Regulation in vivo of the acid-labile subunit of the rat serum insulin-like growth factor-binding protein complex

Endocrine and cellular physiology and pathology of the insulin-like growth factor acid-labile subunit

The acid-labile subunit (ALS) of the insulin-like growth factor (IGF) binding protein (IGFBP) complex, encoded in humans by IGFALS, has a vital role in regulating the endocrine transport and bioavailability of IGF-1 and IGF-2. Accordingly, ALS has a considerable influence on postnatal growth and metabolism. ALS is a leucine-rich glycoprotein that forms high-affinity ternary complexes with IGFBP-3 or IGFBP-5 when they are occupied by either IGF-1 or IGF-2. These complexes constitute a stable reservoir of circulating IGFs, blocking the potentially hypoglycaemic activity of unbound IGFs. ALS is primarily synthesized by hepatocytes and its expression is lower in non-hepatic tissues. ALS synthesis is strongly induced by growth hormone and suppressed by IL-1β, thus potentially serving as a marker of growth hormone secretion and/or activity and of inflammation. IGFALS mutations in humans and Igfals deletion in mice cause modest growth retardation and pubertal delay, accompanied by decreased osteogenesis and enhanced adipogenesis. In hepatocellular carcinoma, IGFALS is described as a tumour suppressor; however, its contribution to other cancers is not well delineated. This Review addresses the endocrine physiology and pathology of ALS, discusses the latest cell and proteomic studies that suggest emerging cellular roles for ALS and outlines its involvement in other disease states.

Expression of acid-labile subunit (ALS) in developing and adult zebrafish and its role in dorso-ventral patterning during development

Mammalian acid-labile subunit (ALS) is a serum protein that binds binary complexes between Insulin-like growth factors (IGFs) and Insulin-like growth factor-binding proteins (IGFBPs) extending their half-life and keeping them in the vasculature. Human ALS deficiency (ACLSD), due to homozygous or compound heterozygous mutations in IGFALS, leads to moderate short stature with reduced levels of IGF-I and IGFBP-3. There is only one corresponding zebrafish ortholog gene and it has not yet been studied. In this study we elucidate the role of igfals during zebrafish development. In zebrafish embryos igfals mRNA is expressed throughout development, mainly in the brain and subsequently also in the gut and swimbladder. To determine its role during development, we knocked down igfals gene product using morpholinos (MOs). Igfals morphant embryos displayed dorsalization in different degrees of severity, including a shortened trunk and loss of tail. Furthermore, co-injection of human IGFALS (hIGFALS) mRNA was able to rescue the MO-induced phenotype. Finally, overexpression of either hIGFALS or zebrafish igfals (zigfals) mRNA leads to ventralization of embryos including a reduced head and enlarged tail. These findings suggest that als plays an important role in dorso-ventral patterning during zebrafish development.

Effect of insulin treatment on circulating insulin-like growth factor I and IGF-binding proteins in cats with diabetes mellitus

BACKGROUND

Insulin-like growth factor-I (IGF-I) is used to screen for acromegaly in diabetic cats. In humans, most circulating IGF-I forms ternary complexes (TC) with IGF-binding protein (IGFBP-3) and an acid-labile subunit. Compared to humans, the amount of TC in cats is more variable. Insulin-like growth factor-I concentrations are reported to increase during insulin treatment, more rapidly in cats achieving remission.

OBJECTIVES

To investigate (i) factors associated with circulating IGF-I concentrations, including IGFBP-profiles (ii) effect of insulin treatment on IGF-I concentrations and (iii) IGF-I as prognostic marker of diabetes mellitus remission.

ANIMALS

Thirty-one privately owned diabetic cats of which 24 were followed 1 year, and 13 healthy cats.

METHODS

Prospective study. Serum insulin, IGF-I, glucose, and fructosamine concentrations were measured. IGF-binding forms were determined by chromatography in 14 diabetic and 13 healthy cats; and IGF-I, IGF-II, IGFBP-3, and IGFBP-5 by mass spectrometry in 3 cats achieving remission.

RESULTS

Insulin-like growth factor-I median (interquartile range) before start of insulin treatment was 300 (160-556) ng/mL. Insulin-like growth factor-I was positively associated with TC (P < .0001) and endogenous insulin (P = .005) and negatively associated with fructosamine (P < .0001). Median IGF-I was higher 2-4 weeks after start of insulin treatment compared with baseline (300 versus 670 ng/mL, P = .0001) and predicted future remission (P = .046). In cats that went into remission, the amount of TC and IGFBP-3 increased, suggesting increase in IGF-I is dependent on TC formation.

CONCLUSIONS

Insulin treatment should be accounted for when interpreting IGF-I in diabetic cats. Insulin-like growth factor-I 2-4 weeks after initiation of insulin treatment shows promise as prognostic marker for remission in diabetic cats.

Deficits in Trabecular Bone Microarchitecture in Young Women With Type 1 Diabetes Mellitus

The pathophysiological mechanism of increased fractures in young adults with type 1 diabetes mellitus (T1DM) is unclear. We conducted a case-control study of trabecular bone microarchitecture and vertebral marrow adiposity in young women with T1DM. Thirty women with T1DM with a median age (range) age of 22.0 years (16.9, 36.1) attending one outpatient clinic with a median age at diagnosis of 9.7 years (0.46, 14.8) were compared with 28 age-matched healthy women who acted as controls. Measurements included MRI-based assessment of proximal tibial bone volume/total volume (appBV/TV), trabecular separation (appTb.Sp), vertebral bone marrow adiposity (BMA), and abdominal adipose tissue and biochemical markers of GH/IGF-1 axis (IGF-1, IGFBP3, ALS) and bone turnover. Median appBV/TV in cases and controls was 0.3 (0.22, 0.37) and 0.33 (0.26, 0.4), respectively (p = 0.018) and median appTb.Sp in T1DM was 2.59 (2.24, 3.38) and 2.32 (2.03, 2.97), respectively (p = 0.012). The median appBV/TV was 0.28 (0.22, 0.33) in those cases with retinopathy (n = 15) compared with 0.33 (0.25, 0.37) in those without retinopathy (p = 0.02). Although median visceral adipose tissue in cases was higher than in controls at 5733 mm(3) (2030, 11,144) and 3460 mm(3) (1808, 6832), respectively (p = 0.012), there was no difference in median BMA, which was 31.1% (9.9, 59.9) and 26.3% (8.5, 49.8) in cases and controls, respectively (p = 0.2). Serum IGF-1 and ALS were also lower in cases, and the latter showed an inverse association to appTbSp (r = -0.30, p = 0.04). Detailed MRI studies in young women with childhood-onset T1DM have shown clear deficits in trabecular microarchitecture of the tibia. Underlying pathophysiological mechanisms may include a microvasculopathy.

Acid-labile subunit levels and the association with response to growth hormone treatment in short children born small for gestational age

AIMS

To determine acid-labile subunit (ALS) levels in short small for gestational age (SGA) children and to assess the relationship between ALS levels and several clinical and laboratory characteristics. Also, to assess whether adding ALS levels to a growth prediction model might improve the long-term growth prediction.

DESIGN/METHODS

ALS levels were measured in 312 short SGA children at the start of growth hormone (GH) treatment.

RESULTS

Median (interquartile range) ALS of all subjects was -0.5 SDS, significantly below the 0 SDS (p < 0.001). In 34 children (11%), ALS levels were ≤-2 SDS. ALS SDS correlated significantly with height SDS (r = 0.24, p < 0.001), weight SDS (r = 0.30, p < 0.001), BMI SDS (r = 0.20, p = 0.001), IGF-I SDS (r = 0.56, p < 0.001) and IGFBP-3 SDS (r = 0.67, p < 0.001). ALS SDS was also positively correlated with fasting insulin (r = 0.41, p < 0.001) and glucose levels (r = 0.33, p < 0.001), and HOMA-IR (r = 0.35, p < 0.001). Baseline ALS levels contributed to the long-term growth prediction of GH treatment (5%, p < 0.001).

CONCLUSION

Short SGA children tend to have lower ALS levels compared to controls, albeit less reduced than IGF-I and IGFBP-3 levels. Our data suggest that ALS may be involved in glucose homeostasis. Determination of ALS levels before the start of GH treatment in short SGA children contributes moderately to a more accurate prediction of the growth response to GH treatment.

Pathological impact of SMN2 mis-splicing in adult SMA mice

Loss-of-function mutations in SMN1 cause spinal muscular atrophy (SMA), a leading genetic cause of infant mortality. The related SMN2 gene expresses suboptimal levels of functional SMN protein, due to a splicing defect. Many SMA patients reach adulthood, and there is also adult-onset (type IV) SMA. There is currently no animal model for adult-onset SMA, and the tissue-specific pathogenesis of post-developmental SMN deficiency remains elusive. Here, we use an antisense oligonucleotide (ASO) to exacerbate SMN2 mis-splicing. Intracerebroventricular ASO injection in adult SMN2-transgenic mice phenocopies key aspects of adult-onset SMA, including delayed-onset motor dysfunction and relevant histopathological features. SMN2 mis-splicing increases during late-stage disease, likely accelerating disease progression. Systemic ASO injection in adult mice causes peripheral SMN2 mis-splicing and affects prognosis, eliciting marked liver and heart pathologies, with decreased IGF1 levels. ASO dose–response and time-course studies suggest that only moderate SMN levels are required in the adult central nervous system, and treatment with a splicing-correcting ASO shows a broad therapeutic time window. We describe distinctive pathological features of adult-onset and early-onset SMA.

Evaluation of insulin-like growth factor acid-labile subunit as a potential biomarker of effect for deoxynivalenol-induced proinflammatory cytokine expression

Consumption of the trichothecene deoxynivalenol (DON) suppresses growth in experimental animals - an adverse effect that was used to establish the tolerable daily intake for this toxin. DON ingestion has been recently found to suppress plasma insulin-like growth factor acid-labile subunit (IGFALS), a protein essential for growth. Studies were conducted to explore the feasibility of using plasma IGFALS as a biomarker of effect for DON. In the first study, weanling mice were fed 0, 1, 2.5, 5 and 10 ppm DON and weight and plasma IGFALS determined at intervals over 9 wk. Reduced body weight gains were detectable beginning at wk 5 in the 10 ppm dose and wk 7 at the 5 ppm dose. Plasma IGFALS was significantly depressed at wk 5 in the 5 and 10 ppm groups at wk 9 in the 10 ppm group. Depressed IGFALS significantly correlated with reduced body weight at wk 5 and 9. Benchmark dose modeling revealed the BMDL and BMD for plasma IGFALS reduction were 1.1 and 3.0 ppm DON and for weight reduction were 2.1 and 4.5 ppm DON. In the second study, it was demonstrated that mice fed 15 ppm DON diet had significantly less plasma IGFALS than mice fed identical amounts of control diet. Thus DON's influence on IGFALS likely reflects the combined effects of reduced food intake as well as its physiological action involving suppressors of cytokine signaling. Taken together, these findings suggest that plasma IGFALS might be a useful biomarker for DON's adverse effects on growth.

Hepatic growth hormone and glucocorticoid receptor signaling in body growth, steatosis and metabolic liver cancer development

Growth hormone (GH) and glucocorticoids (GCs) are involved in the control of processes that are essential for the maintenance of vital body functions including energy supply and growth control. GH and GCs have been well characterized to regulate systemic energy homeostasis, particular during certain conditions of physical stress. However, dysfunctional signaling in both pathways is linked to various metabolic disorders associated with aberrant carbohydrate and lipid metabolism. In liver, GH-dependent activation of the transcription factor signal transducer and activator of transcription (STAT) 5 controls a variety of physiologic functions within hepatocytes. Similarly, GCs, through activation of the glucocorticoid receptor (GR), influence many important liver functions such as gluconeogenesis. Studies in hepatic Stat5 or GR knockout mice have revealed that they similarly control liver function on their target gene level and indeed, the GR functions often as a cofactor of STAT5 for GH-induced genes. Gene sets, which require physical STAT5-GR interaction, include those controlling body growth and maturation. More recently, it has become evident that impairment of GH-STAT5 signaling in different experimental models correlates with metabolic liver disease, ranging from hepatic steatosis to hepatocellular carcinoma (HCC). While GH-activated STAT5 has a protective role in chronic liver disease, experimental disruption of GC-GR signaling rather seems to ameliorate metabolic disorders under metabolic challenge. In this review, we focus on the current knowledge about hepatic GH-STAT5 and GC-GR signaling in body growth, metabolism, and protection from fatty liver disease and HCC development.

Hormone replacement therapy and physical function in healthy older men. Time to talk hormones?

Improving physical function and mobility in a continuously expanding elderly population emerges as a high priority of medicine today. Muscle mass, strength/power, and maximal exercise capacity are major determinants of physical function, and all decline with aging. This contributes to the incidence of frailty and disability observed in older men. Furthermore, it facilitates the accumulation of body fat and development of insulin resistance. Muscle adaptation to exercise is strongly influenced by anabolic endocrine hormones and local load-sensitive autocrine/paracrine growth factors. GH, IGF-I, and testosterone (T) are directly involved in muscle adaptation to exercise because they promote muscle protein synthesis, whereas T and locally expressed IGF-I have been reported to activate muscle stem cells. Although exercise programs improve physical function, in the long-term most older men fail to comply. The GH/IGF-I axis and T levels decline markedly with aging, whereas accumulating evidence supports their indispensable role in maintaining physical function integrity. Several studies have reported that the administration of T improves lean body mass and maximal voluntary strength in healthy older men. On the other hand, most studies have shown that administration of GH alone failed to improve muscle strength despite amelioration of the detrimental somatic changes of aging. Both GH and T are anabolic agents that promote muscle protein synthesis and hypertrophy but work through separate mechanisms, and the combined administration of GH and T, albeit in only a few studies, has resulted in greater efficacy than either hormone alone. Although it is clear that this combined approach is effective, this review concludes that further studies are needed to assess the long-term efficacy and safety of combined hormone replacement therapy in older men before the medical rationale of prescribing hormone replacement therapy for combating the sarcopenia of aging can be established.

Do insulin-like growth factor associated proteins qualify as a tumor marker? Results of a prospective study in 163 cancer patients

OBJECTIVE

Insulin-like growth factor (IGF)-1, -2 and Insulin like growth factor binding proteins (IGFBP) are involved in the proliferation and differentiation of cells. It has never been evaluated, if the IGF-system can serve as a tumor marker in neoplasms.

METHODS

In our prospective study 163 patients with colorectal cancer (22), prostate cancer (21), head and neck tumors (17), lymphomas (20), lung cancer (34) and other entities (49) were analysed for their IGF and IGFBP serum levels at the beginning and the end of radiotherapy and compared to 13 healthy people. Subgroups of patients with local tumor disease versus metastatic disease, primary and recurrent therapy and curative versus palliative therapy were compared.

RESULTS

The serum levels of IGF-2 were significantly elevated in patients with prostate and colorectal cancer. However, sensitivity and specificity were only 70%. IGFBP-2 serum levels were elevated in patients with head and neck tumors. Again sensitivity and specificity were only 73%. A difference between local disease and metastatic disease could not be found. A difference between IGF serum levels before and after radiotherapy could not be detected.

CONCLUSION

The IGF-system cannot serve as a new tumor marker. The detected differences are very small, sensitivity and specificity are too low. IGF measurement is not useful for the evaluation of the success of radiotherapy in malignancies.

Evaluation of IGF-I levels and serum protein profiles of diabetic cats and dogs

In this study, we measured the insulin-like growth factor (IGF)-I levels and evaluated the serum protein profiles of diabetic, insulin-treated, and healthy cats and dogs. The total IGF-I concentrations were 33.74 ± 3.4 ng/mL for normal, 25.8 ± 4.5 ng/mL for diabetic, and 180.4 ± 31.4 ng/mL for insulin-treated cats. IGF-I concentrations were 46.4 ± 6.6 ng/mL for normal, 25.1 ± 4.1 ng/mL for diabetic, and 303.0 ± 61.3 ng/mL for insulin-treated dogs. Total serum protein profiles were analyzed by SDS-PAGE. Fourteen bands ranging from 25 to 240 kDa in size were observed for cats, and 17 bands ranging from 25 to 289 kDa were observed for dogs. The densities of the bands differed among control, diabetic, and insulin-treated animals. In conclusion, we found that serum protein profiles and IGF-I concentrations were altered in both diabetic and insulin-treated animals. When judiciously interpreted in the light of other clinical and laboratory data, the techniques used in our study provide a valuable modality for measuring the severity of diabetes mellitus in dogs and cats.

IGF-I, IGF-II, IGFBP2, IGFBP3 and acid-labile subunit (ALS) in colorectal cancer patients before surgery and during one year follow up in relation to age

PURPOSE

To investigate the changes of IGF system in colon cancer patients in relation to age, the serum IGF-I, IGF-II, IGFBP2, IGFBP3 and ALS were measured by immunochemistry before surgery, as well as one and six months after surgery.

MATERIAL AND METHODS

One hundred and twenty six patients were included into the study: group I (<50 yrs, N=21); group II (50 to <55 yrs, N=16) ; group III (55 to <65 yrs, N=34); group IV (65 to <75 yrs, N=42) and group V (> or =75 yrs, N=13).

RESULTS

Before surgery: only the mean value of IGF-I concentration in group I was significantly higher as compared to group V (p<0.01). One month after surgery: 1) a decrease in the mean values of IGF-I, IGF-II, IGFBP3 and ALS levels was observed, but only for IGF-II (groups II-V), IGFBP3 (groups II-V) and ALS (groups III-V) the changes were significant; 2) the mean value of ALS level in group I was higher as compared to group III-V (p<0.05 to 0.02); 3) higher mean values of IGF-I/alb, IGFBP3/alb and ALS/alb were noted for group I as compared to group V (p<0.01 to 0.001); 4) the mean levels of IGFBP2 were significantly lower in group I as compared to groups II, III, IV and V (p<0.001 in all cases).

CONCLUSIONS

In colon cancer patients IGF-I, IGFBP3 and ALS decrease with age, but the relation between them exists regardless the patient's age and time of observation. Lower IGFBP2 level together with higher IGF-I might contribute to more aggressive course of disease in colon cancer patients below 50 years of age.

The acid-labile subunit is required for full effects of exogenous growth hormone on growth and carbohydrate metabolism

Normal postnatal growth is dependent in part on overlapping actions of GH and IGF-I. These actions reflect GH stimulation of IGF-I production in liver and extrahepatic tissues, representing respectively the endocrine and autocrine/paracrine arms of the IGF system. Recent experiments in genetically modified mice show that each source of IGF-I can compensate for absence of the other but do not resolve their relative role in postnatal growth. In an effort to address this issue, we studied the GH responsiveness of mice harboring a null mutation of the acid-labile subunit (ALS). Null ALS mice have a substantial reduction in endocrine IGF-I but, unlike other models of plasma IGF-I deficiency, have no obvious additional endocrine defects. Wild type and null ALS mice of both sexes received daily sc injections of saline or recombinant bovine GH between d 35 and 63 of postnatal age. The GH-stimulated body weight gain of null ALS mice was reduced by more than 30% relative to wild type mice, irrespective of sex. Reductions in GH responsiveness were also seen for kidney and linear growth. Absence of ALS eliminated the ability of GH to increase plasma IGF-I despite intact GH-dependent stimulation of IGF-I expression in liver, adipose tissue, and skeletal muscle. GH treatment was also less efficient in antagonizing insulin action in null ALS mice. Overall, these results suggest that the GH effects mediated by endocrine IGF-I depends on ALS, and accordingly null ALS mice are less responsive to exogenous GH therapy.

Hepatic gene and protein expression of primary components of the IGF-I axis in long lived Snell dwarf mice

Recent evidence indicates that the GH/IGF-I axis plays a key role in the control of aging and longevity. To better understand this biological relationship we examined the mRNA and corresponding protein levels of primary IGF-I axis genes in the livers of young and aged long-lived Snell dwarf mice relative to their age-matched controls. We demonstrated that the level of IGF-I and ALS mRNAs is dramatically decreased in both young and aged dwarf livers, transcripts encoding IGF-IR and IGFBP-I are elevated in young dwarfs, but normalize to control levels in aged dwarf livers while transcripts encoding IGFBP-3 are elevated only in aged controls. Interestingly, regulation at the protein level of several IGF-I axis components in the Snell dwarf appears to involve both altered gene expression and post-translational regulation. In this study, we reveal both concordant and discordant relationships between mRNA and protein levels for particular components of the IGF-I axis, illustrating that some of these gene products are not solely regulated by transcriptional mechanisms. These results are consistent with a delay in the molecular maturation of the IGF-I axis in dwarf livers, suggesting the preservation of some neonatal characteristics in young adult and aged dwarf livers. Our studies provide gene expression and protein abundance profiles for components of IGF-I axis that are distinguishing characteristics of both young and aged dwarf mice, and suggest that delayed development of the IGF-I axis in the young adult Pit1(dw/dwJ) dwarf liver may play an important role in the endocrine regulation of mammalian longevity.

Regulation of the somatotropic axis by intensive insulin therapy during protracted critical illness

The catabolic state of critical illness has been linked to the suppressed somatotropic GH-IGF-binding protein (IGFBP) axis. In critically ill patients it has been demonstrated that, compared with the conventional approach, which only recommended insulin therapy when blood glucose levels exceeded 12 mmol/liter, strict maintenance of blood glucose levels below 6.1 mmol/liter with intensive insulin therapy almost halved intensive care mortality, acute renal failure, critical illness polyneuropathy, and bloodstream infections. Poor blood glucose control in diabetes mellitus has also been associated with low serum IGF-I levels, which can be increased by insulin therapy. We hypothesized that intensive insulin therapy would improve the IGF-I axis, possibly contributing to the clinical correlates of anabolism. Therefore, this study of 363 patients, requiring intensive care for more than 7 d and randomly assigned to either conventional or intensive insulin therapy, examines the effects of intensive insulin therapy on the somatotropic axis. Contrary to expectation, intensive insulin therapy suppressed serum IGF-I, IGFBP-3, and acid-labile subunit concentrations. This effect was independent of survival of the critically ill patient. Concomitantly, serum GH levels were increased by intensive insulin therapy. The suppression of IGF-I in association with the increased GH levels suggests GH resistance induced by intensive insulin therapy, which was reflected by the decreased serum GH-binding protein levels. Intensive insulin therapy did not affect IGFBP-3 proteolysis, which was markedly higher in protracted critically ill patients compared with healthy controls. Also, intensive insulin therapy did not suppress the urea/creatinine ratio, a clinical correlate of catabolism. In conclusion, our data suggest that intensive insulin therapy surprisingly suppressed the somatotropic axis despite its beneficial effects on patient outcome. GH resistance accompanied this suppression of the IGF-I axis. To what extent and through which mechanisms the changes in the GH-IGF-IGFBP axis contributed to the survival benefit under intensive insulin therapy remain elusive.

Age-dependent regulation of the acid-labile subunit in response to fasting-refeeding in rats

The GH-dependent, hepatocyte-derived acid-labile subunit (ALS) regulates IGF release from the serum by forming ternary complexes containing IGF binding protein (IGFBP)-3 or IGFBP-5. Malnutrition suppresses ALS and IGF-I expression in a development-dependent manner. Our aim was to investigate whether the effect of feeding following fasting was similarly age dependent. We fasted juvenile and adult rats for 48 h and then refed them, collecting serum and liver tissue at 8, 24, and 48 h. These were compared with rats before fasting (0 h controls) and animals fed throughout the study (free-fed controls). During fasting, serum ALS fell to 25 +/- 5.3% of 0 h controls in juveniles but only 56 +/- 6% in adults. Within 24 h of refeeding, ALS in juveniles had returned to 0 h control levels, and by 48 h to free-fed levels, whereas there was no significant refeeding response in adults during this period. Circulating IGF-I and IGFBP-5 showed similar age-dependent responses to refeeding, rising significantly faster in juveniles. IGFBP-3 did not show this response. Furthermore, hepatic ALS and IGF-I mRNA showed no age-differential response to fasting and refeeding, suggesting posttranscriptional regulation. Neither regulation of hepatic GH receptor nor ALS clearance rates could explain the age-dependent effect. We hypothesize that development-dependent regulation of ALS and IGF-I during refeeding may involve a posttranscriptional hepatic response that is not GH dependent.

Regulation of the acid-labile subunit in sustained endotoxemia

The effect of sustained endotoxemia on expression of the acid-labile subunit (ALS) in relation to hepatic markers of altered GH and insulin sensitivity was examined. Juvenile rats were injected with endotoxin twice daily for 48 h, causing reduced food intake and attenuated growth. In pair-fed controls, food restriction caused marked suppression of ALS gene expression and circulating levels within 12 h, and endotoxemia augmented this effect. This acute effect of endotoxin corresponded temporally with transient induction of suppressor of cytokine signaling (SOCS)-3, cytokine-inducible SH2-containing protein (CIS), phosphoenolpyruvate carboxykinase (PEPCK), and insulin-like growth factor-binding protein (IGFBP)-1 and suppression of GH receptor (GHR). During the subsequent 36 h of sustained endotoxin treatment, expression of ALS recovered to, and then rose above, that of their pair-fed controls. This effect was paralleled by other ternary complex components. The inductive effect of sustained endotoxemia relative to pair-fed controls could not be explained by differences in expression of GHR, SOCS-3, or CIS but coincided with normalized PEPCK and IGFBP-1 levels, suggesting better hepatic insulin sensitivity in these animals. These data may indicate that, in sustained endotoxemia, ALS levels are regulated through modulation of hepatic insulin sensitivity.

Insights from insulin-like growth factor binding protein transgenic mice

The existence of abundant high affinity binding proteins for the IGFs, the IGF binding proteins (IGFBPs), was first demonstrated more than 40 yr ago in the very early days of somatomedin research. With the development of molecular techniques and transgenic and knockout mouse models, the nature, complexity, and redundancy of the IGFBPs have now started to be elucidated. Indeed the functional role of the circulating IGFs and the originally proposed endocrine somatomedin hypothesis have recently been questioned. The limited reports to date indicate that IGFBP knockout mice have few phenotypic manifestations. In contrast, overexpression of IGFBPs in transgenic mice is associated with manifestations that provide some insight into the physiological role of the binding proteins. The predominant effect of generalized or tissue-specific overexpression of the IGFBPs has been growth inhibition as would be anticipated from inhibition of the actions of IGF-I and -II. In addition, impaired glucose homeostasis and reduced fecundity have been observed in both IGFBP-1- and IGFBP-3-overexpressing transgenic mice. This review examines the data reported to date for transgenic mouse models that overexpress IGFBPs. In addition, data from transgenic mice that overexpress the acid-labile subunit, an important component of the ternary complex, have also been reviewed.

Insulin-like growth factor (IGF)-I binding to a cell membrane associated IGF binding protein-3 acid-labile subunit complex in human anterior pituitary gland

The binding characteristics of [(125) I]insulin-like growth factor (IGF)-I were studied in human brain and pituitary gland. Competition binding studies with DES(1-3)IGF-I and R(3) -IGF-I, which display high affinity for the IGF-I receptor and low affinity for IGF binding proteins (IGFBPs), were performed to distinguish [(125) I]IGF-I binding to IGF-I receptors and IGFBPs. Specific [(125) I]IGF-I binding in brain regions and the posterior pituitary was completely displaced by DES(1-3)IGF-I and R(3) -IGF-I, indicating binding to IGF-I receptors. In contrast, [(125) I]IGF-I binding in the anterior pituitary was not displaced by DES(1-3)IGF-I and R(3) -IGF-I, suggesting binding to an IGF-binding site that is different from the IGF-I receptor. Binding affinity of IGF-I to this site was about 10-fold lower than for the IGF-I receptor. Using western immunoblotting we were also unable to detect IGF-I receptors in human anterior pituitary. Instead, western immunoblotting and immunoprecipitation experiments showed a 150-kDa IGFBP-3-acid labile subunit (ALS) complex in the anterior pituitary and not in the posterior pituitary and other brain regions. RT-PCR experiments showed the expression of ALS mRNA in human anterior pituitary indicating that the anterior pituitary synthesizes ALS. In the brain regions and posterior pituitary, IGFBP-3 was easily washed away during pre-incubation procedures as used in the [(125) I]IGF-I binding experiments. In contrast, the IGFBP-3 complex in the anterior pituitary could not be removed by these washing procedures. Our results indicate that the human anterior pituitary contains a not previously described tightly cell membrane-bound 150-kDa IGFBP-3-ALS complex that is absent in brain and posterior pituitary.

Dexamethasone does not increase IGF-I and IGFBP-3 levels in man in the absence of endogenous GH

It has been previously shown that short-term glucocorticoid administration increases circulating IGF-I and IGFBP-3 levels both in men and rats. An increase in endogenous GH secretion or a direct hepatic effect have been suggested as possible mechanisms. The aim of this study was to investigate the effect of short-term dexamethasone administration (3 mg orally during 7 days) in 8 patients with Sheehan's syndrome in replacement therapy. All patients had GH values <2.5 pg/l after clonidine administration. Before treatment IGF-I values were 9.3 3.6 microg/l (mean +/- SE) and IGFBP-3 levels were 1,195 +/- 208 microg/l. After dexamethasone administration there were no significant changes either in IGF-I or IGFBP-3 values (10.7 +/- 4.1 and 1,110 +/- 214 microg/l, respectively). A significant increase in insulin values was observed after dexamethasone administration (before: 120 +/- 10 micromol/l; after: 175 +/- 27 pmol/l; p<0.05), while glucose levels did not reach statistical significance (before: 4.6 +/- 0.3 mmol/l; after: 5.9 +/- 1.0 mmol/l). Our data suggest that dexamethasone is unable to increase circulating IGF-I and IGFBP-3 levels in man in the absence of endogenous GH.

The insulin-like growth factor binding protein 3 ternary complex is reduced in cirrhosis

BACKGROUND/AIMS

In healthy adults, serum insulin-like growth factor I (IGF-I), IGF binding protein 3 (IGFBP-3) and acid labile subunit (ALS) form a 150-kDa ternary complex under the control of growth hormone (GH). Approximately 80-90% of circulating IGF-I is bound to the ternary complex. In cirrhosis the GH/IGF axis is severely disturbed and the individual components of the ternary complex are reduced. However, the degree of ternary complex formation in cirrhosis has not previously been described.

METHODS

Serum IGF-I, IGFBP-3, ALS, the 150-kDa ternary complex and IGFBP-3 proteolysis were all measured in six compensated and six decompensated cirrhotic patients and compared to six healthy controls.

RESULTS

Patients with compensated cirrhosis had decreased levels of IGF-I (55%), IGFBP-3 (64%) and ALS (53%), and in the decompensated patients these levels were decreased even further: IGF-I (32%), IGFBP-3 (37%) and ALS (27%) compared to healthy controls. The levels of the ternary complex followed this pattern, with low levels seen in the compensated patients (66%) and a further reduction in the decompensated patients (27%). Ternary complex levels correlated negatively with the Child-Pugh score. No increase in IGFBP-3 proteolysis was found in cirrhotic patients compared to healthy controls.

CONCLUSION

Cirrhosis is associated with reduced levels of the 150-kDa ternary IGFBP-3 complex correlating with the degree of liver disease.

Inactivation of the acid labile subunit gene in mice results in mild retardation of postnatal growth despite profound disruptions in the circulating insulin-like growth factor system

Insulin-like growth factors (IGFs) I and II are important regulators of cell proliferation and differentiation. After birth, plasma IGFs, representing mostly liver-derived IGFs, circulate in ternary complexes of 150 kDa consisting of one molecule each of IGF, IGF-binding protein (IGFBP) 3, and an acid labile subunit (ALS). Onset of ALS synthesis after birth is the primary factor driving the formation of ternary complexes. Capture of IGFs by ALS is thought to allow the development of a plasma reservoir without negative effects such as hypoglycemia and cell proliferation. To evaluate the importance of ALS and ternary complexes, we have created mice in which the ALS gene has been inactivated. The mutation was inherited in a Mendelian manner, without any effects on survival rates and birth weights. A growth deficit was observed in null mice after 3 weeks of life and reached 13% by 10 weeks. This modest phenotype was observed despite reductions of 62 and 88% in the concentrations of plasma IGF-I and IGFBP-3, respectively. Increased turnover accounted for these reductions because indices of synthesis in liver and kidney were not decreased. Surprisingly, absence of ALS did not affect glucose and insulin homeostasis. Therefore, ALS is required for postnatal accumulation of IGF-I and IGFBP-3 but, consistent with findings supporting a predominant role for locally produced IGF-I, is not critical for growth. This model should be useful to determine whether presence of ALS is needed for other actions of liver-derived IGF-I and for maintenance of homeostasis in presence of high circulating levels of IGF-II.

Conservation of a growth hormone-responsive promoter element in the human and mouse acid-labile subunit genes

During extrauterine life, insulin-like growth factors (IGFs) circulate in a ternary serum complex with one IGF-binding protein-3 (IGFBP-3) or IGFBP-5 protein and with a single acid-labile subunit (ALS). GH increases levels of this ternary complex; in mice, this effect is achieved in part by the ability of GH to stimulate mouse ALS (mALS) transcription through an interferon-gamma-activated sequence-like element (GLE) in the mALS promoter. To begin studying how GH regulates human ALS (hALS) gene expression, we cloned the hALS gene and found that it spans approximately 3.3 kb of DNA at chromosomal region 16p13.3. The hALS gene has two exons separated by a 1235-bp intron, which is found at the identical site in rat and mouse ALS genes. Sequence analysis reveals that the hALS 5'-flanking sequence is homologous to the mALS promoter, and that the GH-responsive GLE in the mALS promoter is conserved in both sequence and location in the hALS gene. The region spanning from -755 to -4 bp 5' to the hALS ATG translation start codon directs expression of a luciferase reporter gene in primary rat hepatocytes, and GH increases reporter expression in the presence of the native, but not a mutant, GLE in the hALS promoter. These data suggest that GH stimulates hALS and mALS gene expression by a similar mechanism, which involves at least in part a conserved GLE in the ALS promoter.

Changes in the circulating IGF system during short-term fasting and refeeding in rats

There is little information on free insulin-like growth factor I (IGF-I) and its regulatory proteins during fasting and refeeding. Therefore, we examined rats during fasting (0, 1, 2, and 3 days) and refeeding (3, 6, and 12 h and 1, 2, 3, and 7 days) (n = 6-9). Serum was analyzed for insulin, C-peptide, growth hormone (GH), free and total IGF-I, IGF-binding protein (IGFBP)-1 and -3, and the acid-labile subunit (ALS). Additionally, liver mRNA for IGF-I, IGFBP-1, and ALS was determined. Fasting reduced serum levels of GH, free and total IGF-I, IGFBP-3, and ALS, whereas IGFBP-1 was increased (P < 0.0001). Refeeding normalized IGFBP-1 at 3 h and GH at 12 h. Free IGF-I changed in parallel with total IGF-I, ALS, and IGFBP-3, being normalized at 48 h of refeeding. IGFBP-1 (peptide and mRNA) correlated inversely with insulin and C-peptide (P < 0.001). The correlation between peptide and mRNA was relatively strong for IGFBP-1 (r(2) = 0.36; P < 0.0001), moderate for IGF-I (r(2) = 0.18; P < 0.0005), and insignificant for ALS. In conclusion, insulin appears to regulate IGFBP-1 in fasted and refed rats. However, the normal inverse relationship between free IGF-I and IGFBP-1 was absent, and free IGF-I changed in parallel with total IGF-I and thus ALS and IGFBP-3. Finally, the regulation of the hepatic synthesis of IGF-I, IGFBP-1, and ALS seems to differ substantially.

Decreased serum levels of acid-labile subunit in patients with anorexia nervosa

One of the observations in malnutrition is that serum insulin-like growth factor (IGF)-I levels are decreased, and this decrease is associated with an altered profile of IGF binding proteins (IGFBPs). In human circulation, IGFs are mostly present as an approximately 150-kDa ternary protein complex consisting of IGFs, IGFBP-3, and acid-labile subunit (ALS). In the present study, to clarify the effect of nutrition on serum ALS levels, we investigated 33 patients with anorexia nervosa. Serum levels of ALS were measured by RIA. Furthermore, we measured serum IGF-I, IGF-II, IGFBP-2, and IGFBP-3 levels in the patients. From these data, we investigated which was the best predictor of body mass index (BMI) as a nutritional status marker. In the patients with anorexia nervosa, the serum ALS levels ranged from 0.7-16.9, with a mean of 10.6 +/- 0.7 mg/L, and the levels were significantly lower than those of normal subjects (13.8 +/- 0.8 mg/L, P < 0.05). Serum ALS levels positively correlated with BMI (r = 0.41, P < 0.05), and the levels increased during treatment. The serum IGFBP-2 levels in the patients were increased (871 +/- 91 microg/L), and the levels inversely correlated with BMI (r = -0.52, P < 0.01). The serum IGF-I and IGFBP-3 levels were low (152 +/- 14 microg/L and 2.56 +/- 0.12 mg/L, respectively), and the levels positively correlated with BMI (r = 0.46, P < 0.01; and r = 0.39, P < 0.05, respectively). The serum IGFBP-2, IGF-I, and IGFBP-3 levels returned toward normal ranges as BMI in the patients improved during treatment. Serum IGF-II levels did not correlate with BMI (r = 0.24, P = 0.17). Stepwise regression analysis revealed that serum IGFBP-2 was the best marker of BMI among these variables. The present study suggested that ALS was regulated by nutritional status, the same as IGF-I, IGFBP-2 and IGFBP-3; but the serum IGFBP-2 was the best predictor of BMI as nutritional status marker among the parameters in patients with anorexia nervosa.

Serum free insulin-like growth factor-I is dose-dependently decreased by methylprednisolone and related to body weight changes in rats

Glucocorticoids usually inhibit growth despite a paradoxical increase in total IGF-I. To investigate the effect of methylprednisolone on free IGF-I, rats were treated with for 3 days (0, 1, 2, 4, and 6 mg/kg per day). A dose-dependent decrease in ultrafiltrated serum free IGF-I was observed, being lowest after 6 mg/kg (P < 0.001 all groups vs controls). Total IGF-I was increased in the groups receiving 2 mg/kg (P < 0.05). Weight change in the 24 h prior to blood sampling was positively correlated with free IGF-I (R = 0.46, P = 0.0002), but not with total IGF-I. Immunoassayable IGFBP-1 was decreased in rats given 4 mg/kg (P = 0.001), whereas there was no change in IGFBP-3 or acid-labile subunit. We propose that in rats the glucocorticoid-induced weight loss may in part be due to suppression of circulating free IGF-I.

Interleukin-1 beta suppresses growth hormone-induced acid-labile subunit mRNA levels and secretion in primary hepatocytes

Cytokines are thought to mediate the catabolic states induced by infection and trauma. Recent evidence suggests that the cytokine interleukin-1 beta (IL-1 beta) directly inhibits the anabolic insulin-like growth factor (IGF)-I: growth hormone (GH) axis. The biological activity of circulating IGF is regulated by the hepatocyte derived, GH-dependent acid-labile subunit (ALS) of the 140-kDa IGF binding protein (IGFBP) complex. ALS buffers the growth and metabolic effects of the insulin-like growth factors by sequestering them in a ternary complex with IGFBP-3. To determine whether IL-1 beta has a direct effect on hepatic ALS production, we have examined its effect on ALS mRNA levels and secretion in hepatocytes under GH-induced and basal conditions. In the presence of GH (30 ng/mL) half-maximal reduction of ALS mRNA levels and secretion was induced by between 0.3-3 ng/mL rhIL-1 beta (P < 0.05). However, under basal conditions IL-1 beta had no significant effect on ALS mRNA levels, and only a slight suppression of secretion. Our study suggests that IL-1 beta regulates ALS gene expression and secretion in a way that is dependent, in part, on interaction with the GH signalling pathway.

Expression of insulin-like growth factor-binding protein messenger RNAs in developing rat oligodendrocytes and astrocytes

Insulin-like growth factors, IGF-I and IGF-II, are potent regulators of oligodendrocyte development. Most of the IGF present in vivo is bound to members of a family of six high-affinity IGF-binding proteins (IGFBPs), which can either potentiate or inhibit IGF action, depending on other conditions. Additionally, serum contains a structurally unrelated protein, acid-labile sub-unit (ALS), which forms a ternary complex with IGF and IGFBP3. In this study, we used reverse-transcriptase polymerase chain reaction (RT-PCR) to examine the expression of mRNAs for IGFBP 1-6 and ALS in purified populations of oligodendroglial cells and astrocytes. We found that astrocytes express all six IGFBPs. A2B5+/O4- oligodendrocyte precursors, O4+/O1- intermediate precursors, and O1+ oligodendrocytes express IGFBP3, 5, and 6, while IGFBP4 is expressed in oligodendrocyte precursors but not at more mature stages. We were unable to detect ALS mRNA in whole brain or in cultured oligodendroglial cells. The presence of differentially expressed IGFBPs in developing oligodendrocytes and astrocytes could significantly affect the biological activity of IGF-I and IGF-II in the central nervous system and the IGF-responsiveness of the IGFBP-expressing cells.

Growth hormone stimulates transcription of the gene encoding the acid-labile subunit (ALS) of the circulating insulin-like growth factor-binding protein complex and ALS promoter activity in rat liver

The growth-promoting activity of GH, the principal hormonal determinant of body size, is mediated by insulin-like growth factor I (IGF-I). Most of the IGF-I in plasma circulates in a 150-kDa complex that contains IGF-binding protein-3 (IGFBP-3) and an acid-labile subunit (ALS). The 150-kDa complex serves as a reservoir of IGF-I and determines its bioavailability to the tissues. Formation of the 150-kDa complex depends upon the synthesis of ALS, which is synthesized primarily in liver and is regulated by GH. The present study demonstrates that GH stimulates ALS gene transcription in rat liver and ALS promoter activity in a rat hepatoma cell line. ALS messenger RNA (mRNA) and ALS nuclear transcripts were decreased to similar extents in the livers of GH-deficient hypophysectomized rats. GH increased hepatic ALS mRNA within 3-4 h to about 65% of the levels seen in sham-operated control rats. To confirm that GH stimulated ALS gene transcription, we transiently transfected an ALS promoter-luciferase reporter gene construct into H4-II-E rat hepatoma cells and primary rat hepatocytes. Recombinant human GH (hGH) stimulated promoter activity about 3-fold. In contrast, basal promoter activity was lower, and GH stimulation was absent when the ALS reporter construct was transfected into GH-responsive 3T3-F442A mouse preadipocyte fibroblasts. GH stimulation of ALS promoter activity in H4-II-E cells was mediated by functional GH receptors; nonprimate (rat and bovine) GH gave identical stimulation to hGH, and stimulation by hGH occurred at physiological concentrations. Reverse transcriptase-PCR analysis indicated that GH receptor mRNA was present in H4-II-E cells at approximately 40% of the level seen in rat liver. GH also induced the expression of the endogenous c-fos gene, indicating that the signaling pathway necessary for the activation of gene expression by GH was intact in H4-II-E cells. Thus, H4-II-E cells are a GH-responsive liver cell line that should provide a useful system in which to study the molecular mechanism of transcriptional regulation by GH of ALS and other hepatic genes.

Organization and chromosomal localization of the gene encoding the mouse acid labile subunit of the insulin-like growth factor binding complex

After birth, most of insulin-like growth factor I and II (IGFs) circulate as a ternary complex formed by the association of IGF binding protein 3-IGF complexes with a serum protein called acid-labile subunit (ALS). ALS retains the IGF binding protein-3-IGF complexes in the vascular compartment and extends the t1/2 of IGFs in the circulation. Synthesis of ALS occurs mainly in liver after birth and is stimulated by growth hormone. To study the basis for this regulation, we cloned and characterized the mouse ALS gene. Comparison of genomic and cDNA sequences indicated that the gene is composed of two exons separated by a 1126-bp intron. Exon 1 encodes the first 5 amino acids of the signal peptide and contributes the first nucleotide of codon 6. Exon 2 contributes the last 2 nt of codon 6 and encodes the remaining 17 amino acids of the signal peptide as well as the 580 amino acids of the mature protein. The polyadenylylation signal, ATTAAA, is located 241 bp from the termination codon. The cDNA and genomic DNA diverge 16 bp downstream from this signal. Transcription initiation was mapped to 11 sites over a 140-bp TATA-less region. The DNA fragment extending from nt -805 to -11 (ATG, +1) directed basal and growth hormone-regulated expression of a luciferase reporter plasmid in the rat liver cell line H4-II-E. Finally, the ALS gene was mapped to mouse chromosome 17 by fluorescence in situ hybridization.