Inhibition of glucosylceramide accumulation results in effective blockade of polycystic kidney disease in mouse models

Glucosylceramide synthase modulation ameliorates murine renal pathologies and promotes macrophage effector function in vitro

While significant advances have been made in understanding renal pathophysiology, less is known about the role of glycosphingolipid (GSL) metabolism in driving organ dysfunction. Here, we used a small molecule inhibitor of glucosylceramide synthase to modulate GSL levels in three mouse models of distinct renal pathologies: Alport syndrome (Col4a3 KO), polycystic kidney disease (Nek8jck), and steroid-resistant nephrotic syndrome (Nphs2 cKO). At the tissue level, we identified a core immune-enriched transcriptional signature that was shared across models and enriched in human polycystic kidney disease. Single nuclei analysis identified robust transcriptional changes across multiple kidney cell types, including epithelial and immune lineages. To further explore the role of GSL modulation in macrophage biology, we performed in vitro studies with homeostatic and inflammatory bone marrow-derived macrophages. Cumulatively, this study provides a comprehensive overview of renal dysfunction and the effect of GSL modulation on kidney-derived cells in the setting of renal dysfunction.

Investigational agents for autosomal dominant polycystic kidney disease: preclinical and early phase study insights

INTRODUCTION

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the most common inherited kidney condition caused by a single-gene mutation. It leads patients to kidney failure in more than 50% of cases by the age of 60, and, given the dominant inheritance, this disease is present in the family history in more than 90% of cases.

AREAS COVERED

This review aims to analyze the set of preclinical and early-phase studies to provide a general view of the current progress on ADPKD therapeutic options. Articles from PubMed and the current status of the trials listed in clinicaltrials.gov were examined for the review.

EXPERT OPINION

Many potential therapeutic targets are currently under study for the treatment of ADPKD. A few drugs have reached the clinical phase, while many are currently still in the preclinical phase. Organoids could be a novel approach to the study of drugs in this phase. Other than pharmacological options, very important developing approaches are represented by gene therapy and the use of MiRNA inhibitors.

Glucosylceramide flippases contribute to cellular glucosylceramide homeostasis

Lipid transport is an essential cellular process with importance to human health, disease development, and therapeutic strategies. Type IV P-type ATPases (P4-ATPases) have been identified as membrane lipid flippases by utilizing nitrobenzoxadiazole (NBD)-labeled lipids as substrates. Among the 14 human type IV P-type ATPases, ATP10D was shown to flip NBD-glucosylceramide (GlcCer) across the plasma membrane. Here, we found that conversion of incorporated GlcCer (d18:1/12:0) to other sphingolipids is accelerated in cells exogenously expressing ATP10D but not its ATPase-deficient mutant. These findings suggest that 1) ATP10D flips unmodified GlcCer as well as NBD-GlcCer at the plasma membrane and 2) ATP10D can translocate extracellular GlcCer, which is subsequently converted to other metabolites. Notably, exogenous expression of ATP10D led to the reduction in cellular hexosylceramide levels. Moreover, the expression of GlcCer flippases, including ATP10D, also reduced cellular hexosylceramide levels in fibroblasts derived from patients with Gaucher disease, which is a lysosomal storage disorder with excess GlcCer accumulation. Our study highlights the contribution of ATP10D to the regulation of cellular GlcCer levels and maintaining lipid homeostasis.

Impact of renal tubular Cpt1a overexpression on the kidney metabolome in the folic acid-induced fibrosis mouse model

Background: Chronic kidney disease (CKD) is characterized by the progressive and irreversible deterioration of kidney function and structure with the appearance of renal fibrosis. A significant decrease in mitochondrial metabolism, specifically a reduction in fatty acid oxidation (FAO) in tubular cells, is observed in tubulointerstitial fibrosis, whereas FAO enhancement provides protection. Untargeted metabolomics offers the potential to provide a comprehensive analysis of the renal metabolome in the context of kidney injury. Methodology: Renal tissue from a carnitine palmitoyl transferase 1a (Cpt1a) overexpressing mouse model, which displays enhanced FAO in the renal tubule, subjected to folic acid nephropathy (FAN) was studied through a multiplatform untargeted metabolomics approach based on LC-MS, CE-MS and GC-MS analysis to achieve the highest coverage of the metabolome and lipidome affected by fibrosis. The expression of genes related to the biochemical routes showing significant changes was also evaluated. Results: By combining different tools for signal processing, statistical analysis and feature annotation, we were able to identify variations in 194 metabolites and lipids involved in many metabolic routes: TCA cycle, polyamines, one-carbon metabolism, amino acid metabolism, purine metabolism, FAO, glycerolipids and glycerophospholipids synthesis and degradation, glycosphingolipids interconversion, and sterol metabolism. We found several metabolites strongly altered by FAN, with no reversion induced by Cpt1a overexpression (v.g. citric acid), whereas other metabolites were influenced by CPT1A-induced FAO (v.g. glycine-betaine). Conclusion: It was implemented a successful multiplatform metabolomics approach for renal tissue analysis. Profound metabolic changes accompany CKD-associated fibrosis, some associated with tubular FAO failure. These results highlight the importance of addressing the crosstalk between metabolism and fibrosis when undertaking studies attempting to elucidate the mechanism of CKD progression.

Repurposing small molecules for Nephronophthisis and related renal ciliopathies

Nephronophthisis is an autosomal recessive tubulo-interstitial nephropathy, belonging to the ciliopathy disorders, characterized by fibrosis and/or cysts. It is the most common genetic cause of renal failure in children and young adults. Clinically and genetically heterogeneous, it is caused by variants in ciliary genes resulting in either an isolated kidney disease or syndromic forms in association with other manifestations of ciliopathy disorders. No curative treatment is currently available. Over the past two decades, advances in understanding disease mechanisms have identified several dysregulated signaling pathways, some shared with other cystic kidney diseases. Notably, molecules previously developed to target these pathways have shown promising beneficial effects in orthologous mouse models. In addition to these knowledge-based repurposing approaches, unbiased "in cellulo" phenotypic screens of "repurposing" libraries identified small molecules able to rescue the ciliogenesis defects observed in nephronophthisis conditions. Those compounds appeared to act on relevant pathways and, when tested, showed beneficial nephronophthisis-associated kidney and/or extra-renal defects in mice. In this review, we have summarized those studies which highlight the drug repurposing strategies in the context of a rare disorders such as nephronophthisis-related ciliopathies, with broad genetic heterogeneity and systemic manifestations but with shared disease mechanisms.

Role of UDP-glucose ceramide glucosyltransferase in venous malformation

Venous malformation (VM) results from the abnormal growth of the vasculature; however, the detailed molecular mechanism remains unclear. As a glycosyltransferase, UDP-glucose ceramide glucosyltransferase (UGCG) is localized to the Golgi body and is a key enzyme in the first step of glycosphingolipid synthesis. Here, we aimed to explore the relationship between UGCG and the development of VM. First, investigations using RT-qPCR and Western blotting on the diseased vasculature of VM patients and normal vascular tissues revealed that UGCG expression was markedly elevated in the diseased vessels. Subsequently, immunofluorescence assay showed that UGCG was co-localized with CD31, an endothelial cell marker, in tissues from patients with VM and healthy subjects. Then, we established TIE2-L914F-mutant human umbilical vein endothelial cells (HUVECs) by lentivirus transfection. Next, Western blotting revealed that UGCG expression was considerably higher in HUVECs^TIE2-L914F. In addition, we established a UGCG-overexpressing HUVECs line by plasmid transfection. With the CCK8 cell proliferation experiment, wound healing assay, and tube formation assay, we found that UGCG could promote the proliferation, migration, and tube formation activity of HUVECs, whereas the inhibition of UGCG could inhibit the proliferation, migration, and tube formation activity of HUVECs^TIE2-L914F. Finally, Western blotting revealed that UGCG regulates the AKT/mTOR pathway in HUVECs. These data demonstrated that UGCG can affect the activity of vascular endothelial cells and regulate the AKT/mTOR signaling pathway; this is a potential mechanism underlying VM pathogenesis.

Autosomal Dominant Polycystic Kidney Disease Therapies on the Horizon

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the formation of numerous kidney cysts which leads to kidney failure. ADPKD is responsible for approximately 10% of patients with kidney failure. Overwhelming evidence supports that vasopressin and its downstream cyclic adenosine monophosphate signaling promote cystogenesis, and targeting vasopressin 2 receptor with tolvaptan and other antagonists ameliorates cyst growth in preclinical studies. Tolvaptan is the only drug approved by Food and Drug Administration to treat ADPKD patients at the risk of rapid disease progression. A major limitation of the widespread use of tolvaptan is aquaretic events. This review discusses the potential strategies to improve the tolerability of tolvaptan, the progress on the use of an alternative vasopressin 2 receptor antagonist lixivaptan, and somatostatin analogs. Recent advances in understanding the pathophysiology of PKD have led to new approaches of treatment via targeting different signaling pathways. We review the new pharmacotherapies and dietary interventions of ADPKD that are promising in the preclinical studies and investigated in clinical trials.

Renal ciliopathies: promising drug targets and prospects for clinical trials

INTRODUCTION

Renal ciliopathies represent a collection of genetic disorders characterized by deficiencies in the biogenesis, maintenance, or functioning of the ciliary complex. These disorders, which encompass autosomal dominant polycystic kidney disease (ADPKD), autosomal recessive polycystic kidney disease (ARPKD), and nephronophthisis (NPHP), typically result in cystic kidney disease, renal fibrosis, and a gradual deterioration of kidney function, culminating in kidney failure.

AREAS COVERED

Here we review the advances in basic science and clinical research into renal ciliopathies which have yielded promising small compounds and drug targets, within both preclinical studies and clinical trials.

EXPERT OPINION

Tolvaptan is currently the sole approved treatment option available for ADPKD patients, while no approved treatment alternatives exist for ARPKD or NPHP patients. Clinical trials are presently underway to evaluate additional medications in ADPKD and ARPKD patients. Based on preclinical models, other potential therapeutic targets for ADPKD, ARPKD, and NPHP look promising. These include molecules targeting fluid transport, cellular metabolism, ciliary signaling and cell-cycle regulation. There is a real and urgent clinical need for translational research to bring novel treatments to clinical use for all forms of renal ciliopathies to reduce kidney disease progression and prevent kidney failure.

Inhibitors of Glucosylceramide Synthase

Glucosylceramide synthase can be targeted by high affinity small molecular weight inhibitors for the study of glycosphingolipid metabolism and function or for the treatment of glycosphingolipid storage disorders, including Gaucher and Fabry disease. This work is exemplified by the discovery and development of eliglustat tartrate, the first stand-alone small chemical entity approved for the treatment of Gaucher disease type 1. The development of inhibitors of glucosylceramide synthase that have utility for either research or clinical purposes begins with a testing funnel for screening candidate inhibitors for activity against this enzyme and for activity in lowering the content of glucosylceramide in intact cells. Two common assays for glucosylceramide synthase, one enzyme based and another cell based, are the focus of this chapter.

Metabolism-based approaches for autosomal dominant polycystic kidney disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) leads to end stage kidney disease (ESKD) through the development and expansion of multiple cysts throughout the kidney parenchyma. An increase in cyclic adenosine monophosphate (cAMP) plays an important role in generating and maintaining fluid-filled cysts because cAMP activates protein kinase A (PKA) and stimulates epithelial chloride secretion through the cystic fibrosis transmembrane conductance regulator (CFTR). A vasopressin V2 receptor antagonist, Tolvaptan, was recently approved for the treatment of ADPKD patients at high risk of progression. However additional treatments are urgently needed due to the poor tolerability, the unfavorable safety profile, and the high cost of Tolvaptan. In ADPKD kidneys, alterations of multiple metabolic pathways termed metabolic reprogramming has been consistently reported to support the growth of rapidly proliferating cystic cells. Published data suggest that upregulated mTOR and c-Myc repress oxidative metabolism while enhancing glycolytic flux and lactic acid production. mTOR and c-Myc are activated by PKA/MEK/ERK signaling so it is possible that cAMPK/PKA signaling will be upstream regulators of metabolic reprogramming. Novel therapeutics opportunities targeting metabolic reprogramming may avoid or minimize the side effects that are dose limiting in the clinic and improve on the efficacy observed in human ADPKD with Tolvaptan.

Glucose absorption drives cystogenesis in a human organoid-on-chip model of polycystic kidney disease

In polycystic kidney disease (PKD), fluid-filled cysts arise from tubules in kidneys and other organs. Human kidney organoids can reconstitute PKD cystogenesis in a genetically specific way, but the mechanisms underlying cystogenesis remain elusive. Here we show that subjecting organoids to fluid shear stress in a PKD-on-a-chip microphysiological system promotes cyst expansion via an absorptive rather than a secretory pathway. A diffusive static condition partially substitutes for fluid flow, implicating volume and solute concentration as key mediators of this effect. Surprisingly, cyst-lining epithelia in organoids polarize outwards towards the media, arguing against a secretory mechanism. Rather, cyst formation is driven by glucose transport into lumens of outwards-facing epithelia, which can be blocked pharmacologically. In PKD mice, glucose is imported through cysts into the renal interstitium, which detaches from tubules to license expansion. Thus, absorption can mediate PKD cyst growth in human organoids, with implications for disease mechanism and potential for therapy development.

Venglustat, a Novel Glucosylceramide Synthase Inhibitor, in Patients at Risk of Rapidly Progressing ADPKD: Primary Results of a Double-Blind, Placebo-Controlled, Phase 2/3 Randomized Clinical Trial

RATIONALE & OBJECTIVE

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the formation of multiple kidney cysts that leads to growth in total kidney volume (TKV) and progression to kidney failure. Venglustat is a glucosylceramide synthase inhibitor that has been shown to inhibit cyst growth and reduce kidney failure in preclinical models of ADPKD.

STUDY DESIGN

STAGED-PKD was a 2-stage, multicenter, double-blind, randomized, placebo-controlled phase 2/3 study in adults with ADPKD at risk of rapidly progressive disease, who were selected based on Mayo Clinic imaging classification of ADPKD class 1C, 1D, or 1E and an estimated glomerular filtration rate (eGFR) of 30-89.9mL/min/1.73m².

SETTING & PARTICIPANTS

Enrollment included 236 and 242 patients in stages 1 and 2, respectively.

INTERVENTIONS

In trial stage 1, the patients were randomized 1:1:1 to venglustat, 8mg; venglustat, 15mg; or placebo. In stage 2, the patients were randomized 1:1 to venglustat, 15mg (highest dose identified as safe and well tolerated in stage 1), or placebo.

OUTCOMES

Primary end points were rate of change in TKV over 18 months in stage 1 and eGFR slope over 24 months in stage 2. Secondary end points were eGFR slope over 18 months (stage 1), rate of change in TKV (stage 2), and safety/tolerability, pain, and fatigue (stages 1 and 2).

RESULTS

A prespecified interim futility analysis showed that venglustat treatment had no effect on the annualized rate of change in TKV over 18 months (stage 1) and had a faster rate of decline in eGFR slope over 24 months (stage 2). Due to this lack of efficacy, the study was terminated early.

LIMITATIONS

The short follow-up period after the end of treatment and limited generalizability of the findings.

CONCLUSIONS

In patients with rapidly progressing ADPKD, treatment with venglustat at either 8mg or 15mg showed no change in the rate of change in TKV and a faster rate of eGFR decline in STAGED-PKD despite a dose-dependent decrease in plasma glucosylceramide levels.

FUNDING

This study was funded by Sanofi.

TRIAL REGISTRATION

Registered at ClinicalTrials.gov with study number NCT03523728.

SCF-SKP2 E3 ubiquitin ligase links mTORC1/ER stress/ISR with YAP activation in murine renal cystogenesis

The Hippo pathway nuclear effector Yes-associated protein (YAP) potentiates the progression of polycystic kidney disease (PKD) arising from ciliopathies. The mechanisms underlying the increase in YAP expression and transcriptional activity in PKD remain obscure. We observed that in kidneys from mice with juvenile cystic kidney (jck) ciliopathy, the aberrant hyperactivity of mechanistic target of rapamycin complex 1 (mTORC1), driven by ERK1/2 and PI3K/AKT cascades, induced ER proteotoxic stress. To reduce this stress by reprogramming translation, the protein kinase R-like ER kinase-eukaryotic initiation factor 2α (PERK/eIF2α) arm of the integrated stress response (ISR) was activated. PERK-mediated phosphorylation of eIF2α drove the selective translation of activating transcription factor 4 (ATF4), potentiating YAP expression. In parallel, YAP underwent K63-linked polyubiquitination by SCF S-phase kinase-associated protein 2 (SKP2) E3 ubiquitin ligase, a Hippo-independent, nonproteolytic ubiquitination that enhances YAP nuclear trafficking and transcriptional activity in cancer cells. Defective ISR cellular adaptation to ER stress in eIF2α phosphorylation-deficient jck mice further augmented YAP-mediated transcriptional activity and renal cyst growth. Conversely, pharmacological tuning down of ER stress/ISR activity and SKP2 expression in jck mice by administration of tauroursodeoxycholic acid (TUDCA) or tolvaptan impeded these processes. Restoring ER homeostasis and/or interfering with the SKP2-YAP interaction represent potential therapeutic avenues for stemming the progression of renal cystogenesis.

Parapelvic Cysts: An Imaging Marker of Kidney Disease Potentially Leading to the Diagnosis of Treatable Rare Genetic Disorders? A Narrative Review of the Literature

Simple renal cysts are a common finding during abdominal imaging assessment. The incidence increases with age and it is higher in male gender. Parapelvic cysts are a subset of simple cysts that arise within the renal parenchyma, adjacent to the renal sinus, characterized by being generally single, larger, and incompletely surrounded by renal parenchyma. Noteworthy, parapelvic cysts are a rare and understudied condition which, although considered clinically insignificant due to the absence of influence on renal function, still have a controversial aetiopathogenesis. On the other hand, urological management and differential diagnosis have been thoroughly investigated. The aim of our review is to provide an overall vision on this rare condition, usually misdiagnosed and underestimated, on the basis of more recent data. An accurate differential diagnosis of parapelvic cysts can lead to the identification of treatable conditions such as Fabry disease, autosomal dominant polycystic kidney disease, polycystic liver disease and tuberous sclerosis complex disease.

The STAGED-PKD 2-Stage Adaptive Study With a Patient Enrichment Strategy and Treatment Effect Modeling for Improved Study Design Efficiency in Patients With ADPKD

Rationale & Objective

Venglustat, a glucosylceramide synthase inhibitor, inhibits cyst growth and reduces kidney failure in mouse models of autosomal dominant polycystic kidney disease (ADPKD). STAGED-PKD aims to determine the safety and efficacy of venglustat and was designed using patient enrichment for progression to end-stage kidney disease and modeling from prior ADPKD trials.

Study Design

STAGED-PKD is a 2-stage, international, double-blind, randomized, placebo-controlled trial in adults with ADPKD (Mayo Class 1C-1E) and estimated glomerular filtration rate (eGFR) 45-<90 mL/min/1.73 m² at risk of rapidly progressive disease. Enrichment for rapidly progressing patients was identified based on retrospective analysis of total kidney volume (TKV) and eGFR slope from the combined Consortium for Radiologic Imaging Studies of Polycystic Kidney Disease and HALT Progression of Polycystic Kidney Disease A studies.

Setting & Participants

Target enrollment in stages 1 and 2 was 240 and 320 patients, respectively.

Interventions

Stage 1 randomizes patients 1:1:1 to venglustat 8 mg or 15 mg once daily or placebo. Stage 2 randomizes patients 1:1 to placebo or venglustat, with the preferred dose based on stage 1 safety data.

Outcomes

Primary endpoints are TKV growth rate over 18 months in stage 1 and eGFR slope over 24 months in stage 2. Secondary endpoints include: annualized rate of change in eGFR from baseline to 18 months (stage 1); annualized rate of change in TKV based on magnetic resonance imaging from baseline to 18 months (stage 2); and safety, tolerability, pain, and fatigue (stages 1 and 2).

Limitations

If stage 1 is unsuccessful, patients enrolled in the trial may develop drug-related adverse events that can have long-lasting effects.

Conclusions

Modeling allows the design and powering of a 2-stage combined study to assess venglustat’s impact on TKV growth and eGFR slope. Stage 1 TKV assessment via a nested approach allows early evaluation of efficacy and increased efficiency of the trial design by reducing patient numbers and trial duration.

Funding

This study was funded by Sanofi.

Trial registration

STAGED-PKD has been registered at ClinicalTrials.gov with study number NCT03523728.

The lonidamine derivative H2-gamendazole reduces cyst formation in polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a debilitating renal neoplastic disorder with limited treatment options. It is characterized by the formation of large fluid-filled cysts that develop from kidney tubules through abnormal cell proliferation and cyst-filling fluid secretion driven by cAMP-dependent Cl- secretion. We tested the effectiveness of the indazole carboxylic acid H2-gamendazole (H2-GMZ), a derivative of lonidamine, to inhibit these processes using in vitro and in vivo models of ADPKD. H2-GMZ was effective in rapidly blocking forskolin-induced, Cl--mediated short-circuit currents in human ADPKD cells, and it significantly inhibited both cAMP- and epidermal growth factor-induced proliferation of ADPKD cells. Western blot analysis of H2-GMZ-treated ADPKD cells showed decreased phosphorylated ERK and decreased hyperphosphorylated retinoblastoma levels. H2-GMZ treatment also decreased ErbB2, Akt, and cyclin-dependent kinase 4, consistent with inhibition of heat shock protein 90, and it decreased levels of the cystic fibrosis transmembrane conductance regulator Cl- channel protein. H2-GMZ-treated ADPKD cultures contained a higher proportion of smaller cells with fewer and smaller lamellipodia and decreased cytoplasmic actin staining, and they were unable to accomplish wound closure even at low H2-GMZ concentrations, consistent with an alteration in the actin cytoskeleton and decreased cell motility. Experiments using mouse metanephric organ cultures showed that H2-GMZ inhibited cAMP-stimulated cyst growth and enlargement. In vivo, H2-GMZ was effective in slowing postnatal cyst formation and kidney enlargement in the Pkd1flox/flox: Pkhd1-Cre mouse model. Thus, H2-GMZ treatment decreases Cl- secretion, cell proliferation, cell motility, and cyst growth. These properties, along with its reported low toxicity, suggest that H2-GMZ might be an attractive candidate for treatment of ADPKD.NEW & NOTEWORTHY Autosomal dominant polycystic kidney disease (ADPKD) is a renal neoplastic disorder characterized by the formation of large fluid-filled cysts that develop from kidney tubules through abnormal cell proliferation and cyst-filling fluid secretion driven by cAMP-dependent Cl- secretion. This study shows that the lonidamine derivative H2-GMZ inhibits Cl- secretion, cell proliferation, and cyst growth, suggesting that it might have therapeutic value for the treatment of ADPKD.

Molecular Mechanisms of Epigenetic Regulation, Inflammation, and Cell Death in ADPKD

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder, which is caused by mutations in the PKD1 and PKD2 genes, characterizing by progressive growth of multiple cysts in the kidneys, eventually leading to end-stage kidney disease (ESKD) and requiring renal replacement therapy. In addition, studies indicate that disease progression is as a result of a combination of factors. Understanding the molecular mechanisms, therefore, should facilitate the development of precise therapeutic strategies for ADPKD treatment. The roles of epigenetic modulation, interstitial inflammation, and regulated cell death have recently become the focuses in ADPKD. Different epigenetic regulators, and the presence of inflammatory markers detectable even before cyst growth, have been linked to cyst progression. Moreover, the infiltration of inflammatory cells, such as macrophages and T cells, have been associated with cyst growth and deteriorating renal function in humans and PKD animal models. There is evidence supporting a direct role of the PKD gene mutations to the regulation of epigenetic mechanisms and inflammatory response in ADPKD. In addition, the role of regulated cell death, including apoptosis, autophagy and ferroptosis, have been investigated in ADPKD. However, there is no consensus whether cell death promotes or delays cyst growth in ADPKD. It is therefore necessary to develop an interactive picture between PKD gene mutations, the epigenome, inflammation, and cell death to understand why inherited PKD gene mutations in patients may result in the dysregulation of these processes that increase the progression of renal cyst formation.

Drugs in Clinical Development to Treat Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by progressive cyst formation that ultimately leads to kidney failure in most patients. Approximately 10% of patients who receive kidney replacement therapy suffer from ADPKD. To date, a vasopressin V2 receptor antagonist (V2RA) is the only drug that has been proven to attenuate disease progression. However, aquaresis-related adverse events limit its widespread use. Data on the renoprotective effects of somatostatin analogues differ largely between studies and medications. This review discusses new drugs that are investigated in clinical trials to treat ADPKD, such as cystic fibrosis transmembrane conductance regulator (CFTR) modulators and micro RNA inhibitors, and drugs already marketed for other indications that are being investigated for off-label use in ADPKD, such as metformin. In addition, potential methods to improve the tolerability of V2RAs are discussed, as well as methods to select patients with (likely) rapid disease progression and issues regarding the translation of preclinical data into clinical practice. Since ADPKD is a complex disease with a high degree of interindividual heterogeneity, and the mechanisms involved in cyst growth also have important functions in various physiological processes, it may prove difficult to develop drugs that target cyst growth without causing major adverse events. This is especially important since long-standing treatment is necessary in this chronic disease. This review therefore also discusses approaches to targeted therapy to minimize systemic side effects. Hopefully, these developments will advance the treatment of ADPKD.

Ciliary membrane, localised lipid modification and cilia function

Cilium, a tiny microtubule-based cellular appendage critical for cell signalling and physiology, displays a large variety of receptors. The composition and turnover of ciliary lipids and receptors determine cell behaviour. Due to the exclusion of ribosomal machinery and limited membrane area, a cilium needs adaptive logistics to actively reconstitute the lipid and receptor compositions during development and differentiation. How is this dynamicity generated? Here, we examine whether, along with the Intraflagellar-Transport, targeted changes in sector-wise lipid composition could control the receptor localisation and functions in the cilia. We discuss how an interplay between ciliary lipid composition, localised lipid modification, and receptor function could contribute to cilia growth and signalling. We argue that lipid modification at the cell-cilium interface could generate an added thrust for a selective exchange of membrane lipids and the transmembrane and membrane-associated proteins.

Autosomal Dominant Polycystic Kidney Disease: From Pathophysiology of Cystogenesis to Advances in the Treatment

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic renal disease, with an estimated prevalence between 1:1000 and 1:2500. It is mostly caused by mutations of the PKD1 and PKD2 genes encoding polycystin 1 (PC1) and polycystin 2 (PC2) that regulate cellular processes such as fluid transport, differentiation, proliferation, apoptosis and cell adhesion. Reduction of calcium ions and induction of cyclic adenosine monophosphate (sAMP) promote cyst enlargement by transepithelial fluid secretion and cell proliferation. Abnormal activation of MAPK/ERK pathway, dysregulated signaling of heterotrimeric G proteins, mTOR, phosphoinositide 3-kinase, AMPK, JAK/STAT activator of transcription and nuclear factor kB (NF-kB) are involved in cystogenesis. Another feature of cystic tissue is increased extracellular production and recruitment of inflammatory cells and abnormal connections among cells. Moreover, metabolic alterations in cystic cells including defective glucose metabolism, impaired beta-oxidation and abnormal mitochondrial activity were shown to be associated with cyst expansion. Although tolvaptan has been recently approved as a drug that slows ADPKD progression, some patients do not tolerate tolvaptan because of frequent aquaretic. The advances in the knowledge of multiple molecular pathways involved in cystogenesis led to the development of animal and cellular studies, followed by the development of several ongoing randomized controlled trials with promising drugs. Our review is aimed at pathophysiological mechanisms in cystogenesis in connection with the most promising drugs in animal and clinical studies.

Dysregulated sphingolipid metabolism and autophagy in granulosa cells of women with endometriosis

We evaluated metabolic profiles between cumulus cells (CCs) and mural granulosa cells (MGCs) derived from women with endometriosis to identify their correlations with oocyte quality. CCs and MGCs were collected from women with and without endometriosis undergoing in vitro fertilization/intracytoplasmic sperm injection treatment. The metabolomics of CCs and MGCs were measured by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) followed by a quantitative polymerase chain reaction to further confirm the genes involved in the metabolic results. LC-MS/MS analysis revealed differences in 24 metabolites of CCs and 71 metabolites of MGCs between groups. Among them, five metabolites were upregulated and 19 metabolites were downregulated in CCs with endometriosis, whereas three metabolites were upregulated and 68 metabolites were downregulated in MGCs with endometriosis. Metabolites related to sphingolipid metabolism, which included palmitic acid (PA) and docosahexaenoic acid, increased significantly only in CCs with endometriosis, whereas sphingosine and PA were significantly downregulated in MGCs with endometriosis compared with CCs and MGCs without endometriosis. Gene expression involved in ceramide synthesis (CERS1, SPTL1, and SMPD1) and autophagy (BECN1, LAMP, and PC3) were significantly higher in CCs with endometriosis according to FASN, BECN1, and LAMP protein expressions. However, gene expression involved in ceramide synthesis (SPHK1, ASAH1, and SGPP1) and autophagy (BECN1, LAMP, and PC3) were significantly lower in MGCs with endometriosis, whereas CERS1 and UGCG expression increased. There are differences in sphingolipid metabolites in CCs and MGCs with endometriosis compared with women without endometriosis. These differences seem to be involved in the regulation of autophagic cell death in preovulatory follicles.

[Tolvaptan, a vasopressin V2 receptor antagonist, is the world's first approved drug for treatment of autosomal dominant polycystic kidney disease (ADPKD)]

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic kidney disease. Fluid-filled cysts develop and enlarge in both kidneys, eventually leading to kidney failure. Tolvaptan is a selective vasopressin V₂ receptor antagonist and the first and only drug approved for treatment of ADPKD. It blocks binding of arginine vasopressin (AVP) to V₂ receptors in the collecting duct of kidney, thereby inducing water diuresis (aquaresis) without losing electrolytes. Therefore, tolvaptan was originally developed and approved as the first oral aquaretic agent for treatment of hyponatremia and fluid volume overload in heart failure and cirrhosis. During the development of tolvaptan as aquaretics, efficacy of V₂ antagonist in polycystic kidney animal model was reported and then the development of tolvaptan for ADPKD was also initiated. Cyclic adenosine monophosphate (cAMP) plays an important role in cyst growth by promoting cell proliferation and fluid secretion. Tolvaptan showed suppression of cyst growth through inhibiting AVP-induced cAMP production and delayed the onset of end-stage renal disease in an animal model. In the phase 3 clinical trial in ADPKD patients (TEMPO 3:4 trial), 3-year treatment with tolvaptan slowed the disease progression including increase of kidney volume and decline in renal function. Efficacy of tolvaptan in patients with late-stage ADPKD was confirmed in another 1-year phase 3 REPRISE trial. Tolvaptan is approved for treatment of ADPKD in more than 40 countries and we expect it can contribute to more ADPKD patients worldwide. We also expect that drugs with new mechanisms will be available in the near future.

Nephronophthisis-Pathobiology and Molecular Pathogenesis of a Rare Kidney Genetic Disease

The exponential rise in our understanding of the aetiology and pathophysiology of genetic cystic kidney diseases can be attributed to the identification of cystogenic genes over the last three decades. The foundation of this was laid by positional cloning strategies which gradually shifted towards next-generation sequencing (NGS) based screenings. This shift has enabled the discovery of novel cystogenic genes at an accelerated pace unlike ever before and, most notably, the past decade has seen the largest increase in identification of the genes which cause nephronophthisis (NPHP). NPHP is a monogenic autosomal recessive cystic kidney disease caused by mutations in a diverse clade of over 26 identified genes and is the most common genetic cause of renal failure in children. NPHP gene types present with some common pathophysiological features alongside a diverse range of extra-renal phenotypes associated with specific syndromic presentations. This review provides a timely update on our knowledge of this disease, including epidemiology, pathophysiology, anatomical and molecular features. We delve into the diversity of the NPHP causing genes and discuss known molecular mechanisms and biochemical pathways that may have possible points of intersection with polycystic kidney disease (the most studied renal cystic pathology). We delineate the pathologies arising from extra-renal complications and co-morbidities and their impact on quality of life. Finally, we discuss the current diagnostic and therapeutic modalities available for disease management, outlining possible avenues of research to improve the prognosis for NPHP patients.

Renal involvement in a patient with the chronic visceral subtype of acid sphingomyelinase deficiency resembles Fabry disease

Acid sphingomyelinase deficiency (ASMD) is a lysosomal storage disease (LSD) in which sphingomyelin accumulates due to deficient acid sphingomyelinase. In the chronic visceral subtype, organ manifestations are generally limited to the spleen, liver, and lungs. We report a male patient with the chronic visceral subtype who developed proteinuria and renal insufficiency at the age of 49. In renal tissue, foam cells were observed in the glomeruli as well as sphingomyelin accumulation within podocytes, mesangial cells, endothelial cells, and tubular epithelial cells. Although macrophages are the primary storage cells in both ASMD and Gaucher disease, comparison to the histopathological findings in Gaucher and Fabry disease revealed a diffuse storage pattern in multiple renal cell types, closer resembling the pattern found in Fabry disease.

Pkd1 Mutation Has No Apparent Effects on Peroxisome Structure or Lipid Metabolism

Background

Multiple studies of tissue and cell samples from patients and preclinical models of autosomal dominant polycystic kidney disease report abnormal mitochondrial function and morphology and suggest metabolic reprogramming is an intrinsic feature of this disease. Peroxisomes interact with mitochondria physically and functionally, and congenital peroxisome biogenesis disorders can cause various phenotypes, including mitochondrial defects, metabolic abnormalities, and renal cysts. We hypothesized that a peroxisomal defect might contribute to the metabolic and mitochondrial impairments observed in autosomal dominant polycystic kidney disease.

Methods

Using control and Pkd1-/- kidney epithelial cells, we investigated peroxisome abundance, biogenesis, and morphology by immunoblotting, immunofluorescence, and live cell imaging of peroxisome-related proteins and assayed peroxisomal specific β-oxidation. We further analyzed fatty acid composition by mass spectrometry in kidneys of Pkd1fl/fl;Ksp-Cre mice. We also evaluated peroxisome lipid metabolism in published metabolomics datasets of Pkd1 mutant cells and kidneys. Lastly, we investigated if the C terminus or full-length polycystin-1 colocalize with peroxisome markers by imaging studies.

Results

Peroxisome abundance, morphology, and peroxisome-related protein expression in Pkd1-/- cells were normal, suggesting preserved peroxisome biogenesis. Peroxisomal β-oxidation was not impaired in Pkd1-/- cells, and there was no obvious accumulation of very-long-chain fatty acids in kidneys of mutant mice. Reanalysis of published datasets provide little evidence of peroxisomal abnormalities in independent sets of Pkd1 mutant cells and cystic kidneys, and provide further evidence of mitochondrial fatty acid oxidation defects. Imaging studies with either full-length polycystin-1 or its C terminus, a fragment previously shown to go to the mitochondria, showed minimal colocalization with peroxisome markers restricted to putative mitochondrion-peroxisome contact sites.

Conclusions

Our studies showed that loss of Pkd1 does not disrupt peroxisome biogenesis nor peroxisome-dependent fatty acid metabolism.

Glucosylceramide synthase regulates hepatocyte repair after concanavalin A-induced immune-mediated liver injury

Background

Sphingolipids produce pleiotropic signaling pathways, and participate in the pathological mechanism of hepatocyte apoptosis and necrosis during liver injury. However, the role of glucosylceramide synthase (GCS)-key enzyme that catalyzes the first glycosylation step, in liver injury is still vague.

Methods

All experiments were conducted using 7-9-week-old pathogen-free male C57BL/6 mice. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were detected in murine models of liver disease, in addition to histological characterization of liver injuries. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the relative expression of the GCS, matrix metallopeptidase-1 (MMP-1), and tissue inhibitor of metalloproteinase-1 (TIMP-1) genes. The GCS was observed through a fluorescence microscope, and the flow cytometry was used to detect hepatocyte apoptosis. The concentrations of serum IL-4, IL-6, and IL-10 were measured using enzyme-linked immune-sorbent assay (ELISA) kit. MMP-1 and TIMP-1 protein expression was measured via western blot (WB) analysis.

Results

Con A is often used as a mitogen to activate T lymphocytes and promote mitosis. A single dose of Con A injected intravenously will cause a rapid increase of ALT and AST, which is accompanied by the release of cytokines that cause injury and necrosis of hepatocytes. In this study, we successfully induced acute immune hepatitis in mice by Con A. Con A administration resulted in GCS upregulation in liver tissues. Moreover, the mice in the Con A group had significantly higher levels of ALT, AST, IL-4, IL-6, IL-10 and increased hepatocyte apoptosis than the control group. In contrast, all of the aforementioned genes were significantly downregulated after the administration of a GCS siRNA or Genz-123346 (i.e., a glucosylceramide synthase inhibitor) to inhibit the GCS gene. Additionally, the histopathological changes observed herein were consistent with our ALT, AST, IL-4, IL-6, and IL-10 expression results. However, unlike this, hepatocyte apoptosis has been further increased on the basis of the Con A group. Moreover, our qRT-PCR and WB results indicated that the expression of MMP-1 in the Con A group was significantly lower than that in the control group, whereas TIMP-1 exhibited the opposite trend. Conversely, MMP-1 expression in the GCS siRNA and Genz-123346 groups was higher than that in the Con A group, whereas TIMP-1 expression was lower.

Conclusions

GCS inhibition reduces Con A-induced immune-mediated liver injury in mice, which may be due to the involvement of GCS in the hepatocyte repair process after injury.

Insights Into the Molecular Mechanisms of Polycystic Kidney Diseases

Autosomal dominant (AD) and autosomal recessive (AR) polycystic kidney diseases (PKD) are severe multisystem genetic disorders characterized with formation and uncontrolled growth of fluid-filled cysts in the kidney, the spread of which eventually leads to the loss of renal function. Currently, there are no treatments for ARPKD, and tolvaptan is the only FDA-approved drug that alleviates the symptoms of ADPKD. However, tolvaptan has only a modest effect on disease progression, and its long-term use is associated with many side effects. Therefore, there is still a pressing need to better understand the fundamental mechanisms behind PKD development. This review highlights current knowledge about the fundamental aspects of PKD development (with a focus on ADPKD) including the PC1/PC2 pathways and cilia-associated mechanisms, major molecular cascades related to metabolism, mitochondrial bioenergetics, and systemic responses (hormonal status, levels of growth factors, immune system, and microbiome) that affect its progression. In addition, we discuss new information regarding non-pharmacological therapies, such as dietary restrictions, which can potentially alleviate PKD.

Correction of cilia structure and function alleviates multi-organ pathology in Bardet-Biedl syndrome mice

Bardet–Biedl syndrome (BBS) is a pleiotropic autosomal recessive ciliopathy affecting multiple organs. The development of potential disease-modifying therapy for BBS will require concurrent targeting of multi-systemic manifestations. Here, we show for the first time that monosialodihexosylganglioside accumulates in Bbs2^−/− cilia, indicating impairment of glycosphingolipid (GSL) metabolism in BBS. Consequently, we tested whether BBS pathology in Bbs2^−/− mice can be reversed by targeting the underlying ciliary defect via reduction of GSL metabolism. Inhibition of GSL synthesis with the glucosylceramide synthase inhibitor Genz-667161 decreases the obesity, liver disease, retinal degeneration and olfaction defect in Bbs2^−/− mice. These effects are secondary to preservation of ciliary structure and signaling, and stimulation of cellular differentiation. In conclusion, reduction of GSL metabolism resolves the multi-organ pathology of Bbs2^−/− mice by directly preserving ciliary structure and function towards a normal phenotype. Since this approach does not rely on the correction of the underlying genetic mutation, it might translate successfully as a treatment for other ciliopathies.

Therapeutic advances in ADPKD: the future awaits

Autosomal dominant polycystic kidney disease (ADPKD) is a heterogeneous genetic disorder included in ciliopathies, representing the fourth cause of end stage renal disease (ESRD), with an estimated prevalence between 1:1000 and 1:2500. It is mainly caused by mutations in the PKD1 and PKD2 genes encoding for polycystin 1 (PC1) and polycystin 2 (PC2), which regulate differentiation, proliferation, survival, apoptosis, and autophagy. The advances in the knowledge of multiple molecular pathways involved in the pathophysiology of ADPKD led to the development of several treatments which are currently under investigation. Recently, the widespread approval of tolvaptan and, in Italy, of long-acting release octreotide (octreotide-LAR), represents but the beginning of the new therapeutic management of ADPKD patients. Encouraging results are expected from ongoing randomized controlled trials (RCTs), which are investigating not only drugs acting on the calcium/cyclic adenosin monoposphate (cAMP) pathway, the most studied target so far, but also molecules targeting specific pathophysiological pathways (e.g. epidermal growth factor (EGF) receptor, AMP-activated protein kinase (AMPK) and KEAP1-Nrf2) and sphingolipids. Moreover, studies on animal models and cultured cells have also provided further promising therapeutic strategies based on the role of intracellular calcium, cell cycle regulation, MAPK pathway, epigenetic DNA, interstitial inflammation, and cell therapy. Thus, in a near future, tailored therapy could be the key to changing the natural history of ADPKD thanks to the vigorous efforts that are being made to implement clinical and preclinical studies in this field. Our review aimed to summarize the spectrum of drugs that are available in the clinical practice and the most promising molecules undergoing clinical, animal, and cultured cell studies.

Renal Ciliopathies: Sorting Out Therapeutic Approaches for Nephronophthisis

Nephronophthisis (NPH) is an autosomal recessive ciliopathy and a major cause of end-stage renal disease in children. The main forms, juvenile and adult NPH, are characterized by tubulointerstitial fibrosis whereas the infantile form is more severe and characterized by cysts. NPH is caused by mutations in over 20 different genes, most of which encode components of the primary cilium, an organelle in which important cellular signaling pathways converge. Ciliary signal transduction plays a critical role in kidney development and tissue homeostasis, and disruption of ciliary signaling has been associated with cyst formation, epithelial cell dedifferentiation and kidney function decline. Drugs have been identified that target specific signaling pathways (for example cAMP/PKA, Hedgehog, and mTOR pathways) and rescue NPH phenotypes in in vitro and/or in vivo models. Despite identification of numerous candidate drugs in rodent models, there has been a lack of clinical trials and there is currently no therapy that halts disease progression in NPH patients. This review covers the most important findings of therapeutic approaches in NPH model systems to date, including hypothesis-driven therapies and untargeted drug screens, approached from the pathophysiology of NPH. Importantly, most animal models used in these studies represent the cystic infantile form of NPH, which is less prevalent than the juvenile form. It appears therefore important to develop new models relevant for juvenile/adult NPH. Alternative non-orthologous animal models and developments in patient-based in vitro model systems are discussed, as well as future directions in personalized therapy for NPH.

Ceramide glycosylation and related enzymes in cancer signaling and therapy

Ceramides, the core of the sphingolipid metabolism, draw wide attention as tumor suppressor, and act directly on mitochondria to trigger apoptotic cell death. Ceramide-based therapies are being developed by using promote ceramide generating agents. The ceramide metabolism balance is regulated by multifaceted factors in cancer development. Ceramide metabolic enzymes can increase the elimination of ceramide and counteract the anti-tumor effects of ceramide. However, recent research showed that these metabolic enzymes were highly expressed in several cancers. Especially ceramide glycosyltransferases, they catalyze ceramide glycosylation and synthesis the skeleton of glycosphingolipids (GSLs), play an important role in regulating tumor progression and have a significant correlation with the poor prognosis of cancer patients. To further understand the biological characteristics of ceramide metabolism in tumor, this review focuses on the role of ceramide glycosylation and related enzymes in cancer signaling and therapy. Besides, the research on multidrug resistance and potential inhibitors of ceramide glycosyltransferases are also discussed. Advance study on the structure of ceramide glycosyltransferases and ceramide glycosylation signaling pathway will open the path to new therapies and treatments.

Limitations and opportunities in the pharmacotherapy of ciliopathies

Ciliopathies are a family of rather diverse conditions, which have been grouped based on the finding of altered or dysfunctional cilia, potentially motile, small cellular antennae extending from the surface of postmitotic cells. Cilia-related disorders include embryonically arising conditions such as Joubert, Usher or Kartagener syndrome, but also afflictions with a postnatal or even adult onset phenotype, i.e. autosomal dominant polycystic kidney disease. The majority of ciliopathies are syndromic rather than affecting only a single organ due to cilia being found on almost any cell in the human body. Overall ciliopathies are considered rare diseases. Despite that, pharmacological research and the strive to help these patients has led to enormous therapeutic advances in the last decade. In this review we discuss new treatment options for certain ciliopathies, give an outlook on promising future therapeutic strategies, but also highlight the limitations in the development of therapeutic approaches of ciliopathies.

A Web of Science-based scientometric analysis about mammalian target of rapamycin signaling pathway in kidney disease from 1986 to 2020

Background

The mammalian target of rapamycin (mTOR) signaling pathway is vital for the regulation of cell metabolism, growth and proliferation in the kidney. This study aims to show current research focuses and predict future trends about mTOR pathway in kidney disease by the methods of scientometric analysis.

Methods

We referred to publications from the Web of Science^TM Core Collection (WoSCC) Database. Carrot2, VOSviewer and CiteSpace programs were applied to evaluate the distribution and contribution of authors, institutes and countries/regions of extensive bibliographic metadata, show current research focuses and predict future trends in kidney disease's area.

Results

Until July 10, 2020, there are 2,585 manuscripts about mTOR signaling pathway in kidney disease in total and every manuscript is cited 27.39 times on average. The big name of course is the United States. Research hot spots include "diabetic nephropathy", "kidney transplantation", "autosomal dominant polycystic kidney disease", "tuberous sclerosis complex", "renal cell carcinoma" and "autophagy". Seven key clusters are detected, including "kidney transplantation", "autosomal dominant polycystic kidney disease", "renal transplantation", "renal cell carcinoma", "hamartin", "autophagy" and "tuberous sclerosis complex".

Conclusions

Diabetic nephropathy, kidney transplantation, autosomal dominant polycystic kidney disease, tuberous sclerosis complex, renal cell carcinoma and autophagy are future research hot spots by utilizing scientometric analysis. In the future, it is necessary to research these fields.

Convergence: Lactosylceramide-Centric Signaling Pathways Induce Inflammation, Oxidative Stress, and Other Phenotypic Outcomes

Lactosylceramide (LacCer), also known as CD17/CDw17, is a member of a large family of small molecular weight compounds known as glycosphingolipids. It plays a pivotal role in the biosynthesis of glycosphingolipids, primarily by way of serving as a precursor to the majority of its higher homolog sub-families such as gangliosides, sulfatides, fucosylated-glycosphingolipids and complex neutral glycosphingolipids—some of which confer “second-messenger” and receptor functions. LacCer is an integral component of the “lipid rafts,” serving as a conduit to transduce external stimuli into multiple phenotypes, which may contribute to mortality and morbidity in man and in mouse models of human disease. LacCer is synthesized by the action of LacCer synthase (β-1,4 galactosyltransferase), which transfers galactose from uridine diphosphate galactose (UDP-galactose) to glucosylceramide (GlcCer). The convergence of multiple physiologically relevant external stimuli/agonists—platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), stress, cigarette smoke/nicotine, tumor necrosis factor-α (TNF-α), and in particular, oxidized low-density lipoprotein (ox-LDL)—on β-1,4 galactosyltransferase results in its phosphorylation or activation, via a “turn-key” reaction, generating LacCer. This newly synthesized LacCer activates NADPH (nicotinamide adenine dihydrogen phosphate) oxidase to generate reactive oxygen species (ROS) and a highly “oxidative stress” environment, which trigger a cascade of signaling molecules and pathways and initiate diverse phenotypes like inflammation and atherosclerosis. For instance, LacCer activates an enzyme, cytosolic phospholipase A2 (cPLA2), which cleaves arachidonic acid from phosphatidylcholine. In turn, arachidonic acid serves as a precursor to eicosanoids and prostaglandin, which transduce a cascade of reactions leading to inflammation—a major phenotype underscoring the initiation and progression of several debilitating diseases such as atherosclerosis and cancer. Our aim here is to present an updated account of studies made in the field of LacCer metabolism and signaling using multiple animal models of human disease, human tissue, and cell-based studies. These advancements have led us to propose that previously unrelated phenotypes converge in a LacCer-centric manner. This LacCer synthase/LacCer-induced “oxidative stress” environment contributes to inflammation, atherosclerosis, skin conditions, hair greying, cardiovascular disease, and diabetes due to mitochondrial dysfunction. Thus, targeting LacCer synthase may well be the answer to remedy these pathologies.

The role of neuraminidase in TLR4-MAPK signalling and the release of cytokines by lupus serum-stimulated mesangial cells

Previously, we demonstrated neuraminidase (NEU) activity or NEU1 expression, specifically, is increased in the kidneys of lupus mice and urine of human patients with nephritis. Additionally, NEU activity mediates IL-6 secretion from lupus-prone MRL/lpr primary mouse mesangial cells (MCs) in response to an IgG mimic. IL-6 mediates glomerular inflammation and promotes tissue damage in patients and mouse strains with lupus nephritis. This study further elucidates the mechanisms by which NEU activity and NEU1 specifically mediates the release of IL-6 and other cytokines from lupus-prone MCs. We demonstrate significantly increased release of multiple cytokines and NEU activity in MRL/lpr MCs in response to serum from MRL/lpr mice (lupus serum). Inhibiting NEU activity significantly reduced secretion of three of those cytokines: IL-6, GM-CSF and MIP1α. Message levels of Il-6 and Gm-csf were also increased in response to lupus serum and reduced when NEU activity was inhibited. Neutralizing antibodies to cell-surface receptors and MAPK inhibitors in lupus serum- or LPS-stimulated MCs indicate TLR4 and p38 or ERK MAP kinase signalling play key roles in the NEU-mediated secretion of IL-6. Significantly reduced IL-6 release was observed in C57BL/6 (B6) Neu1+/+ primary MCs compared with wild-type (Neu1+/+) B6 MCs in response to lupus serum. Additional results show inhibiting NEU activity significantly increases sialic acid-containing N-glycan levels. Together, our novel observations support a role for NEU activity, and specifically NEU1, in mediating release of IL-6 from lupus-prone MCs in response to lupus serum through a TLR4-p38/ERK MAPK signalling pathway that likely includes desialylation of glycoproteins.

Gb3-cSrc complex in glycosphingolipid-enriched microdomains contributes to the expression of p53 mutant protein and cancer drug resistance via β-catenin-activated RNA methylation

Glucosylceramide synthase (GCS) is a key enzyme catalyzing ceramide glycosylation to generate glucosylceramide (GlcCer), which in turn serves as the precursor for cells to produce glycosphingolipids (GSLs). In cell membranes, GSLs serve as essential components of GSL-enriched microdomains (GEMs) and mediate membrane functions and cell behaviors. Previous studies showed that ceramide glycosylation correlates with upregulated expression of p53 hotspot mutant R273H and cancer drug resistance. Yet, the underlying mechanisms remain elusive. We report herewith that globotriaosylceramide (Gb3) is associated with cSrc kinase in GEMs and plays a crucial role in modulating expression of p53 R273H mutant and drug resistance. Colon cancer cell lines, either WiDr homozygous for missense-mutated TP53 (R273H+/+) or SW48/TP53-Dox bearing heterozygous TP53 mutant (R273H/+), display drug resistance with increased ceramide glycosylation. Inhibition of GCS with Genz-161 (GENZ 667161) resensitized cells to apoptosis in these p53 mutant-carrying cancer cells. Genz-161 effectively inhibited GCS activity, and substantially suppressed the elevated Gb3 levels seen in GEMs of p53-mutant cells exposed to doxorubicin. Complex formation between Gb3 and cSrc in GEMs to activate β-catenin was detected in both cultured cells and xenograft tumors. Suppression of ceramide glycosylation significantly decreased Gb3-cSrc in GEMs, β-catenin, and methyltransferase-like 3 for m6A RNA methylation, thus altering pre-mRNA splicing, resulting in upregulated expression of wild-type p53 protein, but not mutants, in cells carrying p53 R273H. Altogether, increased Gb3-cSrc complex in GEMs of membranes in response to anticancer drug induced cell stress promotes expression of p53 mutant proteins and accordant cancer drug resistance.

Loss of PKD1/polycystin-1 impairs lysosomal activity in a CAPN (calpain)-dependent manner

Mutations in the PKD1 gene result in autosomal dominant polycystic kidney disease (ADPKD), the most common monogenetic cause of end-stage renal disease (ESRD) in humans. Previous reports suggested that PKD1, together with PKD2/polycystin-2, may function as a receptor-cation channel complex at cilia and on intracellular membranes and participate in various signaling pathways to regulate cell survival, proliferation and macroautophagy/autophagy. However, the exact molecular function of PKD1 and PKD2 has remained enigmatic. Here we used Pkd1-deficient mouse inner medullary collecting duct cells (mIMCD3) genetically deleted for Pkd1, and tubular epithelial cells isolated from nephrons of doxycycline-inducible conditional pkd1^fl/fl;Pax8^rtTA;TetOCre⁺ knockout mice to show that the lack of Pkd1 caused diminished lysosomal acidification, LAMP degradation and reduced CTSB/cathepsin B processing and activity. This led to an impairment of autophagosomal-lysosomal fusion, a lower delivery of ubiquitinated cargo from multivesicular bodies (MVB)/exosomes to lysosomes and an enhanced secretion of unprocessed CTSB into the extracellular space. The TFEB-dependent lysosomal biogenesis pathway was however unaffected. Pkd1-deficient cells exhibited increased activity of the calcium-dependent CAPN (calpain) proteases, probably due to a higher calcium influx. Consistent with this notion CAPN inhibitors restored lysosomal function, CTSB processing/activity and autophagosomal-lysosomal fusion, and blocked CTSB secretion and LAMP degradation in pkd1 knockout cells. Our data reveal for the first time a lysosomal function of PKD1 which keeps CAPN activity in check and ensures lysosomal integrity and a correct autophagic flux.Abbreviations: acCal: acetyl-calpastatin peptide; ADPKD: autosomal dominant polycystic kidney disease; CI-1: calpain inhibitor-1; CQ: chloroquine; Dox: doxycycline; EV: extracellular vesicles; EXO: exosomes; LAMP1/2: lysosomal-associated membrane protein 1/2; LGALS1/GAL1/galectin-1: lectin, galactose binding, soluble 1; LMP: lysosomal membrane permeabilization; mIMCD3: mouse inner medullary collecting duct cells; MV: microvesicles; MVB: multivesicular bodies; PAX8: paired box 8; PKD1/polycystin-1: polycystin 1, transient receptor potential channel interacting; PKD2/polycystin-2: polycystin 2, transient receptor potential cation channel; Tet: tetracycline; TFEB: transcription factor EB; VFM: vesicle-free medium; WT: wild-type.

Pharmacokinetics, Pharmacodynamics, Safety, and Tolerability of Oral Venglustat in Healthy Volunteers

Venglustat is a small‐molecule glucosylceramide synthase (GCS) inhibitor designed to reduce the production of glucosylceramide (GL‐1) and thus is expected to substantially reduce formation of glucosylceramide‐based glycosphingolipids. Because of its effect on glycosphingolipid formation, GCS inhibition has therapeutic potential across many disorders affecting glycosphingolipid metabolism. Therefore, venglustat is under development for substrate reduction therapy in multiple diseases, including Gaucher disease type 3, Parkinson's disease associated with GBA mutations, Fabry disease, GM2 gangliosidosis, and autosomal dominant polycystic kidney disease. Phase 1 studies were conducted in healthy volunteers to determine venglustat pharmacokinetics, pharmacodynamics, safety, and tolerability and to assess food effects on pharmacokinetics (single‐dose and food‐effect studies: NCT01674036; repeated‐dose study: NCT01710826). Following a single oral dose of venglustat l‐malate (2, 5, 15, 25, 50, 100, or 150 mg), venglustat demonstrated linear pharmacokinetics, rapid absorption (median t_max, 3.00–5.50 hours), systemic exposure unaffected by food, low apparent total body clearance (mean CL/F, 5.18–6.43 L/h), and pooled geometric mean t_1/2z of 28.9 hours. Following repeated once‐daily oral doses of venglustat l‐malate (5, 10, or 20 mg) for 14 days, apparent steady state occurred within 5 days of repeated dosing, with pooled accumulation ratios of 2.10 for C_max and 2.22 for AUC_0–24, and no statistically significant effect of dose or sex on accumulation. The mean fraction of dose excreted unchanged in urine (fe_0–24) was 26.3% to 33.1%. Plasma GL‐1 and GM3 decreased time‐ and dose‐dependently. Venglustat demonstrated a favorable safety and tolerability profile.

Sphingolipids controlling ciliary and microvillar function

Cilia and microvilli are membrane protrusions that extend from the surface of many different mammalian cell types. Motile cilia or flagella are only found on specialized cells, where they control cell movement or the generation of fluid flow, whereas immotile primary cilia protrude from the surface of almost every mammalian cell to detect and transduce extracellular signals. Despite these differences, all cilia consist of a microtubule core called the axoneme. Microvilli instead contain bundled linear actin filaments and are mainly localized on epithelial cells, where they modulate the absorption of nutrients. Cilia and microvilli constitute subcellular compartments with distinctive lipid and protein repertoires and specialized functions. Here, we summarize the role of sphingolipids in defining the identity and controlling the function of cilia and microvilli in mammalian cells.

Targeting glycosphingolipid metabolism as a potential therapeutic approach for treating disease in female MRL/lpr lupus mice

Glycosphingolipids (GSLs) hexosylceramides and lactosylceramides are elevated in lupus mice and human patients with nephritis. Whereas other renal diseases characterized by increased GSL levels are thought to be a result of upregulated GSL synthesis, our results suggest elevated hexosylceramides and lactosylceramides in lupus nephritis is a result of increased catabolism of ganglioside GM3 due to significantly increased neuraminidase (NEU) activity. Thus, we hypothesized GM3 would be decreased in lupus nephritis kidneys and blocking NEU activity would reduce GSLs and improve disease in lupus mice. Female MRL/lpr lupus mice were treated with water or the NEU inhibitor oseltamivir phosphate at the onset of proteinuria to block GSL catabolism. Age-matched (non-nephritic) female MRL/MpJ lupus mice served as controls. Renal GM3 levels were significantly higher in the nephritic MRL/lpr water-treated mice compared to non-nephritic MRL/MpJ mice, despite significantly increased renal NEU activity. Blocking GSL catabolism increased, rather than decreased, renal and urine GSL levels and disease was not significantly impacted. A pilot study treating MRL/lpr females with GlcCer synthase inhibitor Genz-667161 to block GSL synthesis resulted in a strong significant negative correlation between Genz-667161 dose and renal GSL hexosylceramide and GM3 levels. Splenomegaly was negatively correlated and serum IgG levels were marginally correlated with increasing Genz-667161 dose. These results suggest accumulation of renal GM3 may be due to dysregulation of one or more of the GSL ganglioside pathways and inhibiting GSL synthesis, but not catabolism, may be a therapeutic approach for treating lupus nephritis.

Glycosphingolipid metabolism and polycystic kidney disease

Sphingolipids and glycosphingolipids are classes of structurally and functionally important lipids that regulate multiple cellular processes, including membrane organization, proliferation, cell cycle regulation, apoptosis, transport, migration, and inflammatory signalling pathways. Imbalances in sphingolipid levels or subcellular localization result in dysregulated cellular processes and lead to the development and progression of multiple disorders, including polycystic kidney disease. This review will describe metabolic pathways of glycosphingolipids with a focus on the evidence linking glycosphingolipid mediated regulation of cell signalling, lipid microdomains, cilia, and polycystic kidney disease. We will discuss molecular mechanisms of glycosphingolipid dysregulation and their impact on cystogenesis. We will further highlight how modulation of sphingolipid metabolism can be translated into new approaches for the treatment of polycystic kidney disease and describe current clinical studies with glucosylceramide synthase inhibitors in Autosomal Dominant Polycystic Kidney Disease.

Apoptosis and autophagy in polycystic kidney disease (PKD)

Apoptosis in the cystic epithelium is observed in most rodent models of polycystic kidney disease (PKD) and in human autosomal dominant PKD (ADPKD). Apoptosis inhibition decreases cyst growth, whereas induction of apoptosis in the kidney of Bcl-2 deficient mice increases proliferation of the tubular epithelium and subsequent cyst formation. However, alternative evidence indicates that both induction of apoptosis as well as increased overall rates of apoptosis are associated with decreased cyst growth. Autophagic flux is suppressed in cell, zebra fish and mouse models of PKD and suppressed autophagy is known to be associated with increased apoptosis. There may be a link between apoptosis and autophagy in PKD. The mammalian target of rapamycin (mTOR), B-cell lymphoma 2 (Bcl-2) and caspase pathways that are known to be dysregulated in PKD, are also known to regulate both autophagy and apoptosis. Induction of autophagy in cell and zebrafish models of PKD results in suppression of apoptosis and reduced cyst growth supporting the hypothesis autophagy induction may have a therapeutic role in decreasing cyst growth, perhaps by decreasing apoptosis and proliferation in PKD. Future research is needed to evaluate the effects of direct autophagy inducers on apoptosis in rodent PKD models, as well as the cause and effect relationship between autophagy, apoptosis and cyst growth in PKD.

ADPKD current management and ongoing trials

Among the diseases that require renal replacement therapy (RRT), ADPKD is the fourth for incidence and prevalence. In Italy, there are at least 32,000 patients affected by ADPKD, of which about 2900 in dialysis. The pure costs of dialysis treatment for the Italian National Health Service can be conservatively estimated at 87 million euros per year. Even a modest slowdown in the evolution of the disease would obtain an important result in terms of reduction of health expenditure. In recent years, many new or repurposed drugs have been evaluated in clinical trials for ADPKD. In this review we will mainly focus on advanced stage clinical trials (phase 2 and 3). We have grouped these studies according to the molecular pathway addressed by the experimental drug or the therapeutic strategy. More than 10 years after the start of the first Phase III clinical trials in ADPKD, the first drug active in slowing disease progression is finally available. It cannot be considered a goal but only the beginning of a journey because of the significant side effects and the high cost of Tolvaptan. An exuberant basic research activity in the field, together with the large number of ongoing protocols, keep the nephrologists and their patients positive with regard to the discovery of new and better therapies in a not-too-distant future.

Metabolic reprogramming and the role of mitochondria in polycystic kidney disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a slowly progressive disease characterized by the relentless growth of renal cysts throughout the life of affected individuals. Early evidence suggested that the epithelia lining the cysts share neoplastic features, leading to the definition of PKD as a "neoplasm in disguise". Recent work from our and other laboratories has identified a profound metabolic reprogramming in PKD, similar to the one reported in cancer and consistent with the reported increased proliferation. Multiple lines of evidence suggest that aerobic glycolysis (a Warburg-like effect) is present in the disease, along with other metabolic dysfunctions such as an increase in the pentose phosphate pathway, in glutamine anaplerosis and fatty acid biosynthesis, while fatty acid oxidation and oxidative phosphorylation (OXPHOS) are decreased. In addition to glutamine, other amino acid-related pathways appear altered, including asparagine and arginine. The precise origin of the metabolic alterations is not entirely clear, but two hypotheses can be formulated, not mutually exclusive. First, the polycystins have been recently shown to regulate directly mitochondrial function and structure either by regulating Ca²⁺ uptake in mitochondria at the Mitochondria Associated Membranes (MAMs) of the Endoplasmic Reticulum, or by a direct translocation of a small fragment of the protein into the matrix of mitochondria. One alternative possibility is that metabolic and mitochondrial dysfunctions in ADPKD are secondary to the de-regulation of proliferation, driven by the multiple signaling pathways identified in the disease, which include mTORC1 and AMPK among the most relevant. While the precise mechanisms underlying these novel alterations identified in ADPKD will need further investigation, it is evident that they offer a great opportunity for novel interventions in the disease.

The role of DNA damage as a therapeutic target in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenic kidney disease and is caused by heterozygous germ-line mutations in either PKD1 (85%) or PKD2 (15%). It is characterised by the formation of numerous fluid-filled renal cysts and leads to adult-onset kidney failure in ~50% of patients by 60 years. Kidney cysts in ADPKD are focal and sporadic, arising from the clonal proliferation of collecting-duct principal cells, but in only 1-2% of nephrons for reasons that are not clear. Previous studies have demonstrated that further postnatal reductions in PKD1 (or PKD2) dose are required for kidney cyst formation, but the exact triggering factors are not clear. A growing body of evidence suggests that DNA damage, and activation of the DNA damage response pathway, are altered in ciliopathies. The aims of this review are to: (i) analyse the evidence linking DNA damage and renal cyst formation in ADPKD; (ii) evaluate the advantages and disadvantages of biomarkers to assess DNA damage in ADPKD and finally, (iii) evaluate the potential effects of current clinical treatments on modifying DNA damage in ADPKD. These studies will address the significance of DNA damage and may lead to a new therapeutic approach in ADPKD.

Design and optimization strategies for the development of new drugs that treat chronic kidney disease

Introduction: Chronic kidney disease (CKD) is characterized by increased risks of progression to end-stage kidney disease requiring dialysis and cardiovascular mortality, predicted to be among the five top causes of death by 2040. Only the design and optimization of novel strategies to develop new drugs to treat CKD will contain this trend. Current therapy for CKD includes nonspecific therapy targeting proteinuria and/or hypertension and cause-specific therapies for diabetic kidney disease, autosomal dominant polycystic kidney disease, glomerulonephritides, Fabry nephropathy, hemolytic uremic syndrome and others.Areas covered: Herein, the authors review the literature on new drugs under development for CKD as well as novel design and development strategies.Expert opinion: New therapies for CKD have become a healthcare priority. Emerging therapies undergoing clinical trials are testing expanded renin-angiotensin system blockade with double angiotensin receptor/endothelin receptor blockers, SGLT2 inhibition, and targeting inflammation, the immune response, fibrosis and the Nrf2 transcription factor. Emerging therapeutic targets include cell senescence, complement activation, Klotho expression preservation and microbiota. Novel approaches include novel model systems that can be personalized (e.g. organoids), unbiased systems biology-based identification of new therapeutic targets, drug databases that speed up drug identification and repurposing, nanomedicines that improve drug delivery and RNA targeting to expand the number of targetable proteins.

Role of Glucosylceramide in Lung Endothelial Cell Fate and Emphysema

Rationale: The loss of pulmonary endothelial cells in emphysema is associated with increased lung ceramide. Ceramide perturbations may cause adaptive alterations in other bioactive sphingolipids, with pathogenic implications. We previously reported a negative correlation between emphysema and circulating glycosphingolipids (GSLs). Glucosylceramide (GlcCer), the initial GSL synthesized from ceramide by GCS (GlcCer synthase), is required for embryonic survival, but its role in the lung is unknown.Objectives: To determine if cigarette smoke (CS) alters lung GlcCer and to elucidate the role of GCS in lung endothelial cell fate.Methods: GlcCer was measured by tandem mass spectrometry in BAL fluid of CS- or elastase-exposed mice, and GCS was detected by Western blotting in chronic obstructive pulmonary disease lungs and CS extract-exposed primary human lung microvascular endothelial cells (HLMVECs). The role of GlcCer and GCS on mTOR (mammalian target of rapamycin) signaling, autophagy, lysosomal function, and cell death were studied in HLMVECs with or without CS exposure.Measurements and Main Results: Mice exposed to chronic CS or to elastase, and patients with chronic obstructive pulmonary disease, exhibited significantly decreased lung GlcCer and GCS. In mice, lung GlcCer levels were negatively correlated with airspace size. GCS inhibition in HLMVEC increased lysosomal pH, suppressed mTOR signaling, and triggered autophagy with impaired lysosomal degradation and apoptosis, recapitulating CS effects. In turn, increasing GlcCer by GCS overexpression in HLMVEC improved autophagic flux and attenuated CS-induced apoptosis.Conclusions: Decreased GSL production in response to CS may be involved in emphysema pathogenesis, associated with autophagy with impaired lysosomal degradation and lung endothelial cell apoptosis.