Sik Lee

Distinct Macrophage Phenotypes Contribute to Kidney Injury and Repair

The ischemically injured kidney undergoes tubular cell necrosis and apoptosis, accompanied by an interstitial inflammatory cell infiltrate. In this study, we show that iNos-positive proinflammatory (M1) macrophages are recruited into the kidney in the first 48 hours after ischemia/reperfusion injury, whereas arginase 1- and mannose receptor-positive, noninflammatory (M2) macrophages predominate at later time points. Furthermore, depletion of macrophages before ischemia/reperfusion diminishes kidney injury, whereas depletion at 3 to 5 days after injury slows tubular cell proliferation and repair. Infusion of Ifnγ-stimulated, bone marrow-derived macrophages into macrophage-depleted mice at the time of kidney reperfusion restored injury to the level seen without macrophage depletion, suggesting that proinflammatory macrophages worsen kidney damage. In contrast, the appearance of macrophages with the M2 phenotype correlated with the proliferative phase of kidney repair. In vitro studies showed that IFNγ-stimulated, proinflammatory macrophages begin to express markers of M2 macrophages when cocultured with renal tubular cells. Moreover, IL-4-stimulated macrophages with an M2 phenotype, but not IFNγ-stimulated proinflammatory macrophages, promoted renal tubular cell proliferation. Finally, tracking fluorescently labeled, IFNγ-stimulated macrophages that were injected after injury showed that inflammatory macrophages can switch to an M2 phenotype in the kidney at the onset of kidney repair. Taken together, these studies show that macrophages undergo a switch from a proinflammatory to a trophic phenotype that supports the transition from tubule injury to tubule repair.

Angiogenic role of adrenomedullin through activation of Akt, mitogen-activated protein kinase, and focal adhesion kinase in endothelial cells

Adrenomedullin (AM) is a multifunctional peptide in human pheochromocytoma. To evaluate whether AM could be an angiogenic factor, we examined its effect on kinases and angiogenic processes. AM induced tyrosine phosphorylation of Akt and mitogen‐activated protein kinase (MAPK)/extracellular signal‐regulated kinase1/2 (ERK1/2) by using distinct signaling pathways in human umbilical vein endothelial cells (HUVECs). AM also phosphorylated focal adhesion kinase, and phosphatidylinositol 3′‐kinase inhibitor inhibited AM‐induced focal adhesion kinase phosphorylation. Pretreatment with high concentrations of AM22‐52, a putative AM receptor antagonist, partially suppressed AM‐induced phosphorylation of Akt, ERK1/2, and focal adhesion kinase. AM and vascular endothelial growth factor produced increases in DNA synthesis and migration in HUVECs. AM induced tube formation in HUVECs, and its effect was inhibited by pretreatment with phosphatidylinositol 3′‐kinase inhibitor or ERK1/2 inhibitor. AM induced sprouting in porcine pulmonary arterial endothelial cells and promoted neovessel formation in a mouse Matrigel plug assay. Inhibitors of phosphatidylinositol 3′‐kinase and ERK1/2 inhibited AM‐induced endothelial sprouting in vitro and angiogenesis in vivo. AM exerts angiogenic activity through activation of Akt, MAPK, and focal adhesion kinase in endothelial cells.

Genistein protects the kidney from cisplatin-induced injury.

Oxidative stress and inflammation contribute to the pathogenesis of cisplatin-induced nephrotoxicity. We found that genistein, a tyrosine kinase inhibitor with broad specificities, and which also has estrogen-like activity, had protective effects on cisplatin-induced renal injury in mice. Genistein significantly decreased reactive oxygen species production, the expression of intercellular adhesion molecule-1 and monocyte chemoattractant protein-1 proteins, as well as the translocation of the p65 subunit of nuclear factor-kappaB into the nucleus and the infiltration of macrophages, all of which were increased in the kidney by cisplatin treatment. Genistein also decreased cisplatin-induced apoptosis by regulating p53 induction in kidney. Genistein significantly reduced reactive oxygen species production in cisplatin-treated normal human kidney HK-2 cells. These studies show that genistein or similar compounds might be useful in prevention of cisplatin-induced renal injury.

SIRT1 activation by resveratrol ameliorates cisplatin-induced renal injury through deacetylation of p53

Nephrotoxicity is one of the important dose-limiting factors during cisplatin treatment. There is a growing body of evidence that activation of p53 has a critical role in cisplatin-induced renal apoptotic injury. The nicotinamide adenine dinucleotide-dependent protein deacetylase SIRT1 decreases apoptosis through deacetylating of p53, and resveratrol is known as an activator of SIRT1. To study the role of SIRT1 in cisplatin-induced renal injury through interaction with p53, mouse proximal tubular cells (MPT) were treated with cisplatin and examined the expression level of SIRT1, acetylation of p53, PUMA-α, Bax, the cytosolic/mitochondrial cytochrome c ratio, and active caspase-3. The expression of SIRT1 was decreased by cisplatin. Resveratrol, a SIRT1 activator, ameliorated cisplatin-induced acetylation of p53, apoptosis, and cytotoxicity in MPT cells. In addition, resveratrol remarkably blocked cisplatin-induced decrease of Bcl-xL in MPT cells. Further specific SIRT1 inhibition with EX 527 or small interference RNA specific to SIRT1 reversed the effect of resveratrol on cisplatin-induced toxicity. Inhibition of p53 by pifithrin-α reversed the effect of EX527 in protein expression of PUMA-α, Bcl-xL, and caspase-3 and cytotoxicity in MPT cells. SIRT1 protein expression after cisplatin treatment was significantly decreased in the kidney. SIRT1 activation by resveratrol decreased cisplatin-induced apoptosis while improving the glomerular filtration rate. Taken together, our findings suggest that the modulation of p53 by SIRT1 could be a possible target to attenuate cisplatin-induced kidney injury.

Alpha-lipoic acid attenuates cisplatin-induced acute kidney injury in mice by suppressing renal inflammation

BACKGROUND Cisplatin is a chemotherapeutic agent used in treatment of malignant tumours. However, cisplatin produces various side effects, such as nephrotoxicity, neurotoxicity, emetogenesis and ototoxicity. Inflammation is an important mechanism of cisplatin nephrotoxicity. Alpha-lipoic acid (alpha-LA) has anti-inflammatory effects that inhibit both adhesion molecule expression in human endothelial cells and monocyte adhesion by suppressing the nuclear factor-kappaB (NF-kappaB) signalling pathway. The goals of this study were to investigate the anti-inflammatory effects of alpha-LA during cisplatin-induced renal injury and to examine the mechanisms of protection. METHODS C57BL/6 mice were given cisplatin (20 mg/kg) with or without alpha-LA treatment (100 mg/kg for 3 days). Renal function, histological changes, adhesion molecule expression and inflammatory cell infiltration were examined. The effect of alpha-LA on NF-kappaB activity was evaluated by examining nuclear translocation and phosphorylation of NF-kappaB p65 subunits in kidney tissue. RESULTS Cisplatin-induced decreases in renal function, measured by blood urea nitrogen, serum creatinine level and renal tubular injury scores, were attenuated by alpha-LA treatment. alpha-LA decreased the tissue levels of tumour necrosis factor-alpha, the expression of intercellular adhesion molecule-1 (ICAM-1) and monocyte chemoattractant protein-1 (MCP-1), and suppressed the infiltration of CD11b-positive macrophages. alpha-LA also attenuated the cisplatin-induced increases in the phosphorylation and nuclear translocation of NF- kappaB p65 subunits in kidney tissue. CONCLUSIONS These results suggest that alpha-LA treatment ameliorates cisplatin-induced acute kidney injury by reducing inflammatory adhesion molecule expression and NF-kappaB activity.

Inhibition of Podocyte FAK Protects against Proteinuria and Foot Process Effacement

Focal adhesion kinase (FAK) is a nonreceptor tyrosine kinase that plays a critical role in cell motility. Movement and retraction of podocyte foot processes, which accompany podocyte injury, suggest focal adhesion disassembly. To understand better the mechanisms by which podocyte foot process effacement leads to proteinuria and kidney failure, we studied the function of FAK in podocytes. In murine models, glomerular injury led to activation of podocyte FAK, followed by proteinuria and foot process effacement. Both podocyte-specific deletion of FAK and pharmacologic inactivation of FAK abrogated the proteinuria and foot process effacement induced by glomerular injury. In vitro, podocytes isolated from conditional FAK knockout mice demonstrated reduced spreading and migration; pharmacologic inactivation of FAK had similar effects on wild-type podocytes. In conclusion, FAK activation regulates podocyte foot process effacement, suggesting that pharmacologic inhibition of this signaling cascade may have therapeutic potential in the setting of glomerular injury.

COMP–Angiopoietin-1 Ameliorates Renal Fibrosis in a Unilateral Ureteral Obstruction Model

Injury to the renal microvasculature may be a major factor in the progression of renal disease; therefore, protection of endothelial cells (EC) in renal vasculature may have a therapeutic role in renal fibrosis. Recently, a soluble, stable, and potent angiopoietin-1 (Ang1) variant, cartilage oligomeric matrix protein (COMP)-Ang1, was developed. The contribution of COMP-Ang1 in renal interstitial fibrosis, however, remains to be clarified. This study investigated the effects of COMP-Ang1 on peritubular capillary EC in the renal cortex and the renal fibrogenic process that is triggered by unilateral ureteral obstruction. COMP-Ang1 preserved renal platelet-EC adhesion molecule-1-and Tie2-positive EC. Morphologic examination indicated less tubular injury and tubulointerstitial fibrosis in mice that received COMP-Ang1 than vehicle-treated mice. Interstitial type I collagen and myofibroblast accumulation were significantly suppressed by COMP-Ang1 treatment. COMP-Ang1 increased Tie2 and Akt phosphorylation in ureteral obstructed kidneys. Renal surface microvasculature and renal blood flow were higher after treatment with COMP-Ang1 than with vehicle. COMP-Ang1 treatment decreased monocyte/macrophage infiltration, tissue levels of TGF-beta1, and Smad 2/3 phosphorylation and increased Smad 7 in the obstructed kidney. These results demonstrate that COMP-Ang1 treatment can decrease the progression of renal fibrosis in unilateral ureteral obstruction. COMP-Ang1 may be an endothelium-specific therapeutic modality in fibrotic renal disease.

Tumor Necrosis Factor-α Induces Fractalkine Expression Preferentially in Arterial Endothelial Cells and Mithramycin A Suppresses TNF-α-Induced Fractalkine Expression

Fractalkine is an unusual tumor necrosis factor (TNF)-α-induced chemokine. The molecule is tethered to cells that express it and produces strong and direct adhesion to leukocytes expressing fractalkine receptor. However, the potential mechanism and significance of TNF-α-induced fractalkine expression in vascular endothelial cells are poorly understood. Here we show that in primary cultured endothelial cells TNF-α-induced fractalkine mRNA expression is mediated mainly through phosphatidylinositol 3′-kinase activation and nuclear factor (NF)-κB mediated transcriptional activation, along with GC-rich DNA-binding protein-mediated transcription. Interestingly, GC-rich DNA-binding protein inhibitors, mithramycin A and chromomycin A3, strongly suppressed TNF-α-induced fractalkine mRNA expression, possibly through inhibition of transcriptional activities by NF-κB and Sp1. In fact, direct inhibition of NF-κB and Sp1 bindings by decoy oligonucleotides suppressed TNF-α-induced fractalkine expression. Histologically, TNF-α-induced fractalkine expression was observed markedly in arterial and capillary endothelial cells, endocardium, and endothelium of intestinal villi, and slightly in venous endothelial cells, but not at all in lymphatic endothelial cells of intestine. Mithramycin A markedly suppressed TNF-α-induced fractalkine expression in vivo. These results indicate that TNF-α-stimulated fractalkine expression could act as part of arterial endothelial adhesion to leukocytes and monocytes during inflammation and atherosclerosis. NF-κB and Sp1 inhibitors such as mithramycin A may provide a pharmacological approach to suppressing these processes.

Protective Effect of α-Lipoic Acid in Lipopolysaccharide-Induced Endothelial Fractalkine Expression

Fractalkine is a unique chemokine that functions as a chemoattractant as well as an adhesion molecule on endothelial cells activated by proinflammatory cytokines. Alpha-lipoic acid (LA), a naturally occurring dithiol compound, is an essential cofactor for mitochondrial bioenergetic enzymes. LA improves glycemic control, reduces diabetic polyneuropathies, and mitigates toxicity associated with heavy metal poisoning. The effects of LA on processes associated with sepsis, however, are unknown. We evaluated the antiinflammatory effect of LA on fractalkine expression in a lipopolysaccharide-induced endotoxemia model. Tumor necrosis factor-&agr; (TNF-&agr;) and interleukin-1&bgr; (IL-1&bgr;) significantly induced fractalkine mRNA and protein expression in endothelial cells. LA strongly suppressed TNF-&agr;– or IL-1&bgr;–induced fractalkine expression in endothelial cells by suppressing the activities of nuclear factor-&kgr;B and specificity protein-1. LA also decreased TNF-&agr;– or IL-1&bgr;–stimulated monocyte adhesion to human umbilical vein endothelial cells. As shown by immunohistochemistry, fractalkine protein expression was markedly increased by treatment with lipopolysaccharide in arterial endothelial cells, endocardium, and endothelium of intestinal villi. LA suppressed lipopolysaccharide-induced fractalkine protein expression and infiltration of endothelin 1-positive cells into the heart and intestine in vivo. LA protected against lipopolysaccharide-induced myocardial dysfunction and improved survival in lipopolysaccharide-induced endotoxemia. These results suggest that LA could be an effective agent to reduce fractalkine-mediated inflammatory processes in endotoxemia.

COMP-angiopoietin-1 decreases lipopolysaccharide-induced acute kidney injury.

During sepsis endothelial dysfunction is an important pathogenetic mechanism in acute kidney injury (AKI). Lipopolysaccharide (LPS)-induced endotoxemia is associated with renal hemodynamic changes such as alterations of renal blood flow (RBF), vascular resistance, and glomerular filtration rate. We used adenoviral delivery of an engineered variant of native angiopoietin-1 (COMP-angiopoietin-1) containing anti-inflammatory and anti-permeability functions, to determine if regulation of renal endothelial cell dysfunction may have a beneficial role in preventing AKI during LPS-induced endotoxemia in mice. This treatment prevented the endotoxin-induced decrease of RBF and mean arterial pressure while improving glomerular filtration rate. Treatment also mitigated the effects of LPS on renal intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 protein expression, the number of ER-HR3-positive macrophages that infiltrated the kidney, serum nitrate/nitrite levels, renal inducible nitric oxide synthase protein expression, the induction of tubular epithelial reactive oxygen and nitrogen species, and renal microvascular permeability. Our findings show that COMP-angiopoietin-1, an endothelium-oriented therapeutic agent, protects against AKI caused by endotoxemia.