What Is the Role for Pediatric Endocrinologists in the Management of Skeletal Dysplasias?

Children with skeletal dysplasias have not been consistently managed by pediatric endocrinologists despite the recognized expertise of these practitioners in managing genetic growth disorders. Growth-altering treatments have broadened the role of the pediatric endocrinologist to manage and sometimes become primary coordinators for genetic disorders such as Turner syndrome and Prader-Willi syndrome. We illustrate how recent advances in understanding the pathophysiology of skeletal disorders and the development of targeted treatments provide an opportunity for pediatric endocrinologists to further expand their role in managing certain skeletal dysplasias, including achondroplasia.

The History of the Insulin-Like Growth Factor System.

The growth hormone (GH)-insulin-like growth factor (IGF) cascade is central to the regulation of growth and metabolism. This article focuses on the history of the components of the IGF system, with an emphasis on the peptide hormones, IGF-I and -II, their cell surface receptors, and the IGF binding proteins (IGFBPs) and IGFBP proteases that regulate the availability of the peptide hormones for interaction with their receptors in relevant target tissues. We describe landmark events in the evolution of the somatomedin hypothesis, including evidence that has become available from experiments at the molecular and cellular levels, whole animal and tissue-specific gene knockouts, studies of cancer epidemiology, identification of prismatic human cases, and short- and long-term clinical trials of IGF-I therapy in humans. In addition, this new evidence has expanded our clinical definition of GH insensitivity (GHI) beyond growth hormone receptor mutations (classic Laron syndrome) to include conditions that cause primary IGF deficiency by impacting post-receptor signal transduction, IGF production, IGF availability to interact with the IGF-I receptor (IGF-1R), and defects in the IGF-1R, itself. We also discuss the clinical aspects of IGFs, from their description as insulin-like activity, to the use of IGF-I in the diagnosis and treatment of GH deficiency, and to the use of recombinant human IGF-I for therapy of children with GHI.

Literature review and expert opinion on the impact of achondroplasia on medical complications and health-related quality of life and expectations for long-term impact of vosoritide: a modified Delphi study.

BACKGROUND: Achondroplasia is associated with disproportionate short stature and significant and potentially severe medical complications. Vosoritide is the first medicine to treat the underlying cause of achondroplasia and data from phase 3 and phase 2 extension studies showed effects on growth and body proportions. However, there are currently no long-term data available on the direct impact on endpoints such as medical complications and health-related quality of life (HRQoL). This study explored the perceived impact of achondroplasia on medical complications, HRQoL, healthcare resource use and mortality, and potential modifying effects of vosoritide, based on published evidence and expert opinion. Structured expert opinion was obtained by an international modified Delphi study among 14 experts in managing achondroplasia performed on a virtual platform and consisting of an explorative phase followed by an anonymous individual rating round. RESULTS: Overall, the panelists expect that in individuals starting long-term treatment between 2 years of age and puberty, growth velocity increases observed in the clinical trials will be maintained until final height is reached (92% agreement) and will likely result in clinically meaningful improvements in upper-to-lower body segment ratio (85%). Earlier treatment initiation will likely result in a greater final height (100%) and more likely improve proportionality (92%) than later treatment. Although current data are limited, ≥ 75% of panelists find it conceivable that the earlier long-term treatment is started, the greater the probability of a positive effect on the lifetime incidence of symptomatic spinal stenosis, kyphosis, obstructive sleep apnea, and foramen magnum stenosis. These are among the most clinically important complications of achondroplasia because of their high impact on comorbidity, mortality, and/or HRQoL. A positive effect of vosoritide on the incidence of surgeries through lifetime was considered more likely with earlier long-term treatment (90%). CONCLUSIONS: This explorative study, based on international expert opinion, provides further insight into the medical and functional impacts of achondroplasia and how these might be modified through long-term use of vosoritide. The results can be used to guide the direction and design of future research to validate the assumptions and to discuss potential treatment outcomes with disease modifying therapies with families and clinicians.

Safety Outcomes During Pediatric GH Therapy: Final Results From the Prospective GeNeSIS Observational Program.

Context: Safety concerns have been raised regarding premature mortality, diabetes, neoplasia, and cerebrovascular disease in association with GH therapy. Objective: To assess incidence of key safety outcomes. Design: Prospective, multinational, observational study (1999 to 2015). Setting: A total of 22,311 GH-treated children from 827 investigative sites in 30 countries. Patients: Children with growth disorders. Interventions: GH treatment. Main outcome measures: Standardized mortality ratio (SMR) and standardized incidence ratio (SIR) with 95% CIs for mortality, diabetes, and primary cancer using general population registries. Results: Predominant short stature diagnoses were GH deficiency (63%), idiopathic short stature (13%), and Turner syndrome (8%), with mean ± SD follow-up of 4.2 ± 3.2 years (∼92,000 person-years [PY]). Forty-two deaths occurred in patients with follow-up, with an SMR (95% CI) of 0.61 (0.44, 0.82); the SMR was elevated for patients with cancer-related organic GH deficiency [5.87 (3.21, 9.85)]. Based on 18 cases, type 2 diabetes mellitus (T2DM) risk was elevated [SIR: 3.77 (2.24, 5.96)], but 72% had risk factors. In patients without cancer history, 14 primary cancers were observed [SIR: 0.71 (0.39, 1.20)]. Second neoplasms occurred in 31 of 622 cancer survivors [5.0%; 10.7 (7.5, 15.2) cases/1000 PY] and intracranial tumor recurrences in 67 of 823 tumor survivors [8.1%; 16.9 (13.3, 21.5) cases/1000 PY]. All three hemorrhagic stroke cases had risk factors. Conclusions: GeNeSIS (Genetics and Neuroendocrinology of Short Stature International Study) data support the favorable safety profile of pediatric GH treatment. Overall risk of death or primary cancer was not elevated in GH-treated children, and no hemorrhagic strokes occurred in patients without risk factors. T2DM incidence was elevated compared with the general population, but most cases had diabetes risk factors.

Mortality in Children Receiving Growth Hormone Treatment of Growth Disorders: Data From the Genetics and Neuroendocrinology of Short Stature International Study.

Context: Although pediatric growth hormone (GH) treatment is generally considered safe for approved indications, concerns have been raised regarding potential for increased risk of mortality in adults treated with GH during childhood. Objective: To assess mortality in children receiving GH. Design: Prospective, multinational, observational study. Setting: Eight hundred twenty-seven study sites in 30 countries. Patients: Children with growth disorders. Interventions: GH treatment during childhood. Main Outcome Measure: Standardized mortality ratios (SMRs) and 95% confidence intervals (CIs) using age- and sex-specific rates from the general population. Results: Among 9504 GH-treated patients followed for ≥4 years (67,163 person-years of follow-up), 42 deaths were reported (SMR, 0.77; 95% CI, 0.56 to 1.05). SMR was significantly elevated in patients with history of malignant neoplasia (6.97; 95% CI, 3.81 to 11.69) and borderline elevated for those with other serious non-GH-deficient conditions (2.47; 95% CI, 0.99-5.09). SMRs were not elevated for children with history of benign neoplasia (1.44; 95% CI, 0.17 to 5.20), idiopathic GHD (0.11; 95% CI, 0.02 to 0.33), idiopathic short stature (0.20; 95% CI, 0.01 to 1.10), short stature associated with small for gestational age (SGA) birth (0.66; 95% CI, 0.08 to 2.37), Turner syndrome (0.51; 95% CI, 0.06 to 1.83), or short stature homeobox-containing (SHOX) gene deficiency (0.83; 95% CI, 0.02 to 4.65). Conclusions: No significant increases in mortality were observed for GH-treated children with idiopathic GHD, idiopathic short stature, born SGA, Turner syndrome, SHOX deficiency, or history of benign neoplasia. Mortality was elevated for children with prior malignancy and those with underlying serious non-GH-deficient medical conditions.

Biology of the somatotroph axis (after the pituitary).

Normal growth requires that pituitary-secreted growth hormone (GH) bind to its specific receptor and activate a complex signaling cascade, leaving to production of insulin-like growth factor-I (IGF-I), which, in turn, activates its own receptor (IGF1R). The GH receptor (GHR) is preformed as a dimer and is transported in a nonligand bound state to the cell surface. Binding of GH to the GHR dimer, results in a conformational change of the dimer, activation of the intracellular Janus Kinase 2 (JAK2) and phosphorylation of signal transducer and activator of transcription (STAT) 5B. Phosphorylated STAT5B dimers are then translocated to the nucleus, where they transcriptionally activate multiple genes, including those for IGF-I, IGF binding protein-3 and the acid-labile subunit (ALS).

Development of additional pituitary hormone deficiencies in pediatric patients originally diagnosed with isolated growth hormone deficiency due to organic causes.

OBJECTIVE: To determine characteristics of children initially diagnosed with isolated growth hormone deficiency (IGHD) of organic aetiology, who later developed multiple pituitary hormone deficiencies (MPHD). DESIGN: Data were analysed for 716 growth hormone-treated children with organic IGHD, who were growth hormone-naïve at baseline in the multinational, observational Genetics and Neuroendocrinology of Short Stature International Study. METHODS: Development of MPHD was ascertained from investigator-provided diagnoses, adverse events and concomitant medications. Analyses were performed for all patients and separately for those who developed MPHD within 4.5 years or had >3.5 years follow-up and continued to have IGHD (4-year cohort). RESULTS: MPHD developed in 71/716 (9.9%) children overall, and in 60/290 (20.7%) in the 4-year cohort. The most frequent additional deficiencies were thyroid-stimulating hormone (47 patients) and gonadotropins (23 patients). Compared with those who remained with IGHD, children who developed MPHD had more severe GHD at study entry, significantly lower baseline insulin-like growth factor1, peak stimulated growth hormone, and more frequent diagnosis of intracranial tumour or mutation of gene(s) controlling hypothalamic-pituitary development and/or function. Multivariate logistic regression analyses identified female gender, longer follow-up, higher baseline age and lower peak stimulated growth hormone as predictors of MPHD development. CONCLUSIONS: MPHD is more likely to develop in patients with severe organic IGHD, especially those with history of intracranial tumour or mutation of gene(s) controlling hypothalamic-pituitary development and/or function. Older baseline age, female gender and longer follow-up duration were also associated with higher incidence of MPHD. Long-term monitoring of pituitary function is recommended, irrespective of the aetiology of GHD.

A novel variant in CDKN1C is associated with intrauterine growth restriction, short stature, and early-adulthood-onset diabetes.

CONTEXT: CDKN1C, a cyclin-dependent kinase inhibitor and negative regulator of cellular proliferation, is paternally imprinted and has been shown to regulate ß-cell proliferation. CDKN1C mutations are associated with growth disorders, including Beckwith-Wiedemann syndrome and IMAGe syndrome. OBJECTIVE: To investigate the genetic basis for a familial disorder characterized by intrauterine growth restriction, short stature, and early-adulthood-onset diabetes. DESIGN, SETTING, AND PARTICIPANTS: Genomic DNA samples (15 affected and 26 unaffected from a six-generation pedigree) were analyzed by genome-wide single nucleotide polymorphism arrays, whole exome and Sanger sequencing, and multiplex ligation-dependent probe amplification. MAIN OUTCOME MEASURE(S): Subjects were assessed for height, weight, adrenal gland size, ACTH, diabetes status, and testis volume. Linkage and sequence analyses were performed, and the identified genetic variant was functionally evaluated in reconstitution studies. RESULTS: The pedigree followed a paternally imprinted pattern of inheritance, and genetic linkage analysis identified a single significant 2.6-megabase locus on chromosome 11p15, within the imprinting center region 2. Multiplex ligation-dependent probe amplification did not detect copy number variants or methylation abnormalities. Whole exome sequencing revealed a single novel variant in the proliferating cell nuclear antigen-binding region of CDKN1C (c.842G>T, p.R281I) that co-segregated with affected status and, unlike variants found in IMAGe, did not entirely abrogate proliferating cell nuclear antigen binding. Clinical assessments revealed that affected individuals had low testicular volume but normal adrenal function. CONCLUSIONS: We report a novel CDKN1C mutation associated with features of IMAGe syndrome, but without adrenal insufficiency or metaphyseal dysplasia, and characterized by early-adulthood-onset diabetes. Our data expand the range of phenotypes observed with CDKN1C defects and suggest that CDKN1C mutations may represent a novel monogenic form of diabetes.

Development of additional pituitary hormone deficiencies in pediatric patients originally diagnosed with idiopathic isolated GH deficiency.

OBJECTIVE: We assessed the characteristics of children initially diagnosed with idiopathic isolated GH deficiency (IGHD) who later developed additional (multiple) pituitary hormone deficiencies (MPHD). DESIGN: Data were analyzed for 5805 pediatric patients with idiopathic IGHD, who were GH-naïve at baseline and GH-treated in the multinational, observational Genetics and Neuroendocrinology of Short Stature International Study. METHODS: Development of MPHD was assessed from investigator diagnoses, adverse events, and concomitant medications. Analyses were performed for all patients and for those who developed MPHD within 4.5 years or had ≥3.5 years, follow-up and continued to have IGHD (4-year cohort). RESULTS: MPHD developed in 118/5805 (2.0%) children overall, and in 96/1757 (5.5%) in the 4-year cohort. Patients who developed MPHD had more profound GHD, with decreased height SDS, IGF1 SDS and peak stimulated GH, and greater height decrement vs target, compared with children who continued to have IGHD (P<0.001 for each variable). Delivery complications, congenital anomalies, and perinatal/neonatal adverse events occurred more frequently in patients who developed MPHD. The most frequent additional deficiency was TSH (82 patients overall); four patients developed two pituitary hormone deficiencies and one developed three deficiencies. Multivariable logistic regression indicated that years of follow-up (odds ratio 1.55), baseline age (1.17), baseline height SDS (0.69), and peak stimulated GH (0.64) were associated with the development of MPHD. CONCLUSIONS: MPHD is more likely to develop in patients with more severe idiopathic IGHD. Older baseline age, lower baseline height SDS, and longer follow-up duration are associated with increased risk of development of MPHD.

Differentiating the roles of STAT5B and STAT5A in human CD4+ T cells.

STAT5A and STAT5B are highly homologous proteins whose distinctive roles in human immunity remain unclear. However, STAT5A sufficiency cannot compensate for STAT5B defects, and human STAT5B deficiency, a rare autosomal recessive primary immunodeficiency, is characterized by chronic lung disease, growth failure and autoimmunity associated with regulatory T cell (Treg) reduction. We therefore hypothesized that STAT5A and STAT5B play unique roles in CD4(+) T cells. Upon knocking down STAT5A or STAT5B in human primary T cells, we found differentially regulated expression of FOXP3 and IL-2R in STAT5B knockdown T cells and down-regulated Bcl-X only in STAT5A knockdown T cells. Functional ex vivo studies in homozygous STAT5B-deficient patients showed reduced FOXP3 expression with impaired regulatory function of STAT5B-null Treg cells, also of increased memory phenotype. These results indicate that STAT5B and STAT5A act partly as non-redundant transcription factors and that STAT5B is more critical for Treg maintenance and function in humans.

Novel microcephalic primordial dwarfism disorder associated with variants in the centrosomal protein ninein.

CONTEXT: Microcephalic primordial dwarfism (MPD) is a rare, severe form of human growth failure in which growth restriction is evident in utero and continues into postnatal life. Single causative gene defects have been identified in a number of patients with MPD, and all involve genes fundamental to cellular processes including centrosome functions. OBJECTIVE: The objective of the study was to find the genetic etiology of a novel presentation of MPD. DESIGN: The design of the study was whole-exome sequencing performed on two affected sisters in a single family. Molecular and functional studies of a candidate gene were performed using patient-derived primary fibroblasts and a zebrafish morpholino oligonucleotides knockdown model. PATIENTS: Two sisters presented with a novel subtype of MPD, including severe intellectual disabilities. MAIN OUTCOME MEASURES: NIN, encoding Ninein, a centrosomal protein critically involved in asymmetric cell division, was identified as a candidate gene, and functional impacts in fibroblasts and zebrafish were studied. RESULTS: From 34,606 genomic variants, two very rare missense variants in NIN were identified. Both probands were compound heterozygotes. In the zebrafish, ninein knockdown led to specific and novel defects in the specification and morphogenesis of the anterior neuroectoderm, resulting in a deformity of the developing cranium with a small, squared skull highly reminiscent of the human phenotype. CONCLUSION: We identified a novel clinical subtype of MPD in two sisters who have rare variants in NIN. We show, for the first time, that reduction of ninein function in the developing zebrafish leads to specific deficiencies of brain and skull development, offering a developmental basis for the myriad phenotypes in our patients.

A novel missense mutation in the SH2 domain of the STAT5B gene results in a transcriptionally inactive STAT5b associated with severe IGF-I deficiency, immune dysfunction, and lack of pulmonary disease.

CONTEXT: Signal transducer and activator of transcription 5b (STAT5b) deficiency, first reported in a patient who carried a p.Ala630Pro missense mutation in the Src homology 2 (SH2) domain, results in a rare clinical condition of GH insensitivity (GHI), IGF-I deficiency (IGFD), and severe immune dysregulation manifesting as progressive worsening of pulmonary function. PATIENT: The new patient presented with severe cutaneous eczema, episodic infections in the first years of life, and autoimmune thyroiditis. Immunological evaluation revealed T lymphopenia, but severe pulmonary symptoms were notably absent. She concomitantly exhibited pronounced growth failure, reaching an adult height of 124.7 cm [-5.90 SD score (SDS)]. Endocrine evaluations (normal provocative GH tests; low serum IGF-I, -3.7 SDS, and IGF-binding protein-3, -4.5 SDS) were consistent with GHI and IGFD. RESULTS: Analysis of the STAT5B gene revealed a novel homozygous missense mutation, p.Phe646Ser, located within the ßD' strand of the SH2 domain. Reconstitution studies demonstrated expression of the p.Phe646Ser variant was less robust than wild type but, in contrast to the previously described STAT5B p.Ala630Pro SH2 mutation, could be phosphorylated in response to GH and interferon-γ. The phosphorylated p.Phe646Ser, however, could not drive transcription. CONCLUSION: A novel STAT5B p.Phe646Ser mutation has been identified in a patient with clinical characteristics of STAT5b deficiency. Only the second STAT5B missense mutation identified, its lack of transcriptional activities despite GH-induced phosphorylation, confirms the crucial role of STAT5b for regulating the expression of IGF1 and provides insights into the importance of the SH2 ßD' strand for full STAT5b transcriptional activities. Whether the phosphorylated p.Phe646Ser variant retained functions that prevented pulmonary distress remains unresolved.

STAT5b deficiency: lessons from STAT5b gene mutations.

Growth hormone (GH) regulates insulin-like growth factor (IGF)-I production primarily through activation of the GH receptor (GHR)-signal transducer and activator of transcription (STAT)-5b signaling cascade. One of four STAT proteins (STAT1, -3, -5a and -5b) activated by the GH-GHR system, the critical importance of STAT5b in IGF-I production became evident with the identification of homozygous, autosomal recessive STAT5b mutations in patients who presented with severe postnatal growth failure, growth hormone insensitivity syndrome (GHIS) and marked IGF-I deficiency. Unlike GHIS due to GHR mutations, patients carrying STAT5b mutations also presented with chronic pulmonary disease and evidence of perturbations of T-cell homeostasis. At present, no single treatment(s) is available to improve both poor statural growth and immune deficiency. Continued clinical evaluations of patients with STAT5b mutations and elucidating the impact of the mutation on STAT5b structure and function, are important to understanding the pathophysiology of this rare, complex, disease (MIM 245590).

IGFBP-3 sensitizes prostate cancer cells to interferon-gamma-induced apoptosis.

OBJECTIVE: Insulin-like growth factor binding protein-3 (IGFBP-3) has been shown to exhibit diverse biological actions, including IGF-independent effects on cell growth and cell death. Here we report that IGFBP-3 sensitizes prostate cancer cells to interferon-gamma (IFN-gamma)-induced apoptosis and inhibition of cell proliferation. DESIGN: The cell growth or cell death of prostate cells in response to the treatments of IGFBPs and/or IFN-gamma was measured, and the signaling pathways mediating these actions assessed. RESULTS: Cell proliferation was minimally affected when M12 prostate cancer cells were treated with exogenous IGFBP-3 (1-5 microg/ml), IGFBP-1 (1-5 microg/ml) or IFN-gamma (20 U/ml). However, strong inhibition of cell growth and significant apoptosis were observed when M12 cells were co-treated with IGFBP-3 and IFN-gamma, but not with IGFBP-1 and IFN-gamma. These effects were IGF-independent and appear not to require intracellular localization of IGFBP-3, as similar results were obtained with mutants of IGFBP-3 that either could not bind IGF or has impaired ability to be internalized. Further analyses revealed that IGFBP-3, but not IGFBP-1, could significantly enhance the weak tyrosine phosphorylation of STAT1 induced by IFN-gamma (20 U/ml) alone. The IGFBP-3-promoted apoptosis in the presence of IFN-gamma could also be abrogated by blockade of the mTOR pathway with its pharmacological inhibitors, LY294002 or rapamycin. CONCLUSIONS: These results demonstrated that in a cancer cell line not responsive to exogenous IGFBP-3 alone, IGFBP-3 sensitized the cells to the anti-proliferative, proapoptotic actions of IFN-gamma through an IGF-independent, STAT1- and mTOR-dependent mechanism.

Short stature in partially corrected X-linked severe combined immunodeficiency--suboptimal response to growth hormone.

BACKGROUND: X-linked severe combined immunodeficiency (XSCID) results from defects in the common cytokine receptor gamma chain (gamma c) required for signaling by receptors for interleukin (IL)-2, -4, -7, -9, -15, and -21. Following haploidentical bone marrow transplant without myelo-conditioning for XSCID, most patients achieve partial reconstitution often limited to T lymphocytes. Many partially corrected patients manifest extreme short stature (<5th percentile). Previous reports have implicated gamma c in growth hormone (GH) receptor signaling, thus severe growth failure in XSCID may be related to the underlying gamma c defect. AIM: To evaluate the GH/insulin-like growth factor-I (IGF-I) axis in three children with XSCID and partial immune reconstitution with profound growth failure. METHODS: The IGF-I generation test was performed by administering recombinant GH subcutaneously for 5 days, and measuring serum levels for IGF-I before GH injection, and on days 5 and 8. RESULTS: Study of the somatotropic axis revealed profoundly diminished IGF-I production following rGH challenge in all three patients. CONCLUSION: The data indicate that the GH/IGF-I axis in these partially corrected XSCID patients with severe short stature is profoundly impaired, and supports previous studies suggesting that the underlying gamma c defect may contribute to the severe growth failure in XSCID. This supports a role for defective gamma c in the extreme short stature of XSCID, and raises the possibility of recombinant IGF-I treatment to bypass this defect.

Insulin resistance is associated with increased serum concentration of IGF-binding protein-related protein 1 (IGFBP-rP1/MAC25).

IGF-binding protein (IGFBP)-related protein 1 (IGFBP-rP1) has been shown to bind both IGFs and insulin, albeit with low affinity, and to inhibit insulin signaling. We hypothesized that IGFBP-rP1 is associated with insulin resistance and components of the IGF system in humans. To this aim, a cross-sectional study was conducted in 113 nondiabetic and 43 type 2 diabetic men. Insulin sensitivity (insulin sensitivity index [S(i)] from intravenous glucose tolerance tests in nondiabetic subjects, or the rate constant for disappearance of glucose [K(ITT)] from insulin tolerance tests in type 2 diabetic subjects), circulating IGFBP-rP1 (from enzyme-linked immunosorbent assay), adiponectin (from radioimmunoassay), C-reactive protein (CRP; from immunoturbidimetry), soluble tumor necrosis factor receptor 2 (sTNFR2; from enzyme-amplified sensitivity immunoassay), and IGF system parameters (IGF-I, free IGF-I, and IGFBP-1 from immunoradiometric assay) were assessed in all subjects. Among nondiabetic men, those in the highest quartile for circulating IGFBP-rP1 exhibited decreased S(i) and adiponectin (both P < 0.01) as well as increased CRP and sTNFR2 (both P < 0.05). Circulating IGFBP-rP1 was also found to be increased in previously undiagnosed type 2 diabetic patients (P = 0.01) but not in known type 2 diabetic patients receiving pharmacological therapy. Although no changes in IGF system components were evident by IGFBP-rP1 quartiles in nondiabetic subjects, independent positive associations of IGFBP-rP1 with circulating fasting IGFBP-1 were evident after adjustment for insulin resistance parameters in both nondiabetic and type 2 diabetic subjects, with IGFBP-rP1 explaining 2 and 11% of IGFBP-1 variance, respectively. In additional multivariate analyses, S(i), sTNFR2, and age stood as independent predictive variables of IGFBP-rP1 (together explaining 18% of its variance) in nondiabetic subjects, and BMI became the only independent predictive variable of IGFBP-rP1 (explaining 26% of its variance) in type 2 diabetic men. These findings show for the first time that circulating IGFBP-rP1 is increased with insulin resistance, and they also suggest novel interactions between IGFBP-rP1 and the IGF system in humans.

In vivo imaging of hepatic growth hormone signaling.

We developed a system to noninvasively and repeatedly image in vivo hepatic GH signaling. GH regulates postnatal growth and metabolism. It affects numerous tissues, but has major effects in liver. We used nude mice for adenoviral-mediated delivery of a signal transducer and activator of transcription 5-dependent GH response element, a luciferase reporter to detect GH signaling pathway activation. We detected by noninvasive bioluminescence imaging GH-induced hepatic GH signaling serially within intact mice. Statistically significant effects of GH dose and time dependence were detected in the liver luciferase signal that peaked 3 h after GH injection. Codelivery of GH receptor significantly enhanced GH response, an effect that was further augmented by fasting. Our imaging system allows detailed in vivo analysis of GH signaling and action and may be a paradigm for studies of additional signaling pathways in liver and other tissues.