Targeting the TWEAK-Fn14 pathway prevents dysfunction in cardiac calcium handling after acute kidney injury.

Heart and kidney have a closely interrelated pathophysiology. Acute kidney injury (AKI) is associated with significantly increased rates of cardiovascular events, a relationship defined as cardiorenal syndrome type 3 (CRS3). The underlying mechanisms that trigger heart disease remain, however, unknown, particularly concerning the clinical impact of AKI on cardiac outcomes and overall mortality. Tumour necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor-inducible 14 (Fn14) are independently involved in the pathogenesis of both heart and kidney failure, and recent studies have proposed TWEAK as a possible therapeutic target; however, its specific role in cardiac damage associated with CRS3 remains to be clarified. Firstly, we demonstrated in a retrospective longitudinal clinical study that soluble TWEAK plasma levels were a predictive biomarker of mortality in patients with AKI. Furthermore, the exogenous application of TWEAK to native ventricular cardiomyocytes induced relevant calcium (Ca2+ ) handling alterations. Next, we investigated the role of the TWEAK-Fn14 axis in cardiomyocyte function following renal ischaemia-reperfusion (I/R) injury in mice. We observed that TWEAK-Fn14 signalling was activated in the hearts of AKI mice. Mice also showed significantly altered intra-cardiomyocyte Ca2+ handling and arrhythmogenic Ca2+ events through an impairment in sarcoplasmic reticulum Ca2+ -adenosine triphosphatase 2a pump (SERCA2a ) and ryanodine receptor (RyR2 ) function. Administration of anti-TWEAK antibody after reperfusion significantly improved alterations in Ca2+ cycling and arrhythmogenic events and prevented SERCA2a and RyR2 modifications. In conclusion, this study establishes the relevance of the TWEAK-Fn14 pathway in cardiac dysfunction linked to CRS3, both as a predictor of mortality in patients with AKI and as a Ca2+ mishandling inducer in cardiomyocytes, and highlights the cardioprotective benefits of TWEAK targeting in CRS3. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Broad protection against invasive fungal disease from a nanobody targeting the active site of fungal b-1,3-glucanosyltransferases.

Invasive fungal disease accounts for ~3.8 million deaths annually, an unacceptable rate that urgently prompts the discovery of new knowledge-driven treatments. We report the use of camelid single-domain nanobodies (Nbs) against fungal ß-1,3-glucanosyltransferases (Gel) involved in ß-1,3-glucan transglycosylation. Crystal structures of two Nbs with Gel4 from Aspergillus fumigatus revealed binding to a dissimilar CBM43 domain and a highly conserved catalytic domain across fungal species, respectively. Anti-Gel4 active site Nb3 showed significant antifungal efficacy in vitro and in vivo prophylactically and therapeutically against different A. fumigatus and Cryptococcus neoformans isolates, reducing the fungal burden and disease severity, thus significantly improving immunocompromised animal survival. Notably, C. deneoformans (serotype D) strains were more susceptible to Nb3 and genetic Gel deletion than C. neoformans (serotype A) strains, indicating a key role for ß-1,3-glucan remodelling in C. deneoformans survival. These findings add new insights about the role of b-1,3-glucan in fungal biology and demonstrate the potential of nanobodies in targeting fungal enzymes to combat invasive fungal diseases.

Dynamics of urine proteomics biomarker and disease progression in patients with IgA nephropathy.

BACKGROUND: Immunoglobulin A nephropathy (IgAN) frequently leads to kidney failure. The urinary proteomics-based classifier IgAN237 may predict disease progression at the time of kidney biopsy. We studied whether IgAN237 also predicts progression later in the course of IgAN. METHODS: Urine from patients with biopsy-proven IgAN was analyzed using capillary electrophoresis-mass spectrometry at baseline (IgAN237-1, n = 103) and at follow-up (IgAN237-2, n = 89). Patients were categorized as "non-progressors" (IgAN237 ≤0.38) and "progressors" (IgAN237 >0.38). Estimated glomerular filtration rate (eGFR) and urinary albumin-creatinine ratio slopes were calculated. RESULTS: Median age at biopsy was 44 years, interval between biopsy and IgAN237-1 was 65 months and interval between IgAN237-1 and IgAN237-2 was 258 days (interquartile range 71-531). IgAN237-1 and IgAN237-2 values did not differ significantly and were correlated (rho = 0.44, P < .001). Twenty-eight percent and 26% of patients were progressors based on IgAN237-1 and IgAN237-2, respectively. IgAN237 inversely correlated with chronic eGFR slopes (rho = -0.278, P = .02 for score-1; rho = -0.409, P = .002 for score-2) and with ±180 days eGFR slopes (rho = -0.31, P = .009 and rho = -0.439, P = .001, respectively). The ±180 days eGFR slopes were worse for progressors than for non-progressors (median -5.98 versus -1.22 mL/min/1.73 m2 per year for IgAN237-1, P < .001; -3.02 vs 1.08 mL/min/1.73 m2 per year for IgAN237-2, P = .0047). In multiple regression analysis baseline progressor/non-progressor according to IgAN237 was an independent predictor of eGFR180days-slope (P = .001). CONCLUSION: The urinary IgAN237 classifier represents a risk stratification tool in IgAN also later in the course of the dynamic disease. It may guide patient management in an individualized manner.

Poacic acid, a ß-1,3-glucan-binding antifungal agent, inhibits cell-wall remodeling and activates transcriptional responses regulated by the cell-wall integrity and high-osmolarity glycerol pathways in yeast.

As a result of the relatively few available antifungals and the increasing frequency of resistance to them, the development of novel antifungals is increasingly important. The plant natural product poacic acid (PA) inhibits ß-1,3-glucan synthesis in Saccharomyces cerevisiae and has antifungal activity against a wide range of plant pathogens. However, the mode of action of PA is unclear. Here, we reveal that PA specifically binds to ß-1,3-glucan, its affinity for which is ~30-fold that for chitin. Besides its effect on ß-1,3-glucan synthase activity, PA inhibited the yeast glucan-elongating activity of Gas1 and Gas2 and the chitin-glucan transglycosylase activity of Crh1. Regarding the cellular response to PA, transcriptional co-regulation was mediated by parallel activation of the cell-wall integrity (CWI) and high-osmolarity glycerol signaling pathways. Despite targeting ß-1,3-glucan remodeling, the transcriptional profiles and regulatory circuits activated by caspofungin, zymolyase, and PA differed, indicating that their effects on CWI have different mechanisms. The effects of PA on the growth of yeast strains indicated that it has a mode of action distinct from that of echinocandins, suggesting it is a unique antifungal agent.

Control of Gene Expression via the Yeast CWI Pathway.

Living cells exposed to stressful environmental situations can elicit cellular responses that guarantee maximal cell survival. Most of these responses are mediated by mitogen-activated protein kinase (MAPK) cascades, which are highly conserved from yeast to humans. Cell wall damage conditions in the yeast Saccharomyces cerevisiae elicit rescue mechanisms mainly associated with reprogramming specific transcriptional responses via the cell wall integrity (CWI) pathway. Regulation of gene expression by this pathway is coordinated by the MAPK Slt2/Mpk1, mainly via Rlm1 and, to a lesser extent, through SBF (Swi4/Swi6) transcription factors. In this review, we summarize the molecular mechanisms controlling gene expression upon cell wall stress and the role of chromatin structure in these processes. Some of these mechanisms are also discussed in the context of other stresses governed by different yeast MAPK pathways. Slt2 regulates both transcriptional initiation and elongation by interacting with chromatin at the promoter and coding regions of CWI-responsive genes but using different mechanisms for Rlm1- and SBF-dependent genes. Since MAPK pathways are very well conserved in eukaryotic cells and are essential for controlling cellular physiology, improving our knowledge regarding how they regulate gene expression could impact the future identification of novel targets for therapeutic intervention.

Urine proteomics for prediction of disease progression in patients with IgA nephropathy.

BACKGROUND: Risk of kidney function decline in immunoglobulin A (IgA) nephropathy (IgAN) is significant and may not be predicted by available clinical and histological tools. To serve this unmet need, we aimed at developing a urinary biomarker-based algorithm that predicts rapid disease progression in IgAN, thus enabling a personalized risk stratification. METHODS: In this multicentre study, urine samples were collected in 209 patients with biopsy-proven IgAN. Progression was defined by tertiles of the annual change of estimated glomerular filtration rate (eGFR) during follow-up. Urine samples were analysed using capillary electrophoresis coupled mass spectrometry. The area under the receiver operating characteristic curve (AUC) was used to evaluate the risk prediction models. RESULTS: Of the 209 patients, 64% were male. Mean age was 42 years, mean eGFR was 63 mL/min/1.73 m2 and median proteinuria was 1.2 g/day. We identified 237 urine peptides showing significant difference in abundance according to the tertile of eGFR change. These included fragments of apolipoprotein C-III, alpha-1 antitrypsin, different collagens, fibrinogen alpha and beta, titin, haemoglobin subunits, sodium/potassium-transporting ATPase subunit gamma, uromodulin, mucin-2, fractalkine, polymeric Ig receptor and insulin. An algorithm based on these protein fragments (IgAN237) showed a significant added value for the prediction of IgAN progression [AUC 0.89; 95% confidence interval (CI) 0.83-0.95], as compared with the clinical parameters (age, gender, proteinuria, eGFR and mean arterial pressure) alone (0.72; 95% CI 0.64-0.81). CONCLUSIONS: A urinary peptide classifier predicts progressive loss of kidney function in patients with IgAN significantly better than clinical parameters alone.

TWEAK and RIPK1 mediate a second wave of cell death during AKI.

Acute kidney injury (AKI) is characterized by necrotic tubular cell death and inflammation. The TWEAK/Fn14 axis is a mediator of renal injury. Diverse pathways of regulated necrosis have recently been reported to contribute to AKI, but there are ongoing discussions on the timing or molecular regulators involved. We have now explored the cell death pathways induced by TWEAK/Fn14 activation and their relevance during AKI. In cultured tubular cells, the inflammatory cytokine TWEAK induces apoptosis in a proinflammatory environment. The default inhibitor of necroptosis [necrostatin-1 (Nec-1)] was protective, while caspase inhibition switched cell death to necroptosis. Additionally, folic acid-induced AKI in mice resulted in increased expression of Fn14 and necroptosis mediators, such as receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed lineage domain-like protein (MLKL). Targeting necroptosis with Nec-1 or by genetic RIPK3 deficiency and genetic Fn14 ablation failed to be protective at early time points (48 h). However, a persistently high cell death rate and kidney dysfunction (72-96 h) were dependent on an intact TWEAK/Fn14 axis driving necroptosis. This was prevented by Nec-1, or MLKL, or RIPK3 deficiency and by Nec-1 stable (Nec-1s) administered before or after induction of AKI. These data suggest that initial kidney damage and cell death are amplified through recruitment of inflammation-dependent necroptosis, opening a therapeutic window to treat AKI once it is established. This may be relevant for clinical AKI, since using current diagnostic criteria, severe injury had already led to loss of renal function at diagnosis.

TRAF3 Modulation: Novel Mechanism for the Anti-inflammatory Effects of the Vitamin D Receptor Agonist Paricalcitol in Renal Disease.

BACKGROUND: CKD leads to vitamin D deficiency. Treatment with vitamin D receptor agonists (VDRAs) may have nephroprotective and anti-inflammatory actions, but their mechanisms of action are poorly understood. METHODS: Modulation of the noncanonical NF-κB2 pathway and its component TNF receptor-associated factor 3 (TRAF3) by the VDRA paricalcitol was studied in PBMCs from patients with ESKD, cytokine-stimulated cells, and preclinical kidney injury models. RESULTS: In PBMCs isolated from patients with ESKD, TRAF3 protein levels were lower than in healthy controls. This finding was associated with evidence of noncanonical NF-κB2 activation and a proinflammatory state. However, PBMCs from patients with ESKD treated with paricalcitol did not exhibit these features. Experiments in cultured cells confirmed the link between TRAF3 and NF-κB2/inflammation. Decreased TRAF3 ubiquitination in K48-linked chains and cIAP1-TRAF3 interaction mediated the mechanisms of paricalcitol action.TRAF3 overexpression by CRISPR/Cas9 technology mimicked VDRA's effects. In a preclinical model of kidney injury, paricalcitol inhibited renal NF-κB2 activation and decreased renal inflammation. In VDR knockout mice with renal injury, paricalcitol prevented TRAF3 downregulation and NF-κB2-dependent gene upregulation, suggesting a VDR-independent anti-inflammatory effect of paricalcitol. CONCLUSIONS: These data suggest the anti-inflammatory actions of paricalcitol depend on TRAF3 modulation and subsequent inhibition of the noncanonical NF-κB2 pathway, identifying a novel mechanism for VDRA's effects. Circulating TRAF3 levels could be a biomarker of renal damage associated with the inflammatory state.

Curcumin reduces renal damage associated with rhabdomyolysis by decreasing ferroptosis-mediated cell death.

Acute kidney injury is a common complication of rhabdomyolysis. A better understanding of this syndrome may be useful to identify novel therapeutic targets because there is no specific treatment so far. Ferroptosis is an iron-dependent form of regulated nonapoptotic cell death that is involved in renal injury. In this study, we investigated whether ferroptosis is associated with rhabdomyolysis-mediated renal damage, and we studied the therapeutic effect of curcumin, a powerful antioxidant with renoprotective properties. Induction of rhabdomyolysis in mice increased serum creatinine levels, endothelial damage, inflammatory chemokines, and cytokine expression, alteration of redox balance (increased lipid peroxidation and decreased antioxidant defenses), and tubular cell death. Treatment with curcumin initiated before or after rhabdomyolysis induction ameliorated all these pathologic and molecular alterations. Although apoptosis or receptor-interacting protein kinase (RIPK)3-mediated necroptosis were activated in rhabdomyolysis, our results suggest a key role of ferroptosis. Thus, treatment with ferrostatin 1, a ferroptosis inhibitor, improved renal function in glycerol-injected mice, whereas no beneficial effects were observed with the pan-caspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-(O-methyl)-fluoromethylketone or in RIPK3-deficient mice. In cultured renal tubular cells, myoglobin (Mb) induced ferroptosis-sensitive cell death that was also inhibited by curcumin. Mechanistic in vitro studies showed that curcumin reduced Mb-mediated inflammation and oxidative stress by inhibiting the TLR4/NF-κB axis and activating the cytoprotective enzyme heme oxygenase 1. Our findings are the first to demonstrate the involvement of ferroptosis in rhabdomyolysis-associated renal damage and its sensitivity to curcumin treatment. Therefore, curcumin may be a potential therapeutic approach for patients with this syndrome.-Guerrero-Hue, M., García-Caballero, C., Palomino-Antolín, A., Rubio-Navarro, A., Vázquez-Carballo, C., Herencia, C., Martín-Sanchez, D., Farré-Alins, V., Egea, J., Cannata, P., Praga, M., Ortiz, A., Egido, J., Sanz, A. B., Moreno, J. A. Curcumin reduces renal damage associated with rhabdomyolysis by decreasing ferroptosis-mediated cell death.

Pathogenic Pathways and Therapeutic Approaches Targeting Inflammation in Diabetic Nephropathy.

Diabetic nephropathy (DN) is associated with an increased morbidity and mortality, resulting in elevated cost for public health systems. DN is the main cause of chronic kidney disease (CKD) and its incidence increases the number of patients that develop the end-stage renal disease (ESRD). There are growing epidemiological and preclinical evidence about the close relationship between inflammatory response and the occurrence and progression of DN. Several anti-inflammatory strategies targeting specific inflammatory mediators (cell adhesion molecules, chemokines and cytokines) and intracellular signaling pathways have shown beneficial effects in experimental models of DN, decreasing proteinuria and renal lesions. A number of inflammatory molecules have been shown useful to identify diabetic patients at high risk of developing renal complications. In this review, we focus on the key role of inflammation in the genesis and progression of DN, with a special interest in effector molecules and activated intracellular pathways leading to renal damage, as well as a comprehensive update of new therapeutic strategies targeting inflammation to prevent and/or retard renal injury.

Advances in understanding the role of angiotensin-regulated proteins in kidney diseases.

Introduction: Renin-angiotensin system (RAS) blockers are in clinical use to treat high blood pressure and proteinuric chronic kidney disease. However, RAS blockade is limited by the risk of hyperkalemia, angiotensin receptor blockers are not clinically superior to angiotensin-converting enzyme inhibitors and dual RAS blockade is formally contraindicated. Areas covered: We review the regulation of protein expression and activation by angiotensin II and RAS blockers as it contributes to kidney disease. Specifically excluded are direct renin actions as well as aldosterone actions. The search strategy included the terms angiotensin, protein, proteomics, inflammation, fibrosis, and kidney and was complemented by additional searches based on initial results. Expert commentary: Recent developments include an improved understanding of the structure, function, and signaling of angiotensin G-protein-coupled receptors; identification of ligands that behave as agonists, antagonists, and even reverse agonists on specific signaling and functional pathways of the same receptor; characterization of further signaling pathways by applying proteomics and phosphoproteomics; and systems biology approaches to characterize signatures of adequate RAS blockade or resistance of kidney injury to RAS blockade. These developments will allow optimization of clinical RAS targeting to improve kidney outcomes through precision nephrology strategies that may include combined approaches, along the path marked by clinically successful dual RAS/neprilysin blockade.

Rlm1 mediates positive autoregulatory transcriptional feedback that is essential for Slt2-dependent gene expression.

Activation of the yeast cell wall integrity (CWI) pathway induces an adaptive transcriptional programme that is largely dependent on the transcription factor Rlm1 and the mitogen-activated protein kinase (MAPK) Slt2. Upon cell wall stress, the transcription factor Rlm1 is recruited to the promoters of RLM1 and SLT2, and exerts positive-feedback mechanisms on the expression of both genes. Activation of the MAPK Slt2 by cell wall stress is not impaired in strains with individual blockade of any of the two feedback pathways. Abrogation of the autoregulatory feedback mechanism on RLM1 severely affects the transcriptional response elicited by activation of the CWI pathway. In contrast, a positive trans-acting feedback mechanism exerted by Rlm1 on SLT2 also regulates CWI output responses but to a lesser extent. Therefore, a complete CWI transcriptional response requires not only phosphorylation of Rlm1 by Slt2 but also concurrent SLT2- and RLM1-mediated positive-feedback mechanisms; sustained patterns of gene expression are mainly achieved by positive autoregulatory circuits based on the transcriptional activation of Rlm1.

Targeting epigenetic DNA and histone modifications to treat kidney disease.

Epigenetics refers to heritable changes in gene expression patterns not caused by an altered nucleotide sequence, and includes non-coding RNAs and covalent modifications of DNA and histones. This review focuses on functional evidence for the involvement of DNA and histone epigenetic modifications in the pathogenesis of kidney disease and the potential therapeutic implications. There is evidence of activation of epigenetic regulatory mechanisms in acute kidney injury (AKI), chronic kidney disease (CKD) and the AKI-to-CKD transition of diverse aetiologies, including ischaemia-reperfusion injury, nephrotoxicity, ureteral obstruction, diabetes, glomerulonephritis and polycystic kidney disease. A beneficial in vivo effect over preclinical kidney injury has been reported for drugs that decrease DNA methylation by either inhibiting DNA methylation (e.g. 5-azacytidine and decitabine) or activating DNA demethylation (e.g. hydralazine), decrease histone methylation by inhibiting histone methyltransferases, increase histone acetylation by inhibiting histone deacetylases (HDACs, e.g. valproic acid, vorinostat, entinostat), increase histone crotonylation (crotonate) or interfere with histone modification readers [e.g. inhibits of bromodomain and extra-terminal proteins (BET)]. Most preclinical studies addressed CKD or the AKI-to-CKD transition. Crotonate administration protected from nephrotoxic AKI, but evidence is conflicting on DNA methylation inhibitors for preclinical AKI. Several drugs targeting epigenetic regulators are in clinical development or use, most of them for malignancy. The BET inhibitor apabetalone is in Phase 3 trials for atherosclerosis, kidney function being a secondary endpoint, but nephrotoxicity was reported for DNA and HDAC inhibitors. While research into epigenetic modulators may provide novel therapies for kidney disease, caution should be exercised based on the clinical nephrotoxicity of some drugs.

Cooperation between SAGA and SWI/SNF complexes is required for efficient transcriptional responses regulated by the yeast MAPK Slt2.

The transcriptional response of Saccharomyces cerevisiae to cell wall stress is mainly mediated by the cell wall integrity (CWI) pathway through the MAPK Slt2 and the transcription factor Rlm1. Once activated, Rlm1 interacts with the chromatin remodeling SWI/SNF complex which locally alters nucleosome positioning at the target promoters. Here we show that the SAGA complex plays along with the SWI/SNF complex an important role for eliciting both early induction and sustained gene expression upon stress. Gcn5 co-regulates together with Swi3 the majority of the CWI transcriptional program, except for a group of genes which are only dependent on the SWI/SNF complex. SAGA subunits are recruited to the promoter of CWI-responsive genes in a Slt2, Rlm1 and SWI/SNF-dependent manner. However, Gcn5 mediates acetylation and nucleosome eviction only at the promoters of the SAGA-dependent genes. This process is not essential for pre-initiation transcriptional complex assembly but rather increase the extent of the remodeling mediated by SWI/SNF. As a consequence, H3 eviction and Rlm1 recruitment is completely blocked in a swi3Δ gcn5Δ double mutant. Therefore, SAGA complex, through its histone acetylase activity, cooperates with the SWI/SNF complex for the mandatory nucleosome displacement required for full gene expression through the CWI pathway.

Mitogen-Activated Protein Kinase 14 Promotes AKI.

An improved understanding of pathogenic pathways in AKI may identify novel therapeutic approaches. Previously, we conducted unbiased liquid chromatography-tandem mass spectrometry-based protein expression profiling of the renal proteome in mice with acute folate nephropathy. Here, analysis of the dataset identified enrichment of pathways involving NFκB in the kidney cortex, and a targeted data mining approach identified components of the noncanonical NFκB pathway, including the upstream kinase mitogen-activated protein kinase kinase kinase 14 (MAP3K14), the NFκB DNA binding heterodimer RelB/NFκB2, and proteins involved in NFκB2 p100 ubiquitination and proteasomal processing to p52, as upregulated. Immunohistochemistry localized MAP3K14 expression to tubular cells in acute folate nephropathy and human AKI. In vivo, kidney expression levels of NFκB2 p100 and p52 increased rapidly after folic acid injection, as did DNA binding of RelB and NFκB2, detected in nuclei isolated from the kidneys. Compared with wild-type mice, MAP3K14 activity-deficient aly/aly (MAP3K14aly/aly) mice had less kidney dysfunction, inflammation, and apoptosis in acute folate nephropathy and less kidney dysfunction and a lower mortality rate in cisplatin-induced AKI. The exchange of bone marrow between wild-type and MAP3K14aly/aly mice did not affect the survival rate of either group after folic acid injection. In cultured tubular cells, MAP3K14 small interfering RNA targeting decreased inflammation and cell death. Additionally, cell culture and in vivo studies identified the chemokines MCP-1, RANTES, and CXCL10 as MAP3K14 targets in tubular cells. In conclusion, MAP3K14 promotes kidney injury through promotion of inflammation and cell death and is a promising novel therapeutic target.

Lyso-Gb3 activates Notch1 in human podocytes.

Podocyte injury is an early feature of Fabry nephropathy, but the molecular mechanisms of podocyte injury are poorly understood. Lyso-Gb3 accumulates in serum in Fabry disease and increases extracellular matrix synthesis in podocytes. We explored the contribution of Notch1 signaling, a mediator of podocyte injury, to lyso-Gb3-elicited responses in cultured human podocytes. At clinically relevant concentrations, lyso-Gb3 activates podocyte Notch1 signaling, resulting in increased active Notch1 and HES1, a canonical Notch transcriptional target. A γ-secretase inhibitor or specific Notch1 small interfering RNA (siRNA) inhibited HES1 upregulation in response to lyso-Gb3. Notch1 siRNA or γ-secretase inhibition also prevented the lyso-Gb3-induced upregulation of Notch1, Notch ligand Jagged1 and chemokine (MCP1, RANTES) expression. Notch siRNA prevented the activation of nuclear factor kappa B (NFκB), and NFκB activation contributed to Notch1-mediated inflammatory responses as the NFκB inhibitor, parthenolide, prevented lyso-Gb3-induced chemokine upregulation. Notch1 also mediates fibrogenic responses in podocytes as Notch siRNA prevented lyso-Gb3 upregulation of fibronectin mRNA. Supporting the clinical relevance of cell culture findings, active Notch1, Jagged1 and HES1 were observed in Fabry kidney biopsies. Lyso-Gb3 elicited similar responses in mouse kidney. In conclusion, lyso-Gb3 promotes Notch1-mediated inflammatory and fibrogenic responses in podocytes that may contribute to Fabry nephropathy.

'Strengthening the fungal cell wall through chitin-glucan cross-links: effects on morphogenesis and cell integrity'.

The cross-linking of polysaccharides to assemble new cell wall in fungi requires transglycosylation mechanisms by which preexisting glycosidic linkages are broken and new linkages are created between the polysaccharides. The molecular mechanisms for these processes, which are essential for fungal cell biology, are only now beginning to be elucidated. Recent development of in vivo and in vitro biochemical approaches has allowed characterization of important aspects about the formation of chitin-glucan covalent cell wall cross-links by cell wall transglycosylases of the CRH family and their biological function. Covalent linkages between chitin and glucan mediated by Crh proteins control morphogenesis and also play important roles in the remodeling of the fungal cell wall as part of the compensatory responses necessary to counterbalance cell wall stress. These enzymes are encoded by multigene families of redundant proteins very well conserved in fungal genomes but absent in mammalian cells. Understanding the molecular basis of fungal adaptation to cell wall stress through these and other cell wall remodeling enzymatic activities offers an opportunity to explore novel antifungal treatments and to identify potential fungal virulence factors.

Downregulation of kidney protective factors by inflammation: role of transcription factors and epigenetic mechanisms.

Chronic kidney disease (CKD) is associated to an increased risk of death, CKD progression, and acute kidney injury (AKI) even from early stages, when glomerular filtration rate (GFR) is preserved. The link between early CKD and these risks is unclear, since there is no accumulation of uremic toxins. However, pathological albuminuria and kidney inflammation are frequent features of early CKD, and the production of kidney protective factors may be decreased. Indeed, Klotho expression is already decreased in CKD category G1 (normal GFR). Klotho has anti-aging and nephroprotective properties, and decreased Klotho levels may contribute to increase the risk of death, CKD progression, and AKI. In this review, we discuss the downregulation by mediators of inflammation of molecules with systemic and/or renal local protective functions, exemplified by Klotho and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), a transcription factor that promotes mitochondrial biogenesis. Cytokines such as TWEAK, TNF-α, or transforming growth factor -ß1 produced locally during kidney injury or released from inflammatory sites at other organs may decrease kidney expression of Klotho and PGC-1α or lead to suboptimal recruitment of these nephroprotective proteins. Transcription factors (e.g., Smad3 and NF-κB) and epigenetic mechanisms (e.g., histone acetylation or methylation) contribute to downregulate the expression of Klotho and/or PGC-1α, while histone crotonylation promotes PGC-1α expression. NF-κBiz facilitates the repressive effect of NF-κB on Klotho expression. A detailed understanding of these mediators may contribute to the development of novel therapeutic approaches to prevent CKD progression and its negative impact on mortality and AKI.

PCSK9 in diabetic kidney disease.

BACKGROUND: Chronic Kidney Disease (CKD) and, specifically, diabetic kidney disease (DKD)+, is among the fastest increasing causes of death worldwide. A better understanding of the factors contributing to the high mortality may help design novel monitoring and therapeutic approaches, since protection offered by statins in CKD patients is not satisfactory. Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) promotes hypercholesterolemia and may be targeted therapeutically. Adding anti-PCSK9 agents to standard lipid lowering therapy further reduces the incidence of cardiovascular events. DESIGN: We studied plasma PCSK9 in a cross-sectional study of 134 diabetic kidney disease patients with estimated glomerular filtration rate (eGFR) categories G1-G4 and albuminuria categories A1-A3, in order to identify factors influencing plasma PCSK9 in this population. RESULTS: Mean±SD plasma PCSK9 levels were 309.8±113.9 ng/ml. Plasma PCSK9 was not influenced by eGFR or albuminuria, but was higher in patients on lipid lowering therapy. In univariate analysis, plasma PCSK9 showed a significant positive correlation with serum total iron binding capacity, vitamin E, plasma renin and phosphaturia, and there was a trend towards a positive correlation with total serum cholesterol. In multivariate models, only therapy with fibrate and statin, and renin remained independently correlated with plasma PCSK9. However, multivariate models explained very little of the PCSK9 variability. CONCLUSIONS: In DKD, therapy with lipid lowering drugs and specially the fibrate/statin combination were independently associated with higher PCSK9 levels. The biomarker potential of PCSK9 levels to identify DKD patients that may benefit from anti-PCSK9 strategies should be studied.

Chronicity following ischaemia-reperfusion injury depends on tubular-macrophage crosstalk involving two tubular cell-derived CSF-1R activators: CSF-1 and IL-34.

Two structurally unrelated ligands activate the macrophage colony stimulating factor receptor (CSF-1R, c-fms, CD115): M-CSF/CSF-1 and interleukin-34 (IL-34). Both ligands promote macrophage proliferation, survival and differentiation. IL-34 also activates the protein-tyrosine phosphatase ζ receptor (PTP-ζ, PTPRZ1). Both receptors and cytokines are increased during acute kidney injury. While tubular cell-derived CSF-1 is required for kidney repair, Baek et al (J Clin Invest 2015; 125: 3198-3214) have now identified tubular epithelial cell-derived IL-34 as a promoter of kidney neutrophil and macrophage infiltration and tubular cell destruction during experimental kidney ischaemia-reperfusion, leading to chronic injury. IL-34 promoted proliferation of both intrarenal macrophages and bone marrow cells, increasing circulating neutrophils and monocytes and their kidney recruitment. Thus, injured tubular cells release two CSF-1R activators, one (CSF-1) that promotes tubular cell survival and kidney repair and another (IL-34) that promotes chronic kidney damage. These results hold promise for the development of IL-34-targeting strategies to prevent ischaemia-reperfusion kidney injury in contexts such as kidney transplantation. However, careful consideration should be given to the recent characterization by Bezie et al. (J Clin Invest 2015; 125: 3952-3964) of IL-34 as a T regulatory cell (Treg) cytokine that modulates macrophage responses so that IL-34-primed macrophages potentiate the immune suppressive capacity of Tregs and promote graft tolerance.