The proteasome and intracellular redox status: implications for apoptotic regulation in lens epithelial cells

Effect of an MG132-Sustained Drug Delivery Capsular Ring on the Inhibition of Posterior Capsule Opacification in a Rabbit Model

PURPOSE

To design an MG132-sustained drug delivery capsular ring (SDDCR) and investigate its effect on the inhibition of posterior capsule opacification (PCO) in a rabbit model.

METHODS

The SDDCRs were prepared by forming a slice of film made by the mixture of poly lactic-co-glycolic acid (PLGA) and MG132 on the surface of capsular tension rings (CTRs). The drug-loading capacity, entrapment efficiency, and in vitro release of the drug-containing film were detected. Eighteen New Zealand white rabbits were operated with phacoemulsification and MG132-SDDCRs/PLGA-CTRs/CTRs implantation in the single eye. The images of the anterior segments were acquired at certain days, and the epithelial-mesenchymal transition (EMT) markers were detected by western blot and immunofluorescence.

RESULTS

The drug-loading capacity and entrapment efficiency of MG132-SDDCRs were 1.15% ± 0.04% and 66.16% ± 0.027%, respectively, and the drug released well within a month. The PCO degree of the MG132-SDDCR group was significantly lower than the other groups. The expression of alpha-smooth muscle actin, fibronectin, vimentin, and collagen-I was lower, and the expression of E-cadherin (E-cad) was higher in the MG132-SDDCR group than the other groups.

CONCLUSIONS

MG132-SDDCRs could be established successfully. The PCO process was prevented, and the expression of EMT markers was inhibited by the implantation of MG132-SDDCRs, indicating that this could be a potential treatment against PCO.

Integrin αVβ5-mediated Removal of Apoptotic Cell Debris by the Eye Lens and Its Inhibition by UV Light Exposure

Accumulation of apoptotic material is toxic and associated with cataract and other disease states. Identification of mechanisms that prevent accumulation of apoptotic debris is important for establishing the etiology of these diseases. The ocular lens is routinely assaulted by UV light that causes lens cell apoptosis and is associated with cataract formation. To date, no molecular mechanism for removal of toxic apoptotic debris has been identified in the lens. Vesicular debris within lens cells exposed to UV light has been observed raising speculation that lens cells themselves could act as phagocytes to remove toxic apoptotic debris. However, phagocytosis has not been confirmed as a function of the intact eye lens, and no mechanism for lens phagocytosis has been established. Here, we demonstrate that the eye lens is capable of phagocytizing extracellular lens cell debris. Using high throughput RNA sequencing and bioinformatics analysis, we establish that lens epithelial cells express members of the integrin αVβ5-mediated phagocytosis pathway and that internalized cell debris co-localizes with αVβ5 and with RAB7 and Rab-interacting lysosomal protein that are required for phagosome maturation and fusion with lysosomes. We demonstrate that the αVβ5 receptor is required for lens epithelial cell phagocytosis and that UV light treatment of lens epithelial cells results in damage to the αVβ5 receptor with concomitant loss of phagocytosis. These data suggest that loss of αVβ5-mediated phagocytosis by the eye lens could result in accumulation of toxic cell debris that could contribute to UV light-induced cataract formation.

Thiol-protease oxidation in age-related neuropathology

Increased oxidative stress is a hallmark of every major neurodegenerative disease that has been studied. Numerous biomarkers of oxidative stress have been found, indicating that waves of oxidation had, at one time or another, overwhelmed antioxidant defenses, leaving behind a host of oxidized DNA, lipids, and proteins in their path. Although some level of oxidation may be beneficial, perhaps mediated by a hormetic response, the extent and types of oxidation detected in neuropathological states would suggest that oxidative stress contributes to a loss of homeostasis and cellular dysfunction. Although there are many targets of oxidants, this review emphasizes protein oxidation with a focus on an important group of redox-sensitive enzymes, the thiol-proteases. Both the direct and the indirect effects of oxidation and their potential importance in neurodegeneration are considered.

Effect of estrogen replacement therapy on lens epithelial cell apoptosis in an experimental rat model

Epidemiologic studies have revealed a higher incidence of cataracts in estrogen-deprived postmenopausal women, although the pathogenic mechanism has not yet been elucidated. Apoptosis of lens epithelial cells has been associated with cataractogenesis. The aim of the study reported here was to investigate the effect of estrogen replacement therapy (ERT) on lens epithelial cell apoptosis in an experimental rat model. Forty female Wistar rats were randomized into four groups: ERT (17beta-estradiol, 10 microg/kg/day) for 3 months without ovariectomy (group 1) and with ovariectomy (group 2); only ovariectomy (group 3); sham operated (group 4). At the end of the third month, all rats were sacrificed in estrous cycle, as determined by the vaginal smear test, and their right eyes were enucleated. Enucleated eyes were analyzed by immunohistochemical methods for the expression of terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end (TUNEL), caspase-3, and bcl-2 labeling. The TUNEL, caspase-3, and bcl-2 staining scores were found to increase in group 3 rats following the ovariectomy compared to the sham-operated group. The ERT decreased these scores in rats with or without the ovariectomy; however, these differences were not statistically significant. These data suggest that estrogen does not significantly affect lens epithelial cell apoptosis. Further studies are needed to gain a better understanding of the protective mechanism of estrogen and to provide new ideas for the treatment and prevention of cataract.

On to the road to degradation: atherosclerosis and the proteasome

Protein metabolism is a central element of every living cell. The ubiquitin-proteasome system (UPS) is an integral part of the protein metabolism machinery mediating post-transcriptional processing and degradation of the majority of intracellular proteins. Over the past few years, remarkable progress has been made in our understanding of the role of the UPS in vascular biology and pathobiology, particularly atherosclerosis. This review reflects on the recent developments from the effects on endothelial cells and the initial stage of atherosclerosis to the effects on vascular smooth muscle and the progression stage of atherosclerosis and finally to the effects on cell viability and the complication stage of atherosclerosis. It will conclude with the integration of the available information in a synoptic view of the involvement of the UPS in atherosclerosis.

Comprehensive proteomic and transcriptomic analysis reveals early induction of a protective anti-oxidative stress response by low-dose proteasome inhibition

Effective inhibition of the proteasome by high doses of proteasome inhibitors induces apoptotic cell death. In contrast, partial proteasome inhibition by low inhibitor doses mediates a protective cellular stress response. The early targets and mediators of these dose-dependent effects of proteasome inhibitors are unknown. Primary human umbilical cord vein endothelial cells were treated with low and high doses of the proteasome inhibitor MG132 for 2 h. In a combined 2-DE and MS approach, we identified more than 20 new targets of proteasome inhibition. These proteins are involved in cell cycle regulation, signaling, cytoskeletal rearrangement, and cellular stress response. Accompanying Affymetrix analysis revealed that these proteins are not regulated on the transcriptional level but are mainly stabilized by proteasome inhibition. The proteasome-dependent accumulation of the anti-oxidative sensor proteins DJ-1, peroxiredoxin-1 and -6 was accompanied by dose-dependent induction of oxidative stress after 2 h of proteasome inhibition and contributed to the differential transcriptional stress response to low- and high-dose proteasome inhibition: Whereas low-dose proteasome inhibition induces a transcriptional profile reminiscent of a physiological stress response that preconditions and protects endothelial cells from oxidative stress, high inhibitor doses induce massive transcriptional dysregulation and pronounced oxidative stress triggering apoptosis.

Mitochondrial function and redox control in the aging eye: role of MsrA and other repair systems in cataract and macular degenerations

Oxidative stress occurs when the level of prooxidants exceeds the level of antioxidants in cells resulting in oxidation of cellular components and consequent loss of cellular function. Oxidative stress is implicated in wide range of age-related disorders including Alzheimer's disease, Parkinson's disease amyotrophic lateral sclerosis (ALS), Huntington's disease and the aging process itself. In the anterior segment of the eye, oxidative stress has been linked to lens cataract and glaucoma while in the posterior segment of the eye oxidative stress has been associated with macular degeneration. Key to many oxidative stress conditions are alterations in the efficiency of mitochondrial respiration resulting in superoxide (O(2)(-)) production. Superoxide production precedes subsequent reactions that form potentially more dangerous reactive oxygen species (ROS) species such as the hydroxyl radical (OH), hydrogen peroxide (H(2)O(2)) and peroxynitrite (OONO(-)). The major source of ROS in the mitochondria, and in the cell overall, is leakage of electrons from complexes I and III of the electron transport chain. It is estimated that 0.2-2% of oxygen taken up by cells is converted to ROS, through mitochondrial superoxide generation, by the mitochondria. Generation of superoxide at complexes I and III has been shown to occur at both the matrix side of the inner mitochondrial membrane and the cytosolic side of the membrane. While exogenous sources of ROS such as UV light, visible light, ionizing radiation, chemotherapeutics, and environmental toxins may contribute to the oxidative milieu, mitochondria are perhaps the most significant contribution to ROS production affecting the aging process. In addition to producing ROS, mitochondria are also a target for ROS which in turn reduces mitochondrial efficiency and leads to the generation of more ROS in a vicious self-destructive cycle. Consequently, the mitochondria have evolved a number of antioxidant and key repair systems to limit the damaging potential of free oxygen radicals and to repair damaged proteins (Fig. 1). The aging eye appears to be at considerable risk from oxidative stress. This review will outline the potential role of mitochondrial function and redox balance in age-related eye diseases, and detail how the methionine sulfoxide reductase (Msr) protein repair system and other redox systems play key roles in the function and maintenance of the aging eye.