Erratum: Proof-of-concept study for liver-directed miQURE technology in a dyslipidemic mouse model.

[This corrects the article DOI: 10.1016/j.omtn.2023.04.004.].

Semaglutide Has Beneficial Effects on Non-Alcoholic Steatohepatitis in Ldlr-/-.Leiden Mice.

Semaglutide, a glucagon-like peptide-1 receptor agonist, is an antidiabetic medication that has recently been approved for the treatment of obesity as well. Semaglutide is postulated to be a promising candidate for the treatment of non-alcoholic steatohepatitis (NASH). Here, Ldlr-/-.Leiden mice received a fast-food diet (FFD) for 25 weeks, followed by another 12 weeks on FFD with daily subcutaneous injections of semaglutide or vehicle (control). Plasma parameters were evaluated, livers and hearts were examined, and hepatic transcriptome analysis was performed. In the liver, semaglutide significantly reduced macrovesicular steatosis (-74%, p < 0.001) and inflammation (-73%, p < 0.001) and completely abolished microvesicular steatosis (-100%, p < 0.001). Histological and biochemical assessment of hepatic fibrosis showed no significant effects of semaglutide. However, digital pathology revealed significant improvements in the degree of collagen fiber reticulation (-12%, p < 0.001). Semaglutide did not affect atherosclerosis relative to controls. Additionally, we compared the transcriptome profile of FFD-fed Ldlr-/-.Leiden mice with a human gene set that differentiates human NASH patients with severe fibrosis from those with mild fibrosis. In FFD-fed Ldlr-/-.Leiden control mice, this gene set was upregulated as well, while semaglutide predominantly reversed this gene expression. Using a translational model with advanced NASH, we demonstrated that semaglutide is a promising candidate with particular potential for the treatment of hepatic steatosis and inflammation, while for the reversal of advanced fibrosis, combinations with other NASH agents may be necessary.

Atorvastatin Attenuates Diet-Induced Non-Alcoholic Steatohepatitis in APOE*3-Leiden Mice by Reducing Hepatic Inflammation.

Patients with metabolic syndrome are often prescribed statins to prevent the development of cardiovascular disease. Conversely, data on their effects on non-alcoholic steatohepatitis (NASH) are lacking. We evaluated these effects by feeding APOE*3-Leiden mice a Western-type diet (WTD) with or without atorvastatin to induce NASH and hepatic fibrosis. Besides the well-known plasma cholesterol lowering (-30%) and anti-atherogenic effects (severe lesion size -48%), atorvastatin significantly reduced hepatic steatosis (-22%), the number of aggregated inflammatory cells in the liver (-80%) and hepatic fibrosis (-92%) compared to WTD-fed mice. Furthermore, atorvastatin-treated mice showed less immunohistochemically stained areas of inflammation markers. Atorvastatin prevented accumulation of free cholesterol in the form of cholesterol crystals (-78%). Cholesterol crystals are potent inducers of the NLRP3 inflammasome pathway and atorvastatin prevented its activation, which resulted in reduced expression of the pro-inflammatory cytokines interleukin (IL)-1ß (-61%) and IL-18 (-26%). Transcriptome analysis confirmed strong reducing effects of atorvastatin on inflammatory mediators, including NLRP3, NFκB and TLR4. The present study demonstrates that atorvastatin reduces hepatic steatosis, inflammation and fibrosis and prevents cholesterol crystal formation, thereby precluding NLRP3 inflammasome activation. This may render atorvastatin treatment as an attractive approach to reduce NAFLD and prevent progression into NASH in dyslipidemic patients.

Proof-of-concept study for liver-directed miQURE technology in a dyslipidemic mouse model.

A gene-silencing platform (miQURE) has been developed and successfully used to deliver therapeutic microRNA (miRNA) to the brain, reducing levels of neurodegenerative disease-causing proteins/RNAs via RNA interference and improving the disease phenotype in animal models. This study evaluates the use of miQURE technology to deliver therapeutic miRNA for liver-specific indications. Angiopoietin-like 3 (ANGPTL3) was selected as the target mRNA because it is produced in the liver and because loss-of-function ANGPTL3 mutations and/or pharmacological inhibition of ANGPTL3 protein lowers lipid levels and reduces cardiovascular risk. Overall, 14 candidate miRNA constructs were tested in vitro, the most potent of which (miAngE) was further evaluated in mice. rAAV5-miAngE led to dose-dependent (≤-77%) decreases in Angptl3 mRNA in WT mice with ≤-90% reductions in plasma ANGPTL3 protein. In dyslipidemic APOE∗3-Leiden.CETP mice, AAV5-miAngE significantly reduced cholesterol and triglyceride levels vs. vehicle and scrambled (miSCR) controls when administrated alone, with greater reductions when co-administered with lipid-lowering therapy (atorvastatin). A significant decrease in total atherosclerotic lesion area (-58% vs. miSCR) was observed in AAV5-miAngE-treated dyslipidemic mice, which corresponded with the maintenance of a non-diseased plaque phenotype and reduced lesion severity. These results support the development of this technology for liver-directed indications.

NLRX1 Prevents M2 Macrophage Polarization and Excessive Renal Fibrosis in Chronic Obstructive Nephropathy.

BACKGROUND: Chronic kidney disease often leads to kidney dysfunction due to renal fibrosis, regardless of the initial cause of kidney damage. Macrophages are crucial players in the progression of renal fibrosis as they stimulate inflammation, activate fibroblasts, and contribute to extracellular matrix deposition, influenced by their metabolic state. Nucleotide-binding domain and LRR-containing protein X (NLRX1) is an innate immune receptor independent of inflammasomes and is found in mitochondria, and it plays a role in immune responses and cell metabolism. The specific impact of NLRX1 on macrophages and its involvement in renal fibrosis is not fully understood. METHODS: To explore the specific role of NLRX1 in macrophages, bone-marrow-derived macrophages (BMDMs) extracted from wild-type (WT) and NLRX1 knockout (KO) mice were stimulated with pro-inflammatory and pro-fibrotic factors to induce M1 and M2 polarization in vitro. The expression levels of macrophage polarization markers (Nos2, Mgl1, Arg1, and Mrc1), as well as the secretion of transforming growth factor ß (TGFß), were measured using RT-PCR and ELISA. Seahorse-based bioenergetics analysis was used to assess mitochondrial respiration in naïve and polarized BMDMs obtained from WT and NLRX1 KO mice. In vivo, WT and NLRX1 KO mice were subjected to unilateral ureter obstruction (UUO) surgery to induce renal fibrosis. Kidney injury, macrophage phenotypic profile, and fibrosis markers were assessed using RT-PCR. Histological staining (PASD and Sirius red) was used to quantify kidney injury and fibrosis. RESULTS: Compared to the WT group, an increased gene expression of M2 markers-including Mgl1 and Mrc1-and enhanced TGFß secretion were found in naïve BMDMs extracted from NLRX1 KO mice, indicating functional polarization towards the pro-fibrotic M2 subtype. NLRX1 KO naïve macrophages also showed a significantly enhanced oxygen consumption rate compared to WT cells and increased basal respiration and maximal respiration capacities that equal the level of M2-polarized macrophages. In vivo, we found that NLRX1 KO mice presented enhanced M2 polarization markers together with enhanced tubular injury and fibrosis demonstrated by augmented TGFß levels, fibronectin, and collagen accumulation. CONCLUSIONS: Our findings highlight the unique role of NLRX1 in regulating the metabolism and function of macrophages, ultimately protecting against excessive renal injury and fibrosis in UUO.

A Novel, Orally Bioavailable, Small-Molecule Inhibitor of PCSK9 With Significant Cholesterol-Lowering Properties In Vivo.

Proprotein convertase subtilisin kexin type 9 (PCSK9) inhibits the clearance of low-density lipoprotein (LDL) cholesterol (LDL-C) from plasma by directly binding with the LDL receptor (LDLR) and sending the receptor for lysosomal degradation. As the interaction promotes elevated plasma LDL-C levels, and therefore a predisposition to cardiovascular disease, PCSK9 has attracted intense interest as a therapeutic target. Despite this interest, an orally bioavailable small-molecule inhibitor of PCSK9 with extensive lipid-lowering activity is yet to enter the clinic. We report herein the discovery of NYX-PCSK9i, an orally bioavailable small-molecule inhibitor of PCSK9 with significant cholesterol-lowering activity in hyperlipidemic APOE∗3-Leiden.CETP mice. NYX-PCSK9i emerged from a medicinal chemistry campaign demonstrating potent disruption of the PCSK9-LDLR interaction in vitro and functional protection of the LDLR of human lymphocytes from PCSK9-directed degradation ex vivo. APOE∗3-Leiden.CETP mice orally treated with NYX-PCSK9i demonstrated a dose-dependent decrease in plasma total cholesterol of up to 57%, while its combination with atorvastatin additively suppressed plasma total cholesterol levels. Importantly, the majority of cholesterol lowering by NYX-PCSK9i was in non-HDL fractions. A concomitant increase in total plasma PCSK9 levels and significant increase in hepatic LDLR protein expression strongly indicated on-target function by NYX-PCSK9i. Determinations of hepatic lipid and fecal cholesterol content demonstrated depletion of liver cholesteryl esters and promotion of fecal cholesterol elimination with NYX-PCSK9i treatment. All measured in vivo biomarkers of health indicate that NYX-PCSK9i has a good safety profile. NYX-PCSK9i is a potential new therapy for hypercholesterolemia with the capacity to further enhance the lipid-lowering activities of statins.

Dual targeting of hepatic fibrosis and atherogenesis by icosabutate, an engineered eicosapentaenoic acid derivative.

BACKGROUND & AIMS: While fibrosis stage predicts liver-associated mortality, cardiovascular disease (CVD) is still the major overall cause of mortality in patients with NASH. Novel NASH drugs should thus ideally reduce both liver fibrosis and CVD. Icosabutate is a semi-synthetic, liver-targeted eicosapentaenoic acid (EPA) derivative in clinical development for NASH. The primary aims of the current studies were to establish both the anti-fibrotic and anti-atherogenic efficacy of icosabutate in conjunction with changes in lipotoxic and atherogenic lipids in liver and plasma respectively. METHODS: The effects of icosabutate on fibrosis progression and lipotoxicity were investigated in amylin liver NASH (AMLN) diet (high fat, cholesterol and fructose) fed ob/ob mice with biopsy-confirmed steatohepatitis and fibrosis and compared with the activity of obeticholic acid. APOE*3Leiden.CETP mice, a translational model for hyperlipidaemia and atherosclerosis, were used to evaluate the mechanisms underlying the lipid-lowering effect of icosabutate and its effect on atherosclerosis. RESULTS: In AMLN ob/ob mice, icosabutate significantly reduced hepatic fibrosis and myofibroblast content in association with downregulation of the arachidonic acid cascade and a reduction in both hepatic oxidised phospholipids and apoptosis. In APOE*3Leiden.CETP mice, icosabutate reduced plasma cholesterol and TAG levels via increased hepatic uptake, upregulated hepatic lipid metabolism and downregulated inflammation pathways, and effectively decreased atherosclerosis development. CONCLUSIONS: Icosabutate, a structurally engineered EPA derivative, effectively attenuates both hepatic fibrosis and atherogenesis and offers an attractive therapeutic approach to both liver- and CV-related morbidity and mortality in NASH patients.

Deletion of NLRX1 increases fatty acid metabolism and prevents diet-induced hepatic steatosis and metabolic syndrome.

NOD-like receptor (NLR)X1 (NLRX1) is an ubiquitously expressed inflammasome-independent NLR that is uniquely localized in mitochondria with as yet unknown effects on metabolic diseases. Here, we report that NLRX1 is essential in regulating cellular metabolism in non-immune parenchymal hepatocytes by decreasing mitochondrial fatty acid-dependent oxidative phosphorylation (OXPHOS) and promoting glycolysis. NLRX1 loss in mice has a profound impact on the prevention of diet-induced metabolic syndrome parameters, non-alcoholic fatty liver disease (NAFLD) progression, and renal dysfunction. Despite enhanced caloric intake, NLRX1 deletion in mice fed a western diet (WD) results in protection from liver steatosis, hepatic fibrosis, obesity, insulin resistance, glycosuria and kidney dysfunction parameters independent from inflammation. While mitochondrial content was equal, NLRX1 loss in hepatocytes leads to increased fatty acid oxidation and decreased steatosis. In contrast, glycolysis was decreased in NLRX1-deficient cells versus controls. Thus, although first implicated in immune regulation, we show that NLRX1 function extends to the control of hepatocyte energy metabolism via the restriction of mitochondrial fatty acid-dependent OXPHOS and enhancement of glycolysis. As such NLRX1 may be an attractive novel therapeutic target for NAFLD and metabolic syndrome.

Aryl hydrocarbon receptor expression by macrophages and lymphocytes within infiltrates in BK polyomavirus associated nephropathy.

BACKGROUND: BK virus nephropathy (BKPyVN) is a major complication after renal transplantation. Little is known about the intra renal immune response during BKPyVN. The role of macrophages remains elusive. The activation of aryl hydrocarbon receptor (AHR) - a transcription factor involved in drug metabolism - plays a key role in inflammation and viral tolerance through modulation of macrophages polarization. Since AHR has not been studied in kidney transplantation, our aim was to compare the AHR expression within renal grafts in BKPyVN with T-cell mediated rejection (TCMR) as a control. METHODS: We evaluated AHR expression in kidney grafts from BKPyVN (n=8) with TCMR as control (n=6) among cases with available frozen material for AHR gene intragraft transcription measurement and stainings for AHR, CD68 and CD45. RESULTS: AHR transcription was higher in BKPyVN grafts versus TCMR (p=0.03). While CD68+ or CD45+ cell expression did not differ within infiltrates (median score=3 in both groups; p=1.0 and 0.69, respectively), a higher proportion of nuclear AHR expression was found in BKPyVN for CD68+ and CD45+ cells when compared with TCMR (score median 2 vs 0; p=0.007 and 1 vs 0; p=0.013, respectively). CONCLUSIONS: We describe for the first time a higher expression of AHR in inflammatory cell infiltrates from BKPyVN versus TCMR renal biopsies. Further studies are required to explore AHR as a potential target in the modulation of inflammatory response in BKPyVN with known modulating ligands.

NLRX1 dampens oxidative stress and apoptosis in tissue injury via control of mitochondrial activity.

Mitochondrial dysfunction is the most prominent source of oxidative stress in acute and chronic kidney disease. NLRX1 is a receptor of the innate immune system that is ubiquitously expressed and localized in mitochondria. We investigated whether NLRX1 may act at the interface of metabolism and innate immunity in a model of oxidative stress. Using a chimeric mouse model for renal ischemia-reperfusion injury, we found that NLRX1 protects against mortality, mitochondrial damage, and epithelial cell apoptosis in an oxidative stress-dependent fashion. We found that NLRX1 regulates oxidative phosphorylation and cell integrity, whereas loss of NLRX1 results in increased oxygen consumption, oxidative stress, and subsequently apoptosis in epithelial cells during ischemia-reperfusion injury. In line, we found that NLRX1 expression in human kidneys decreased during acute renal ischemic injury and acute cellular rejection. Although first implicated in immune regulation, we propose that NLRX1 function extends to the control of mitochondrial activity and prevention of oxidative stress and apoptosis in tissue injury.

Depletion of Gut Microbiota Protects against Renal Ischemia-Reperfusion Injury.

An accumulating body of evidence shows that gut microbiota fulfill an important role in health and disease by modulating local and systemic immunity. The importance of the microbiome in the development of kidney disease, however, is largely unknown. To study this concept, we depleted gut microbiota with broad-spectrum antibiotics and performed renal ischemia-reperfusion (I/R) injury in mice. Depletion of the microbiota significantly attenuated renal damage, dysfunction, and remote organ injury and maintained tubular integrity after renal I/R injury. Gut flora-depleted mice expressed lower levels of F4/80 and chemokine receptors CX3CR1 and CCR2 in the F4/80+ renal resident macrophage population and bone marrow (BM) monocytes than did control mice. Additionally, compared with control BM monocytes, BM monocytes from gut flora-depleted mice had decreased migratory capacity toward CX3CL1 and CCL2 ligands. To study whether these effects were driven by depletion of the microbiota, we performed fecal transplants in antibiotic-treated mice and found that transplant of fecal material from an untreated mouse abolished the protective effect of microbiota depletion upon renal I/R injury. In conclusion, we show that depletion of gut microbiota profoundly protects against renal I/R injury by reducing maturation status of F4/80+ renal resident macrophages and BM monocytes. Therefore, dampening the inflammatory response by targeting microbiota-derived mediators might be a promising therapy against I/R injury.

Predominant Tubular Interleukin-18 Expression in Polyomavirus-Associated Nephropathy.

Polyomavirus-associated nephropathy (PVAN) occurs in a significant percentage of renal transplant recipients, with BK virus reactivation as the main causative agent. PVAN leads to tubular damage and may result in allograft loss. In this study, we analyzed the antiviral immune response in PVAN. Transcription of the proinflammatory cytokine interleukin-18 (IL-18) was significantly higher in PVAN biopsies compared with T cell-mediated rejection (TCMR) (1.42 ± 0.20 and 0.69 ± 0.10, respectively; *P = 0.0021). Tubular expression of IL-18 was significantly increased in PVAN compared with TCMR (2.00 ± 0.24 and 1.333 ± 0.13, respectively; *P = 0.028). In contrast, in TCMR, IL-18 was expressed predominantly by CD163-positive macrophages. These data suggest that the antiviral immune response in PVAN is partly coordinated by the tubular epithelium, whereas in TCMR, this may be controlled by inflammatory cells.

Intragraft Blood Dendritic Cell Antigen-1-Positive Myeloid Dendritic Cells Increase during BK Polyomavirus-Associated Nephropathy.

Although both polyomavirus infection and T cell-mediated rejection (TCMR) are characterized by tubulointerstitial inflammation in the renal allograft, these conditions are treated with opposing therapeutic regimens. To gain more insight into the differences between antiviral and alloimmune responses, we performed a case-control study, in which we immunophenotyped the inflammatory infiltrates in renal biopsy specimens with BK polyomavirus-associated nephropathy (BKPyVAN) and specimens with TCMR. Compared with TCMR, BKPyVAN was diagnosed later after transplantation; therefore, BKPyVAN specimens showed more chronic damage than TCMR specimens showed. However, TCMR and BKPyVAN specimens had comparable levels of tubulointerstitial inflammation. Adjustment for confounders in various multivariable models revealed more blood dendritic cell antigen-1(+) (BDCA-1(+)) myeloid dendritic cells (mDCs) present during BKPyVAN (odds ratio, 2.31; 95% confidence interval, 1.03 to 5.16; P=0.04) than during TCMR. Double immunostaining for SV40 and BDCA-1 showed that, during BKPyVAN, BDCA-1(+) mDCs localized in proximity to the polyomavirus-infected tubular epithelial cells. We ensured that time of biopsy after transplantation was not a confounding factor by including additional specimens with late TCMR and protocol biopsy specimens matched for biopsy time. These additional specimens showed amounts of BDCA-1(+) mDCs comparable with amounts in the early TCMR specimens. These results suggest that BDCA-1(+) mDCs, known to be involved in the antiviral immune response during various viral infections, might have a pivotal role during BKPyVAN infection in the grafted kidney.

The interplay between antiviral immunity and allo-immune reactivity after renal transplantation: consortium between the Centres Amsterdam, Leiden and Nijmegen (ALLOVIR).

In the consortium "ALLOVIR" we aim to characterize the effect of CMV and BKV infections on the innate immune responses to viral and alloantigens. Furthermore, we want to characterize the interplay between adaptive immune responses to viral and alloantigens with emphasis on the role of heterologous immunity. Thirdly, we will characterize the manifestations of these immune responses in the allograft, as reflected in tissue and urine, and their correlation with graft function. Finally, we will assess how immunosuppressive drugs interfere with these cross-reactive immune responses.

Epac-Rap signaling reduces oxidative stress in the tubular epithelium.

Activation of Rap1 by exchange protein activated by cAMP (Epac) promotes cell adhesion and actin cytoskeletal polarization. Pharmacologic activation of Epac-Rap signaling by the Epac-selective cAMP analog 8-pCPT-2'-O-Me-cAMP during ischemia-reperfusion (IR) injury reduces renal failure and application of 8-pCPT-2'-O-Me-cAMP promotes renal cell survival during exposure to the nephrotoxicant cisplatin. Here, we found that activation of Epac by 8-pCPT-2'-O-Me-cAMP reduced production of reactive oxygen species during reoxygenation after hypoxia by decreasing mitochondrial superoxide production. Epac activation prevented disruption of tubular morphology during diethyl maleate-induced oxidative stress in an organotypic three-dimensional culture assay. In vivo renal targeting of 8-pCPT-2'-O-Me-cAMP to proximal tubules using a kidney-selective drug carrier approach resulted in prolonged activation of Rap1 compared with nonconjugated 8-pCPT-2'-O-Me-cAMP. Activation of Epac reduced antioxidant signaling during IR injury and prevented tubular epithelial injury, apoptosis, and renal failure. Our data suggest that Epac1 decreases reactive oxygen species production by preventing mitochondrial superoxide formation during IR injury, thus limiting the degree of oxidative stress. These findings indicate a new role for activation of Epac as a therapeutic application in renal injury associated with oxidative stress.

Bile acids trigger cholemic nephropathy in common bile-duct-ligated mice.

UNLABELLED: Tubular epithelial injury represents an underestimated but important cause of renal dysfunction in patients with cholestasis and advanced liver disease, but the underlying mechanisms are unclear. To address the hypothesis that accumulation and excessive alternative urinary elimination of potentially toxic bile acids (BAs) may contribute to kidney injury in cholestasis, we established a mouse model for detailed in vivo time course as well as treatment studies. Three-day common bile duct ligation (CBDL) induced renal tubular epithelial injury predominantly at the level of aquaporin 2-positive collecting ducts with tubular epithelial and basement membrane defects. This was followed by progressive interstitial nephritis and tubulointerstitial renal fibrosis in 3-, 6-, and 8-week CBDL mice. Farnesoid X receptor knockout mice (with a hydrophilic BA pool) were completely protected from CBDL-induced renal fibrosis. Prefeeding of hydrophilic norursodeoxycholic acid inhibited renal tubular epithelial injury in CBDL mice. In addition, we provide evidence for renal tubular injury in cholestatic patients with cholemic nephropathy. CONCLUSION: We characterized a novel in vivo model for cholemic nephropathy, which offers new perspectives to study the complex pathophysiology of this condition. Our findings suggest that urinary-excreted toxic BAs represent a pivotal trigger for renal tubular epithelial injury leading to cholemic nephropathy in CBDL mice.

cAMP signalling protects proximal tubular epithelial cells from cisplatin-induced apoptosis via activation of Epac.

BACKGROUND AND PURPOSE: Nephrotoxicity is the principal dose-limiting factor for cisplatin chemotherapy and is primarily associated with proximal tubular epithelial cells, including disruption of cell adhesions and induction of apoptosis. Cell adhesion and survival is regulated by, amongst other factors, the small GTPase Rap and its activator, the exchange protein directly activated by cAMP (Epac). Epac is particularly enriched in renal tubule epithelium. This study investigates the cytoprotective effects of cAMP-Epac-Rap signalling in a model of cisplatin-induced renal cell injury. EXPERIMENTAL APPROACH: The Epac-selective cAMP analogue 8-pCPT-2'-O-Me-cAMP was used to activate the Epac-Rap signalling pathway in proximal tubular epithelial cells. Cells were exposed to cisplatin, in the presence or absence of 8-pCPT-2'-O-Me-cAMP, and nephrotoxicity was determined by monitoring cell-cell junctions and cell apoptosis. KEY RESULTS: Activation of Epac-Rap signalling preserves cell-cell junctions and protects against cell apoptosis of mouse proximal tubular cells during cisplatin treatment. Activation with the Epac-selective cAMP analogue 8-pCPT-2'-O-Me-cAMP or receptor-mediated induction of cAMP both induced cytoprotection against cisplatin, whereas a PKA-selective cAMP analogue was not cytoprotective. 8-pCPT-2'-O-Me-cAMP mediated cytoprotection was blocked by RNAi-mediated silencing of Epac-Rap signalling in these cells. In contrast, 8-pCPT-2'-O-Me-cAMP did not protect against cisplatin-induced cell death of cancer cells that lacked Epac1 expression. CONCLUSIONS AND IMPLICATIONS: Our study identifies activation of Epac-Rap signalling as a potential strategy for reducing the nephrotoxicity associated with cisplatin treatments and, as a result, broadens the therapeutic window of this chemotherapeutic agent.

Focal adhesion kinase signaling mediates acute renal injury induced by ischemia/reperfusion.

Renal ischemia/reperfusion (I/R) injury is associated with cell matrix and focal adhesion remodeling. Focal adhesion kinase (FAK) is a nonreceptor protein tyrosine kinase that localizes at focal adhesions and regulates their turnover. Here, we investigated the role of FAK in renal I/R injury, using a novel conditional proximal tubule-specific fak-deletion mouse model. Tamoxifen treatment of FAK(loxP/loxP)//γGT-Cre-ER(T2) mice caused renal-specific fak recombination (FAK(ΔloxP/ΔloxP)) and reduction of FAK expression in proximal tubules. In FAK(ΔloxP/ΔloxP) mice compared with FAK(loxP/loxP) controls, unilateral renal ischemia followed by reperfusion resulted in less tubular damage with reduced tubular cell proliferation and lower expression of kidney injury molecule-1, which was independent from the postischemic inflammatory response. Oxidative stress is involved in the pathophysiology of I/R injury. Primary cultured mouse renal cells were used to study the role of FAK deficiency for oxidative stress in vitro. The conditional fak deletion did not affect cell survival after hydrogen peroxide-induced cellular stress, whereas it impaired the recovery of focal adhesions that were disrupted by hydrogen peroxide. This was associated with reduced c-Jun N-terminal kinase-dependent phosphorylation of paxillin at serine 178 in FAK-deficient cells, which is required for focal adhesion turnover. Our findings support a role for FAK as a novel factor in the initiation of c-Jun N-terminal kinase-mediated cellular stress response during renal I/R injury and suggest FAK as a target in renal injury protection.

Epac-Rap signaling reduces cellular stress and ischemia-induced kidney failure.

Renal ischemia-reperfusion injury is associated with the loss of tubular epithelial cell-cell and cell-matrix interactions which contribute to renal failure. The Epac-Rap signaling pathway is a potent regulator of cell-cell and cell-matrix adhesion. The cyclic AMP analogue 8-pCPT-2'-O-Me-cAMP has been shown to selectively activate Epac, whereas the addition of an acetoxymethyl (AM) ester to 8-pCPT-2'-O-Me-cAMP enhanced in vitro cellular uptake. Here we demonstrate that pharmacological activation of Epac-Rap signaling using acetoxymethyl-8-pCPT-2'-O-Me-cAMP preserves cell adhesions during hypoxia in vitro, maintaining the barrier function of the epithelial monolayer. Intrarenal administration in vivo of 8-pCPT-2'-O-Me-cAMP also reduced renal failure in a mouse model for ischemia-reperfusion injury. This was accompanied by decreased expression of the tubular cell stress marker clusterin-α, and lateral expression of ß-catenin after ischemia indicative of sustained tubular barrier function. Our study emphasizes the undervalued importance of maintaining tubular epithelial cell adhesion in renal ischemia and demonstrates the potential of pharmacological modulation of cell adhesion as a new therapeutic strategy to reduce the extent of injury in kidney disease and transplantation.

Application of siRNA in targeting protein expression in kidney disease.

Although it is one of the major targeted organs by systemically administered siRNA, when compared to other tissues the kidney receives only moderate interest regarding therapeutic siRNA delivery. Here we review recent approaches to target renal protein expression under normal and pathological conditions. Experimental evidence to support the clinical relevance of siRNA administration in the treatment of renal disease is discussed. High-throughput screening using recently available genome-wide RNA interference libraries provides a new, powerful tool that can be applied to conventional and 3D in vitro culture models for lead finding or the identification of signal pathway involvement in renal disease.