The RGD sequence present in IGFBP-2 is required for reduced glucose clearance after oral glucose administration in female transgenic mice

Abstract

-Recent studies suggest that insulin-like growth factor-binding protein-2 (IGFBP-2) affects both growth and metabolism. Whereas negative growth effects are primarily due to negative interference with IGF-I, the mechanisms for metabolic interference of IGFBP-2 are less clear. As we demonstrate, overexpression of IGFBP-2 in transgenic mice is correlated with a decelerated clearance of blood glucose after oral administration. IGFBP-2 carries an integrin-binding domain (RGD motif), which has been shown to also mediate IGF-independent effects. We thus asked if higher serum levels of IGFBP-2 without an intact RGD motif would also partially block blood glucose clearance after oral glucose application. In fact, transgenic mice overexpressing mutated IGFBP-2 with higher levels of IGFBP-2 carrying an RGE motif instead of an RGD were not characterized by decelerated glucose clearance. Impaired glucose tolerance was correlated with lower levels of GLUT4 present in plasma membranes isolated from muscle tissues after glucose challenge. At the same time, activation of TBC1D1 was depressed in mice overexpressing wild-type but not mutated IGFBP-2. Although we do not have reason to assume altered activation of IGF-I receptor or PDK1/Akt activation in both models, we have identified increased levels of integrin-linked kinase and focal adhesion kinase dependent on the presence of the RGD motif. From our results we conclude that impaired glucose clearance in female IGFBP-2 transgenic mice is dependent on the presence of the RGD motif and that translocation of GLUT4 in the muscle may be regulated by IGFBP-2 via RGDdependent mechanisms.WITH THE EPIDEMIC INCREASE of metabolic diseases worldwide, a better understanding of metabolic control in vivo is required. The insulin-like growth factor (IGF) system is known to have metabolic effects, and IGF-I is capable of improving cellular defects present in type 2 diabetes (T2D) (25). In addition, IGF-binding proteins (IGFBPs) have well-recognized metabolic but also therapeutic potential due to IGF-dependent or -independent effects (12, 37). Beyond all other IGFBPs, metabolic effects of IGFBP-1 and IGFBP-2 have received a detailed discussion recently (A. Hoeflich and V. C. Russo, unpublished data). IGFBP-2 is reduced in obesity and further suppressed in obese subjects with T2D (9). IGFBP-2 has also been identified as a marker of the metabolic syndrome (11). Interestingly, serum IGFBP-2 levels correlated positively with insulin sensitivity and negatively with fat mass in young adult subjects (6). IGFBP-2 was identified in sheep as a mediator of leptin effects and insulin sensitivity in muscles (38). In mice, Wheatcroft et al. (36) have demonstrated that IGFBP-2 protects against the development of age-related glucose intolerance, insulin resistance, and hypertension. IGFBP-2 contains an RGD sequence motif in addition to heparin-binding domains located in the linker domain or in the COOH-terminal region, respectively (8). The RGD motif of IGFBP-2 seems to particularly mediate IGF-independent effe...

Skeletal muscle-specific overexpression of IGFBP-2 promotes a slower muscle phenotype in healthy but not dystrophic mdx mice and does not affect the dystrophic pathology

“…Therefore it is possible that impaired nNOS activity in the mdx mouse might affect the ability of IGFBP-2 to promote a slower muscle phenotype. IGFBP-2 exerts IGF-independent effects via interactions with integrin-5, and a link between integrin-5 and AMPK has been reported [58][59][60]. Interestingly, α5β1 integrin has been suggested to interact with dystrophin in cultured myotubes [61] indicating a potential link between the presence of dystrophin and a signal downstream of α5β1 integrin.…”

Peripheral versus Central Index of Metabolic Dysfunction and Associations with Clinical and Pathological Outcomes in Alzheimer’s Disease

“…IGFBP-2, in particular, binds to both IGF-1 and IGF-2, and can inhibit IGF functions such as DNA synthesis, cell proliferation, and cell death, as well as glucose and amino acid uptake in cells [3, 4]. For example, transgenic mice that overexpressed IGFBP-2 showed significantly higher blood glucose levels than controls at 30, 60 and 90 minutes during an oral glucose tolerance test, as well as lower levels of GLUT4–the insulin-dependent glucose transporter–at cell surfaces compared to controls [5]. Abnormally high IGFBP-2 levels are often an indicator of severe catabolic events, such as gastric cancer, anorexia nervosa and renal failure [6-8].…”

40 YEARS OF IGF1: IGF-binding proteins

“…In contrast, constitutive IGFBP-2 overexpression reduced postnatal body 302 weight gain in transgenic mice (Hoeflich, et al 1999). Constitutive overexpression also impaired 303 glucose tolerance and decreased GLUT4 glucose transporter translocation to the cell membrane via 304 its Arg-Gly-Asp sequence, suggesting the involvement of integrins rather than the IGF-I receptor 305 (Reyer, et al 2015). 306…”