Liliana Karabatas

Decreased Tubular Uptake of L-3,4-Dihydroxyphenylalanine in Streptozotocin-Induced Diabetic Rats

Background/Aims: This study determined alterations in renal dopamine production in streptozotocin-treated rats and explored the mechanisms underlying this alteration. Methods: Streptozotocin (65 mg/kg) or vehicle was administered to 3-month-old male Wistar rats. Treated animals had hyperglycemia, glycosuria and increased diuresis, natriuresis and excretion of L-dopa. Urinary dopamine and dihydroxyphenylacetic acid were similar to those in control animals. The production of dopamine by renal cortex slices from treated rats was significantly less than that from control animals. The addition of glucose (8.4–18.4 mM) to the incubation medium decreased about 40% the uptake of L-dopa by isolated proximal tubular cells. Scatchard analysis of the saturation curves obtained in this condition showed a decrease in the Vmax without changes in the Km. Results: Our results confirm previous studies suggesting a renal dopaminergic deficiency in insulin-dependent diabetes and provide evidence strongly suggesting that a decrease in the number of tubular L-dopa transport sites is the underlying defect of this deficiency. Conclusion: These results highlight the role of the uptake of dopa as an important modulator of renal dopamine synthesis.

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.

Heterozygous IGFALS Gene Variants in Idiopathic Short Stature and Normal Children: Impact on Height and the IGF System

Background: In acid-labile subunit (ALS)-deficient families, heterozygous carriers of IGFALS gene mutations are frequently shorter than their wild-type relatives, suggesting that IGFALS haploinsufficiency could result in short stature. We have characterized IGFALS gene variants in idiopathic short stature (ISS) and in normal children, determining their impact on height and the IGF system. Patients and Methods: In 188 normal and 79 ISS children levels of IGF-1, IGFBP-3, ALS, ternary complex formation (TCF) and IGFALS gene sequence were determined. Results: In sum, 9 nonsynonymous or frameshift IGFALS variants (E35Gfs*17, G83S, L97F, R277H, P287L, A330D, R493H, A546V and R548W) were found in 10 ISS children and 6 variants (G170S, V239M, N276S, R277H, G506R and R548W) were found in 7 normal children. If ISS children were classified according to the ability for TCF enhanced by the addition of rhIGFBP-3 (TCF+), carriers of pathogenic IGFALS gene variants were shorter and presented lower levels of IGF-1, IGFBP-3 and ALS in comparison to carriers of benign variants. In ISS families, subjects carrying pathogenic variants were shorter and presented lower IGF-1, IGFBP-3 and ALS levels than noncarriers. Conclusions: These findings suggest that heterozygous IGFALS gene variants could be responsible for short stature in a subset of ISS children with diminished levels of IGF-1, IGFBP-3 and ALS.

Characterization of four Latin American families confirms previous findings and reveals novel features of acid-labile subunit deficiency

Acid‐labile subunit deficiency (ACLSD), caused by inactivating mutations in both IGFALS gene alleles, is characterized by marked reduction in IGF‐I and IGFBP‐3 levels associated with mild growth retardation. The aim of this study was to expand the known phenotype and genetic characteristics of ACLSD by reporting data from four index cases and their families.

Partial growth hormone insensitivity and dysregulatory immune disease associated with de novo germline activating STAT3 mutations

Germinal heterozygous activating STAT3 mutations represent a novel monogenic defect associated with multi-organ autoimmune disease and, in some cases, severe growth retardation. By using whole-exome sequencing, we identified two novel STAT3 mutations, p.E616del and p.C426R, in two unrelated pediatric patients with IGF-I deficiency and immune dysregulation. The functional analyses showed that both variants were gain-of-function (GOF), although they were not constitutively phosphorylated. They presented differences in their dephosphorylation kinetics and transcriptional activities under interleukin-6 stimulation. Both variants increased their transcriptional activities in response to growth hormone (GH) treatment. Nonetheless, STAT5b transcriptional activity was diminished in the presence of STAT3 GOF variants, suggesting a disruptive role of STAT3 GOF variants in the GH signaling pathway. This study highlights the broad clinical spectrum of patients presenting activating STAT3 mutations and explores the underlying molecular pathway responsible for this condition, suggesting that different mutations may drive increased activity by slightly different mechanisms.

Genotyping IGFBP3 Gene Polymorphism Improves the Diagnostic Efficiency of IGFBP-3 Measurements in the Differential Diagnosis between Growth Hormone Deficiency and Idiopathic Short Stature

(IRMA), and levels were expressed as standard deviation score (SDS). The following polymorphisms were determined: IGF1.PCR1 and rs6220 (C/T) in the IGF1 gene; rs2854744 (–202 A/C) and rs13241830 (–185 C/T) in the IGFBP3 gene, and rs3751893 (C/T, D70D) and five single nucleotide polymorphisms in the promoter region of the IGFALS gene. Cutoff levels for maximal DE were calculated by receiver operating characteristic (ROC) analysis.

Contents Vol. 55, 2001

W.F. Blum, Bad Homburg J.-P. Bourguignon, Liège H.G. Burger, Melbourne P.G. Chatelain, Lyon G. Chiumello, Milan P.E. Clayton, Manchester G. Copinschi, Brussels H.J. Degenhart, Rotterdam M.G. Forest, Lyon J. Girard, Basel P.D. Gluckman, Auckland A. Grüters, Berlin Z. Hochberg, Haifa R.P. Kelch, Iowa City, Iowa P.J. Keller, Zurich S.W.J. Lamberts, Rotterdam F. Leidenberger, Hamburg C.J. Migeon, Baltimore, Md. E. Milgrom, Bicêtre J. Müller, Copenhagen (Book Reviews) O.H. Pescovitz, Indianapolis, Ind. D.A. Price, Manchester R.G. Rosenfeld, Portland, Ohio G. Saggese, Pisa M.O. Savage, London S.M. Shalet, Manchester T. Tanaka, Tokyo G. Van Vliet, Montreal R.J. Voutilainen, Kuopio G.A. Werther, Parkville, Australia J.-M. Wit, Leiden M. Zachmann, Zurich