Why Do Normal Children Have Acromegalic Levels of IGF-I During Puberty?

Metabolic control of puberty: 60 years in the footsteps of Kennedy and Mitra's seminal work

An individual's nutritional status has a powerful effect on sexual maturation. Puberty onset is delayed in response to chronic energy insufficiency and is advanced under energy abundance. The consequences of altered pubertal timing for human health are profound. Late puberty increases the chances of cardiometabolic, musculoskeletal and neurocognitive disorders, whereas early puberty is associated with increased risks of adult obesity, type 2 diabetes mellitus, cardiovascular diseases and various cancers, such as breast, endometrial and prostate cancer. Kennedy and Mitra's trailblazing studies, published in 1963 and using experimental models, were the first to demonstrate that nutrition is a key factor in puberty onset. Building on this work, the field has advanced substantially in the past decade, which is largely due to the impressive development of molecular tools for experimentation and population genetics. In this Review, we discuss the latest advances in basic and translational sciences underlying the nutritional and metabolic control of pubertal development, with a focus on perspectives and future directions.

Insulin-like Growth Factor 1, Growth Hormone, and Anti-Müllerian Hormone Receptors Are Differentially Expressed during GnRH Neuron Development

Gonadotropin-releasing hormone (GnRH) neurons are key neuroendocrine cells in the brain as they control reproduction by regulating hypothalamic-pituitary-gonadal axis function. In this context, anti-Müllerian hormone (AMH), growth hormone (GH), and insulin-like growth factor 1 (IGF1) were shown to improve GnRH neuron migration and function in vitro. Whether AMH, GH, and IGF1 signaling pathways participate in the development and function of GnRH neurons in vivo is, however, currently still unknown. To assess the role of AMH, GH, and IGF1 systems in the development of GnRH neuron, we evaluated the expression of AMH receptors (AMHR2), GH (GHR), and IGF1 (IGF1R) on sections of ex vivo mice at different development stages. The expression of AMHR2, GHR, and IGF1R was assessed by immunofluorescence using established protocols and commercial antibodies. The head sections of mice were analyzed at E12.5, E14.5, and E18.5. In particular, at E12.5, we focused on the neurogenic epithelium of the vomeronasal organ (VNO), where GnRH neurons, migratory mass cells, and the pioneering vomeronasal axon give rise. At E14.5, we focused on the VNO and nasal forebrain junction (NFJ), the two regions where GnRH neurons originate and migrate to the hypothalamus, respectively. At E18.5, the median eminence, which is the hypothalamic area where GnRH is released, was analyzed. At E12.5, double staining for the neuronal marker ß-tubulin III and AMHR2, GHR, or IGF1R revealed a signal in the neurogenic niches of the olfactory and VNO during early embryo development. Furthermore, IGF1R and GHR were expressed by VNO-emerging GnRH neurons. At E14.5, a similar expression pattern was found for the neuronal marker ß-tubulin III, while the expression of IGF1R and GHR began to decline, as also observed at E18.5. Of note, hypothalamic GnRH neurons labeled for PLXND1 tested positive for AMHR2 expression. Ex vivo experiments on mouse sections revealed differential protein expression patterns for AMHR2, GHR, and IGF1R at any time point in development between neurogenic areas and hypothalamic compartments. These findings suggest a differential functional role of related systems in the development of GnRH neurons.

Tracking and Cumulative Lifetime Exposure to IGF-I in 6459 Healthy Individuals and in SGA Children Treated With GH

CONTEXT

Supraphysiological serum insulin-like growth factor-I (IGF-I) concentrations have been a matter of concern in children treated with GH because high IGF-I levels were associated with risk of later disease in former epidemiological studies.

OBJECTIVE

To determine whether a single IGF-I measurement reliably reflects lifetime IGF-I exposure we evaluated intraindividual longitudinal tracking of IGF-I and IGF-binding protein-3 (IGFBP-3) levels and we estimated cumulative lifetime exposure to IGF-I in healthy and GH-treated individuals.

METHODS

We included 6459 healthy participants (cross-sectional = 5326; longitudinal = 1133) aged 0-76 years (9963 serum samples) and 9 patients born small-for-gestational-age (SGA) with 238 serum samples during GH treatment. Intraindividual tracking of IGF-I and IGFBP-3 (SD score [SDS]) was determined by intraclass correlation coefficients (ICCs). Cumulative lifetime IGF-I exposure was estimated by area under the curve of the predicted SDS trajectory from 0 to 76 years.

RESULTS

For IGF-I (SDS), ICCs were 0.50 (95% CI, 0.47-0.53) for male and 0.53 (0.50-0.56) for female participants. Lifetime IGF-I exposure was significantly higher in female (mean 12 723 ± 3691 SD) than in male participants (12 563 ± 3393); P = 0.02. In SGA children, treatment with GH increased the lifetime exposure to IGF-I from 9512 ± 1889 to 11 271 ± 1689, corresponding to an increase in lifetime IGF-I trajectory from -0.89 SD ± 0.57 to -0.35 SD ± 0.49.

CONCLUSION

Because IGF-I and IGFBP-3 levels track throughout life, a single measurement reliably reflects lifetime exposure. GH therapy increased the lifetime exposure to IGF-I only slightly and it remained below the average lifetime exposure in the reference population.

Reproductive Markers of Testicular Function and Size During Puberty in Boys With and Without a History of Cryptorchidism

CONTEXT

Longitudinal data on levels of hypothalamic-pituitary-gonadal axis hormones and insulin-like growth factor I (IGF-I) during puberty in boys with a history of cryptorchidism are largely missing.

OBJECTIVE

We aimed to compare pubertal hormone levels between boys with a history of congenital cryptorchidism who experienced spontaneous testicular descent or underwent orchiopexy and boys without a history of cryptorchidism.

METHODS

This was a nested case-control study within a population-based birth cohort, with a prospective, longitudinal pubertal follow-up every 6 months (2005 to 2019). Participants were 109 Finnish boys, including boys with a history of unilateral cryptorchidism who underwent orchiopexy (n = 15), unilateral cryptorchidism who had spontaneous testicular descent (n = 15), bilateral cryptorchidism who underwent orchiopexy (n = 9), bilateral cryptorchidism who had spontaneous testicular descent (n = 7), and controls (n = 63). Serum reproductive hormone levels and testicular volumes were measured.

RESULTS

From around onset of puberty, boys with bilateral cryptorchidism who underwent orchiopexy had significantly higher follicle-stimulating hormone (FSH) and lower inhibin B levels than controls. Boys with unilateral cryptorchidism who underwent orchiopexy had significantly higher FSH than controls, whereas inhibin B levels were similar. Testosterone, luteinizing hormone, insulin-like factor 3, and IGF-I were generally similar between groups. Testicular volume of boys with unilateral or bilateral cryptorchidism who underwent orchiopexy was smaller than that of the controls from 1 year after pubertal onset (P < 0.05).

CONCLUSION

Cryptorchid boys, particularly those with bilateral cryptorchidism who underwent orchiopexy, had altered levels of serum biomarkers of Sertoli cells and germ cells and smaller testicular volumes compared with controls.

Are androstenedione, dihydrotestosterone, thyroid-stimulating hormone, insulin-like growth factor I, and insulin-like growth factor binding protein 3 necessary for isolated micropenis healthy boys' evaluation without any phenotypic abnormalities? A cross-sectional study

The study aimed to familiarise primary care physicians and specialists with the minimum hormonal diagnostic tests necessary to assay isolated micropenis in healthy children without any phenotypic abnormality. Children aged 6-15 years (mean 11.6 ± 1.68) were assessed from May 2010 to September 2021 (N = 247). Multiple regression analysis showed correlations between stretched penile length (SPL) and hormonal assays as follows: follicle-stimulating hormone (FSH): r = 0.097, p = 0.035; luteinizing hormone (LH): r = 0.139, p = 0.012, thyroid-stimulating hormone (TSH): r = -0.001, p = 0.321; testosterone (T): r = 0.118, p = 0.004; dihydrotestosterone (DHT): r = 0.002, p = 0.243; androstenedione (Δ4And): r = -0.004, p = 0.502; insulin-like growth factor I (IGF-I): r = -0.003, p = 0.062; and IFG-binding protein 3 (IGF-BP₃ ): r = 0.052, p = 0.051. The most hormonal disorder was testosterone deficiency. TSH, Δ4And, and DHT were normal in all boys. SPL was significantly correlated with FSH, LH, and T, but there was no significant correlation between SPL and TSH, DHT, Δ4And, IGF-I, and IGF-BP₃ . Whenever the isolated micropenis is seen without other anomalies, it is sufficient to assay testosterone, FSH, and LH in the first step.

Development of male-larger sexual size dimorphism in a lizard: IGF1 peak long after sexual maturity overlaps with pronounced growth in males

Squamate reptiles have been considered to be indeterminate growers for a long time. However, recent studies demonstrate that bone prolongation is stopped in many lizards by the closure of bone growth plates. This shift in the paradigm of lizard growth has important consequences for questions concerning the proximate causes of sexual size dimorphism. The traditional model of highly plastic and indeterminate growth would correspond more to a long-term action of a sex-specific growth regulator. On the other hand, determinate growth would be more consistent with a regulator acting in a sex-specific manner on the activity of bone growth plates operating during the phase when a dimorphism in size develops. We followed the growth of males and females of the male-larger Madagascar ground gecko (Paroedura picta) and monitored the activity of bone growth plates, gonad size, levels of steroids, expression of their receptors (AR, ESR1), and expression of genes from the insulin-like growth factor network (IGF1, IGF2, IGF1R, and IGF2R) in livers. Specifically, we measured gene expression before the onset of dimorphic growth, at the time when males have more active bone growth plates and sexual size dimorphism was clearly visible, and after a period of pronounced growth in both sexes. We found a significant spike in the expression of IGF1 in males around the time when dimorphism develops. This overexpression in males comes long after an increase in circulating testosterone levels and sexual maturation in males, and it might be suppressed by ovarian hormones in females. The results suggest that sexual size dimorphism in male-larger lizards can be caused by a positive effect of high levels of IGF1 on bone growth. The peak in IGF1 resembles the situation during the pubertal growth spurt in humans, but in lizards, it seems to be sex-specific and disconnected from sexual maturation.

Growth variations with opposite clinical outcomes and the emerging role of IGF-1

Normal growth pattern variations [i.e., constitutional advancement and constitutional delay of growth and puberty (CAGP and CDGP)] are the mirror image of each other and are associated with early puberty (EP) and delayed puberty (DP), respectively. Differences between CAGP and CDGP relate not only to auxological characteristics (height, weight) but also to insulin-like growth factor-1 (IGF-1). IGF-1 levels in CAGP are above average whereas in CDGP they are below average, suggesting a role for IGF-1 in the induction of these growth patterns. Herein, we provide data suggesting that early activation of the growth hormone (GH)/IGF-1 axis induces the growth pattern of CAGP. Moreover, we suggest that IGF-1 is a decisive factor for the release of the gonadotropin-releasing hormone (GnRH) inhibition brake that occurs in prepuberty. It is therefore crucial for puberty onset.

Sex steroid priming in short stature children unresponsive to GH stimulation tests: Why, who, when and how

Despite decades of experience, the diagnosis of growth hormone deficiency (GHD) remains challenging, especially in peripubertal children. Failure to respond to GH stimulation tests (GHSTs) is needed to confirm GHD, but long-standing controversies regarding the number of tests needed and the interpretation of GH peaks are still a matter of debate worldwide. Diagnostic workup is even more problematic in short children with slow growth and delayed sexual development: they often exhibit low GH peaks under GHST, which often normalize as puberty progresses. Consequently, this transient suboptimal response to GHST may result in GH overtreatment, carrying both health and economic concerns. Considering the complex and bound link between GH axis and sex steroids, the use of sex steroid priming prior to GHST might be helpful in peripubertal setting. However, its use is still controversial. There is no consensus regarding patient selection, timing, dose, and preparation of sex steroids. In this review, we aim to overview the use of sex steroid priming in clinical practice, highlighting the need to develop appropriate guidelines in order to overcome diagnostic pitfalls in peripubertal age.

Role of the GH-IGF1 axis on the hypothalamus-pituitary-testicular axis function: lessons from Laron syndrome

BACKGROUND

Animal studies suggest that insulin-like growth factor 1 (IGF1) may influence the function of the hypothalamus-pituitary-testicular axis, especially in childhood, but the evidence in humans is scanty. Laron syndrome, a human model of IGF1 deficiency, may help to solve this issue.

PURPOSE

This systematic review aims to analyze puberty onset and progression, testicular volume, gonadotropin, and total testosterone serum levels, sperm parameters and fertility, and penile length in patients with Laron syndrome.

METHODS

Specific keywords were used. All data on male patients with Laron syndrome were included.

RESULTS

Seventeen articles matched the inclusion criteria and were entered in the analysis, for a total of 125 male patients. Puberty was absent in 8.9% and delayed in 35.6% of untreated patients of pubertal age. After onset, the duration of the pubertal process was prolonged in 76.9% of untreated patients. The growth spurt was absent in 52.6% and delayed in 31.6% of untreated patients. The testicular volume was small in the two patients who did not receive any treatment. Treatment with IGF1 increased gonadotropin and testosterone serum levels in five out of five patients of pubertal age. No effect was found in four out of four patients younger than 5 years. No study reported data on sperm parameters and fertility. Micropenis occurred in 67.2% of patients.

CONCLUSION AND FUTURE PERSPECTIVES

Delayed puberty is common in patients with Laron syndrome. The growth hormone-IGF1 axis may influence the time of puberty onset. Serum levels of IGF1 should be investigated in children with delayed puberty, scarce progression of testicular growth, and/or micropenis. IGF1 levels might be measured in children with delayed puberty, poor testicular growth, and/or micropenis.

Pubarche and Gonadarche Onset and Progression Are Differently Associated With Birth Weight and Infancy Growth Patterns

Context

Controversy exists regarding associations between early-life growth patterns and timing of puberty.

Objective

This work aims to investigate associations between birth anthropometry, early growth patterns, and onset/progression of pubertal milestones in boys and girls.

Methods

Among children examined at birth (1997-2003) and at age 36 months in a mother-child cohort, pubertal Tanner stages (B1-5, PH1-5, G1-5) and testicular volume were examined by trained physicians at 1 to 5 follow-up examinations during childhood and adolescence (672 girls and 846 boys, 2006-2013).With parametric survival models we analyzed associations between birth weight, changes in SD scores (SDS) from birth to 36 months (ΔSDS 0-36 > 0.67 SD defining catch-up growth), and age at pubertal onset/attainment of late pubertal stages/menarche.

Results

A 1-kg higher birth weight was associated with earlier onset of B2+ (thelarche): -3.9 months (CI, -6.7 to -1.1 months), G2+ (gonadarche): -2.7 months (-5.3 to -0.1 months), Tvol3+ (testis size > 3 mL): -2.8 months (CI, -4.9 to -0.7 months), but with later G4+ and PH4+ in boys, and a slower progression from B2 to menarche (5.3 months [CI, 1.2 to 9.4 months]) in girls. Catch-up growth was associated with earlier PH2+ (pubarche) in girls (-4.1 months [CI, -7.6 to -0.6 months]), earlier PH2+ in boys (-3.4 months [CI, -6.6 to -0.2 months]), faster progression from B2 to menarche in girls (-9.1 months [CI, 14.6 to 3.5 months]), and earlier G4+ and PH4+ in boys.

Conclusion

Associations between birthweight and infancy catch-up growth differed for gonadarche and pubarche, and for early and late pubertal markers, with similar patterns in both sexes.

Anti-Müllerian Hormone, Growth Hormone, and Insulin-Like Growth Factor 1 Modulate the Migratory and Secretory Patterns of GnRH Neurons

Anti-Müllerian hormone (AMH) is secreted by Sertoli or granulosa cells. Recent evidence suggests that AMH may play a role in the pathogenesis of hypogonadotropic hypogonadism (HH) and that its serum levels could help to discriminate HH from delayed puberty. Moreover, the growth hormone (GH)/insulin-like growth factor 1 (IGF1) system may be involved in the function of gonadotropin-releasing hormone (GnRH) neurons, as delayed puberty is commonly found in patients with GH deficiency (GHD) or with Laron syndrome, a genetic form of GH resistance. The comprehension of the stimuli enhancing the migration and secretory activity of GnRH neurons might shed light on the causes of delay of puberty or HH. With these premises, we aimed to better clarify the role of the AMH, GH, and IGF1 on GnRH neuron migration and GnRH secretion, by taking advantage of previously established models of immature (GN11 cell line) and mature (GT1-7 cell line) GnRH neurons. Expression of Amhr, Ghr, and Igf1r genes was confirmed in both cell lines. Cells were then incubated with increasing concentrations of AMH (1.5–150 ng/mL), GH (3–1000 ng/mL), or IGF1 (1.5–150 ng/mL). All hormones were able to support GN11 cell chemomigration. AMH, GH, and IGF1 significantly stimulated GnRH secretion by GT1-7 cells after a 90-min incubation. To the best of our knowledge, this is the first study investigating the direct effects of GH and IGF1 in GnRH neuron migration and of GH in the GnRH secreting pattern. Taken together with previous basic and clinical studies, these findings may provide explanatory mechanisms for data, suggesting that AMH and the GH-IGF1 system play a role in HH or the onset of puberty.

Testicular Growth and Pubertal Onset in GH-Deficient Children Treated With Growth Hormone: A Retrospective Study

The prevalence of idiopathic oligozoospermia has been esteemed as high as 75%. An Italian survey has reported bilateral testicular hypotrophy in 14% of final-year high school students. The search for determinants of testicular growth in childhood is important for the primary prevention of spermatogenic failure. Therefore, this retrospective study aimed to evaluate the testicular growth and pubertal onset in deficient children treated recombinant human growth hormone (rhGH). To accomplish this, the clinical charts of 93 patients with GH deficiency (GHD) were carefully reviewed. Their mean age at the time of diagnosis was 11.2 ± 2.4 years. rhGH was administered for 44.0 ± 22.4 months, and the onset of puberty was recorded after a mean of 25.8 ± 22.4 months from the first rhGH administration. As expected, serum insulin-like growth factor 1 (IGF1) levels increased significantly after treatment. Before rhGH therapy, the Tanner stage was I in 59 out of 70 boys (84.3%), II in 8/70 (11.4%), III in 3/70 (4.3%). No one was on stage IV or V. The mean Tanner stage was 1.19 ± 0.51. At the last visit, the Tanner stage was I in 8/72 boys (11.1%), II in 6/72 (8.3%), III in 6/72 (8.3%), IV in 16/72 (22.2%), and V in 36/72 (50.0%). After a mean of 44.0 ± 22.4 months of rhGH treatment, the mean Tanner stage was 4.05 ± 1.30. Patients treated with rhGH showed a significant testicular volume (TV) growth over time, whereas no growth was observed in age-matched but not yet treated patients, even when the age was compatible with a spontaneous start of puberty. The multivariate regression analysis showed that the duration of treatment and the mean rhGH dose significantly predicted the percentage of TV increase. In contrast, age, serum FSH, and IGF1 levels, and final rhGH dose did not impact TV growth over time. In conclusion, these findings suggest that GH may play a role in testicular growth and pubertal onset, despite the descriptive nature of this study. Further properly designed studies are needed to confirm these findings. This knowledge may be useful to implement the diagnostic-therapeutic algorithm in case of a lack of testicular growth in childhood.

Somatotropic-Testicular Axis: A crosstalk between GH/IGF-I and gonadal hormones during development, transition, and adult age

BACKGROUND

The hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-somatotropic (HPS) axes are strongly interconnected. Interactions between these axes are complex and poorly understood. These interactions are characterized by redundancies in reciprocal influences at each level of regulation and the combination of endocrine and paracrine effects that change during development.

OBJECTIVES

To comprehensively review the crosstalk between the HPG and HPS axes and related pathological and clinical aspects during various life stages of male subjects.

MATERIALS AND METHODS

A thorough search of publications available in PubMed was performed using proper keywords.

RESULTS

Molecular studies confirmed the expressions of growth hormone (GH) and insulin-like growth factor-I (IGF-I) receptors on the HPG axis and reproductive organs, indicating a possible interaction between HPS and HPG axes at various levels. Insulin growth factors participate in sexual differentiation during fetal development, indicating that normal HPS axis activity is required for proper testicular development. IGF-I contributes to correct testicular position during minipuberty, determines linear growth during childhood, and promotes puberty onset and pace through gonadotropin-releasing hormone activation. IGF-I levels are high during transition age, even when linear growth is almost complete, suggesting its role in reproductive tract maturation. Patients with GH deficiency (GHD) and insensitivity (GHI) exhibit delayed puberty and impaired genital development; replacement therapy in such patients induces proper pubertal development. In adults, few studies have suggested that lower IGF-I levels are associated with impaired sperm parameters.

DISCUSSION AND CONCLUSION

The role of GH-IGF-I in testicular development remains largely unexplored. However, it is important to evaluate gonadic development in children with GHD. Additionally, HPS axis function should be evaluated in children with urogenital malformation or gonadal development alterations. Correct diagnosis and prompt therapeutic intervention are needed for healthy puberty, attainment of complete gonadal development during transition age, and fertility potential in adulthood.

Unravelling the role of epigenetics in reproductive adaptations to early-life environment

Reproductive function adjusts in response to environmental conditions in order to optimize success. In humans, this plasticity includes age of pubertal onset, hormone levels and age at menopause. These reproductive characteristics vary across populations with distinct lifestyles and following specific childhood events, and point to a role for the early-life environment in shaping adult reproductive trajectories. Epigenetic mechanisms respond to external signals, exert long-term effects on gene expression and have been shown in animal and cellular studies to regulate normal reproductive function, strongly implicating their role in these adaptations. Moreover, human cohort data have revealed differential DNA methylation signatures in proxy tissues that are associated with reproductive phenotypic variation, although the cause-effect relationships are difficult to discern, calling for additional complementary approaches to establish functionality. In this Review, we summarize how adult reproductive function can be shaped by childhood events. We discuss why the influence of the childhood environment on adult reproductive function is an important consideration in understanding how reproduction is regulated and necessitates consideration by clinicians treating women with diverse life histories. The resolution of the molecular mechanisms responsible for human reproductive plasticity could also lead to new approaches for intervention by targeting these epigenetic modifications.

CENTRAL PRECOCIOUS PUBERTY IN TWO BOYS WITH PRADER-WILLI SYNDROME ON GROWTH HORMONE TREATMENT

Objective

Prader-Willi syndrome (PWS) is a rare genetic neuroendocrine disorder characterized by hypotonia, obesity, short stature, and mental retardation. Incomplete or delayed pubertal development as well as premature adrenarche are usually found in PWS, whereas central precocious puberty is rarely seen.

Methods

This study reports the clinical, biochemical, and histologic findings in 2 boys with PWS who developed central precocious puberty.

Results

Both boys were started on growth hormone therapy during the first years of life according to the PWS indication. They had both bilateral cryptorchidism at birth and had orchidopexy in early childhood. Retrospective histologic analysis of testicular biopsies demonstrated largely normal tissue architecture and germ cell maturation, but severely decreased number of prespermatogonia in one of the patients. Both boys had premature adrenarche around the age of 6. Precocious puberty was diagnosed in both boys with enlargement of testicular volume (>3 mL), signs of virilization and a pubertal response to a gonadotropin-releasing hormone (GnRH) test and they were both treated with GnRH analog.

Conclusion

The cases described here displayed typical characteristics for PWS, a considerable heterogeneity of the hypothalamic-pituitary function, as well as testicular histology. Central precocious puberty is extremely rare in PWS boys, but growth hormone treatment may play a role in the pubertal timing.