The roles and mechanisms of the Hippo/YAP signaling pathway in the nervous system.

The Hippo signaling pathway, consisting of a highly conserved kinase cascade and downstream transcription co-activators YAP (Yes-associated protein)/TAZ (transcriptional coactivator with PDZ-binding motif), plays a key role in tissue homeostasis and organ size control by regulating the proliferation, differentiation and apoptosis of cells. During normal development, the precise control of neural cell numbers and spatial distributions of these neural cells is important for brain development. Recent studies have shown that the Hippo/YAP signaling pathway is actively involved in the self-renewal of neural stem cells, proliferation of neural progenitor cells, differentiation and activation of glial cells, and myelination of glial cells as well as in the development of neurological diseases. Due to its prominent role in the nervous system, it is necessary to further study on this pathway. In this review, we summarize the recent studies and focus on the roles and mechanisms of the Hippo/YAP signaling pathway in the nervous system, and provide insights for neural development and neural injury diseases.

Polarized Distribution of Active Myosin II Regulates Directional Migration of Cultured Olfactory Ensheathing Cells.

Migration of olfactory ensheathing cells (OECs) is critical for development of olfactory system and essential for neural regeneration after OEC transplantation into nerve injury site. However, the molecular mechanisms underlying the regulation of directional migration of OECs remain unclear. In this study, we found that in migrating OECs, phosphorylated myosin light chain (p-MLC, active myosin II) displayed a polarized distribution, with the leading front exhibiting higher than soma and trailing process. Over-expression of GFP-MLC significantly reduced OEC migration. Moreover, decreasing this front-to-rear difference of myosin II activity by the frontal application of a ML-7 (myosin II inhibitors) gradient induced the collapse of leading front and reversed soma translocation of OECs, whereas, increasing this front-to-rear difference of myosin II activity by the rear application of a ML-7 or BDM gradient or the frontal application of a Caly (myosin II activator) gradient accelerated the soma translocation of OECs. Finally, myosin II as a downstream signaling of repulsive factor Slit-2 mediated the reversal of soma translocation induced by Slit-2. Taken together, these results suggest that the polarized distribution of active myosin II regulates the directional migration of OECs during spontaneous migration or upon to extracellular stimulation such as Slit-2.

Atorvastatin attenuates homocysteine-induced migration of smooth muscle cells through mevalonate pathway involving reactive oxygen species and p38 MAPK.

Statins have been reported to have an antioxidant effect against homocysteine (Hcy)-induced endothelial dysfunction. It is unknown whether they have the same effect against migration of vascular smooth muscle cells (VSMCs) induced by Hcy. In this study, it was investigated whether and how atorvastatin could inhibit the Hcy-induced migration in cultured VSMCs and revealed the possible redox mechanism. VSMCs were isolated from the thoracic aortas of Sprague-Dawley rats. The migration of VSMCs was examined using a transwell technique and cell viability was determined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazoliumbromide (MTT) assay. Reactive oxygen species (ROS) were measured using the fluoroprobe 2'7'-dichlorodihydrofluorescein diacetate. The activity of NADPH oxidase was assessed by lucigenin enhanced chemiluminescence. Expressions of Nox1 mRNA and p-p38MAPK protein were measured by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis, respectively. The results showed that atorvastatin inhibited the migration of VSMCs induced by Hcy, which was reversed by the mevalonate. In addition, pretreatment with the NADPH oxidase inhibitor DPI, the free radical scavenger NAC and the p38 MAPK inhibitor SB203580 blocked Hcy-induced VSMCs migration. Furthermore, atorvastatin suppressed Hcy-induced activation of NADPH oxidase and ROS, attenuated Hcy-induced overexpression of Nox1mRNA. Similar effects occurred with VSMCs transfected with Nox1 siRNA. Moreover, atorvastatin other than DPI, NAC, SB203580 and Nox1 siRNA transfection blocked Hcy-induced p38 MAPK phosphorylation, which was also reversed by the mevalonate. The data demonstrates that atorvastatin inhibits Hcy-induced VSMCs migration in a mevalonate pathway. Furthermore, a part of the biological effect of atorvastatin involves a decrease in the levels of Nox1-dependent ROS generation and p38 MAPK activation.

Atorvastatin inhibits homocysteine-induced dysfunction and apoptosis in endothelial progenitor cells.

AIM: To investigate the protective effects of atorvastatin on homocysteine (Hcy)-induced dysfunction and apoptosis in endothelial progenitor cells (EPCs) and the possible molecular mechanisms. METHODS: EPCs were divided into six groups: Hcy treatment groups (0, 50, and 500 micromol/L) and atorvastatin pretreatment groups (0.1, 1, and 10 micromol/L). EPC proliferation, migration, in vitro vasculogenesis activity, and apoptosis rate were assayed by the MTT assay, modified Boyden chamber assay, in vitro vasculogenesis kit, and AnnexinV-FITC apoptosis detection kit, respectively. The level of reactive oxygen species (ROS) in cells was measured using H(2)DCF-DA as a fluorescence probe. The activity of NADPH oxidase was evaluated with lucigenin-enhanced chemiluminescence. NO in the supernatant was detected by the nitrate reductase assay. The eNOS mRNA expression and p-eNOS, p-Akt, p-p38MAPK protein expression were measured by RT-PCR and Western blotting analysis, respectively. Caspase-3 activity was determined by colorimetric assay. RESULTS: Hcy does-dependently impaired the proliferation, migration and in vitro vasculogenesis capacity of EPCs, induced cell apoptosis, increased ROS accumulation and NADPH oxidase activation, and decreased the secretion of NO compared with the control group (P<0.05 or P<0.01). The detrimental effects of Hcy were attenuated by atorvastatin pretreatment. Furthermore, Hcy caused a significant downregulation of eNOS mRNA, p-eNOS, and p-Akt protein expression as well as an upregulation of p-p38MAPK protein expression and caspase-3 activity. These effects of Hcy on EPCs were reversed by atorvastatin in a does-dependent manner. CONCLUSION: Atorvastatin inhibited homocysteine-induced dysfunction and apoptosis in endothelial progenitor cells, which may be related to its effects on suppressing oxidative stress, up-regulating Akt/eNOS and down-regulating the p38MAPK/caspase-3 signaling pathway.

Atorvastatin inhibits homocysteine-induced oxidative stress and apoptosis in endothelial progenitor cells involving Nox4 and p38MAPK.

Previous studies showed that homocysteine (Hcy) reduces endothelial progenitor cells (EPCs) numbers and impairs functional activity. Atorvastatin, HMG-CoA inhibition has been showed to have protective effects on EPCs. Recent studies have demonstrated that reduced EPCs numbers and activity are associated with EPCs apoptosis. However, the protective mechanisms of atorvastatin on HHcy-induced EPCs apoptosis remain to be determined. This study was designed to examine the effect of atorvastatin on homocysteine-induced reactive oxygen species (ROS) production and apoptosis in EPCs. EPCs were isolated from peripheral blood and characterized, then challenged with Hcy (50-500 micromol/L) in the presence or absence of atorvastatin (0.01-1 micromol/L) or various stress signaling inhibitors, including mevalonate (100 micromol/L), antioxidants N-acetyl cysteine (NAC, 10 micromol/L), the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor diphenylene iodonium (DPI 10 micromol/L), the eNOS inhibitor N(G)mono-methyl-l-arginine LNMA (1mmol/L), and the p38 mitogen-activated protein kinase (p38 MAPK) inhibitor SB203580 (10 micromol/L). Apoptosis was evaluated by FACS analysis and cell viability was determined by MTT assay. ROS were detected by 2',7'-dichlorodihydrofluorescein diacetate (H(2)DCFH-DA). NADPH oxidases were evaluated with lucigenin-enhanced chemiluminescence. Expression of Nox4 mRNA and p-p38MAPK protein was measured by RT-PCR and Western blot analysis, respectively. Our data revealed that atorvastatin significantly suppressed Hcy-induced ROS accumulation and EPCs apoptosis. Atorvastatin also antagonized homocysteine-induced activation of NADPH oxidase and overexpression of Nox4 mRNA and p-p38MAPK protein. Similar effects occurred with EPCs transfected with Nox4 siRNA. These findings demonstrated that atorvastatin may inhibit Hcy-induced NADPH oxidase activation, ROS accumulation, and EPCs apoptosis through Nox4/p38MAPK dependent mechanisms, all of which may contribute to atorvastatin-induced beneficial effects on EPCs function.

Atorvastatin attenuates homocysteine-induced apoptosis in human umbilical vein endothelial cells via inhibiting NADPH oxidase-related oxidative stress-triggered p38MAPK signaling.

AIM: To examine the effect of atorvastatin on homocysteine (Hcy)-induced reactive oxygen species (ROS) production and apoptosis in human umbilical vein endothelial cells (HUVECs). METHODS: HUVECs were cultured with Hcy (0.1-5 mmol/L) in the presence or absence of atorvastatin (1-100 micromol//L) or various stress signaling inhibitors, including the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor diphenylene iodonium (DPI, 10 micromol/L), the p38 mitogen-activated protein kinase (p38 MAPK) inhibitor SB203580 (10 micromol/L) and antioxidants N-acetyl cysteine (NAC, 1 mmol/L). Cell apoptosis was evaluated by Annexin V/propidium iodide staining and flow cytometry. ROS were detected by 2',7'-dichlorodihydrofluorescein diacetate (H(2)DCFH-DA). NADPH oxidases were evaluated with lucigenin-enhanced chemiluminescence. Hcy-induced expression of p38MAPK protein was measured by Western blotting analysis. RESULTS: Atorvastatin inhibited endothelial cell apoptosis induced by 1 mmol/L Hcy in a dose-dependent manner and the maximal inhibitory effect was reached at 100 micromol/L. Atorvastatin (10 micromol/L) significantly suppressed Hcy (1 mmol/L for 30 min) induced ROS accumulation (3.17+/-0.33 vs 4.34+/-0.31, P<0.05). Atorvastatin (10 micromol/L) also antagonized Hcy (1 mmol/L for 30 min) induced activation of NADPH oxidase (2.57+/-0.49 vs 3.33+/-0.6, P<0.05). Furthermore, atorvastatin inhibited Hcy-induced phosphorylation of p38 MAPK (1.7+/-0.1 vs 2.22+/-0.25, P<0.05), similar effects occurred with DPI, NAC and SB203580. CONCLUSION: Atorvastatin may inhibit Hcy-induced ROS accumulation and endothelium cell apoptosis through an NADPH oxidase and/or p38MAPK-dependent mechanisms, all of which may contribute to atorvastatin-induced beneficial effect on endothelial function.