A high concentration of glucose alters the production of tPA, uPA and PAI-1 antigens from human mesangial cells

Plasminogen deficiency is associated with improved glucose tolerance, and lower DPP-4 activity

Plasminogen (Plg), which is the inactive form of plasmin, deficiency enhanced insulin secretion, and was associated with improved oral glucose tolerance in mice. Additionally, Plg deficiency was associated with lower dipeptidyl peptidase-4 (DPP-4) activity, and enhanced glucagons-like peptide-1 (GLP-1) expression. Plg may regulate the DPP-4 activity and the glucose metabolism.

Effects of uPA on mesangial matrix changes in the kidney of diabetic rats

OBJECTIVE

To investigate the effect of urokinase-type plasminogen activator (uPA) on mesangial matrix in the kidney of diabetic rats and its related mechanisms.

METHODS

Diabetic Sprague-Dawley (SD) rats induced by intraperitoneal injection of streptozotocin (STZ) were randomly and evenly divided into two groups: DM + vehicle, and DM + uPA (2500 U kg(-1) uPA via tail vein once a day for four weeks). The normal SD rats without diabetes were considered as control group. Rats in the three groups were executed and the heart blood was sampled for determination of blood glucose and serum creatinine. Meanwhile, kidney tissues of rats were also harvest for measurement of glomerular area, volume, and mesangial area by periodic acid silver methenamine (PASA) staining. The expression of urokinase-type plasminogen activator receptor (uPAR), plasminogen activator inhibitor-1 (PAI-1), and collagen IV in renal tissues was tested with immunohistochemistry.

RESULTS

Compared with control, the DM rats had obvious albuminuria, significantly (p < 0.01) increased glomerular volume and mesangial matrix area, and significantly (p < 0.05) higher expression of uPAR, PAI-1 and collagen IV in mesangial matrix, significantly up-regulated (p < 0.05) glomerular uPAR, PAI-1, and collagen IV expression. After treated with uPA, the diabetic rats had significantly (p < 0.05) reduced albuminuria, significantly (p < 0.01) improved glomerular volume and mesangial matrix, significantly (p < 0.05) down-regulated PAI-1 and collagen IV expression in mesangial matrix. However, the uPAR expression in renal tissues were unchangeable (p > 0.05) and PAI-1 and collagen IV expression were significantly (p < 0.05) reduced when diabetic rats were treated with uPA.

CONCLUSION

uPA can down-regulate glomerular PAI-1 expression in the DM rats but not significantly influence uPAR expression, suggesting that uPA might regulate the mesangial cell (MC) and its matrix expression and improve diseased diabetic mesangial matrix via its combination with uPAR to uptake PAI-1 and accelerate its degradation.

Metabolic reprogramming of macrophages: glucose transporter 1 (GLUT1)-mediated glucose metabolism drives a proinflammatory phenotype

Glucose is a critical component in the proinflammatory response of macrophages (MΦs). However, the contribution of glucose transporters (GLUTs) and the mechanisms regulating subsequent glucose metabolism in the inflammatory response are not well understood. Because MΦs contribute to obesity-induced inflammation, it is important to understand how substrate metabolism may alter inflammatory function. We report that GLUT1 (SLC2A1) is the primary rate-limiting glucose transporter on proinflammatory-polarized MΦs. Furthermore, in high fat diet-fed rodents, MΦs in crown-like structures and inflammatory loci in adipose and liver, respectively, stain positively for GLUT1. We hypothesized that metabolic reprogramming via increased glucose availability could modulate the MΦ inflammatory response. To increase glucose uptake, we stably overexpressed the GLUT1 transporter in RAW264.7 MΦs (GLUT1-OE MΦs). Cellular bioenergetics analysis, metabolomics, and radiotracer studies demonstrated that GLUT1 overexpression resulted in elevated glucose uptake and metabolism, increased pentose phosphate pathway intermediates, with a complimentary reduction in cellular oxygen consumption rates. Gene expression and proteome profiling analysis revealed that GLUT1-OE MΦs demonstrated a hyperinflammatory state characterized by elevated secretion of inflammatory mediators and that this effect could be blunted by pharmacologic inhibition of glycolysis. Finally, reactive oxygen species production and evidence of oxidative stress were significantly enhanced in GLUT1-OE MΦs; antioxidant treatment blunted the expression of inflammatory mediators such as PAI-1 (plasminogen activator inhibitor 1), suggesting that glucose-mediated oxidative stress was driving the proinflammatory response. Our results indicate that increased utilization of glucose induced a ROS-driven proinflammatory phenotype in MΦs, which may play an integral role in the promotion of obesity-associated insulin resistance.

Signs of dysregulated fibrinolysis precede the development of type 2 diabetes mellitus in a population-based study

Background

Diabetic patients experience stimulated coagulation and dysfibrinolysis, which is associated with an increased risk of cardiovascular events. This imbalance may precede the manifest diagnosis. We investigated whether elevated antigen levels of tissue plasminogen activator (tPA), plasminogen activator inhibitor-1 (PAI-1), the tPA/PAI-1 complex, or von Willebrand Factor (VWF) precede type 2 diabetes mellitus (T2DM) diagnosis, and whether this elevation occurs before increased fasting plasma glucose (FPG) or 2-hour plasma glucose (2hPG) in individuals who later develop T2DM.

Methods

We conducted a prospective incident case-referent study within the Västerbotten Intervention Programme. Cardiovascular risk factor data as well as FPG and 2hPG and blood samples for future research were collected at a baseline health examination between 1989 and 2000, (n= 28 736). During follow-up in January 2001, 157 cases had developed T2DM. Referents without T2DM were matched for sex, age, and year of participation (n=277). Subgroup analysis was performed for cases with normal baseline glucose levels (FPG <6.1 mmol/L and 2hPG < 8.9 mmol/L) and cases with elevated levels (FPG 6.1-6.9 mmol/L and/or 2hPG 8.9-12.1 mmol/L).

Results

After adjusting for BMI, family history of diabetes, physical activity, smoking, systolic blood pressure and levels of C-reactive protein and triglycerides, independent associations were found between incident T2DM and elevated levels of tPA (OR=1.54, 95% CI 1.06-2.23), PAI-1 (OR=1.61, 95% CI 1.14-2.28), and tPA/PAI-1 complex (OR=2.45, 95% CI 1.56-3.84). In participants with normal glucose levels, PAI-1 (OR=2.06, 95% CI 1.10 - 3.86) exhibited an independent relationship with incident T2DM after the adjustments.

Conclusions

Elevated levels of fibrinolytic variables precede the manifestation of T2DM after adjusting for metabolic and cardiovascular risk factors and can be detected several years before changes in glucose tolerance.

Diabetes-induced renal injury in rats is attenuated by suramin

Progression of hyperglycemia-induced renal injury is a contributing factor for diabetic nephropathy (DN)-induced end-stage renal disease (ESRD), and development of novel therapeutic strategies that act early to prevent progression of DN and ESRD are important. We examined the efficacy and mechanism(s) of suramin on hyperglycemia-induced renal injury before development of overt histological damage. Two groups of male Sprague-Dawley rats received streptozotocin (STZ) and one group received saline. Three weeks later, one STZ group received suramin (10 mg/kg). All animals were euthanized 1 week later (4 weeks). Although there was a decrease in creatinine clearance between control and STZ ± suramin rats, there was no difference in creatinine clearance between STZ rats ± suramin intervention. Liquid chromatography-tandem mass spectroscopy-based analysis revealed increases in urinary proteins that are early indicators of DN (e.g., cystatin C, clusterin, cathepsin B, retinol binding protein 4, and peroxiredoxin-1) in the STZ group, which were blocked by suramin. Endothelial intracellular adhesion molecule-1 (ICAM-1) activation, leukocyte infiltration, and inflammation; transforming growth factor-β1 (TGF-β1) signaling; TGF-β1/SMAD-3-activated fibrogenic markers fibronectin-1, α-smooth muscle actin, and collagen 1A2; activation of proinflammatory and profibrotic transcription factors nuclear factor-κB (NF-κB) and signal transducer and activator of transcription factor-3 (STAT-3), respectively, were all increased in STZ rats and suramin blocked these changes. In conclusion, delayed administration of suramin attenuated 1) urinary markers of DN, 2) inflammation by blocking NF-κB activation and ICAM-1-mediated leukocyte infiltration, and 3) fibrosis by blocking STAT-3 and TGF-β1/SMAD-3 signaling. These results support the potential use of suramin in DN.

Functional characterization of the plasmacytoma variant translocation 1 gene (PVT1) in diabetic nephropathy

We previously observed association between variants in the plasmacytoma variant translocation 1 gene (PVT1) and end-stage renal disease (ESRD) attributed to both type 1 and type 2 diabetes, and demonstrated PVT1 expression in a variety of renal cell types. While these findings suggest a role for PVT1 in the development of ESRD, potential mechanisms for involvement remain unknown. The goal of this study was to identify possible molecular mechanisms by which PVT1 may contribute to the development and progression of diabetic kidney disease. We knocked-down PVT1 expression in mesangial cells using RNA interference, and analyzed RNA and protein levels of fibronectin 1 (FN1), collagen, type IV, alpha 1 (COL4A1), transforming growth factor beta 1 (TGFB1) and plasminogen activator inhibitor-1 (SERPINE1 or PAI-1) by qPCR and ELISA, respectively. PVT1 expression was significantly upregulated by glucose treatment in human mesangial cells, as were levels of FN1, COL4A1, TGFB1, and PAI-1. Importantly, PVT1 knockdown significantly reduced mRNA and protein levels of the major ECM proteins, FN1 and COL4A1, and two key regulators of ECM proteins, TGFB1 and PAI-1. However, we observed a higher and more rapid reduction in levels of secreted FN1, COL4A1, and PAI-1 compared with TGFB1, suggesting that at least some of the PVT1 effects on ECM proteins may be independent of this cytokine. These results indicate that PVT1 may mediate the development and progression of diabetic nephropathy through mechanisms involving ECM accumulation.

A peptide inhibitor of the urokinase/urokinase receptor system inhibits alteration of the blood-retinal barrier in diabetes

One of the major complications of diabetes is the alteration of the blood-retinal barrier, leading to retinal edema and consequent vision loss. The aim of this study was to evaluate the role of the urokinase plasminogen activator (uPA)/uPA receptor (uPAR) system in the regulation of retinal vascular permeability. Biochemical, molecular, and histological techniques were used to examine the role of uPA and uPAR in the regulation of retinal vascular permeability in diabetic rats and cultured retinal endothelial cells. The increased retinal vascular permeability in diabetic rats was associated with a decrease in vascular endothelial (VE) -cadherin expression in retinal vessels. Treatment with the uPA/uPAR-inhibiting peptide (A6) was shown to reduce diabetes-induced permeability and the loss of VE-cadherin. The increased permeability of cultured cells in response to advanced glycation end products (AGEs) was significantly inhibited with A6. Treatment of endothelial cells with specific matrix metalloproteinases or AGEs resulted in loss of VE-cadherin from the cell surface, which could be inhibited by A6. uPA/uPAR physically interacts with AGEs/receptor for advanced glycation end products on the cell surface and regulates its activity. uPA and its receptor uPAR play important roles in the alteration of the blood-retinal barrier through proteolytic degradation of VE-cadherin. The ability of A6 to block retinal vascular permeability in diabetes suggests a potential therapeutic approach for the treatment of diabetic macular edema.

Reactive oxygen species mediate high glucose-induced plasminogen activator inhibitor-1 up-regulation in mesangial cells and in diabetic kidney

BACKGROUND

Plasminogen activator inhibitor-1 (PAI-1) plays an important role in remodeling of extracellular matrix (ECM) in the glomeruli. PAI-1 is up-regulated by high glucose and is overexpressed in diabetic kidney. Since reactive oxygen species (ROS) mediate ECM accumulation in diabetic glomeruli and was recently found to mediate transforming growth factor-beta1 (TGF-beta1)-induced PAI-1 up-regulation in glomerular mesangial cells, we examined the role of ROS in high glucose-induced PAI-1 expression in cultured glomerular mesangial cells and in streptozotocin-induced diabetic rat glomeruli.

METHODS

Growth arrested and synchronized primary rat mesangial cells were treated with different concentrations of glucose in the presence or absence of N-acetylcysteine (NAC) or trolox, or after cellular reduced form of glutathione (GSH) depleted with DL-buthionine-(S,R)-sulfoximine (BSO). Taurine was administered to diabetic rats from 2 days to 4 weeks after streptozotocin injection. Urinary protein excretion, glomerular volume, and fractional mesangial area were measured as markers of renal injury and lipid peroxide (LPO) as an oxidative stress marker. PAI-1 mRNA expression was measured by Northern blot analysis in mesangial cells and reverse transcription-polymerase chain reaction (RT-PCR) in glomeruli, PAI-1 protein by Western blot analysis and enzyme-linked immunosorbent assay (ELISA), and plasmin activity by fluorometry.

RESULTS

High glucose significantly increased PAI-1 mRNA and protein expression and decreased plasmin activity in mesangial cells. Equimolar concentrations of l-glucose or mannitol did not affect PAI-1 expression. BSO pretreatment significantly increased basal PAI-1 expression and amplified the response to high glucose. NAC effectively inhibited high glucose-induced, but not basal, PAI-1 expression. Reduced plasmin activity in mesangial cells by high glucose was rescued by antioxidants. Anti-TGF-beta antibody inhibited both high glucose- and H(2)O(2)-induced PAI-1 up-regulation. Taurine significantly reduced plasma LPO, glomerular PAI-1 expression, glomerular volume, fractional mesangial area, and proteinuria in streptozotocin-induced diabetic rats.

CONCLUSION

These results demonstrate that ROS mediate high glucose-induced up-regulation of PAI-1 expression in cultured mesangial cells and in diabetic glomeruli. Since both high glucose and TGF-beta1 induce cellular ROS and ROS mediate both high glucose- and TGF-beta1-induced PAI-1, ROS appear to amplify TGF-beta1 signaling in high glucose-induced PAI-1 up-regulation. Antioxidants can prevent accumulation of ECM protein in diabetic glomeruli partly by abrogating up-regulation of PAI-1 and suppression of plasmin activity.

Renal synthesis of urokinase type-plasminogen activator, its receptor, and plasminogen activator inhibitor-1 in diabetic nephropathy in rats: modulation by angiotensin-converting-enzyme inhibitor

Plasmin is an important factor in the degradation of extracellular matrix. In the study reported here we examined the expression of plasminogen-activator inhibitor-1 (PAI-1), urokinase-type plasminogen activator (uPA), and uPA receptor (uPAR), as well as the relevance of such expression to the production of type IV collagen, a major component of extracellular matrix, in the renal tissue of rats with streptozotocin-induced diabetes. Because angiotensin II is involved in the synthesis of PAI-1 and uPA, we also examined the effect of benazepril, an angiotensin-converting-enzyme inhibitor, on the expression of PAI-1, uPA, and uPAR messenger RNAs (mRNAs) and type IV collagen protein. Rats with streptozocin-induced diabetes-some untreated and some treated with 30 mg/L benazepril-and nondiabetic control rats were sacrificed at 4, 12, or 24 weeks after induction of diabetes. We examined the expression of PAI-1, uPA, and uPAR mRNAs through the use of in situ hybridization and that of type IV collagen by means of immunohistochemical methods. In control rats, we detected weak signals for PAI-1, uPA, and uPAR mRNAs in glomeruli. Diabetic rats exhibited high levels of expression of PAI-1, uPA, and uPAR mRNAs and type IV collagen protein, mainly in mesangial cells. These mRNAs were synthesized in various renal cells (epithelial, mesangial, and endothelial cells and Bowman's capsule). Benazepril inhibited increases in all 3 mRNAs, especially in the mesangium; reduced type IV collagen expression; and attenuated mesangial expansion. Our results indicated that altered expression of PAI-1, uPA, and uPAR in diabetic nephropathy was associated with mesangial expansion and that the beneficial effects of ACE-I may be at least associated with such expression.

Hyperglycemia induces PAI-1 gene expression in adipose tissue by activation of the hexosamine biosynthetic pathway

We examined whether acute in vivo increases in either plasma glucose or insulin concentrations stimulate PAI-1 gene expression in fat tissue. We studied chronically catheterized unstressed and awake, lean (approximately 300 g, n=12) and obese (approximately 450 g, n=12) Sprague-Dawley rats. Hyperglycemia (approximately 18mM) was induced for 3 h by glucose infusion during a pancreatic clamp (somatostatin inhibited endogenous insulin secretion). Compared with equivalent saline infusion, hyperglycemia induced a 6-7 fold increase in PAI-1 gene expression in both lean and obese rats (P<0.001). When the rate of cellular glucose uptake was matched during a euglycemic hyperinsulinemic (approximately 60 microU/ml) clamp, PAI-1 gene expression in both obese and lean rats was proportionately and significantly increased (P<0.001). We further examined whether induction of the hexosamine biosynthetic pathway would mimic the effects of hyperglycemia and hyperinsulinemia on PAI-1 gene expression. Indeed, infusion of glucosamine (GlcN, 30 micromol/kg/min), induced a approximately 3-4 fold increase (P<0.01) in PAI-1 gene expression in both lean and obese animals. While obese rats had a four times greater fat mass then the lean rats, PAI-1 gene expression remained significantly higher when expressed as per gram fat. Our results support the hypothesis that increased glucose uptake induces PAI-1 gene expression in adipose tissue, probably through the activation of the hexosamine biosynthetic pathway. These findings may account for some of the fibrinolytic alterations seen in obese type 2 diabetic humans.

Role of PKC and TGF-beta receptor in glucose-induced proliferation of smooth muscle cells

The role of protein kinase C (PKC) and transforming growth factor (TGF)-beta in the proliferation of vascular smooth muscle cells (SMCs) under a high glucose condition was investigated. [3H]-thymidine incorporation under 20 mM glucose was significantly accelerated compared with that under 5.5 mM glucose, and this increase was inhibited by an anti-TGF-beta antibody or a PKC-beta specific inhibitor, LY333531. The amount of active and total TGF-beta1 in the conditioned media did not differ between 5.5 and 20 mM glucose. However, the expression of TGF-beta receptor type II under 20 mM glucose was significantly increased, but that of the TGF-beta receptor type I was not. This increased expression of the TGF-beta receptor type II was prevented by LY333531. These observations suggest that the increased expression of the TGF-beta receptor type II via PKC-beta plays an important role in the accelerated proliferation of SMCs under a high glucose condition, leading to the development of diabetic macroangiopathy.

High glucose reduces generation of plasmin activity by mesangial cells

Mesangium enlargement is a central feature of diabetic nephropathy and almost certainly plays a pathogenic role in this condition. Previous studies have shown that mesangium degradation is reduced in a high glucose mileau. Plasmin has been shown to play an important role in extracellular matrix degradation, both directly and through its ability to activate the matrix metalloproteinases. We therefore investigated how high glucose concentration may affect the various components of the plasminogen cascade on mesangial cells and whether it impairs the ability of the mesangial cell to generate plasmin activity. Result showed decreased binding of plasminogen and the urokinase type plasminogen activator to the mesangial cell surface while the tissue type plasminogen activator and the plasminogen activator-1 associated with mesangial cells were increased. The net effect of these changes was a reduced capacity of mesangial cell layers to generate plasmin activity in a high glucose environment. We postulate that this may be of importance in the reduced mesangium degradation which occurs in diabetes.