Dual inhibiting senescence and epithelial-to-mesenchymal transition by erythropoietin preserve tubular epithelial cell regeneration and ameliorate renal fibrosis in unilateral ureteral obstruction

Targeting senescence to prevent diabetic kidney disease: Exploring molecular mechanisms and potential therapeutic targets for disease management

BACKGROUND/AIMS

As a microvascular complication, diabetic kidney disease is the leading cause of chronic kidney disease and end-stage renal disease worldwide. While the underlying pathophysiology driving transition of diabetic kidney disease to renal failure is yet to be fully understood, recent studies suggest that cellular senescence is central in disease development and progression. Consequently, understanding the molecular mechanisms which initiate and drive senescence in response to the diabetic milieu is crucial in developing targeted therapies that halt progression of renal disease.

METHODS

To understand the mechanistic pathways underpinning cellular senescence in the context of diabetic kidney disease, we reviewed the literature using PubMed for English language articles that contained key words related to senescence, inflammation, fibrosis, senescence-associated secretory phenotype (SASP), autophagy, and diabetes.

RESULTS

Aberrant accumulation of metabolically active senescent cells is a notable event in the progression of diabetic kidney disease. Through autocrine- and paracrine-mediated mechanisms, resident senescent cells potentiate inflammation and fibrosis through increased expression and secretion of pro-inflammatory cytokines, chemoattractants, recruitment of immune cells, myofibroblast activation, and extracellular matrix remodelling. Compounds that eliminate senescent cells and/or target the SASP - including senolytic and senomorphics drugs - demonstrate promising results in reducing the senescent cell burden and associated pro-inflammatory effect.

CONCLUSIONS

Here we evidence the link between senescence and diabetic kidney disease and highlight underlying molecular mechanisms and potential therapeutic targets that could be exploited to delay disease progression and improve outcomes for individuals with the disease. Trials are now required to translate their therapeutic potential to a clinical setting.

Bone morphogenetic protein 4 inhibits pulmonary fibrosis by modulating cellular senescence and mitophagy in lung fibroblasts

BACKGROUND

Accumulation of myofibroblasts is critical to fibrogenesis in idiopathic pulmonary fibrosis (IPF). Senescence and insufficient mitophagy in fibroblasts contribute to their differentiation into myofibroblasts, thereby promoting the development of lung fibrosis. Bone morphogenetic protein 4 (BMP4), a multifunctional growth factor, is essential for the early stage of lung development; however, the role of BMP4 in modulating lung fibrosis remains unknown.

METHODS

The aim of this study was to evaluate the role of BMP4 in lung fibrosis using BMP4-haplodeleted mice, BMP4-overexpressed mice, primary lung fibroblasts and lung samples from patients with IPF.

RESULTS

BMP4 expression was downregulated in IPF lungs and fibroblasts compared to control individuals, negatively correlated with fibrotic genes, and BMP4 decreased with transforming growth factor (TGF)-β1 stimulation in lung fibroblasts in a time- and dose-dependent manner. In mice challenged with bleomycin, BMP4 haploinsufficiency perpetuated activation of lung myofibroblasts and caused accelerated lung function decline, severe fibrosis and mortality. BMP4 overexpression using adeno-associated virus 9 vectors showed preventative and therapeutic efficacy against lung fibrosis. In vitro, BMP4 attenuated TGF-β1-induced fibroblast-to-myofibroblast differentiation and extracellular matrix (ECM) production by reducing impaired mitophagy and cellular senescence in lung fibroblasts. Pink1 silencing by short-hairpin RNA transfection abolished the ability of BMP4 to reverse the TGF-β1-induced myofibroblast differentiation and ECM production, indicating dependence on Pink1-mediated mitophagy. Moreover, the inhibitory effect of BMP4 on fibroblast activation and differentiation was accompanied with an activation of Smad1/5/9 signalling and suppression of TGF-β1-mediated Smad2/3 signalling in vivo and in vitro.

CONCLUSION

Strategies for enhancing BMP4 signalling may represent an effective treatment for pulmonary fibrosis.

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.

Gasotransmitters: Potential Therapeutic Molecules of Fibrotic Diseases

Fibrosis is defined as the pathological progress of excessive extracellular matrix (ECM), such as collagen, fibronectin, and elastin deposition, as the regenerative capacity of cells cannot satisfy the dynamic repair of chronic damage. The well-known features of tissue fibrosis are characterized as the presence of excessive activated and proliferated fibroblasts and the differentiation of fibroblasts into myofibroblasts, and epithelial cells undergo the epithelial-mesenchymal transition (EMT) to expand the number of fibroblasts and myofibroblasts thereby driving fibrogenesis. In terms of mechanism, during the process of fibrosis, the activations of the TGF-β signaling pathway, oxidative stress, cellular senescence, and inflammatory response play crucial roles in the activation and proliferation of fibroblasts to generate ECM. The deaths due to severe fibrosis account for almost half of the total deaths from various diseases, and few treatment strategies are available for the prevention of fibrosis as yet. Recently, numerous studies demonstrated that three well-defined bioactive gasotransmitters, including nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), generally exhibited anti-inflammatory, antioxidative, antiapoptotic, and antiproliferative properties. Besides these effects, a number of studies have reported that low-dose exogenous and endogenous gasotransmitters can delay and interfere with the occurrence and development of fibrotic diseases, including myocardial fibrosis, idiopathic pulmonary fibrosis, liver fibrosis, renal fibrosis, diabetic diaphragm fibrosis, and peritoneal fibrosis. Furthermore, in animal and clinical experiments, the inhalation of low-dose exogenous gas and intraperitoneal injection of gaseous donors, such as SNAP, CINOD, CORM, SAC, and NaHS, showed a significant therapeutic effect on the inhibition of fibrosis through modulating the TGF-β signaling pathway, attenuating oxidative stress and inflammatory response, and delaying the cellular senescence, while promoting the process of autophagy. In this review, we first demonstrate and summarize the therapeutic effects of gasotransmitters on diverse fibrotic diseases and highlight their molecular mechanisms in the process and development of fibrosis.

Biodegradable Stent with mTOR Inhibitor-Eluting Reduces Progression of Ureteral Stricture

In this study, we investigated the effect of mTOR inhibitor (mTORi) drug-eluting biodegradable stent (DE stent), a putative restenosis-inhibiting device for coronary artery, on thermal-injury-related ureteral stricture in rabbits. In vitro evaluation confirmed the dose-dependent effect of mTORi, i.e., rapamycin, on fibrotic markers in ureteral component cell lines. Upper ureteral fibrosis was induced by ureteral thermal injury in open surgery, which was followed by insertion of biodegradable stents, with or without rapamycin drug-eluting. Immunohistochemistry and Western blotting were performed 4 weeks after the operation to determine gross anatomy changes, collagen deposition, expression of epithelial–mesenchymal transition markers, including Smad, α-SMA, and SNAI 1. Ureteral thermal injury resulted in severe ipsilateral hydronephrosis. The levels of type III collagen, Smad, α-SMA, and SNAI 1 were increased 28 days after ureteral thermal injury. Treatment with mTORi-eluting biodegradable stents significantly attenuated thermal injury-induced urinary tract obstruction and reduced the level of fibrosis proteins, i.e., type III collagen. TGF-β and EMT signaling pathway markers, Smad and SNAI 1, were significantly modified in DE stent-treated thermal-injury-related ureteral stricture rabbits. These results suggested that intra-ureteral administration of rapamycin by DE stent provides modification of fibrosis signaling pathway, and inhibiting mTOR may result in fibrotic process change.

Targeting Premature Renal Aging: from Molecular Mechanisms of Cellular Senescence to Senolytic Trials

The biological process of renal aging is characterized by progressive structural and functional deterioration of the kidney leading to end-stage renal disease, requiring renal replacement therapy. Since the discovery of pivotal mechanisms of senescence such as cell cycle arrest, apoptosis inhibition, and the development of a senescence-associated secretory phenotype (SASP), efforts in the understanding of how senescent cells participate in renal physiological and pathological aging have grown exponentially. This has been encouraged by both preclinical studies in animal models with senescent cell clearance or genetic depletion as well as due to evidence coming from the clinical oncologic experience. This review considers the molecular mechanism and pathways that trigger premature renal aging from mitochondrial dysfunction, epigenetic modifications to autophagy, DNA damage repair (DDR), and the involvement of extracellular vesicles. We also discuss the different pharmaceutical approaches to selectively target senescent cells (namely, senolytics) or the development of systemic SASP (called senomorphics) in basic models of CKD and clinical trials. Finally, an overview will be provided on the potential opportunities for their use in renal transplantation during ex vivo machine perfusion to improve the quality of the graft.

SGLT2i and GLP-1RA in Cardiometabolic and Renal Diseases: From Glycemic Control to Adipose Tissue Inflammation and Senescence

Background. Over the last few years, the use of sodium-glucose cotransporter 2 inhibitors (SGLT2i) and glucagon-like peptide 1 receptor agonists (GLP-1RA) has increased substantially in medical practice due to their documented benefits in cardiorenal and metabolic health. In this sense, and in addition to being used for glycemic control in diabetic patients, these drugs also have other favorable effects such as weight loss and lowering blood pressure, and more recently, they have been shown to have cardio and renoprotective effects with anti-inflammatory properties. Concerning the latter, the individual or associated use of these antihyperglycemic agents has been linked with a decrease in proinflammatory cytokines and with an improvement in the inflammatory profile in chronic endocrine-metabolic diseases. Hence, these drugs have been positioned as first-line therapy in the management of diabetes and its multiple comorbidities, such as obesity, which has been associated with persistent inflammatory states that induce dysfunction of the adipose tissue. Moreover, other frequent comorbidities in long-standing diabetic patients are chronic complications such as diabetic kidney disease, whose progression can be slowed by SGLT2i and/or GLP-1RA. The neuroendocrine and immunometabolism mechanisms underlying adipose tissue inflammation in individuals with diabetes and cardiometabolic and renal diseases are complex and not fully understood. Summary. This review intends to expose the probable molecular mechanisms and compile evidence of the synergistic or additive anti-inflammatory effects of SGLT2i and GLP-1RA and their potential impact on the management of patients with obesity and cardiorenal compromise.

Recombinant Erythropoietin Provides Protection against Renal Fibrosis in Adenine-Induced Chronic Kidney Disease

Chronic kidney disease (CKD) causes anemia by renal damage. In CKD, the kidney is submitted to hypoxia, persistent inflammation, leading to fibrosis and permanent loss of renal function. Human recombinant erythropoietin (rEPO) has been widely used to treat CKD-associated anemia and is known to possess organ-protective properties that are independent from its well-established hematopoietic effects. Nonhematopoietic effects of EPO are mediated by an alternative receptor that is proposed to consist of a heterocomplex between the erythropoietin receptor (EPOR) and the beta common receptor (βcR). The present study explored the effects of rEPO to prevent renal fibrosis in adenine-induced chronic kidney disease (Ad-CKD) and their association with the expression of the heterodimer EPOR/βcR. Male Wistar rats were randomized to control group (CTL), adenine-fed rats (Ad-CKD), and Ad-CKD with treatment of rEPO (1050 IU/kg, once weekly for 4 weeks). Ad-CKD rats exhibited anemia, uremia, decreased renal function, increased infiltration of inflammatory cells, tubular atrophy, and fibrosis. rEPO treatment not only corrected anemia but reduced uremia and partially improved renal function as well. In addition, we observed that rEPO diminishes tubular injury, prevents fibrosis deposition, and induces the EPOR/βcR heteroreceptor. The findings may explain the extrahematopoietic effects of rEPO in CKD and provide new strategies for the treatment of renal fibrosis in CKD.

Advances in Understanding the Effects of Erythropoietin on Renal Fibrosis

Renal fibrosis is the common manifestation of the pathogenesis of end-stage renal disease that results from different types of renal insult, and is a hallmark of chronic kidney disease (CKD). The main pathologic characteristics of renal fibrosis are renal interstitial fibroblast hyperplasia and the aberrant and excessive deposition of extracellular matrix, pathologies that lead to the destruction of normal renal tubules and interstitial structures. However, the biological significance of fibrosis during the progression of CKD is not clear, and there are no approved clinical treatments for delaying or reversing renal fibrosis. Studies of the mechanism of renal fibrosis and of potential measures of prevention and treatment have focused on erythropoietin (EPO), a hormone best known as a regulator of red blood cell production. These recent studies have found that EPO may also provide efficient protection against renal fibrosis. Future therapeutic approaches using EPO offer new hope for patients with CKD. The aim of the present review is to briefly discuss the role of EPO in renal fibrosis, to identify its possible mechanisms in preventing renal fibrosis, and to provide novel ideas for the use of EPO in future treatments of renal fibrosis.

End-stage renal disease is different from chronic kidney disease in upregulating ROS-modulated proinflammatory secretome in PBMCs - A novel multiple-hit model for disease progression

Background

The molecular mechanisms underlying chronic kidney disease (CKD) transition to end-stage renal disease (ESRD) and CKD acceleration of cardiovascular and other tissue inflammations remain poorly determined.

Methods

We conducted a comprehensive data analyses on 7 microarray datasets in peripheral blood mononuclear cells (PBMCs) from patients with CKD and ESRD from NCBI-GEO databases, where we examined the expressions of 2641 secretome genes (SG).

Results

1) 86.7% middle class (molecular weight >500 Daltons) uremic toxins (UTs) were encoded by SGs; 2) Upregulation of SGs in PBMCs in patients with ESRD (121 SGs) were significantly higher than that of CKD (44 SGs); 3) Transcriptomic analyses of PBMC secretome had advantages to identify more comprehensive secretome than conventional secretomic analyses; 4) ESRD-induced SGs had strong proinflammatory pathways; 5) Proinflammatory cytokines-based UTs such as IL-1β and IL-18 promoted ESRD modulation of SGs; 6) ESRD-upregulated co-stimulation receptors CD48 and CD58 increased secretomic upregulation in the PBMCs, which were magnified enormously in tissues; 7) M1-, and M2-macrophage polarization signals contributed to ESRD- and CKD-upregulated SGs; 8) ESRD- and CKD-upregulated SGs contained senescence-promoting regulators by upregulating proinflammatory IGFBP7 and downregulating anti-inflammatory TGF-β1 and telomere stabilizer SERPINE1/PAI-1; 9) ROS pathways played bigger roles in mediating ESRD-upregulated SGs (11.6%) than that in CKD-upregulated SGs (6.8%), and half of ESRD-upregulated SGs were ROS-independent.

Conclusions

Our analysis suggests novel secretomic upregulation in PBMCs of patients with CKD and ESRD, act synergistically with uremic toxins, to promote inflammation and potential disease progression. Our findings have provided novel insights on PBMC secretome upregulation to promote disease progression and may lead to the identification of new therapeutic targets for novel regimens for CKD, ESRD and their accelerated cardiovascular disease, other inflammations and cancers. (Total words: 279).

The emerging role of cellular senescence in renal diseases

Cellular senescence represents the state of irreversible cell cycle arrest during cell division. Cellular senescence not only plays a role in diverse biological events such as embryogenesis, tissue regeneration and repair, ageing and tumour occurrence prevention, but it is also involved in many cardiovascular, renal and liver diseases through the senescence-associated secretory phenotype (SASP). This review summarizes the molecular mechanisms underlying cellular senescence and its possible effects on a variety of renal diseases. We will also discuss the therapeutic approaches based on the regulation of senescent and SASP blockade, which is considered as a promising strategy for the management of renal diseases.

Unilateral Ureteral Obstruction as a Model to Investigate Fibrosis-Attenuating Treatments

Renal fibrosis is the common pathway for most forms of progressive renal disease. The Unilateral Ureteral Obstruction (UUO) model is used to cause renal fibrosis, where the primary feature of UUO is tubular injury as a result of obstructed urine flow. Furthermore, experimental UUO in rodents is believed to mimic human chronic obstructive nephropathy in an accelerated manner. Renal fibrosis is the common pathway for most forms of progressive renal disease. Removing the obstruction may not be sufficient to reverse fibrosis, so an accompanying treatment may be of benefit. In this review, we have done a revision on treatments shown to ameliorate fibrosis in the context of the UUO experimental model. The treatments inhibit the production of fibrotic and inflammatory proteins such as Transforming Growth Factor β1 (TGF-β₁), Tumor Necrosis Factor α (TNF-α), collagen and fibronectin, Heat Shock Protein 47 (HSP47), suppress the proliferation of fibroblasts, prevent epithelial-to-mesenchymal transition, reduce oxidative stress, inhibit the action of the Nuclear Factor κB (NF-κB), reduce the phosphorylation of mothers against decapentaplegic homolog (SMAD) family members 2 and 3 (Smad2/3) or Mitogen-Activated Protein Kinases (MAPKs), inhibit the activation of the renin-angiotensin system. Summaries of the UUO experimental methods and alterations observed in the UUO experiments are included.

Mesenchymal stem cells-microvesicle-miR-451a ameliorate early diabetic kidney injury by negative regulation of P15 and P19

Microvesicles (MVs) from mesenchymal stem cells (MSCs) have been reported as a new communicated way between cells. This study evaluated the influence and underlying mechanism of MVs-shuttled miR-451a on renal fibrosis and epithelial mesenchymal transformation (EMT) in diabetic nephropathy (DN) with hyperuricemia. MVs were isolated from MSCs-cultured medium by gradient ultracentrifugation. The level of miR-451a in MSCs and MVs was analyzed by qPCR. The changes of miR-451a, E-cadherin, α-SMA, P15INK4b (P15), and P19INK4d (P19) were measured in hyperglycosis and hyperuricemia-induced cell (HK-2) and mouse models. The changes of cell cycle were analyzed by flow cytometry. The ability of proliferation and viability was measured by BrdU and CCK8, respectively. Dual-luciferase reporter assays were conducted to determine the target binding sites. The renal function and histological changes of mice were analyzed. MVs showed the same surface markers as MSCs but much higher miR-451a expression (4.87 ± 2.03 fold higher than MSCs). miR-451a was decreased to 26% ± 11% and 6.7% ± 0.82% in injured HK-2 cells and kidney, respectively. MV-miR-451a enhanced the HK2 cells proliferation and viability in vitro, and decreased the morphologic and functional injury of kidney in vivo. Moreover, infusion of MV-miR-451a reduced the level of α-SMA and raised E-cadherin expression. These effects were responsible for the improved arrested cell cycle and down-regulation of P15 and P19 via miR-451a targeting their 3′-UTR sites. This study demonstrated that MSC–MV-miR-451a could inhibit cell cycle inhibitors P15 and P19 to restart the blocked cell cycle and reverse EMT in vivo and in vitro, and thus miR-451a is potentially a new target for DN therapy.

Impact statement

The mechanism of MSCs repairing the injured kidney in diabetic nephropathy is not yet clear. In the research, MVs showed the same surface markers as MSCs but much higher MiR-451a expression. miR-451a was decreased in both injured HK-2 cells and kidneys. MV-miR-451a stimulated the cell proliferation and viability in vitro and promoted structural and functional improvements of injured kidney in vivo. Infusion of MV-miR-451a ameliorated EMT by reducing α-SMA and increasing E-cadherin. These effects relied on the improved cell cycle arrest and the down-regulation of P15 and P19 via miR-451a binding to their 3′-UTR region. This study demonstrated that MSC–MV-miR-451a could specifically inhibit cell cycle inhibitors to restart the blocked cell cycle and reverse EMT in vivo and in vitro. Therefore, miR-451a may be a new target for DN therapy.

Erythropoiesis and chronic kidney disease-related anemia: From physiology to new therapeutic advancements

Erythropoiesis is triggered by hypoxia and is strictly regulated by hormones, growth factors, cytokines, and vitamins to ensure an adequate oxygen delivery to all body cells. Abnormalities in one or more of these factors may induce different kinds of anemia requiring different treatments. A key player in red blood cell production is erythropoietin. It is a glycoprotein hormone, mainly produced by the kidneys, that promotes erythroid progenitor cell survival and differentiation in the bone marrow and regulates iron metabolism. A deficit in erythropoietin synthesis is the main cause of the normochromic normocytic anemia frequently observed in patients with progressive chronic kidney disease. The present review summarizes the most recent findings about each step of the erythropoietic process, going from the renal oxygen sensing system to the cascade of events induced by erythropoietin through its own receptor in the bone marrow. The paper also describes the new class of drugs designed to stabilize the hypoxia-inducible factor by inhibiting prolyl hydroxylase, with a discussion about their metabolism, disposition, efficacy, and safety. According to many trials, these drugs seem able to simulate tissue hypoxia and then stimulate erythropoiesis in patients affected by renal impairment. In conclusion, the in-depth investigation of all events involved in erythropoiesis is crucial to understand anemia pathophysiology and to identify new therapeutic strategies, in an attempt to overcome the potential side effects of the commonly used erythropoiesis-stimulating agents.

Cellular senescence, senescence-associated secretory phenotype, and chronic kidney disease

Chronic kidney disease (CKD) is increasingly being accepted as a type of renal ageing. The kidney undergoes age-related alterations in both structure and function. To date, a comprehensive analysis of cellular senescence and senescence-associated secretory phenotype (SASP) in CKD is lacking. Hence, this review mainly discusses the relationship between the two phenomena to show the striking similarities between SASP and CKD-associated secretory phenotype (CASP). It has been reported that replicative senescence, stress-induced premature ageing, and epigenetic abnormalities participate in the occurrence and development of CKD. Genomic damage and external environmental stimuli cause increased levels of oxidative stress and a chronic inflammatory state as a result of irreversible cell cycle arrest and low doses of SASP. Similar to SASP, CASP factors activate tissue repair by multiple mechanisms. Once tissue repair fails, the accumulated SASP or CASP species aggravate DNA damage response (DDR) and cause the senescent cells to secrete more SASP factors, accelerating the process of cellular ageing and eventually leading to various ageing-related changes. It is concluded that cellular senescence and SASP participate in the pathological process of CKD, and correspondingly CKD accelerated the progression of cell senescence and the secretion of SASP. These results will facilitate the integration of these mechanisms into the care and management of CKD and other age-related diseases.

P16 INK4a Deletion Ameliorated Renal Tubulointerstitial Injury in a Stress-induced Premature Senescence Model of Bmi-1 Deficiency

To determine whether p16 ^INK4a deletion ameliorated renal tubulointerstitial injury by inhibiting a senescence-associated secretory phenotype (SASP) in Bmi-1-deficient (Bmi-1 ^-/-) mice, renal phenotypes were compared among 5-week-old Bmi-1 and p16 ^INK4a double-knockout, and Bmi-1 ^-/- and wild-type mice. Fifth-passage renal interstitial fibroblasts (RIFs) from the three groups were analyzed for senescence and proliferation. The effect of Bmi-1 deficiency on epithelial-to-mesenchymal transition (EMT) was examined in Bmi-1-knockdown human renal proximal tubular epithelial (HK2) cells, which were treated with concentrated conditioned medium (CM) from the fifth-passage renal interstitial fibroblasts (RIFs) of above three group mice or with exogenous TGF-β1. Our results demonstrated that p16 ^INK4a deletion largely rescued renal aging phenotypes caused by Bmi-1 deficiency, including impaired renal structure and function, decreased proliferation, increased apoptosis, senescence and SASP, DNA damage, NF-κB and TGF-β1/Smad signal activation, inflammatory cell infiltration, and tubulointerstitial fibrosis and tubular atrophy. P16 ^INK4a deletion also promoted proliferation, reduced senescence and SASP of RIFs and subsequently inhibited EMT of Bmi-1-knockdown HK2 cells. TGF-β1 further induced the EMT of Bmi-1-knockdown HK2 cells. Thus, p16 ^INK4a positive senescent cells would be a therapeutic target for preventing renal tubulointerstitial injury.

Erythropoietin protects the tubular basement membrane by promoting the bone marrow to release extracellular vesicles containing tPA-targeting miR-144

Renal fibrosis is an inevitable outcome of chronic kidney disease (CKD). Erythropoietin (EPO) has been recently reported to be able to mitigate renal fibrosis. The mechanism underlying the protective effect of EPO, however, remains elusive. In the present study, employing a mouse model of renal tubulointerstitial fibrosis induced by unilateral ureteral obstruction (UUO), we demonstrated that EPO markedly reduced the disruption of the tubular basement membrane (TBM) through attenuating the activation of tissue plasminogen activator (tPA) and matrix metalloproteinase 9 (MMP9), the major matrix proteolytic network in the obstructed kidney. Instead of acting directly on tPA in the kidney, EPO strongly increased the level of circulating microRNA (miR)-144, which was delivered to the injured renal fibroblasts via extracellular vesicles (EVs) to target the tPA 3′-untranslated region and suppress tPA expression. The protective effect of EPO on mouse TBM was inhibited by miR-144 antagomir. Furthermore, in vitro results confirmed that EPO could stimulate bone marrow-derived Sca-1+CD44+CD11b−CD19− cells to secrete miR-144-containing EVs, which markedly suppressed tPA expression, as well as metalloproteinase 9 (MMP9) level and activity, in cultured renal fibroblasts. In conclusion, our study provides the first evidence that EPO protects mouse renal TBM through promoting bone marrow cells to generate and secrete miR-144, which, in turn, is efficiently delivered into the mouse kidney via EVs to inhibit the activation of the tPA/MMP9-mediated proteolytic network. This finding thus suggests that EPO, a hormone widely used to treat anemia in CKD, is a potential therapeutic strategy for renal fibrosis.

Diverse origins of the myofibroblast—implications for kidney fibrosis

Fibrosis is the common end point of chronic kidney disease. The persistent production of inflammatory cytokines and growth factors leads to an ongoing process of extracellular matrix production that eventually disrupts the normal functioning of the organ. During fibrosis, the myofibroblast is commonly regarded as the predominant effector cell. Accumulating evidence has demonstrated a diverse origin of myofibroblasts in kidney fibrosis. Proposed major contributors of myofibroblasts include bone marrow-derived fibroblasts, tubular epithelial cells, endothelial cells, pericytes and interstitial fibroblasts; the published data, however, have not yet clearly defined the relative contribution of these different cellular sources. Myofibroblasts have been reported to originate from various sources, irrespective of the nature of the initial damage responsible for the induction of kidney fibrosis. Here, we review the possible relevance of the diversity of myofibroblast progenitors in kidney fibrosis and the implications for the development of novel therapeutic approaches. Specifically, we discuss the current status of preclinical and clinical antifibrotic therapy and describe targeting strategies that might help support resident and circulating cells to maintain or regain their original functional differentiation state. Such strategies might help these cells resist their transition to a myofibroblast phenotype to prevent, or even reverse, the fibrotic state.