Characterization of mRNA and genes for aldose reductase in rat

The betaine/GABA transporter and betaine: roles in brain, kidney, and liver

The physiological roles of the betaine/GABA transporter (BGT1; slc6a12) are still being debated. BGT1 is a member of the solute carrier family 6 (the neurotransmitter, sodium symporter transporter family) and mediates cellular uptake of betaine and GABA in a sodium- and chloride-dependent process. Most of the studies of BGT1 concern its function and regulation in the kidney medulla where its role is best understood. The conditions here are hostile due to hyperosmolarity and significant concentrations of NH₄Cl and urea. To withstand the hyperosmolarity, cells trigger osmotic adaptation, involving concentration of a transcriptional factor TonEBP/NFAT5 in the nucleus, and accumulate betaine and other osmolytes. Data from renal cells in culture, primarily MDCK, revealed that transcriptional regulation of BGT1 by TonEBP/NFAT5 is relatively slow. To allow more acute control of the abundance of BGT1 protein in the plasma membrane, there is also post-translation regulation of BGT1 protein trafficking which is dependent on intracellular calcium and ATP. Further, betaine may be important in liver metabolism as a methyl donor. In fact, in the mouse the liver is the organ with the highest content of BGT1. Hepatocytes express high levels of both BGT1 and the only enzyme that can metabolize betaine, namely betaine:homocysteine –S-methyltransferase (BHMT1). The BHMT1 enzyme removes a methyl group from betaine and transfers it to homocysteine, a potential risk factor for cardiovascular disease. Finally, BGT1 has been proposed to play a role in controlling brain excitability and thereby represents a target for anticonvulsive drug development. The latter hypothesis is controversial due to very low expression levels of BGT1 relative to other GABA transporters in brain, and also the primary location of BGT1 at the surface of the brain in the leptomeninges. These issues are discussed in detail.

Aldose reductase deficiency improves Wallerian degeneration and nerve regeneration in diabetic thy1-YFP mice

This study examined the role of aldose reductase (AR) in diabetes-associated impaired nerve regeneration using thy1-YFP (YFP) mice. Sciatic nerves of nondiabetic and streptozotocin-induced diabetic AR(+/+)YFP and AR(-/-)YFP mice were transected after 4 weeks of diabetes. Wallerian degeneration and nerve regeneration were evaluated at 1 and 2 weeks postaxotomy by fluorescence microscopy. Motor nerve conduction velocity recovery and regenerating nerve morphometric parameters were determined at 10 and 20 weeks, respectively. There was no difference in the extent of Wallerian degeneration, size of regenerating stump, motor nerve conduction velocity recovery, or caliber of regenerating fibers between nondiabetic AR(+/+)YFP and AR(-/-)YFP mice. In diabetic AR(+/+)YFP mice, Wallerian degeneration was delayed, associated with slower macrophage invasion and abnormal vascularization. Those mice had smaller regenerating stumps, slower motor nerve conduction velocity, and smaller regenerating fibers compared with nondiabetic mice. These features of impaired nerve regeneration were largely attenuated in diabetic AR(-/-)YFP mice. Retarded macrophage invasion and vascularization associated with Wallerian degeneration were normalized in diabetic AR(-/-)YFP mice. These results indicate that AR plays an important role in diabetes-associated impaired nerve regeneration, in part by affecting vascularization and macrophage invasion during Wallerian degeneration. The thy1-YFP mice are valuable tools for further investigation of the mechanism of diabetes-associated nerve regeneration.

Up-regulation of aldose reductase by the substrate, methylglyoxal

Methylglyoxal (MG), a reactive dicarbonyl produced during glucose metabolism, is known as a preferred substrate of aldose reductase (AR; AKR1B1) that concomitantly catalyzes the reduction of glucose in the polyol pathway. MG modifies cellular proteins to form cross-links of amino groups, generating so-called advanced glycation end products. Increased rates of MG formation under hyperglycemic conditions and ensuing high serum levels of MG are reported in diabetic patients. As involvement of AR in the pathogenesis of diabetic complications has been suggested, we investigated the effects of MG on AR activity using cultured vascular smooth muscle cells (SMC) isolated from rat aorta. MG-induced a dose- and time-dependent increase in AR mRNA levels to a maximum of 4.5-fold. This increase in mRNA was accompanied by elevated enzyme activity and protein levels. Pretreatment of SMC with N-acetyl-L-cysteine significantly suppressed the MG-induced AR expression, while DL-buthionine-(S,R)-sulfoximine further augmented the MG-induced increase in AR mRNA level. Intracellular levels of reactive oxygen species determined using 2',7'-dichlorofluorescein diacetate were significantly elevated in SMC treated with MG, suggesting the involvement of oxidative stress in this process. Under oxidative stress generated by hydrogen peroxide, the major signaling pathway mediating the up-regulation of AR expression was demonstrated to be the epidermal growth factor receptor-ERK pathway. In contrast, the p38 kinase pathway appears to mediate MG-induced AR expression. The cytotoxic effect of MG was significantly enhanced in the presence of the AR inhibitor ponalrestat, indicating a protective role of AR against MG-induced cell damage.

Plasma 3-deoxyglucosone elevation in chronic renal failure is associated with increased aldose reductase in erythrocytes

BACKGROUND

Serum concentrations of 3-deoxyglucosone (3DG), a highly reactive dicarbonyl compound, are elevated in uremic patients. Aldose reductase (AR) is an enzyme involved in both the detoxification of 3DG and producing precursors of 3DG.

METHODS

We examined the relationship between plasma 3DG and erythrocyte AR content in uremic patients. Patients were divided into three groups: (1) progressive renal disease without hemodialysis (HD; chronic renal failure [CRF] group), (2) patients without diabetes mellitus (DM) treated with maintenance HD (HD group), and (3) patients with DM treated with maintenance HD (DM-HD group). High-performance liquid chromatography was used to measure 3DG, and erythrocyte AR was measured by means of enzyme-linked immunosorbent assay.

RESULTS

Both 3DG and erythrocyte AR levels were significantly greater in the CRF, HD, and DM-HD groups than in healthy controls. These results did not change after HD sessions in the HD or DM-HD groups. Serum creatinine levels correlated with 3DG and erythrocyte AR levels in the control and CRF groups (3DG: r = 0.67; P < 0.001; erythrocyte AR: r = 0.71; P < 0.001). Both erythrocyte AR and 3DG levels then increased as renal function declined. A positive correlation was seen between 3DG and erythrocyte AR levels in all groups (r = 0.65; P < 0.001), and also between plasma osmolality and erythrocyte AR level (r = 0.46; P < 0.001).

CONCLUSION

Both erythrocyte AR and 3DG levels are increased in uremic patients, and these increases could possibly contribute to the development of uremic symptoms.

Substrate-induced up-regulation of aldose reductase by methylglyoxal, a reactive oxoaldehyde elevated in diabetes

Methylglyoxal (MG), a reactive dicarbonyl produced during glucose metabolism, induced a dose- and time-dependent increase in aldose reductase (AR) mRNA level in rat aortic smooth muscle cells (SMCs). AR has been implicated in the pathogenesis of diabetic complications, whereas the clinical efficacy of AR inhibitors has not been unequivocally proven. The enzyme catalyzes the reduction of glucose in the polyol pathway, as well as that of MG, which is known to be a preferred substrate of AR. A maximum of 4.5-fold induction of AR mRNA by MG was accompanied by elevated enzyme activity and protein levels and was completely abolished in the presence of cycloheximide or actinomycin D. Pretreatment of SMCs with N-acetyl-L-cysteine significantly suppressed the MG-induced AR expression, whereas DL-buthionine-(S,R)-sulfoximine further augmented the MG-induced increase in AR mRNA level. Intracellular levels of reactive oxygen species determined using 2',7'-dichlorofluorescein diacetate were significantly elevated in SMCs treated with MG, suggesting the involvement of oxidative stress in this process. However, inconsistent with our previous findings on oxidative stress-induced up-regulation of AR, the inhibition of extracellular signal-regulated kinase by 2'-amino-3'-methoxyflavone (PD98059) did not affect MG-induced AR expression, whereas blockade of the p38 mitogen-activated protein kinase pathway by 4-(4-fluorophenyl)-2-(4-methylsulfonylphenyl)-5-(4-pyridyl) imidazol (SB203580) significantly suppressed the induction. The cytotoxic effect of MG on SMCs was significantly enhanced in the presence of the AR inhibitor ponalrestat, indicating a protective role of AR against MG-induced cell damage. Taken together, these observations indicated that substrate-induced induction of AR by MG during hyperglycemic conditions may hinder vascular remodeling and accelerate the development of vascular lesions in diabetes.

EGF receptor-ERK pathway is the major signaling pathway that mediates upregulation of aldose reductase expression under oxidative stress

Acceleration of the polyol pathway and enhanced oxidative stress are implicated in the pathogenesis of diabetic complications. We and others recently reported that aldose reductase (AR), the rate-limiting enzyme in the polyol pathway, was upregulated by reactive oxygen and nitrogen species in vascular smooth muscle cells. To clarify the molecular mechanisms underlying these findings, we investigated the signal transduction pathways mediating AR expression using the rat vascular smooth muscle cell line A7r5. A selective epidermal growth factor (EGF) receptor kinase inhibitor, tyrphostin AG1478, significantly suppressed the hydrogen peroxide (H2O2)-induced increase in AR mRNA and enzyme activity. Activation of extracellular signal-regulated protein kinase (ERK) by H2O2 was blunted by AG1478. PD98059, a specific inhibitor of ERK kinase (MEK1), reduced H2O2-induced AR expression. EGF alone elicited activation of ERK and induction of AR expression. Increased level of AR transcript was demonstrated in cells treated with oxidized low-density lipoprotein, and this increase was also suppressed by AG1478. Inhibition of p38 MAP kinase by SB203580 also partially suppressed the H2O2-initiated AR induction. The presence of ponalrestat, an AR inhibitor, significantly accelerated H2O2-induced cell death. These results suggested that AR may act as a survival factor in these cells and that the EGF receptor-ERK pathway is the major signaling pathway involved in the upregulation of AR expression under oxidative stress.

Expression of aldose reductase and sorbitol dehydrogenase genes in Schwann cells isolated from rat: effects of high glucose and osmotic stress

To investigate the polyol pathway activity in Schwann cells, we determined the mRNA levels of aldose reductase (AR) and sorbitol dehydrogenase (SDH) in cultured cells under hyperglycemic or hyperosmotic conditions using competitive RT-PCR technique. The expressions of AR and SDH mRNAs in Schwann cells were unaltered by high (30 mM) glucose content in the medium. On the other hand, osmotic stress elicited significant increases in AR mRNA without any effect on SDH mRNA expression. The levels of AR mRNA determined by this RT-PCR system were significantly correlated with AR activity, as well as the levels of sorbitol accumulated in Schwann cells cultured under hyperosmotic conditions. These findings suggest that in contrast to the induction of AR expression by osmotic stress, high glucose per se does not up-regulate expression of the enzymes constituting the polyol pathway in Schwann cells. The RT-PCR system developed in this study may be a useful tool in ascertaining the relative contributions of AR and SDH to the metabolic derangements leading to diabetic complications.

Isolation of differentially expressed aldose reductase in ovaries after estrogen withdrawal from hypophysectomized diethylstilbestrol treated rats: increased expression during apoptosis

More than 99% of the follicles are eliminated by apoptosis before reaching ovulation. Several growth factors and hormones inhibit apoptosis in the ovary, including estrogen. Using differential display of mRNA, aldose reductase was shown to increase in the ovary of diethylstilbestrol treated hypophysectomized rats after estrogen withdrawal, inducing apoptosis. The aldose reductase mRNA expression was confirmed to be 2.2 +/- 0.2-fold higher after estrogen withdrawal using northern blot analysis. In addition, untreated immature rats showed a 1.7 +/- 0.3-fold higher expression of ovarian aldose reductase mRNA compared to ovaries 24 h after pregnant mare's serum gonadotropin treatment, decreasing apoptosis in the ovary. In the prostate, the level of aldose reductase was increased 3.1 +/- 1.1-fold 2 days after castration induced apoptosis. Although the physiological role of aldose reductase in the ovary is not known, these data suggest that aldose reductase may be part of a hormonally regulated apoptotic pathway in the ovary and prostate.

Characterization of genomic regions directing the cell-specific expression of the mouse aldose reductase gene

Aldose reductase (AR), an enzyme implicated in the pathogenesis of diabetic complications, is highly expressed in such target organs of complications as the lens and peripheral nerve of experimental animals. In mouse, however, a very low level of the transcript was expressed in these tissues. To explore the unique expression pattern of AR in mice, genomic structure and upstream regions regulating the basal expression of the enzyme were determined. In NIH3T3 cells, a -1.1-kb upstream portion demonstrated the highest promoter activity. The ability to drive the luciferase reporter gene was reduced by 56% when the -1.1/-0.86-kb region was deleted. In Chinese hamster ovary (CHO) cells, deletion up to -0.67 kb did not affect basal promoter activity. The activity in CHO cells was reduced by 73% when the -0. 67/-0.24-kb region was deleted. These findings indicate that a genomic region directing the cell-specific transcription of the mouse AR gene exists.

Identification of a novel cis-element required for the constitutive activity and osmotic response of the rat aldose reductase promoter

A new and essential cis-element AEE (aldose reductase enhancer element), necessary for the constitutive activity and the osmotic stress response of rat aldose reductase transcription in a rat liver cell line, has been identified. In transient transfection assays, an increase in promoter activity, up to 3.8-fold, was observed with osmotic stress (600 mosm/kg H2O) using a luciferase reporter gene construct containing aldose reductase promoter sequence from -1,094 base pair (bp) to +23 bp. A deletion between -1,071 and -895 bp reduced the constitutive activity and abolished the osmotic response of the promoter. Exonuclease III mediated in vivo DNA footprinting and dimethyl sulfate in vivo footprinting revealed DNA protection of a 32-bp region and two guanosines (G) within this region protected from methylation, respectively. Electrophoretic gel mobility shift assays using whole liver cell extracts showed protein binding, under both normal and stressed conditions. Deletion of the sequence between the two guanosines protected by in vivo dimethyl sulfate DNA footprinting (GAAGAGTG) in a luciferase construct (-1,094 bp to +23 bp) abolished the constitutive promoter activity. One copy of AEE fused to the thymidine kinase promoter gave a maximum constitutive activity of 7.7-fold and a maximum osmotic response activity of 6. 7-fold.

Further characterization of a rat hepatoma-derived aldose-reductase-like protein--organ distribution and modulation in vitro

A protein detected in N-methyl-N-nitrosourea-initiated rat hepatomas by two-dimensional electrophoresis at 35 kDa/pI 7.4 was identified in a previous study by internal amino acid micro sequencing as an aldose-reductase-like protein [Zeindl-Eberhart, E., Jungblut, P. R., Otto, A. & Rabes, H. M. (1994) Identification of tumor-associated protein variants during rat hepatocarcinogenesis, J. Biol. Chem. 269, 14589-14594]. Two-dimensional electrophoresis of rat lens proteins revealed a spot at 37 kDa/pI 6.8 that showed a high degree of identity (98.5%) with rat lens aldose reductase after amino acid sequencing and 80% sequence identity to the rat-hepatoma-derived aldose-reductase-like protein. This suggests that hepatoma-derived aldose-reductase-like protein and rat lens aldose reductase are related proteins encoded by different genes. A different expression profile of these proteins was found in various rat organs. Rat lens aldose reductase is present, in addition to in lens, in heart, brain, muscle, lung, duodenum, kidney, spleen and bone marrow, while the hepatoma-derived aldose-reductase-like protein is found preferentially in hepatomas and in embryonic liver. Though different in organ expression, an identical response was found for both proteins after stimulation with fibroblast growth factor-1 and after exposure to increased glucose concentrations. Since rat hepatoma-derived aldose-reductase-like protein is expressed in embryonic, but not in adult liver, it is assumed that it is expressed in hepatomas as a functionally active embryonal type of aldose reductase during hepatocarcinogenesis. Immunohistochemistry revealed that the hepatoma-derived aldose-reductase-like protein is expressed already in the preneoplastic stage of hepatocarcinogenesis and might potentially serve as a marker enzyme in early hepatic neoplasia.

Induction of aldose reductase gene expression in LEC rats during the development of the hereditary hepatitis and hepatoma

We examined age-related changes in the protein and the mRNA expression of aldose reductase in livers of Long-Evans with a cinnamon-like color (LEC) rats, which develop hereditary hepatitis and hepatoma with aging, using Long-Evans with an agouti color rats as controls. The levels of the protein and mRNA of aldose reductase increased after 20 weeks, at the stage of acute hepatitis, and were maintained at 60 weeks of age, while those of aldehyde reductase seemed to be constant at all ages. The expression of aldose reductase was marked in cancerous lesions in hepatoma-bearing LEC rat liver compared to uninvolved surrounding tissues. These results indicated that elevation of aldose reductase accompanied hepatocarcinogenesis and may be related to the acquisition of immortality of the cancer cells through detoxifying cytotoxic aldehyde compounds.

Hormonal regulation of aldose reductase in rat ovary during the estrous cycle

The physiological roles of aldose reductase [alditol:NAD(P)+1-oxidoreductase] have not been fully elucidated yet, although it has been implicated in the pathogenesis of diabetic complications. In the rat ovary we found remarkable changes in the enzyme level during the 4-day estrous cycle. After diestrus, the activity and protein content of aldose reductase increased to the maximum level on proestrous morning and rapidly fell off to the lowest level on the early morning of estrus. At this time its mRNA level in the ovary was significantly decreased compared with that on the morning of proestrus. Immunohistochemical staining of the diestrous ovary demonstrated localization of the enzyme protein in the granulosa cells and in the oocytes. At the end of proestrus when its level was low, immunoreactive aldose reductase in the granulosa cells was localized preferentially to the antrum side, with lesser staining in the cells lining the follicles. Administration of chlorpromazine to the rats on proestrus significantly restored the enzyme level on the following morning of the expected estrus. This effect of chlorpromazine was abolished when human chorionic gonadotropin was administered to the chlorpromazine-treated rats. When chlorpromazine was administered to the rats treated with bromocriptine, an inhibitor of pituitary prolactin secretion, aldose reductase activity in the ovary was significantly elevated compared with that in the rats treated with chlorpromazine alone. These findings suggest that in the rat ovary it is under hormonal regulation during the estrous cycle. The enzyme may possess a new functional role in the reproductive system of the female rat, which can be disordered under diabetic conditions.

Elevation of aldose reductase gene expression in rat primary hepatoma and hepatoma cell lines: implication in detoxification of cytotoxic aldehydes

Aldose reductase and aldehyde reductase are members of the aldo-keto reductase superfamily, and participate in the reduction of a wide range of carbonyl compounds. We have purified aldose reductase from rat lens and raised antiserum against it in rabbits. Immunoblot analyses using this antibody showed that a significant amount of aldose reductase was expressed in cell lines derived from hepatomas while it was negligible in normal hepatocytes. Elevated expression of aldose reductase was also observed in cancerous lesions of 3'-methyl-4-dimethyl-aminoazobenzene (3'-Me-DAB)-induced hepatocarcinomas. Expression of aldose reductase mRNA was confirmed in these cells by Northern-blot analysis, suggesting that the induction occurred at the stage of gene transcription. The level of aldehyde reductase, however, did not change in cancerous tissue or in the cell lines. The viability of hepatoma cells in the presence of 3-deoxyglucosone and glyceraldehyde was decreased by an aldose reductase inhibitor, ONO-2235 (5-[1Z,2E)-2-methyl-3-phenylpropenylidene]-4-oxo-2-thioxo -3- thiazolidineacetic acid). Taken together, induction of aldose reductase gene expression during hepatocarcinogenesis may render cancer cells resistant to various toxic carbonyl compounds produced during metabolism or administered as anti-cancer drugs.

Long-term induction of an aldose reductase protein by basic fibroblast growth factor in rat astrocytes in vitro

Basic fibroblast growth factor (bFGF) is known to elicit various developmental-like effects on astrocytes in vitro, but these effects were studied mainly over short-term periods. In this work we asked the question whether bFGF could induce long-term effects on rat astrocytes in culture. This factor was found to induce only a transient mitogenic effect lasting less than 48 h, even when the treatment was carried on for 4 days. By contrast, it induced long-term effects on the rate of synthesis of several proteins as seen by two-dimensional polyacrylamide gel electrophoresis after labeling the cells with [35S]methionine. The most upregulated protein was extracted from preparative gels of soluble extracts of cultured bFGF-treated astrocytes and of normal brain. It was characterized by internal amino acid microsequencing. Two tryptic digest peptides had N-terminal sequences similar to rat lens aldose reductase. This protein was also expressed in oligodendroglial and neuronal cells in culture, but it was not upregulated by bFGF. Aldose reductase is thought to be involved in a minor pathway of glucose metabolism and in diabetic complications. Its long-term regulation by bFGF will possibly help in the understanding of its actual physiological role.

Presence of a closely related subgroup in the aldo-ketoreductase family of the mouse

Aldose reductase (alditol:NAD(P)+ 1-oxidoreductase), an enzyme implicated in the pathogenesis of various diabetic complications, catalyzes the reduction of a variety of aldehydes. From a mouse kidney library, we isolated aldose reductase cDNA that encodes a 316-amino-acid protein with approximately 97% identity to rat lens aldose reductase, approximately 69% identity to the mouse vas deferens protein and also approximately 69% identity to mouse fibroblast growth-factor-1-regulated protein. RNA-blot analysis demonstrated abundant expression of the enzyme transcript in the testis, skeletal muscle and kidney. However, a very low level of the transcript was detected in the sciatic nerve and lens, where abundant expression and involvement of the enzyme in diabetic complications were documented in other animals species. The isolated cDNA was expressed in Escherichia coli and the recombinant protein was purified to homogeneity by affinity chromatography and chromatofocusing. The expressed enzyme demonstrated reductase activity for various aldo sugars but not for the steroids. The enzyme reaction with DL-glyceraldehyde was, however, competitively inhibited by progesterone or 17 alpha-hydroxyprogesterone. The results not only indicate a unique tissue distribution and enzyme attribute of mouse aldose reductase, but also the presence of a closely related subgroup within the aldo-oxidoreductase superfamily in mouse tissues.

Regulation of aldose reductase gene expression in renal cortex and medulla of rats

A role for aldose reductase-mediated production of polyol in the aetiology of diabetic nephropathy has been supported by both animal and clinical studies. In the renal medulla, the rate of polyol production is influenced in part by regulated changes in the level of aldose reductase gene expression. However, little is known about the expression of aldose reductase in the renal cortex. In this study, we evaluated the regulation of aldose reductase gene expression in the renal cortex and medulla in response to galactose feeding. Four groups of rats (n = 6) were treated for 9 weeks with control or galactose diet in the presence or absence of sorbinil, an aldose reductase inhibitor. In the renal medulla, galactose treatment produced a significant (p < 0.01) decrease in aldose reductase mRNA, to approximately 10% of control levels. Coadministration of sorbinil partially prevented the effect of galactose feeding on medullary aldose reductase mRNA (to 43% of control). Under basal conditions, the concentration of aldose reductase mRNA in the cortex was only 1% that of the renal medulla. Galactose feeding significantly reduced cortical aldose reductase mRNA by 29% relative to control (p < 0.01), and this was completely reversed by addition of sorbinil. Sorbinil administration to rats fed a control diet also decreased aldose reductase expression in the renal medulla and cortex. These results demonstrate that galactose feeding results in dynamic, polyol-dependent regulation of aldose reductase gene expression in the renal cortex as well as the medulla.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of tumor-associated protein variants in chemically induced rat hepatomas and transformed rat liver cell lines determined by two-dimensional electrophoresis

High resolution two-dimensional electrophoresis (2-DE), using the rat liver as a model, was applied to study hepatocarcinogenesis induced by different chemical carcinogens. Several tumor-associated protein variants were detected by 2-DE in chemically induced rat hepatomas and transformed rat liver cell lines compared to normal rat liver tissue. Proliferation-related protein changes and/or protein alterations due to culture conditions were corrected for by comparison with 2-DE patterns of isolated cells from regenerating liver and short-term cultivated liver cells. Some of the tumor-associated variants were further characterized: (i) By peptide mapping with limited proteolysis we detected clear relationships between several variants. (ii) By studying post-translational modifications phosphorylated and glycosylated variants could be determined. (iii) A tumor-associated protein variant was identified by amino acid analysis and amino acid sequencing.

Restriction fragment length polymorphisms of the human aldose reductase gene: a preliminary report

Abnormal metabolism through the polyol pathway during episodes of hyperglycaemia is implicated in the development of the chronic complications of diabetes. Since aldose reductase is the first and ratelimiting enzyme of the polyol pathway, it is predicted that restriction fragment length polymorphisms at the aldose reductase gene locus may influence catalytic activity and determine individual susceptibility to the diabetic complications. This paper reports the existence of EcoRI and TaqI restriction fragment length polymorphisms at the human aldose reductase locus.

Aldose reductase expression and prostaglandin E2 production are coordinately regulated in cultured rat mesangial cells

There is increasing evidence that a link between the polyol pathway and prostaglandins is important in the pathogenesis of diabetic nephropathy. The presence of the polyol pathway in the kidneys of normal animals, the galactose-fed rat, and animals with experimental diabetes has been established. While aldose reductase (AR) immunoreactive protein (AR-IRP) and AR mRNA are expressed at high levels in renal medulla, the sites of AR synthesis and regulation and metabolic consequences of AR activity in renal cortex are uncertain. The present study was conducted to test the hypothesis that AR expression and PGE2 production are coordinately regulated in glomerular mesangial cells. To test this hypothesis, we measured AR-IRP, AR mRNA, and PGE2 production in mesangial cells isolated from rats maintained on diets containing normal chow (MC-N), 50% galactose (MC-G), and 50% dextrin (MC-D). The rank order for each parameter studied (AR-IRP, AR mRNA, PGE2) was MC-N > MC-G > MC-D. Western blot analysis demonstrated that MC-N (optical density [OD] 1.0), MC-G (OD 0.59), and MC-D (OD 0.25) express AR-IRP. Slot-blot analyses demonstrated that levels of AR mRNA were greatest in MC-N (1.0), intermediate in MC-G (0.49), and lowest in MC-D (0.31). Ribonuclease (RNase) protection analyses demonstrated a similar pattern of AR mRNA expression, with MC-N at 1.0, MC-G at 0.60, and MC-D at 0.33. PGE2 production (pg/5 x 10(4) cells/30 min) was highest in MC-N (278 +/- 29), intermediate in MC-G (110 +/- 9), and lowest in MC-D (37 +/- 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Aldose reductase mRNA expression and its activity are induced by glucose in fetal rat aortic smooth muscle (A10) cells

The induction of aldose reductase (AR) mRNA expression and its activity by glucose were investigated in fetal rat aortic smooth muscle (A10) cells. The increase in the expression of AR mRNA was observed at 6 h, and reached a maximum (2.3 fold) at 12 h after exposure to 80 mM glucose. On the other hand, increase in AR activity was observed at 12 h and reached a maximum (2 fold) at 48 h after exposure to 80 mM glucose. AR mRNA levels as well as its activity increased almost linearly in a concentration dependent manner up to 80 mM. Although not significant, there was a consistent increase in AR mRNA level and its activity at 23.75 mM glucose. There was a good correlation between AR mRNA level and AR activity. In the presence of 1 microgram/ml actinomycin D, the increase in the expression of AR mRNA level by glucose was almost completely abolished, suggesting its transcriptional regulation by glucose. Other osmolytes were also effective in inducing AR mRNA expression as well as its activity at 80 mOsm/kg. Therefore, the increase in AR mRNA level and its activity by glucose in A10 cells may be a response to the increase in osmolarity.

Characterization of the aldose reductase-encoding gene family in rat

Although the enzyme aldose reductase (AR) is implicated in the development of tissue pathology in diabetes, the exact mechanism of this involvement remains unclear. To better understand the role that expression of the aldose reductase-encoding gene (ALR) may play in diabetic complications, we have begun to analyze the gene and its regulatory regions, and we present here the sequence of four ALR genes in the rat. The putative functional gene is 14.1 kb long, has ten exons which show perfect sequence identity to the rat lens AR RNA sequence, and nine introns with classical splice-site consensus sequences. Potential regulatory elements in the 5'-flanking region of this gene include a TATA box and two CCAAT boxes. Probing rat genomic Southern blots with a fragment from the first intron indicates that there is probably only one copy of this gene in the rat genome. The other three genes are processed pseudogenes which show approx. 90% identity to the rat lens AR RNA sequence, contain no introns, and have poly(A) regions at their 3' ends. Chromosomal localization studies show the presence of ALR genes on chromosomes 3, 4 and 6 in the rat with the putative functional gene mapped on chromosome 4.

Degenerated intramural pericytes ('ghost cells') in the retinal capillaries of diabetic rats

One of the earliest histopathological signs of diabetic retinopathy is a selective loss of intramural pericytes from retinal capillaries. In the present study, the retinal vessels of rats with streptozotocin-induced diabetes (STZ Wistar) and rats with genetically-induced insulin dependent diabetes mellitus (BB Wistar) and non-insulin dependent diabetes mellitus (SHR/N-corpulent) were examined after 6 to 8 months duration for diabetes-related retinal microangiopathies. The SHR/N-corpulent (cp) rats were fed a 54% sucrose diet, whereas the STZ Wistar and BB Wistar rats were fed laboratory chow for 32 to 36 weeks. In all the diabetic rats, the retinal capillaries in enzyme-digested flat mounts exhibited an increase in periodic-acid-Schiff (PAS) staining and loss of pericytes compared to their respective euglycemic controls. Pericyte "ghosts", like those defined in human diabetes as intramural pockets lacking normal cell contents, were documented by high resolution micrographs in all the diabetic rats. Endothelial cell proliferation, capillary dilation, and varicose loop formation were noted in some of the diabetic rats. Hence, similar capillary lesions were found in very different groups of diabetic rats. The findings suggest that a chronic high tissue concentration of glucose is the underlying factor which triggers pathogenesis in the pericyte. Hyperglycemia-induced activation of endogenous aldose reductase of the polyol pathway is probably the initial insult, but other factors such as advanced glycosylation products may affect the final outcome.

Resolving isoforms of aldose reductase by preparative isoelectric focusing in the Rotofor

We have resolved and characterized isoforms of aldose reductase from bovine and porcine lenses by preparative isoelectric focusing with narrow pH gradients using the Rotofor. Both bovine and porcine lens aldose reductases were resolved as two enzyme isoforms. The bovine isoforms were Mr40400 +/- 445 polypeptides of pI4.71 and 5.19. Porcine isoforms were Mr41500 +/- 450 polypeptides of pI 4.90 and 5.30. Staphylococcus aureus V-8 protease digestion patterns for each set of isoforms were essentially identical and all isoforms probably contain blocked amino terminal amino acids. Antiserum to bovine lens aldose reductase cross-reacted with porcine lens aldose reductase. Each isoform displayed substrate preferences characteristic of mammalian aldose reductases. With purification, both bovine and porcine lens aldose reductases became less sensitive to inhibition by 6-fluoro-spiro-(chroman-4.4'-imidazolidine)-2',5'-dione (sorbinil).

A thirty year journey in the polyol pathway

The development of the concept that aldose reductase (AR) is involved in diabetic complications is presented from its early beginning when Dr Van Heyningen first found polyols in sugar cataracts in 1959. The involvement of the polyol theory of sugar cataract is described. The prevention of sugar cataract formation by aldose reductase inhibitors dramatically demonstrates the role of this enzyme in sugar-induced cataracts. The possibility of AR involvement of other diabetic complications was an obvious extension of the polyol theory. The use of AR inhibitors in preventing diabetic changes in nerve and retina in animals strongly suggest that AR may play a role in the development of other diabetic complications.

Increase in aldose reductase mRNA in dog lens epithelial cells under hypertonic conditions

Aldose reductase (AR) mRNA levels increase when dog lens epithelial cells are exposed to hypertonic conditions. Hybridization of mRNA to an AR cDNA, using Northern and slot blots, showed that AR mRNA is elevated at least fourfold when primary dog lens epithelial cells are grown in media (300 mosmol kg-1) supplemented with 150 mM NaCl (600 mosmol kg-1 final). A time course showed an increase in AR mRNA of approximately twofold by 24 hr with a maximum increase of between four- and eightfold by 48 hr. AR mRNA remained elevated for the duration of the experiment, 8 days. The addition of Tolrestat, an inhibitor of aldose reductase, had no effect on the increased level of AR mRNA in these hypertonically stressed cells. Cells grown in media supplemented with 250 mM sorbitol also showed a substantial increase in AR mRNA. These data indicate, as in other cell types, the lens, a target tissue of diabetes, responds to hypersomotic stress with an induction of AR expression and suggests that AR may play a role in intracellular osmotic regulation.

Isolation and characterization of cDNA clones encoding aldose reductase

The action of aldose reductase has been implicated in the etiology of a variety of diabetic complications affecting the visual system. However, very little is known regarding the structure and functional organization of the genes encoding this key enzyme. In the present study, we have isolated and characterized complementary DNA clones encoding bovine lens aldose reductase. Nucleotide sequencing of four independently isolated clones was used to establish a 1154 nucleotide composite cDNA sequence. The cDNA sequence encodes 296 amino acids of the aldose reductase primary structure, and contains an additional 261 nucleotides of apparently untranslated sequence downstream from the coding region. No nucleotide sequence differences were found among the four independently isolated aldose reductase cDNA clones. The aldose reductase amino acid sequence deduced from the cDNA shows high homology to that reported for aldose reductase of the rat lens. Significant similarities are also evident between bovine lens aldose reductase and both human liver aldehyde reductase and frog lens rho-crystallin.

A superfamily of NADPH-dependent reductases in eukaryotes and prokaryotes

Aldose reductase (AR) is implicated in some of the disabling complications of diabetes, including neuropathy, retinopathy and cataracts. Our studies are aimed at further clarifying the role of AR in diabetes and facilitating the design of new classes of potent, specific AR inhibitors by gaining an understanding of the protein structure of AR. To this end, we have determined the complete protein sequence of rat lens AR using cDNA analysis and primer extension of mRNA. By comparing protein sequences, we have found that the structural relatedness (41% to 57%) among the vertebrate proteins, aldose reductase, aldehyde reductase, prostaglandin F synthase and the frog lens protein rho-crystallin can now be extended to prokaryotes by the inclusion of Corynebacterium 2,5-diketo-D-gluconate reductase. This more distantly related protein shares 30-40% identity with the vertebrate enzymes. Sequence alignments reveal that 18% of the amino acids are completely conserved in all members of the superfamily, many of them in clusters, suggesting that they mark important structural features such as the nucleotide binding site and substrate binding site. rho-Crystallin, which is structurally related to this superfamily of NADPH-dependent reductases, does not appear to reduce PGH2, PGD2, xylose or glyceraldehyde to any appreciable extent. It does, however, bind NADPH.