Molecular phenotypes of acute kidney injury in kidney transplants.
ABSTRACT: Little is known regarding the molecular phenotype of kidneys with AKI because biopsies are performed infrequently. However, all kidney transplants experience acute injury, making early kidney transplants an excellent model of acute injury, provided the absence of rejection, because donor kidneys should not have CKD, post-transplant biopsies occur relatively frequently, and follow-up is excellent typically. Here, we used histopathology and microarrays to compare indication biopsies from 26 transplants with acute injury with 11 pristine protocol biopsies of stable transplants. Kidneys with acute injury showed increased expression of 394 transcripts associated with the repair response to injury, including many epithelium-like injury molecules tissue, remodeling molecules, and inflammation molecules. Many other genes also predicted the phenotype, including the acute injury biomarkers HAVCR1 and IL18. Pathway analysis of the injury-repair transcripts revealed similarities to cancer, development, and cell movement. The injury-repair transcript score in kidneys with acute injury correlated with reduced graft function, future renal recovery, brain death, and need for dialysis, but not with future graft loss. In contrast, histologic features of acute tubular injury did not correlate with function or with the molecular changes. Thus, the transcripts associated with repair of injury suggest a massive coordinated response of the kidney parenchyma to acute injury, providing both an objective measure for assessing the severity of injury in kidney biopsies and validation for many biomarkers of AKI.
Project description:Microarray analysis of human kidneys with acute kidney injury (AKI) has been limited because such kidneys are seldom biopsied. However, all kidney transplants experience AKI, and early kidney transplants without rejection are an excellent model for human AKI: they are screened to exclude chronic kidney disease, frequently biopsied, and have extensive follow-up. We used histopathology and microarrays to compare indication biopsies from 28 transplants with AKI to 11 pristine protocol biopsies of stable transplants. Kidneys with AKI showed increased expression of 394 injury-repair response associated transcripts, including many known epithelial injury molecules (e.g. ITGB6, LCN2), tissue remodeling molecules (e.g. VCAN), and inflammation molecules (S100A8, ITGB3). Many other genes also predict the phenotype, depending on statistical filtering rules, including AKI biomarkers as HAVCR1 and IL18. Most mouse orthologs of the top injury-repair transcripts were increased in published mouse AKI models. Pathway analysis of the injury-repair transcripts revealed similarities to cancer, development, and cell movement. The injury-repair transcript score AKI kidneys correlated with reduced function, future recovery, brain death, and need for dialysis, but not future graft loss. In contrast, histologic features of "acute tubular injury" did not correlate with function or with the molecular changes. Thus the injury-repair associated transcripts represent a massive coordinate injury-repair response of kidney parenchyma to AKI, similar to mouse AKI models, and provide an objective measure for assessing the severity of AKI in kidney biopsies and validation for the use of many AKI biomarkers. AKI biopsies sample names and CEL files are from GSE21374. All consenting renal transplant patients undergoing biopsies for cause as standard of care between 09/2004 and 10/2007 at the university of Alberta or between 11/2006 and 02/2007 at the University of Illinois were included in the analysis. In addition to the cores required for standard histopathology, we collected one core for gene expression studies. the relationship between gene expression in the biopsy and subsequent graft loss was analyzed.
Project description:BACKGROUND:Kidney transplant biopsies offer an opportunity to understand the pathogenesis of organ fibrosis. We studied the relationships between the time of biopsy after transplant (TxBx), histologic fibrosis, diseases, and transcript expression. METHODS:Expression microarrays from 681 kidney transplant indication biopsies taken either early (n = 282, <1 year) or late (n = 399, >1 year) after transplant were used to analyze the molecular landscape of fibrosis in relationship to histologic fibrosis and diseases. RESULTS:Fibrosis was absent at transplantation but was present in some early biopsies by 4 months after transplant, apparently as a self-limited response to donation implantation injury not associated with progression to failure. The molecular phenotype of early biopsies represented the time sequence of the response to wounding: immediate expression of acute kidney injury transcripts, followed by fibrillar collagen transcripts after several weeks, then by the appearance of immunoglobulin and mast cell transcripts after several months as fibrosis appeared. Fibrosis in late biopsies correlated with injury, fibrillar collagen, immunoglobulin, and mast cell transcripts, but these were independent of time. Pathway analysis revealed epithelial response-to-wounding pathways such as Wnt/?-catenin. CONCLUSION:Fibrosis in late biopsies had different associations because many kidneys had potentially progressive diseases and subsequently failed. Molecular correlations with fibrosis in late biopsies were independent of time, probably because ongoing injury obscured the response-to-wounding time sequence. The results indicate that fibrosis in kidney transplants is driven by nephron injury and that progression to failure reflects continuing injury, not autonomous fibrogenesis. TRIAL REGISTRATION:INTERCOM study (www.clinicalTrials.gov; NCT01299168). FUNDING:Canada Foundation for Innovation and Genome Canada.
Project description:Macrophages (Mø) are integral in ischemia/reperfusion injury-incited (I/R-incited) acute kidney injury (AKI) that leads to fibrosis and chronic kidney disease (CKD). IL-34 and CSF-1 share a receptor (c-FMS), and both cytokines mediate Mø survival and proliferation but also have distinct features. CSF-1 is central to kidney repair and destruction. We tested the hypothesis that IL-34-dependent, Mø-mediated mechanisms promote persistent ischemia-incited AKI that worsens subsequent CKD. In renal I/R, the time-related magnitude of Mø-mediated AKI and subsequent CKD were markedly reduced in IL-34-deficient mice compared with controls. IL-34, c-FMS, and a second IL-34 receptor, protein-tyrosine phosphatase ? (PTP-?) were upregulated in the kidney after I/R. IL-34 was generated by tubular epithelial cells (TECs) and promoted Mø-mediated TEC destruction during AKI that worsened subsequent CKD via 2 distinct mechanisms: enhanced intrarenal Mø proliferation and elevated BM myeloid cell proliferation, which increases circulating monocytes that are drawn into the kidney by chemokines. CSF-1 expression in TECs did not compensate for IL-34 deficiency. In patients, kidney transplants subject to I/R expressed IL-34, c-FMS, and PTP-? in TECs during AKI that increased with advancing injury. Moreover, IL-34 expression increased, along with more enduring ischemia in donor kidneys. In conclusion, IL-34-dependent, Mø-mediated, CSF-1 nonredundant mechanisms promote persistent ischemia-incited AKI that worsens subsequent CKD.
Project description:BACKGROUND:Given the gap between patients in need of a renal transplantation (RTx) and organs available, transplantation centers increasingly accept organs of suboptimal quality, e.g. from donors with acute kidney injury (AKI). METHODS:To determine the outcome of kidney transplants from deceased donors with AKI (defined as ? AKIN stage 1), all 107 patients who received a RTx from donors with AKI between August 2004 and July 2014 at our center were compared to their respective consecutively transplanted patients receiving kidneys from donors without AKI. 5-year patient and graft survival, frequencies of delayed graft function (DGF), acute rejections and glomerular filtration rate (eGFR, CKD-EPI) were assessed. RESULTS:Patient survival was similar in both groups, whereas death-censored and overall graft survival were decreased in AKI kidney recipients. AKI kidney recipients showed higher frequencies of DGF and had a reduced eGFR at 7 days, three months and one and three years after RTx. However, mortality was noticeably lower compared to waiting list candidates. Rejection-free survival was similar between groups. CONCLUSIONS:In our cohort, both short-term and long-term renal function was inferior in recipients of AKI kidneys, while patient survival was similar. Our data indicates that recipients of donor AKI kidneys should be carefully selected and additional factors impairing short- and long-term outcome should be minimized to prevent further deterioration of graft function.
Project description:After acute kidney injury (AKI), patients either recover or alternatively develop fibrosis and chronic kidney disease. Interactions between injured epithelia, stroma, and inflammatory cells determine whether kidneys repair or undergo fibrosis, but the molecular events that drive these processes are poorly understood. Here, we use single nucleus RNA sequencing of a mouse model of AKI to characterize cell states during repair from acute injury. We identify a distinct proinflammatory and profibrotic proximal tubule cell state that fails to repair. Deconvolution of bulk RNA-seq datasets indicates that this failed-repair proximal tubule cell (FR-PTC) state can be detected in other models of kidney injury, increasing during aging in rat kidney and over time in human kidney allografts. We also describe dynamic intercellular communication networks and discern transcriptional pathways driving successful vs. failed repair. Our study provides a detailed description of cellular responses after injury and suggests that the FR-PTC state may represent a therapeutic target to improve repair.
Project description:MicroRNAs (miRNAs) are endogenous noncoding RNA molecules that are involved in post-transcriptional gene silencing. Using global miRNA expression profiling, we found miR-21, -155, and 18a to be highly upregulated in rat kidneys following tubular injury induced by ischemia/reperfusion (I/R) or gentamicin administration. Mir-21 and -155 also showed decreased expression patterns in blood and urinary supernatants in both models of kidney injury. Furthermore, urinary levels of miR-21 increased 1.2-fold in patients with clinical diagnosis of acute kidney injury (AKI) (n = 22) as compared with healthy volunteers (n = 25) (p < 0.05), and miR-155 decreased 1.5-fold in patients with AKI (p < 0.01). We identified 29 messenger RNA core targets of these 3 miRNAs using the context likelihood of relatedness algorithm and found these predicted gene targets to be highly enriched for genes associated with apoptosis or cell proliferation. Taken together, these results suggest that miRNA-21 and -155 could potentially serve as translational biomarkers for detection of AKI and may play a critical role in the pathogenesis of kidney injury and tissue repair process.
Project description:Although macrophages are important players in the injury/repair processes in animal models of acute kidney injury (AKI), their roles in human AKI remains uncertain owing to a paucity of human biopsy studies. We investigated the role of macrophages in 72 cases of biopsy-proven acute tubular necrosis (ATN) and six cases of healthy kidney. Macrophages were identified by CD68 and CD163 immunohistochemistry and analyzed for their effect on renal outcomes. CD163+ M2 macrophages outnumbered CD68+ cells in the healthy kidneys, suggesting that CD163+ macrophages are resident macrophages. The infiltration of both subtypes of macrophages increased significantly in ATN. The density of the CD68+ macrophages was significantly higher in advanced-stage AKI, whereas CD163+ M2 macrophages was not. Eighty percent of patients exhibited renal functional recovery during follow-up. Older age and a higher density of CD163+ macrophages predicted non-recovery, whereas the AKI stage, tubular injury score, and density of CD68+ cells did not. The density of CD163+ M2 macrophages was an independent predictor of low eGFR at 3 months in advanced-stage AKI. This is the first human study demonstrating the possible role of macrophages in the injury and repair phases of AKI.
Project description:The mechanisms initiating late immune responses to an allograft are poorly understood. Here we show, via transcriptome analysis of serial protocol biopsies from kidney transplants, that the initial responses to kidney injury correlate with a late B lymphocyte signature relating to renal dysfunction and fibrosis. With a potential link between dysfunctional repair and immunoreactivity, we investigate the immunological consequences of dysfunctional repair examining chronic disease in mouse kidneys 18 months after a bilateral ischemia/reperfusion injury event. In the absence of foreign antigens, a sustained immune response involving both innate and adaptive immune systems accompanies a transition to chronic kidney damage. At late stages, B lymphocytes exhibite an antigen-driven proliferation, selection and maturation into broadly-reacting antibody-secreting cells. These findings reveal a previously unappreciated role for dysfunctional tissue repair in local immunomodulation that may have particular relevance to transplant-associated immunobiology.
Project description: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.
Project description:Cisplatin and its derivatives are widely used chemotherapeutic drugs for cancer treatment. However, they have debilitating side effects in normal tissues and induce ototoxicity, neurotoxicity, and nephrotoxicity. In kidneys, cisplatin preferentially accumulates in renal tubular cells causing tubular cell injury and death, resulting in acute kidney injury (AKI). Recent studies have suggested that DNA damage and the associated DNA damage response (DDR) are an important pathogenic mechanism of AKI following cisplatin treatment. Activation of DDR may lead to cell cycle arrest and DNA repair for cell survival or, in the presence of severe injury, kidney cell death. Modulation of DDR may provide novel renoprotective strategies for cancer patients undergoing cisplatin chemotherapy.