Molecular cloning and baculovirus expression of the rabbit corneal aldehyde dehydrogenase (ALDH1A1) cDNA

The role of ALDHs in lipid peroxidation-related diseases

Lipid peroxidation presents the oxidative degradation of polyunsaturated fatty acids lincited by reactive species. Excessive accumulation of lipid peroxidation byproducts, including 4-hydroxy-2-nonenal (4-HNE) and malondialdehyde (MDA), causes protein dysfunction and various illnesses. Aldehyde dehydrogenases (ALDHs) catalyze the metabolism of both endogenous and exogenous aldehydes. These enzymes participate in detoxification and intermediary metabolism. Contemporary research has affirmed the involvement of both enzymatic and non-enzymatic pathways of ALDHs in modulating the evolution of diseases associated with lipid peroxidation. This review provides an overview of the biological functions and clinical implications concerning the enzymatic and non-enzymatic pathways of ALDHs in diseases related to lipid peroxidation, such as, non-alcoholic fatty liver disease (NAFLD), atherosclerosis, and type 2 diabetes (T2DM). Furthermore, the activators or inhibitors of ALDHs represent a promising therapeutic strategy for lipid peroxidation-related diseases.

Molecular characterization and expression profile of the ALDH1A1 gene and its functions in yak luteal cells

The ALDH1A1 gene encodes a cytoplasmic member of the aldehyde dehydrogenase 1 family, which plays an important role in regulating animal reproductive performance, including estrus cycle and embryonic development. The aim of this study was to characterize ALDH1A1 activity in ovaries of 3-5 year-old yaks and to determine its effects on cell proliferation, apoptosis, and progesterone secretion in luteal cells (LCs). The coding sequence (CDS) of the ALDH1A1 gene was cloned by reverse transcription-PCR and immunohistochemical analysis was used to confirm localization of the ALDH1A1 protein in the ovary. To assess the activity of ALDH1A1 in regulating progesterone secretion, si-ALDH1A1 was transfected into LCs in vitro and progesterone levels in LC supernatants were measured by ELISA. The interference efficiency was assessed by real-time quantitative PCR (RT-qPCR) and immunofluorescence staining, and cell proliferation and apoptosis were evaluated by EdU and TUNEL staining, respectively. The cloned ALDH1A1 sequence contained 1462 bp, encoding 487 amino acids. Immunohistochemical analysis showed that ALDH1A1 protein expression, which was significantly higher in LCs, was mainly found in antral follicles and the corpus luteum (CL). The expression of ALDH1A1 mRNA in LCs was effectively inhibited by si-ALDH1A1transfection, and progesterone secretion was markedly decreased along with the significant down-regulation of progesterone pathway-related genes, STAR, CYP11A1, CYP19A1, CYP17A1, 3β-HSD, and HSD17B1. Knockdown of ALDH1A1 mRNA expression decreased cell proliferation and increased apoptosis in LCs. The mRNA expression of the proliferation-related genes, PCNA, CCND1, CCNB1 and CDC25A, was significantly down-regulated, while expression of the apoptosis-promoting CASP3 gene was significantly increased. In summary, we characterized the yak ALDH1A1 gene and revealed that ALDH1A1 knockdown promoted apoptosis, repressed cell proliferation, and decreased progesterone secretion by yak LCs, potentially by regulating the mRNA expression of genes related to proliferation, apoptosis, and progesterone synthesis and secretion.

Moonlighting in drug metabolism

Drug metabolizing enzymes catalyze the biotransformation of many of drugs and chemicals. The drug metabolizing enzymes are distributed among several evolutionary families and catalyze a range of detoxication reactions, including oxidation/reduction, conjugative, and hydrolytic reactions that serve to detoxify potentially toxic compounds. This detoxication function requires that drug metabolizing enzymes exhibit substrate promiscuity. In addition to their catalytic functions, many drug metabolizing enzymes possess functions unrelated to or in addition to catalysis. Such proteins are termed 'moonlighting proteins' and are defined as proteins with multiple biochemical or biophysical functions that reside in a single protein. This review discusses the diverse moonlighting functions of drug metabolizing enzymes and the roles they play in physiological functions relating to reproduction, vision, cell signaling, cancer, and transport. Further research will likely reveal new examples of moonlighting functions of drug metabolizing enzymes.

Composition, structure and function of the corneal stroma

No other tissue in the body depends more on the composition and organization of the extracellular matrix (ECM) for normal structure and function than the corneal stroma. The precise arrangement and orientation of collagen fibrils, lamellae and keratocytes that occurs during development and is needed in adults to maintain stromal function is dependent on the regulated interaction of multiple ECM components that contribute to attain the unique properties of the cornea: transparency, shape, mechanical strength, and avascularity. This review summarizes the contribution of different ECM components, their structure, regulation and function in modulating the properties of the corneal stroma. Fibril forming collagens (I, III, V), fibril associated collagens with interrupted triple helices (XII and XIV), network forming collagens (IV, VI and VIII) as well as small leucine-rich proteoglycans (SLRP) expressed in the stroma: decorin, biglycan, lumican, keratocan, and fibromodulin are some of the ECM components reviewed in this manuscript. There are spatial and temporal differences in the expression of these ECM components, as well as interactions among them that contribute to stromal function. Unique regions within the stroma like Bowman's layer and Descemet's layer are discussed. To define the complexity of corneal stroma composition and structure as well as the relationship to function is a daunting task. Our knowledge is expanding, and we expect that this review provides a comprehensive overview of current knowledge, definition of gaps and suggests future research directions.

Impaired dopamine metabolism in Parkinson's disease pathogenesis

A full understanding of Parkinson's Disease etiopathogenesis and of the causes of the preferential vulnerability of nigrostriatal dopaminergic neurons is still an unsolved puzzle. A multiple-hit hypothesis has been proposed, which may explain the convergence of familial, environmental and idiopathic forms of the disease. Among the various determinants of the degeneration of the neurons in Substantia Nigra pars compacta, in this review we will focus on the endotoxicity associated to dopamine dyshomeostasis. In particular, we will discuss the relevance of the reactive dopamine metabolite 3,4-dihydroxyphenylacetaldehyde (DOPAL) in the catechol-induced neurotoxicity. Indeed, the synergy between the catechol and the aldehyde moieties of DOPAL exacerbates its reactivity, resulting in modification of functional protein residues, protein aggregation, oxidative stress and cell death. Interestingly, αSynuclein, whose altered proteostasis is a recurrent element in Parkinson's Disease pathology, is considered a preferential target of DOPAL modification. DOPAL triggers αSynuclein oligomerization leading to synapse physiology impairment. Several factors can be responsible for DOPAL accumulation at the pre-synaptic terminals, i.e. dopamine leakage from synaptic vesicles, increased rate of dopamine conversion to DOPAL by upregulated monoamine oxidase and decreased DOPAL degradation by aldehyde dehydrogenases. Various studies report the decreased expression and activity of aldehyde dehydrogenases in parkinsonian brains, as well as genetic variants associated to increased risk in developing the pathology. Thus, we discuss how the deregulation of these enzymes might be considered a contributing element in the pathogenesis of Parkinson's Disease or a down-stream effect. Finally, we propose that a better understanding of the impaired dopamine metabolism in Parkinson's Disease would allow a more refined patients stratification and the design of more targeted and successful therapeutic strategies.

UPLC-MS-based metabolomics reveals metabolic dysregulation in ALDH1A1-overexpressed lung adenocarcinoma cells

INTRODUCTION

Specific oncogenotypes can produce distinct metabolic changes in cancer. Recently it is considered that metabolic reprograming contributes heavily to drug resistance. Aldehyde dehydrogenase 1A1 (ALDH1A1), is overexpressed in drug resistant lung adenocarcinomas and may be the cause of acquired drug resistance. However, how ALDH1A1 affects metabolic profiling in lung adenocarcinoma cells remains elusive.

OBJECTIVE

We sought to investigate metabolic alterations induced by ALDH1A1 in lung adenocarcinoma in order to better understand the reprogramming and metabolic mechanism of resistance induced by ALDH1A1.

METHODS

Metabolic alterations in lung adenocarcinoma HCC827-ALDH1A1 cells were analyzed by ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS). HCC827-ALDH1A1 metabolic signatures were extracted by univariate and multivariate statistical analysis. Furthermore, metabolite enrichment analysis and pathway analysis were performed using MetaboAnalyst 4.0 software.

RESULTS

Twenty-two metabolites were positively identified using authentic standards, including uridine monophosphate (UMP), uridine diphosphate (UDP), adenosine diphosphate (ADP), malic acid, malonyl-coenzyme A, nicotinamide adenine dinucleotide (NAD), coenzyme A and so on. Furthermore, metabolic pathway analysis revealed several dysregulated pathways in HCC827-ALDH1A1 cells, including nucleotide metabolism, urea cycle, tricarboxylic acid (TCA) cycle, and glycerol phospholipid metabolism etc. CONCLUSION: Lung cancer is the most frequent cause of cancer-related deaths worldwide. Nearly all patients eventually undergo disease progression due to acquired resistance. Mechanisms of biological acquired resistance need to be identified. Our study identified altered metabolites in HCC827-ALDH1A1 cells, enhancing our knowledge of lung adenocarcinoma metabolic alterations induced by ALDH1A1, creating a novel therapeutic pathway. These metabolic signatures of ALDH1A1 overexpression may shed light on molecular mechanisms in drug-resistant tumors, and on candidate drug targets. Furthermore, new molecular targets may provide the foundation for potential anticancer strategies for lung cancer therapy.

Aldehyde dehydrogenase 1B1: a novel immunohistological marker for colorectal cancer

Background:

Aldehyde dehydrogenase (ALDH) 1A1 is an immunohistological biomarker of various solid tumours, but has not been successfully proved as a colorectal cancer (CRC) marker. We recently reported that ALDH1B1, which has functional roles in tumourigenesis, may be a better CRC marker than ALDH1A1.

Methods:

Human CRC explants and cell lines were analysed to identify candidate CRC markers from eight ALDH isozymes including ALDH1A1 and ALDH1B1. A tissue microarray, including paired specimens of normal and tumour tissues, was subsequently analysed to determine if candidate ALDHs could distinguish CRC from normal tissue.

Results:

Based on mRNA analysis, ALDH1B1 and ALDH2 were selected as suitable candidates. These were strongly and regularly expressed in tumour tissue and cell lines, including highly tumourigenic cell populations (ALDH⁺CD44⁺ cells), while other ALDHs, including ALDH1A1, showed differential or low expression. No genetic alteration of ALDH1B1 in CRC was suggested by the relationships between mRNA and protein levels/enzymatic activities, and cDNA sequences of CRC cell lines. Tissue microarray findings showed that ALDH1B1, but not ALDH2, could distinguish CRC from normal tissue. Furthermore, ratios of ALDH1B1 to ALDH1A1 or ALDH2 were found to be powerful CRC indicators.

Conclusions:

These results suggest that ALDH1B1 is a novel human CRC biomarker.

ALDH1A3, a metabolic target for cancer diagnosis and therapy

Metabolism reprogramming has been linked with the initiation, metastasis, and recurrence of cancer. The aldehyde dehydrogenase (ALDH) family is the most important enzyme system for aldehyde metabolism. The human ALDH family is composed of 19 members. ALDH1A3 participates in various physiological processes in human cells by oxidizing all-trans-retinal to retinoic acid. ALDH1A3 expression is regulated by many factors, and it is associated with the development, progression, and prognosis of cancers. In addition, ALDH1A3 influences a diverse range of biological characteristics within cancer stem cells and can act as a marker for these cells. Thus, growing evidence indicates that ALDH1A3 has the potential to be used as a target for cancer diagnosis and therapy.

Aldehyde dehydrogenases in cellular responses to oxidative/electrophilic stress

Reactive oxygen species (ROS) are continuously generated within living systems and the inability to manage ROS load leads to elevated oxidative stress and cell damage. Oxidative stress is coupled to the oxidative degradation of lipid membranes, also known as lipid peroxidation. This process generates over 200 types of aldehydes, many of which are highly reactive and toxic. Aldehyde dehydrogenases (ALDHs) metabolize endogenous and exogenous aldehydes and thereby mitigate oxidative/electrophilic stress in prokaryotic and eukaryotic organisms. ALDHs are found throughout the evolutionary gamut, from single-celled organisms to complex multicellular species. Not surprisingly, many ALDHs in evolutionarily distant, and seemingly unrelated, species perform similar functions, including protection against a variety of environmental stressors such as dehydration and ultraviolet radiation. The ability to act as an "aldehyde scavenger" during lipid peroxidation is another ostensibly universal ALDH function found across species. Upregulation of ALDHs is a stress response in bacteria (environmental and chemical stress), plants (dehydration, salinity, and oxidative stress), yeast (ethanol exposure and oxidative stress), Caenorhabditis elegans (lipid peroxidation), and mammals (oxidative stress and lipid peroxidation). Recent studies have also identified ALDH activity as an important feature of cancer stem cells. In these cells, ALDH expression helps abrogate oxidative stress and imparts resistance against chemotherapeutic agents such as oxazaphosphorine, taxane, and platinum drugs. The ALDH superfamily represents a fundamentally important class of enzymes that contributes significantly to the management of electrophilic/oxidative stress within living systems. Mutations in various ALDHs are associated with a variety of pathological conditions in humans, highlighting the fundamental importance of these enzymes in physiological and pathological processes.

Aldehyde dehydrogenases: from eye crystallins to metabolic disease and cancer stem cells

The aldehyde dehydrogenase (ALDH) superfamily is composed of nicotinamide adenine dinucleotide (phosphate) (NAD(P)(+))-dependent enzymes that catalyze the oxidation of aldehydes to their corresponding carboxylic acids. To date, 24 ALDH gene families have been identified in the eukaryotic genome. In addition to aldehyde metabolizing capacity, ALDHs have additional catalytic (e.g. esterase and reductase) and non-catalytic activities. The latter include functioning as structural elements in the eye (crystallins) and as binding molecules to endobiotics and xenobiotics. Mutations in human ALDH genes and subsequent inborn errors in aldehyde metabolism are the molecular basis of several diseases. Most recently ALDH polymorphisms have been associated with gout and osteoporosis. Aldehyde dehydrogenase enzymes also play important roles in embryogenesis and development, neurotransmission, oxidative stress and cancer. This article serves as a comprehensive review of the current state of knowledge regarding the ALDH superfamily and the contribution of ALDHs to various physiological and pathophysiological processes.

Ocular surface development and gene expression

The ocular surface-a continuous epithelial surface with regional specializations including the surface and glandular epithelia of the cornea, conjunctiva, and lacrimal and meibomian glands connected by the overlying tear film-plays a central role in vision. Molecular and cellular events involved in embryonic development, postnatal maturation, and maintenance of the ocular surface are precisely regulated at the level of gene expression by a well-coordinated network of transcription factors. A thorough appreciation of the biological characteristics of the ocular surface in terms of its gene expression profiles and their regulation provides us with a valuable insight into the pathophysiology of various blinding disorders that disrupt the normal development, maturation, and/or maintenance of the ocular surface. This paper summarizes the current status of our knowledge related to the ocular surface development and gene expression and the contribution of different transcription factors to this process.

Ocular aldehyde dehydrogenases: protection against ultraviolet damage and maintenance of transparency for vision

Aldehyde dehydrogenase (ALDH) enzymes catalyze the NAD(P)(+)-dependent oxidation of a wide variety of endogenous and exogenous aldehydes to their corresponding acids. Some members of the ALDH superfamily of enzymes are abundantly expressed in the mammalian cornea and lens in a taxon-specific manner. Considered to be corneal and lens crystallins, they confer protective and transparent properties upon these ocular tissues. ALDH3A1 is highly expressed in the cornea of most mammals, with the exception of rabbit that expresses exclusively ALDH1A1 in the cornea. ALDH1A1 is present in both the cornea and lens of several animal species. As a result of their catalytic and non-catalytic functions, ALDH3A1 and ALDH1A1 proteins protect inner ocular tissues from ultraviolet radiation and reactive oxygen-induced damage. In addition, these corneal crystallins contribute to cellular transparency in corneal stromal keratocytes, supporting a structural role of these ALDH proteins. A putative regulatory function of ALDH3A1 on corneal cell proliferation has also been proposed. Finally, the three retinaldehyde dehydrogenases cooperatively mediate retinoic acid signaling during the eye development.

Characterization of aldehyde dehydrogenase isozymes in ovarian cancer tissues and sphere cultures

BACKGROUND

Aldehyde dehydrogenases belong to a superfamily of detoxifying enzymes that protect cells from carcinogenic aldehydes. Of the superfamily, ALDH1A1 has gained most attention because current studies have shown that its expression is associated with human cancer stem cells. However, ALDH1A1 is only one of the 19 human ALDH subfamilies currently known. The purpose of the present study was to determine if the expression and activities of other major ALDH isozymes are associated with human ovarian cancer and ovarian cancer sphere cultures.

METHODS

Immunohistochemistry was used to delineate ALDH isozyme localization in clinical ovarian tissues. Western Blot analyses were performed on lysates prepared from cancer cell lines and ovarian cancer spheres to confirm the immunohistochemistry findings. Quantitative reverse transcription-polymerase chain reactions were used to measure the mRNA expression levels. The Aldefluor® assay was used to measure ALDH activity in cancer cells from the four tumor subtypes.

RESULTS

Immunohistochemical staining showed significant overexpression of ALDH1A3, ALDH3A2, and ALDH7A1 isozymes in ovarian tumors relative to normal ovarian tissues. The expression and activity of ALDH1A1 is tumor type-dependent, as seen from immunohistochemisty, Western blot analysis, and the Aldefluor® assay. The expression was elevated in the mucinous and endometrioid ovarian epithelial tumors than in serous and clear cell tumors. In some serous and most clear cell tumors, ALDH1A1 expression was found in the stromal fibroblasts. RNA expression of all studied ALDH isozymes also showed higher expression in endometrioid and mucinous tumors than in the serous and clear cell subtypes. The expression of ALDH enzymes showed tumor type-dependent induction in ovarian cancer cells growing as sphere suspensions in serum-free medium.

CONCLUSIONS

The results of our study indicate that ALDH enzyme expression and activity may be associated with specific cell types in ovarian tumor tissues and vary according to cell states. Elucidating the function of the ALDH isozymes in lineage differentiation and pathogenesis may have significant implications for ovarian cancer pathophysiology.

Molecular mechanisms of ALDH3A1-mediated cellular protection against 4-hydroxy-2-nonenal

Evidence suggests that aldehydic molecules generated during lipid peroxidation (LPO) are causally involved in most pathophysiological processes associated with oxidative stress. 4-Hydroxy-2-nonenal (4-HNE), the LPO-derived product, is believed to be responsible for much of the cytotoxicity. To counteract the adverse effects of this aldehyde, many tissues have evolved cellular defense mechanisms, which include the aldehyde dehydrogenases (ALDHs). Our laboratory has previously characterized the tissue distribution and metabolic functions of ALDHs, including ALDH3A1, and demonstrated that these enzymes may play a significant role in protecting cells against 4-HNE. To further characterize the role of ALDH3A1 in the oxidative stress response, a rabbit corneal keratocyte cell line (TRK43) was stably transfected to overexpress human ALDH3A1. These cells were studied after treatment with 4-HNE to determine their abilities to: (a) maintain cell viability, (b) metabolize 4-HNE and its glutathione conjugate, (c) prevent 4-HNE-protein adduct formation, (d) prevent apoptosis, (e) maintain glutathione homeostasis, and (f) preserve proteasome function. The results demonstrated a protective role for ALDH3A1 against 4-HNE. Cell viability assays, morphological evaluations, and Western blot analyses of 4-HNE-adducted proteins revealed that ALDH3A1 expression protected cells from the adverse effects of 4-HNE. Based on the present results, it is apparent that ALDH3A1 provides exceptional protection from the adverse effects of pathophysiological concentrations of 4-HNE such as may occur during periods of oxidative stress.

Myofibroblast differentiation modulates keratocyte crystallin protein expression, concentration, and cellular light scattering

PURPOSE

The purpose of this study was to determine whether myofibroblast differentiation altered keratocyte crystallin protein concentration and increased cellular light scattering.

METHODS

Serum-free cultured rabbit corneal keratocytes and TGFβ (5 ng/mL) induced myofibroblasts were harvested and counted and protein/RNA extracted. Expression of myofibroblast and keratocyte markers was determined by real-time PCR and Western blot analysis. The cell volume of calcein AM-loaded keratocytes and myofibroblasts was determined by using nonlinear optical microscopy. Cellular light scattering of transformed myofibroblasts expressing human keratocyte crystallins was measured by reflectance confocal microscopy.

RESULTS

Differentiated myofibroblasts showed a significant decrease in RNA levels for the keratocyte markers ALDH1A1, lumican, and keratocan and a significant increase in the myofibroblast marker α-smooth muscle actin. Volumetric and protein measurements showed that myofibroblast differentiation significantly increased cytoplasmic volume (293%; P < 0.001) and water-soluble and -insoluble protein content per cell (respectively, 442% and 431%; P < 0.002) compared to keratocytes. Western blot analysis showed that the level of ALDH1A1 protein per cell was similar between myofibroblasts and keratocytes, but was substantially reduced as a percentage of total water-soluble protein. Light scattering measurements showed that induced expression of corneal crystallins significantly decreased light scattering.

CONCLUSIONS

These data suggest that myofibroblast differentiation leads to a marked increase in cell volume and dilution of corneal crystallins associated with an increase in cellular light scattering.

Proteomic analysis of endothelial cold-adaptation

BACKGROUND

Understanding how human cells in tissue culture adapt to hypothermia may aid in developing new clinical procedures for improved ischemic and hypothermic protection. Human coronary artery endothelial cells grown to confluence at 37°C and then transferred to 25°C become resistant over time to oxidative stress and injury induced by 0°C storage and rewarming. This protection correlates with an increase in intracellular glutathione at 25°C. To help understand the molecular basis of endothelial cold-adaptation, isolated proteins from cold-adapted (25°C/72 h) and pre-adapted cells were analyzed by quantitative proteomic methods and differentially expressed proteins were categorized using the DAVID Bioinformatics Resource.

RESULTS

Cells adapted to 25°C expressed changes in the abundance of 219 unique proteins representing a broad range of categories such as translation, glycolysis, biosynthetic (anabolic) processes, NAD, cytoskeletal organization, RNA processing, oxidoreductase activity, response-to-stress and cell redox homeostasis. The number of proteins that decreased significantly with cold-adaptation exceeded the number that increased by 2:1. Almost half of the decreases were associated with protein metabolic processes and a third were related to anabolic processes including protein, DNA and fatty acid synthesis. Changes consistent with the suppression of cytoskeletal dynamics provided further evidence that cold-adapted cells are in an energy conserving state. Among the specific changes were increases in the abundance and activity of redox proteins glutathione S-transferase, thioredoxin and thioredoxin reductase, which correlated with a decrease in oxidative stress, an increase in protein glutathionylation, and a recovery of reduced protein thiols during rewarming from 0°C. Increases in S-adenosylhomocysteine hydrolase and nicotinamide phosphoribosyltransferase implicate a central role for the methionine-cysteine transulfuration pathway in increasing glutathione levels and the NAD salvage pathway in increasing the reducing capacity of cold-adapted cells.

CONCLUSIONS

Endothelial adaptation to mild-moderate hypothermia down-regulates anabolic processes and increases the reducing capacity of cells to enhance their resistance to oxidation and injury associated with 0°C storage and rewarming. Inducing these characteristics in a clinical setting could potentially limit the damaging effects of energy insufficiency due to ischemia and prevent the disruption of integrated metabolism at low temperatures.

Ultraviolet radiation: cellular antioxidant response and the role of ocular aldehyde dehydrogenase enzymes

Solar ultraviolet radiation (UVR) exposes the human eye to near constant oxidative stress. Evidence suggests that UVR is the most important environmental insult leading to the development of a variety of ophthalmoheliosis disorders. UVR-induced reactive oxygen species (ROS) are highly reactive with DNA, proteins, and cellular membranes, resulting in cellular and tissue damage. Antioxidant defense systems present in ocular tissues function to combat ROS and protect the eye from oxidative damage. Important enzymatic antioxidants are the superoxide dismutases, catalase, glutathione peroxidases, glutathione reductase, and members of the aldehyde dehydrogenase (ALDH) superfamily. Glutathione, ascorbic and uric acids, α-tocopherol, nicotinamide-adenine dinucleotide phosphate, and ferritin serve as small molecule, nonenzymatic antioxidants. Ocular tissues have high levels of these antioxidants, which are essential for the maintenance of reduction-oxidation homeostasis in the eye and protection against oxidative damage. ALDH1A1 and ALDH3A1, present abundantly in the cornea and lens, have been shown to have unique roles in the defense against UVR and the downstream effects of oxidative stress. This review presents the properties and functions of ocular antioxidants that play critical roles in the cellular response to UVR exposure, including a focused discussion of the unique roles that the ALDH1A1 and ALDH3A1 enzymes have as multifunctional ocular antioxidants.

Widespread increases in malondialdehyde immunoreactivity in dopamine-rich and dopamine-poor regions of rat brain following multiple, high doses of methamphetamine

Treatment with multiple high doses of methamphetamine (METH) can induce oxidative damage, including dopamine (DA)-mediated reactive oxygen species (ROS) formation, which may contribute to the neurotoxic damage of monoamine neurons and long-term depletion of DA in the caudate putamen (CPu) and substantia nigra pars compacta (SNpc). Malondialdehyde (MDA), a product of lipid peroxidation by ROS, is commonly used as a marker of oxidative damage and treatment with multiple high doses of METH increases MDA reactivity in the CPu of humans and experimental animals. Recent data indicate that MDA itself may contribute to the destruction of DA neurons, as MDA causes the accumulation of toxic intermediates of DA metabolism via its chemical modification of the enzymes necessary for the breakdown of DA. However, it has been shown that in human METH abusers there is also increased MDA reactivity in the frontal cortex, which receives relatively fewer DA afferents than the CPu. These data suggest that METH may induce neuronal damage regardless of the regional density of DA or origin of DA input. The goal of the current study was to examine the modification of proteins by MDA in the DA-rich nigrostriatal and mesoaccumbal systems, as well as the less DA-dense cortex and hippocampus following a neurotoxic regimen of METH treatment. Animals were treated with METH (10 mg/kg) every 2 h for 6 h, sacrificed 1 week later, and examined using immunocytochemistry for changes in MDA-adducted proteins. Multiple, high doses of METH significantly increased MDA immunoreactivity (MDA-ir) in the CPu, SNpc, cortex, and hippocampus. Multiple METH administration also increased MDA-ir in the ventral tegmental area and nucleus accumbens. Our data indicate that multiple METH treatment can induce persistent and widespread neuronal damage that may not necessarily be limited to the nigrostriatal DA system.

Aldehyde dehydrogenase 7A1 (ALDH7A1) attenuates reactive aldehyde and oxidative stress induced cytotoxicity

Mammalian aldehyde dehydrogenase 7A1 (ALDH7A1) is homologous to plant ALDH7B1 which protects against various forms of stress such as increased salinity, dehydration and treatment with oxidants or pesticides. Deleterious mutations in human ALDH7A1 are responsible for pyridoxine-dependent and folinic acid-responsive seizures. In previous studies, we have shown that human ALDH7A1 protects against hyperosmotic stress presumably through the generation of betaine, an important cellular osmolyte, formed from betaine aldehyde. Hyperosmotic stress is coupled to an increase in oxidative stress and lipid peroxidation (LPO). In this study, cell viability assays revealed that stable expression of mitochondrial ALDH7A1 in Chinese hamster ovary (CHO) cells provides significant protection against treatment with the LPO-derived aldehydes hexanal and 4-hydroxy-2-nonenal (4HNE) implicating a protective function for the enzyme during oxidative stress. A significant increase in cell survival was also observed in CHO cells expressing either mitochondrial or cytosolic ALDH7A1 treated with increasing concentrations of hydrogen peroxide (H(2)O(2)) or 4HNE, providing further evidence for anti-oxidant activity. In vitro enzyme activity assays indicate that human ALDH7A1 is sensitive to oxidation and that efficiency can be at least partially restored by incubating recombinant protein with the thiol reducing agent β-mercaptoethanol (BME). We also show that after reactivation with BME, recombinant ALDH7A1 is capable of metabolizing the reactive aldehyde 4HNE. In conclusion, ALDH7A1 mechanistically appears to provide cells protection through multiple pathways including the removal of toxic LPO-derived aldehydes in addition to osmolyte generation.

Molecular characterization, expression analysis, and role of ALDH3B1 in the cellular protection against oxidative stress

Aldehyde dehydrogenase (ALDH) enzymes are critical in the detoxification of aldehydes. The human genome contains 19 ALDH genes, mutations in which are the basis of several diseases. The expression, subcellular localization, enzyme kinetics, and role of ALDH3B1 in aldehyde- and oxidant-induced cytotoxicity were investigated. ALDH3B1 was purified from Sf9 cells using chromatographic methods, and enzyme kinetics were determined spectrophotometrically. ALDH3B1 demonstrated high affinity for hexanal (K(m)=62 μM), octanal (K(m)=8 μM), 4-hydroxy-2-nonenal (4HNE; K(m)=52 μM), and benzaldehyde (K(m)=46 μM). Low affinity was seen toward acetaldehyde (K(m)=23.3 mM), malondialdehyde (K(m)=152 mM), and the ester p-nitrophenyl acetate (K(m)=3.6 mM). ALDH3B1 mRNA was abundant in testis, lung, kidney, and ovary. ALDH3B1 protein was highly expressed in these tissues and the liver. Immunofluorescence microscopy of ALDH3B1-transfected human embryonic kidney (HEK293) cells and subcellular fractionation of mouse kidney and liver revealed a cytosolic protein localization. ALDH3B1-transfected HEK293 cells were significantly protected from the lipid peroxidation-derived aldehydes trans-2-octenal, 4HNE, and hexanal and the oxidants H(2)O(2) and menadione. In addition, ALDH3B1 protein expression was up-regulated by 4HNE in ARPE-19 cells. The results detailed in this study support a pathophysiological role for ALDH3B1 in protecting cells from the damaging effects of oxidative stress.

Aldehyde dehydrogenase 1B1: molecular cloning and characterization of a novel mitochondrial acetaldehyde-metabolizing enzyme

Ethanol-induced damage is largely attributed to its toxic metabolite, acetaldehyde. Clearance of acetaldehyde is achieved by its oxidation, primarily catalyzed by the mitochondrial class II aldehyde dehydrogenase (ALDH2). ALDH1B1 is another mitochondrial aldehyde dehydrogenase (ALDH) that shares 75% peptide sequence homology with ALDH2. Recent population studies in whites suggest a role for ALDH1B1 in ethanol metabolism. However, to date, no formal documentation of the biochemical properties of ALDH1B1 has been forthcoming. In this current study, we cloned and expressed human recombinant ALDH1B1 in Sf9 insect cells. The resultant enzyme was purified by affinity chromatography to homogeneity. The kinetic properties of purified human ALDH1B1 were assessed using a wide range of aldehyde substrates. Human ALDH1B1 had an exclusive preference for NAD(+) as the cofactor and was catalytically active toward short- and medium-chain aliphatic aldehydes, aromatic aldehydes, and the products of lipid peroxidation, 4-hydroxynonenal and malondialdehyde. Most importantly, human ALDH1B1 exhibited an apparent K(m) of 55 μM for acetaldehyde, making it the second low K(m) ALDH for metabolism of this substrate. The dehydrogenase activity of ALDH1B1 was sensitive to disulfiram inhibition, a feature also shared with ALDH2. The tissue distribution of ALDH1B1 in C57BL/6J mice and humans was examined by quantitative polymerase chain reaction, Western blotting, and immunohistochemical analysis. The highest expression occurred in the liver, followed by the intestinal tract, implying a potential physiological role for ALDH1B1 in these tissues. The current study is the first report on the expression, purification, and biochemical characterization of human ALDH1B1 protein.

Aldehyde dehydrogenase 7A1 (ALDH7A1) is a novel enzyme involved in cellular defense against hyperosmotic stress

Mammalian ALDH7A1 is homologous to plant ALDH7B1, an enzyme that protects against various forms of stress, such as salinity, dehydration, and osmotic stress. It is known that mutations in the human ALDH7A1 gene cause pyridoxine-dependent and folic acid-responsive seizures. Herein, we show for the first time that human ALDH7A1 protects against hyperosmotic stress by generating osmolytes and metabolizing toxic aldehydes. Human ALDH7A1 expression in Chinese hamster ovary cells attenuated osmotic stress-induced apoptosis caused by increased extracellular concentrations of sucrose or sodium chloride. Purified recombinant ALDH7A1 efficiently metabolized a number of aldehyde substrates, including the osmolyte precursor, betaine aldehyde, lipid peroxidation-derived aldehydes, and the intermediate lysine degradation product, alpha-aminoadipic semialdehyde. The crystal structure for ALDH7A1 supports the enzyme's substrate specificities. Tissue distribution studies in mice showed the highest expression of ALDH7A1 protein in liver, kidney, and brain, followed by pancreas and testes. ALDH7A1 protein was found in the cytosol, nucleus, and mitochondria, making it unique among the aldehyde dehydrogenase enzymes. Analysis of human and mouse cDNA sequences revealed mitochondrial and cytosolic transcripts that are differentially expressed in a tissue-specific manner in mice. In conclusion, ALDH7A1 is a novel aldehyde dehydrogenase expressed in multiple subcellular compartments that protects against hyperosmotic stress by generating osmolytes and metabolizing toxic aldehydes.

Corneal aldehyde dehydrogenases: multiple functions and novel nuclear localization

Aldehyde dehydrogenases (ALDHs) represent a superfamily of NAD(P)(+)-dependent enzymes which catalyze the oxidation of a wide variety of endogenous and exogenous aldehydes to their corresponding acids. Some ALDHs have been identified as corneal crystallins and thereby contribute to the protective and refractive properties of the cornea. ALDH3A1 is highly expressed in the cornea of most mammals with the exception of rabbit that abundantly expresses ALDH1A1 in the cornea instead of ALDH3A1. In this study, we examined the gene expression of other ALDHs and found high messenger levels of ALDH1B1, ALDH2 and ALDH7A1 in mouse cornea and lens. Substantial evidence supports a protective role for ALDH3A1 and ALDH1A1 against ultraviolet radiation (UVR)-induced oxidative damage to ocular tissues. The mechanism by which this protection occurs includes UVR filtering, detoxification of reactive aldehydes generated by UVR exposure and antioxidant activity. We recently have identified ALDH3A1 as a nuclear protein in corneal epithelium. Herein, we show that ALDH3A1 is also found in the nucleus of rabbit keratocytes. The nuclear presence of ALDH3A1 may be involved in cell cycle regulation.

Molecular cloning and oxidative modification of human lens ALDH1A1: implication in impaired detoxification of lipid aldehydes

Earlier studies showed that human lens ALDH1A1 plays a critical role in protection against oxidative stress-induced cytotoxicity in human lens epithelial cells (HLEC), and opacification of rat and mouse lens. The complete coding sequence of ALDH1A1 was cloned from human lens cDNA library by using PCR methods and expressed it in Escherichia coli. The cloned human lens ALDH1A1 cDNA encodes a 501-amino-acid protein (molecular mass = 54.8 kD) that is 100% identical to human liver ALDH1A1 and shares significant identity with the same isozyme from other tissues and species. The purified recombinant human lens ALDH1A1 exhibited optimal catalytic activity at pH 8 and preferred NAD(+) as cofactor and specifically catalyzed the oxidation of toxic lipid aldehydes such as 4-hydroxynonenal (HNE; K(m) = 4.8 microM) and malonaldehyde (K(m) MDA = 3.5 microM). Citral, disulfiram, and cyanamide were found to inhibit human lens ALDH1A1 at IC50 values of 55, 101, and 22610 microM, respectively, whereas diethylstilbestrol (DES) was found to be an activator (EC(50), 1.3 microM). Further, modification of recombinant human lens ALDH1A1 with nitric oxide donors such as S-nitroso-N-acetylpenicillamine (SNAP) and S-nitrosoglutathione (GSNO) significantly inhibited the enzyme activity. It therefore appears that activation of ALDH1A1, which efficiently catalyzes the detoxification of lipid-derived toxic aldehydes, and/or prevention of its oxidative modification may be novel therapeutic interventions against oxidative stress-induced lens pathologies.

Non-P450 aldehyde oxidizing enzymes: the aldehyde dehydrogenase superfamily

BACKGROUND

Aldehydes are highly reactive molecules. While several non-P450 enzyme systems participate in their metabolism, one of the most important is the aldehyde dehydrogenase (ALDH) superfamily, composed of NAD(P)+-dependent enzymes that catalyze aldehyde oxidation.

OBJECTIVE

This article presents a review of what is currently known about each member of the human ALDH superfamily including the pathophysiological significance of these enzymes.

METHODS

Relevant literature involving all members of the human ALDH family was extensively reviewed, with the primary focus on recent and novel findings.

CONCLUSION

To date, 19 ALDH genes have been identified in the human genome and mutations in these genes and subsequent inborn errors in aldehyde metabolism are the molecular basis of several diseases, including Sjögren-Larsson syndrome, type II hyperprolinemia, gamma-hydroxybutyric aciduria and pyridoxine-dependent seizures. ALDH enzymes also play important roles in embryogenesis and development, neurotransmission, oxidative stress and cancer. Finally, ALDH enzymes display multiple catalytic and non-catalytic functions including ester hydrolysis, antioxidant properties, xenobiotic bioactivation and UV light absorption.

The role of corneal crystallins in the cellular defense mechanisms against oxidative stress

The refracton hypothesis describes the lens and cornea together as a functional unit that provides the proper ocular transparent and refractive properties for the basis of normal vision. Similarities between the lens and corneal crystallins also suggest that both elements of the refracton may also contribute to the antioxidant defenses of the entire eye. The cornea is the primary physical barrier against environmental assault to the eye and functions as a dominant filter of UV radiation. It is routinely exposed to reactive oxygen species (ROS)-generating UV light and molecular O(2) making it a target vulnerable to UV-induced damage. The cornea is equipped with several defensive mechanisms to counteract the deleterious effects of UV-induced oxidative damage. These comprise both non-enzymatic elements that include proteins and low molecular weight compounds (ferritin, glutathione, NAD(P)H, ascorbate and alpha-tocopherol) as well as various enzymes (catalase, glucose-6-phosphate dehydrogenase, glutathione peroxidase, glutathione reductase, and superoxide dismutase). Several proteins accumulate in the cornea at unusually high concentrations and have been classified as corneal crystallins based on the analogy of these proteins with the abundant taxon-specific lens crystallins. In addition to performing a structural role related to ocular transparency, corneal crystallins may also contribute to the corneal antioxidant systems through a variety of mechanisms including the direct scavenging of free radicals, the production of NAD(P)H, the metabolism and/or detoxification of toxic compounds (i.e. reactive aldehydes), and the direct absorption of UV radiation. In this review, we extend the discussion of the antioxidant defenses of the cornea to include these highly expressed corneal crystallins and address their specific capacities to minimize oxidative damage.

Corneal crystallins and the development of cellular transparency

Past studies have established that the cornea like the lens abundantly expresses a few water-soluble enzyme/proteins in a taxon specific fashion. Based on these similarities it has been proposed that the lens and the cornea form a structural unit, the 'refracton', that has co-evolved through gene sharing to maximize light transmission and refraction to the retina. Thus far, the analogy between corneal crystallins and lens crystallins has been limited to similarities in the abundant expression, with few reports concerning their structural function. This review covers recent studies that establish a clear relationship between expression of corneal crystallins and light scattering from corneal stromal cells, i.e. keratocytes, that support a structural role for corneal crystallins in the development of transparency similar to that of lens crystallins that would be consistent with the 'refracton' hypothesis.

Multiple and additive functions of ALDH3A1 and ALDH1A1: cataract phenotype and ocular oxidative damage in Aldh3a1(-/-)/Aldh1a1(-/-) knock-out mice

ALDH3A1 (aldehyde dehydrogenase 3A1) is abundant in the mouse cornea but undetectable in the lens, and ALDH1A1 is present at lower (catalytic) levels in the cornea and lens. To test the hypothesis that ALDH3A1 and ALDH1A1 protect the anterior segment of the eye against environmentally induced oxidative damage, Aldh1a1(-/-)/Aldh3a1(-/-) double knock-out and Aldh1a1(-/-) and Aldh3a1(-/-) single knock-out mice were evaluated for biochemical changes and cataract formation (lens opacification). The Aldh1a1/Aldh3a1- and Aldh3a1-null mice develop cataracts in the anterior and posterior subcapsular regions as well as punctate opacities in the cortex by 1 month of age. The Aldh1a1-null mice also develop cataracts later in life (6-9 months of age). One- to three-month-old Aldh-null mice exposed to UVB exhibited accelerated anterior lens subcapsular opacification, which was more pronounced in Aldh3a1(-/-) and Aldh3a1(-/-)/Aldh1a1(-/-) mice compared with Aldh1a1(-/-) and wild type animals. Cataract formation was associated with decreased proteasomal activity, increased protein oxidation, increased GSH levels, and increased levels of 4-hydroxy-2-nonenal- and malondialdehyde-protein adducts. In conclusion, these findings support the hypothesis that corneal ALDH3A1 and lens ALDH1A1 protect the eye against cataract formation via nonenzymatic (light filtering) and enzymatic (detoxification) functions.

Expression and initial characterization of human ALDH3B1

Aldehyde dehydrogenases (ALDHs) are critical enzymes in the metabolism of endogenous and exogenous aldehydes. The human genome contains 19 putatively functional ALDH genes; ALDH3B1 belongs to the ALDH3 family. While recent studies have linked the ALDH3B1 locus to schizophrenia, nothing was known, until now, about the properties and significance of the ALDH3B1 protein. The aim of this study was to characterize the ALDH3B1 protein. Human ALDH3B1 was baculovirus-expressed and found to be catalytically active towards medium- and long-chain aliphatic aldehydes and the aromatic aldehyde benzaldehyde. Western blot analyses indicate that ALDH3B1 is highly expressed in kidney and liver and moderately expressed in various brain regions. ALDH3B1-transfected HEK293 cells were significantly protected against cytotoxicity induced by the lipid peroxidation product octanal when compared to vector-transfected cells. This study shows for the first time the functionality, expression and protective role of ALDH3B1 and indicates a potential physiological role of ALDH3B1 against oxidative stress.

Mechanisms involved in the protection of UV-induced protein inactivation by the corneal crystallin ALDH3A1

Various lines of evidence have shown that ALDH3A1 (aldehyde dehydrogenase 3A1) plays a critical and multifaceted role in protecting the cornea from UV-induced oxidative stress. ALDH3A1 is a corneal crystallin, which is defined as a protein recruited into the cornea for structural purposes without losing its primary function (i.e. metabolism). Although the primary role of ALDH3A1 in the metabolism of toxic aldehydes has been clearly demonstrated, including the detoxification of aldehydes produced during UV-induced lipid peroxidation, the structural role of ALDH3A1 in the cornea remains elusive. We therefore examined the potential contribution of ALDH3A1 in maintaining the optical integrity of the cornea by suppressing the aggregation and/or inactivation of other proteins through chaperone-like activity and other protective mechanisms. We found that ALDH3A1 underwent a structural transition near physiological temperatures to form a partially unfolded conformation that is suggestive of chaperone activity. Although this structural transition alone did not correlate with any protection, ALDH3A1 substantially reduced the inactivation of glucose-6-phosphate dehydrogenase by 4-hydroxy-2-nonenal and malondialdehyde when co-incubated with NADP(+), reinforcing the importance of the metabolic function of this corneal enzyme in the detoxification of toxic aldehydes. A large excess of ALDH3A1 also protected glucose-6-phosphate dehydrogenase from inactivation because of direct exposure to UVB light, which suggests that ALDH3A1 may shield other proteins from damaging UV rays. Collectively, these data demonstrate that ALDH3A1 can reduce protein inactivation and/or aggregation not only by detoxification of reactive aldehydes but also by directly absorbing UV energy. This study provides for the first time mechanistic evidence supporting the structural role of the corneal crystallin ALDH3A1 as a UV-absorbing constituent of the cornea.

Scallop lens Ω-crystallin (ALDH1A9): A novel tetrameric aldehyde dehydrogenase

Scallop eye lens Omega-crystallin is an inactive aldehyde dehydrogenase (ALDH1A9) related to cytoplasmic ALDH1A1 and mitochondrial ALDH2 that migrates by gel filtration chromatography as a homodimer. Because mammalian ALDH1A1 and ALDH2 are homotetramers, we investigated the native molecular mass of scallop Omega-crystallin by multi-angle laser light scattering. The results indicate that the scallop Omega-crystallin is a tetrameric, not a dimeric protein. Moreover, phylogenetic tree analysis shows that scallop Omega-crystallin clusters with the mitochondrial ALDH2 and ALDH1B1 rather than the cytoplasmic ALDH1A, yet it lacks the mitochondrial N-terminal leader sequence characteristic of the mitochondrial ALDHs. The mitochondrial grouping, enzymatic inactivity, and anomalous gel filtration behavior make scallop cytoplasmic Omega-crystallin an interesting protein for structural studies of evolutionary adaptations to become an enzyme-crystallin.

Seabream antiquitin: molecular cloning, tissue distribution, subcellular localization and functional expression

Subsequent to our earlier report on the first purification of antiquitin protein from seabream liver and demonstration of its enzymatic activity [FEBS Letters 516 (2002) 183-186], we report herein the cloning of its full-length cDNA sequence. The open reading frame encodes a protein of 511 amino acids. Results of RT-PCR indicate that antiquitin is highly expressed in both the seabream liver and kidney. Transfection studies in cultured eukaryotic cells provided further evidence that it is a cytosolic protein. Bacterial expression of the enzyme was also performed. The purified recombinant protein was demonstrated to exhibit similar kinetic properties as the native enzyme.

Molecular cloning, baculovirus expression, and tissue distribution of the zebrafish aldehyde dehydrogenase 2

Ethanol is metabolized to acetaldehyde mainly by the alcohol dehydrogenase pathway and, to a lesser extent, through microsomal oxidation (CYP2E1) and the catalase-H(2)O(2) system. Acetaldehyde, which is responsible for some of the deleterious effects of ethanol, is further oxidized to acetic acid by aldehyde dehydrogenases (ALDHs), of which mitochondrial ALDH2 is the most efficient. The aim of this study was to evaluate zebrafish (Danio rerio) as a model for ethanol metabolism by cloning, expressing, and characterizing the zebrafish ALDH2. The zebrafish ALDH2 cDNA was cloned and found to be 1892 bp in length and encoding a protein of 516 amino acids (M(r) = 56,562), approximately 75% identical to mammalian ALDH2 proteins. Recombinant zebrafish ALDH2 protein was expressed using the baculovirus expression system and purified to homogeneity by affinity chromatography. We found that zebrafish ALDH2 is catalytically active and efficiently oxidizes acetaldehyde (K(m) = 11.5 microM) and propionaldehyde (K(m) = 6.1 microM). Similar kinetic properties were observed with the recombinant human ALDH2 protein, which was expressed and purified using comparable experimental conditions. Western blot analysis revealed that ALDH2 is highly expressed in the heart, skeletal muscle, and brain with moderate expression in liver, eye, and swim bladder of the zebrafish. These results are the first reported on the cloning, expression, and characterization of a zebrafish ALDH, and indicate that zebrafish is a suitable model for studying ethanol metabolism and, therefore, toxicity.

Role of human aldehyde dehydrogenases in endobiotic and xenobiotic metabolism

The human genome contains at least 17 genes that are members of the aldehyde dehydrogenase (ALDH) superfamily. These genes encode NAD(P)(+)-dependent enzymes that oxidize a wide range of aldehydes to their corresponding carboxylic acids. Aldehydes are highly reactive molecules that are intermediates or products involved in a broad spectrum of physiologic, biologic, and pharmacologic processes. Aldehydes are generated during retinoic acid biosynthesis and the metabolism of amino acids, lipids, carbohydrates, and drugs. Mutations in several ALDH genes are the molecular basis of inborn errors of metabolism and contribute to environmentally induced diseases.

Preferential transcription of rabbit Aldh1a1 in the cornea: implication of hypoxia-related pathways

Here we examine the molecular basis for the known preferential expression of rabbit aldehyde dehydrogenase class 1 (ALDH1A1) in the cornea. The rabbit Aldh1a1 promoter-firefly luciferase reporter transgene (-3519 to +43) was expressed preferentially in corneal cells in transfection tests and in transgenic mice, with an expression pattern resembling that of rabbit Aldh1a1. The 5' flanking region of the rabbit Aldh1a1 gene resembled that in the human gene (60.2%) more closely than that in the mouse (46%) or rat (51.5%) genes. We detected three xenobiotic response elements (XREs) and one E-box consensus sequence in the rabbit Aldh1a1 upstream region; these elements are prevalent in other highly expressed corneal genes and can mediate stimulation by dioxin and repression by CoCl(2), which simulates hypoxia. The rabbit Aldh1a1 promoter was stimulated fourfold by dioxin in human hepatoma cells and repressed threefold by CoCl(2) treatment in rabbit corneal stromal and epithelial cells. Cotransfection, mutagenesis, and gel retardation experiments implicated the hypoxia-inducible factor 3alpha/aryl hydrocarbon nuclear translocator heterodimer for Aldh1a1 promoter activation via the XREs and stimulated by retinoic acid protein 13 for promoter repression via the E-box. These experiments suggest that XREs, E-boxes, and PAS domain/basic helix-loop-helix transcription factors (bHLH-PAS) contribute to preferential rabbit Aldh1a1 promoter activity in the cornea, implicating hypoxia-related pathways.

Human aldehyde dehydrogenase 3A1 (ALDH3A1): biochemical characterization and immunohistochemical localization in the cornea

ALDH3A1 (aldehyde dehydrogenase 3A1) is expressed at high concentrations in the mammalian cornea and it is believed that it protects this vital tissue and the rest of the eye against UV-light-induced damage. The precise biological function(s) and cellular distribution of ALDH3A1 in the corneal tissue remain to be elucidated. Among the hypotheses proposed for ALDH3A1 function in cornea is detoxification of aldehydes formed during UV-induced lipid peroxidation. To investigate in detail the biochemical properties and distribution of this protein in the human cornea, we expressed human ALDH3A1 in Sf9 insect cells using a baculovirus vector and raised monoclonal antibodies against ALDH3A1. Recombinant ALDH3A1 protein was purified to homogeneity with a single-step affinity chromatography method using 5'-AMP-Sepharose 4B. Human ALDH3A1 demonstrated high substrate specificity for medium-chain (6 carbons and more) saturated and unsaturated aldehydes, including 4-hydroxy-2-nonenal, which are generated by the peroxidation of cellular lipids. Short-chain aliphatic aldehydes, such as acetaldehyde, propionaldehyde and malondialdehyde, were found to be very poor substrates for human ALDH3A1. In addition, ALDH3A1 metabolized glyceraldehyde poorly and did not metabolize glucose 6-phosphate, 6-phosphoglucono-delta-lactone and 6-phosphogluconate at all, suggesting that this enzyme is not involved in either glycolysis or the pentose phosphate pathway. Immunohistochemistry in human corneas, using the monoclonal antibodies described herein, revealed ALDH3A1 expression in epithelial cells and stromal keratocytes, but not in endothelial cells. Overall, these cumulative findings support the metabolic function of ALDH3A1 as a part of a corneal cellular defence mechanism against oxidative damage caused by aldehydic products of lipid peroxidation. Both recombinant human ALDH3A1 and the highly specific monoclonal antibodies described in the present paper may prove to be useful in probing biological functions of this protein in ocular tissue.

Aldh3a1 protects human corneal epithelial cells from ultraviolet- and 4-hydroxy-2-nonenal-induced oxidative damage

Aldehyde dehydrogenase 3A1 (ALDH3A1) is one of the most abundant proteins found in corneal epithelial cells of mammalian species, with several postulated protective roles that include detoxification of peroxidic aldehydes, scavenging of free radicals, and direct absorption of ultraviolet (UV) radiation. In the present study, the protective role of ALDH3A1 against UV- and 4-hydroxy-2-nonenal- (4-HNE-) induced oxidative damage was studied. For this purpose, human ALDH3A1 was stably transfected in a human corneal epithelial cell line (HCE) lacking endogenous enzyme. Cells transfected with ALDH3A1 were more resistant to UV- and 4-HNE-induced cytotoxicity than mock-transfected cells. DNA fragmentation assays revealed that both treatments induced apoptosis in mock-transfected cells, but not in ALDH3A1-expressing cells. Apoptosis appeared to occur via caspase-3 activation and subsequent PARP cleavage. The Michaelis-Menten constant (K(m)) for 4-HNE was 54 microM in ALDH3A1-transfected cells; the addition of 100 microM 4-HNE increased NAD(P)H levels by 50% above that in mock-transfected cells. We also found that ALDH3A1 expression prevented 4-HNE-induced protein adduct formation. Taken together, these data suggest that ALDH3A1 is a regulatory element of the cellular defense system that protects corneal epithelium against UV- and 4-HNE-induced oxidative damage.