Visfatin/extracellular-nicotinamide-phosphoribosyltranferase-(eNampt) is a multifaceted adipokine enhanced in type-2-diabetes and obesity. Visfatin/eNampt cause in vitro endothelial dysfunction and vascular inflammation, although whether the same effects are achieved in vivo is unknown. Toll-like receptor-4 (TLR4), a main surface pattern recognition receptor of innate immune system is a potential target for visfatin/eNampt. We studied its capacity to generate vascular dysfunction in vivo, focusing on TLR4 role and downstream activation of nod-like-receptor-protein-3 (NLRP3)-inflammasome. 4 month-old C57BL/6 mice were exposed to 7 days infusion of visfatin/eNampt, alone or together with FK 866 (Nampt enzymatic inhibitor), CLI 095 (TLR4 blocker), MCC 950 (NLRP3-inflammasome inhibitor), or anakinra (interleukin(IL)-1-receptor antagonist). Endothelial dysfunction was tested in isolated microvessels. In human umbilical endothelial cells (HUVEC), proteins related to the NLRP3-inflammasome phosphorylated p-65, NLRP3, caspase-1, pro-IL-1β, and mature IL-1β were determined by Western blot, while the inflammasome related apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC-specks) was studied by immunofluorescence. Impaired endothelium-dependent relaxations were observed in isolated mesenteric microvessels from visfatin/eNampt-infused mice. This effect was attenuated by co-treatment with FK 866 or CLI 095, supporting a role for Nampt enzymatic activity and TLR4 activation. Moreover, cultured HUVEC exposed to visfatin/eNampt showed higher expression and activation of NLRP3-inflammasome. Again, this effect relied on Nampt enzymatic activity and TLR4 activation, and it was abrogated by the inflammasome assembly blockade with MCC 950. The endothelial dysfunction evoked by visfatin/eNampt infusion in vivo was also sensitive to both MCC 950 and anakinra treatments, suggesting that the NLRP3-inflammasome-driven tissular release of IL-1β is the final mediator of endothelial damage. We conclude that Visfatin/eNampt produces in vivo vascular dysfunction in mice by a Nampt-dependent TLR4-mediated pathway, involving NLRP3-inflammasome and paracrine IL-1β. Thus, those targets may become therapeutic strategies for attenuating the adipokine-mediated vascular dysfunction associated to obesity and/or type-2-diabetes.
Bibliographical noteFunding Information:
Supported by a grant from Plan Nacional I+D+i (SAF2017-84776-R). T.R. was supported by a Juan de la Cierva Incorporación contract (IJCI-2015-24474). M.R.-G. was supported by a fellowship from Pronabec (Perú) A.S.-H.L. and I.V. are the recipients of FPI-UAM (2015), and FPU-MEC (FPU16/02612) contracts, respectively. A.R. is the recipient of a research contract from Comunidad Autónoma de Madrid (PEJ-2017-AI/SAL-6867).
© 2020, The Author(s).