Mouse Model Of Chronic Kidney Disease Research Articles

The Pathophysiologic Role of Gelsolin in Chronic Kidney Disease: Focus on Podocytes.

Chronic kidney disease (CKD) is normally related to proteinuria, a common finding in a compromised glomerular filtration barrier (GFB). GFB is a structure composed of glomerular endothelial cells, the basement membrane, and the podocytes. CKD with podocyte damage may be associated with actin cytoskeleton reorganization, resulting in podocyte effacement. Gelsolin plays a critical role in several diseases, including cardiovascular diseases and cancer. Our current study aimed to determine the connection between gelsolin and podocyte, and thus the mechanism underlying podocyte injury in CKD. Experiments were carried out on Drosophila to demonstrate whether gelsolin had a physiological role in maintaining podocyte. Furthermore, the survival rate of gelsolin-knocked down Drosophila larvae was extensively reduced after AgNO3 exposure. Secondly, the in vitro podocytes treated with puromycin aminonucleoside (PAN) enhanced the gelsolin protein expression, as well as small GTPase RhoA and Rac1, which also regulated actin dynamic expression incrementally with the PAN concentrations. Thirdly, we further demonstrated in vivo that GSN was highly expressed inside the glomeruli with mitochondrial dysfunction in a CKD mouse model. Our findings suggest that an excess of gelsolin may contribute to podocytes damage in glomeruli.

A Monoclonal Antibody Targeting ALK2 As a Potential Therapeutic Agent for Anemia of Inflammation

Background: Iron homeostasis is primarily regulated by hepcidin, a hormone predominantly expressed in the liver. Hepcidin activates the degradation of the transmembrane iron exporter ferroportin, thereby downregulating the release of iron from cells. Hepcidin expression is, at least partly, regulated in response to signaling of the type I TGF-β receptor ALK2, via SMAD2/3 phosphorylation. IL-6, which is commonly elevated in chronic kidney disease (CKD) and other inflammatory conditions, upregulates hepcidin expression and reduces serum iron bioavailability. As a result, chronic inflammatory conditions are often accompanied by secondary anemia of inflammation (AI).We have previously demonstrated that ALK2 inhibition suppressed hepcidin expression in rodents, monkeys and healthy humans. We further described that administration of a selective small molecule ALK2 kinase inhibitor (KTI-2338) reversed changes in hepcidin and iron in a mouse model of CKD, supporting the potential benefit of ALK2 inhibition in AI. Another approach to targeting ALK2 signaling is use of a neutralizing antibody. KTI-018 is a neutralizing ALK2 antibody with high affinity and selectivity for ALK2. This biologic has been demonstrated to reduce serum hepcidin and increase serum iron in healthy non-human primates.Aims: To further elucidate the specific contribution of ALK2 signaling as a driver in AI, and to determine the therapeutic potential of the antibody in this type of anemia, we assessed the effect of KTI-018 in the CKD mouse model.Methods: The study was conducted with 6-week-old male C57Bl/6 mice. Mice in the CKD cohort (CKD) were treated with once daily oral administration of adenine, a compound that metabolizes to 2,8-dihydroxyadenine, forming crystals in the proximal tubular epithelia and causing inflammation and fibrosis in the kidneys. Mice in the control cohort (healthy) received once daily oral administration of vehicle.Upon confirmation of disease, the CKD cohort was subdivided into two groups. The treatment group received twice weekly intraperitoneal treatment with KTI-018 (CKD-KTI-018), and the control group received tris-buffered saline (CKD-TBS). Healthy mice received TBS only. All mice were maintained on their assigned daily adenine or vehicle regimen. At day 53, the study was terminated and hematologic parameters, serum hepcidin, iron, and IL-6 levels were assessed.Results: After 42 days of adenine or vehicle administration, serum hepcidin, serum iron, and hematologic parameters were assessed in representative cohorts of CKD-TBS and healthy mice. The CKD-TBS cohort experienced changes associated with anemia of inflammation as compared to the healthy mice, including increased hepcidin, decreased serum iron, and decreased hematologic parameters. The differences between the healthy and CKD-TBS groups were maintained through the duration of the study.At study termination, CKD-TBS mice had increased serum IL-6 levels (218%), elevated serum hepcidin (149%), and reduced serum iron (-30%) as compared to the healthy mice. Laboratory findings characteristic of anemia were present in the CKD-TBS group, including decreased red blood cells (-6.1%), hemoglobin (-13.2%), and reticulocyte hemoglobin content (-9.3%) as compared to healthy mice.In contrast, CKD-KTI-018 mice had decreased serum hepcidin (-25%) and increased serum iron (59%) as compared to CKD-TBS mice. This restoration of serum iron corresponded to improvements in red blood cells, hemoglobin, and reticulocyte hemoglobin content, which were increased by 7.6%, 9.6%, and 6.7%, respectively, in the CKD-KTI-018 mice as compared to the CKD-TBS mice. These results demonstrate that, by decreasing serum hepcidin, KTI-018 increased the bioavailability of iron, which led to the restoration of hematologic parameters and appeared to reverse AI in mice.Discussion: In this study, a neutralizing ALK2 antibody decreased serum hepcidin, increased serum iron and consequently reversed AI in a mouse model of CKD. These results support the role of ALK2 signaling in AI and suggest that inhibition of ALK2 may be a potential treatment approach for anemia resulting from CKD and other chronic inflammatory diseases. Future studies will explore if ALK2 inhibition may prevent or treat progression of CKD itself, and the role that ALK2 inhibition may play in other chronic inflammatory conditions associated with elevated hepcidin. DisclosuresMedeiros: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company. Backus: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company. Materna: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company. Fisher: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company. Lachey: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees. Seehra: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company.

Dimethylamine enhances platelet hyperactivity in chronic kidney disease model.

Chronic kidney disease (CKD) remains a major health threat worldwide which is associated with elevated blood level of dimethylamine (DMA) and unbalanced platelet functions. Dimethylamine, a simple aliphatic amine, is abundantly found in human urine as well as other body fluids like plasma. However, the relation between dimethylamine and platelet activation is unclear. This study aims to unravel the mechanism of DMA and platelet function in chronic kidney disease. Through in vitro platelet characterization assay and in vivo CKD mouse model, the level of DMA, platelet activity and renal function were assessed by established methods. PKCδ and its downstream kinase MEK1/2 were examined by immunoblotting analysis of human platelet extract. Rescue experiments with PKCδ inhibitor or choline deficient diet were also conducted. DMA level in plasma of mouse CKD model was elevated along with enhanced platelet activation and comprised renal function. DMA can activate platelet in vitro and in vivo. Inhibition of PKCδ could antagonize the effect of DMA on platelet activation. When choline as the dietary source of DMA was deprived from CKD mouse, the level DMA was reduced and platelet activation was attenuated. Our results demonstrate that dimethylamine could enhance platelet activation in CKD model, potentially through activation of PKCδ.

ALKBH1 reduces DNA N6-methyladenine to allow for vascular calcification in chronic kidney disease.

Vascular calcification is a common complication of chronic kidney disease (CKD), and one of the main risk factors for increased cardiovascular morbidity and mortality in patients with CKD. In this issue of the JCI, Ouyang and Su et al. report that Alkb homolog 1 (ALKBH1), a DNA demethylase, reduced DNA N6-methyladenine (6mA) in vascular smooth muscle cells (VSMCs) and leukocytes, thus leading to aortic arch calcification in the patients with CKD. During the progression of vascular calcification, increased ALKBH1 expression was linked to decreased 6mA levels, findings that the authors noted in both patients with CKD and CKD mouse models. The kidney and vascular disease risk factor soluble urokinase receptor (suPAR) was also elevated in the plasma. Notably, lower 6mA levels induced BMP2-mediated osteogenic reprogramming in the VSMCs. These findings present a function of ALKBH1 in vascular calcification and provide a framework for therapeutic strategies.

Melatonin Protects Chronic Kidney Disease Mesenchymal Stem/Stromal Cells against Accumulation of Methylglyoxal via Modulation of Hexokinase-2 Expression.

Treatment options for patients with chronic kidney disease (CKD) are currently limited; therefore, there has been significant interest in applying mesenchymal stem/stromal cell (MSC)-based therapy to treat CKD. However, MSCs harvested from CKD patients tend to show diminished viability and proliferation due to sustained exposure to uremic toxins in the CKD environment, which limits their utility for cell therapy. The application of melatonin has been demonstrated to improve the therapeutic efficacy of MSCs derived from and engrafted to tissues in patients suffering from CKD, although the underlying biological mechanism has not been elucidated. In this study, we observed overexpression of hexokinase-2 (HK2) in serum samples of CKD patients and MSCs harvested from an adenine-fed CKD mouse model (CKD-mMSCs). HK2 upregulation led to increased production levels of methylglyoxal (MG), a toxic metabolic intermediate of abnormal glycolytic processes. The overabundance of HK2 and MG was associated with impaired mitochondrial function and low cell proliferation in CKD-mMSCs. Melatonin treatment inhibited the increases in HK2 and MG levels, and further improved mitochondrial function, glycolytic metabolism, and cell proliferation. Our findings suggest that identifying and characterizing metabolic regulators such as HK2 in CKD may improve the efficacy of MSCs for treating CKD and other kidney disorders.

Early inflammatory changes and CC chemokine ligand-8 upregulation in the heart contribute to uremic cardiomyopathy.

Uremic cardiomyopathy is a common complication in chronic kidney disease (CKD) patients, accounting for a high mortality rate. Several mechanisms have been proposed to link CKD and cardiac alterations; however, the early cardiac modifications that occur in CKD that may trigger cardiac remodeling and dysfunction remain largely unexplored. Here, in a mouse model of CKD induced by 5/6 nephrectomy, we first analyzed the early transcriptional and inflammatory changes that occur in the heart. Five days after 5/6 nephrectomy, RNA-sequencing showed the upregulation of 54 genes in the cardiac tissue of CKD mice and the enrichment of biological processes related to immune system processes. Increased cardiac infiltration of T-CD4+ lymphocytes, myeloid cells, and macrophages during early CKD was observed. Next, since CC chemokine ligand-8 (CCL8) was one of the most upregulated genes in the heart of mice with early CKD, we investigated the effect of acute and transient CCL8 inhibition on uremic cardiomyopathy severity. An increase in CCL8 protein levels was confirmed in the heart of early CKD mice. CCL8 inhibition attenuated the early infiltration of T-CD4+ lymphocytes and macrophages to the cardiac tissue, leading to a protection against chronic cardiac fibrotic remodeling, inflammation and cardiac dysfunction induced by CKD. Altogether, our data show the occurrence of transcriptional and inflammatory changes in the heart during the early phases of CKD and identify CCL8 as a key contributor to the early cardiac inflammatory state that triggers further cardiac remodeling and dysfunction in uremic cardiomyopathy.

Preventive Effects of Lactobacillus Mixture against Chronic Kidney Disease Progression through Enhancement of Beneficial Bacteria and Downregulation of Gut-Derived Uremic Toxins.

Gut dysbiosis is a major contributor to adverse chronic kidney disease (CKD) progression, and microbiota-based strategies could be considered as a novel therapeutic and preventative target. In this study, a probiotic screening platform based on gut-derived uremic toxin-reducing probiotics was developed and the underlying mechanism was further verified through a 0.2% adenine-induced CKD mouse model. Two strains (Lactobacillus paracasei and Lactobacillus plantarum) were selected due to their high clearance ability and named Lactobacillus mix (Lm). The results showed that Lm significantly improved the kidney function by reducing kidney injury and fibrotic-related proteins. Furthermore, Lm decreased oxidative stress and proinflammatory reactions and elevated immune responses in the kidney. Importantly, Lm reversed gut dysbiosis and restored the abundance of commensal bacteria, especially short-chain fatty acid producers, leading to improved intestinal barrier integrity via modulation of microbial composition and metabolite production. Taken together, these findings provided evidence that Lm could be a preventive approach against CKD.

Chrono-Drug Discovery and Development Based on Circadian Rhythm of Molecular, Cellular and Organ Level.

The paired suprachiasmatic nuclei (SCN) is the circadian pacemaker in mammals. Clock genes ultimately regulates a vast array of circadian rhythms involved in biological, physiological and behavioral process. The clock genes are closely related to sleep disorders, metabolic syndromes, and cancer diseases. Monitoring rhythm, overcoming rhythm disruption, and manipulating rhythm from the perspective of the clock genes play an important role to improve chronopharmacotherapy. Such an approach should be achieved by overcoming the new challenges in drug delivery systems that match the circadian rhythm (Chrono-DDS). Gene and antibody delivery, targeting specific molecules for certain diseases have been focused in recent studies on pharmacotherapy. One of important candidates should also be clock genes. New drugs targeting the molecular clock are being developed to manage diseases in humans. The circadian dynamics of cancer stem cells are controlled by the tumor microenvironment and provide proof for its implication in chronotherapy against triple-negative breast cancer. To examine the relationship between the circadian clock and chronic kidney disease (CKD) exacervation leads to clarify the novel molecular mechanisms causing renal malfunction in mice with CKD. A novel inhibitor of cell cycle regulatory factors has been identified and the inhibitor repressed renal inflammation in a CKD mouse model. Therefore, this review aims to introduce the role of the molecular clock in the time-dependent dosing changes in the therapeutic effect and safety of a drug and the possibility of drug discovery and development based on the molecular clock.

Pro-cachectic factors link experimental and human chronic kidney disease to skeletal muscle wasting programs.

Skeletal muscle wasting is commonly associated with chronic kidney disease (CKD), resulting in increased morbidity and mortality. However, the link between kidney and muscle function remains poorly understood. Here, we took a complementary interorgan approach to investigate skeletal muscle wasting in CKD. We identified increased production and elevated blood levels of soluble pro-cachectic factors, including activin A, directly linking experimental and human CKD to skeletal muscle wasting programs. Single-cell sequencing data identified the expression of activin A in specific kidney cell populations of fibroblasts and cells of the juxtaglomerular apparatus. We propose that persistent and increased kidney production of pro-cachectic factors, combined with a lack of kidney clearance, facilitates a vicious kidney/muscle signaling cycle, leading to exacerbated blood accumulation and, thereby, skeletal muscle wasting. Systemic pharmacological blockade of activin A using soluble activin receptor type IIB ligand trap as well as muscle-specific adeno-associated virus-mediated downregulation of its receptor ACVR2A/B prevented muscle wasting in different mouse models of experimental CKD, suggesting that activin A is a key factor in CKD-induced cachexia. In summary, we uncovered a crosstalk between kidney and muscle and propose modulation of activin signaling as a potential therapeutic strategy for skeletal muscle wasting in CKD.

Inhibition of CTCF-regulated miRNA-185-5p mitigates renal interstitial fibrosis of chronic kidney disease.

Aim: The present study aimed to elucidate the effect of CTCFon renal interstitial fibrosis in chronic kidney disease (CKD) and underlying mechanisms. Materials & methods: We measured NPHS2 expression and investigated its function in a unilateral ureteral obstruction-induced mouse model of CKD. Results: NPHS2 was poorly expressed in CKD mice. miR-185-5p targeted NPHS2 and reduced its expression, leading to increased α-SMAand COLI/IIIexpression, increased renal interstitial fibrosis areaand elevated phosphorylated vasodilator-stimulated phosphoprotein/vasodilator-stimulated phosphoprotein ratio. Co-treatment with CTCF downregulated miR-185-5p expression and abolished its effects in the CKD model. Conclusion: CTCF suppressed miR-185-5p and upregulated its target NPHS2, with a net effect of alleviating renal interstitial fibrosis in CKD.

Ophiocordyceps lanpingensis polysaccharides alleviate chronic kidney disease through MAPK/NF-κB pathway

Ethnopharmacological relevanceOphiocordyceps lanpingensis (O. lanpingensis) is a traditional ethno-medicine distributed in Eastern Himalayas, which has been used by local minorities to prevent and treat urinary diseases for hundreds of years. However, the corresponding active components and related pharmacological mechanism of such medication are not clear yet. Aims of the studyThis study was performed to investigate the effects and potential mechanisms of O. lanpingensis polysaccharides (OLP) in the treatment of chronic kidney disease (CKD) based on our previous research results. Materials and methodsMethylation analysis was used to investigate the monosaccharide composition and glycosidic linkages in OLP. The animals were divided into the control group, CKD model group, losartan group and three different doses of OLP groups. The CKD mouse model was established by the adenine gavage. The histological changes of renal tissue were observed by Hematoxylin-eosin and Masson staining. Biochemical indicators, including blood urea nitrogen (BUN), serum creatinine (Scr), serum phosphorus (P), plasma calcium (Ca), reactive oxygen species (ROS), superoxide dismutase (SOD), glutathione peroxidase (GSH-PX) and malondialdehyde (MDA) were measured to evaluate the alleviation of CKD by OLP. Moreover, the expression levels of a series of cytokines related to the inflammation, apoptosis and fibrosis were analyzed to explore the possible mechanisms of OLP to treat CKD. ResultsOLP is composed of three kinds of monosaccharides. There are eight kinds of glycosidic linkages in OLP, among which →4)-Glcp-(1→ is the main linkage. OLP could significantly attenuate CKD in mice and the tubulointerstitial damage was recovered to almost normal after the treatment of OLP. Compared with the CKD model group, the levels of Scr, BUN, MDA, P in OLP treatment groups were significantly decreased; and the levels of SOD and Ca were increased after OLP treatment. Furthermore, OLP could reduce the oxidative stress of the renal tissues, decrease the expression levels of pro-inflammatory factors through TLR4-mediated MAPK and NF-κB pathway, inhibit the apoptosis of renal cells by MAPK pathway, and relieve the renal fibrosis by down-regulating the expression of TGF-β1. ConclusionsOLP is composed of three kinds of monosaccharides and →4)-Glcp-(1→ is the main glycosidic linkage in the polysaccharide. OLP could ameliorate CKD in mice by declining the oxidative stress, inflammation, apoptosis and fibrosis in the kidneys. The study provided some evidences for the potential application of OLP in alleviating CKD.

Hyperphosphatemia Contributes to Skeletal Muscle Atrophy in Chronic Kidney Disease

Alterations in mineral metabolism involve changes in serum levels of phosphate as well as its key regulators, fibroblast growth factor 23 (FGF23), vitamin D, parathyroid hormone and klotho. Chronic Kidney Disease (CKD) is a public health epidemic that affects an estimated 37 million Americans, and is associated with elevated serum levels of phosphate (hyperphosphatemia) and FGF23 as well as various pathologies, such vascular calcification, cardiac hypertrophy, and skeletal muscle atrophy. We previously found that elevated FGF23 directly targets cardiac myocytes and contributes to cardiac hypertrophy. Furthermore, elevated phosphate has direct effects on smooth muscle cells and induces vascular calcification. In order to determine whether FGF23 and/or phosphate might also contribute to CKD-associated skeletal muscle atrophy, we tested if skeletal muscle cells can respond to elevations of FGF23 or phosphate. Since the skeletal muscle phenotype in CKD is not well characterized, we analyzed skeletal muscle on a functional, histological, and molecular level in two established mouse models of CKD. We studied the C2C12 skeletal muscle cell line during the differentiation process from myoblasts to myotubes as well as fully differentiated myotubes. Myoblast differentiation was induced with horse serum; cells were co-treated with 25 ng/ml FGF23 or 5 mM phosphate for 5 days, followed by the expression analysis of differentiation markers by qPCR. In a separate study, differentiated C2C12 myotubes were treated with FGF23 or phosphate for 24 hours, followed by the qPCR analysis of atrophy genes (atrogenes), including MT1, Murf1, and Fbox32. Furthermore, we studied mice with global deletion of collagen 4a3 (Col4a3-/-) and wildtype littermates at 10 weeks of age, as well as C57Bl/6 mice receiving an adenine-rich (0.2%) diet or regular chow for 12 weeks. In all mice we studied grip strength, hindlimb circumference by MRI, cross-sectional area of individual muscle fibers that were immuno-labeled with anti-laminin by fluorescence microscopy, and expression levels of atrogenes by qPCR. Phosphate but not FGF23 affected the differentiation process of C2C12 myoblasts and differentiated C2C12 myotubes. Phosphate treatments significantly reduced expression levels of MyoD and MyoG and increased expression of MT1. In both mouse models, grip strength and areas of hindlimb and myotubes were significantly reduced, and expression levels of MT1 and Murf1 were significantly elevated when compared to their controls. FGF23 does not target skeletal muscle cells suggesting that it cannot directly contribute to skeletal muscle atrophy. Elevated phosphate impairs myoblast differentiation and induces atrophy in vitro. We have characterized two CKD mouse models with associated skeletal muscle atrophy, where we will now determine the contribution of hyperphosphatemia to the injury process. Pharmacological approaches targeting phosphate uptake or excretion, or phosphate's direct actions on tissues might alleviate various CKD-associated pathologies.

Tracking Acoustic and Electrophysiological Changes Associated with CKD-induced Cardiac and Valvular Remodeling in a Mouse Model

Objective: Patients with chronic kidney disease (CKD) are at a higher risk of developing heart and valvular diseases than the general population. Non-invasive screening methods are needed to identify cardiovascular abnormalities in this population. In this study, we use a diet-induced CKD mouse to study AV and cardiac remodeling. We hypothesize that structural differences in AV and cardiac remodeling occur in CKD mice, and can be identified through phonocardiogram (PCG) and electrocardiogram (ECG) signals. Methods: Eight-week old C57BL/6J mice were assigned to the following groups: 1) control group, fed a normal chow diet for 12 weeks, and 2) CKD group, fed a chow containing 0.2% adenine, with normal (0.6%) phosphorus for 6 weeks to induce CKD, and 3) CKD+high phosphate (HP) group, fed CKD inducing diet for 6 weeks, and then fed for 6 weeks with a 0.2% adenine/1.8% phosphorus diet to induce cardiovascular calcification. PCG and ECG signals were recorded weekly and echocardiogram parameters were recorded at the experimental end-point. Results: The HP diet induced aortic valve calcification in the CKD+HP group. CKD and CKD+HP group had increased end-diastolic volume, which is indicative of left ventricular hypertrophy. Changes in ECG parameters indicate that CKD groups have delayed cardiac repolarization time, an early ECG marker associated with arrhythmias. PCG signals indicate the presence of a systolic and diastolic murmur in the CKD+HP group, a characteristic of both valve disease and cardiac dysfunction. Conclusions: We demonstrate that the diet-induced CKD mouse model can be used to study valve and cardiac remodeling, and ECG and PCG signals can noninvasively track valve and cardiac changes. Future studies will determine the adequacy of using these signals to predict cardiovascular diseases.

Therapeutic Effect of Endothelin-Converting Enzyme Inhibitor on Chronic Kidney Disease through the Inhibition of Endoplasmic Reticulum Stress and the NLRP3 Inflammasome.

Chronic inflammation and oxidative stress significantly contribute to the development and progression of chronic kidney disease (CKD). The NOD-like receptor family pyrin containing domain-3 (NLRP3) inflammasome plays a key role in the inflammatory response. The renal endothelin (ET) system is activated in all cases of CKD. Furthermore, ET-1 promotes renal cellular injury, inflammation, fibrosis and proteinuria. Endothelin-converting enzymes (ECEs) facilitate the final processing step of ET synthesis. However, the roles of ECEs in CKD are not clear. In this study, we investigated the effects of ETs and ECEs on kidney cells. We found that ET-1 and ET-2 expression was significantly upregulated in the renal tissues of CKD patients. ET-1 and ET-2 showed no cytotoxicity on human kidney tubular epithelial cells. However, ET-1 and ET-2 caused endoplasmic reticulum (ER) stress and NLRP3 inflammasome activation in tubular epithelial cells. The ECE inhibitor phosphoramidon induced autophagy. Furthermore, phosphoramidon inhibited ER stress and the NLRP3 inflammasome in tubular epithelial cells. In an adenine diet-induced CKD mouse model, phosphoramidon attenuated the progression of CKD by regulating autophagy, the NLRP3 inflammasome and ER stress. In summary, these findings showed a new strategy to delay CKD progression by inhibiting ECEs through autophagy activation and restraining ER stress and the NLRP3 inflammasome.

The Non-coding MicroRNA-223 is a Promising Biomarker of Chronic Kidney Disease

Renal diseases are consecutive to a deregulation of gene expression regulated by non-coding RNAs. These non-coding RNAs were discovered at the turn of the 21st century when it was established that post-transcriptional regulation was performed through small non-coding RNAs, known as microRNAs (miRNAs). Up to 3,000 miRNAs are expressed by human cells. They are small, single-stranded nucleic acids, which trigger translational repression of mRNA by base-pairing with the 3′ untranslated region of their mRNA targets. In addition to miRNA regulation, it was also demonstrated that 60,000 long non-coding RNAs are expressed in the human cell and that they are able to regulate gene expression at all levels. The roles of these various RNA families are just beginning to be understood in the field of nephrology. In the past decade, the authors and various others have published that several miRNAs are deregulated during the onset of chronic kidney disease (CKD) and are associated with cardiovascular damage. This review focuses on miRNA-223 (miR-223) as its expression is increased in vivo in the large vessels of a mouse model of CKD, whereas it is diminished in the serum of both mice and human patients with CKD. In patients, miR-223 expression was correlated with all-cause mortality, as well as cardiovascular and renal events. Molecular clues were given by a multi-omics approach, indicating that miR-223 modulates gene regulation at all levels including mRNA expression, protein amounts, and metabolic molecule accumulation. miR-223 is thus a potential target to prevent or treat complications of CKD pathogenesis.

Metformin Attenuates Renal Fibrosis in a Mouse Model of Adenine-Induced Renal Injury Through Inhibiting TGF-β1 Signaling Pathways.

It is well-known that all progressive chronic kidney disease (CKD) is pathologically characterized by tubulointerstitial fibrosis process. Multiple studies have shown the critical role of inflammation and fibrosis in the development of CKD. Hence strategies that target inflammatory and fibrotic signaling pathways may provide promising opportunities to protect against renal fibrosis. Metformin has been used as the first-line glucose-lowering agent to treat patients with type 2 diabetes mellitus (T2DM) for over 50 years. Accumulating evidence suggests the potential for additional therapeutic applications of metformin, including mitigation of renal fibrosis. In this study, the anti-fibrotic effects of metformin independent of its glucose-lowering mechanism were examined in an adenine -induced mouse model of CKD. Expressions of inflammatory markers MCP-1, F4/80 and ICAM, fibrotic markers type IV collagen and fibronectin, and the cytokine TGF-β1 were increased in adenine-induced CKD when compared to control groups and significantly attenuated by metformin treatment. Moreover, treatment with metformin inhibited the phosphorylation of Smad3, ERK1/2, and P38 and was associated with activation of the AMP-activated protein kinase (AMPK) in the kidneys of adenine-treated mice. These results indicate that metformin attenuates adenine-induced renal fibrosis through inhibition of TGF-β1 signaling pathways and activation of AMPK, independent of its glucose-lowering action.

Nicotinamide Attenuates the Progression of Renal Failure in a Mouse Model of Adenine-Induced Chronic Kidney Disease.

Nicotinamide adenine dinucleotide (NAD+) supplies energy for deoxidation and anti-inflammatory reactions fostering the production of adenosine triphosphate (ATP). The kidney is an essential regulator of body fluids through the excretion of numerous metabolites. Chronic kidney disease (CKD) leads to the accumulation of uremic toxins, which induces chronic inflammation. In this study, the role of NAD+ in kidney disease was investigated through the supplementation of nicotinamide (Nam), a precursor of NAD+, to an adenine-induced CKD mouse model. Nam supplementation reduced kidney inflammation and fibrosis and, therefore, prevented the progression of kidney disease. Notably, Nam supplementation also attenuated the accumulation of glycolysis and Krebs cycle metabolites that occurs in renal failure. These effects were due to increased NAD+ supply, which accelerated NAD+-consuming metabolic pathways. Our study suggests that Nam administration may be a novel therapeutic approach for CKD prevention.

Exosomes isolated from melatonin-stimulated mesenchymal stem cells improve kidney function by regulating inflammation and fibrosis in a chronic kidney disease mouse model

Chronic kidney disease (CKD) is defined as structural and functional abnormalities of the kidney due to inflammation and fibrosis. We investigated the therapeutic effects of exosomes secreted by melatonin-stimulated mesenchymal stem cells (Exocue) on the functional recovery of the kidney in a CKD mouse model. Exocue upregulated gene expression of micro RNAs (miRNAs) associated with anti-inflammatory and anti-fibrotic effects. Exocue-treated groups exhibited low tumor necrosis factor-α and transforming growth factor-β levels in serum and fibrosis inhibition in kidney tissues mediated through regulation of cell apoptosis and proliferation of fibrosis-related cells. Exocue treatment decreased the gene expression of CKD progression-related miRNAs. Moreover, the CKD severity was alleviated in the Exocue group via upregulation of aquaporin 2 and 5 levels and reduction of blood urea nitrogen and creatinine, resulting in functional recovery of the kidney. In conclusion, Exocue could be a novel therapeutic agent for treating CKD by regulating inflammation and fibrosis.

Glycolysis and Lactate Dehydrogenase A in Iron-Mediated Suppression of Osteoblast Function

Background/Objective: 
 An estimated 37 million Americans have Chronic Kidney Disease (CKD), a condition in characterized by gradual decline in kidney function1. Patients with CKD are often afflicted with skeletal fractures, increasing morbidity and mortality. CKD has also shown a strong correlation with iron-deficiency anemia. The underlying mechanisms of how iron-deficiency anemia of CKD affects bone loss are not well understood. Based on RNA-sequencing results, we hypothesize that lactate dehydrogenase A (LDHA) may play a role in iron-deficiency mediated suppression of osteoblast differentiation and function. 
 
 Methods: 
 Mouse Progenitor Cells (MPC2) were incubated in osteogenic media along with deferoxamine (DFO) to induce differentiation in chronic iron deficiency; samples were collected after 7 and 14 days. Quantitative real-time PCR and western blot were used to validate LDHA mRNA and protein levels in DFO treated MPCs versus control cells. RNA levels of osteoblast genes and LDHA were also assessed in a pre-clinical mouse model of CKD. 
 
 Results: 
 In vitro, MPCs cultured in DFO media showed a significant increase of LDHA mRNA at 7 days (p=0.015) and returned to near control levels by day 14. Western blots showed a slight increase of total LDHA protein in DFO treated MPCs at 7 days and a large increase of protein at the 14-day mark (p=0.051). In vivo, CKD bone marrow showed a reduction in osteoblast gene expression (osteocalcin and type 1 collagen; p<0.05). LDHA mRNA expression was increased in CKD mice bone marrow when compared to wild-type mice (p=0.051), suggesting an inverse relationship. 
 
 Conclusion and Potential Impact: 
 Inappropriate activation of glycolysis and LDHA appears to play a role in iron-deficiency mediated suppression of osteoblast function in relation to CKD, both in vitro and in vivo. Further exploration of this relationship could be critical to the development of improved treatment options to maintain bone homeostasis during CKD.

The HIF-PHI BAY 85-3934 (Molidustat) Improves Anemia and Is Associated With Reduced Levels of Circulating FGF23 in a CKD Mouse Model.

Fibroblast growth factor-23 (FGF23) is a critical factor in chronic kidney disease (CKD), with elevated levels causing alterations in mineral metabolism and increased odds for mortality. Patients with CKD develop anemia as the kidneys progressively lose the ability to produce erythropoietin (EPO). Anemia is a potent driver of FGF23 secretion; therefore, a hypoxia-inducible factor prolyl hydroxylase inhibitor (HIF-PHI) currently in clinical trials to elevate endogenous EPO to resolve anemia was tested for effects on iron utilization and FGF23-related parameters in a CKD mouse model. Mice were fed either a casein control diet or an adenine-containing diet to induce CKD. The CKD mice had markedly elevated iFGF23 and blood urea nitrogen (BUN), hyperphosphatemia, and anemia. Cohorts of mice were then treated with a patient-equivalent dose of BAY 85-3934 (BAY; Molidustat), which elevated EPO and completely resolved aberrant complete blood counts (CBCs) in the CKD mice. iFGF23 was elevated in vehicle-treated CKD mice (120-fold), whereas circulating iFGF23 was significantly attenuated (>60%) in the BAY-treated CKD mice. The BAY-treated mice with CKD also had reduced BUN, but there was no effect on renal vitamin D metabolic enzyme expression. Consistent with increased EPO, bone marrow Erfe, Transferrin receptor (Tfrc), and EpoR mRNAs were increased in BAY-treated CKD mice, and in vitro hypoxic marrow cultures increased FGF23 with direct EPO treatment. Liver Bmp-6 and hepcidin expression were downregulated in all BAY-treated groups. Femur trabecular parameters and cortical porosity were not worsened with BAY administration. In vitro, differentiated osteocyte-like cells exposed to an iron chelator to simulate iron depletion/hypoxia increased FGF23; repletion with holo-transferrin completely suppressed FGF23 and normalized Tfrc1. Collectively, these results support that resolving anemia using a HIF-PHI during CKD was associated with lower BUN and reduced FGF23, potentially through direct restoration of iron utilization, thus providing modifiable outcomes beyond improving anemia for this patient population. © 2021 American Society for Bone and Mineral Research (ASBMR).