Hepcidin Removal during Continuous Renal Replacement Therapy.

INTRODUCTION: Patients with acute kidney injury (AKI) or end stage kidney disease (ESKD) may require continuous renal replacement therapy (CRRT) as a supportive intervention. While CRRT is effective at achieving solute control and fluid balance, the indiscriminate nature of this procedure raises the possibility that beneficial substances may similarly be removed. Hepcidin, an antimicrobial peptide with pivotal roles in iron homeostasis and pathogen clearance, has biochemical properties amenable to direct removal via CRRT. We hypothesized that serum hepcidin levels would significantly decrease after initiation of CRRT. METHODS: In this prospective, observational trial, we enrolled 13 patients who required CRRT: 11 due to stage 3 AKI, and 2 due to critical illness in the setting of ESKD. Plasma was collected at the time of enrollment, and then plasma and effluent were collected at 10:00 a.m. on the following 3 days. Plasma samples were also collected from healthy controls, and we compared hepcidin concentrations in those with renal disease compared to normal controls, evaluated trends in hepcidin levels over time, and calculated the hepcidin sieving coefficient. RESULTS: Plasma hepcidin levels were significantly higher in patients initiating CRRT than in normal controls (158 ± 60 vs. 17 ± 3 ng/mL respectively, p < 0.001). Hepcidin levels were highest prior to CRRT initiation (158 ± 60 ng/mL), and were significantly lower on day 1 (102 ± 24 ng/mL, p < 0.001) and day 2 (56 ± 14 ng/mL, p < 0.001) before leveling out on day 3 (51 ± 11 ng/mL). The median sieving coefficient was consistent at 0.82-0.83 for each of 3 days. CONCLUSIONS: CRRT initiation is associated with significant decreases in plasma hepcidin levels over the first 2 days of treatment regardless of indication for CRRT, or presence of underlying ESKD. Since reduced hepcidin levels are associated with increased mortality and our data implicate CRRT in hepcidin removal, larger clinical studies evaluating relevant clinical outcomes based on hepcidin trends in this population should be pursued.

Alveolar epithelial glycocalyx degradation mediates surfactant dysfunction and contributes to acute respiratory distress syndrome.

Acute respiratory distress syndrome (ARDS) is a common cause of respiratory failure yet has few pharmacologic therapies, reflecting the mechanistic heterogeneity of lung injury. We hypothesized that damage to the alveolar epithelial glycocalyx, a layer of glycosaminoglycans interposed between the epithelium and surfactant, contributes to lung injury in patients with ARDS. Using mass spectrometry of airspace fluid noninvasively collected from mechanically ventilated patients, we found that airspace glycosaminoglycan shedding (an index of glycocalyx degradation) occurred predominantly in patients with direct lung injury and was associated with duration of mechanical ventilation. Male patients had increased shedding, which correlated with airspace concentrations of matrix metalloproteinases. Selective epithelial glycocalyx degradation in mice was sufficient to induce surfactant dysfunction, a key characteristic of ARDS, leading to microatelectasis and decreased lung compliance. Rapid colorimetric quantification of airspace glycosaminoglycans was feasible and could provide point-of-care prognostic information to clinicians and/or be used for predictive enrichment in clinical trials.

Loss of endothelial sulfatase-1 after experimental sepsis attenuates subsequent pulmonary inflammatory responses.

Sepsis patients are at increased risk for hospital-acquired pulmonary infections, potentially due to postseptic immunosuppression known as the compensatory anti-inflammatory response syndrome (CARS). CARS has been attributed to leukocyte dysfunction, with an unclear role for endothelial cells. The pulmonary circulation is lined by an endothelial glycocalyx, a heparan sulfate-rich layer essential to pulmonary homeostasis. Heparan sulfate degradation occurs early in sepsis, leading to lung injury. Endothelial synthesis of new heparan sulfates subsequently allows for glycocalyx reconstitution and endothelial recovery. We hypothesized that remodeling of the reconstituted endothelial glycocalyx, mediated by alterations in the endothelial machinery responsible for heparan sulfate synthesis, contributes to CARS. Seventy-two hours after experimental sepsis, coincident with glycocalyx reconstitution, mice demonstrated impaired neutrophil and protein influx in response to intratracheal lipopolysaccharide (LPS). The postseptic reconstituted glycocalyx was structurally remodeled, with enrichment of heparan sulfate disaccharides sulfated at the 6-O position of glucosamine. Increased 6-O-sulfation coincided with loss of endothelial sulfatase-1 (Sulf-1), an enzyme that specifically removes 6-O-sulfates from heparan sulfate. Intravenous administration of Sulf-1 to postseptic mice restored the pulmonary response to LPS, suggesting that loss of Sulf-1 was necessary for postseptic suppression of pulmonary inflammation. Endothelial-specific knockout mice demonstrated that loss of Sulf-1 was not sufficient to induce immunosuppression in non-septic mice. Knockdown of Sulf-1 in human pulmonary microvascular endothelial cells resulted in downregulation of the adhesion molecule ICAM-1. Taken together, our study indicates that loss of endothelial Sulf-1 is necessary for postseptic suppression of pulmonary inflammation, representing a novel endothelial contributor to CARS.

Circulating heparin oligosaccharides rapidly target the hippocampus in sepsis, potentially impacting cognitive functions.

Sepsis induces heparanase-mediated degradation of the endothelial glycocalyx, a heparan sulfate-enriched endovascular layer critical to vascular homeostasis, releasing highly sulfated domains of heparan sulfate into the circulation. These domains are oligosaccharides rich in heparin-like trisulfated disaccharide repeating units. Using a chemoenzymatic approach, an undecasaccharide containing a uniformly 13C-labeled internal 2-sulfoiduronic acid residue was synthesized on a p-nitrophenylglucuronide acceptor. Selective periodate cleavage afforded a heparin nonasaccharide having a natural structure. This 13C-labeled nonasaccharide was intravenously administered to septic (induced by cecal ligation and puncture, a model of polymicrobial peritonitis-induced sepsis) and nonseptic (sham) mice. Selected tissues and biological fluids from the mice were harvested at various time points over 4 hours, and the 13C-labeled nonasaccharide was recovered and digested with heparin lyases. The resulting 13C-labeled trisulfated disaccharide was quantified, without interference from endogenous mouse heparan sulfate/heparin, using liquid chromatography-mass spectrometry with sensitive and selective multiple reaction monitoring. The 13C-labeled heparin nonasaccharide appeared immediately in the blood and was rapidly cleared through the urine. Plasma nonasaccharide clearance was only slightly prolonged in septic mice (t1/2 ∼ 90 minutes). In septic mice, the nonasaccharide penetrated into the hippocampus but not the cortex of the brain; no hippocampal or cortical brain penetration occurred in sham mice. The results of this study suggest that circulating heparan sulfates are rapidly cleared from the plasma during sepsis and selectively penetrate the hippocampus, where they may have functional consequences.

Epithelial Heparan Sulfate Contributes to Alveolar Barrier Function and Is Shed during Lung Injury.

The lung epithelial glycocalyx is a carbohydrate-enriched layer lining the pulmonary epithelial surface. Although epithelial glycocalyx visualization has been reported, its composition and function remain unknown. Using immunofluorescence and mass spectrometry, we identified heparan sulfate (HS) and chondroitin sulfate within the lung epithelial glycocalyx. In vivo selective enzymatic degradation of epithelial HS, but not chondroitin sulfate, increased lung permeability. Using mass spectrometry and gel electrophoresis approaches to determine the fate of epithelial HS during lung injury, we detected shedding of 20 saccharide-long or greater HS into BAL fluid in intratracheal LPS-treated mice. Furthermore, airspace HS in clinical samples from patients with acute respiratory distress syndrome correlated with indices of alveolar permeability, reflecting the clinical relevance of these findings. The length of HS shed during intratracheal LPS-induced injury (≥20 saccharides) suggests cleavage of the proteoglycan anchoring HS to the epithelial surface, rather than cleavage of HS itself. We used pharmacologic and transgenic animal approaches to determine that matrix metalloproteinases partially mediate HS shedding during intratracheal LPS-induced lung injury. Although there was a trend toward decreased alveolar permeability after treatment with the matrix metalloproteinase inhibitor, doxycycline, this did not reach statistical significance. These studies suggest that epithelial HS contributes to the lung epithelial barrier and its degradation is sufficient to increase lung permeability. The partial reduction of HS shedding achieved with doxycycline is not sufficient to rescue epithelial barrier function during intratracheal LPS-induced lung injury; however, whether complete attenuation of HS shedding is sufficient to rescue epithelial barrier function remains unknown.

More than a biomarker: the systemic consequences of heparan sulfate fragments released during endothelial surface layer degradation (2017 Grover Conference Series).

Advances in tissue fixation and imaging techniques have yielded increasing appreciation for the glycosaminoglycan-rich endothelial glycocalyx and its in vivo manifestation, the endothelial surface layer (ESL). Pathological loss of the ESL during critical illness promotes local endothelial dysfunction and, consequently, organ injury. Glycosaminoglycan fragments, such as heparan sulfate, are released into the plasma of animals and humans after ESL degradation and have thus served as a biomarker of endothelial injury. The development of state-of-the-art glycomic techniques, however, has revealed that these circulating heparan sulfate fragments are capable of influencing growth factor and other signaling pathways distant to the site of ESL injury. This review summarizes the current state of knowledge concerning the local (i.e. endothelial injury) and systemic (i.e. para- or endocrine) consequences of ESL degradation and identifies opportunities for future, novel investigations.

Circulating Heparan Sulfate Fragments Attenuate Histone-Induced Lung Injury Independently of Histone Binding.

Extracellular histones are cationic damage-associated molecular pattern molecules capable of directly inducing cellular injury via charge-mediated interactions with plasma membranes. Accordingly, histones released into the plasma during critical illness are known to contribute to the onset and propagation of lung injury. Vascular injury (with consequent degradation of the endothelial glycocalyx) simultaneously releases anionic heparan sulfate fragments (hexa- to octasaccharides in size) into the plasma. It is unknown whether this endogenous release of heparan sulfate fragments modulates charge-dependent histone cytotoxicity, or if exogenous heparan sulfate fragments could therapeutically attenuate histone-induced lung injury. Using isothermic calorimetry, we found that extracellular histones only bind to heparan sulfate fragments ≥ 10 saccharides in size, suggesting that glycocalyx-derived heparan sulfate hexa/octasaccharides are incapable of intercepting/neutralizing circulating histones. However, we found that even heparan sulfate fragments incapable of histone binding (e.g., tetrasaccharides) attenuated histone-induced lung injury in vivo, suggesting a direct, size-independent protective effect of heparan sulfate. We found that histones had no effect on human neutrophils ex vivo but exerted toll-like receptor-independent cytotoxicity on human pulmonary microvascular endothelial cells in vitro. This cytotoxicity could be prevented by either the addition of negatively charged (i.e., highly sulfated) heparan sulfate tetrasaccharides (incapable of binding histones) or decasaccharides (capable of binding histones). Taken together, our findings suggest that heparan sulfate oligosaccharides may directly exert pulmonary endothelial-protective effects that attenuate histone-mediated lung injury.

A model-specific role of microRNA-223 as a mediator of kidney injury during experimental sepsis.

Sepsis outcomes are heavily dependent on the development of septic organ injury, but no interventions exist to interrupt or reverse this process. microRNA-223 (miR-223) is known to be involved in both inflammatory gene regulation and host-pathogen interactions key to the pathogenesis of sepsis. The goal of this study was to determine the role of miR-223 as a mediator of septic kidney injury. Using miR-223 knockout mice and multiple models of experimental sepsis, we found that miR-223 differentially influences acute kidney injury (AKI) based on the model used. In the absence of miR-223, mice demonstrated exaggerated AKI in sterile models of sepsis (LPS injection) and attenuated AKI in a live-infection model of sepsis (cecal ligation and puncture). We demonstrated that miR-223 expression is induced in kidney homogenate after cecal ligation and puncture, but not after LPS or fecal slurry injection. We investigated additional potential mechanistic explanations including differences in peritoneal bacterial clearance and host stool virulence. Our findings highlight the complex role of miR-223 in the pathogenesis of septic kidney injury, as well as the importance of differences in experimental sepsis models and their consequent translational applicability.

Fibroblast Growth Factor Signaling Mediates Pulmonary Endothelial Glycocalyx Reconstitution.

The endothelial glycocalyx is a heparan sulfate (HS)-rich endovascular structure critical to endothelial function. Accordingly, endothelial glycocalyx degradation during sepsis contributes to tissue edema and organ injury. We determined the endogenous mechanisms governing pulmonary endothelial glycocalyx reconstitution, and if these reparative mechanisms are impaired during sepsis. We performed intravital microscopy of wild-type and transgenic mice to determine the rapidity of pulmonary endothelial glycocalyx reconstitution after nonseptic (heparinase-III mediated) or septic (cecal ligation and puncture mediated) endothelial glycocalyx degradation. We used mass spectrometry, surface plasmon resonance, and in vitro studies of human and mouse samples to determine the structure of HS fragments released during glycocalyx degradation and their impact on fibroblast growth factor receptor (FGFR) 1 signaling, a mediator of endothelial repair. Homeostatic pulmonary endothelial glycocalyx reconstitution occurred rapidly after nonseptic degradation and was associated with induction of the HS biosynthetic enzyme, exostosin (EXT)-1. In contrast, sepsis was characterized by loss of pulmonary EXT1 expression and delayed glycocalyx reconstitution. Rapid glycocalyx recovery after nonseptic degradation was dependent upon induction of FGFR1 expression and was augmented by FGF-promoting effects of circulating HS fragments released during glycocalyx degradation. Although sepsis-released HS fragments maintained this ability to activate FGFR1, sepsis was associated with the downstream absence of reparative pulmonary endothelial FGFR1 induction. Sepsis may cause vascular injury not only via glycocalyx degradation, but also by impairing FGFR1/EXT1-mediated glycocalyx reconstitution.

Heparan Sulfate in the Developing, Healthy, and Injured Lung.

Remarkable progress has been achieved in understanding the regulation of gene expression and protein translation, and how aberrancies in these template-driven processes contribute to disease pathogenesis. However, much of cellular physiology is controlled by non-DNA, nonprotein mediators, such as glycans. The focus of this Translational Review is to highlight the importance of a specific glycan polymer-the glycosaminoglycan heparan sulfate (HS)-on lung health and disease. We demonstrate how HS contributes to lung physiology and pathophysiology via its actions as both a structural constituent of the lung parenchyma as well as a regulator of cellular signaling. By highlighting current uncertainties in HS biology, we identify opportunities for future high-impact pulmonary and critical care translational investigations.

Smad4 loss promotes lung cancer formation but increases sensitivity to DNA topoisomerase inhibitors.

Non-small-cell lung cancer (NSCLC) is a common malignancy with a poor prognosis. Despite progress targeting oncogenic drivers, there are no therapies targeting tumor-suppressor loss. Smad4 is an established tumor suppressor in pancreatic and colon cancer; however, the consequences of Smad4 loss in lung cancer are largely unknown. We evaluated Smad4 expression in human NSCLC samples and examined Smad4 alterations in large NSCLC data sets and found that reduced Smad4 expression is common in human NSCLC and occurs through a variety of mechanisms, including mutation, homozygous deletion and heterozygous loss. We modeled Smad4 loss in lung cancer by deleting Smad4 in airway epithelial cells and found that Smad4 deletion both initiates and promotes lung tumor development. Interestingly, both Smad4(-/-) mouse tumors and human NSCLC samples with reduced Smad4 expression demonstrated increased DNA damage, whereas Smad4 knockdown in lung cancer cells reduced DNA repair and increased apoptosis after DNA damage. In addition, Smad4-deficient NSCLC cells demonstrated increased sensitivity to both chemotherapeutics that inhibit DNA topoisomerase and drugs that block double-strand DNA break repair by non-homologous end joining. In sum, these studies establish Smad4 as a lung tumor suppressor and suggest that the defective DNA repair phenotype of Smad4-deficient tumors can be exploited by specific therapeutic strategies.

Role of PTEN in basal cell derived lung carcinogenesis.

Lung adenocarcinoma (AdC) and lung squamous cell carcinoma (SCC) are the most common non-small cell lung cancer (NSCLC) subtypes, however, most genetic mouse models of lung cancer produce predominantly, if not exclusively, AdC. Whether this is secondary to targeting mutations to the distal airway cells or to the use of activating Kras mutations that drive AdC formation is unknown. We previously showed that targeting Kras(G12D) activation and transforming growth factor ß receptor type II (TGFßRII) deletion to airway basal cells via a keratin promoter induced formation of both lung AdC and SCC. In this study we assessed if targeting phosphatase and tensin homologue (PTEN) deletion to airway basal cells could initiate lung tumor formation or increase lung SCC formation. We found that PTEN deletion is capable of initiating both lung AdC and SCC formation when targeted to basal cells and although PTEN deletion is a weaker tumor initiator than Kras(G12D) with low tumor multiplicity and long latency, tumors initiated by PTEN deletion were larger and displayed more malignant conversion than Kras(G12D) initiated tumors. That PTEN deletion did not increase lung SCC formation compared to Kras(G12D) activation, suggests that the initiating genetic event does not dictate tumor histology when genetic alterations are targeted to a specific cell. These studies also confirm that basal cells of the conducting airway are capable of giving rise to multiple NSCLC tumor types.

Redirecting valvular myofibroblasts into dormant fibroblasts through light-mediated reduction in substrate modulus.

Fibroblasts residing in connective tissues throughout the body are responsible for extracellular matrix (ECM) homeostasis and repair. In response to tissue damage, they activate to become myofibroblasts, which have organized contractile cytoskeletons and produce a myriad of proteins for ECM remodeling. However, persistence of myofibroblasts can lead to fibrosis with excessive collagen deposition and tissue stiffening. Thus, understanding which signals regulate de-activation of myofibroblasts during normal tissue repair is critical. Substrate modulus has recently been shown to regulate fibrogenic properties, proliferation and apoptosis of fibroblasts isolated from different organs. However, few studies track the cellular responses of fibroblasts to dynamic changes in the microenvironmental modulus. Here, we utilized a light-responsive hydrogel system to probe the fate of valvular myofibroblasts when the Young's modulus of the substrate was reduced from ~32 kPa, mimicking pre-calcified diseased tissue, to ~7 kPa, mimicking healthy cardiac valve fibrosa. After softening the substrata, valvular myofibroblasts de-activated with decreases in α-smooth muscle actin (α-SMA) stress fibers and proliferation, indicating a dormant fibroblast state. Gene signatures of myofibroblasts (including α-SMA and connective tissue growth factor (CTGF)) were significantly down-regulated to fibroblast levels within 6 hours of in situ substrate elasticity reduction while a general fibroblast gene vimentin was not changed. Additionally, the de-activated fibroblasts were in a reversible state and could be re-activated to enter cell cycle by growth stimulation and to express fibrogenic genes, such as CTGF, collagen 1A1 and fibronectin 1, in response to TGF-ß1. Our data suggest that lowering substrate modulus can serve as a cue to down-regulate the valvular myofibroblast phenotype resulting in a predominantly quiescent fibroblast population. These results provide insight in designing hydrogel substrates with physiologically relevant stiffness to dynamically redirect cell fate in vitro.

Loss of transforming growth factor beta type II receptor increases aggressive tumor behavior and reduces survival in lung adenocarcinoma and squamous cell carcinoma.

PURPOSE: Lung adenocarcinoma and lung squamous cell carcinoma (SCC) are the most common non-small cell lung cancer (NSCLC) subtypes. This study was designed to determine whether reduced expression of TGFß type II receptor (TGFßRII) promotes lung adenocarcinoma and SCC carcinogenesis. EXPERIMENTAL DESIGN: We examined TGFßRII expression at the protein and mRNA levels in human NSCLC samples and assessed the relationship between TGFßRII expression and clinicopathologic parameters. To determine whether sporadic TGFßRII deletion in airway epithelial cells induces NSCLC formation, we targeted TGFßRII deletion alone and in combination with oncogenic Kras(G12D) to murine airways using a keratin 5 (K5) promoter and inducible Cre recombinase. RESULTS: Reduced TGFßRII expression in human NSCLC is associated with male gender, smoking, SCC histology, reduced differentiation, increased tumor stage, increased nodal metastasis, and reduced survival. Homozygous or heterozygous TGFßRII deletion in mouse airway epithelia increases the size and number of Kras(G12D)-initiated adenocarcinoma and SCC. TGFßRII deletion increases proliferation, local inflammation, and TGFß ligand elaboration; TGFßRII knockdown in airway epithelial cells increases migration and invasion. CONCLUSIONS: Reduced TGFßRII expression in human NSCLC is associated with more aggressive tumor behavior and inflammation that is, at least partially, mediated by increased TGFß1 expression. TGFßRII deletion in mouse airway epithelial cells promotes adenocarcinoma and SCC formation, indicating that TGFßRII loss plays a causal role in lung carcinogenesis. That TGFßRII shows haploid insufficiency suggests that a 50% TGFßRII protein reduction would negatively impact lung cancer prognosis.

Epidermal Smad4 deletion results in aberrant wound healing.

In the present study, we assessed the role of Smad4, a component of the transforming growth factor-beta signaling pathway, in cutaneous wound repair. Interestingly, when Smad4 was deleted in the epidermis, several defects in wound healing were observed in non-keratinocyte compartments. In comparison with wounded wild-type mouse skin, Smad4-deficient wounds had delayed wound closure and remodeling. Increased angiogenesis and inflammation were found in Smad4-deficient skin; these effects were exacerbated throughout the entire wound healing process. In addition, increased numbers of myofibroblasts but reduced collagen levels were found in Smad4-deficient wounds in comparison with wild-type wounds. Since Smad4 is not a secreted protein, we assessed if the above non-cell autonomous alterations were the result of molecular alterations in Smad4-deficient keratinocytes, which exert paracrine effects on wound stroma. Smad4-deficient skin and wounds had elevated levels of transforming growth factor-beta1, which have been shown to induce similar phenotypes, as well as of several transforming growth factor-beta1 target genes, such as matrix metalloproteinases, vascular endothelial growth factor-A, and chemokine (C-C motif) ligand 5. Furthermore, the above pathological and molecular alterations were exacerbated in skin cancer lesions that spontaneously developed from Smad4-deficient skin. Therefore, loss of Smad4 in the epidermis appears to significantly affect the microenvironment during wound healing and carcinogenesis.