Activation of a stress pathway is a primary cause of many types of cataracts. A search of the literatures has indicated that misfolded protein conformations in the endoplasmic reticulum (ER) induce ER stress, and prolonged ER stress oxidizes and kills numerous cell types. Our laboratory has previously proposed that many cataractogenic stressors also exhibit endoplasmic reticulum (ER) stress and induce well-defined protective and death pathways called the unfolded protein response (UPR). The first stage of the UPR protects cells against stress, and cells eliminate the unfolded modified proteins from the ER by the ubiquitin dependent ER-associated degradation (ERAD). However, prolonged ER stress activates the second stage of the UPR, which leads to activation of the UPR dependent death pathway. The UPR death pathway activates specific proteins including caspases, stimulates Ca++ release and the over production of reactive oxygen species (ROS), and results in LEC death. Lens epithelial cell derived growth factor (LEDGF) is known to be a transcriptional activator and survival factor and rescues various cell types under stress conditions by up-regulating expression of the stress associated genes. A recent study has suggested that prolonged ER stress activates the expression of the ledgf gene. Thus, we propose that the UPR also activates an eclectic survival pathway, which activates the ledgf gene and downstream survival genes to promote cell survival under prolonged ER stress. Chemical chaperones (PBA and TMAO) and TUDCA are reported to suppress ER stress. Recently we showed that these drugs reduced ER stress, delayed LEC death, and alleviated cataract formation. These results opened novel opportunities of research to develop prophylactic drugs for LEC and cataract development.
Aim 1 is to test that A) diabetes induces the UPR, which produces ROS, induces LEC death, and promotes cataract formation in rats, B) the UPR induces abnormal LEC proliferation in galactosemic rat LECs, and C) these proliferative LECs are preferentially attacked by ER stress. We believe that these above events are involved in cataract development.
Aim 2 is to test whether LEDGF is a prosurvival downstream activator in the UPR and if the UPR pathway regulates the transcription of the ledgf gene in galactosemic LECs. Stimulation of the LEDGF protective pathway could be another way of alleviating cataract in chronic diabetes.
Aim 3 is to test whether chemical chaperones and TUDCA can be used as prophylactic agents to suppress the death of LECs in galactosemic and diabetic cataract. The drugs will be trapped in poly-lactide-co-glycolides (PLGA) nanoparticles and directly inject into the vitreal space. The PLGA can deliver larger amounts of drugs and slowly release these drugs over a long time.
Activation of stress pathway is a primary cause of many types of diseases including cataracts. One form of stress, so called endoplasmic reticulum (ER) stress, is caused by misfolded protein conformation. The ER stress produces reactive oxygen species (ROS) to oxidize free glutathione and proteins and induces cell death in the lens. We will study the roles of the UPR in lens epithelial cell death and cataract fromation in diabetic and galactosemic rats. Furthermore, lens epithelial derived growth factor (LEDGF) is elevated in cells under ER stress, we will study the basic notion of up-regulation of LEDGF in the UPR pathway, which may open an alternative survival pathway. Finally, chemical chaperones and TUDCA are known to reduce ER stress dependent cell death. We will study whether these chaperones and TUDCA can be used as prophylactic drugs to suppress ER stress, ROS production, LEC death, and cataract development. Modulating ER stress by these chaperones and TUDCA may offer a novel therapeutic approach to the treatment of human patients with cataract.
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