RAGE does not contribute to renal injury and damage upon ischemia/reperfusion-induced injury.

Item does not contain fulltextThe receptor for advanced glycation end products (RAGE) mediates a variety of inflammatory responses in renal diseases, but its role in renal ischemia/reperfusion (I/R) injury is unknown. We showed that during renal I/R, RAGE ligands HMGB1 and S100B are expressed. However, RAGE deficiency does not affect renal injury and function upon I/R-induced injury

The Role of Toll-Like Receptor 2 in Inflammation and Fibrosis during Progressive Renal Injury

Tissue fibrosis and chronic inflammation are common causes of progressive organ damage, including progressive renal disease, leading to loss of physiological functions. Recently, it was shown that Toll-like receptor 2 (TLR2) is expressed in the kidney and activated by endogenous danger signals. The expression and function of TLR2 during renal fibrosis and chronic inflammation has however not yet been elucidated. Therefore, we studied TLR2 expression in human and murine progressive renal diseases and explored its role by inducing obstructive nephropathy in TLR2−/− or TLR2+/+ mice. We found that TLR2 is markedly upregulated on tubular and tubulointerstitial cells in patients with chronic renal injury. In mice with obstructive nephropathy, renal injury was associated with a marked upregulation and change in distribution of TLR2 and upregulation of murine TLR2 danger ligands Gp96, biglycan, and HMGB1. Notably, TLR2 enhanced inflammation as reflected by a significantly reduced influx of neutrophils and production of chemokines and TGF-β in kidneys of TLR2−/− mice compared with TLR2+/+ animals. Although, the obstructed kidneys of TLR2−/− mice had less interstitial myofibroblasts in the later phase of obstructive nephropathy, tubular injury and renal matrix accumulation was similar in both mouse strains. Together, these data demonstrate that TLR2 can initiate renal inflammation during progressive renal injury and that the absence of TLR2 does not affect the development of chronic renal injury and fibrosis

Mitochondrial DNA is Released in Urine of SIRS Patients With Acute Kidney Injury and Correlates With Severity of Renal Dysfunction

Systemic inflammatory response syndrome (SIRS) is characterized by the activation of the innate immune system resulting in stimulation of inflammatory responses, coagulation, and platelet activation that may contribute to complication such as the development of acute kidney injury (AKI). AKI importantly worsens the outcome of SIRS, implying the existence of a detrimental cross talk via systemic messages. Mitochondria are a source of damage-associated molecular patterns (DAMPs) and are thought to form a molecular link between tissue injury and stimulation of innate immunity. The role of mitochondrial DNA (mtDNA) in the cross talk between the onset of SIRS and subsequent development of AKI is unknown. Hence, we performed a case control study in critically ill patients with SIRS diagnosed with or without AKI, in which we determined mtDNA levels in plasma and urine, and correlated these to markers of renal impairment, inflammation, coagulation, and platelet activation. In addition, we exposed mice, primary renal tubular epithelial cells (TECs), and platelets to mtDNA or purified mitochondrial ligands, and measured their response to elucidate underlying pathophysiological mechanisms. Our data reveal that increased systemic mtDNA levels in SIRS patients do not correlate with systemic inflammation and renal disease activity. Moreover, AKI does not have an additional effect on circulating mtDNA levels. In contrast, we found that urinary mtDNA levels correlate with an elevated albumin creatinine ratio (ACR) as well as with increased urinary markers of inflammation, coagulation, and platelet activation. Both renal TECs and platelets respond to mtDNA and mtDNA ligands, leading to increased expression of, respectively, inflammatory cytokines and P-selectin. Moreover, activation of platelets results in mtDNA release. Together, these data suggest that circulating mtDNA is probably not important in the detrimental cross talk between SIRS and AKI, whereas renal mtDNA accumulation may be related to intrarenal inflammation, coagulation processes, and renal dysfunction in the pathophysiology of SIR

Toll-like receptor-4 coordinates the innate immune response of the kidney to renal ischemia/reperfusion injury.

Toll-like receptors (TLRs) can detect endogenous danger molecules released upon tissue injury resulting in the induction of a proinflammatory response. One of the TLR family members, TLR4, is constitutively expressed at RNA level on renal epithelium and this expression is enhanced upon renal ischemia/reperfusion (I/R) injury. The functional relevance of this organ-specific upregulation remains however unknown. We therefore investigated the specific role of TLR4 and the relative contribution of its two downstream signaling cascades, the MyD88-dependent and TRIF-dependent cascades in renal damage by using TLR4-/-, MyD88-/- and TRIF-mutant mice that were subjected to renal ischemia/reperfusion injury. Our results show that TLR4 initiates an exaggerated proinflammatory response upon I/R injury, as reflected by lower levels of chemokines and infiltrating granulocytes, less renal damage and a more preserved renal function in TLR4-/- mice as compared to wild type mice. In vitro studies demonstrate that renal tubular epithelial cells can coordinate an immune response to ischemic injury in a TLR4-dependent manner. In vivo we found that epithelial- and leukocyte-associated functional TLR4 contribute in a similar proportion to renal dysfunction and injury as assessed by bone marrow chimeric mice. Surprisingly, no significant differences were found in renal function and inflammation in MyD88-/- and TRIF-mutant mice compared with their wild types, suggesting that selective targeting of TLR4 directly may be more effective for the development of therapeutic tools to prevent I/R injury than targeting the intracellular pathways used by TLR4. In conclusion, we identified TLR4 as a cellular sentinel for acute renal damage that subsequently controls the induction of an innate immune response

Expression (A) and activity (B) of the MMP-mediated collagen degradation pathway in TLR2^+/+ (□) and TLR2^−/− (▪) mice 3, 7, and 14 days after UUO or in contralateral non-obstructed kidneys.

<p>Both MMPs and TIMPs were significantly reduced in TLR2^−/− mice compared to TLR2^+/+ mice 14 days after UUO-injury (A). Data are mean and SEM of six mice per group, *p<0.05. Gel zymography (B) illustrates that renal MMP-9 activity was lower in kidneys TLR2^−/− mice at this time point. No difference between TLR2^−/− and TLR2^+/+ mice was observed for MMP-2 activity at 14 days post-UUO.</p

Total and active TGF-β levels in kidneys from TLR2^+/+ (□) and TLR2^−/− (▪) mice 3, 7, and 14 days after UUO or in contralateral non-obstructed kidneys.

<p>The amount of total TGFβ and activated TGFβ was significantly lower in kidneys from TLR2^−/− mice compared to TLR2^−/− mice 7 days after UUO-induced injury. Data are mean and SEM of six mice per group. *p<0.05.</p

Expression and localization of TLR2 in UUO-injured kidney of TLR2^+/+ mice at several time points.

<p>The amount of TLR2 mRNA (A) and protein (B) was markedly upregulated after UUO injury. Data are mean and SEM of six mice per group; *p<0.05. High magnification images (inserts) show that 3 and 7 days after UUO TLR2 was mainly located at the apical side of renal tubules in both cortex and medulla. After 14 days, apical tubular TLR2 staining in cortex and medulla is lost and extended into the cytoplasm and the interstitium.</p

TLR2 expression and localization in renal biopsy specimens of patients with obstructive hydronephrosis (B), severe forms of IgA nephropathy (C, D) or in control renal biopsy specimens (A).

<p>TLR2 was clearly upregulated in kidneys of patients with obstructive hydronephrosis or IgA nephropathy and mainly expressed by tubulointerstitial cells. Some expression was found at the apical side of renal tubules (asterisks, D). Double staining showed coexpression of various myofibroblasts (blue) (asterisks E), and numerous macrophages (blue) with TLR2 (red) (asterisks F). No immunoreactivity of TLR2 was observed in negative control sections derived from IgA nephropathy patients (insert A, primary antibody omitted).</p

Apoptotic and proliferating tubular cells in kidneys from TLR2^+/+ (□) and TLR2^−/− (▪) mice 3, 7, and 14 days after UUO or in contralateral kidneys.

<p>The number of apoptotic (t = 7) tubular cells and proliferating (t = 14) cells were significantly lower in kidneys from TLR2^−/− mice compared to kidneys from TLR2^+/+ animals as counted in 10 randomly selected high-power fields. Cells were counted on renal tissue sections stained for active caspase-3 (apoptosis) and Ki67 (proliferation). Due to severe tubular atrophy, it is impossible to identify apoptotic TECs after 14 days. Therefore we analyzed at this time point the total amount of apoptotic cells (both interstitial cells and tubular cells). Data are mean and SEM of six mice per group, *p<0.05.</p