Endothelial NO/cGMP/VASP Signaling Attenuates Kupffer Cell Activation and Hepatic Insulin Resistance Induced by High-Fat Feeding

Abstract

OBJECTIVEProinflammatory activation of Kupffer cells is implicated in the effect of high-fat feeding to cause liver insulin resistance. We sought to determine whether reduced endothelial nitric oxide (NO) signaling contributes to the effect of high-fat feeding to increase hepatic inflammatory signaling and if so, whether this effect 1) involves activation of Kupffer cells and 2) is ameliorated by increased NO signaling.RESEARCH DESIGN AND METHODSEffect of NO/cGMP signaling on hepatic inflammation and on isolated Kupffer cells was examined in C57BL/6 mice, eNos−/− mice, and Vasp−/− mice fed a low-fat or high-fat diet.RESULTSWe show that high-fat feeding induces proinflammatory activation of Kupffer cells in wild-type mice coincident with reduced liver endothelial nitric oxide synthase activity and NO content while, conversely, enhancement of signaling downstream of endogenous NO by phosphodiesterase-5 inhibition protects against high fat–induced inflammation in Kupffer cells. Furthermore, proinflammatory activation of Kupffer cells is evident in eNos−/− mice even on a low-fat diet. Targeted deletion of vasodilator-stimulated phosphoprotein (VASP), a key downstream target of endothelially derived NO, similarly predisposes to hepatic and Kupffer cell inflammation and abrogates the protective effect of NO signaling in both macrophages and hepatocytes studied in a cell culture model.CONCLUSIONSThese results collectively imply a physiological role for endothelial NO to limit obesity-associated inflammation and insulin resistance in hepatocytes and support a model in which Kupffer cell activation during high-fat feeding is dependent on reduced NO signaling. Our findings also identify the NO/VASP pathway as a novel potential target for the treatment of obesity-associated liver insulin resistance.

Deficiency of lymphotoxin-α does not exacerbate high-fat diet-induced obesity but does enhance inflammation in mice

“…The character of the accumulated macrophages in LT Ϫ/Ϫ mice was likely to be weighted toward an M2 transcript profile due to elevated levels of markers MGL1 and Arg1 for chow-fed mice and decreased levels of TNF for both diets in LT Ϫ/Ϫ as opposed to WT adipose tissue (34). The M2 phenotype is thought to be anti-inflammatory in nature (69) and not associated with insulin resistance, although we did see a preponderance of Arg1 mRNA for WT HFHS diet-fed mice in our study. This may be due to experimental design since macrophage phenotype marker expression is dynamic and influenced by diet duration (62).…”

Guanylin-Guanylyl cyclase-C signaling in macrophages regulates mesenteric fat inflammation induced by high-fat diet

“…In addition, the hepatic triacylglycerol content of VASP knockout mice was higher than that of WT mice [14]. Furthermore, an in vitro study showed that lipopolysaccharide-induced expression of TNFα or iNOS in macrophages is attenuated in the presence of agents that increase VASP signaling, such as diazen-1-IM1, 2-diolate, and 8-bromoguanosine-3′,5′-cGMP [14]. Similarly increases in TNFα or iNOS expression induced by combined treatment with lipopolysaccharide and interferon γ were attenuated in macrophages that overexpressed VASP [14].…”

“…Recently, it was reported that the expression of proinflammatory markers in the Kupffer cells of VASP knockout mice was significantly higher than that of WT mice. In addition, the hepatic triacylglycerol content of VASP knockout mice was higher than that of WT mice [14]. Furthermore, an in vitro study showed that lipopolysaccharide-induced expression of TNFα or iNOS in macrophages is attenuated in the presence of agents that increase VASP signaling, such as diazen-1-IM1, 2-diolate, and 8-bromoguanosine-3′,5′-cGMP [14].…”

“…PKG phosphorylates targets such as vasodilator-stimulated phosphoprotein (VASP) [12], a protein implicated in the control of cytoskeletal dynamics and cell migration [13]. It recently was shown that the expression of inflammatory cytokines was increased significantly in the macrophages of VASP knockout mice [14], suggesting that the cGMP-PKG-VASP pathway controls the proinflammatory state. Therefore, we investigated the phosphorylation of VASP and the protein levels of inhibitors of kappa B α (IκBα) in the mesenteric fat of dTg and WT rats.…”

“…Furthermore, an in vitro study showed that lipopolysaccharide-induced expression of TNFα or iNOS in macrophages is attenuated in the presence of agents that increase VASP signaling, such as diazen-1-IM1, 2-diolate, and 8-bromoguanosine-3′,5′-cGMP [14]. Similarly increases in TNFα or iNOS expression induced by combined treatment with lipopolysaccharide and interferon γ were attenuated in macrophages that overexpressed VASP [14]. We here showed that the phosphorylation of VASP at Ser239 in the mesenteric fat was markedly increased in HFD dTg rats compared with HFD WT rats.…”