Cellular and molecular pathways of renal repair after acute kidney injury

Molecular Mechanisms of the Acute Kidney Injury to Chronic Kidney Disease Transition: An Updated View

Increasing evidence has demonstrated the bidirectional link between acute kidney injury (AKI) and chronic kidney disease (CKD) such that, in the clinical setting, the new concept of a unified syndrome has been proposed. The pathophysiological reasons, along with the cellular and molecular mechanisms, behind the ability of a single, acute, apparently self-limiting event to drive chronic kidney disease progression are yet to be explained. This acute injury could promote progression to chronic disease through different pathways involving the endothelium, the inflammatory response and the development of fibrosis. The interplay among endothelial cells, macrophages and other immune cells, pericytes and fibroblasts often converge in the tubular epithelial cells that play a central role. Recent evidence has strengthened this concept by demonstrating that injured tubules respond to acute tubular necrosis through two main mechanisms: The polyploidization of tubular cells and the proliferation of a small population of self-renewing renal progenitors. This alternative pathophysiological interpretation could better characterize functional recovery after AKI.

TGF-β1-p53 cooperativity regulates a profibrotic genomic program in the kidney: molecular mechanisms and clinical implications

Chronic kidney disease affects >15% of the U.S. population and >850 million individuals worldwide. Fibrosis is the common outcome of many chronic renal disorders and, although the etiology varies (i.e., diabetes, hypertension, ischemia, acute injury, and urologic obstructive disorders), persistently elevated renal TGF-β1 levels result in the relentless progression of fibrotic disease. TGF-β1 orchestrates the multifaceted program of renal fibrogenesis involving proximal tubular dysfunction, failed epithelial recovery and redifferentiation, and subsequent tubulointerstitial fibrosis, eventually leading to chronic renal disease. Recent findings implicate p53 as a cofactor in the TGF-β1-induced signaling pathway and a transcriptional coregulator of several TGF-β1 profibrotic response genes by complexing with receptor-activated SMADs, which are homologous to the small worms (SMA) and Drosophilia mothers against decapentaplegic (MAD) gene families. The cooperative p53-TGF-β1 genomic cluster includes genes involved in cell growth control and extracellular matrix remodeling [e.g., plasminogen activator inhibitor-1 (PAI-1; serine protease inhibitor, clade E, member 1), connective tissue growth factor, and collagen I]. Although the molecular basis for this codependency is unclear, many TGF-β1-responsive genes possess p53 binding motifs. p53 up-regulation and increased p53 phosphorylation; moreover, they are evident in nephrotoxin- and ischemia/reperfusion-induced injury, diabetic nephropathy, ureteral obstructive disease, and kidney allograft rejection. Pharmacologic and genetic approaches that target p53 attenuate expression of the involved genes and mitigate the fibrotic response, confirming a key role for p53 in renal disorders. This review focuses on mechanisms whereby p53 functions as a transcriptional regulator within the TGF-β1 cluster with an emphasis on the potent fibrosis-promoting PAI-1 gene.-Higgins, C. E., Tang, J., Mian, B. M., Higgins, S. P., Gifford, C. C., Conti, D. J., Meldrum, K. K., Samarakoon, R., Higgins, P. J. TGF-β1-p53 cooperativity regulates a profibrotic genomic program in the kidney: molecular mechanisms and clinical implications.

Human mesenchymal stromal cells ameliorate complement induced inflammatory cascade and improve renal functions in a rat model of ischemia-reperfusion induced acute kidney injury

Introduction

The primary rational for using mesenchymal stromal cells (MSCs) to rejuvenate damaged tissue is mostly based on their capacity to trans-differentiate and repair injured organs. However, previous studies have demonstrated that MSCs are beneficial even at very early stages, before differentiation and proliferation can be expected. The aim of the current study was to investigate the multifaceted immunological effects of systemically administrating MSCs in the setting of acute kidney injury (AKI) induced by ischemic-reperfusion (I/R).

Methods

A rat model of I/R induced AKI was used. The rats underwent a unilateral nephrectomy with simultaneously clamping the contralateral kidney for 60 minutes. Four treatment groups received intravenously, increasing doses of human MSCs and after 48 hours, the rats were sacrificed. Blood was taken to evaluate renal functions and to measure systemic inflammatory markers. Kidneys were taken for histopathologic examinations and evaluations of intra-renal complement activation and inflammatory mediators.

Results

Renal functions improved in U shaped dose dependent manner. Mean serum creatinine levels were 4.5, 2.9, 2.6, 1.7 and 4.1 mg/dL in I/R + placebo, I/R + 150x10³ cells, I/R + 250x10³ cells, I/R + 500x10³ cells and I/R + 1,000x10³ cells respectfully (p-values<0.05). Urea demonstrated consistent results with the same U shape improvement manner. The extensive activation of the complement system was ameliorated in the MSCs treatment groups. In addition, MSCs significantly decreased intra-renal levels of IL-1β and TNF-α. It should be noted that the highest doses of MSCs induced renal hypoxia, marked by the Hypoxy-probe staining.

Conclusions

The early beneficial effect of MSCs in the setting of AKI may be attributed to their immunomodulatory effects. Safe treatment with MSCs can block the deleterious activation of the complement cascade and alleviate the hazardous inflammatory mediator-related cascade.

Renal subcapsular transplantation of hepatocyte growth factor-producing mesothelial cell sheets improves ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) is a clinically important cause of acute kidney injury leading to chronic kidney disease. Furthermore, IRI in renal transplantation still remains a risk factor for delayed graft function. Previous studies on IRI have had some limitations, and few of the studied therapies have been clinically applicable. Therefore, a new method for treating renal IRI is needed. We examined the effects of human mesothelial cell (MC) sheets and hepatocyte growth factor (HGF)-transgenic MC (tg MC) sheets transplanted under the renal capsule in an IRI rat model and compared these two treatments with the intravenous administration of HGF protein and no treatment through serum, histological, and mRNA analyses over 28 days. MC sheets and HGF-tg MC sheets produced HGF protein and significantly improved acute renal dysfunction, acute tubular necrosis, and survival rate. The improvement in necrosis was likely due to the cell sheets promoting the migration and proliferation of renal tubular cells, as observed in vitro. Expression of α-smooth muscle actin at day 14 and renal fibrosis at day 28 after IRI were significantly suppressed in MC sheet and HGF-tg MC sheet treatment groups compared with the other groups, and these effects tended to be reinforced by the HGF-tg MC sheets. These results suggest that the cell sheets locally and continuously affect renal paracrine factors, such as HGF, and support recovery from acute tubular necrosis and improvement of renal fibrosis in chronic disease.

Acute kidney injury overview: From basic findings to new prevention and therapy strategies

Acute kidney injury (AKI) is defined as a decrease in kidney function within hours, which encompasses both injury and impairment of renal function. AKI is not considered a pathological condition of single organ failure, but a syndrome in which the kidney plays an active role in the progression of multi-organ dysfunction. The incidence rate of AKI is increasing and becoming a common (8-16% of hospital admissions) and serious disease (four-fold increased hospital mortality) affecting public health costs worldwide. AKI also affects the young and previously healthy individuals affected by infectious diseases in Latin America. Because of the multifactorial pathophysiological mechanisms, there is no effective pharmacological therapy that prevents the evolution or reverses the injury once established; therefore, renal replacement therapy is the only current alternative available for renal patients. The awareness of an accurate and prompt recognition of AKI underlying the various clinical phenotypes is an urgent need for more effective therapeutic interventions to diminish mortality and socio-economic impacts of AKI. The use of biomarkers as an indicator of the initial stage of the disease is critical and the cornerstone to fulfill the gaps in the field. This review discusses emerging strategies from basic science toward the anticipation of features, treatment of AKI, and new treatments using pharmacological and stem cell therapies. We will also highlight bioartificial kidney studies, addressing the limitations of the development of this innovative technology.

Early detection of unilateral ureteral obstruction by desorption electrospray ionization mass spectrometry

Desorption electrospray ionization mass spectrometry (DESI-MS) is an emerging analytical tool for rapid in situ assessment of metabolomic profiles on tissue sections without tissue pretreatment or labeling. We applied DESI-MS to identify candidate metabolic biomarkers associated with kidney injury at the early stage. DESI-MS was performed on sections of kidneys from 80 mice over a time course following unilateral ureteral obstruction (UUO) and compared to sham controls. A predictive model of renal damage was constructed using the LASSO (least absolute shrinkage and selection operator) method. Levels of lipid and small metabolites were significantly altered and glycerophospholipids comprised a significant fraction of altered species. These changes correlate with altered expression of lipid metabolic genes, with most genes showing decreased expression. However, rapid upregulation of PG(22:6/22:6) level appeared to be a hitherto unknown feature of the metabolic shift observed in UUO. Using LASSO and SAM (significance analysis of microarrays), we identified a set of well-measured metabolites that accurately predicted UUO-induced renal damage that was detectable by 12 h after UUO, prior to apparent histological changes. Thus, DESI-MS could serve as a useful adjunct to histology in identifying renal damage and demonstrates early and broad changes in membrane associated lipids.

A mouse model of renal fibrosis to overcome the technical variability in ischaemia/reperfusion injury among operators

The ischaemia-reperfusion (I/R) model is a widely used model of acute kidney injury (AKI) and renal fibrosis. However, the ischaemia duration that is long enough to cause broad fibrosis shows that a high mortality rate and a short ischaemia duration does not cause fibrosis, resulting in a large variation in fibrosis progression in this experimental model. Inter-operator variation occurs for I/R injury severity because the I/R procedure is complex, which results in poor reproducibility of subsequent fibrosis in the model. In the present study, we developed a renal fibrosis model in which the fibrosis progression for 8 weeks is predictable within 8 days. Three operators independently performed I/R followed by uninephrectomy at day 7 in mice. The aim was to create a model that would show a blood urea nitrogen (BUN) level >100 mg/dL at day 8 after I/R (day 1 after uninephrectomy). Although the ischaemia duration to satisfy this BUN criterion differed among operators, the mice developed anaemia, polyuria, and fibrosis in a similar manner under the same BUN criterion with a low mortality rate. Interstitial fibrosis had developed at week 8, which was strongly correlated with the BUN at day 8. This protocol allows operators to adjust the ischaemia duration based on the BUN criterion and to separate mice into the desired number of groups based on the BUN to study interventions against renal fibrosis.

Urine macrophages reflect kidney macrophage content during acute tubular interstitial and glomerular injury

Macrophage polarization is a major contributing factor in acute kidney injury (AKI). We aim to determine its biomarker value in differentiating etiologic causes of various intrinsic renal AKI. A total of 205 patients with renal intrinsic AKI were enrolled. Urinary sCD163 was quantified and macrophage subtypes in urine and in renal biopsy were determined. Compared to healthy controls and AKI due to interstitial or tubular injuries (0 pg/μmol), urinary sCD163 was markedly higher in glomerulopathy, especially in diffuse proliferative glomerulonephritis (275.5 pg/μmol) and significantly correlated with cellular crescent formation. Urine sediment analysis of M1/M2 ratio could differentiate acute tubulointerstitial nephritis (M1/M2 > 2.35) from crescentic glomerulonephritis (M1/M2 < 0.27). Urinary sCD163 levels and M2 subtype positively correlated with infiltrated M2 in the glomeruli, whereas urine M1 positively correlated with infiltrated M1 in the interstitium. Of note, urinary sCD163 showed better diagnositic performance in differentiating disease etiologies compared to tradiational urinary biomarkers of AKI (NGAL and KIM-1) and markers of myeloid cells (CD11b) and pan macrophages (CD68). Thus markers of macrophage polarization could be viewed as the noninvasive "liquid biopsy" in the presence of various intrinsic kidney diseases.

Arsenic and sulfur dioxide co-exposure induce renal injury via activation of the NF-κB and caspase signaling pathway

Although emerging evidence suggests positive association of arsenic (As) or sulfur dioxide (SO₂) exposure with human diseases, reports concerning the effects of co-exposure of As and SO₂ are lacking. Moreover, there is insufficient information in the literature about As and SO₂ co-exposure to renal injury. In this study, we focus on the environmental problems of excessive As and SO₂ that co-exist in many coal consumption areas. We used both C57BL/6 mice and 293T cells to detect toxicities of As and SO₂ exposure alone or in combination. Our results showed that co-exposure significantly increased the hazard compared with exposure to As or SO₂ alone. Mouse kidney tissue slices showed that co-exposure caused more severe diffuse sclerosing glomerulonephritis than As and SO₂ exposure alone. Meanwhile experiments showed that apoptosis was aggravated by co-exposure of As and SO₂ in 293T cells. Because As and SO₂ cause cell toxicity through increasing oxidative stress, next we detected ROS and other oxidative stress parameters, and the results showed oxidative stress was increased by co-exposure compared with the other three groups. The expression levels of downstream genes in the NF-κB and caspase pathways were higher in the co-exposure group than in the groups of As or SO₂ exposure alone in mice and 293T cells. Based on the above results, co-exposure could induce higher toxicity in vitro and in vivo compared with single exposure to As or SO₂, indicating that people living in places that contaminated by As and SO₂ may have higher chance to get renal injury.

Lithium ameliorates tubule-interstitial injury through activation of the mTORC2/protein kinase B pathway

Tubule-interstitial injury (TII) is a critical step in the progression of renal disease. It has been proposed that changes in proximal tubule (PT) albumin endocytosis plays an important role in the development of TII. Some reports have shown protective effects of lithium on kidney injury animal models that was correlated to proteinuria. We tested the hypothesis that lithium treatment ameliorates the development of TII due to changes in albumin endocytosis. Two experimental models were used: (1) TII induced by albumin overload in an animal model; (2) LLC-PK1 cells, a PT cell line. Lithium treatment ameliorates TII induced by albumin overload measured by (1) proteinuria; (2) collagen deposition; (3) area of tubule-interstitial space, and (4) macrophage infiltration. Lithium treatment increased mTORC2 activity leading to the phosphorylation of protein kinase B (PKB) at Ser473 and its activation. This mechanism enhanced albumin endocytosis in PT cells, which decreased the proteinuria observed in TII induced by albumin overload. This effect did not involve changes in the expression of megalin, a PT albumin receptor. In addition, activation of this pathway decreased apoptosis in LLC-PK1 cells, a PT cell line, induced by higher albumin concentration, similar to that found in pathophysiologic conditions. Our results indicate that the protective role of lithium treatment on TII induced by albumin overload involves an increase in PT albumin endocytosis due to activation of the mTORC2/PKB pathway. These results open new possibilities in understanding the effects of lithium on the progression of renal disease.

Acute kidney injury to chronic kidney disease transition: insufficient cellular stress response

PURPOSE OF REVIEW

Recent epidemiological and preclinical mechanistic studies provide strong evidence that acute kidney injury (AKI) and chronic kidney disease (CKD) form an interconnected syndrome. Injured kidneys undergo a coordinated reparative process with an engagement of multiple cell types after injury; however, maladaptation to the injury subjects kidneys to a vicious cycle of fibrogenesis and nephron loss. In this review, we will outline and discuss the pathogenesis of AKI-to-CKD transition with an emphasis on dysregulated 'cellular stress adaptation' as a potential therapeutic target.

RECENT FINDINGS

Recent studies identify the crucial role of injured tubular epithelial cells in the transition from AKI to CKD. Damaged tubular cells undergo reactivation of developmental and epithelial-mesenchymal transition signaling, metabolic alteration, and cell-cycle arrest, thereby driving inflammation and fibrogenesis. Recent work highlights that cellular stress-adaptive pathways against hypoxic and oxidative stress provide insufficient protection after severe AKI episode.

SUMMARY

Insufficient cellular stress adaptation may underpin the persistent activation of inflammatory and fibrogenic signaling in damaged kidneys. We propose that harnessing cellular stress-adaptive responses will be a promising therapeutic strategy to halt or even reverse the deleterious process of AKI-to-CKD transition.

Biglycan evokes autophagy in macrophages via a novel CD44/Toll-like receptor 4 signaling axis in ischemia/reperfusion injury

Biglycan, a small leucine-rich proteoglycan, acts as a danger signal and is classically thought to promote macrophage recruitment via Toll-like receptors (TLR) 2 and 4. We have recently shown that biglycan signaling through TLR 2/4 and the CD14 co-receptor regulates inflammation, suggesting that TLR co-receptors may determine whether biglycan-TLR signaling is pro- or anti-inflammatory. Here, we sought to identify other co-receptors and characterize their impact on biglycan-TLR signaling. We found a marked increase in the number of autophagic macrophages in mice stably overexpressing soluble biglycan. In vitro, stimulation of murine macrophages with biglycan triggered autophagosome formation and enhanced the flux of autophagy markers. Soluble biglycan also promoted autophagy in human peripheral blood macrophages. Using macrophages from mice lacking TLR2 and/or TLR4, CD14, or CD44, we demonstrated that the pro-autophagy signal required TLR4 interaction with CD44, a receptor involved in adhesion, migration, lymphocyte activation, and angiogenesis. In vivo, transient overexpression of circulating biglycan at the onset of renal ischemia/reperfusion injury (IRI) enhanced M1 macrophage recruitment into the kidneys of Cd44^+/+ and Cd44^-/- mice but not Cd14^-/- mice. The biglycan-CD44 interaction increased M1 autophagy and the number of renal M2 macrophages and reduced tubular damage following IRI. Thus, CD44 is a novel signaling co-receptor for biglycan, an interaction that is required for TLR4-CD44-dependent pro-autophagic activity in macrophages. Interfering with the interaction between biglycan and specific TLR co-receptors could represent a promising therapeutic intervention to curtail kidney inflammation and damage.

A phase I/II, double-blind, placebo-controlled study assessing safety and efficacy of C1 esterase inhibitor for prevention of delayed graft function in deceased donor kidney transplant recipients

Delayed graft function (DGF) is defined as need for dialysis early posttransplant. DGF is related to ischemia-reperfusion injury (IRI) that diminishes allograft function and may be complement dependent. Here, we investigate the ability of C1 esterase inhibitor (C1INH) to prevent IRI/DGF in kidney transplant recipients. Seventy patients receiving deceased donor kidney transplants at risk for DGF were randomized to receive C1INH 50 U/kg (#35) or placebo (#35) intraoperatively and at 24 hours. The primary end point was need for hemodialysis during the first week posttransplant. Assessments of glomerular filtration rate and dialysis dependence were accomplished. Complications and safety of therapy were recorded. Similar characteristics with no significant differences in cold-ischemia time or risk factors for DGF were seen. C1INH did not result in reduction of dialysis sessions at 1 week posttransplant, but significantly fewer dialysis sessions (P = .0232) were required 2 to 4 weeks posttransplant. Patients at highest risk for DGF (Kidney Donor Profile Index ≥85) benefited most from C1INH therapy. Significantly better renal function was seen at 1 year in C1INH patients (P = .006). No significant adverse events were noted with C1INH. Although the primary end point was not met, significant reductions in need for dialysis and improvements in long-term allograft function were seen with C1INH treatment.

A High-Throughput Screen Identifies DYRK1A Inhibitor ID-8 that Stimulates Human Kidney Tubular Epithelial Cell Proliferation

BACKGROUND

The death of epithelial cells in the proximal tubules is thought to be the primary cause of AKI, but epithelial cells that survive kidney injury have a remarkable ability to proliferate. Because proximal tubular epithelial cells play a predominant role in kidney regeneration after damage, a potential approach to treat AKI is to discover regenerative therapeutics capable of stimulating proliferation of these cells.

METHODS

We conducted a high-throughput phenotypic screen using 1902 biologically active compounds to identify new molecules that promote proliferation of primary human proximal tubular epithelial cells in vitro.

RESULTS

The primary screen identified 129 compounds that stimulated tubular epithelial cell proliferation. A secondary screen against these compounds over a range of four doses confirmed that eight resulted in a significant increase in cell number and incorporation of the modified thymidine analog EdU (indicating actively proliferating cells), compared with control conditions. These eight compounds also stimulated tubular cell proliferation in vitro after damage induced by hypoxia, cadmium chloride, cyclosporin A, or polymyxin B. ID-8, an inhibitor of dual-specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A), was the top candidate identified as having a robust proproliferative effect in two-dimensional culture models as well as a microphysiologic, three-dimensional cell culture system. Target engagement and genetic knockdown studies and RNA sequencing confirmed binding of ID-8 to DYRK1A and upregulation of cyclins and other cell cycle regulators, leading to epithelial cell proliferation.

CONCLUSIONS

We have identified a potential first-in-class compound that stimulates human kidney tubular epithelial cell proliferation after acute damage in vitro.

P53 in kidney injury and repair: Mechanism and therapeutic potentials

Acute kidney injury (AKI) is a major kidney disease with poor clinical outcome. Besides its acute consequence of high mortality, AKI may also contribute significantly to the occurrence and progression of chronic kidney diseases (CKD). Accumulating evidence has demonstrated that maladaptive and incomplete kidney repair after AKI leads to the development of renal fibrosis and, ultimately, CKD. p53, a well-known tumor suppressor, plays a critical role in AKI and subsequent kidney repair through the regulation of various cell biologic processes, including apoptosis, cell cycle arrest, and autophagy. Despite the notable progress in deciphering the involvement of p53 in kidney injury and repair, the underlying mechanisms of p53 in these pathological processes remain largely unknown. Further investigation in this area is essential for the application of p53 as therapeutic target to prevent and treat AKI or impede its progression to CKD. In this review, we summarize the recent advances in understanding p53 regulation of AKI and kidney repair, pinpoint the potential of p53 as a therapeutic target, and present future research interests and directions.

Microvascular rarefaction and hypertension in the impaired recovery and progression of kidney disease following AKI in preexisting CKD states

Acute kidney injury (AKI) is a major complication in hospitalized patients and is associated with elevated mortality rates. Numerous recent studies indicate that AKI also significantly increases the risk of chronic kidney disease (CKD), end-stage renal disease (ESRD), hypertension, cardiovascular disease, and mortality in those patients who survive AKI. Moreover, the risk of ESRD and mortality after AKI is substantially higher in patients with preexisting CKD. However, the underlying mechanisms by which AKI and CKD interact to promote ESRD remain poorly understood. The recently developed models that superimpose AKI on rodents with preexisting CKD have provided new insights into the pathogenic mechanisms mediating the deleterious interactions between AKI and CKD. These studies show that preexisting CKD impairs recovery from AKI and promotes the development of mechanisms of CKD progression. Specifically, preexisting CKD exacerbates microvascular rarefaction, failed tubular redifferentiation, disruption of cell cycle regulation, hypertension, and proteinuria after AKI. The purpose of this review is to discuss the potential mechanisms by which microvascular rarefaction and hypertension contribute to impaired recovery from AKI and the subsequent progression of renal disease in preexisting CKD states.

Immune cells and inflammation in AKI to CKD progression

Acute kidney injury (AKI) is a common clinical state resulting from pathogenic conditions such as ischemic and toxic insults. The pathophysiology of AKI shares common pathogenic denominators including cell death/injury, inflammation, and fibrosis, regardless of the initiating insults. Recent clinical studies have shown that a single episode of AKI can lead to subsequent chronic kidney disease (CKD). Although the involvement of multiple types of cells in the pathophysiology of AKI is becoming increasingly clear, the precise mechanisms for this "AKI to CKD progression" are still unknown, and no drug has been shown to halt this progression. An increasing number of epidemiological studies have also revealed that the presence of aging greatly increases the risk of AKI to CKD progression, and chronic inflammation is increasingly recognized as an important determinant factor for this progression. In this review article, we first describe the current understanding of the pathophysiology of AKI to CKD progression based on multiple types of cells. In particular, we will highlight the recent findings in regard to the mechanisms for chronic inflammation after AKI. Subsequently, we will focus on the mechanisms responsible for the increased risk of AKI to CKD progression in the elderly. Finally, we highlight our recent finding of age-dependent tertiary lymphoid tissue formation and its roles in AKI to CKD progression and speculate on the potential therapeutic opportunities that come from targeting aberrant inflammation after AKI.

Tisp40 deficiency limits renal inflammation and promotes tubular cell proliferation in renal ischemia reperfusion injury

Renal ischemia reperfusion (IR) is a common cause of acute kidney injury (AKI), and no effective treatment is available to date. In our previous studies, we demonstrated that Tisp40 exacerbates tubular cell apoptosis and tubulointerstitial fibrosis after renal IR injury. However, the role of Tisp40 in renal inflammatory responses and tubular cell proliferation during renal IR injury remains unknown. In this study, Tisp40 knockout (KO) and wild-type (WT) mice were induced with or without renal IR injury. For renal IR, bilateral renal pedicels were exposed and clamped to induce 30 min of ischemia. After 48 h of reperfusion, the kidneys were collected for analyses. Results showed that Tisp40 deficiency attenuates neutrophil and macrophage infiltration after renal IR. Consistently, the protein levels of TNF-α and MCP-1 were markedly decreased, and the phosphorylation levels of IκBα and P65 were inhibited in Tisp40-deficient mice than in WT mice in renal IR injury. In addition, compared with WT mice, Tisp40 deficiency significantly increased the expression levels of proliferative cellular nuclear antigen and phosphorylated Erk1/2 after renal IR injury. In conclusion, Tisp40 deficiency limits renal inflammatory responses and promotes tubular cell proliferation in ischemic AKI.

Enhancing in vivo renal ischemia assessment by high-dynamic-range fluorescence molecular imaging

Fluorescence imaging has been used to evaluate the physiological features of renal ischemia in animal model. However, the fluorophore distribution details of the ischemia model could not be fully represented due to the limited dynamic range of the charged-couple device. A high-dynamic-range (HDR) strategy was adopted in renal ischemia fluorescence imaging, both ex vivo and in vivo. The HDR strategy successfully combined ischemia relevant biological features that could only be captured with different exposure times, and then presented these features in the HDR results. The HDR results effectively highlighted the renal ischemic areas with relatively better perfusion and diminished the saturation that resulted from long exposure time. The relative fluorescence intensities of the ischemic kidneys and the image entropy values were significantly higher in the HDR images than in the original images, therefore enhancing the visualization of the renal ischemia model. The results suggest that HDR could serve as a postprocessing strategy to enhance the assessment of in vivo renal ischemia, and HDR fluorescence molecular imaging could be a valuable imaging tool for future studies of clinical ischemia detection and evaluation.

Targeting TGFβ Signaling to Address Fibrosis Using Antisense Oligonucleotides

Fibrosis results from the excessive accumulation of extracellular matrix in chronically injured tissue. The fibrotic process is governed by crosstalk between many signaling pathways. The search for an effective treatment is further complicated by the fact that there is a degree of tissue-specificity in the pathways involved, although the process is not completely understood for all tissues. A plethora of drugs have shown promise in pre-clinical models, which is not always borne out translationally in clinical trial. With the recent approvals of two antisense oligonucleotides for the treatment of the genetic diseases Duchenne muscular dystrophy and spinal muscular atrophy, we explore here the potential of antisense oligonucleotides to knockdown the expression of pro-fibrotic proteins. We give an overview of the generalized fibrotic process, concentrating on key players and highlight where antisense oligonucleotides have been used effectively in cellular and animal models of different fibrotic conditions. Consideration is given to the advantages antisense oligonucleotides would have as an anti-fibrotic therapy alongside factors that would need to be addressed to improve efficacy. A prospective outlook for the development of antisense oligonucleotides to target fibrosis is outlined.

Inhibition of maternally expressed gene 3 attenuated lipopolysaccharide-induced apoptosis through sponging miR-21 in renal tubular epithelial cells

Acute kidney injury (AKI) results in retention of waste products and dysregulation of extracellular volume and electrolytes, thus leading to a variety of complications. Recent advances in long noncoding RNAs suggested their close relationship with disease progression. In the current study, we investigated the role and mechanism of maternally expressed gene 3 (MEG3) on AKI pathogenesis. Real-time polymerase chain reaction found that the expression of MEG3 was significantly increased in both kidney tissues and TKPTS cells induced by lipopolysaccharide (LPS). Western blot assay showed that the expression of apoptosis regulator Bcl-2 was increased in MEG3-inhibited TKPTS cells. Flow cytometry assay confirmed that LPS-induced apoptosis was significantly attenuated after transfection of si-MEG3. The RNAhybrid informatics algorithm predicted that there was a strong binding capacity between miR-21 and MEG3. Luciferase reporter assay confirmed that MEG3 could function as a competing endogenous RNA of miR-21. The antiapoptotic effect of si-MEG3 could be neutralized by a miR-21 inhibitor, demonstrated by the decreased expression of Bcl-2 and flow cytometry results. Further investigation showed that programmed cell death protein 4 (PDCD4), a validated target of miR-21, was highly expressed in both injured kidney tissues and LPS-stimulated TKPTS cells. Meanwhile, the protein expression of PDCD4 was significantly reduced by inhibition of MEG3, but retrieved by coinhibition of MEG3 and miR-21. In conclusion, our results demonstrated that inhibition of MEG3 could attenuate LPS-induced apoptosis in TKPTS cells by regulating the miR-21/PDCD4 pathway, suggesting that the MEG3/miR-21/PDCD4 axis could be developed as a potential therapeutic target of AKI.

Are Pax proteins potential therapeutic targets in kidney disease and cancer?

Pax genes encode developmental regulators that are expressed in a variety of tissues and control critical events in morphogenesis. In the kidney, Pax2 and Pax8 are expressed in embryonic development and in specific renal diseases associated with aberrant epithelial cell proliferation. Prior genetic and cell biological studies suggest that reducing the activity of Pax proteins in renal cancer or in polycystic kidney disease can slow the progression of these conditions. The Pax proteins may be critical for providing tissue and locus specificity to recruit epigenetic modifiers that control gene expression and chromatin structure. Although they are nuclear, targeting Pax proteins to inhibit function may be feasible with small molecules. Such inhibition of Pax protein function may provide novel therapies for subsets of renal disorders that are tissue- and cell type-specific and avoid systemic effects on non-Pax-expressing cells and tissues. Given the paucity of effective treatments for renal cancer and cystic disease, the Pax family of proteins represents new pharmaceutical targets that merit exploration and further development.