Identification of thrombospondin 1 (TSP-1) as a novel mediator of cell injury in kidney ischemia

Knockdown of KLF6 ameliorates myocardial infarction by regulating autophagy via transcriptional regulation of PTTG1

Krüppel-like factor 6 (KLF6) knockdown provides protection against kidney ischemia/reperfusion injury and ischemic stroke. However, it is unclear whether it plays a role in myocardial infarction (MI). Here, the expression of KLF6 was analyzed using the Gene Expression Omnibus (GEO) database and determined in patients with MI. The impact of KLF6 knockdown was further confirmed in in vivo and in vitro models of MI. The interaction between KLF6 and pituitary tumor-transforming gene 1 (PTTG1) was also evaluated. According to the GEO database, KLF6 expression was found to be upregulated in mouse hearts after MI compared to sham-operated mice. The upregulation of KLF6 in hearts from mice post-MI and in patients with MI was confirmed. KLF6 knockdown was found to alleviate myocardial injury, diminish infarct size, and suppress apoptosis and autophagy in mice with MI. In addition, inactivation of the AMP-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) signaling was observed after KLF6 knockdown in mice with MI. In an in vitro model of MI, the knockdown of KLF6 increased cell survival and inhibited autophagy through the AMPK/mTOR pathway. In addition, KLF6 interacted with the promoter of PTTG1 and negatively regulated its expression. Knockdown of PTTG1 abolished the function of KLF6 knockdown in vitro. This study demonstrates the protective effect of KLF6 knockdown against MI, which is attributed to the elevation of PTTG1 expression and inhibition of the AMPK/mTOR pathway. These findings provide a novel insight into MI treatment.NEW & NOTEWORTHY Our study demonstrates for the first time the role of Krüppel-like factor 6 (KLF6)/PTTG1 axis in myocardial infarction (MI). This study demonstrates the protective effect of KLF6 knockdown against MI, which is attributed to the elevation of PTTG1 expression and inhibition of the AMPK/mTOR pathway. These findings provide a novel insight into MI treatment.

GWAS Meta-analysis of Kidney Function Traits in Japanese Populations

BACKGROUND

Genetic epidemiological evidence for the kidney function traits in East Asian populations, including Japanese, remain still relatively unclarified. Especially, the number of genome-wide association studies (GWASs) for kidney traits reported still remains limited, and the sample size of each independent study is relatively small. Given the genetic variability between ancestries/ethnicities, implementation of GWAS with sufficiently large sample sizes in specific population of Japanese is considered meaningful.

METHODS

We conducted the GWAS meta-analyses of kidney traits by leveraging the GWAS summary data of the representative large genome cohort studies with about 200,000 Japanese participants (n = 202,406 for estimated glomerular filtration rate [eGFR] and n = 200,845 for serum creatinine [SCr]).

RESULTS

In the present GWAS meta-analysis, we identified 110 loci with 169 variants significantly associated with eGFR (on chromosomes 1-13 and 15-22; P < 5 × 10-8), whereas we also identified 112 loci with 176 variants significantly associated with SCr (on chromosomes 1-22; P < 5 × 10-8), of which one locus (more than 1 Mb distant from known loci) with one variant (CD36 rs146148222 on chromosome 7) for SCr was considered as the truly novel finding.

CONCLUSION

The present GWAS meta-analysis of the largest genome cohort studies in Japanese subjects provided some original genomic loci associated with kidney function, which may contribute to the possible development of personalized prevention of kidney diseases based on genomic information in the near future.

Role of TSP-1 and its receptor ITGB3 in the renal tubulointerstitial injury of focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS), a common cause of primary glomerulonephritis, has a poor prognosis and is pathologically featured by tubulointerstitial injury. Thrombospondin-1 (TSP-1) is an extracellular matrix protein that acts in combination with different receptors in the kidney. Here, we analyzed the tubular expression of TSP-1 and its receptor integrin β3 (ITGB3) in FSGS. Previously the renal interstitial chip analysis of FSGS patients with tubular interstitial injury showed that the expression of TSP-1 and ITGB3 were upregulated. We found that the expression of TSP-1 and ITGB3 increased in the tubular cells of FSGS patients. The plasma level of TSP-1 increased and was correlated to the degree of tubulointerstitial lesions in FSGS patients. TSP-1/ITGB3 signaling induced renal tubular injury in HK-2 cells exposure to bovine serum albumin and the adriamycin (ADR)-induced nephropathy model. THBS1 KO ameliorated tubular injury and renal fibrosis in ADR-treated mice. THBS1 knockdown decreased the expression of KIM-1 and caspase 3 in the HK-2 cells treated with bovine serum albumin, while THBS1 overexpression could induce tubular injury. In vivo, we identified cyclo-RGDfK as an agent to block the binding of TSP-1 to ITGB3. Cyclo-RGDfK treatment could alleviate ADR-induced renal tubular injury and interstitial fibrosis in mice. Moreover, TSP-1 and ITGB3 were colocalized in tubular cells of FSGS patients and ADR-treated mice. Taken together, our data showed that TSP-1/ITGB3 signaling contributed to the development of renal tubulointerstitial injury in FSGS, potentially identifying a new therapeutic target for FSGS.

Nanotechnology-based Strategies for Molecular Imaging, Diagnosis, and Therapy of Organ Transplantation

Organ transplantation is the preferred paradigm for patients with end-stage organ failures. Despite unprecedented successes, complications such as immune rejection, ischemia-reperfusion injury, and graft dysfunction remain significant barriers to long-term recipient survival after transplantation. Conventional immunosuppressive drugs have limited efficacy because of significant drug toxicities, high systemic immune burden, and emergence of transplant infectious disease, leading to poor quality of life for patients. Nanoparticle-based drug delivery has emerged as a promising medical technology and offers several advantages by enhancing the delivery of drug payloads to their target sites, reducing systemic toxicity, and facilitating patient compliance over free drug administration. In addition, nanotechnology-based imaging approaches provide exciting diagnostic methods for monitoring molecular and cellular changes in transplanted organs, visualizing immune responses, and assessing the severity of rejection. These noninvasive technologies are expected to help enhance the posttransplantation patient survival through real time and early diagnosis of disease progression. Here, we present a comprehensive review of nanotechnology-assisted strategies in various aspects of organ transplantation, including organ protection before transplantation, mitigation of ischemia-reperfusion injury, counteraction of immune rejection, early detection of organ dysfunction posttransplantation, and molecular imaging and diagnosis of immune rejection.

Single-Cell Spatial Transcriptomics Unveils Platelet-Fueled Cycling Macrophages for Kidney Fibrosis

With the increasing incidence of kidney diseases, there is an urgent need to develop therapeutic strategies to combat post-injury fibrosis. Immune cells, including platelets, play a pivotal role in this repair process, primarily through their released cytokines. However, the specific role of platelets in kidney injury and subsequent repair remains underexplored. Here, the detrimental role of platelets in renal recovery following ischemia/reperfusion injury and its contribution to acute kidney injury  to chronic kidney disease transition is aimed to investigated. In this study, it is shown that depleting platelets accelerates injury resolution and significantly reduces fibrosis. Employing advanced single-cell and spatial transcriptomic techniques, macrophages as the primary mediators modulated by platelet signals is identified. A novel subset of macrophages, termed "cycling M2", which exhibit an M2 phenotype combined with enhanced proliferative activity is uncovered. This subset emerges in the injured kidney during the resolution phase and is modulated by platelet-derived thrombospondin 1 (THBS1) signaling, acquiring profibrotic characteristics. Conversely, targeted inhibition of THBS1 markedly downregulates the cycling M2 macrophage, thereby mitigating fibrotic progression. Overall, this findings highlight the adverse role of platelet THBS1-boosted cycling M2 macrophages in renal injury repair and suggest platelet THBS1 as a promising therapeutic target for alleviating inflammation and kidney fibrosis.

Thrombospondin-1 Drives Cardiac Remodeling in Chronic Kidney Disease

Patients with chronic kidney disease (CKD) face a high risk of cardiovascular disease. Previous studies reported that endogenous thrombospondin 1 (TSP1) involves right ventricular remodeling and dysfunction. Here we show that a murine model of CKD increased myocardial TSP1 expression and produced left ventricular hypertrophy, fibrosis, and dysfunction. TSP1 knockout mice were protected from these features. In vitro, indoxyl sulfate is driving deleterious changes in cardiomyocyte through the TSP1. In patients with CKD, TSP1 and aryl hydrocarbon receptor were both differentially expressed in the myocardium. Our findings summon large clinical studies to confirm the translational role of TSP1 in patients with CKD.

Integrin β1-rich extracellular vesicles of kidney recruit Fn1+ macrophages to aggravate ischemia-reperfusion-induced inflammation

Ischemia-reperfusion injury-induced (IRI-induced) acute kidney injury is accompanied by mononuclear phagocyte (MP) invasion and inflammation. However, systematic analysis of extracellular vesicle-carried (EV-carried) proteins mediating intercellular crosstalk in the IRI microenvironment is still lacking. Multiomics analysis combining single-cell RNA-Seq data of kidney and protein profiling of kidney-EV was used to elucidate the intercellular communication between proximal tubular cells (PTs) and MP. Targeted adhesion and migration of various MPs were caused by the secretion of multiple chemokines as well as integrin β1-rich EV by ischemic-damaged PTs after IRI. These recruited MPs, especially Fn1+ macrophagocyte, amplified the surviving PT's inflammatory response by secreting the inflammatory factors TNF-α, MCP-1, and thrombospondin 1 (THBS-1), which could interact with integrin β1 to promote more MP adhesion and interact with surviving PT to further promote the secretion of IL-1β. However, GW4869 reduced MP infiltration and maintained a moderate inflammatory level likely by blocking EV secretion. Our findings establish the molecular bases by which chemokines and kidney-EV mediate PT-MP crosstalk in early IRI and provide insights into systematic intercellular communication.

Engineered Bone Marrow Stem Cell-Sheets Alleviate Renal Damage in a Rat Chronic Glomerulonephritis Model

Although mesenchymal stem cell (MSC)-based regenerative therapy is being developed for the treatment of kidney diseases, cell delivery and engraftment still need to be improved. Cell sheet technology has been developed as a new cell delivery method, to recover cells as a sheet form retaining intrinsic cell adhesion proteins, which promotes its transplantation efficiency to the target tissue. We thus hypothesized that MSC sheets would therapeutically reduce kidney disease with high transplantation efficiency. When the chronic glomerulonephritis was induced by two injections of the anti-Thy 1.1 antibody (OX-7) in rats, the therapeutic efficacy of rat bone marrow stem cell (rBMSC) sheet transplantation was evaluated. The rBMSC-sheets were prepared using the temperature-responsive cell-culture surfaces and transplanted as patches onto the surface of two kidneys of each rat at 24 h after the first injection of OX-7. At 4 weeks, retention of the transplanted MSC-sheets was confirmed, and the animals with MSC-sheets showed significant reductions in proteinuria, glomerular staining for extracellular matrix protein, and renal production of TGFß1, PAI-1, collagen I, and fibronectin. The treatment also ameliorated podocyte and renal tubular injury, as evidenced by a reversal in the reductions of WT-1, podocin, and nephrin and by renal overexpression of KIM-1 and NGAL. Furthermore, the treatment enhanced gene expression of regenerative factors, and IL-10, Bcl-2, and HO-1 mRNA levels, but reduced TSP-1 levels, NF-kB, and NAPDH oxidase production in the kidney. These results strongly support our hypothesis that MSC-sheets facilitated MSC transplantation and function, and effectively retarded progressive renal fibrosis via paracrine actions on anti-cellular inflammation, oxidative stress, and apoptosis and promoted regeneration.

Trained immunity - basic concepts and contributions to immunopathology

Trained immunity is a functional state of the innate immune response and is characterized by long-term epigenetic reprogramming of innate immune cells. This concept originated in the field of infectious diseases - training of innate immune cells, such as monocytes, macrophages and/or natural killer cells, by infection or vaccination enhances immune responses against microbial pathogens after restimulation. Although initially reported in circulating monocytes and tissue macrophages (termed peripheral trained immunity), subsequent findings indicate that immune progenitor cells in the bone marrow can also be trained (that is, central trained immunity), which explains the long-term innate immunity-mediated protective effects of vaccination against heterologous infections. Although trained immunity is beneficial against infections, its inappropriate induction by endogenous stimuli can also lead to aberrant inflammation. For example, in systemic lupus erythematosus and systemic sclerosis, trained immunity might contribute to inflammatory activity, which promotes disease progression. In organ transplantation, trained immunity has been associated with acute rejection and suppression of trained immunity prolonged allograft survival. This novel concept provides a better understanding of the involvement of the innate immune response in different pathological conditions, and provides a new framework for the development of therapies and treatment strategies that target epigenetic and metabolic pathways of the innate immune system.

A biocompatible nanoparticle-based approach to inhibiting renal ischemia reperfusion injury in mice by blocking thrombospondin-1 activity

Thrombospondin-1 (TSP-1) is a key mediator of renal ischemia-reperfusion injury (IRI), a major cause of kidney dysfunction under various disease conditions and a risk factor of renal allograft rejection. In this study, we developed a nanotechnology-based therapy targeting TSP-1 to prevent renal IRI. A biocompatible nanoparticle (NP) capable of specific binding to TSP-1 was prepared by conjugating NPs with TSP-1-binding (LSKL) peptides. LSKL/NPs not only effectively adsorbed recombinant TSP-1 proteins in vitro, but also efficiently neutralized TSP-1 in mice undergoing renal IRI. IRI-induced elevation of TSP-1 in the kidney was significantly inhibited by post-IR treatment with LSKL/NPs, but not free LSKL or NPs. Furthermore, TSP-1 proteins adsorbed on LSKL/NPs were functionally inactive and unable to induce apoptosis in renal tubular epithelial cells. Importantly, LSKL/NPs induced strong protection against renal IRI, as shown by markedly diminished serum creatinine levels and improved histological lesions of the kidney. Thus, LSKL/NPs provide a useful means of depleting and inactivating TSP-1 and a potential therapy for renal IRI.

Neuroblastoma suppressor of tumorigenicity 1 is a circulating protein associated with progression to end-stage kidney disease in diabetes

Circulating proteins associated with transforming growth factor-β (TGF-β) signaling are implicated in the development of diabetic kidney disease (DKD). It remains to be comprehensively examined which of these proteins are involved in the pathogenesis of DKD and its progression to end-stage kidney disease (ESKD) in humans. Using the SOMAscan proteomic platform, we measured concentrations of 25 TGF-β signaling family proteins in four different cohorts composed in total of 754 Caucasian or Pima Indian individuals with type 1 or type 2 diabetes. Of these 25 circulating proteins, we identified neuroblastoma suppressor of tumorigenicity 1 (NBL1, aliases DAN and DAND1), a small secreted protein known to inhibit members of the bone morphogenic protein family, to be most strongly and independently associated with progression to ESKD during 10-year follow-up in all cohorts. The extent of damage to podocytes and other glomerular structures measured morphometrically in 105 research kidney biopsies correlated strongly with circulating NBL1 concentrations. Also, in vitro exposure to NBL1 induced apoptosis in podocytes. In conclusion, circulating NBL1 may be involved in the disease process underlying progression to ESKD, and its concentration in circulation may identify subjects with diabetes at increased risk of progression to ESKD.

The Innate Cellular Immune Response in Xenotransplantation

Xenotransplantation is very attractive strategy for addressing the shortage of donors. While hyper acute rejection (HAR) caused by natural antibodies and complement has been well defined, this is not the case for innate cellular xenogeneic rejection. An increasing body of evidence suggests that innate cellular immune responses contribute to xenogeneic rejection. Various molecular incompatibilities between receptors and their ligands across different species typically have an impact on graft outcome. NK cells are activated by direct interaction as well as by antigen dependent cellular cytotoxicity (ADCC) mechanisms. Macrophages are activated through various mechanisms in xenogeneic conditions. Macrophages recognize CD47 as a "marker of self" through binding to SIRPα. A number of studies have shown that incompatibility of porcine CD47 against human SIRPα contributes to the rejection of xenogeneic target cells by macrophages. Neutrophils are an early responder cell that infiltrates xenogeneic grafts. It has also been reported that neutrophil extracellular traps (NETs) activate macrophages as damage-associated pattern molecules (DAMPs). In this review, we summarize recent insights into innate cellular xenogeneic rejection.

Thrombospondin 1 Promotes Endoplasmic Reticulum Stress and Apoptosis in HK-2 Cells by Upregulating ATF6-CHOP

OBJECTIVE

The goal of this study is to investigate the role and mechanism of endoplasmic reticulum stress and apoptosis regulated by thrombospondin 1 (TSP1) in human renal tubular epithelial cells (HK-2 cells).

METHODS

HK-2 cells were exposed to high concentrations of glucose (HG). The endoplasmic reticulum stress inhibitor 4-phenylbutyric acid (4-PBA) was administered by transfecting TSP1 or an empty vector to explore the mechanism of the endoplasmic reticulum response regulated by TSP1 and stress in renal cell apoptosis. The effects of TSP1 and 4-PBA on the proliferation and apoptosis of HK-2 cells under HG conditions were assessed using Cell counting kit-8 and flow cytometry. Western blotting was used to detect the apoptosis- and endoplasmic reticulum stress-related protein expression regulated by TSP1 and 4-PBA.

RESULTS

HG treatment induced high cell apoptosis, abundantly expressed TSP1 level and restrained viability in HK-2 cells. Overexpression of TSP1 significantly inhibited the proliferation of and facilitated apoptosis of HK-2 cells under HG conditions. Administration of endoplasmic reticulum stress inhibitor 4-PBA after overexpression of TSP1 antagonized the inhibitory proliferation and promoted apoptosis rate in HG-triggered HK-2 cells induced by TSP1 overexpression. 4-PBA treatment significantly hindered the expression of endoplasmic reticulum stress markers, such as PERK, ATF4, ATF6, p-eIF2α, IRE1, CHOP and XBP1, suggesting that the administration of 4-PBA was successful.

CONCLUSION

Overexpression of TSP1 activated endoplasmic reticulum stress by regulating the ATF6-CHOP axis. TSP1 restrained cell proliferation, and promoted apoptosis and endoplasmic reticulum stress by activating the ATF6-CHOP axis.

USF2 knockdown downregulates THBS1 to inhibit the TGF-β signaling pathway and reduce pyroptosis in sepsis-induced acute kidney injury

OBJECTIVE

Acute kidney injury (AKI) is a serious complication of sepsis. This study was performed to explore the mechanism that THBS1 mediated pyroptosis by regulating the TGF-β signaling pathway in sepsis-induced AKI.

METHODS

Gene expression microarray related to sepsis-induced AKI was obtained from the GEO database, and the mechanism in sepsis-induced AKI was predicted by bioinformatics analysis. qRT-PCR and ELISA were performed to detect expressions of THBS1, USF2, TNF-α, IL-1β, and IL-18 in sepsis-induced AKI patients and healthy volunteers. The mouse model of sepsis-induced AKI was established, with serum creatinine, urea nitrogen, 24-h urine output measured, and renal tissue lesions observed by HE staining. The cell model of sepsis-induced AKI was cultured in vitro, with expressions of TNF-α, IL-1β, and IL-18, pyroptosis, Caspase-1 and GSDMD-N, and activation of TGF-β/Smad3 pathway detected. The upstream transcription factor USF2 was knocked down in cells to explore its effect on sepsis-induced AKI.

RESULTS

THBS1 and USF2 were highly expressed in patients with sepsis-induced AKI. Silencing THBS1 protected mice against sepsis-induced AKI, and significantly decreased the expressions of NLRP3, Caspase-1, GSDMD-N, IL-1β, and IL-18, increased cell viability, and decreased LDH activity, thus partially reversing the changes in cell morphology. Mechanistically, USF2 promoted oxidative stress responses by transcriptionally activating THBS1 to activate the TGF-β/Smad3/NLRP3/Caspase-1 signaling pathway and stimulate pyroptosis, and finally exacerbated sepsis-induced AKI.

CONCLUSION

USF2 knockdown downregulates THBS1 to inhibit the TGF-β/Smad3 signaling pathway and reduce pyroptosis and further ameliorate sepsis-induced AKI.

Efficient Ex Vivo Screening of Agents Targeting Thrombospondin1-Induced Vascular Dysfunction Using a Digital Multiwire Myograph System

Homeostasis of vascular tone is intricately and delicately maintained systemically and locally, by autonomic nerves and hormones in the blood and by intimal vasoactive substances, respectively. The balance can be acutely or chronically interrupted secondary to many alterations, especially under pathological conditions. Excessive matricellular glycoprotein thrombospondin 1 (TSP1) levels in circulation have been found to play an important role in ischemia-reperfusion injuries of different organs, by acutely suppressing vasorelaxation and chronically remodeling vascular bed. Our laboratory has been interested in identifying new drug moieties, which can selectively and effectively counteract TSP1-induced vascular dysfunction, in order to address associated clinical complications. Preliminary studies using computational docking and molecular models revealed potential drug candidates for further evaluation via vascular functional bioassay to prove the antagonism using an ex vivo vascular model. Herein, we described an efficient screening method for the identification of active drug candidates, by adapting a multiwire myograph system to perform a protocol with different treatments, in the presence of pathological levels of TSP1. We discussed the promising pharmacological evaluation results and suggested suitable modification for versatile applications. We also described the necessity of pre-determination of optimal resting tension to obtain the maximal response, if the experimental test model is different from those with determined optimal resting tension.

Expression of human CD47 in pig glomeruli prevents proteinuria and prolongs graft survival following pig-to-baboon xenotransplantation

BACKGROUND

Nephrotic syndrome is a common complication of pig-to-baboon kidney xenotransplantation (KXTx) that adversely affects outcomes. We have reported that upregulation of CD80 and down-regulation of SMPDL-3b in glomeruli have an important role in the development of proteinuria following pig-to-baboon KXTx. Recently we found induced expression of human CD47 (hCD47) on endothelial cells and podocytes isolated from hCD47 transgenic (Tg) swine markedly reduced phagocytosis by baboon and human macrophages. These observations led us to hypothesize that transplanting hCD47 Tg porcine kidneys could overcome the incompatibility of the porcine CD47-baboon SIRPα interspecies ligand-receptor interaction and prevent the development of proteinuria following KXTx.

METHODS

Ten baboons received pig kidneys with vascularized thymic grafts (n = 8) or intra-bone bone marrow transplants (n = 2). Baboons were divided into three groups (A, B, and C) based on the transgenic expression of hCD47 in GalT-KO pigs. Baboons in Group A received kidney grafts with expression of hCD47 restricted to glomerular cells (n = 2). Baboons in Group B received kidney grafts with high expression of hCD47 on both glomerular and tubular cells of the kidneys (n = 4). Baboons in Group C received kidney grafts with low/no glomerular expression of hCD47, and high expression of hCD47 on renal tubular cells (n = 4).

RESULTS

Consistent with this hypothesis, GalT-KO/hCD47 kidney grafts with high expression of hCD47 on glomerular cells developed minimal proteinuria. However, high hCD47 expression in all renal cells including renal tubular cells induced an apparent destructive inflammatory response associated with upregulated thrombospondin-1. This response could be avoided by a short course of weekly anti-IL6R antibody administration, resulting in prolonged survival without proteinuria (mean 170.5 days from 47.8 days).

CONCLUSION

Data showed that transgenic expression of hCD47 on glomerular cells in the GalT-KO donor kidneys can prevent xenograft nephropathy, a significant barrier for therapeutic applications of xenotransplantation. The ability to prevent nephrotic syndrome following KXTx overcomes a critical barrier for future clinical applications of KXTx.

Endothelial-Derived miR-17∼92 Promotes Angiogenesis to Protect against Renal Ischemia-Reperfusion Injury

BACKGROUND

Damage to the renal microvasculature is a hallmark of renal ischemia-reperfusion injury (IRI)-mediated AKI. The miR-17∼92 miRNA cluster (encoding miR-17, -18a, -19a, -20a, -19b-1, and -92a-1) regulates angiogenesis in multiple settings, but no definitive role in renal endothelium during AKI pathogenesis has been established.

METHODS

Antibodies bound to magnetic beads were utilized to selectively enrich for renal endothelial cells from mice. Endothelial-specific miR-17∼92 knockout (miR-17∼92endo-/- ) mice were generated and given renal IRI. Mice were monitored for the development of AKI using serum chemistries and histology and for renal blood flow using magnetic resonance imaging (MRI) and laser Doppler imaging. Mice were treated with miRNA mimics during renal IRI, and therapeutic efficacies were evaluated.

RESULTS

miR-17, -18a, -20a, -19b, and pri-miR-17∼92 are dynamically regulated in renal endothelial cells after renal IRI. miR-17∼92endo-/- exacerbates renal IRI in male and female mice. Specifically, miR-17∼92endo-/- promotes renal tubular injury, reduces renal blood flow, promotes microvascular rarefaction, increases renal oxidative stress, and promotes macrophage infiltration to injured kidneys. The potent antiangiogenic factor thrombospondin 1 (TSP1) is highly expressed in renal endothelium in miR-17∼92endo-/- after renal IRI and is a target of miR-18a and miR-19a/b. miR-17∼92 is critical in the angiogenic response after renal IRI, which treatment with miR-18a and miR-19b mimics can mitigate.

CONCLUSIONS

These data suggest that endothelial-derived miR-17∼92 stimulates a reparative response in damaged renal vasculature during renal IRI by regulating angiogenic pathways.

Improving Liver Graft Function Using CD47 Blockade in the Setting of Normothermic Machine Perfusion

BACKGROUND

Towards the goal of utilizing more livers for transplantation, transplant centers are looking to increase the use of organs from "marginal" donors. Livers from these donors, however, have been shown to be more susceptible to preservation and reperfusion injury.

METHODS

Using a porcine model of donation after circulatory death (DCD), we studied the use of antibody-mediated CD47 blockade to further improve liver graft function undergoing normothermic machine perfusion. Livers from 20 pigs (5 per group) were brought under either 30 or 60 minutes of warm ischemia time (WIT) followed by the administration of CD47mAb treatment or IgG control antibodies and 6 hours of normothermic extracorporeal liver perfusion (NELP).

RESULTS

After 6 hours of NELP, CD47mAb-treated livers with 30 or 60 minutes WIT had significantly lower ALT levels and higher bile production compared to their respective control groups. Blockade of the CD47 signaling pathway resulted in significantly lower TSP-1 protein levels, lower expression of Caspase-3, and higher expression of pERK.

CONCLUSIONS

These findings suggested that CD47mAb treatment decreases ischemia/reperfusion injury through CD47/TSP-1 signaling downregulation and the presence of necrosis/apoptosis after reperfusion, and could increase liver regeneration during normothermic perfusion of the liver.Supplemental Visual Abstract; http://links.lww.com/TP/C146.

Peritubular Capillary Rarefaction: An Underappreciated Regulator of CKD Progression

Peritubular capillary (PTC) rarefaction is commonly detected in chronic kidney disease (CKD) such as hypertensive nephrosclerosis and diabetic nephropathy. Moreover, PTC rarefaction prominently correlates with impaired kidney function and predicts the future development of end-stage renal disease in patients with CKD. However, it is still underappreciated that PTC rarefaction is a pivotal regulator of CKD progression, primarily because the molecular mechanisms of PTC rarefaction have not been well-elucidated. In addition to the established mechanisms (reduced proangiogenic factors and increased anti-angiogenic factors), recent studies discovered significant contribution of the following elements to PTC loss: (1) prompt susceptibility of PTC to injury, (2) impaired proliferation of PTC, (3) apoptosis/senescence of PTC, and (4) pericyte detachment from PTC. Mainly based on the recent and novel findings in basic research and clinical study, this review describes the roles of the above-mentioned elements in PTC loss and focuses on the major factors regulating PTC angiogenesis, the assessment of PTC rarefaction and its surrogate markers, and an overview of the possible therapeutic agents to mitigate PTC rarefaction during CKD progression. PTC rarefaction is not only a prominent histological characteristic of CKD but also a central driving force of CKD progression.

A novel biomarker of chronic allograft dysfunction in renal transplant recipients (serum calreticulin and CD47)

Background

Chronic allograft dysfunction (CAD) is considered the leading cause of late allograft loss. The cluster of differentiation 47 (CD47) and calreticulin (CRT) are involved in many and diverse cellular processes. The present study was designed to study the role of the pro-phagocytic CRT and anti-phagocytic CD47 signals in patients with renal transplantation in relation to graft function.

Thirty renal transplantation recipients (RTR) for more than 6 months [15 with stable renal function and 15 with chronic allograft dysfunction (CAD)] and 15 healthy controls were enrolled in the study. Quantification of CRT, CD47, and high-sensitivity C-reactive protein (hsCRP) levels in serum was done using standardized enzyme-linked immunosorbent assay (ELISA) kits. Measurement of renal function and urinary alkaline phosphatase (U.ALP) was done. Renal interstitial fibrosis (IF) was graded in renal biopsies of CAD.

Results

Serum CRT and urinary ALP levels were statistically significant higher (P < 0.001) while serum CD47 level was statistically significant lower (P < 0.001) in patients with CAD than patients with stable graft function and controls. There was statistically insignificant difference between controls and patients with stable graft function. Serum CRT and serum CD47 levels were positively correlated with each other and with worsening renal and tubular function, serum hsCRP in RTR and with degree of renal IF in patients with CAD (P < 0.05).

Conclusions

The activation and dysregulation of CRT and CD47 could play a role in the development of CAD and could be a potential biomarker for renal allograft dysfunction.

The role of thrombospondin-1 in the pathogenesis of antiphospholipid syndrome

OBJECTIVE

Antiphospholipid syndrome (APS) is an acquired thrombophilia characterized by recurrent thrombosis and/or pregnancy morbidity, in the presence of antibodies to β2 glycoprotein-I (β2GPI), prothrombin or Lupus anticoagulant (LA). Anti-β2GPI antibodies recognize complexes of β2GPI dimers with CXCL4 chemokine and activate platelets. Thrombospondin 1 (TSP-1) is secreted by platelets and exhibits prothrombotic and proinflammatory properties. Therefore, we investigated its implication in APS.

METHODS

Plasma from APS patients (n = 100), Systemic Lupus Erythematosus (SLE) (n = 27) and healthy donors (HD) (n = 50) was analyzed for TSP-1, IL-1β, IL-17A and free active TGF-β1 by ELISA. Human Umbilical Vein Endothelial Cells (HUVECs) and HD monocytes were treated with total HD-IgG or anti-β2GPI, β2GPI and CXCL4 and CD4⁺ T-cells were stimulated by monocyte supernatants. TSP-1, IL-1β, IL-17A TGF-β1 levels were quantified by ELISA and Real-Time PCR.

RESULTS

Higher plasma levels of TSP-1 and TGF-β1, which positively correlated each other, were observed in APS but not HDs or SLE patients. Patients with arterial thrombotic events or those undergoing a clinical event had the highest TSP-1 levels. These patients also had detectable IL-1β, IL-17A in their plasma. HD-derived monocytes and HUVECs stimulated with anti-β2GPI-IgG-β2GPI-CXCL4 secreted the highest TSP-1 and IL-1β levels. Supernatants from anti-β2GPI-β2GPI-CXCL4 treated monocytes induced IL-17A expression from CD4⁺ T-cells. Transcript levels followed a similar pattern.

CONCLUSIONS

TSP-1 is probably implicated in the pathogenesis of APS. In vitro cell treatments along with high TSP-1 levels in plasma of APS patients suggest that high TSP-1 levels could mark a prothrombotic state and an underlying inflammatory process.

Thrombospondin-1 in maladaptive aging responses: a concept whose time has come

Numerous age-dependent alterations at the molecular, cellular, tissue and organ systems levels underlie the pathophysiology of aging. Herein, the focus is upon the secreted protein thrombospondin-1 (TSP1) as a promoter of aging and age-related diseases. TSP1 has several physiological functions in youth, including promoting neural synapse formation, mediating responses to ischemic and genotoxic stress, minimizing hemorrhage, limiting angiogenesis, and supporting wound healing. These acute functions of TSP1 generally require only transient expression of the protein. However, accumulating basic and clinical data reinforce the view that chronic diseases of aging are associated with accumulation of TSP1 in the extracellular matrix, which is a significant maladaptive contributor to the aging process. Identification of the relevant cell types that chronically produce and respond to TSP1 and the molecular mechanisms that mediate the resulting maladaptive responses could direct the development of therapeutic agents to delay or revert age-associated maladies.

Current Status of Novel Biomarkers for the Diagnosis of Acute Kidney Injury: A Historical Perspective

Acute kidney injury (AKI) is a common and serious medical condition associated with significant increases in morbidity, mortality, and cost of care. Because of the high incidence and poor outcomes associated with AKI, there has been significant interest in the development of new therapies for the prevention and treatment of the disease. A lack of efficacy in drug trials led to the concern that AKI was not being diagnosed early enough for an effective intervention and that a rise in serum creatinine itself is not a sensitive-enough marker. Researchers have been searching for novel biomarkers that can not only assess a decline in kidney function but also demonstrate structural damage to the kidney and at time points earlier than increases in serum creatinine measurements allow. Over the past 10 years, there have been 3300 new publications and hundreds of new biomarkers investigated, yet concern still remains regarding AKI biomarker performance. The AKI biomarkers are yet to be widely utilized in clinical practice, leading some to question whether AKI biomarkers will ever reach their initial promise. However, we believe that biomarkers are an important part of current and future AKI research and clinical management. In this review, we compare the historical contexts of acute myocardial ischemia and AKI biomarker development to illustrate the progress that has been made within AKI biomarker research in a relatively short period of time and also to point out key differences between the disease processes that have been barriers to widespread AKI biomarker adoption. Finally, we discuss potential paths by which biomarkers can lead to appropriate AKI treatment responses that lower morbidity and mortality.

LncRNA GAS5 promotes apoptosis as a competing endogenous RNA for miR-21 via thrombospondin 1 in ischemic AKI

Mounting evidence has indicated that long noncoding RNAs (lncRNAs) and microRNAs (miRNAs) played important roles in renal ischemia/reperfusion (I/R) injury. However, the involvement of lncRNA growth arrest specific 5 (GAS5) in acute kidney injury (AKI) remained largely unexplored. This study aimed to determine possible mechanisms of GAS5 in the renal I/R process. We found that GAS5, noticeably upregulated by renal I/R injury, was further suppressed by delayed IPC while knockdown of miR-21 in vivo before IPC could significantly increased the GAS5 levels. Concurrently, TSP-1 was negatively regulated by miR-21 in vivo and vitro. Additionally, Reciprocal repression of GAS5 and miR-21 was identified. Knockdown of miR-21 in H6R0.5 treated HK-2 cells promoted apoptosis. Co-transfection of miR-21 mimic and pcDNA-GAS5 or pcDNA-Vector were performed, results of which showed that inhibition of miR-21 on TSP-1 could be rescued by overexpression of GAS5. This study suggested that GAS5 facilitated apoptosis by competitively sponging miR-21, which negatively regulated TSP-1 in renal I/R injury. This novel regulatory axis could act as a therapeutic target for AKI in the future.

A Boolean Model of Microvascular Rarefaction to Predict Treatment Outcomes in Renal Disease

Despite advances in renovascular disease (RVD) research, gaps remain between experimental and clinical outcomes, translation of results, and the understanding of pathophysiological mechanisms. A predictive tool to indicate support (or lack of) for biological findings may aid clinical translation of therapies. We created a Boolean model of RVD and hypothesized that it would predict outcomes observed in our previous studies using a translational swine model of RVD. Our studies have focused on developing treatments to halt renal microvascular (MV) rarefaction in RVD, a major feature of renal injury. A network topology of 20 factors involved in renal MV rarefaction that allowed simulation of 5 previously tested treatments was created. Each factor was assigned a function based upon its interactions with other variables and assumed to be “on” or “off”. Simulations of interventions were performed until outcomes reached a steady state and analyzed to determine pathological processes that were activated, inactivated, or unchanged vs. RVD with no intervention. Boolean simulations mimicked the results of our previous studies, confirming the importance of MV integrity on treatment outcomes in RVD. Furthermore, our study supports the potential application of a mathematical tool to predict therapeutic feasibility, which may guide the design of future studies for RVD.

The role of CD47 in pathogenesis and treatment of renal ischemia reperfusion injury

Ischemia reperfusion (IR) injury is a process defined by the temporary loss of blood flow and tissue perfusion followed later by restoration of the same. Brief periods of IR can be tolerated with little permanent deficit, but sensitivity varies for different target cells and tissues. Ischemia reperfusion injuries have multiple causes including peripheral vascular disease and surgical interventions that disrupt soft tissue and organ perfusion as occurs in general and reconstructive surgery. Ischemia reperfusion injury is especially prominent in organ transplantation where substantial effort has been focused on protecting the transplanted organ from the consequences of IR. A number of factors mediate IR injury including the production of reactive oxygen species and inflammatory cell infiltration and activation. In the kidney, IR injury is a major cause of acute injury and secondary loss of renal function. Transplant-initiated renal IR is also a stimulus for innate and adaptive immune-mediated transplant dysfunction. The cell surface molecule CD47 negatively modulates cell and tissue responses to stress through limitation of specific homeostatic pathways and initiation of cell death pathways. Herein, a summary of the maladaptive activities of renal CD47 will be considered as well as the possible therapeutic benefit of interfering with CD47 to limit renal IR.

The Protective Effects of Thymosin-β-4 in a Rat Model of Ischemic Acute Kidney Injury

BACKGROUND

Despite the progress in the treatment of acute kidney injury (AKI), current curative approaches fail to provide adequate treatment. In this study, we aimed to investigate the possible protective effects of thymosin-β-4(Tβ4) on an ischemic AKI model in rats.

METHODS

Rats were randomly assigned into four groups (n = 8/group): The control group (sham-operated), the ischemia-reperfusion (I/R) group; renal ischemia (90 min) by infrarenal abdominal aortic occlusion followed by reperfusion (3 h), the Tβ4 + I/R group; treated with Tβ4 before I/R, and the I/Tβ4/R group; treated with Tβ4 just before reperfusion. Besides renal function determination (creatinine (Cr) and blood urea nitrogen (BUN)); histological evaluation was also conducted. Renal tissue caspase-9, matrix metalloproteinase (MMP-9) activities, and hyaluronan levels were measured. Additionally, renal tissue oxidative stress (lipid hydroperoxide, malondialdehyde, superoxide dismutase, glutathione, pro-oxidant-antioxidant balance, ferric reducing antioxidant power, nitric oxide), inflammation (tumor necrosis factor-α, interleukin-1β, interleukin-6, nuclear factor-κβ) were evaluated.

RESULTS

I/R increased the level of caspase-9, MMP-9 activity, and hyaluronan (p < 0.001) and these were significantly decreased in both Tβ4 groups. Moreover, I/R led to increases in oxidative stress and inflammation parameters (p < 0.001) while the levels of antioxidants were decreased. Nevertheless, Tβ4 in both groups were able to restore oxidative stress and inflammation parameters. Furthermore, Tβ4 attenuated histologic injury caused by I/R (p < 0.01) and diminished serum urea-creatinine levels (p < 0.001).

CONCLUSION

These results suggest that Tβ4 has significant improving effects in ischemic acute kidney injury. This beneficial effect might be a result of the inhibition of extracellular matrix remodeling and apoptosis cascade via modulation in renal redox status and inflammation.

CD47 limits autophagy to promote acute kidney injury

Acute kidney injury (AKI) initiates a complex pathophysiological cascade leading to epithelial cell death. Recent studies identify autophagy, a key intracellular process that degrades cytoplasmic constituents, as protective against AKI. We have previously reported that the protein thrombospondin-1 and its receptor CD47 are induced in AKI; however, the mechanism underlying their regulation of injury is unknown. Here, we investigated whether CD47 signaling affects autophagy to regulate AKI. Wild-type (WT) and CD47^-/- mice were challenged with renal ischemia-reperfusion injury. All animals underwent analysis of renal function and biomolecular phenotyping. CD47^-/- mice were resistant to AKI, with decreased serum creatinine and ameliorated histologic changes compared with WT animals. These mice also displayed increased abundance of key autophagy genes, including autophagy-related gene (Atg)5, Atg7, beclin-1, and microtubule-associated proteins 1A/1B light chain 3 (LC3) at baseline and post-AKI, which were significantly reduced in WT mice. Changes in protein expression correlated with increased autophagosome and autolysosome formation in renal tubular epithelial cells (RTECs). In mouse kidney transplantation, treatment with a CD47-blocking antibody that improved function was associated with increased autophagy compared with control mice. Primary isolated RTECs from CD47^-/- mice demonstrated increased basal expression of several autophagy components that was preserved under hypoxic stress. These data suggest that activated CD47 promotes AKI through inhibition of autophagy and point to CD47 as a target to preserve renal function following injury.-El-Rashid, M., Ghimire, K., Sanganeria, B., Lu, B., Rogers, N. M. CD47 limits autophagy to promote acute kidney injury.

CD47 deficiency protects cardiomyocytes against hypoxia/reoxygenation injury by rescuing autophagic clearance

To assess the effect of cluster of differentiation (CD47) downregulation on autophagy in hypoxia/reoxygenation (H/R)‑treated H9c2 cardiomyocytes. H9c2 cells were maintained in normoxic conditions (95% air, 5% CO2, 37˚C) without CD47 antibodies, Si‑CD47 or chloroquine (CQ) treatment; H9c2 cells in the H/R group were subjected to 24 h of hypoxia (1% O2, 94% N2, 5% CO2, 37˚C) followed by 12 h of reoxygenation (95% air, 5% CO2, 37˚C). All assays were controlled, triplicated and repeated on three separately initiated cultures. The biochemical parameters in the medium supernatant were measured to evaluate the oxidative stress in cardiomyocytes. The Annexin V‑fluorescein isothiocyanate assay was used to detect the apoptotic rate in the H9c2 cells. Transmission electron microscope, immunofluorescent staining and western blot analysis were performed to detect the effect of the CD47 antibody on autophagic flux in H/R‑treated H9c2 cardiomyocytes. The cardiomyocytic oxidative stress and apoptotic rate decreased and autophagic clearance increased after CD47 downregulation. H/R triggered cell autophagy, autophagosome accumulation and apoptosis in H9c2 cell lines. However, these effects can be attenuated by CD47 downregulation. This study demonstrates its clinical implications in ischemia/reperfusion injury treatment.

Effect of long non-coding RNA growth arrest-specific 5 on apoptosis in renal ischaemia/reperfusion injury

AIM

Long non-coding RNA (lncRNAs) have been shown to play a critical role in a variety of pathophysiological processes, such as cell proliferation, apoptosis and migration. However, there were few studies addressing the function of lncRNAs in renal ischaemia/reperfusion (I/R) injury. Apoptosis is an important pathogenesis during I/R injury. Here, we identified the effect of hypoxia-responsive lncRNA growth arrest-specific 5 (GAS5) on apoptosis in renal I/R injury.

METHODS

Ischaemia/reperfusion injury in mice or hypoxia/re-oxygenation (H/R) in human proximal renal tubular epithelial cells (HK-2) was practiced to induce apoptosis. The kidneys and blood were collected at 24 h after reperfusion. The GAS5 messenger RNA (mRNA) expression and apoptosis-related gene mRNA and protein levels, including p53, cellular inhibitor of apoptosis protein 2 (cIAP2) and thrombospondin-1 (TSP-1), were analysed. GAS5 small-interfering RNA was transfected with H/R induced cells. Over-expression of GAS5 was performed by plasmid transfection.

RESULTS

Apoptotic cells significantly increased in I/R-injured kidneys. GAS5 could be up-regulated in kidneys at 24 h after reperfusion and 3 h after re-oxygenation, combined with increased expression of its downstream apoptosis-related proteins p53 and cIAP2. GAS5 small-interfering RNA treatment down-regulated the mRNA and protein levels of p53 and TSP-1, and attenuated apoptosis induced by H/R in HK-2 cells. Conversely, over-expression of GAS5 up-regulated the mRNA and protein levels of p53 and TSP-1, and promoted apoptosis in HK-2 cells.

CONCLUSION

Long non-coding RNA GAS5 induced by I/R injury could promote apoptosis in kidney. TSP-1 might be one of the downstream effectors of GAS5, which will be explored in the future.

Elimination of donor CD47 protects against vascularized allograft rejection in mice

CD47 is a ubiquitously expressed transmembrane glycoprotein that plays a complex role in regulation of cell survival and function. We have previously shown that the interspecies incompatibility of CD47 plays an important role in triggering rejection of cellular xenografts by macrophages. However, the role of CD47 in solid organ transplantation remains undetermined. Here, we explored this question in mouse models of heart allotransplantation. We observed that the lack of CD47 in donor hearts had no deleterious effect on graft survival in syngeneic or single MHC class I-mismatched recipients, in which both wild-type (WT) and CD47 knockout (CD47 KO) mouse hearts survived long term with no sign of rejection. Paradoxically, elimination of donor CD47 was beneficial for graft survival in signal MHC class II- and class I- plus class II-mismatched combinations, in which CD47 KO donor hearts showed significantly improved survival compared to WT donor hearts. Similarly, CD47 KO donor hearts were more resistant than WT hearts to humoral rejection in α1,3-galactosyltransferase-deficient mice. Moreover, a significant prolongation of WT allografts was observed in recipient mice treated with antibodies against a CD47 ligand thrombospondin-1 (TSP1) or with TSP1 deficiency, indicating that TSP1-CD47 signaling may stimulate vascularized allograft rejection. Thus, unlike cellular transplantation, donor CD47 expression may accelerate the rejection of vascularized allografts.

Hypercholesterolemia-induced increase in plasma oxidized LDL abrogated pro angiogenic response in kidney grafts

BACKGROUND

Renal transplantation is increasingly associated with the presence of comorbidity factors such as dyslipidemia which could influence the graft outcome. We hypothesized that hypercholesterolemia could affect vascular repair processes and promote post-transplant renal vascular remodeling through the over-expression of the anti-angiogenic thrombospondin-1 interacting with vascular endothelial growth factor-A levels.

METHODS

We tested this hypothesis in vitro, in vivo and in a human cohort using (1) endothelial cells; (2) kidney auto-transplanted pig subjected (n = 5) or not (n = 6) to a diet enriched in cholesterol and (3) a renal transplanted patient cohort (16 patients).

RESULTS

Cells exposed to oxidized LDL showed reduced proliferation and an increased expression of thrombospondin-1. In pigs, 3 months after transplantation of kidney grafts, we observed a deregulation of the hypoxia inducible factor 1a-vascular endothelial growth factor-A axis induced in cholesterol-enriched diet animals concomitant with an overexpression of thrombospondin-1 and a decrease in cortical microvessel density promoting vascular remodeling. In patients, hypercholesterolemia was associated with decreased vascular endothelial growth factor-A plasma levels during early follow up after renal transplantation and increased chronic graft dysfunction.

CONCLUSIONS

These results support a potential mechanism through which a high fat-diet impedes vascular repair in kidney graft and suggest the value of controlling cholesterolemia in recipient even at the early stage of renal transplantation.

Podocyte-Specific Induction of Krüppel-Like Factor 15 Restores Differentiation Markers and Attenuates Kidney Injury in Proteinuric Kidney Disease

BACKGROUND

Podocyte injury is the hallmark of proteinuric kidney diseases, such as FSGS and minimal change disease, and destabilization of the podocyte's actin cytoskeleton contributes to podocyte dysfunction in many of these conditions. Although agents, such as glucocorticoids and cyclosporin, stabilize the actin cytoskeleton, systemic toxicity hinders chronic use. We previously showed that loss of the kidney-enriched zinc finger transcription factor Krüppel-like factor 15 (KLF15) increases susceptibility to proteinuric kidney disease and attenuates the salutary effects of retinoic acid and glucocorticoids in the podocyte.

METHODS

We induced podocyte-specific KLF15 in two proteinuric murine models, HIV-1 transgenic (Tg26) mice and adriamycin (ADR)-induced nephropathy, and used RNA sequencing of isolated glomeruli and subsequent enrichment analysis to investigate pathways mediated by podocyte-specific KLF15 in Tg26 mice. We also explored in cultured human podocytes the potential mediating role of Wilms Tumor 1 (WT1), a transcription factor critical for podocyte differentiation.

RESULTS

In Tg26 mice, inducing podocyte-specific KLF15 attenuated podocyte injury, glomerulosclerosis, tubulointerstitial fibrosis, and inflammation, while improving renal function and overall survival; it also attenuated podocyte injury in ADR-treated mice. Enrichment analysis of RNA sequencing from the Tg26 mouse model shows that KLF15 induction activates pathways involved in stabilization of actin cytoskeleton, focal adhesion, and podocyte differentiation. Transcription factor enrichment analysis, with further experimental validation, suggests that KLF15 activity is in part mediated by WT1.

CONCLUSIONS

Inducing podocyte-specific KLF15 attenuates kidney injury by directly and indirectly upregulating genes critical for podocyte differentiation, suggesting that KLF15 induction might be a potential strategy for treating proteinuric kidney disease.

Matricellular protein thrombospondin-1 in pulmonary hypertension: multiple pathways to disease

Matricellular proteins are secreted molecules that have affinities for both extracellular matrix and cell surface receptors. Through interaction with structural proteins and the cells that maintain the matrix these proteins can alter matrix strength. Matricellular proteins exert control on cell activity primarily through engagement of membrane receptors that mediate outside-in signaling. An example of this group is thrombospondin-1 (TSP1), first identified as a component of the secreted product of activated platelets. As a result, TSP1 was initially studied in relation to coagulation, growth factor signaling and angiogenesis. More recently, TSP1 has been found to alter the effects of the gaseous transmitter nitric oxide (NO). This latter capacity has provided motivation to study TSP1 in diseases associated with loss of NO signaling as observed in cardiovascular disease and pulmonary hypertension (PH). PH is characterized by progressive changes in the pulmonary vasculature leading to increased resistance to blood flow and subsequent right heart failure. Studies have linked TSP1 to pre-clinical animal models of PH and more recently to clinical PH. This review will provide analysis of the vascular and non-vascular effects of TSP1 that contribute to PH, the experimental and translational studies that support a role for TSP1 in disease promotion and frame the relevance of these findings to therapeutic strategies.

Fenofibrate protects against acute myocardial I/R injury in rat by suppressing mitochondrial apoptosis as decreasing cleaved caspase-9 activation

BACKGROUND AND AIMS

Peroxisome proliferator-activated receptor-α (PPAR-α) activation has been reported to reduce myocardial ischemia-reperfusion (I/R) injury by inhibiting cell apoptosis. However, the antiapoptotic mechanism of PPAR-α is still unknown. Fenofibrate is a PPAR-α agonist In the present study, we investigate the effects and relevant mechanism of fenofibrate on experimental myocardial ischemia-reperfusion (I/R) injury in rats.

METHODS

Adult male Wistar rats were pretreated with fenofibrate (80 mg/kg) daily for a period of 7 days. After the treatment period, myocardial I/R injury model was made by left anterior descending coronary artery ligation for 45 min and reperfusion for 120 min. Myocardial infarct size, malondialdehyde (MDA) cleaved-caspase-9 protein expression, PPARα and uncoupling protein 2 (UCP2) mRNA levels in myocardial tissue were detected Cell apoptosis was detected by Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). Serum lactate dehydrogenase and creatine kinase activities were measured in rats pretreated with fenofibrate The ultrastructure of myocardial tissues was observed.

RESULTS

Significant increases in myocardial cell apoptosis, malondialdehyde (MDA) level and cleaved-caspase-9 protein expression level in myocardial tissue were observed, along with reductions of PPARα and uncoupling protein 2 (UCP2) mRNA levels in myocardial tissue of the experimental myocardial ischemia-reperfusion (I/R) injury in rats. Impaired mitochondria were also observed under electron microscopic. However, pretreatment of ischemia/reperfusion rats with fenofibrate brought the biochemical parameters and related genes expression levels to near normalcy, indicating the protective effect of fenofibrate against myocardial ischemia/reperfusion injury in rats.

CONCLUSIONS

The PPAR-α activator fenofibrate conferred cytoprotective effect against myocardial ischemia-reperfusion (I/R) injury in rats. Associated mechanisms involved decreased cleaved-caspase-9 expression and decreased cell apoptosis.

Regulation of Cellular Redox Signaling by Matricellular Proteins in Vascular Biology, Immunology, and Cancer

SIGNIFICANCE

In contrast to structural elements of the extracellular matrix, matricellular proteins appear transiently during development and injury responses, but their sustained expression can contribute to chronic disease. Through interactions with other matrix components and specific cell surface receptors, matricellular proteins regulate multiple signaling pathways, including those mediated by reactive oxygen and nitrogen species and H2S. Dysregulation of matricellular proteins contributes to the pathogenesis of vascular diseases and cancer. Defining the molecular mechanisms and receptors involved is revealing new therapeutic opportunities. Recent Advances: Thrombospondin-1 (TSP1) regulates NO, H2S, and superoxide production and signaling in several cell types. The TSP1 receptor CD47 plays a central role in inhibition of NO signaling, but other TSP1 receptors also modulate redox signaling. The matricellular protein CCN1 engages some of the same receptors to regulate redox signaling, and ADAMTS1 regulates NO signaling in Marfan syndrome. In addition to mediating matricellular protein signaling, redox signaling is emerging as an important pathway that controls the expression of several matricellular proteins.

CRITICAL ISSUES

Redox signaling remains unexplored for many matricellular proteins. Their interactions with multiple cellular receptors remains an obstacle to defining signaling mechanisms, but improved transgenic models could overcome this barrier.

FUTURE DIRECTIONS

Therapeutics targeting the TSP1 receptor CD47 may have beneficial effects for treating cardiovascular disease and cancer and have recently entered clinical trials. Biomarkers are needed to assess their effects on redox signaling in patients and to evaluate how these contribute to their therapeutic efficacy and potential side effects. Antioxid. Redox Signal. 27, 874-911.

Renal Protection Mediated by Hypoxia Inducible Factor-1α Depends on Proangiogenesis Function of miR-21 by Targeting Thrombospondin 1

Background

Angiogenesis contributes to the repair process after renal ischemia/reperfusion (I/R) injury. In the present study, we tested the role of miR-21 in the angiogenesis induced by hypoxia inducible factor (HIF)-1α through inhibiting a predicted target gene thrombospondin 1 (TSP-1).

Methods

To stabilize HIF-1α, hypoxia (1% O₂ for 24 hours) was performed in human umbilical vein endothelial cells and cobalt chloride (CoCl₂) was pretreated intraperitoneally 24 hours before renal I/R in mice. Locked nucleic acid modified anti-miR-21 and scrambled control was transfected with hypoxic cells or delivered into the mice via tail vein 1 hour before CoCl₂ injection. The kidneys and blood were collected at 24 hours after reperfusion.

Results

HIF-1α induced by hypoxia and CoCl₂ upregulated vascular endothelial growth factor and miR-21, and increased angiogenesis. It was found that expression of TSP-1 was inversely related with miR-21 in vitro and in vivo. Targeting of TSP-1 by miR-21 was further confirmed in vitro. Furthermore, HIF-1α improved renal function, accompanied with increased angiogenesis after I/R injury in mice. The protective effect of HIF-1α was attenuated by inhibition of miR-21.

Conclusions

HIF-1α induced angiogenesis by upregulating not only vascular endothelial growth factor but also miR-21 via inhibiting a novel target gene TSP-1. Both of them may contribute to the protective effect of HIF-1α on renal I/R injury.

Hypoxia induces HIF-1α which upregulates not only VEGF but also miR-21, and this last one inhibits a novel target gene, thrombospondin 1. Angiogenesis induced by hypoxia depends at least partially on production of VEGF and inhibition of thrombospondin 1 through miR-21.

Ischemia as a factor affecting innate immune responses in kidney transplantation

PURPOSE OF REVIEW

Ischemic injury inevitably occurs during the procurement of organs for transplantation, and the injury is worsened by inflammation following reperfusion. The purpose of this review is to describe the role of the innate immune system in ischemia-induced renal injury in kidneys procured for transplantation. The key role of pattern recognition receptors in immune responses to ischemia is described. Innate immune receptors are emerging novel targets for the amelioration of ischemic injury of donor kidneys.

RECENT FINDINGS

Several families of pattern recognition receptors are direct mediators of early injurious events during kidney procurement, and also innate and adaptive immune responses after transplantation. The deleterious events associated with the activation of the innate immune system in donor kidneys significantly contribute to short and long-term allograft outcomes.

SUMMARY

Although a number of therapies have been proposed to decrease ischemic donor kidney injury, targeting the innate immune system is an exciting new area that is gaining significant interest in transplantation. As we learn more about how these important receptors are regulated by ischemia, strategies will likely evolve to allow their modulation in ischemic renal injury.

A systems approach to renal inflammation in SLE

Lupus disease and its complications including lupus nephritis (LN) are very disabling and significantly impact the quality of life and longevity of patients. Broadly immunosuppressive treatments do not always provide the expected clinical benefits and have significant side effects that contribute to patient morbidity. In the era of systems biology, new strategies are being deployed integrating diverse sources of information (molecular and clinical) so as to identify individual disease specificities and select less aggressive treatments. In this review, we summarize integrative approaches linking molecular disease profiles (mainly tissue transcriptomics) and clinical phenotypes. The main goals are to better understand the pathogenesis of lupus nephritis, to identify the risk factors for renal flare and to find the predictors of both short and long-term clinical outcome. Identification of common key drivers and additional patient-specific key drivers can open the door to improved and individualized therapy to prevent and treat LN.

The multifaceted role of the renal microvasculature during acute kidney injury

Pediatric acute kidney injury (AKI) represents a complex disease process for clinicians as it is multifactorial in cause and only limited treatment or preventatives are available. The renal microvasculature has recently been implicated in AKI as a strong therapeutic candidate involved in both injury and recovery. Significant progress has been made in the ability to study the renal microvasculature following ischemic AKI and its role in repair. Advances have also been made in elucidating cell-cell interactions and the molecular mechanisms involved in these interactions. The ability of the kidney to repair post AKI is closely linked to alterations in hypoxia, and these studies are elucidated in this review. Injury to the microvasculature following AKI plays an integral role in mediating the inflammatory response, thereby complicating potential therapeutics. However, recent work with experimental animal models suggests that the endothelium and its cellular and molecular interactions are attractive targets to prevent injury or hasten repair following AKI. Here, we review the cellular and molecular mechanisms of the renal endothelium in AKI, as well as repair and recovery, and potential therapeutics to prevent or ameliorate injury and hasten repair.

CD47 regulates renal tubular epithelial cell self-renewal and proliferation following renal ischemia reperfusion

Defects in renal tubular epithelial cell repair contribute to renal ischemia reperfusion injury, cause acute kidney damage, and promote chronic renal disease. The matricellular protein thrombospondin-1 and its receptor CD47 are involved in experimental renal ischemia reperfusion injury, although the role of this interaction in renal recovery is unknown. We found upregulation of self-renewal genes (transcription factors Oct4, Sox2, Klf4 and cMyc) in the kidney of CD47(-/-) mice after ischemia reperfusion injury. Wild-type animals had minimal self-renewal gene expression, both before and after injury. Suggestive of cell autonomy, CD47(-/-) renal tubular epithelial cells were found to increase expression of the self-renewal genes. This correlated with enhanced proliferative capacity compared with cells from wild-type mice. Exogenous thrombospondin-1 inhibited self-renewal gene expression in renal tubular epithelial cells from wild-type but not CD47(-/-) mice, and this was associated with decreased proliferation. Treatment of renal tubular epithelial cells with a CD47 blocking antibody or CD47-targeting small interfering RNA increased expression of some self-renewal transcription factors and promoted cell proliferation. In a syngeneic kidney transplant model, treatment with a CD47 blocking antibody increased self-renewal transcription factor expression, decreased tissue damage, and improved renal function compared with that in control mice. Thus, thrombospondin-1 via CD47 inhibits renal tubular epithelial cell recovery after ischemia reperfusion injury through inhibition of proliferation/self-renewal.

Hantavirus Infection Suppresses Thrombospondin-1 Expression in Cultured Endothelial Cells in a Strain-Specific Manner

Hantavirus infection is associated with two frequently fatal diseases in humans: Hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). The pathogenesis of hantavirus infection is complex and not fully understood; however, it is believed to involve virus-induced hyperinflammatory immune responses. Thrombospondin-1 (THBS1) is a large homotrimeric protein that plays a putative role in regulating blood homeostasis. Hyperresponsiveness to inflammatory stimuli has also been associated with defects in the THBS1 gene. Our data suggest that hantavirus infection of human umbilical cord vein endothelial cells (HUVEC) suppress the accumulation of THBS1 in the extracellular matrix. Additionally, this suppression is dependent on virus replication, implying a direct mechanism of action. Our data also imply that the pathogenic Andes and Hantaan strains inhibit THBS1 expression while the non-pathogenic Prospect Hill strain showed little inhibition. These observations suggest that a dysregulation of THBS1 may contribute to the pathogenesis of hantavirus infection.

Thrombospondin 1 Deficiency Ameliorates the Development of Adriamycin-Induced Proteinuric Kidney Disease

Accumulating evidence suggests that thrombospondin 1 (TSP1) is an important player in diabetic nephropathy. However, the role of TSP1 in podocyte injury and the development of non-diabetic proteinuric kidney disease is largely unknown. In the current study, by using a well-established podocyte injury model (adriamycin-induced nephropathy mouse model), we examined the contribution of TSP1 to the development of proteinuric kidney disease. We found that TSP1 was up-regulated in the glomeruli, notably in podocytes, in adriamycin injected mice before the onset of proteinuria. ADR treatment also stimulated TSP1 expression in cultured human podocytes in vitro. Moreover, increased TSP1 mediated ADR-induced podocyte apoptosis and actin cytoskeleton disorganization. This TSP1's effect was through a CD36-dependent mechanism and involved in the stimulation of p38MAPK pathway. Importantly, in vivo data demonstrated that TSP1 deficiency protected mice from ADR induced podocyte loss and foot process effacement. ADR induced proteinuria, glomerulosclerosis, renal macrophage infiltration and inflammation was also attenuated in TSP1 deficient mice. Taken together, these studies provide new evidence that TSP1 contributes to the development of non-diabetic proteinuric kidney disease by stimulating podocyte injury and the progression of renal inflammation.

Oxidative Stress and Lung Ischemia-Reperfusion Injury

Ischemia-reperfusion (IR) injury is directly related to the formation of reactive oxygen species (ROS), endothelial cell injury, increased vascular permeability, and the activation of neutrophils and platelets, cytokines, and the complement system. Several studies have confirmed the destructiveness of the toxic oxygen metabolites produced and their role in the pathophysiology of different processes, such as oxygen poisoning, inflammation, and ischemic injury. Due to the different degrees of tissue damage resulting from the process of ischemia and subsequent reperfusion, several studies in animal models have focused on the prevention of IR injury and methods of lung protection. Lung IR injury has clinical relevance in the setting of lung transplantation and cardiopulmonary bypass, for which the consequences of IR injury may be devastating in critically ill patients.

Innate and adaptive immune responses subsequent to ischemia-reperfusion injury in the kidney

Understanding innate immune responses and their correlation to alloimmunity after solid organ transplantation is key to optimizing long term graft outcome. While Ischemia/Reperfusion injury (IRI) has been well studied, new insight into central mechanisms of innate immune activation, i.e. chemokine mediated cell trafficking and the role of Toll-like receptors have evolved recently. The mechanistic implications of Neutrophils, Macrophages/Monocytes, NK-cells, Dendritic cells in renal IRI has been proven by selective depletion of these cell types, thereby offering novel therapeutic interventions. At the same time, the multi-faceted role of different T-cell subsets in IRI has gained interest, highlighting the dichotomous effects of differentiated T-cells and suggesting more selective therapeutic approaches. Targeting innate immune cells and their activation and migration pathways, respectively, has been promising in experimental models holding translational potential. This review will summarize the effects of innate immune activation and potential strategies to interfere with the immunological cascade following renal IRI.

Regulated cell death in AKI

AKI is pathologically characterized by sublethal and lethal damage of renal tubules. Under these conditions, renal tubular cell death may occur by regulated necrosis (RN) or apoptosis. In the last two decades, tubular apoptosis has been shown in preclinical models and some clinical samples from patients with AKI. Mechanistically, apoptotic cell death in AKI may result from well described extrinsic and intrinsic pathways as well as ER stress. Central converging nodes of these pathways are mitochondria, which become fragmented and sensitized to membrane permeabilization in response to cellular stress, resulting in the release of cell death-inducing factors. Whereas apoptosis is known to be regulated, tubular necrosis was thought to occur by accident until recent work unveiled several RN subroutines, most prominently receptor-interacting protein kinase-dependent necroptosis and RN induced by mitochondrial permeability transition. Additionally, other cell death pathways, like pyroptosis and ferroptosis, may also be of pathophysiologic relevance in AKI. Combination therapy targeting multiple cell-death pathways may, therefore, provide maximal therapeutic benefits.