Concept: Insulin-like growth factor 1
Insulin-like growth factor 1 (IGF-1), the most abundant growth factor in the bone matrix, maintains bone mass in adulthood. We now report that IGF-1 released from the bone matrix during bone remodeling stimulates osteoblastic differentiation of recruited mesenchymal stem cells (MSCs) by activation of mammalian target of rapamycin (mTOR), thus maintaining proper bone microarchitecture and mass. Mice with knockout of the IGF-1 receptor (Igf1r) in their pre-osteoblastic cells showed lower bone mass and mineral deposition rates than wild-type mice. Further, MSCs from Igf1rflox/flox mice with Igf1r deleted by a Cre adenovirus in vitro, although recruited to the bone surface after implantation, were unable to differentiate into osteoblasts. We also found that the concentrations of IGF-1 in the bone matrix and marrow of aged rats were lower than in those of young rats and directly correlated with the age-related decrease in bone mass. Likewise, in age-related osteoporosis in humans, we found that bone marrow IGF-1 concentrations were 40% lower in individuals with osteoporosis than in individuals without osteoporosis. Notably, injection of IGF-1 plus IGF binding protein 3 (IGFBP3), but not injection of IGF-1 alone, increased the concentration of IGF-1 in the bone matrix and stimulated new bone formation in aged rats. Together, these results provide mechanistic insight into how IGF-1 maintains adult bone mass, while also providing a further rationale for its therapeutic targeting to treat age-related osteoporosis.
Measurement of insulin-like growth factor-1 (IGF-I) has utility for the diagnosis and management of growth disorders, but inter-assay comparison of results has been complicated by a multitude of reference standards, antibodies, detection methods, and pre-analytical preparation strategies. We developed a quantitative LC-MS method for intact IGF-I, which has advantages in throughput and complexity when compared to mass spectrometric approaches that rely on stable isotope dilution analysis of tryptic peptides. Since the method makes use of full-scan data, the assay was easily extended to provide quantitative measurement of IGF-II using the same assay protocol. The validated LC-MS assay for IGF-I and IGF-II provides accurate results across the pediatric and adult reference range and is suitable for clinical use.
Insulin-like growth factor II (IGF-II) is a major embryonic growth factor belonging to the insulin-like growth factor family which includes insulin and IGF-I. Its expression in humans is tightly controlled by maternal imprinting, a genetic restraint which is lost in many cancers, resulting in upregulation of both mature IGF-II mRNA and protein expression. Additionally, increased expression of several longer isoforms of IGF-II, termed pro- and big-IGF-II, has been observed. To date, it is ambiguous as to what role these IGF-II isoforms have in initiating and sustaining tumorigenesis and whether they are bioavailable. We have expressed each individual IGF-II isoform in their proper O-glycosylated format and established that all bind to the IGF-IR, IR-A and IR-B receptors, resulting in their activation and subsequent stimulation of fibroblast proliferation. We also confirmed that all isoforms are able to be sequestered into binary complex with several IGF binding proteins (IGFBP-2, IGFBP-3 and IGFBP-5). In contrast to this, ternary complex formation with IGFBP-3/IGFBP-5 and the auxillary protein, acid labile subunit (ALS) was severely diminished. Furthermore, big-IGF-II isoforms bound much more weakly to purified ectodomain of the natural IGF-II scavenging receptor, IGF-IIR. IGF-II isoforms thus possess unique biological properties which may enable them to escape normal sequestration avenues and remain bioavailable in vivo in order to sustain oncogenic signaling.
The NEPROCHECK test (Astute Medical, San Diego, CA, USA) combines urinary tissue inhibitor of metalloproteinases-2 (TIMP-2) and insulin-like growth factor binding protein 7 (IGFBP7) to identify patients at high risk for acute kidney injury (AKI). In a US Food and Drug Administration registration trial (NCT01573962), AKI was determined by a three-member clinical adjudication committee. The objectives were to examine agreement among adjudicators as well as between adjudicators and consensus criteria for AKI and to determine the relationship of biomarker concentrations and adjudicator agreement.
Although both growth hormone (GH) and insulin-like growth factor 1 (IGF-1) signaling were shown to regulate life span in lower organisms, the role of GH signaling in human longevity remains unclear. Because a GH receptor exon 3 deletion (d3-GHR) appears to modulate GH sensitivity in humans, we hypothesized that this polymorphism could play a role in human longevity. We report a linear increased prevalence of d3-GHR homozygosity with age in four independent cohorts of long-lived individuals: 841 participants [567 of the Longevity Genes Project (LGP) (8% increase; P = 0.01), 152 of the Old Order Amish (16% increase; P = 0.02), 61 of the Cardiovascular Health Study (14.2% increase; P = 0.14), and 61 of the French Long-Lived Study (23.5% increase; P = 0.02)]. In addition, mega analysis of males in all cohorts resulted in a significant positive trend with age (26% increase; P = 0.007), suggesting sexual dimorphism for GH action in longevity. Further, on average, LGP d3/d3 homozygotes were 1 inch taller than the wild-type (WT) allele carriers (P = 0.05) and also showed lower serum IGF-1 levels (P = 0.003). Multivariate regression analysis indicated that the presence of d3/d3 genotype adds approximately 10 years to life span. The LGP d3/d3-GHR transformed lymphocytes exhibited superior growth and extracellular signal-regulated kinase activation, to GH treatment relative to WT GHR lymphocytes (P < 0.01), indicating a GH dose response. The d3-GHR variant is a common genetic polymorphism that modulates GH responsiveness throughout the life span and positively affects male longevity.
GH-IGF system regulation of attenuated muscle growth and lipolysis in Atlantic salmon reared at elevated sea temperatures
- Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology
- Published over 6 years ago
Growth regulation in adult Atlantic salmon (1.6 kg) was investigated during 45 days in seawater at 13, 15, 17, and 19 °C. We focused on feed intake, nutrient uptake, nutrient utilization, and endocrine regulation through growth hormone (GH), insulin-like growth factors (IGF), and IGF-binding proteins (IGFBP). During prolonged thermal exposure, salmon reduced feed intake and growth. Feed utilization was reduced at 19 °C after 45 days compared with fish at lower temperatures, and body lipid storage was depleted with increasing water temperature. Although plasma IGF-1 concentrations did not change, 32-Da and 43-kDa IGFBP increased in fish reared at ≤17 °C, and dropped in fish reared at 19 °C. Muscle igf1 mRNA levels were reduced at 15 and 45 days in fish reared at 15, 17, and 19 °C. Muscle igf2 mRNA levels did not change after 15 days in response to increasing temperature, but were reduced after 45 days. Although liver igf2 mRNA levels were reduced with increasing temperatures after 15 and 45 days, temperature had no effect on igf1 mRNA levels. The liver igfbp2b mRNA level, which corresponds to circulating 43-kDa IGFBP, exhibited similar responses after 45 days. IGFBP of 23 kDa was only detected in plasma in fish reared at 17 °C, and up-regulation of the corresponding igfbp1b gene indicated a time-dependent catabolic response, which was not observed in fish reared at 19 °C. However, higher muscle ghr mRNA levels were detected in fish at 17 and 19 °C than in fish at lower temperatures, indicating lipolytic regulation in muscle. These results show that the reduction of muscle growth in large salmon is mediated by decreased igf1 and igf2 mRNA levels in addition to GH-associated lipolytic action to cope with prolonged thermal exposure. Accordingly, 13 °C appears to be a more optimal temperature for the growth of adult Atlantic salmon at sea.
Background:In preterm infants, low levels of insulin-like growth factor-I (IGF-I) and IGF binding protein 3 (IGFBP-3) are associated with impaired brain growth and retinopathy of prematurity (ROP). Treatment with IGF-I/IGFBP-3 may be beneficial for brain development and may decrease the prevalence of ROP.Methods:In a phase II pharmacokinetics and safety study, five infants (three girls) with a median (range) gestational age (GA) of 26 wk + 6 d (26 wk + 0 d to 27 wk + 2 d) and birth weight of 990 (900-1,212) g received continuous intravenous infusion of recombinant human (rh)IGF-I/rhIGFBP-3. Treatment was initiated during the first postnatal day and continued for a median (range) duration of 168 (47-168) h in dosages between 21 and 111 µg/kg/24 h.Results:Treatment with rhIGF-I/rhIGFBP-3 was associated with higher serum IGF-I and IGFBP-3 concentrations (P < 0.001) than model-predicted endogenous levels. Of 74 IGF-I samples measured during study drug infusion, 37 (50%) were within the target range, 4 (5%) were above, and 33 (45%) were below. The predicted dose of rhIGF-I/rhIGFBP-3 required to establish circulating levels of IGF-I within the intrauterine range in a 1,000 g infant was 75-100 µg/kg/24 h. No hypoglycemia or other adverse effects were recorded.Conclusion:In this study, continuous intravenous infusion of rhIGF-I/rhIGFBP-3 was effective in increasing serum concentrations of IGF-I and IGFBP-3, and was found to be safe.
Liver resection offers a chance of cure for patients with hepatocellular carcinoma (HCC). Hepatic pedicle clamping (HPC) is commonly used to reduce blood loss during hepatectomy. Hepatic ischemia-reperfusion (I/R) injury has recently been reported to be a major factor in accelerated tumor growth. We therefore evaluated the effect of intermittent HPC on the prognosis of patients after liver resection.
The IGF system plays important roles in growth. Nevertheless, few data have been reported so far on the expression of IGF system members and their relationship with growth in domestic animals, especially pigs. In this study, hepatic transcript level of IGF1, IGF2, IGF binding protein 2 (IGFBP2), IGFBP3 and IGF 1 receptor (IGF1R), plasma protein level of IGF1 and IGFBP3, and eight growth or carcass traits, including chest circumference, body length, body height (BH), body weight, carcass weight, loin muscle area (LMA), back fat thickness and average daily gain, were measured in fast-growing Landrace and slow-growing Lantang pigs at the age of 1, 27, 90, 150 and 180 days. The results showed that liver mRNA level of IGF1, IGF2 and IGF1R, and blood protein level of IGF1 have a similar developmental profile in both Landrace and Lantang pigs. Their levels were higher at the early age than that at other older ages. Hepatic transcript abundances of the two growth inhibitors, IGFBP2 and IGFBP3, were mostly higher in Lantang pigs than that in Landrace pigs, at 5 examined postnatal stages. The IGF system members' liver mRNA level and/or serum protein level have significant correlation with each other in different age of Landrace or Lantang pigs. Hepatic mRNA level or serum protein level of IGF system members also has significant correlation with investigated traits, especially with BH and LMA, in different age of Lantang or Landrace pigs. Our results revealed the change profiles of porcine IGF system members' liver transcript level and plasma protein level between different pig breeds and different postnatal developmental ages. Moreover, the correlation analysis results suggest that the IGF system members act coordinately to regulate the growth performance and carcass composition in pigs. The information obtained from the present study is important for elucidation of the regulatory mechanism of IGF system underlying growth, and for genetic improvement in pigs.
Excessive apoptosis in intervertebral disc (IVD) cells is important in IVD degeneration. Interleukin (IL)-1β has been shown to induce apoptosis in these cells. However, whether insulin-like growth factor-1 (IGF-1) inhibits IL-1β-induced apoptosis in the nucleus pulposus remains unclear. The purpose of this study was to investigate the effects of IGF-1 on IL-1β-induced apoptosis in the nucleus pulposus. Cells isolated from the nucleus pulposus were grown in culture to a monolayer. These cells were identified using immuno-histochemistry for type II collagen and toluidine blue staining for glycosaminoglycans. Following exposure to IGF-1 or IL-1β, the cells were observed using light microscopy. Giemsa staining, TdT-mediated dUTP-biotin nick end-labeling (TUNEL) and flow cytometry (FCM) were used to detect the rate of early cell death, which served as an indicator of apoptosis. In the IL-1β group, a large number of these cells underwent apoptosis and demonstrated morphological changes associated with apoptosis. A small proportion of cells exposed to IGF-1 alone underwent apoptosis. No obvious signs of apoptosis were observed in the control group. TUNEL results revealed that the rate of apoptosis in the IGF-1 group was significantly reduced compared with that in the IL-1β group (P<0.01), confirmed using FCM. Compared with the control group, the apoptotic rate was also significantly increased in IL-1β-exposed cells (P<0.01). These findings strongly suggested that IGF-1 inhibits IL-1β-induced apoptosis in the nucleus pulposus.