Chronic Kidney Disease: A Vicarious Relation to Premature Cell Senescence

Cellular senescence of granulosa cells in the pathogenesis of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders in women of reproductive age, but its pathology has not been fully characterized and the optimal treatment strategy remains unclear. Cellular senescence is a permanent state of cell-cycle arrest that can be induced by multiple stresses. Senescent cells contribute to the pathogenesis of various diseases, owing to an alteration in secretory profile, termed 'senescence-associated secretory phenotype' (SASP), including with respect to pro-inflammatory cytokines. Senolytics, a class of drugs that selectively eliminate senescent cells, are now being used clinically, and a combination of dasatinib and quercetin (DQ) has been extensively used as a senolytic. We aimed to investigate whether cellular senescence is involved in the pathology of PCOS and whether DQ treatment has beneficial effects in patients with PCOS. We obtained ovaries from patients with or without PCOS, and established a mouse model of PCOS by injecting dehydroepiandrosterone. The expression of the senescence markers p16INK4a, p21, p53, γH2AX, and senescence-associated β-galactosidase and the SASP-related factor interleukin-6 was significantly higher in the ovaries of patients with PCOS and PCOS mice than in controls. To evaluate the effects of hyperandrogenism and DQ on cellular senescence in vitro, we stimulated cultured human granulosa cells (GCs) with testosterone and treated them with DQ. The expression of markers of senescence and a SASP-related factor was increased by testosterone, and DQ reduced this increase. DQ reduced the expression of markers of senescence and a SASP-related factor in the ovaries of PCOS mice and improved their morphology. These results indicate that cellular senescence occurs in PCOS. Hyperandrogenism causes cellular senescence in GCs in PCOS, and senolytic treatment reduces the accumulation of senescent GCs and improves ovarian morphology under hyperandrogenism. Thus, DQ might represent a novel therapy for PCOS.

Permissive role of vascular endothelium in fibrosis: focus on the kidney

Fibrosis, the morphologic end-result of a plethora of chronic conditions and the scorch for organ function, has been thoroughly investigated. One aspect of its development and progression, namely the permissive role of vascular endothelium, has been overshadowed by studies into (myo)fibroblasts and TGF-β; thus, it is the subject of the present review. It has been established that tensile forces of the extracellular matrix acting on cells are a prerequisite for mechanochemical coupling, leading to liberation of TGF-β and formation of myofibroblasts. Increased tensile forces are prompted by elevated vascular permeability in response to diverse stressors, resulting in the exudation of fibronectin, fibrinogen/fibrin, and other proteins, all stiffening the extracellular matrix. These processes lead to the development of endothelial cells dysfunction, endothelial-to-mesenchymal transition, premature senescence of endothelial cells, perturbation of blood flow, and gradual obliteration of microvasculature, leaving behind "string" vessels. The resulting microvascular rarefaction is not only a constant companion of fibrosis but also an adjunct mechanism of its progression. The deepening knowledge of the above chain of pathogenetic events involving endothelial cells, namely increased permeability-stiffening of the matrix-endothelial dysfunction-microvascular rarefaction-tissue fibrosis, may provide a roadmap for therapeutic interventions deemed to curtail and reverse fibrosis.

Klotho-derived peptide 1 inhibits cellular senescence in the fibrotic kidney by restoring Klotho expression via posttranscriptional regulation

Background: Klotho deficiency is a common feature of premature aging and chronic kidney disease (CKD). As such, restoring Klotho expression could be a logic strategy for protecting against various nephropathies. In this study, we demonstrate that KP1, a Klotho-derived peptide, inhibits cellular senescence by restoring endogenous Klotho expression. Methods: The effects of KP1 on cellular senescence and Klotho expression were assessed in mouse models of CKD. RNA-sequencing was employed to identify the microRNA involved in regulating Klotho by KP1. Gain- or loss-of-function approaches were used to assess the role of miR-223-3p and IncRNA-TUG1 in regulating Klotho and cellular senescence. Results: KP1 inhibited senescence markers p21, p16 and γ-H2AX in tubular epithelial cells of diseased kidneys, which was associated with its restoration of Klotho expression at the posttranscriptional level. Profiling of kidney microRNAs by RNA sequencing identified miR-223-3p that bound to Klotho mRNA and inhibited its protein expression. Overexpression of miR-223-3p inhibited Klotho and induced p21, p16 and γ-H2AX, which were negated by KP1. Conversely, inhibition of miR-223-3p restored Klotho expression, inhibited cellular senescence. Furthermore, miR-223-3p interacted with lncRNA-TUG1 and inhibited its expression. Knockdown of lncRNA-TUG1 increased miR-223-3p, aggravated Klotho loss and worsened cellular senescence, whereas KP1 mitigated all these changes. Conclusion: These studies demonstrate that KP1 inhibits cellular senescence and induces Klotho expression via posttranscriptional regulation mediated by miR-223-3p and lncRNA-TUG1. By restoring endogenous Klotho, KP1 elicits a broad spectrum of protective actions and could serve as a promising therapeutic agent for fibrotic kidney disorders.

Radioprotective Effects of Carvacrol and/or Thymol against Gamma Irradiation-Induced Acute Nephropathy: In Silico and In Vivo Evidence of the Involvement of Insulin-like Growth Factor-1 (IGF-1) and Calcitonin Gene-Related Peptide

Radiotherapy (RT) is an effective curative cancer treatment. However, RT can seriously damage kidney tissues resulting in radiotherapy nephropathy (RN) where oxidative stress, inflammation, and apoptosis are among the common pathomechanisms. Carvacrol and thymol are known for their antioxidative, anti-inflammatory, and radioprotective activities. Therefore, this study investigated the nephroprotective potentials of carvacrol and/or thymol against gamma (γ) irradiation-induced nephrotoxicity in rats along with the nephroprotection mechanisms, particularly the involvement of insulin-like growth factor-1 (IGF-1) and calcitonin gene-related peptide (CGRP). Methods: Male rats were injected with carvacrol and/or thymol (80 and 50 mg/kg BW in the vehicle, respectively) for five days and exposed to a single dose of irradiation (6 Gy). Then, nephrotoxicity indices, oxidative stress, inflammatory, apoptotic biomarkers, and the histopathological examination were assessed. Also, IGF-1 and CGRP renal expressions were measured. Results: Carvacrol and/or thymol protected kidneys against γ-irradiation-induced acute RN which might be attributed to their antioxidative, anti-inflammatory, and antiapoptotic activities. Moreover, both reserved the γ -irradiation-induced downregulation of CGRP- TNF-α loop in acute RN that might be involved in the pathomechanisms of acute RN. Additionally, in Silico molecular docking simulation of carvacrol and thymol demonstrated promising fitting and binding with CGRP, IGF-1, TNF-α and NF-κB through the formation of hydrogen, hydrophobic and alkyl bonds with binding sites of target proteins which supports the reno-protective properties of carvacrol and thymol. Collectively, our findings open a new avenue for using carvacrol and/or thymol to improve the therapeutic index of γ-irradiation.

Dual-Signal Triple-Mode Optical Sensing Platform for Assisting in the Diagnosis of Kidney Disorders

As known biomarkers of kidney diseases, N-acetyl-β-d-glucosaminidase (NAG) and β-galactosidase (β-GAL) are of great importance for the diagnosis and treatment of diseases. The feasibility of using multiplex sensing methods to simultaneously report the outcome of the two enzymes in the same sample is even more alluring. Herein, we establish a simple sensing platform for the concurrent detection of NAG and β-GAL using silicon nanoparticles (SiNPs) as a fluorescent indicator synthesized by a one-pot hydrothermal route. p-Nitrophenol (PNP), as a common enzymatic hydrolysis product of the two enzymes, led to the attenuation of fluorometric signal caused by the inner filter effect on SiNPs, the enhancement of colorimetric signal due to the increase of intensity of the characteristic absorption peak at around 400 nm with increasing reaction time, and the changes of RGB values of images obtained through a color recognition application on a smartphone. The fluorometric/colorimetric approach combined with the smartphone-assisted RGB mode was able to detect NAG and β-GAL with good linear response. Applying this optical sensing platform to clinical urine samples, we found that the two indicators in healthy individuals and patients (glomerulonephritis) with kidney diseases were significantly different. By expanding to other renal lesion-related specimens, this tool may show great potentials in clinical diagnosis and visual inspection.

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 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.

The interaction between cellular senescence and chronic kidney disease as a therapeutic opportunity

Chronic kidney disease (CKD) is an increasingly serious public health problem in the world, but the effective therapeutic approach is quite limited at present. Cellular senescence is characterized by the irreversible cell cycle arrest, senescence-associated secretory phenotype (SASP) and senescent cell anti-apoptotic pathways (SCAPs). Renal senescence shares many similarities with CKD, including etiology, mechanism, pathological change, phenotype and outcome, however, it is difficult to judge whether renal senescence is a trigger or a consequence of CKD, since there is a complex correlation between them. A variety of cellular signaling mechanisms are involved in their interactive association, which provides new potential targets for the intervention of CKD, and then extends the researches on senotherapy. Our review summarizes the common features of renal senescence and CKD, the interaction between them, the strategies of senotherapy, and the open questions for future research.

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

Acute kidney injury (AKI) is a common clinical problem, and patients who survive AKI have a high risk of chronic kidney disease (CKD). The mechanism of CKD post-AKI, characterized by progressive renal fibrosis, is still unclear. Maladaptive tubular epithelial cells (TECs) after AKI are considered a leading cause of renal fibrosis post-AKI. TECs under maladaptive repair manifest characteristics of senescence. Removing senescent TECs by genetic ablation has been proven effective in reducing renal fibrosis. Senolytics, which eliminate senescent cells by pharmacological intervention, have been studied in a series of degenerative diseases. To our knowledge, the effects of senolytics on renal fibrosis post-AKI have not been verified before. Here, we confirmed renal senescence in the unilateral ischemia/reperfusion injury murine model. Senescent TECs could activate fibroblasts and senolytics specifically induced apoptosis of senescent TECs. Next, we demonstrated that senolytics could reduce renal senescence and ameliorate renal fibrosis in both unilateral renal ischemia/reperfusion injury and multiple-cisplatin-treatment murine models. Our results indicate senescent TECs as a vital factor in renal fibrosis progression, and senolytic therapy might be promising for treating CKD post-AKI.

Radiation-induced kidney toxicity: molecular and cellular pathogenesis

Radiation nephropathy (RN) is a kidney injury induced by ionizing radiation. In a clinical setting, ionizing radiation is used in radiotherapy (RT). The use and the intensity of radiation therapy is limited by normal-tissue damage including kidney toxicity. Different thresholds for kidney toxicity exist for different entities of RT. Histopathologic features of RN include vascular, glomerular and tubulointerstitial damage. The different molecular and cellular pathomechanisms involved in RN are not fully understood. Ionizing radiation causes double-stranded breaks in the DNA, followed by cell death including apoptosis and necrosis of renal endothelial, tubular and glomerular cells. Especially in the latent phase of RN oxidative stress and inflammation have been proposed as putative pathomechanisms, but so far no clear evidence was found. Cellular senescence, activation of the renin–angiotensin–aldosterone-system and vascular dysfunction might contribute to RN, but only limited data is available. Several signalling pathways have been identified in animal models of RN and different approaches to mitigate RN have been investigated. Drugs that attenuate cell death and inflammation or reduce oxidative stress and renal fibrosis were tested. Renin–angiotensin–aldosterone-system blockade, anti-apoptotic drugs, statins, and antioxidants have been shown to reduce the severity of RN. These results provide a rationale for the development of new strategies to prevent or reduce radiation-induced kidney toxicity.

Association between dynapenic abdominal obesity and inflammatory profile in diabetic older community-dwelling patients with end-stage renal disease

BACKGROUND

Obesity and poor strength impose higher risk factor for end-stage renal disease (ESRD) patients. It is expected that the combination of both conditions might be critically associated with the inflammatory profile in this population, especially in community-dwelling elderly. So, diagnosis of dynapenic obesity and inflammation is an important tool in the management of chronic kidney disease patients at imminent risk of hospitalization.

PURPOSE

To investigate the association between dynapenic abdominal obesity and inflammatory markers in community-swelling elderly with ESRD.

METHODS

Two hundred and forty-seven community-dwelling older patients (66.74 ± 3.20 years; n = 150, 60.73%, males) undergoing maintenance phase hemodialysis volunteered for this study. The study sample was categorized into four groups according to handgrip strength and waist circumference as follows: control, dynapenia (low strength alone), abdominal obesity (high waist circumference alone), and dynapenic obesity (D/AO) (the combination of low strength and high waist circumference). Blood samples were collected for tumor necrosis factor alpha (TNF-α), interleukin (IL)- 6 and IL- 10. Results were considered significant at P < 0.05.

RESULTS

Proportions for control, abdominal obesity, dynapenic, and D/AO were 38.5%, 15.8%, 25.9%, and 19.8%, respectively. Higher concentrations of TNF-α were found in the D/AO group (P < 0.0001). This group also displayed lower levels of IL-10 (P < 0.0001). Further, the D/AO traits were strongly associated with TNF-α and IL-10 (P < 0.0001).

CONCLUSION

The closely relation between D/AO and inflammatory profile provides evidence that the pooled information of low muscle strength and abdominal obesity may be clinically relevant for the management of ESRD patients.

Cellular Senescence in Kidney Fibrosis: Pathologic Significance and Therapeutic Strategies

Age-related disorders such as chronic kidney disease (CKD) are increasingly prevalent globally and pose unprecedented challenges. In many aspects, CKD can be viewed as a state of accelerated and premature aging. Aging kidney and CKD share many common characteristic features with increased cellular senescence, a conserved program characterized by an irreversible cell cycle arrest with altered transcriptome and secretome. While developmental senescence and acute senescence may positively contribute to the fine-tuning of embryogenesis and injury repair, chronic senescence, when unresolved promptly, plays a crucial role in kidney fibrogenesis and CKD progression. Senescent cells elicit their fibrogenic actions primarily by secreting an assortment of inflammatory and profibrotic factors known as the senescence-associated secretory phenotype (SASP). Increasing evidence indicates that senescent cells could be a promising new target for therapeutic intervention known as senotherapy, which includes depleting senescent cells, modulating SASP and restoration of senescence inhibitors. In this review, we discuss current understanding of the role and mechanism of cellular senescence in kidney fibrosis. We also highlight potential options of targeting senescent cells for the treatment of CKD.

Cellular Senescence in Renal and Urinary Tract Disorders

Cellular senescence is a state of cell cycle arrest induced by repetitive cell mitoses or different stresses, which is implicated in various physiological or pathological processes. The beneficial or adverse effects of senescent cells depend on their transitory or persistent state. Transient senescence has major beneficial roles promoting successful post-injury repair and inhibiting malignant transformation. On the other hand, persistent accumulation of senescent cells has been associated with chronic diseases and age-related illnesses like renal/urinary tract disorders. The deleterious effects of persistent senescent cells have been related, in part, to their senescence-associated secretory phenotype (SASP) characterized by the release of a variety of factors responsible for chronic inflammation, extracellular matrix adverse remodeling, and fibrosis. Recently, an increase in senescent cell burden has been reported in renal, prostate, and bladder disorders. In this review, we will summarize the molecular mechanisms of senescence and their implication in renal and urinary tract diseases. We will also discuss the differential impacts of transient versus persistent status of cellular senescence, as well as the therapeutic potential of senescent cell targeting in these diseases.

Klotho, Aging, and the Failing Kidney

Klotho has been recognized as a gene involved in the aging process in mammals for over 30 years, where it regulates phosphate homeostasis and the activity of members of the fibroblast growth factor (FGF) family. The α-Klotho protein is the receptor for Fibroblast Growth Factor-23 (FGF23), regulating phosphate homeostasis and vitamin D metabolism. Phosphate toxicity is a hallmark of mammalian aging and correlates with diminution of Klotho levels with increasing age. As such, modulation of Klotho activity is an attractive target for therapeutic intervention in the diseasome of aging; in particular for chronic kidney disease (CKD), where Klotho has been implicated directly in the pathophysiology. A range of senotherapeutic strategies have been developed to directly or indirectly influence Klotho expression, with varying degrees of success. These include administration of exogenous Klotho, synthetic and natural Klotho agonists and indirect approaches, via modulation of the foodome and the gut microbiota. All these approaches have significant potential to mitigate loss of physiological function and resilience accompanying old age and to improve outcomes within the diseasome of aging.

Metabolic Flexibility and Innate Immunity in Renal Ischemia Reperfusion Injury: The Fine Balance Between Adaptive Repair and Tissue Degeneration

Renal ischemia reperfusion injury (IRI), a common event after renal transplantation, causes acute kidney injury (AKI), increases the risk of delayed graft function (DGF), primes the donor kidney for rejection, and contributes to the long-term risk of graft loss. In the last decade, epidemiological studies have linked even mild episodes of AKI to chronic kidney disease (CKD) progression, and innate immunity seems to play a crucial role. The ischemic insult triggers an acute inflammatory reaction that is elicited by Pattern Recognition Receptors (PRRs), expressed on both infiltrating immune cells as well as tubular epithelial cells (TECs). Among the PRRs, Toll-like receptors (TLRs), their synergistic receptors, Nod-like receptors (NLRs), and the inflammasomes, play a pivotal role in shaping inflammation and TEC repair, in response to renal IRI. These receptors represent promising targets to modulate the extent of inflammation, but also function as gatekeepers of tissue repair, protecting against AKI-to-CKD progression. Despite the important considerations on timely use of therapeutics, in the context of IRI, treatment options are limited by a lack of understanding of the intra- and intercellular mechanisms associated with the activation of innate immune receptors and their impact on adaptive tubular repair. Accumulating evidence suggests that TEC-associated innate immunity shapes the tubular response to stress through the regulation of immunometabolism. Engagement of innate immune receptors provides TECs with the metabolic flexibility necessary for their plasticity during injury and repair. This could significantly affect pathogenic processes within TECs, such as cell death, mitochondrial damage, senescence, and pro-fibrotic cytokine secretion, well-known to exacerbate inflammation and fibrosis. This article provides an overview of the past 5 years of research on the role of innate immunity in experimental and human IRI, with a focus on the cascade of events activated by hypoxic damage in TECs: from programmed cell death (PCD) and mitochondrial dysfunction-mediated metabolic rewiring of TECs to maladaptive repair and progression to fibrosis. Finally, we will discuss the important crosstalk between metabolism and innate immunity observed in TECs and their therapeutic potential in both experimental and clinical research.

Cellular Senescence Is Associated with Faster Progression of Focal Segmental Glomerulosclerosis

BACKGROUND

A current, albeit unproven, hypothesis is that an acceleration of cellular senescence is involved in impaired renal repair and progression of glomerular diseases. Focal segmental glomerulosclerosis (FSGS) is a glomerular disease with a substantial risk for progression to ESRD. However, if and to what extent cell senescence predicts a negative outcome in FSGS is still unknown.

METHODS

The hypothesis that cell senescence represents a proximate mechanism by which the kidney is damaged in FSGS (NOS phenotype) was investigated in 26 consecutive kidney biopsies from adult FSGS cases (eGFR 72 ± 4 mL/min, proteinuria 2.3 ± 0.6 g/day) who were incident for 2 years in a Northern Italian nephrology center and had a 6-year clinical follow-up.

RESULTS

Cell senescence (p16INK4A, SA-β-galactosidase [SA-β-Gal]) was upregulated by ∼3- to 4-fold in both glomerular and tubular cells in kidney biopsies of FSGS as compared to age-matched controls (p < 0.05-0.01). Tubular SA-β-Gal correlated with proteinuria and glomerulosclerosis, while only as a trend, tubular p16INK4A was directly associated with interstitial fibrosis. At univariate analysis, basal eGFR, proteinuria, and tubular expression of SA-β-Gal and p16INK4A were significantly directly related to the annual loss of eGFR. No correlation was observed between glomerular p16INK4A and eGFR loss. However, at multivariate analysis, eGFR, proteinuria, and tubular p16INK4A, but not SA-β-Gal, contributed significantly to the prediction of eGFR loss.

CONCLUSIONS

The results indicate that an elevated cell senescence rate, expressed by an upregulation of p16INK4A in tubules at the time of initial biopsy, represents an independent predictor of progression to ESRD in adult patients with FSGS.