eNAMPT is a novel therapeutic target for mitigation of coronary microvascular disease in type 2 diabetes.

AIMS/HYPOTHESIS: Individuals with diabetes are at high risk of cardiovascular complications, which significantly increase morbidity/mortality. Coronary microvascular disease (CMD) is recognised as a critical contributor to the increased cardiac mortality observed in people with diabetes. Therefore, there is an urgent need for treatments that are specific to CMD. eNAMPT (extracellular nicotinamide phosphoribosyltransferase) is a damage-associated molecular pattern and TLR4 ligand, whose plasma levels are elevated in people with diabetes. This study was thus designed to investigate the pathogenic role of intracellular nicotinamide phosphoribosyltransferase (iNAMPT) and eNAMPT in promoting the development of CMD in a preclinical murine model of type 2 diabetes. METHODS: An inducible type 2 diabetic mouse model was generated by a single injection of low-dose streptozocin (75 mg/kg, i.p.) combined with a high-fat diet for 16 weeks. The in vivo effects of i/eNAMPT inhibition on cardiac endothelial cell (CEC) function were evaluated by using Nampt+/- heterozygous mice, chronic administration of eNAMPT-neutralising monoclonal antibody (mAb) or use of an NAMPT enzymatic inhibitor (FK866). RESULTS: As expected, diabetic wild-type mice exhibited significantly lower coronary flow velocity reserve (CFVR), a determinant of coronary microvascular function, compared with control wild-type mice. eNAMPT plasma levels or expression in CECs were significantly greater in diabetic mice than in control mice. Furthermore, in comparison with diabetic wild-type mice, diabetic Nampt+/- heterozygous mice showed markedly improved CFVR, accompanied by increased left ventricular capillary density and augmented endothelium-dependent relaxation (EDR) in the coronary artery. NAMPT inhibition by FK866 or an eNAMPT-neutralising mAb significantly increased CFVR in diabetic mice. Furthermore, administration of the eNAMPT mAb upregulated expression of angiogenesis- and EDR-related genes in CECs from diabetic mice. Treatment with either eNAMPT or NAD+ significantly decreased CEC migration and reduced EDR in coronary arteries, partly linked to increased production of mitochondrial reactive oxygen species. CONCLUSIONS/INTERPRETATION: These data indicate that increased i/eNAMPT expression contributes to the development of diabetic coronary microvascular dysfunction, and provide compelling support for eNAMPT inhibition as a novel and effective therapeutic strategy for CMD in diabetes.

Involvement of eNAMPT/TLR4 inflammatory signaling in progression of non-alcoholic fatty liver disease, steatohepatitis, and fibrosis.

Although the progression of non-alcoholic fatty liver disease (NAFLD) from steatosis to steatohepatitis (NASH) and cirrhosis remains poorly understood, a critical role for dysregulated innate immunity has emerged. We examined the utility of ALT-100, a monoclonal antibody (mAb), in reducing NAFLD severity and progression to NASH/hepatic fibrosis. ALT-100 neutralizes eNAMPT (extracellular nicotinamide phosphoribosyltransferase), a novel damage-associated molecular pattern protein (DAMP) and Toll-like receptor 4 (TLR4) ligand. Histologic and biochemical markers were measured in liver tissues and plasma from human NAFLD subjects and NAFLD mice (streptozotocin/high-fat diet-STZ/HFD, 12 weeks). Human NAFLD subjects (n = 5) exhibited significantly increased NAMPT hepatic expression and significantly elevated plasma levels of eNAMPT, IL-6, Ang-2, and IL-1RA compared to healthy controls, with IL-6 and Ang-2 levels significantly increased in NASH non-survivors. Untreated STZ/HFD-exposed mice displayed significant increases in NAFLD activity scores, liver triglycerides, NAMPT hepatic expression, plasma cytokine levels (eNAMPT, IL-6, and TNFα), and histologic evidence of hepatocyte ballooning and hepatic fibrosis. Mice receiving the eNAMPT-neutralizing ALT-100 mAb (0.4 mg/kg/week, IP, weeks 9 to 12) exhibited marked attenuation of each index of NASH progression/severity. Thus, activation of the eNAMPT/TLR4 inflammatory pathway contributes to NAFLD severity and NASH/hepatic fibrosis. ALT-100 is potentially an effective therapeutic approach to address this unmet NAFLD need.

eNAMPT Is a Novel Damage-associated Molecular Pattern Protein That Contributes to the Severity of Radiation-induced Lung Fibrosis.

The paucity of therapeutic strategies to reduce the severity of radiation-induced lung fibrosis (RILF), a life-threatening complication of intended or accidental ionizing radiation exposure, is a serious unmet need. We evaluated the contribution of eNAMPT (extracellular nicotinamide phosphoribosyltransferase), a damage-associated molecular pattern (DAMP) protein and TLR4 (Toll-like receptor 4) ligand, to the severity of whole-thorax lung irradiation (WTLI)-induced RILF. Wild-type (WT) and Nampt+/- heterozygous C57BL6 mice and nonhuman primates (NHPs, Macaca mulatta) were exposed to a single WTLI dose (9.8 or 10.7 Gy for NHPs, 20 Gy for mice). WT mice received IgG1 (control) or an eNAMPT-neutralizing polyclonal or monoclonal antibody (mAb) intraperitoneally 4 hours after WTLI and weekly thereafter. At 8-12 weeks after WTLI, NAMPT expression was assessed by immunohistochemistry, biochemistry, and plasma biomarker studies. RILF severity was determined by BAL protein/cells, hematoxylin and eosin, and trichrome blue staining and soluble collagen assays. RNA sequencing and bioinformatic analyses identified differentially expressed lung tissue genes/pathways. NAMPT lung tissue expression was increased in both WTLI-exposed WT mice and NHPs. Nampt+/- mice and eNAMPT polyclonal antibody/mAb-treated mice exhibited significantly attenuated WTLI-mediated lung fibrosis with reduced: 1) NAMPT and trichrome blue staining; 2) dysregulated lung tissue expression of smooth muscle actin, p-SMAD2/p-SMAD1/5/9, TGF-ß, TSP1 (thrombospondin-1), NOX4, IL-1ß, and NRF2; 3) plasma eNAMPT and IL-1ß concentrations; and 4) soluble collagen. Multiple WTLI-induced dysregulated differentially expressed lung tissue genes/pathways with known tissue fibrosis involvement were each rectified in mice receiving eNAMPT mAbs.The eNAMPT/TLR4 inflammatory network is essentially involved in radiation pathobiology, with eNAMPT neutralization an effective therapeutic strategy to reduce RILF severity.

An Actin-, Cortactin- and Ena-VASP-Linked Complex Contributes to Endothelial Cell Focal Adhesion and Vascular Barrier Regulation.

BACKGROUND/AIMS: Increase in vascular permeability is a cardinal feature of all inflammatory diseases and represents an imbalance in vascular contractile forces and barrier-restorative forces, both of which are highly dependent on actin cytoskeletal dynamics. In addition to the involvement of key vascular barrier-regulatory, actin-binding proteins, such as nmMLCK and cortactin, we recently demonstrated a role for a member of the Ena-VASP family known as Ena-VASP-like (EVL) in promoting vascular focal adhesion (FA) remodeling and endothelial cell (EC) barrier restoration/preservation. METHODS: To further understand the role of EVL in EC barrier-regulatory processes, we examined EVL-cytoskeletal protein interactions in FA dynamics in vitro utilizing lung EC and in vivo murine models of acute inflammatory lung injury. Deletion mapping studies and immunoprecipitation assays were performed to detail the interaction between EVL and cortactin, and further evaluated by assessment of changes in vascular EC permeability following disruption of EVL-cortactin interaction. RESULTS: Initial studies focusing on the actin-binding proteins, nmMLCK and cortactin, utilized deletion mapping of the cortactin gene (CTTN) to identify cortactin domains critical for EVL-cortactin interaction and verified the role of actin in promoting EVL-cortactin interaction. A role for profilins, actin-binding proteins that regulate actin polymerization, was established in facilitating EVL-FA binding. CONCLUSION: In summary, these studies further substantiate EVL participation in regulation of vascular barrier integrity and in the highly choreographed cytoskeletal interactions between key FA and cytoskeletal partners.

Circulating eNAMPT as a biomarker in the critically ill: acute pancreatitis, sepsis, trauma, and acute respiratory distress syndrome.

BACKGROUND: Nicotinamide phosphoribosyltransferase (NAMPT) exhibits dual functionality - as an intracellular enzyme regulating nicotinamide adenine dinucleotide metabolism and as an extracellular secreted protein (eNAMPT) to function as a cytokine regulator of innate immunity via binding to Toll-Like receptor 4 and NF-κB activation. In limited preclinical and clinical studies, eNAMPT was implicated in the pathobiology of acute respiratory distress syndrome (ARDS) suggesting that eNAMPT could potentially serve as a diagnostic and prognostic biomarker. We investigated the feasibility of circulating eNAMPT levels to serve as a biomarker in an expanded cohort of patients with ARDS and ARDS-predisposing conditions that included acute pancreatitis, sepsis, and trauma with comparisons to controls. METHODS: A total of 671 patients and 179 healthy controls were included in two independent cohorts. Plasma and serum eNAMPT levels were quantified using one of two complementary Enzyme-linked Immunosorbent Assays. After log base 2 variance stabilizing transformation of plasma/serum eNAMPT measurements, differences between healthy controls and each disease cohort were compared using linear regression or a generalized estimating equation (GEE) model where applicable. Complementary analyses included sensitivity, specificity, positive predictive values, negative predictive values, and the area under the receiver operating curve. RESULTS: Compared to controls, circulating eNAMPT levels were significantly elevated in subjects with acute pancreatitis, sepsis, trauma, and ARDS (all p < 0.01). In the acute pancreatitis cohort, circulating eNAMPT levels positively correlated with disease severity (p < 0.01). CONCLUSIONS: Circulating eNAMPT levels are novel biomarker in the critically ill with acute pancreatitis, sepsis, trauma, and/or ARDS with the potential to reflect disease severity.

Endothelial eNAMPT amplifies pre-clinical acute lung injury: efficacy of an eNAMPT-neutralising monoclonal antibody.

RATIONALE: The severe acute respiratory syndrome coronavirus 2/coronavirus disease 2019 pandemic has highlighted the serious unmet need for effective therapies that reduce acute respiratory distress syndrome (ARDS) mortality. We explored whether extracellular nicotinamide phosphoribosyltransferase (eNAMPT), a ligand for Toll-like receptor (TLR)4 and a master regulator of innate immunity and inflammation, is a potential ARDS therapeutic target. METHODS: Wild-type C57BL/6J or endothelial cell (EC)-cNAMPT -/- knockout mice (targeted EC NAMPT deletion) were exposed to either a lipopolysaccharide (LPS)-induced ("one-hit") or a combined LPS/ventilator ("two-hit")-induced acute inflammatory lung injury model. A NAMPT-specific monoclonal antibody (mAb) imaging probe (99mTc-ProNamptor) was used to detect NAMPT expression in lung tissues. Either an eNAMPT-neutralising goat polyclonal antibody (pAb) or a humanised monoclonal antibody (ALT-100 mAb) were used in vitro and in vivo. RESULTS: Immunohistochemical, biochemical and imaging studies validated time-dependent increases in NAMPT lung tissue expression in both pre-clinical ARDS models. Intravenous delivery of either eNAMPT-neutralising pAb or mAb significantly attenuated inflammatory lung injury (haematoxylin and eosin staining, bronchoalveolar lavage (BAL) protein, BAL polymorphonuclear cells, plasma interleukin-6) in both pre-clinical models. In vitro human lung EC studies demonstrated eNAMPT-neutralising antibodies (pAb, mAb) to strongly abrogate eNAMPT-induced TLR4 pathway activation and EC barrier disruption. In vivo studies in wild-type and EC-cNAMPT -/- mice confirmed a highly significant contribution of EC-derived NAMPT to the severity of inflammatory lung injury in both pre-clinical ARDS models. CONCLUSIONS: These findings highlight both the role of EC-derived eNAMPT and the potential for biologic targeting of the eNAMPT/TLR4 inflammatory pathway. In combination with predictive eNAMPT biomarker and NAMPT genotyping assays, this offers the opportunity to identify high-risk ARDS subjects for delivery of personalised medicine.

Genetic and epigenetic regulation of the non-muscle myosin light chain kinase isoform by lung inflammatory factors and mechanical stress.

RATIONALE: The myosin light chain kinase gene, MYLK, encodes three proteins via unique promoters, including the non-muscle isoform of myosin light chain kinase (nmMLCK), a cytoskeletal protein centrally involved in regulation of vascular integrity. As MYLK coding SNPs are associated with severe inflammatory disorders (asthma, acute respiratory distress syndrome (ARDS)), we explored clinically relevant inflammatory stimuli and promoter SNPs in nmMLCK promoter regulation. METHODS: Full-length or serially deleted MYLK luciferase reporter promoter activities were measured in human lung endothelial cells (ECs). SNP-containing non-muscle MYLK (nmMYLK) DNA fragments were generated and nmMYLK promoter binding by transcription factors (TFs) detected by protein-DNA electrophoretic mobility shift assay (EMSA). Promoter demethylation was evaluated by 5-aza-2'-deoxycytidine (5-Aza). A preclinical mouse model of lipopolysaccharide (LPS)-induced acute lung injury (ALI) was utilized for nmMLCK validation. RESULTS: Lung EC levels of nmMLCK were significantly increased in LPS-challenged mice and LPS, tumor necrosis factor-α (TNF-α), 18% cyclic stretch (CS) and 5-Aza each significantly up-regulated EC nmMYLK promoter activities. EC exposure to FG-4592, a prolyl hydroxylase inhibitor that increases hypoxia-inducible factor (HIF) expression, increased nmMYLK promoter activity, confirmed by HIF1α/HIF2α silencing. nmMYLK promoter deletion studies identified distal inhibitory and proximal enhancing promoter regions as well as mechanical stretch-, LPS- and TNFα-inducible regions. Insertion of ARDS-associated SNPs (rs2700408, rs11714297) significantly increased nmMYLK promoter activity via increased transcription binding (glial cells missing homolog 1 (GCM1) and intestine-specific homeobox (ISX), respectively). Finally, the MYLK rs78755744 SNP (-261G/A), residing within a nmMYLK CpG island, significantly attenuated 5-Aza-induced promoter activity. CONCLUSION: These findings indicate nmMYLK transcriptional regulation by clinically relevant inflammatory factors and ARDS-associated nmMYLK promoter variants are consistent with nmMLCK as a therapeutic target in severe inflammatory disorders.

Direct Extracellular NAMPT Involvement in Pulmonary Hypertension and Vascular Remodeling. Transcriptional Regulation by SOX and HIF-2α.

We previously demonstrated involvement of NAMPT (nicotinamide phosphoribosyltransferase) in pulmonary arterial hypertension (PAH) and now examine NAMPT regulation and extracellular NAMPT's (eNAMPT's) role in PAH vascular remodeling. NAMPT transcription and protein expression in human lung endothelial cells were assessed in response to PAH-relevant stimuli (PDGF [platelet-derived growth factor], VEGF [vascular endothelial growth factor], TGF-ß1 [transforming growth factor-ß1], and hypoxia). Endothelial-to-mesenchymal transition was detected by SNAI1 (snail family transcriptional repressor 1) and PECAM1 (platelet endothelial cell adhesion molecule 1) immunofluorescence. An eNAMPT-neutralizing polyclonal antibody was tested in a PAH model of monocrotaline challenge in rats. Plasma eNAMPT concentrations, significantly increased in patients with idiopathic pulmonary arterial hypertension, were highly correlated with indices of PAH severity. eNAMPT increased endothelial-to-mesenchymal transition, and each PAH stimulus significantly increased endothelial cell NAMPT promoter activity involving transcription factors STAT5 (signal transducer and activator of transcription 5), SOX18 (SRY-box transcription factor 18), and SOX17 (SRY-box transcription factor 17), a PAH candidate gene newly defined by genome-wide association study. The hypoxia-induced transcription factor HIF-2α (hypoxia-inducible factor-2α) also potently regulated NAMPT promoter activity, and HIF-2α binding sites were identified between -628 bp and -328 bp. The PHD2 (prolyl hydroxylase domain-containing protein 2) inhibitor FG-4592 significantly increased NAMPT promoter activity and protein expression in an HIF-2α-dependent manner. Finally, the eNAMPT-neutralizing polyclonal antibody significantly reduced monocrotaline-induced vascular remodeling, PAH hemodynamic alterations, and NF-κB activation. eNAMPT is a novel and attractive therapeutic target essential to PAH vascular remodeling.

Nicotinamide phosphoribosyltransferase purification using SUMO expression system.

Nicotinamide phosphoribosyltransferase (NAMPT) is a rate-limiting enzyme in the salvage pathway required for nicotinamide adenine dinucleotide synthesis. The secreted NAMPT protein serves as a master regulatory cytokine involved in activation of evolutionarily conserved inflammatory networks. Appreciation of the role of NAMPT as a damage-associated molecular pattern protein (DAMP) has linked its activities to several disorders via Toll-like receptor 4 (TLR4) binding and inflammatory cascade activation. Information is currently lacking concerning the precise mode of the NAMPT protein functionality due to limited availability of purified protein for use in in vitro and in vivo studies. Here we report successful NAMPT expression using the pET-SUMO expression vector in E. coli strain SHuffle containing a hexa-His tag for purification. The Ulp1 protease was used to cleave the SUMO and hexa-His tags, and the protein was purified by immobilized-metal affinity chromatography. The protein yield was ~4 mg/L and initial biophysical characterization of the protein using circular dichroism revealed the secondary structural elements, while dynamic light scattering demonstrated the presence of oligomeric units. The NAMPT-SUMO showed a predominantly dimeric protein with functional enzymatic activity. Finally, we report NAMPT solubilization in n-dodecyl-ß-d-maltopyranoside (DDM) detergent in monomeric form, thus enhancing the opportunity for further structural and functional investigations.

Development of a biomarker mortality risk model in acute respiratory distress syndrome.

BACKGROUND: There is a compelling unmet medical need for biomarker-based models to risk-stratify patients with acute respiratory distress syndrome. Effective stratification would optimize participant selection for clinical trial enrollment by focusing on those most likely to benefit from new interventions. Our objective was to develop a prognostic, biomarker-based model for predicting mortality in adult patients with acute respiratory distress syndrome. METHODS: This is a secondary analysis using a cohort of 252 mechanically ventilated subjects with the diagnosis of acute respiratory distress syndrome. Survival to day 7 with both day 0 (first day of presentation) and day 7 sample availability was required. Blood was collected for biomarker measurements at first presentation to the intensive care unit and on the seventh day. Biomarkers included cytokine-chemokines, dual-functioning cytozymes, and vascular injury markers. Logistic regression, latent class analysis, and classification and regression tree analysis were used to identify the plasma biomarkers most predictive of 28-day ARDS mortality. RESULTS: From eight biologically relevant biomarker candidates, six demonstrated an enhanced capacity to predict mortality at day 0. Latent-class analysis identified two biomarker-based phenotypes. Phenotype A exhibited significantly higher plasma levels of angiopoietin-2, macrophage migration inhibitory factor, interleukin-8, interleukin-1 receptor antagonist, interleukin-6, and extracellular nicotinamide phosphoribosyltransferase (eNAMPT) compared to phenotype B. Mortality at 28 days was significantly higher for phenotype A compared to phenotype B (32% vs 19%, p = 0.04). CONCLUSIONS: An adult biomarker-based risk model reliably identifies ARDS subjects at risk of death within 28 days of hospitalization.

Genome-Wide Association Study in African Americans with Acute Respiratory Distress Syndrome Identifies the Selectin P Ligand Gene as a Risk Factor.

RATIONALE: Genetic factors are involved in acute respiratory distress syndrome (ARDS) susceptibility. Identification of novel candidate genes associated with increased risk and severity will improve our understanding of ARDS pathophysiology and enhance efforts to develop novel preventive and therapeutic approaches. OBJECTIVES: To identify genetic susceptibility targets for ARDS. METHODS: A genome-wide association study was performed on 232 African American patients with ARDS and 162 at-risk control subjects. The Identify Candidate Causal SNPs and Pathways platform was used to infer the association of known gene sets with the top prioritized intragenic SNPs. Preclinical validation of SELPLG (selectin P ligand gene) was performed using mouse models of LPS- and ventilator-induced lung injury. Exonic variation within SELPLG distinguishing patients with ARDS from sepsis control subjects was confirmed in an independent cohort. MEASUREMENTS AND MAIN RESULTS: Pathway prioritization analysis identified a nonsynonymous coding SNP (rs2228315) within SELPLG, encoding P-selectin glycoprotein ligand 1, to be associated with increased susceptibility. In an independent cohort, two exonic SELPLG SNPs were significantly associated with ARDS susceptibility. Additional support for SELPLG as an ARDS candidate gene was derived from preclinical ARDS models where SELPLG gene expression in lung tissues was significantly increased in both ventilator-induced (twofold increase) and LPS-induced (5.7-fold increase) murine lung injury models compared with controls. Furthermore, Selplg-/- mice exhibited significantly reduced LPS-induced inflammatory lung injury compared with wild-type C57/B6 mice. Finally, an antibody that neutralizes P-selectin glycoprotein ligand 1 significantly attenuated LPS-induced lung inflammation. CONCLUSIONS: These findings identify SELPLG as a novel ARDS susceptibility gene among individuals of European and African descent.

Novel Mechanism for Nicotinamide Phosphoribosyltransferase Inhibition of TNF-α-mediated Apoptosis in Human Lung Endothelial Cells.

Nicotinamide phosphoribosyltransferase (NAMPT) exists as both intracellular NAMPT and extracellular NAMPT (eNAMPT) proteins. eNAMPT is secreted into the blood and functions as a cytokine/enzyme (cytozyme) that activates NF-κB signaling via ligation of Toll-like receptor 4 (TLR4), further serving as a biomarker for inflammatory lung disorders such as acute respiratory distress syndrome. In contrast, intracellular NAMPT is involved in nicotinamide mononucleotide synthesis and has been implicated in the regulation of cellular apoptosis, although the exact mechanisms for this regulation are poorly understood. We examined the role of NAMPT in TNF-α-induced human lung endothelial cell (EC) apoptosis and demonstrated that reduced NAMPT expression (siRNA) increases EC susceptibility to TNF-α-induced apoptosis as reflected by PARP-1 cleavage and caspase-3 activation. In contrast, overexpression of NAMPT served to reduce degrees of TNF-α-induced EC apoptosis. Inhibition of nicotinamide mononucleotide synthesis by FK866 (a selective NAMPT enzymatic inhibitor) failed to alter TNF-α-induced human lung EC apoptosis, suggesting that NAMPT-dependent NAD+ generation is unlikely to be involved in regulation of TNF-α-induced EC apoptosis. We next confirmed that TNF-α-induced EC apoptosis is attributable to NAMPT secretion into the EC culture media and subsequent eNAMPT ligation of TLR4 on the EC membrane surface. Silencing of NAMPT expression, direct neutralization of secreted eNAMPT by an NAMPT-specific polyclonal antibody (preventing TLR4 ligation), or direct TLR4 antagonism all served to significantly increase EC susceptibility to TNF-α-induced EC apoptosis. Together, these studies provide novel insights into NAMPT contributions to lung inflammatory events and to novel mechanisms of EC apoptosis regulation.

Nicotinamide Phosphoribosyltransferase Promotes Pulmonary Vascular Remodeling and Is a Therapeutic Target in Pulmonary Arterial Hypertension.

BACKGROUND: Pulmonary arterial hypertension is a severe and progressive disease, a hallmark of which is pulmonary vascular remodeling. Nicotinamide phosphoribosyltransferase (NAMPT) is a cytozyme that regulates intracellular nicotinamide adenine dinucleotide levels and cellular redox state, regulates histone deacetylases, promotes cell proliferation, and inhibits apoptosis. We hypothesized that NAMPT promotes pulmonary vascular remodeling and that inhibition of NAMPT could attenuate pulmonary hypertension. METHODS: Plasma, mRNA, and protein levels of NAMPT were measured in the lungs and isolated pulmonary artery endothelial cells from patients with pulmonary arterial hypertension and in the lungs of rodent models of pulmonary hypertension. Nampt+/- mice were exposed to 10% hypoxia and room air for 4 weeks, and the preventive and therapeutic effects of NAMPT inhibition were tested in the monocrotaline and Sugen hypoxia models of pulmonary hypertension. The effects of NAMPT activity on proliferation, migration, apoptosis, and calcium signaling were tested in human pulmonary artery smooth muscle cells. RESULTS: Plasma and mRNA and protein levels of NAMPT were increased in the lungs and isolated pulmonary artery endothelial cells from patients with pulmonary arterial hypertension, as well as in lungs of rodent models of pulmonary hypertension. Nampt+/- mice were protected from hypoxia-mediated pulmonary hypertension. NAMPT activity promoted human pulmonary artery smooth muscle cell proliferation via a paracrine effect. In addition, recombinant NAMPT stimulated human pulmonary artery smooth muscle cell proliferation via enhancement of store-operated calcium entry by enhancing expression of Orai2 and STIM2. Last, inhibition of NAMPT activity attenuated monocrotaline and Sugen hypoxia-induced pulmonary hypertension in rats. CONCLUSIONS: Our data provide evidence that NAMPT plays a role in pulmonary vascular remodeling and that its inhibition could be a potential therapeutic target for pulmonary arterial hypertension.

An update on sphingosine-1-phosphate receptor 1 modulators.

Sphingolipids represent an essential class of lipids found in all eukaryotes, and strongly influence cellular signal transduction. Autoimmune diseases like asthma and multiple sclerosis (MS) are mediated by the sphingosine-1-phosphate receptor 1 (S1P1) to express a variety of symptoms and disease patterns. Inspired by its natural substrate, an array of artificial sphingolipid derivatives has been developed to target this specific G protein-coupled receptor (GPCR) in an attempt to suppress autoimmune disorders. FTY720, also known as fingolimod, is the first oral disease-modifying therapy for MS on the market. In pursuit of improved stability, bioavailability, and efficiency, structural analogues of this initial prodrug have emerged over time. This review covers a brief introduction to the sphingolipid metabolism, the mechanism of action on S1P1, and an updated overview of synthetic sphingosine S1P1 agonists.

The Consequences of Overlapping G-Quadruplexes and i-Motifs in the Platelet-Derived Growth Factor Receptor ß Core Promoter Nuclease Hypersensitive Element Can Explain the Unexpected Effects of Mutations and Provide Opportunities for Selective Targeting of Both Structures by Small Molecules To Downregulate Gene Expression.

The platelet-derived growth factor receptor ß (PDGFR-ß) signaling pathway is a validated and important target for the treatment of certain malignant and nonmalignant pathologies. We previously identified a G-quadruplex-forming nuclease hypersensitive element (NHE) in the human PDGFR-ß promoter that putatively forms four overlapping G-quadruplexes. Therefore, we further investigated the structures and biological roles of the G-quadruplexes and i-motifs in the PDGFR-ß NHE with the ultimate goal of demonstrating an alternate and effective strategy for molecularly targeting the PDGFR-ß pathway. Significantly, we show that the primary G-quadruplex receptor for repression of PDGFR-ß is the 3'-end G-quadruplex, which has a GGA sequence at the 3'-end. Mutation studies using luciferase reporter plasmids highlight a novel set of G-quadruplex point mutations, some of which seem to provide conflicting results on effects on gene expression, prompting further investigation into the effect of these mutations on the i-motif-forming strand. Herein we characterize the formation of an equilibrium between at least two different i-motifs from the cytosine-rich (C-rich) sequence of the PDGFR-ß NHE. The apparently conflicting mutation results can be rationalized if we take into account the single base point mutation made in a critical cytosine run in the PDGFR-ß NHE that dramatically affects the equilibrium of i-motifs formed from this sequence. We identified a group of ellipticines that targets the G-quadruplexes in the PDGFR-ß promoter, and from this series of compounds, we selected the ellipticine analog GSA1129, which selectively targets the 3'-end G-quadruplex, to shift the dynamic equilibrium in the full-length sequence to favor this structure. We also identified a benzothiophene-2-carboxamide (NSC309874) as a PDGFR-ß i-motif-interactive compound. In vitro, GSA1129 and NSC309874 downregulate PDGFR-ß promoter activity and transcript in the neuroblastoma cell line SK-N-SH at subcytotoxic cell concentrations. GSA1129 also inhibits PDGFR-ß-driven cell proliferation and migration. With an established preclinical murine model of acute lung injury, we demonstrate that GSA1129 attenuates endotoxin-mediated acute lung inflammation. Our studies underscore the importance of considering the effects of point mutations on structure formation from the G- and C-rich sequences and provide further evidence for the involvement of both strands and associated structures in the control of gene expression.

A genetic variant of cortactin linked to acute lung injury impairs lamellipodia dynamics and endothelial wound healing.

Inflammatory mediators released in acute lung injury (ALI) trigger the disruption of interendothelial junctions, leading to loss of vascular barrier function, protein-rich pulmonary edema, and severe hypoxemia. Genetic signatures that predict patient recovery or disease progression are poorly defined, but recent genetic screening of ALI patients has identified an association between lung inflammatory disease and a single nucleotide polymorphism (SNP) in the gene for the actin-binding and barrier-regulatory protein cortactin. This study investigated the impact of this disease-linked cortactin variant on wound healing processes that may contribute to endothelial barrier restoration. A microfabricated platform was used to quantify wound healing in terms of gap closure speed, lamellipodia dynamics, and cell velocity. Overexpression of wild-type cortactin in endothelial cells (ECs) improved directional cell motility and enhanced lamellipodial protrusion length, resulting in enhanced gap closure rates. By contrast, the cortactin SNP impaired wound closure and cell locomotion, consistent with the observed reduction in lamellipodial protrusion length and persistence. Overexpression of the cortactin SNP in lung ECs mitigated the barrier-enhancing activity of sphingosine 1-phosphate. These findings suggest that this common cortactin variant may functionally contribute to ALI predisposition by impeding endothelial wound healing.

The NAMPT promoter is regulated by mechanical stress, signal transducer and activator of transcription 5, and acute respiratory distress syndrome-associated genetic variants.

Increased nicotinamide phosphoribosyltransferase (NAMPT) transcription is mechanistically linked to ventilator-induced inflammatory lung injury (VILI), with VILI severity attenuated by reduced NAMPT bioavailability. The molecular mechanisms of NAMPT promoter regulation in response to excessive mechanical stress remain poorly understood. The objective of this study was to define the contribution of specific transcription factors, acute respiratory distress syndrome (ARDS)-associated single nucleotide polymorphisms (SNPs), and promoter demethylation to NAMPT transcriptional regulation in response to mechanical stress. In vivo NAMPT protein expression levels were examined in mice exposed to high tidal volume mechanical ventilation. In vitro NAMPT expression levels were examined in human pulmonary artery endothelial cells exposed to 5 or 18% cyclic stretch (CS), with NAMPT promoter activity assessed using NAMPT promoter luciferase reporter constructs with a series of nested deletions. In vitro NAMPT transcriptional regulation was further characterized by measuring luciferase activity, DNA demethylation, and chromatin immunoprecipitation. VILI-challenged mice exhibited significantly increased NAMPT expression in bronchoalveolar lavage leukocytes and in lung endothelium. A mechanical stress-inducible region (MSIR) was identified in the NAMPT promoter from -2,428 to -2,128 bp. This MSIR regulates NAMPT promoter activity, mRNA expression, and signal transducer and activator of transcription 5 (STAT5) binding, which is significantly increased by 18% CS. In addition, NAMPT promoter activity was increased by pharmacologic promoter demethylation and inhibited by STAT5 silencing. ARDS-associated NAMPT promoter SNPs rs59744560 (-948G/T) and rs7789066 (-2,422A/G) each significantly elevated NAMPT promoter activity in response to 18% CS in a STAT5-dependent manner. Our results show that NAMPT is a key novel ARDS therapeutic target and candidate gene with genetic/epigenetic transcriptional regulation in response to excessive mechanical stress.

Nicotinamide phosphoribosyltransferase inhibitor is a novel therapeutic candidate in murine models of inflammatory lung injury.

We previously identified the intracellular nicotinamide phosphoribosyltransferase (iNAMPT, aka pre-B-cell colony enhancing factor) as a candidate gene promoting acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury (VILI) with circulating nicotinamide phosphoribosyltransferase potently inducing NF-κB signaling in lung endothelium. iNAMPT also synthesizes intracellular nicotinamide adenine dinucleotide (iNAD) in response to extracellular oxidative stress, contributing to the inhibition of apoptosis via ill-defined mechanisms. We now further define the role of iNAMPT activity in the pathogenesis of ARDS/VILI using the selective iNAMPT inhibitor FK-866. C57/B6 mice were exposed to VILI (40 ml/kg, 4 h) or LPS (1.5 mg/kg, 18 h) after osmotic pump delivery of FK-866 (100 mg/kg/d, intraperitoneally). Assessment of total bronchoalveolar lavage (BAL) protein, polymorphonuclear neutrophil (PMN) levels, cytokine levels (TNF-α, IL-6, IL-1α), lung iNAD levels, and injury scores revealed that FK-866-mediated iNAMPT inhibition successfully reduced lung tissue iNAD levels, BAL injury indices, inflammatory cell infiltration, and lung injury scores in LPS- and VILI-exposed mice. FK-866 further increased lung PMN apoptosis, as reflected by caspase-3 activation in BAL PMNs. These findings support iNAMPT inhibition via FK-866 as a novel therapeutic agent for ARDS via enhanced apoptosis in inflammatory PMNs.

FTY720 (s)-phosphonate preserves sphingosine 1-phosphate receptor 1 expression and exhibits superior barrier protection to FTY720 in acute lung injury.

OBJECTIVE: Effective therapies are needed to reverse the increased vascular permeability that characterizes acute inflammatory diseases such as acute lung injury. FTY720 is a pharmaceutical analog of the potent barrier-enhancing phospholipid, sphingosine 1-phosphate. Because both FTY720 and sphingosine 1-phosphate have properties that may limit their usefulness in patients with acute lung injury, alternative compounds are needed for therapeutic use. The objective of this study is to characterize the effects of FTY720 (S)-phosphonate, a novel analog of FTY720-phosphate, on variables of pulmonary vascular permeability in vitro and alveolar-capillary permeability in vivo. SETTING: University-affiliated research institute. SUBJECTS: Cultured human pulmonary endothelial cells; C57BL/6 mice. INTERVENTIONS: Endothelial cells were stimulated with sphingosine 1-phosphate receptor 1 agonists to determine effects on sphingosine 1-phosphate receptor 1 expression. Acute lung injury was induced in C57BL/6 mice with bleomycin to assess effects of sphingosine 1-phosphate receptor 1 agonists. MEASUREMENTS AND MAIN RESULTS: FTY720 (S)-phosphonate potently increases human pulmonary endothelial cell barrier function in vitro as measured by transendothelial electrical resistance. Reduction of sphingosine 1-phosphate receptor 1 with small interference RNA significantly attenuates this transendothelial electrical resistance elevation. FTY720 (S)-phosphonate maintains endothelial sphingosine 1-phosphate receptor 1 protein expression in contrast to greater than 50% reduction after incubation with sphingosine 1-phosphate, FTY720, or other sphingosine 1-phosphate receptor 1 agonists. FTY720 (S)-phosphonate does not induce ß-arrestin recruitment, sphingosine 1-phosphate receptor 1 ubiquitination, and proteosomal degradation that occur after other agonists. Intraperitoneal administration of FTY720 (S)-phosphonate every other day for 1 week in normal or bleomycin-injured mice maintains significantly higher lung sphingosine 1-phosphate receptor 1 expression compared with FTY720. FTY720 fails to protect against bleomycin-induced acute lung injury in mice, while FTY720 (S)-phosphonate significantly decreases lung leak and inflammation. CONCLUSION: FTY720 (S)-phosphonate is a promising barrier-promoting agent that effectively maintains sphingosine 1-phosphate receptor 1 levels and improves outcomes in the bleomycin model of acute lung injury.

Extracellular Nicotinamide Phosphoribosyltransferase Is a Therapeutic Target in Experimental Necrotizing Enterocolitis.

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency of prematurity. Postulated mechanisms leading to inflammatory necrosis of the ileum and colon include activation of the pathogen recognition receptor Toll-like receptor 4 (TLR4) and decreased levels of transforming growth factor beta (TGFß). Extracellular nicotinamide phosphoribosyltransferase (eNAMPT), a novel damage-associated molecular pattern (DAMP), is a TLR4 ligand and plays a role in a number of inflammatory disease processes. To test the hypothesis that eNAMPT is involved in NEC, an eNAMPT-neutralizing monoclonal antibody, ALT-100, was used in a well-established animal model of NEC. Preterm Sprague-Dawley pups delivered prematurely from timed-pregnant dams were exposed to hypoxia/hypothermia and randomized to control-foster mother dam-fed rats, injected IP with saline (vehicle) 48 h after delivery; control + mAB-foster dam-fed rats, injected IP with 10 µg of ALT-100 at 48 h post-delivery; NEC-orally gavaged, formula-fed rats injected with saline; and NEC + mAb-formula-fed rats, injected IP with 10 µg of ALT-100 at 48 h. The distal ileum was processed 96 h after C-section delivery for histological, biochemical, molecular, and RNA sequencing studies. Saline-treated NEC pups exhibited markedly increased fecal blood and histologic ileal damage compared to controls (q < 0.0001), and findings significantly reduced in ALT-100 mAb-treated NEC pups (q < 0.01). Real-time PCR in ileal tissues revealed increased NAMPT in NEC pups compared to pups that received the ALT-100 mAb (p < 0.01). Elevated serum levels of tumor necrosis factor alpha (TNFα), interleukin 6 (IL-6), interleukin-8 (IL-8), and NAMPT were observed in NEC pups compared to NEC + mAb pups (p < 0.01). Finally, RNA-Seq confirmed dysregulated TGFß and TLR4 signaling pathways in NEC pups that were attenuated by ALT-100 mAb treatment. These data strongly support the involvement of eNAMPT in NEC pathobiology and eNAMPT neutralization as a strategy to address the unmet need for NEC therapeutics.