(1630) Modulation of NAMPT in Systemic Inflammation Exhibits Tissue-Specific Roles

Introduction: Cellular NAD+ levels are defended by a biosynthetic pathway rate-limited by the enzyme NAMPT (nicotinamide phosphoribosyltransferase). Acute kidney injury (AKI), a common condition of rapid loss of function often linked with sepsis, is associated with low NAD+. In murine models of acute systemic inflammation, NAMPT transcription is unexpectedly upregulated in the whole kidney, leading us to hypothesize that inflammatory triggers induce NAMPT expression in distinct renal cell populations.

Methods: In vivo, a murine model of systemic inflammation with LPS 17.5 mg/kg BW was utilized, and murine pulmonary endothelial cells were isolated. SiRNA was used to lower NAMPT expression in human umbilical vein endothelial cells (HUVECs) and human kidney cells (HK2). In vitro, septic conditions were simulated, and various readouts such as bulk RNAseq, RT-qPCR, Western Blot, NAD(H) levels, immunohistochemistry, and transendothelial electrical resistance were assessed.

Results: Endotoxemic mice developed AKI and, unexpectedly, whole-kidney elevation of NAMPT (p < 0.05). To model this further, we inflamed HK2 and HUVECs with TNFα. Whereas HUVECs showed NAMPT induction (p < 0.001), HK2 did not (p>0.05). Knockdown of NAMPT blunted TNFα-dependent expression of inflammatory markers ICAM-1 (Intercellular adhesion molecule 1) (p < 0.05) and IL-6 (Interleukin-6) (p < 0.05) in HUVECs and prevented inflammatory barrier dysfunction (p < 0.01).  Conversely in HK2, NAMPT knockdown increased TNFα-dependent expression of the injury marker LCN2 (Lipocalin-2) (p < 0.01).

Conclusions: Despite a decrease in kidney NAD+ arising during endotoxemia, we find that the major enzyme responsible for its biosynthesis, NAMPT, is upregulated. Inflammatory NAMPT induction may be limited to the vascular endothelium, where it may potentiate inflammatory responses through unknown mechanisms. These findings support the development of both endothelial and epithelial-specific inducible NAMPT knockout mouse models to explore cell-specific mechanisms of inflammation.