The effect of hydrogen peroxide on sarco/endoplasmic and plasma membrane calcium ATPase gene expression in cultured human lens epithelial cells

The Plasma Membrane Calcium ATPases and Their Role as Major New Players in Human Disease

The Ca²⁺ extrusion function of the four mammalian isoforms of the plasma membrane calcium ATPases (PMCAs) is well established. There is also ever-increasing detail known of their roles in global and local Ca²⁺ homeostasis and intracellular Ca²⁺ signaling in a wide variety of cell types and tissues. It is becoming clear that the spatiotemporal patterns of expression of the PMCAs and the fact that their abundances and relative expression levels vary from cell type to cell type both reflect and impact on their specific functions in these cells. Over recent years it has become increasingly apparent that these genes have potentially significant roles in human health and disease, with PMCAs1-4 being associated with cardiovascular diseases, deafness, autism, ataxia, adenoma, and malarial resistance. This review will bring together evidence of the variety of tissue-specific functions of PMCAs and will highlight the roles these genes play in regulating normal physiological functions and the considerable impact the genes have on human disease.

Excessive hydrogen peroxide enhances the attachment of amyloid β1-42 in the lens epithelium of UPL rats, a hereditary model for cataracts

Several studies have reported that hydrogen peroxide (H2O2) is related to the toxicity of amyloid β (Aβ), and that the accumulation of Aβ in the lenses of humans causes lens opacification. In this study, we investigate the accumulation of Aβ1-42 in the lenses of UPL rats, which then leads to lens opacification. In addition, we demonstrate the effect of disulfiram eye drops (DSF), a potent radical scavenger, on Aβ1-42 accumulation in the lenses of UPL rats. The H2O2 levels in 46- to 60-day-old UPL rat lenses are significantly higher than in normal rats, and the Aβ1-42 levels in 53- and 60-day-old UPL rats are also increased only in lens epithelium containing capsules (capsule-epithelium), not in the lens cortex and nucleus. However, no increases in amyloid precursor protein (APP), β- or γ-secretase mRNA were observed in lenses of the corresponding ages. It has been thought that Aβ1-42 that accumulates in the lenses of UPL rats is actually produced in another tissue containing neuronal cells, such as brain or retina. Aβ1-42 levels in the brain and retina rise with aging, and the levels of APP, β- and γ-secretase mRNA in the retinas of 53-day-old UPL rats with opaque lenses are significantly higher than in 25-day-old UPL rats with transparent lenses. In contrast to the results in retinas, the levels of APP, β- and γ-secretase mRNA in the brains of 25- and 53-day-old UPL rats are similar. On the other hand, in an in vitro study, Aβ1-42 attachment in the lens capsule-epithelium of UPL rats was found to increase in H2O2. In addition, in an in vivo study, the inhibition of H2O2 by DSF was found to attenuate the increase in Aβ1-42 in the lens capsule-epithelium of 60-day-old UPL rats. Taken together, we hypothesize that excessive H2O2 in the lens enhances the attachment of Aβ1-42 in the lens capsule-epithelium of UPL rats, and that the instillation of DSF has the ability to attenuate the attachment of Aβ1-42 by inhibiting H2O2 production in lens. These findings provide significant information that can be used to design further studies aimed at developing anti-cataract drugs.

Ca2+-dependent transcriptional control of Ca2+ homeostasis

Intracellular free Ca(2+) ions regulate many cellular functions, and in turn, the cell devotes many genes/proteins to keep tight control of the level of intracellular free Ca(2+). Here, we review recent work on Ca(2+)-dependent mechanisms and effectors that regulate the transcription of genes encoding proteins involved in the maintenance of the homeostasis of Ca(2+) in the cell.

Correlation between hyper-sensitivity to hydrogen peroxide and low defense against Ca(2+) influx in cataractogenic lens of Ihara cataract rats

Our previous studies have demonstrated that lipid peroxidation in the lenses of hereditary cataract model rats (Ihara cataract rat (ICR)/f rats) caused a dysfunction in Ca(2+) regulation. In the present study, we investigated the effect of in vitro hydrogen peroxide (H(2)O(2)) stimulation on lipid peroxide (LPO) and the activities of sarco-/endoplasmic reticulum and plasma membrane Ca(2+)-ATPase (SERCA and PMCA) in the ICR/f rat lenses. An increase in LPO level and decreases in the SERCA and PMCA activities were observed with increasing H(2)O(2) concentration, and pretreatment with diethyldithiocarbamate, a potent radical scavenger, attenuated these changes in normal and ICR/f rat lenses. The glutathione levels, glutathione peroxidase and glutathione reductase activities are significantly lower in ICR/f rat lenses than in normal rat lenses. Furthermore, we presented as two kinetic parameters such as DP (defense point) and K(s) (reactive constant) analyzed from above various biological responses vs. H(2)O(2) concentration-profile curves using a one-exponential equation. The DPs for LPO, SERCA and PMCA in ICR/f rat lenses is lower than in normal rat lenses. In contrast to the results in DP, the K(s) for LPO, SERCA and PMCA in ICR/f rat lenses is higher than in normal rat lenses. In addition, the closed relationship of was observed between DP and K(s) for LPO, SERCA and PMCA. These results show that the resistance to H(2)O(2) in the ICR/f rat lenses is lower than that of normal rats. The DP and K(s) values can provide an useful information for resistances to various stimuli in cells and tissues.

Allosteric inhibitors of plasma membrane Ca2+ pumps: Invention and applications of caloxins

Plasma membrane Ca²⁺ pumps (PMCA) play a major role in Ca²⁺ homeostasis and signaling by extruding cellular Ca²⁺ with high affinity. PMCA isoforms are encoded by four genes which are expressed differentially in various cell types in normal and disease states. Therefore, PMCA isoform selective inhibitors would aid in delineating their role in physiology and pathophysiology. We are testing the hypothesis that extracellular domains of PMCA can be used as allosteric targets to obtain a novel class of PMCA-specific inhibitors termed caloxins. This review presents the concepts behind the invention of caloxins and our progress in this area. A section is also devoted to the applications of caloxins in literature. We anticipate that isoform-selective caloxins will aid in understanding PMCA physiology in health and disease. With strategies to develop therapeutics from bioactive peptides, caloxins may become clinically useful in cardiovascular diseases, neurological disorders, retinopathy, cancer and contraception.

Mitochondria induce oxidative stress, generation of reactive oxygen species and redox state unbalance of the eye lens leading to human cataract formation: disruption of redox lens organization by phospholipid hydroperoxides as a common basis for cataract disease

The aging eye appears to be at considerable risk from oxidative stress. Lipid peroxidation (LPO) is one of the mechanisms of cataractogenesis, initiated by enhanced promotion of oxygen free radicals in the eye fluids and tissues and impaired enzymatic and non-enzymatic antioxidant defenses of the crystalline lens. The present study proposes that mitochondria are one of the major sources of reactive oxygen species (ROS) in mammalian and human lens epithelial cells and that therapies that protect mitochondria in lens epithelial cells from damage and reduce damaging ROS generation may potentially ameliorate the effects of free radical-induced oxidation that occur in aging ocular tissues and in human cataract diseases. It has been found that rather than complete removal of oxidants by the high levels of protective enzyme activities such as superoxide dismutase (SOD), catalase, lipid peroxidases in transparent lenses, the lens conversely, possess a balance between peroxidants and antioxidants in a way that normal lens tends to generate oxidants diffusing from lenticular tissues, shifting the redox status of the lens to become more oxidizing during both morphogenesis and aging. Release of the oxidants (O(2)(-)·, H(2)O(2) , OH·, and lipid hydroperoxides) by the intact lenses in the absence of respiratory inhibitors indicates that these metabolites are normal physiological products inversely related to the lens life-span potential (maturity of cataract) generated through the metal-ion catalyzed redox-coupled pro-oxidant activation of the lens reductants (ascorbic acid, glutathione). The membrane-bound phospholipid (PL) hydroperoxides escape detoxification by the lens enzymatic reduction. The lens cells containing these species would be vulnerable to peroxidative attack which trigger the PL hydroperoxide-dependent chain propagation of LPO and other damages in membrane (lipid and protein alterations). The increased concentrations of primary LPO products (diene conjugates, lipid hydroperoxides) and end fluorescent LPO products were detected in the lipid moiety of the aqueous humor samples obtained from patients with cataract as compared to normal donors. Since LPO is clinically important in many of the pathological effects and aging, new therapeutic modalities, such as patented N-acetylcarnosine prodrug lubricant eye drops, should treat the incessant infliction of damage to the lens cells and biomolecules by reactive lipid peroxides and oxygen species and "refashion" the affected lens membranes in the lack of important metabolic detoxification of PL peroxides. Combined in ophthalmic formulations with N-acetylcarnosine, mitochondria-targeted antioxidants are promising to become investigated as a potential tool for treating a number of ROS-related ocular diseases, including human cataracts.

Plasma membrane Ca2+-ATPases: Targets of oxidative stress in brain aging and neurodegeneration

The plasma membrane Ca²⁺-ATPase (PMCA) pumps play an important role in the maintenance of precise levels of intracellular Ca²⁺ [Ca²⁺]_i, essential to the functioning of neurons. In this article, we review evidence showing age-related changes of the PMCAs in synaptic plasma membranes (SPMs). PMCA activity and protein levels in SPMs diminish progressively with increasing age. The PMCAs are very sensitive to oxidative stress and undergo functional and structural changes when exposed to oxidants of physiological relevance. The major signatures of oxidative modification in the PMCAs are rapid inactivation, conformational changes, aggregation, internalization from the plasma membrane and proteolytic degradation. PMCA proteolysis appears to be mediated by both calpains and caspases. The predominance of one proteolytic pathway vs the other, the ensuing pattern of PMCA degradation and its consequence on pump activity depends largely on the type of insult, its intensity and duration. Experimental reduction of PMCA expression not only alters the dynamics of cellular Ca²⁺ handling but also has a myriad of downstream consequences on various aspects of cell function, indicating a broad role of these pumps. Age- and oxidation-related down-regulation of the PMCAs may play an important role in compromised neuronal function in the aging brain and its several-fold increased susceptibility to neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, and stroke. Therapeutic approaches that protect the PMCAs and stabilize [Ca²⁺]_i homeostasis may be capable of slowing and/or preventing neuronal degeneration. The PMCAs are therefore emerging as a new class of drug targets for therapeutic interventions in various chronic degenerative disorders.