IL-6/IL-6R Axis Plays a Critical Role in Acute Kidney Injury

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IL-6 can mediate proinflammatory effects, and IL-6 receptor (IL-6R) blockade as a treatment for inflammatory diseases has entered clinical practice. However, opposing effects of IL-6 have been observed in models of GN. Although IL-6 is proinflammatory in murine lupus nephritis, protective effects have been observed for IL-6 in the nephrotoxic nephritis (NTN) model of acute crescentic GN. In light of the potential dangers of IL-6-directed treatment, we studied the mechanisms underlying the contradictory findings in GN. IL-6 can signal through the membrane-bound IL-6R, which is expressed only on hepatocytes and certain leukocytes (classic), or through the soluble IL-6R, which binds the ubiquitously expressed gp130 (alternative). Preemptive treatment of mice with anti-IL-6R or anti-IL-6 worsened NTN, whereas selective blockade of alternative IL-6 signaling by the fusion protein sgp130Fc did not. FACS analysis of mouse spleen cells revealed proinflammatory macrophages express the highest levels of IL-6Ra, and in vitro treatment with IL-6 blocked macrophage proliferation. Furthermore, proinflammatory macrophages were expanded during inflammation in IL-6 2/2 mice. Late application of anti-IL-6 after establishment of adaptive nephritogenic immunity was sufficient to aggravate NTN within 2.5 days, a period when macrophages are active. Finally, NTN was aggravated in mice with macrophage-specific impairment of IL-6 classic signaling, coincident with enhanced macrophage proliferation and accumulation in the kidney. Our data thus reveal a novel mechanism in which IL-6-mediated dampening of macrophage activation protects tissues from overshooting immune responses. This finding has important implications for potential IL-6-directed therapies and supports the careful choice of recipient patients and timing.

Section: Discussionmentioning

confidence: 99%

“…In addition to the anti-inflammatory role of IL-6 in NTN, a more recent study found protective effects of IL-6 trans-signaling in AKI. 43 Regarding the situation in humans, IL-6 secretion from PBMCs correlated with renal disease activity in lupus nephritis. 44 Urinary IL-6 has also been suggested as a marker for renal inflammation in different forms of GN.…”

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confidence: 99%

Inflammation-Induced IL-6 Functions as a Natural Brake on Macrophages and Limits GN

Luig¹,

Kluger²,

Goerke³

et al. 2015

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“…IL-6 is a major proinflammatory mediator well characterized in the orchestration of the inflammatory response following acute renal insult 4,5 and has been shown to be a superior marker in renal patients compared with other proinflammatory candidates, such as the systemic inflammatory marker C-reactive protein. [6][7][8][9] On the other hand, IL-10, while not as established in kidney injury, is appreciated to be a prototypical anti-inflammatory cytokine that carries out the critical function of modulating inflammation.…”

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confidence: 99%

Plasma IL-6 and IL-10 Concentrations Predict AKI and Long-Term Mortality in Adults after Cardiac Surgery

Zhang

Garg

Coca

et al. 2015

169

119

Inflammation has an integral role in the pathophysiology of AKI. We investigated the associations of two biomarkers of inflammation, plasma IL-6 and IL-10, with AKI and mortality in adults undergoing cardiac surgery. Patients were enrolled at six academic centers (n=960). AKI was defined as a $50% or $0.3-mg/dl increase in serum creatinine from baseline. Pre-and postoperative IL-6 and IL-10 concentrations were categorized into tertiles and evaluated for associations with outcomes of in-hospital AKI or postdischarge all-cause mortality at a median of 3 years after surgery. Preoperative concentrations of IL-6 and IL-10 were not significantly associated with AKI or mortality. Elevated first postoperative IL-6 concentration was significantly associated with higher risk of AKI, and the risk increased in a dose-dependent manner (second tertile adjusted odds ratio [OR], 1.61 [95% confidence interval (95% CI), 1.10 to 2.36]; third tertile adjusted OR, 2.13 [95% CI, 1.45 to 3.13]). First postoperative IL-6 concentration was not associated with risk of mortality; however, the second tertile of peak IL-6 concentration was significantly associated with lower risk of mortality (adjusted hazard ratio, 0.75 [95% CI, 0.57 to 0.99]). Elevated first postoperative IL-10 concentration was significantly associated with higher risk of AKI (adjusted OR, 1.57 [95% CI, 1.04 to 2.38]) and lower risk of mortality (adjusted HR, 0.72 [95% CI, 0.56 to 0.93]). There was a significant interaction between the concentration of neutrophil gelatinase-associated lipocalin, an established AKI biomarker, and the association of IL-10 concentration with mortality (P=0.01). These findings suggest plasma IL-6 and IL-10 may serve as biomarkers for perioperative outcomes. AKI is a common complication of cardiac surgery, leading to increased morbidity and mortality. 1 Current paradigms of diagnosis and treatment are based on serum creatinine and are thus insensitive. These limitations have spurred the search for novel proteins that are involved in the process of kidney injury. 2,3 While AKI is traditionally recognized and diagnosed by renal functional impairment and structural damage, it is also an inflammatory condition. Understanding and measuring the processes of inflammation in AKI may provide unique tools for its assessment and prediction.To this end, we developed an ancillary study to our large, multicenter cohort study of adult patients

“…12 STAT3 is also activated in renal tubule cells during AKI and plays a critical role in the response to injury. 13 Following AKI, SOCS3 levels are depressed, corresponding with increased STAT3 activity associated with the tubule repair process. 14 Both the loss and overexpression of SOCS3 have been associated with renal disease.…”

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confidence: 99%

The Cleaved Cytoplasmic Tail of Polycystin-1 Regulates Src-Dependent STAT3 Activation

Talbot¹,

Song²,

Wang³

et al. 2014

Polycystin-1 (PC1) mutations result in proliferative renal cyst growth and progression to renal failure in autosomal dominant polycystic kidney disease (ADPKD). The transcription factor STAT3 (signal transducer and activator of transcription 3) was shown to be activated in cyst-lining cells in ADPKD and PKD mouse models and may drive renal cyst growth, but the mechanisms leading to persistent STAT3 activation are unknown. A proteolytic fragment of PC1 corresponding to the cytoplasmic tail, PC1-p30, is overexpressed in ADPKD. Here, we show that PC1-p30 interacts with the nonreceptor tyrosine kinase Src, resulting in Srcdependent activation of STAT3 by tyrosine phosphorylation. The PC1-p30-mediated activation of Src/ STAT3 was independent of JAK family kinases and insensitive to the STAT3 inhibitor suppressor of cytokine signaling 3. Signaling by the EGF receptor (EGFR) or cAMP amplified the activation of Src/STAT3 by PC1-p30. Expression of PC1-p30 changed the cellular response to cAMP signaling. In the absence of PC1-p30, cAMP dampened EGFR-or IL-6-dependent activation of STAT3; in the presence of PC1-p30, cAMP amplified Src-dependent activation of STAT3. In the polycystic kidney (PCK) rat model, activation of STAT3 in renal cystic cells depended on vasopressin receptor 2 (V2R) signaling, which increased cAMP levels. Genetic inhibition of vasopressin expression or treatment with a pharmacologic V2R inhibitor strongly suppressed STAT3 activation and reduced renal cyst growth. These results suggest that PC1, via its cleaved cytoplasmic tail, integrates signaling inputs from EGFR and cAMP, resulting in Src-dependent activation of STAT3 and a proliferative response.