Expression of the Insulin-like Growth Factor 1 (IGF-1) and Type I IGF Receptor mRNAs in Human HLE-B3 Lens Epithelial Cells (original) (raw)
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Molecular and Cellular Endocrinology, 1990
Insulin and insulin-like growth factor I (IGF-I) stimulate overall growth and development of the chick embryo in early organogenesis. Turning to individual organs, to clarify the cellular effects of these peptides and the activity of the receptors involved, we had demonstrated with developing lens that insulin and IGF-I increase the accumulation of &crystallin mRNA, a marker for lens differentiation, in part by stimulation of transcription. In this study we expand our previous work on lens receptors to an earlier time in organogenesis, day 4, which marks the beginning of differentiation of the lens epithelial cells into elongated fibers. Insulin receptors are demonstrable by affinity cross-linking in epithelial cells at day 6, and specific binding of ['251]insulin and ['251]IGF-I is detectable in day 4 lenses. Insulin and IGF-I stimulation of substrate phosphorylation in the presence of solubilized receptors occurs only with high concentrations (lo-100 nM) of either peptide in day 4 lenses, while a clear response with low concentrations (1 nM) is elicited by day 6 of development. Low concentrations of both insulin and IGF-I (0.1-l nM) increase the incorporation of [3H]leucine and [3H]uridine in day 6 lens cells, suggesting that each peptide acts through its own receptor. These results confirm and extend the finding of insulin and IGF-I receptors in the developing chicken lens, and demonstrate their functional activity. This embryonic model should be valuable for further analysis of the action of insulin and IGF-I in growth and differentiation processes during early development.
Scientific Reports
Insulin and insulin-like growth factor-1 (IGF-1) are present in human tears and likely play an important role in mediating ocular surface homeostasis. We previously characterized the IGF-1/insulin hybrid receptor (Hybrid-R) in corneal epithelial cells and found that it was activated by IGF-1 and not insulin; and reported the novel finding that it localized to the corneal epithelial cell nucleus. Since the corneal epithelium is an insulin insensitive tissue and does not require insulin for glucose uptake, this study investigated the function of insulin in corneal epithelial cells. We show that stress induced by growth factor deprivation triggers transcriptional upregulation and de novo nuclear accumulation of Hybrid-R through the homodimeric insulin receptor (INSR). This occurs independent of PI3K/Akt signaling. Nuclear accumulation of Hybrid-R was associated with partial cell cycle arrest and a corresponding reduction in mitochondrial respiration. Treatment with insulin, and not IGF-1, attenuated IGF-1R and INSR transcription and restored cell cycle and metabolic homeostasis. Together, these findings support that insulin mediates receptor homeostasis in corneal epithelial cells, favoring an IGF-1 mediated pathway. This may have important implications in diabetic corneal disease and wound healing. Insulin Receptor (INSR) and Insulin-like Growth Factor Type 1 Receptor (IGF-1R) are members of the receptor tyrosine kinase superfamily 1. They play an important role in the regulation of essential biological and molecular processes including proliferation, migration, metabolism, differentiation, and survival 2. This occurs through ligand binding of the receptor at the plasma membrane, leading to autophosphorylation and downstream activation of phosphoinositide 3-kinase (PI3K) and extracellular signal regulated kinase (ERK) pathways 3. Known extracellular ligands for INSR and IGF-1R include insulin, IGF-1, and IGF-2, all of which display different affinities for each receptor 1. Structurally, INSR and IGF-1R are transmembrane glycoproteins composed of two extracellular alpha subunits that form the ligand-binding domain and two transmembrane beta subunits that possess tyrosine kinase activity 4. Overall, the two receptors exhibit greater than 50% homology in their amino acid sequences. This ranges from 45% to 65% in the alpha subunit binding domain, rising to 84% homology within the tyrosine kinase domain. The structural similarity between INSR and IGF-1R make possible the formation of insulin and IGF-1 hybrid receptors (Hybrid-R) 5-7. It is unknown what drives formation of Hybrid-R. Some hypothesize that formation of Hybrid-R is driven by the ratio between IGF-1R and INSR 8. Others speculate that Hybrid-R is regulated developmentally 9. In addition to formation of Hybrid-R, the functional significance of Hybrid-R remains controversial. An increase in Hybrid-R expression has been reported in skeletal muscle and adipose tissue in diabetes 10-12. Hybrid-R has also been shown to bind IGF-1 with a greater affinity than insulin 13,14. Thus, increased expression of Hybrid-R in diabetic tissue may alter insulin sensitivity 7,10-12. A reduction in insulin sensitivity represents a key hallmark of diabetes. In the diabetic cornea, epithelial erosions, persistent epithelial defects, corneal neuropathy and ulceration can result in painful and often permanent loss of vision 15-18. While the corneal epithelium has been previously reported to be an insulin-insensitive tissue, meaning that it does not require insulin for glucose uptake, studies have shown that supraphysiological levels of insulin applied topically to the eye promotes corneal wound healing
Increased ocular levels of IGF-1 in transgenic mice lead to diabetes-like eye disease
Journal of Clinical Investigation, 2004
IGF-1 has been associated with the pathogenesis of diabetic retinopathy, although its role is not fully understood. Here we show that normoglycemic/normoinsulinemic transgenic mice overexpressing IGF-1 in the retina developed most alterations seen in human diabetic eye disease. A paracrine effect of IGF-1 in the retina initiated vascular alterations that progressed from nonproliferative to proliferative retinopathy and retinal detachment. Eyes from 2-month-old transgenic mice showed loss of pericytes and thickening of basement membrane of retinal capillaries. In mice 6 months and older, venule dilatation, intraretinal microvascular abnormalities, and neovascularization of the retina and vitreous cavity were observed. Neovascularization was consistent with increased IGF-1 induction of VEGF expression in retinal glial cells. In addition, IGF-1 accumulated in aqueous humor, which may have caused rubeosis iridis and subsequently adhesions between the cornea and iris that hampered aqueous humor drainage and led to neovascular glaucoma. Furthermore, all transgenic mice developed cataracts. These findings suggest a role of IGF-1 in the development of ocular complications in long-term diabetes. Thus, these transgenic mice may be used to study the mechanisms that lead to diabetes eye disease and constitute an appropriate model in which to assay new therapies. Nonstandard abbreviations used: glial fibrillar acidic protein (GFAP); intraocular pressure (IOP); intraretinal microvascular abnormalities (IRMAs); rat insulin promoter-I (RIP-I); streptozotocin (STZ); von Willebrand factor (vWF).
The IGF/Insulin-IGFBP Axis in Corneal Development, Wound Healing, and Disease
Frontiers in Endocrinology
The insulin-like growth factor (IGF) family plays key roles in growth and development. In the cornea, IGF family members have been implicated in proliferation, differentiation, and migration, critical events that maintain a smooth refracting surface that is essential for vision. The IGF family is composed of multiple ligands, receptors, and ligand binding proteins. Expression of IGF type 1 receptor (IGF-1R), IGF type 2 receptor (IGF-2R), and insulin receptor (INSR) in the cornea has been well characterized, including the presence of the IGF-1R and INSR hybrid (Hybrid-R) in the corneal epithelium. Recent data also indicates that each of these receptors display unique intracellular localization. Thus, in addition to canonical ligand binding at the plasma membrane and the initiation of downstream signaling cascades, IGF-1R, INSR, and Hybrid-R also function to regulate mitochondrial stability and nuclear gene expression. IGF-1 and IGF-2, two of three principal ligands, are polypeptide growth factors that function in all cellular layers of the cornea. Unlike IGF-1 and IGF-2, the hormone insulin plays a unique role in the cornea, different from many other tissues in the body. In the corneal epithelium, insulin is not required for glucose uptake, due to constitutive activation of the glucose transporter, GLUT1. However, insulin is needed for the regulation of metabolism, circadian rhythm, autophagy, proliferation, and migration after wounding. There is conflicting evidence regarding expression of the six IGF-binding proteins (IGFBPs), which function primarily to sequester IGF ligands. Within the cornea, IGFBP-2 and IGFBP-3 have identified roles in tissue homeostasis. While IGFBP-3 regulates growth control and intracellular receptor localization in the corneal epithelium, both IGFBP-2 and IGFBP-3 function in corneal fibroblast differentiation and myofibroblast proliferation, key events in stromal wound healing. IGFBP-2 has also been linked to cellular overgrowth in pterygium. There is a clear role for IGF family members in regulating tissue homeostasis in the cornea. This review summarizes what is known regarding the function of IGF and related proteins in corneal development, during wound healing, and in the pathophysiology of disease. Finally, we highlight key areas of research that are in need of future study.
Mutual regulation between IGF‐1R and IGFBP‐3 in human corneal epithelial cells
Journal of Cellular Physiology, 2018
The Insulin-like growth factor type 1 receptor (IGF-1R) is part of the receptor tyrosine kinase (RTK) superfamily. Activation of IGF-1R regulates several key signaling pathways responsible for maintaining cellular homeostasis, including survival, growth and proliferation. In addition to mediating signal transduction at the plasma membrane, in serum-based models, IGF-1R undergoes SUMOylation by SUMO1 and translocates to the nucleus in response to IGF-1. In corneal epithelial cells grown in serum free culture however, IGF-1R has been shown to accumulate in the nucleus independent of IGF-1. In this study, we report that the insulin-like growth factor binding protein 3 (IGFBP-3) mediates nuclear translocation of IGF-1R in response to growth factor withdrawal. This occurs via SUMOylation by SUMO2/3. Further, IGF-1R and IGFBP-3 undergo reciprocal regulation independent of PI3k/Akt signaling. Thus, under healthy growth conditions, IGFBP-3 functions as a gatekeeper to arrest the cell cycle in G0/G1, but does not alter mitochondrial respiration in cultured cells. When stressed, IGFBP-3 functions as a caretaker to maintain levels of IGF-1R in the nucleus. These results demonstrate mutual regulation between IGF-1R and IGFBP-3 to maintain cell survival under stress. This is the first study to show a direct relationship between IGF-1R and IGFBP-3 in the maintenance of corneal epithelial homeostasis.
Regulation of growth factor mRNA levels in the eyes of diabetic rats
Metabolism, 1995
The underlying etiology of diabetic microvascular disease remains unknown. To examine the potential contribution of basic fibroblast growth factor (bFGF), which is an angiogenic factor, and insulin-like growth factor-I (IGF-I) to the development of diabetic microvascular disease, bFGF and IGF-I mRNA levels were measured in tissues of control, diabetic, and insulin-treated diabetic rats. Diabetes was induced in rats by intravenous injection of streptozotocin (STZ) 65 mg/kg, and the rats were maintained for 21 days. bFGF mRNA levels increased threefold in the eyes of diabetic versus control rats, whereas a consistent change in bFGF mRNA levels was not observed in other tissues. In contrast, IGF-I mRNA levels decreased in the eyes and other tissues, including kidney, lung, and skeletal muscle, of diabetic as compared with control rats. Insulin treatment prevented the diabetes-induced increase in bFGF and decrease in IGF-I mRNA levels. Acidic FGF (aFGF) mRNA levels were unchanged in eyes from diabetic versus control rats. In partially purified retinas, diabetes increased bFGF mRNA levels twofold as compared with levels in control retinas, whereas IGF-I mRNA levels decreased to 58% of control levels in retinas from diabetic rats. Insulin treatment again prevented the diabetes-induced increase in IGF-I mRNA levels in the retina but had no effect on the diabetes-induced increase in bFGF mRNA levels, bFGF peptide levels were minimally increased in diabetic versus control retinas. Treatment of diabetic rats with the aldose reductase inhibitor sorbinil prevented the diabetes-induced increase in sorbitol accumulation and myo.inositol depletion in the lens, but it did not affect the diabetes-induced increase in bFGF and decrease in IGF-I mRNA levels in the retina. Induction of hypoinsulinemia by fasting the animals did decrease IGF-I mRNA levels but did not reproduce the diabetes-induced increase in bFGF mRNA levels in the eye. In conclusion, these data demonstrate that the effect of diabetes on growth factor mRNA levels in the eye is gene-specific, suggest that different metabolic abnormalities are responsible for diabetes-induced alterations in the production of different growth factors in the eye, and are consistent with a role for bFGF in the development of diabetic retinopathy.
Molecular vision, 2011
Insulin stimulates eye growth in chicks and this effect is greatly enhanced if the retinal image is degraded by the defocus of either sign. However, it is unclear whether the insulin receptor (IR) is expressed at all in the chicken retina in animals 1-2 weeks post-hatching. We have investigated IR expression and whether IR transcript abundance varies in the fundal layers. To elucidate the possible role of insulin and insulin-like growth factor (IGF)-1 signaling in eye growth regulation, mRNA (mRNA) levels were measured for insulin, IGF-1, IR, and IGF-1 receptor (IGF-1R) during imposed negative or positive defocus. Chicks were treated binocularly with positive or negative spectacle lenses for 4 or 24 h, or they remained untreated (n=6, for each treatment group). Northern blot analyses were performed to screen for transcription variants in the different fundal layers of untreated animals. Real-time PCR was used to quantify IR, IGF-1R, IGF-1, and insulin mRNA levels in the different fu...
Insulinlike Growth Factor I Affects Ocular Development
Ophthalmology, 2006
To evaluate the ocular dimensions in patients with primary growth hormone receptor insensitivity (Laron syndrome [LS]) and to study the effect of supplemental insulinlike growth factor I (IGF-I) on ocular growth.