Angiotensin II upregulates toll-like receptor 4 on mesangial cells

TLR2 and TLR4 gene expression in peripheral monocytes in nondiabetic hypertensive patients: the effect of intensive blood pressure-lowering

The activation of innate immune receptors, such as Toll-like receptors (TLRs), participates in the pathogenesis of cardiovascular diseases. The authors evaluated TLR2 and TLR4 gene expression in the peripheral monocytes of nondiabetic hypertensive patients compared with normotensive individuals and investigated the effect of intensive systolic blood pressure (SBP)-lowering. Included were 43 nondiabetic hypertensive patients with essential hypertension who were randomly assigned to an intensive treatment arm, with an SBP target of <130 mm Hg, or a standard arm, with an SBP target of <140 mm Hg. TLR2 and TLR4 messenger RNA (mRNA) levels in monocytes were estimated before and 12 weeks after therapy initiation. Sixteen healthy individuals were included for comparison. Hypertensives revealed significantly higher TLR4 mRNA levels compared with normotensives (985 ± 885 vs 554 ± 234, P=.005). In contrast, no statistically significant difference was found in TLR2. Compared with standard treatment, intensive treatment significantly downregulated TLR2 and TLR4 mRNAs, expressed as fold induction (0.66 ± 0.49 vs 1.38 ± 1.65 and 0.62 ± 0.3 vs 1.9 ± 1.2, respectively; P<.001 for both). In conclusion, TLR4 mRNA levels in peripheral monocytes are significantly elevated in nondiabetic hypertensive patients. Intensive control of SBP results in attenuation of TLR2 and TLR4 gene expression in those patients. Our findings suggest that a strict SBP target in nondiabetic hypertensive patients may offer additional benefits.

Toll-like receptor 4 promotes tubular inflammation in diabetic nephropathy

Inflammation contributes to the tubulointerstitial lesions of diabetic nephropathy. Toll-like receptors (TLRs) modulate immune responses and inflammatory diseases, but their role in diabetic nephropathy is not well understood. In this study, we found increased expression of TLR4 but not of TLR2 in the renal tubules of human kidneys with diabetic nephropathy compared with expression of TLR4 and TLR2 in normal kidney and in kidney disease from other causes. The intensity of tubular TLR4 expression correlated directly with interstitial macrophage infiltration and hemoglobin A1c level and inversely with estimated glomerular filtration rate. The tubules also upregulated the endogenous TLR4 ligand high-mobility group box 1 in diabetic nephropathy. In vitro, high glucose induced TLR4 expression via protein kinase C activation in a time- and dose-dependent manner, resulting in upregulation of IL-6 and chemokine (C-C motif) ligand 2 (CCL-2) expression via IκB/NF-κB activation in human proximal tubular epithelial cells. Silencing of TLR4 with small interfering RNA attenuated high glucose-induced IκB/NF-κB activation, inhibited the downstream synthesis of IL-6 and CCL-2, and impaired the ability of conditioned media from high glucose-treated proximal tubule cells to induce transmigration of mononuclear cells. We observed similar effects using a TLR4-neutralizing antibody. Finally, streptozotocin-induced diabetic and uninephrectomized TLR4-deficient mice had significantly less albuminuria, renal dysfunction, renal cortical NF-κB activation, tubular CCL-2 expression, and interstitial macrophage infiltration than wild-type animals. Taken together, these data suggest that a TLR4-mediated pathway may promote tubulointerstitial inflammation in diabetic nephropathy.

Toll-like receptor 4 signaling is involved in IgA-stimulated mesangial cell activation

PURPOSE

Deposition of polymeric IgA1 in the kidney mesangium is the hallmark of IgA nephropathy, but the molecular mechanisms of IgA-mediated mesangial responses and inflammatory injuries remain poorly understood. We hypothesize that Toll-like receptor 4 (TLR4) is involved in IgA-induced mesangial cell activation.

MATERIALS AND METHODS

Mouse mesangial cells were stimulated with lipopolysaccharide (LPS) (1 μg/mL), IgA (20 μg/mL), or both, and TLR4 expression was measured by real time RT-PCR and Western blot. Intracellular responses to LPS or IgA were assessed by Western blot for ERK1/2, JNK, p38 MAP kinases (MAPKs), Iκ-Bα degradation and fibronectin secretion. MCP-1 secretion was assessed by ELISA. Small interfering RNA (siRNA) of TLR4 was used to confirm that the effects were caused by TLR4 activity.

RESULTS

LPS- or IgA-treatment upregulated the levels of TLR4 mRNA and protein in cultured MMC at 24 h. LPS and IgA induced rapid phosphorylation of MAPKs, but degradation of Iκ-Bα was observed only in LPS-treated MMC. LPS, but not IgA, induced increased secretion of MCP-1 and fibronectin at 24 h or 48 h. Combined LPS and IgA treatment did not cause additional increases in TLR4 mRNA and protein levels or Iκ-Bα degradation, and MCP-1 and fibronectin secretions were less than with LPS alone. LPS- or IgA-induced TLR4 protein levels and MAPK activation were inhibited by transfection with TLR4 siRNA.

CONCLUSION

These results indicate that the activation of MAPKs and MCP-1 secretion are mediated by TLR4, at least in part, in IgA-treated mesangial cells. TLR4 is involved in mesangial cell injury by induction of pro-inflammatory cytokines in IgA nephropathy.

Toll-like receptor 4 (TLR4) expression in human and murine pancreatic beta-cells affects cell viability and insulin homeostasis

Background

Toll-like receptor 4 (TLR4) is widely recognized as an essential element in the triggering of innate immunity, binding pathogen-associated molecules such as Lipopolysaccharide (LPS), and in initiating a cascade of pro-inflammatory events. Evidence for TLR4 expression in non-immune cells, including pancreatic β-cells, has been shown, but, the functional role of TLR4 in the physiology of human pancreatic β-cells is still to be clearly established. We investigated whether TLR4 is present in β-cells purified from freshly isolated human islets and confirmed the results using MIN6 mouse insulinoma cells, by analyzing the effects of TLR4 expression on cell viability and insulin homeostasis.

Results

CD11b positive macrophages were practically absent from isolated human islets obtained from non-diabetic brain-dead donors, and TLR4 mRNA and cell surface expression were restricted to β-cells. A significant loss of cell viability was observed in these β-cells indicating a possible relationship with TLR4 expression. Monitoring gene expression in β-cells exposed for 48h to the prototypical TLR4 ligand LPS showed a concentration-dependent increase in TLR4 and CD14 transcripts and decreased insulin content and secretion. TLR4-positive MIN6 cells were also LPS-responsive, increasing TLR4 and CD14 mRNA levels and decreasing cell viability and insulin content.

Conclusions

Taken together, our data indicate a novel function for TLR4 as a molecule capable of altering homeostasis of pancreatic β-cells.

Hydroxysafflor Yellow A suppresses thrombin generation and inflammatory responses following focal cerebral ischemia-reperfusion in rats

Hydroxysafflor Yellow A has been demonstrated to attenuate pressure overloaded hypertrophy in rats and inhibit platelet aggregation. Herein we found that Hydroxysafflor Yellow A prevented cerebral ischemia-reperfusion injury by inhibition of thrombin generation. In addition, treatment with Hydroxysafflor Yellow A significantly inhibited NF-kappaB p65 nuclear translation and p65 binding activity, both mRNA and protein levels of ICAM-1 and the infiltration of neutrophils. Mean while, Hydroxysafflor Yellow A had the capacity to improve neurological deficit scores, increase the number of the surviving hippocampal CA1 pyramidal cells and decrease the plasma angiotensin II level. These results illustrated that anti-cerebral ischemic mechanism of Hydroxysafflor Yellow A may be due to its suppression of thrombin generation and inhibition of thrombin-induced inflammatory responses by reducing angiotensin II content.

Innate immune receptors and autophagy: implications for autoimmune kidney injury

Inflammation is the immune system's response to infectious or noninfectious sources of danger. Danger recognition is facilitated by various innate immune receptor families including the Toll-like receptors (TLRs), which detect danger signals in extracellular and intracellular compartments. It is an evolving concept that renal damage triggers intrarenal inflammation by immune recognition of molecules that are being released by dying cells. Such danger-associated molecules act as immunostimulatory agonists to TLRs and other innate immune receptors and induce cytokine and chemokine secretion, leukocyte recruitment, and tissue remodeling. As a new entry to this concept, autophagy allows stressed cells to reduce intracellular microorganisms, protein aggregates, and cellular organelles by moving and subsequently digesting them in autophagolysosomes. Within the autophagolysosome, endogenous molecules and danger-associated molecules may be presented to TLRs or loaded onto the major histocompatibility complex and presented as autoantigens. Here we discuss the current evidence for the danger signaling concept in autoimmune kidney injury and propose that autophagy-related processing of self-proteins provides a source of immunostimulatory molecules and autoantigens. A better understanding of danger signaling should enable us to unravel yet unknown triggers for renal immunopathology and progressive kidney disease.

Cyclic stretch enhances the expression of toll-like receptor 4 gene in cultured cardiomyocytes via p38 MAP kinase and NF-kappaB pathway

Background

Toll-like receptor 4 (TLR4) plays an important role in innate immunity. The role of TLR4 in stretched cardiomyocytes is not known. We sought to investigate whether mechanical stretch could regulate TLR4 expression, as well as the possible molecular mechanisms and signal pathways mediating the expression of TLR4 by cyclic mechanical stretch in cardiomyocytes.

Methods

Neonatal Wistar rat cardiomyocytes grown on a flexible membrane base were stretched by vacuum to 20% of maximum elongation at 60 cycles/min. Western blot, real-time polymerase chain reaction, and promoter activity assay were performed. In vitro monocyte adhesion to stretched myocyte was detected.

Results

Cyclic stretch significantly increased TLR4 protein and mRNA expression after 2 h to 24 h of stretch. Addition of SB203580, TNF-α antibody, and p38α MAP kinase siRNA 30 min before stretch inhibited the induction of TLR4 protein. Cyclic stretch increased, while SB203580 abolished the phosphorylated p38 protein. Gel shifting assay showed significant increase of DNA-protein binding activity of NF-κB after stretch and SB203580 abolished the DNA-protein binding activity induced by cyclic stretch. DNA-binding complexes induced by cyclic stretch could be supershifted by p65 monoclonal antibody. Cyclic stretch increased TLR4 promoter activity while SB203580 and NF-κB siRNA decreased TLR4 promoter activity. Cyclic stretch increased adhesion of monocyte to cardiomyocytes while SB203580, TNF-α antibody, and TLR4 siRNA attenuated the adherence of monocyte. TNF-α and Ang II significantly increased TLR4 protein expression. Addition of losartan, TNF-α antibody, or p38α siRNA 30 min before Ang II and TNF-α stimulation significantly blocked the increase of TLR4 protein by AngII and TNF-α.

Conclusions

Cyclic mechanical stretch enhances TLR4 expression in cultured rat neonatal cardiomyocytes. The stretch-induced TLR4 is mediated through activation of p38 MAP kinase and NF-κB pathways. TLR4 up-regulation by cyclic stretch increases monocyte adherence.

Glucose-based peritoneal dialysis fluids downregulate toll-like receptors and trigger hyporesponsiveness to pathogen-associated molecular patterns in human peritoneal mesothelial cells

The objective of this study was to investigate the effects of glucose-based peritoneal dialysis (PD) fluids and icodextrin-based PD fluids on the expression of Toll-like receptor 2 (TLR2)/TLR4 and subsequent ligand-induced mitogen-activated protein kinase (MAPK) and NF-kappaB signaling and tumor necrosis factor alpha (TNF-alpha) and interleukin-1beta (IL-1beta) mRNA expression in human peritoneal mesothelial cells (HPMCs). A human peritoneal mesothelial cell line (HMrSV5) was stimulated with glucose-based and icodextrin-based peritoneal dialysis fluids. Cell viability was assessed using MTT [3-(4,5-dimethylthiazolyl)-2,5-diphenyl-2H-tetrazolium bromide]. TLR2/TLR4 expression was determined by real-time PCR, Western blotting, and an immunofluorescence assay. In addition, cells were pretreated with different PD solutions and then incubated with Pam3CSK4 or lipopolysaccharide (LPS), and the degrees of MAPK and NF-kappaB activation were reflected by detecting the phosphorylation levels of extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), p38, and p65, using a Western blot method. TNF-alpha and IL-1beta mRNA expression was measured by real-time PCR. Glucose-based peritoneal dialysis fluids suppressed the expression of TLR2 and TLR4 proteins in HPMCs. Challenge of cells with either Pam3CSK4 or LPS resulted in impaired TNF-alpha and IL-1beta production. Moreover, reduced TLR2 and TLR4 levels in glucose-based peritoneal dialysis solution-treated mesothelial cells were accompanied by reduced p42/44 (ERK1/2), JNK, p38 MAPK, and NF-kappaB p65 phosphorylation upon TLR ligand engagement. No significant changes in MAPK and NF-kappaB signaling and TNF-alpha and IL-1beta mRNA expression were observed in icodextrin-based PD solution-treated mesothelial cells. Glucose-based PD solution, but not icodextrin-based PD solution, downregulates expression of TLR2/TLR4 by human peritoneal mesothelial cells and triggers hyporesponsiveness to pathogen-associated molecular patterns.

Morg1 heterozygous mice are protected from acute renal ischemia-reperfusion injury

Renal ischemia and reperfusion injury leads to acute renal failure when proinflammatory and apoptotic processes in the kidney are activated. The increase in hypoxia-inducible transcription factor-alpha (HIF-alpha), an important transcription factor for several genes, can attenuate ischemic renal injury. We recently identified a novel WD-repeat protein designated Morg1 (MAPK organizer 1) that interacts with prolyl hydroxylase 3 (PHD3), an important enzyme involved in the regulation of HIF-1alpha and HIF-2alpha expression. While homozygous Morg1 -/- mice are embryonic lethal, heterozygous Morg1 +/- mice have a normal phenotype. We show here that Morg1 +/- were partially protected from renal ischemia-reperfusion injury compared with wild-type Morg1 +/+ animals. Morg1 +/- mice compared with wild-type animals revealed a stronger increase in HIF-1alpha and HIF-2alpha expression in the ischemic-reperfused kidney associated with enhanced serum erythropoietin levels. However, no significant expression of HIF-1alpha and HIF-2alpha was found in nonischemic kidneys without any difference between Morg1 +/- and Morg1 +/+ mice. Ischemic kidneys of Morg1 +/- mice expressed more erythropoietin mRNA than ischemic kidneys from wild-type animals. Renal ischemia in Morg1 +/- mice resulted in a decrease in renal inflammation and reduction of proinflammatory cytokines (MCP-1, IP-10, MIP-2) compared with wild-type mice. Furthermore, there was significantly less apoptosis and tubular damage in Morg1 +/- kidneys after ischemia-reperfusion, and this was also reflected in significantly improved renal function compared with wild-type. Thus Morg1 may be a novel therapeutic target to limit renal injury after ischemia-reperfusion.

Osteopontin modulates angiotensin II-induced inflammation, oxidative stress, and fibrosis of the kidney

Osteopontin, a secreted glycoprotein has been implicated in several renal pathological conditions such as those due to ureteral obstruction, ischemia, and cyclosporine toxicity. We studied its possible role in angiotensin II-mediated renal injury by infusing wild-type and osteopontin knockout mice with angiotensin II and found that it raised blood pressure and increased urinary albumin/creatinine ratios in both strains of mice. However, while wild-type mice responded to the infusion by macrophage infiltration and increased expression of alpha-smooth muscle actin, fibronectin, and transforming growth factor-beta; the osteopontin knockout mice developed none of these. Further, the knockout mice had increased expression of monocyte chemoattractant protein-1; NADPH oxidase subunits such as NOX2, gp47phox, and NOX4; and plasminogen activator inhibitor-1 compared to the wild type animals. Proximal tubule epithelial cells in culture treated with recombinant osteopontin and angiotensin II had increased alpha-smooth muscle actin and transforming growth factor-beta expression. The effect of angiotensin II was blocked by an antibody to osteopontin. In addition, osteopontin attenuated angiotensin II-induced plasminogen activator inhibitor-1 expression. These studies show that osteopontin is a promoter and an inhibitor of inflammation, oxidative stress, and fibrosis that is capable of modulating angiotensin II-induced renal damage.

Angiotensin II upregulates Toll-like receptor 4 and enhances lipopolysaccharide-induced CD40 expression in rat peritoneal mesothelial cells

OBJECTIVE

Activation of Toll-like receptor 4 (TLR4) in peritoneal mesothelial cells by endotoxin contributes to peritoneal inflammation and fibrosis. Here we investigated TLR4 expression induced by angiotensin II (Ang II) and functional consequences of nuclear factor-kappaB (NF-kappaB) activation and CD40 expression in rat peritoneal mesothelial cells (RPMCs).

METHODS

TLR4, CD40, tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) were determined by reverse transcription polymerase chain reaction (RT-PCR) and TLR4, IkappaBalpha, phospho-IkappaBalpha, NF-kappaB p65, and phospho-NF-kappaB p65 were analyzed by Western blot. The intracellular distribution of NF-kappaB p65 was detected by immunofluorescence.

RESULTS

Treatment of RPMCs with Ang II resulted in an increase in the expression of TLR4 mRNA and protein levels. Preincubation of RPMCs with Ang II significantly increased lipopolysaccharide (LPS)-induced phospho-IkappaBalpha and phospho-NF-kappaB p65 protein (P < 0.05 vs. LPS alone) and CD40, TNF-alpha, and IL-6 mRNA levels (P < 0.05 vs. LPS alone). A significantly increased nuclear staining of NF-kappaB p65 in cells treated with Ang II plus LPS was also observed.

CONCLUSIONS

Ang II upregulates the expression of TLR4 by RPMCs, resulting in enhanced NF-kappaB signaling and induction of CD40, TNF-alpha, and IL-6 expression. Locally produced Ang II in the peritoneum may have an amplified role in LPS-induced peritoneal inflammation.

Candesartan attenuates Angiotensin II-induced mesangial cell apoptosis via TLR4/MyD88 pathway

Angiotensin II (Ang II) can stimulate Toll-like receptor 4 (TLR4) expression in mesangial cells (MCs), but the role of TLR4 in the Ang II-induced apoptosis and the effect of candesartan on TLR4 expression remain unclear. Here, we report that Ang II-induced MC apoptosis in a time-dependent manner and up-regulated TLR4/MyD88 expression, and that the intracellular ROS was subsequently increased. We also show that candesartan attenuated the Ang II-induced MC apoptosis, and that this protective effect was dependent on decreased TLR4/MyD88 expression as well as reduced intracellular ROS formation. Furthermore, Ang II increased the apoptosis inducing factor protein level, while candesartan markedly reduced this increase. These results demonstrate that TLR4/MyD88 pathway was involved in the Ang II promoted MC apoptosis, which was related to TLR4/MyD88 mediated oxidative stress. These data also suggest that candesartan exerted anti-apoptotic effect as an antioxidant by modulating this pathway.

Losartan chemistry and its effects via AT1 mechanisms in the kidney

Besides the importance of the renin-angiotensin system (RAS) in the circulation and other organs, the local RAS in the kidney has attracted a great attention in research in last decades. The renal RAS plays an important role in the body fluid homeostasis and long-term cardiovascular regulation. All major components and key enzymes for the establishment of a local RAS as well as two important angiotensin II (Ang II) receptor subtypes, AT1 and AT2 receptors, have been confirmed in the kidney. In additional to renal contribution to the systemic RAS, the intrarenal RAS plays a critical role in the regulation of renal function as well as in the development of kidney disease. Notably, kidney AT1 receptors locating at different cells and compartments inside the kidney are important for normal renal physiological functions and abnormal pathophysiological processes. This mini-review focuses on: 1) the local renal RAS and its receptors, particularly the AT1 receptor and its mechanisms in physiological and pathophysiological processes; and 2) the chemistry of the selective AT1 receptor blocker, losartan, and the potential mechanisms for its actions in the renal RAS-mediated disease.

Toll-like receptors, wound healing, and carcinogenesis

Following acute injury, the concerted action of resident and nonresident cell populations evokes wound healing responses that entail a temporary increase in inflammation, extracellular matrix production, and proliferation to ultimately restore normal organ architecture. However, chronic injury evokes a perpetuating wound healing response promoting the development of fibrosis, organ failure, and cancer. Recent evidence points toward toll-like receptors (TLRs) as important regulators of inflammatory signals in wound healing. Here, we will review the activation of TLRs by different endogenous and bacterial TLR ligands during wound healing, and the contribution of TLR-induced signals to injury, fibrogenesis, regeneration, and carcinogenesis. We will discuss the hypothesis that TLRs act as sensors of danger signals in injured tissue to switch the wound healing response toward fibrogenesis and regeneration as a protective response to imminent danger at the cost of an increased long-term risk of developing scars and cancer.

PPAR{alpha} attenuates the proinflammatory response in activated mesangial cells

The activated mesangial cell is an important therapeutic target for the control of glomerulonephritis. The peroxisome proliferator-activated receptor alpha (PPARalpha) has attracted considerable attention for its anti-inflammatory effects; however, its roles in the mesangial cells remain unknown. To determine the anti-inflammatory function of PPARalpha in mesangial cells, wild-type and Ppara-null cultured mesangial cells were exposed to lipopolysaccharide (LPS). LPS treatment caused enhanced proinflammatory responses in the Ppara-null cells compared with wild-type cells, as revealed by the induction of interleukin-6, enhanced cell proliferation, and the activation of the nuclear factor (NF)-kappaB signaling pathway. In wild-type cells resistant to inflammation, constitutive expression of PPARalpha was undetectable. However, LPS treatment induced the significant appearance and substantial activation of PPARalpha, which would attenuate the proinflammatory responses through its antagonizing effects on the NF-kappaB signaling pathway. The induction of PPARalpha was coincident with the appearance of alpha-smooth muscle actin, which might be associated with the phenotypic changes of mesangial cells. Moreover, another examination using LPS-injected wild-type mice demonstrated the appearance of PPARalpha-positive cells in glomeruli, suggesting in vivo correlation with PPARalpha induction. These results suggest that PPARalpha plays crucial roles in the attenuation of inflammatory response in activated mesangial cells. PPARalpha might be a novel therapeutic target against glomerular diseases.

Transcription Factor PU.1 Controls Transcription Start Site Positioning and Alternative TLR4 Promoter Usage

Human and mouse show markedly different sensitivities toward bacterial endotoxins, and recent evidence suggests that a species-specific regulation of the lipopolysaccharide receptor Toll-like receptor 4 (Tlr4) may contribute to this phenomenon. To gain further insight into mechanisms of Tlr4 regulation, we conducted a detailed in vivo and in vitro study of the murine Tlr4 gene, including analysis of transcription start site location, transcription factor occupancy, and activities of its proximal regulatory sequences. Our analyses identified a PU.1-dependent myeloid promoter, which is conserved between humans and mouse. We also identified an additional, distal promoter, located approximately 200 bp upstream of the myeloid-specific promoter, which is a functional target of E-box binding factors. In contrast to humans, where non-myeloid cells utilize both promoters, the distal Tlr4 promoter initiates all Tlr4 transcripts in murine non-myeloid cells, indicating that species-specific differences in TLR4 mRNA regulation may primarily exist in non-myeloid cell types. Interestingly, PU.1 null murine myeloid progenitor cells predominantly use the distal promoter, and the conditional induction of PU.1 expression in these cells leads to the rapid switch of transcription initiation to the proximal myeloid promoter. This indicates a direct role for PU.1 in determining the transcriptional start site and in recruiting the basal transcription machinery to myeloid promoters.

Influence of angiotensin II on expression of toll-like receptor 2 and maturation of dendritic cells in chronic cyclosporine nephropathy

BACKGROUND

Angiotensin (Ang) II plays an important role in immune regulation. We evaluate the influence of the renin-angiotensin system (RAS) in the innate immune response caused by cyclosporine A (CsA)-induced renal injury.

METHODS

Two separate studies were performed in Sprague Dawley rats. First, losartan (LSRT, 10 mg/kg per day) was concurrently administered with CsA (15 mg/kg per day) for 28 days. Second, AngII (435 ng/kg/min) was infused with or without LSRT for 14 days.

RESULTS

AngII blockade with LSRT decreased toll-like receptor (TLR) 2 mRNA and protein expression, expression of tumor necrosis factor (TNF)-alpha mRNA, and expression of major histocompatibility complex class II antigen, which was upregulated in CsA-induced renal injury. The increased number of matured dendritic cells (DCs) in CsA-induced renal injury was also decreased by concomitant treatment of LSRT. Direct infusion of AngII increased TNF-alpha mRNA, TLR2 mRNA, and protein and the number of DCs, compared with the control rat kidney. In contrast, concomitant treatment of LSRT decreased all parameters.

CONCLUSION

AngII plays a pivotal role in activating the innate immune response in CsA-induced renal injury.

Differential regulation of Toll-like receptor 4 gene expression in renal cells by angiotensin II: dependency on AP1 and PU.1 transcriptional sites

BACKGROUND

Toll-like receptor 4 (TLR4) is involved in the sensing of lipopolysaccharide and, therefore, plays a central role in innate immune responses to gram-negative bacteria. Interestingly, TLR4 expression occurs within the kidney. We have previously demonstrated that angiotensin II (ANG II) upregulates TLR4 expression on mesangial cells. However, the factors controlling transcriptional activation of the Tlr4 gene in mesangial cells are not known, and the specificity of this response for other renal cells is unclear.

METHODS

Cultured murine proximal tubular cells (mouse cortical tubule cell line; MCT cells), murine mesangial cells (MMCs), and murine podocytes were treated with ANG II. The expression of ANG II receptor mRNA and TLR4 mRNA and protein was determined by polymerase chain reaction and Western blotting. The transcriptional activity of wild-type and mutant mouse TLR4 promoter reporter constructs was determined upon transient transfection of the three cell types.

RESULTS

Although MMCs, podocytes, and syngeneic proximal MCT cells similarly expressed ANG II receptors, ANG II stimulated TLR4 mRNA and protein expression in MMCs and podocytes only. A mouse TLR4 promoter construct (-518/+129), previously shown to contain all important transcriptional regulatory elements in various cell types, was activated by ANG II in MMCs and podocytes, but not in MCT cells. Mutation of a proximal PU.1-binding consensus site or an AP1 site abolished ANG-II-mediated transcriptional activation of the TLR4 promoter. Finally, basal transcription of the Tlr4 gene depended in all three cell lines on an intact AP1 site and additionally on the proximal PU.1 site in MMCs.

CONCLUSIONS

ANG II stimulates TLR4 transcription through AP1 and PU.1 sites in a cell-specific manner. Since the intrarenal ANG II concentrations are enhanced in many pathophysiological situations, ANG-II-stimulated transcription of TLR4 on MMCs and podocytes may contribute to renal inflammation.

Renin-angiotensin-aldosterone system and progression of renal disease

Inhibition of the renin-angiotensin-aldosterone system (RAAS) is one of the most powerful maneuvers to slow progression of renal disease. Angiotensin II (AngII) has emerged in the past decade as a multifunctional cytokine that exhibits many nonhemodynamic properties, such as acting as a growth factor and profibrogenic cytokine, and even having proinflammatory properties. Many of these deleterious functions are mediated by other factors, such as TGF-beta and chemoattractants that are induced in the kidney by AngII. Moreover, understanding of the RAAS has become much more complex in recent years with the identification of novel peptides (e.g., AngIV) that could bind to specific receptors, elucidating deleterious effects, and non-angiotensin-converting enzyme (ACE)-mediated generation of AngII. The ability of renal cells to produce AngII in a concentration that is much higher than what is found in the systemic circulation and the observation that aldosterone may be engaged directly in profibrogenic processes independent of hypertension have added to the complexity of the RAAS. Even renin has now been identified to have a "life on its own" and mediates profibrotic effects via binding to specific receptors. Finally, drugs that are used to block the RAAS, such as ACE inhibitors or certain AngII type 1 receptor antagonists, may have properties on cells independent of AngII (ACE inhibitor-mediated outside-inside signaling and peroxisome proliferator-activated receptor-gamma stimulatory effects of certain sartanes). Although blockade of the RAAS with ACE inhibitors, AngII type 1 receptor antagonists, or the combination of both should be part of every strategy to slow progression of renal disease, a better understanding of the novel aspects of the RAAS should contribute to the development of innovative strategies not only to completely halt progression but also to induce regression of human renal disease.