| 1. |
- Bornfeldt, Karin E.
(författare)
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Actions and interactions of insulin-like growth factor-I and insulin in vascular smooth muscle
- 1991
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Insulin-like growth factor-I (IGF-I) is a polypeptide with structural and biological similarities with insulin, and the receptors for IGF-I and insulin are homologous. The present investigation was devoted to the actions and interactions of IGF-I and insulin in vascular smooth muscle. In vascular smooth muscle from intact arteries and in cultured vascular smooth muscle cells there are abundant IGF-I receptors, but very few insulin receptors. IGF-I and insulin stimulated proliferation of cultured vascular smooth muscle cells, and the effects were probably mediated via the IGF-I receptor. However, the maximal growthpromoting effect of IGF-I was twice the maximal effect of insulin. If an acidic amino acid was substituted for the basic amino acid histidine in insulin B-chain (BlO His:::} Asp), like in IGF-I, the maximal growth-promoting activity reached the effect of IGF-1. The amino acid in position 10 in insulin B-chain may thus be important for the growthpromoting activity of insulin. Vascular smooth muscle cells express IGF-1 mRNA and produce imm1,1noreactive IGF-1 in vitro. Levels of IGF-1 m RNA were decreased by platelet-derived growth factor (PDGF-BB), basic fibroblast growth factor (bFGF) and serum, whereas IGF-1 and high concentrations of insulin increased IGF-I rnRNA and immunoreactive IGF-I. It is thus possible that IGF-1 is able to increase its own production in an autocrine loop withpositive feedback. The growth-promoting effects of IGF-1 and insulin were weak compared to the effects ofPDGF-BB and bFGF. The results indicate qualitative as well as quantitative differences between IGF-1 and insulin compared to PDGF-BB and bFGF. IGF-1 gene expression in aortic tissue was found to be decreased by diabetes and fasting in vivo, and the levels were restored if diabetic rats were treated with insulin. Vascular smooth muscle proliferation induced by balloon catheterization was found to be impaired by diabetes and increased by insulin-treatment in vivo, although not to the levels in normal rats. IGF-1 stimulated vascular smooth muscle proliferation in diabetic rats in vivo without affecting the diabetic state, and IGF-I gene expression was increased in proliferating vascular smooth muscle. The results suggest that IGF-I is involved in vascular smooth muscle proliferation in vivo. In conclusion, insulin is less potent than IGF-1 in stimulating proliferation of vascular smooth muscle, and the growth-promoting effects of insulin are weaker than the effects ofiGF-1, suggesting that insulin in concentrations found in plasma has little direct effect on vascular smooth muscle proliferation. IGF-1 is probably of importance for vascular smooth muscle proliferation, and the results suggest that IGF-1 can be locally produced and regulated in the vascular wall.
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| 2. |
- Dekker Nitert, Marloes, et al.
(författare)
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IGF-I/insulin hybrid receptors in human endothelial cells
- 2005
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Ingår i: Molecular and Cellular Endocrinology. - : Elsevier BV. - 1872-8057 .- 0303-7207. ; 229:1-2, s. 31-37
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Tidskriftsartikel (refereegranskat)abstract
- Vascular complications are common in diabetes. IGF-I receptors (IGF-IR) and insulin receptors (IR) in endothelial cells might respond to altered levels of IGF-I and insulin, resulting in altered endothelial function in diabetes. We therefore studied IGF-IR and IR gene expression, ligand binding, receptor protein, and phosphorylation in human umbilical vein endothelial cells (HUVEC). IGF-IR mRNA was more abundant than IR mRNA in freshly isolated HUVEC (IGF-IR/IR ratio 7.1 +/- 1.5) and in cultured HUVEC (ratio 3.5 +/- 0.51). Accordingly, specific binding of (125)I-IGF-I (0.64 +/- 0.25%) was higher than that of (125)I-insulin (0.25 +/- 0.09%). Protein was detected for both receptors and IGF-I/insulin hybrid receptors. IGF-IR phosphorylation was stimulated by 10(-10) to 10(-8) M IGF-I. IR were activated by 10(-9) to 10(-8) M insulin and IGF-I. We conclude that HUVEC express more IGF-IR than IR, and also express hybrid receptors. Both IGF-I and insulin phosphorylate their own receptors but only IGF-I seems to phosphorylate hybrid receptors.
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| 3. |
- Nilsson, Ulrika K., 1969-
(författare)
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Lysophosphatidic acid : Physiological effects and structure-activity relationships
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lipids havepreviously been considered primarily as building blocks of the cell membrane, but are now also recognized as important cell signaling molecules. Lysophosphatidic acid (LPA) is a glycerophospholipid consisting of a phosphate head group, a linker region, and a lipophilic tail. LPA has earlier been shown to exert a diversity of cellular effects such as aggregation, apoptosis, contraction, migration, and proliferation. The effects of LPA are elicited by activation of its cognate G protein-coupled receptors LPA1, LPA2, and LPA3. In the present study we have used cultures of human smooth muscle cells (SMCs) and erythroleukemia cells (HEL), and isolated human platelets to characterize physiological effects of LPA compared with adrenaline and noradrenaline as well as structure-activity relationships of LPA. SMCs were isolated from biopsies of human myometrium obtained at cesarean sections. We show that cultured myometrial SMCs express multiple LPA and α2-adrenergic receptor subtypes. Treatment of SMCs with LPA and noradrenaline resulted in increases in proliferation. However, LPA elicits a much more pronounced stimulatory effect than noradrenaline. The ability to increase calcium might be one explanation why LPA is more effective. Further studies indicated that several pathways mediate the growth stimulatory effect of LPA where transactivation of epidermal growth factor receptors through matrix metalloproteinases as well as calcium/calmodulin-dependent protein kinases appears to be important. LPA enantiomers and LPA analogues were synthesized and characterized due to their capacity to increase calcium in HEL cells. Our study is the first to show that both natural (R) and unnatural (S) LPA enantiomers are capable of stimulating cells, suggesting LPA receptors are not stereoselective. Moreover, we have synthesized a LPA analogue with higher maximal effect than LPA by reducing the hydrocarbon chain length. In platelets we demonstrated that LPA is a weak calciumelevating compound which failed to stimulate aggregation. However, in combination with adrenaline, another weak platelet agonist, a complete aggregatory response was obtained in blood from some healthy individuals. These results are important since platelet activation is a key step in distinguishing normal from pathological hemostasis. Since LPA is present at high concentrations in atherosclerotic lesions, the synergistic effect of LPA and adrenaline might be a new risk factor for arterial thrombosis.
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