The chromatin landscape of healthy and injured cell types in the human kidney

There is a need to define regions of gene activation or repression that control human kidney cells in states of health, injury, and repair to understand the molecular pathogenesis of kidney disease and design therapeutic strategies. Comprehensive integration of gene expression with epigenetic features that define regulatory elements remains a significant challenge. We measure dual single nucleus RNA expression and chromatin accessibility, DNA methylation, and H3K27ac, H3K4me1, H3K4me3, and H3K27me3 histone modifications to decipher the chromatin landscape and gene regulation of the kidney in reference and adaptive injury states. We establish a spatially-anchored epigenomic atlas to define the kidney's active, silent, and regulatory accessible chromatin regions across the genome. Using this atlas, we note distinct control of adaptive injury in different epithelial cell types. A proximal tubule cell transcription factor network of ELF3, KLF6, and KLF10 regulates the transition between health and injury, while in thick ascending limb cells this transition is regulated by NR2F1. Further, combined perturbation of ELF3, KLF6, and KLF10 distinguishes two adaptive proximal tubular cell subtypes, one of which manifested a repair trajectory after knockout. This atlas will serve as a foundation to facilitate targeted cell-specific therapeutics by reprogramming gene regulatory networks.

Molecular Signatures of Glomerular Neovascularization in a Patient with Diabetic Kidney Disease

The Kidney Precision Medicine Project (KPMP) aims to create a kidney tissue atlas, define disease subgroups, and identify critical cells, pathways, and targets for novel therapies through molecular investigation of human kidney biopsies obtained from participants with acute kidney injury (AKI) or chronic kidney disease (CKD). We present the case of a 66-year-old woman with diabetic kidney disease who underwent a protocol KPMP kidney biopsy. Her clinical history included diabetes mellitus complicated by neuropathy and eye disease, increased insulin resistance, hypertension, albuminuria, and relatively preserved glomerular filtration rate (early CKD stage 3a). The patient's histopathology was consistent with diabetic nephropathy and arterial and arteriolar sclerosis. Three-dimensional, immunofluorescence imaging of the kidney biopsy specimen revealed extensive peri-glomerular neovascularization that was underestimated by standard histopathologic approaches. Spatial transcriptomics was performed to obtain gene expression signatures at discrete areas of the kidney biopsy. Gene expression in the areas of glomerular neovascularization revealed increased expression of genes involved in angiogenic signaling, proliferation and survival of endothelial cells, as well as new vessel maturation and stability. This molecular correlation provides additional insights into the development of kidney disease in patients with diabetes and spotlights how novel molecular techniques employed by the KPMP can supplement and enrich the histopathologic diagnosis obtained from a kidney biopsy.

The chromatin landscape of healthy and injured cell types in the human kidney

There is a need to define regions of gene activation or repression that control human kidney cells in states of health, injury, and repair to understand the molecular pathogenesis of kidney disease and design therapeutic strategies. However, comprehensive integration of gene expression with epigenetic features that define regulatory elements remains a significant challenge. We measured dual single nucleus RNA expression and chromatin accessibility, DNA methylation, and H3K27ac, H3K4me1, H3K4me3, and H3K27me3 histone modifications to decipher the chromatin landscape and gene regulation of the kidney in reference and adaptive injury states. We established a comprehensive and spatially-anchored epigenomic atlas to define the kidney's active, silent, and regulatory accessible chromatin regions across the genome. Using this atlas, we noted distinct control of adaptive injury in different epithelial cell types. A proximal tubule cell transcription factor network of ELF3 , KLF6 , and KLF10 regulated the transition between health and injury, while in thick ascending limb cells this transition was regulated by NR2F1 . Further, combined perturbation of ELF3 , KLF6 , and KLF10 distinguished two adaptive proximal tubular cell subtypes, one of which manifested a repair trajectory after knockout. This atlas will serve as a foundation to facilitate targeted cell-specific therapeutics by reprogramming gene regulatory networks.

Integrated Cytometry With Machine Learning Applied to High-Content Imaging of Human Kidney Tissue for In Situ Cell Classification and Neighborhood Analysis

The human kidney is a complex organ with various cell types that are intricately organized to perform key physiological functions and maintain homeostasis. New imaging modalities, such as mesoscale and highly multiplexed fluorescence microscopy, are increasingly being applied to human kidney tissue to create single-cell resolution data sets that are both spatially large and multidimensional. These single-cell resolution high-content imaging data sets have great potential to uncover the complex spatial organization and cellular makeup of the human kidney. Tissue cytometry is a novel approach used for the quantitative analysis of imaging data; however, the scale and complexity of such data sets pose unique challenges for processing and analysis. We have developed the Volumetric Tissue Exploration and Analysis (VTEA) software, a unique tool that integrates image processing, segmentation, and interactive cytometry analysis into a single framework on desktop computers. Supported by an extensible and open-source framework, VTEA's integrated pipeline now includes enhanced analytical tools, such as machine learning, data visualization, and neighborhood analyses, for hyperdimensional large-scale imaging data sets. These novel capabilities enable the analysis of mesoscale 2- and 3-dimensional multiplexed human kidney imaging data sets (such as co-detection by indexing and 3-dimensional confocal multiplexed fluorescence imaging). We demonstrate the utility of this approach in identifying cell subtypes in the kidney on the basis of labels, spatial association, and their microenvironment or neighborhood membership. VTEA provides an integrated and intuitive approach to decipher the cellular and spatial complexity of the human kidney and complements other transcriptomics and epigenetic efforts to define the landscape of kidney cell types.

Serving on a Graduate Medical Education Diversity, Equity, Inclusion, and Justice Committee: Lessons Learned From a Journey of Growth and Healing

Efforts toward achieving diversity, equity, inclusion, and justice (DEIJ) within graduate medical education (GME) often begin with the formation of a DEIJ committee that steers the work. Little is known about the experiences and the challenges faced by those serving on such committees. We sought to describe the experiences of members of our institutional GME DEIJ committee to gain knowledge that would propel this work forward. An open-ended survey was electronically administered to members of our institutional GME DEIJ committee. Responses were analyzed using a rapid qualitative analytical approach. Eighteen members (58%) responded. Of these, (67%) were women and five (28%) were Black. Six domains emerged: “motivation,” “challenges,” “emotional response,” “highs,” “facilitators,” and “advice.” Black respondents more often cited the need to increase diversity as a motivator to join this work. Women and Black respondents more often identified time constraints as a challenge to participation. Some members found the work emotionally draining; others described it as uplifting. Two themes emerged as high points of participation-pride and achievement around the work completed and the personal benefits of building a community with a shared purpose. Three themes emerged as facilitators: effective leadership, support, and establishing psychological safety during the meetings. Many arrived at the realization that change would take time and advocated for patience and perseverance. Protected time and DEIJ expertise were identified as integral to successful committee work. Our findings provide novel insights into the experience of serving on a GME DEIJ committee and highlights infrastructural and institutional prerequisites for success.

Alterations in Protein Translation and Carboxylic Acid Catabolic Processes in Diabetic Kidney Disease

Diabetic kidney disease (DKD) remains the leading cause of end-stage kidney disease despite decades of study. Alterations in the glomerulus and kidney tubules both contribute to the pathogenesis of DKD although the majority of investigative efforts have focused on the glomerulus. We sought to examine the differential expression signature of human DKD in the glomerulus and proximal tubule and corroborate our findings in the db/db mouse model of diabetes. A transcriptogram network analysis of RNAseq data from laser microdissected (LMD) human glomerulus and proximal tubule of DKD and reference nephrectomy samples revealed enriched pathways including rhodopsin-like receptors, olfactory signaling, and ribosome (protein translation) in the proximal tubule of human DKD biopsy samples. The translation pathway was also enriched in the glomerulus. Increased translation in diabetic kidneys was validated using polyribosomal profiling in the db/db mouse model of diabetes. Using single nuclear RNA sequencing (snRNAseq) of kidneys from db/db mice, we prioritized additional pathways identified in human DKD. The top overlapping pathway identified in the murine snRNAseq proximal tubule clusters and the human LMD proximal tubule compartment was carboxylic acid catabolism. Using ultra-performance liquid chromatography–mass spectrometry, the fatty acid catabolism pathway was also found to be dysregulated in the db/db mouse model. The Acetyl-CoA metabolite was down-regulated in db/db mice, aligning with the human differential expression of the genes ACOX1 and ACACB. In summary, our findings demonstrate that proximal tubular alterations in protein translation and carboxylic acid catabolism are key features in both human and murine DKD.

Integration of spatial and single-cell transcriptomics localizes epithelial cell-immune cross-talk in kidney injury

Single-cell sequencing studies have characterized the transcriptomic signature of cell types within the kidney. However, the spatial distribution of acute kidney injury (AKI) is regional and affects cells heterogeneously. We first optimized coordination of spatial transcriptomics and single-nuclear sequencing data sets, mapping 30 dominant cell types to a human nephrectomy. The predicted cell-type spots corresponded with the underlying histopathology. To study the implications of AKI on transcript expression, we then characterized the spatial transcriptomic signature of 2 murine AKI models: ischemia/reperfusion injury (IRI) and cecal ligation puncture (CLP). Localized regions of reduced overall expression were associated with injury pathways. Using single-cell sequencing, we deconvoluted the signature of each spatial transcriptomic spot, identifying patterns of colocalization between immune and epithelial cells. Neutrophils infiltrated the renal medulla in the ischemia model. Atf3 was identified as a chemotactic factor in S3 proximal tubules. In the CLP model, infiltrating macrophages dominated the outer cortical signature, and Mdk was identified as a corresponding chemotactic factor. The regional distribution of these immune cells was validated with multiplexed CO-Detection by indEXing (CODEX) immunofluorescence. Spatial transcriptomic sequencing complemented single-cell sequencing by uncovering mechanisms driving immune cell infiltration and detection of relevant cell subpopulations.

Large-scale, three-dimensional tissue cytometry of the human kidney: a complete and accessible pipeline

The advent of personalized medicine has driven the development of novel approaches for obtaining detailed cellular and molecular information from clinical tissue samples. Tissue cytometry is a promising new technique that can be used to enumerate and characterize each cell in a tissue and, unlike flow cytometry and other single-cell techniques, does so in the context of the intact tissue, preserving spatial information that is frequently crucial to understanding a cell's physiology, function, and behavior. However, the wide-scale adoption of tissue cytometry as a research tool has been limited by the fact that published examples utilize specialized techniques that are beyond the capabilities of most laboratories. Here we describe a complete and accessible pipeline, including methods of sample preparation, microscopy, image analysis, and data analysis for large-scale three-dimensional tissue cytometry of human kidney tissues. In this workflow, multiphoton microscopy of unlabeled tissue is first conducted to collect autofluorescence and second-harmonic images. The tissue is then labeled with eight fluorescent probes, and imaged using spectral confocal microscopy. The raw 16-channel images are spectrally deconvolved into 8-channel images, and analyzed using the Volumetric Tissue Exploration and Analysis (VTEA) software developed by our group. We applied this workflow to analyze millimeter-scale tissue samples obtained from human nephrectomies and from renal biopsies from individuals diagnosed with diabetic nephropathy, generating a quantitative census of tens of thousands of cells in each. Such analyses can provide useful insights that can be linked to the biology or pathology of kidney disease. The approach utilizes common laboratory techniques, is compatible with most commercially-available confocal microscope systems and all image and data analysis is conducted using the VTEA image analysis software, which is available as a plug-in for ImageJ.

Clinical, histopathologic and molecular features of idiopathic and diabetic nodular mesangial sclerosis in humans

BACKGROUND

Idiopathic nodular mesangial sclerosis, also called idiopathic nodular glomerulosclerosis (ING), is a rare clinical entity with an unclear pathogenesis. The hallmark of this disease is the presence of nodular mesangial sclerosis on histology without clinical evidence of diabetes mellitus or other predisposing diagnoses. To achieve insights into its pathogenesis, we queried the clinical, histopathologic and transcriptomic features of ING and nodular diabetic nephropathy (DN).

METHODS

All renal biopsy reports accessioned at Indiana University Health from 2001 to 2016 were reviewed to identify 48 ING cases. Clinical and histopathologic features were compared between individuals with ING and DN (n = 751). Glomeruli of ING (n = 5), DN (n = 18) and reference (REF) nephrectomy (n = 9) samples were isolated by laser microdissection and RNA was sequenced. Immunohistochemistry of proline-rich 36 (PRR36) protein was performed.

RESULTS

ING subjects were frequently hypertensive (95.8%) with a smoking history (66.7%). ING subjects were older, had lower proteinuria and had less hyaline arteriolosclerosis than DN subjects. Butanoate metabolism was an enriched pathway in ING samples compared with either REF or DN samples. The top differentially expressed gene, PRR36, had increased expression in glomeruli 248-fold [false discovery rate (FDR) P = 5.93 × 10-6] compared with the REF and increased 109-fold (FDR P = 1.85 × 10-6) compared with DN samples. Immunohistochemistry revealed a reduced proportion of cells with perinuclear reaction in ING samples as compared to DN.

CONCLUSIONS

Despite similar clinical and histopathologic characteristics in ING and DN, the uncovered transcriptomic signature suggests that ING has distinct molecular features from nodular DN. Further study is warranted to understand these relationships.

Molecular characterization of the human kidney interstitium in health and disease

The gene expression signature of the human kidney interstitium is incompletely understood. The cortical interstitium (excluding tubules, glomeruli, and vessels) in reference nephrectomies (N = 9) and diabetic kidney biopsy specimens (N = 6) was laser microdissected (LMD) and sequenced. Samples underwent RNA sequencing. Gene signatures were deconvolved using single nuclear RNA sequencing (snRNAseq) data derived from overlapping specimens. Interstitial LMD transcriptomics uncovered previously unidentified markers including KISS1, validated with in situ hybridization. LMD transcriptomics and snRNAseq revealed strong correlation of gene expression within corresponding kidney regions. Relevant enriched interstitial pathways included G-protein coupled receptor. binding and collagen biosynthesis. The diabetic interstitium was enriched for extracellular matrix organization and small-molecule catabolism. Cell type markers with unchanged expression (NOTCH3, EGFR, and HEG1) and those down-regulated in diabetic nephropathy (MYH11, LUM, and CCDC3) were identified. LMD transcriptomics complements snRNAseq; together, they facilitate mapping of interstitial marker genes to aid interpretation of pathophysiology in precision medicine studies.

Application of Laser Microdissection to Uncover Regional Transcriptomics in Human Kidney Tissue

Gene expression analysis of human kidney tissue is an important tool to understand homeostasis and disease pathophysiology. Increasing the resolution and depth of this technology and extending it to the level of cells within the tissue is needed. Although the use of single nuclear and single cell RNA sequencing has become widespread, the expression signatures of cells obtained from tissue dissociation do not maintain spatial context. Laser microdissection (LMD) based on specific fluorescent markers would allow the isolation of specific structures and cell groups of interest with known localization, thereby enabling the acquisition of spatially-anchored transcriptomic signatures in kidney tissue. We have optimized an LMD methodology, guided by a rapid fluorescence-based stain, to isolate five distinct compartments within the human kidney and conduct subsequent RNA sequencing from valuable human kidney tissue specimens. We also present quality control parameters to enable the assessment of adequacy of the collected specimens. The workflow outlined in this manuscript shows the feasibility of this approach to isolate sub-segmental transcriptomic signatures with high confidence. The methodological approach presented here may also be applied to other tissue types with substitution of relevant antibody markers.

Quantitative Large-Scale Three-Dimensional Imaging of Human Kidney Biopsies: A Bridge to Precision Medicine in Kidney Disease

Kidney biopsy remains the gold standard for uncovering the pathogenesis of acute and chronic kidney diseases. However, the ability to perform high resolution, quantitative, molecular and cellular interrogation of this precious tissue is still at a developing stage compared to other fields such as oncology. Here, we discuss recent advances in performing large-scale, three-dimensional (3D), multi-fluorescence imaging of kidney biopsies and quantitative analysis referred to as 3D tissue cytometry. This approach allows the accurate measurement of specific cell types and their spatial distribution in a thick section spanning the entire length of the biopsy. By uncovering specific disease signatures, including rare occurrences, and linking them to the biology in situ, this approach will enhance our understanding of disease pathogenesis. Furthermore, by providing accurate quantitation of cellular events, 3D cytometry may improve the accuracy of prognosticating the clinical course and response to therapy. Therefore, large-scale 3D imaging and cytometry of kidney biopsy is poised to become a bridge towards personalized medicine for patients with kidney disease.

Live-Animal Imaging of Renal Function by Multiphoton Microscopy

Intravital microscopy, microscopy of living animals, is a powerful research technique that combines the resolution and sensitivity found in microscopic studies of cultured cells with the relevance and systemic influences of cells in the context of the intact animal. The power of intravital microscopy has recently been extended with the development of multiphoton fluorescence microscopy systems capable of collecting optical sections from deep within the kidney at subcellular resolution, supporting high-resolution characterizations of the structure and function of glomeruli, tubules, and vasculature in the living kidney. Fluorescent probes are administered to an anesthetized, surgically prepared animal, followed by image acquisition for up to 3 hr. Images are transferred via a high-speed network to specialized computer systems for digital image analysis. This general approach can be used with different combinations of fluorescent probes to evaluate processes such as glomerular permeability, proximal tubule endocytosis, microvascular flow, vascular permeability, mitochondrial function, and cellular apoptosis/necrosis. © 2018 by John Wiley & Sons, Inc.

Endothelial STAT3 Modulates Protective Mechanisms in a Mouse Ischemia-Reperfusion Model of Acute Kidney Injury

STAT3 is a transcriptional regulator that plays an important role in coordinating inflammation and immunity. In addition, there is a growing appreciation of the role STAT3 signaling plays in response to organ injury following diverse insults. Acute kidney injury (AKI) from ischemia-reperfusion injury is a common clinical entity with devastating consequences, and the recognition that endothelial alterations contribute to kidney dysfunction in this setting is of growing interest. Consequently, we used a mouse with a genetic deletion of Stat3 restricted to the endothelium to examine the role of STAT3 signaling in the pathophysiology of ischemic AKI. In a mouse model of ischemic AKI, the loss of endothelial STAT3 signaling significantly exacerbated kidney dysfunction, morphologic injury, and proximal tubular oxidative stress. The increased severity of ischemic AKI was associated with more robust endothelial-leukocyte adhesion and increased tissue accumulation of F4/80+ macrophages. Moreover, important proximal tubular adaptive mechanisms to injury were diminished in association with decreased tissue mRNA levels of the epithelial cell survival cytokine IL-22. In aggregate, these findings suggest that the endothelial STAT3 signaling plays an important role in limiting kidney dysfunction in ischemic AKI and that selective pharmacologic activation of endothelial STAT3 signaling could serve as a potential therapeutic target.

Quantitative Three-Dimensional Tissue Cytometry to Study Kidney Tissue and Resident Immune Cells

Analysis of the immune system in the kidney relies predominantly on flow cytometry. Although powerful, the process of tissue homogenization necessary for flow cytometry analysis introduces bias and results in the loss of morphologic landmarks needed to determine the spatial distribution of immune cells. An ideal approach would support three-dimensional (3D) tissue cytometry: an automated quantitation of immune cells and associated spatial parameters in 3D image volumes collected from intact kidney tissue. However, widespread application of this approach is limited by the lack of accessible software tools for digital analysis of large 3D microscopy data. Here, we describe Volumetric Tissue Exploration and Analysis (VTEA) image analysis software designed for efficient exploration and quantitative analysis of large, complex 3D microscopy datasets. In analyses of images collected from fixed kidney tissue, VTEA replicated the results of flow cytometry while providing detailed analysis of the spatial distribution of immune cells in different regions of the kidney and in relation to specific renal structures. Unbiased exploration with VTEA enabled us to discover a population of tubular epithelial cells that expresses CD11C, a marker typically expressed on dendritic cells. Finally, we show the use of VTEA for large-scale quantitation of immune cells in entire human kidney biopsies. In summary, we show that VTEA is a simple and effective tool that supports unique digital interrogation and analysis of kidney tissue from animal models or biobanked human kidney biopsies. We have made VTEA freely available to interested investigators via electronic download.

Inhibition of Toll-Like Receptor 4 Signaling Mitigates Microvascular Loss but Not Fibrosis in a Model of Ischemic Acute Kidney Injury

The development of chronic kidney disease (CKD) following an episode of acute kidney injury (AKI) is an increasingly recognized clinical problem. Inhibition of toll-like receptor 4 (TLR4) protects renal function in animal models of AKI and has become a viable therapeutic strategy in AKI. However, the impact of TLR4 inhibition on the chronic sequelae of AKI is unknown. Consequently, we examined the chronic effects of TLR4 inhibition in a model of ischemic AKI. Mice with a TLR4-deletion on a C57BL/6 background and wild-type (WT) background control mice (C57BL/6) were subjected to bilateral renal artery clamping for 19 min and reperfusion for up to 6 weeks. Despite the acute protective effect of TLR4 inhibition on renal function (serum creatinine 1.6 ± 0.4 mg/dL TLR4-deletion vs. 2.8 ± 0.3 mg/dL·WT) and rates of tubular apoptosis following ischemic AKI, we found no difference in neutrophil or macrophage infiltration. Furthermore, we observed significant protection from microvascular rarefaction at six weeks following injury with TLR4-deletion, but this did not alter development of fibrosis. In conclusion, we validate the acute protective effect of TLR4 signal inhibition in AKI but demonstrate that this protective effect does not mitigate the sequential fibrogenic response in this model of ischemic AKI.

Novel application of complementary imaging techniques to examine in vivo glucose metabolism in the kidney

The metabolic status of the kidney is a determinant of injury susceptibility and a measure of progression for many disease processes; however, noninvasive modalities to assess kidney metabolism are lacking. In this study, we employed positron emission tomography (PET) and intravital multiphoton microscopy (MPM) to assess cortical and proximal tubule glucose tracer uptake, respectively, following experimental perturbations of kidney metabolism. Applying dynamic image acquisition PET with 2-¹⁸fluoro-2-deoxyglucose (¹⁸F-FDG) and tracer kinetic modeling, we found that an intracellular compartment in the cortex of the kidney could be distinguished from the blood and urine compartments in animals. Given emerging literature that the tumor suppressor protein p53 is an important regulator of cellular metabolism, we demonstrated that PET imaging was able to discern a threefold increase in cortical ¹⁸F-FDG uptake following the pharmacological inhibition of p53 in animals. Intravital MPM with the fluorescent glucose analog 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG) provided increased resolution and corroborated these findings at the level of the proximal tubule. Extending our observation of p53 inhibition on proximal tubule glucose tracer uptake, we demonstrated by intravital MPM that pharmacological inhibition of p53 diminishes mitochondrial potential difference. We provide additional evidence that inhibition of p53 alters key metabolic enzymes regulating glycolysis and increases intermediates of glycolysis. In summary, we provide evidence that PET is a valuable tool for examining kidney metabolism in preclinical and clinical studies, intravital MPM is a powerful adjunct to PET in preclinical studies of metabolism, and p53 inhibition alters basal kidney metabolism.

Muc1 enhances the β-catenin protective pathway during ischemia-reperfusion injury

The hypoxia-inducible factor (HIF)-1 and β-catenin protective pathways represent the two most significant cellular responses that are activated in response to acute kidney injury. We previously reported that murine mucin (Muc)1 protects kidney function and morphology in a mouse model of ischemia-reperfusion injury (IRI) by stabilizing HIF-1α, enhancing HIF-1 downstream signaling, and thereby preventing metabolic stress (Pastor-Soler et al. Muc1 is protective during kidney ischemia-reperfusion injury. Am J Physiol Renal Physiol 308: F1452-F1462, 2015). We asked if Muc1 regulates the β-catenin protective pathway during IRI as 1) β-catenin nuclear targeting is MUC1 dependent in cultured human cells, 2) β-catenin is found in coimmunoprecipitates with human MUC1 in extracts of both cultured cells and tissues, and 3) MUC1 prevents β-catenin phosphorylation by glycogen synthase kinase (GSK)3β and thereby β-catenin degradation. Using the same mouse model of IRI, we found that levels of active GSK3β were significantly lower in kidneys of control mice compared with Muc1 knockout (KO) mice. Consequently, β-catenin was significantly upregulated at 24 and 72 h of recovery and appeared in the nuclear fraction at 72 h in control mouse kidneys. Both β-catenin induction and nuclear targeting were absent in Muc1 KO mice. We also found downstream induction of β-catenin prosurvival factors (activated Akt, survivin, transcription factor T cell factor 4 (TCF4), and its downstream target cyclin D1) and repression of proapoptotic factors (p53, active Bax, and cleaved caspase-3) in control mouse kidneys that were absent or aberrant in kidneys of Muc1 KO mice. Altogether, the data clearly indicate that Muc1 protection during acute kidney injury proceeds by enhancing both the HIF-1 and β-catenin protective pathways.

Muc1 is protective during kidney ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) due to hypotension is a common cause of human acute kidney injury (AKI). Hypoxia-inducible transcription factors (HIFs) orchestrate a protective response in renal endothelial and epithelial cells in AKI models. As human mucin 1 (MUC1) is induced by hypoxia and enhances HIF-1 activity in cultured epithelial cells, we asked whether mouse mucin 1 (Muc1) regulates HIF-1 activity in kidney tissue during IRI. Whereas Muc1 was localized on the apical surface of the thick ascending limb, distal convoluted tubule, and collecting duct in the kidneys of sham-treated mice, Muc1 appeared in the cytoplasm and nucleus of all tubular epithelia during IRI. Muc1 was induced during IRI, and Muc1 transcripts and protein were also present in recovering proximal tubule cells. Kidney damage was worse and recovery was blocked during IRI in Muc1 knockout mice compared with congenic control mice. Muc1 knockout mice had reduced levels of HIF-1α, reduced or aberrant induction of HIF-1 target genes involved in the shift of glucose metabolism to glycolysis, and prolonged activation of AMP-activated protein kinase, indicating metabolic stress. Muc1 clearly plays a significant role in enhancing the HIF protective pathway during ischemic insult and recovery in kidney epithelia, providing a new target for developing therapies to treat AKI. Moreover, our data support a role specifically for HIF-1 in epithelial protection of the kidney during IRI as Muc1 is present only in tubule epithelial cells.

The role of APOE-ɛ4 and beta amyloid in the differential rate of recovery from ECT: a review

Individual biological differences may contribute to the variability of outcomes, including cognitive effects, observed following electroconvulsive treatment (ECT). A narrative review of the research literature on carriage of the apolipoprotein E ɛ4 allele (APOE-ɛ4) and the protein biomarker beta amyloid (Aβ) with ECT cognitive outcome was undertaken. ECT induces repeated brain seizures and there is debate as to whether this causes brain injury and long-term cognitive disruption. The majority of ECT is administered to the elderly (over age 65 years) with drug-resistant depression. Depression in the elderly may be a symptom of the prodromal stage of Alzheimer's disease (AD). Carriage of the APOE-ɛ4 allele and raised cerebral Aβ are consistently implicated in AD, but inconsistently implicated in brain injury (and related syndromes) recovery rates. A paucity of brain-related recovery, genetic and biomarker research in ECT responses in the elderly was found: three studies have examined the effect of APOE-ɛ4 allele carriage on cognition in the depressed elderly receiving ECT, and two have examined Aβ changes after ECT, with contradictory findings. Cognitive changes in all studies of ECT effects were measured by a variety of psychological tests, making comparisons of such changes between studies problematic. Further, psychological test data-validity measures were not routinely administered, counter to current testing recommendations. The methodological issues of the currently available literature as well as the need for well-designed, hypothesis driven, longitudinal studies are discussed.

Endothelial HIF-2 mediates protection and recovery from ischemic kidney injury

The hypoxia-inducible transcription factors HIF-1 and HIF-2 mediate key cellular adaptions to hypoxia and contribute to renal homeostasis and pathophysiology; however, little is known about the cell type-specific functions of HIF-1 and HIF-2 in response to ischemic kidney injury. Here, we used a genetic approach to specifically dissect the roles of endothelial HIF-1 and HIF-2 in murine models of hypoxic kidney injury induced by ischemia reperfusion or ureteral obstruction. In both models, inactivation of endothelial HIF increased injury-associated renal inflammation and fibrosis. Specifically, inactivation of endothelial HIF-2α, but not endothelial HIF-1α, resulted in increased expression of renal injury markers and inflammatory cell infiltration in the postischemic kidney, which was reversed by blockade of vascular cell adhesion molecule-1 (VCAM1) and very late antigen-4 (VLA4) using monoclonal antibodies. In contrast, pharmacologic or genetic activation of HIF via HIF prolyl-hydroxylase inhibition protected wild-type animals from ischemic kidney injury and inflammation; however, these same protective effects were not observed in HIF prolyl-hydroxylase inhibitor-treated animals lacking endothelial HIF-2. Taken together, our data indicate that endothelial HIF-2 protects from hypoxia-induced renal damage and represents a potential therapeutic target for renoprotection and prevention of fibrosis following acute ischemic injury.

Live-animal imaging of renal function by multiphoton microscopy

Intravital microscopy, microscopy of living animals, is a powerful research technique that combines the resolution and sensitivity found in microscopic studies of cultured cells with the relevance and systemic influences of cells in the context of the intact animal. The power of intravital microscopy has recently been extended with the development of multiphoton fluorescence microscopy systems capable of collecting optical sections from deep within the kidney at subcellular resolution, supporting high-resolution characterizations of the structure and function of glomeruli, tubules, and vasculature in the living kidney. Fluorescent probes are administered to an anesthetized, surgically prepared animal, followed by image acquisition for up to 3 hr. Images are transferred via a high-speed network to specialized computer systems for digital image analysis. This general approach can be used with different combinations of fluorescent probes to evaluate processes such as glomerular permeability, proximal tubule endocytosis, microvascular flow, vascular permeability, mitochondrial function, and cellular apoptosis/necrosis.

p53 is renoprotective after ischemic kidney injury by reducing inflammation

In the rat, p53 promotes tubular apoptosis after ischemic AKI. Acute pharmacologic inhibition of p53 is protective in this setting, but chronic inhibition enhances fibrosis, demonstrating that the role of p53 in ischemic AKI is incompletely understood. Here, we investigated whether genetic absence of p53 is also protective in ischemic AKI. Surprisingly, p53-knockout mice (p53(-/-)) had worse kidney injury, compared with wild-type mice, and exhibited increased and prolonged infiltration of leukocytes after ischemia. Acute inhibition of p53 with pifithrin-α in wild-type mice mimicked the observations in p53(-/-) mice. Chimeric mice that lacked p53 in leukocytes sustained injury similar to p53(-/-) mice, suggesting an important role for leukocyte p53 in ischemic AKI. Compared with wild-type mice, a smaller proportion of macrophages in the kidneys of p53(-/-) and pifithrin-α-treated mice after ischemic injury were the anti-inflammatory M2 phenotype. Ischemic kidneys of p53(-/-) and pifithrin-α-treated mice also showed reduced expression of Kruppel-like factor-4. Finally, models of peritonitis in p53(-/-) and pifithrin-α-treated mice confirmed the anti-inflammatory role of p53 and its effect on the polarization of macrophage phenotype. In summary, in contrast to the rat, inflammation characterizes ischemic AKI in mice; leukocyte p53 is protective by reducing the extent and duration of this inflammation and by promoting the anti-inflammatory M2 macrophage phenotype.

Pathophysiology of acute kidney injury

Acute kidney injury (AKI) is the leading cause of nephrology consultation and is associated with high mortality rates. The primary causes of AKI include ischemia, hypoxia, or nephrotoxicity. An underlying feature is a rapid decline in glomerular filtration rate (GFR) usually associated with decreases in renal blood flow. Inflammation represents an important additional component of AKI leading to the extension phase of injury, which may be associated with insensitivity to vasodilator therapy. It is suggested that targeting the extension phase represents an area potential of treatment with the greatest possible impact. The underlying basis of renal injury appears to be impaired energetics of the highly metabolically active nephron segments (i.e., proximal tubules and thick ascending limb) in the renal outer medulla, which can trigger conversion from transient hypoxia to intrinsic renal failure. Injury to kidney cells can be lethal or sublethal. Sublethal injury represents an important component in AKI, as it may profoundly influence GFR and renal blood flow. The nature of the recovery response is mediated by the degree to which sublethal cells can restore normal function and promote regeneration. The successful recovery from AKI depends on the degree to which these repair processes ensue and these may be compromised in elderly or chronic kidney disease (CKD) patients. Recent data suggest that AKI represents a potential link to CKD in surviving patients. Finally, earlier diagnosis of AKI represents an important area in treating patients with AKI that has spawned increased awareness of the potential that biomarkers of AKI may play in the future.

Soluble thrombomodulin reduces inflammation and prevents microalbuminuria induced by chronic endothelial activation in transgenic mice

Chronic kidney disease pathogenesis involves both tubular and vascular injuries. Despite abundant investigations to identify the risk factors, the involvement of chronic endothelial dysfunction in developing nephropathies is insufficiently explored. Previously, soluble thrombomodulin (sTM), a cofactor in the activation of protein C, has been shown to protect endothelial function in models of acute kidney injury. In this study, the role for sTM in treating chronic kidney disease was explored by employing a mouse model of chronic vascular activation using endothelial-specific TNF-α-expressing (tie2-TNF) mice. Analysis of kidneys from these mice after 3 mo showed no apparent phenotype, whereas 6-mo-old mice demonstrated infiltration of CD45-positive leukocytes accompanied by upregulated gene expression of inflammatory chemokines, markers of kidney injury, and albuminuria. Intervention with murine sTM with biweekly subcutaneous injections during this window of disease development between months 3 and 6 prevented the development of kidney pathology. To better understand the mechanisms of these findings, we determined whether sTM could also prevent chronic endothelial cell activation in vitro. Indeed, treatment with sTM normalized increased chemokines, adhesion molecule expression, and reduced transmigration of monocytes in continuously activated TNF-expressing endothelial cells. Our results suggest that vascular inflammation associated with vulnerable endothelium can contribute to loss in renal function as suggested by the tie2-TNF mice, a unique model for studying the role of vascular activation and inflammation in chronic kidney disease. Furthermore, the ability to restore the endothelial balance by exogenous administration of sTM via downregulation of specific adhesion molecules and chemokines suggests a potential for therapeutic intervention in kidney disease associated with chronic inflammation.

The p53 inhibitor pifithrin-α can stimulate fibrosis in a rat model of ischemic acute kidney injury

Inhibition of the tumor suppressor p53 diminishes tubular cell apoptosis and protects renal function in animal models of acute kidney injury (AKI). Therefore, targeting p53 has become an attractive therapeutic strategy in the approach to AKI. Although the acute protective effects of p53 inhibition in AKI have been examined, there is still relatively little known regarding the impact of acute p53 inhibition on the chronic sequelae of AKI. Consequently, we utilized the p53 inhibitor pifithrin-α to examine the long-term effects of p53 inhibition in a rodent model of ischemic AKI. Male Sprague-Dawley rats were subjected to bilateral renal artery clamping for 30 min followed by reperfusion for up to 8 wk. Pifithrin-α or vehicle control was administered at the time of surgery and then daily for 2 days [brief acute administration (BA)] or 7 days [prolonged acute administration (PA)]. Despite the acute protective effect of pifithrin-α in models of ischemic AKI, we found no protection in the microvascular rarefaction at 4 wk or development fibrosis at 8 wk with pifithrin-α administered on the BA schedule compared with vehicle control-treated animals. Furthermore, pifithrin-α administered on a PA schedule actually produced worse fibrosis compared with vehicle control animals after ischemic injury [21%/area (SD4.4) vs.16%/area (SD3.6)] as well as under sham conditions [2.6%/area (SD1.8) vs. 4.7%/area (SD1.3)]. The development of fibrosis with PA administration was independent of microvascular rarefaction. We identified enhanced extracellular matrix production, epithelial-to-mesenchymal transition, and amplified inflammatory responses as potential contributors to the augmented fibrosis observed with PA administration of pifithrin-α.

Fueling the fire in acute kidney injury: endothelial cells collect their Toll

Chen et al. demonstrate endothelial expression of Toll-like receptor 4 (TLR4) in the outer medulla of the kidney early in the course of ischemic acute kidney injury. Furthermore, they provide data that support the hypothesis that activation of endothelial TLR4 in the early extension phase of AKI by damage-associated molecular pattern molecules released from injured tubules results in endothelial activation. This activation can serve to amplify inflammation and tubular damage.

MMP-9 gene deletion mitigates microvascular loss in a model of ischemic acute kidney injury

Microvascular rarefaction following an episode of acute kidney injury (AKI) is associated with renal hypoxia and progression toward chronic kidney disease. The mechanisms contributing to microvascular rarefaction are not well-understood, although disruption in local angioregulatory substances is thought to contribute. Matrix metalloproteinase (MMP)-9 is an endopeptidase important in modifying the extracellular matrix (ECM) and remodeling the vasculature. We examined the role of MMP-9 gene deletion on microvascular rarefaction in a rodent model of ischemic AKI. MMP-9-null mice and background control (FVB/NJ) mice were subjected to bilateral renal artery clamping for 20 min followed by reperfusion for 14, 28, or 56 days. Serum creatinine level in MMP-9-null mice 24 h after injury [1.4 (SD 0.8) mg/dl] was not significantly different from FVB/NJ mice [1.5 (SD 0.6) mg/dl]. Four weeks after ischemic injury, FVB/NJ mice demonstrated a 30-40% loss of microvascular density compared with sham-operated (SO) mice. In contrast, microvascular density was not significantly different in the MMP-9-null mice at this time following injury compared with SO mice. FVB/NJ mice had a 50% decrease in tissue vascular endothelial growth factor (VEGF) 2 wk after ischemic insult compared with SO mice. A significant difference in VEGF was not observed in MMP-9-null mice compared with SO mice. There was no significant difference in the liberation of angioinhibitory fragments from the ECM between MMP-9-null mice and FVB/NJ mice following ischemic injury. In conclusion, MMP-9 deletion stabilizes microvascular density following ischemic AKI in part by preserving tissue VEGF levels.

Impaired endothelial proliferation and mesenchymal transition contribute to vascular rarefaction following acute kidney injury

Acute kidney injury induces the loss of renal microvessels, but the fate of endothelial cells and the mechanism of potential vascular endothelial growth factor (VEGF)-mediated protection is unknown. Cumulative cell proliferation was analyzed in the kidney of Sprague-Dawley rats following ischemia-reperfusion (I/R) injury by repetitive administration of BrdU (twice daily) and colocalization in endothelial cells with CD31 or cablin. Proliferating endothelial cells were undetectable for up to 2 days following I/R and accounted for only ∼1% of BrdU-positive cells after 7 days. VEGF-121 preserved vascular loss following I/R but did not affect proliferation of endothelial, perivascular cells or tubular cells. Endothelial mesenchymal transition states were identified by localizing endothelial markers (CD31, cablin, or infused tomato lectin) with the fibroblast marker S100A4. Such structures were prominent within 6 h and sustained for at least 7 days following I/R. A Tie-2-cre transgenic crossed with a yellow fluorescent protein (YFP) reporter mouse was used to trace the fate of endothelial cells and demonstrated interstititial expansion of YFP-positive cells colocalizing with S100A4 and smooth muscle actin following I/R. The interstitial expansion of YFP cells was attenuated by VEGF-121. Multiphoton imaging of transgenic mice revealed the alteration of YFP-positive vascular cells associated with blood vessels characterized by limited perfusion in vivo. Taken together, these data indicate that vascular dropout post-AKI results from endothelial phenotypic transition combined with an impaired regenerative capacity, which may contribute to progressive chronic kidney disease.

Alteration of microvascular permeability in acute kidney injury

Functional and structural abnormalities in the renal microvasculature are important processes contributing to the pathophysiology of ischemic acute kidney injury (AKI). Renewed interest in the complex interplay between tubular injury, inflammation and microvascular alterations has emerged in order to gain a better understanding of acute kidney injury syndromes. This review examines alterations of the renal microvasculature as they relate to ischemic and septic AKI with an emphasis on the mechanisms involved in altered microvascular permeability.

p53 regulates renal expression of HIF-1{alpha} and pVHL under physiological conditions and after ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) is a common cause of acute kidney injury (AKI) and is characterized by widespread tubular and microvascular damage. The tumor suppressor p53 is upregulated after IRI and contributes to renal injury in part by promoting apoptosis. Acute, short-term inhibition of p53 with pifithrin-alpha conveys significant protection after IRI. The hypoxia-inducible factor-1 (HIF-1) pathway is also activated after IRI and has opposing effects to those promoted by p53. The balance between the HIF-1 and p53 responses can determine the outcome of IRI. In this manuscript, we investigate whether p53 regulates the HIF-1 pathway in a rodent model of IRI. HIF-1alpha is principally expressed in the collecting tubules (CT) and thick ascending limbs (TAL) under physiological conditions. However, inhibition of p53 with pifithrin-alpha increases the faint expression of HIF-1alpha in proximal tubules (PT) under physiological conditions. Twenty-four hours after IRI, HIF-1alpha expression is decreased in both CT and TAL. HIF-1alpha expression in the PT is not significantly altered after IRI. Acute inhibition of p53 significantly increases HIF-1alpha expression in the PT after IRI. Additionally, pifithrin-alpha prevents the IRI-induced decrease in HIF-1alpha in the CT and TAL. Parallel changes are observed in the HIF-1alpha transcriptive target, carbonic anhydrase-9. Finally, inhibition of p53 prevents the dramatic changes in Von Hippel-Lindau protein morphology and expression after IRI. We conclude that activation of p53 after IRI mitigates the concomitant activation of the protective HIF-1 pathway. Modulating the interactions between the p53 and HIF-1 pathway can provide novel options in the treatment of AKI.

Preservation of peritubular capillary endothelial integrity and increasing pericytes may be critical to recovery from postischemic acute kidney injury

Decreased renal blood flow following an ischemic insult contributes to a reduction in glomerular filtration. However, little is known about the underlying cellular or subcellular mechanisms mediating reduced renal blood flow in human ischemic acute kidney injury (AKI) or acute renal failure (ARF). To examine renal vascular injury following ischemia, intraoperative graft biopsies were performed after reperfusion in 21 cadaveric renal allografts. Confocal fluorescence microscopy was utilized to examine vascular smooth muscle and endothelial cell integrity as well as peritubular interstitial pericytes in the biopsies. The reperfused, transplanted kidneys exhibited postischemic injury to the renal vasculature, as demonstrated by disorganization/disarray of the actin cytoskeleton in vascular smooth muscle cells and disappearance of von Willebrand factor from vascular endothelial cells. Damage to peritubular capillary endothelial cells was more severe in subjects destined to have sustained ARF than in those with rapid recovery of their graft function. In addition, peritubular pericytes/myofibroblasts were more pronounced in recipients destined to recover than those with sustained ARF. Taken together, these data suggest damage to the renal vasculature occurs after ischemia-reperfusion in human kidneys. Preservation of peritubular capillary endothelial integrity and increasing pericytes may be critical to recovery from postischemic AKI.

Acute and chronic microvascular alterations in a mouse model of ischemic acute kidney injury

Functional and structural abnormalities in the renal microvasculature are important processes contributing to the pathophysiology of ischemic acute kidney injury (AKI). In this study, we examine the contribution of endothelial cell loss via apoptosis on microvascular permeability and rarefaction in a mouse model of ischemic AKI. Three-dimensional reconstructions of microvascular networks obtained 24 h following acute ischemic injury demonstrate an intact endothelial monolayer in areas of increased microvascular permeability. A 45% decrease in microvascular density was observed 4 wk after acute ischemic injury. Examination of microvascular endothelial cells following acute ischemic injury did not reveal evidence of positive terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling staining at 1, 2, 8, and 16 days following ischemia; however, activation of caspase-3 was evident in endothelial cells following acute ischemic injury. Examination of angiopoietin (Ang) protein expression in the kidney 24 h after ischemic injury revealed an eightfold increase in Ang-1 but no significant change in Ang-2. No significant difference in the expression of vascular endothelial growth factor or Ang-2 was observed 4 wk after ischemic injury, although an almost twofold elevation in Ang-1 was observed. An increase in angiostatic breakdown products of collagen IV was observed at both 24 h and 4 wk after ischemic injury. Taken together, these findings indicate that the loss of endothelial cells following ischemic injury is not a major contributor to altered microvascular permeability, although renal microvascular endothelial cells are vulnerable to the initiation of apoptotic mechanisms following ischemic injury that can ultimately impact microvascular density.

Organic cation transport in the rat kidney in vivo visualized by time-resolved two-photon microscopy

Secretion of cationic drugs and endogenous metabolites is a major function of the kidney accomplished by tubular organic cation transport systems. A cationic styryl dye (ASP(+)) was developed as a fluorescent substrate for renal organic cation transporters. The dye was injected intravenously and continuously monitored in externalized rat kidneys by time-resolved two-photon laser scanning microscopy. To investigate changes in transport activity, cimetidine, a competitive inhibitor of organic cation transport was co-injected with ASP(+). Shortly after injection, fluorescence increased in peritubular capillaries. Simultaneously, fluorescence was transiently found at the basolateral membrane of the proximal and distal tubules at a higher intensity and shorter wavelength indicating membrane association of ASP(+). Subsequently, intracellular fluorescence increased steeply within 10 s. In the proximal tubules, intracellular fluorescence decreased by 50% within 5 min, while in the distal tubules the fluorescence decreased by only 5% within the same time frame. Intracellular uptake of ASP(+) into proximal tubules was significantly reduced by cimetidine. Our studies show that organic cation transport of the kidney can be visualized in vivo by two-photon laser scanning microscopy.

Imaging vascular pathology

Examining the mechanisms of renal microvascular alterations in disease and the ramifications they have for overall organ function has remained a challenge due to the complexity of the renal microvascular system and the inability to examine it with sufficient resolution in vivo. However, advances in intravital microscopy have provided opportunities to meet these challenges. In this review we will examine specific areas where intravital imaging has advanced our knowledge of renal disease processes and present areas where these techniques, especially intravital multiphoton microscopy, have even further potential to integrate our knowledge of renal vascular pathology.

Minocycline reduces renal microvascular leakage in a rat model of ischemic renal injury

Tetracyclines exhibit significant anti-inflammatory properties, inhibit matrix metalloproteinases (MMPs), and are protective in models of ischemia-reperfusion injury (IRI). Both inflammatory cascades and MMP activation have been demonstrated to modulate microvascular permeability. Because increased microvascular permeability occurs during IRI in a variety of organ systems including the kidney, we hypothesized that minocycline, a semisynthetic tetracycline, would diminish microvascular leakage during renal IRI. To test this hypothesis, we used intravital 2-photon microscopy to examine leakage of fluorescent dextrans from the vasculature in a rodent model of IRI. Minocycline significantly reduced the extent of dextran (500 kDa) leakage from the renal microvasculature 24 h after ischemia. Although minocycline diminished leukocyte accumulation in the kidney following ischemia, areas of leukocyte accumulation did not correlate with areas of microvascular permeability in either the saline- or minocycline-pretreated animals. Minocycline diminished the perivascular increase in MMP-2 and MMP-9, as well as the increase in MMP-2 activity 24 h after ischemia. ABT-518, a specific inhibitor of MMP-2 and MMP-9, also significantly reduced the extent of dextran (500 kDa) leakage from the renal microvasculature 24 h after ischemia. Our results indicate that minocycline mitigates the renal microvascular permeability defect following IRI. This effect is spatially distinct from the effect of minocycline on leukocyte accumulation and may be related to diminished activity of MMPs on the integrity of the perivascular matrix.

Endothelial injury and dysfunction: role in the extension phase of acute renal failure

The pathophysiology of ischemic acute renal failure (ARF) involves a complex interplay between renal hemodynamics, tubular and endothelial cell injury, and inflammatory processes. A growing body of evidence supports the contribution of altered renal vascular function, especially at the microvascular level, in initiating and subsequently extending the initial tubular injury. The extension phase of ischemic ARF involves continued reduction in renal perfusion, ongoing hypoxia, and inflammatory processes that occur during reperfusion and contribute to continued tubular cell injury. Vascular endothelial cell injury and dysfunction play a vital part in this extension phase. With injury, the endothelial cell loses its ability to regulate vascular tone, perfusion, permeability and inflammation/adhesion. This loss of regulatory function has a detrimental impact upon renal function. Vascular congestion, edema formation, diminished blood flow, and infiltration of inflammatory cells have been documented in the corticomedullary junction of the kidney. However, linking their genesis to microvascular endothelial injury and dysfunction has been difficult. New diagnostic and therapeutic approaches to ischemic ARF must incorporate these finding to devise early recognition strategies and therapeutic approaches.

Minocycline inhibits apoptosis and inflammation in a rat model of ischemic renal injury

Tetracyclines exhibit significant anti-inflammatory properties in a variety of rheumatologic and dermatologic conditions. They have also been shown to inhibit apoptosis in certain neurodegenerative disorders. Because ischemic renal injury is characterized by both apoptosis and inflammation, we investigated the therapeutic potential of tetracyclines in a rat model of renal ischemia-reperfusion. Male Sprague-Dawley rats underwent bilateral renal artery clamp for 30 min followed by reperfusion and received either minocycline or saline for 36 h before ischemia. Minocycline reduced tubular cell apoptosis 24 h after ischemia as determined by terminal transferase-mediated dUTP nick end-labeling staining and nuclear morphology. It also decreased cytochrome c release into the cytoplasm and reduced upregulation of p53 and Bax after ischemia. The minocycline-treated group showed a significant reduction in tubular injury and cast formation. In addition, minocycline reduced the number of infiltrating leukocytes, decreased leukocyte chemotaxis both in vitro and ex vivo, and downregulated the expression of ICAM-1. Serum creatinine 24-h postischemia was significantly reduced in the minocycline-treated group. We conclude that minocycline has potent antiapoptotic and anti-inflammatory properties and protects renal function in this model of ischemia-reperfusion. Tetracyclines are among the safest and best-studied antibiotics. They are thus attractive candidates for the therapy of human ischemic acute renal failure.

Injury of the renal microvascular endothelium alters barrier function after ischemia

The role of renal microvascular endothelial cell injury in the pathophysiology of ischemic acute renal failure (ARF) remains largely unknown. No consistent morphological alterations have been ascribed to the endothelium of the renal microvasculature as a result of ischemia-reperfusion injury. Therefore, the purpose of this study was to examine biochemical markers of endothelial injury and morphological changes in the renal microvascular endothelium in a rodent model of ischemic ARF. Circulating von Willebrand factor (vWF) was measured as a marker of endothelial injury. Twenty-four hours after ischemia, circulating vWF peaked at 124% over baseline values (P = 0.001). The FVB-TIE2/GFP mouse was utilized to localize morphological changes in the renal microvascular endothelium. Immediately after ischemia, there was a marked increase in F-actin aggregates in the basal and basolateral aspect of renal microvascular endothelial cells in the corticomedullary junction. After 24 h of reperfusion, the pattern of F-actin staining was more similar to that observed under physiological conditions. In addition, alterations in the integrity of the adherens junctions of the renal microvasculature, as demonstrated by loss of localization in vascular endothelial cadherin immunostaining, were observed after 24 h of reperfusion. This observation temporally correlated with the greatest extent of permeability defect in the renal microvasculature as identified using fluorescent dextrans and two-photon intravital imaging. Taken together, these findings indicate that renal vascular endothelial injury occurs in ischemic ARF and may play an important role in the pathophysiology of ischemic ARF.

Microvascular endothelial injury and dysfunction during ischemic acute renal failure

The pathophysiology of ischemic acute renal failure (ARF) appears to involve a complex interplay between renal hemodynamics, tubular injury, and inflammatory processes. While the current paradigm of the pathophysiology of ischemic ARF invokes both sublethal and lethal tubular injury as being of paramount importance to diminished renal function, a growing body of evidence supports the contribution of altered renal vascular function in potentially initiating and subsequently extending the initial tubular injury. We propose that the "extension phase" of ischemic ARF involves alterations in renal perfusion, continued hypoxia, and inflammatory processes that all contribute to continued tubular cell injury. Vascular endothelial cell injury and dysfunction play a vital part in this extension phase. In the constitutive state the endothelium regulates migration of inflammatory cells into tissue, vascular tone and perfusion, vasopermeability, and prevents coagulation. Upon injury, the endothelial cell loses its ability to regulate these functions. This loss of regulatory function can have a subsequent detrimental impact upon renal function. Vascular congestion, edema formation, diminished blood flow, and infiltration of inflammatory cells have been documented in the corticomedullary junction of the kidney, but linking their genesis to vascular endothelial injury and dysfunction has been difficult. However, new investigative approaches, including multiphoton microscopy and the Tie2-GFP mouse, have been developed that will further our understanding of the roles endothelial injury and dysfunction play in the pathophysiology of ischemic ARF. This knowledge should provide new diagnostic and therapeutic approaches to ischemic ARF.

Endothelial injury and dysfunction in ischemic acute renal failure

Ischemic acute renal failure is the most common cause of acute renal failure in hospitalized patients and has an average mortality rate of 50%. Although epithelial and vascular smooth muscle cell abnormalities have been clearly delineated in association with this condition, the extent of endothelial injury and dysfunction has been difficult to document, primarily for anatomic reasons. However, endothelial tight junction separation and endothelial cell detachment, blebbing, and necrosis have been observed after ischemia in other organs. In addition, adenosine triphosphate depletion studies in cultured endothelial cells have demonstrated that multiple actin-based alterations occur in a reversible and duration-dependent fashion. After an ischemic insult, total renal blood flow returns toward normal, but marked, regional alterations occur. Most affected is the outer medullary or corticomedullary junction region where blood flow remains approximately 10% of normal. In this area, the microvasculature becomes congested. Interstitial edema, red blood cell trapping, leukocyte adherence, and extravasation all contribute to this congestion. Increased expression of both P selectin and E selectin has been documented in renal endothelial cells after ischemic injury, and treatment with antibodies to either intercellular adhesion molecule-1, P selectins, or E selectins has been shown to minimize renal injury. During ischemia in vivo and adenosine triphosphate depletion in cell culture studies, F-actin destruction occurs, with polymerization leading to accumulation of intracellular actin aggregates. By using multiphoton microscopy, Voxx software, and the Tie-2 mouse with selective endothelial cell green fluorescent protein expression driven by the Tie-2 promoter, we have been able to identify macrovascular and microvascular endothelial cells in four dimensions (three dimensions plus time) intravitally. By using Texas red-labeled large molecular weight dextrans, we can document blood flow and vascular dysfunction. Intravital studies using multiphoton imaging techniques can now be conducted to identify and quantify endothelial cell injury and dysfunction in functioning organs.

Rho-kinase regulates myosin II activation in MDCK cells during recovery after ATP depletion

Alterations in the actin cytoskeleton of renal tubular epithelial cells during periods of ischemic injury and recovery have important consequences for normal cell and kidney function. Myosin II has been demonstrated to be an important effector in organizing basal actin structures in some cell types. ATP depletion in vitro has been demonstrated to recapitulate alterations of the actin cytoskeleton in renal tubular epithelial cells observed during renal ischemia in vivo. We utilized this reversible cell culture model of ischemia to examine the correlation of the activation state and cellular distribution of myosin II with disruption of actin stress fibers in Madin-Darby canine kidney (MDCK) cells during ATP depletion and recovery from ATP depletion. We found that myosin II inactivation occurs rapidly and precedes dissociation of myosin II from actin stress fibers during ATP depletion. Myosin II activation temporally correlates with colocalization of myosin II to reorganizing stress fibers during recovery from ATP depletion. Furthermore, myosin activation and actin stress fiber formation were found to be Rho-associated Ser/Thr protein kinase dependent during recovery from ATP depletion.

Mechanisms of cellular injury in ischemic acute renal failure

Significant advances have been made in understanding the pathophysiology of injury at the cellular level in ischemic acute renal failure. Alterations in the actin cytoskeleton are of central importance to the structural, physiological, and biochemical changes that occur in proximal tubule cells during acute ischemic injury. These cytoskeletal alterations occur rapidly and are dependent on the severity and duration of ischemic injury. Most importantly, alterations in the actin cytoskeleton are responsible for changes in the cell surface membrane that modify cell polarity, cell-cell interactions, and cell-matrix interactions. Ultimately, these cytoskeletal alterations play a major role in the decrement in glomerular filtration rate that is the hallmark of ischemic acute renal failure.

Phosphorylation by protein kinase C of the 20,000-dalton light chain of myosin in intact and chemically skinned vascular smooth muscle

In the present study we tested the hypothesis that phosphorylation of the 20,000-dalton light chain subunit of smooth muscle myosin (LC20) by the calcium-activated and phospholipid-dependent protein kinase C regulates contraction of chemically-permeabilized (glycerinated) porcine carotid artery smooth muscle. Purified protein kinase C and oleic acid were used to phosphorylate LC20 in glycerinated muscles in the presence of a CaEGTA/EGTA buffer system (pCa 8) to prevent activation of myosin light chain kinase. Phosphorylation of the light chain to 1.3 mol of PO4/mol of LC20 did not stimulate contraction. Tryptic digests of glycerinated carotid artery LC20 contained two major phosphopeptides which contained phosphoserine but not phosphothreonine. Incubation of glycerinated muscles with calcium (20 microM) and calmodulin (10 microM) resulted in contraction and LC20 phosphorylation to 1.1 mol of PO4/mol of LC20; tryptic digests of LC20 from these muscles contained a single phosphopeptide which could be distinguished by phosphopeptide mapping from the two phosphopeptides derived from muscles phosphorylated with protein kinase C. Further phosphorylation of Ca2+/calmodulin-activated muscles to 2.0 mol of PO4/mol of LC20, by incubation with protein kinase C, had no effect on either the level of isometric force or the lightly-loaded shortening velocity (after-load = 0.1 peak active force); removal of Ca2+ and calmodulin, but not protein kinase C and oleic acid, resulted in normal relaxation in spite of maintained phosphorylation to 1.2 mol of PO4/mol of LC20. Comparison of LC20 phosphopeptide maps from glycerinated muscles incubated with protein kinase C plus Ca2+/calmodulin (2.0 mol of PO4/mol of LC20) to maps from intact muscles stimulated with 10(-6) M phorbol 12,13-dibutyrate (0.05 mol of PO4/mol of LC20) showed that the same three phosphopeptides were present in both the intact and glycerinated muscles. These findings show that phosphorylation of LC20 by protein kinase C in glycerinated muscles to levels at least 40 times higher than those present during contraction of intact, phorbol ester-stimulated muscles does not activate contraction nor does it significantly modify the contraction of smooth muscle which occurs in response to the Ca2+/calmodulin-dependent phosphorylation of Ser19 by myosin light chain kinase.

Phosphorylation of two sites on smooth muscle myosin. Effects on contraction of glycerinated vascular smooth muscle

Contraction of glycerinated porcine carotid artery smooth muscle in response to calcium (20 microM), calmodulin (10 microM), and MgATP was associated with phosphorylation of the 20,000-dalton myosin light chain (LC20) to an average stoichiometry of 1.47 mol of PO4/mol of LC20. Tryptic and chymotryptic phosphopeptide maps of the mono- and diphosphorylated forms of LC20 purified from skinned muscles demonstrated the presence of a single phosphopeptide in all cases. Phosphoamino acid analysis indicated that the monophosphorylated form contained primarily phosphoserine, whereas the diphosphorylated form contained both phosphoserine and phosphothreonine. Thiophosphorylation of LC20 by adenosine 5'-O-(thiotriphosphate) resulted in the incorporation of 1 mol of thiophosphate into phosphoserine. Thiophosphorylated LC20 could be subsequently phosphorylated at a threonine residue to a stoichiometry of 1.7 mol of PO4/mol of LC20 by incubation in the presence of MgATP, calcium, and calmodulin. The extent of multiple site phosphorylation of LC20 was dependent upon both the ionic strength and the free Mg2+ concentration in the muscle bath; increasing either ionic strength (0.07-0.15 M) or [Mg2+] (1-20 mM) resulted in lower stoichiometries of LC20 phosphorylation. The effect of multiple site phosphorylation on contraction was examined in muscles which were seqentially phosphorylated at serine followed by threonine. Full activation (21 degrees C) of both isometric force (1.4 newtons/cm2) and unloaded shortening velocity (0.016 L0/s) was achieved following thiophosphorylation to 1.1 mol of PO4/mol of LC20. No further activation of either isometric force (1.5 newtons/cm2) or unloaded shortening velocity (0.015 L0/s) occurred following phosphorylation to 1.7 mol of PO4/mol of LC20.