concentrations during an OGTT in obese children reflect the presence of peripheral insulin resistance and/or cardiovascular risk factors more closely than single measurements of fasting plasma glucose (FPG).

METHODS

One hundred and twenty-two obese children attending our Paediatric Obesity Service underwent formal OGTTs, following the measurement of blood pressure and fasting levels of insulin, glucose and lipid profiles in the majority. Fasting insulin was used as a surrogate measure of insulin sensitivity. Three different child-specific definitions for metabolic syndrome were used to identify clustering of cardiovascular risk factors in 65 of these children.

RESULTS

In the whole group, 10.7% had IGT but changes in glucose during the OGTT were not influenced by age, sex, pubertal status or raw (or age- and sex-adjusted) body mass index (BMI). During the OGTT, FPG, glucose at 60 min and area under the glucose curve correlated highly with fasting insulin. Children with metabolic syndrome (defined using any of three definitions) had comparable FPG levels to those without metabolic syndrome, but they demonstrated significantly elevated glucose levels at 60 min. On sub-group analysis, obese children with normal carbohydrate metabolism were significantly more likely to have a 1 h glucose level > or = 7.8 mmol/l if they had metabolic syndrome (P = 0.026).

CONCLUSIONS

These data suggest that an elevated 1 h post-load glucose measurement is seen in obese children who have a coexistent clustering of cardiovascular risk factors.

The insulin-like growth factor system and its pleiotropic functions in brain

In recent years, much interest has been devoted to defining the role of the IGF system in the nervous system. The ubiquitous IGFs, their cell membrane receptors, and their carrier binding proteins, the IGFBPs, are expressed early in the development of the nervous system and are therefore considered to play a key role in these processes. In vitro studies have demonstrated that the IGF system promotes differentiation and proliferation and sustains survival, preventing apoptosis of neuronal and brain derived cells. Furthermore, studies of transgenic mice overexpressing components of the IGF system or mice with disruptions of the same genes have clearly shown that the IGF system plays a key role in vivo.

Insulin-like growth factor binding protein-2 binding to extracellular matrix plays a critical role in neuroblastoma cell proliferation, migration, and invasion

IGF binding proteins (IGFBPs) modulate IGF cellular bioavailability and may directly regulate tumor growth and invasion. We have previously shown that IGFBP-2 binds and localizes IGF-I to the pericellular matrix and have provided some evidence suggesting that the heparin binding domain (HBD) or the arginine-glycine-aspartic acid (RGD) integrin binding motif may be involved in these interactions. However, the precise mechanisms involved remain to be elucidated. We therefore mutated the HBD or RGD sequence of IGFBP-2 and investigated consequent effects on extracellular matrix (ECM) binding, IGF-induced proliferation, and migration of neuroblastoma cells. IGFBP-2 and its arginine-glycine-glutamic acid (RGE) mutant similarly bound ECM components, whereas binding of mutant HBD-IGFBP-2 to each of the ECM substrates was markedly reduced by 70-80% (P < 0.05). IGF-I (100 ng/ml) increased incorporation of 3H-thymidine in neuroblastoma SK-N-SHEP cells by approximately 30%, an effect blunted by exogenously added native or either mutant IGFBP-2. Overexpression of IGFBP-2 and its RGE mutant potently promoted SHEP cell proliferation (5-fold), whereas SHEP cell proliferation was negligible when HBD-IGFBP-2 was overexpressed. Addition or overexpression of IGFBP-2 and its RGE mutant potently (P < 0.05) enhanced SHEP cell migration/invasion through the ECM. However, overexpression of the HBD-IGFBP-2 mutant potently inhibited (50-60%) SHEP cell invasion through ECM. Thus, IGFBP-2, which binds to the ECM, enhances proliferation and metastatic behavior of neuroblastoma cells, functions that directly or indirectly use the HBD but not the integrin binding sequence. Our novel findings thus point to a key role for the HBD of IGFBP-2 in the control and regulation of neuroblastoma growth and invasion.

Insulin-like growth factor binding protein-3 (IGFBP-3) localizes to and modulates proliferative epidermal keratinocytes in vivo

BACKGROUND

The colocalization of insulin-like growth factor binding protein-3 (IGFBP-3) and IGF-I receptor (IGF-IR) in the basal/germinative layer of the epidermis suggests a key role in modulating epidermal homeostasis.

OBJECTIVES

We aimed to clarify both the specific cellular localization and the effect of excess epidermal IGFBP-3 on keratinocyte proliferation.

METHODS

(i) Total RNA was isolated from fluorescence-activated cell sorted basal human keratinocyte subtypes [keratinocyte stem cells, transit amplifying keratinocytes (TA), postmitotic differentiating keratinocytes (PMD)], and real-time polymerase chain reaction analysis was used to determine the abundance of IGFBP-3 and IGF-IR mRNAs. (ii) An IGFBP-3 transgenic mouse model was then used to assess the effect of excess epidermal IGFBP-3 on keratinocyte proliferation. Excess epidermal IGFBP-3 mRNA and protein was determined by in situ hybridization and immunohistochemistry, respectively.

RESULTS

(i) The highest levels of IGFBP-3 mRNA were detected in TA keratinocytes, in contrast to IGF-IR mRNA levels which were highest in PMD keratinocytes. (ii) Elevated human IGFBP-3 mRNA and protein was confirmed in the epidermis of skin derived from transgenic mice. Excess IGFBP-3 reduced the relative percentage of proliferative keratinocytes (Ki67 positive) irrespective of skin location (belly, back and tail). Thus, in the epidermis, IGFBP-3 mRNA is highly expressed by proliferative keratinocytes (TA) and overexpression of IGFBP-3 inhibits keratinocyte proliferation.

CONCLUSIONS

We conclude that in vivo IGFBP-3 ensures epidermal homeostasis via downregulation of keratinocyte proliferation, and thus modulates the early stages of keratinocyte differentiation.

Insights into the acute cerebral metabolic changes associated with childhood diabetes

AIMS

Type 1 diabetes is a prevalent chronic disease in childhood with the commonest single cause of death being cerebral oedema in the context of diabetic ketoacidosis (DKA). The nature of the alterations in cerebral metabolism that may result in vulnerability to neuronal injury remains unknown. The aim of this study was to analyse the magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) brain data from eight children with diabetes following acute presentation with hyperglycaemia with or without ketoacidosis, to determine the nature and timing of any alterations in cerebral structure and metabolism.

METHODS

This study used MRI and MRS to investigate regional cerebral abnormalities in a small series of diabetic patients with and without DKA. Changes were compared with the clinical and biochemical features of the patients studied.

RESULTS

Our small series of patients all demonstrated abnormal signal changes in the frontal region on fluid attenuated inversion recovery (FLAIR) MR imaging, suggestive of oedema, and spectroscopic abnormalities of increased taurine, myoinositol and glucose levels. The MR abnormalities varied in severity but did not correlate with any clinical or biochemical parameters.

CONCLUSIONS

These changes indicate that many diabetic children, particularly at presentation, may have alterations in cerebral metabolism with implications for the pathogenesis and treatment of the cerebral complications of DKA. In addition, our findings suggest that increased taurine may be one of the important differentiating factors in the response of the brain of diabetic children to DKA that may reflect an increase in their vulnerability to cerebral oedema compared with diabetic adults.

A novel approach to continuous glucose analysis utilizing glycemic variation

BACKGROUND

Various methodologies have been proposed for analysis of continuous glucose measurements. These methods have mainly focused on the proportion of low or high glucose readings and have not attempted to analyze other dimensions of the data obtained. This study proposes an algorithm for analysis of continuous glucose data including a novel method of assessing glycemic variability.

METHODS

Mean blood glucose and mean of daily differences (MODD) assessed the degree that the Continuous Glucose Monitoring System (CGMS, Medtronic MiniMed, Northridge, CA) trace was representative of the 3-month glycemic pattern. Percentages of times in low, normal, and high glucose ranges were used to assess marked glycemic excursion. Continuous overall net glycemic action (CONGA), a novel method developed by the authors, assessed intra-day glycemic variability. These methods were applied to 10 CGMS traces chosen randomly from those completed by children with type 1 diabetes from the Royal Children's Hospital, Melbourne, Victoria, Australia and 10 traces recorded by healthy volunteer controls.

RESULTS

The healthy controls had lower values for mean blood glucose, MODD, and CONGA. Patients with diabetes had higher percentages of time spent in high and low glucose ranges. There was no overlap between the CONGA values for patients with diabetes and for controls, and the difference between controls and patients with diabetes increased markedly as the CONGA time period increased.

CONCLUSIONS

We advocate an approach to the analysis of CGMS data based upon a hierarchy of relevant clinical questions alluding to the representative nature of the data, the amount of time spent in glycemic excursions, and the degree of glycemic variation. Integrated use of these algorithms distinguishes between various patterns of glycemic control in those with and without diabetes.

Rates of diabetes mellitus-related complications in a contemporary adolescent cohort

BACKGROUND

Ten years after the Diabetes Control and Complications Trial there is a paucity of data as to what are current rates of diabetes-related complications in adolescence.

OBJECTIVE

To assess the incidence of diabetes-related complications in a contemporary cohort of adolescents with type 1 diabetes mellitus.

DESIGN

Retrospective cross-sectional survey.

PATIENTS

Adolescents aged >10 years with type 1 diabetes mellitus for >5 years from the Royal Children's Hospital, Melbourne Diabetes Clinic.

RESULTS

382 patients were studied (191 male). The mean HbA1c for males was 8.72% and for females was 8.80%. The rates of hypothyroidism and hypercholesterolaemia were 1.5% and 22% respectively. Twenty-five patients (8%) had intermittent microalbuminuria and six (2%) had persistent microalbuminuria. Only one patient had macroalbuminuria (0.3%). Only two patients (0.7%) with mild non-were diagnosed proliferative diabetic retinopathy. Coeliac disease was diagnosed in 6% of patients.

CONCLUSIONS

In this representative and contemporary cohort of diabetic adolescents the incidence of microvascular diabetes-related complications is quite low.

Psychiatric morbidity and health outcome in Type 1 diabetes--perspectives from a prospective longitudinal study

AIMS

To describe psychiatric status and relationship to metabolic control in adolescents with Type 1 diabetes studied prospectively from diagnosis.

METHODS

Adolescents (n = 41) completed a self-report measure of psychiatric status 10 years after disease onset. Metabolic control information was recorded prospectively from diagnosis. The rate and type of psychiatric disorder were determined and the relationship between mental health status and metabolic control history examined.

RESULTS

Thirty-seven per cent of the adolescents met criteria for a DSM-IV psychiatric disorder, two to three times higher than community levels of psychiatric morbidity. Females were significantly more likely to receive a diagnoses (chi2 = 4.98, P < 0.05). Two thirds of participants had experienced at least one serious hypoglycaemic episode and one third had a history of chronic poor metabolic control. DSM-IV diagnoses were present in half of those with a history of chronic poor control, one third of the hypoglycaemia group and one quarter of well controlled participants. Adolescents with a current Mood (t = -2.83, P < 0. 01), Anxiety (t = -3.77, P = 0.001) or Behaviour (t = 2.56, P < 0.05) disorder and those with a history of poorly controlled diabetes (F (2,29) = 5.4, P = 0.01) had higher externalizing behaviour problem scores at diagnosis than those without current disorder.

CONCLUSIONS

Adolescents with Type 1 diabetes are at high risk for psychiatric disorder. Poorly controlled diabetes over the first 10 years of illness was associated with pre-existing behaviour problems at diagnosis and there was a trend for an association with current psychiatric status.

Antiapoptotic effects of leptin in human neuroblastoma cells

Many factors regulate nervous system development, including complex cross-talk between local neuroendocrine systems. The adipocyte-secreted hormone leptin, mainly known for its key roles in nutrition and reproductive balance, may also be involved in neuroanatomical organization, myelination processes, and neuronal/glia maturation. SK-N-SH-SY5Y neuroblastoma cells were employed as an in vitro model of human neuronal cells to determine whether leptin exerts neuroprotective activities. We show that SH-SY5Y cells express leptin, the long and short isoforms of the leptin receptor (ObRl, ObRs). In SH-SY5Y cells, leptin induced signal transducer and activator of transcription (STAT)-3 phosphorylation and suppressor of cytokine signaling-3 mRNA expression. Leptin dose-dependently increased cell number (up to 200% at 1 microm by 48 h, P < 0.01), and at 24-48 h, leptin at 100 nm increased SH-SY5Y cell number by 30-50%, respectively. SH-SY5Y cell viability was reduced in serum-free conditions at 24 h, and addition of leptin at 100 nm significantly reduced apoptosis by approximately 20% (P < 0.001). Leptin's antiapoptotic activity required Janus kinase/STAT, MAPK, and phosphatidylinositol-3-kinase activation because the antiapoptotic effects of leptin were abolished, and caspase-3 immunoreactivity increased in the presence of the specific blockers AG490, U0126, or LY294002. Gene array demonstrated that leptin inhibits apoptosis via potent down-regulation of caspase-10 and TNF-related apoptosis-inducing ligand. Our data thus demonstrate, for the first time, that leptin stimulates, in a time- and dose-dependent manner, neuroblastoma cell proliferation and that the underlying mechanisms involve suppression of apoptosis via the Janus kinase-STAT, phosphatidylinositol-3 kinase, and MAPK pathways that culminate altogether in the down-regulation of the apoptotic factors caspase-10 and TNF-related apoptosis-inducing ligand.

Fibroblast growth factor-2 over-rides insulin-like growth factor-I induced proliferation and cell survival in human neuroblastoma cells

The insulin-like growth factor (IGF) system is a key regulator of cell growth, survival and differentiation, and these functions are co-modulated by other growth factors including fibroblast growth factor-2 (FGF-2). To investigate IGF/FGF interactions in neuronal cells, we employed neuroblastoma cells (SK-N-MC). In serum free conditions proliferation of the SK-N-MC cells was promoted by IGF-I (25 ng/ml), but blunted by FGF-2 (50 ng/ml). IGF-I-induced proliferation was abolished in the presence of FGF-2 even when IGF-I was used at 100 ng/ml. In addition to our previously described FGF-2 induced proteolytic cleavage of IGFBP-2, we found that FGF-2 increased IGFBP-6 levels in conditioned medium (CM) without affecting IGFBP-6 mRNA abundance. Modulation of IGFBP-2 and -6 levels were not significant mechanisms involved in the blockade of IGF-I action since the potent IGF-I analogues [QAYL]IGF-I and des(1-3)IGF-I (minimal IGFBP affinity) were unable to overcome FGF-2 inhibition of cell proliferation. FGF-2 treated cells showed morphological differentiation expressing the TUJ1 neuronal marker while cells treated with IGF-I alone showed no morphological change. When IGF-I was combined with FGF-2, however, cell morphology was indistinguishable from that seen with FGF-2 alone. FGF-2 inhibited proliferation and enhanced differentiation was also associated with a 70% increase in cell death. Although IGF-I alone was potently anti-apoptotic (60% decreased), IGF-I was unable to prevent apoptosis when administrated in combination with FGF-2. Gene-array analysis confirmed FGF-2 activation of the intrinsic and extrinsic apoptotic pathways and blockade of IGF anti-apoptotic signaling. FGF-2, directly and indirectly, overcomes the proliferative and anti-apoptotic activity of IGF-I by complex mechanisms, including enhancement of differentiation and apoptotic pathways, and inhibition of IGF-I induced anti-apoptotic signalling. Modulation of IGF binding protein abundance by FGF-2 does not play a significant role in inhibition of IGF-I induced mitogenesis.

Neuronal protection from glucose deprivation via modulation of glucose transport and inhibition of apoptosis: a role for the insulin-like growth factor system

Glucose is the brain's major energy source; therefore, loss of neuronal cells is a potential consequence of hypoglycaemia. Since apoptosis is a major mechanism of neuronal loss following a range of insults, we explored potent anti-apoptotic systems (IGF-I and bcl-2) as means of enhancing neuronal survival in the face of glucose deprivation. Human neuroblastoma cells (SH-SY5Y, SHEP and SHEP-bcl-2) were exposed to low glucose as a model of glucopenia-induced neuronal damage. Administration of IGF-I and/or over-expression of the survival gene bcl-2 were exploited to attempt to limit neuronal loss. Neuronal survival mechanisms and interactions between these systems were investigated. Low glucose (0.25-2.5 mM) adversely affected cell growth and survival; however, IGF-I ameliorated these outcomes. Over-expression of bcl-2 blunted low glucose-induced apoptosis and up-regulated IGF-I receptor, with the effect of IGF-I addition being negligible on apoptosis, while significantly enhancing mitochondrial activity. In SH-SY5Y cells, IGF-I significantly changed >two-fold mRNA levels of the apoptosis-related genes gadd45, fas, iNOS, NFkB, TRAIL, without further affecting bcl-2 expression. In low glucose, IGF-I acutely enhanced glucose transport and translocation of GLUT1 protein to the cell membrane. GLUT1 mRNA expression was up-regulated by both IGF-I and bcl-2. The potent anti-apoptotic systems IGF-I and bcl-2 are both thus able to enhance cell survival in a glucose-deprived human neuronal model. Although we clearly show evidence of positive cross-talk via bcl-2 modulation of IGF-I receptor, IGF-I also has enhancing effects on mitochondrial function outside the bcl-2 pathway. The common effect of both systems on enhancement of GLUT-1 expression suggests that this is a key mechanism for enhanced survival. These studies also point to the potential use of IGF-I therapy in prevention or amelioration of hypoglycaemic brain injury.

Regional and urban Victorian diabetic youth: clinical and quality-of-life outcomes

OBJECTIVES

To compare groups of urban and regional Victorian diabetic children and assess their quality of life, diabetes knowledge, access to services and metabolic control.

METHODS

Forty-seven children from three regional Victorian communities (Horsham, Warrnambool and Sale; n = 16, 18 and 13, respectively) were compared with 120 age-, sex- and duration of diabetes-matched children attending the Royal Children's Hospital (RCH) diabetes clinic in Melbourne. Quality of life, diabetes knowledge, use of services, and metabolic control were assessed using the child health questionnaire (CHQ PF-50/CF-80); a diabetes-knowledge questionnaire; access to a diabetes nurse educator (DNE), dietitian and complication screening; and indices of mean HbA1C (values are taken every 3 months in the 'yearly HbA1C'), respectively.

RESULTS

Comparisons of CHQ data showed that regional diabetic youth scored significantly lower on most subscales. The greatest deficits were seen in areas of mental health, self-esteem, parent impact (emotional) and family cohesion. Diabetes knowledge and median yearly HbA1C for patients were not significantly different between the regional and urban centres (8.1%, 8.9%, 8.4% and 8.6% at RCH, Horsham, Warrnambool and Sale, respectively). Patients in regional centres had reportedly less access to team-based diabetes care.

CONCLUSIONS

Regional youth in Victoria, with similar levels of metabolic control and diabetes knowledge as their urban counterparts, have a markedly lower quality of life, implying a negative synergy between diabetes and the demands of regional lifestyles.

Neuropsychological profiles of children with type 1 diabetes 6 years after disease onset

OBJECTIVE

To describe neuropsychological profiles and their relationship to metabolic control in children with type 1 diabetes 6 years after the onset of disease.

RESEARCH DESIGN AND METHODS

Children with type 1 diabetes (n = 90), aged 6-17 years, who had previously been assessed soon after diagnosis and 2 years later, were reevaluated 6 years after the onset of disease. Their neuropsychological profiles were compared with those of individuals in a community control group (n = 84), who had been assessed at similar intervals. Relationships between illness variables, such as age at the onset of disease and metabolic control history, and neuropsychological status were also examined.

RESULTS

Six years after onset of disease, children with type 1 diabetes performed more poorly than control subjects on measures of intelligence, attention, processing speed, long-term memory, and executive skills. Attention, processing speed, and executive skills were particularly affected in children with onset of disease before 4 years of age, whereas severe hypoglycemia was associated with lower verbal and full-scale intelligence quotient scores.

CONCLUSIONS

Neuropsychological profiles of children with type 1 diabetes 6 years after the onset of disease are consistent with subtle compromise of anterior and medial temporal brain regions. Severe hypoglycemia, particularly in very young children, is the most plausible explanation for neuropsychological deficits, but the contributory role of chronic hyperglycemia warrants further exploration.

The effect of flexible low glycemic index dietary advice versus measured carbohydrate exchange diets on glycemic control in children with type 1 diabetes

OBJECTIVE

To determine the long-term effect of low glycemic index dietary advice on metabolic control and quality of life in children with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Children with type 1 diabetes (n = 104) were recruited to a prospective, stratified, randomized, parallel study to examine the effects of a measured carbohydrate exchange (CHOx) diet versus a more flexible low-glycemic index (GI) dietary regimen on HbA(1c) levels, incidence of hypo- and hyperglycemia, insulin dose, dietary intake, and measures of quality of life over 12 months.

RESULTS

At 12 months, children in the low-GI group had significantly better HbA(1c) levels than those in the CHOx group (8.05 +/- 0.95 vs. 8.61 +/- 1.37%, P = 0.05). Rates of excessive hyperglycemia (>15 episodes per month) were significantly lower in the low-GI group (35 vs. 66%, P = 0.006). There were no differences in insulin dose, hypoglycemic episodes, or dietary composition. The low-GI dietary regimen was associated with better quality of life for both children and parents.

CONCLUSIONS

Flexible dietary instruction based on the food pyramid with an emphasis of low-GI foods improves HbA(1c) levels without increasing the risk of hypoglycemia and enhances the quality of life in children with diabetes.

Calcium regulates the expression of insulin-like growth factor binding protein-3 by the human keratinocyte cell line HaCaT

The insulin-like growth factor (IGF) system is essential for epidermal homeostasis. Insulin-like growth factor binding protein 3 (IGFBP-3), a modulator of IGF action that also exhibits IGF-independent activity, is localized to selected keratinocytes in the basal epidermal layer and may thus contribute to keratinocyte differentiation. We have utilized the human keratinocyte cell line, HaCaT, to examine the effect of calcium on the regulation of components of the IGF system. Western ligand and northern blot analyses revealed secreted IGFBP-3 and IGFBP-3 mRNA were reduced by an elevation in calcium levels in the culture medium. At 1.0 and 1.2 mM CaCl2 culture conditions IGFBP-3 abundance was reduced to 36% +/- 1.6% and 26% +/- 7.1%, respectively, of that from cells grown at 0.03 mM CaCl2. IGFBP-3 mRNA levels in 0.7 mM and 1.2 mM CaCl2 were reduced to 46% +/- 17.4% and 24% +/- 4.6%, respectively, compared with IGFBP-3 mRNA levels at 0.03 mM CaCl2. The observed reduction of IGFBP-3 was not associated with IGFBP-3 proteolysis. In contrast IGF-I receptor protein and mRNA levels remained unchanged. The IGF-I stimulated proliferative response of HaCaT keratinocytes showed that under low (0.03 mM) and high (1.2 mM) CaCl2 conditions IGF-I at 100 and 1000 ng per ml similarly increased cell number 2.4- and 2.7-fold, respectively, with similar dose-response curves. HaCaT keratinocytes grown under medium (0.7 mM) and high (1.2 mM), but not low (0.03 mM), CaCl2 conditions for 21 d revealed an induction of profilaggrin mRNA, a marker of keratinocyte differentiation. These studies indicate that the exposure of HaCaT keratinocytes to elevated calcium levels is associated with a decline in IGFBP-3 but not IGF-I receptor levels. These findings suggest a potential mechanism for the distribution of IGFBP-3 in the epidermis, which may be involved in the process of keratinocyte differentiation.

The role of the insulin-like growth factor system in the developing brain

Insulin-like growth factors (IGFs) play a central role in brain growth and development, with IGF-1, its receptors and binding proteins (IGFBPs) being highly expressed, particularly in the olfactory bulb (OB), representing a local paracrine system. A potential role of IGFBPs in transporting and targeting IGFs to their receptors is supported by the finding that abundant IGFBP-2 is associated with cell surface proteoglycans. An OB organ culture system expressing IGF-1 and IGFBPs represents an in vitro injury model. Although IGF-1 is potently antiapoptotic for neurons and oligodendrocytes, marked gliosis and IGFBP-3 expression are seen, similar to in vivo injury responses, where intraventricular injection of IGF-1 postinjury enhances neuronal survival by blocking apoptosis. In contrast, des (1-3) IGF-1, which has low affinity for IGFBPs, is ineffective, supporting a transport or receptor targeting role for local IGFBPs. We conclude that the IGF system plays a crucial cell survival and growth role in the developing and injured brain and that IGFs have significant therapeutic potential.

Growth hormone receptor abundance in tibial growth plates of uremic rats: GH/IGF-I treatment

BACKGROUND

Children with chronic renal failure (CRF) exhibit growth retardation and a disturbed growth hormone/insulin-like growth factor-I (GH/IGF-I) axis. Treatment of children with CRF with GH or GH/IGF-I can partially restore linear growth. The molecular basis for decreased longitudinal growth is not known but may involve an impaired action of GH.

METHODS

We used the growth-retarded uremic rat model to determine the abundance and distribution of GH receptors (GHRs) in the tibial epiphyseal growth plate and the influence of GH, IGF-I, or combined GH/IGF-I treatment. Pair-fed rats were used as the control.

RESULTS

While all treatment regimes increased body length and weight in both rat groups, only GH/IGF-I treatment increased the total growth plate width. This involved an increase in cell number in the hypertrophic zone, which could also be induced by IGF-I alone. Immunohistochemical analysis showed that uremic rats had decreased abundance of GHRs in the proliferative zone, and only GH/IGF-I therapy could overcome this decrease. These data thus suggest that growth retardation in uremic rats is, at least in part, due to a decrease in GHR abundance in chondrocytes of the proliferative zone of the tibial growth plate. This decreased GHR abundance can be overcome by combined GH/IGF-I therapy, thus enhancing generation and proliferation of hypertrophic zone chondrocytes and increasing growth-plate width.

CONCLUSION

These studies point to a mechanism for the growth retardation seen in children with CRF, and suggest that combined GH/IGF-I treatment may provide more effective therapy for these patients than GH alone.

Antisense inhibition of IGF receptor expression in HaCaT keratinocytes: a model for antisense strategies in keratinocytes

Antisense strategies targeting skin conditions are attractive in concept, with a number of possible pathologic conditions, such a psoriasis, apparently suitable for such an approach. Because in vitro screening of candidate sequences is usually desirable, we have attempted to use a range of new generation cationic lipids to produce significant antisense oligodeoxynucleotide (ODN) uptake in an immortalized keratinocyte cell line (HaCaT). A large number of commercially available lipids were screened for the ability to induce nuclear ODN localization: Tfx-50, Tfx-20, Tfx-10, Superfect, Cytofectin GSV, Perfect lipids 1-8, Lipofectin, and Lipofectamine. All lipids were used at a range of concentrations (1-20 microg/ml) and with a range of ODN concentrations (1-1000) nM). Of all lipids used, only Cytofectin GSV and Superfect produced significant (>30% of cells) levels of nuclear positive cells, with Superfect also producing significant toxicity at the effective concentration used. Only two treatments produced a significant reduction in target mRNA: insulin-like growth factor-1 receptor (IGF-1R)-ODN 64 complexed with Cytofectin GSV (27.1% +/- 3.5% of IGF-1R mRNA in untreated cells,p < 0.01) and ODN 64 complexed with 10 microg/ml Lipofectin (62.2% +/- 3.4% of IGF-1R mRNA in untreated cells, p < 0.05). Only one treatment, ODN 64 complexed with Cytofectin GSV, produced a reduction in cell growth and survival as assessed by amido black assay. These results demonstrate that in HaCaT keratinocytes, Cytofectin GSV alone of all commercially available cationic lipids was effective in delivering antisense ODN into cell nuclei such that a profound antisense effect could be demonstrated.

Reversal of epidermal hyperproliferation in psoriasis by insulin-like growth factor I receptor antisense oligonucleotides

Epidermal hyperplasia is a key feature of the common skin disorder psoriasis. Stimulation of epidermal keratinocytes by insulin-like growth factor I (IGF-I) is essential for cell division, and increased sensitivity to IGF-I may occur in psoriasis. We hypothesized that inhibition of IGF-I receptor expression in the psoriasis lesion would reverse psoriatic epidermal hyperplasia by slowing the rate of keratinocyte cell division. Here we report the use of C5-propynyl-dU,dC-phosphorothioate antisense oligonucleotides to inhibit IGF-I receptor expression in keratinocytes. We identified several inhibitory antisense oligonucleotides and demonstrated IGF-I receptor inhibition in vitro through an mRNA targeting mechanism. Repeated injection of these oligonucleotides into human psoriasis lesions, grafted onto nude mice, caused a dramatic normalization of the hyperplastic epidermis. The findings indicate that IGF-I receptor stimulation is a rate-limiting step in psoriatic epidermal hyperplasia and that IGF-I receptor targeting by cutaneous administration of antisense oligonucleotides forms the basis of a potential new psoriasis therapy.

Ambulatory blood pressure, microalbuminuria, and autonomic neuropathy in adolescents with type 1 diabetes

OBJECTIVE

To examine the relationship between 24-h blood pressure (BP) measurements, urinary albumin excretion rates, and autonomic neuropathy (AN) in adolescents with type 1 diabetes.

RESEARCH DESIGN AND METHODS

A total of 31 patients with microalbuminuria (MA), 20 patients with intermittent MA (I-MA) and 11 patients with persistent MA (P-MA) were identified from the diabetes clinics at two major Australian tertiary care pediatric hospitals. Two control groups were used; one consisted of 19 age-, sex-, and diabetes duration-matched adolescents with normoalbuminuria (NA), and the other consisted of 46 age- and sex-matched nondiabetic control subjects. A medical history and physical examination were followed by a series of noninvasive tests of cardiovascular and pupillary autonomic function and then by 24-h ambulatory blood pressure monitoring (ABPM).

RESULTS

ABPM showed an incremental increase in all BP parameters from nondiabetic control subjects through subjects with NA. A parallel incremental increase in diurnal and nocturnal ambulatory heart rates was also evident. Subjects with MA had significantly reduced pupillary adaptation to darkness compared with nondiabetic subjects and subjects with NA. The above results paralleled an incremental increase in HbAlc levels in adolescents with type 1 diabetes from subjects with NA to subjects with P-MA.

CONCLUSIONS

Higher 24-h BP values and evidence of subclinical signs of AN are present before P-MA develops and may have important implications for timing the introduction of treatments designed to prevent or retard the microvascular complications of type 1 diabetes in adolescents.

Endogenous IGF-1 regulates the neuronal differentiation of adult stem cells

Stem cells from the adult forebrain of mice were stimulated to form clones in vitro using fibroblast growth factor-2 (FGF-2). At concentrations above 10 ng/ml of FGF-2, very few clones gave rise to neurons; however, if FGF-2 was removed after 5 days, 20-30% of clones subsequently gave rise to neurons. The number of neuron-containing clones and the number of neurons per clone was significantly enhanced, if insulin-like growth factor (IGF)-1 or heparin were added subsequent to FGF-2 removal. The spontaneous production of neurons after FGF-2 removal was shown to be due to endogenous IGF-1, since antibodies to IGF-1 and an IGF-1 binding protein totally inhibited neuronal production. Similarly, these reagents also abrogated the neuron-promoting effects of heparin. Thus, it appears that endogenous IGF-1 may be a major regulator of stem cell differentiation into neurons. Furthermore, it was found that high levels of IGF-1 or insulin promoted the maturation and affected the neurotransmitter phenotype of the neurons generated.

Interactions between bcl-2 and the IGF system control apoptosis in the developing mouse brain

The IGF system and the pro-survival Bcl-2 proteins protect cells from apoptosis and play a key role in brain development. In order to examine a possible relationship between these two potent anti-apoptotic systems, we utilised two transgenic mice models overexpressing either Bcl-2 or IGF-I proteins in olfactory bulb (OB) or cerebellar neurons, respectively. We have demonstrated that while the organization of the defined layers of the OB from the bcl-2 transgenic and wildtype mice cultured in serum free medium (SF) was similarly poor, the mitral cell layer from the transgenic mice was expanded and their neurons were well preserved. Addition of IGF-I improved the definition of the layers normally present within the OB, in both wildtype and bcl-2 transgenic mice, and restored wildtype mitral cell layer structure and neuronal survival similar to that in bcl-2 mice, whose mitral cell survival was not further enhanced by IGF-I. Immunoreactivity for IGF-I and IGFBP-2 was markedly increased in these Bcl-2-expressing mitral cells compared to wildtype mice. In newborn IGF-I transgenic mice, cerebellar Purkinje cells overexpressing IGF-I showed markedly increased immunoreactivity for Bcl-2 and IGFBP-2. These studies indicate that in the developing brain IGF-I modulates expression of its major binding protein IGFBP-2, as well as the Bcl-2 protein. In addition apoptosis caused by culturing OBs in SF medium, is inhibited by expression of Bcl-2 in the mitral neurons and is associated with enhanced expression of the IGF system, including IGF-I and IGFBP-2. The later may thus play a role in IGF targeting. This complex interaction between the two potent anti-apoptotic systems is likely to provide a robust system of cell protection during brain development and repair.

Predictors of change in the neuropsychological profiles of children with type 1 diabetes 2 years after disease onset

OBJECTIVE

To identify type 1 diabetes-related predictors of change in the neuropsychological profiles of children over the first 2 years of the illness.

RESEARCH DESIGN AND METHODS

Children (n = 116) aged 3-14 years were assessed soon after diagnosis and re-evaluated 2 years later to examine relationships between illness variables, such as age of onset and metabolic control history, and changes in neuropsychological status over the first 2 years of type 1 diabetes.

RESULTS

Illness variables were significant predictors of change in neuropsychological test scores within 2 years of onset of type 1 diabetes. Age of onset of type 1 diabetes predicted negative change on Performance Intelligence Quotient, whereas both recurrent severe hypoglycemia and chronic hyperglycemia were associated with reduced memory and learning capacity.

CONCLUSIONS

These results suggest that the relationship between metabolic control and neuropsychological risk is nonlinear in that children with either recurrent severe hypoglycemia or chronically elevated blood sugars exhibit negative changes in their neuropsychological profiles. Onset of type 1 diabetes very early in life adds another dimension of risk, particularly affecting the acquisition of visuospatial skills.

GH-receptor distribution in the ovine foetal adrenal gland: ontogenic and functional studies

In order to examine the role of GH in the regulation of foetal adrenal development and function, we have localized GH-receptor mRNA and protein in adrenal glands of ovine foetuses at specific stages of gestation. Adrenals from 60-75 day (n=4), 100-110 day (n=4) and 140-145 day (n=3) foetal sheep (term is 145-150 days) and non-pregnant adult animals (n=3) were dissected and fixed. GH-receptor mRNA localization was studied by in situ hybridization using a (35)S-labelled antisense cRNA probe, and protein by immunohistochemistry using a specific monoclonal antibody to the GH-receptor. At all ages studied, GH-receptor mRNA and immunoreactivity could be detected throughout the adrenocortical region. In adult adrenals, GH-receptor mRNA and immunoreactivity were also evident throughout the adrenocortical zone, with the strongest expression confined to a defined region of cells at the interface between the zona glomerulosa and zona fasciculata. Northern blot analysis of 100 day and 140 day foetal adrenals confirmed the presence of a 4.4 kb GH-receptor mRNA transcript, while immunoblotting of foetal adrenals at approximately 110 days of gestation revealed a 55 kDa GH-receptor species. To study the effect of GH on the function and growth of the immature foetal adrenal gland in vivo, chronically catheterized ovine foetuses (n=4), between 100 and 110 days of gestation, were given a pulsatile infusion of recombinant bovine GH (125 microgram/15 min, 24 pulses/24 h) for 72 h. Plasma cortisol and aldosterone levels were compared with age-matched controls receiving saline infusion alone (n=4). It was found that there was no difference in the basal plasma level of cortisol or aldosterone, and that infusion of GH did not alter steroid levels or gross adrenal size and morphology. These studies demonstrate strong expression of the GH-receptor in the developing ovine foetal adrenal cortex. However, in the immature foetus GH infusion is without effect on plasma steroid levels, suggesting that the steroidogenic action of GH in the ovine foetus may be gestationally dependent.

Autonomic nerve function in adolescents with Type 1 diabetes mellitus: relationship to microalbuminuria

AIMS

Thirty adolescent patients with Type 1 diabetes mellitus and microalbuminuria were studied for evidence of early autonomic neuropathy.

METHODS

Using tests involving cardiovascular and pupillary reflexes, the adolescents were compared with a normoalbuminuric group of patients with diabetes, who were matched for age, sex, puberty and duration of diabetes.

RESULTS

There was an increased prevalence of autonomic nerve dysfunction in the patients with microalbuminuria. These patients had higher resting heart rates (86 beats/min in the microalbuminuric group vs. 77 beats/min in normoalbuminuric controls, P = 0.002), and impaired pupillary dilatation in darkness (pupillary diameter % 56.5% vs. 62.5%, P = 0.003). Patients with microalbuminuria also had poorer long term glycaemic control (mean HbA1C 8.7% vs. 7.8%, P = 0.002) and higher blood pressures (systolic 125 vs. 116 mmHg, P = 0.001; diastolic 69 vs. 62 mmHg, P = 0.0001; mean arterial pressure 90 vs. 83 mmHg, P = 0.002) than those with normal urinary albumin excretion.

CONCLUSIONS

Microalbuminuria and autonomic nerve dysfunction co-exist in patients with Type 1 DM. Longitudinal studies will determine whether these findings have implications for the identification of patients at higher risk of progression of early renal complications.

Basic fibroblast growth factor induces proteolysis of secreted and cell membrane-associated insulin-like growth factor binding protein-2 in human neuroblastoma cells

Insulin-like growth factor (IGF) action in the brain is modulated by IGF-binding proteins (IGFBPs) whose abundance can be altered by other locally expressed growth factors. However, the mechanisms involved are unclear. We here employed the neuroblastoma cell line SK-N-MC as a model to define the mechanisms involved in modulation of IGFBPs in neuronal cells. Western ligand blotting analysis and immunoprecipitation of conditioned media (CM) from SK-N-MC cells showed that in these cells, as in the brain, the most abundantly expressed IGFBP was IGFBP-2. However, IGFBP-2 was barely detectable in CM from cells treated with basic fibroblast growth factor (bFGF) without a change in IGFBP-2 messenger RNA (mRNA) abundance. These CM contained specific IGFBP-2 proteolytic activity, resulting in two IGFBP-2 fragments of 14 and 22 kDa. The activity was inhibited by EDTA/phenylmethylsulfonyl fluoride or aprotinin. Competitive binding studies indicated that IGFBP-2 fragments had reduced binding affinity for IGF-I. bFGF induced IGFBP-3 mRNA and protein. Affinity cross-linking of [125I]IGF-I to neuroblastoma cell membranes followed by immunoprecipitation revealed a approximately 38 kDa [125I]IGF-I/IGFBP-2 complex. Cell surface-associated IGFBP-2 was also susceptible to bFGF-induced proteolysis, with the appearance of a single cross-linked 21-kDa complex with low affinity for IGF-I. These findings indicate that intact IGFBP-2 and the 14-kDa, but not the 22-kDa fragment, bind to the cell surface. Our data suggest that induction of IGFBP-2 proteolysis on neuronal cell surface is a novel mechanism whereby IGF availability is modulated by the local growth factor bFGF.

Live confocal microscopy of oligonucleotide uptake by keratinocytes in human skin grafts on nude mice

Anti-sense oligonucleotide uptake by keratinocytes in human skin grafts on athymic mice was examined using live confocal microscopy. Fluorescein isothiocyanate-labeled 15-mer C-5 propyne modified phosphorothioate anti-sense oligonucleotide (10-50 microM) was intradermally injected into normal human skin grafts on athymic mice, and the localization of the anti-sense oligonucleotide was assessed after 1-24 h postinjection. Anti-sense oligonucleotide was found to localize in the nuclei of basal and suprabasal keratinocytes after 1-2 h, and this localization was still observed after 24 h. This live in vivo observation of anti-sense oligonucleotide uptake in basal keratinocytes was confirmed using conventional fluorescence microscopy of fixed sections of skin grafts. Neither single nucleotides which were fluorescein isothiocyanate-labeled nor fluorescein isothiocyanate alone was able to penetrate into the nuclei of human skin graft keratinocytes after intradermal injection, and hence it is likely that the anti-sense oligonucleotide was not degraded prior to intracellular localization. Topical administration of anti-sense oligonucleotide and anti-sense oligonucleotide-liposome complexes resulted primarily in localization in the stratum corneum of human skin grafts. When grafts were tape stripped prior to anti-sense oligonucleotide administration, however, as little as 5 microM anti-sense oligonucleotide was required to observe nuclear anti-sense oligonucleotide accumulation. These results suggest that cutaneous anti-sense strategies can be tested using delivery via intradermal anti-sense oligonucleotide injection in human skin grafts on athymic mice, and that agents providing penetration of anti-sense oligonucleotide across the stratum corneum are likely to be required for successful topical therapies.

Interactions between growth hormone, insulin-like growth factor I, and basic fibroblast growth factor in melanocyte growth

Melanocytes, highly differentiated neural crest-derived cells, are located in the basal layer of the epidermis, where they play a role in protecting against UV damage in the skin. Previous studies suggest that both growth hormone (GH) and the insulin-like growth factor I (GH/IGF-I) system may be important for melanocyte growth and function. We have therefore characterized the role of the GH/IGF system in melanocyte growth in vitro and its interaction with the local growth factor basic fibroblast growth factor (bFGF). Analysis of the effects of GH, IGF-I, and bFGF and combinations of these growth factors on melanocyte growth in vitro revealed that 1) GH stimulates the growth of melanocytes when combined with IGF-I, des(1-3)IGF-I [an analog of IGF-I that has a reduced binding affinity for IGF-binding proteins (IGFBPs)], or bFGF, either separately or in combination; 2) in contrast to the lack of effect of GH or bFGF alone, both IGF-I and des(1-3)IGF-I enhance melanocyte growth in a dose-dependent manner; and 3) IGF-I is more efficacious in eliciting a growth response at low concentrations compared to des(1-3)IGF-I. Using Western ligand blotting, affinity cross-linking, immunoprecipitation, RIA, and Northern analysis, we show that cultured human melanocytes synthesize and secrete minimal amounts of IGFBP. IGFBP-4 is the major IGFBP produced by these cells when cultured in complete growth medium or in the presence of either IGF-I or des(1-3)IGF-I alone. In conclusion, these studies provide support for a role for both GH and IGF-I in the growth of human melanocytes in vitro, involving synergy with bFGF. Low levels of melanocyte-derived IGFBP-4 may play a role in enhancing the modulation of IGF action.

Oligonucleotide uptake in cultured keratinocytes: influence of confluence, cationic liposomes, and keratinocyte cell type

The success of anti-sense strategies has been limited, at least in part, by the poor uptake of these agents into the target cells. In keratinocytes, there is conflicting evidence as to the amount and location of oligonucleotide uptake into these cells, with variable proportions of cells reported to take up oligodeoxynucleotide, and also cytoplasmic and nuclear localization reported. In this study, the uptake of oligodeoxynucleotides in cultured normal human keratinocytes and the HaCaT cell line was quantitated in the presence of various lipids designed to enhance uptake and in varying culture conditions. About 12% of cells in a confluent normal human keratinocyte culture showed nuclear uptake, with a small and variable proportion showing cytoplasmic localization after 24 h incubation with 1 microM oligodeoxynucleotide. Uptake of oligodeoxynucleotide was found to be increased by liposome encapsulation (to a maximum of 28.1% +/- 2.1% of cells), low confluence (39.5% +/- 2.5%), and further increased by a combination of the two conditions (55.4% +/- 4.3%). HaCaT cell populations showed sparse but consistent uptake of oligodeoxynucleotide, with about 1% of cells showing nuclear localization in the presence of 1 microM oligodeoxynucleotide, increasing to 13.5% +/- 4.9% in the presence of cationic lipid (Tfx-50) in low confluence HaCaT monolayers. We conclude that normal keratinocytes exhibit reliable, substantial uptake of oligonucleotides in conditions controlled for confluence and aided by liposome encapsulation.

Expression of insulin-like growth factor binding protein-3 (IGFBP-3) in human keratinocytes is regulated by EGF and TGFbeta1

Insulin-like growth factor-I (IGF-I) is essential for normal epidermal homeostasis; however, the role of IGF binding proteins (IGFBPs), regulators of IGF action, remains unclear. Here we examine the regulation of human keratinocyte-produced IGFBPs by epidermal growth factor (EGF), transforming growth factor beta 1 (TGFbeta1), and IGF-I, growth factors known to be active in skin. In the absence of added growth factors, IGFBP-3 was the major binding protein secreted into the medium by primary keratinocytes. Addition of EGF or TGFbeta1 to keratinocyte cultures resulted in a significant decrease in IGFBP-3 abundance in conditioned medium when compared with control, untreated cells. Specifically, EGF (50 ng/ml) and TGFbeta1 (50 ng/ml) reduced IGFBP-3 abundance to 15+/-6% and 22+/-9%, respectively. Using Northern blot analysis, we found EGF and TGFbeta1 (50 ng/ml) to reduce IGFBP-3 mRNA levels in keratinocytes to 51+/-12% and 50+/-38%, respectively, when compared with control, untreated cells. Treatment with IGF-I or its analogue des(1-3)IGF-I did not lead to any consistent change in IGFBP-3 abundance. However, both IGF-I and des(1-3)IGF-I at 100 ng/ml led to a modest increase in IGFBP-3 mRNA levels in keratinocytes, suggesting posttranscriptional regulation of IGFBP-3 abundance. We propose that local modulation of IGFBP-3 abundance may represent another level of regulation of growth factor action in the epidermis, where EGF and TGFbeta1 and possibly other local growth factors specifically regulate the availability of IGF-I to its keratinocyte receptors.

Co-ordinated and cellular specific induction of the components of the IGF/IGFBP axis in the rat brain following hypoxic-ischemic injury

Insulin-like growth factor 1 (IGF-1) is induced after hypoxic-ischemic (HI) brain injury, and therapeutic studies suggest that IGF-1 may restrict delayed neuronal and glial cell loss. We have used a well-characterised rat model of HI injury to extend our understanding of the modes of action of the IGF system after injury. The induction of the IGF system by injury was examined by in situ hybridization, immunohistochemistry, Northern blot analysis, RNase protection assay and reverse transcriptase-polymerase chain reaction (RT-PCR). IGF-1 accumulated in blood vessels of the damaged hemisphere within 5 h after a severe injury. By 3 days, IGF-1 mRNA was expressed by reactive microglia in regions of delayed neuronal death, and immunoreactive IGF-1 was associated with these microglia and reactive astrocytes juxtaposed to surviving neurones surrounding the infarct. Total IGF-1 receptor mRNA was unchanged by the injury. IGFBP-2 mRNA was strongly induced in reactive astrocytes throughout the injured hemisphere, and IGFBP-3 and IGFBP-5 mRNA were moderately induced in reactive microglia and neurones of the injured hippocampus, respectively. IGFBP-6 mRNA was induced in the damaged hemisphere by 3 days and increased protein was seen on the choroid plexus, ependyma and reactive glia. In contrast, insulin II was not induced. These results indicate cell type-specific expression for IGF-1, IGFBP-2,3,5 and 6 after injury. Our findings suggest that the IGF-1 produced by microglia after injury is transferred to perineuronal reactive astrocytes expressing IGFBP-2. Thus, modulation of IGF-1 action by IGFBP-2 might represent a key mechanism that restricts neuronal cell loss following HI brain injury.

Intranuclear localization of insulin-like growth factor binding protein-3 (IGFBP-3) during cell division in human keratinocytes

Insulin-like growth factor-I (IGF-I) stimulation of basal keratinocytes is an essential component of normal epidermal homeostasis. In addition to the IGF receptor, basal keratinocytes synthesize insulin-like growth factor binding protein-3 (IGFBP-3). The HaCaT keratinocyte cell line, which has many characteristics of basal keratinocytes, synthesizes IGFBP-3 that in vitro reduces its IGF-I responsiveness. IGFBP-3 has attracted interest as a potential growth arrest protein, both via its ability to modulate IGF-I responsiveness, and more controversially via IGF-I-independent mechanisms. Intracellular modes of action have been proposed, and a nuclear localization consensus sequence has previously been identified within IGFBP-3. Using immunocytochemistry with a biotinylated antibody specific for IGFBP-3, we investigated the intracellular localization of IGFBP-3 in subconfluent monolayer cultures of HaCaT cells. Diffuse cellular staining was visible, potentially corresponding to cell surface and nascent cytoplasmic IGFBP-3. Of particular interest however, was the localization of staining over the nuclei of a large proportion of cells that were undergoing cell division. Antibody staining was specific for IGFBP-3 because addition of recombinant human IGFBP-3 to the antibody prior to incubation with the cells inhibited these staining patterns. Optical sections obtained using a confocal laser scanning microscope showed that in keratinocytes undergoing cell division, IGFBP-3 was localized inside the nucleus. These results show that intracellular IGFBP-3 localization is altered during the cell cycle and suggest a possible nuclear role for IGFBP-3 during cell division.

The Melbourne Pre-Diabetes Study: prediction of type 1 diabetes mellitus using antibody and metabolic testing

OBJECTIVES

To determine the utility of various autoantibodies in predicting progression to clinical diabetes in first-degree relatives of patients with type 1 diabetes mellitus.

PARTICIPANTS

3315 first-degree relatives of patients with type 1 diabetes (1161 parents, 1206 siblings and 948 offspring) recruited through diabetes clinics, private endocrinologists, Diabetes Australia and the Juvenile Diabetes Foundation.

MAIN OUTCOME MEASURES

Prevalence of islet cell antibodies (ICA) levels > or = 20 JDFu, insulin autoantibodies (IAA) levels > 100 nU/mL, and antibodies to glutamic acid decarboxylase (GADAb) and tyrosine phosphatase IA2 (IA2Ab); change in beta cell function over time; and development of clinical diabetes.

RESULTS

2.6% of relatives had elevated ICA levels, 1.3% had elevated IAA levels and 0.3% had both. High ICA levels were significantly more frequent in siblings than in offspring or parents, and were more frequent in relatives younger than 20 years. GADAb were detected in 68% and IA2Ab in 57% of relatives with elevated ICA and/or IAA levels. Diabetes developed in 33 relatives (25 siblings, 2 offspring and 6 parents). Before diagnosis of clinical diabetes, high ICA levels were detected in 18 (58%), high IAA levels in 7 (23%), both in 5 (15%), and either in 19 (61%); GADAb were detected in 26 (84%), IA2Ab in 13 (42%), both in 11 (35%), and either in 28 (90%). First phase insulin release (FPIR) less than 50 mU/L was very strongly associated with progression to diabetes. In relatives with FPIR initially greater than 50 mU/L who eventually developed diabetes, there was a gradual and continuous reduction in FPIR over time before diagnosis.

CONCLUSIONS

Type 1 diabetes can be diagnosed in the preclinical stage. The recently described antibodies to glutamic acid decarboxylase and tyrosine phosphatase IA2 appear superior to ICA as screening tools for the preclinical diagnosis of type 1 diabetes.

Neuropsychological complications of IDDM in children 2 years after disease onset

OBJECTIVE

To compare the neuropsychological profiles of children with IDDM with a community control group at two time points: 3 months after disease onset and 2 years after the baseline assessment.

RESEARCH DESIGN AND METHODS

A total of 123 children (age 3-14 years) with recent IDDM onset were compared with 129 community control subjects, stratified for age and sex, on standardized measures of general intelligence, attention, speed of processing, memory, learning, executive skills, and behavioral adjustment soon after diagnosis and 2 years later. Exclusion criteria were premorbid evidence of central nervous system disease or trauma, or English not spoken in the home.

RESULTS

There were no differences between children with IDDM and control subjects on any measure at the initial assessment 3 months after disease onset. Two years later, children with IDDM tended to show a less positive change, relative to control subjects, in their standardized scores on measures of general intelligence, and significantly so on the vocabulary (P < 0.01) and block design (P < 0.05) subtests. Multivariate group differences were also apparent on speed of processing (P < 0.05) and learning (P < 0.01) subtests, reflecting smaller developmental gains in the children with IDDM when compared with control subjects.

CONCLUSIONS

The findings are consistent with previous reports, suggesting that IDDM is associated with an increased risk of mild neuropsychological dysfunction. The skills most affected in this cohort were information processing speed, acquisition of new knowledge, and conceptual reasoning abilities. Clinicians and educators should be made aware of the risk of specific neuropsychological deficits in children with IDDM.

Insulin-like growth factor binding protein-2 binds to cell surface proteoglycans in the rat brain olfactory bulb

A family of six insulin-like growth factor binding proteins (IGFBPs) bind IGF-I and modulate its biological activity. IGFBPs may bind to macromolecules on the cell surface or pericellular extracellular matrix, and this interaction may modulate their effect on IGF activity. To date, little is known about the specificity of IGFBPs in the regulation of IGF action in the brain. We therefore explored whether IGFBPs were associated with cell membrane or extracellular matrix components in the rat brain. IGF-I binding sites with the characteristics of an IGFBP were found in the olfactory bulb mitral cell layer. This IGFBP was identified as IGFBP-2 by immunoprecipitation of both solubilized membrane preparations and cross-linked 125I-IGF: IGFBP complexes. While binding of IGFBP-2 to cell membranes was unaffected by RGD-containing peptide, it was inhibited by high salt concentration, suggesting interaction with proteoglycans. IGFBP-2 bound in vitro to the glycosaminoglycans chondroitin-4 and -6-sulfate, keratan sulfate, and heparin. IGFBP-2 also bound the proteoglycan aggrecan, an effect reduced by digestion of its glycosaminoglycans. Binding of IGFBP-2 to chondroitin-6-sulfate decreased the binding affinity of IGFBP-2 for IGF-I approximately 3-fold. Finally, an IGFBP-2 antibody coimmunoprecipitated IGFBP-2 and an approximately 200 kDa proteoglycan containing chondroitin-sulfate side chains from the rat olfactory bulb, providing definitive evidence for IGFBP-2 binding to olfactory bulb proteoglycans. These findings indicate that IGFBP-2 binds to proteoglycans in cell membranes of the rat olfactory bulb. Because we have previously shown that IGFs are highly expressed in the rat olfactory bulb, cell associated IGFBP-2 may have an important role in directing IGFs to specific sites in this brain region.

Expression of insulin-like growth factor binding protein-3 (IGFBP-3) in the psoriatic lesion

Epidermal hyper-proliferation is a key feature of psoriasis, and a role for IGF-I in this process has previously been proposed. Herein we investigated the expression of IGF binding proteins in the psoriatic lesion and compared it with normal skin. With in situ hybridization, we found that IGFBP-3 mRNA was expressed in the basal layer of the epidermis in normal skin. IGFBP-3 was also detected immunohistochemically, exclusively in the basal layer. In the psoriatic lesion, IGFBP-3 mRNA was similarly limited to the basal layer despite the characteristic expansion of the basaloid keratinocyte compartment and was detected only in the suprapapillary epidermis, where IGFBP-3 mRNA was more abundant than in normal or uninvolved epidermis, and IGFBP-3 protein could be readily detected with specific antibody. As with IGFBP-3 mRNA, which represents the likely site of IGFBP-3 synthesis, IGFBP-3 was strictly limited to the basal keratinocytes of the suprapapillary epidermis. By using an antibody to the cell cycle antigen Ki67, we also showed that the suprapapillary epidermis, where IGFBP-3 expression was maximal, contained few keratinocytes undergoing mitosis, whereas the tips of the rete pegs, where IGFBP-3 expression was conspicuously absent, contained many keratinocytes undergoing mitosis. We suggest that IGFBP-3 is a growth inhibitor in basal keratinocytes and that absence of IGFBP-3 in the tips of rete pegs may contribute to epidermal hyper-proliferation in the psoriatic lesion.

Cell-specific regulation of mRNAs for IGF-I and IGF-binding proteins-4 and -5 in streptozotocin-diabetic rat kidney

Streptozotocin (STZ)-induced diabetes in the rat causes early renal enlargement preceded by a transient elevation in IGF-I content and an increase in IGF-I tissue binding. The effects of IGF-I are mainly mediated through the IGF-I receptor (IGF-IR) and modulated by six specific IGF-binding proteins (IGFBPs). We investigated the gene expression of IGF-I, IGF-IR and IGFBPs at a cellular level within the kidney using in situ hybridisation techniques in short-term (7 day) STZ-diabetic, insulin-treated euglycaemic and normal rats. In diabetes, IGFBP-1 mRNA showed markedly increased expression in distal tubules, collecting ducts and thick ascending limbs of Henle (TALs). IGF-I, and IGFBP-4 and -5 mRNAs showed site-specific tubular changes whilst remaining unchanged in other parts of the kidney normally expressing the genes: IGF-I and IGFBP-4 mRNAs were reduced in TALs and proximal tubules respectively; IGFBP-5 mRNA was reduced in most distal tubular cells but strongly expressed in a few of these cells. IGF-IR mRNA and the mRNAs for IGFBP-2, -3 and -6 were unchanged in STZ diabetes. There was no difference between control and insulin-treated kidneys. These complex changes suggest possible involvement of the IGF/IGFBP system in the early stages of diabetic renal hypertrophy.

Localization of mRNAs for insulin-like growth factor-I (IGF-I), IGF-I receptor, and IGF binding proteins in rat eye

PURPOSE

To localize mRNAs for insulin-like growth factor (IGF)-I, IGF-I receptor (IGF-IR), and IGF binding protein (BP)-1 to IGFBP-6 in the rat eye.

METHODS

cDNA sequences for IGF-I, IGF-IR, and IGFBP-1 to IGFBP-6 were used to synthesize 35S-CTP labeled antisense and sense probes for in situ hybridization on 5-microns sections of the rat eye, including the retina, choroid, sclera, ciliary body, and cornea.

RESULTS

IGF-I mRNA was demonstrated over ganglion cells of the retina and endothelial cells of the choroid and ciliary processes. IGF-IR mRNA showed more extensive distribution, localizing to the retinal ganglion cell layer, inner nuclear layer, and outer limiting membrane and also the outer nonpigmented epithelium of the ciliary processes and cornea, conjunctiva, and lens. IGFBP-2 mRNA localized to outer nonpigmented epithelia of the ciliary processes and the germinal layer of corneal epithelium as well as iris, conjunctiva, and sclera. Messenger RNAs for IGFBP-3 to IGFBP-6 localized to choroidal endothelial cells and chromatophores and also to the inner pigmented epithelium of the ciliary processes. Messenger RNAs for IGFBP-5 and IGFBP-6 were seen in the inner and outer nuclear layers of the neural retina. IGFBP-1 mRNA was not detected within the rat eye.

CONCLUSIONS

Using in situ hybridization, we have demonstrated mRNAs for IGF-I, IGF-IR, and IGFBP-2 to IGFBP-6 in specific histologic layers of the retina, choroid, ciliary body, and cornea in the rat. The characterization of the IGF system in vivo suggests specific roles in the normal eye and provides a basis for studying the IGF system in eye pathology.

Growth hormone measurements versus auxology in treatment decisions: the Australian experience

Growth hormone (GH) therapy is regulated in Australia by an expert national government committee. A national database (OZGROW) enables regular audits and rational guideline revisions. In 1988 the guidelines were revised to allow eligibility on auxologic criteria alone because of difficulties in diagnosing GH deficiency (GHD) and GH responses in non-GH-deficient children. Initial entry criteria were height less than the 3rd percentile and growth velocity less than the 25th percentile of bone age. Growth hormone testing was continued in most children. More than 3100 children have been treated since 1988 (35 percent with GHD, 12.5% with Turner syndrome, and 52% with other non-GHDs). Five-year responses (change in height SD scores) were best in the group with complete GHD (+2) (which received the lowest dose of GH) and similar in other groups, including those with partial GHD (+1.5). The increase in final height is 4 to 6 cm in subjects with Turner syndrome. This data is not yet available for subjects with other non-GHDs. In 1994 the guidelines were revised to restrict use of GH therapy to subjects with height less than the 1st percentile, and cessation of GH therapy was brought forward to bone age 13.5 years for girls and 15 years for boys. Subjects with maturational delay were excluded because of the finding that in the presence of significant bone age delay height prognosis was good. New patient accruals have decreased since 1992, from 100/yr to less than 50/yr. Expenditures have also fallen, from $31 to $16 in 1994-1995, because of reduced patient numbers and GH pricing. Australian use of GH is 68.7% that of the United States and 42.2% that of Sweden and is in the midrange internationally. In conclusion, an auxology-based GH program coupled with a comprehensive national database enables rational and economic use of GH in short children.

Identification and localization of insulin-like growth factor-binding protein (IGFBP) messenger RNAs in human hair follicle dermal papilla

The role of the insulin-like growth factors (IGFs) in hair follicle biology has recently been recognized, although their actions, sites of production, and modulation by the insulin-like growth factor-binding proteins (IGFBPs) have not to date been defined. IGF-I is essential for normal hair growth and development, and may be important in regulation of the hair growth cycle. In many culture systems, IGF-I actions are modulated by the IGFBPs. Thus, if IGFBPs are produced in the human hair follicle, they may play a role in targeting IGF-I to its receptor or may modulate IGF-I action by interaction with matrix proteins. We have used in situ hybridization to localize messenger RNA for the six IGFBPs in anagen hair follicles. Anti-sense and sense RNA probes for the IGFBPs (IGFBP-1 to -6) were produced, and 5-micrometer sections of adult facial skin were probed. Messenger RNA for IGFBP-3, -4, and -5 were identified, with predominantly IGFBP-3 and -5 mRNA found in the dermal papilla, and to a lesser extent IGFBP-4 mRNA. IGFBP-4 mRNA was also found at the dermal papilla/epithelial matrix border. Messenger RNAs for both IGFBP-4 and -5 were also demonstrated in the dermal sheath surrounding the hair follicle. Messenger RNAs for IGFBP-1, -2, and -6 were not identified. These studies demonstrate specific localization of IGFBP mRNAs in hair follicles, suggesting that they each play specific roles in the local modulation of IGF action during the hair growth cycle.

Skeletal dysplasias: response to growth hormone therapy

OBJECTIVE

This study was conducted to determine the response of children with skeletal dysplasia and short stature to growth hormone therapy and whether such therapy is appropriate in skeletal dysplasia.

METHODOLOGY

A retrospective analysis of the Australia-wide group of children with skeletal dysplasia registered on the Ozgrow database, using growth data at commencement and at 12 monthly intervals. Eighteen females and 35 males received growth hormone (GH) therapy for at least 12 months. Patients were aged 10.3 +/- 3.3 (mean +/- s.d.) years and had severe short stature with height standard deviation score (SDS) of -3.5 +/- 1.0 (mean +/- s.d.).

RESULTS

Hypochondroplasia (N = 7), metaphyseal dysplasia (N = 5) and dyschondrosteosis (N = 5) were the most frequently represented specific skeletal dysplasia subgroups. These groups and the remaining heterogeneous group did not differ significantly at baseline or subsequent growth response. Duration of GH therapy was mean (range) 36 mo (12-60 mo). Sex, age or degree of short stature did not correlate with response to GH therapy. delta height SDS was 0.3 (mean) after 12 months of GH therapy, which corresponded to an increase in mean growth velocity from 4.3 cm/yr to 6.9 cm/yr. Mean GV declined after the first year, and by 36 months was only 1.1 cm/year above baseline, while delta height SDS was 0.8

CONCLUSIONS

The results suggest that growth hormone therapy is not generally effective for treatment of short stature in skeletal dysplasia.

Localization of growth hormone receptor/binding protein messenger ribonucleic acid (mRNA) during rat fetal development: relationship to insulin-like growth factor-I mRNA

Although GH plays a key role in postnatal growth, prenatal growth is thought to be GH independent. However, recent data has shown GH receptor/binding protein (GHR/BP) to be present in rat fetal tissues as early as fetal stage E12. The aim of the present study was to investigate tissue-specific production of the GHR/BP messenger RNA (mRNA) and its relationship to locally transcribed insulin-like growth factor-I (IGF-I) mRNA in the fetus. We have used in situ hybridization to localize GHR/BP and IGF-I mRNAs in 16.5-, 18.5-, and 20.5-day-old rat fetuses. Furthermore, because the two parameters of the IGF-I gene differentially respond to GH stimulation, we have also investigated the presence and localization of promoter-specific IGF-I mRNAs. We found the distribution of IGF-I and GHR/BP mRNAs to be widespread but distinct during the fetal stages examined. High levels of IGF-I mRNA were found in connective tissues or their precursors, including the dermis, perichondrium, and gut. In contrast, GHR/BP mRNA exhibited three distinct patterns of distribution. First, GHR/BP mRNA was found at epithelial sites adjacent to sites of IGF-I transcription. Second, GHR/BP and IGF-I mRNAs were found to colocalize in some connective tissues, but GHR/BP mRNA levels in these sites were often lower than at other sites (i.e. epithelial) of GHR/BP gene transcription. Third, GHR/BP mRNA was also found in regions remote from IGF-I mRNA, including the nerve ganglia and inner olfactory bulb. Using promoter-specific IGF-I RNA probes, we detected only promoter 1 transcripts in all fetal tissues examined. The only exception occurred in specialized epithelial cells of the cochlea where we detected high levels of both promoter 1- and 2-derived IGF-I transcripts. We have thus demonstrated a distinct distribution of GHR/BP and IGF-I mRNAs in the developing rat fetus with coordinate expression at some sites. These findings suggest a role of GH or a GH-like peptide, acting both directly and indirectly via IGF-I, in fetal growth and development.

Insulin-like growth factor-I and epidermal growth factor regulate insulin-like growth factor binding protein-3 (IGFBP-3) in the human keratinocyte cell line HaCaT

The human keratinocyte cell line HaCaT has a basal phenotype and secretes an insulin-like growth factor (IGF) binding protein, IGFBP-3, which modulates its IGF-I response. Keratinocytes are highly responsive to mitogenic stimulation by IGF-I and epidermal growth factor (EGF), but the effect of these growth factors on IGFBP secretion by keratinocytes is not known. We investigated the effects of IGF-I and EGF, as well as three other skin-growth regulators, retinoic acid, basic fibroblast growth factor, and dexamethasone, on mitogenic stimulation and IGFBP-3 production in HaCaT cells. IGF-I and EGF were strongly mitogenic, whereas retinoic acid, basic fibroblast growth factor, and dexamethasone were not significantly mitogenic. IGF-I increased the level of IGFBP-3 in cell-conditioned medium by up to twofold, whereas EGF caused a twentyfold reduction in IGFBP-3. Retinoic acid and basic fibroblast growth factor had only minor effects on IGFBP-3 and dexamethasone had no effect. IGF-I stimulation of IGFBP-3 did not involve increases in IGFBP-3 mRNA; however, EGF, consistent with its effect on IGFBP-3 protein, caused a fivefold reduction in IGFBP-3 mRNA. In summary, EGF profoundly inhibited IGFBP-3 synthesis in basal keratinocytes, whereas IGF-I increased IGFBP-3 levels by a posttranscriptional mechanism. We hypothesize that by inhibiting IGFBP-3 production in basal keratinocytes, epidermal mitogens such as EGF might stimulate epidermal growth indirectly by increasing local IGF-I availability.

Localization of mRNAs for insulin-like growth factor binding proteins 1 to 6 in rat kidney

Insulin-like growth factor-I (IGF-I) is a peptide growth factor whose activity is modulated by interaction with the family of six IGF binding proteins (IGFBPs). IGF-I is detected in rat kidney and has metabolic and growth effects. We have used in situ hybridization to localize mRNAs for the IGFBPs in rat kidney. Messenger RNAs for all six IGFBPs were detected, each with a distinctive distribution. IGFBP-1 mRNA was expressed in the distal nephron, from the thick ascending limb of the loop of Henle to the cortical collecting ducts. IGFBP-2 mRNA expression was confined to epithelial cells of the glomeruli and the thin limbs of the loop of Henle. IGFBP-3 mRNA was localized to the cortical interstitium while IGFBP-4 was the only IGFBP mRNA found in the proximal tubule. IGFBP-5 mRNA, the most abundant and widely distributed of the IGFBP mRNAs in the kidney, occurred in the glomerular mesangium and the medullary interstitium as well as in the epithelial cells of the distal nephron. IGFBP-6 mRNA, the least abundant, was expressed mainly in fibroblasts associated with renal blood vessels and the ureter. This heterogeneous distribution of the IGFBPs may enable IGF action to be regulated by multiple factors in a site-specific manner.