Postnatally elevated levels of insulin-like growth factor (IGF)-II fail to rescue the dwarfism of IGF-I-deficient mice except kidney weight

Insulin-like growth factor-1 effects on kidney development in preterm piglets

BACKGROUND

Preterm birth disrupts fetal kidney development, potentially leading to postnatal acute kidney injury. Preterm infants are deficient in insulin-like growth factor 1 (IGF-1), a growth factor that stimulates organ development. By utilizing a preterm pig model, this study investigated whether IGF-1 supplementation enhances preterm kidney maturation.

METHODS

Cesarean-delivered preterm pigs were treated systemically IGF-1 or vehicle control for 5, 9 or 19 days after birth. Blood, urine, and kidney tissue were collected for biochemical, histological and gene expression analyses. Age-matched term-born pigs were sacrificed at similar postnatal ages and served as the reference group.

RESULTS

Compared with term pigs, preterm pigs exhibited impaired kidney maturation, as indicated by analyses of renal morphology, histopathology, and inflammatory and injury markers. Supplementation with IGF-1 reduced signs of kidney immaturity, particularly in the first week of life, as indicated by improved morphology, upregulated expression of key developmental genes, reduced severity and incidence of microscopic lesions, and decreased levels of inflammatory and injury markers. No association was seen between the symptoms of necrotizing enterocolitis and kidney defects.

CONCLUSION

Preterm birth in pigs impairs kidney maturation and exogenous IGF-1 treatment partially reverses this impairment. Early IGF-1 supplementation could support the development of preterm kidneys.

IMPACT

Preterm birth may disrupt kidney development in newborns, potentially leading to morphological changes, injury, and inflammation. Preterm pigs have previously been used as models for preterm infants, but not for kidney development. IGF-1 supplementation promotes kidney maturation and alleviates renal impairments in the first week of life in preterm pigs. IGF-1 may hold potential as a supportive therapy for preterm infants sensitive to acute kidney injury.

Liver fat metabolism of broilers regulated by Bacillus amyloliquefaciens TL via stimulating IGF-1 secretion and regulating the IGF signaling pathway

Bacillus amyloliquefaciens TL (B.A-TL) is well-known for its capability of promoting protein synthesis and lipid metabolism, in particular, the abdominal fat deposition in broilers. However, the underlying molecular mechanism remains unclear. In our study, the regulations of lipid metabolism of broilers by B.A-TL were explored both in vivo and in vitro. The metabolites of B.A-TL were used to simulate in vitro the effect of B.A-TL on liver metabolism based on the chicken hepatocellular carcinoma cell line (i.e., LMH cells). The effects of B.A-TL on lipid metabolism by regulating insulin/IGF signaling pathways were investigated by applying the signal pathway inhibitors in vitro. The results showed that the B.A-TL metabolites enhanced hepatic lipid synthesis and stimulated the secretion of IGF-1. The liver transcriptome analysis revealed the significantly upregulated expressions of four genes (SI, AMY2A, PCK1, and FASN) in the B.A-TL treatment group, mainly involved in carbohydrate digestion and absorption as well as biomacromolecule metabolism, with a particularly prominent effect on fatty acid synthase (FASN). Results of cellular assays showed that B.A-TL metabolites were involved in the insulin/IGF signaling pathway, regulating the expressions of lipid metabolism genes (e.g., FASN, ACCα, LPIN, and ACOX) and the FASN protein, ultimately regulating the lipid metabolism via the IGF/PI3K/FASN pathway in broilers.

Renal effects of growth hormone in health and in kidney disease

Growth hormone (GH) and its mediator insulin-like growth factor-1 (IGF-1) have manifold effects on the kidneys. GH and IGF receptors are abundantly expressed in the kidney, including the glomerular and tubular cells. GH can act either directly on the kidneys or via circulating or paracrine-synthesized IGF-1. The GH/IGF-1 system regulates glomerular hemodynamics, renal gluconeogenesis, tubular sodium and water, phosphate, and calcium handling, as well as renal synthesis of 1,25 (OH)2 vitamin D3 and the antiaging hormone Klotho. The latter also acts as a coreceptor of the phosphaturic hormone fibroblast-growth factor 23 in the proximal tubule. Recombinant human GH (rhGH) is widely used in the treatment of short stature in children, including those with chronic kidney disease (CKD). Animal studies and observations in acromegalic patients demonstrate that GH-excess can have deleterious effects on kidney health, including glomerular hyperfiltration, renal hypertrophy, and glomerulosclerosis. In addition, elevated GH in patients with poorly controlled type 1 diabetes mellitus was thought to induce podocyte injury and thereby contribute to the development of diabetic nephropathy. This manuscript gives an overview of the physiological actions of GH/IGF-1 on the kidneys and the multiple alterations of the GH/IGF-1 system and its consequences in patients with acromegaly, CKD, nephrotic syndrome, and type 1 diabetes mellitus. Finally, the impact of short- and long-term treatment with rhGH/rhIGF-1 on kidney function in patients with kidney diseases will be discussed.

Effects of GH/IGF axis on bone and cartilage

Growth hormone (GH) and its mediator, the insulin-like growth factor-1 (IGF-1) regulate somatic growth, metabolism and many aspects of aging. As such, actions of GH/IGF have been studied in many tissues and organs over decades. GH and IGF-1 are part of the hypothalamic/pituitary somatotrophic axis that consists of many other regulatory hormones, receptors, binding proteins, and proteases. In humans, GH/IGF actions peak during pubertal growth and regulate skeletal acquisition through stimulation of extracellular matrix production and increases in bone mineral density. During aging the activity of these hormones declines, a state called somatopaguss, which associates with deleterious effects on the musculoskeletal system. In this review, we will focus on GH/IGF-1 action in bone and cartilage. We will cover many studies that have utilized congenital ablation or overexpression of members of this axis, as well as cell-specific gene-targeting approaches used to unravel the nature of the GH/IGF-1 actions in the skeleton in vivo.

Overlap of Peak Growth Activity and Peak IGF-1 to IGFBP Ratio: Delayed Increase of IGFBPs versus IGF-1 in Serum as a Mechanism to Speed up and down Postnatal Weight Gain in Mice

Forced expression of insulin-like growth factor binding proteins (IGFBPs) in transgenic mice has clearly revealed inhibitory effects on somatic growth. However, by this approach, it cannot be solved if or how IGFBPs rule insulin-like growth factor (IGF)-dependent growth under normal conditions. In order to address this question, we have used growth-selected mouse models (obese and lean) and studied IGF-1 and IGFBPs in serum with respect to longitudinal growth activity in males and females compared with unselected controls. In mice of both genders, body weights were recorded and daily weight gains were calculated. Between 2 and 54 weeks of age, serum IGF-1 was determined by ELISA and intact IGFBP-2, -3 and -4 were quantified by Western ligand blotting. The molar ratio of IGF-1 to the sum of IGFBP-2 to -4 was calculated for all groups and plotted against the daily weight gain curve. Growth-selected mice are characterized by higher daily weight gains and extended periods of elevated growth activity if compared to matched unselected controls. Therefore, adult mice from the obese and lean groups can achieve more than twofold increased body weight in both genders (p < 0.001). Between 2 and 11 weeks of age, in obese and lean mice of both genders, serum IGF-1 concentrations are increased more prominently if compared to unselected controls (p < 0.001). Instead, substantial decreases of IGFBPs, particularly of IGFBP-2, are observed in males and females of all groups at the age of 2 to 4 weeks (p < 0.001). Due to the strong increase of IGF-1 but not of IGFBPs between two and four weeks of age, the ratio of IGF-1 to IGFBP-2 to -4 in serum significantly increased in all groups and genders (p < 0.05). Notably, the IGF-1 to IGFBP ratio was higher in male and female obese mice if compared to unselected controls (p < 0.05).

Intrauterine programming of the glucocorticoid-insulin-like growth factor 1 (GC-IGF1) axis mediates glomerulosclerosis in female adult offspring rats induced by prenatal ethanol exposure

Prenatal ethanol exposure (PEE) causes intrauterine growth retardation (IUGR), and the occurrence of glomerulosclerosis is closely related to IUGR. This study aimed to confirm the kidney toxic effect of PEE and explore its intrauterine programming mechanism in female offspring. The Wistar female fetuses on gestational day (GD) 20 and the adult offspring at postnatal week 24 were anesthetized and decapitated. The adult offspring kidneys in the PEE group displayed glomerular hyperplasia and glomerulosclerosis. Blood urea nitrogen (BUN) and the BUN / Serum creatinine (Scr) concentration ratio in the PEE group was increased significantly compared to the control group (P<0.01, P<0.05). Meanwhile, the renal glucocorticoid-activation system was inhibited, whereas the insulin-like growth factor 1 (IGF1) signaling pathway was activated in the female adult offspring of the PEE group. In the fetal kidney of the PEE group, pathological observation showed kidney dysplasia, and the gene expression of the glial-cell-line-derived neurotrophic factor/tyrosine kinase receptor (GDNF/c-Ret) signaling pathway was reduced compared to that of the control group. Moreover, the glucocorticoid-activation system was activated, whereas the IGF1 signaling pathway was inhibited in the fetal kidneys of the PEE group. In conclusion, PEE caused fetal kidney dysplasia and adult glomerulosclerosis in the female offspring rats, and the intrauterine programming alteration of glucocorticoid-insulin-like growth factor 1 (GC-IGF1) axis might be involved in fetal-originated glomerulosclerosis.

Insulin-like growth factors: actions on the skeleton

The discovery of the growth hormone (GH)-mediated somatic factors (somatomedins), insulin-like growth factor (IGF)-I and -II, has elicited an enormous interest primarily among endocrinologists who study growth and metabolism. The advancement of molecular endocrinology over the past four decades enables investigators to re-examine and refine the established somatomedin hypothesis. Specifically, gene deletions, transgene overexpression or more recently, cell-specific gene-ablations, have enabled investigators to study the effects of the Igf1 and Igf2 genes in temporal and spatial manners. The GH/IGF axis, acting in an endocrine and autocrine/paracrine fashion, is the major axis controlling skeletal growth. Studies in rodents have clearly shown that IGFs regulate bone length of the appendicular skeleton evidenced by changes in chondrocytes of the proliferative and hypertrophic zones of the growth plate. IGFs affect radial bone growth and regulate cortical and trabecular bone properties via their effects on osteoblast, osteocyte and osteoclast function. Interactions of the IGFs with sex steroid hormones and the parathyroid hormone demonstrate the significance and complexity of the IGF axis in the skeleton. Finally, IGFs have been implicated in skeletal aging. Decreases in serum IGFs during aging have been correlated with reductions in bone mineral density and increased fracture risk. This review highlights many of the most relevant studies in the IGF research landscape, focusing in particular on IGFs effects on the skeleton.

Somatotropic Axis Regulation Unravels the Differential Effects of Nutritional and Environmental Factors in Growth Performance of Marine Farmed Fishes

The Gh/Prl/Sl family has evolved differentially through evolution, resulting in varying relationships between the somatotropic axis and growth rates within and across fish species. This is due to a wide range of endogenous and exogenous factors that make this association variable throughout season and life cycle, and the present minireview aims to better define the nutritional and environmental regulation of the endocrine growth cascade over precisely defined groups of fishes, focusing on Mediterranean farmed fishes. As a result, circulating Gh and Igf-i are revitalized as reliable growth markers, with a close association with growth rates of gilthead sea bream juveniles with deficiency signs in both macro- or micro-nutrients. This, together with other regulated responses, promotes the use of Gh and Igf-i as key performance indicators of growth, aerobic scope, and nutritional condition in gilthead sea bream. Moreover, the sirtuin-energy sensors might modulate the growth-promoting action of somatotropic axis. In this scenario, transcripts of igf-i and gh receptors mirror changes in plasma Gh and Igf-i levels, with the ghr-i/ghr-ii expression ratio mostly unaltered over season. However, this ratio is nutritionally regulated, and enriched plant-based diets or diets with specific nutrient deficiencies downregulate hepatic ghr-i, decreasing the ghr-i/ghr-ii ratio. The same trend, due to a ghr-ii increase, is found in skeletal muscle, whereas impaired growth during overwintering is related to increase in the ghr-i/ghr-ii and igf-ii/igf-i ratios in liver and skeletal muscle, respectively. Overall, expression of insulin receptors and igf receptors is less regulated, though the expression quotient is especially high in the liver and muscle of sea bream. Nutritional and environmental regulation of the full Igf binding protein 1-6 repertoire remains to be understood. However, tissue-specific expression profiling highlights an enhanced and nutritionally regulated expression of the igfbp-1/-2/-4 clade in liver, whereas the igfbp-3/-5/-6 clade is overexpressed and regulated in skeletal muscle. The somatotropic axis is, therefore, highly informative of a wide-range of growth-disturbing and stressful stimuli, and multivariate analysis supports its use as a reliable toolset for the assessment of growth potentiality and nutrient deficiencies and requirements, especially in combination with selected panels of other nutritionally regulated metabolic biomarkers.

An essential role for IGF2 in cartilage development and glucose metabolism during postnatal long bone growth

Postnatal bone growth involves a dramatic increase in length and girth. Intriguingly, this period of growth is independent of growth hormone and the underlying mechanism is poorly understood. Recently, an IGF2 mutation was identified in humans with early postnatal growth restriction. Here, we show that IGF2 is essential for longitudinal and appositional murine postnatal bone development, which involves proper timing of chondrocyte maturation and perichondrial cell differentiation and survival. Importantly, the Igf2 null mouse model does not represent a simple delay of growth but instead uncoordinated growth plate development. Furthermore, biochemical and two-photon imaging analyses identified elevated and imbalanced glucose metabolism in the Igf2 null mouse. Attenuation of glycolysis rescued the mutant phenotype of premature cartilage maturation, thereby indicating that IGF2 controls bone growth by regulating glucose metabolism in chondrocytes. This work links glucose metabolism with cartilage development and provides insight into the fundamental understanding of human growth abnormalities.

Regulation of skeletal growth and mineral acquisition by the GH/IGF-1 axis: Lessons from mouse models

The growth hormone (GH) and its downstream mediator, the insulin-like growth factor-1 (IGF-1), construct a pleotropic axis affecting growth, metabolism, and organ function. Serum levels of GH/IGF-1 rise during pubertal growth and associate with peak bone acquisition, while during aging their levels decline and associate with bone loss. The GH/IGF-1 axis was extensively studied in numerous biological systems including rodent models and cell cultures. Both hormones act in an endocrine and autocrine/paracrine fashion and understanding their distinct and overlapping contributions to skeletal acquisition is still a matter of debate. GH and IGF-1 exert their effects on osteogenic cells via binding to their cognate receptor, leading to activation of an array of genes that mediate cellular differentiation and function. Both hormones interact with other skeletal regulators, such as sex-steroids, thyroid hormone, and parathyroid hormone, to facilitate skeletal growth and metabolism. In this review we summarized several rodent models of the GH/IGF-1 axis and described key experiments that shed new light on the regulation of skeletal growth by the GH/IGF-1 axis.

Genetic dissection of IGF1-dependent and -independent effects of permanent GH excess on postnatal growth and organ pathology of mice

To study insulin-like growth factor 1 (IGF1)-independent effects of permanent growth hormone (GH) excess on body and organ growth and pathology in vivo, hemizygous bovine GH transgenic mice with homozygous disruption of the Igf1 gene (Igf1(-/-)/GH) were generated, and examined in comparison to Igf1(-/-), Igf1(+/-), wild-type (WT), Igf1(+/-)/GH, and GH mice. GH mice and Igf1(+/-)/GH mice showed increased serum IGF1 levels and the well-known giant-phenotype of GH transgenic mice. In contrast, the typical dwarf-phenotype of Igf1(-/-) mice was only slightly ameliorated in Igf1(-/-)/GH mice. Similar to GH mice, Igf1(-/-)/GH mice displayed hepatocellular hypertrophy, glomerulosclerosis, and reduced volumes of acidophilic cells in the pituitary gland. However, GH excess associated skin lesions of male GH mice were not observed in Igf1(-/-)/GH mice. Therefore, development of GH excess induced liver-, kidney-, and pituitary gland-alterations in GH transgenic mice is independent of IGF1 whereas GH stimulated body growth depends on IGF1.

Insulin-like growth factors and kidney disease

Insulin-like growth factors (IGF-1 and IGF-2) are necessary for normal growth and development. They are related structurally to proinsulin and promote cell proliferation, differentiation, and survival, as well as insulin-like metabolic effects, in most cell types and tissues. In particular, IGFs are important for normal pre- and postnatal kidney development. IGF-1 mediates many growth hormone actions, and both growth hormone excess and deficiency are associated with perturbed kidney function. IGFs affect renal hemodynamics both directly and indirectly by interacting with the renin-angiotensin system. In addition to the IGF ligands, the IGF system includes receptors for IGF-1, IGF-2/mannose-6-phosphate, and insulin, and a family of 6 high-affinity IGF-binding proteins that modulate IGF action. Disordered regulation of the IGF system has been implicated in a number of kidney diseases. IGF activity is enhanced in early diabetic nephropathy and polycystic kidneys, whereas IGF resistance is found in chronic kidney failure. IGFs have a potential role in enhancing stem cell repair of kidney injury. Most IGF actions are mediated by the tyrosine kinase IGF-1 receptor, and inhibitors recently have been developed. Further studies are needed to determine the optimal role of IGF-based therapies in kidney disease.

Genetic mechanisms and signaling pathways in autosomal dominant polycystic kidney disease

Recent advances in defining the genetic mechanisms of disease causation and modification in autosomal dominant polycystic kidney disease (ADPKD) have helped to explain some extreme disease manifestations and other phenotypic variability. Studies of the ADPKD proteins, polycystin-1 and -2, and the development and characterization of animal models that better mimic the human disease, have also helped us to understand pathogenesis and facilitated treatment evaluation. In addition, an improved understanding of aberrant downstream pathways in ADPKD, such as proliferation/secretion-related signaling, energy metabolism, and activated macrophages, in which cAMP and calcium changes may play a role, is leading to the identification of therapeutic targets. Finally, results from recent and ongoing preclinical and clinical trials are greatly improving the prospects for available, effective ADPKD treatments.

Growth hormone, insulin-like growth factor-1, and the kidney: pathophysiological and clinical implications

Besides their growth-promoting properties, GH and IGF-1 regulate a broad spectrum of biological functions in several organs, including the kidney. This review focuses on the renal actions of GH and IGF-1, taking into account major advances in renal physiology and hormone biology made over the last 20 years, allowing us to move our understanding of GH/IGF-1 regulation of renal functions from a cellular to a molecular level. The main purpose of this review was to analyze how GH and IGF-1 regulate renal development, glomerular functions, and tubular handling of sodium, calcium, phosphate, and glucose. Whenever possible, the relative contributions, the nephronic topology, and the underlying molecular mechanisms of GH and IGF-1 actions were addressed. Beyond the physiological aspects of GH/IGF-1 action on the kidney, the review describes the impact of GH excess and deficiency on renal architecture and functions. It reports in particular new insights into the pathophysiological mechanism of body fluid retention and of changes in phospho-calcium metabolism in acromegaly as well as of the reciprocal changes in sodium, calcium, and phosphate homeostasis observed in GH deficiency. The second aim of this review was to analyze how the GH/IGF-1 axis contributes to major renal diseases such as diabetic nephropathy, renal failure, renal carcinoma, and polycystic renal disease. It summarizes the consequences of chronic renal failure and glucocorticoid therapy after renal transplantation on GH secretion and action and questions the interest of GH therapy in these conditions.

Serum IGF-1 is insufficient to restore skeletal size in the total absence of the growth hormone receptor

States of growth hormone (GH) resistance, such those observed in Laron dwarf patients, are characterized by mutations in the GH receptor (GHR), decreased serum and tissue IGF-1 levels, impaired glucose tolerance, and impaired skeletal acquisition. IGF-1 replacement therapy in such patients increases growth velocity but does not normalize growth. Herein we combined the GH-resistant (GHR knockout [GHRKO]) mouse model with mice expressing the hepatic Igf-1 transgene (HIT) to generate the GHRKO-HIT mouse model. In GHRKO-HIT mice, serum IGF-1 levels were restored via transgenic expression of Igf-1, allowing us to study how endocrine IGF-1 affects growth, metabolic homeostasis, and skeletal integrity. We show that in a GH-resistant state, normalization of serum IGF-1 improved body adiposity and restored glucose tolerance but was insufficient to support normal skeletal growth, resulting in an osteopenic skeletal phenotype. The inability of serum IGF-1 to restore skeletal integrity in the total absence of GHR likely resulted from reduced skeletal Igf-1 gene expression, blunted GH-mediated effects on the skeleton that are independent of serum or tissue IGF-1, and poor delivery of IGF-1 to the tissues. These findings are consistent with clinical data showing that IGF-I replacement therapy in patients with Laron syndrome does not achieve full skeletal growth.

Insulin-like growth factors in normal and diseased kidney

This article reviews the physiology of the insulin-like growth factor (IGF) system in the kidney and the changes and potential role of this system in selected renal diseases. The potential therapeutic uses of recombinant human IGF-I for the treatment of acute and chronic kidney failure are briefly discussed.

Growth factors, nutrient signaling, and cardiovascular aging

Growth factors regulated by specific macronutrients have been shown to promote aging and accelerate mortality in the majority of the organisms studied. In particular, the enzymes activated by growth hormone, insulin, and insulin-like growth factor-1 in mammals and their orthologs in simple model organisms represent perhaps the best-understood proteins involved in the aging process. Dietary restriction, which reduces the level of insulin-like growth factor-1 and of other growth factors, has been associated with protection from diabetes, cancer, and cardiovascular diseases, and deficiencies in growth hormone signaling and insulin-like growth factor-1 are strongly associated with protection from cancer and diabetes in both mice and humans; however, their role in cardiac function and cardiovascular diseases is controversial. Here, we review the link between growth factors, cardiac function, and heart disease with focus on the cardioprotective and sensitizing effect of growth factors in both model organisms and humans.

The insulin-like growth factor system in kidney disease and hypertension

PURPOSE OF REVIEW

The insulin-like growth factor system plays an important role in renal physiology and it is perturbed in a range of kidney diseases.

RECENT FINDINGS

Some insulin-like growth factor (IGF) actions in the kidney are mediated by nitric oxide. Growth hormone and IGF-binding proteins may contribute to renal diseases via effects on podocytes and proximal tubule cells. In contrast, growth hormone and IGF-I may counteract the catabolic consequences of end-stage renal disease. Polymorphisms in the IGF system are associated with hypertension.

SUMMARY

Further studies are needed to determine whether modulating the IGF system may have a role in treating kidney diseases and/or hypertension.

Insulin-like growth factor (IGF)-I and IGF-II contribute differentially to the phenotype of pregnancy associated plasma protein-A knock-out mice

CONTEXT

Insulin-like growth factor (IGF) signaling is essential for achieving optimal body size during fetal development, peak bone mass during puberty, and maximal fecundity in the reproductive period. IGF-II is considered the main fetal IGF, whereas IGF-I is more important postnatally. Pregnancy-associated plasma protein-A (PAPP-A) enhances local IGF signaling through cleavage of inhibitory IGF binding proteins. Conversely, inhibition of PAPP-A results in reduced local IGF action. Thus, PAPP-A knock-out (KO) mice are born as proportional dwarfs due to the dysregulation of IGF-II signaling during early embryogenesis that impacts body size. Relaxation of IgfII imprinting through mutation of a reciprocally imprinted downstream gene, H19, which allowed transcription of IGF-II from the normally silent maternal allele, rescued the dwarf phenotype of PAPP-A KO mice.

OBJECTIVE

To determine the effect of increased IGF-II expression on postnatal phenotypes of PAPP-A KO mice.

DESIGN

Young adult wild-type (WT), PAPP-A KO, H19 mutant (ΔH19/WT) and ΔH19/PAPP-A KO mice were characterized for skeletal phenotype (peripheral quantitative computed tomography at the midshaft and distal metaphysis of the femur) and reproductive phenotype (time to first litter, time between litters, pups per litter).

RESULTS

Serum IGF-II levels were significantly increased in ΔH19/WT and ΔH19/PAPP-A KO mice compared to WT and PAPP-A KO mice; serum IGF-I levels were not affected by H19 mutation. PAPP-A KO mice had reductions in cortical thickness and in cortical and trabecular area, bone mineral content and bone mineral density compared to WT mice. There were no significant differences between PAPP-A KO and ΔH19/PAPP-A KO mice in any of the bone parameters. PAPP-A KO crossed with (×) PAPP-A KO had a longer time until first litter, normal time between subsequent litters, and significantly reduced number of pups per litter compared to WT×WT. ΔH19/PAPP-A KO×ΔH19/PAPP-A KO had an even longer time to first litter, but also longer time between litters. This phenotype was associated with female ΔH19/PAPP-A KO mice. Furthermore, these ΔH19/PAPP-A KO mouse mothers failed to care for their pups.

CONCLUSIONS

An increase in IGF-II expression did not rescue the skeletal and reproductive deficiencies associated with reduced local IGF-I signaling in PAPP-A KO mice. In addition, the data suggest a potential new role for genomic imprinting at the IgfII/H19 locus affecting maternal behavior.

Effect of growth hormone administration to mature miniature Brahman cattle treated with or without insulin on circulating concentrations of insulin-like growth factor-I and other metabolic hormones and metabolites

Previously, we determined that a primary cause of proportional stunted growth in a line of Brahman cattle was related to an apparent refractoriness in metabolic response to GH in young animals. The objective of this study was to determine the effect of administration of GH, insulin (INS), and GH plus INS to mature miniature Brahman cows (n = 6; 9.7 ± 2.06 y; 391 ± 48.6 kg) and bulls (n = 8; 9.4 ± 2.00 y; 441 ± 54.0 kg) on circulating concentrations of metabolic hormones and metabolites, primarily IGF-I and IGF-I binding proteins. We hypothesized that IGF-I secretion could be enhanced by concomitant administration of exogenous GH and INS, and neither alone would be effective. Animals were allotted to a modified crossover design that included four treatments: control (CON), GH, INS, and GH + INS. At the start of the study, one-half of the cattle were administered GH (Posilac; 14-d slow release) and the other one-half served as CON for 7 d. Beginning on day 8, and for 7 d, INS (Novolin L) was administered (0.125 IU/kg BW) twice daily (7:00 AM and 7:00 PM) to all animals; hence, the INS and GH + INS treatments. Cattle were rested for 14 d and then were switched to the reciprocal crossover treatments. Blood samples were collected at 12-hour intervals during the study. Compared with CON, GH treatment increased (P < 0.01) mean plasma concentrations of GH (11.1 vs 15.7 ± 0.94 ng/mL), INS (0.48 vs 1.00 ± 0.081 ng/mL), IGF-I (191.3 vs 319.3 ± 29.59 ng/mL), and glucose (73.9 vs 83.4 ± 2.12 mg/dL) but decreased (P < 0.05) plasma urea nitrogen (14.2 vs 11.5 ± 0.75 mg/dL). Compared with INS, GH + INS treatment increased (P < 0.05) mean plasma concentration of INS (0.71 vs 0.96 ± 0.081 ng/mL), IGF-I (228.7 vs 392.3 ± 29.74 ng/mL), and glucose (48.1 vs 66.7 ± 2.12 mg/dL), decreased (P < 0.01) plasma urea nitrogen (13.6 vs 10.4 ± 0.76 mg/dL), and did not affect GH (13.5 vs 12.7 ± 0.95 ng/mL). In the miniature Brahman model, both the GH and GH + INS treatments dramatically increased circulating concentrations of IGF-I in mature cattle, suggesting that this line of Brahman cattle is capable of responding to bioactive GH.

Comparative analysis of clinical, biochemical and genetic aspects associated with bone mineral density in small for gestational age children

Clinical, biochemical and genetic analysis related to bone mineral density (BMD) were carried out in children born small for gestational age (SGA) that failed to achieve postnatal catch-up growth (CUG), SGA children that completed CUG and adequate for gestational age (AGA) children. Serum IGF-I, IGF-II, IGF binding protein-3 and acid-labile subunit were lower in the SGA-CUG children as compared with the other groups. Frequencies of polymorphic variants of vitamin D receptor, estrogen receptor and collagen genes were similar among groups. The genotype 194-192 of the IGF-I gene was higher in the SGA-CUG and 196-192 was higher in the SGA+CUG group. In the SGA-CUG group, the genotype SS of the COLIA1 gene was associated with lower BMD. Therefore, IGF system and COLIA1 polymorphism distinguish prepubertal SGA-CUG children from the SGA+CUG children of the same age. Furthermore, COLIA1 polymorphism could be useful to predict osteopenia in SGA-CUG children.

IGF-1 and bone: New discoveries from mouse models

Insulin-like growth factor-1 (IGF-1) plays a central role in cellular growth, differentiation, survival, and cell cycle progression. It is expressed early during development and its effects are mediated through binding to a tyrosine kinase receptor, the insulin-like growth factor-1 receptor (IGF-1R). In the circulation, the IGFs bind to IGF-binding proteins (IGFBPs), which determine their bioavailability and regulate the interaction between the IGFs and IGF-1R. Studies in animal models and in humans have established critical roles for IGFs in skeletal growth and development. In this review we present new and old findings from mouse models of the IGF system and discuss their clinical relevance to normal and pathological skeletal physiology.

Mice lacking the orphan receptor ror1 have distinct skeletal abnormalities and are growth retarded

Ror1 is a member of the Ror-family receptor tyrosine kinases. Ror1 is broadly expressed in various tissues and organs during mouse embryonic development. However, so far little is known about its function. The closely related family member Ror2 was shown to play a crucial role in skeletogenesis and has been shown to act as a co-receptor for Wnt5a mediating non-canonical Wnt-signaling. Previously, it has been shown that during embryonic development Ror1 acts in part redundantly with Ror2 in the skeletal and cardiovascular systems. In this study, we report that loss of the orphan receptor Ror1 results in a variety of phenotypic defects within the skeletal and urogenital systems and that Ror1 mutant mice display a postnatal growth retardation phenotype.

Longevity is not influenced by prenatal programming of body size

Insulin-like growth factor (IGF) signaling is essential for achieving optimal body size during fetal development, whereas, in the adult, IGFs are associated with aging and age-related diseases. However, it is unclear as to what extent lifespan is influenced by events that occur during development. Here, we provide direct evidence that the exceptional longevity of mice with altered IGF signaling is not linked to prenatal programming of body size. Mice null for pregnancy-associated plasma protein-A (PAPP-A), an IGF-binding protein proteinase that increases local IGF bioavailability, are 60-70% the size of their wild-type littermates at birth and have extended median and maximum lifespan of 30-40%. In this study, PAPP-A(-/-) mice whose body size was normalized during fetal development through disruption of IgfII imprinting did not lose their longevity advantage. Adult-specific moderation of IGF signaling through PAPP-A inhibition may present a unique opportunity to improve lifespan without affecting important aspects of early life physiology.

A comparative study of age-related hearing loss in wild type and insulin-like growth factor I deficient mice

Insulin-like growth factor-I (IGF-I) belongs to the family of insulin-related peptides that fulfils a key role during the late development of the nervous system. Human IGF1 mutations cause profound deafness, poor growth and mental retardation. Accordingly, Igf1^−/− null mice are dwarfs that have low survival rates, cochlear alterations and severe sensorineural deafness. Presbycusis (age-related hearing loss) is a common disorder associated with aging that causes social and cognitive problems. Aging is also associated with a decrease in circulating IGF-I levels and this reduction has been related to cognitive and brain alterations, although there is no information as yet regarding the relationship between presbycusis and IGF-I biodisponibility. Here we present a longitudinal study of wild type Igf1^+/+ and null Igf1^−/− mice from 2 to 12 months of age comparing the temporal progression of several parameters: hearing, brain morphology, cochlear cytoarchitecture, insulin-related factors and IGF gene expression and IGF-I serum levels. Complementary invasive and non-invasive techniques were used, including auditory brainstem-evoked response (ABR) recordings and in vivo MRI brain imaging. Igf1^−/− null mice presented profound deafness at all the ages studied, without any obvious worsening of hearing parameters with aging. Igf1^+/+ wild type mice suffered significant age-related hearing loss, their auditory thresholds and peak I latencies augmenting as they aged, in parallel with a decrease in the circulating levels of IGF-I. Accordingly, there was an age-related spiral ganglion degeneration in wild type mice that was not evident in the Igf1 null mice. However, the Igf1^−/− null mice in turn developed a prematurely aged stria vascularis reminiscent of the diabetic strial phenotype. Our data indicate that IGF-I is required for the correct development and maintenance of hearing, supporting the idea that IGF-I-based therapies could contribute to prevent or ameliorate age-related hearing loss.

Elevated levels of insulin-like growth factor (IGF)-I in serum rescue the severe growth retardation of IGF-I null mice

IGF-I plays a vital role in growth and development and acts in an endocrine and an autocrine/paracrine fashion. The purpose of the current study was to clarify whether elevated levels of IGF-I in serum can rescue the severe growth retardation and organ development and function of igf-I null mice. To address that, we overexpressed a rat igf-I transgene specifically in the liver of igf-I null mice. We found that in the total absence of tissue IGF-I, elevated levels of IGF-I in serum can support normal body size at puberty and after puberty but are insufficient to fully support the female reproductive system (evident by irregular estrous cycle, impaired development of ovarian corpus luteum, reduced number of uterine glands and endometrial hypoplasia, all leading to decreased number of pregnancies and litter size). We conclude that most autocrine/paracrine actions of IGF-I that determine organ growth and function can be compensated by elevated levels of endocrine IGF-I. However, in mice, full compensatory responses are evident later in development, suggesting that autocrine/paracrine IGF-I is critical for neonatal development. Furthermore, we show that tissue IGF-I is necessary for the development of the female reproductive system and cannot be compensated by elevated levels of serum IGF-I.

The role of liver-derived insulin-like growth factor-I

IGF-I is expressed in virtually every tissue of the body, but with much higher expression in the liver than in any other tissue. Studies using mice with liver-specific IGF-I knockout have demonstrated that liver-derived IGF-I, constituting a major part of circulating IGF-I, is an important endocrine factor involved in a variety of physiological and pathological processes. Detailed studies comparing the impact of liver-derived IGF-I and local bone-derived IGF-I demonstrate that both sources of IGF-I can stimulate longitudinal bone growth. We propose here that liver-derived circulating IGF-I and local bone-derived IGF-I to some extent have overlapping growth-promoting effects and might have the capacity to replace each other (= redundancy) in the maintenance of normal longitudinal bone growth. Importantly, and in contrast to the regulation of longitudinal bone growth, locally derived IGF-I cannot replace (= lack of redundancy) liver-derived IGF-I for the regulation of a large number of other parameters including GH secretion, cortical bone mass, kidney size, prostate size, peripheral vascular resistance, spatial memory, sodium retention, insulin sensitivity, liver size, sexually dimorphic liver functions, and progression of some tumors. It is clear that a major role of liver-derived IGF-I is to regulate GH secretion and that some, but not all, of the phenotypes in the liver-specific IGF-I knockout mice are indirect, mediated via the elevated GH levels. All of the described multiple endocrine effects of liver-derived IGF-I should be considered in the development of possible novel treatment strategies aimed at increasing or reducing endocrine IGF-I activity.

The C-terminal cytoplasmic domain of human proEGF is a negative modulator of body and organ weights in transgenic mice

We generated transgenic mice to study the in vivo role of the cytoplasmic domain of human proEGF (proEGFcyt). Post-pubertal proEGFcyt transgenic (tg) mice displayed an up to 15% reduction in body weight, including smaller kidney and brain weights as compared to control littermates. Renal histology, gene expression profiles, and functional parameters were normal. In both sexes, serum levels of IGFBP-3 were reduced. Circulating IGF-I/IGF-II levels were unchanged. Histomorphological analysis revealed isolated foci of liver necrosis specific to proEGFcyt tg mice. In conclusion, we identified proEGF cytoplasmic domain as a novel modulator of whole body and organ-specific growth in mice.

Decreased p44/42 mitogen-activated protein kinase phosphorylation in gender- or hormone-related but not during age-related adrenal gland growth in mice

Postnatal growth of the mouse adrenal gland shows a characteristic gender-dependent pattern, resulting in an almost 2-fold higher adrenal weight in 11-wk-old female vs. male mice. We demonstrated that the higher weight of the adrenal glands in female mice is due to a significantly (P < 0.05) increased growth rate in female mice and a shorter growth phase of the adrenal glands in male mice (P < 0.05). To address the signaling mechanisms underlying these differential growth patterns, we evaluated the phosphorylation levels of p44/42 and p38 MAPK. In female mice, age-dependent reductions of p38 MAPK phosphorylation were found between wk 3 and 9 (47% reduction; P < 0.05). At the age of 11 wk, the p38 MAPK phosphorylation level in female adrenal glands was about 60% lower than in the male counterparts (P < 0.01). Similarly, the phosphorylation level of p44/42 MAPK was 50% lower in female adrenal glands (P < 0.001). Reduced activation of p44/42 MAPK was also observed after growth stimulation of the adrenal glands in male mice after ACTH treatment (-36%; P < 0.001) or by expression of a GH transgene (-34%; P < 0.001), whereas p38 MAPK, JNK, or PDK1 activation was unaffected. From our findings in three independent mouse models where partial deactivation of p44/42 MAPK was observed under conditions of elevated growth, we suggest a function of p44/42 MAPK for adrenal growth and a role of p44/42 MAPK for the integration of different endocrine stimuli.

Conditional deletion of insulin-like growth factor-I in collagen type 1alpha2-expressing cells results in postnatal lethality and a dramatic reduction in bone accretion

IGF-I acts through endocrine and local, autocrine/paracrine routes. Disruption of both endocrine and local IGF-I action leads to neonatal lethality and impaired growth in various tissues including bone; however, the severity of growth and skeletal phenotype caused by disruption of endocrine IGF-I action is far less than with total IGF-I disruption. Based on these data and the fact that bone cells express IGF-I in high abundance, we and others predicted that locally produced IGF-I is also critical in regulating growth and bone accretion. To determine the role of local IGF-I, type 1alpha2 collagen-Cre mice were crossed with IGF-I loxP mice to generate Cre+ (conditional mutant) and Cre- (control) loxP homozygous mice. Surprisingly, approximately 40-50% of the conditional mutants died at birth, which is similar to total IGF-I disruption, but not observed in mice lacking circulating IGF-I. Expression of IGF-I in bone and muscle but not liver and brain was significantly decreased in the conditional mutant. Accordingly, circulating levels of serum IGF-I were also not affected. Disruption of local IGF-I dramatically reduced body weight 28-37%, femur areal bone mineral density 10-25%, and femur bone size 18-24% in growing mice. In addition, mineralization was reduced as early as during embryonic development. Consistently, histomorphometric analysis determined impaired osteoblast function as demonstrated by reduced mineral apposition rate (14-30%) and bone formation rate (35-57%). In conclusion, both local and endocrine IGF-I actions are involved in regulating growth of various tissues including bone, but they act via different mechanisms.