Developmental regulation of insulin-like growth factor-I and growth hormone receptor gene expression

Insulin-Like Growth Factor Signaling in Alzheimer's Disease: Pathophysiology and Therapeutic Strategies

Alzheimer's disease (AD) is the leading cause of dementia among the elderly population, posing a significant public health challenge due to limited therapeutic options that merely delay cognitive decline. AD is associated with impaired energy metabolism and reduced neurotrophic signaling. The insulin-like growth factor (IGF) signaling pathway, crucial for central nervous system (CNS) development, metabolism, repair, cognition, and emotion regulation, includes IGF-1, IGF-2, IGF-1R, IGF-2R, insulin receptor (IR), and six insulin-like growth factor binding proteins (IGFBPs). Research has identified abnormalities in IGF signaling in individuals with AD and AD models. Dysregulated expression of IGFs, receptors, IGFBPs, and disruptions in downstream phosphoinositide 3-kinase-protein kinase B (PI3K/AKT) and mitogen-activated protein kinase (MAPK) pathways collectively increase AD susceptibility. Studies suggest modulating the IGF pathway may ameliorate AD pathology and cognitive decline. This review explores the CNS pathophysiology of IGF signaling in AD progression and assesses the potential of targeting the IGF system as a novel therapeutic strategy. Further research is essential to elucidate how aberrant IGF signaling contributes to AD development, understand underlying molecular mechanisms, and evaluate the safety and efficacy of IGF-based treatments.

6-benzylaminopurine exposure induced development toxicity and behaviour alteration in zebrafish (Danio rerio)

6-benzylaminopurine (6-BA) is one of the first synthetic hormones and has been widely used in fruit cultivation, gardening and agriculture. However, excessive use of 6-BA will cause potential harm to the environment and humans. Therefore, our research focused on assessing the impact of 6-BA on the development and neurobehavior of zebrafish. The results showed that 6-BA had little effect on the embryos from 2 hpf to 10 hpf. However, delayed development, decreased survival and hatchability were observed under 30 and 40 mg/L 6-BA from 24 hpf. 6-BA also reduced surface tension of embryonic chorions at 24 hpf. In addition, 6-BA caused abnormal morphology and promoted the accumulation of oxidative stress. Transcription of genes in connection with development and oxidative stress was also strikingly altered. Results of movement assay showed that zebrafish were less active and their behavior was significantly inhibited under the 20 and 30 mg/L 6-BA treatments. Locomotion-related genes th and mao were down-regulated by gradient, while the transcription of dbh was upregulated at a low concentration (2 mg/L) but decreased as the concentration increased. Moreover, 6-BA exposure caused increased arousal and decreased sleep. Sleep/wake related genes hcrt and hcrtr2 were upregulated, but decreased at 30 mg/L, while the mRNA level of aanat2 was reduced in a concentration-dependent manner. To sum up, our results showed that 6-BA induced developmental toxicity, promoted the accumulation of oxidative stress, and damaged locomotion and sleep/wake behavior.

Toxic effects and potential mechanisms of Fluxapyroxad to zebrafish (Danio rerio) embryos

Fluxapyroxad is a broad-spectrum and high-efficiency succinate dehydrogenase inhibitor fungicide that can control plant fungal pathogens on many crops. However, fluxapyroxad can enter the aquatic environment when applied in the field, which has an impact on the aquatic environment. The potential threat and toxicological mechanisms of fluxapyroxad in aquatic organisms remain poorly understood. In this study, zebrafish embryos were exposed to fluxapyroxad to investigate the toxic effects and potential mechanisms of fluxapyroxad. In the acute toxicity test, the lethal sensitivity rank of the zebrafish during the three stages was larvae (0.699 mg/L) > adult fish (0.913 mg/L) > embryo (1.388 mg/L). Fluxapyroxad induced abnormal spontaneous movement, malformations and decreased heartbeat, hatching percentage, and body length of the embryos. In the sublethal toxicity test, succinate dehydrogenase activity was significantly increased in all treatment groups, while the activities of the electron transport chain complex II and ATPase were markedly inhibited in 0.347 and 0.694 mg/L fluxapyroxad groups compared to that of the control group. Exposure to fluxapyroxad resulted in significant increases in MDA production, and GPx activity was significantly reduced at 0.694 mg/L. Moreover, caspase-3 activity was significantly increased in the 0.694 mg/L group, and the expression of the genes related to growth (bmp4 and lox) was inhibited after fluxapyroxad exposure. These results indicated that oxidative stress, cell apoptosis and mitochondrial damage might be the potential mechanism underlying the toxic effects of fluxapyroxad on zebrafish embryos.

Distribution of growth hormone-responsive cells in the brain of rats and mice

A growth hormone (GH) injection is able to induce the phosphorylated form of the signal transducer and activator of transcription 5 (pSTAT5) in a large number of cells throughout the mouse brain. The present study had the objective to map the distribution of GH-responsive cells in the brain of rats that received an intracerebroventricular injection of GH and compare it to the pattern found in mice. We observed that rats and mice exhibited a similar distribution of GH-induced pSTAT5 in the majority of areas of the telencephalon, hypothalamus and brainstem. However, rats exhibited a higher density of GH-responsive cells than mice in the horizontal limb of the diagonal band of Broca (HDB), supraoptic and suprachiasmatic nuclei, whereas mice displayed more GH-responsive cells than rats in the hippocampus, lateral hypothalamic area and dorsal motor nucleus of the vagus (DMX). Since both HDB and DMX contain acetylcholine-producing neurons, pSTAT5 was co-localized with choline acetyltransferase in GH-injected animals. We found that 50.0 ± 4.5% of cholinergic neurons in the rat HDB coexpressed GH-induced pSTAT5, whereas very few co-localizations were observed in the mouse HDB. In contrast, rats displayed fewer cholinergic neurons responsive to GH in the DMX at the level of the area postrema. In summary, pSTAT5 can be used as a marker of GH-responsive cells in the rat brain. Although rats and mice exhibit a relatively similar distribution of GH-responsive neurons, some species-specific differences exist, as exemplified for the responsiveness to GH in distinct populations of cholinergic neurons.

Dysregulation of circadian rhythm in zebrafish (Danio rerio) by thifluzamide: Involvement of positive and negative regulators

Thifluzamide as a fungicide is toxic to brain of zebrafish embryos. Brain can regulate biological rhythms. To clarify whether thifluzamide would influence circadian rhythms, zebrafish embryos were treated with thifluzamide (0, 0.19, 1.90 and 2.85 mg/L) for 4 days. Exposure to thifluzamide induced pronounced changes in embryo brain and melatonin levels. The mRNA levels of genes related to circadian rhythms were apparently altered. Among these, the transcripts of cry1ba and clock1 were extremely correlated with exposure concentrations. Importantly, the content of cry1 showed no apparent changes, but the clock level was dramatically increased. Moreover, consistent with the inhibition of development and behavior, the levels of GH and DA were significantly inhibited. In addition, the expression levels of genes related to development, behavior and reproduction were significantly changed by thifluzamide. Therefore, we speculated that circadian disruption due to thifluzamide exposure were primarily attributed to increases in expression of clock1a and contents of clock, which might be at least in part responsible for abnormal development and behavior of zebrafish. In addition, our research will provide important insights into the grouped assessment of SDHI pesticides in future.

Flutolanil affects circadian rhythm in zebrafish (Danio rerio) by disrupting the positive regulators

Circadian rhythms are fundamental to behavior and physiology of organisms. Flutolanil as a fungicide is toxic to zebrafish embryos. The aims of this study were to determine whether flutolanil would influence circadian rhythms of zebrafish and the mechanism involved. Zebrafish embryos were exposed to flutolanil (0, 0.125, 0.5 and 2 mg/L) for 4 days. Here we report that flutolanil increased the melatonin levels of zebrafish. The mRNA levels of genes related to circadian rhythms were significantly altered. The clock level was significantly increased, but the content of cry1 showed no apparent changes. Moreover, our findings that the level of GH was significantly decreased were consistent with the abnormal development of zebrafish embryos. The expression levels of genes related to development, behavior and reproduction were significantly altered by flutolanil. These results indicate that flutolanil disturbed circadian rhythms of zebrafish primarily by affecting the positive elements, which were at least in partial responsible for abnormal development and behavior of zebrafish. And we speculate that flutolanil is toxic to zebrafish embryos at least in part via dysregulation of circadian rhythms involving clock.

Developmental toxicity by thifluzamide in zebrafish (Danio rerio): Involvement of leptin

Although previous trials have indicated that thifluzamide induces developmental inhibition in zebrafish, understanding the distinct mechanism of thifluzamide in this process remains challenging. This study investigated the effect of thifluzamide on zebrafish development and the underlying related signaling pathway. Thifluzamide repressed glucagon (GC) levels but increased growth hormone (GH) levels, and changed the expression of the genes related to growth and development. Additionally, protein kinase A (PKA) and leptin levels were obviously decreased in zebrafish after exposure to thifluzamide for 28 days, but the phosphorylation of cAMP responsive element-binding protein (CREB) was increased. Our results suggested that the anti-developmental effects of thifluzamide in zebrafish are largely associated with alterations in expressions of genes related to growth and development through modulation of leptin.

Atlas of tissue- and developmental stage specific gene expression for the bovine insulin-like growth factor (IGF) system

The insulin-like growth factor (IGF) axis is fundamental for mammalian growth and development. However, no comprehensive reference data on gene expression across tissues and pre- and postnatal developmental stages are available for any given species. Here we provide systematic promoter- and splice variant specific information on expression of IGF system components in embryonic (Day 48), fetal (Day 153), term (Day 277, placenta) and juvenile (Day 365–396) tissues of domestic cow, a major agricultural species and biomedical model. Analysis of spatiotemporal changes in expression of IGF1, IGF2, IGF1R, IGF2R, IGFBP1-8 and IR genes, as well as lncRNAs H19 and AIRN, by qPCR, indicated an overall increase in expression from embryo to fetal stage, and decrease in expression from fetal to juvenile stage. The stronger decrease in expression of lncRNAs (average ―16-fold) and ligands (average ―12.1-fold) compared to receptors (average ―5.7-fold) and binding proteins (average ―4.3-fold) is consistent with known functions of IGF peptides and supports important roles of lncRNAs in prenatal development. Pronounced overall reduction in postnatal expression of IGF system components in lung (―12.9-fold) and kidney (―13.2-fold) are signatures of major changes in organ function while more similar hepatic expression levels (―2.2-fold) are evidence of the endocrine rather than autocrine/paracrine role of IGFs in postnatal growth regulation. Despite its rapid growth, placenta displayed a more stable expression pattern than other organs during prenatal development. Quantitative analyses of contributions of promoters P0-P4 to global IGF2 transcript in fetal tissues revealed that P4 accounted for the bulk of transcript in all tissues but skeletal muscle. Demonstration of IGF2 expression in fetal muscle and postnatal liver from a promoter orthologous to mouse and human promoter P0 provides further evidence for an evolutionary and developmental shift from placenta-specific P0-expression in rodents and suggests that some aspects of bovine IGF expression may be closer to human than mouse.

Acetylcholine Modulates the Hormones of the Growth Hormone/Insulinlike Growth Factor-1 Axis During Development in Mice

Pituitary growth hormone (GH) and insulinlike growth factor (IGF)-1 are anabolic hormones whose physiological roles are particularly important during development. The activity of the GH/IGF-1 axis is controlled by complex neuroendocrine systems including two hypothalamic neuropeptides, GH-releasing hormone (GHRH) and somatostatin (SRIF), and a gastrointestinal hormone, ghrelin. The neurotransmitter acetylcholine (ACh) is involved in tuning GH secretion, and its GH-stimulatory action has mainly been shown in adults but is not clearly documented during development. ACh, together with these hormones and their receptors, is expressed before birth, and somatotroph cells are already responsive to GHRH, SRIF, and ghrelin. We thus hypothesized that ACh could contribute to the modulation of the main components of the somatotropic axis during development. In this study, we generated a choline acetyltransferase knockout mouse line and showed that heterozygous mice display a transient deficit in ACh from embryonic day 18.5 to postnatal day 10, and they recover normal ACh levels from the second postnatal week. This developmental ACh deficiency had no major impact on weight gain and cardiorespiratory status of newborn mice. Using this mouse model, we found that endogenous ACh levels determined the concentrations of circulating GH and IGF-1 at embryonic and postnatal stages. In particular, serum GH level was correlated with brain ACh content. ACh also modulated the levels of GHRH and SRIF in the hypothalamus and ghrelin in the stomach, and it affected the levels of these hormones in the circulation. This study identifies ACh as a potential regulator of the somatotropic axis during the developmental period.

The developmental effects of low-level procymidone towards zebrafish embryos and involved mechanism

Procymidone (PCM), a dicarboximide fungicide, is widely used in agriculture to control plant diseases. In the present study, zebrafish embryos were exposed to PCM at 0, 10, 100 and 1000 ng/L for 72 h, the development and cardiac functioning of larvae were observed and determined. The results showed that hatching rate was significantly decreased in the 1000 ng/L treatment, and pericardial edema rate and spine curvature rate were significantly increased in the 100 and 1000 ng/L groups. The PCM-treated larvae exhibited an increased heart rate as well as arrhythmia, and shortened low jaw. The transcription levels of cardiac development-related genes tbx5, nkx2.5, tnnt2, gata4, myh6, myl7, cdh2, ryr2 were altered, which might be responsible for the cardiac developmental and functioning defects in the larvae. The deformation in bone development might be related with the impaired transcription levels of ihh, shh, bmp2b, bmp4, gh, igf1, sox9, gli2. The activities of Na⁺/K⁺-ATPase and Ca²⁺-ATPase were significantly inhibited by 100 ng/L and 1000 ng/L PCM exposure, which might be a cause for the occurrence of pericardial edema and skeletal deformation. The results of this study will be helpful in evaluating the potential threat of PCM to fish population in the aquatic environment.

IGF1 stimulates greater muscle hypertrophy in the absence of myostatin in male mice

Insulin-like growth factors (IGFs) and myostatin have opposing roles in regulating the growth and size of skeletal muscle, with IGF1 stimulating, and myostatin inhibiting, growth. However, it remains unclear whether these proteins have mutually dependent, or independent, roles. To clarify this issue, we crossed myostatin null (Mstn^-/-) mice with mice overexpressing Igf1 in skeletal muscle (Igf1⁺) to generate six genotypes of male mice; wild type (Mstn^+/+ ), Mstn^+/-, Mstn^-/-, Mstn^+/+:Igf1⁺, Mstn^+/-:Igf1⁺ and Mstn^-/-:Igf1⁺ Overexpression of Igf1 increased the mass of mixed fibre type muscles (e.g. Quadriceps femoris) by 19% over Mstn^+/+ , 33% over Mstn^+/- and 49% over Mstn^-/- (P < 0.001). By contrast, the mass of the gonadal fat pad was correspondingly reduced with the removal of Mstn and addition of Igf1 Myostatin regulated the number, while IGF1 regulated the size of myofibres, and the deletion of Mstn and Igf1⁺ independently increased the proportion of fast type IIB myosin heavy chain isoforms in T. anterior (up to 10% each, P < 0.001). The abundance of AKT and rpS6 was increased in muscles of Mstn^-/-mice, while phosphorylation of AKT^S473 was increased in Igf1⁺mice (Mstn^+/+:Igf1⁺, Mstn^+/-:Igf1⁺ and Mstn^-/-:Igf1⁺). Our results demonstrate that a greater than additive effect is observed on the growth of skeletal muscle and in the reduction of body fat when myostatin is absent and IGF1 is in excess. Finally, we show that myostatin and IGF1 regulate skeletal muscle size, myofibre type and gonadal fat through distinct mechanisms that involve increasing the total abundance and phosphorylation status of AKT and rpS6.

Oxygen-sensitive regulation and neuroprotective effects of growth hormone-dependent growth factors during early postnatal development

Perinatal hypoxia severely disrupts metabolic and somatotrophic development, as well as cerebral maturational programs. Hypoxia-inducible transcription factors (HIFs) represent the most important endogenous adaptive mechanisms to hypoxia, activating a broad spectrum of growth factors that contribute to cell survival and energy homeostasis. To analyze effects of systemic hypoxia and growth hormone (GH) therapy (rhGH) on HIF-dependent growth factors during early postnatal development, we compared protein (using ELISA) and mRNA (using quantitative RT PCR) levels of growth factors in plasma and brain between normoxic and hypoxic mice (8% O2, 6 h; postnatal day 7, P7) at P14. Exposure to hypoxia led to reduced body weight ( P < 0.001) and length ( P < 0.04) compared with controls and was associated with significantly reduced plasma levels of mouse GH ( P < 0.01) and IGF-1 ( P < 0.01). RhGH abrogated these hypoxia-induced changes of the GH/IGF-1 axis associated with normalization of weight and length gain until P14 compared with controls. In addition, rhGH treatment increased cerebral IGF-1, IGF-2, IGFBP-2, and erythropoietin mRNA levels, resulting in significantly reduced apoptotic cell death in the hypoxic, developing mouse brain. These data indicate that rhGH may functionally restore hypoxia-induced systemic dysregulation of the GH/IGF-1 axis and induce upregulation of neuroprotective, HIF-dependent growth factors in the hypoxic developing brain.

Reproductive parameters of some native bovine breeds: Sanmartinero and Casanareño

En bovinos, la reducción de la eficiencia reproductiva de los sistemas de producción de carne y doble propósito se atribuye a factores nutricionales, sanitarios, climáticos y en última instancia a características genéticas de los animales. Sin embargo, en condiciones de trópico cálido húmedo, variaciones genéticas entre razas podrían reducir la edad al primer parto, el intervalo entre partos y aumentar la vida útil de las vacas. Las razas Sanmartinero y Casanareño podrían mejorar los sistemas de producción bovina debido al aporte de variantes genéticas que emergieron en el proceso de adaptación a las duras condiciones de la Orinoquía Colombiana. Actualmente, los genes con función biológica conocida se usan como marcadores moleculares para estimar parámetros de diversidad genética pecuaria facilitando la identificación y ubicación dentro del genoma de regiones que codifican o regulan la expresión de rasgos de interés económico. En ganado criollo colombiano Romosinuano se han identificado genes candidatos del eje Hormona de crecimiento/Factor de crecimiento similar a la insulina que se asocian positivamente con edad al primer parto, intervalo entre partos, longevidad y protección del embrión al estrés calórico. No obstante en las razas criollas Sanmartinero y Casanareño reconocidas empíricamente por estas características, no han sido sometidas a dichos análisis de genes candidatos que permitan promover un valor agregado a los animales. El objetivo de esta revisión es documentar algunos parámetros reproductivos y genéticos de las razas criollas Sanmartinero y Casanareño que soportan la necesidad de desarrollar estudios moleculares y justificar su uso en los sistemas de producción de carne y doble propósito de la Orinoquía colombiana.

The developmental effect of difenoconazole on zebrafish embryos: A mechanism research

Difenoconazole is a widely used triazole fungicide and has been reported to have negative impacts on zebrafish embryos. To investigate the mechanism of its developmental toxicity, zebrafish embryos were exposed to 0.5 and 2.0 mg/L difenoconazole for 96 h. The morphological and physiological indicators of embryo development were tested. The total cholesterol (TCHO) level, triglyceride (TG) level and malondialdehyde (MDA) content were measured at 96 hpf (hours post-fertilization). In addition, the transcription of genes related to embryo development, the antioxidant system, lipid synthesis and metabolism was quantified. Our results showed that a large suite of symptoms were induced by difenoconazole, including hatching regression, heart rate decrease, growth inhibition and teratogenic effects. 0.5 mg/L difenoconazole could significantly increase the TG content of zebrafish embryos at 96 hpf, while no apparent change in the TCHO and MDA level was observed post 96 h exposure. Q-PCR (quantitative real-time polymerase chain reaction) results showed that the transcription of genes related to embryonic development was decreased after exposure. Genes related to hatching, retinoic acid metabolism and lipid homeostasis were up-regulated by difenoconazole.

Regulation of neurotrophin receptor (Trk) signaling: suppressor of cytokine signaling 2 (SOCS2) is a new player

The classic neurotrophins Nerve Growth Factor (NGF), Brain Derived Neurotrophic Factor (BDNF) and Neurotrophins NT-3 and NT-4 are well known to regulate various aspects of neuronal differentiation, survival and growth. They do this by binding to their cognate receptors, members of the Tropomyosin-related kinase (Trk) receptor tyrosine kinase family, namely TrkA, TrkB, and TrkC. These receptors are then internalized and localized to different cellular compartments, where signal transduction occurs. Conversely, members of the suppressor of cytokine signaling (SOCS) family are best known as negative regulators of signaling via the JAK/STAT pathway. Some members of the family, and in particular SOCS2, have roles in the nervous system that at least partially overlap with that of neurotrophins, namely neuronal differentiation and neurite outgrowth. Recent evidence suggests that SOCS2 is a novel regulator of NGF signaling, altering TrkA cellular localization and downstream signaling to affect neurite growth but not neuronal survival. This review first discusses regulation of Trk receptor signaling, followed by the role of SOCS2 in the nervous system and finishes with a discussion of possible mechanisms by which SOCS2 may regulate TrkA function.

Microstructural brain changes in acromegaly: quantitative analysis by diffusion tensor imaging

OBJECTIVE

We examined brain diffusion changes of patients with acromegaly. We searched whether there are differences in apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values between remission and non-remission patients with acromegaly and investigated any effect of time of hormone exposure on diffusion metrics.

METHODS

The values of FA and ADC were calculated in a total of 35 patients with acromegaly and 28 control subjects. Patients were subdivided into remission and non-remission groups. We looked at brain FA and ADC differences among the groups and looked for any relation between the diffusion changes and time of hormone exposure among the patients with acromegaly.

RESULTS

We found decreased FA and increased ADC values in some of the growth hormone responsive areas. There were no significant brain diffusion changes between remission and non-remission groups. The most affected areas were the hypothalamus, parietal white matter and pre-motor cortex in patients with acromegaly. In terms of hormone exposure time among the patients with acromegaly, there was no effect of disease duration on brain microstructural changes.

CONCLUSION

All patients with acromegaly showed increased brain diffusion with no relation to disease duration and treatment status. We suggested that in patients with acromegaly, brain damage had already occurred in the subclinical period before symptom onset.

ADVANCES IN KNOWLEDGE

This study contributes to the understanding of the mechanisms in acromegaly.

The Regulation of IGF-1 Gene Transcription and Splicing during Development and Aging

It is commonly known that the insulin-like growth factor-I gene contains six exons that can be differentially spliced to create multiple transcript variants. Further, there are two mutually exclusive leader exons each having multiple promoter sites that are variably used. The mature IGF-I protein derived from the multiplicity of transcripts does not differ suggesting a regulatory role for the various transcript isoforms. The variant forms possess different stabilities, binding partners, and activity indicating a pivotal role for the isoforms. Research has demonstrated differential expression of the IGF-I mRNA transcripts in response to steroids, growth hormone, and developmental cues. Many studies of different tissues have focused on assessing the presence, or putative action, of the transcript isoforms with little consideration of the transcriptional mechanisms that generate the variants or the translational use of the transcript isoforms. Control points for the latter include epigenetic regulation of splicing and promoter usage in response to development or injury, RNA binding proteins and microRNA effects on transcript stability, and preferential use of two leader exons by GH and other hormones. This review will detail the current knowledge of the mechanical, hormonal, and developmental stimuli regulating IGF-1 promoter usage and splicing machinery used to create the variants.

Serum IGF-1 affects skeletal acquisition in a temporal and compartment-specific manner

Insulin-like growth factor-1 (IGF-1) plays a critical role in the development of the growing skeleton by establishing both longitudinal and transverse bone accrual. IGF-1 has also been implicated in the maintenance of bone mass during late adulthood and aging, as decreases in serum IGF-1 levels appear to correlate with decreases in bone mineral density (BMD). Although informative, mouse models to date have been unable to separate the temporal effects of IGF-1 depletion on skeletal development. To address this problem, we performed a skeletal characterization of the inducible LID mouse (iLID), in which serum IGF-1 levels are depleted at selected ages. We found that depletion of serum IGF-1 in male iLID mice prior to adulthood (4 weeks) decreased trabecular bone architecture and significantly reduced transverse cortical bone properties (Ct.Ar, Ct.Th) by 16 weeks (adulthood). Likewise, depletion of serum IGF-1 in iLID males at 8 weeks of age, resulted in significantly reduced transverse cortical bone properties (Ct.Ar, Ct.Th) by 32 weeks (late adulthood), but had no effect on trabecular bone architecture. In contrast, depletion of serum IGF-1 after peak bone acquisition (at 16 weeks) resulted in enhancement of trabecular bone architecture, but no significant changes in cortical bone properties by 32 weeks as compared to controls. These results indicate that while serum IGF-1 is essential for bone accrual during the postnatal growth phase, depletion of IGF-1 after peak bone acquisition (16 weeks) is compartment-specific and does not have a detrimental effect on cortical bone mass in the older adult mouse.

TISSUE-SPECIFIC REGULATION OF INSULIN-LIKE GROWTH FACTORS AND INSULIN-LIKE GROWTH FACTOR BINDING PROTEINS IN MALE DIABETIC RATS IN VIVO AND IN VITRO

1. Insulin-like growth factors (IGFs) are associated with the development of diabetes mellitus. The liver, kidney and heart have been implicated as important organs in the onset of diabetes mellitus. However, the effect of diabetes on the IGF system in these organs has not been fully described. Thus, we investigated changes in IGF-I, IGF-II and IGF binding proteins (IGFBPs) in male steptozotocin-induced diabetic rats, as well as in a high glucose-induced in vitro model. 2. Serum levels of IGF-I were decreased, but the levels of IGF-II were increased, in diabetic rats compared with controls. The expression of IGFBP-3 in the serum was markedly decreased; in contrast, the expression of IGFBP-1 and -2 was increased in diabetic rats. The expression of IGF-I, IGF-II, IGFBP-1, IGFBP-2, IGFBP-3 and IGFBP-4 in the liver of the diabetic group was similar to that in the serum of diabetic rats. 3. In heart tissue of the diabetic group, IGF-I levels were decreased, but IGF-II levels were increased. In addition, the expression of IGFBP-3, IGFBP-1 and IGFBP-2 was decreased in diabetic rats. 4. In the kidney of the diabetic group, IGF-I and IGF-II levels were increased. There was only slight expression of IGFBP-3 in the kidney and this was not altered in diabetic rats. Levels of IGFBP-1 and -2 were markedly increased in the kidney of diabetic rats. 5. Insulin treatment recovered the changes in expression of IGF-I, IGF-II and IGFBPs in the serum, liver, heart and kidney. In the liver, heart and kidney, the expression of the insulin receptor was increased in male diabetic rats. 6. In conclusion, diabetes tissue-specifically alters the IGF system in the liver, heart and kidney in rats; this effect can be recovered by insulin treatment.

A liver specific gene that is expressed in growth hormone transgenic mice and in normal female mice as a function of age

Growth hormone (GH) acts on various organs to exert its growth and metabolic effects. GH induces transcription of a number of genes in different organs including liver. By performing subtractive hybridization analysis on liver cDNAs of GH transgenic and non-transgenic mice, differentially expressed cDNAs were obtained. This paper describes the isolation and characterization of a liver cDNA, termed cDNA #5, that contains 1897 bp and is predicted to encode a protein (P5) of 512 aa residues. P5 has five immunoglobulin related domains thus allowing it to be classified as a member of the immunoglobulin super family (IGSF). Also, P5 shows significant similarity to both rat and human alpha-1-B glycoprotein which is an acidic serum protein of unknown function. mRNA #5 was detected in the liver hepatocytes of male and female GH transgenic mice and in the liver of female, but not of male, non-transgenic mice. mRNA #5 was not present in dwarf mice including the Ames dwarf, those that express a GH antagonist and those with the GH receptor and binding protein gene disrupted. These findings suggest that induction of mRNA #5 in the liver requires a continuous pattern of GH secretion and an intact GH-GH receptor-signaling complex. mRNA #5 levels in female non-transgenic mice were observed to vary with age implying that gender-specific age-dependent factor(s) may be involved in the induction of mRNA #5. The appearance of mRNA #5 in post-hepatectomized liver that coincides with the proliferative phase of liver regeneration suggests that it may be involved in hepatocyte proliferation. Together these data suggest that expression of cDNA #5 is liver-specific, sexually dimorphic, age-dependent, and may be involved in hepatocyte hyperplasia and liver enlargement.

Dendritic stability in a model of adult-onset IGF-I deficiency

OBJECTIVE

A significant decrease in plasma levels of insulin-like growth factor-I (IGF-I) is one of the most robust hallmarks of aging and may contribute to functional changes associated with senescence. This study examined the role of IGF-I in the maintenance of adult dendritic morphology.

DESIGN

We utilized a model of the aging-related decrease in plasma IGF-I to examine whether such a decrease, in itself, leads to dendritic changes in the cerebral cortex. The dw/dw rat, originally of the Lewis strain, suffers from a spontaneous mutation in which growth hormone (GH) production is severely decreased. Since GH is responsible for the production of circulating IGF-I by the liver, these animals are deficient in plasma IGF-I. Homozygous dw/dw rats were administered porcine GH to sustain IGF-I levels during development and then GH injections were stopped as adults in order to examine the effects of adult-onset GH and IGF-I deficiency. Animals sacrificed after two or eight weeks of GH and IGF-I deficiency were compared to age-matched dw/dw animals that received GH both developmentally and throughout adulthood (GH/IGF-I replete). The dendritic arbors of pyramidal neurons in cingulate cortex were labeled by intracellular injection and reconstructed in three dimensions.

RESULTS

Comparing GH/IGF-I replete and deficient dw/dw rats, we found no differences in the apical or basal arbors of either layer two or layer five pyramidal neurons.

CONCLUSIONS

These findings indicate that a decrease in plasma levels of IGF-I is not sufficient in itself to produce dendritic changes like those seen in aging animals.

Growth hormone expression in the perinatal and postnatal rat lung

It is now established that the lung is a target site for pituitary growth hormone (GH) action, because pathophysiological states of pituitary GH excess and deficiency are associated with impaired pulmonary function. The onset of lung development and differentiation is, however, before the ontogenic differentiation of pituitary somatotrophs. GH may be involved, nevertheless, in lung development, because it is present in extrapituitary tissues of preimplantation mouse embryos and in the lung buds of embryonic chickens. The possibility that GH may be expressed in the rat lung during fetal and neonatal development, therefore, has been assessed. GH mRNA was detected in the lung, and its 693-bp sequence was identical to that in the pituitary gland. By in situ hybridization, this transcript was found to be abundantly expressed in the lungs of embryonic day (ED) 17 rats in mesenchymal, mucosal epithelial, and smooth muscle cells. This transcript was expressed in neonates until at least day 14 postnatally and was localized to type I and II epithelial cells and to pulmonary tissue macrophages and alveolar macrophages. GH immunoreactivity paralleled GH mRNA cellular localization throughout the time course studied. This immunoreactivity was specific and was lost after antibody preabsorption. The perinatal and postnatal lung is, therefore, an extrapituitary site of GH gene expression during development. Given that the GH receptor is present in the lung from early development, lung GH may have autocrine and/or paracrine roles in lung growth or differentiation or in pulmonary function.

Age-dependent onset of liver-specific IGF-I gene deficiency and its persistence in old age: implications for postnatal growth and insulin resistance in LID mice

To explore the limitations of the liver-specific IGF-I gene-deficient (LID) model and to further evaluate the role of endocrine IGF-I in early postnatal life and old age, we have studied these mice during the prepubertal period (from birth to 3 wk of age) and when they are 2 yr old. During the first 2 wk of life, IGF-I gene deficiency and the resulting reduction in serum IGF-I levels in LID mice did not reach sufficiently low levels when mice experience the most rapid and growth hormone (GH)-independent growth. It suggests that the role of liver-derived IGF-I in prepubertal, GH-independent postnatal growth cannot be established. From our previous studies, liver IGF-I mRNA level was abolished in adult LID mice, which causes elevated GH level, insulin resistance, pancreatic islet enlargement, and hyperinsulinemia. Interestingly in 2-yr-old LID mice, although liver IGF-I mRNA and serum IGF-I levels were still suppressed, serum insulin and GH levels had returned to normal. Compared with same-sex control littermates, aged male LID mice had significantly reduced body weight and fat mass and exhibited normal insulin sensitivity. On the other hand, aged female LID mice exhibited normal weight and marginal resistance to insulin actions. The pancreatic islet percentage (reflecting islet cell mass) was also restored to normal levels in aged LID mice. Thus, although the IGF-I gene deficiency is well maintained into old age, the insulin sensitivity, islet enlargement, and hyperinsulinemia that occurred in young adult mice have been mostly restored to normal levels, further supporting the age-dependent and sexual dimorphic features of the LID mice.

Potential role of IGF-I in hypoxia tolerance using a rat hypoxic-ischemic model: activation of hypoxia-inducible factor 1alpha

Hypoxia preconditioning and subsequent tolerance to hypoxia-ischemia damage is a well-known phenomenon and has significant implications in clinical medicine. In this investigation, we tested the hypothesis that the transcriptional activation of IGF-I is one of the underlying mechanisms for hypoxia-induced neuroprotection. In a rodent model of hypoxia-ischemia, hypoxia preconditioning improved neuronal survival as demonstrated by decreased hypoxia-ischemia-induced neuronal apoptosis. To study the role of IGF-I in hypoxia tolerance, we used in situ hybridization to examine IGF-I mRNA distribution on adjacent tissue sections. In cerebral cortex and hippocampus, hypoxia preconditioning resulted in an increase in neuronal IGF-I mRNA levels with or without hypoxia-ischemia. To test its direct effects, we added IGF-I to primary neuronal culture under varying oxygen concentrations. As oxygen concentration decreased, neuronal survival also decreased, which could be reversed by IGF-I, especially at the lowest oxygen concentration. Interestingly, IGF-I treatment resulted in an activation of hypoxia-inducible factor 1alpha (HIF-1alpha), a master transcription factor for hypoxia-induced metabolic adaptation. To evaluate whether IGF-I transcriptional activation correlates with HIF-1alpha activity, we studied the time course of HIF-1alpha DNA binding activity in the same rat model of hypoxia-ischemia. After hypoxia-ischemia, there was an increase in HIF-1alpha DNA binding activity in cortical tissues, with the highest increase around 24 h. Like IGF-I mRNA levels, hypoxia preconditioning increased HIF-1alpha DNA binding activity alone or with subsequent hypoxia ischemia. Overall, our results suggest that IGF-I transcriptional activation is one of the metabolic adaptive responses to hypoxia, which is likely mediated by a direct activation of HIF-1alpha.

Proliferation and differentiation of spermatogonial stem cells in the w/wv mutant mouse testis

Mutations in the dominant-white spotting (W; c-kit) and stem cell factor (Sl; SCF) genes, which encode the transmembrane tyrosine kinase receptor and its ligand, respectively, affect both the proliferation and differentiation of many types of stem cells. Almost all homozygous W or Sl mutant mice are sterile because of the lack of differentiated germ cells or spermatogonial stem cells. To characterize spermatogenesis in c-kit/SCF mutants and to understand the role of c-kit signal transduction in spermatogonial stem cells, the existence, proliferation, and differentiation of spermatogonia were examined in the W/Wv mutant mouse testis. In the present study, some of the W/Wv mutant testes completely lacked spermatogonia, and many of the remaining testes contained only a few spermatogonia. Examination of the proliferative activity of the W/Wv mutant spermatogonia by transplantation of enhanced green fluorescent protein (eGFP)-labeled W/Wv spermatogonia into the seminiferous tubules of normal SCF (W/Wv) or SCF mutant (Sl/Sld) mice demonstrated that the W/Wv spermatogonia had the ability to settle and proliferate, but not to differentiate, in the recipient seminiferous tubules. Although the germ cells in the adult W/Wv testis were c-kit-receptor protein-negative undifferentiated type A spermatogonia, the juvenile germ cells were able to differentiate into spermatogonia that expressed the c-kit-receptor protein. Furthermore, differentiated germ cells with the c-kit-receptor protein on the cell surface could be induced by GnRH antagonist treatment, even in the adult W/Wv testis. These results indicate that all the spermatogonial stem cell characteristics of settlement, proliferation, and differentiation can be demonstrated without stimulating the c-kit-receptor signal. The c-kit/SCF signal transduction system appears to be necessary for the maintenance and proliferation of differentiated c-kit receptor-positive spermatogonia but not for the initial step of spermatogonial cell differentiation.

Abundance of message for insulin-like growth factors-I and -II and for receptors for growth hormone, insulin-like growth factors-I and -II, and insulin in the intestine and liver of pre- and full-term calves

The somatotropic axis and insulin are involved in pre- and postnatal development. In pre- and full-term calves (GrP0 and GrN0; born after 277 and 290 d of pregnancy, respectively) and in preterm calves on d 8 of life after being fed for 7 d (GrP8), we studied whether there are differences in the abundance of messenger RNA (mRNA) of IGF-I and IGF-II and of receptors for GH, IGF-I, IGF-II, and insulin among different intestinal sites (duodenum, jejunum, ileum, and colon) and whether there are ontogenetic differences during the perinatal period in intestine and liver. Intestinal site differences (P < 0.05) existed in mRNA levels of IGF-I and IGF-II and receptors for GH, IGF-I, IGF-II, and insulin. Abundance of mRNA of IGF-I and -II and of receptors for IGF-I and GH was highest (P < 0.05) in the colon, abundance of the receptor for IGF-II was comparably high in the colon and ileum, and that of the receptor for insulin was similarly high in colon, ileum, and jejunum. Among GrP0, GrN0, and GrP8 groups, there were differences (P < 0.05) in mRNA levels of IGF-I and IGF-II and of receptors for GH, IGF-I, IGF-II and insulin. Abundance of mRNA of IGF-I and IGF-II and of receptors for GH, IGF-I, IGF-II and insulin was highest (P < 0.05) in GrP0 calves immediately after birth and was primarily seen in the ileum. In liver, the mRNA levels differed (P < 0.05) among groups for IGF-II and receptors for IGF-I, IGF-II, and insulin, and were highest (P < 0.05) for IGF-II in GrP0, for receptors of IGF-I in GrN0, and were higher (P < 0.05) in GrP0 than GrP8 for receptors of IGF-II. In conclusion, mRNA levels of IGF-I and IGF-II and of receptors for GH, IGF-I, IGF-II, and insulin were different at different intestinal sites and in intestine and liver and changed during the perinatal period.

Growth hormone action on proliferation and differentiation of cerebral cortical cells from fetal rat

To define the role of GH during central nervous system development, we performed studies in cultured rat cerebral cortical cells from 14- (E14) and 17-d-old embryos (E17). The expression of GH receptor, IGF-I receptor, and IGF-I mRNAs was confirmed. In E17, GH increased total cell number (3.9-fold), [(3)H]-thymidine incorporation (3.5-fold), proliferating cell nuclear antigen levels (2.5-fold), and bromodeoxyuridine (BrdU)-positive cells (2.5-fold). GH action on nestin/BrdU-positive cells was increased in E14 cells at 3 d in vitro (80-fold) but not at 7 d in vitro. In E14 cells, GH increased (9.5-fold) beta-tubulin/BrdU cells. In E17 cells, GH induced neuronal differentiation, as indicated by the absence of beta-tubulin/BrdU-positive cells and the 5.9-fold increment of beta-tubulin protein, and increased glial fibrillary acidic protein/BrdU-positive cells (2.5-fold) and glial fibrillary acidic protein expression (4.5-fold). GH-induced proliferation and differentiation was blocked by IGF-I antiserum. GH increased IGF-binding protein-3 (IGFBP-3), IGF-I receptor protein and its phosphorylation. This study shows that GH promotes proliferation of neural precursors, neurogenesis, and gliogenesis during brain development. These responses are mediated by locally produced IGF-I. GH-induced IGFBP-3 may also have a role in these responses. Therefore, GH is able to activate the IGF-I/IGFBP-3 system in these cerebral cells and induce a physiological action of IGF-I.

IL-6-overexpression brings about growth impairment potentially through a GH receptor defect

This paper is concerned with growth retardation associated with overproduction of interleukin-6 (IL-6). As a model, we used MUP/hIL-6 transgenic mice in which human IL-6 cDNA is overexpressed under the control of a MUP gene enhancer/promoter. The growth-retardation of MUP/hIL-6 transgenic mice was paralleled by reduced serum levels of IGF-I. As shown, hepatic IGF-I mRNA levels were reduced in the transgenic mice. MUP/hIL-6 transgenic mice are in a state of growth hormone (GH)-resistance, since their serum GH levels are either normal or elevated. To identify possible steps in GH signaling which might be perturbed in the transgenic mice, we examined the synthesis of GH receptor (GHR) mRNA. We noted a twofold reduction of hepatic GHR mRNA in the transgenic mice. We therefore conclude that overexpression of IL-6 brings about growth impairment in part through a GH receptor defect.

Growth hormone increases the total number of cardiac myocyte nuclei in young rats but not in old rats

Previously we have shown that growth hormone (GH) increases the total number of myocyte nuclei of the left ventricle in adult rats (8 months old). In the present study, we investigated whether GH could increase the total number of myocyte nuclei of the left ventricle in young and old rats. Female rats, 3 months old and 20 months old, were injected with GH or vehicle for 80 days. Using immersion-fixed left ventricles, unbiased stereological methods were applied. The weight of the left ventricle was increased by 49% (P<0.001) in the GH-injected young rats and by 32% (P<0.01) in the GH-injected old rats compared with the controls. Compared with the control groups, there was a 31% increase in the total number of myocyte nuclei in the GH-injected young group (P<0.05), but no significant increase in the GH-injected old group. The total number of non-myocyte nuclei was increased by 59% in the young GH-injected group (P<0.001) and by 25% in the old GH-injected group (P<0.01). In conclusion, GH induced a substantial left ventricle growth in both young and old rats. GH increased the total number of myocyte nuclei in the left ventricle of young rats, but not in old rats. This study shows that the myocyte response to GH declines with ageing.

Body growth and substrate partitioning for fat and protein gain in weaned BALB/c mice treated with growth hormone

Previously we have found that recombinant human growth hormone (rhGH) (GH; 74 ng g body wt.(-1)) administration to weaned BALB/c male mice (fed 12% or 20% protein diet) induced a growth lag and subsequent repletion similar to the catch-up growth process. We studied the partitioning of feed and protein intakes between adipose and protein body stores through the linear relationships among them. The non-linear relationship of protein intake with body fat gain/protein gain (FG/PG) ratio was especially adequate in determining the partitioning of substrates. rhGH induced an increase in feed and protein intake utilization for body weight gain (50%) and fat gain (75-140%) over saline; macronutrient utilization was the greatest in rhGH-treated mice fed 20% protein. However, growth recovery of rhGH mice was anomalous and protein intake was derived primarily for fat gain. Mice fed 12% protein (treated and control) also derived protein intake in preference to fat stores. Treatment and diet had a cumulative effect with the result that rhGH-treated animals fed 12% protein showed the greatest FG/PG ratio (1.6), and therefore, the lowest efficiency to gain protein. Weaning is a critical stage in mice when treating with rhGH, as this could provoke a growth lag. The study showed that a high protein level is required to surpass the rhGH-induced lag, but it is not enough to obtain an enhanced protein deposition. Feeding a 12% protein diet was even worse as mice did not improve on the growth lag and substrates were directed mainly to body fat.

GH regulation of IGF-I and suppressor of cytokine signaling gene expression in C2C12 skeletal muscle cells

GH is required for normal postnatal growth and metabolism. GH stimulates postnatal growth through induction of IGF-I gene expression. Although the liver is the major site of GH-regulated IGF-I, recent evidence indicates that GH-regulated IGF-I expression in nonhepatic tissues is sufficient for normal postnatal growth. One potentially important nonhepatic site of GH-stimulated IGF-I expression is skeletal muscle, as injection of GH into animals leads to increased IGF-I mRNA in this tissue. Nevertheless, direct effects of GH in skeletal muscle cells in culture have not been reported. We therefore tested the C2C12 myogenic cell line for its response to GH and demonstrate that C2C12 skeletal muscle cells rapidly respond to physiological levels of GH with increased tyrosine phosphorylation of the GH receptor, Janus kinase 2, signal transducer and activator of transcription-5a and -5b, insulin receptor substrate-1, and activation of MAPKs/ERKs and protein kinase B/Akt. In these cells, GH stimulates the expression of IGF-I and two members of the suppressors of cytokine signaling family, cytokine-inducible SH2-containing protein and suppressor of cytokine signaling-2. Treatment of C2C12 myoblasts with either the MAPK kinase inhibitor PD98059 or the PI3K inhibitor wortmannin results in higher levels of GH-induced IGF-I and suppressor of cytokine signaling-2 mRNA expression, suggesting that activation of MAPK and PI3K pathways has an inhibitory role in IGF-I and suppressor of cytokine signaling-2 gene regulation. Therefore, C2C12 cells provide the first in vitro model system to study various aspects of GH action in skeletal muscle.

Lack of Socs2 expression causes the high-growth phenotype in mice

Characterizing causal molecular defects in mouse models of overgrowth or dwarfism helps to identify the key genes and pathways that regulate the growth process. We report here the molecular basis for high growth (hg), a spontaneous mutation that causes a 30-50% increase in postnatal growth. We conclude that hg is an allele of the suppressor of cytokine signaling 2 (Socs2), a member of a family of regulators of cytokine signal transduction. We demonstrate mapping of Socs2 to the hg region, lack of Socs2 mRNA expression, a disruption of the Socs2 locus in high-growth (HG) mice, and a similarity of phenotypes of HG mice and Socs2(-/-) mice generated by gene targeting. Characteristics of the HG phenotype suggest that Socs2 deficiency affects growth prenatally and postnatally most likely through deregulating the growth hormone (GH)/insulin-like growth factor I (IGF1). These results demonstrate a critical role for Socs2 in controlling growth.

Gigantism in mice lacking suppressor of cytokine signalling-2

Suppressor of cytokine signalling-2 (SOCS-2) is a member of the suppressor of cytokine signalling family, a group of related proteins implicated in the negative regulation of cytokine action through inhibition of the Janus kinase (JAK) signal transducers and activators of transcription (STAT) signal-transduction pathway. Here we use mice unable to express SOCS-2 to examine its function in vivo. SOCS-2(-/-) mice grew significantly larger than their wild-type littermates. Increased body weight became evident after weaning and was associated with significantly increased long bone lengths and the proportionate enlargement of most organs. Characteristics of deregulated growth hormone and insulin-like growth factor-I (IGF-I) signalling, including decreased production of major urinary protein, increased local IGF-I production, and collagen accumulation in the dermis, were observed in SOCS-2-deficient mice, indicating that SOCS-2 may have an essential negative regulatory role in the growth hormone/IGF-I pathway.

Platelet-derived growth factor and lysophosphatidic acid inhibit growth hormone binding and signaling via a protein kinase C-dependent pathway

Growth hormone (GH) regulates body growth and metabolism. GH exerts its biological action by stimulating JAK2, a GH receptor (GHR)-associated tyrosine kinase. Activated JAK2 phosphorylates itself and GHR, thus initiating multiple signaling pathways. In this work, we demonstrate that platelet-derived growth factor (PDGF) and lysophosphatidic acid (LPA) down-regulate GH signaling via a protein kinase C (PKC)-dependent pathway. PDGF substantially reduces tyrosyl phosphorylation of JAK2 induced by GH but not interferon-gamma or leukemia inhibitory factor. PDGF, but not epidermal growth factor, decreases tyrosyl phosphorylation of GHR (by approximately 90%) and the amount of both total cellular GHR (by approximately 80%) and GH binding (by approximately 70%). The inhibitory effect of PDGF on GH-induced tyrosyl phosphorylation of JAK2 and GHR is abolished by depletion of 4beta-phorbol 12-myristate 13-acetate (PMA)-sensitive PKCs with chronic PMA treatment and is severely inhibited by GF109203X, an inhibitor of PKCs. In contrast, extracellular signal-regulated kinases 1 and 2 and phosphatidylinositol 3-kinase appear not to be involved in this inhibitory effect of PDGF. LPA, a known activator of PKC, also inhibits GH-induced tyrosyl phosphorylation of JAK2 and GHR and reduces the number of GHR. We propose that ligands that activate PKC, including PDGF, LPA, and PMA, down-regulate GH signaling by decreasing the number of cell surface GHR through promoting GHR internalization and degradation and/or cleavage of membrane GHR and release of the extracellular domain of GHR.