Flavia Pricci

Accelerated diabetic glomerulopathy in galectin-3/AGE receptor 3 knockout mice

Several molecules were shown to bind advanced glycation end products (AGEs) in vitro, but it is not known whether they all serve as AGE receptors and which functional role they play in vivo. We investigated the role of galectin‐3, a multifunctional lectin with (anti)adhesive and growth‐regulating properties, as an AGE receptor and its contribution to the development of diabetic glomerular disease, using a knockout mouse model. Galectin‐3 knockout mice obtained by gene ablation and the corresponding wild‐type mice were rendered diabetic with streptozotocin and killed 4 months later, together with age‐matched nondiabetic controls. Despite a comparable degree of metabolic derangement, galectin‐3‐deficient mice developed ac‐celerated glomerulopathy vs. the wild‐type animals, as evidenced by the more pronounced increase in protein‐uria, extracellular matrix gene expression, and mesan‐gial expansion. This was associated with a more marked renal/glomerular AGE accumulation, indicating it was attributable to the lack of galectin‐3 AGE receptor function. The galectin‐3‐deficient genotype was associated with reduced expression of receptors implicated in AGE removal (macrophage scavenger receptor A and AGE‐R1) and increased expression of those mediating cell activation (RAGE and AGE‐R2). These results show that the galectin‐3‐regulated AGE receptor pathway is operating in vivo and protects toward AGE‐induced tissue injury in contrast to that through RAGE.—Pugliese, G., Pricci, F., Iacobini, C., Leto, G., Amadio, L., Barsotti, P., Frigeri L., Hsu, D. K., Vlassara, H., Liu, F.‐T., Di Mario, U. Accelerated diabetic glomerulopathy in galectin‐3/AGE receptor 3 knockout mice. FASEB J. 15, 2471–2479 (2001)

Upregulation of Mesangial Growth Factor and Extracellular Matrix Synthesis by Advanced Glycation End Products Via a Receptor-Mediated Mechanism

Enhanced advanced glycosylation end product (AGE) formation has been shown to participate in the patho-genesis of diabetes-induced glomerular injury by mediating the increased extracellular matrix (ECM) deposition and altered cell growth and turnover leading to mesangial expansion. These effects could be exerted via an AGE-receptor-mediated upregulation of growth factors, such as the IGFs and transforming growth factor-β (TGF-β). We tested this hypothesis in human and rat mesangial cells grown on nonglycated or native bovine serum albumin (BSA), glycated BSA with AGE formation (BSA-AGE), or glycated BSA in which AGE formation was prevented by the use of aminoguanidine (BSA-AM), in the presence or absence of an antibody, α-p60, directed against the p60/OST protein named AGE-receptor 1 (AGE-R1), or normal control (pre-immune) serum. The mRNA and/or protein levels of IGF-I, IGF-II, IGF receptors, IGF binding proteins (IGFBPs), TGF-β1 and the ECM components fibronectin, laminin, and collagen IV were measured, together with cell proliferation. Both human and rat mesangial cells grown on BSA-AGE showed increased IGF-I and total and bioac-tive TGF-β medium levels and enhanced IGF-I, IGF-II, and TGF-β1 gene expression, compared with cells grown on BSA, whereas total IGFBP and IGFBP-3 medium content, IGF receptor density and affinity, and IGF-I receptor transcripts were unchanged. Moreover, cells grown on BSA-AGE showed increased ECM protein and mRNA levels versus cells cultured on BSA, whereas cell proliferation was unchanged in human mesangial cells and slightly reduced in rat mesangial cells. Growing cells on BSA-AM did not affect any of the measured parameters. Co-incubation of BSA-AGE with anti-AGE-R1, but not with pre-immune serum, prevented AGE-induced increases in IGF-I, TGF-β1, and ECM production or gene expression; anti-AGE-R1 also reduced growth factor and matrix synthesis in cells grown on BSA. These results demonstrate that mesangial IGF and TGF-β1 synthesis is upregulated by AGE-modified proteins through an AGE-receptor-mediated mechanism. The parallelism with increased ECM production raises the speculation that the enhanced synthesis of these growth factors resulting from advanced nonen-zymatic glycation participates in the pathogenesis of hyperglycemia-induced mesangial expansion.

Mechanisms of glucose-enhanced extracellular matrix accumulation in rat glomerular mesangial cells

In view of the importance of mesangial extracellular matrix (ECM) accumulation in the pathogenesis of diabetic glomerulosclerosis, we investigated 1) the effects of high glucose on ECM production by rat glomerular mesangial cells in culture (study A) and 2) the mechanisms underlying these effects, particularly the role of high sugar levels irrespective of intracellular metabolism (study B1) and of excess glucose disposal via the polyol pathway and associated biochemical alterations (study B2). Cells were cultured for 4 weeks, through six to eight passages, under the experimental conditions indicated below and, at each passage, the levels of fibronectin (FN), laminin (LAM), and collagen types I (C-I), III (C-III), IV (C-IV), and VI (C-VI) in media and cell extracts were quantified by an enzyme immunoassay. In study A, medium and cell content of matrix were assessed, together with [3H]leucine and [3H]thymidine incorporation into monolayers, polyol, fructose, and myo-inositol levels and the cytosolic redox state, in cells grown in high (30 mM) D-glucose or iso-osmolar mannitol versus cells cultured in normal (5.5 mM) D-glucose. FN, LAM, C-IV, and C-VI accumulation, but not C-I and C-III accumulation, was increased by 30 mM glucose, but not by iso-osmolar mannitol, when compared with 5.5 mM glucose, starting at week 2 and, except for C-VI, persisting throughout the remaining 2 weeks, whereas no change was observed in the measured indexes of total protein synthesis and DNA synthesis/cell proliferation. At any time point, polyol levels were increased, whereas myo-inositol was reduced by high glucose; in cells grown under elevated glucose concentrations, the lactate/pyruvate (L/P) ratio, an index of the cytosolic redox state, progressively increased. In study B1, the effects of high D-glucose were compared with those of iso-osmolar concentrations of sugars that are partly or not metabolized but are capable of inducing nonenzymatic glycosylation, such as D-galactose and L-glucose, and of mannitol, which does not enter the cell. Both D-galactose and L-glucose, but not mannitol, partly mimicked D-glucose-induced ECM overproduction. Although D-galactose is metabolized via the polyol pathway and alters the cytosolic redox state, ECM changes induced by high galactose were not prevented by the use of an aldose reductase inhibitor (ARI), Alcon 1576 (14 μM). In study B2, agents interfering with intracellular metabolism of excess glucose via the polyol pathway (14 μM Alcon 1576) and associated changes in myo-inositol metabolism (1 mM myo-inositol) and cytosolic redox state (1 mM sodium pyruvate, which corrects glucose-induced polyol pathway-dependent increased NADH/NAD+) were added to cells cultured in 30 and 5.5 mM D-glucose. Alcon 1576 inhibited polyol pathway activity with decreasing efficacy during the 4-week period, whereas myo-inositol and pyruvate produced complete and persistent prevention of reduced myo-inositol levels and increased L/P ratio, respectively. High glucose-induced ECM overproduction was transiently reduced by pyruvate and, to a lesser extent, by the ARI and myo-inositol. These results suggest that 1) high glucose selectively increases accumulation of basement membrane components and 2) multiple mechanisms seem to be operating in the pathogenesis of glucose-induced ECM overproduction, including elevated sugar levels per se, possibly via nonenzymatic glycosylation, and to a lesser extent, intracellular glucose metabolism via the polyol pathway and associated changes in myo-inositol metabolism and cytosolic redox state.

Galectin-3/AGE-receptor 3 knockout mice show accelerated AGE-induced glomerular injury: evidence for a protective role of galectin-3 as an AGE receptor

We previously showed that mice lacking galectin‐3/AGE‐receptor 3 develop accelerated diabetic glomerulopathy. To further investigate the role of galectin‐3/AGE‐receptor function in the pathogenesis of diabetic renal disease, galectin‐3 knockout (KO) and coeval wild‐type (WT) mice were injected for 3 months with 30 μg/day of Nε‐carboxymethyllysine (CML)‐modified or unmodified mouse serum albumin (MSA). Despite receiving equal doses of CML, KO had higher circulating and renal AGE levels and showed more marked renal functional and structural changes than WT mice, with significantly higher proteinuria, albuminuria, glomerular, and mesangial area and glomerular sclerosis index. Renal 4‐hydroxy‐2‐nonenal content and NFκB activation were also more pronounced in KO‐CML vs. WT‐CML. Kidney mRNA levels of fibronectin, laminin, collagen IV, and TGF‐β were up‐regulated, whereas those of matrix metalloproteinase‐2 and ‐14 were down‐regulated, again more markedly in KO‐CML than WT‐CML mice. Basal and CML‐induced RAGE and 80K‐H mRNA levels were higher in KO vs. WT mice. MSA injection did not produce any significant effect in both genotypes. The association of galectin‐3 ablation with enhanced susceptibility to AGE‐induced renal disease, increased AGE levels and signaling, and altered AGE‐receptor pattern indicates that galectin‐3 is operating in vivo as an AGE receptor to afford protection toward AGE‐dependent tissue injury.

Role of Galectin-3 in Diabetic Nephropathy

The advanced glycosylation end products (AGE) participate in the pathogenesis of nephropathy and other diabetic complications through several mechanisms, including their binding to cell surface receptors. The AGE receptors include RAGE, the macrophage scavenger receptors, OST-48 (AGE-R1), 80K-H (AGE-R2), and galectin-3 (AGE-R3). Galectin-3 interacts with the beta-galactoside residues of cell surface and matrix glycoproteins via the carbohydrate recognition domain and with intracellular proteins via peptide-peptide associations mediated by its N-terminus domain. These structural properties enable galectin-3 to exert multiple functions, including the mRNA splicing activity, the control of cell cycle, the regulation of cell adhesion, the modulation of allergic reactions, and the binding of AGE. The lack of transmembrane anchor sequence or signal peptide suggests that it is associated with other AGE receptors, possibly AGE-R1 and AGE-R2, to form an AGE-receptor complex, rather than playing an independent role. In target tissues of diabetic vascular complications, such as the endothelium and mesangium, galectin-3 is weakly expressed under basal conditions and is markedly upregulated by the diabetic milieu (and to a lesser extent by aging). Galectin-3-deficient mice were found to develop accelerated diabetic glomerulopathy versus the wild-type animals, as evidenced by the more pronounced increase in proteinuria, mesangial expansion, and matrix gene expression. This was associated with a more marked renal/glomerular AGE accumulation, suggesting that it was attributable to the lack of galectin-3 AGE-receptor function. These data indicate that galectin-3 is upregulated under diabetic conditions and is operating in vivo to provide protection toward AGE-induced tissue injury, as opposed to RAGE.

Oxidative stress in diabetes-induced endothelial dysfunction involvement of nitric oxide and protein kinase C.

Reactive oxygen species (ROS) formation plays a major role in diabetes-induced endothelial dysfunction, though the molecular mechanism(s) involved and the contribution of nitric oxide (NO) are still unclear. This study using bovine retinal endothelial cells was aimed at assessing (i) the role of oxygen-dependent vs. NO-dependent oxidative stress in the endothelial cell permeability alterations induced by the diabetic milieu and (ii) whether protein kinase C (PKC) activation ultimately mediates these changes. Superoxide, lipid peroxide, and PKC activity were higher under high glucose (HG) vs. normal glucose throughout the 30 d period. Nitrite/nitrate and endothelial NO synthase levels increased at 1 d and decreased thereafter. Changes in monolayer permeability to 125I-BSA induced by 1 or 30 d incubation in HG or exposure to advanced glycosylation endproduct were reduced by treatment with antioxidants or PKC inhibitors, whereas NO blockade prevented only the effect of 1 d HG. HG-induced changes were mimicked by a PKC activator, a superoxide generating system, an NO and superoxide donor, or peroxynitrite (attenuated by PKC inhibition), but not a NO donor. The short-term effect of HG depends on a combined oxidative and nitrosative stress with peroxynitrite formation, whereas the long-term effect is related to ROS generation; in both cases, PKC ultimately mediates permeability changes.

Accelerated Lipid-Induced Atherogenesis in Galectin-3-Deficient Mice Role of Lipoxidation via Receptor-Mediated Mechanisms

Objective—Modified lipoproteins, particularly oxidized LDLs, are believed to evoke an inflammatory response which participates in all stages of atherosclerosis. Disposal of these particles is mediated through receptors which may trigger proinflammatory signaling pathways leading to vascular injury. This study was aimed at assessing the role in atherogenesis of one of these receptors, galectin-3. Methods and Results—Galectin-3–deficient and wild-type mice were fed an atherogenic diet or standard chow for 8 months. Lesion area and length were higher in galectin-3–deficient versus wild-type mice. At the level of the aortic sinus, wild-type animals showed only fatty streaks, whereas galectin-3–deficient mice developed complex lesions, associated with extensive inflammatory changes. This was indicated by the presence of T lymphocytes with activated Th1-phenotype and by more marked monocyte-macrophage infiltration, inflammatory mediator expression, vascular cell apoptosis, and proinflammatory transcription factor activation. Increased accumulation of oxidixed LDLs and lipoxidation products and upregulation of other receptors for these compounds, including the proinflammatory RAGE, were detected in galectin-3–deficient versus wild-type mice. Conclusions—These data suggest a unique protective role for galectin-3 in the uptake and effective removal of modified lipoproteins, with concurrent downregulation of proinflammatory pathways responsible for atherosclerosis initiation and progression.

Advanced lipoxidation end-products mediate lipid-induced glomerular injury: role of receptor-mediated mechanisms

Atherosclerosis and renal disease are related conditions, sharing several risk factors. This includes hyperlipidaemia, which may result in enhanced lipoprotein accumulation and chemical modification, particularly oxidation, with formation of advanced lipoxidation endproducts (ALEs). We investigated whether increased lipid peroxidation plays a major role in the pathogenesis of lipid‐induced renal disease, via receptor‐mediated mechanisms involving the scavenger and advanced glycation endproduct (AGE) receptors. Mice knocked out for galectin‐3 (Gal3−/−), an AGE receptor previously shown to protect from AGE‐induced renal injury, and the corresponding wild‐type (Gal3+/+) animals, were fed an atherogenic high‐fat diet (HFD; 15% fat, 1.25% cholesterol and 0.5% sodium cholate); mice fed a normal‐fat diet (NFD; 4% fat) served as controls. Gal3+/+ mice fed a HFD developed glomerular disease, as indicated by proteinuria, mesangial expansion and glomerular hypertrophy and sclerosis. Glomerular injury was associated with increased glomerular matrix protein expression, ALE and oxidized LDL content, oxidative stress, AGE and scavenger receptor expression and macrophage infiltration, with only modest renal/glomerular fat accumulation and changes in lipid metabolism. Fibrotic and inflammatory changes, together with accumulation of ALEs, such as 4‐hydroxy‐2‐nonenal adducts and Nε‐carboxymethyllysine, oxidative stress and expression of the receptor of AGEs (RAGE), were significantly more marked in Gal3−/− animals, whereas fat deposition and abnormalities in lipid metabolism remained modest. Thus, lipid‐induced renal damage is mainly dependent on lipid peroxidation with formation of carbonyl reactive species and ALEs, which accumulate within the kidney tissue, thus triggering receptor‐mediated pro‐inflammatory signalling pathways, as in atherogenesis. Moreover, galectin‐3 exerts a significant role in the uptake and effective removal of modified lipoproteins, with diversion of these products from RAGE‐dependent pro‐inflammatory pathways associated with downregulation of RAGE expression. Copyright

Galectin-3 ablation protects mice from diet-induced NASH: a major scavenging role for galectin-3 in liver.

BACKGROUND & AIMS Excess fatty acid oxidation and generation of reactive carbonyls with formation of advanced lipoxidation endproducts (ALEs) is involved in nonalcoholic steatohepatitis (NASH) by triggering inflammation, hepatocyte injury, and fibrosis. This study aimed at verifying the hypothesis that ablation of the ALE-receptor galectin-3 prevents experimental NASH by reducing receptor-mediated ALE clearance and downstream events. METHODS Galectin-3-deficient (Lgals3(-/-)) and wild type (Lgals3(+/+)) mice received an atherogenic diet or standard chow for 8 months. Liver tissue was analyzed for morphology, inflammation, cell and matrix turnover, lipid metabolism, ALEs, and ALE-receptors. RESULTS Steatosis was significantly less pronounced in Lgals3(-/-) than Lgals3(+/+) animals on atherogenic diet. NASH, invariably detected in Lgals3(+/+) mice, was observed, to a lower extent, only in 3/8 Lgals3(-/-) mice, showing less inflammatory, degenerative, and fibrotic phenomena than Lgals3(+/+) mice. This was associated with higher circulating ALE levels and lower tissue ALE accumulation and expression of other ALE-receptors. Up-regulation of hepatic fatty acid synthesis and oxidation, inflammatory cell infiltration, pro-inflammatory cytokines, endoplasmic reticulum stress, hepatocyte apoptosis, myofibroblast transdifferentiation, and impaired Akt phosphorylation were also significantly attenuated in Lgals3(-/-) animals. Galectin-3 silencing in liver endothelial cells resulted in reduced N(ε)-carboxymethyllysine-modified albumin uptake and ALE-receptor expression. CONCLUSIONS Galectin-3 ablation protects from diet-induced NASH by decreasing hepatic ALE accumulation, with attenuation of inflammation, hepatocyte injury, and fibrosis. It also reduced up-regulation of lipid synthesis and oxidation causing less fat deposition, oxidative stress, and possibly insulin resistance. These data suggest that galectin-3 is a major receptor involved in ALE uptake by the liver.

Increased activity of the insulin-like growth factor system in mesangial cells cultured in high glucose conditions. Relation to glucose-enhanced extracellular matrix production.

SummaryRecent evidence suggests that several growth factors participate in diabetic glomerular disease by mediating increased extracellular matrix accumulation and altered cell growth and turnover leading to mesangial expansion. Transforming growth factor (TGF)-β has been demonstrated to be upregulated both in vivo and in vitro, whereas studies on the activity of the renal insulin-like growth factor (IGF) system in experimental diabetes have provided conflicting results. We investigated the effects of prolonged exposure (4 weeks) of cultured human and rat mesangial cells to high (30 mmol/1) glucose vs iso-osmolar mannitol or normal (5.5 mmol/1) glucose levels on: 1) the autocrine/paracrine activity of the IGF system (as assessed by measuring IGF-I and II, IGF-I and II receptors, and IGF binding proteins); and, in parallel, on 2) TGF-βl gene expression; 3) matrix production; and 4) cell proliferation. High glucose levels progressively increased the medium content of IGF-I and the mRNA levels for IGF-I and IGF-II, increased IGF-I and IGF-II binding and IGF-I receptor gene expression, and reduced IGF binding protein production. TGF-βl transcripts and matrix accumulation and gene expression were increased in parallel, whereas cell proliferation was reduced. Iso-osmolar mannitol did not affect any of the above parameters. These experiments demonstrated that high glucose levels induce enhanced mesangial IGF activity, together with enhanced TGF-βl gene expression, increased matrix production, and reduced cell proliferation. It is possible that IGFs participate in mediating diabetes-induced changes in matrix turnover leading to mesangial expansion, by acting in a paracrine/autocrine fashion within the glomerulus. [Diabetologia (1996) 39: 775-784]