Camilla A. M. Glad

The GH/IGF-1 axis in obesity: pathophysiology and therapeutic considerations

Obesity has become one of the most common medical problems in developed countries, and this disorder is associated with high incidences of hypertension, dyslipidaemia, cardiovascular disease, type 2 diabetes mellitus and specific cancers. Growth hormone (GH) stimulates the production of insulin-like growth factor 1 in most tissues, and together GH and insulin-like growth factor 1 exert powerful collective actions on fat, protein and glucose metabolism. Clinical trials assessing the effects of GH treatment in patients with obesity have shown consistent reductions in total adipose tissue mass, in particular abdominal and visceral adipose tissue depots. Moreover, studies in patients with abdominal obesity demonstrate a marked effect of GH therapy on body composition and on lipid and glucose homeostasis. Therefore, administration of recombinant human GH or activation of endogenous GH production has great potential to influence the onset and metabolic consequences of obesity. However, the clinical use of GH is not without controversy, given conflicting results regarding its effects on glucose metabolism. This Review provides an introduction to the role of GH in obesity and summarizes clinical and preclinical data that describe how GH can influence the obese state.

Identification of Adipocyte Genes Regulated by Caloric Intake

CONTEXT Changes in energy intake have marked and rapid effects on metabolic functions, and some of these effects may be due to changes in adipocyte gene expression that precede alterations in body weight. OBJECTIVE The aim of the study was to identify adipocyte genes regulated by changes in caloric intake independent of alterations in body weight. RESEARCH DESIGN AND METHODS Obese subjects given a very low-caloric diet followed by gradual reintroduction of ordinary food and healthy subjects subjected to overfeeding were investigated. Adipose tissue biopsies were taken at multiple time-points, and gene expression was measured by DNA microarray. Genes regulated in the obese subjects undergoing caloric restriction followed by refeeding were identified using two-way ANOVA corrected with Bonferroni. From these, genes regulated by caloric restriction and oppositely during the weight-stable refeeding phase were identified in the obese subjects. The genes that were also regulated, in the same direction as the refeeding phase, in the healthy subjects after overfeeding were defined as being regulated by caloric intake. Results were confirmed using real-time PCR or immunoassay. RESULTS Using a significance level of P < 0.05 for all comparisons, 52 genes were down-regulated, and 50 were up-regulated by caloric restriction and regulated in the opposite direction by refeeding and overfeeding. Among these were genes involved in lipogenesis (ACLY, ACACA, FASN, SCD), control of protein synthesis (4EBP1, 4EBP2), β-oxidation (CPT1B), and insulin resistance (PEDF, SPARC). CONCLUSIONS Metabolic genes involved in lipogenesis, protein synthesis, and insulin resistance are central in the transcriptional response of adipocytes to changes in caloric intake.

Cell death–inducing DFF45-like effector C is reduced by caloric restriction and regulates adipocyte lipid metabolism

Members of the cell death-inducing DFF45-like effector (CIDE) gene family have been shown to regulate lipid metabolism. In this article, we report that the third member of the human CIDE family, CIDEC, is down-regulated in response to a reduced caloric intake. The down-regulation was demonstrated by microarray and real-time polymerase chain reaction analysis of subcutaneous adipose tissue in 2 independent studies on obese patients undergoing treatment with a very low calorie diet. By analysis of CIDEC expression in 65 human tissues, we conclude that human CIDEC is predominantly expressed in subcutaneous adipocytes. Together, these observations led us to investigate the effect of decreased CIDEC expression in cultured 3T3-L1 adipocytes. Small interfering RNA-mediated knockdown of CIDEC resulted in an increased basal release of nonesterified fatty acids, decreased responsiveness to adrenergic stimulation of lipolysis, and increased oxidation of endogenous fatty acids. Thus, we suggest that CIDEC is a regulator of adipocyte lipid metabolism and may be important for the adipocyte to adapt to changes in energy availability.

Influence of the Exon 3-Deleted/Full-Length Growth Hormone (GH) Receptor Polymorphism on the Response to GH Replacement Therapy in Adults with Severe GH Deficiency

CONTEXT There is considerable individual variation in the clinical response to GH replacement therapy in GH deficient (GHD) adults. Useful predictors of treatment response are lacking. OBJECTIVE The aim of the study was to assess the influence of the exon 3-deleted (d3-GHR) and full-length (fl-GHR) GH receptor isoforms on the response to GH replacement therapy in adults with severe GHD. DESIGN AND PATIENTS A total of 124 adult GHD patients (79 men; median age, 50 yr) were studied before and after 12 months of GH therapy. GHD patients were divided into those bearing fl/fl alleles (group 1) and those bearing at least one d3-GHR allele (group 2), and the genotype was related to the effects of GH therapy on IGF-I levels and total body fat (BF). INTERVENTION GH dose was individually titrated to obtain normal serum IGF-I levels. MAIN OUTCOME MEASURES GHR genotype was determined by PCR amplification, IGF-I levels by immunoassay, and BF by a four-compartment model. RESULTS Seventy-two (58%) patients had fl/fl genotype and were classified as group 1, whereas 52 (42%) had at least one d3-GHR allele and were classified as group 2 (40 were heterozygous and 12 were homozygous). At baseline, there were no significant differences in the study groups. Changes in IGF-I and BF after 12 months of GH treatment did not differ significantly between the two genotype groups. CONCLUSION The presence of d3-GHR allele did not influence the response to GH replacement therapy in our cohort of adults with severe GHD.

Common Genetic Variants in the Glucocorticoid Receptor and the 11β-Hydroxysteroid Dehydrogenase Type 1 Genes Influence Long-Term Cognitive Impairments in Patients With Cushing's Syndrome in Remission

CONTEXT Cognitive function is impaired in patients with Cushings syndrome (CS) in remission. OBJECTIVE The objective of the investigation was to study the effects of polymorphisms in genes associated with glucocorticoid (GC) sensitivity on cognitive function in patients with CS in long-term remission. DESIGN This was a cross-sectional, case-controlled, single-center study. PATIENTS Fifty-three patients with CS in remission and 53 controls matched for age, gender, and educational level participated in the study. MAIN OUTCOME MEASURES Cognitive function, studied using standardized neuropsychological testing, and polymorphisms in the GC receptor (NR3C1; Bcl1 and A3669G), mineralocorticoid receptor (NR3C2; I180V), 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1; rs11119328), and ATP binding cassette B1 (ABCB1; rs1045642) genes were measured. The association between cognitive function and polymorphisms were analyzed using linear regression with adjustments for age and educational level. RESULTS The mean age in patients and controls was 53 ± 14 years. The median (interquartile range) duration of remission was 13 (5-18) years. In patients, the single-nucleotide polymorphism rs11119328 was associated with impairments in processing speed, auditory attention, auditory working memory, and reading speed. This association was not seen in matched controls. The Bcl1 polymorphism was associated with fatigue and worse visual attention and working memory. The remaining single-nucleotide polymorphisms were not associated with cognitive performance. CONCLUSION In this study, polymorphisms in the 11βHSD1 and NR3C1 genes were associated with impaired cognitive function, indicating that GC sensitivity and prereceptor regulation of GC action may play a role in the long-term consequences of CS. The study provides a novel insight into the etiology of cognitive dysfunction in patients with CS in remission.

Rapid and high throughput genotyping of the growth hormone receptor exon 3 deleted/full-length polymorphism using a tagSNP

OBJECTIVE The growth hormone (GH) receptor (GHR) exon 3 deleted/full-length (d3/fl) polymorphism has been suggested to affect GH sensitivity. The conventional genotyping method used for this polymorphism (multiplex PCR with fragment detection by gel electrophoresis) is laborious and requires large amount of DNA template. This has restricted analysis of this polymorphism to small cohorts. Our aim was to evaluate the accuracy of using a tagging single nucleotide polymorphism (tagSNP) as a marker for the d3/fl polymorphism. DESIGN The d3/fl polymorphism was analyzed using TaqMan SNP genotyping of the tagSNP rs6873545 in 183 patients with adult GH deficiency (GHD). The results were compared to d3/fl genotypes determined by the conventional method. RESULTS Genotyping success rate for the tagSNP was 100%. Frequency of the d3-allele was 24.0% (d3/d3 7.7%, d3/fl 32.2% and fl/fl 60.1%) and the results from the two different methods were identical. Moreover, three samples previously undetermined when genotyped using the conventional method were successfully analyzed using the tagSNP. CONCLUSION The GHR d3/fl polymorphism can be studied by TaqMan SNP genotyping. Use of the tagSNP facilitates investigations of the effects of the d3/fl polymorphism in large cohorts.

SNPs within the GH-signaling pathway are associated with the early IGF1 response to GH replacement therapy in GHD adults

OBJECTIVE GH-deficient (GHD) adults have reduced serum concentrations of IGF1. GH replacement therapy increases serum IGF1 concentrations, but the interindividual variation in treatment response is large and likely influenced by genetic factors. This study was designed to test the hypothesis that single-nucleotide polymorphisms (SNPs) in genes within the GH signaling pathway influence the serum IGF1 response to GH replacement. DESIGN AND METHODS A total of 313 consecutive GHD adults (58.1% men; mean age 49.7 years) were studied before and after 1 week, 6 months, and 1 year of GH treatment. GH dose was individually titrated to normalize serum IGF1 levels. Six SNPs in the GH receptor (GHR) and the GH signaling pathway (JAK2, STAT5B, SOCS2, and PIK3CB) genes were selected for genotyping. The GHR exon 3-deleted/full-length (d3/fl) polymorphism was analyzed using tagSNP rs6873545. RESULTS After 1 week of GH replacement, homozygotes of the fl-GHR showed a better IGF1 response to GH than carriers of the d3-GHR (P=0.016). Conversely, homozygotes of the minor allele of PIK3CB SNP rs361072 responded better than carriers of the major allele (P=0.025). Compared with baseline, both SNPs were associated with the IGF1 response at 6 months (P=0.041 and P=0.047 respectively), and SNP rs6873545 was further associated with the IGF1 response at 1 year (P=0.041). CONCLUSIONS Our results indicate that common genetic variants in the GH signaling pathway may be of functional relevance to the response to GH replacement in GHD adults.

Body composition and bone mineral density in women with Cushing's syndrome in remission and the association with common genetic variants influencing glucocorticoid sensitivity

OBJECTIVE Adverse body compositional features and low bone mineral density (BMD) are the characteristic of patients with active Cushings syndrome (CS). The aim of this study was to evaluate body composition and BMD in women with CS in long-term remission and the influence of polymorphisms in genes affecting glucocorticoid (GC) sensitivity on these end-points. DESIGN, PATIENTS AND METHODS This was a cross-sectional, case-controlled study, including 50 women previously treated for CS and 50 age and gender-matched controls. Median (interquartile range) remission time was 13 (5-19) years. Body composition and BMD were measured with dual-energy X-ray absorptiometry. Five polymorphisms in four genes associated with GC sensitivity were analysed using TaqMan or Sequenom single-nucleotide polymorphism genotyping. RESULTS Patients with CS in remission had increased abdominal fat mass (P<0.01), whereas BMD was not significantly different at any site between patients and controls. In patients, the NR3C1 Bcl1 polymorphism was associated with reduced total (P<0.05) and femur neck BMD (P<0.05). The polymorphism rs1045642 in the ABCB1 gene was associated with increased abdominal fat mass (P<0.05) and decreased appendicular skeletal muscle mass (P<0.05). GC replacement was associated with reduced total BMD (P<0.01), BMD at lumbar spine (P<0.05) and increased abdominal fat (P<0.01). CONCLUSION Ongoing GC replacement therapy together with polymorphisms in two genes related with GC sensitivity is associated with abdominal obesity and adverse skeletal health in patients with CS in long-term remission.

Genotypes associated with lipid metabolism contribute to differences in serum lipid profile of GH-deficient adults before and after GH replacement therapy

OBJECTIVE GH deficiency (GHD) in adults is associated with an altered serum lipid profile that responds to GH replacement therapy (GHRT). This study evaluated the influence of polymorphisms in genes related to lipid metabolism on serum lipid profile before and after 1 year of GHRT in adults. DESIGN AND METHODS In 318 GHD patients, total cholesterol (TC) serum concentrations, LDL-C, HDL-C, and triglycerides (TG) were assessed. Using a candidate gene approach, 20 single nucleotide polymorphisms (SNPs) were genotyped. GH dose was individually titrated to obtain normal serum IGF1 concentrations. RESULTS At baseline, the minor alleles of cholesteryl ester transfer protein (CETP) gene SNPs rs708272 and rs1800775 were associated with higher serum TC and apolipoprotein E (APOE) gene SNP rs7412 with lower TC concentrations; CETP SNPs rs708272, rs1800775, and rs3764261 and apolipoprotein B (APOB) gene SNP rs693 with higher serum HDL-C; APOE SNP rs7412, peroxisome proliferator-activated receptor gamma (PPARG) gene SNP rs10865710 with lower LDL-C, and CETP SNP rs1800775 with higher LDL-C; and APOE/C1/C4/C2 cluster SNP rs35136575 with lower serum TG. After treatment, APOB SNP rs676210 GG genotype was associated with larger reductions in TC and LDL-C and PPARG SNP rs10865710 CC genotype with greater TC reduction. All associations remained significant when adjusted for age, sex, and BMI. CONCLUSIONS In GHD adults, multiple SNPs in genes related to lipid metabolism contributed to individual differences in baseline serum lipid profile. The GH treatment response in TC and LDL-C was influenced by polymorphisms in the APOB and PPARG genes.

Reverse feeding suppresses the activity of the GH axis in rats and induces a preobesogenic state.

Reversed feeding (RF) is known to disrupt hormone rhythmicity and metabolism. Although these effects may be mediated in part by phase inversion of glucocorticoid secretion, the precise mechanism is incompletely characterized. In this study, we demonstrate that acute nocturnal food deprivation in male rats suppressed the amplitude of spontaneous GH secretion during the dark phase by 62% (P < 0.001), without affecting baseline secretion. Prolonged RF, which reduced pituitary weight (by 22%; P < 0.05), also suppressed GH pulse height sufficiently to reduce skeletal growth (by 4-5%; P < 0.01) and terminal liver weight (by 11%; P < 0.001). Despite this suppression of the GH axis, proportionate adiposity was not elevated, probably due to the accompanying 16% reduction in cumulative food intake (P < 0.01). We demonstrate that RF also resulted in phase inversion of core clock gene expression in liver, abdominal white adipose tissue (WAT) and skeletal muscle, without affecting their expression patterns in the suprachiasmatic nucleus. In addition, RF resulted in phase inversion of hepatic peroxisome proliferator-activated receptor γ2 mRNA expression, a 3- to 5-fold elevation in fatty acid synthase mRNA in WAT in both light- and dark-phase samples (P < 0.01) and an elevation in muscle uncoupling protein 3 mRNA expression at the beginning of the light phase (P < 0.01). Consumption of a high-fat diet increased inguinal (by 36%; P < 0.05) and retroperitoneal WAT weight (by 72%; P < 0.01) only in RF-maintained rats, doubling the efficiency of lipid accumulation (P < 0.05). Thus, RF not only desynchronizes central and peripheral circadian clocks, and suppresses nocturnal GH secretion, but induces a preobesogenic state.