Héctor G. Jasper

Serum complexes of insulin-like growth factor-1 modulate skeletal integrity and carbohydrate metabolism

Serum insulin‐like growth factor (IGF) ‐1 is secreted mainly by the liver and circulates bound to IGF‐binding proteins (IGFBPs), either as binary complexes or ternary complexes with IGFBP‐3 or IGFBP‐5 and an acid‐labile subunit (ALS). The purpose of this study was to genetically dissect the role of IGF‐1 circulatory complexes in somatic growth, skeletal integrity, and metabolism. Phenotypic comparisons of controls and four mouse lines with genetic IGF‐1 deficits— liver‐specific IGF‐1 deficiency (LID), ALS knockout (ALSKO), IGFBP‐3 (BP3) knockout, and a triply deficient LID/ALSKO/BP3 line—produced several novel findings. 1) All deficient strains had decreased serum IGF‐1 levels, but this neither predicted growth potential or skeletal integrity nor defined growth hormone secretion or metabolic abnormalities. 2) IGF‐1 deficiency affected development of both cortical and trabecular bone differently, effects apparently dependent on the presence of different circulating IGF‐1 complexes. 3) IGFBP‐3 deficiency resulted in increased linear growth. In summary, each IGF‐1 complex constituent appears to play a distinct role in determining skeletal phenotype, with different effects on cortical and trabecular bone compartments.— Yakar, S., Rosen, C. J., Bouxsein, M. L., Sun, H., Mejia, W., Kawashima, Y., Wu, Y., Emerton, K., Williams, V., Jepsen, K., Schaffler, M. B., Majeska, R. J., Gavrilova, O., Gutierrez, M., Hwang, D., Pennisi, P., Frystyk, J., Boisclair, Y., Pintar, J., Jasper, H., Domene, H., Cohen, P., Clemmons, D., LeRoith, D. Serum complexes of insulin‐like growth factor‐1 modulate skeletal integrity and carbohydrate metabolism. FASEB J. 23, 709–719 (2009)

Human Acid-Labile Subunit Deficiency: Clinical, Endocrine and Metabolic Consequences

The majority of insulin-like growth factor (IGF)-I and IGF-II circulate in the serum as a complex with the insulin-like growth factor binding protein (IGFBP)-3 or IGFBP-5, and an acid-labile subunit (ALS). The function of ALS is to prolong the half-life of the IGF-I-IGFBP-3/IGFBP-5 binary complexes. Fourteen different mutations of the human IGFALS gene have been identified in 17 patients, suggesting that ALS deficiency may be prevalent in a subset of patients with extraordinarily low serum levels of IGF-I and IGFBP-3 that remain abnormally low upon growth hormone stimulation. Postnatal growth was clearly affected. Commonly, the height standard deviation score before puberty was between –2 and –3, and approximately 1.4 SD shorter than the midparental height SDS. Pubertal delay was found in 50% of the patients. Circulating IGF-II, IGFBP-1, -2 and -3 levels were reduced, with the greatest reduction observed for IGFBP-3. Insulin insensitivity was a common finding, and some patients presented low bone mineral density. Human ALS deficiency represents a unique condition in which the lack of ALS proteins results in the disruption of the entire IGF circulating system. Despite a profound circulating IGF-I deficiency, there is only a mild impact on postnatal growth. The preserved expression of locally produced IGF-I might be responsible for the preservation of linear growth near normal limits.

Differential impact of simple childhood obesity on the components of the growth hormone-insulin-like growth factor (IGF)-IGF binding proteins axis.

Simple childhood obesity is characterized by normal or even accelerated growth in spite of reduced growth hormone (GH) secretion. There are conflicting reports on the effects of obesity upon components of the GH-insulin-like growth factor-I (IGF-I)-IGF binding proteins (IGFBPs) system. In the present study we aimed to determine GH, IGF-I, IGFBP-3 and IGFBP-2 as well as some of the less explored components of this axis (IGFBP-3 proteolytic activity, IGFBP-3 plasma fragments, and total acid labile subunit [ALS]) in 22 obese and 17 age-matched control children. We also evaluated not only total GH binding protein (GHBP) serum levels but also GHBP bound to GH (complexed) in both groups. Obese and control groups strongly differed in BMI (obese: 4.7 +/- 0.36 vs control: 0.37 +/- 0.25 SDS, p <0.0001). In the obese group, we found lower GH serum levels, but normal serum levels of GH-GHBP complex, IGF-I, IGFBP-3, IGF-I/IGFBP-3 molar ratio, IGFBP-3 proteolytic activity, IGFBP-3 plasma fragments and total ALS. Obese children presented higher total circulating GHBP (6.0 +/- 0.44 vs 2.9 +/- 0.29 nmol/l, p <0.001) and insulin levels (10.5 +/- 1.5 vs 5.1 +/- 0.8 mU/l, p <0.001), while IGFBP-2 (4.6 +/- 0.5 vs 6.6 +/- 0.7%, p <0.05) and the ratio IGFBP-2/IGF-I (0.032 +/- 0.019 vs 0.095 +/- 0.01, p = 0.013) were lower than in controls. BMI and insulin were directly, and IGFBP-2 serum levels inversely, correlated to total GHBP serum levels when multiple regression analysis was performed (r = 0.74, p <0.001). By stepwise regression analysis, insulin (r = -0.37, p <0.05) and BMI (r = -0.52, p <0.01) inversely determined IGFBP-2. In summary, obese children present normal growth in spite of reduced GH secretion, probably because the combination of increased total GHBP and normal GH-GHBP complex serum levels (suggesting increased GH receptor [GHR] number and a normal serum GH reservoir, respectively) allow for the achievement of normal levels of IGF-I, IGFBP-3, IGFBP-3 proteolytic activity, IGFBP-3 plasma fragments and total ALS. Reduced IGFBP-2 serum levels and a lower ratio of IGFBP-2/IGF-I in obese children may suggest an increase of tissue IGF-I bioavailability, thus promoting its action. Normal IGF-I and GH availability may be contributing to maintain normal growth in obese children.

Effect of deflazacort versus methylprednisone on growth, body composition, lipid profile, and bone mass after renal transplantation

Abstract Kidney function, growth velocity, weight/ height ratio, body composition, lipid profile, and bone mass were studied in a randomized, multicenter trial of deflazacort versus methylprednisone in 27 prepubertal patients with kidney transplantation. Methylprednisone (0.20±0.03) was replaced by deflazacort (13 patients, 0.30±0.03 mg/kg per day). After 12 months, creatinine clearance decreased significantly only during methylprednisone therapy. Growth velocity increased only in patients treated with deflazacort from 3.3±0.6 to 5.6±0.5 cm/year. Serum levels of several components of the insulin-like growth factor axis did not change. Weight/height ratio was increased in methylprednisone-treated patients (P<0.05) and decreased in deflazacort-treated patients (P<0.005). Lean body mass increased in both groups (P<0.005). Fat body mass and serum leptin increased only in methylprednisone-treated patients (P<0.025). Total cholesterol and low-density lipoprotein-cholesterol increased in methylprednisone-treated patients by 9.9% (P<0.05) and 12.5% (P<0.025). High-density lipoprotein-cholesterol increased by 21% (P<0.005) and apolipoprotein B decreased by 11% (P<0.005) in deflazacort-treated patients. Total skeleton and lumbar spine bone mineral density decreased in both groups, but at 1 year methylprednisone-treated patients had lost 50% more bone. Bone mineral content decreased only in methylprednisone-treated patients (P<0.01). Our data suggest that substituting deflazacort for maintenance methylprednisone might prevent height loss, excessive bone loss, and fat accumulation; and leads to an improvement in the lipoproteins of these children.

Impact of Heterozygosity for Acid-Labile Subunit (IGFALS) Gene Mutations on Stature: Results from the International Acid-Labile Subunit Consortium

CONTEXT To date, 16 IGFALS mutations in 21 patients with acid-labile subunit (ALS) deficiency have been reported. The impact of heterozygosity for IGFALS mutations on growth is unknown. OBJECTIVE The study evaluates the impact of heterozygous expression of IGFALS mutations on phenotype based on data collected by the International ALS Consortium. SUBJECTS/METHODS Patient information was derived from the IGFALS Registry, which includes patients with IGFALS mutations and family members who were either heterozygous carriers or homozygous wild-type. Within each family, the effect of IGFALS mutations on stature was analyzed as follows: 1) effect of two mutant alleles (2ALS) vs. wild-type (WT); 2) effect of two mutant alleles vs. one mutant allele (1ALS); and 3) effect of one mutant allele vs. wild-type. The differences in height sd score (HtSDS) were then pooled and evaluated. RESULTS Mean HtSDS in 2ALS was -2.31 +/- 0.87 (less than -2 SDS in 62%); in 1ALS, -0.83 +/- 1.34 (less than -2 SDS in 26%); and in WT, -1.02 +/- 1.04 (less than -2 SDS in 12.5%). When analyses were performed within individual families and pooled, the difference in mean HtSDS between 2ALS and WT was -1.93 +/- 0.79; between 1ALS and WT, -0.90 +/- 1.53; and between 2ALS and 1ALS, -1.48 +/- 0.83. CONCLUSIONS Heterozygosity for IGFALS mutations results in approximately 1.0 SD height loss in comparison with wild type, whereas homozygosity or compound heterozygosity gives a further loss of 1.0 to 1.5 SD, suggestive of a gene-dose effect. Further studies involving a larger cohort are needed to evaluate the impact of heterozygous IGFALS mutations not only on auxology, but also on other aspects of the GH/IGF system.

Normal Growth Spurt and Final Height despite Low Levels of All Forms of Circulating Insulin-Like Growth Factor-I in a Patient with Acid-Labile Subunit Deficiency

Background: In a recently described patient with acid-labile subunit (ALS) deficiency, the inability to form ternary complexes resulted in a marked reduction in circulating total insulin-like growth factor (IGF)-I, whereas skeletal growth was only marginally affected. To further study the role of circulating versus locally produced IGF-I in skeletal growth in this patient, we now describe in detail growth changes and their relationship with several components of the circulating IGF system. Design and Methods: We followed growth and development up to the final height in a patient with complete ALS deficiency and determined both spontaneous and growth hormone (GH)-stimulated changes in the IGF system, including measurements of total, free and bioactive IGF-I, total IGF-II and insulin-like growth factor binding protein (IGFBP)-1, IGFBP-2 and IGFBP-3. Results: The patient had a delayed growth and pubertal onset. Six months of GH treatment had no effect on growth. At the age of 19.3 years, he spontaneously completed puberty and had a normal growth spurt for a late adolescent (peak height velocity of 8.4 cm/year). A normal final height was attained at 21.3 years (167.5 cm; –0.78 SDS). During as well as after puberty, basal levels of total, free and bioactive IGF-I were low, as were total IGF-II, IGFBP-1, IGFBP-2 and IGFBP-3. GH treatment for 6 months normalized free IGF-I and increased bioactive IGF-I, but had no effect on growth velocity. Conclusions: This case story shows that in the presence of complete ALS deficiency, a height within normal limits can be obtained despite low levels of all forms of circulating IGF-I. Furthermore, the patient presented a delayed but normal growth spurt without any marked increment of circulating IGF-I.

Mutations in pregnancy‐associated plasma protein A2 cause short stature due to low IGF‐I availability

Mutations in multiple genes of the growth hormone/IGF‐I axis have been identified in syndromes marked by growth failure. However, no pathogenic human mutations have been reported in the six high‐affinity IGF‐binding proteins (IGFBPs) or their regulators, such as the metalloproteinase pregnancy‐associated plasma protein A2 (PAPP‐A2) that is hypothesized to increase IGF‐I bioactivity by specific proteolytic cleavage of IGFBP‐3 and ‐5. Multiple members of two unrelated families presented with progressive growth failure, moderate microcephaly, thin long bones, mildly decreased bone density and elevated circulating total IGF‐I, IGFBP‐3, and ‐5, acid labile subunit, and IGF‐II concentrations. Two different homozygous mutations in PAPPA2, p.D643fs25* and p.Ala1033Val, were associated with this novel syndrome of growth failure. In vitro analysis of IGFBP cleavage demonstrated that both mutations cause a complete absence of PAPP‐A2 proteolytic activity. Size‐exclusion chromatography showed a significant increase in IGF‐I bound in its ternary complex. Free IGF‐I concentrations were decreased. These patients provide important insights into the regulation of longitudinal growth in humans, documenting the critical role of PAPP‐A2 in releasing IGF‐I from its BPs.

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

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

Unbound (bioavailable) IGF1 enhances somatic growth

SUMMARY Understanding insulin-like growth factor-1 (IGF1) biology is of particular importance because, apart from its role in mediating growth, it plays key roles in cellular transformation, organ regeneration, immune function, development of the musculoskeletal system and aging. IGF1 bioactivity is modulated by its binding to IGF-binding proteins (IGFBPs) and the acid labile subunit (ALS), which are present in serum and tissues. To determine whether IGF1 binding to IGFBPs is necessary to facilitate normal growth and development, we used a gene-targeting approach and generated two novel knock-in mouse models of mutated IGF1, in which the native Igf1 gene was replaced by Des-Igf1 (KID mice) or R3-Igf1 (KIR mice). The KID and KIR mutant proteins have reduced affinity for the IGFBPs, and therefore present as unbound IGF1, or ‘free IGF1’. We found that both KID and KIR mice have reduced serum IGF1 levels and a concomitant increase in serum growth hormone levels. Ternary complex formation of IGF1 with the IGFBPs and the ALS was markedly reduced in sera from KID and KIR mice compared with wild type. Both mutant mice showed increased body weight, body and bone lengths, and relative lean mass. We found selective organomegaly of the spleen, kidneys and uterus, enhanced mammary gland complexity, and increased skeletal acquisition. The KID and KIR models show unequivocally that IGF1-complex formation with the IGFBPs is fundamental for establishing normal body and organ size, and that uncontrolled IGF bioactivity could lead to pathological conditions.

Effects of deflazacort immunosuppression on long-term growth and growth factors after renal transplantation.

Abstract. Deflazacort is an oxazoline compound derived from prednisolone. We studied changes in kidney function, growth velocity, weight/height ratio, insulin-like growth factor (IGF-I), and IGF binding proteins before and after substitution of deflazacort for methylprednisone in 27 transplanted patients aged 3.1 – 20 years. Methylprednisone (mean±SEM 0.17±0.01 mg/kg per day) was replaced by deflazacort (0.29±0.01 mg/kg per day) for a period of 1 – 5 years. Calculated creatinine clearance did not change significantly during deflazacort treatment. Growth velocity increased from 2.6±0.5 cm/year to 5.2±0.7 cm/year (1st year) in 14 prepubertal patients. After 4 years of deflazacort treatment, height standard deviation score for chronological age did not change in 7 prepubertal patients. Mean weight/height ratio decreased by 50% (1st year) and remained reduced during follow-up. Serum IGF-I, IGF binding protein -3 (IGFBP3), IGF/IGFBP3 molar ratio, and IGF-I and -II binding capacities showed no significant change; however in 5 of 6 patients IGFBP2 decreased during deflazacort therapy. Our findings suggest that immunosuppressive treatment with deflazacort is as effective as methylprednisone and may lead to an improvement in the growth prognosis of children with renal transplantation.