Reduced Tie2 in Microvascular Endothelial Cells Is Associated with Organ-Specific Adhesion Molecule Expression in Murine Health and Endotoxemia.

Endothelial cells (ECs) in the microvasculature in organs are active participants in the pathophysiology of sepsis. Tyrosine protein kinase receptor Tie2 (Tek; Tunica interna Endothelial cell Kinase) is thought to play a role in their inflammatory response, yet data are inconclusive. We investigated acute endotoxemia-induced changes in the expression of Tie2 and inflammation-associated endothelial adhesion molecules E-selectin and VCAM-1 (vascular cell adhesion molecule-1) in kidneys and lungs in inducible, EC-specific Tie2 knockout mice. The extent of Tie2 knockout in healthy mice differed between microvascular beds, with low to absent expression in arterioles in kidneys and in capillaries in lungs. In kidneys, Tie2 mRNA dropped more than 70% upon challenge with lipopolysaccharide (LPS) in both genotypes, with no change in protein. In renal arterioles, tamoxifen-induced Tie2 knockout was associated with higher VCAM-1 protein expression in healthy conditions. This did not increase further upon challenge of mice with LPS, in contrast to the increased expression occurring in control mice. Also, in lungs, Tie2 mRNA levels dropped within 4 h after LPS challenge in both genotypes, while Tie2 protein levels did not change. In alveolar capillaries, where tamoxifen-induced Tie2 knockout did not affect the basal expression of either adhesion molecule, a 4-fold higher E-selectin protein expression was observed after exposure to LPS compared to controls. The here-revealed heterogeneous effects of absence of Tie2 in ECs in kidney and lung microvasculature in health and in response to acute inflammatory activation calls for further in vivo investigations into the role of Tie2 in EC behavior.

Pattern of tamoxifen-induced Tie2 deletion in endothelial cells in mature blood vessels using endo SCL-Cre-ERT transgenic mice.

Tyrosine-protein kinase receptor Tie2, also known as Tunica interna Endothelial cell Kinase or TEK plays a prominent role in endothelial responses to angiogenic and inflammatory stimuli. Here we generated a novel inducible Tie2 knockout mouse model, which targets mature (micro)vascular endothelium, enabling the study of the organ-specific contribution of Tie2 to these responses. Mice with floxed Tie2 exon 9 alleles (Tie2floxed/floxed) were crossed with end-SCL-Cre-ERT transgenic mice, generating offspring in which Tie2 exon 9 is deleted in the endothelial compartment upon tamoxifen-induced activation of Cre-recombinase (Tie2ΔE9). Successful deletion of Tie2 exon 9 in kidney, lung, heart, aorta, and liver, was accompanied by a heterogeneous, organ-dependent reduction in Tie2 mRNA and protein expression. Microvascular compartment-specific reduction in Tie2 mRNA and protein occurred in arterioles of all studied organs, in renal glomeruli, and in lung capillaries. In kidney, lung, and heart, reduced Tie2 expression was accompanied by a reduction in Tie1 mRNA expression. The heterogeneous, organ- and microvascular compartment-dependent knockout pattern of Tie2 in the Tie2floxed/floxed;end-SCL-Cre-ERT mouse model suggests that future studies using similar knockout strategies should include a meticulous analysis of the knockout extent of the gene of interest, prior to studying its role in pathological conditions, so that proper conclusions can be drawn.

Early Heterogenic Response of Renal Microvasculature to Hemorrhagic Shock/Resuscitation and the Influence of NF-κB Pathway Blockade.

Hemorrhagic shock (HS) is associated with low blood pressure due to excessive loss of circulating blood and causes both macrocirculatory and microcirculatory dysfunction. Fluid resuscitation after HS is used in the clinic to restore tissue perfusion. The persistent microcirculatory damage caused by HS and/or resuscitation can result in multiple organ damage, with the kidney being one of the involved organs. The kidney microvasculature consists of different segments that possess a remarkable heterogeneity in functional properties. The aim of this study was to investigate the inflammatory responses of these different renal microvascular segments, i.e., arterioles, glomeruli, and postcapillary venules, to HS and resuscitation (HS/R) in mice and to explore the effects of intervention with a nuclear factor-kappa B (NF-κB) inhibitor on these responses. We found that HS/R disturbed the balance of the angiopoietin-Tie2 ligand-receptor system, especially in the glomeruli. Furthermore, endothelial adhesion molecules, proinflammatory cytokines, and chemokines were markedly upregulated by HS/R, with the strongest responses occurring in the glomerular and postcapillary venous segments. Blockade of NF-κB signaling during the resuscitation period only slightly inhibited HS/R-induced inflammatory activation, possibly because NF-κB p65 nuclear translocation already occurred during the HS period. In summary, although all three renal microvascular segments were activated upon HS/R, responses of endothelial cells in glomeruli and postcapillary venules to HS/R, as well as to NF-κB inhibition were stronger than those in arterioles. NF-κB inhibition during the resuscitation phase does not effectively counteract NF-κB p65 nuclear translocation initiating inflammatory gene transcription.

Heterogenous Renal Injury Biomarker Production Reveals Human Sepsis-Associated Acute Kidney Injury Subtypes.

To identify mechanisms associated with sepsis-acute kidney injury based on the expression levels of renal injury biomarkers, neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1 in renal biopsies which may allow the identification of sepsis-acute kidney injury patient subtypes. DESIGN: Prospective, clinical laboratory study using "warm" human postmortem sepsis-acute kidney injury kidney biopsies. SETTING: Research laboratory at university teaching hospital. SUBJECTS: Adult patients who died of sepsis in the ICU and control patients undergoing tumor nephrectomy. MEASUREMENTS AND MAIN RESULTS: Reverse transcription quantitative polymerase chain reaction and immunohistochemical staining were used to quantify messenger RNA and protein expression levels of neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 in the kidney of sepsis-acute kidney injury patients and control subjects. Morphometric analysis was used to quantify renal and glomerular neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 protein levels. Neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 messenger RNA and protein levels were increased in kidneys of sepsis-acute kidney injury patients compared with control kidney tissue. Neutrophil gelatinase-associated lipocalin was localized in the distal tubules, collecting ducts, the adventitia of the renal arterioles, and in the glomerular tufts of renal biopsies from sepsis-acute kidney injury patients. In contrast, kidney injury molecule-1 was localized at the brush border of the proximal tubules. There was no correlation between neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 levels. Furthermore, renal neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 levels were not associated with the extent of renal injury, the severity of critical illness, or serum creatinine levels at either ICU admission or day of expiration. By laser microdissecting glomeruli, followed by reverse transcription quantitative polymerase chain reaction, we identified heterogenous glomerular neutrophil gelatinase-associated lipocalin production in the kidney of sepsis-acute kidney injury patients. CONCLUSION: We found differences in the expression of neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 in patients with the same syndrome "sepsis-acute kidney injury" meaning there is no single pathway leading to sepsis-acute kidney injury. This underscores the beliefs that there are many/different pathophysiological pathways that can cause sepsis-acute kidney injury. Hence, patients with criteria that meet the definitions of both acute kidney injury and sepsis can be divided into subtypes based on pathophysiological features.

Partial Deletion of Tie2 Affects Microvascular Endothelial Responses to Critical Illness in A Vascular Bed and Organ-Specific Way.

Tyrosine kinase receptor (Tie2) is mainly expressed by endothelial cells. In animal models mimicking critical illness, Tie2 levels in organs are temporarily reduced. Functional consequences of these reduced Tie2 levels on microvascular endothelial behavior are unknown. We investigated the effect of partial deletion of Tie2 on the inflammatory status of endothelial cells in different organs. Newly generated heterozygous Tie2 knockout mice (exon 9 deletion, ΔE9/Tie2) exhibiting 50% reduction in Tie2 mRNA and protein, and wild-type littermate controls (Tie2), were subjected to hemorrhagic shock and resuscitation (HS + R), or challenged with i.p. lipopolysaccharide (LPS). Kidney, liver, lung, heart, brain, and intestine were analyzed for mRNA levels of adhesion molecules E-selectin, vascular cell adhesion molecule 1 (VCAM-1), and intercellular cell adhesion molecule 1 (ICAM-1), and CD45. Exposure to HS + R did not result in different expression responses of these molecules between organs from Tie2 or Tie2 mice and sham-operated mice. In contrast, the LPS-induced mRNA expression levels of E-selectin, VCAM-1, and ICAM-1, and CD45 in organs were attenuated in Tie2 mice when compared with Tie2 mice in kidney and liver, but not in the other organs studied. Furthermore, reduced expression of E-selectin and VCAM-1 protein, and reduced influx of CD45 cells upon LPS exposure, was visible in a microvascular bed-specific pattern in kidney and liver of Tie2 mice compared with controls. In contrast to the hypothesis that a disbalance in the Ang/Tie2 system leads to increased microvascular inflammation, heterozygous deletion of Tie2 is associated with an organ-restricted, microvascular bed-specific attenuation of endothelial inflammatory response to LPS.

Kidney histopathology in lethal human sepsis.

PURPOSE: The histopathology of sepsis-associated acute kidney injury (AKI) in critically ill patients remains an understudied area. Previous studies have identified that acute tubular necrosis (ATN) is not the only driver of sepsis-AKI. The focus of this study was to identify additional candidate processes that may drive sepsis-AKI. To do this we immunohistochemically characterized the histopathological and cellular features in various compartments of human septic kidneys. METHODS: We studied the following histopathological features: leukocyte subsets, fibroblast activation, cellular proliferation, apoptosis, and fibrin deposition in the glomerulus and the tubulointerstitium in human post-mortem kidney biopsy tissue. Biopsy tissue samples from 27 patients with sepsis-AKI were collected 33 min (range 24-150) after death in the ICU. The unaffected part of the kidneys from 12 patients undergoing total nephrectomy as a result of renal carcinoma served as controls. RESULTS: Immunohistochemical analysis revealed the presence of more neutrophils and macrophages in the glomeruli and more neutrophils in the tubulointerstitium of renal tissue from patients with sepsis compared to control renal tissue. Type II macrophages were predominant, with some macrophages expressing both type I and type II markers. In contrast, there were almost no macrophages found in control kidneys. The number of activated (myo)fibroblasts was low in the glomeruli of sepsis-AKI kidneys, yet this was not observed in the tubulointerstitium. Cell proliferation and fibrin deposition were more pronounced in the glomeruli and tubulointerstitium of sepsis-AKI than in control kidneys. CONCLUSIONS: The extensive heterogeneity of observations among and within patients emphasizes the need to thoroughly characterize patients with sepsis-AKI in a large sample of renal biopsy tissue from patients with sepsis.

Renal Klotho is Reduced in Septic Patients and Pretreatment With Recombinant Klotho Attenuates Organ Injury in Lipopolysaccharide-Challenged Mice.

OBJECTIVES: To determine the applicability of recombinant Klotho to prevent inflammation and organ injury in sepsis in man and mice. DESIGN: Prospective, clinical laboratory study using "warm" human postmortem sepsis-acute kidney injury biopsies. Laboratory study using a mouse model of endotoxemia. SETTING: Research laboratory at a university teaching hospital. SUBJECTS: Adult patients who died of sepsis in the ICU and control patients undergoing total nephrectomy secondary to renal cancer; male C57BL/6 and Klotho haploinsufficient mice. INTERVENTIONS: Lipopolysaccharide (0.05 mg/kg) injection and kill after 4, 8, and 24 hours. Mice received recombinant Klotho (0.05 mg/kg) 30 minutes prior to lipopolysaccharide (1 mg/kg) injection. Mice treated with saline were included as controls. MEASUREMENTS AND MAIN RESULTS: Quantitative reverse transcription polymerase chain reaction and immunohistochemical staining were used to quantify Klotho messenger RNA and protein expression in the kidney of sepsis-acute kidney injury patients and the kidney and brain of mice. The messenger RNA and protein expression of damage markers, inflammatory cytokine, chemokines, and endothelial adhesion molecules were also determined in mice. Renal neutrophil influx was quantified. We found significantly lower renal Klotho messenger RNA and protein levels in sepsis-acute kidney injury biopsies than in control subjects. These findings were recapitulated in the kidney and brain of lipopolysaccharide-challenged mice. Decreased Klotho expression paralleled an increase in kidney damage markers neutrophil gelatinase-associated lipocalin and kidney injury molecule-1. Administration of recombinant Klotho prior to lipopolysaccharide injection attenuated organ damage, inflammation and endothelial activation in the kidney and brain of mice. Furthermore, less neutrophils infiltrated into the kidneys of recombinant Klotho mice compared with lipopolysaccharide only treated mice. CONCLUSIONS: Renal Klotho expression in human sepsis-acute kidney injury and in mouse models of sepsis was significantly decreased and correlated with renal damage. Recombinant Klotho intervention diminished organ damage, inflammation, and endothelial activation in the kidney and brain of lipopolysaccharide-challenged mice. Systemic Klotho replacement may potentially be an organ-protective therapy for septic patients to halt acute, inflammatory organ injury.

Endothelial Interferon Regulatory Factor 1 Regulates Lipopolysaccharide-Induced VCAM-1 Expression Independent of NFκB.

Sepsis is a severe systemic inflammatory response to infection. Endothelial activation and dysfunction play a critical role in the pathophysiology of sepsis and represent an important therapeutic target to reduce sepsis mortality. Interferon regulatory factor 1 (IRF-1) was recently identified as a downstream target of TNF-α-mediated signal transduction in endothelial cells. The aim of this study was to explore the importance of IRF-1 as a regulator of lipopolysaccharide (LPS)-induced endothelial proinflammatory activation. We found that renal IRF-1 was upregulated by LPS in vivo as well as in LPS-stimulated endothelial cells in vitro. Furthermore, we identified intracellular retinoic acid inducible gene-I (RIG-I) as a regulator of LPS-mediated IRF-1 induction. IRF-1 depletion specifically resulted in diminished induction of VCAM-1 in response to LPS, but not of E-selectin or ICAM-1, which was independent of NFκB signaling. When both IRF-1 and the RIG-I adapter protein mitochondrial antiviral signaling (MAVS) were absent, VCAM-1 induction was not additionally inhibited, suggesting that MAVS and IRF-1 reside in the same signaling pathway. Surprisingly, E-selectin and IL-6 induction were no longer inhibited by MAVS knockdown when IRF-1 was also absent, revealing a redundant endothelial activation pathway. In summary, we report an IRF-1-mediated proinflammatory signaling pathway that specifically regulates LPS-mediated VCAM-1 expression, independent of NFκB.

Organ-Specific Differences in Endothelial Permeability-Regulating Molecular Responses in Mouse and Human Sepsis.

In patients with sepsis-induced multi-organ dysfunction syndrome, diverging patterns of oedema formation and loss of function in organs such as lung and kidney suggest that endothelial permeability-regulating molecular responses are differentially regulated. This potential differential regulation has been insufficiently studied at the level of components of adherens and tight junctions. We hypothesized that such a regulation by endothelial cells in sepsis takes place in an organ-specific manner. We addressed our hypothesis by studying by quantitative real time polymerase chain reaction the expression of a predefined subset of EC permeability-related molecules (occludin, claudin-5, PV-1, CD-31, endomucin, Angiopoietin-1, Angiopoietin-2, Tie2, VEGFA, VEGFR1, VEGFR2, and VE-cadherin) in kidney and lung after systemic lipopolysacharide injection in mice, and in kidneys of patients who died of sepsis. We showed that baseline endothelial expression of permeability-related molecules differs in mouse kidney and lung. Moreover, we showed differential regulation of these molecules after lipopolysacharide injection in the two mouse organs. In lung we found a decrease in expression levels of molecules of the adherence and tight junctions complex and related signaling systems, compatible with increased permeability. In contrast, in kidney we found expression patterns of these molecules compatible with decreased permeability. Finally, we partially corroborated our findings in mouse kidney in human kidneys from septic patients. These findings may help to understand the clinical difference in the extent of oedema formation in kidney and lung in sepsis-associated organ failure.

Microsphere-Based Rapamycin Delivery, Systemic Versus Local Administration in a Rat Model of Renal Ischemia/Reperfusion Injury.

PURPOSE: The increasing prevalence and treatment costs of kidney diseases call for innovative therapeutic strategies that prevent disease progression at an early stage. We studied a novel method of subcapsular injection of monodisperse microspheres, to use as a local delivery system of drugs to the kidney. METHODS: We generated placebo- and rapamycin monodisperse microspheres to investigate subcapsular delivery of drugs. Using a rat model of acute kidney injury, subcapsular injection of placebo and rapamycin monodisperse microspheres (monospheres) was compared to subcutaneous injection, mimicking systemic administration. RESULTS: We did not find any adverse effects related to the delivery method. Irrespective of the injection site, a similar low dose of rapamycin was present in the circulation. However, only local intrarenal delivery of rapamycin from monospheres led to decreased macrophage infiltration and a significantly lower amount of myofibroblasts in the kidney, where systemic administration did not. Local delivery of rapamycin did cause a transient increase in the deposition of collagen I, but not of collagen III. CONCLUSIONS: We conclude that therapeutic effects can be increased when rapamycin is delivered subcapsularly by monospheres, which, combined with low systemic concentrations, may lead to an effective intrarenal delivery method.

Local therapeutic efficacy with reduced systemic side effects by rapamycin-loaded subcapsular microspheres.

Kidney injury triggers fibrosis, the final common pathway of chronic kidney disease (CKD). The increase of CKD prevalence worldwide urgently calls for new therapies. Available systemic treatment such as rapamycin are associated with serious side effects. To study the potential of local antifibrotic therapy, we administered rapamycin-loaded microspheres under the kidney capsule of ureter-obstructed rats and assessed the local antifibrotic effects and systemic side effects of rapamycin. After 7 days, microsphere depots were easily identifiable under the kidney capsule. Both systemic and local rapamycin treatment reduced intrarenal mTOR activity, myofibroblast accumulation, expression of fibrotic genes, and T-lymphocyte infiltration. Upon local treatment, inhibition of mTOR activity and reduction of myofibroblast accumulation were limited to the immediate vicinity of the subcapsular pocket, while reduction of T-cell infiltration was widespread. In contrast to systemically administered rapamycin, local treatment did not induce off target effects such as weight loss. Thus subcapsular delivery of rapamycin-loaded microspheres successfully inhibited local fibrotic response in UUO with less systemic effects. Therapeutic effect of released rapamycin was most prominent in close vicinity to the implanted microspheres.

Epithelial-to-mesenchymal transition in fibrosis: collagen type I expression is highly upregulated after EMT, but does not contribute to collagen deposition.

The hallmark of fibrosis is an accumulation of fibrillar collagens, especially of collagen type I. There is considerable debate whether in vivo type II epithelial-to-mesenchymal transition (EMT) is involved in organ fibrosis. Lineage tracing experiments by various groups show opposing data concerning the relative contribution of epithelial cells to the pool of myofibroblasts. We hypothesized that EMT-derived cells might directly contribute to collagen deposition. To study this, EMT was induced in human epithelial lung and renal cell lines in vitro by means of TGF-ß1 stimulation, and we compared the collagen type I (COL1A1) expression levels of transdifferentiated cells with that of myofibroblasts obtained by TGF-ß1 stimulation of human dermal and lung fibroblasts. COL1A1 expression levels of transdifferentiated epithelial cells appeared to be at least one to two orders of magnitude lower than that of myofibroblasts. This was confirmed at immunohistochemical level: in contrast to myofibroblasts, collagen type I deposition by EMT-derived cells was not or hardly detectable. We postulate that, even when type II EMT occurs in vivo, the direct contribution of EMT-derived cells to collagen accumulation is rather limited.

Macrophage phenotypes in the collagen-induced foreign body reaction in rats.

Implantation of biomaterials into the body elicits a material-dependent inflammatory response called the foreign body reaction (FBR). Macrophages play a pivotal role in the FBR by orchestrating the pro-inflammatory microenvironment around the biomaterials by secreting cytokines, chemokines and growth factors. When the biomaterial is porous or degradable, macrophages can migrate into the material and continue the generation of a pro-inflammatory microenvironment inside the materials. They also regulate the degradation of biomaterials by secreting proteolytic enzymes and by phagocytosis. We hypothesize that macrophages present in the different microenvironments of the FBR have different phenotypes. Fundamental knowledge of the phenotypes of macrophages and their dynamics during the FBR will contribute to our overall understanding of the mechanisms involved in the FBR, and may provide us with additional tools to modulate the FBR. To investigate the phenotype of macrophages in the FBR, we validated phenotype-specific markers for rat macrophages in vitro by stimulating them with IFNγ/LPS, IL4/IL13 or IL4/dexamethasone to induce classically activated macrophages (M1φ) or alternatively activated macrophages (M2φ). Gene expression analysis, Western blot and immunohistochemistry revealed that iNOS and CD206 are specifically expressed by M1φ and M2φ, respectively. Using these markers, we investigated the distribution of M1φ and M2φ in the FBR induced by subcutaneously implanted hexamethylenediisocyanate cross-linked dermal sheep collagen (HDSC) disks in AO rats. We found that part of the macrophages display an M2 phenotype, whereas the M1phenotype was not detected. Our data suggest that many macrophages in the FBR induced by HDSC do not fit into the classical M1 or M2 dichotomy.

Development and in-vivo characterization of supramolecular hydrogels for intrarenal drug delivery.

Intrarenal drug delivery from a hydrogel carrier implanted under the kidney capsule is an innovative way to induce kidney tissue regeneration and/or prevent kidney inflammation or fibrosis. We report here on the development of supramolecular hydrogels for this application. We have synthesized two types of supramolecular hydrogelators by connecting the hydrogen bonding moieties to poly(ethylene glycols) in two different ways in order to obtain hydrogels with different physico-chemical properties. Chain-extended hydrogelators containing hydrogen bonding units in the main chain, and bifunctional hydrogelators end-functionalized with hydrogen bonding moieties, were made. The influence of these hydrogels on the renal cortex when implanted under the kidney capsule was studied. The overall tissue response to these hydrogels was found to be mild, and minimal damage to the cortex was observed, using the infiltration of macrophages, formation of myofibroblasts, and the deposition of collagen III as relevant read-out parameters. Differences in tissue response to these hydrogels could be related to the different physico-chemical properties of the three hydrogels. The strong, flexible and slow eroding chain-extended hydrogels are proposed to be suitable for long-term intrarenal delivery of organic drugs, while the weaker, soft and fast eroding bifunctional hydrogel is eminently suitable for short-term, fast delivery of protein drugs to the kidney cortex. The favourable biological behaviour of the supramolecular hydrogels makes them exquisite candidates for subcapsular drug delivery, and paves the way to various opportunities for intrarenal therapy.

Hierarchical formation of supramolecular transient networks in water: a modular injectable delivery system.

A modular one-component supramolecular transient network in water, based on poly(ethylene glycol) and end-capped with four-fold hydrogen bonding units, is reported. Due to its nonlinear structural formation, this system allows active proteins to be added to the hydrogel during formation. Once implanted in vivo it releases the protein by erosion of both the protein and polymer via dissolution.

From kidney development to drug delivery and tissue engineering strategies in renal regenerative medicine.

Deterioration of renal function is typically slow but progressive, and therefore renal disease is often diagnosed in a late stage when already serious complaints occur. Ultimately when renal function has dropped below 10%, renal replacement is required. Renal transplantation provides a long-term solution but due to shortage of donor kidneys most patients receive hemodialysis therapy. Although hemodialysis is an effect method to correct disturbances in water and electrolyte balances in the body, it does not substitute for the important endocrine and metabolic renal functions that are critical for homeostasis. Among these functions are, the renal production of renin which controls blood pressure, the secretion of erythropoietin which stimulates the synthesis of red blood cells, and the excretion of protein bound waste products. As a consequence, many dialysis patients remain in poor health. With the development of regenerative medicine, and particularly tissue engineering and novel drug delivery strategies, alternative routes for renal replacement are emerging. Increasing understanding of (stem) cells, growth factors and regeneration in the kidney has contributed to a whole new view on restoration and reconstruction of (parts of) renal tissue that may be used to improve current renal replacement therapies. Here, an overview of critical interactions between cells, growth factors and extracellular matrix molecules in kidney development and regeneration will be described. Ultimately, we will discuss how these interactions can be translated to strategies for in-vivo regeneration and in-vitro reconstruction of the kidney.

TOF-secondary ion mass spectrometry imaging of polymeric scaffolds with surrounding tissue after in vivo implantation.

Supramolecular polymeric materials are of increasing interest for the use as drug delivery carriers. A thorough insight in the biocompatibility and the degradation of these materials in vivo are of fundamental importance to further their development and application in medical practice. Molecular imaging techniques are powerful tools that enable the elucidation of molecular distributions in and around such polymer implants. A supramolecular polymeric hydrogel was implanted under the renal capsule to study its biocompatibility with TOF-SIMS. This results in a molecular cartography of the polymer implant combined with the cellular signature of the implantation environment. In this experiment, molecular signals are observed from cells that are involved in the biological response to the implant, e.g., macrophages. These molecular signatures are compared with macrophage standards cultured in different polarization environments. On the basis of this comparison, information can be acquired on the various macrophage differentiations that are connected to different stages in the foreign body response. Mass spectrometric imaging techniques offer the opportunity to visualize different histological phenomena in a single experiment without the need for specific immunohistochemical markers. Cellular infiltration into the polymer is visualized, offering a clear view on both biological and polymer features in a single imaging experiment.

Donor and recipient contribution to transplant vasculopathy in chronic renal transplant dysfunction.

BACKGROUND: Chronic transplant dysfunction is the leading cause of long-term renal allograft loss. One of the histologic hallmarks of chronic transplant dysfunction is transplant vasculopathy characterized by accumulation of smooth muscle cells (SMCs) in the arterial subendothelial space, leading to ischemic graft failure. Currently, no therapy is available for transplant vasculopathy, and knowledge of the origin (donor vs. recipient) of neointimal cells may contribute to develop adequate strategies. METHODS: Origin of neointimal SMCs, endothelial, and tubular cells was determined in four nephrectomy samples from male recipients transplanted with a female kidney. Recipient-derived cells were detected using X- and Y-chromosome-specific fluorescent in situ hybridization combined with immunofluorescent staining. Specificity and sensitivity of fluorescent in situ hybridization were determined with corresponding controls. RESULTS: No Y-chromosome-positive cells were detected in the female to female graft, whereas approximately 31% of nucleated cells in male to male grafts had a detectable Y-chromosome. In female to male grafts, a recipient-derived population of neointimal alpha-smooth muscle actin-positive SMCs were detected (6%, range 3%-11%). Percentages of recipient-derived arterial endothelial cells, glomerular endothelial cells, and tubular epithelial cells were 14% (range 4%-32%), 19% (range 7%-31%) and 3% (range 2%-5%), respectively. CONCLUSIONS: Both donor- and recipient-derived cells contribute to vascular remodeling in clinical renal transplantation. The presence of alpha-smooth muscle actin in donor- and recipient-derived cells supports a constructive role for these cells in neointimal formation. However, the predominance of donor-derived cells in the neointima points to these cells as the likely therapeutic target.

Endothelial progenitor cell dysfunction in patients with progressive chronic kidney disease.

Endothelial progenitor cells (EPC) contribute to repair and maintenance of the vascular system, but in patients with chronic kidney disease (CKD), the number and function of EPC may be affected by kidney dysfunction. We assessed numbers and the angiogenic function of EPC from patients with CKD in relation to disease progression. In a cross-sectional, prospective study, 50 patients with varying degrees of CKD, including 20 patients undergoing dialysis and 10 healthy controls, were included. Mononuclear cells were isolated, and circulating EPC were quantified by flow cytometry based on expression of CD14 and CD34. EPC were cultured on fibronectin-coated supramolecular films of oligocaprolactone under angiogenic conditions to determine their angiogenic capacity and future use in regenerative medicine. CKD patients had normal numbers of circulating CD14+ EPC but reduced numbers of circulating CD34+ EPC. Furthermore, EPC from patients with CKD displayed functional impairments, i.e., hampered adherence, reduced endothelial outgrowth potential, and reduced antithrombogenic function. These impairments were already observed at stage 1 CKD and became more apparent when CKD progressed. Dialysis treatment only partially ameliorated EPC impairments in patients with CKD. In conclusion, EPC number and function decrease with advancing CKD, which may hamper physiological vascular repair and can add to the increased risk for cardiovascular diseases observed in CKD patients.

Ciclosporin does not influence bone marrow-derived cell differentiation to myofibroblasts early after renal ischemia/reperfusion.

BACKGROUND: Ischemia/reperfusion injury (IRI) is a risk factor for the development of interstitial fibrosis. Previously we had shown that after renal IRI, bone marrow-derived cells (BMDC) can differentiate to interstitial myofibroblasts. Here we hypothesized that the immunosuppressant ciclosporin A (CsA), known for its profibrotic side effect, promotes myofibroblast differentiation of BMDC in the postischemic kidney. METHODS: Using a model of unilateral renal IRI in rats reconstituted with R26-human placental alkaline phosphatase transgenic bone marrow, CsA was administered in a previously defined critical window for differentiation of BMDC to myofibroblasts. We evaluated fibrotic changes in the kidney and myofibroblast differentiation of BMDC on day 14 after CsA treatment. RESULTS: CsA treatment for 14 days led to increased transforming growth factor-beta transcript levels and collagen III deposition in the postischemic kidney. However, neither the total number of alpha-smooth-muscle-actin-positive interstitial myofibroblasts, nor the bone marrow-derived fraction thereof was affected by CsA administration, irrespective of dosage and duration of treatment. CONCLUSIONS: In the critical postischemic window of BMDC differentiation to myofibroblasts, CsA did not promote BMDC differentiation to myofibroblasts, suggesting that, in the clinical setting, CsA is not involved in myofibroblastic differentiation of BMDC.