LDL stimulates collagen mRNA synthesis in mesangial cells through induction of PKC and TGF-beta expression

Aberrant DNA methylation of Tgfb1 in diabetic kidney mesangial cells

Epigenetic modulation may underlie the progression of diabetic nephropathy (DN). Involvement of TGFB1 in mesangial fibrosis of DN led us to hypothesize that Tgfb1 DNA demethylation contributes to progression of DN. In primary mesangial cells from diabetic (db/db) mouse kidneys, demethylation of Tgfb1 DNA and upregulation of Tgfb1 mRNA progressed simultaneously. USF1 binding site in Tgfb1 promoter region were demethylated, and binding of USF1 increased, with decreased binding of DNMT1 in db/db compared with control. Given downregulation of Tgfb1 expression by folic acid, antioxidant Tempol reversed DNA demethylation, with increased and decreased recruitment of DNMT1 and USF1 to the promoter, resulting in decreased Tgfb1 expression in db/db mice. Addition of H₂O₂ to mesangial cells induced DNA demethylation and upregulated Tgfb1 expression. Finally, Tempol attenuated mesangial fibrosis in db/db mice. We conclude that aberrant DNA methylation of Tgfb1 due to ROS overproduction play a key to mesangial fibrosis during DN progression.

Synergistic action of inflammation and lipid dysmetabolism on kidney damage in rats

In kidney disease, inflammation and lipid dysmetabolism are often associated together, however, the effect and mechanism of inflammatory mediators and lipid dysmetabolism on kidney damage is still unclear. In this study, Wistar rats were randomized into four groups: normal diet + saline (Group N), high-fat diet (HF)+ saline (Group HF), normal diet + adriamycin (Group ADR), HF + adriamycin (Group ADR + HF). After 10 weeks of feeding, rats in each group were randomly sacrificed. We found that the protein content of urine in ADR and ADR + HF groups were significantly higher than that of group N and HF while the serum levels of total protein and albumin in the ADR and ADR + HF groups decreased correspondingly. The serum levels of triglyceride, total cholesterol and low-density lipoprotein in the HF, ADR and ADR + HF groups increased. In the treatment groups, mesangial proliferation, matrix accumulation, tubular vacuolization, inflammatory cell infiltration and fat deposition were detected. These pathological changes were the most serious in the ADR + HF group. The expression of tumor necrosis factor-α (TNF-α) and transforming growth factor-β1 (TGF-β1) were increased in each treatment group, especially in the ADR + HF group. Our results suggested that the inflammatory factors and abnormal lipid levels can activate the inflammatory response in kidney of the Wistar rats, and lead to a series of pathological changes in renal tissue, and inflammatory factors and lipid dysmetabolism can aggravate damage in the kidney.

Renal Lipotoxicity-Associated Inflammation and Insulin Resistance Affects Actin Cytoskeleton Organization in Podocytes

In the last few decades a change in lifestyle has led to an alarming increase in the prevalence of obesity and obesity-associated complications. Obese patients are at increased risk of developing hypertension, heart disease, insulin resistance (IR), dyslipidemia, type 2 diabetes and renal disease. The excess calories are stored as triglycerides in adipose tissue, but also may accumulate ectopically in other organs, including the kidney, which contributes to the damage through a toxic process named lipotoxicity. Recently, the evidence suggests that renal lipid accumulation leads to glomerular damage and, more specifically, produces dysfunction in podocytes, key cells that compose and maintain the glomerular filtration barrier. Our aim was to analyze the early mechanisms underlying the development of renal disease associated with the process of lipotoxicity in podocytes. Our results show that treatment of podocytes with palmitic acid produced intracellular accumulation of lipid droplets and abnormal glucose and lipid metabolism. This was accompanied by the development of inflammation, oxidative stress and endoplasmic reticulum stress and insulin resistance. We found specific rearrangements of the actin cytoskeleton and slit diaphragm proteins (Nephrin, P-Cadherin, Vimentin) associated with this insulin resistance in palmitic-treated podocytes. We conclude that lipotoxicity accelerates glomerular disease through lipid accumulation and inflammation. Moreover, saturated fatty acids specifically promote insulin resistance by disturbing the cytoarchitecture of podocytes. These data suggest that renal lipid metabolism and cytoskeleton rearrangements may serve as a target for specific therapies aimed at slowing the progression of podocyte failure during metabolic syndrome.

Global Gene Expression Analysis in PKCα-/- Mouse Skin Reveals Structural Changes in the Dermis and Defective Wound Granulation Tissue

The skin's mechanical integrity is maintained by an organized and robust dermal extracellular matrix (ECM). Resistance to mechanical disruption hinges primarily on homeostasis of the dermal collagen fibril architecture, which is regulated, at least in part, by members of the small leucine-rich proteoglycan (SLRP) family. Here we present data linking protein kinase C alpha (PKCα) to the regulated expression of multiple ECM components including SLRPs. Global microarray profiling reveals deficiencies in ECM gene expression in PKCα-/- skin correlating with abnormal collagen fibril morphology, disorganized dermal architecture, and reduced skin strength. Detailed analysis of the skin and wounds from wild-type and PKCα-/- mice reveals a failure to upregulate collagen and other ECM components in response to injury, resulting in delayed granulation tissue deposition in PKCα-/- wounds. Thus, our data reveal a previously unappreciated role for PKCα in the regulation of ECM structure and deposition during skin wound healing.

Effect and mechanism of the Ang-(1-7) on human mesangial cells injury induced by low density lipoprotein

Hyperlipidemia is an independent risk factor for renal disease, and lipid deposition is associated with glomerulosclerosis. The angiotensin converting enzyme 2-angiotensin-(1-7)-Mas axis (ACE2-Ang-(1-7)-Mas axis) has been reported to participate in lipid metabolic regulation but its mechanism remains unclear. We hypothesized Ang-(1-7) would reduce lipid uptake in human mesangial cells (HMCs) by regulating the low density lipoprotein receptor-sterol regulatory element binding proteins 2-SREBP cleavage activating protein (LDLr-SREBP2-SCAP) negative feedback system, and improve glomerulosclerosis by regulating the transforming growth factor-β1 (TGF-β1). In this study we found that ACE2 was undetected in HMCs. The administration of LDL caused normal LDLr-SREBPs-SCAP negative feedback effect. Exogenous Ang-(1-7) enhanced this negative feedback effect via down-regulating LDLr, SREBP2, and SCAP expression, and effectively inhibited LDL-induced lipid deposition and cholesterol increases. This enhanced inhibitory effect was reversed by the Mas receptor antagonist A-779. Meanwhile, Ang-(1-7) significantly decreased the high LDL-induced production of TGF-β1, an effect blocked by A-779. Interestingly, HMCs treated with Ang-(1-7) alone activated the TGF-β1 expression. Our results suggested that Ang-(1-7) inhibits LDL accumulation and decreases cholesterol levels via modulating the LDLr-SREBPs-SCAP negative feedback system through the Mas receptor. Moreover, Ang-(1-7) exhibits a dual regulatory effect on TGF-β1 in HMCs.

Reversibility of renal injury with cholesterol lowering in hyperlipidemic diabetic mice

Hyperlipidemia is a risk factor for development and progression of diabetic nephropathy. However, it is not known if reduction of hyperlipidemia is protective against progression of disease. The goal of this study was to determine if reduction of hypercholesterolemia could limit progression of diabetic nephropathy. Diabetic and nondiabetic LDL receptor deficient (LDLR(-/-)) mice were fed diets containing either no cholesterol (0%) or high cholesterol (0.12%) for 36 weeks. One group each of diabetic and nondiabetic mice were fed the high-cholesterol diet for 26 weeks then changed to the 0% cholesterol diet for the last 10 weeks. Consumption of the high-cholesterol diet exacerbated the development of diabetic nephropathy with elevations in urine albumin excretion, glomerular and renal hypertrophy, and mesangial matrix expansion. Increased glomerular lipid and apolipoprotein B accumulation was found in diabetic mice that consumed the 0.12% cholesterol diet compared with other groups. However, diabetic mice that changed from the high-cholesterol diet to the 0% cholesterol diet for the last 10 weeks had lower urine albumin excretion and mesangial matrix expansion compared with mice that consumed the 0.12% cholesterol diet throughout. This suggests that hyperlipidemia causes continuous renal injury, and that lowering cholesterol levels by dietary means can improve renal function in diabetic LDLR(-/-) mice.

Lovastatin inhibits oxidized low-density lipoprotein-induced plasminogen activator inhibitor and transforming growth factor-beta1 expression via a decrease in Ras/extracellular signal-regulated kinase activity in mesangial cells

Oxidized low-density lipoprotein (Ox-LDL) might be involved in the progression of renal disease. Ox-LDL stimulation of plasminogen activator inhibitor-1 (PAI-1) expression via transforming growth factor-beta (TGF-beta)/Smad signaling in mesangial cells required activation of extracellular signal-regulated kinase (ERK). Mevalonate depletion by 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase inhibitors, or statins, decreases the levels of farnesyl pyrophosphate (FPP) for isoprenylation of Ras. We postulate that statins may ameliorate the Ox-LDL-induced mesangial matrix accumulation by inhibiting Ras/ERK activation with subsequent downregulation of TGF-beta target genes. Quiescent mesangial cells were incubated for 18 h with and without the presence of lovastatin before 50 microg/mL of Ox-LDL treatment for 1 h. Lovastatin inhibited markedly the stimulatory effects of Ox-LDL on ERK1/2 activation, nuclear Smad3 expression, TGF-beta1 and PAI-1 mRNA and protein expression, and PAI-1 luciferase activity. These inhibitory effects of lovastatin were reversed almost completely by mevalonate or FPP. Similar to lovastatin, FTI-277, which is an inhibitor of Ras farnesylation, decreased the Ox-LDL-induced activation of ERK/Smad3 and induction of TGF-beta1/PAI-1. These results indicate that lovastatin prevents the Ox-LDL-induced Ras/ERK activation that results in inhibition of Smad3 activation in mesangial cells with subsequent downregulation of TGF-beta target genes. Thus, statins seem to have antifibrotic effects through their anti-TGF-beta response that are relevant in the treatment of chronic renal disease with dyslipidemia.

Role of CAGA boxes in the plasminogen activator inhibitor-1 promoter in mediating oxidized low-density lipoprotein-induced transcriptional activation in mesangial cells

Oxidized low-density lipoprotein (Ox-LDL) activates transforming growth factor-beta (TGF-beta)/Smad signaling to stimulate plasminogen activator inhibitor-1 (PAI-1) expression in mesangial cells. Smad-binding sequences, termed CAGA boxes, are present in the promoter of human PAI-1 gene, and they mediate TGF-beta transcriptional induction. However, the functional role of each CAGA box in the Ox-LDL-induced PAI-1 promoter activation is unknown. In this study, mutation of 1 of the 3 CAGA boxes located at -730, -580, and -280 of the PAI-1 promoter decreased the Ox-LDL-induced luciferase activity by 40 to 58%, whereas mutations in 2 sites reduced it over 75% or completely abolished it. Overexpression of Smad3 in N-terminal tagged Smad3-transfected cells increased the Ox-LDL-induced transcriptional activation of the PAI-1 promoter, whereas mutation of Smad3 abolished it. Electrophoretic mobility shift assay showed that the labeled -280, -580, and -730 CAGA box probes detected DNA/protein complexes induced by Ox-LDL, whereas mutant probes did not. When nuclear extracts were preincubated with a 100-fold of an unlabeled -280, -580, and -730 CAGA oligonucleotide, the formation of complexes was prevented but not with mutant CAGA box competitors. The addition of anti-Smad3 to the reaction with the labeled -280 or -580 CAGA box probe resulted in a supershift, but not with the -730 CAGA box probe. These results suggest that the 3 CAGA elements in the PAI-1 promoter mediate the Ox-LDL-induced PAI-1 transcription to a different degree, of which the -280 and -580 CAGA regions directly bind to Smad3.

Mechanisms of low-density lipoprotein-induced expression of connective tissue growth factor in human aortic endothelial cells

Hyperlipidemia is a recognized risk factor for atherosclerotic vascular disease. The underlying mechanisms that link lipoproteins and vascular disease are undefined. Connective tissue growth factor (CTGF) is emerging as a key determinant of progressive fibrotic diseases, and its expression is upregulated by diabetes. To define the mechanisms through which low-density lipoproteins (LDL) promote vascular injury, we evaluated whether LDL can modulate the expression of CTGF and collagen IV in human aortic endothelial cells (HAECs). Treatment of HAECs with LDL (50 microg/ml) for 24 h produced a significant increase in the mRNA and the protein levels of CTGF and collagen IV compared with unstimulated controls. To explore the mechanisms by which LDL regulates CTGF and collagen IV expression in HAECs, we determined first if CTGF and collagen IV are downstream targets for regulation by transforming growth factor-beta (TGF-beta). The results demonstrated that TGF-beta produced a concentration-dependent increase in the protein levels of CTGF. To assess whether the induction of CTGF in response to LDL is mediated via autocrine activation of TGF-beta, HAECs were treated with LDL for 24 h in the presence and absence of anti-TGF-beta neutralizing antibodies (anti-TGF-beta NA). The results demonstrated that the increase in CTGF induced by LDL was significantly inhibited by the anti-TGF-beta NA. To investigate the upstream mediators of TGF-beta on activity of CTGF in response to LDL, HAECs were treated with LDL for 24 h in the presence and absence of cell-permeable MAPK inhibitors. Inhibition of p38(mapk) activities did not affect LDL-induced TGF-beta1, CTGF, and collagen IV expression. On the other hand, SP-600125, a specific inhibitor of c-Jun NH(2)-terminal kinase, suppressed LDL-induced TGF-beta, CTGF, and collagen IV expression, and PD-98059, a selective inhibitor of p44/42(mapk), suppressed LDL-induced TGF-beta and CTGF expression. These findings are the first to implicate the MAPK pathway and TGF-beta as key players in LDL signaling, leading to CTGF and collagen IV expression in HAECs. The data also point to a potential mechanistic pathway through which lipoproteins may promote vascular injury.

Oxidized LDL activates PAI-1 transcription through autocrine activation of TGF-beta signaling in mesangial cells

BACKGROUND

Lipid abnormalities and oxidative stress may be involved in the development of glomerulosclerosis. Plasminogen activator inhibitor-1 (PAI-1) is a component of extracellular matrix (ECM) and target gene of transforming growth factor-beta (TGF-beta). Smad proteins play a key role in TGF-beta signaling, and Smad binding CAGA boxes are present in the PAI-1 promoter. This study examined whether oxidized low-density lipoprotein (Ox-LDL) activates PAI-1 transcription in human mesangial cells, mediated by increased Smad/DNA interactions.

METHODS

Quiescent HMC were incubated with 50 microg/mL of Cu(++)-catalyzed Ox-LDL for 15 minutes to 4 hours, and the effects of Ox-LDL on TGF-beta1 and PAI-1 mRNA expression, PAI-1 promoter activity, and DNA binding activity of Smad proteins were examined.

RESULTS

Ox-LDL induced TGF-beta1 and PAI-1 mRNA expression. Ox-LDL increased the transiently transfected PAI-1 promoter activity as compared with controls to 3.9-fold. Ox-LDL-treated cells increased Smad3 protein levels two times the control levels in the nuclei. Electrophoretic mobility shift assay (EMSA) performed using a CAGA sequence probe and nuclear extracts showed that Ox-LDL increased DNA/protein complexes. When nuclear extracts were preincubated with 100 molar excess of unlabeled CAGA oligonucleotide or SB-431542, an inhibitor of the TGF-beta type I receptor, the formation of complex was prevented. The DNA binding protein was shown to be Smad3 by antibody supershift. Transfection of phosphorothioate CAGA oligonucleotides, which compete with the CAGA-containing PAI-1 promoter for Smad3 binding, inhibited the Ox-LDL-induced PAI-1 mRNA expression. Cotransfection of phosphorothioate CAGA oligonucleotides with PAI-1 reporter vector also blocked the Ox-LDL-induced PAI-1 promoter activity.

CONCLUSION

These results suggest that Ox-LDL activates TGF-beta/Smad signaling to stimulate PAI-1 transcription in human mesangial cells. Thus, progression of glomerular disease may be promoted by PAI-1 up-regulation in human mesangial cells mediated by the Ox-LDL-induced TGF-beta/Smad signaling pathways.

The leaf extract of Ginkgo Biloba L. suppresses oxidized LDL-stimulated fibronectin production through an antioxidant action in rat mesangial cells

1 The leaf extract of Ginkgo Biloba L. exhibits a variety of pharmacological effects through an antioxidant action. We examined the effects of the leaf extract (Ginkgolon-24) on the production of fibronectin induced by oxidized low-density lipoprotein (oxLDL) in rat mesangial cells. 2 Stimulation with oxLDL accelerated the production of fibronectin with the preceding generation of reactive oxygen species (ROS). Pretreatment with Ginkgolon-24 inhibited the oxLDL-induced fibronectin production as well as ROS generation. 3 oxLDL also elicited the activation of SP-1, nuclear factor-kappaB, and cAMP response element-binding protein, which are transcription factors involved in the fibronectin production. Among these activated transcription factors, Ginkgolon-24 inhibited the activation of SP-1 only. 4 Furthermore, 7-ketocholesterol, an oxidized lipid in oxLDL particles, induced the production of fibronectin and the activation of SP-1, which were also suppressed by Ginkgolon-24. 5 These results suggest that the leaf extract of Ginkgo Biloba L. inhibits the oxLDL-induced production of fibronectin probably through inhibitory effects on ROS generation and SP-1 activation in rat mesangial cells.

Angiotensin II mediates LDL-induced superoxide generation in mesangial cells

Lipid abnormalities and activation of the local renin-angiotensin system (RAS) may be involved in the pathogenesis of chronic glomerular disease. This study investigated whether low-density lipoprotein (LDL) activates local RAS in cultured human mesangial cells (HMC) and, at the same time, whether ANG II mediates LDL-induced mesangial cell proliferation, hypertrophy, and superoxide (O2-) generation. Quiescent HMC were exposed to 50 to 200 microg/ml of LDL or 10-7 to 10-10 M ANG II for 0.5 to 24 h in the presence or absence of 10-6 M losartan, an ANG II type I (AT1) receptor antagonist, or 10-5 M diphehylendieodonium (DPI) or 10-4 M apocynin, inhibitors of nicotinamide adenine dinucleotide phosphate oxidase. LDL induced an up to threefold increase in the ANG II levels in the culture medium of HMC. LDL upregulated AT1 receptor and angiotensinogen mRNA expression in HMC. LDL incubated with HMC increased O2- production by up to 3.3 times compared with the level of control cells. The LDL-induced, increased O2- generation was suppressed by losartan, DPI, or apocynin. LDL significantly increased mesangial [3H]thymidine or [3H]leucine incorporation, whereas these processes were abrogated by losartan. In conclusion, LDL increases ANG II production by mesangial cells, which in turn results in increased O2- production, and cell proliferation and hypertrophy, these effects of ANG II being mediated by the AT1 receptor.

Biphasic regulation of plasminogen activator/inhibitor by LDL in mesangial cells

Lipid abnormalities and dysregulation of the plasminogen activator (PA)/plasmin system may be involved in the development of glomerulosclerosis. We investigated the effects of low-density lipoprotein (LDL) on PA inhibitor-1 (PAI-1), urokinase-type PA (uPA), and tissue-type PA (tPA) in relationship to protein kinase C (PKC) in cultured human mesangial cells (HMC). LDL (200 microg/ml) induced two peaks of PKC activation at hours 0.25 and 6, with translocation of PKC-alpha, -beta(1), and -delta from cytosol to the membrane. The second increase in PKC activity gradually decreased to the control value by hour 18. LDL downregulated 2.4-kb PAI-1, uPA, and tPA mRNA expression within 6 h of incubation with HMC. On the other hand, after 12-48 h, LDL-treated cells showed a significant increase in PAI-1, tPA, and uPA mRNA levels. LDL induced up to a twofold increase in PAI-1 antigen levels in the extracellular matrix of HMC after 24-48 h as well as increased PA inhibitory activity in the culture medium. Analysis of the adhesion plaques from cells incubated with LDL for 48 h by zymography showed increased intensity of lysis near molecular weights of approximately 55,000 and 100,000. LDL slightly increased tPA release at hours 24 and 48 but did not increase PA activity in culture medium. The stimulatory effects of LDL on PAI-1, tPA, and uPA gene regulation in HMC were blocked by the inhibition of PKC using GF-109203X 12 h after treatment with LDL or downregulation of PKC using phorbol myristate acetate. In summary, LDL regulates PAI-1, uPA, and tPA in biphasic patterns in HMC, and the upregulation of PAI-1, uPA, and tPA after long-term LDL exposure seems to be mediated by a delayed PKC activation associated with an increased PA inhibitory activity. These results suggest that LDL, after prolonged incubations with HMC, causes a PA/inhibitor imbalance favoring accumulation of matrix.