Sphingosine 1-phosphate receptor 1 governs endothelial barrier function and angiogenesis by upregulating endoglin signaling.

Background: The sphingosine 1-phosphate (S1P)/S1P receptor (S1pr) 1 signaling plays an essential role in regulating vascular integrity and angiogenesis. We have previously shown that cell-surface expression of endoglin (Eng) is sustained by S1P/S1pr1 signaling in endothelial cells (ECs). However, whether S1pr1 mediates Eng signaling, or vice versa, remains unknown. Methods: S1pr1 inhibitors were used to study whether pharmacological inhibition induces basal vascular leakage in vivo. An acute respiratory distress syndrome (ARDS) model was used to study whether S1pr1 inhibition evoked greater inflammation in lungs. A S1pr1 inhibitor, a bone morphogenetic protein 9 (BMP9) blocking antibody, or lentivirus-mediated expression of soluble extracellular domain of Eng (sEng) were used to test whether blocking both S1P/S1pr1 and BMP9/Eng signaling axes would impose any interaction in retinal angiogenesis. To clarify whether S1P and BMP9 function in a linear pathway, a study of trans-endothelial electrical resistance (TEER) measurement was carried out using a mouse islet EC line MS1; time course studies were executed to exam downstream effectors of S1P and BMP9 signaling pathways in ECs; two stable MS1 cell lines were generated, one with overexpression of human S1PR1 and the other with knockdown of Eng, to validate S1pr1 and Eng were the key players for the crosstalk. Inhibitor of extracellular regulated protein kinases (ERK) was used to check whether this signaling was involved in S1P-induced cell-surface localization of Eng. Results: The present study elucidated that S1pr1 and Eng are both pivotal for angiogenesis in the postnatal mouse retina, and that the activation of S1pr1 or Eng increases vascular barrier function. Activation of S1pr1 enhanced the phosphorylation of Smad family members 1, 5, and 8 (pSmad1/5/8), while the inhibition of S1pr1 reduced the levels of pSma1/5/8 induced by BMP9 treatment. Activation or loss of Eng did not affect S1pr1 signaling. Moreover, activation of ERK was involved in promoting EC-surface expression of Eng by S1pr1. Conclusions: Our data demonstrates for the first time that there exists a linear pathway of S1pr1-Eng signaling axis in ECs, which governs vascular homeostasis. Functional BMP9/Eng signaling requires S1P/S1pr1 activation, and S1pr1 signaling acts as a vascular protection mechanism upstream of Eng.

Regulatory mechanism of NOV/CCN3 in the inflammation and apoptosis of lung epithelial alveolar cells upon lipopolysaccharide stimulation.

Lipopolysaccharide (LPS) induces stress inflammation and apoptosis. Pulmonary epithelial cell apoptosis, which accelerates the progression of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), is the leading cause of mortality in patients with ALI/ARDS. The nephroblastoma overexpressed protein (CCN3), an inflammatory modulator, is reported to be a biomarker in ALI. Using the LPS-induced ALI model, this study investigated the expression of CCN3 and its possible molecular mechanism in lung alveolar epithelial cell inflammation and apoptosis. Our data revealed that LPS treatment greatly increased the level of CCN3 in A549 cells. The A549 cells were transfected with specific CCN3 small interfering RNA (siRNA) using transfection reagent. CCN3 siRNA not only largely attenuated the expressions of the inflammatory cytokines interleukin (IL)-1ß and transforming growth factor (TGF)-ß1, but also reduced the apoptotic rate of the AEC II cells and affected the expressions of the apoptosis-associated proteins (Bcl-2 and caspase-3). Furthermore, CCN3 knockdown greatly inhibited the activation of nuclear factor-κB p65 in A549 cells. In addition, TGF-ß/p-Smad inhibitor (TP0427736) and NF-κB inhibitor (PDTC) significantly attenuated the expression level of CCN3 in A549 cells. In conclusion, our data indicated that CCN3 siRNA affected downstream signal through TGF-ß/ p-Smad or NF-κB pathway, leading to the inhibition of cell inflammation and apoptosis in human alveolar epithelial cells.

Can glypican-3 be a disease-specific biomarker?

BACKGROUND: Glypican-3 (GPC3) is a cell surface-bound proteoglycan which has been identified as a potential biomarker candidate in hepatocellular carcinoma, lung carcinoma, severe pneumonia, and acute respiratory distress syndrome (ARDS). The aim of our review is to evaluate whether GPC3 has utility as a disease-specific biomarker, to discuss the potential involvement of GPC3 in cell biology, and to consider the changes of GPC3 gene and protein expression and regulation in hepatocellular carcinoma, lung cancer, severe pneumonia, and ARDS. RESULTS: Immunohistochemical studies have suggested that over-expression of GPC3 is associated with a poorer prognosis for hepatocellular carcinoma patients. Expression of GPC3 leads to an increased apoptosis response in human lung carcinoma tumor cells, and is considered to be a candidate lung tumor suppressor gene. Increased serum levels of GPC3 have been demonstrated in ARDS patients with severe pneumonia. CONCLUSIONS: Glypican-3 could be considered as a clinically useful biomarker in hepatocellular carcinoma, lung carcinoma, and ARDS, but further research is needed to confirm and expand on these findings.