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Objective: We sought to compare the relationship between body composition, insulin resistance, and inflammatory adipokines in Aboriginal Canadian women, who are at high risk of vascular disease, with white women., Research Design and Methods: A subgroup of the First Nations Bone Health Study population, consisting of 131 Aboriginal women and 132 matched white women, was utilized. Body composition was determined by whole-body dual X-ray absorptiometry, and blood analytes were measured after an overnight fast., Results: After excluding individuals with diabetes, A1C, BMI, percent trunk fat, and homeostasis model assessment of insulin resistance (HOMA-IR) were greater in First Nation women compared with white women, whereas adiponectin, retinol binding protein (RBP)4, and insulin-like growth factor binding protein-1 (IGFBP-1) were lower. First Nation women had more trunk fat for any given level of total fat than white women. There were no differences in resistin, leptin, tumor necrosis factor (TNF)-alpha, or C-reactive protein (CRP) levels between First Nation and white women. Insulin resistance correlated with leptin and inversely with adiponectin levels in both First Nation and white women. There were weak correlations between insulin resistance and TNF-alpha, interleukin-6, and CRP, but these were not significant after correction for body fat. No correlation was found between RBP4 and insulin resistance. ANCOVA revealed a higher HOMA-IR adjusted for total body fat in First Nation women than in white women (P = 0.015) but not HOMA-IR adjusted for trunk fat (P > 0.2)., Conclusions: First Nation women are more insulin resistant than white women, and this is explained by trunk fat but not total fat. Despite the increased insulin resistance, inflammatory adipokines are not significantly increased in First Nation women compared with white women.

Objective: The relationship between adipokine levels and body composition has not been carefully examined. Most studies in humans are cross-sectional, and the few studies in mice have been restricted to a comparison of control animals with markedly obese, insulin-resistant mice. Our objective was to study changes in adipokine levels and body composition in response to modest dietary intervention., Research Methods and Procedures: Plasma resistin, adiponectin, and leptin levels were examined in mice fed ad libitum, a 75% restricted diet, or a diet supplemented with 10% sucrose. Body composition was determined by whole-body DXA., Results: The percentage body fat was reduced in mice subjected to the restricted diet and increased in mice supplemented with 10% dextrose. Adipokine levels were not different in either of these groups compared with the control mice. A significant inverse correlation was observed between resistin levels and total body fat, whereas there was no significant correlation between body fat and adiponectin levels. Positive correlations were observed between leptin levels and percentage body fat, total body fat, and abdominal fat. Leptin levels correlated with plasma glucose, but multivariate analysis revealed that this correlation was the result of a strong positive correlation between leptin and insulin levels. There were no correlations between glycemia and resistin or glycemia and adiponectin levels, and no correlation was observed between any of the adipokine levels and bone mineral content or density., Discussion: These data suggest that in the mouse, modest dietary perturbations have little effect on resistin and adiponectin levels despite significant effects on glycemia, insulin levels, and bone parameters.

Estrogen and progestin participate in the regulation of adipose tissue metabolism, and peroxisome proliferator-activated receptor-gamma (PPARgamma) and retinoic acid receptor-alpha (RXRalpha) are absolutely required for adipose tissue development. The present study is to investigate the changes in parametrial fat mass and expression of PPARgamma and RXRalpha during estrous cycle in mice. Parametrial white adipose tissues (WAT), inter-scapula brown adipose tissues, and uteri from female mice were weighed. Blood samples were collected for the measurement of 17 beta-estradiol and progesterone levels. An RNase protection assay and Western blot analysis were used to compare the expression of PPARgamma and RXRalpha in adipose tissue. The mass of parametrial WAT in diestrus was significantly higher compared with estrus. However, there is no significant difference on the mass of brown adipose tissues during estrous cycle. The expression of PPARgamma in WAT in diestrus was significantly higher than that in estrus. The expression of RXRalpha during estrous cycle was unchanged in both white and brown adipose tissues. In conclusion, the variation in parametrial WAT mass during the mouse estrous cycle correlates with changes in the expression of PPARgamma in WAT.

IGF binding protein (IGFBP)-3 inhibits cell growth and promotes apoptosis by sequestering free IGFs. In addition IGFBP-3 has IGF-independent, proapoptotic, antiproliferative effects on prostate cancer cells in vitro. Expression of the large T-antigen (Tag) under the long probasin promoter (LPB) in LPB-Tag mice results in prostate tumorigenesis. To investigate the IGF-dependent and IGF-independent effects of IGFBP-3 on prostate tumor growth, we crossed LPB-Tag mice with cytomegalovirus (CMVBP-3) and phosphoglycerate kinase (PGKBP-3) mice that overexpress IGFBP-3 under the cytomegalovirus promoter and the phosphoglycerate kinase promoter, respectively, and also I56G/L80G/L81G-mutant IGFBP-3 (PGKmBP-3) mice that express I56G/L80G/L81G-IGFBP-3, a mutant, that does not bind IGF-I but retains IGF-independent proapoptotic effects in vitro. Prostate tumor size and the steady-state level of p53 were attenuated in LPB-Tag/CMVBP-3 and LPB-Tag/PGKBP-3 mice, compared with LPB-Tag/wild-type (Wt) mice. A more marked effect was observed in LPB-Tag/CMVBP-3, compared with LPB-Tag/PGKBP-3, reflecting increased levels of transgene expression in CMVBP-3 prostate tissue. No attenuation of tumor growth was observed in LPB-Tag/PGKmBP-3 mice during the early tumor development, indicating that the inhibitory effects of IGFBP-3 were most likely IGF dependent during the initiation of tumorigenesis. At 15 wk of age, epidermal growth factor receptor expression was increased in LPB-Tag/Wt and LPB-Tag/PGKmBP-3 tissue, compared with LPB-Tag/PGKBP-3. IGF receptor was increased in all transgenic mice, but pAkt expression, a marker of downstream IGF-I action, was increased only in LPB-Tag/Wt and LPB-Tag/PGKmBP-3. After 15 wk of age, a marked reduction in tumor growth was apparent in LPB-Tag/PGKmBP-3 mice, indicating that the IGF-independent effects of IGFBP-3 may be important in inhibiting tumor progression.

Background: Adipose tissue produces both vascular growth factors and inhibitors. Since obesity is associated with expansion of the capillary bed in regional adipose depots the balance between these factors may favor angiogenesis., Objective: To investigate the relationship between body mass index and serum concentrations of vascular growth factors in human subjects., Methods: Vascular endothelial growth factor (VEGF), VEGF-C, VEGF-D, soluble VEGF receptor-2 (sVEGFr2), hepatocyte growth factor (HGF), angiopoietin-2, angiogenin and endostatin concentrations were measured in serum collected from 58 lean (24 males, 34 female, mean BMI, 22.2+/-0.3) and 42 overweight and obese (16 males and 26 females, mean BMI, 33.5+/-1.2) subjects after an overnight fast., Results: Sexual dimorphism was apparent in the serum concentrations of VEGF-C, VEFG-D and angiopoietin-2 with significantly higher levels in female compared to male subject. VEGF, VEGF-C, VEGF-D, soluble VEGF receptor-2, angiopoietin-2, angiogenin and endostatin but not HGF were significantly elevated in overweight and obese subjects. Positive correlations between BMI and the serum concentrations of VEGF-C, VEGF-D, sVEGF-R2, angiopoietin-2, angiogenin and endostatin were observed even after adjustment for gender and age., Conclusions: Increased levels of vascular growth factors as well as the angiogenesis inhibitor endostatin are present in overweight and obese subjects and may contribute to previously documented increased risk of metastatic disease in obese subjects with cancer.

Background: Vascular growth factors are important not only in angiogenesis but also for the maintenance of normal endothelial integrity and function. Elevated levels of vascular endothelial growth factor (VEGF), angiopoietin-2, hepatocyte growth factor (HGF), endostatin and angiogenin have been associated with endothelial dysfunction and atherosclerosis. Both acromegaly and growth hormone deficiency (GHD) are associated with endothelial dysfunction and changes in blood vessel morphology., Aim: To investigate the effect of GH status on the circulating levels of angiogenic factors., Design: We measured the levels of six endothelial growth modulators, four angiogenic growth factors and two inhibitors of angiogenesis in 35 untreated acromegalics, 36 untreated GH-deficient subjects and 101 normal control subjects. Fifteen GH-deficient subjects were also studied before and 1 year after treatment with GH., Results: Mean angiogenin concentrations were increased in acromegaly and decreased in GH-deficient subjects compared to control subjects. Endostatin levels showed a similar pattern although the elevated levels in acromegalic subjects did not achieve statistical significance. Angiogenin and endostatin levels both correlated significantly with IGF-I levels (R = 0.61, P < 0.001 and R = 0.22, P < 0.01, respectively). The relationship between angiogenin and IGF-I levels remained significant even after correction for gender, age, body mass index (BMI) and insulin resistance. There were no significant differences in the levels of HGF, VEGF, VEGF-C or angiopoietin-2 between the three groups. VEGF-D levels were elevated in both acromegalic and GH-deficient male subjects. A similar pattern was apparent in female subjects. After GH treatment, a significant reduction in VEGF-D levels and a significant rise in endostatin levels were observed in GH-deficient subjects. A nonsignificant increase in angiogenin levels was also observed., Conclusion: These data indicate that significant perturbations in the levels of vascular growth modulators are present in both acromegaly and GHD. While changes in endostatin and angiogenin levels appear to correlate with IGF-I levels, VEGF-D levels show similar perturbations in both acromegaly and GHD. Further studies are required to determine the relationship of the perturbations to endothelial dysfunction in these conditions.

The majority of insulin-like growth factor-I (IGF-I) in the adult rodent circulation is bound to high affinity IGF binding proteins. We investigated the changes in IGF-I clearance, blood glucose and plasma insulin levels, and tissue 2-deoxyglucose uptake after intravenous administration of the IGF aptamer, NBI-31772, which selectively competes with IGF-I for binding to the IGFBPs, but has no effect at the IGF-I receptor. Clearance of 125I-IGF-I was significantly increased in NBI-31772-treated mice compared with vehicle-treated mice (t1/2 = 45.0 +/- 1.9 vs. 56.3 +/- 3.9 min, respectively; p = 0.021). However, NBI-31772 had no significant effect on glucose levels, and no insulin sparing effect was apparent neither under basal conditions nor during an intravenous glucose challenge. The decline in the specific activity after 3H-2-deoxyglucose administration was significantly less rapid in NBI-31772-treated mice compared with controls, suggesting that the IGF-I aptamer had an inhibitory effect on hepatic gluconeogenesis. In contrast, no insulin-like effect was apparent in other tissues examined. 3H-2-deoxyglucose accumulation was similar in all tissues analyzed, including skeletal muscle, which is thought to be particularly sensitive to IGF-I. These data suggest that the IGF-I aptamer affects clearance of radiolabeled IGF-I from the circulation, but has no marked effects on glucose nor insulin homeostasis. The search for hydrophilic IGF aptamers with longer duration of action that could be used in the treatment of diabetes may be rewarding.

IGF-independent effects of IGF-binding protein-3 (IGFBP-3) have been demonstrated in vitro; however, the physiological significance of these effects in vivo is unclear. We generated two transgenic (Tg) mouse strains that overexpress a human Gly56/Gly80/Gly81-mutant IGFBP-3 cDNA. This mutant has a markedly reduced affinity for the IGFs, but retains the IGF-independent effects. Serum levels of mutant IGFBP-3 were 156 +/- 12 and 400 +/- 24 ng/ml in hemizygous mice of strains 5005 and 5012, respectively. When Tg and wild-type mice were compared, there was no reduction in birth weight, litter size, or postnatal growth. Despite differences in transgene expression in various tissues, relative organ weight was similar in Tg and wild-type mice, with exception of brain, where a modest reduction in brain weight was observed in the high-expressing 5012 lineage. There was also a significant reduction in proliferating cell nuclear antigen-staining cells observed in the periventricular region of the developing brain in embryonic d 18 Tg embryos. In the higher expressing 5012 Tg strain, IGF-I and murine IGFBP-3 levels, marker of GH action were increased. Furthermore, there was a positive correlation between mutant IGFBP-3 levels and IGF-I levels and between mutant IGFBP-3 levels and murine IGFBP-3 (P = 0.002 and P < 0.001, respectively). These data indicate that overexpression of mutant IGFBP-3 is not associated with growth retardation. The higher levels of IGF-I and murine IGFBP-3 in the 5012 Tg strain suggest that the growth inhibitory effect of mutant IGFBP-3 may be compensated for by other mechanisms.

Background: The colocalization of insulin-like growth factor binding protein-3 (IGFBP-3) and IGF-I receptor (IGF-IR) in the basal/germinative layer of the epidermis suggests a key role in modulating epidermal homeostasis., Objectives: We aimed to clarify both the specific cellular localization and the effect of excess epidermal IGFBP-3 on keratinocyte proliferation., Methods: (i) Total RNA was isolated from fluorescence-activated cell sorted basal human keratinocyte subtypes [keratinocyte stem cells, transit amplifying keratinocytes (TA), postmitotic differentiating keratinocytes (PMD)], and real-time polymerase chain reaction analysis was used to determine the abundance of IGFBP-3 and IGF-IR mRNAs. (ii) An IGFBP-3 transgenic mouse model was then used to assess the effect of excess epidermal IGFBP-3 on keratinocyte proliferation. Excess epidermal IGFBP-3 mRNA and protein was determined by in situ hybridization and immunohistochemistry, respectively., Results: (i) The highest levels of IGFBP-3 mRNA were detected in TA keratinocytes, in contrast to IGF-IR mRNA levels which were highest in PMD keratinocytes. (ii) Elevated human IGFBP-3 mRNA and protein was confirmed in the epidermis of skin derived from transgenic mice. Excess IGFBP-3 reduced the relative percentage of proliferative keratinocytes (Ki67 positive) irrespective of skin location (belly, back and tail). Thus, in the epidermis, IGFBP-3 mRNA is highly expressed by proliferative keratinocytes (TA) and overexpression of IGFBP-3 inhibits keratinocyte proliferation., Conclusions: We conclude that in vivo IGFBP-3 ensures epidermal homeostasis via downregulation of keratinocyte proliferation, and thus modulates the early stages of keratinocyte differentiation.

IGFBPs regulate growth and development by regulating IGF transport to tissues and IGF bioavailability to IGF receptors at cell membrane level. IGFBP excess leads predominantly to inhibition of IGF action and growth retardation with impaired organogenesis. Absence of human and also mouse ALS leads to decreased IGF-I levels in circulation and causes mild growth retardation. Although IGFBP KO mice demonstrate relatively minor phenotypes, the possibility of compensatory mechanisms that mask the phenotypic manifestation of lack of individual binding proteins needs to be further investigated. Recent studies of hepatic regeneration in IGFBP-1 KO mice and also with mutant IGFBP-3 Tg mice provide some limited support for the existence of IGF-independent mechanism of action in vivo.

Objective: To examine gender differences and hormonal regulation of resistin, adiponectin, and leptin., Research Methods and Procedures: Plasma levels were measured, and mRNA expression in perigonadal fat was quantified by RNase protection assays., Results: Plasma resistin declined with age despite an increase in adiposity in both genders. In male mice, plasma leptin increased, whereas adiponectin levels were constant. In females, both adiponectin and leptin levels increased with age. Resistin mRNA levels were significantly higher in female than male mice at all ages, whereas leptin and adiponectin mRNA levels were similar in fat from 6-week-old male and female mice, and sexual dimorphism was apparent only in the older mice, with higher levels apparent in females. Castration did not abolish gender differences in plasma levels or resistin, adiponectin, or leptin mRNAs. Castration of male mice did not significantly change adipokine mRNA levels or plasma levels of resistin or leptin; however, adiponectin was significantly increased. Dihydrotestosterone treatment had no effect on adipokine mRNA expression or resistin and adiponectin levels but increased leptin levels. In contrast, ovariectomy significantly increased resistin mRNA abundance and decreased leptin and adiponectin mRNAs. Plasma leptin levels were also increased by ovariectomy, whereas resistin and adiponectin levels were unchanged. Estrogen replacement significantly reduced resistin mRNA and increased leptin and adiponectin mRNA levels but had no effect on plasma adipokine levels., Discussion: The gender differences in adipokine mRNA expression and plasma levels were not ablated by castration and seem to be dependent on other factors in addition to gonadal steroids.

Background: Growth hormone deficiency (GHD) in adult life has been associated with increased central adiposity, decreased insulin sensitivity, dyslipidaemia and increased risk of cardiovascular disease. The effects of GH replacement on adiponectin and resistin, adipokines which have a role in modulating insulin sensitivity have not been previously reported., Aim: To examine the effects of GH replacement on adipokine levels and insulin resistance in GHD patients., Design: Seventeen adult GHD patients were examined at baseline and after 1 year of treatment with recombinant human GH (mean dose 0.31 mg/day, range 0.13-0.67 mg/day)., Results: GH replacement significantly increased IGF-I levels. The mean IGF-I SD score increased from -1.98 at baseline to 0.76 at study end. GH replacement was associated with a significant reduction in percentage body fat (34.11 +/- 1.33 vs. 30.65 +/- 1.27%, P < 0.0005) and a significant increase in lean body mass (63.57 +/- 1.24 vs. 66.96 +/- 1.18%, P < 0.0004), before and after treatment, respectively. Surprisingly, there was no effect of GH replacement on the plasma levels of leptin, resistin or adiponectin or on plasma lipid profile. Insulin sensitivity did not deteriorate during GH replacement despite the known 'anti-insulin' effect of GH. Fasting glucose, insulin and insulin resistance as calculated using the homeostasis model assessment insulin resistance index (HOMA-R) were unchanged by GH treatment., Conclusion: These data demonstrate GH replacement in adult subjects with GHD is effective in changing body composition and restoring IGF-I levels over a 12-month period; however, in our study, these changes were not accompanied by changes in adipokine levels or beneficial effects on plasma lipids or insulin resistance.

Background: Cushing's syndrome (CS) is associated with central adiposity, insulin resistance and impaired glucose homeostasis. Adipose tissue is thought to regulates glucose homeostasis via circulating adipokines, such as resistin, leptin and adiponectin, although their role in the insulin resistance associated with CS has not been established., Design: We examined the relationship between insulin resistance and adipokine levels in CS patients. We compared plasma levels of resistin, leptin and adiponectin in 10 women and four men patients with CS, with 14 health subjects matched for age, gender and body mass index. A subgroup of three women and four men with pituitary-dependent CS were re-examined at least 9 months after curative surgery., Results: CS patients had significantly more truncal fat and less lean body mass as assessed by DEXA compared to control subjects. Total cholesterol, triglycerides and insulin resistance, as calculated using the homeostasis model assessment of insulin resistance (HOMA-R), was significantly increased in CS patients. Of the adipokines measured, only resistin was significantly different between female CS patients and female control subjects (5.05 +/- 0.56 vs. 2.91 +/- 0.39 micro g/l, P = 0.015). Curative surgery significantly reduced total body fat and truncal fat, leptin, total and low-density lipoprotein (LDL) cholesterol, glucose and HOMA-R. A reduction in both resistin and adiponectin was also observed but the differences between pre- and post-treatment levels did not achieve statistical significance., Conclusion: Here we report for the first time that resistin levels are significantly elevated in CS patients and may be important in the insulin resistance associated with glucocorticoid excess.

Unlabelled: IGF-I and their binding proteins are important in bone health. Examination of BMD, osteoblast proliferation, and markers of bone resorption in transgenic mice that constitutively overexpress IGFBP-3 indicates that overexpression of IGFBP-3 increases osteoclast number and bone resorption, impairs osteoblast proliferation, and has a significant negative effect on bone formation., Introduction: Low serum insulin-like growth factor I (IGF-I) levels correlate with an increased risk of osteoporotic fractures. Serum IGF-I is largely bound to IGF-binding protein-3 (IGFBP-3), which can inhibit IGF-I action and enhance delivery of IGF-I to tissues. Its role in bone biology is unclear., Methods: Bone mineral density (BMD), osteoblast proliferation, and markers of bone resorption were examined in transgenic (Tg) mice that constitutively overexpressed human IGFBP-3 cDNA driven by either the cytomegalovirus (CMV) or phosphoglycerate kinase (PGK) promoter., Results: Cultured calvarial osteoblasts from Tg mice expressed the transgene and grew more slowly than cells from wild-type (Wt) mice, and the mitogenic response to IGF-I was attenuated in osteoblasts from Tg mice. Total volumetric BMD and cortical BMD, measured in the femur using peripheral quantitative computed tomography (pQCT) were significantly reduced in both Tg mouse strains compared with Wt mice. PGKBP-3 Tg mice showed the most marked reduction in bone density. Osteocalcin levels were similar in Wt and CMVBP-3 Tg mice but were significantly reduced in PGKBP-3 Tg mice. Urinary deoxypyridinoline and osteoclast perimeter, markers of bone resorption, were significantly increased in both Tg mouse strains compared with Wt mice. Using double labeling with tetracycline, we demonstrated that pericortical and endocortical mineral apposition rate was significantly reduced in PGKBP-3 Tg mice compared with Wt mice., Conclusions: These data show that overexpression of IGFBP-3 increases osteoclast number and bone resorption, impairs osteoblast proliferation, and has a significant negative effect on bone formation.

We investigated the changes in insulin resistance and adipose tissue expression of the adipokines resistin, adiponectin, and leptin and the transcription factors peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and retinoid X receptor-alpha (RXR-alpha) during 48 h of food deprivation. Insulin sensitivity (SI) declined, whereas glucose effectiveness (SG) increased. Plasma adiponectin levels declined in the first 8 h and remained constant thereafter. There was no correlation between either SI or SG and adiponectin protein or mRNA levels. PPAR-gamma mRNA abundance remained constant, whereas leptin and resistin mRNAs and plasma leptin declined and RXR-alpha mRNA abundance increased in both white and brown fat. Leptin mRNA abundance was closely correlated with SI (R2 = 0.91 and 0.87 for white and brown fat, respectively). Resistin mRNA abundance correlated inversely with SG (R2 = 0.99 and 0.84 for white and brown fat, respectively). These data indicate that changes in the expression of leptin are more closely correlated with the insulin resistance of fasting than with changes in other adipokines or RXR-alpha and PPAR-gamma expression.

Background: Insulin resistance, impaired glucose tolerance and type 2 diabetes are common in acromegalic subjects. The mechanism underlying this insulin resistance is unclear., Design: We investigated the levels of the adipocytokines, resistin, adiponectin and leptin in a group of 18 acromegalic subjects and 18 control subjects matched for age, gender and body mass index., Results: Here we demonstrate for the first time significant elevation in adiponectin levels in acromegalic subjects compared to control subjects 12.5 +/- 1.2 vs. 8.97 +/- 1.1 mg/l, P = 0.029. The resistin levels were similar in acromegalic subjects and controls; 20.65 +/- 2.99 vs. 19.03 +/- 4.72 micro g/l. No evidence of a correlation between adiponectin and insulin resistance as calculated from HOMA-R was found. No correlation was observed either between adiponectin or resistin levels and GH levels, total IGF-I or free IGF-I levels. Leptin levels were significantly reduced in acromegalic subjects, 8.22 +/- 2.26 vs. 18.3 +/- 4.1 micro g/l, P = 0.004. In control subjects, significant correlations between leptin levels and HOMA-R and between resistin levels and HOMA-R were observed. These relationships were not apparent in acromegalic subjects., Conclusion: From these data we conclude that changes in resistin and adiponectin levels are unlikely to account for the insulin resistance of acromegaly.

Glucose homeostasis was examined in male transgenic (Tg) mice that overexpressed the human insulin-like growth factor (IGF)-binding protein (IGFBP)-3 cDNA, driven by either the cytomegalovirus (CMV) or the phosphoglycerate kinase (PGK) promoter. The Tg mice of both lineages demonstrated increased serum levels of human (h) IGFBP-3 and total IGF-I compared with wild-type (Wt) mice. Fasting blood glucose levels were significantly elevated in 8-wk-old CMV-binding protein (CMVBP)-3- and PGK binding protein (PGKBP)-3-Tg mice compared with Wt mice: 6.35 +/- 0.22 and 5.22 +/- 0.39 vs. 3.99 +/- 0.26 mmol/l, respectively. Plasma insulin was significantly elevated only in CMVBP-3-Tg mice. The responses to a glucose challenge were significantly increased in both Tg strains: area under the glucose curve = 1,824 +/- 65 and 1,910 +/- 115 vs. 1,590 +/- 67 mmol. l(-1). min for CMVBP-3, PGKBP-3, and Wt mice, respectively. The hypoglycemic effects of insulin and IGF-I were significantly attenuated in Tg mice compared with Wt mice. There were no differences in adipose tissue resistin, retinoid X receptor-alpha, or peroxisome proliferator-activated receptor-gamma mRNA levels between Tg and Wt mice. Uptake of 2-deoxyglucose was reduced in muscle and adipose tissue from Tg mice compared with Wt mice. These data demonstrate that overexpression of hIGFBP-3 results in fasting hyperglycemia, impaired glucose tolerance, and insulin resistance.

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.

The ternary complex, composed of IGF-I or IGF-II, IGF-binding protein-3, and the acid-labile subunit, is responsible for transport of the majority of the IGF-I and IGF-II present in the circulation. Acid-labile subunit is developmentally and hormonally regulated, suggesting an important, although unclear, role in regulating the availability and action of the IGFs. To investigate the biological role of acid-labile subunit, we generated transgenic mice, which constitutively overexpress a human acid-labile subunit cDNA driven by the cytomegalovirus promoter. Two independent transgenic strains, CMVALS-1 and CMVALS-2, with mean serum levels of human acid-labile subunit of 19.3 +/- 4.2 and 20.2 +/- 3.2 microg/ml respectively, were characterized. Total acid-labile subunit, endogenous plus transgene derived, was measured by Western blotting and was found to be significantly increased in transgenic compared with wild-type mice (1.51 +/- 0.02-fold; P < 0.001). There were no significant differences in serum IGF-binding protein-3 or IGF-I levels between transgenic and wild-type mice. Similar chromatographic elution patterns were observed when sera from transgenic and wild-type mice were preincubated with [(125)I]IGF-I, indicating that acid-labile subunit overexpression had no measurable effect on compartmentalization of IGF-I in the circulation. Transgene-derived human acid-labile subunit mRNA was detected in 17-d-old embryos and all adult mouse tissues examined. A significant reduction in litter size was also observed in each of the acid-labile subunit transgenic mouse strains. This reduction in litter size was due to a maternal effect, as it was apparent when transgenic female mice were crossed with wild-type male mice, but not when male transgenic mice were crossed with female wild-type mice. The transgenic mice were phenotypically normal at birth, but demonstrated a significant reduction in postnatal body weight gain, particularly during the first 3 wk of life. Over the first 3 months of life, average body weights were significantly reduced by 5.3 +/- 0.6%, 4.2 +/- 0.6%, 8.1 +/- 0.9%, and 5.6 +/- 0.8%, compared with those in wild-type mice, for male and female CMVALS-1 mice and male and female CMVALS-2 mice, respectively. Double transgenic mice, generated by crossing acid-labile subunit transgenic mice with transgenic mice that overexpress IGF-binding protein-3, demonstrated a significantly more marked reduction in body weight gain than acid-labile subunit transgenic mice. These data demonstrate that overexpression of acid-labile subunit has significant effects on postnatal growth and reproduction. As there is little measurable alteration in the circulating components of the IGF system, these effects are most likely to be mediated via disturbances in tissue IGF availability.

In cell culture systems insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) can both enhance and inhibit IGF-I action. To investigate the biological role of IGFBP-3 in vivo, transgenic (Tg) mice that constitutively overexpress the human IGFBP-3 complementary DNA (cDNA) driven by the mouse phosphoglycerate kinase I (PGK) and the cytomegalovirus (CMV) promoters were examined. Serum levels of human IGFBP-3 in CMVBP-3 and PGKBP-3 Tg mice were 4.7 and 5.8 microgram/ml, respectively and total IGFBP-3 was increased 4.9- and 7.7-fold compared with that in wild-type (Wt) mice. In PGKBP-3 Tg mice the levels of transgene expression were similar in all tissues. Although CMVBP-3 mice demonstrated similar levels of expression of the transgene as PGKBP-3 mice in most tissues, markedly elevated expression was apparent in the kidney and heart. The transgene-derived IGFBP-3 circulated as a 150-kDa ternary complex, and serum IGF-I levels were elevated 1.9- to 2.8-fold in Tg mice compared with Wt mice. A significant reduction in birth weight of approximately 10% and a modest reduction in litter size were apparent in both Tg strains. Early postnatal growth, as assessed by both body weight and length, was significantly reduced in Tg mice compared with Wt mice. This was more marked in PGKBP-3 than in CMVBP-3 mice, who demonstrated a propensity to adiposity after weaning. The relative organ weights of brain and kidney were reduced in both Tg strains, whereas liver size and epididymal fat were significantly increased in CMVBP-3, but not PGKBP-3, mice. Our data indicate that overexpression of IGFBP-3 is associated with modest intrauterine and postnatal growth retardation despite elevated circulating IGF-I levels.