Role of Endothelial eNAMPT Secretion and TLR4 Signaling in the ARDS Vascular Endotype

本A1应用的重点是细胞外烟酰胺磷酸核糖基转移酶的关键作用

This A1 application is focused on the critical role of extracellular nicotinamide phosphoribosyltransferase (eNAMPT) in driving lung vascular inflammation and multi-organ endothelial cell (EC) permeability, events that are central to increasing ARDS mortality and the COVID-19-ARDS vascular endotype. We initially identified eNAMPT as a novel ARDS and ventilator-induced lung injury (VILI) therapeutic target utilizing genomic–intensive approaches and cellular and preclinical studies of excessive mechanical stress/VILI. We showed eNAMPT is a novel ARDS biomarker with plasma eNAMPT levels increasing in response to viral/bacterial infection and expo- sure to mechanical ventilation. Importantly, utilizing conditional EC–specific NAMPT KO mice, we have recently shown that EC contributions to ARDS pathobiology includes eNAMPT secretion into the circulation thereby driv- ing preclinical ARDS inflammatory lung injury and severity. We have shown that eNAMPT produces these inju- rious effects by functioning as a damage-associated molecular pattern protein (DAMP) and master regulator of evolutionarily-conserved inflammatory cascades via novel ligation of the Toll–like receptor 4 (TLR4). Our ex- citing preclinical data in both rat and porcine ARDS/VILI models have validated the efficacy of the eNAMPT- neutralizing humanized mAb (ALT-100) in reducing eNAMPT- and LPS-induced TLR4 activation and NFκB- driven cytokine production, lung permeability and inflammatory lung injury. To further interrogate and validate eNAMPT as a ARDS therapeutic target, Specific Aim #1 will extend prior studies which showed ROS-generating ARDS stimuli (hypoxia, hyperoxia, mechanical stress, cytokines) to induce NAMPT expression and NAMPT pro- moter SNPs to significantly increase eNAMPT plasma levels and risk of ARDS mortality (reduced ventilator-free days, increased ARDS mortality). SA #1 will characterize the role of three key transcription factors (hypoxia- inducible factors HIF1/2, NRF2), NAMPT and TLR4 promoter SNPs, and DNA methylation sites in genetic/ep- igenetic regulation of NAMPT and TLR4 promoter activities. As eNAMPT secretion is key to initiation of inflam- matory cascade activation, SA #2 will mechanistically explore novel regulation of TLR4- and mechanical stress- stimulated eNAMPT secretion via extracellular vesicle formation, inflammasome activation, and ABC transport- ers. As treatment with the eNAMPT-neutralizing ALT-100 mAb reversed the dramatic increases in Akt1 nitration, MAP kinase effector activation, and reduced Akt/mTOR deubiquitination, SA #3 will dissect the structure/function mechanisms involved in eNAMPT-TLR4 binding and stimulated increases in EC permeability with specific focus on MAP kinase effector p90rsk, Akt1 nitration, and UCHL1 activity in EC cytoskeletal-driven barrier dysfunction. Finally, SA #4 will optimize eNAMPT ALT-100 mAb dosing and time of delivery as a therapeutic strategy in preclinical rat and porcine ARDS/VILI models. The dissection of EC secretion of eNAMPT and eNAMPT/TLR4 participation in ARDS/VILI pathobiology will accelerate ALT-100 mAb development, an actionable strategy to attenuate inflammatory lung injury, EC permeability and ARDS/VILI mortality.