The effect of glucose on proteoglycans produced by cultured mesangial cells

Renal accumulation of biglycan and lipid retention accelerates diabetic nephropathy

Hyperlipidemia worsens diabetic nephropathy, although the mechanism by which renal lipids accumulate is unknown. We previously demonstrated that renal proteoglycans have high low-density lipoprotein (LDL) binding affinity, suggesting that proteoglycan-mediated LDL retention may contribute to renal lipid accumulation. The aim of this study was to determine the relative effect of diabetes and hyperlipidemia on renal proteoglycan content. Diabetic and non-diabetic LDL receptor-deficient mice were fed diets containing 0% or 0.12% cholesterol for 26 weeks, and then kidneys were analyzed for renal lipid and proteoglycan content. Diabetic mice on the high-cholesterol diet had accelerated development of diabetic nephropathy with elevations in urine albumin excretion, glomerular and renal hypertrophy, and mesangial matrix expansion. Renal lipid accumulation was significantly increased by consumption of the 0.12% cholesterol diet, diabetes, and especially by both. The renal proteoglycans biglycan and decorin were detectable in glomeruli, with a significant increase in renal biglycan content in diabetic mice on the high-cholesterol diet. Renal biglycan and renal apolipoprotein B were colocalized, and regression analyses showed a significant relation between renal biglycan and renal apolipoprotein B content. The increased renal biglycan content in diabetic nephropathy probably contributes to renal lipid accumulation and the development of diabetic nephropathy.

High glucose-induced membrane translocation of PKC betaI is associated with Arf6 in glomerular mesangial cells

Protein kinase C (PKC)-induced changes in glomerular mesangial cell (MC) phenotypic behavior has been implicated in diabetes. The activity of diacylglycerol-sensitive PKC isoforms in MCs is altered by ambient changes in glucose, but the regulation of PKC activity and subsequent intracellular signaling events are not yet clearly defined. Small GTP-binding proteins of the ADP-ribosylation factor (Arfs) family, may regulate protein kinase membrane recruitment and hence its activity in signaling events of non-polarized cells. Members of the ARF family may coordinate membrane dynamics and other cellular functions through their interaction with PKC. We studied the activation of Arf, PKC betaI and phospholipase D (PLD) in MCs cultured under normal or high glucose conditions. MCs cultured in high glucose medium exhibited predominantly cytosolic localization of PKC betaI, Arf3 and Arf6. However, phorbol ester (PMA) stimulation of cells cultured in high glucose significantly enhanced membrane association of PKC betaI and Arf6, but not Arf3. Using [3H]choline chloride to prelabel MCs and measuring [3H]choline-containing metabolite release as PLD activity, PMA stimulated a significant increase of PLD activity under high glucose condition. Our data suggest that Arf6 plays a specific role in activation of PKC betaI and PLD under high glucose condition, and may be a significant intracellular event in the change of the mesangial cell phenotype associated with diabetic nephropathy.

Activation of PKC-beta(I) in glomerular mesangial cells is associated with specific NF-kappaB subunit translocation

Changes in expression and activity of protein kinase C (PKC) isoforms and early transcription factors may account for alterations in cell behavior seen in diabetes. We studied the expression of PKC-beta(I) in rat glomerular mesangial cells (MCs) cultured in normal or high glucose and compared it with the temporal and spatial expression of dimeric transcription factor (NF-kappaB) p50 and p65. The results show that in unstimulated cells PKC-beta(I) and NF-kappaB p50 are distributed in the cytosol and, on stimulation, their distribution is perinuclear and they are localized to the membrane. Serum-starved MCs cultured in high-glucose medium exhibit a predominantly cytosolic localization of PKC-beta(I) and both p50 and p65 NF-kappaB. However, phorbol 12-myristate 13-acetate (PMA) stimulation of cells grown in the presence of high glucose resulted in membrane translocation of PKC-beta(I) that was associated with nuclear translocation of NF-kappaB p65, but not NF-kappaB p50. Moreover, the translocation to the nucleus for NF-kappaB p65 was significantly higher in MCs exposed to high glucose compared with those exposed to normal glucose. These observations indicate that the NF-kappaB p65, but not NF-kappaB p50, expression and translocation pattern mirrors that of PKC-beta(I), which may be one important pathway by which signaling is enhanced in the high-glucose state.

Influence of glucose on production and N-sulfation of heparan sulfate in cultured adipocyte cells

Altered lipoprotein lipase regulation associated with diabetes leading to the development of hypertriglyceridemia might be attributed to possible changes in content and the fine structure of heparan sulfate and its associated lipoprotein lipase. Adipocyte cell surface is the primary site of synthesis of lipoprotein lipase and the enzyme is bound to cell surface heparan sulfate proteoglycans via heparan sulfate side chains. In this study, the effect of diabetes on the production of adipocyte heparan sulfate and its sulfation (especially N-sulfation) were examined. Mouse 3T3-L1 adipocytes were exposed to high glucose (25 mM) and low glucose (5.55 mM) in the medium and cell-associated heparan sulfate was isolated and characterized. A significant decrease in total content of heparan sulfate was observed in adipocytes cultured under high glucose as compared to low glucose conditions. The degree of N-sulfation was-assessed through oligosaccharide mapping of heparan sulfate after chemical cleavages involving low pH (1.5) nitrous acid and hydrazinolysis/high pH (4.0) nitrous acid treatments; N-sulfation was found to be comparable between the adipocyte heparan sulfates produced under these glucose conditions. The activity and message levels for N-deacetylase/N-sulfotransferase, the enzyme responsible for N-sulfation in the biosynthesis of heparan sulfate, did not vary in adipocytes whether they were exposed to low or high glucose. While most cells or tissues in diabetic situations produce heparan sulfate with low-charge density concomitant with a decrease in N-sulfation, adipocyte cell system is an exception in this regard. Heparan sulfate from adipocytes cultured in low glucose conditions binds to lipoprotein lipase by the same order of magnitude as that derived from high glucose conditions. It is apparent that adipocytes cultured under high glucose conditions produce diminished levels of heparan sulfate (without significant changes in N-sulfation). In conclusion, it is possible that the reduction in heparan sulfate in diabetes could contribute to the decreased levels of heparan sulfate associated lipoprotein lipase, leading to diabetic hypertriglyceridemia.

Glomerular heparan sulfate alterations: mechanisms and relevance for proteinuria

Heparan sulfate (HS) is the anionic polysaccharide side chain of HS proteoglycans (HSPGs) present in basement membranes, in extracellular matrix, and on cell surfaces. Recently, agrin was identified as a major HSPG present in the glomerular basement membrane (GBM). An increased permeability of the GBM for proteins after digestion of HS by heparitinase or after antibody binding to HS demonstrated the importance of HS for the permselective properties of the GBM. With recently developed antibodies directed against the GBM HSPG (agrin) core protein and the HS side chain, we demonstrated a decrease in HS staining in the GBM in different human proteinuric glomerulopathies, such as systemic lupus erythematosus (SLE), minimal change disease, membranous glomerulonephritis, and diabetic nephropathy, whereas the staining of the agrin core protein remained unaltered. This suggested changes in the HS side chains of HSPG in proteinuric glomerular diseases. To gain more insight into the mechanisms responsible for this observation, we studied GBM HS(PG) expression in experimental models of proteinuria. Similar HS changes were found in murine lupus nephritis, adriamycin nephropathy, and active Heymann nephritis. In these models, an inverse correlation was found between HS staining in the GBM and proteinuria. From these investigations, four new and different mechanisms have emerged. First, in lupus nephritis, HS was found to be masked by nucleosomes complexed to antinuclear autoantibodies. This masking was due to the binding of cationic moieties on the N-terminal parts of the core histones to anionic determinants in HS. Second, in adriamycin nephropathy, glomerular HS was depolymerized by reactive oxygen species (ROS), mainly hydroxyl radicals, which could be prevented by scavengers both in vitro (exposure of HS to ROS) and in vivo. Third, in vivo renal perfusion of purified elastase led to a decrease of HS in the GBM caused by proteolytic cleavage of the agrin core protein near the attachment sites of HS by the HS-bound enzyme. Fourth, in streptozotocin-induced diabetic nephropathy and during culture of glomerular cells under high glucose conditions, evidence was obtained that hyperglycemia led to a down-regulation of HS synthesis, accompanied by a reduction in the degree of HS sulfation.

High glucose induces the activity and expression of Na(+)/H(+) exchange in glomerular mesangial cells

Changes in activity or expression of transporters may account for alterations in cell behavior in diabetes. We sought to ascertain if mesangial cells (MC) grown in different glucose concentrations exhibit changes in activity and expression of acid-extruding transporters, the Na(+)/H(+) and Na(+)-dependent Cl(-)/HCO(-)(3) exchanger. pH(i) was determined by the use of the fluorescent pH-sensitive dye BCECF. In MCs grown in 5 mM glucose (control), the Na(+)/H(+) exchanger was responsible for 31.8 +/- 5.1% of steady-state pH(i), whereas Na(+)-dependent Cl(-)/HCO(-)(3) contributed 62.9 +/- 4.0% (n = 11). In MCs grown in high glucose for 2 wk, Na(+)/H(+) exchange contribution to acid-extrusion increased as follows: 42.3 +/- 4.6% [n = 8, 10 mM, not significant (NS)], 51.1 +/- 5.1% (n = 8, 20 mM, P < 0.01), and 64.8 +/- 5.5% (n = 7, 30 mM, P < 0.001). The Na(+)-dependent Cl(-)/HCO(-)(3) exchanger contributed less [47.0 +/- 4.6, 38.6 +/- 5.8, and 21.1 +/- 3.8%, for 10, 20, and 30 mM glucose, respectively (n > 7)]. We sought to ascertain if the magnitude of the acute stimulated response to ANG II by the Na(+)/H(+) and Na(+)-dependent Cl(-)/HCO(-)(3) exchanger is changed. Na(+)/H(+) exchanger (1.89-fold increase in 30 vs. 5 mM, P < 0.002), but not Na(+)-dependent Cl(-)/HCO(-)(3) exchange (0. 17-fold, NS), exhibited an enhanced response to ANG II (1 microM). Na(+)/H(+) exchange (NHE1) expression was significantly different (1. 72-fold) after prolonged exposure to high glucose. These results suggest that the Na(+)/H(+) exchanger, but not Na(+)-dependent Cl(-)/HCO(-)(3) exchanger, may play an early role in the response to hyperglycemia in the diabetic state.

High glucose-induced transforming growth factor beta1 production is mediated by the hexosamine pathway in porcine glomerular mesangial cells

Previous studies revealed that exposure of mesangial cells to high glucose concentration induces the production of matrix proteins mediated by TGF-beta1. We tested if structural analogues of D-glucose may mimic the high glucose effect and found that D-glucosamine was strikingly more potent than D-glucose itself in enhancing the production of TGF-beta protein and subsequent production of the matrix components heparan sulfate proteoglycan and fibronectin in a time- and dose-dependent manner. D-Glucosamine also promoted conversion of latent TGF-beta to the active form. Therefore, we suggested that the hexosamine biosynthetic pathway (the key enzyme of which is glutamine:fructose-6-phosphate amidotransferase [GFAT]) contributes to the high glucose-induced TGF-beta1 production. Inhibition of GFAT by the substrate analogue azaserine or by inhibition of GFAT protein synthesis with antisense oligonucleotide prevented the high glucose-induced increase in cellular glucosamine metabolites and TGF-beta1 expression and bioactivity and subsequent effects on mesangial cell proliferation and matrix production. Overall, our study indicates that the flux of glucose metabolism through the GFAT catalyzed hexosamine biosynthetic pathway is involved in the glucose-induced mesangial production of TGF-beta leading to increased matrix production.

High concentration of glucose increases mitogenic responsiveness to heparin-binding epidermal growth factor-like growth factor in rat vascular smooth muscle cells

The effect of a high extracellular glucose concentration on the mitogenic response of rat vascular smooth muscle cells (SMCs) to heparin-binding epidermal growth factor-like growth factor (HB-EGF) was investigated. The mitogenic effect of HB-EGF was significantly greater in SMCs cultured in high glucose (25 mmol/L) than in cells cultured in low glucose (5.5 mmol/L) or at high osmolarity (5.5 mmol/L glucose plus 19.5 mmol/L mannitol). The mitogenic effect of epidermal growth factor (EGF), which shares the EGF receptor with HB-EGF, was not affected by glucose concentration. The mitogenic effect of HB-EGF was greater when incubated with heparan sulfate (HS) isolated from SMCs cultured in high glucose than with HS from cells cultured in low glucose. HS synthesized by cells in high glucose was of smaller molecular size and less sulfated than HS synthesized by cells in low glucose. The abundance of mRNA encoding HS-N-deacetylase/N-sulfotransferase (HS-NdAc/NST), a regulatory enzyme in the biosynthesis of HS, was decreased by high glucose in a protein kinase C-independent manner. These observations suggest that the enhanced mitogenic response to HB-EGF in SMCs cultured in high glucose may be attributable to changes in cell-associated HS. Downregulation of HS-NdAc/NST gene expression by high glucose may be related to the altered HS biosynthesis.

Expression of extracellular matrix molecules in human mesangial cells in response to prolonged hyperglycaemia

Post-mitotic cultures of human mesangial cells were maintained in media containing 4-30 mM D-glucose for up to 28 days. Changes in mRNA and protein levels for specific macromolecules occurred between 7 and 14 days after initiating hyperglycaemic conditions. Slot blot analysis showed 2-3-fold increases in mRNAs for collagen type I, fibronectin, versican and perlecan, whereas mRNA for decorin was increased by up to 20-fold. Levels of mRNAs for biglycan and syndecan were unaffected by hyperglycaemic culture. Reverse transcriptase PCR (RT-PCR) confirmed that decorin mRNA levels are greatly elevated and also showed increased transcription of the TGF-beta 1 gene in hyperglycaemic cultures. Western analysis and ELISA indicated accumulations of collagen types I and III, laminin and fibronectin in the cell layers and media of hyperglycaemic cultures with increasing time. Type IV collagen did not accumulate in either compartment of hyperglycaemic mesangial cell cultures. Collagen types I, III, and fibronectin did not accumulate in the cell layers of hyperglycaemic human dermal fibroblasts, indicating a cell-specific response in mesangial cultures. Decorin and versican, but not biglycan, were increased in the hyperglycaemic mesangial cell culture media. There were no apparent changes in core proteins for decorin and biglycan in fibroblast media. Transforming growth factor beta 1 (TGF-beta 1) in hyperglycaemic mesangial cell cultures increased 5-fold after 7 days, but decreased thereafter to only approx. 2-fold after 28 days. The changes in TGF-beta 1 mRNA, as detected by RT-PCR, and protein followed one another closely.

Effects of high glucose on the production of heparan sulfate proteoglycan by mesangial and epithelial cells

Changes in heparan sulfate metabolism may be important in the pathogenesis of diabetic nephropathy. Recent studies performed on renal biopsies from patients with diabetic nephropathy revealed a decrease in heparan sulfate glycosaminoglycan staining in the glomerular basement membrane without changes in staining for heparan sulfate proteoglycan-core protein. To understand this phenomenon at the cellular level, we investigated the effect of high glucose conditions on the synthesis of heparan sulfate proteoglycan by glomerular cells in vitro. Human adult mesangial and glomerular visceral epithelial cells were cultured under normal (5 mM) and high glucose (25 mM) conditions. Immunofluorescence performed on cells cultured in 25 mM glucose confirmed and extended the in vivo histological observations. Using metabolic labeling we observed an altered proteoglycan production under high glucose conditions, with predominantly a decrease in heparan sulfate compared to dermatan sulfate or chondroitin sulfate proteoglycan. N-sulfation analysis of heparan sulfate proteoglycan produced under high glucose conditions revealed less di- and tetrasaccharides compared to larger oligosaccharides, indicating an altered sulfation pattern. Furthermore, with quantification of glomerular basement membrane heparan sulfate by ELISA, a significant decrease was observed when mesangial and visceral epithelial cells were cultured in high glucose conditions. We conclude that high glucose concentration induces a significant alteration of heparan sulfate production by mesangial cells and visceral epithelial cells. Changes in sulfation and changes in absolute quantities are both observed and may explain the earlier in vivo observations. These changes may be of importance for the altered integrity of the glomerular charge-dependent filtration barrier and growth-factor matrix interactions in diabetic nephropathy.

Proteoglycan synthesis by bovine myocardial endothelial cells is increased by long-term exposure to high concentrations of glucose

The role of the metabolic milieu in control of proteoglycan synthesis was investigated using bovine myocardial endothelial cells (BMEC) grown for six to eight passages in media containing either 5.6 or 25 mM glucose. Macromolecular Na[35S]sulfate incorporation into proteoglycans was increased by exposure to 25 mM when compared with 5.6 mM glucose (7.05 +/- 0.40 [SD] vs. 3.5 +/- 0.50 x 10(-4) dpm/microgram DNA). In contrast, [3H]leucine incorporation was unaffected by glucose (11.27 +/- 0.85 vs. 9.88 +/- 1.23 x 10(-5) dpm/microgram DNA). The distribution of isotopes between media and cell layer fractions was not different in the two conditions. Addition of 19.4 mM mannitol to 5.6 mM glucose containing media had no effect on isotope incorporation. The HPLC-DEAE and Sepharose CL-6B elution profiles of media 35S-proteoglycans synthesized under each condition were similar. A Sepharose CL-4B Kav 0.08 heparan sulfate proteoglycan accounted for 20% of the total 35S-incorporation. Perlecan domain III mRNA was identified by Northern analysis and domain 1 by the polymerase chain reaction (PCR) in total BMEC RNA. A mixture of chondroitin/dermatan sulfate proteoglycans accounted for 67% of 35S-incorporation. They eluted from Sepharose CL-6B at Kav 0 and 0.22. Two [3H]leucine labeled core proteins of 135 and 50 kD were identified in each of these 35S-proteoglycan peaks. Biglycan but not decorin mRNAs were detected by Northern analysis and by PCR. These data demonstrate that prolonged exposure to high glucose concentrations in vitro stimulate the accumulation of [35S]sulfate into microvascular endothelial cell proteoglycans without significant alterations in their overall hydrodynamic or charge related properties. Modulation of proteoglycan synthesis by glucose may participate in the pathogenesis of the small vessel complications of diabetes.

Reduction of heparan sulphate-associated anionic sites in the glomerular basement membrane of rats with streptozotocin-induced diabetic nephropathy

Heparan sulphate-associated anionic sites in the glomerular basement membrane were studied in rats 8 months after induction of diabetes by streptozotocin and in age- adn sex-matched control rats, employing the cationic dye cuprolinic blue. Morphometric analysis at the ultrastructural level was performed using a computerized image processor. The heparan sulphate specificity of the cuprolinic blue staining was demonstrated by glycosaminoglycan-degrading enzymes, showing that pretreatment of the sections with heparitinase abolished all staining, whereas chondroitinase ABC had no effect. The majority of anionic sites (74% in diabetic and 81% in control rats) were found within the lamina rara externa of the glomerular basement membrane. A minority of anionic sites were scattered throughout the lamina densa and lamina rara interna, and were significantly smaller than those in the lamina rara externa of the glomerular basement membrane (p<0.001 and p<0.01 for diabetic and control rats, respectively). Diabetic rats progressively developed albuminuria reaching 40.3 (32.2-62.0) mg/24 h after 8 months in contrast to the control animals (0.8 (0.2-0.9) mg/24 h, p<0.002). At the same time, the number of heparan sulphate anionic sites and the total anionic site surface (number of anionic sites x mean anionic site surface) in the lamina rara externa of the glomerular basement membrane was reduced by 19% (p<0.021) and by 26% (p<0.02), respectively. Number and total anionic site surface in the remaining part of the glomerular basement membrane (lamina densa and lamina rara interna) were not significantly changed. We conclude that in streptozotocin-diabetic rats with an increased urinary albumin excretion, a reduced heparan sulphate charge barrier/density is found at the lamina rara externa of the glomerular basement membrane.

Increased hyaluronan production in the glomeruli from diabetic rats: a link between glucose-induced prostaglandin production and reduced sulphated proteoglycan

Exposure in vivo or in vitro to elevated glucose increases production of vasoactive prostaglandins by glomeruli and mesangial cells. This study aimed to determine whether this increased prostaglandin production could provide a link with later structural changes in diabetic nephropathy. Glomerular cores were prepared from control rats and streptozotocin-diabetic rats (3 weeks' duration). Over 24 h in culture hyaluronan production from diabetic glomerular cores was higher than production from control glomerular cores whether maintained in 5.6 mmol/l glucose (105.6 +/- 15.5 vs 53.6 +/- 8.5 ng hyaluronan per 250 glomerular cores, p < 0.001); in 25 mmol/l glucose (149.3 +/- 34.8 vs 62.7 +/- 7.8 ng hyaluronan per 250 glomerular cores, p < 0.01); or in 45 mmol/l glucose (176.8 +/- 23.3 vs 102.0 +/- 17.9 ng hyaluronan per 250 glomerular cores, p < 0.01). At 5.6 mmol/l glucose, exposure in vitro to prostaglandin E2 caused an increase in hyaluronan production [maximal at 10(-9) mol/l prostaglandin E2, 237 +/- 19 vs 42 +/- 4, ng hyaluronan per 250 glomerular cores, p < 0.001 (control) and 195 +/- 7 vs 103 +/- 5, ng hyaluronan per 250 glomerular cores, p < 0.001 (diabetic)]. In both control and diabetic glomerular cores hyaluronan production was reduced significantly by the cyclooxygenase inhibitor indomethacin (10(-5) mol/l) [24.7 +/- 3.33 vs. 40.25 +/- 4.11 ng hyaluronan per 250 glomerular cores, p < 0.05 (control) and 36.5 +/- 6.25 vs 118.0 +/- 22.6, p < 0.01 (diabetic)]. A direct spectrophotometric microassay was used to determine the concentration of sulphated glycosaminoglycans derived from papain-digested glomerular core proteoglycans.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of different antihypertensive treatments on morphologic progression of diabetic nephropathy in uninephrectomized dogs

We previously reported the renal hemodynamic effects of different antihypertensive regimens in uninephrectomized, alloxan-induced, diabetic (DM) beagle dogs following one year of treatment. Dogs were prospectively randomized to one of five groups (N = 26): nondiabetic controls, Group I; dogs with DM on no antihypertensive drugs, Group II; dogs on a converting enzyme inhibitor, lisinopril (L), Group III; dogs on a calcium antagonist, TA3090 (diltiazem-like), Group IV; and dogs on a combination of each drug, in reduced doses, Group V. The current paper extends our previous studies by describing the morphologic changes that occurred within each group of dogs studied. More than 100 glomeruli from the renal cortex of each dog were evaluated for increases in mesangial volume fraction (Vv), glomerulosclerosis (GS) and ateriolar hyalinosis. The interstitium was also evaluated for associated changes. Increases in Vv were attenuated in all treated groups (0.28 +/- 0.04, DM alone versus 0.16 +/- 0.05 L; 0.21 +/- 0.07, TA-3090; 0.19 +/- 0.06 micron 2/micron 2, L+TA 3090; P < 0.05) compared to untreated DM. An attenuated increase in Vv also correlated with a blunted rise in proteinuria in Groups III (r = 0.79) and V (r = 0.81) but not Group IV (r = 0.29). Development of focal GS was blunted in all treated groups; however, global GS was fourfold greater in Group IV compared to untreated DM. The degree of interstitial fibrosis also correlated with the degree of global GS. These data support the concept that both a converting enzyme inhibitor and heart rate lowering calcium antagonist attenuate morphologic progression of diabetic renal disease.(ABSTRACT TRUNCATED AT 250 WORDS)