Inhibition of Aerobic Glycolysis Attenuates Disease Progression in Polycystic Kidney Disease

Therapeutic Potential of Ketogenic Interventions for Autosomal-Dominant Polycystic Kidney Disease: A Systematic Review

BACKGROUND

Recent findings have highlighted that abnormal energy metabolism is a key feature of autosomal-dominant polycystic kidney disease (ADPKD). Emerging evidence suggests that nutritional ketosis could offer therapeutic benefits, including potentially slowing or even reversing disease progression. This systematic review aims to synthesise the literature on ketogenic interventions to evaluate the impact in ADPKD.

METHODS

A systematic search was conducted in Medline, Embase, and Scopus using relevant Medical Subject Headings (MeSH) and keywords. Studies assessing ketogenic interventions in the management of ADPKD in both human and animal models were selected for data extraction and analysis.

RESULTS

Three animal reports and six human studies were identified. Ketogenic diets (KD) significantly slowed polycystic kidney disease (PKD) progression in rats with improved renal function and reduced cystic areas. There was reduced renal fibrosis and cell proliferation. The supplementation of beta-hydroxybutyrate (BHB) in rats also reduced PKD progression in a dose-dependent manner. Human studies (n = 129) on KD in ADPKD reported consistent body mass index (BMI) reduction across trials, with an average weight loss of ∼4 kg. Improvements in blood pressure were also noted. Ketosis was achieved in varying degrees. Effects on kidney function (eGFR) were beneficial. Results for kidney volume were mixed but most studies were underpowered for this outcome. Lipid profiles showed increases in total cholesterol (∼1 mmol/L) and LDL cholesterol (∼0.4 mmol/L) in most studies. Safety concerns such as "keto flu" symptoms, elevated uric acid levels, and occasional kidney stones were noted. Overall feasibility and adherence to the KD were rated positively by most participants.

CONCLUSIONS

Human studies are promising; however, they have been limited by small sample sizes and short durations. Larger, long-term trials are needed to assess the efficacy, adherence, and safety of ketogenic diets in people with ADPKD.

Impaired Glucose Metabolism, Primary Cilium Defects, and Kidney Cystogenesis in Glycogen Storage Disease Type Ia

Key Points

Metabolism adaptations due to glucose-6 phosphate accumulation in glycogen storage disease type Ia kidneys, toward a Warburg-like metabolism, promoted cell proliferation. Metabolic perturbations directly affected primary cilium structure and cystogenesis in glycogen storage disease type Ia kidneys.

Background

Glycogen storage disease type Ia (GSDIa) is a rare metabolic disorder caused by mutations in the catalytic subunit of glucose-6 phosphatase (G6PC1). This leads to severe hypoglycemia, and most young patients with GSDIa develop CKD. The kidney pathology is characterized by the development of cysts, which typically occur at an advanced stage of CKD.

Methods

To elucidate the molecular mechanisms responsible for cyst formation, we characterized renal metabolism, molecular pathways involved in cell proliferation, and primary cilium integrity using mice in which G6pc1 was specifically deleted in the kidney from an in utero stage.

Results

GSDIa mice exhibited kidney fibrosis, high inflammation, and cyst formation, leading to kidney dysfunction. In addition, the loss of G6PC1 led to the ectopic accumulation of glycogen and lipids in the kidneys and a metabolic shift toward a Warburg-like metabolism. This metabolic adaptation was due to an excess of glucose-6 phosphate, which supports cell proliferation, driven by the mitogen-activated protein kinase/extracellular signal–regulated kinases and protein kinase B/mammalian target of rapamycin pathways. Treatment of GSDIa mice with rapamycin, a target of the mammalian target of rapamycin pathway, reduced cell proliferation and kidney damage. Our results also identified lipocalin 2 as a contributor to renal inflammation and an early biomarker of CKD progression in GSDIa mice. Its inactivation partially prevented kidney lesions in GSDIa. Importantly, primary cilium defects were observed in the kidneys of GSDIa mice.

Conclusions

Metabolic adaptations because of glucose-6 phosphate accumulation in GSDIa renal tubules, toward a Warburg-like metabolism, promoted cell proliferation and cyst formation in a similar manner to that observed in various cystic kidney diseases. This was associated with downregulation of primary cilium gene expression and, consequently, altered cilium morphology.

Early treatment with 2-deoxy-d-glucose reduces proliferative proteins in the kidney and slows cyst growth in a hypomorphic Pkd1 mouse model of autosomal dominant polycystic kidney disease (PKD)

In autosomal dominant polycystic kidney disease (ADPKD) there is cyst growth in the kidneys that leads to chronic kidney disease often requiring dialysis or kidney transplantation. There is enhanced aerobic glycolysis (Warburg effect) in the cyst lining epithelial cells that contributes to cyst growth. The glucose mimetic, 2-Deoxy-d-glucose (2-DG) inhibits glycolysis. The effect of early and late administration of 2-DG on cyst growth and kidney function was determined in Pkd1RC/RC mice, a hypomorphic PKD model orthologous to human disease. Early administration of 2-DG resulted in decreased kidney weight, cyst index, cyst number and cyst size, but no change in kidney function. 2-DG decreased proliferation. a major mediator of cyst growth, of cells lining the cyst. Late administration of 2-DG did not have an effect on cyst growth or kidney function. To determine mechanisms of decreased proliferation, an array of mTOR and autophagy proteins was measured in the kidney. 2-DG suppressed autophagic flux in Pkd1RC/RC kidneys and decreased autophagy proteins, ATG3, ATG5 and ATG12-5. 2-DG had no effect on p-mTOR or p-S6 (mTORC1) and decreased p-AMPK. 2-DG decreased p-4E-BP1, p-c-Myc and p-ERK that are known to promote proliferation and cyst growth in PKD. 2-DG decreased p-AKTS473, a marker of mTORC2. So the role of mTORC2 in cyst growth was determined. Knockout of Rictor (mTORC2) in Pkd1 knockout mice did not change the PKD phenotype. In summary, 2-DG decreases proliferation in cells lining the cyst and decreases cyst growth by decreasing proteins that are known to promote proliferation. In conclusion, the present study reinforces the therapeutic potential of 2-DG for use in patients with ADPKD.

Potential Add-On Benefits of Dietary Intervention in the Treatment of Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited cause of renal failure. The pathogenesis of the disease encompasses several pathways and metabolic alterations, including the hyperactivation of mTOR and suppression of AMPK signaling pathways, as well as mitochondrial dysfunction. This metabolic reprogramming makes epithelial cyst-lining cells highly dependent on glucose for energy and unable to oxidize fatty acids. Evidence suggests that high-carbohydrate diets may worsen the progression of ADPKD, providing the rationale for treating ADPKD patients with calorie restriction and, in particular, with ketogenic dietary interventions, already used for other purposes such as in overweight/obese patients or in the treatment of refractory epilepsy in children. Preclinical studies have demonstrated that calorie restriction may prevent and/or slow disease progression by inducing ketosis, particularly through increased beta-hydroxybutyrate (BHB) levels, which may modulate the metabolic signaling pathways altered in ADKPK. In these patients, although limited, ketogenic intervention studies have shown promising beneficial effects. However, larger and longer randomized controlled trials are needed to confirm their tolerability and safety in long-term maintenance and their additive role in the therapy of polycystic kidney disease.

Reprogramming of Energy Metabolism in Human PKD1 Polycystic Kidney Disease: A Systems Biology Analysis

Multiple alterations of cellular metabolism have been documented in experimental studies of autosomal dominant polycystic kidney disease (ADPKD) and are thought to contribute to its pathogenesis. To elucidate the molecular pathways and transcriptional regulators associated with the metabolic changes of renal cysts in ADPKD, we compared global gene expression data from human PKD1 renal cysts, minimally cystic tissues (MCT) from the same patients, and healthy human kidney cortical tissue samples. We found gene expression profiles of PKD1 renal cysts were consistent with the Warburg effect with gene pathway changes favoring increased cellular glucose uptake and lactate production, instead of pyruvate oxidation. Additionally, mitochondrial energy metabolism was globally depressed, associated with downregulation of gene pathways related to fatty acid oxidation (FAO), branched-chain amino acid (BCAA) degradation, the Krebs cycle, and oxidative phosphorylation (OXPHOS) in renal cysts. Activation of mTORC1 and its two target proto-oncogenes, HIF-1α and MYC, was predicted to drive the expression of multiple genes involved in the observed metabolic reprogramming (e.g., GLUT3, HK1/HK2, ALDOA, ENO2, PKM, LDHA/LDHB, MCT4, PDHA1, PDK1/3, MPC1/2, CPT2, BCAT1, NAMPT); indeed, their predicted expression patterns were confirmed by our data. Conversely, we found AMPK inhibition was predicted in renal cysts. AMPK inhibition was associated with decreased expression of PGC-1α, a transcriptional coactivator for transcription factors PPARα, ERRα, and ERRγ, all of which play a critical role in regulating oxidative metabolism and mitochondrial biogenesis. These data provide a comprehensive map of metabolic pathway reprogramming in ADPKD and highlight nodes of regulation that may serve as targets for therapeutic intervention.

Inhibition of asparagine synthetase effectively retards polycystic kidney disease progression

Polycystic kidney disease (PKD) is a genetic disorder characterized by bilateral cyst formation. We showed that PKD cells and kidneys display metabolic alterations, including the Warburg effect and glutaminolysis, sustained in vitro by the enzyme asparagine synthetase (ASNS). Here, we used antisense oligonucleotides (ASO) against Asns in orthologous and slowly progressive PKD murine models and show that treatment leads to a drastic reduction of total kidney volume (measured by MRI) and a prominent rescue of renal function in the mouse. Mechanistically, the upregulation of an ATF4-ASNS axis in PKD is driven by the amino acid response (AAR) branch of the integrated stress response (ISR). Metabolic profiling of PKD or control kidneys treated with Asns-ASO or Scr-ASO revealed major changes in the mutants, several of which are rescued by Asns silencing in vivo. Indeed, ASNS drives glutamine-dependent de novo pyrimidine synthesis and proliferation in cystic epithelia. Notably, while several metabolic pathways were completely corrected by Asns-ASO, glycolysis was only partially restored. Accordingly, combining the glycolytic inhibitor 2DG with Asns-ASO further improved efficacy. Our studies identify a new therapeutic target and novel metabolic vulnerabilities in PKD.

Cross-Species Insights into Autosomal Dominant Polycystic Kidney Disease: Provide an Alternative View on Research Advancement

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a prevalent hereditary disorder that affects the kidneys, characterized by the development of an excessive number of fluid-filled cysts of varying sizes in both kidneys. Along with the progression of ADPKD, these enlarged cysts displace normal kidney tissue, often accompanied by interstitial fibrosis and inflammation, and significantly impair renal function, leading to end-stage renal disease. Currently, the precise mechanisms underlying ADPKD remain elusive, and a definitive cure has yet to be discovered. This review delineates the epidemiology, pathological features, and clinical diagnostics of ADPKD or ADPKD-like disease across human populations, as well as companion animals and other domesticated species. A light has been shed on pivotal genes and biological pathways essential for preventing and managing ADPKD, which underscores the importance of cross-species research in addressing this complex condition. Treatment options are currently limited to Tolvaptan, dialysis, or surgical excision of large cysts. However, comparative studies of ADPKD across different species hold promise for unveiling novel insights and therapeutic strategies to combat this disease.

A combination of β-hydroxybutyrate and citrate ameliorates disease progression in a rat model of polycystic kidney disease

Our research has shown that interventions producing a state of ketosis are highly effective in rat, mouse, and cat models of polycystic kidney disease (PKD), preventing and partially reversing cyst growth and disease progression. The ketone β-hydroxybutyrate (BHB) appears to underlie this effect. In addition, we have demonstrated that naturally formed microcrystals within kidney tubules trigger a renoprotective response that facilitates tubular obstruction clearance in healthy animals but, alternatively, leads to cyst formation in PKD. The administration of citrate prevents microcrystal formation and slows PKD progression. Juvenile Cy/+ rats, a nonorthologous PKD model, were supplemented from 3 to 8 wk of age with water containing titrated BHB, citrate, or in combination to find minimal effective and optimal dosages, respectively. Adult rats were given a reduced BHB/citrate combination or equimolar control K/NaCl salts from 8 to 12 wk of age. In addition, adult rats were placed in metabolic cages following BHB, citrate, and BHB/citrate administration to determine the impact on mineral, creatinine, and citrate excretion. BHB or citrate alone effectively ameliorates disease progression in juvenile rats, decreasing markers of cystic disease and, in combination, producing a synergistic effect. BHB/citrate leads to partial disease regression in adult rats with established cystic disease, inhibiting cyst formation and kidney injury. BHB/citrate confers benefits via multiple mechanisms, increases creatinine and citrate excretion, and normalizes mineral excretion. BHB and citrate are widely available and generally recognized as safe compounds and, in combination, exhibit high promise for supporting kidney health in polycystic kidney disease.NEW & NOTEWORTHY Combining β-hydroxybutyrate (BHB) and citrate effectively slows and prevents cyst formation and expansion in young Cy/+ rats using less BHB and citrate than when used alone, demonstrating synergy. In adult rats, the combination causes a partial reversal of existing disease, reducing cyst number and cystic area, preserving glomerular health, and decreasing markers of kidney injury. Our results suggest a safe and feasible strategy for supporting kidney health in polycystic kidney disease (PKD) using a combination of BHB and citrate.

Long-Term Effects of Tolvaptan in Autosomal Dominant Polycystic Kidney Disease: Predictors of Treatment Response and Safety over 6 Years of Continuous Therapy

Tolvaptan, an oral vasopressin V2 receptor antagonist, reduces renal volume expansion and loss of renal function in patients with autosomal dominant polycystic kidney disease (ADPKD). Data for predictive factors indicating patients more likely to benefit from long-term tolvaptan are lacking. Data were retrospectively collected from 55 patients on tolvaptan for 6 years. Changes in renal function, progression of renal dysfunction (estimated glomerular filtration rate [eGFR], 1-year change in eGFR [ΔeGFR/year]), and renal volume (total kidney volume [TKV], percentage 1-year change in TKV [ΔTKV%/year]) were evaluated at 3-years pre-tolvaptan, at baseline, and at 6 years. In 76.4% of patients, ΔeGFR/year improved at 6 years. The average 6-year ΔeGFR/year (range) minus baseline ΔeGFR/year: 3.024 (-8.77-20.58 mL/min/1.73 m2). The increase in TKV was reduced for the first 3 years. A higher BMI was associated with less of an improvement in ΔeGFR (p = 0.027), and family history was associated with more of an improvement in ΔeGFR (p = 0.044). Hypernatremia was generally mild; 3 patients had moderate-to-severe hyponatremia due to prolonged, excessive water intake in response to water diuresis-a side effect of tolvaptan. Family history of ADPKD and baseline BMI were contributing factors for ΔeGFR/year improvement on tolvaptan. Hyponatremia should be monitored with long-term tolvaptan administration.

The Han:SPRD Rat: A Preclinical Model of Polycystic Kidney Disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) stands as the most prevalent hereditary renal disorder in humans, ultimately culminating in end-stage kidney disease. Animal models carrying mutations associated with polycystic kidney disease have played an important role in the advancement of ADPKD research. The Han:SPRD rat model, carrying an R823W mutation in the Anks6 gene, is characterized by cyst formation and kidney enlargement. The mutated protein, named Samcystin, is localized in cilia of tubular epithelial cells and seems to be involved in cystogenesis. The homozygous Anks6 mutation leads to end-stage renal disease and death, making it a critical factor in kidney development and function. This review explores the utility of the Han:SPRD rat model, highlighting its phenotypic similarity to human ADPKD. Specifically, we discuss its role in preclinical trials and its importance for investigating the pathogenesis of the disease and developing new therapeutic approaches.

Hexokinase-linked glycolytic overload and unscheduled glycolysis in hyperglycemia-induced pathogenesis of insulin resistance, beta-cell glucotoxicity, and diabetic vascular complications

Hyperglycemia is a risk factor for the development of insulin resistance, beta-cell glucotoxicity, and vascular complications of diabetes. We propose the hypothesis, hexokinase-linked glycolytic overload and unscheduled glycolysis, in explanation. Hexokinases (HKs) catalyze the first step of glucose metabolism. Increased flux of glucose metabolism through glycolysis gated by HKs, when occurring without concomitant increased activity of glycolytic enzymes-unscheduled glycolysis-produces increased levels of glycolytic intermediates with overspill into effector pathways of cell dysfunction and pathogenesis. HK1 is saturated with glucose in euglycemia and, where it is the major HK, provides for basal glycolytic flux without glycolytic overload. HK2 has similar saturation characteristics, except that, in persistent hyperglycemia, it is stabilized to proteolysis by high intracellular glucose concentration, increasing HK activity and initiating glycolytic overload and unscheduled glycolysis. This drives the development of vascular complications of diabetes. Similar HK2-linked unscheduled glycolysis in skeletal muscle and adipose tissue in impaired fasting glucose drives the development of peripheral insulin resistance. Glucokinase (GCK or HK4)-linked glycolytic overload and unscheduled glycolysis occurs in persistent hyperglycemia in hepatocytes and beta-cells, contributing to hepatic insulin resistance and beta-cell glucotoxicity, leading to the development of type 2 diabetes. Downstream effector pathways of HK-linked unscheduled glycolysis are mitochondrial dysfunction and increased reactive oxygen species (ROS) formation; activation of hexosamine, protein kinase c, and dicarbonyl stress pathways; and increased Mlx/Mondo A signaling. Mitochondrial dysfunction and increased ROS was proposed as the initiator of metabolic dysfunction in hyperglycemia, but it is rather one of the multiple downstream effector pathways. Correction of HK2 dysregulation is proposed as a novel therapeutic target. Pharmacotherapy addressing it corrected insulin resistance in overweight and obese subjects in clinical trial. Overall, the damaging effects of hyperglycemia are a consequence of HK-gated increased flux of glucose metabolism without increased glycolytic enzyme activities to accommodate it.

ALTERATIONS IN HISTIDINE METABOLISM IS A FEATURE OF EARLY AUTOSOMAL DOMINANT POLYCYSTIC KIDNEY DISEASE (ADPKD)

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by epithelial proliferation and progressive cyst enlargement. Using a non-targeted high-resolution metabolomics approach, we analyzed biofluids from 36 ADPKD and 18 healthy controls with estimated glomerular filtration rate (eGFR) > 60 ml/min to identify features specific to ADPKD or that associate with disease severity [eGFR or height-corrected total kidney volume (htTKV)]. Multiple pathways differed between ADPKD subjects and controls, with the histidine pathway being the most highly represented. Plasma histidine, urinary N-methylhistamine, methylimidazole-acetaldehyde, and imidazole-acetaldehyde, as well as 3-methylhistidine and anserine were increased, while plasma N-acetylhistamine and urinary imidazole-acetic acid were decreased in ADPKD compared to controls. In ADPKD, urinary histidine and a histidine derivative, urocanate (a precursor of glutamate), were significantly associated. HtTKV and eGFR were inversely associated with urinary glutamine and plasma 4-imidazolone-5-propionic acid, respectively. Supernatant from cultured human ADPKD renal cystic epithelia demonstrated increased aspartate and glutamate levels at 8 and 24 hours compared to primary tubular epithelia (p < 0.001). Following exposure over 48 hours to α-fluromethylhistidine, an inhibitor of histamine production, primary human PKD1 cyst epithelia proliferation increased significantly from baseline (p < 0.01) and greater than non-cystic epithelia (p < 0.05). The histidine ammonia lyase inhibitor nitromethane reversed α-fluromethylhistidine-induced cyst epithelia proliferation indicating a role for glutamate in cyst growth. In conclusion, histidine metabolism is altered preferentially leading to glutamate production and epithelial proliferation in ADPKD and associates with disease severity.

Short-Term Dapagliflozin Administration in Autosomal Dominant Polycystic Kidney Disease-A Retrospective Single-Arm Case Series Study

Treatment with sodium-glucose cotransporter-2 (SGLT2) inhibitors may have pleiotropic and beneficial effects in terms of ameliorating of risk factors for the progression of autosomal dominant polycystic kidney disease (ADPKD). However, there is insufficient evidence regarding the use of these drugs in patients with ADPKD, as they were excluded from several clinical trials conducted to explore kidney protection provided by SGLT2 inhibitors. This retrospective single-arm case series study was performed to investigate the effects of dapagliflozin, a selective SGLT2 inhibitor administered at 10 mg/day, on changes in height-adjusted kidney volume (htTKV) and estimated glomerular filtration rate (eGFR) in ADPKD patients. During a period of 102 ± 20 days (range 70-156 days), eGFR was decreased from 47.9 (39.7-56.9) to 40.8 (33.7-44.5) mL/min/1.73 m2 (p < 0.001), while htTKV was increased from 599 (423-707) to 617 (446-827) mL/m (p = 0.002) (n = 20). The annual increase in htTKV rate was significantly promoted, and urinary phosphate change was found to be correlated with the change in htTKV (rs = 0.575, p = 0.020). In the examined patients, eGFR was decreased and htTKV increased during short-term administration of dapagliflozin. To confirm the possibility of the effects of dapagliflozin on ADPKD, additional interventional studies are required.

Functions of the primary cilium in the kidney and its connection with renal diseases

The nonmotile primary cilium is a sensory structure found on most mammalian cell types that integrates multiple signaling pathways involved in tissue development and postnatal function. As such, mutations disrupting cilia activities cause a group of disorders referred to as ciliopathies. These disorders exhibit a wide spectrum of phenotypes impacting nearly every tissue. In the kidney, primary cilia dysfunction caused by mutations in polycystin 1 (Pkd1), polycystin 2 (Pkd2), or polycystic kidney and hepatic disease 1 (Pkhd1), result in polycystic kidney disease (PKD), a progressive disorder causing renal functional decline and end-stage renal disease. PKD affects nearly 1 in 1000 individuals and as there is no cure for PKD, patients frequently require dialysis or renal transplantation. Pkd1, Pkd2, and Pkhd1 encode membrane proteins that all localize in the cilium. Pkd1 and Pkd2 function as a nonselective cation channel complex while Pkhd1 protein function remains uncertain. Data indicate that the cilium may act as a mechanosensor to detect fluid movement through renal tubules. Other functions proposed for the cilium and PKD proteins in cyst development involve regulation of cell cycle and oriented division, regulation of renal inflammation and repair processes, maintenance of epithelial cell differentiation, and regulation of mitochondrial structure and metabolism. However, how loss of cilia or cilia function leads to cyst development remains elusive. Studies directed at understanding the roles of Pkd1, Pkd2, and Pkhd1 in the cilium and other locations within the cell will be important for developing therapeutic strategies to slow cyst progression.

The Interplay between Immune and Metabolic Pathways in Kidney Disease

Kidney disease is a significant health problem worldwide, affecting an estimated 10% of the global population. Kidney disease encompasses a diverse group of disorders that vary in their underlying pathophysiology, clinical presentation, and outcomes. These disorders include acute kidney injury (AKI), chronic kidney disease (CKD), glomerulonephritis, nephrotic syndrome, polycystic kidney disease, diabetic kidney disease, and many others. Despite their distinct etiologies, these disorders share a common feature of immune system dysregulation and metabolic disturbances. The immune system and metabolic pathways are intimately connected and interact to modulate the pathogenesis of kidney diseases. The dysregulation of immune responses in kidney diseases includes a complex interplay between various immune cell types, including resident and infiltrating immune cells, cytokines, chemokines, and complement factors. These immune factors can trigger and perpetuate kidney inflammation, causing renal tissue injury and progressive fibrosis. In addition, metabolic pathways play critical roles in the pathogenesis of kidney diseases, including glucose and lipid metabolism, oxidative stress, mitochondrial dysfunction, and altered nutrient sensing. Dysregulation of these metabolic pathways contributes to the progression of kidney disease by inducing renal tubular injury, apoptosis, and fibrosis. Recent studies have provided insights into the intricate interplay between immune and metabolic pathways in kidney diseases, revealing novel therapeutic targets for the prevention and treatment of kidney diseases. Potential therapeutic strategies include modulating immune responses through targeting key immune factors or inhibiting pro-inflammatory signaling pathways, improving mitochondrial function, and targeting nutrient-sensing pathways, such as mTOR, AMPK, and SIRT1. This review highlights the importance of the interplay between immune and metabolic pathways in kidney diseases and the potential therapeutic implications of targeting these pathways.

Advanced glycation end products promote the progression of chronic kidney diseases by targeting calpain 6

Advanced glycation end products (AGEs) are produced by glycosylation or oxidation of proteins and lipids and are tightly involved in the chronic kidney disease (CKD) process. Calpain 6 (CAPN6) is a non-classical calpain that has been reported to be overexpressed in CKD. This study aimed to explore the effects of AGEs in CKD progress and their correlation with CAPN6. AGEs production was measured using ELISA. The CCK-8 assay was used to test cell proliferation. mRNA and protein levels were tested using qRT-PCR and western blot. The progress of glycolysis was tested by calculating the ATP and ECAR content in HK-2 cells. The expression of AGEs and CAPN6 was significantly increased in patients with CKD3, CKD4, and CKD5. AGEs treatment inhibited cell proliferation and glycolysis and accelerated apoptosis. Additionally, CAPN6 knockdown effectively reversed the effects of AGEs in HK-2 cells. In addition, overexpressed CAPN6 played similar role to AGEs, which suppressed cell proliferation and glycolysis and facilitated apoptosis. Moreover, the administration of 2-DG, a glycolysis inhibitor, counteracted the effects of CAPN6 silencing in HK-2 cells. Mechanistically, CAPN6 interacts with NF-κB and PDTC reduced CAPN6 expression in HK-2 cells. This investigation revealed that AGEs facilitate CKD development in vitro by modulating the expression of CAPN6.

The PI3K-Akt-mTOR pathway mediates renal pericyte-myofibroblast transition by enhancing glycolysis through HKII

BACKGROUND

Pericyte-myofibroblast transition (PMT) has been confirmed to contribute to renal fibrosis in several kidney diseases, and transforming growth factor-β1 (TGF-β1) is a well-known cytokine that drives PMT. However, the underlying mechanism has not been fully established, and little is known about the associated metabolic changes.

METHODS

Bioinformatics analysis was used to identify transcriptomic changes during PMT. PDGFRβ + pericytes were isolated using MACS, and an in vitro model of PMT was induced by 5 ng/ml TGF-β1. Metabolites were analyzed by ultraperformance liquid chromatography (UPLC) and tandem mass spectrometry (MS). 2-Deoxyglucose (2-DG) was used to inhibit glycolysis via its actions on hexokinase (HK). The hexokinase II (HKII) plasmid was transfected into pericytes for HKII overexpression. LY294002 or rapamycin was used to inhibit the PI3K-Akt-mTOR pathway for mechanistic exploration.

RESULTS

An increase in carbon metabolism during PMT was detected through bioinformatics and metabolomics analysis. We first detected increased levels of glycolysis and HKII expression in pericytes after stimulation with TGF-β1 for 48 h, accompanied by increased expression of α-SMA, vimentin and desmin. Transdifferentiation was blunted when pericytes were pretreated with 2-DG, an inhibitor of glycolysis. The phosphorylation levels of PI3K, Akt and mTOR were elevated during PMT, and after inhibition of the PI3K-Akt-mTOR pathway with LY294002 or rapamycin, glycolysis in the TGF-β1-treated pericytes was decreased. Moreover, PMT and HKII transcription and activity were blunted, but the plasmid-mediated overexpression of HKII rescued PMT inhibition.

CONCLUSIONS

The expression and activity of HKII as well as the level of glycolysis were increased during PMT. Moreover, the PI3K-Akt-mTOR pathway regulates PMT by increasing glycolysis through HKII regulation.

Preclinical evaluation of tolvaptan and salsalate combination therapy in a Pkd1-mouse model

Background: Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic disorder and an important cause of end stage renal disease (ESRD). Tolvaptan (a V2R antagonist) is the first disease modifier drug for treatment of ADPKD, but also causes severe polyuria. AMPK activators have been shown to attenuate cystic kidney disease. Methods: In this study, we tested the efficacy of the combined administration of salsalate (a direct AMPK activator) and tolvaptan using clinically relevant doses in an adult-onset conditional Pkd1 knock-out (KO) mouse model. Results: Compared to untreated Pkd1 mutant mice, the therapeutic effects of salsalate were similar to that of tolvaptan. The combined treatment tended to be more effective than individual drugs used alone, and was associated with improved kidney survival (p < 0.0001) and reduced kidney weight to body weight ratio (p < 0.0001), cystic index (p < 0.001) and blood urea levels (p < 0.001) compared to untreated animals, although the difference between combination and single treatments was not statistically significant. Gene expression profiling and protein expression and phosphorylation analyses support the mild beneficial effects of co-treatment, and showed that tolvaptan and salsalate cooperatively attenuated kidney injury, cell proliferation, cell cycle progression, inflammation and fibrosis, and improving mitochondrial health, and cellular antioxidant response. Conclusion: These data suggest that salsalate-tolvaptan combination, if confirmed in clinical testing, might represent a promising therapeutic strategy in the treatment of ADPKD.

SUPPRESION OF MITOCHONDRIAL RESPIRATION IS A FEATURE OF CELLULAR GLUCOSE TOXICITY

Glucose toxicity is central to the myriad complications of diabetes and is now believed to encompass neurodegenerative diseases and cancer as well as microvascular and macrovascular disease. Due to the widespread benefits of SGLT2 inhibitors, which affect glucose uptake in the kidney proximal tubular cell, a focus on cell metabolism in response to glucose has important implications for overall health. We previously found that a -Warburg-type effect underlies diabetic kidney disease and involves metabolic reprogramming. This is now supported by quantitative measurements of superoxide measurement in the diabetic kidney and systems biology analysis of urine metabolites in patients. Further exploration of mechanisms underlying mediators of mitochondrial suppression will be critical in understanding the chronology of glucose-induced toxicity and developing new therapeutics to arrest the systemic glucose toxicity of diabetes.

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.

Emerging therapies for autosomal dominant polycystic kidney disease with a focus on cAMP signaling

Autosomal dominant polycystic kidney disease (ADPKD), with an estimated genetic prevalence between 1:400 and 1:1,000 individuals, is the third most common cause of end stage kidney disease after diabetes mellitus and hypertension. Over the last 3 decades there has been great progress in understanding its pathogenesis. This allows the stratification of therapeutic targets into four levels, gene mutation and polycystin disruption, proximal mechanisms directly caused by disruption of polycystin function, downstream regulatory and signaling pathways, and non-specific pathophysiologic processes shared by many other diseases. Dysfunction of the polycystins, encoded by the PKD genes, is closely associated with disruption of calcium and upregulation of cyclic AMP and protein kinase A (PKA) signaling, affecting most downstream regulatory, signaling, and pathophysiologic pathways altered in this disease. Interventions acting on G protein coupled receptors to inhibit of 3',5'-cyclic adenosine monophosphate (cAMP) production have been effective in preclinical trials and have led to the first approved treatment for ADPKD. However, completely blocking cAMP mediated PKA activation is not feasible and PKA activation independently from cAMP can also occur in ADPKD. Therefore, targeting the cAMP/PKA/CREB pathway beyond cAMP production makes sense. Redundancy of mechanisms, numerous positive and negative feedback loops, and possibly counteracting effects may limit the effectiveness of targeting downstream pathways. Nevertheless, interventions targeting important regulatory, signaling and pathophysiologic pathways downstream from cAMP/PKA activation may provide additive or synergistic value and build on a strategy that has already had success. The purpose of this manuscript is to review the role of cAMP and PKA signaling and their multiple downstream pathways as potential targets for emergent therapies for ADPKD.

Is autosomal dominant polycystic kidney disease an early sweet disease?

The clinical course of autosomal dominant polycystic kidney disease (ADPKD) starts in childhood. Evidence of the beneficial impact of early nephron-protective strategies and lifestyle modifications on ADPKD prognosis is accumulating. Recent studies have described the association of overweight and obesity with rapid disease progression in adults with ADPKD. Moreover, defective glucose metabolism and metabolic reprogramming have been reported in distinct ADPKD models highlighting these pathways as potential therapeutic targets in ADPKD. Several "metabolic" approaches are currently under evaluation in adults, including ketogenic diet, food restriction, and metformin therapy. No data are available on the impact of these approaches in childhood thus far. Yet, according to World Health Organization (WHO), we are currently facing a childhood obesity crisis with an increased prevalence of overweight/obesity in the pediatric population associated with a cardio-metabolic risk profile. The present review summarizes the knowledge about the role of glucose metabolism in the pathophysiology of ADPKD and underscores the possible harm of overweight and obesity in ADPKD especially in terms of long-term cardiovascular outcomes and renal prognosis.

Shared pathobiology identifies AMPK as a therapeutic target for obesity and autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common Mendelian kidney disease, affecting approximately one in 1,000 births and accounting for 5% of end-stage kidney disease in developed countries. The pathophysiology of ADPKD is strongly linked to metabolic dysregulation, which may be secondary to defective polycystin function. Overweight and obesity are highly prevalent in patients with ADPKD and constitute an independent risk factor for progression. Recent studies have highlighted reduced AMP-activated protein kinase (AMPK) activity, increased mammalian target of rapamycin (mTOR) signaling, and mitochondrial dysfunction as shared pathobiology between ADPKD and overweight/obesity. Notably, mTOR and AMPK are two diametrically opposed sensors of energy metabolism that regulate cell growth and proliferation. However, treatment with the current generation of mTOR inhibitors is poorly tolerated due to their toxicity, making clinical translation difficult. By contrast, multiple preclinical and clinical studies have shown that pharmacological activation of AMPK provides a promising approach to treat ADPKD. In this narrative review, we summarize the pleiotropic functions of AMPK as a regulator of cellular proliferation, macromolecule metabolism, and mitochondrial biogenesis, and discuss the potential for pharmacological activation of AMPK to treat ADPKD and obesity-related kidney disease.

Pharmacological Effects of Panduratin A on Renal Cyst Development in In Vitro and In Vivo Models of Polycystic Kidney Disease

Renal cyst expansion in polycystic kidney disease (PKD) involves abnormalities in both cyst-lining-cell proliferation and fluid accumulation. Suppression of these processes may retard the progression of PKD. Evidence suggests that the activation of 5' AMP-activated protein kinase (AMPK) inhibits cystic fibrosis transmembrane conductance regulator (CFTR)-mediated chloride secretion, leading to reduced progression of PKD. Here we investigated the pharmacological effects of panduratin A, a bioactive compound known as an AMPK activator, on CFTR-mediated chloride secretion and renal cyst development using in vitro and animal models of PKD. We demonstrated that AMPK was activated in immortalized normal renal cells and autosomal dominant polycystic kidney disease (ADPKD) cells following treatment with panduratin A. Treatment with panduratin A reduced the number of renal cyst colonies corresponding with a decrease in cell proliferation and phosphorylated p70/S6K, a downstream target of mTOR signaling. Additionally, panduratin A slowed cyst expansion via inhibition of the protein expression and transport function of CFTR. In heterozygous Han:Sprague-Dawley (Cy/+) rats, an animal model of PKD, intraperitoneal administration of panduratin A (25 mg/kg BW) for 5 weeks significantly decreased the kidney weight per body weight ratios and the cystic index. Panduratin A also reduced collagen deposition in renal tissue. Intraperitoneal administration of panduratin A caused abdominal bleeding and reduced body weight. However, 25 mg/kg BW of panduratin A via oral administration in the PCK rats, another non-orthologous PKD model, showed a significant decrease in the cystic index without severe adverse effects, indicating that the route of administration is critical in preventing adverse effects while still slowing disease progression. These findings reveal that panduratin A might hold therapeutic properties for the treatment of PKD.

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.

A Comprehensive Biological and Synthetic Perspective on 2-Deoxy-d-Glucose (2-DG), A Sweet Molecule with Therapeutic and Diagnostic Potentials

Glucose, the primary substrate for ATP synthesis, is catabolized during glycolysis to generate ATP and precursors for the synthesis of other vital biomolecules. Opportunistic viruses and cancer cells often hijack this metabolic machinery to obtain energy and components needed for their replication and proliferation. One way to halt such energy-dependent processes is by interfering with the glycolytic pathway. 2-Deoxy-d-glucose (2-DG) is a synthetic glucose analogue that can inhibit key enzymes in the glycolytic pathway. The efficacy of 2-DG has been reported across an array of diseases and disorders, thereby demonstrating its broad therapeutic potential. Recent approval of 2-DG in India as a therapeutic approach for the management of the COVID-19 pandemic has brought renewed attention to this molecule. The purpose of this perspective is to present updated therapeutic avenues as well as a variety of chemical synthetic strategies for this medically useful sugar derivative, 2-DG.

Metabolic reprogramming in a slowly developing orthologous model of polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease and affects 1 in 1,000 individuals. There is accumulating evidence suggesting that there are shared cellular mechanisms responsible for cystogenesis in human and murine PKD and that reprogramming of metabolism is a key disease feature. In this study, we used a targeted metabolomics approach in an orthologous mouse model of PKD (Pkd1RC/RC) to investigate the metabolic modifications a cystic kidney undergoes during disease progression. Using the Kyoto Encyclopedia of Genes and Genomes pathway database, we identified several biologically relevant metabolic pathways that were altered early in this disease (in 3-mo-old Pkd1RC/RC mice), the most highly represented being arginine biosynthesis and metabolism and tryptophan and phenylalanine metabolism. During the next 6 mo of disease progression, multiple uremic solutes accumulated in the kidney of cystic mice, including several established markers of oxidative stress and endothelial dysfunction (allantoin, asymmetric dimethylarginine, homocysteine, malondialdehyde, methionine sulfoxide, and S-adenosylhomocysteine). Levels of kynurenines and polyamines were also augmented in kidneys of Pkd1RC/RC versus wild-type mice, as were the levels of bacteria-produced indoles, whose increase within PKD kidneys suggests microbial dysbiosis. In summary, we confirmed previously published and identified novel metabolic markers and pathways of PKD progression that may prove helpful for diagnosis and monitoring of cystic kidney disease in patients. Furthermore, they provide targets for novel therapeutic approaches that deserve further study and hint toward currently understudied pathomechanisms.NEW & NOTEWORTHY This report delineates the evolution of metabolic changes occurring during autosomal dominant polycystic kidney disease (ADPKD) progression. Using an orthologous model, we performed kidney metabolomics and confirmed dysregulation of metabolic pathways previously found altered in nonorthologous or rapidly-progressive PKD models. Importantly, we identified novel alterations, including augmentation of kynurenines, polyamines, and indoles, suggesting increased inflammation and microbial dysbiosis that provide insights into PKD pathomechanisms and may prove helpful for diagnosing, monitoring, and treating ADPKD.

Dietary Interventions in Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the progressive growth of renal cysts, leading to the loss of functional nephrons. Recommendations for individuals with ADPKD to maintain a healthy diet and lifestyle are largely similar to those for the general population. However, recent evidence from preclinical models suggests that more tightly specified dietary regimens, including caloric restriction, intermittent fasting, and ketogenic diets, hold promise to slow disease progression, and the results of ongoing human clinical trials are eagerly awaited. These dietary interventions directly influence nutrient signaling and substrate availability in the cystic kidney, while also conferring systemic metabolic benefits. The present review focuses on the importance of local and systemic metabolism in ADPKD and summarizes current evidence for dietary interventions to slow disease progression and improve quality of life.

Disruption of polycystin-1 cleavage leads to cardiac metabolic rewiring in mice

Cardiovascular manifestations account for marked morbi-mortality in autosomal dominant polycystic kidney disease (ADPKD). Pkd1- and Pkd2-deficient mice develop cardiac dysfunction, however the underlying mechanisms remain largely unclear. It is unknown whether impairment of polycystin-1 cleavage at the G-protein-coupled receptor proteolysis site, a significant ADPKD mutational mechanism, is involved in this process. We analyzed the impact of polycystin-1 cleavage on heart metabolism using Pkd1^V/V mice, a model unable to cleave this protein and with early cardiac dysfunction. Pkd1^V/V hearts showed lower levels of glucose and amino acids and higher lipid levels than wild-types, as well as downregulation of p-AMPK, p-ACCβ, CPT1B-Cpt1b, Ppara, Nppa and Acta1. These findings suggested decreased fatty acid β-oxidation, which was confirmed by lower oxygen consumption by Pkd1^V/V isolated mitochondria using palmitoyl-CoA. Pkd1^V/V hearts also presented increased oxygen consumption in response to glucose, suggesting that alternative substrates may be used to generate energy. Pkd1^V/V hearts displayed a higher density of decreased-size mitochondria, a finding associated with lower MFN1, Parkin and BNIP3 expression. These derangements were correlated with increased apoptosis and inflammation but not hypertrophy. Notably, Pkd1^V/V neonate cardiomyocytes also displayed shifts in oxygen consumption and p-AMPK downregulation, suggesting that, at least partially, the metabolic alterations are not induced by kidney dysfunction. Our findings reveal that disruption of polycystin-1 cleavage leads to cardiac metabolic rewiring in mice, expanding the understanding of heart dysfunction associated with Pkd1 deficiency and likely with human ADPKD.

OUP accepted manuscript

Autosomal dominant polycystic kidney disease (ADPKD) is the most prevalent hereditary kidney disease. Recent evidence suggests that the pathogenesis of ADPKD is a complex web of abnormal cellular processes including altered cell signaling, disordered cell metabolism, impaired autophagy, increased apoptosis, mitochondrial dysfunction and chronic inflammation. Sodium–glucose cotransporter (SGLT) inhibitors (SGLTi) reduce body weight, blood pressure and blood glucose levels, have kidney and cardiovascular protective activity, and have been reported to decrease inflammation, increase autophagy and improve mitochondrial dysfunction. We now review results from preclinical studies on SGLTi for ADPKD identified through a systematic search of the MEDLINE, Cochrane Library, Embase and PubMed databases. Potential underlying mechanisms for the conflicting results reported as well as implications for clinical translation are discussed, as ADPKD patients were excluded from clinical trials exploring kidney protection by SGLT2 inhibitors (SGLT2i). However, they were not excluded from cardiovascular safety trials or trials for cardiovascular conditions. A post-hoc analysis of the kidney function trajectories and safety of SGLT2i in ADPKD patients enrolled in such trials may provide additional information. In conclusion, SGLT2i are cardio- and nephroprotective in diverse clinical situations. Currently, it is unclear whether ADPKD patients may benefit from SGLT2i in terms of kidney function preservation, and their safety in this population remains unexplored. We propose a roadmap to address this unmet clinical need.

Metabolic Reprogramming and Reconstruction: Integration of Experimental and Computational Studies to Set the Path Forward in ADPKD

Metabolic reprogramming is a key feature of Autosomal Dominant Polycystic Kidney Disease (ADPKD) characterized by changes in cellular pathways occurring in response to the pathological cell conditions. In ADPKD, a broad range of dysregulated pathways have been found. The studies supporting alterations in cell metabolism have shown that the metabolic preference for abnormal cystic growth is to utilize aerobic glycolysis, increasing glutamine uptake and reducing oxidative phosphorylation, consequently resulting in ADPKD cells shifting their energy to alternative energetic pathways. The mechanism behind the role of the polycystin proteins and how it leads to disease remains unclear, despite the identification of numerous signaling pathways. The integration of computational data analysis that accompanies experimental findings was pivotal in the identification of metabolic reprogramming in ADPKD. Here, we summarize the important results and argue that their exploitation may give further insights into the regulative mechanisms driving metabolic reprogramming in ADPKD. The aim of this review is to provide a comprehensive overview on metabolic focused studies and potential targets for treatment, and to propose that computational approaches could be instrumental in advancing this field of research.

Metformin induces lactate accumulation and accelerates renal cyst progression in Pkd1-deficient mice

Metabolic reprogramming is a potential treatment strategy for autosomal dominant polycystic kidney disease (ADPKD). Metformin has been shown to inhibit the early stages of cyst formation in animal models. However, metformin can lead to lactic acidosis in diabetic patients with advanced chronic kidney disease, and its efficacy in ADPKD is still not fully understood. Here, we investigated the effect of metformin in an established hypomorphic mouse model of PKD that presents stable and heritable knockdown of Pkd1. The Pkd1 miRNA transgenic mice of both genders were randomized to receive metformin or saline injections. Metformin was administrated through daily intraperitoneal injection from postnatal day 35 for 4 weeks. Unexpectedly, metformin treatment at a concentration of 150 mg/kg increased disease severity, including kidney-to-body weight ratio, cystic index and plasma BUN levels, and was associated with increased renal tubular cell proliferation and plasma lactate levels. Functional enrichment analysis for cDNA microarrays from kidney samples revealed significant enrichment of several pro-proliferative pathways including β-catenin, hypoxia-inducible factor-1α, protein kinase Cα and Notch signaling pathways in the metformin-treated mutant mice. The plasma metformin concentrations were still within the recommended therapeutic range for type 2 diabetic patients. Short-term metformin treatment in a second Pkd1 hypomorphic model (Pkd1RC/RC) was however neutral. These results demonstrate that metformin may exacerbate late-stage cyst growth associated with the activation of lactate-related signaling pathways in Pkd1 deficiency. Our findings indicate that using metformin in the later stage of ADPKD might accelerate disease progression and call for the cautious use of metformin in these patients.

Tubular Cell Glucose Metabolism Shift During Acute and Chronic Injuries

Acute and chronic kidney disease are responsible for large healthcare costs worldwide. During injury, kidney metabolism undergoes profound modifications in order to adapt to oxygen and nutrient shortage. Several studies highlighted recently the importance of these metabolic adaptations in acute as well as in chronic phases of renal disease, with a potential deleterious effect on fibrosis progression. Until recently, glucose metabolism in the kidney has been poorly studied, even though the kidney has the capacity to use and produce glucose, depending on the segment of the nephron. During physiology, renal proximal tubular cells use the beta-oxidation of fatty acid to generate large amounts of energy, and can also produce glucose through gluconeogenesis. In acute kidney injury, proximal tubular cells metabolism undergo a metabolic shift, shifting away from beta-oxidation of fatty acids and gluconeogenesis toward glycolysis. In chronic kidney disease, the loss of fatty acid oxidation is also well-described, and data about glucose metabolism are emerging. We here review the modifications of proximal tubular cells glucose metabolism during acute and chronic kidney disease and their potential consequences, as well as the potential therapeutic implications.

Chronic activation of AMP-activated protein kinase leads to early-onset polycystic kidney phenotype

AMP-activated protein kinase (AMPK) plays a key role in the cellular response to low energy stress and has emerged as an attractive therapeutic target for tackling metabolic diseases. Whilst significant progress has been made regarding the physiological role of AMPK, its function in the kidney remains only partially understood. We use a mouse model expressing a constitutively active mutant of AMPK to investigate the effect of AMPK activation on kidney function in vivo. Kidney morphology and changes in gene and protein expression were monitored and serum and urine markers were measured to assess kidney function in vivo. Global AMPK activation resulted in an early-onset polycystic kidney phenotype, featuring collecting duct cysts and compromised renal function in adult mice. Mechanistically, the cystic kidneys had increased cAMP levels and ERK activation, increased hexokinase I (Hk I) expression, glycogen accumulation and altered expression of proteins associated with autophagy. Kidney tubule-specific activation of AMPK also resulted in a polycystic phenotype, demonstrating that renal tubular AMPK activation caused the cystogenesis. Importantly, human autosomal dominant polycystic kidney disease (ADPKD) kidney sections revealed similar protein localisation patterns to that observed in the murine cystic kidneys. Our findings show that early-onset chronic AMPK activation leads to a polycystic kidney phenotype, suggesting dysregulated AMPK signalling is a contributing factor in cystogenesis.

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.

Metformin and Glaucoma-Review of Anti-Fibrotic Processes and Bioenergetics

Glaucoma is the leading cause of irreversible blindness globally. With an aging population, disease incidence will rise with an enormous societal and economic burden. The treatment strategy revolves around targeting intraocular pressure, the principle modifiable risk factor, to slow progression of disease. However, there is a clear unmet clinical need to find a novel therapeutic approach that targets and halts the retinal ganglion cell (RGC) degeneration that occurs with fibrosis. RGCs are highly sensitive to metabolic fluctuations as a result of multiple stressors and thus their viability depends on healthy mitochondrial functioning. Metformin, known for its use in type 2 diabetes, has come to the forefront of medical research in multiple organ systems. Its use was recently associated with a 25% reduced risk of glaucoma in a large population study. Here, we discuss its application to glaucoma therapy, highlighting its effect on fibrotic signalling pathways, mitochondrial bioenergetics and NAD oxidation.

Molecular Pathophysiology of Autosomal Recessive Polycystic Kidney Disease

Autosomal recessive polycystic kidney disease (ARPKD) is a rare disorder and one of the most severe forms of polycystic kidney disease, leading to end-stage renal disease (ESRD) in childhood. PKHD1 is the gene that is responsible for the vast majority of ARPKD. However, some cases have been related to a new gene that was recently identified (DZIP1L gene), as well as several ciliary genes that can mimic a ARPKD-like phenotypic spectrum. In addition, a number of molecular pathways involved in the ARPKD pathogenesis and progression were elucidated using cellular and animal models. However, the function of the ARPKD proteins and the molecular mechanism of the disease currently remain incompletely understood. Here, we review the clinics, treatment, genetics, and molecular basis of ARPKD, highlighting the most recent findings in the field.

Overweight and Obesity and Progression of ADPKD

BACKGROUND AND OBJECTIVES

On the basis of earlier observations, we evaluated the association between overweight and obesity and rapid progression of autosomal dominant polycystic kidney disease in participants in the Tolvaptan Efficacy and Safety in Management of Autosomal Dominant Polycystic Kidney Disease and Its Outcomes (TEMPO) 3:4 trial. More importantly, we also determined whether efficacy of tolvaptan was attenuated in individuals with baseline overweight or obesity.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A total of 1312 study participants with relatively early-stage autosomal dominant polycystic kidney disease (mean eGFR 78±22 ml/min per 1.73 m2) who were at high risk of rapid progression were categorized by body mass index (BMI; calculated using nonkidney weight) as normal weight (18.5-24.9 kg/m2; n=670), overweight (25.0-29.9 kg/m2; n=429), or obese (≥30 kg/m2; n=213). Linear and multinomial logistic regression models were used to determine the association of baseline overweight and obesity with change in total kidney volume (TKV) over the 3-year study period.

RESULTS

In fully adjusted models, higher BMI was associated with greater annual percent change in TKV (difference of 1.20 [95% confidence interval (95% CI), 0.85 to 1.55] per five-unit higher BMI). Overweight and obesity were associated with higher odds of annual percent change in TKV of ≥7% versus <5% (overweight: odds ratio, 2.04 [95% CI, 1.45 to 2.87]; obese: odds ratio, 4.31 [95% CI, 2.83 to 6.57] versus normal weight). eGFR decline did not differ according to BMI (fully adjusted difference in decline of -0.95 [95% CI, -2.32 to 0.40] ml/min per 1.73 m2 per year per five-unit higher BMI). The three-way interaction (treatment×time×BMI group) was not statistically significant in linear mixed models with an outcome of TKV (log-transformed estimated coefficient comparing the treatment effect for overweight versus normal weight: 0.56% [95% CI, -0.70% to 1.84%] per year; P=0.38; obese versus normal weight: 0.07% [95% CI, -1.47% to 1.63%] per year; P=0.93) or eGFR (estimated coefficient comparing overweight versus normal weight: -0.07 [95% CI, -0.95 to 0.82] ml/min per 1.73 m2 per year; P=0.88; obese versus normal weight: 0.22 [95% CI, -0.93 to 1.36] ml/min per 1.73 m2 per year; P=0.71).

CONCLUSIONS

Overweight and particularly obesity are strongly and independently associated with kidney growth, but not eGFR slope, in the TEMPO 3:4 trial, and tolvaptan efficacy is irrespective of BMI categorization.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Tolvaptan Efficacy and Safety in Management of Autosomal Dominant Polycystic Kidney Disease and Its Outcomes (TEMPO) 3:4, NCT00428948.

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.

Reduced Oxidative Phosphorylation and Increased Glycolysis in Human Glaucoma Lamina Cribrosa Cells

Purpose

The lamina cribrosa (LC) is a key site of damage in glaucomatous optic neuropathy. We previously found that glaucoma LC cells have an increased profibrotic gene expression, with mitochondrial dysfunction in the form of decreased mitochondrial membrane potential. Altered cell bioenergetics have recently been reported in organ fibrosis and in cancer. In this study, we carried out a systematic mitochondrial bioenergetic assessment and measured markers of alternative sources of cellular energy in normal and glaucoma LC cells.

Methods

LC cells from three glaucoma donors and three age-matched normal controls were assessed using VICTOR X4 Perkin Elmer (Waltham, MA) plate reader with different phosphorescent and luminescent probes. adenosine triphosphate levels, oxygen consumption rate, and extracellular acidification were measured and normalized to total protein content. RNA and protein expression levels of MCT1, MCT4, MTFHD2, and GLS2 were quantified using real-time RT-PCR and Western blotting.

Results

Glaucoma LC cells contain significantly less adenosine triphosphate (P < .05) when supplied with either glucose or galactose. They also showed significantly diminished oxygen consumption in both basal and maximal respiration with more lactic acid contribution in ECA. Both mRNA and protein expression levels of MCT1, MCT4, MTHFD2, and GLS2 were significantly increased in glaucoma LC cells.

Conclusions

We demonstrate evidence of metabolic reprogramming (The Warburg effect) in glaucoma LC cells. Expression of markers of glycolysis, glutamine, and one carbon metabolism are elevated in glaucoma cells at both the mRNA and protein levels. A better understanding of bioenergetics in glaucoma may help in the development of new therapeutics.

Reprogramming of Metabolism in Kidney Cancer

Metabolic reprogramming is one of the major steps that tumor cells take during cancer progression. This process allows the cells to survive in a nutrient- and oxygen-deprived environment, to become stress tolerant, and to metastasize to different sites. Recent studies have shown that reprogramming happens in stromal cells and involves the cross-talk of the cancer cell/tumor microenvironment. There are similarities between the metabolic reprogramming that occurs in both noncancerous kidney diseases and renal cell carcinoma (RCC), suggesting that such reprogramming is a means by which renal epithelial cells survive injury and repair the tissue, and that RCC cells hijack this system. This article reviews reprogramming of major metabolism pathways in RCC, highlighting similarities and differences from kidney diseases and potential therapeutic strategies against it.

Inhibition of aerobic glycolysis alleviates sepsis‑induced acute kidney injury by promoting lactate/Sirtuin 3/AMPK‑regulated autophagy

Metabolism reprogramming influences the severity of organ dysfunction, progression to fibrosis, and development of disease in acute kidney injury (AKI). Previously we showed that inhibition of aerobic glycolysis improved survival rates and protected septic mice from kidney injury. However, the underlying mechanisms remain unclear. In the present study, it was revealed that sepsis or lipopolysaccharide (LPS) enhanced aerobic glycolysis as evidenced by increased lactate production and upregulated mRNA expression of glycolysis-related genes in kidney tissues and human renal tubular epithelial (HK-2) cells. The aerobic glycolysis inhibitor 2-deoxy-D-glucose (2-DG) downregulated glycolysis, and improved kidney injury induced by sepsis. 2-DG treatments increased the expression of sirtuin 3 (SIRT3) and phosphorylation-AMP-activated protein kinase (p-AMPK), following promoted autophagy and attenuated apoptosis of tubular epithelial cells in septic mice and in LPS-treated HK-2 cells. However, the glycolysis metabolite lactate downregulated SIRT3 and p-AMPK expression, inhibited autophagy and enhanced apoptosis in LPS-treated HK-2 cells. Furthermore, pharmacological blockade of autophagy with 3-methyladenine (3-MA) partially abolished the protective effect of 2-DG in sepsis-induced AKI. These findings indicated that inhibition of aerobic glycolysis protected against sepsis-induced AKI by promoting autophagy via the lactate/SIRT3/AMPK pathway.

Prostaglandins as potential targets for the treatment of polycystic kidney disease

Polycystic kidney disease (PKD) is characterized by the proliferation of fluid-filled kidney cysts that enlarge over time, causing damage to the surrounding kidney and ultimately resulting in kidney failure. Both increased cell proliferation and fluid secretion are stimulated by increased cyclic adenosine monophosphate (cAMP) in PKD kidneys, so many treatments for the disease target cAMP lowering. Prostaglandins (PG) levels are elevated in multiple animal models of PKD and mediate many of their effects by elevating cAMP levels. Inhibiting the production of PG with cyclooxygenase 2 (COX2) inhibitors reduces PG levels and reduces disease progression. However, COX inhibitors also block beneficial PG and can cause nephrotoxicity. In an orthologous model of the main form of PKD, PGD₂ and PGI₂ were the two PG highest in kidneys and most affected by a COX2 inhibitor. Future studies are needed to determine whether specific blockage of PGD₂ and/or PGI₂ activity would lead to more targeted and effective treatments with fewer undesirable side-effects.

Roles of telomeres and telomerase in age‑related renal diseases (Review)

Age‑related renal diseases, which account for various progressive renal disorders associated with cellular and organismal senescence, are becoming a substantial public health burden. However, their aetiologies are complicated and their pathogeneses remain poorly understood. Telomeres and telomerase are known to be essential for maintaining the integrity and stability of eukaryotic genomes and serve crucial roles in numerous related signalling pathways that activate renal functions, such as repair and regeneration. Previous studies have reported that telomere dysfunction served a role in various types of age‑related kidney disease through various different molecular pathways. The present review aimed to summarise the current knowledge of the association between telomeres and ageing‑related kidney diseases and explored the contribution of dysfunctional telomeres to these diseases. The findings may help to provide novel strategies for treating patients with renal disease.

Loss of Mitochondrial Control Impacts Renal Health

Disruption of mitochondrial biosynthesis or dynamics, or loss of control over mitochondrial regulation leads to a significant alteration in fuel preference and metabolic shifts that potentially affect the health of kidney cells. Mitochondria regulate metabolic networks which affect multiple cellular processes. Indeed, mitochondria have established themselves as therapeutic targets in several diseases. The importance of mitochondria in regulating the pathogenesis of several diseases has been recognized, however, there is limited understanding of mitochondrial biology in the kidney. This review provides an overview of mitochondrial dysfunction in kidney diseases. We describe the importance of mitochondria and mitochondrial sirtuins in the regulation of renal metabolic shifts in diverse cells types, and review this loss of control leads to increased cell-to-cell transdifferentiation processes and myofibroblast-metabolic shifts, which affect the pathophysiology of several kidney diseases. In addition, we examine mitochondrial-targeted therapeutic agents that offer potential leads in combating kidney diseases.

Mutation of regulatory phosphorylation sites in PFKFB2 worsens renal fibrosis

Fatty acid oxidation is the major energy pathway used by the kidney, although glycolysis becomes more important in the low oxygen environment of the medulla. Fatty acid oxidation appears to be reduced in renal fibrosis, and drugs that reverse this improve fibrosis. Expression of glycolytic genes is more variable, but some studies have shown that inhibiting glycolysis reduces renal fibrosis. To address the role of glycolysis in renal fibrosis, we have used a genetic approach. The crucial control point in the rate of glycolysis is 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase. Phosphorylation of the kidney isoform, PFKFB2, on residues Ser⁴⁶⁸ and Ser⁴⁸⁵ stimulates glycolysis and is the most important mechanism regulating glycolysis. We generated transgenic mice with inactivating mutations of Ser⁴⁶⁸ and Ser⁴⁸⁵ in PFKFB2 (PFKFB2 KI mice). These mutations were associated with a reduced ability to increase glycolysis in primary cultures of renal tubular cells from PFKFB2 KI mice compared to WT cells. This was associated in PFKFB2 KI mice with increased renal fibrosis, which was more severe in the unilaternal ureteric obstruction (UUO) model compared with the folic acid nephropathy (FAN) model. These studies show that phosphorylation of PFKFB2 is important in limiting renal fibrosis after injury, indicating that the ability to regulate and maintain adequate glycolysis in the kidney is crucial for renal homeostasis. The changes were most marked in the UUO model, probably reflecting a greater effect on distal renal tubules and the greater importance of glycolysis in the distal nephron.

Sodium-glucose cotransporter-2 inhibitors for diabetic kidney disease: Targeting Warburg effects in proximal tubular cells

Inhibitors of sodium-glucose cotransporter 2 (SGLT2) have undoubtedly shifted the paradigm for diabetes medicine and research and, especially, diabetic kidney disease (DKD). The pharmacological action of SGLT2 inhibitors is simply the release of glucose into urine; however, precisely how SGLT2 inhibitors contribute to the health of those with diabetes has still not been completely elucidated. Towards this end, the present review provides a novel insight into the action of SGLT2 inhibitors by highlighting a neglected fuel-burning system found in proximal tubular cells-'glycolysis'. In addition, exploring the details of the molecular mechanisms and clinical biomarkers of the organ protection conferred by SGLT2 inhibitors is now required to prepare for the next stage of clinical diabetes medicine-the 'post-SGLT2 inhibitor era'.