Short chain fatty acids (SCFAs), a family of gut microbial metabolites, have been reported to promote preservation of endothelial function and thereby exert anti-atherosclerotic action. However, the precise mechanism mediating this protective action of SCFAs remains unknown. The present study investigated the effects of SCFAs (acetate, propionate and butyrate) on the activation of Nod-like receptor pyrin domain 3 (Nlrp3) inflammasome in endothelial cells (ECs) and associated carotid neointima formation. Using a partial ligated carotid artery (PLCA) mouse model fed with the Western diet (WD), we found that butyrate significantly decreased Nlrp3 inflammasome formation and activation in the carotid arterial wall of wild type mice (Asc+/+), which was comparable to the effect of gene deletion of the adaptor protein apoptosis-associated speck-like protein gene (Asc-/-). Nevertheless, both acetate and propionate markedly enhanced the formation and activation of the Nlrp3 inflammasome as well as carotid neointima formation in the carotid arteries with PLCA in Asc+/+, but not Asc-/- mice. In cultured ECs (EOMA cells), butyrate was found to significantly decrease the formation and activation of Nlrp3 inflammasomes induced by 7-ketocholesterol (7-Ket) or cholesterol crystals (CHC), while acetate did not inhibit Nlrp3 inflammasome activation induced by either 7-Ket or CHC, but itself even activated Nlrp3 inflammsomes. Mechanistically, the inhibitory action of butyrate on the Nlrp3 inflammasome was attributed to a blockade of lipid raft redox signaling platforms to produce O2•- upon 7-Ket or CHC stimulations. These results indicate that SCFAs have differential effects on endothelial Nlrp3 inflammasome activation and associated carotid neointima formation.

Expression and activity of serum- and glucocorticoid-inducible kinase 1 (SGK1) are associated with many metabolic and inflammatory diseases. In this study, we report that SGK1 promotes alternative macrophage polarization and restrains inflammation in the infectious milieu of the gingiva. Inhibition of SGK1 expression or activity enhances characteristics of classically activated (M1) macrophages by directly activating the transcription of genes encoding iNOS, IL-12P40, TNF-α, and IL-6 and repressing IL-10 at message and protein levels. Moreover, SGK1 inhibition robustly reduces the expression of alternatively activated (M2) macrophage molecular markers, including arginase-1, Ym-1, Fizz1, and Mgl-1. These results were confirmed by multiple gain- and loss-of-function approaches, including small interfering RNA, a plasmid encoding SGK1, and LysM-Cre–mediated sgk1 gene knockout. Further mechanistic analysis showed that SGK1 deficiency decreases STAT3 but increases FoxO1 expression in macrophages under M2 or M1 macrophage–priming conditions, respectively. Combined with decreased FoxO1 phosphorylation and the subsequent suppressed cytoplasmic translocation observed, SGK1 deficiency robustly enhances FoxO1 activity and drives macrophage to preferential M1 phenotypes. Furthermore, FoxO1 inhibition abrogates M1 phenotypes, and STAT3 overexpression results in a significant increase of M2 phenotypes, indicating that both FoxO1 and STAT3 are involved in SGK1-mediated macrophage polarization. Additionally, SGK1 differentially regulates the expression of M1 and M2 molecular markers, including CD68 and F4/F80 and CD163 and CD206, respectively, and protects against Porphyromonas gingivalis–induced alveolar bone loss in a mouse model. Taken together, these results have demonstrated that SGK1 is critical for macrophage polarization and periodontal bone loss, and for the first time, to our knowledge, we elucidated a bifurcated signaling circuit by which SGK1 promotes alternative, while suppressing inflammatory, macrophage polarization.

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We hypothesized that autophagy and associated lysosome function serve as a critical modulator during Nod-like receptor family pyrin domain containing 3 (Nlrp3) inflammasome activation on proatherogenic stimuli. We first demonstrated that 7-ketocholesterol stimulated Nlrp3 inflammasome formation and activation as shown by increased colocalization of inflammasome components [Nlrp3 versus apoptosis associated speck-like protein (Asc) or caspase-1] and enhanced cleavage of caspase-1 into active caspase-1 to generate IL-1b in coronary artery smooth muscle cells. Deletion of the CD38 gene (CD38 À/À ) that regulates lysosome function and autophagic flux also led to Nlrp3 inflammasome formation and activation. In the presence of rapamycin, the effects of either 7-ketocholesterol treatment or CD38 gene deletion were abolished. The autophagy inhibitor spautin-1 and the lysosome function blocker bafilomycin A1 also enhanced Nlrp3 inflammasome formation and activation. In animal experiments, we found that increased colocalization of Nlrp3 versus Asc or caspase-1 enhanced IL-1b accumulation and caspase-1 activity in the coronary arterial wall of CD38 À/À mice on the Western diet compared with CD38 þ/þ mice. This increased colocalization was blocked by treatment with rapamycin but enhanced by chloroquine, a water-soluble blocker of autophagic flux. Morphologic examinations confirmed that the media of coronary arteries was significantly thicker in CD38 À/À mice on the Western diet than CD38 þ/þ mice. In conclusion, the deficiency of autophagic flux promotes Nlrp3 inflammasome formation and activation in coronary artery smooth muscle cells on proatherogenic stimulation, leading to medial thickening of the coronary arterial wall.

Supplemental Digital Content is Available in the Text.Deep learning-based analysis of large-scale bioimages of the dorsal root ganglion after nerve injury reveals satellite glial cell plasticity but no loss of sensory neurons.