Novel mechanism for nicotinamide phosphoribosyltransferase inhibition of TNF-α-mediated apoptosis in human lung endothelial cells

Radu C. Oita, Sara M. Camp, Wenli Ma, Ermelinda Ceco, Mark Harbeck, Patrick Singleton, Joe Messana, Xiaoguang Sun, Ting Wang, Joe GN Garcia

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

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-kB 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 TNFa- 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.

Original languageEnglish (US)
Pages (from-to)36-44
Number of pages9
JournalAmerican Journal of Respiratory Cell and Molecular Biology
Volume59
Issue number1
DOIs
StatePublished - Jul 1 2018

Fingerprint

Nicotinamide Phosphoribosyltransferase
Endothelial cells
Endothelial Cells
Apoptosis
Lung
Toll-Like Receptor 4
Nicotinamide Mononucleotide
Ligation
NF-kappa B
Adult Respiratory Distress Syndrome
Biomarkers
Cell membranes
Cell culture
Caspase 3

Keywords

  • Acute lung injury
  • Apoptosis
  • NAD
  • Nicotinamide phosphoribosyltransferase

ASJC Scopus subject areas

  • Molecular Biology
  • Pulmonary and Respiratory Medicine
  • Clinical Biochemistry
  • Cell Biology

Cite this

Novel mechanism for nicotinamide phosphoribosyltransferase inhibition of TNF-α-mediated apoptosis in human lung endothelial cells. / Oita, Radu C.; Camp, Sara M.; Ma, Wenli; Ceco, Ermelinda; Harbeck, Mark; Singleton, Patrick; Messana, Joe; Sun, Xiaoguang; Wang, Ting; Garcia, Joe GN.

In: American Journal of Respiratory Cell and Molecular Biology, Vol. 59, No. 1, 01.07.2018, p. 36-44.

Research output: Contribution to journalArticle

Oita, Radu C. ; Camp, Sara M. ; Ma, Wenli ; Ceco, Ermelinda ; Harbeck, Mark ; Singleton, Patrick ; Messana, Joe ; Sun, Xiaoguang ; Wang, Ting ; Garcia, Joe GN. / Novel mechanism for nicotinamide phosphoribosyltransferase inhibition of TNF-α-mediated apoptosis in human lung endothelial cells. In: American Journal of Respiratory Cell and Molecular Biology. 2018 ; Vol. 59, No. 1. pp. 36-44.
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AU - Oita, Radu C.

AU - Camp, Sara M.

AU - Ma, Wenli

AU - Ceco, Ermelinda

AU - Harbeck, Mark

AU - Singleton, Patrick

AU - Messana, Joe

AU - Sun, Xiaoguang

AU - Wang, Ting

AU - Garcia, Joe GN

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AB - 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-kB 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 TNFa- 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.

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