Methylation in pericytes after acute injury promotes chronic kidney disease

Adenine-induced animal model of chronic kidney disease: current applications and future perspectives

Chronic kidney disease (CKD) with high morbidity and mortality all over the world is characterized by decreased kidney function, a condition which can result from numerous risk factors, including diabetes, hypertension and obesity. Despite significant advances in our understanding of the pathogenesis of CKD, there are still no treatments that can effectively combat CKD, which underscores the urgent need for further study into the pathological mechanisms underlying this condition. In this regard, animal models of CKD are indispensable. This article reviews a widely used animal model of CKD, which is induced by adenine. While a physiologic dose of adenine is beneficial in terms of biological activity, a high dose of adenine is known to induce renal disease in the organism. Following a brief description of the procedure for disease induction by adenine, major mechanisms of adenine-induced CKD are then reviewed, including inflammation, oxidative stress, programmed cell death, metabolic disorders, and fibrillation. Finally, the application and future perspective of this adenine-induced CKD model as a platform for testing the efficacy of a variety of therapeutic approaches is also discussed. Given the simplicity and reproducibility of this animal model, it remains a valuable tool for studying the pathological mechanisms of CKD and identifying therapeutic targets to fight CKD.

Crosstalk among proximal tubular cells, macrophages, and fibroblasts in acute kidney injury: single-cell profiling from the perspective of ferroptosis

The link between ferroptosis, a form of cell death mediated by iron and acute kidney injury (AKI) is recently gaining widespread attention. However, the mechanism of the crosstalk between cells in the pathogenesis and progression of acute kidney injury remains unexplored. In our research, we performed a non-negative matrix decomposition (NMF) algorithm on acute kidney injury single-cell RNA sequencing data based specifically focusing in ferroptosis-associated genes. Through a combination with pseudo-time analysis, cell-cell interaction analysis and SCENIC analysis, we discovered that proximal tubular cells, macrophages, and fibroblasts all showed associations with ferroptosis in different pathways and at various time. This involvement influenced cellular functions, enhancing cellular communication and activating multiple transcription factors. In addition, analyzing bulk expression profiles and marker genes of newly defined ferroptosis subtypes of cells, we have identified crucial cell subtypes, including Egr1 + PTC-C1, Jun + PTC-C3, Cxcl2 + Mac-C1 and Egr1 + Fib-C1. All these subtypes which were found in AKI mice kidneys and played significantly distinct roles from those of normal mice. Moreover, we verified the differential expression of Egr1, Jun, and Cxcl2 in the IRI mouse model and acute kidney injury human samples. Finally, our research presented a novel analysis of the crosstalk of proximal tubular cells, macrophages and fibroblasts in acute kidney injury targeting ferroptosis, therefore, contributing to better understanding the acute kidney injury pathogenesis, self-repairment and acute kidney injury-chronic kidney disease (AKI-CKD) progression.

DNA methylation in peripheral blood is associated with renal aging and renal function decline: a national community study

BACKGROUND

Older patients are at risk for acute kidney injury and chronic kidney disease. Age-related increases in DNA methylation at CpG islands have been linked to aging-related diseases like cancer and cardiovascular disease, but the exact causal relationship between methylation in renal aging and other kidney diseases remains unclear. This study aimed to elucidate the methylation status of peripheral blood mononuclear cells (PBMCs) in the Asian population. Using human whole blood DNA methylation analysis from the Taiwan Biobank, we included participants with both whole blood genome-wide methylation data and follow-up data on serum creatinine. We investigated hyper- and hypomethylated genes in comparison of participants with higher and lower estimated glomerular filtration (eGFR) decline rate in overall cohort as well as in comparison of old and young participants in subgroup of participants with higher eGFR decline rate. Common genes and signaling pathways in both comparative analyses were identified.

RESULTS

Among 1587 participants in the analysis, 187 participants had higher eGFR decline rate. According to the comparison of methylation in participants with different eGFR declines and at different ages, respectively, we identified common hypermethylated genes, including DNMT3A and GGACT, as well as hypomethylated genes such as ARL6IP5, CYB5D1, BCL6, RPRD2, ZNF451, and MIAT in both participants with higher eGFR decline and those of older age. We observed associations between the methylation status of signaling pathways and aging as well as renal function decline. These pathways notably included autophagy, p38 mitogen-activated protein kinases, and sirtuins, which were associated with autophagy process and cytokine production.

CONCLUSIONS

Through methylation analysis of PBMCs, we identified genes and signaling pathways which could play crucial roles in the interplay of renal aging and renal function decline. These findings contribute to the development of novel biomarkers for identifying at-risk groups and even for therapeutic agent discovery.

Fibroblast expression of transmembrane protein smoothened governs microenvironment characteristics after acute kidney injury

The smoothened (Smo) receptor facilitates hedgehog signaling between kidney fibroblasts and tubules during acute kidney injury (AKI). Tubule-derived hedgehog is protective in AKI, but the role of fibroblast-selective Smo is unclear. Here, we report that Smo-specific ablation in fibroblasts reduced tubular cell apoptosis and inflammation, enhanced perivascular mesenchymal cell activities, and preserved kidney function after AKI. Global proteomics of these kidneys identified extracellular matrix proteins, and nidogen-1 glycoprotein in particular, as key response markers to AKI. Intriguingly, Smo was bound to nidogen-1 in cells, suggesting that loss of Smo could affect nidogen-1 accessibility. Phosphoproteomics revealed that the 'AKI protector' Wnt signaling pathway was activated in these kidneys. Mechanistically, nidogen-1 interacted with integrin β1 to induce Wnt in tubules to mitigate AKI. Altogether, our results support that fibroblast-selective Smo dictates AKI fate through cell-matrix interactions, including nidogen-1, and offers a robust resource and path to further dissect AKI pathogenesis.

TNIK depletion induces inflammation and apoptosis in injured renal proximal tubule epithelial cells

In the aftermath of acute kidney injury (AKI), surviving proximal tubule epithelia repopulate injured tubules to promote repair. However, a portion of cells fail to repair [termed failed-repair proximal tubule cells (FR-PTCs)] and exert ongoing proinflammatory and profibrotic effects. To better understand the molecular drivers of the FR-PTC state, we reanalyzed a mouse ischemia-reperfusion injury single-nucleus RNA-sequencing (snRNA-seq) atlas to identify Traf2 and Nck interacting kinase (Tnik) to be exclusively expressed in FR-PTCs but not in healthy or acutely injured proximal tubules after AKI (2 and 6 wk) in mice. We confirmed expression of Tnik protein in injured mouse and human tissues by immunofluorescence. Then, to determine the functional role of Tnik in FR-PTCs, we depleted TNIK with siRNA in two human renal proximal tubule epithelial cell lines (primary and immortalized hRPTECs) and analyzed each by bulk RNA-sequencing. Pathway analysis revealed significant upregulation of inflammatory signaling pathways, whereas pathways associated with differentiated proximal tubules such as organic acid transport were significantly downregulated. TNIK gene knockdown drove reduced cell viability and increased apoptosis, including differentially expressed poly(ADP-ribose) polymerase (PARP) family members, cleaved PARP-1 fragments, and increased annexin V binding to phosphatidylserine. Together, these results indicate that Tnik upregulation in FR-PTCs acts in a compensatory fashion to suppress inflammation and promote proximal tubule epithelial cell survival after injury. Modulating TNIK activity may represent a prorepair therapeutic strategy after AKI.NEW & NOTEWORTHY The molecular drivers of successful and failed repair in the proximal tubule after acute kidney injury (AKI) are incompletely understood. We identified Traf2 and Nck interacting kinase (Tnik) to be exclusively expressed in failed-repair proximal tubule cells after AKI. We tested the effect of siTNIK depletion in two proximal tubule cell lines followed by bulk RNA-sequencing analysis. Our results indicate that TNIK acts to suppress inflammatory signaling and apoptosis in injured renal proximal tubule epithelial cells to promote cell survival.

Hypoxic Inducible Factor Stabilization in Pericytes beyond Erythropoietin Production: The Good and the Bad

The paracrine signaling pathways for the crosstalk between pericytes and endothelial cells are essential for the coordination of cell responses to challenges such as hypoxia in both healthy individuals and pathological conditions. Ischemia-reperfusion injury (IRI), one of the causes of cellular dysfunction and death, is associated with increased expression of genes involved in cellular adaptation to a hypoxic environment. Hypoxic inducible factors (HIFs) have a central role in the response to processes initiated by IRI not only linked to erythropoietin production but also because of their participation in inflammation, angiogenesis, metabolic adaptation, and fibrosis. While pericytes have an essential physiological function in erythropoietin production, a lesser-known role of HIF stabilization during IRI is that pericytes' HIF expression could influence vascular remodeling, cell loss and organ fibrosis. Better knowledge of mechanisms that control functions and consequences of HIF stabilization in pericytes beyond erythropoietin production is advisable for the development of therapeutic strategies to influence disease progression and improve treatments. Thus, in this review, we discuss the dual roles-for good or bad-of HIF stabilization during IRI, focusing on pericytes, and consequences in particular for the kidneys.

Nucleic acid and protein methylation modification in renal diseases

Although great efforts have been made to elucidate the pathological mechanisms of renal diseases and potential prevention and treatment targets that would allow us to retard kidney disease progression, we still lack specific and effective management methods. Epigenetic mechanisms are able to alter gene expression without requiring DNA mutations. Accumulating evidence suggests the critical roles of epigenetic events and processes in a variety of renal diseases, involving functionally relevant alterations in DNA methylation, histone methylation, RNA methylation, and expression of various non-coding RNAs. In this review, we highlight recent advances in the impact of methylation events (especially RNA m6A methylation, DNA methylation, and histone methylation) on renal disease progression, and their impact on treatments of renal diseases. We believe that a better understanding of methylation modification changes in kidneys may contribute to the development of novel strategies for the prevention and management of renal diseases.

Update of pericytes function and their roles in kidney diseases

Studies have highlighted the significant involvement of kidney pericytes in renal fibrosis. Kidney pericytes, classified as interstitial mesenchymal cells, are extensively branched, collagen-producing cells that closely interact with endothelial cells. This article aims to provide an overview of the recent advancements in understanding the physiological functions of pericytes and their roles in kidney diseases. In a healthy kidney, pericytes have essential physiological function in angiogenesis, erythropoietin (EPO) production, and the regulation of renal blood flow. Nevertheless, pericyte-myofibroblast transition has been identified as the primary cause of disease progression in acute kidney injury (AKI)-to-chronic kidney disease (CKD) continuum. Our recent research has demonstrated that hypoxia-inducible factor-2α (HIF-2α) regulates erythropoietin production in pericytes. However, this production is repressed by EPO gene hypermethylation and HIF-2α downregulation which were induced by transforming growth factor-β1-activated DNA methyltransferase and activin receptor-like kinase-5 signaling pathway during renal fibrosis, respectively. Additionally, AKI induces epigenetic modifications in pericytes, rendering them more prone to extracellular matrix production, cell migration and proliferation, thereby contributing to subsequent capillary rarefaction and renal fibrosis. Further investigation into the specific functions and roles of different subpopulations of pericytes may contribute for the development of targeted therapies aimed at attenuating kidney disease and mitigating their adverse effects.

Integrin β8 prevents pericyte-myofibroblast transition and renal fibrosis through inhibiting the TGF-β1/TGFBR1/Smad3 pathway in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the leading causes to develop end-stage kidney disease worldwide. Pericytes are implicated in the development of tissue fibrosis. However, the underlying mechanisms of pericytes in DKD remain largely unknown. We isolated and cultured primary pericytes and rat mesangial cells (HBZY-1). Western blot and qRT-PCR analysis were used to explore the role and regulatory mechanism of Integrin β8/transforming growth factor beta 1 (TGF-β1) pathway. We also constructed pericyte-specific Integrin β8 knock-in mice as the research objects to determine the role of Integrin β8 in vivo. We discovered that reduced Integrin β8 expression was closely associated with pericyte transition in DKD. Overexpressed Integrin β8 in pericytes dramatically suppressed TGF-β1/TGF beta receptor 1 (TGFBR1)/Smad3 signaling pathway and protected glomerular endothelial cells (GECs) in vitro. In vivo, pericyte-specific Integrin β8 knock-in ameliorated pericyte transition, endothelium injury and renal fibrosis in STZ-induced diabetic mice. Mechanistically, Murine double minute 2 (MDM2) was found to increase the degradation of Integrin β8 and caused TGF-β1 release and activation. Knockdown MDM2 could partly reverse the decline of Integrin β8 and suppress pericytes transition. In conclusion, the present findings suggested that upregulated MDM2 expression contributes to the degradation of Integrin β8 and activation of TGF-β1/TGFBR1/Smad3 signaling pathway, which ultimately leads to pericyte transition during DKD progression. These results indicate MDM2/Integrin β8 might be considered as therapeutic targets for DKD.

Role of epigenetically regulated inflammation in renal diseases

In recent decades, renal disease research has witnessed remarkable advances. Experimental evidence in this field has highlighted the role of inflammation in kidney disease. Epigenetic dynamics and immunometabolic reprogramming underlie the alterations in cellular responses to intrinsic and extrinsic stimuli; these factors determine cell identity and cell fate decisions and represent current research hotspots. This review focuses on recent findings and emerging concepts in epigenetics and inflammatory regulation and their effect on renal diseases. This review aims to summarize the role and mechanisms of different epigenetic modifications in renal inflammation and injury and provide new avenues for future research on inflammation-related renal disease and drug development.

Pyruvate kinase M2 regulates kidney fibrosis through pericyte glycolysis during the progression from acute kidney injury to chronic kidney disease

We aimed to investigate the role of renal pericyte pyruvate kinase M2 (PKM2) in the progression of acute kidney injury (AKI) to chronic kidney disease (CKD). The role of PKM2 in renal pericyte-myofibroblast transdifferentiation was investigated in an AKI-CKD mouse model. Platelet growth factor receptor beta (PDGFRβ)-iCreERT2; tdTomato mice were used for renal pericyte tracing. Western blotting and immunofluorescence staining were used to examine protein expression. An 5-ethynyl-2'-deoxyuridine assay was used to measure renal pericyte proliferation. A scratch cell migration assay was used to analyse cell migration. Seahorse experiments were used to examine glycolytic rates. Enzyme-linked immunoassay was used to measure pyruvate kinase enzymatic activity and lactate concentrations. The PKM2 nuclear translocation inhibitors Shikonin and TEPP-46 were used to alter pericyte transdifferentiation. In AKI-CKD, renal pericytes proliferated and transdifferentiated into myofibroblasts and PKM2 is highly expressed in renal pericytes. Shikonin and TEPP-46 inhibited pericyte proliferation, migration, and pericyte-myofibroblast transdifferentiation by reducing nuclear PKM2 entry. In the nucleus, PKM2 promoted downstream lactate dehydrogenase A (LDHA) and glucose transporter 1 (GLUT1) transcription, which are critical for glycolysis. Therefore, PKM2 regulates pericyte glycolytic and lactate production, which regulates renal pericyte-myofibroblast transdifferentiation. PKM2-regulated renal pericyte-myofibroblast transdifferentiation by regulating downstream LDHA and GLUT1 transcription and lactate production. Reducing nuclear PKM2 import can reduce renal pericytes-myofibroblasts transdifferentiation, providing new ideas for AKI-CKD treatment.

Epigenetic reprogramming driving successful and failed repair in acute kidney injury

Acute kidney injury (AKI) causes epithelial damage followed by subsequent repair. While successful repair restores kidney function, this process is often incomplete and can lead to chronic kidney disease (CKD) in a process called failed repair. To better understand the epigenetic reprogramming driving this AKI-to-CKD transition we generated a single nucleus multiomic atlas for the full mouse AKI time course, consisting of ~280,000 single nucleus transcriptomes and epigenomes. We reveal cell-specific dynamic alterations in gene regulatory landscapes reflecting especially activation of proinflammatory pathways. We further generated single nucleus multiomic data from four human AKI samples including validation by genome-wide identification of NF-kB binding sites. A regularized regression analysis identifies key regulators involved in both successful and failed repair cell fate, identifying the transcription factor CREB5 as a regulator of both successful and failed tubular repair that also drives proximal tubule cell proliferation after injury. Our interspecies multiomic approach provides a foundation to comprehensively understand cell states in AKI.

Pericytes in the disease spotlight

Pericytes are known as the mural cells in small-caliber vessels that interact closely with the endothelium. Pericytes play a key role in vasculature formation and homeostasis, and when dysfunctional contribute to vasculature-related diseases such as diabetic retinopathy and neurodegenerative conditions. In addition, significant extravascular roles of pathological pericytes are being discovered with relevant implications for cancer and fibrosis. Pericyte research is challenged by the lack of consistent molecular markers and clear discrimination criteria versus other (mural) cells. However, advances in single-cell approaches are uncovering and clarifying mural cell identities, biological functions, and ontogeny across organs. We discuss the latest developments in pericyte pathobiology to inform future research directions and potential outcomes.

Acute kidney disease: an overview of the epidemiology, pathophysiology, and management

Acute kidney injury (AKI) increases the risk of chronic kidney disease (CKD), and AKI and CKD are seen as interconnected syndromes. Acute kidney disease (AKD) is defined as subacute damage and/or loss of kidney function occurring 7 to 90 days after AKI, during which period key interventions may be initiated to hinder the development of CKD. While AKD is usually under-recognized, it is associated with high morbidity and mortality globally. This review article aims to summarize the current knowledge concerning the epidemiology, pathophysiology, and management of AKD with the aim to develop monitoring strategies and therapeutic agents of AKD. Generally, AKD tends to occur more frequently in the elderly and those with chronic diseases, such as hypertension, diabetes mellitus, and metabolic syndrome. In addition, the severity, duration, and frequency of AKI are independent risk factors for AKD. Investigations of several mechanisms of AKD, such as renal tubular epithelium cell-cycle arrest, epigenetic change, chronic inflammation, mitochondria dysfunction, failed regeneration of tubular cells, metabolic reprogramming, and renin-angiotensin system (RAS) activation, have identified additional potential pharmacotherapy targets. Management of AKD includes prevention of repeated AKI, early and regular follow-up by a nephrologist, resumption and adjustment of essential medication, optimization of blood pressure control and nutrition management, and development of new pharmaceutical agents including RAS inhibitors. Finally, we outline a care bundle for AKD patients based on important lessons learned from studies and registries and identify the need for clinical trials of RAS inhibitors or other novel agents to impede ensuing CKD development.

Role of perivascular cells in kidney homeostasis, inflammation, repair and fibrosis

Perivascular niches in the kidney comprise heterogeneous cell populations, including pericytes and fibroblasts, with distinct functions. These perivascular cells have crucial roles in preserving kidney homeostasis as they maintain microvascular networks by stabilizing the vasculature and regulating capillary constriction. A subset of kidney perivascular cells can also produce and secrete erythropoietin; this ability can be enhanced with hypoxia-inducible factor-prolyl hydroxylase inhibitors, which are used to treat anaemia in chronic kidney disease. In the pathophysiological state, kidney perivascular cells contribute to the progression of kidney fibrosis, partly via transdifferentiation into myofibroblasts. Moreover, perivascular cells are now recognized as major innate immune sentinels in the kidney that produce pro-inflammatory cytokines and chemokines following injury. These mediators promote immune cell infiltration, leading to persistent inflammation and progression of kidney fibrosis. The crosstalk between perivascular cells and tubular epithelial, immune and endothelial cells is therefore a key process in physiological and pathophysiological states. Here, we examine the multiple roles of kidney perivascular cells in health and disease, focusing on the latest advances in this field of research.

Novel Approaches in Chronic Renal Failure without Renal Replacement Therapy: A Review

Chronic kidney disease (CKD) is characterized by renal parenchymal damage leading to a reduction in the glomerular filtration rate. The inflammatory response plays a pivotal role in the tissue damage contributing to renal failure. Current therapeutic options encompass dietary control, mineral salt regulation, and management of blood pressure, blood glucose, and fatty acid levels. However, they do not effectively halt the progression of renal damage. This review critically examines novel therapeutic avenues aimed at ameliorating inflammation, mitigating extracellular matrix accumulation, and fostering renal tissue regeneration in the context of CKD. Understanding the mechanisms sustaining a proinflammatory and profibrotic state may offer the potential for targeted pharmacological interventions. This, in turn, could pave the way for combination therapies capable of reversing renal damage in CKD. The non-replacement phase of CKD currently faces a dearth of efficacious therapeutic options. Future directions encompass exploring vaptans as diuretics to inhibit water absorption, investigating antifibrotic agents, antioxidants, and exploring regenerative treatment modalities, such as stem cell therapy and novel probiotics. Moreover, this review identifies pharmaceutical agents capable of mitigating renal parenchymal damage attributed to CKD, targeting molecular-level signaling pathways (TGF-β, Smad, and Nrf2) that predominate in the inflammatory processes of renal fibrogenic cells.

Biomarkers of the End-Stage Renal Disease Progression: Beyond the GFR

Chronic kidney disease can progress to the end-stage renal disease (ESRD) characterized by a high risk of morbidity and mortality. ESRD requires immediate therapy or even dialysis or kidney transplantation, therefore, its timely diagnostics is critical for many patients. ESRD is associated with pathological changes, such as inflammation, fibrosis, endocrine disorders, and epigenetic changes in various cells, which could serve as ESRD markers. The review summarizes information on conventional and new ESRD biomarkers that can be assessed in kidney tissue, blood, and urine. Some biomarkers are specific to a particular pathology, while others are more universal. Here, we suggest several universal inflammatory, fibrotic, hormonal, and epigenetic markers indicative of severe deterioration of renal function and ESRD progression for improvement of ESRD diagnostics.

Nestin and Notch3 collaboratively regulate angiogenesis, collagen production, and endothelial-mesenchymal transition in lung endothelial cells

BACKGROUND

Nestin, an intermediate filament protein, participates in various pathophysiological processes, including wound healing, angiogenesis, endothelial-mesenchymal transition (EndoMT), and fibrosis. However, the pathophysiological roles of lung nestin-expressing cells remain unclear due to conflicting reports. The objective of this study is to elucidate the characteristics and functions of lung nestin-expressing cells.

METHODS

We conducted a series of in vitro and in vivo experiments using endothelial cell line MS1 and nestin-GFP mice. This animal model allows for nestin-expressing cell detection without the use of anti-nestin antibodies.

RESULTS

Lung nestin-expressing cells occurred in approximately 0.2% of CD45- cells and was co-expressed with epithelial, endothelial, and mesenchymal cell-surface markers. Importantly, virtually all nestin-expressing cells co-expressed CD31. When compared to lung nestin-nonexpressing endothelial cells, nestin-expressing endothelial cells showed robust angiogenesis with frequent co-expression of PDGFRβ and VEGFR2. During TGFβ-mediated EndoMT, the elevation of Nes mRNA expression preceded that of Col1a1 mRNA, and nestin gene silencing using nestin siRNA resulted in further upregulation of Col1a1 mRNA expression. Furthermore, Notch3 expression was regulated by nestin in vitro and in vivo; nestin siRNA resulted in reduced Notch3 expression accompanied with enhanced EndoMT. Contrary to previous reports, neither Nes mRNA expression nor nestin-expressing cells were increased during pulmonary fibrosis.

CONCLUSIONS

Our study showed that (1) lung nestin-expressing cells are an endothelial lineage but are distinct from nestin-nonexpressing endothelial cells; (2) nestin regulates Notch3 and they act collaboratively to regulate angiogenesis, collagen production, and EndoMT; and (3) nestin plays novel roles in lung angiogenesis and fibrosis. Video Abstract.

Mitapivat, a pyruvate kinase activator, improves transfusion burden and reduces iron overload in β-thalassemic mice

Not available.

Hypermethylation suppresses microRNA-219a-2 to activate the ALDH1L2/GSH/PAI-1 pathway for fibronectin degradation in renal fibrosis

Epigenetic regulations, such as DNA methylation and microRNAs, play an important role in renal fibrosis. Here, we report the regulation of microRNA-219a-2 (mir-219a-2) by DNA methylation in fibrotic kidneys, unveiling the crosstalk between these epigenetic mechanisms. Through genome-wide DNA methylation analysis and pyro-sequencing, we detected the hypermethylation of mir-219a-2 in renal fibrosis induced by unilateral ureter obstruction (UUO) or renal ischemia/reperfusion, which was accompanied by a significant decrease in mir-219a-5p expression. Functionally, overexpression of mir-219a-2 enhanced fibronectin induction during hypoxia or TGF-β1 treatment of cultured renal cells. In mice, inhibition of mir-219a-5p suppressed fibronectin accumulation in UUO kidneys. ALDH1L2 was identified to be the direct target gene of mir-219a-5p in renal fibrosis. Mir-219a-5p suppressed ALDH1L2 expression in cultured renal cells, while inhibition of mir-219a-5p prevented the decrease of ALDH1L2 in UUO kidneys. Knockdown of ALDH1L2 enhanced PAI-1 induction during TGF-β1 treatment of renal cells, which was associated with fibronectin expression. In conclusion, the hypermethylation of mir-219a-2 in response to fibrotic stress attenuates mir-219a-5p expression and induces the up-regulation of its target gene ALDH1L2, which may reduce fibronectin deposition by suppressing PAI-1.

Regulation of pericyte metabolic reprogramming restricts the AKI to CKD transition

BACKGROUND AND AIMS

Acute kidney injury (AKI) is associated with high morbidity and mortality and is recognized as a long-term risk factor for progression to chronic kidney disease (CKD). The AKI to CKD transition is characterized by interstitial fibrosis and the proliferation of collagen-secreting myofibroblasts. Pericytes are the major source of myofibroblasts in kidney fibrosis. However, the underlying mechanism of pericyte-myofibroblast transition (PMT) is still unclear. Here we investigated the role of metabolic reprogramming in PMT.

METHODS

Unilateral ischemia/reperfusion-induced AKI to CKD mouse model and TGF-β-treated pericyte-like cells were used to detect the levels of fatty acid oxidation (FAO) and glycolysis, and the critical signaling pathways during PMT under the treatment of drugs regulating metabolic reprogramming.

RESULTS

PMT is characterized by a decrease in FAO and an increase in glycolysis. Enhancement of FAO by the peroxisome proliferator-activated receptor gamma coactivator-1α (PGC1α) activator ZLN-005 or suppression of glycolysis by the hexokinase 2 (HK2) inhibitor 2-DG can inhibit PMT, preventing the transition of AKI to CKD. Mechanistically, AMPK modulates various pathways involved in the metabolic switch from glycolysis to FAO. Specifically, the PGC1α-CPT1A pathway activates FAO, while inhibition of the HIF1α-HK2 pathway drives glycolysis inhibition. The modulations of these pathways by AMPK contribute to inhibiting PMT.

CONCLUSIONS

Metabolic reprogramming controls the fate of pericyte transdifferentiation and targets the abnormal metabolism of pericytes can effectively prevent AKI to CKD transition.

Prevascularization techniques for dental pulp regeneration: potential cell sources, intercellular communication and construction strategies

One of the difficulties of pulp regeneration is the rapid vascularization of transplanted engineered tissue, which is crucial for the initial survival of the graft and subsequent pulp regeneration. At present, prevascularization techniques, as emerging techniques in the field of pulp regeneration, has been proposed to solve this challenge and have broad application prospects. In these techniques, endothelial cells and pericytes are cocultured to induce intercellular communication, and the cell coculture is then introduced into the customized artificial vascular bed or induced to self-assembly to simulate the interaction between cells and extracellular matrix, which would result in construction of a prevascularization system, preformation of a functional capillary network, and rapid reconstruction of a sufficient blood supply in engineered tissue after transplantation. However, prevascularization techniques for pulp regeneration remain in their infancy, and there remain unresolved problems regarding cell sources, intercellular communication and the construction of prevascularization systems. This review focuses on the recent advances in the application of prevascularization techniques for pulp regeneration, considers dental stem cells as a potential cell source of endothelial cells and pericytes, discusses strategies for their directional differentiation, sketches the mechanism of intercellular communication and the potential application of communication mediators, and summarizes construction strategies for prevascularized systems. We also provide novel ideas for the extensive application and follow-up development of prevascularization techniques for dental pulp regeneration.

Key circRNAs, lncRNAs, and mRNAs of ShenQi Compound in Protecting Vascular Endothelial Cells From High Glucose Identified by Whole Transcriptome Sequencing

ABSTRACT

Vascular endothelial cells, which make up the inner wall of blood arteries, are susceptible to damage from oxidative stress and apoptosis caused by hyperglycemia. According to certain reports, noncoding RNAs are involved in controlling oxidative stress and apoptosis. ShenQi Compound (SQC), a traditional herbal remedy, has been successfully treating diabetic vascular disease in China for more than 20 years. Although it is well established that SQC protects the vascular endothelium, the molecular mechanism remains unknown. Goto-Kakizaki rats, spontaneous type II diabetes rats, that consistently consume a high-fat diet were chosen as model animals. Six groups (control group, model group, metformin group, and 7.2 g/kg/d SQC group, 14.4 g/kg/d SQC group, and 28.8 g/kg/d SQC group) were included in this work, 15 rats each group. The approach of administration was gavage, and the same volume (5.0 mL/kg/d) was given in each group, once a day, 12 weeks. The thoracic aortas were removed after the rats were sacrificed. Oxidative reduction profile in thoracic aorta, histopathological observation of thoracic aorta, endothelial cell apoptosis in thoracic aorta, whole transcriptome sequencing, bioinformatic analyses, and qRT-PCR were conducted. As a result, SQC prevented the oxidative stress and apoptosis induced by a high glucose concentration. Under hyperglycemia condition, noncoding RNAs, including 1 downregulated novel circRNA (circRNA.3121), 3 downregulated lncRNAs (Skil.cSep08, Shawso.aSep08-unspliced, and MSTRG.164.2), and 1 upregulated mRNA (Pcdh17), were clearly reverse regulated by SQC. SQC plays a role in protecting vascular endothelial cells from high glucose mainly by mediating ncRNA to inhibit cell apoptosis and oxidative stress.

Regulated cell death pathways in kidney disease

Disorders of cell number that result from an imbalance between the death of parenchymal cells and the proliferation or recruitment of maladaptive cells contributes to the pathogenesis of kidney disease. Acute kidney injury can result from an acute loss of kidney epithelial cells. In chronic kidney disease, loss of kidney epithelial cells leads to glomerulosclerosis and tubular atrophy, whereas interstitial inflammation and fibrosis result from an excess of leukocytes and myofibroblasts. Other conditions, such as acquired cystic disease and kidney cancer, are characterized by excess numbers of cyst wall and malignant cells, respectively. Cell death modalities act to clear unwanted cells, but disproportionate responses can contribute to the detrimental loss of kidney cells. Indeed, pathways of regulated cell death - including apoptosis and necrosis - have emerged as central events in the pathogenesis of various kidney diseases that may be amenable to therapeutic intervention. Modes of regulated necrosis, such as ferroptosis, necroptosis and pyroptosis may cause kidney injury directly or through the recruitment of immune cells and stimulation of inflammatory responses. Importantly, multiple layers of interconnections exist between different modalities of regulated cell death, including shared triggers, molecular components and protective mechanisms.

LncRNA GAS5 suppresses TGF-β1-induced transformation of pulmonary pericytes into myofibroblasts by recruiting KDM5B and promoting H3K4me2/3 demethylation of the PDGFRα/β promoter

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a condition that may cause persistent pulmonary damage. The transformation of pericytes into myofibroblasts has been recognized as a key player during IPF progression. This study aimed to investigate the functions of lncRNA growth arrest-specific transcript 5 (GAS5) in myofibroblast transformation during IPF progression.

METHODS

We created a mouse model of pulmonary fibrosis (PF) via intratracheal administration of bleomycin. Pericytes were challenged with exogenous transforming growth factor-β1 (TGF-β1). To determine the expression of target molecules, we employed quantitative reverse transcription-polymerase chain reaction, Western blotting, and immunohistochemical and immunofluorescence staining. The pathological changes in the lungs were evaluated via H&E and Masson staining. Furthermore, the subcellular distribution of GAS5 was examined using FISH. Dual-luciferase reporter assay, ChIP, RNA pull-down, and RIP experiments were conducted to determine the molecular interaction.

RESULTS

GAS5 expression decreased whereas PDGFRα/β expression increased in the lungs of IPF patients and mice with bleomycin-induced PF. The in vitro overexpression of GAS5 or silencing of PDGFRα/β inhibited the TGF-β1-induced differentiation of pericytes to myofibroblasts, as evidenced by the upregulation of pericyte markers NG2 and desmin as well as downregulation of myofibroblast markers α-SMA and collagen I. Further mechanistic analysis revealed that GAS5 recruited KDM5B to promote H3K4me2/3 demethylation, thereby suppressing PDGFRα/β expression. In addition, KDM5B overexpression inhibited pericyte-myofibroblast transformation and counteracted the promotional effect of GAS5 knockdown on pericyte-myofibroblast transformation. Lung fibrosis in mice was attenuated by GAS5 overexpression but promoted by GAS5 deficiency.

CONCLUSION

GAS5 represses pericyte-myofibroblast transformation by inhibiting PDGFRα/β expression via KDM5B-mediated H3K4me2/3 demethylation in IPF, identifying GAS5 as an intervention target for IPF.

Progress and Challenges of Understanding Cardiorenal Syndrome Type 3

The pathologies of the kidney and heart have instigated a large number of researchers around the world to try to better understand what the exact connectors responsible for the emergence and establishment of these diseases are. The classification of these pathologies into different types of cardiorenal syndromes (CRSs) over the last 15 years has greatly contributed to understanding pathophysiological and diagnostic aspects, as well as treatment strategies. However, with the advent of new technologies classified as "Omics", a new range of knowledge and new possibilities have opened up in order to effectively understand the intermediaries between the kidney-heart axis. The universe of micro-RNAs (miRNAs), epigenetic factors, and components present in extracellular vesicles (EVs) have been protagonists in studying different types of CRSs. Thus, the new challenge that is imposed is to select and link the large amount of information generated from the use of large-scale analysis techniques. The present review seeks to present some of the future perspectives related to understanding CRSs, with an emphasis on CRS type 3.

Pleotropic effects of hypoxia-inducible factor-prolyl hydroxylase domain inhibitors: are they clinically relevant?

Anemia is common in patients with chronic kidney disease (CKD) and is mainly caused by insufficient production of erythropoietin from fibrotic kidney. Because anemia impairs quality of life and overall prognosis, recombinant human erythropoietin-related products (erythropoiesis-stimulating agents, ESAs) have been developed to increase hemoglobin level for decades. However, many safety concerns have been announced regarding the use of ESAs, including an increased occurrence of cardiovascular events, vascular access thrombosis, cancer progression, and recurrence. Hypoxia-inducible factor (HIF) is crucial to erythropoietin production, as a result, prolyl hydroxylase domain (PHD) enzyme inhibitors have been new therapeutic agents for the treatment of anemia in CKD. They can be administered orally, which is a preferred route for patients not undergoing hemodialysis. In clinical trials, PHD inhibitor could induce noninferior effect on erythropoiesis and improve functional iron deficiency compared with ESAs. Although no serious adverse events were reported, safety is still a concern because HIF stabilization induced by PHD inhibitor has pleotropic effects, such as angiogenesis, metabolic change, and cell survival, which might lead to unwanted deleterious effects, including fibrosis, inflammation, cardiovascular risk, and tumor growth. More molecular mechanisms of PHD inhibition and long-term clinical trials are needed to observe these pleotropic effects for the confirmation of safety and efficacy of PHD inhibitors.

Microvessels derived from hiPSCs are a novel source for angiogenesis and tissue regeneration

The establishment of effective vascularization represents a key challenge in regenerative medicine. Adequate sources of vascular cells and intact vessel fragments have not yet been explored. We herein examined the potential application of microvessels induced from hiPSCs for rapid angiogenesis and tissue regeneration. Microvessels were generated from human pluripotent stem cells (iMVs) under a defined induction protocol and compared with human adipose tissue-derived microvessels (ad-MVs) to illustrate the similarity and differences of the alternative source. Then, the therapeutic effect of iMVs was detected by transplantation in vivo. The renal ischemia-reperfusion model and skin damage model were applied to explore the potential effect of vascular cells derived from iMVs (iMVs-VCs). Besides, the subcutaneous transplantation model and muscle injury model were established to explore the ability of iMVs for angiogenesis and tissue regeneration. The results revealed that iMVs had remarkable similarities to natural blood vessels in structure and cellular composition, and were potent for vascular formation and self-organization. The infusion of iMVs-VCs promoted tissue repair in the renal and skin damage model through direct contribution to the reconstruction of blood vessels and modulation of the immune microenvironment. Moreover, the transplantation of intact iMVs could form a massive perfused blood vessel and promote muscle regeneration at the early stage. The infusion of iMVs-VCs could facilitate the reconstruction and regeneration of blood vessels and modulation of the immune microenvironment to restore structures and functions of damaged tissues. Meanwhile, the intact iMVs could rapidly form perfused vessels and promote muscle regeneration. With the advantages of abundant sources and high angiogenesis potency, iMVs could be a candidate source for vascularization units for regenerative medicine.

No safe renal warm ischemia time-The molecular network characteristics and pathological features of mild to severe ischemia reperfusion kidney injury

Ischemic acute kidney injury (AKI) has always been a hot and difficult research topic in the field of renal diseases. This study aims to illustrate the safe warm ischemia time of kidney and the molecular network characteristics and pathological features of mild to severe ischemia reperfusion kidney injury. We established varying degrees of renal injury due to different ischemia time (0 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min, and 30 min) on unilateral (left kidney) ischemia-reperfusion injury and contralateral (right kidney) resection (uIRIx) mouse model. Mice were sacrificed 24 h after uIRIx, blood samples were harvested to detect serum creatinine (Scr), and kidney tissue samples were harvested to perform Periodic Acid-Schiff (PAS) staining and RNA-Seq. Differentially expressed genes (DEGs) were identificated, time-dependent gene expression patterns and functional enrichment analysis were further performed. Finally, qPCR was performed to validated RNA-Seq results. Our results indicated that there was no absolute safe renal warm ischemia time, and every minute of ischemia increases kidney damage. Warm ischemia 26min or above in mice makes severe kidney injury, renal pathology and SCr were both significantly changed. Warm ischemia between 18 and 26 min makes mild kidney injury, with changes in pathology and renal molecular expression, while SCr did not change. No obvious pathological changes but significant differences in molecular expression were found less than 16min warm ischemia. There are two key time intervals in the process of renal ischemia injury, 0 min-16 min (short-term) and 26 min-28 min (long-term). Gene expression of immune-related pathways were most significantly down-regulated in short-term ischemia, while metabolism-related pathways were the mainly enriched pathway in long-term ischemia. Taken together, this study provides novel insights into safe renal artery occlusion time in partial nephrectomy, and is of great value for elucidating molecular network characteristics and pathological features of mild to severe ischemia reperfusion kidney injury, and key genes related to metabolism and immune found in this study also provide potential diagnostic and therapeutic biomarkers for AKI.

Protocol for renal ischemia-reperfusion injury by flank incisions in mice

Ischemia-reperfusion injury (IRI) contributes to acute kidney injury (AKI) and development of chronic kidney disease. We describe an IRI protocol for mice via flank incisions approach, using a pedicle clamp to cause ischemic injury. Compared with trans-abdominal approach, it is technically easier with lesser fluid loss and organ injury. Technical challenges during the dissection of renal pedicles are highlighted. For complete details on the execution of this protocol, please refer to Lai et al. (2014).

Transforming growth factor-β1 decreases erythropoietin production through repressing hypoxia-inducible factor 2α in erythropoietin-producing cells

BACKGROUND

Renal erythropoietin (EPO)-producing (REP) cells produce EPO through hypoxia-inducible factor (HIF) 2α-activated gene transcription. Insufficient EPO production leads to anemia in patients with chronic kidney disease. Although recombinant EPO is effective to improve anemia, no reliable REP cell lines limit further progress of research and development of novel treatment.

METHODS

We screened Epo mRNA expression in mouse fibroblast cell lines. Small interfering RNA specific for HIF1α or HIF2α was transfected to study Epo expression in C3H10T1/2 cells. The effect of transforming growth factor-β1 (TGF-β1) on HIF-EPO axis was studied in C3H10T1/2 cells and mice.

RESULTS

Similar to mouse REP pericytes, C3H10T1/2 cells differentiated to α-smooth muscle actin⁺ myofibroblasts after exposure to TGF-β1. Specific HIF knockdown demonstrated the role of HIF2α in hypoxia-induced Epo expression. Sustained TGF-β1 exposure increased neither DNA methyltransferase nor methylation of Epas1 and Epo genes. However, TGF-β1 repressed HIF2α-encoding Epas1 promptly through activating activin receptor-like kinase-5 (ALK5), thereby decreasing Epo induction by hypoxia and prolyl hydroxylase domain inhibitor roxadustat. In mice with pro-fibrotic injury induced by ureteral obstruction, upregulation of Tgfb1 was accompanied with downregulation of Epas1 and Epo in injured kidneys and myofibroblasts, which were reversed by ALK5 inhibitor SB431542.

CONCLUSION

C3H10T1/2 cells possessed the property of HIF2α-dependent Epo expression in REP pericytes. TGF-β1 induced not only the transition to myofibroblasts but also a repressive effect on Epas1-Epo axis in C3H10T1/2 cells. The repressive effect of TGF-β1 on Epas1-Epo axis was confirmed in REP pericytes in vivo. Inhibition of TGF-β1-ALK5 signaling might provide a novel treatment to rescue EPO expression in REP pericytes of injured kidney.

Kidney pericyte hypoxia-inducible factor regulates erythropoiesis but not kidney fibrosis

Prolyl hydroxylase domain enzyme (PHD) inhibitors are effective in the treatment of chronic kidney disease (CKD)-associated anemia by stabilizing hypoxia inducible factor (HIF), thereby increasing erythropoietin and consequently erythropoiesis. However, concern for CKD progression needs to be addressed in clinical trials. Although pre-clinical studies showed an anti-inflammatory effect in kidney disease models, the effect of PHD inhibitors on kidney fibrosis was inconsistent probably because the effects of HIF are cell type and context dependent. The major kidney erythropoietin-producing cells are pericytes that produce erythropoietin through HIF-2α-dependent gene transcription. The concern for the impact of HIF in pericytes on kidney fibrosis arises from the fact that pericytes are the major precursor cells of myofibroblasts in CKD. Since cells expressing Gli1 fulfill the morphologic and anatomic criteria for pericytes, we induced Gli1⁺ cell-specific HIF stabilization or knockout to study the impact of HIF in pericytes on kidney pathology of mice with or without fibrotic injury induced by unilateral ureteral obstruction. Compared with the littermate controls, mice with pericyte-specific HIF stabilization due to von Hippel-Lindau protein or PHD2 knockout showed increased serum erythropoietin and polycythemia rather than a discernible difference in kidney fibrosis. Compared with Gli1⁺ pericytes sorted from littermate controls, Gli1⁺ pericytes sorted from PHD2 knockout mice showed increased erythropoietin gene expression rather than discernible changes in Col1a1 or Acta2 expression. Furthermore, pericyte-specific knockout of HIF-1α or HIF-2α did not affect kidney fibrosis. Thus, our study supports the absence of negative effects of PHD inhibitors on kidney fibrosis of mice despite HIF stabilization in pericytes.

A Metabolic Reprogramming of Glycolysis and Glutamine Metabolism Is a Requisite for Renal Fibrogenesis-Why and How?

Chronic Kidney Disease (CKD) is characterized by organ remodeling and fibrosis due to failed wound repair after on-going or severe injury. Key to this process is the continued activation and presence of matrix-producing renal fibroblasts. In cancer, metabolic alterations help cells to acquire and maintain a malignant phenotype. More recent evidence suggests that something similar occurs in the fibroblast during activation. To support these functions, pro-fibrotic signals released in response to injury induce metabolic reprograming to meet the high bioenergetic and biosynthetic demands of the (myo)fibroblastic phenotype. Fibrogenic signals such as TGF-β1 trigger a rewiring of cellular metabolism with a shift toward glycolysis, uncoupling from mitochondrial oxidative phosphorylation, and enhanced glutamine metabolism. These adaptations may also have more widespread implications with redirection of acetyl-CoA directly linking changes in cellular metabolism and regulatory protein acetylation. Evidence also suggests that injury primes cells to these metabolic responses. In this review we discuss the key metabolic events that have led to a reappraisal of the regulation of fibroblast differentiation and function in CKD.

Targeting fibroblast CD248 attenuates CCL17-expressing macrophages and tissue fibrosis

The role of fibroblasts in tissue fibrosis has been extensively studied. Activated fibroblasts, namely myofibroblasts, produce pathological extracellular matrix. CD248, a type I transmembrane glycoprotein, is expressed in fibroblasts after birth. In human chronic kidney disease, upregulated CD248 in myofibroblasts is linked to poor renal survival. In this study, we demonstrated a novel interaction between CD248 and macrophages to be a key step in mediating tissue fibrosis. CD248 was upregulated in myofibroblasts in murine models of renal and peritoneal fibrosis. Cd248 knockout (Cd248^–/–) could attenuate both renal and peritoneal fibrosis. By parabiosis of GFP reporter mice and Cd248^–/– mice, we showed that attenuation of renal fibrosis was associated with a decrease of macrophage infiltration in Cd248^–/– mice. Moreover, decrease of chemokine (C–C motif) ligand 17 and Ccl22 was found in macrophages isolated from the fibrotic kidneys of Cd248^–/– mice. Because galectin-3-deficient macrophages showed decreased Ccl17 and Ccl22 in fibrotic kidneys, we further demonstrated that CD248 interacted specifically with galectin-3 of macrophages who then expressed CCL17 to activate collagen production in myofibroblasts. Mice with DNA vaccination targeting CD248 showed decreased fibrosis. We thus propose that CD248 targeting should be studied in the clinical tissue fibrosis setting.