Differential inflammasome activation predisposes to acute-on-chronic liver failure in human and experimental cirrhosis with and without previous decompensation.

OBJECTIVE: Systemic inflammation predisposes acutely decompensated (AD) cirrhosis to the development of acute-on-chronic liver failure (ACLF). Supportive treatment can improve AD patients, becoming recompensated. Little is known about the outcome of patients recompensated after AD. We hypothesise that different inflammasome activation is involved in ACLF development in compensated and recompensated patients. DESIGN: 249 patients with cirrhosis, divided into compensated and recompensated (previous AD), were followed prospectively for fatal ACLF development. Two external cohorts (n=327) (recompensation, AD and ACLF) were included. Inflammasome-driving interleukins (ILs), IL-1α (caspase-4/11-dependent) and IL-1ß (caspase-1-dependent), were measured. In rats, bile duct ligation-induced cirrhosis and lipopolysaccharide exposition were used to induce AD and subsequent recompensation. IL-1α and IL-1ß levels and upstream/downstream gene expression were measured. RESULTS: Patients developing ACLF showed higher baseline levels of ILs. Recompensated patients and patients with detectable ILs had higher rates of ACLF development than compensated patients. Baseline CLIF-C (European Foundation for the study of chronic liver failure consortium) AD, albumin and IL-1α were independent predictors of ACLF development in compensated and CLIF-C AD and IL-1ß in recompensated patients. Compensated rats showed higher IL-1α gene expression and recompensated rats higher IL-1ß levels with higher hepatic gene expression. Higher IL-1ß detection rates in recompensated patients developing ACLF and higher IL-1α and IL-1ß detection rates in patients with ACLF were confirmed in the two external cohorts. CONCLUSION: Previous AD is an important risk factor for fatal ACLF development and possibly linked with inflammasome activation. Animal models confirmed the results showing a link between ACLF development and IL-1α in compensated cirrhosis and IL-1ß in recompensated cirrhosis.

Activation of Rac-1 and RhoA contributes to podocyte injury in chronic kidney disease.

Rho-family GTPases like RhoA and Rac-1 are potent regulators of cellular signaling that control gene expression, migration and inflammation. Activation of Rho-GTPases has been linked to podocyte dysfunction, a feature of chronic kidney diseases (CKD). We investigated the effect of Rac-1 and Rho kinase (ROCK) inhibition on progressive renal failure in mice and studied the underlying mechanisms in podocytes. SV129 mice were subjected to 5/6-nephrectomy which resulted in arterial hypertension and albuminuria. Subgroups of animals were treated with the Rac-1 inhibitor EHT1846, the ROCK inhibitor SAR407899 and the ACE inhibitor Ramipril. Only Ramipril reduced hypertension. In contrast, all inhibitors markedly attenuated albumin excretion as well as glomerular and tubulo-interstitial damage. The combination of SAR407899 and Ramipril was more effective in preventing albuminuria than Ramipril alone. To study the involved mechanisms, podocytes were cultured from SV129 mice and exposed to static stretch in the Flexcell device. This activated RhoA and Rac-1 and led via TGFß to apoptosis and a switch of the cells into a more mesenchymal phenotype, as evident from loss of WT-1 and nephrin and induction of α-SMA and fibronectin expression. Rac-1 and ROCK inhibition as well as blockade of TGFß dramatically attenuated all these responses. This suggests that Rac-1 and RhoA are mediators of podocyte dysfunction in CKD. Inhibition of Rho-GTPases may be a novel approach for the treatment of CKD.

Deficiency of biglycan causes cardiac fibroblasts to differentiate into a myofibroblast phenotype.

Myocardial infarction (MI) is followed by extracellular matrix (ECM) remodeling, which is on the one hand required for the healing response and the formation of stable scar tissue. However, on the other hand, ECM remodeling can lead to fibrosis and decreased ventricular compliance. The small leucine-rich proteoglycan (SLRP), biglycan (bgn), has been shown to be critically involved in these processes. During post-infarct remodeling cardiac fibroblasts differentiate into myofibroblasts which are the main cell type mediating ECM remodeling. The aim of the present study was to characterize the role of bgn in modulating the phenotype of cardiac fibroblasts. Cardiac fibroblasts were isolated from hearts of wild-type (WT) versus bgn(-/0) mice. Phenotypic characterization of the bgn(-/0) fibroblasts revealed increased proliferation. Importantly, this phenotype of bgn(-/0) fibroblasts was abolished to the WT level by reconstitution of biglycan in the ECM. TGF-ß receptor II expression and phosphorylation of SMAD2 were increased. Furthermore, indicative of a myofibroblast phenotype bgn(-/0) fibroblasts were characterized by increased α-smooth muscle actin (α-SMA) incorporated into stress fibers, increased formation of focal adhesions, and increased contraction of collagen gels. Administration of neutralizing antibodies to TGF-ß reversed the pro-proliferative, myofibroblastic phenotype. In vivo post-MI α-SMA, TGF-ß receptor II expression, and SMAD2 phosphorylation were markedly increased in bgn(-/0) mice. Collectively, the data suggest that bgn deficiency promotes myofibroblast differentiation and proliferation in vitro and in vivo likely due to increased responses to TGF-ß and SMAD2 signaling.

Peroxisome proliferator-activated receptor (PPAR)gamma can inhibit chronic renal allograft damage.

Chronic inflammation and fibrosis are the leading causes of chronic allograft failure. The nuclear receptor peroxisome proliferator-activated receptor (PPAR)gamma is a transcription factor known to have antidiabetogenic and immune effects, and PPARgamma forms obligate heterodimers with the retinoid X receptor (RXR). We have reported that a retinoic acid (RAR)/RXR-agonist can potently influence the course of renal chronic allograft dysfunction. In this study, in a Fischer to Lewis rat renal transplantation model, administration of the PPARgamma-agonist, rosiglitazone, independent of dose (3 or 30 mg/kgBW/day), lowered serum creatinine, albuminuria, and chronic allograft damage with a chronic vascular damage score as follows: 35.0 +/- 5.8 (controls) vs. 8.1 +/- 2.4 (low dose-Rosi; P < 0.05); chronic tubulointerstitial damage score: 13.6 +/- 1.8 (controls) vs. 2.6 +/- 0.4 (low dose-Rosi; P < 0.01). The deposition of extracellular matrix proteins (collagen, fibronectin, decorin) was strikingly lower. The expression of transforming growth factor-beta1 was inhibited, whereas that of bone morphogenic protein-7 (BMP-7) was increased. Intragraft mononuclear cells and activated fibroblast numbers were reduced by 50%. In addition, the migratory and proliferative activity of these cells was significantly inhibited in vitro. PPARgamma activation diminished the number of cells expressing the proinflammatory and fibrogenic proteoglycan biglycan. In macrophages its secretion was blocked by rosiglitazone in a predominantly PPARgamma-dependent manner. The combination of PPARgamma- and RAR/RXR-agonists resulted in additive effects in the inhibition of fibrosis. In summary, PPARgamma activation was potently immunosuppressive and antifibrotic in kidney allografts, and these effects were enhanced by a RAR/RXR-agonist.

Characterization of CXCL16 and ADAM10 in the normal and transplanted kidney.

The chemokine CXCL16 plays an important role in the recruitment of leukocytes to sites of inflammation influencing the course of experimental glomerulonephritis. Here we show that human kidneys highly express CXCL16 in the distal tubule, connecting tubule and principal cells of the collecting duct with weak expression in the thick ascending limb of Henle. Beside the membrane localization, a soluble form of CXCL16 can be proteolytically released which acts as a chemotactic factor. In human renal tissue the expression pattern of the disintegrin-like metalloproteinase ADAM10 is similar to that of CXCL16, suggesting ADAM10 can potentially cleave CXCL16 in vivo. When we tested this in primary tubular cells we found that blockade of ADAM10 activity inhibited the IFN-gamma induced release of soluble CXCL16. Acute tubular damage in renal allografts was associated with elevated urinary CXCL16 and this correlated with focally increased apical CXCL16 expression in the distal tubules and collecting ducts. Renal allograft biopsies, with a histopathological diagnosis of acute interstitial rejection, showed increased basolateral ADAM10 expression together with high numbers of infiltrating T cells. Our results suggest that CXCL16 and ADAM10 are involved in the recruitment of T cells to the kidney and play an important role in inflammatory kidney diseases.