Corneal complications from diabetes are common, often very painful, can negatively impact quality of life, and lead to permanent visual impairment. Owing to the vast array of molecular pathways that are altered in the diabetic cornea, traditional therapies are often not sufficient, due to abnormal cellular responses and the loss of trophic support from corneal nerves. Our prior studies have shown that the insulin-like growth factor (IGF) system is altered in diabetes. This includes a significant increase in the pleiotropic secretory protein, IGF-binding protein-3 (IGFBP-3) in diabetic human tears that correlates with loss of the corneal subbasal nerve plexus. While corneal epithelial cells do not require insulin for glucose uptake, our laboratory has found instead that insulin has an essential role in mediating expression of the IGF type 1 receptor (IGF-1R), insulin receptor (INSR), and IGFBP-3. Further interrogation of these pathways led to the generation of novel and exciting findings in corneal epithelial cells (CECs) that form the basis for the current proposal. Of high relevance to this proposal, all of our findings implicate the IGF-1 system as a mediator of mitochondrial function and stability. This is clinically significant since mitochondrial damage is a major underlying cause of disease morbidity in diabetes and other systemic diseases. Based on these findings, we propose to test two central hypotheses: (1) that insulin and IGFBP-3 regulate mitochondrial quality control and stability by coordinating mitochondrial-nuclear crosstalk in response to stress; and, (2) that interactions between the voltage dependent anion channel VDAC1, IGF-1R, and INSR mediate mitochondrial biogenesis and stability. We will test these hypotheses in the following aims.
Aim 1. Compare the effects of IGF-related ligands, receptors, and IGFBP-3 on signaling, proliferation, and metabolism in normoglycemic versus hyperglycemic CEC culture in vitro and the diabetic mouse corneal epithelium in vivo.
Aim 2 : Compare the effects of IGF-related ligands, receptors, and IGFBP-3 on mitochondrial biogenesis, stability through interactions with VDAC1, and dynamics (fission/fusion) in CECs in vitro and the diabetic mouse corneal epithelium in vivo.
Aim 3 : Compare the effects of IGF-related ligands, receptors, and IGFBP-3 on mitophagy and apoptosis in CECs in vitro and the diabetic mouse corneal epithelium in vivo. Mitochondria are well known to regulate signals that drive energy production and cell survival, and their dysfunction has been implicated in a wide range of diseases. These studies will provide the first comprehensive picture detailing the role of the IGF family in mediating mitochondrial stability and function in the healthy cornea and in the pathobiology of disease. The outcomes could represent a major paradigm shift in our understanding and future treatment of the diabetic corneal epithelium and other corneal diseases and dystrophies where mitochondrial function is altered.
Diabetes is a worldwide epidemic with serious health impact and significant economic burden. With the continued rise in costs of insulin in the United States, lack of patient compliance is an increasingly important factor, translating into an increased risk of ocular complications and blindness due to non-controlled diabetes. This proposal seeks to test how the insulin-like growth factor (IGF) family is altered in the diabetic cornea, with the goal of translating these findings into novel therapies to treat and ameliorate corneal disease.
