Inactivation of the acid labile subunit gene in mice results in mild retardation of postnatal growth despite profound disruptions in the circulating insulin-like growth factor system

Endocrine and cellular physiology and pathology of the insulin-like growth factor acid-labile subunit

The acid-labile subunit (ALS) of the insulin-like growth factor (IGF) binding protein (IGFBP) complex, encoded in humans by IGFALS, has a vital role in regulating the endocrine transport and bioavailability of IGF-1 and IGF-2. Accordingly, ALS has a considerable influence on postnatal growth and metabolism. ALS is a leucine-rich glycoprotein that forms high-affinity ternary complexes with IGFBP-3 or IGFBP-5 when they are occupied by either IGF-1 or IGF-2. These complexes constitute a stable reservoir of circulating IGFs, blocking the potentially hypoglycaemic activity of unbound IGFs. ALS is primarily synthesized by hepatocytes and its expression is lower in non-hepatic tissues. ALS synthesis is strongly induced by growth hormone and suppressed by IL-1β, thus potentially serving as a marker of growth hormone secretion and/or activity and of inflammation. IGFALS mutations in humans and Igfals deletion in mice cause modest growth retardation and pubertal delay, accompanied by decreased osteogenesis and enhanced adipogenesis. In hepatocellular carcinoma, IGFALS is described as a tumour suppressor; however, its contribution to other cancers is not well delineated. This Review addresses the endocrine physiology and pathology of ALS, discusses the latest cell and proteomic studies that suggest emerging cellular roles for ALS and outlines its involvement in other disease states.

Plasma Proteomic Analysis Reveals the Potential Role of Lectin and Alternative Complement Pathways in IgA Vasculitis Pathogenesis

BACKGROUND

IgA vasculitis (IgAV) is the most common form of childhood vasculitis. A better understanding of its pathophysiology is required to identify new potential biomarkers and treatment targets.

OBJECTIVE

to assess the underlying molecular mechanisms in the pathogenesis of IgAV using an untargeted proteomics approach.

METHODS

Thirty-seven IgAV patients and five healthy controls were enrolled. Plasma samples were collected on the day of diagnosis before any treatment was initiated. We used nano-liquid chromatography-tandem mass spectrometry (nLC-MS/MS) to investigate the alterations in plasma proteomic profiles. For the bioinformatics analyses, databases including Uniprot, PANTHER, KEGG, Reactome, Cytoscape, and IntAct were used.

RESULTS

Among the 418 proteins identified in the nLC-MS/MS analysis, 20 had significantly different expressions in IgAV patients. Among them, 15 were upregulated and 5 were downregulated. According to the KEGG pathway and function classification analysis, complement and coagulation cascades were the most enriched pathways. GO analyses showed that the differentially expressed proteins were mainly involved in defense/immunity proteins and the metabolite interconversion enzyme family. We also investigated molecular interactions in the identified 20 proteins of IgAV patients. We extracted 493 interactions from the IntAct database for the 20 proteins and used Cytoscape for the network analyses.

CONCLUSION

Our results clearly suggest the role of the lectin and alternate complement pathways in IgAV. The proteins defined in the pathways of cell adhesion may serve as biomarkers. Further functional studies may lead the way to better understanding of the disease and new therapeutic options for IgAV treatment.

Nutritional status affects Igf1 regulation of skeletal muscle myogenesis, myostatin, and myofibrillar protein degradation pathways in gopher rockfish (Sebastes carnatus)

Insulin-like growth factor-1 (Igf1) regulates skeletal muscle growth in fishes by increasing protein synthesis and promoting muscle hypertrophy. When fish experience periods of insufficient food intake, they undergo slower muscle growth or even muscle wasting, and those changes emerge in part from nutritional modulation of Igf1 signaling. Here, we examined how food deprivation (fasting) modulates Igf1 regulation of liver and skeletal muscle gene expression in gopher rockfish (Sebastes carnatus), a nearshore rockfish of importance for commercial and recreational fisheries in the northeastern Pacific Ocean, to understand how food limitation impacts Igf regulation of muscle growth pathways. Rockfish were either fed or fasted for 14 d, after which a subset of fish from each group was treated with recombinant Igf1 from sea bream (Sparus aurata). Fish that were fasted lost body mass and had lower body condition, reduced hepatosomatic index, and lower plasma Igf1 concentrations, as well as a decreased abundance of igf1 gene transcripts in the liver, increased hepatic mRNAs for Igf binding proteins igfbp1a, igfbp1b, and igfbp3a, and decreased mRNA abundances for igfbp2b and a putative Igf acid labile subunit (igfals) gene. In skeletal muscle, fasted fish showed a reduced abundance of intramuscular igf1 mRNAs but elevated gene transcripts encoding Igf1 receptors A (igf1ra) and B (igf1rb), which also showed downregulation by Igf1. Fasting increased skeletal muscle mRNAs for myogenin and myostatin1, as well as ubiquitin ligase F-box only protein 32 (fbxo32) and muscle RING-finger protein-1 (murf1) genes involved in muscle atrophy, while concurrently downregulating mRNAs for myoblast determination protein 2 (myod2), myostatin2, and myogenic factors 5 (myf5) and 6 (myf6 encoding Mrf4). Treatment with Igf1 downregulated muscle myostatin1 and fbxo32 under both feeding conditions, but showed feeding-dependent effects on murf1, myf5, and myf6/Mrf4 gene expression indicating that Igf1 effects on muscle growth and atrophy pathways is contingent on recent food consumption experience.

Novel IGFALS mutations with predicted pathogenetic effects by the analysis of AlphaFold structure

PURPOSE

According to the American College of Medical Genetics (ACMG) classification, variants of uncertain significance (VUS) are gene variations whose impact on the disease risk is not yet known. VUS, therefore, represent an unmet need for genetic counselling. Aim of the study is the use the AlphaFold artificial intelligence algorithm to predict the impact of novel mutations of the IGFALS gene, detected in a subject with short stature and initially classified as VUS according to the ACMG classification.

METHODS

A short-stature girl and her parents have been investigated. IGFALS mutations have been detected through clinical exome and confirmed by Sanger sequencing. The potential presence of co-occurring gene alterations was investigated in the proband by whole exome and CGH array. Structure of the ALS protein (encoded by the IGFALS gene) was evaluated through the AlphaFold artificial intelligence algorithm.

RESULTS

Two IGFALS variants were found in the proband: c.1349T > C (p.Leu450Pro) and c.1363_1365delCTC (p.Leu455del), both classified as VUS, according to ACMG. Parents' analysis highlighted the in trans position of the two variants. AlphaFold showed that the mutated positions were found the concave side a horseshoe structure of the ALS protein, likely interfering with protein-protein interactions. According to a loss of function (LoF) effect of the two variants, reduced levels of the IGF1 and IGFBP-3 proteins, as well as a growth hormone (GH) excess were detected in the proband's serum.

CONCLUSIONS

By using the AlphaFold structure we were able to predict two IGFALS gene mutations initially classified as VUS, as potentially pathogenetic. Our proof-of-concept showed a potential application of AlphaFold as tool to a better inform VUS interpretation of genetic tests.

Insulin signaling in the long-lived reproductive caste of ants

In most organisms, reproduction is correlated with shorter life span. However, the reproductive queen in eusocial insects exhibits a much longer life span than that of workers. In Harpegnathos ants, when the queen dies, workers can undergo an adult caste switch to reproductive pseudo-queens (gamergates), exhibiting a five-times prolonged life span. To explore the relation between reproduction and longevity, we compared gene expression during caste switching. Insulin expression is increased in the gamergate brain that correlates with increased lipid synthesis and production of vitellogenin in the fat body, both transported to the egg. This results from activation of the mitogen-activated protein kinase (MAPK) branch of the insulin signaling pathway. By contrast, the production in the gamergate developing ovary of anti-insulin Imp-L2 leads to decreased signaling of the AKT/forkhead box O (FOXO) branch in the fat body, which is consistent with their extended longevity.

The role of the IGF system in mammary physiology of ruminants

The IGF system plays a central role in all stages of mammary development, lactation and involution. IGFs exert their effects on the mammary gland through both endocrine and paracrine/autocrine mechanisms and the importance of circulating versus local IGF action remains an open question, especially in ruminants. At the whole organ level, a critical role for IGFs in ductal morphogenesis and lobuloalveolar development has been established, while at the cellular level the ability of IGFs to stimulate cell proliferation and control cell survival contributes to the number of milk-secreting cells in the gland. Much of this work has been conducted in rodents which provide an affordable research model and allow for genetic manipulation of specific components of the IGF system. Research into the role of the IGF system in dairy cows has generally supported information obtained with rodents though large gaps in our knowledge remain and species differences are not well defined. Examples include whether exogenous somatotropin exerts its effects on the mammary gland through local IGF-1 synthesis which is accepted dogma in rodents, what the role of IGF-1 versus IGF-2 is in the mammary gland, and how the IGFBPs regulate IGF bioactivity. This last area is particularly under-investigated in ruminants both at the whole animal and the cellular and molecular levels. Given that the IGF system may underlie many management practices that could contribute to enhancing productive efficiency of lactation, more research into the basic biology of this important system is warranted.

Mice with gene alterations in the GH and IGF family

Much of our understanding of GH's action stems from animal models and the generation and characterization of genetically altered or modified mice. Manipulation of genes in the GH/IGF1 family in animals started in 1982 when the first GH transgenic mice were produced. Since then, multiple laboratories have altered mouse DNA to globally disrupt Gh, Ghr, and other genes upstream or downstream of GH or its receptor. The ability to stay current with the various genetically manipulated mouse lines within the realm of GH/IGF1 research has been daunting. As such, this review attempts to consolidate and summarize the literature related to the initial characterization of many of the known gene-manipulated mice relating to the actions of GH, PRL and IGF1. We have organized the mouse lines by modifications made to constituents of the GH/IGF1 family either upstream or downstream of GHR or to the GHR itself. Available data on the effect of altered gene expression on growth, GH/IGF1 levels, body composition, reproduction, diabetes, metabolism, cancer, and aging are summarized. For the ease of finding this information, key words are highlighted in bold throughout the main text for each mouse line and this information is summarized in Tables 1, 2, 3 and 4. Most importantly, the collective data derived from and reported for these mice have enhanced our understanding of GH action.

Identification of serum prognostic biomarkers of severe COVID-19 using a quantitative proteomic approach

The COVID-19 pandemic is an unprecedented threat to humanity that has provoked global health concerns. Since the etiopathogenesis of this illness is not fully characterized, the prognostic factors enabling treatment decisions have not been well documented. Accurately predicting the progression of the disease would aid in appropriate patient categorization and thus help determine the best treatment option. Here, we have introduced a proteomic approach utilizing data-independent acquisition mass spectrometry (DIA-MS) to identify the serum proteins that are closely associated with COVID-19 prognosis. Twenty-seven proteins were differentially expressed between severely ill COVID-19 patients with an adverse or favorable prognosis. Ingenuity Pathway Analysis revealed that 15 of the 27 proteins might be regulated by cytokine signaling relevant to interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF), and their differential expression was implicated in the systemic inflammatory response and in cardiovascular disorders. We further evaluated practical predictors of the clinical prognosis of severe COVID-19 patients. Subsequent ELISA assays revealed that CHI3L1 and IGFALS may serve as highly sensitive prognostic markers. Our findings can help formulate a diagnostic approach for accurately identifying COVID-19 patients with severe disease and for providing appropriate treatment based on their predicted prognosis.

Applying Bioinformatic Platforms, In Vitro, and In Vivo Functional Assays in the Characterization of Genetic Variants in the GH/IGF Pathway Affecting Growth and Development

Heritability accounts for over 80% of adult human height, indicating that genetic variability is the main determinant of stature. The rapid technological development of Next-Generation Sequencing (NGS), particularly Whole Exome Sequencing (WES), has resulted in the characterization of several genetic conditions affecting growth and development. The greatest challenge of NGS remains the high number of candidate variants identified. In silico bioinformatic tools represent the first approach for classifying these variants. However, solving the complicated problem of variant interpretation requires the use of experimental approaches such as in vitro and, when needed, in vivo functional assays. In this review, we will discuss a rational approach to apply to the gene variants identified in children with growth and developmental defects including: (i) bioinformatic tools; (ii) in silico modeling tools; (iii) in vitro functional assays; and (iv) the development of in vivo models. While bioinformatic tools are useful for a preliminary selection of potentially pathogenic variants, in vitro—and sometimes also in vivo—functional assays are further required to unequivocally determine the pathogenicity of a novel genetic variant. This long, time-consuming, and expensive process is the only scientifically proven method to determine causality between a genetic variant and a human genetic disease.

Insulin-like growth factors: Ligands, binding proteins, and receptors

BACKGROUND

The insulin-like growth factor family of ligands (IGF-I, IGF-II, and insulin), receptors (IGF-IR, M6P/IGF-IIR, and insulin receptor [IR]), and IGF-binding proteins (IGFBP-1-6) play critical roles in normal human physiology and disease states.

SCOPE OF REVIEW

Insulin and insulin receptors are the focus of other chapters in this series and will therefore not be discussed further. Here we review the basic components of the IGF system, their role in normal physiology and in critical pathology's. While this review concentrates on the role of IGFs in human physiology, animal models have been essential in providing understanding of the IGF system, and its regulation, and are briefly described.

MAJOR CONCLUSIONS

IGF-I has effects via the circulation and locally within tissues to regulate cellular growth, differentiation, and survival, thereby controlling overall body growth. IGF-II levels are highest prenatally when it has important effects on growth. In adults, IGF-II plays important tissue-specific roles, including the maintenance of stem cell populations. Although the IGF-IR is closely related to the IR it has distinct physiological roles both on the cell surface and in the nucleus. The M6P/IGF-IIR, in contrast, is distinct and acts as a scavenger by mediating internalization and degradation of IGF-II. The IGFBPs bind IGF-I and IGF-II in the circulation to prolong their half-lives and modulate tissue access, thereby controlling IGF function. IGFBPs also have IGF ligand-independent cell effects.

Mouse models of growth hormone insensitivity

Growth hormone (GH) induces pleiotropic effects on growth and metabolism via binding and subsequent activation of the growth hormone receptor (GHR) and its downstream signaling pathways. Growth hormone insensitivity (GHI) describes a group of disorders in which there is resistance to the action of GH and resultant insulin-like growth factor I (IGF-I) deficiency. GHI is commonly due to genetic disorders of the GH receptor causing GH receptor deficiency (e.g. Laron Syndrome (LS)), decreased activation of GHR, or defects in post-receptor signaling molecules. Genetically altered mouse lines have been invaluable to better understand the physiological impact of GHI due to the ability to do invasive and longitudinal measures of metabolism, growth, and health on a whole animal or in individual tissues/cells. In the current review, the phenotype of mouse lines with GHI will be reviewed. Mouse lines to be discussed include: 1) GHR-/- mice with a gene disruption in the GHR that results in no functional GHR throughout life, also referred to as the Laron mouse, 2) mice with temporal loss of GHR (aGHRKO) starting at 6 weeks of age, 3) mice transgenic for a GHR antagonist (GHA mice), 4) mice with GHI in select tissues or cells generated via Cre-lox or related technology, and 5) assorted mice with defects in post-receptor signaling molecules. Collectively, these mouse lines have revealed an intriguing role of GH action in health, disease, and aging.

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.

The role of acid-labile subunit (ALS) in the modulation of GH-IGF-I action

Acid-labile subunit (ALS) deficiency (ACLSD) constitutes the first monogenic defect involving a member of the Insulin-like Growth Factor (IGF) binding protein system. The lack of ALS completely disrupts the circulating IGF system. Autocrine/paracrine action of local produced IGF-I could explain the mild effect on growth. In the present work we have revised the more relevant clinical and biochemical consequences of complete ACLSD in 61 reported subjects from 31 families. Low birth weight and/or length, reduced head circumference, height between -2 and -3 SD, pubertal delay and insulin resistance are commonly observed. Partial ACLSD could be present in children initially labeled as idiopathic short stature, presenting low IGF-I levels, suggesting that one functional IGFALS allele is insufficient to stabilize ternary complexes. Dysfunction of the GH-IGF axis observed in ACLSD may eventually result in increased risk for type-2 diabetes and tumor progression. Consequently, long term surveillance is recommended in these patients.

Expression of acid-labile subunit (ALS) in developing and adult zebrafish and its role in dorso-ventral patterning during development

Mammalian acid-labile subunit (ALS) is a serum protein that binds binary complexes between Insulin-like growth factors (IGFs) and Insulin-like growth factor-binding proteins (IGFBPs) extending their half-life and keeping them in the vasculature. Human ALS deficiency (ACLSD), due to homozygous or compound heterozygous mutations in IGFALS, leads to moderate short stature with reduced levels of IGF-I and IGFBP-3. There is only one corresponding zebrafish ortholog gene and it has not yet been studied. In this study we elucidate the role of igfals during zebrafish development. In zebrafish embryos igfals mRNA is expressed throughout development, mainly in the brain and subsequently also in the gut and swimbladder. To determine its role during development, we knocked down igfals gene product using morpholinos (MOs). Igfals morphant embryos displayed dorsalization in different degrees of severity, including a shortened trunk and loss of tail. Furthermore, co-injection of human IGFALS (hIGFALS) mRNA was able to rescue the MO-induced phenotype. Finally, overexpression of either hIGFALS or zebrafish igfals (zigfals) mRNA leads to ventralization of embryos including a reduced head and enlarged tail. These findings suggest that als plays an important role in dorso-ventral patterning during zebrafish development.

Disorders of IGFs and IGF-1R signaling pathways

The insulin-like growth factor (IGF) system comprises two ligands, IGF-I and IGF-II, that regulate multiple physiological processes, including mammalian development, metabolism and growth, through the type 1 IGF receptor (IGF-1R). The growth hormone (GH)-IGF-I axis is the major regulator of longitudinal growth. IGF-II is expressed in many tissues, notably the placenta, to regulate human pre- and post-natal growth and development. This review provides a brief introduction to the IGF system and summarizes findings from reports arising from recent larger genomic sequencing studies of human genetic mutations in IGF1 and IGF2 and genes of proteins regulating IGF action, namely the IGF-1R, IGF-1R signaling pathway components and the IGF binding proteins (IGFBPs). A perspective on the effect of homozygous mutations on structure and function of the IGFs and IGF-1R is also given and this is related to the effects on growth.

The Actions of IGF-1 in the Growth Plate and Its Role in Postnatal Bone Elongation

PURPOSE OF REVIEW

Bone elongation is a complex process driven by multiple intrinsic (hormones, growth factors) and extrinsic (nutrition, environment) variables. Bones grow in length by endochondral ossification in cartilaginous growth plates at ends of developing long bones. This review provides an updated overview of the important factors that influence this process.

RECENT FINDINGS

Insulin-like growth factor-1 (IGF-1) is the major hormone required for growth and a drug for treating pediatric skeletal disorders. Temperature is an underrecognized environmental variable that also impacts linear growth. This paper reviews the current state of knowledge regarding the interaction of IGF-1 and environmental factors on bone elongation. Understanding how internal and external variables regulate bone lengthening is essential for developing and improving treatments for an array of bone elongation disorders. Future studies may benefit from understanding how these unique relationships could offer realistic new approaches for increasing bone length in different growth-limiting conditions.

An internal deletion of ADAR rescued by MAVS deficiency leads to a minute phenotype

The RNA-editing protein ADAR is essential for early development in the mouse. Genetic evidence suggests that A to I editing marks endogenous RNAs as ‘self’. Today, different Adar knockout alleles have been generated that show a common phenotype of apoptosis, liver disintegration, elevated immune response and lethality at E12.5. All the Adar knockout alleles can be rescued by a concomitant deletion of the innate immunity genes Mavs or Ifih1 (MDA5), albeit to different extents. This suggests multiple functions of ADAR. We analyze Adar^Δ7-9 mice that show a unique growth defect phenotype when rescued by Mavs. We show that Adar^Δ7-9 can form a truncated, unstable, editing deficient protein that is mislocalized. Histological and hematologic analysis of these mice indicate multiple tissue- and hematopoietic defects. Gene expression profiling shows dysregulation of Rps3a1 and Rps3a3 in rescued Adar^Δ7-9. Consistently, a distortion in 40S and 60S ribosome ratios is observed in liver cells. This dysregulation is also seen in Adar^Δ2-13; Mavs^−/− but not in Adar^E861A/E861A; Ifih1^−/− mice, suggesting editing-independent functions of ADAR in regulating expression levels of Rps3a1 and Rps3a3. In conclusion, our study demonstrates the importance of ADAR in post-natal development which cannot be compensated by ADARB1.

The IGF system and longitudinal growth in preterm infants in relation to gestational age, birth weight and gender

OBJECTIVE

Growth factors in the blood of very preterm infants may reflect growth and contribute to the understanding of early development. We investigated postnatal levels of insulin-like growth factors (IGFs) in infants born very preterm and related them to early growth development.

DESIGN

Blood samples were analyzed weekly for IGF-I, IGF-II, IGF binding protein (BP)-1, IGFBP-3, and acid-label subunit (ALS).

METHODS

73 children born very preterm (gestational age (GA) <32 weeks) were divided according to their gender-specific birth weight standard deviation score (SDS) into either appropriate for GA (AGA) or small for GA (SGA). Fifty-two (71%) and forty-three (59%) infants completed follow-up with anthropometry at approximately 3 years and at 5 years of age respectively. Thirty-six subjects (49%) had blood sampling for IGF-I and IGFBP-3 measurements up to 3 years of age.

RESULTS

IGF-I, IGFBP-3, and ALS levels increased in all groups from week 31 to week 36, with generally lower levels in the SGAs, with a concomitant lower growth velocity. Postnatal ALS was strongly associated with IGF-I and IGFBP-3 in boys, girls and AGA infants. IGF-II was higher in earlier born preterms (GA < 27 weeks) at postmenstrual ages 27.5-29.9 weeks compared with SGAs and late GA (GA ≥ 27 weeks) preterms (p < .0001). IGF-II, in contrast to IGF-I, did not differ between SGAs and AGAs at weeks 31-36. Mean IGFBP-1 was highest in the SGAs compared to AGAs at mean week 28,5 and 31 (p = .001) and IGFBP-1 levels were elevated in relation to IGF-I in the SGAs at that period. At follow-up, the increase in IGF-I between week 31 and 33.5 was a significant positive determinant of height SDS at 3 and 5 years of age in forward multiple regression analysis, independent of target height.

CONCLUSION

This is the first study to investigate postnatal ALS levels in preterm infants. In very preterm infants, IGF-II is less affected by size at birth during early postnatal weeks compared with IGF-I. Early elevated IGFBP-1 might protect the SGA infants from an intense metabolic rate. Our results indicate that anabolic and metabolic processes during weeks 31-36 predicts later height.

Neuron-specific Mafb knockout causes growth retardation accompanied by an impaired growth hormone/insulin-like growth factor I axis

Mammalian postnatal growth is regulated primarily by the growth hormone (GH)/insulin-like growth factor I (IGF-I) axis. MafB is a basic leucine zipper (bZip) transcription factor that has pleiotropic functions. Although MafB plays a critical role in fetal brain development, such as in guidance for hindbrain segmentation, its postnatal role in neurons remains to be elucidated. To investigate this, we used neuron-specific Mafb conditional knockout (cKO) mice. In addition to an approximately 50% neonatal viability, the Mafb cKO mice exhibited growth retardation without apparent signs of low energy intake. Notably, serum IGF-I levels of these mice in the postnatal stage were lower than those of control mice. They seemed to have a neuroendocrine dysregulation, as shown by the upregulation of serum GH levels in the resting state and an inconsistent secretory response of GH upon administration of growth hormone-releasing hormone. These findings reveal that neuronal MafB plays an important role in postnatal development regulated by the GH/IGF-I axis.

The tammar wallaby: a non-traditional animal model to study growth axis maturation

Maturation of the growth hormone (GH)/insulin-like growth factor 1 (IGF1) axis is a critical developmental event that becomes functional over the peripartum period in precocial eutherian mammals such as sheep. In mice and marsupials that give birth to altricial young, the GH/IGF1 axis matures well after birth, suggesting that functional maturation is associated with developmental stage, not parturition. Recent foster-forward studies in one marsupial, the tammar wallaby (Macropus eugenii), have corroborated this hypothesis. 'Fostering' tammar young not only markedly accelerates their development and growth rates, but also affects the timing of maturation of the growth axis compared with normal growing young, providing a novel non-traditional animal model for nutritional manipulation. This review discusses how nutrition affects the maturation of the growth axis in marsupials compared with traditional eutherian animal models.

Nonclassical GH Insensitivity: Characterization of Mild Abnormalities of GH Action

GH insensitivity (GHI) presents in childhood with growth failure and in its severe form is associated with extreme short stature and dysmorphic and metabolic abnormalities. In recent years, the clinical, biochemical, and genetic characteristics of GHI and other overlapping short stature syndromes have rapidly expanded. This can be attributed to advancing genetic techniques and a greater awareness of this group of disorders. We review this important spectrum of defects, which present with phenotypes at the milder end of the GHI continuum. We discuss their clinical, biochemical, and genetic characteristics. The objective of this review is to clarify the definition, identification, and investigation of this clinically relevant group of growth defects. We also review the therapeutic challenges of mild GHI.

Adipocyte GR Inhibits Healthy Adipose Expansion Through Multiple Mechanisms in Cushing Syndrome

In Cushing syndrome, excessive glucocorticoids lead to metabolic disturbances, such as insulin resistance, adipocyte hypertrophy, and liver steatosis. In vitro experiments have highlighted the importance of adipocyte glucocorticoid receptor (GR), but its metabolic roles in vivo have not been fully elucidated in Cushing syndrome. In this study, using clinical samples from patients with Cushing syndrome and adipocyte-specific GR knockout (AGRKO) mice, we investigated the roles of adipocyte GR and its clinical relevance in Cushing syndrome. Under chronic treatment with corticosterone, AGRKO mice underwent healthy adipose expansion with diminished ectopic lipid deposition and improved insulin sensitivity. These changes were associated with Atgl-mediated lipolysis through a novel intronic glucocorticoid-responsive element. Additionally, integrated analysis with RNA sequencing of AGRKO mice and clinical samples revealed that healthy adipose expansion was associated with dysregulation of tissue remodeling, preadipocyte proliferation, and expression of the circadian gene. Thus, our study revealed the roles of adipocyte GR on healthy adipose expansion and its multiple mechanisms in Cushing syndrome.

The insulin-like growth factor-1 system in the adult mammalian brain and its implications in central maternal adaptation

Our knowledge on the bioavailability and actions of insulin-like growth factor-1 (IGF-1) has markedly expanded in recent years as novel mechanisms were discovered on IGF binding proteins (IGFBPs) and their ability to release IGF-1. The new discoveries allowed a better understanding of the endogenous physiological actions of IGF-1 and also its applicability in therapeutics. The focus of the present review is to summarize novel findings on the neuronal, neuroendocrine and neuroplastic actions of IGF-1 in the adult brain. As most of the new regulatory mechanisms were described in the periphery, their implications on brain IGF system will also be covered. In addition, novel findings on the effects of IGF-1 on lactation and maternal behavior are described. Based on the enormous neuroplastic changes related to the peripartum period, IGF-1 has great but largely unexplored potential in maternal adaptation of the brain, which is highlighted in the present review.

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.

Differential tissue response to growth hormone in mice

Growth hormone (GH) has been shown to act directly on multiple tissues throughout the body. Historically, it was believed that GH acted directly in the liver and only indirectly in other tissues via insulin-like growth hormone 1 (IGF-1). Despite extensive work to describe GH action in individual tissues, a comparative analysis of acute GH signaling in key metabolic tissues has not been performed. Herein, we address this knowledge gap. Acute tissue response to human recombinant GH was assessed in mice by measuring signaling via phospho-STAT5 immunoblotting. STAT5 activation is an easily and reliably detected early marker of GH receptor engagement. We found differential tissue sensitivities; liver and kidney were equally GH-sensitive and more sensitive than white adipose tissue, heart, and muscle (gastrocnemius). Gastrocnemius had the greatest maximal response compared to heart, liver, white adipose tissue, and whole kidney. Differences in maximum responsiveness were positively correlated with tissue STAT5 abundance, while differences in sensitivity were not explained by differences in GH receptor levels. Thus, GH sensitivity and responsiveness of distinct metabolic tissues differ and may impact physiology and disease.

Extensive phenotypic characterization of a new transgenic mouse reveals pleiotropic perturbations in physiology due to mesenchymal hGH minigene expression

The human growth hormone (hGH) minigene used for transgene stabilization in mice has been recently identified to be locally expressed in the tissues where transgenes are active and associated with phenotypic alterations. Here we extend these findings by analyzing the effect of the hGH minigene in TgC6hp55 transgenic mice which express the human TNFR1 under the control of the mesenchymal cell-specific CollagenVI promoter. These mice displayed a fully penetrant phenotype characterized by growth enhancement accompanied by perturbations in metabolic, skeletal, histological and other physiological parameters. Notably, this phenotype was independent of TNF-TNFR1 signaling since the genetic ablation of either Tnf or Tradd did not rescue the phenotype. Further analyses showed that the hGH minigene was expressed in several tissues, also leading to increased hGH protein levels in the serum. Pharmacological blockade of GH signaling prevented the development of the phenotype. Our results indicate that the unplanned expression of the hGH minigene in CollagenVI expressing mesenchymal cells can lead through local and/or systemic mechanisms to enhanced somatic growth followed by a plethora of primary and/or secondary effects such as hyperphagia, hypermetabolism, disturbed glucose homeostasis, altered hematological parameters, increased bone formation and lipid accumulation in metabolically critical tissues.

Comparison of pulsatile vs. continuous administration of human placental growth hormone in female C57BL/6J mice

Exogenous growth hormone has different actions depending on the method of administration. However, the effects of different modes of administration of the placental variant of growth hormone on growth, body composition and glucose metabolism have not been investigated. In this study, we examined the effect of pulsatile vs. continuous administration of recombinant variant of growth hormone in a normal mouse model. Female C57BL/6J mice were randomized to receive vehicle or variant of growth hormone (2 or 5 mg/kg per day) by daily subcutaneous injection (pulsatile) or osmotic pump for 6 days. Pulsatile treatment with 2 and 5 mg/kg per day significantly increased body weight. There was also an increase in liver, kidney and spleen weight via pulsatile treatment, whereas continuous treatment did not affect body weight or organ size. Pulsatile treatment with 5 mg/kg per day significantly increased fasting plasma insulin concentration, whereas with continuous treatment, fasting insulin concentration was not significantly different from the vehicle-treated control. However, a dose-dependent increase in fasting insulin concentration and decrease in insulin sensitivity, as assessed by HOMA, was observed with both modes of treatment. At 5 mg/kg per day, hepatic growth hormone receptor expression was increased compared to vehicle-treated animals, by both modes of administration. Pulsatile variant of growth hormone did not alter the plasma insulin-like growth factor-1 concentration, whereas a slight decrease was observed with continuous variant of growth hormone treatment. Neither pulsatile nor continuous treatment affected hepatic insulin-like growth factor-1 mRNA expression. Our findings suggest that pulsatile variant of growth hormone treatment was more effective in stimulating growth but caused marked hyperinsulinemia in mice.

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.

Pappa2 deletion alters IGFBPs but has little effect on glucose disposal or adiposity

OBJECTIVE

Insulin-like growth factor binding proteins (IGFBPs) are involved in glucose and lipid metabolism, and their actions are modulated by proteases. The aim of this study was to examine the effects of an IGFBP-5 protease, pregnancy associated plasma protein-A2 (PAPP-A2), on glucose metabolism and susceptibility to diet-induced obesity.

DESIGN

Postnatal growth, circulating IGF-I, IGFBP-3 and IGFBP-5 levels, and glucose tolerance were measured in Pappa2 deletion mice and littermate controls on a chow diet. Males were subsequently fed a high-fat diet for 8 weeks to measure weight gain and adiposity, as well as glucose tolerance in response to a metabolic challenge.

RESULTS

Circulating IGFBP-5 levels were ~2-fold higher in mice with no functional PAPP-A2 than in littermate controls, as expected. In contrast, circulating IGFBP-3 levels were reduced by ~15-fold, and total IGF-I levels were ~60% higher in Pappa2 deletion mice. There was no effect of Pappa2 deletion on fasting blood glucose levels or glucose clearance after intraperitoneal injection of 2g glucose/kg body weight in mice on a chow diet. In males on a high-fat diet, there was no difference between genotypes in weight gain or adiposity, adjusting for differences in initial body weight, or in fasting blood glucose or insulin levels, or in glucose clearance.

CONCLUSIONS

Despite a dramatic disruption of the balance between circulating IGF-I, IGFBP-3 and -5, we found no effects of Pappa2 deletion on glucose metabolism, weight gain or adiposity on a high-fat diet.

Dysregulation of energy balance by trichothecene mycotoxins: Mechanisms and prospects

Trichothecenes are toxic metabolites produced by fungi that constitute a worldwide hazard for agricultural production and both animal and human health. More than 40 countries have introduced regulations or guidelines for food and feed contamination levels of the most prevalent trichothecene, deoxynivalenol (DON), on the basis of its ability to cause growth suppression. With the development of analytical tools, evaluation of food contamination and exposure revealed that a significant proportion of the human population is chronically exposed to DON doses exceeding the provisional maximum tolerable daily dose. Accordingly, a better understanding of trichothecene impact on health is needed. Upon exposure to low or moderate doses, DON and other trichothecenes induce anorexia, vomiting and reduced weight gain. Several recent studies have addressed the mechanisms by which trichothecenes induce these symptoms and revealed a multifaceted action targeting gut, liver and brain and causing dysregulation in neuroendocrine signaling, immune responses, growth hormone axis, and central neurocircuitries involved in energy homeostasis. Newly identified trichothecene toxicosis biomarkers are just beginning to be exploited and already open up new questions on the potential harmful effects of chronic exposure to DON at apparently asymptomatic very low levels. This review summarizes our current understanding of the effects of DON and other trichothecenes on food intake and weight growth.

Heterogeneity of the growth phenotype and birth size in acid-labile subunit (ALS) deficiency

PURPOSE

The IGFALS gene encodes the acid-labile subunit (ALS) protein, which regulates circulating IGF-1. Human IGFALS mutations cause growth hormone insensitivity (GHI) associated with ALS, IGF-1 and IGFBP-3 deficiencies and mild to moderate postnatal growth impairment (height SDS -2 to -4). Prenatal growth impairment is not a recognised feature of this disorder, but heterozygous carriers may show an intermediate phenotype.

METHODS

We report a family of five subjects, including three children born small for gestational age, who were investigated for IGFALS gene mutations.

RESULTS

The proband, an 8.7 years female with pre- and postnatal growth failure (BW SDS -3.04, Ht SDS -3.86) and biochemical features of GHI, had a homozygous mutation of IGFALS, c.401T>A; p.L134Q. Her 6.1 years brother (BW SDS -2.11, Ht SDS -2.0) had the same homozygous IGFALS mutation. Both parents [adult height SDS -1.76 (father) and -1.82 (mother)] and her 2.7 years sister (BW SDS -2.60, Ht SDS -2.04) were heterozygous for the IGFALS mutation.

CONCLUSION

Significant phenotypic heterogeneity was observed between family members, in particular varying degrees of prenatal growth retardation were present in the three siblings, which may have contributed to the variation in the postnatal growth phenotype.

The histone H3K9 demethylase Kdm3b is required for somatic growth and female reproductive function

Kdm3b is a Jumonji C domain-containing protein that demethylates mono- and di-methylated lysine 9 of histone H3 (H3K9me1 and H3K9me2). Although the enzyme activity of Kdm3b is well characterized in vitro, its genetic and physiological function remains unknown. Herein, we generated Kdm3b knockout (Kdm3bKO) mice and observed restricted postnatal growth and female infertility in these mice. We found that Kdm3b ablation decreased IGFBP-3 expressed in the kidney by 53% and significantly reduced IGFBP-3 in the blood, which caused an accelerated degradation of IGF-1 and a 36% decrease in circulating IGF-1 concentration. We also found Kdm3b was highly expressed in the female reproductive organs including ovary, oviduct and uterus. Knockout of Kdm3b in female mice caused irregular estrous cycles, decreased 45% of the ovulation capability and 47% of the fertilization rate, and reduced 44% of the uterine decidual response, which were accompanied with a more than 50% decrease in the circulating levels of the 17beta-estradiol. Importantly, these female reproductive phenotypes were associated with significantly increased levels of H3K9me1/2/3 in the ovary and uterus. These results demonstrate that Kdm3b-mediated H3K9 demethylation plays essential roles in maintenance of the circulating IGF-1, postnatal somatic growth, circulating 17beta-estradiol, and female reproductive function.

A novel homozygous mutation of the IGFALS gene in a female adolescent: indirect evidence for a contributing role of the circulating IGF-I pool in the pubertal growth spurt

BACKGROUND

Mutations of the IGFALS gene have been reported since 2004 in 24 patients, but only 5 of these are females.

CASE REPORT

We describe a 14.7-year-old female of a consanguineous Moroccan family with growth retardation and normal-onset but slow progression of puberty without manifest pubertal height gain.

RESULTS

At age 3.2 years, the patient's height was 85.5 cm (-2.9 SDS) and her weight 9.9 kg (-2.9 SDS) with a head circumference of 44.5 cm (-3.3 SDS). Serum IGF-I and IGFBP-3 concentrations were low with normal basal and stimulated growth hormone (GH) levels. An IGF-I generation test confirmed a lack of response to GH administration. While onset of puberty occurred at a normal age, no significant pubertal growth acceleration was observed despite progression of breast development. Sequencing of the IGFALS gene revealed a novel homozygous frameshift mutation (c.1291delT) with a stop codon (p.W431GfsX10) leading to undetectable serum levels of acid-labile subunit.

CONCLUSION

We report the phenotype of an adolescent girl with primary IGF-I deficiency due to a novel homozygous mutation of the IGFALS gene, who presented with growth delay, normal pubertal onset with slow progression and no pubertal growth acceleration indirectly suggesting a contributing role of the circulating IGF-I pool in the pubertal growth spurt.

Acid-labile subunit levels and the association with response to growth hormone treatment in short children born small for gestational age

AIMS

To determine acid-labile subunit (ALS) levels in short small for gestational age (SGA) children and to assess the relationship between ALS levels and several clinical and laboratory characteristics. Also, to assess whether adding ALS levels to a growth prediction model might improve the long-term growth prediction.

DESIGN/METHODS

ALS levels were measured in 312 short SGA children at the start of growth hormone (GH) treatment.

RESULTS

Median (interquartile range) ALS of all subjects was -0.5 SDS, significantly below the 0 SDS (p < 0.001). In 34 children (11%), ALS levels were ≤-2 SDS. ALS SDS correlated significantly with height SDS (r = 0.24, p < 0.001), weight SDS (r = 0.30, p < 0.001), BMI SDS (r = 0.20, p = 0.001), IGF-I SDS (r = 0.56, p < 0.001) and IGFBP-3 SDS (r = 0.67, p < 0.001). ALS SDS was also positively correlated with fasting insulin (r = 0.41, p < 0.001) and glucose levels (r = 0.33, p < 0.001), and HOMA-IR (r = 0.35, p < 0.001). Baseline ALS levels contributed to the long-term growth prediction of GH treatment (5%, p < 0.001).

CONCLUSION

Short SGA children tend to have lower ALS levels compared to controls, albeit less reduced than IGF-I and IGFBP-3 levels. Our data suggest that ALS may be involved in glucose homeostasis. Determination of ALS levels before the start of GH treatment in short SGA children contributes moderately to a more accurate prediction of the growth response to GH treatment.

Modulation of the somatotropic axis in periparturient dairy cows

This review focuses on modulation of growth hormone (GH) and its downstream actions on periparturient dairy cows undergoing physiological and metabolic adaptations. During the periparturient period, cows experience a negative energy balance implicating that the feed intake does not meet the total energy demand for the onset of lactation. To regulate this metabolic condition, key hormones of somatotropic axis such as GH, IGF-I and insulin must coordinate adaptations required for the preservation of metabolic homeostasis. The hepatic GHR1A transcript and GHR protein are reduced at parturition, but recovers on postpartum. However, plasma IGF-I concentration remains low even though hepatic abundance of the GHR and IGF-I mRNA return to pre-calving value. This might be caused by alternation in IGFBPs and ALS genes, which consequently affect the plasma IGF-I stability. Plasma insulin level declines in a parallel manner with the decrease in plasma IGF-I after parturition. Increased GH stimulates the lipolytic effects and hepatic glucose synthesis to meet the energy requirement for mammary lactose synthesis, suggesting that GH antagonizes insulin-dependent glucose uptake and attenuates insulin action to decrease gluconeogenesis.

Association of umbilical cord plasma acid-labile subunit of the insulin-like growth factor ternary complex with anthropometry in term newborns

BACKGROUND

Birth size can affect neonatal morbidity and mortality. The insulin-like growth factor (IGF) system is the most important endocrine factor influencing fetal growth. In the circulation, IGFs (mostly IGF-I) are bound to IGF-binding protein 3 (IGFBP-3) and an acid-labile subunit (ALS) to form a ternary complex. The ALS protects IGFs from decay and facilitates their endocrine activity. However, the function of ALS in fetal growth has not yet been fully determined.

METHODS

Venous umbilical plasma samples were obtained from 98 term neonates and analyzed using enzyme-linked immunosorbent assays. The ALS, IGF-I, and IGFBP-3 umbilical cord plasma levels were analyzed for their association with anthropometric measurements of the neonates.

RESULTS

The ALS, IGF-I, and IGFBP-3 cord plasma levels were positively correlated with birth weight (r = 0.42, p < 0.001; r = 0.43, p < 0.001; and r = 0.27, p < 0.01, respectively) and placental weight (r = 0.37, p < 0.001; r = 0.31, p < 0.01; and r = 0.30, p < 0.01, respectively). In addition, the ALS cord plasma levels were also positively correlated with head circumference (r = 0.29, p < 0.01). Multiple linear regression analyses showed that both ALS and IGF-I cord plasma levels were independent predictive variables for birth weight (p < 0.01 and p < 0.005, respectively). The ALS cord plasma levels were the only independent predictive variables, however, for head circumference and placental weight (p < 0.01 and p < 0.05, respectively).

CONCLUSION

The ALS umbilical cord plasma levels are one important factor, in addition to IGF-I, in the IGF system for predicting birth anthropometry, at least for near-term gestation. Our results suggest that the influence of ALS on the IGF system may develop prior to birth and affect fetal growth.

Skeletal response of male mice to anabolic hormone therapy in the absence of the Igfals gene

IGF-I is a critical regulator of skeletal acquisition, which acts in endocrine and autocrine/paracrine modes. In serum, IGF-I is carried by the IGF-binding proteins in binary complexes. Further stabilization of these complexes is achieved by binding to the acid labile subunit (ALS) in a ternary complex (of IGF-I-IGF-binding protein 3/5-ALS). Ablation of the Igfals gene in humans (ALS deficiency) and mice (ALS knockout [ALSKO]) leads to markedly decreased serum IGF-I levels, growth retardation, and impaired skeletal acquisition. To investigate whether hormonal replacement therapy would improve the skeletal phenotype in cases of Igfals gene ablation, we treated male ALSKO mice with GH, IGF-I, or a combination of both. Treatments were administered to animals between 4 and 16 weeks of age or from 8 to 16 weeks of age. Although all treatment groups showed an increase (20%) in serum IGF-I levels, there was no increase in body weight, weight gain, or bone length in either age group. Despite the blunted linear growth in response to hormone therapy, ALSKO mice treated with GH showed radial bone growth, which contributed to bone strength tested by 4-point bending. We found that ALSKO mice treated with GH showed increased total cross-sectional area, cortical bone area, and cortical thickness by microtomography. Dynamic histomorphometry showed that although GH and double treatment groups resulted in trends towards increased bone formation parameters, these did not reach significance. However, bone resorption parameters were significantly increased in all treatment groups. ALSKO mice treated between 4 and 16 weeks of age showed minor differences in bone traits compared with vehicle-treated mice. In conclusion, treatment with GH and IGF-I do not work synergistically to rescue the stunted growth found in mice lacking the Igfals gene. Although GH alone appears to increase bone parameters slightly, it does not affect body weight or linear growth.

Tumors, IGF-2, and hypoglycemia: insights from the clinic, the laboratory, and the historical archive

Tumors of mesenchymal and epithelial origin produce IGF-2, which activates pathways in the tumors. In a minority of patients, the tumors (hepatomas, fibromas, and fibrosarcomas are the most common among many) release into the circulation enough IGF-2-related peptides to mimic the fasting hypoglycemia characteristic of patients with insulin-producing islet-cell tumors. Rarely, markedly elevated IGF-2 levels produce somatic changes suggestive of acromegaly. Typically, the elevated IGF-2 levels are associated with suppressed plasma levels of insulin, IGF-1, and GH. Complicating the pathophysiology are the IGF binding proteins (IGFBPs) that can bind IGF-2 and IGF-1, modifying hormone metabolism and action. IGFBP concentrations are often altered in the presence of these tumors. At the cellular level, the 3 hormone-related ligands, IGF-2, IGF-1, and insulin, all bind to 4 (or more) types of IGF-1 receptor (IGF-1R) and insulin receptor (IR). Each receptor has its own characteristic affinity for each ligand, a tyrosine kinase, and overlapping profiles of action in the target cells. The IGF-2R, in addition to binding mannose-6-phosphate-containing proteins, provides an IGF-2 degradation pathway. Recent evidence suggests IGF-2R involvement also in signal transduction. Surgery, the treatment of choice, can produce a cure. For patients not cured by surgery, multiple therapies exist, for the tumor and for hypoglycemia. Potential future therapeutic approaches are sketched. From 1910 to 1930, hypoglycemia, insulin, insulinomas, and non-islet-cell tumors were recognized. The latter third of the century witnessed the emergence of the immunoassay for insulin; the IGFs, their binding proteins, and assays to measure them; and receptors for the insulin-related peptides as well as the intracellular pathways beyond the receptor. In closing, we replace non-islet-cell tumor hypoglycemia, an outdated and misleading label, with IGF-2-oma, self-explanatory and consistent with names of other hormone-secreting tumors.

A novel mutation in IGFALS, c.380T>C (p.L127P), associated with short stature, delayed puberty, osteopenia and hyperinsulinaemia in two siblings: insights into the roles of insulin growth factor-1 (IGF1)

BACKGROUND

The acid-labile subunit (ALS) protein is crucial for maintaining the circulating IGF/IGFBP system. Inactivating mutations of IGFALS result in IGF1 deficiency associated with growth retardation. Although the first IGFALS mutation in humans was described in 2004, only 16 mutations have been reported since. Moreover, the phenotype of affected patients as a consequence of ALS deficiency is still highly variable. We assessed whether children with idiopathic short stature (ISS) harbour mutations in IGFALS and characterized affected patients' phenotype.

DESIGN

Sixty-five children with ISS were enrolled in the study. Serum ALS levels were measured by ELISA, and IGFALS was sequenced.

RESULTS

A novel homozygous mutation in IGFALS, c.380T>C (p.L127P), was identified in two siblings of a consanguineous family. The proband, a 17·75-year-old male, was -1·9 SDS in height and -4·5 SDS in weight. Exaggerated stimulated GH (38 ng/ml) and extremely low IGF1 and IGFBP3 (<25 and <500 ng/ml, respectively) indicated GH insensitivity. Both affected siblings had low or no ALS (43 and 0 mU/ml, respectively). They were also mildly small for gestational age, severely underweight and showed osteopenia, insulin insensitivity and delayed and slow puberty progression.

CONCLUSIONS

Acid-labile subunit deficiency due to IGFALS mutations is a rare cause of growth retardation in children. The unique combination of features presented by the two affected siblings emphasizes the important role of IGF1 in bone formation, insulin regulation and the pubertal process, in addition to its crucial effect on growth. Long-term follow-up is indicated since the clinical outcome with respect to osteoporosis, diabetes mellitus and fertility has not been recognized.

Evaluation of insulin-like growth factor acid-labile subunit as a potential biomarker of effect for deoxynivalenol-induced proinflammatory cytokine expression

Consumption of the trichothecene deoxynivalenol (DON) suppresses growth in experimental animals - an adverse effect that was used to establish the tolerable daily intake for this toxin. DON ingestion has been recently found to suppress plasma insulin-like growth factor acid-labile subunit (IGFALS), a protein essential for growth. Studies were conducted to explore the feasibility of using plasma IGFALS as a biomarker of effect for DON. In the first study, weanling mice were fed 0, 1, 2.5, 5 and 10 ppm DON and weight and plasma IGFALS determined at intervals over 9 wk. Reduced body weight gains were detectable beginning at wk 5 in the 10 ppm dose and wk 7 at the 5 ppm dose. Plasma IGFALS was significantly depressed at wk 5 in the 5 and 10 ppm groups at wk 9 in the 10 ppm group. Depressed IGFALS significantly correlated with reduced body weight at wk 5 and 9. Benchmark dose modeling revealed the BMDL and BMD for plasma IGFALS reduction were 1.1 and 3.0 ppm DON and for weight reduction were 2.1 and 4.5 ppm DON. In the second study, it was demonstrated that mice fed 15 ppm DON diet had significantly less plasma IGFALS than mice fed identical amounts of control diet. Thus DON's influence on IGFALS likely reflects the combined effects of reduced food intake as well as its physiological action involving suppressors of cytokine signaling. Taken together, these findings suggest that plasma IGFALS might be a useful biomarker for DON's adverse effects on growth.

Conceptus-endometrium crosstalk during maternal recognition of pregnancy in cattle

Successful growth and development of the posthatching blastocyst and pregnancy establishment are a result of the interaction between a competent embryo and a receptive uterine environment. We examined the global transcriptome profiles of the Day 16 bovine conceptus and pregnant endometrium tissues using RNA-Seq to identify genes that contribute to the dialogue during the period of pregnancy recognition. Using stringent filtering criterion, a total of 16 018 and 16 262 transcripts of conceptus and pregnant endometrium origin, respectively, were identified with distinct tissue-specific expression profiles. Of these, 2261 and 2505 transcripts were conceptus and endometrium specific. Using Cytoscape software, a total of 133 conceptus ligands that interact with corresponding receptors on the endometrium and 121 endometrium ligands that interact with corresponding receptors on the conceptus were identified. While 87 ligands were commonly detected, 46 were conceptus specific and 34 endometrium specific. This study is one of the first to provide a comprehensive list of potentially secreted molecules in the conceptus that interact with receptors on the endometrium and vice versa during the critical window of maternal recognition of pregnancy. The identified tissue-specific genes may serve as candidates to study pregnancy recognition and they or downstream products may represent potential early markers of pregnancy.

Identification of IGF1, SLC4A4, WWOX, and SFMBT1 as hypertension susceptibility genes in Han Chinese with a genome-wide gene-based association study

Hypertension is a complex disorder with high prevalence rates all over the world. We conducted the first genome-wide gene-based association scan for hypertension in a Han Chinese population. By analyzing genome-wide single-nucleotide-polymorphism data of 400 matched pairs of young-onset hypertensive patients and normotensive controls genotyped with the Illumina HumanHap550-Duo BeadChip, 100 susceptibility genes for hypertension were identified and also validated with permutation tests. Seventeen of the 100 genes exhibited differential allelic and expression distributions between patient and control groups. These genes provided a good molecular signature for classifying hypertensive patients and normotensive controls. Among the 17 genes, IGF1, SLC4A4, WWOX, and SFMBT1 were not only identified by our gene-based association scan and gene expression analysis but were also replicated by a gene-based association analysis of the Hong Kong Hypertension Study. Moreover, cis-acting expression quantitative trait loci associated with the differentially expressed genes were found and linked to hypertension. IGF1, which encodes insulin-like growth factor 1, is associated with cardiovascular disorders, metabolic syndrome, decreased body weight/size, and changes of insulin levels in mice. SLC4A4, which encodes the electrogenic sodium bicarbonate cotransporter 1, is associated with decreased body weight/size and abnormal ion homeostasis in mice. WWOX, which encodes the WW domain-containing protein, is related to hypoglycemia and hyperphosphatemia. SFMBT1, which encodes the scm-like with four MBT domains protein 1, is a novel hypertension gene. GRB14, TMEM56 and KIAA1797 exhibited highly significant differential allelic and expressed distributions between hypertensive patients and normotensive controls. GRB14 was also found relevant to blood pressure in a previous genetic association study in East Asian populations. TMEM56 and KIAA1797 may be specific to Taiwanese populations, because they were not validated by the two replication studies. Identification of these genes enriches the collection of hypertension susceptibility genes, thereby shedding light on the etiology of hypertension in Han Chinese populations.

Mex3c regulates insulin-like growth factor 1 (IGF1) expression and promotes postnatal growth

Mex3c is highly expressed in the testis, brain, and developing bone. Mex3c mutation causes postnatal growth retardation and background-dependent perinatal lethality, possibly through impairing the translation of insulin-like growth factor 1 mRNA in bone-forming cells.

Insulin-like growth factor 1 (IGF1) mediates the growth-promoting activities of growth hormone. How Igf1 expression is regulated posttranscriptionally is unclear. Caenorhabditis elegans muscle excess 3 (MEX-3) is involved in cell fate specification during early embryonic development through regulating mRNAs involved in specifying cell fate. The function of its mammalian homologue, MEX3C, is unknown. Here we show that MEX3C deficiency in Mex3c homozygous mutant mice causes postnatal growth retardation and background-dependent perinatal lethality. Hypertrophy of chondrocytes in growth plates is significantly impaired. Circulating and bone local production of IGF1 are both decreased in mutant mice. Mex3c mRNA is strongly expressed in the testis and the brain, and highly expressed in resting and proliferating chondrocytes of the growth plates. MEX3C is able to enrich multiple mRNA species from tissue lysates, including Igf1. Igf1 expression in bone is decreased at the protein level but not at the mRNA level, indicating translational/posttranslational regulation. We propose that MEX3C protein plays an important role in enhancing the translation of Igf1 mRNA, which explains the perinatal lethality and growth retardation observed in MEX3C-deficient mice.

Insulin-like growth factor binding proteins: a structural perspective

Insulin-like growth factor binding proteins (IGFBP-1 to -6) bind insulin-like growth factors-I and -II (IGF-I and IGF-II) with high affinity. These binding proteins maintain IGFs in the circulation and direct them to target tissues, where they promote cell growth, proliferation, differentiation, and survival via the type 1 IGF receptor. IGFBPs also interact with many other molecules, which not only influence their modulation of IGF action but also mediate IGF-independent activities that regulate processes such as cell migration and apoptosis by modulating gene transcription. IGFBPs-1 to -6 are structurally similar proteins consisting of three distinct domains, N-terminal, linker, and C-terminal. There have been major advances in our understanding of IGFBP structure in the last decade and a half. While there is still no structure of an intact IGFBP, several structures of individual N- and C-domains have been solved. The structure of a complex of N-BP-4:IGF-I:C-BP-4 has also been solved, providing a detailed picture of the structural features of the IGF binding site and the mechanism of binding. Structural studies have also identified features important for interaction with extracellular matrix components and integrins. This review summarizes structural studies reported so far and highlights features important for binding not only IGF but also other partners. We also highlight future directions in which structural studies will add to our knowledge of the role played by the IGFBP family in normal growth and development, as well as in disease.

Genetic Defects in the Growth Hormone-IGF-I Axis Causing Growth Hormone Insensitivity and Impaired Linear Growth

Human genetic defects in the growth hormone (GH)-IGF-I axis affecting the IGF system present with growth failure as their principal clinical feature. This is usually associated with GH insensitivity (GHI) presenting in childhood as severe or mild short stature. Dysmorphic features and metabolic abnormalities may also be present. The field of GHI due to mutations affecting GH action has evolved rapidly since the first description of the extreme phenotype related to homozygous GH receptor (GHR) mutations in 1966. A continuum of genetic, phenotypic, and biochemical abnormalities can be defined associated with clinically relevant defects in linear growth. The mechanisms of the GH-IGF-I axis in the regulation of normal human growth is discussed followed by descriptions of mutations in GHR, STAT5B, IGF-I, IGFALS, IGF1R, and GH1 defects causing bio-inactive GH or anti-GH antibodies. These GH-IGF-I axis defects are associated with a range of clinical, and hormonal characteristics. An up-dated approach to the clinical assessment of the patient with GHI focusing on investigation of the GH-IGF-I axis and relevant molecular studies contributing to the identification of causative genetic defects is also discussed.

Evidence for a continuum of genetic, phenotypic, and biochemical abnormalities in children with growth hormone insensitivity

GH insensitivity (GHI) presents in childhood as growth failure and in its severe form is associated with dysmorphic and metabolic abnormalities. GHI may be caused by genetic defects in the GH-IGF-I axis or by acquired states such as chronic illness. This article discusses the former category. The field of GHI due to mutations affecting GH action has evolved considerably since the original description of the extreme phenotype related to homozygous GH receptor (GHR) mutations over 40 yr ago. A continuum of genetic, phenotypic, and biochemical abnormalities can be defined associated with clinically relevant defects in linear growth. The role and mechanisms of the GH-IGF-I axis in normal human growth is discussed, followed by descriptions of mutations in GHR, STAT5B, PTPN11, IGF1, IGFALS, IGF1R, and GH1 defects causing bioinactive GH or anti-GH antibodies. These defects are associated with a range of genetic, clinical, and hormonal characteristics. Genetic abnormalities causing growth failure that is less severe than the extreme phenotype are emphasized, together with an analysis of height and serum IGF-I across the spectrum of different types of GHR defects. An overall view of genotype and phenotype relationships is presented, together with an updated approach to the assessment of the patient with GHI, focusing on investigation of the GH-IGF-I axis and relevant molecular studies contributing to this diagnosis.

Acid-labile subunit (ALS) deficiency

The acid-labile subunit (ALS) protein is crucial for maintaining the integrity of the circulating IGF/IGFBP system. In humans, complete ALS deficiency is characterized by severely reduced serum IGF-I and IGFBP-3 concentrations that is incongruent with the associated mild growth retardation (height SDS -2 to -3 SDS before and during puberty). Twenty-one patients have been described with ALS deficiency, representing 16 unique homozygous or compound heterozygous inactivating mutations of the IGFALS gene. Pubertal delay in boys and insulin insensitivity are common findings. In the assessment of a child with short stature ALS deficiency should be consider in those patients presenting: 1) a normal response to GH stimulation test, 2) low IGF-I levels associated with more profoundly reduced IGFBP-3 levels, 3) a mild growth retardation, apparently out of proportion to the degree of IGF-I and IGFBP-3 deficits, 4) lack of response to an IGF generation test and 5) insulin insensitivity.

D440N mutation in the acid-labile subunit of insulin-like growth factor complexes inhibits secretion and complex formation

The acid-labile subunit (ALS) regulates IGF bioavailability by forming heterotrimeric complexes with IGFs and IGF-binding protein-3 (IGFBP-3). A homozygous missense mutation (D440N) resulting in undetectable circulating levels of ALS with a concomitant reduction in IGF-I and IGFBP-3 has been reported to cause mild growth retardation. To understand how this particular mutation affects ALS circulating levels and IGF-transport function, we expressed recombinant ALS and its variants, D440N-ALS, T442A-ALS, and D440N/T442A-ALS, using adenovirus vectors. Compared with wild-type ALS, the secretion of D440N-ALS was 80% lower. The D440N mutation was proposed to generate an N-glycosylation site additional to the seven existing motifs in ALS. D440N-ALS appeared larger than ALS, attributable to N-linked glycans because deglycosylation with N-glycosidase F reduced both proteins to the same molecular mass. When ALS was incubated with IGF-I and IGFBP-3, 70-80% of IGF-I was detected by gel-filtration chromatography in forms corresponding to the 150-kDa ternary complex. In contrast, when D440N-ALS was tested, less than 30% of IGF-I was found in high molecular mass complexes. Two other ALS variants mutated in the same putative glycosylation site, D440N/T442A-ALS and T442A-ALS, showed similar chromatographic profiles to wild-type ALS. The D440N mutation in ALS generates a hyperglycosylated form with impaired secretion and complex formation, potentially leading to dysregulation of endocrine IGF, thus contributing to the growth retardation observed in the affected patient. This is the first study to explain how a natural mutation, D440N, in ALS impairs its function.

Effect of dietary n-3 polyunsaturated fatty acid supplementation on bovine uterine endometrial and hepatic gene expression of the insulin-like growth factor system

Supplementation of cattle diets with n-3 polyunsaturated fatty acids (n-3 PUFA) has been suggested to have positive effects on fertility. In addition, the actions of the insulin-like growth factor (IGF) system both systemically and locally have been shown to influence reproductive processes. The objective of this study was to evaluate the effect of dietary n-3 PUFA supplementation on hepatic and endometrial expression of IGF signalling genes in cattle. Beef heifers were supplemented with a rumen protected source of either a saturated fatty acid (palmitic acid; CON) or high n-3 PUFA diet (n-3 PUFA) for 45 days before slaughter and tissue recovery. Transcription level of candidate IGF signalling genes was measured by reverse transcription quantitative real-time PCR (RT-qPCR) in total RNA isolated from uterine endometrial and liver tissue from seven CON and seven n-3 PUFA supplemented animals. Compared to controls, mRNA abundance in n-3 PUFA liver tissues was higher for IGF-2R, IGFBP-1 and IGFBP-5 (P < 0.05); lower for GHR-1A (P < 0.05); and unchanged for IGF-1, IGF-2, IGF-1R, IGFBP-2, IGFBP-3, IGFBP-4, IGFBP-6, ALS and GHR(total) (P > 0.05). Compared to controls, mRNA abundance in n-3 PUFA endometrial tissues was higher for IGF-2, IGF-1R, IGF-2R and IGFBP-2 (P < 0.05); lower for IGF-1, IGFBP-3 and IGFBP-6 (P < 0.05); and unchanged for IGFBP-1, IGFBP-4, IGFBP-5 and GHR(total) (P > 0.05). Thus, dietary supplementation of cattle with n-3 PUFA affects transcription of genes involved in IGF signalling, in a tissue dependent fashion.

Sex-specific regulation of body size and bone slenderness by the acid labile subunit

Insulin-like growth factor 1 (IGF-1) is a crucial mediator of body size and bone mass during growth and development. In serum, IGF-1 is stabilized by several IGF-1-binding proteins (IGFBPs) and the acid labile subunit (ALS). Previous research using ALS knockout (ALSKO) mice indicated a growth retardation phenotype, and clinical reports of humans have indicated short stature and low bone mineral density (BMD) in patients with ALS deficiency. To determine the temporal and sex-specific effects of ALS deficiency on body size and skeletal development during growth, we characterized control and ALSKO mice from 4 to 16 weeks of age. We found that female ALSKO mice had an earlier-onset reduction in body size (4 weeks) but that both female and male ALSKO mice were consistently smaller than control mice. Interestingly, skeletal analyses at multiple ages showed increased slenderness of ALSKO femurs that was more severe in females than in males. Both male and female ALSKO mice appeared to compensate for their more slender bones through increased bone formation on their endosteal surfaces during growth, but ALSKO females had increased endosteal bone formation compared with ALSKO males. This study revealed age- and sex-specific dependencies of body size and bone size on the ALS. These findings may explain the heterogeneity in growth and BMD measurements reported in human ALS-deficient patients.