Senolytic therapy ameliorates renal fibrosis postacute kidney injury by alleviating renal senescence

Wuling San regulates AVPR2-cAMP-PKA-CREB pathway to delay cellular senescence and ameliorate acute kidney injury

ETHNOPHARMACOLOGICAL RELEVANCE

Cellular senescence in renal resident cells plays a pivotal role in the progression of acute kidney injury (AKI), necessitating the expansion of effective drug targets. Traditional Chinese medicine (TCM) formulations, characterized by their multi-target effects, offer a promising perspective for advancing research on AKI. Wuling San (WLS), a well-established compound used in treating urological disorders, has yet to elucidate its potential pharmacological targets and mechanisms in ameliorating AKI and delaying cellular senescence.

AIM OF THE STUDY

This study sought to elucidate the mechanisms by which WLS modulates the AVPR2-cAMP-PKA-CREB pathway to mitigate cellular senescence and promote recovery from AKI.

METHODS

We first prepared WLS-containing serum and performed RT-qPCR experiments to screen for GPCRs that were differentially expressed in response to WLS. Next, we established an in vitro AKI mouse model to assess the renal protective effects of the WLS by measuring renal function, renal pathology, and oxidative stress levels. After this, we performed RNA sequencing (RNA-Seq) profiling to identify differentially expressed genes (DEGs) affected by WLS treatment. We also conducted Gene Ontology (GO) functional enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses to identify potential signaling pathways involved. We then utilized the Gene Expression Omnibus (GEO) data to screen for cellular senescence related differentially expressed genes (CSRDEGs) in AKI patients and performed enrichment analysis, as well as a joint analysis of specific genes in relation to the RNA-Seq profiling results. We also examined how WLS affects the expression of proteins linked to cellular senescence in the AKI mouse model by targeting the AVPR2-cAMP-PKA-CREB pathway.

RESULTS

WLS markedly enhanced the expression of Arginine Vasopressin Receptor 2 (AVPR2) and ameliorated renal function indicators, as well as pathological changes and oxidative stress levels in the mouse model of AKI. RNA-Seq profiling revealed significant enrichment of the cAMP signaling pathway following WLS intervention. Bioinformatics analysis indicated that genes associated with cellular senescence in AKI patients were notably enriched in the p53 signaling pathway. Data mining from the GEO database, in conjunction with RNA-Seq profiling, demonstrated a substantial reduction in key genes after WLS treatment. Additionally, WLS elevated both the expression and phosphorylation of pivotal proteins within the AVPR2-cAMP-PKA-CREB pathway, while concurrently decreasing proteins associated with cellular senescence.

CONCLUSION

The results demonstrated that WLS significantly elevated the expression of AVPR2, which may underlie its nephroprotective effects and facilitate the mitigation of AKI by modulating the AVPR2-cAMP-PKA-CREB pathway, ultimately contributing to a delay in cellular senescence.

The context-dependent effect of cellular senescence: From embryogenesis and wound healing to aging

Aging is characterized by a steady loss of physiological integrity, leading to impaired function and increased vulnerability to death. Cell senescence is a biological process that progresses with aging and is believed to be a key driver of age-related diseases. Senescence, a hallmark of aging, also demonstrates its beneficial physiological aspects as an anti-cancer, pro-regenerative, homeostatic, and developmental mechanism. A transitory response in which the senescent cells are quickly formed and cleared may promote tissue regeneration and organismal fitness. At the same time, senescence-related secretory phenotypes associated with extended senescence can have devastating effects. The fact that the interaction between senescent cells and their surroundings is very context-dependent may also help to explain this seemingly opposing pleiotropic function. Further, mitochondrial dysfunction is an often-unappreciated hallmark of cellular senescence and figures prominently in multiple feedback loops that induce and maintain the senescent phenotype. This review summarizes the mechanism of cellular senescence and the significance of acute senescence. We concisely introduced the context-dependent role of senescent cells and SASP, aspects of mitochondrial biology altered in the senescent cells, and their impact on the senescent phenotype. Finally, we conclude with recent therapeutic advancements targeting cellular senescence, focusing on acute injuries and age-associated diseases. Collectively, these insights provide a future roadmap for the role of senescence in organismal fitness and life span extension.

Update of cellular senescence in kidney fibrosis: from mechanism to potential interventions

Kidney fibrosis is the final common pathway of virtually all chronic kidney disease (CKD). However, despite great progress in recent years, no targeted antifibrotic therapies have been approved. Epidemiologic, clinical, and molecular evidence suggest that aging is a major contributor to the increasing incidence of CKD. Senescent renal tubular cells, fibroblasts, endothelial cells, and podocytes have been detected in the kidneys of patients with CKD and animal models. Nonetheless, although accumulated evidence supports the essential role of cellular senescence in CKD, the mechanisms that promote cell senescence and how senescent cells contribute to CKD remain largely unknown. In this review, we summarize the features of the cellular senescence of the kidney and discuss the possible functions of senescent cells in the pathogenesis of kidney fibrosis. We also address whether pharmacological approaches targeting senescent cells can be used to retard the the progression of kidney fibrosis.

Dasatinib and Quercetin Limit Gingival Senescence, Inflammation, and Bone Loss

Cellular senescence has emerged as one of the central hallmarks of aging and drivers of chronic comorbidities, including periodontal diseases. Senescence can also occur in younger tissues and instigate metabolic alterations and dysfunction, culminating in accelerated aging and pathological consequences. Senotherapeutics, such as the combination of dasatinib and quercetin (DQ), are being increasingly used to improve the clinical outcomes of chronic disorders and promote a healthy life span through the reduction of senescent cell burden and senescence-associated secretory phenotype (SASP). Recent evidence suggests that senescent cells and SASP can contribute to the pathogenesis of periodontal diseases as well. In this study, we investigated the effect of DQ interventions on periodontal tissue health using preclinical models of aging. In vitro, DQ ameliorated biological signatures of senescence in human gingival keratinocytes upon persistent exposure to periodontal bacteria, Fusobacterium nucleatum, by modulating the levels of key senescence markers such as p16, SA-β-galactosidase, and lamin-B1 and inflammatory mediators associated with SASP including interleukin-8, matrix metalloproteinase (MMP)-1, and MMP-3. In vivo, the oral administration of DQ mitigated senescent cell burden and SASP in gingival tissues and reduced naturally progressing periodontal bone loss in aged mice. Collectively, our findings provide proof-of-concept evidence for translational studies and reveal that targeting gingival senescence and the senescence-associated secretome can be an effective strategy to improve periodontal health, particularly in vulnerable populations.

Cells of all trades - on the importance of spatial positioning of senescent cells in development, healing and aging

Biological processes are often spatially regulated, ensuring molecular and cellular events occur in their most strategically advantageous locations. Cellular senescence, marked by cell cycle arrest and hypersecretion, is recognized as an important part of physiological processes like development and healing, but it also contributes to aging and disease. However, the spatial distribution of senescent cells and its physiological and pathological impact remain unclear. Here we compile evidence on senescent cell localization in development, healing, and aging. We emphasize the significance of their spatial patterns and speculate on the effects of disrupted spatial positioning of senescence in relation to pathologies. To summarize the specific spatial functions of senescent cells, we propose to refer to them as 'barrier' and 'conductor' functions. The 'barrier' function of senescent cells, due to their altered morphology and apoptosis resistance, separates tissues and builds a border between two environments. The conductor function, with the secretion of signaling factors, influences the surrounding area and stimulates migration, differentiation, or proliferation, among other processes. Overall, this Review explores the spatial patterning of cellular senescence in biological processes, highlighting its dual roles as 'barrier' and 'conductor' functions, and examines the implications of senescent cell distribution in development, healing, aging, and disease.

Senolytic procyanidin C1 alleviates renal fibrosis by promoting apoptosis of senescent renal tubular epithelial cells

Renal fibrosis is a common pathological process in various chronic kidney diseases. The accumulation of senescent renal tubular epithelial cells (TECs) in renal tissues plays an important role in the development of renal fibrosis. Eliminating senescent TECs has been proven to effectively reduce renal fibrosis. Procyanidin C1 (PCC1) plays a senolytic role by specifically eliminating senescent cells and extending its overall lifespan. However, whether PCC1 can alleviate unilateral ureteral obstruction (UUO)-induced renal fibrosis and the associated therapeutic mechanisms remains unclear. Here, we observed a marked increase in senescent TECs within obstructed human renal tissue and demonstrated the positive correlation between the accumulation of senescent TECs and renal fibrosis in UUO-induced renal fibrosis in mice. We found that PCC1 reduced the number of senescent TECs, restored the regenerative phenotype in kidneys with reduced fibrosis, and improved tubular repair after UUO-induced injury. In vitro, PCC1 effectively cleared senescent HK2 cells by inducing apoptosis via ANGPTL4/NOX4 signaling. Incubation with culture medium from senescent HK2 cells promoted fibroblast activation, whereas PCC1 impeded profibrotic effects by downregulating senescence-associated secretory phenotype (SASP) factors from senescent HK2 cells. Therefore, PCC1 alleviated interstitial renal fibrosis not only by clearing senescent TECs and improving tubular repair but also by indirectly attenuating myofibroblast activation by reducing the level of SASP. In summary, PCC1 may be a novel therapeutic senolytic agent for treating renal fibrosis.

High glucose induces renal tubular epithelial cell senescence by inhibiting autophagic flux

Autophagy, a cellular degradation process involving the formation and clearance of autophagosomes, is mediated by autophagic proteins, such as microtubule-associated protein 1 light chain 3 (LC3) and sequestosome 1 (p62), and modulated by 3-methyladenine (3-MA) as well as chloroquine (CQ). Senescence, characterised by permanent cell cycle arrest, is marked by proteins such as cyclin-dependent kinase inhibitor 1 (p21) and tumour protein 53 (p53). This study aims to investigate the relationship between cell senescence and renal function in diabetic kidney disease (DKD) and the effect of autophagy on high-glucose-induced cell senescence. We categorised 46 patients with DKD diagnosed by renal biopsy into classes I, IIa, IIb, III and IV and used four normal kidney specimens from patients with renal trauma as controls. We evaluated pathological changes, LC3 and p21. We used streptozotocin-induced DKD models in rats and 35 mM glucose-cultured human proximal tubular epithelial cells (HK-2) with or without 3-MA and CQ. We assessed p53, p21, LC3 and p62. We observed autophagosomes and detected senescence-associated galactosidase (SA-β-gal) activity. In patients with DKD, p21 and LC3 expression levels increased over time and correlated positively with blood creatinine and proteinuria. In DKD rats and HK-2 cells, p21, p53, LC3 and p62 expression levels were higher than in the controls, as were SA-β-gal-positive cells, renal tubular autophagosomes and co-expression of p21 and LC3. The 3-MA reduced p16, p21 and p53 expression compared with the high glucose group, whereas CQ had the opposite effect. These results suggest that renal tubular cell senescence is associated with the progression of DKD. Additionally, autophagic flux may play a role in mediating high-glucose-induced senescence in renal tubular cells.

Yishen paidu pills attenuates 5/6 nephrectomy induced kidney disease via inhibiting the PI3K/AKT/mTOR signaling pathway

Introduction

Chronic kidney disease (CKD) is a substantial global health issue with high morbidity and mortality. Yishen Paidu Pills (YSPDP) are effective concentrated water pills composed of four herbs developed by Wuhan Union Hospital to treat CKD. However, the mechanism of YSPDP action is largely unknown. This study combined metabolomics, network pharmacology, transcriptomics, and experimental verification to elucidate and identify the effects and potential mechanisms of YSPDP against CKD.

Methods

Firstly, we used metabolomics analyses to identify the chemical components of YSPDP. Then, network pharmacology was conducted and indicated the predicted signaling pathways regulated by YSPDP. Next, we conducted a 5/6 subtotal nephrectomy (5/6 SNx) rat model and treated these rats with YSPDP or Losartan for 10 weeks to evaluate the effect of YSPDP on CKD. To further analyze the underlying mechanism of YSPDP in CKD, the kidney tissues of 5/6 SNx rats treated with vehicle and YSPDP were performed with transcriptome sequencing. Finally, the western blot was performed to validate the signaling pathways of YSPDP against CKD.

Results

Twenty-four classes of chemicals were identified by metabolomics in YSPDP. YSPDP markedly hindered CKD progression, characterized by the restoration of body weight and serum albumin levels, improved renal function, diminished tissue injury, and hampered renal fibrosis in 5/6 SNx rats. The efficacy of YSPDP in ameliorating the progression of CKD was comparable to that of losartan. Furthermore, network pharmacology, transcriptomics, and functional enrichment analysis indicated the PI3K/AKT/mTOR signaling pathway was the key pathway regulated by YSPDP. Western blot validated the inhibition of PI3K/AKT/mTOR signaling in the kidney of 5/6 SNx rats treated by YSPDP.

Conclusion

The study identified the chemicals of YSPDP and revealed that YSPDP prevented the progression of CKD by inhibiting PI3K/AKT/mTOR signaling in 5/6 SNx rats.

The deleterious effects of CDK4/6 inhibition on renal recovery post-acute kidney injury

Acute kidney injury (AKI) is a common clinical problem, and patients who survive AKI have a high risk of chronic kidney disease (CKD). The acute protective effects of Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors in AKI have been examined, there is still relatively little known regarding the impact of acute CDK4/6 inhibition on the chronic sequence of AKI. Therefore, we utilized the CDK4/6 inhibitor Palbociclib to examine the long-term effects of CDK4/6 inhibition in a rodent model of ischemic AKI. Palbociclib (Palb) was administered during the acute stage or post the acute stage of AKI and mice were sacrificed 21 days post injury. We found that Palb could cause renal senescence and renal fibrosis. Furthermore, dasatinib (D) plus quercetin (Q) were used to eliminate senescent cells in ischemic AKI murine model and Palb was administered post the treatment of D + Q. We found that Palb could reverse the senolytic and antifibrotic effects induced by D + Q, which indicates that the profibrotic effect of Palb could be ascribed to its pro-senescent effects. Our results demonstrate that CDK4/6 inhibitors treatment might be deleterious on the chronic sequence of AKI.

The novel peptide PEP-Z-2 potentially treats renal fibrosis in vivo and in vitro by regulating TGF-β/Smad/AKT/MAPK signaling

Renal fibrosis is a process in which excessive deposition of extracellular matrix leads to an increase in tissue hardness and gradual destruction of the renal parenchyma. Chronic kidney disease (CKD) commonly progresses to end-stage renal disease (ESRD), ultimately leading to renal failure. This disease has high incidence and mortality rates, but to date, effective treatment options are lacking. PEP-Z-2 is a collagen peptide isolated from redlip croaker scales and may have potential fibroprotective activity. In this study, PEP-Z-2 was found to alleviate unilateral ureteral obstruction (UUO)- and folic acid (FA)-induced kidney injury in a mouse model, reduce collagen deposition in tissues, normalize renal function, reduce the expression of fibrosis markers, reduce reactive oxygen species (ROS) production, and restore the balance of the oxidant/antioxidant system. In vitro experiments also demonstrated that PEP-Z-2 inhibits the TGF-β-induced differentiation of fibroblasts and renal tubular epithelial cells into myofibroblasts and reduces the production of extracellular matrix (ECM) proteins such as fibronectin, Col I, and α-SMA, demonstrating notable therapeutic effects on renal fibrosis. This effect is achieved by regulating the TGF-β/Smad/AKT/MAPK pathway. Our research suggested that PEP-Z-2 is a potential therapeutic drug for renal fibrosis, and peptides from aquatic organisms may constitute a new class of candidate drugs for the treatment of renal fibrosis and even other types of organ fibrosis.

Management of inflammaging in kidney diseases: focusing on the current investigational drugs

INTRODUCTION

To improve kidney disease treatments, it is crucial to understand how inflammaging affects patients´ longevity. We could potentially slow down kidney disease progression and enhance longevity by targeting specific pathways involved in inflammaging with potential drugs.

AREAS OF COVERED

This review offers an updated overview of 'anti-inflammaging' drugs currently in the kidney disease research pipeline, as well as those with potential for future therapeutic use. Furthermore, these drugs are categorized according to their mechanisms, including targeting inflammation, immune and metabolic regulation, oxidative stress, senescence, and autophagy, as demonstrated in preclinical and early clinical trials. Additionally, the review provides insights into key challenges and opinions for future advancements in this field.

EXPERT OPINION

We reviewed recent advancements in applying different therapies to mitigate inflammaging in kidney diseases. We underscore the need for continued research to elucidate the complex pathways underlying inflammaging, which will be essential for the development of more precise and effective treatments. As research in this field advances, several emerging drugs appear promising for future investigation. While current findings are encouraging, further clinical studies are required to validate the therapeutic potential of these agents in kidney diseases, ultimately paving the way for more targeted and efficacious interventions.

APC and ZBTB2 May Mediate M2 Macrophage Infiltration to Promote the Development of Renal Fibrosis: A Bioinformatics Analysis

Background and Purpose: The continuous accumulation of M2 macrophages may potentially contribute to the development of kidney fibrosis in chronic kidney disease (CKD). The purpose of this study was to analyze the infiltration of M2 macrophages in uremic patients and to seek new strategies to slow down the progression of renal fibrosis. Methods: We conducted a comprehensive search for expression data pertaining to uremic samples within the Gene Expression Omnibus (GEO) database, encompassing the time frame from 2010 to 2022. Control and uremic differentially expressed genes (DEGs) were identified. Immune cell infiltration was investigated by CIBERSORT and modules associated with M2 macrophage infiltration were identified by weighted gene coexpression network analysis (WGCNA). Consistent genes were identified using the least absolute shrinkage and selection operator (LASSO) and selection and visualization of the most relevant features (SVM-RFE) methods to search for overlapping genes. Receiver operating characteristic (ROC) curves were examined for the diagnostic value of candidate genes. Quantitative real-time PCR (qPCR) examined the expression levels of candidate genes obtained from uremic patients in M2 macrophage. Results: A total of 1298 DEGs were identified within the GSE37171 dataset. Significant enrichment of DEGs was observed in 20 biological processes (BP), 19 cellular components (CC), 6 molecular functions (MF), and 70 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. CIBERSORT analysis observed a significant increase in B-cell memory, dendritic cell activation, M0, M1, M2, and plasma cell numbers in uremic samples. We identified the 10 most interrelated genes. In particular, adenomatous polyposis coli (APC) and zinc finger and BTB structural domain 2 (ZBTB2) were adversely associated with the infiltration of M2 macrophages. Importantly, the expression levels of APC and ZBTB2 were far lower in M2 macrophages from uremic patients than those in healthy individuals. Conclusion: The development of renal fibrosis may be the result of M2 macrophage infiltration promoted by APC and ZBTB2.

From premature birth to premature kidney disease: does accelerated aging play a role?

As the limits of fetal viability have increased over the past 30 years, there has been a growing body of evidence supporting the idea that chronic disease should be taken into greater consideration in addition to survival after preterm birth. Accumulating evidence also suggests there is early onset of biologic aging after preterm birth. Similarly, chronic kidney disease (CKD) is also associated with a phenotype of advanced biologic age which exceeds chronologic age. Yet, significant knowledge gaps remain regarding the link between premature biologic age after preterm birth and kidney disease. This review summarizes the four broad pillars of aging, the evidence of premature aging following preterm birth, and in the setting of CKD. The aim is to provide additional plausible biologic mechanisms to explore the link between preterm birth and CKD. There is a need for more research to further elucidate the biologic mechanisms of the premature aging paradigm and kidney disease after preterm birth. Given the emerging research on therapies for premature aging, this paradigm could create pathways for prevention of advanced CKD.

The potential for senotherapy as a novel approach to extend life quality in veterinary medicine

Cellular senescence, a condition where cells undergo arrest and can assume an inflammatory phenotype, has been associated with initiation and perpetuation of inflammation driving multiple disease processes in rodent models and humans. Senescent cells secrete inflammatory cytokines, proteins, and matrix metalloproteinases, termed the senescence associated secretory phenotype (SASP), which accelerates the aging processes. In preclinical models, drug interventions termed "senotherapeutics" selectively clear senescent cells and represent a promising strategy to prevent or treat multiple age-related conditions in humans and veterinary species. In this review, we summarize the current available literature describing in vitro evidence for senotheraputic activity, preclinical models of disease, ongoing human clinical trials, and potential clinical applications in veterinary medicine. These promising data to date provide further justification for future studies identifying the most active senotherapeutic combinations, dosages, and routes of administration for use in veterinary medicine.

Induction of p16Ink4a Gene Expression in Heme Protein-Induced AKI and by Heme: Pathophysiologic Implications

Key Points

In heme protein–mediated AKI (HP-AKI), a senescence phenotype promptly occurs, and increased expression of p16Ink4a contributes to HP-AKI. Renal p16Ink4a expression is induced by hemoglobin, myoglobin, and heme in vivo and in renal epithelial cells exposed to heme in vitro . Impairing the binding or degradation of heme by hemopexin deficiency or heme oxygenase-1 deficiency, respectively, further upregulates p16Ink4a.

Background

Understanding the pathogenetic basis for AKI involves the study of ischemic and nephrotoxic models of AKI, the latter including heme protein–mediated AKI (HP-AKI). Recently, interest has grown regarding the role of senescence as a mechanism of kidney injury, including AKI. We examined whether senescence occurs in HP-AKI and potential inducers of and the role of a key driver of senescence, namely, p16Ink4a, in HP-AKI.

Methods

The long-established murine glycerol model of HP-AKI was used, and indices of senescence were examined. To evaluate the interaction of heme and p16Ink4a expression, murine models of genetic deficiency of hemopexin (HPX ) and heme oxygenase-1 (HO-1 ) were used. To determine the involvement of p16Ink4a in HP-AKI, the population of p16Ink4a-expressing cells was reduced using the INK-ATTAC model.

Results

Using multiple indices, a senescence phenotype appears in the kidney within hours after the induction of HP-AKI. This phenotype includes significant upregulation of p16Ink4a. p16Ink4a is upregulated in the kidney after the individual administration of myoglobin, hemoglobin, and heme, as well as in renal epithelial cells exposed to heme in vitro . Genetic deficiencies of HPX and HO-1 , which, independently, are expected to increase heme content in the kidney, exaggerate induction of p16Ink4a in the kidney and exacerbate HP-AKI, the latter shown in the present studies involving HPX −/− mice and in previous studies involving HO-1 −/− mice. Finally, reduction in the population of p16Ink4a-expressing cells in the kidney improves renal function in HP-AKI even within 24 hours.

Conclusions

The pathogenesis of HP-AKI involves senescence and the induction of p16Ink4a, the latter driven, in part, by hemoglobin, myoglobin, and heme.

Intervention treatment reducing cellular senescence inhibits tubulointerstitial fibrosis in diabetic mice following acute kidney injury

Senescence of kidney tubules leads to tubulointerstitial fibrosis (TIF). Proximal tubular epithelial cells undergo stress-induced senescence during diabetes and episodes of acute kidney injury (AKI), and combining these injuries promotes the progression of diabetic kidney disease (DKD). Since TIF is crucial to progression of DKD, we examined the therapeutic potential of targeting senescence with a senolytic drug (HSP90 inhibitor) and/or a senostatic drug (ASK1 inhibitor) in a model of TIF in which AKI is superimposed on diabetes. After 8 weeks of streptozotocin-induced diabetes, mice underwent bilateral clamping of renal pedicles to induce mild AKI, followed by 28 days of reperfusion. Groups of mice (n=10-12) received either vehicle, HSP90 inhibitor (alvespimycin), ASK1 inhibitor (GS-444217), or both treatments. Vehicle-treated mice displayed tubular injury at day 3 and extensive tubular cell senescence at day 10, which remained unresolved at day 28. Markers of senescence (Cdkn1a and Cdkn2a), inflammation (Cd68, Tnf, and Ccl2), and TIF (Col1a1, Col4a3, α-Sma/Acta2, and Tgfb1) were elevated at day 28, coinciding with renal function impairment. Treatment with alvespimycin alone reduced kidney senescence and levels of Col1a1, Acta2, Tgfb1, and Cd68; however, further treatment with GS-444217 also reduced Col4a3, Tnf, Ccl2, and renal function impairment. Senolytic therapy can inhibit TIF during DKD, but its effectiveness can be improved by follow-up treatment with a senostatic inhibitor, which has important implications for treating progressive DKD.

Shared and Distinct Renal Transcriptome Signatures in 3 Standard Mouse Models of Chronic Kidney Disease

INTRODUCTION

Several mouse models with diverse disease etiologies are used in preclinical research for chronic kidney disease (CKD). Here, we performed a head-to-head comparison of renal transcriptome signatures in standard mouse models of CKD to assess shared and distinct molecular changes in three mouse models commonly employed in preclinical CKD research and drug discovery.

METHODS

All experiments were conducted on male C57BL/6J mice. Mice underwent sham, unilateral ureter obstruction (UUO), or unilateral ischemic-reperfusion injury (uIRI) surgery and were terminated two- and 6-weeks post-surgery, respectively. The adenine-supplemented diet-induced (ADI) model of CKD was established by feeding with adenine diet for 6 weeks and compared to control diet feeding. For all models, endpoints included plasma biochemistry, kidney histology, and RNA sequencing.

RESULTS

All models displayed increased macrophage infiltration (F4/80 IHC) and fibrosis (collagen 1a1 IHC). Compared to corresponding controls, all models were characterized by an extensive number of renal differentially expressed genes (≥11,000), with a notable overlap in transcriptomic signatures across models. Gene expression markers of fibrosis, inflammation, and kidney injury supported histological findings. Interestingly, model-specific transcriptome signatures included several genes representing current drug targets for CKD, emphasizing advantages and limitations of the three CKD models in preclinical target and drug discovery.

CONCLUSION

The UUO, uIRI, and ADI mouse models of CKD have significant commonalities in their renal global transcriptome profile. Model-specific renal transcriptional signatures should be considered when selecting the specific model in preclinical target and drug discovery.

Perioperative acute kidney injury: The renoprotective effect and mechanism of dexmedetomidine

Dexmedetomidine (DEX) is a highly selective and potent α2-adrenoceptor (α2-AR) agonist that is widely used as a clinical anesthetic to induce anxiolytic, sedative, and analgesic effects. In recent years, a growing body of evidence has demonstrated that DEX protects against acute kidney injury (AKI) caused by sepsis, drugs, surgery, and ischemia-reperfusion (I/R) in organs or tissues, indicating its potential role in the prevention and treatment of AKI. In this review, we summarized the evidence of the renoprotective effects of DEX on different models of AKI and explored the mechanism. We found that the renoprotective effects of DEX mainly involved antisympathetic effects, reducing inflammatory reactions and oxidative stress, reducing apoptosis, increasing autophagy, reducing ferroptosis, protecting renal tubular epithelial cells (RTECs), and inhibiting renal fibrosis. Thus, the use of DEX is a promising strategy for the management and treatment of perioperative AKI. The aim of this review is to further clarify the renoprotective mechanism of DEX to provide a theoretical basis for its use in basic research in various AKI models, clinical management, and the treatment of perioperative AKI.

Cellular senescence of renal tubular epithelial cells in acute kidney injury

Cellular senescence represents an irreversible state of cell-cycle arrest during which cells secrete senescence-associated secretory phenotypes, including inflammatory factors and chemokines. Additionally, these cells exhibit an apoptotic resistance phenotype. Cellular senescence serves a pivotal role not only in embryonic development, tissue regeneration, and tumor suppression but also in the pathogenesis of age-related degenerative diseases, malignancies, metabolic diseases, and kidney diseases. The senescence of renal tubular epithelial cells (RTEC) constitutes a critical cellular event in the progression of acute kidney injury (AKI). RTEC senescence inhibits renal regeneration and repair processes and, concurrently, promotes the transition of AKI to chronic kidney disease via the senescence-associated secretory phenotype. The mechanisms underlying cellular senescence are multifaceted and include telomere shortening or damage, DNA damage, mitochondrial autophagy deficiency, cellular metabolic disorders, endoplasmic reticulum stress, and epigenetic regulation. Strategies aimed at inhibiting RTEC senescence, targeting the clearance of senescent RTEC, or promoting the apoptosis of senescent RTEC hold promise for enhancing the renal prognosis of AKI. This review primarily focuses on the characteristics and mechanisms of RTEC senescence, and the impact of intervening RTEC senescence on the prognosis of AKI, aiming to provide a foundation for understanding the pathogenesis and providing potentially effective approaches for AKI treatment.

Mosaic loss of Y chromosome is associated with aging and epithelial injury in chronic kidney disease

BACKGROUND

Mosaic loss of Y chromosome (LOY) is the most common chromosomal alteration in aging men. Here, we use single-cell RNA and ATAC sequencing to show that LOY is present in the kidney and increases with age and chronic kidney disease.

RESULTS

The likelihood of a cell having LOY varies depending on its location in the nephron. Cortical epithelial cell types have a greater proportion of LOY than medullary or glomerular cell types, which may reflect their proliferative history. Proximal tubule cells are the most abundant cell type in the cortex and are susceptible to hypoxic injury. A subset of these cells acquires a pro-inflammatory transcription and chromatin accessibility profile associated with expression of HAVCR1, VCAM1, and PROM1. These injured epithelial cells have the greatest proportion of LOY and their presence predicts future kidney function decline. Moreover, proximal tubule cells with LOY are more likely to harbor additional large chromosomal gains and express pro-survival pathways. Spatial transcriptomics localizes injured proximal tubule cells to a pro-fibrotic microenvironment where they adopt a secretory phenotype and likely communicate with infiltrating immune cells.

CONCLUSIONS

We hypothesize that LOY is an indicator of increased DNA damage and potential marker of cellular senescence that can be applied to single-cell datasets in other tissues.

Quercetin antagonized advanced glycated end products induced apoptosis and functional inhibition of fibroblasts from the prolapsed uterosacral ligament

The altered behaviors and functions of pelvic floor fibroblasts are pathophysiological changes of pelvic organ prolapse (POP). Our previous study showed that advanced glycated end products (AGEs) accumulated in the pelvic tissues of POP and induced fibroblast apoptosis. The study was designed to investigate whether quercetin antagonize AGEs-induced apoptosis and functional inhibition of fibroblasts. The uptake of 5-ethynyl-2'-deoxyuridine (EdU) was evaluated for cell proliferation. Flow cytometric analysis was applied for cell apoptosis. Intracellular reactive oxygen species (ROS) content was determined by the fluorescence of dichlorofluorescein (DCF). The contractility of fibroblasts was measured by collagen gel contraction assay. The expressions of extracellular matrix (ECM) related genes and the expression of miR-4429 and caspase-3 were quantified by qPCR. The expressions of phosphatase and tensin homolog (PTEN), phosphoinositide 3-kinase (PI3K), serine-threonine kinase (Akt), and phosphorylated Akt (p-Akt) were analyzed by Western Blot. The down-regulation of miR-4429 was achieved by cell transfection. Quercetin antagonized AGEs-induced apoptosis, proliferation inhibition, and ROS increase in fibroblasts. Quercetin did not alleviate AGEs-induced contractile impairment of fibroblasts. Quercetin reduced the gene expressions of lysyl oxidase like protein 1 (LOXL1)and matrix metallopeptidase 1 (MMP1), and increased the gene expressions of lysyl oxidase (LOX) and fibrillin 2 (FBN2) in fibroblasts. Quercetin reversed AGEs-induced upregulation of PTEN and downregulation of PI3K, P-Akt, and miR-4429 in fibroblasts. The inhibitory effect of quercetin on AGEs-induced fibroblast apoptosis was inhibited by downregulating the expression of miR-4429. In conclusion, quercetin antagonized AGEs-induced apoptosis and functional inhibition of fibroblasts from the prolapsed uterosacral ligament. And inhibiting AGEs-induced down-regulation of miR-4429/PTEN/PI3K/Akt pathway was the mechanism underlying the antagonistic effect of quercetin on AGEs-induced apoptosis.

Targeting Senescent Cells as Therapy for CKD

Senescent cells accumulate in the kidney with aging, after acute and chronic injuries, and are present in increased numbers in deteriorating kidney transplants. Senescent cells have undergone permanent cell cycle arrest and release many proinflammatory cytokines/chemokines and profibrotic factors: the senescence-associated secretory phenotype. Recent work from several groups including our own has shown that senescent cells play a causative role in progression of kidney disease. Experimental evidence also indicates that targeting senescent cells has potential to alter the renal regenerative response, reducing progressive fibrosis and improving functional recovery after injury. Research and clinical interest is focused on understanding how accumulating chronic senescent cells link acute injury to progressive fibrosis, dysfunction, and mortality in human CKD. In this review, we outline current protocols for the identification of how senescent cells are identified in vitro and in vivo . We discuss the proposed mechanisms of actions of first-generation senolytic and senomorphic agents, such as ABT-263 (navitoclax) which targets the BCL2 family of survival factors, and senomorphic agents such as metformin which targets aspects of the senescence-associated secretory phenotype. We also review that emerging technologies, such as nanocarriers, are now being developed to have safer delivery systems for senolytics, greater specificity, fewer off-target effects, and less toxicity. Other methods of senescent cell elimination being developed target various immune evasion tactics displayed by these cells. By understanding the role of senescence in kidney homeostasis and disease, developing new, targeted compounds and the tools to allow their efficacy to be charted noninvasively, it should become possible for senolytic treatments to move from the bench to bedside.

Cellular senescence and frailty: a comprehensive insight into the causal links

Senescent cells may have a prominent role in driving inflammation and frailty. The impact of cellular senescence on frailty varies depending on the assessment tool used, as it is influenced by the criteria or items predominantly affected by senescent cells and the varying weights assigned to these items across different health domains. To address this challenge, we undertook a thorough review of all available studies involving gain- or loss-of-function experiments as well as interventions targeting senescent cells, focusing our attention on those studies that examined outcomes based on the individual frailty phenotype criteria or specific items used to calculate two humans (35 and 70 items) and one mouse (31 items) frailty indexes. Based on the calculation of a simple "evidence score," we found that the burden of senescent cells related to musculoskeletal and cerebral health has the strongest causal link to frailty. We deem that insight into these mechanisms may not only contribute to clarifying the role of cellular senescence in frailty but could additionally provide multiple therapeutic opportunities to help the future development of a desirable personalized therapy in these extremely heterogeneous patients.

Podocyte Senescence and Aging

As the population in many industrial countries is aging, the risk, incidence, and prevalence of CKD increases. In the kidney, advancing age results in a progressive decrease in nephron number and an increase in glomerulosclerosis. In this review, we focus on the effect of aging on glomerular podocytes, the post-mitotic epithelial cells critical for the normal integrity and function of the glomerular filtration barrier. The podocytes undergo senescence and transition to a senescence-associated secretory phenotype typified by the production and secretion of inflammatory cytokines that can influence neighboring glomerular cells by paracrine signaling. In addition to senescence, the aging podocyte phenotype is characterized by ultrastructural and functional changes; hypertrophy; cellular, oxidative, and endoplasmic reticulum stress; reduced autophagy; and increased expression of aging genes. This results in a reduced podocyte health span and a shortened life span. Importantly, these changes in the pathways/processes characteristic of healthy podocyte aging are also often similar to pathways in the disease-induced injured podocyte. Finally, the better understanding of podocyte aging and senescence opens therapeutic options to slow the rate of podocyte aging and promote kidney health.

Dihydroartemisinin attenuates ischemia/reperfusion-induced renal tubular senescence by activating autophagy

Acute kidney injury (AKI) is an important factor for the occurrence and development of CKD. The protective effect of dihydroartemisinin on AKI and and reported mechanism have not been reported. In this study, we used two animal models including ischemia-reperfusion and UUO, as well as a high-glucose-stimulated HK-2 cell model, to evaluate the protective effect of dihydroartemisinin on premature senescence of renal tubular epithelial cells in vitro and in vivo. We demonstrated that dihydroartemisinin improved renal aging and renal injury by activating autophagy. In addition, we found that co-treatment with chloroquine, an autophagy inhibitor, abolished the anti-renal aging effect of dihydroartemisinin in vitro. These findings suggested that activation of autophagy/elimination of senescent cell might be a useful strategy to prevent AKI/UUO induced renal tubular senescence and fibrosis.

Increased cellular senescence in doxorubicin-induced murine ovarian injury: effect of senolytics

Ovarian injury caused by chemotherapy can lead to early menopause, infertility, and even premature senility in female cancer patients, impairing the quality of life and overall health of the cancer survivors seriously. However, there is still a lack of effective protection strategies against such injury. Cellular senescence can be induced by chemotherapeutic agents in multiple organs and may corrode the structure and function of normal tissues. We hypothesized that the widely used first-line chemotherapy drug, doxorubicin, could increase senescent cell burden in normal ovarian tissue during the therapeutic process and that elimination of senescent cells with senolytics would ameliorate doxorubicin-induced ovarian injury. Here, we demonstrated an accumulation of cellular senescence in doxorubicin-treated ovaries through detecting p16 and p21 expression levels and senescence-associated β-galactosidase (SA-β-gal) activity as well as senescence-associated secretory phenotype (SASP) factors. Short-term intervention with the classic senolytic combination dasatinib and quercetin (DQ) or fisetin significantly reduced the load of senescent cells in ovaries after doxorubicin treatment. However, neither DQ nor fisetin alleviated doxorubicin-related ovarian dysfunction. Further experiments showed that ovarian apoptosis and fibrosis following doxorubicin exposure could not be improved by senolytics. Collectively, our study shows that senolytic treatment can eliminate accumulated senescent cells, but cannot reverse the massive follicle loss and ovarian stromal fibrosis caused by doxorubicin, suggesting that cellular senescence may not be one of the key mechanisms in doxorubicin-induced ovarian injury.

Cellular senescence and the host immune system in aging and age-related disorders

Cellular senescence is a complex process involving a close-to-irreversible arrest of the cell cycle, the acquisition of the senescence-associated secretory phenotype (SASP), as well as profound changes in the expression of cell surface proteins that determine the recognition of senescent cells by innate and cognate immune effectors including macrophages, NK, NKT and T cells. It is important to note that senescence can occur in a transient fashion to improve the homeostatic response of tissues to stress. Moreover, both the excessive generation and the insufficient elimination of senescent cells may contribute to pathological aging. Attempts are being made to identify the mechanisms through which senescent cell avoid their destruction by immune effectors. Such mechanisms involve the cell surface expression of immunosuppressive molecules including PD-L1 and PD-L2 to ligate PD-1 on T cells, as well as tolerogenic MHC class-I variants. In addition, senescent cells can secrete factors that attract immunosuppressive and pro-inflammatory cells into the microenvironment. Each of these immune evasion mechanism offers a target for therapeutic intervention, e.g., by blocking the interaction between PD-1 and PD-L1 or PD-L2, upregulating immunogenic MHC class-I molecules and eliminating immunosuppressive cell types. In addition, senescent cells differ in their antigenic makeup and immunopeptidome from their normal counterparts, hence offering the opportunity to stimulate immune response against senescence-associated antigens. Ideally, immunological anti-senescence strategies should succeed in selectively eliminating pathogenic senescent cells but spare homeostatic senescence.

Tubular cell senescence promotes maladaptive kidney repair and chronic kidney disease after cisplatin nephrotoxicity

Cisplatin is a widely used chemotherapy drug; however, it induces both acute and chronic kidney diseases (CKD) in patients with cancer. The pathogenesis of cisplatin-induced CKD is unclear, and effective renoprotective approaches are not available. Here, we report that repeated low-dose cisplatin (RLDC) treatment of C57BL/6 mice induced chronic cellular senescence in kidney tubules, accompanied with tubular degeneration and profibrotic phenotype transformation that culminated in maladaptive repair and renal fibrosis. Suppression of tubular senescence by senolytic drugs ABT-263 and Fisetin attenuated renal fibrosis and improved tubular repair, as indicated by restoration of tubular regeneration and renal function. In vitro, RLDC also induced senescence in mouse proximal tubular (BUMPT) cells. ABT-263 eliminated senescent BUMPT cells following RLDC treatment, reversed the profibrotic phenotype of the cells, and increased their clonogenic activity. Moreover, ABT-263 alleviated the paracrine effect of RLDC-treated BUMPT cells on fibroblasts for fibrosis. Consistently, knockdown of p16 suppressed post-RLDC senescence and fibrotic changes in BUMPT cells and alleviated their paracrine effects on renal fibroblast proliferation. These results indicate that persistent induction of tubular senescence plays an important role in promoting cisplatin-induced CKD. Targeting senescent tubular cells may be efficient for improvement of kidney repair and for the prevention and treatment of cisplatin-induced CKD.

The expression of fibrosis-related genes is elevated in doxorubicin-induced senescent human dermal fibroblasts, but their secretome does not trigger a paracrine fibrotic response in non-senescent cells

Tissue fibrosis is associated with the aging process of most of our organs, and organ aging correlates with the chronic accumulation of senescent cells. Fibrosis occurs when fibroblasts proliferate and deposit pathological amounts of extracellular matrix (ECM), leading to progressive tissue scarring and organ dysfunction. Fibroblasts play a key role in fibrosis, especially in the skin where fibroblasts are the most abundant cell type in the dermis and are mainly responsible for the synthesis of ECM. This study aims to investigate how senescent fibroblasts and their secretome influence dermal fibrosis. Here we used human dermal fibroblasts (HDFs) treated with doxorubicin (doxo) to induce senescence. The senescent phenotype of these stress-induced premature senescent (SIPS) cells was confirmed with several markers. The expression of pro-fibrotic genes was quantified and finally, the impact of their secretome on the fibrotic response of non-senescent fibroblasts was assessed. Doxorubicin treatment, induced senescence in fibroblasts which has been confirmed with elevated senescence-associated β- galactosidase (SA-β-gal) activity, absence of BrdU incorporation, upregulation of p21, and loss of Lamin b1. Expression levels of the pro-fibrotic genes ACTA2 and FN1 increased in SIPS cells, but in contrast to studies using lung fibroblasts the secretome of these cells failed to induce a paracrine fibrotic response in non-senescent cells. In general, these results suggest that these senescent cells are potentially profibrotic, and their accumulation can trigger fibrosis in organs.

Senescent cardiac fibroblasts: A key role in cardiac fibrosis

Cardiac fibroblasts are a cell population that controls the homeostasis of the extracellular matrix and orchestrates a damage response to maintain cardiac architecture and performance. Due to these functions, fibroblasts play a central role in cardiac fibrosis development, and there are large differences in matrix protein secretion profiles between fibroblasts from aged versus young animals. Senescence is a multifactorial and complex process that has been associated with inflammatory and fibrotic responses. After damage, transient cellular senescence is usually beneficial, as these cells promote tissue repair. However, the persistent presence of senescent cells within a tissue is linked with fibrosis development and organ dysfunction, leading to aging-related diseases such as cardiovascular pathologies. In the heart, early cardiac fibroblast senescence after myocardial infarction seems to be protective to avoid excessive fibrosis; however, in non-infarcted models of cardiac fibrosis, cardiac fibroblast senescence has been shown to be deleterious. Today, two new classes of drugs, termed senolytics and senostatics, which eliminate senescent cells or modify senescence-associated secretory phenotype, respectively, arise as novel therapeutical strategies to treat aging-related pathologies. However, further studies will be needed to evaluate the extent of the utility of senotherapeutic drugs in cardiac diseases, in which pathological context and temporality of the intervention must be considered.

Context-dependent roles of cellular senescence in normal, aged, and disease states

Cellular senescence is a state of irreversible cell cycle arrest that often emerges after tissue damage and in age-related diseases. Through the production of a multicomponent secretory phenotype (SASP), senescent cells can impact the regeneration and function of tissues. However, the effects of senescent cells and their SASP are very heterogeneous and depend on the tissue environment and type as well as the duration of injury, the degree of persistence of senescent cells and the organism's age. While the transient presence of senescent cells is widely believed to be beneficial, recent data suggest that it is detrimental for tissue regeneration after acute damage. Furthermore, although senescent cell persistence is typically associated with the progression of age-related chronic degenerative diseases, it now appears to be also necessary for correct tissue function in the elderly. Here, we discuss what is currently known about the roles of senescent cells and their SASP in tissue regeneration in ageing and age-related diseases, highlighting their (negative and/or positive) contributions. We provide insight for future research, including the possibility of senolytic-based therapies and cellular reprogramming, with aims ranging from enhancing tissue repair to extending a healthy lifespan.

Cellular senescence of renal tubular epithelial cells in renal fibrosis

Renal fibrosis (RF) is the common pathological manifestation of virtually all chronic kidney diseases (CKD) and one of the major causes of end-stage renal disease (ESRD), but the pathogenesis of which is still unclear. Renal tubulointerstitial lesions have been identified as a key pathological hallmark of RF pathology. Renal tubular epithelial cells are the resident cells of the tubulointerstitium and play an important role in kidney recovery versus renal fibrosis following injury. Studies in recent years have shown that senescence of renal tubular epithelial cells can accelerate the progression of renal fibrosis. Oxidative stress(OS), telomere attrition and DNA damage are the major causes of renal tubular epithelial cell senescence. Current interventions and therapeutic strategies for cellular senescence include calorie restriction and routine exercise, Klotho, senolytics, senostatics, and other related drugs. This paper provides an overview of the mechanisms and the key signaling pathways including Wnt/β-catenin/RAS, Nrf2/ARE and STAT-3/NF-κB pathway involved in renal tubular epithelial cell senescence in RF and therapies targeting renal tubular epithelial cell senescence future therapeutic potential for RF patients. These findings may offer promise for the further treatment of RF and CKD.

Cisplatin nephrotoxicity: new insights and therapeutic implications

Cisplatin is an effective chemotherapeutic agent for various solid tumours, but its use is limited by adverse effects in normal tissues. In particular, cisplatin is nephrotoxic and can cause acute kidney injury and chronic kidney disease. Preclinical studies have provided insights into the cellular and molecular mechanisms of cisplatin nephrotoxicity, which involve intracellular stresses including DNA damage, mitochondrial pathology, oxidative stress and endoplasmic reticulum stress. Stress responses, including autophagy, cell-cycle arrest, senescence, apoptosis, programmed necrosis and inflammation have key roles in the pathogenesis of cisplatin nephrotoxicity. In addition, emerging evidence suggests a contribution of epigenetic changes to cisplatin-induced acute kidney injury and chronic kidney disease. Further research is needed to determine how these pathways are integrated and to identify the cell type-specific roles of critical molecules involved in regulated necrosis, inflammation and epigenetic modifications in cisplatin nephrotoxicity. A number of potential therapeutic targets for cisplatin nephrotoxicity have been identified. However, the effects of renoprotective strategies on the efficacy of cisplatin chemotherapy needs to be thoroughly evaluated. Further research using tumour-bearing animals, multi-omics and genome-wide association studies will enable a comprehensive understanding of the complex cellular and molecular mechanisms of cisplatin nephrotoxicity and potentially lead to the identification of specific targets to protect the kidney without compromising the chemotherapeutic efficacy of cisplatin.

Cellular communication network 2 (connective tissue growth factor) aggravates acute DNA damage and subsequent DNA damage response-senescence-fibrosis following kidney ischemia reperfusion injury

Chronic allograft dysfunction with progressive fibrosis of unknown cause remains a major issue after kidney transplantation, characterized by ischemia-reperfusion injury (IRI). One hypothesis to account for this is that spontaneous progressive tubulointerstitial fibrosis following IRI is driven by cellular senescence evolving from a prolonged, unresolved DNA damage response (DDR). Since cellular communication network factor 2 ((CCN2), formerly called connective tissue growth factor), an established mediator of kidney fibrosis, is also involved in senescence-associated pathways, we investigated the relation between CCN2 and cellular senescence following kidney transplantation. Tubular CCN2 overexpression was found to be associated with DDR, loss of kidney function and tubulointerstitial fibrosis in both the early and the late phase in human kidney allograft biopsies. Consistently, CCN2 deficient mice developed reduced senescence and tubulointerstitial fibrosis in the late phase; six weeks after experimental IRI. Moreover, tubular DDR markers and plasma urea were less elevated in CCN2 knockout than in wild-type mice. Finally, CCN2 administration or overexpression in epithelial cells induced upregulation of tubular senescence-associated genes including p21, while silencing of CCN2 alleviated DDR induced by anoxia-reoxygenation injury in cultured proximal tubule epithelial cells. Thus, our observations indicate that inhibition of CCN2 can mitigate IRI-induced acute kidney injury, DNA damage, and the subsequent DDR-senescence-fibrosis sequence. Hence, targeting CCN2 might help to protect the kidney from transplantation-associated post-IRI chronic kidney dysfunction.

Cellular senescence in ischemia/reperfusion injury

Ischemia/reperfusion (IR) injury, a main reason of mortality and morbidity worldwide, occurs in many organs and tissues. As a result of IR injury, senescent cells can accumulate in multiple organs. Increasing evidence shows that cellular senescence is the underlying mechanism that transforms an acute organ injury into a chronic one. Several recent studies suggest senescent cells can be targeted for the prevention or elimination of acute and chronic organ injury induced by IR. In this review, we concisely introduce the underlying mechanism and the pivotal role of premature senescence in the transition from acute to chronic IR injuries. Special focus is laid on recent advances in the mechanisms as well as on the basic and clinical research, targeting cellular senescence in multi-organ IR injuries. Besides, the potential directions in this field are discussed in the end. Together, the recent advances reviewed here will act as a comprehensive overview of the roles of cellular senescence in IR injury, which could be of great significance for the design of related studies, or as a guide for potential therapeutic target.

Tubular cell polyploidy protects from lethal acute kidney injury but promotes consequent chronic kidney disease

Acute kidney injury (AKI) is frequent, often fatal and, for lack of specific therapies, can leave survivors with chronic kidney disease (CKD). We characterize the distribution of tubular cells (TC) undergoing polyploidy along AKI by DNA content analysis and single cell RNA-sequencing. Furthermore, we study the functional roles of polyploidization using transgenic models and drug interventions. We identify YAP1-driven TC polyploidization outside the site of injury as a rapid way to sustain residual kidney function early during AKI. This survival mechanism comes at the cost of senescence of polyploid TC promoting interstitial fibrosis and CKD in AKI survivors. However, targeting TC polyploidization after the early AKI phase can prevent AKI-CKD transition without influencing AKI lethality. Senolytic treatment prevents CKD by blocking repeated TC polyploidization cycles. These results revise the current pathophysiological concept of how the kidney responds to acute injury and identify a novel druggable target to improve prognosis in AKI survivors.

Acute kidney injury is frequent, often fatal and can leave survivors with chronic kidney disease. Here the authors show that tubular cell polyploidy reduces early fatality sustaining residual function but promotes chronic kidney disease, which can be prevented by blocking YAP1

Inhibition of Malate Dehydrogenase-2 Protects Renal Tubular Epithelial Cells from Anoxia-Reoxygenation-Induced Death or Senescence

Ischemia-reperfusion injury is the leading cause of acute kidney injury. Reactive oxygen species (ROS) production causes cell death or senescence. In cultures of primary human renal tubular epithelial cells (RPTECs) subjected to anoxia-reoxygenation, inhibition of the Krebs cycle at the level of malate dehydrogenase-2 (MDH-2) decreases hypoxia-inducible factor-1α and oxidative stress and protects from apoptotic or ferroptotic cell death. Inhibition of MDH-2 decreased reoxygenation-induced upregulation of p53 and p21, restored the levels of the proliferation marker Ki-67, and prevented the upregulation of the senescence marker beta-galactosidase and interleukin-1β production. MDH-2 inhibition reduced the reoxygenation-induced upregulation of ATP, but the alterations of critical cell metabolism enzymes allowed enough ATP production to prevent cell energy collapse. Thus, inhibition of the Krebs cycle at the level of MDH-2 protects RPTECs from anoxia-reoxygenation-induced death or senescence. MDH-2 may be a promising pharmaceutical target against ischemia-reperfusion injury.

Cellular senescence: the good, the bad and the unknown

Cellular senescence is a ubiquitous process with roles in tissue remodelling, including wound repair and embryogenesis. However, prolonged senescence can be maladaptive, leading to cancer development and age-related diseases. Cellular senescence involves cell-cycle arrest and the release of inflammatory cytokines with autocrine, paracrine and endocrine activities. Senescent cells also exhibit morphological alterations, including flattened cell bodies, vacuolization and granularity in the cytoplasm and abnormal organelles. Several biomarkers of cellular senescence have been identified, including SA-βgal, p16 and p21; however, few markers have high sensitivity and specificity. In addition to driving ageing, senescence of immune and parenchymal cells contributes to the development of a variety of diseases and metabolic disorders. In the kidney, senescence might have beneficial roles during development and recovery from injury, but can also contribute to the progression of acute kidney injury and chronic kidney disease. Therapies that target senescence, including senolytic and senomorphic drugs, stem cell therapies and other interventions, have been shown to extend lifespan and reduce tissue injury in various animal models. Early clinical trials confirm that senotherapeutic approaches could be beneficial in human disease. However, larger clinical trials are needed to translate these approaches to patient care.

Protective effect of quercetin on kidney diseases: From chemistry to herbal medicines

Kidney injuries may trigger renal fibrosis and lead to chronic kidney disease (CKD), but effective therapeutic strategies are still limited. Quercetin is a natural flavonoid widely distributed in herbal medicines. A large number of studies have demonstrated that quercetin may protect kidneys by alleviating renal toxicity, apoptosis, fibrosis and inflammation in a variety of kidney diseases. Therefore, quercetin could be one of the promising drugs in the treatment of renal disorders. In the present study, we review the latest progress and highlight the beneficial role of quercetin in kidney diseases and its underlying mechanisms. The pharmacokinetics and bioavailability of quercetin and its proportion in herbal medicine will also be discussed.

VNN1 contributes to the acute kidney injury-chronic kidney disease transition by promoting cellular senescence via affecting RB1 expression

The mechanisms underlying acute kidney injury (AKI) and chronic kidney disease (CKD) progression include interstitial inflammation, cellular senescence, and oxidative stress (OS). Although vanin-1 (VNN1) plays an important role in OS, its contribution to the AKI-CKD transition remains unknown. Here, we explored the roles and mechanisms of VNN1 in the progression of the AKI-CKD transition. We observed that VNN1 expression was upregulated after ischemia/reperfusion (I/R) injury and high VNN1 expression levels were associated with poor renal repair after I/R injury. In VNN1 knockout (KO) mice, recovery of serum creatinine and blood urea nitrogen levels after I/R injury was accelerated and renal fibrosis was inhibited after severe I/R injury. Furthermore, in VNN1 KO mice, senescence of renal tubular cells was inhibited after severe I/R injury, as assessed by P16 expression and SA-β-Gal assays. However, our results also revealed that VNN1 KO renal tubular cells did not resist senescence when OS was blocked. To elucidate the mechanism underlying VNN1-mediated regulation of senescence during the AKI-CKD transition, retinoblastoma 1 (RB1) was identified as a potential target. Our results suggest that the reduced senescence in VNN1 KO renal tubular cells was caused by suppressed RB1 expression and phosphorylation. Collectively, our results unveil a novel molecular mechanism by which VNN1 promotes AKI-CKD transition via inducing senescence of renal tubular cells by activating RB1 expression and phosphorylation after severe renal injury. The present study proposes a new strategy for designing therapies wherein VNN1 can be targeted to obstruct the AKI-CKD transition.

Quercetin Alleviates Pulmonary Fibrosis in Mice Exposed to Silica by Inhibiting Macrophage Senescence

Quercetin exerts anti-inflammatory, anti-oxidant and other protective effects. Previous studies have shown that senescent cells, such as fibroblasts and type II airway epithelial cells, are strongly implicated in the development of pulmonary fibrosis pathology. However, the role of senescent macrophages during silicosis remains unclear. We investigated the effects of quercetin on macrophage senescence and pulmonary fibrosis, and explored underlying mechanisms. Mice were randomized to six model groups. Vitro model was also established by culturing RAW264.7 macrophages with silica (SiO₂). We examined the effects of quercetin on fibrosis, senescence-associated β-galactosidase (SA-β-Gal) activity, and senescence-specific genes (p16, p21, and p53). We showed that quercetin reduced pulmonary fibrosis and inhibited extracellular matrix (ECM) formation. Quercetin also attenuated macrophage senescence induced by SiO₂ both in vitro and in vivo. In addition, quercetin significantly decreased the expressions of the senescence-associated secretory phenotype (SASP), including proinflammatory factors (interleukin-1α (Il-1α), Il-6, tumor necrosis factor-α (TNF-α), and transforming growth factor-β1 (TGF-β1)) and matrix metalloproteinases (MMP2, MMP9, and MMP12). In conclusion, quercetin mediated its anti-fibrotic effects by inhibiting macrophage senescence, possibly via SASP.

Primary Graft Dysfunction: The Role of Aging in Lung Ischemia-Reperfusion Injury

Transplant centers around the world have been using extended criteria donors to remedy the ongoing demand for lung transplantation. With a rapidly aging population, older donors are increasingly considered. Donor age, at the same time has been linked to higher rates of lung ischemia reperfusion injury (IRI). This process of acute, sterile inflammation occurring upon reperfusion is a key driver of primary graft dysfunction (PGD) leading to inferior short- and long-term survival. Understanding and improving the condition of older lungs is thus critical to optimize outcomes. Notably, ex vivo lung perfusion (EVLP) seems to have the potential of reconditioning ischemic lungs through ex-vivo perfusing and ventilation. Here, we aim to delineate mechanisms driving lung IRI and review both experimental and clinical data on the effects of aging in augmenting the consequences of IRI and PGD in lung transplantation.

Nanoparticles Formulation Improves the Antifibrogenic Effect of Quercetin on an Adenine-Induced Model of Chronic Kidney Disease

Renal fibrosis is the final stage of chronic kidney injury characterized by glomerulosclerosis and tubulointerstitial fibrosis with parenchymal destruction. Quercetin belongs to the most studied flavonoids with antioxidant, anti-inflammatory, antifibrogenic, and antitumor activity. It modifies the TGF-β/Smad signaling pathway, decreasing profibrogenic expression molecules and inducing the expression of antioxidant, anti-inflammatory, and antifibrogenic molecules. However, quercetin exhibits poor water solubility and low absorption and bioavailability. This limitation was solved by developing a nanoparticles formulation that improves the solubility and bioavailability of several bioactive compounds. Therefore, we aimed to investigate the in vivo antifibrogenic effect of a quercetin nanoparticles formulation. Male C57BL/6 mice were induced into chronic renal failure with 50 mg/kg of adenine for four weeks. The animals were randomly grouped and treated with 25, 50, or 100 mg/kg of quercetin, either macroparticles or nanoparticles formulation. We performed biochemical, histological, and molecular analyses to evaluate and compare the effect of macroparticles versus nanoparticles formulation on kidney damage. Here, we demonstrated that smaller doses of nanoparticles exhibited the same beneficial effect as larger doses of macroparticles on preventing kidney damage. This finding translates into less quercetin consumption reaching the desired therapeutic effect.

Enhanced Autophagic Flux, Suppressed Apoptosis and Reduced Macrophage Infiltration by Dasatinib in Kidneys of Obese Mice

Obesity causes renal changes (ORC), characterized by defective renal autophagy, lipogenesis, enhanced macrophage infiltration and apoptosis. We hypothesize that Dasatinib, a tyrosine kinase inhibitor, may ameliorate changes associated with obesity. We the mice with either Obesogenic diet (OD) or a standard basal diet. After 12 weeks, the mice received either vehicle or Dasatinib 4 mg/kg/d for an additional four weeks. We examined serum creatinine, urea, lipid profile and renal cortical mRNA expression for lipogenesis marker SREBP1, inflammatory macrophage marker iNOS and fibrosis markers; TGFβ and PDGFA genes; immunohistochemical (IHC) staining for CD68; inflammatory macrophage marker and ASMA; fibrosis marker, LC3 and SQSTM1/P62; autophagy markers and western blotting (WB) for caspase-3; and, as an apoptosis marker, LC3II/I and SQSTM1/P62 in addition to staining for H&E, PAS, Sirius red and histopathological scoring. Dasatinib attenuated renal cortical mRNA expression for SREBP1, iNOS, PDGFA and TGFβ and IHC staining for CD68, ASMA and SQSTM1/P62 and WB for caspase-3 and SQSTM1/P62, while elevating LC3 expression. Moreover, Dasatinib ameliorated ORC; glomerulosclerosis, glomerular expansion, tubular dilatation, vacuolation and casts; inflammatory cellular infiltration; and fibrosis. Dasatinib is a promising therapy for ORC by correcting autophagy impairment, attenuating lipogenesis, apoptosis and macrophage infiltration by inducing antifibrotic activity.

Emergent players in renovascular disease

Renovascular disease (RVD) remains a common etiology of secondary hypertension. Recent clinical trials revealed unsatisfactory therapeutic outcomes of renal revascularization, leading to extensive investigation to unravel key pathophysiological mechanisms underlying irreversible functional loss and structural damage in the chronically ischemic kidney. Research studies identified complex interactions among various players, including inflammation, fibrosis, mitochondrial injury, cellular senescence, and microvascular remodeling. This interplay resulted in a shift of our understanding of RVD from a mere hemodynamic disorder to a pro-inflammatory and pro-fibrotic pathology strongly influenced by systemic diseases like metabolic syndrome (MetS), hypertension, diabetes mellitus, and hyperlipidemia. Novel diagnostic approaches have been tested for early detection and follow-up of RVD progression, using new imaging techniques and biochemical markers of renal injury and dysfunction. Therapies targeting some of the pathological pathways governing the development of RVD have shown promising results in animal models, and a few have moved from bench to clinical research. This review summarizes evolving understanding in chronic ischemic kidney injury.

Molecular Mechanisms of Kidney Injury and Repair

Chronic kidney disease (CKD) will become the fifth global cause of death by 2040, thus emphasizing the need to better understand the molecular mechanisms of damage and regeneration in the kidney. CKD predisposes to acute kidney injury (AKI) which, in turn, promotes CKD progression. This implies that CKD or the AKI-to-CKD transition are associated with dysfunctional kidney repair mechanisms. Current therapeutic options slow CKD progression but fail to treat or accelerate recovery from AKI and are unable to promote kidney regeneration. Unraveling the cellular and molecular mechanisms involved in kidney injury and repair, including the failure of this process, may provide novel biomarkers and therapeutic tools. We now review the contribution of different molecular and cellular events to the AKI-to-CKD transition, focusing on the role of macrophages in kidney injury, the different forms of regulated cell death and necroinflammation, cellular senescence and the senescence-associated secretory phenotype (SAPS), polyploidization, and podocyte injury and activation of parietal epithelial cells. Next, we discuss key contributors to repair of kidney injury and opportunities for their therapeutic manipulation, with a focus on resident renal progenitor cells, stem cells and their reparative secretome, certain macrophage subphenotypes within the M2 phenotype and senescent cell clearance.

Obesity-related kidney disease: Beyond hypertension and insulin-resistance

Chronic kidney disease (CKD) causes considerable morbidity, mortality, and health expenditures worldwide. Obesity is a significant risk factor for CKD development, partially explained by the high prevalence of diabetes mellitus and hypertension in obese patients. However, adipocytes also possess potent endocrine functions, secreting a myriad of cytokines and adipokines that contribute to insulin resistance and induce a chronic low-grade inflammatory state thereby damaging the kidney. CKD development itself is associated with various metabolic alterations that exacerbate adipose tissue dysfunction and insulin resistance. This adipose-renal axis is a major focus of current research, given the rising incidence of CKD and obesity. Cellular senescence is a biologic hallmark of aging, and age is another significant risk factor for obesity and CKD. An elevated senescent cell burden in adipose tissue predicts renal dysfunction in animal models, and senotherapies may alleviate these phenotypes. In this review, we discuss the direct mechanisms by which adipose tissue contributes to CKD development, emphasizing the potential clinical importance of such pathways in augmenting the care of CKD.

Deletion of SA β-Gal+ cells using senolytics improves muscle regeneration in old mice

Systemic deletion of senescent cells leads to robust improvements in cognitive, cardiovascular, and whole-body metabolism, but their role in tissue reparative processes is incompletely understood. We hypothesized that senolytic drugs would enhance regeneration in aged skeletal muscle. Young (3 months) and old (20 months) male C57Bl/6J mice were administered the senolytics dasatinib (5 mg/kg) and quercetin (50 mg/kg) or vehicle bi-weekly for 4 months. Tibialis anterior (TA) was then injected with 1.2% BaCl2 or PBS 7- or 28 days prior to euthanization. Senescence-associated β-Galactosidase positive (SA β-Gal+) cell abundance was low in muscle from both young and old mice and increased similarly 7 days following injury in both age groups, with no effect of D+Q. Most SA β-Gal+ cells were also CD11b+ in young and old mice 7- and 14 days following injury, suggesting they are infiltrating immune cells. By 14 days, SA β-Gal+/CD11b+ cells from old mice expressed senescence genes, whereas those from young mice expressed higher levels of genes characteristic of anti-inflammatory macrophages. SA β-Gal+ cells remained elevated in old compared to young mice 28 days following injury, which were reduced by D+Q only in the old mice. In D+Q-treated old mice, muscle regenerated following injury to a greater extent compared to vehicle-treated old mice, having larger fiber cross-sectional area after 28 days. Conversely, D+Q blunted regeneration in young mice. In vitro experiments suggested D+Q directly improve myogenic progenitor cell proliferation. Enhanced physical function and improved muscle regeneration demonstrate that senolytics have beneficial effects only in old mice.

Cellular senescence and acute kidney injury

Acute kidney injury (AKI) is a common clinical complication characterized by a sudden deterioration of the kidney's excretory function, which normally occurs secondary to another serious illness. AKI is an important risk factor for chronic kidney disease (CKD) occurrence and progression to kidney failure. It is, therefore, crucial to block the development of AKI as early as possible. To date, existing animal studies have shown that senescence occurs in the early stage of AKI and is extremely critical to prognosis. Cellular senescence is an irreversible process of cell cycle arrest that is accompanied by alterations at the transcriptional, metabolic, and secretory levels along with modified cellular morphology and chromatin organization. Acute cellular senescence tends to play an active role, whereas chronic senescence plays a dominant role in the progression of AKI to CKD. The occurrence of chronic senescence is inseparable from senescence-associated secretory phenotype (SASP) and senescence-related pathways. SASP acts on normal cells to amplify the senescence signal through senescence-related pathways. Senescence can be improved by initiating reprogramming, which plays a crucial role in blocking the progression of AKI to CKD. This review integrates the existing studies on senescence in AKI from several aspects to find meaningful research directions to improve the prognosis of AKI and prevent the progression of CKD.