CSF-1 and Notch signaling cooperate in macrophage instruction and tissue repair during peripheral limb ischemia

Ischemia causes an inflammatory response featuring monocyte-derived macrophages (MF) involved in angiogenesis and tissue repair. Angiogenesis and ischemic macrophage differentiation are regulated by Notch signaling via Notch ligand Delta-like 1 (Dll1). Colony stimulating factor 1 (CSF-1) is an essential MF lineage factor, but its role in ischemic macrophage development and the interaction with Notch signaling is so far unclear. Using a mouse model of hind limb ischemia with CSF-1 inhibitor studies and Dll1 heterozygous mice we show that CSF-1 is induced in the ischemic niche by a subpopulation of stromal cells expressing podoplanin, which was paralleled by the development of ischemic macrophages. Inhibition of CSF-1 signaling with small molecules or blocking antibodies impaired macrophage differentiation but prolonged the inflammatory response, resulting in impaired perfusion recovery and tissue regeneration. Yet, despite high levels of CSF-1, macrophage maturation and perfusion recovery were impaired in mice with Dll1 haploinsufficiency, while inflammation was exaggerated. In vitro, CSF-1 was not sufficient to induce full MF differentiation from donor monocytes in the absence of recombinant DLL1, while the presence of DLL1 in a dose-dependent manner stimulated MF differentiation in combination with CSF-1. Thus, CSF-1 is an ischemic niche factor that cooperates with Notch signaling in a non-redundant fashion to instruct macrophage cell fate and maturation, which is required for ischemic perfusion recovery and tissue repair.

Strikingly conserved gene expression changes of polyamine regulating enzymes among various forms of acute and chronic kidney injury

The polyamines spermidine and spermine and their common precursor molecule putrescine are involved in tissue injury and repair. Here, we test the hypothesis that impaired polyamine homeostasis contributes to various kidney pathologies in mice during experimental models of ischemia-reperfusion, transplantation, rhabdomyolysis, cyclosporine treatment, arterial hypertension, diabetes, unilateral ureteral obstruction, high oxalate feeding, and adenine-induced injuries. We found a remarkably similar pattern in most kidney pathologies with reduced expression of enzymes involved in polyamine synthesis together with increased expression of polyamine degrading enzymes. Transcript levels of amine oxidase copper-containing 1 (Aoc1), an enzyme which catalyzes the breakdown of putrescine, were barely detectable by in situ mRNA hybridization in healthy kidneys. Aoc1 was highly expressed upon various experimental kidney injuries resulting in a significant reduction of kidney putrescine content. Kidney levels of spermine were also significantly reduced, whereas spermidine was increased in response to ischemia-reperfusion injury. Increased Aoc1 expression in injured kidneys was mainly accounted for by an Aoc1 isoform that harbors 22 additional amino acids at its N-terminus and shows increased secretion. Mice with germline deletion of Aoc1 and injured kidneys showed no decrease of kidney putrescine content; although they displayed no overt phenotype, they had fewer tubular casts upon ischemia-reperfusion injury. Hyperosmotic stress stimulated AOC1 expression at the transcriptional and post-transcription levels in metanephric explants and kidney cell lines. AOC1 expression was also significantly enhanced after kidney transplantation in humans. These data demonstrate that the kidneys respond to various forms of injury with down-regulation of polyamine synthesis and activation of the polyamine breakdown pathway. Thus, an imbalance in kidney polyamines may contribute to various etiologies of kidney injury.

[What is confirmed in the treatment of chronic kidney disease?]

Chronic kidney disease (CKD) is defined as a relevant excretion of albumin into the urine or a reduction of the glomerular filtration rate (GFR) over a longer time period of ≥ 3 months. The causes of CKD are manifold, whereby the association with diabetes mellitus is the most frequent cause. Early stages of CKD affect approximately 10% of the total population. The frequency of cardiovascular events, the risk of dependency on dialysis and the all-cause mortality increase exponentially with a decrease in the GFR and an increase in albuminuria. The guidelines of the German College of General Practitioners and Family Physicians (DEGAM) and the organization Kidney Disease: Improving Global Outcomes (KDIGO) recommend referral to a nephrologist with a GFR of ≤ 30 or ≤ 60 ml/min/1.73 m² in the presence of various cofactors. This means that the majority of CKD patients are treated by general internists or general practitioners. This article gives a concise summary of current data on the treatment of CKD and its associated complications in clinical practice. It refers to the current guidelines and also new study results which could perspectively expand the therapeutic repertoire.

[Hypo- and hypernatremia in the intensive care unit : Pitfalls in volume management]

Hypo- and hypernatremias are very frequent in intensive care unit (ICU) patients and are closely related to volume disturbances and volume management in the ICU. They are associated with longer ICU stays and significant increases in mortality. Treating them is more complex than it may initially appear. Hyponatremias are differentiated based on tonicity and volume status. With hypertonic and isotonic hyponatremias, the primary focus of treatment is the underlying hyperglycemia. In case of hypotonic hypovolemic hyponatremia, the condition is treated with balanced crystalloid solutions. In eu-/hypervolemic hypotonic hyponatremias acute treatment with hypertonic saline is necessary. Hypervolemic hypernatremia occurs almost exclusively in ICU patients, often due to infusion of hypertonic solutions. There is little evidence to guide treatment, although hypotonic infusions in conjunction with diuretics may represent a legitimate approach. Great emphasis should be placed on prevention and the infusion of hypertonic solutions should be avoided. Disturbances in plasma sodium concentrations are common, requiring close attention. Exact diagnostic classification needs to be made and volume managed accordingly.

Parallel generation of easily selectable multiple nephronal cell types from human pluripotent stem cells

Human pluripotent stem cells (hPSCs) provide a source for the generation of defined kidney cells and renal organoids applicable in regenerative medicine, disease modeling, and drug screening. These applications require the provision of hPSC-derived renal cells by reproducible, scalable, and efficient methods. We established a chemically defined protocol by application of Activin A, BMP4, and Retinoic acid followed by GDNF, which steered hPSCs to the renal lineage and resulted in populations of SIX2⁺/CITED1⁺ metanephric mesenchyme- (MM) and of HOXB7⁺/GRHL2⁺ ureteric bud (UB)-like cells already by 6 days. Transcriptome analysis corroborated that the PSC-derived cell types at day 8 resemble their renal vesicle and ureteric epithelial counterpart in vivo, forming tubular and glomerular renal cells 6 days later. We demonstrate that starting from hPSCs, our in vitro protocol generates a pool of nephrogenic progenitors at the renal vesicle stage, which can be further directed into specialized nephronal cell types including mesangial-, proximal tubular-, distal tubular, collecting duct epithelial cells, and podocyte precursors after 14 days. This simple and rapid method to produce renal cells from a common precursor pool in 2D culture provides the basis for scaled-up production of tailored renal cell types, which are applicable for drug testing or cell-based regenerative therapies.

Correction: Does NGAL reduce costs? A cost analysis of urine NGAL (uNGAL) & serum creatinine (sCr) for acute kidney injury (AKI) diagnosis

[This corrects the article DOI: 10.1371/journal.pone.0178091.].

Calprotectin and neutrophil gelatinase-associated lipocalin in the differentiation of pre-renal and intrinsic acute kidney injury

BACKGROUND

Urinary calprotectin has recently been identified as a promising biomarker for the differentiation of pre-renal and intrinsic acute kidney injury (AKI). This study compares the diagnostic performance of calprotectin and neutrophil gelatinase-associated lipocalin (NGAL) in this differential diagnosis.

METHODS

Urinary calprotectin and NGAL concentrations were assessed in a study population of 87 subjects including 38 cases of intrinsic AKI, 24 cases of pre-renal AKI and 25 healthy controls. Urinary tract obstruction, renal transplantation and metastatic cancer were defined as exclusion criteria.

RESULTS

Mean calprotectin concentrations were significantly lower in pre-renal (190.2 ± 205.7 ng mL(-1) ) than in intrinsic AKI (6250.1 ± 7167.2 ng mL(-1) , P < 0.001). Receiver-operating characteristic (ROC) analysis provided an AUC of 0.99. Mean NGAL concentrations were significantly higher in intrinsic than in pre-renal AKI as well (458.1 ± 695.3 vs. 64.8 ± 62.1 ng mL(-1) , P = 0.001) providing an AUC of 0.82. A combination of the present study population with the cohort of the proof of concept study led to a population of 188 subjects (58 pre-renal AKI, 90 intrinsic AKI, 40 healthy controls). ROC analyses provided an AUC of 0.97 for calprotectin and 0.76 for NGAL yielding sensitivity and specificity values of 93.3 and 94.8% (calprotectin) vs. 75.3 and 72.4% (NGAL). Optimal cut-off values were 440 ng mL(-1) (calprotectin) and 52 ng mL(-1) (NGAL). Pyuria increased calprotectin concentrations independent of renal failure.

CONCLUSION

This study shows that both calprotectin and NGAL are able to differentiate between pre-renal and intrinsic AKI after exclusion of pyuria. In the present population, calprotectin presents a higher sensitivity and specificity than NGAL.

Detection of intracellular iron by its regulatory effect

Intracellular iron regulates gene expression by inhibiting the interaction of iron regulatory proteins (IRPs) with RNA motifs called iron-responsive elements (IREs). To assay this interaction in living cells we have developed two fluorescent IRE-based reporters that rapidly, reversibly, and specifically respond to changes in cellular iron status as well as signaling that modifies IRP activity. The reporters were also sufficiently sensitive to distinguish apo- from holotransferrin in the medium, to detect the effect of modifiers of the transferrin pathway such as HFE, and to detect the donation or chelation of iron by siderophores bound to the lipocalin neutrophil gelatinase-associated lipocalin (Ngal). In addition, alternative configurations of the IRE motif either enhanced or repressed fluorescence, permitting a ratio analysis of the iron-dependent response. These characteristics make it possible to visualize iron-IRP-IRE interactions in vivo.

Vigilant vector: heart-specific promoter in an adeno-associated virus vector for cardioprotection

Repeated bouts of ischemia in the heart lead to fibrosis and eventually to heart failure. Although certain genes, such as SOD or hemoxygenase and antisense to AT(1)R, ACE, and (beta(1)-AR can provide short-term protection of the heart from ischemia, there is no known mechanism for constantly responding to repeated incidences of ischemia. We hypothesized that a "vigilant vector," designed to be expressed specifically in the heart and switch on therapeutic genes only during hypoxia, would provide cardioprotection. To attain cardiac specificity, we inserted an MLC2v promoter into an adeno-associated virus (AAV) designed to deliver AS to AT(1)R and gfp. In in vitro experiments in cardiomyocytes (H9C2 cells), the MLC2v-AAV-gfp drove gene expression in all cells at levels comparable to a cytomegalovirus (CMV) promoter. In in vivo experiments, the rAAV-MLC2v-gfp was injected intravenously into mice or rats. Green fluorescence protein (GFP) DNA was located in kidney, heart (right and left ventricle), lung, adrenal and spleen. GFP mRNA, however, was expressed only in the heart and absent in other tissues. To switch on the rAAV transgene during ischemia, we inserted a hypoxia response element (HRE). This upregulates transcription when O(2) levels are low. Thus, there are 4 components to the vigilant vector; a gene switch (HRE), a heart-specific promoter (MLC2v), a therapeutic gene (AS-AT(1)R) and a reporter gene (gfp). To silence or lower basal level of expression while retaining specificity, we have reduced the length of the MLC2v promoter from 3 kb to 1775 bp or 281 bp. The truncated promoter is equally effective in heart specific expression. Preliminary studies with the rAAV-HRE-gfp in vitro show an increased expression in 1% O(2) in 4 to 6 hours. By adding additional hypoxia-inducible factor (HIFalpha) (5 microg), the MLC2v-gfp expression is increased by 4-fold in 1% O(2). Further amplification of the gene to 400-fold in 1% O(2) can be achieved with a double plasmid. The construct may serve as a prototype "vigilant vector" to switch on therapeutic genes in specific tissue with physiological signals.