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Macrophage-derived Lipocalin-2 contributes to ischemic resistance mechanisms by protecting from renal injury.

ABSTRACT: Renal ischemia-reperfusion injury triggers an inflammatory response associated to infiltrating macrophages which determines the further outcome of disease. Brown Norway rats are known to show endogenous resistance to ischemia-induced renal damage. By contrast, Sprague Dawley rats exhibit a higher susceptibility to ischemic injury. In order to ascertain cytoprotective mechanisms, we focused on the implication of lipocalin-2 protein in main resistance mechanisms in renal ischemia/reperfusion injury by using adoptive macrophage administration, genetically modified ex vivo either to overexpress or to knockdown lipocalin-2. In vitro experiments with bone marrow-derived macrophages both from Brown Norway rats and from Sprague Dawley rats under hypoxic conditions showed endogenous differences regarding cytokine and lipocalin-2 expression profile in the two strains. Most interestingly, we observed that macrophages of the resistant strain express significantly more lipocalin-2. In vivo studies showed that tubular epithelial cell apoptosis and renal injury significantly increased and reparative markers decreased in Brown Norway rats after injection of lipocalin-2-knockdown macrophages, while the administration of lipocalin-2-overexpressing cells significantly decreased Sprague Dawley susceptibility. These data point to a crucial role of macrophage-derived lipocalin-2 in endogenous cytoprotective mechanisms. We conclude that expression of lipocalin-2 in tissue-infiltrating macrophages is pivotal for kidney-intrinsic cytoprotective pathways during ischemia reperfusion injury.

SUBMITTER: Jung M

PROVIDER: S-EPMC4766505 | biostudies-literature | 2016 Feb

REPOSITORIES: biostudies-literature

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Macrophage-derived Lipocalin-2 contributes to ischemic resistance mechanisms by protecting from renal injury.

Jung Michaela M Brüne Bernhard B Hotter Georgina G Sola Anna A

Scientific reports 20160225

Renal ischemia-reperfusion injury triggers an inflammatory response associated to infiltrating macrophages which determines the further outcome of disease. Brown Norway rats are known to show endogenous resistance to ischemia-induced renal damage. By contrast, Sprague Dawley rats exhibit a higher susceptibility to ischemic injury. In order to ascertain cytoprotective mechanisms, we focused on the implication of lipocalin-2 protein in main resistance mechanisms in renal ischemia/reperfusion injur ...[more]

PMID: 26911537

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Project description:BackgroundRecent researches indicate that the intestinal consequences of renal ischemia reperfusion (IR) would predispose to the translocation of gut-derived endotoxin. Here, we designed experiments to test the hypothesis that the gut-derived endotoxin has a potential role in mediating local inflammatory processes in the acutely injured kidney.MethodsRats were performed sham or renal IR surgery (60?min of bilateral renal ischemia, then 24?h of reperfusion) (n?=?5). The intestinal structural and mucosa permeability were evaluated. Serum endotoxin and bacterial load in liver and mesenteric lymph nodes (MLN) were measured. Separate groups were pretreated with oral norfloxacin 20?mg/kg/day or saline for 4?weeks and divided into sham plus saline, sham plus norfloxacin, renal IR plus saline and renal IR plus norfloxacin group. Serum biochemistry and endotoxin were determined. Kidney pathological changes were scored. Protein or mRNA expression of toll-like receptor 4 (TLR4) and proinflammatory mediators were measured in kidney homogenate.ResultsRenal IR led to marked intestinal integrity disruption and increase in intestinal permeability. These are accompanied by low grade of endotoxemia as well as increased bacterial load in liver and MLN. The group pretreated with norfloxacin showed significant attenuation of the increase in serum urea, ALAT, ASAT and endotoxin. The increased renal protein or mRNA of TLR4 and proinflammatory mediators (IL-6 and MCP-1) in the unpretreated animals was significantly attenuated in the norfloxacin-pretreated animals. However, norfloxacin pretreatment did not produce any protective effects on renal tubular integrity.ConclusionsOur results show for the first time that gut-derived endotoxin, resulting from an increased intestinal permeability after severe renal IR, subsequently amplifies intrarenal inflammatory response by activation renal TLR4 signaling. Our study results do not establish that antibiotic administration was effective in improving the overall renal outcome. However, our findings may be the first step to understanding how to tailor therapies to mitigate intrarenal inflammation in select groups of patients.

Project description:Acute kidney injury (AKI) is associated with an abrupt loss of kidney function that results in significant morbidity and mortality. Considerable effort has focused around the identification of diagnostic biomarkers and the analysis of molecular events. Most studies have adopted organ-wide approaches that do not fully capture the interplay among different cell types in the pathophysiology of AKI. To extend our understanding of molecular and cellular events in AKI, we developed a mouse line that enables the identification of translational profiles in specific cell types by CRE recombinase-dependent activation of an eGFP-tagged L10a ribosomal protein subunit, and consequently, translating ribosome affinity purification (TRAP) of mRNA populations. By utilizing cell-type specific CRE-driver lines, in this study we identify distinct cellular responses in an ischemia reperfusion injury (IRI) model of AKI. Cell-specific translational expression profiles were uncovered 24 hours after IRI from four populations enriched for distinct anatomical and cellular subgroups: nephron, interstitial cell populations, vascular endothelium, and macrophages/monocytes by Affymetrix microarray. A construct containing the CAGGS promoter driving eGFP-L10a, with a loxP-site flanked triple SV40 polyA cassette between promoter and eGFP-L10a cassette was targeted into the ubiquitously active Rosa26 locus. The upstream polyA cassette is designed to block activity of the downstream eGFP-L10a cassette. CRE-dependent removal of this transcriptional block activates eGFP::L10a production within the CRE-producing cell, and all of its descendants. Mice carrying the conditional eGFP-L10a allele, referred to as L10a, were maintained in a homozygous state. L10a mice were crossed to four CRE strains to activate eGFP::L10a expression in four predominantly non-overlapping cellular compartments in the kidney. A Six2-Tet-GFP::CRE allele is active exclusively within nephron progenitors; consequently, historical labeling results in eGFP::L10a expression throughout the main body of the nephron. A Foxd1-GFP::CRE allele is active in the progenitors of many of the interstitial cell lineages including those generating mesangial and non-glomerular pericytes. In addition, Foxd1 is normally expressed in podocytes. Cdh5-CRE is reported to be active throughout the vascular endothelium, and finally, Lyz2-CRE specifically labels cells of the myeloid lineage, notably macrophages, monocytes and dendritic cells. Mice carrying any CRE allele and the L10a allele are designated generically CRE-L10a. six2-L10a, foxd1-L10a, cdh5-L10a and lyz2-L10a denote specifically mice that are compound heterozygotes for the indicated CRE driver and L10a. CRE-L10a, L10a heterozygous littermates without CRE allele, C57BL/6 wild type mice were subjected to renal bilateral warm ischemia 28 minutes followed by 24-hour reperfusion when the kidney TRAP RNA and total RNA were isolated and subjected to Affymetrix microarray. Biological triplicates for each CRE-L10a line underwent no Surgery; sham Surgery and IRI treatment.

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Macrophage-derived Lipocalin-2 contributes to ischemic resistance mechanisms by protecting from renal injury.

Publications

Macrophage-derived Lipocalin-2 contributes to ischemic resistance mechanisms by protecting from renal injury.

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