The purpose of this study was to investigate the direct effect of vascular endothelial growth factor (VEGF) on microvascular permeability and its signaling mechanisms. The apparent permeability coefficient to albumin was measured in isolated coronary venules. Topical application of VEGF dose-dependently and transiently increased albumin permeability by two- to threefold. Inhibition of nitric oxide (NO) synthesis with NG-monomethyl-L-arginine abolished VEGF-induced venular hyperpermeability. Furthermore, because NO exerts vasoactive effects through stimulation of guanylate cyclase (GC) and the subsequent production of guanosine 3',5'-cyclic monophosphate (cGMP), we examined the role of GC and cGMP-dependent protein kinase (PKG) in the mediation of VEGF's action. The permeability response to VEGF was measured in the presence of the selective GC inhibitor 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one and the specific PKG inhibitor KT-5823. Both inhibitors reduced basal permeability and prevented the hyperpermeability response to VEGF. Therefore, we suggest that VEGF modulates microvascular permeability via a signaling cascade involving NO synthesis, GC stimulation, and PKG activation.

The vascular endothelium is a layer of cells lining the inner surface of vessels, serving as a barrier that mediates microenvironment homeostasis. Deterioration of either the structure or function of endothelial cells (ECs) results in a variety of cardiovascular diseases. Previous studies have shown that reactive oxygen species (ROS) is a key factor that contributes to the impairment of ECs and the subsequent endothelial dysfunction. The longevity regulator Sirt1 is a NAD+-dependent deacetylase that has a potential antioxidative stress activity in vascular ECs. The mechanisms underlying the protective effects involve Sirt1/FOXOs, Sirt1/NF-κB, Sirt1/NOX, Sirt1/SOD, and Sirt1/eNOs pathways. In this review, we summarize the most recent reports in this field to recapitulate the potent mechanisms involving the protective role of Sirt1 in oxidative stress and to highlight the beneficial effects of Sirt1 on cardiovascular functions.

Sepsis‐induced liver injury is recognized as a key problem in intensive care units. The gut microbiota has been touted as an important mediator of liver disease development; however, the precise roles of gut microbiota in regulating sepsis‐induced liver injury are unknown. Here, we aimed to investigate the role of the gut microbiota in sepsis‐induced liver injury and the underlying mechanism. Cecal ligation and puncture (CLP) was used to induce polymicrobial sepsis and related liver injury. Fecal microbiota transplantation (FMT) was used to validate the roles of gut microbiota in these pathologies. Metabolomics analysis was performed to characterize the metabolic profile differences between sepsis‐resistant (Res; survived to 7 days after CLP) and sepsis‐sensitive (Sen; moribund before or approximately 24 hours after CLP) mice. Mice gavaged with feces from Sen mice displayed more‐severe liver damage than did mice gavaged with feces from Res mice. The gut microbial metabolic profile between Sen and Res mice was different. In particular, the microbiota from Res mice generated more granisetron, a 5‐hydroxytryptamine 3 (5‐HT3) receptor antagonist, than the microbiota from Sen mice. Granisetron protected mice against CLP‐induced death and liver injury. Moreover, proinflammatory cytokine expression by macrophages after lipopolysaccharide (LPS) challenge was markedly reduced in the presence of granisetron. Both treatment with granisetron and genetic knockdown of the 5‐HT3A receptor in cells suppressed nuclear factor kappa B (NF‐кB) transactivation and phosphorylated p38 (p‐p38) accumulation in macrophages. Gut microbial granisetron levels showed a significantly negative correlation with plasma alanine aminotransferase (ALT)/aspartate aminotransferase (AST) levels in septic patients. Conclusion: Our study indicated that gut microbiota plays a key role in the sensitization of sepsis‐induced liver injury and associates granisetron as a hepatoprotective compound during sepsis development.

Substance P (SP) is involved in the proliferation of cholangiocytes in bile duct ligated (BDL) mice and human cholangiocarcinoma growth by interacting with the neurokinin-1 receptor (NK-1R). To identify whether SP regulates liver fibrosis during cholestasis, wild type (WT) or NK-1R knockout (NK-1R−/−) mice that received BDL or sham surgery and Mdr2−/− mice treated with either an NK-1R antagonist (L-733,060) or saline were used. Additionally, WT mice were treated with SP or saline intraperitoneally. In vivo, there was increased expression of TAC1 (coding SP) and NK-1R in both BDL and Mdr2−/− mice compared to WT mice. The expression of TAC1 and NK-1R was significantly higher in liver samples from PSC patients compared to healthy controls. Knockout of NK-1R decreased BDL-induced liver fibrosis and treatment with L-733,060 resulted in decreased liver fibrosis in Mdr2−/− mice, which was shown by decreased Sirius red staining, fibrosis gene and protein expression and reduced transforming growth factor-β1 levels in serum and cholangiocytes supernatants. Furthermore, we observed that reduced liver fibrosis in NK-1R−/− mice with BDL surgery or Mdr2−/− mice treated with L-733,060 was associated with enhanced cellular senescence of hepatic stellate cells (HSCs) and decreased senescence of cholangiocytes. In vitro, L-733,060 inhibited SP-induced expression of fibrotic genes in HSCs and cholangiocytes. Treatment with L-733,060 partially reversed SP-induced decrease of senescence genes expression in cultured HSCs and SP-induced increase of senescence-related genes expression in cultured cholangiocytes. Collectively, our results demonstrated the regulatory effects of the SP/NK-1R axis on liver fibrosis through changes in cellular senescence during cholestatic liver injury.

We have previously demonstrated that agonists increase microvascular permeability through a phospholipase C-nitric oxide synthase-guanylate cyclase cascade. The aim of this study was to further investigate the downstream end of the signaling pathway with a focus on myosin light chain (MLC) phosphorylation. The apparent permeability coefficient to albumin was measured in isolated coronary venules. Under control conditions, the nitric oxide donor sodium nitroprusside, as well as the guanosine 3',5'-cyclic monophosphate-dependent protein kinase (PKG) activator 8-bromoguanosine 3',5'-cyclic monophosphate, increased venular permeability two- to threefold. Similarly, activation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate significantly elevated permeability. Inhibition of MLC phosphorylation with ML-7 significantly attenuated the hyperpermeability responses to the agonists. Furthermore, ML-7 dose dependently reduced basal venular permeability. Consistently, inhibition of dephosphorylation with the protein phosphatase inhibitor calyculin dramatically increased basal permeability. These results suggest that 1) PKG and PKC play an important signaling role in the regulation of endothelial barrier function and 2) MLC phosphorylation contributes to basal and agonist-stimulated microvascular permeability.