Yu-Hua Li

Curcumin protects against glutamate excitotoxicity in rat cerebral cortical neurons by increasing brain-derived neurotrophic factor level and activating TrkB

Curcumin is a major active component isolated from Curcuma longa. Previously, we have reported its significant antidepressant effect. However, the mechanisms underlying the antidepressant effects are still obscure. In the present study, we explored the effect of curcumin against glutamate excitotoxicity, mainly focusing on the neuroprotective effects of curcumin on the expression of Brain-Derived Neurotrophic Factor (BDNF), which is deeply involved in the etiology and treatment of depression. Exposure of rat cortical neurons to 10 microM glutamate for 24 h caused a significant decrease in BDNF level, accompanied with reduced cell viability and enhanced cell apoptosis. Pretreatment of neurons with curcumin reversed the BDNF expression and cell viability in a dose- and time-dependent manner. However, K252a, a Trk receptor inhibitor which is known to inhibit the activity of BDNF, could block the survival-promoting effect of curcumin. In addition, the up-regulation of BDNF levels by curcumin was also suppressed by K252a. Taken together, these results suggest that the neuroprotective effect of curcumin might be mediated via BDNF/TrkB signaling pathway.

Reciprocal interaction with G-actin and tropomyosin is essential for aquaporin-2 trafficking

Trafficking of water channel aquaporin-2 (AQP2) to the apical membrane and its vasopressin and protein kinase A (PKA)–dependent regulation in renal collecting ducts is critical for body water homeostasis. We previously identified an AQP2 binding protein complex including actin and tropomyosin-5b (TM5b). We show that dynamic interactions between AQP2 and the actin cytoskeleton are critical for initiating AQP2 apical targeting. Specific binding of AQP2 to G-actin in reconstituted liposomes is negatively regulated by PKA phosphorylation. Dual color fluorescence cross-correlation spectroscopy reveals local AQP2 interaction with G-actin in live epithelial cells at single-molecule resolution. Cyclic adenosine monophosphate signaling and AQP2 phosphorylation release AQP2 from G-actin. In turn, AQP2 phosphorylation increases its affinity to TM5b, resulting in reduction of TM5b bound to F-actin, subsequently inducing F-actin destabilization. RNA interference–mediated knockdown and overexpression of TM5b confirm its inhibitory role in apical trafficking of AQP2. These findings indicate a novel mechanism of channel protein trafficking, in which the channel protein itself critically regulates local actin reorganization to initiate its movement.

Curcumin produces neuroprotective effects via activating brain-derived neurotrophic factor/TrkB-dependent MAPK and PI-3K cascades in rodent cortical neurons.

Curcumin is a major constituent of curcuma longa, a traditional medicine used to manage mental disorders effectively in China. The neuroprotective effects of curcumin have been demonstrated in our previous studies. In the present research, we confirmed this effect by showing that curcumin application promoted the viability of cultured rodent cortical neurons. Moreover, when neurons were pretreated with tyrosine kinase B (TrkB) antibody, known to inhibit the activity of brain-derived neurotrophic factor (BDNF), the protective effect of curcumin was blocked. Additionally, treatment of curcumin increased BDNF and phosphor-TrkB and both of these enhancements can be suppressed by ERK and PI-3K inhibitors. The administration of curcumin led to increased levels of phosphor-ERK and AKT, which were each blocked by MAPK and PI-3K inhibitors. Furthermore, the curcumin-induced increase in phosphorylated cyclic AMP response element binding protein (CREB), which has been implicated as a possible mediator of antidepressant actions, was prevented by MAPK and PI-3K inhibitors. Therefore, we hypothesize the neuroprotection of curcumin might be mediated via BDNF/TrkB-MAPK/PI-3K-CREB signaling pathway.

Salvianolic acid B protects human endothelial cells from oxidative stress damage: a possible protective role of glucose-regulated protein 78 induction

AIMS The purposes of the present study were to both evaluate the protective effects of Salvianolic acid B (Sal B) and to determine the possible molecular mechanisms by which Sal B protects endothelial cells from damage caused by oxidative stress. METHODS AND RESULTS Pretreatment with Sal B markedly attenuated H(2)O(2)-induced viability loss, lactate dehydrogenase leakage and apoptosis in human umbilical vein endothelial cells (HUVECs). The mechanism of Sal B protection was studied using two-dimensional gel electrophoresis coupled with hybrid quadrupole time-of-flight mass spectrometry. Database searching implicated that glucose-regulated protein 78 (GRP78), a central regulator for endoplasmic reticulum (ER) stress, was up-regulated in Sal B-exposed HUVECs. GRP78 expression regulation was confirmed by western blot and RT-PCR (reverse transcription-polymerase chain reaction) analyses. Additionally, GRP94, which shares significant sequence homology with GRP78, was also up-regulated in Sal B-treated cells. Sal B caused pancreatic ER kinase (PKR)-like ER kinase (PERK) activation followed by the phosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2 alpha) and the expression of activating transcription factor 4 (ATF4). Knockdown of endogenous ATF4 expression partially repressed Sal B-induced GRP78 induction. Further investigation showed that ATF6 was also activated by Sal B. Knockdown of GRP78 by siRNA significantly reduced the protective effects of Sal B. CONCLUSION The results suggest that Sal B induces the expression of GRP78 by activating ATF6 and the PERK-eIF2 alpha-ATF4 pathway. Furthermore, up-regulation of GRP78 by Sal B may play an important role in protecting human endothelial cells from oxidative stress-induced cellular damage.

Transgelin 2 Participates in Lovastatin-Induced Anti-Angiogenic Effects in Endothelial Cells through a Phosphorylated Myosin Light Chain-Related Mechanism

Background Anti-angiogenic activity is considered to play a key role in the statin-induced anti-tumor effects. We aimed to identify new targets underlying this pleiotropic effect of lovastatin. Methodology/Principal Findings We investigated the inhibitory effects of lovastatin on endothelial cell biology and angiogenesis in vitro. Lovastatin at high doses inhibited endothelial cell migration and tube formation. Using two-dimensional gel electrophoresis followed by mass spectrometry, we identified the up-regulation of the actin-binding protein transgelin 2 in endothelial cells following treatment with lovastatin. Changes in transgelin 2 levels were confirmed by Western blot and confocal microscopy. We further demonstrated that the Rho signaling inactivation and actin depolymerization contributed to the up-regulation of transgelin 2. The knockdown of transgelin 2 by siRNA dramatically enhanced endothelial migration and tube formation, and meanwhile attenuated the inhibitory effects of lovastatin on cell motility. Moreover, the lovastatin-induced inhibition of myosin light chain phosphorylation was also reversed by transgelin 2 knockdown. The activation of Rho GTPase in the absence of transgelin 2 may represent a mechanism underlying the regulation of phosphorylated myosin light chain by transgelin 2. Conclusions/Significance These results strongly imply a novel role for transgelin 2 in the angiostatic activities of lovastatin.

Aquaporin-2 regulates cell volume recovery via tropomyosin.

Cell volume regulation is particularly important for kidney collecting duct cells. These cells are the site of water reabsorption regulated by vasopressin and aquaporin-2 (AQP2) trafficking to the apical membrane, and subject to changes in osmolality. Here, we examined the role of AQP2 in regulatory volume decrease (RVD), which is a cellular defensive process against hypotonic stress. Stable expression of AQP2 increases RVD in MDCK cells and its phosphorylation levels decrease during the RVD process. We then examined the involvement of AQP2 phosphorylation at serine 256 and serine 261 in RVD using cells stably expressing the phosphorylation mutants. Both S256A- and S256D-AQP2 decrease RVD compared to wild type (WT)-AQP2 although only S256A mutation decreases the initial osmotic swelling, indicating that AQP2-enhanced RVD is independent of osmotic swelling induced by the water permeability of AQP2. S261A and S261D mutations do not induce changes compared with WT-AQP2. These findings indicate that switching between phosphorylation and dephosphorylation at S256 is important for RVD. We previously reported that AQP2 interacts with tropomyosin 5b (TM5b), which regulates actin stability. AQP2 interactions with TM5b are rapidly increased by hypotonicity and then decreased, which are consistent with AQP2 phosphorylation levels. Knockdown and overexpression of TM5b show its essential role in WT-AQP2-enhanced RVD. RVD in S256A- and S256D-AQP2-expressing cells is not changed by TM5b knockdown or overexpression. The present study shows that AQP2 regulates RVD via TM5b and switching between phosphorylation and dephosphorylation at S256 in AQP2 is critical for this process.

Inhibitive effects of low oxygen and glucose deprivation on brain-pancreas relative protein expression via hypoxia- inducible factor-1 pathways.

Background: Brain-Pancreas Relative Protein (BPRP), a novel protein discovered in our lab, was decreased in ischemic rat brain. However, the mechanisms regulating BPRP expression during ischemia need further investigation. Methods: In the present study we cultured PC12 cells with low oxygen and glucose deprivation (LOGD, a model of ischemia in vitro) media, then examined the signal transduction pathways of BPRP expression under LOGD. Results: It was found that LOGD significantly decreased BPRP expression, but increased the intracellular Ca2+ concentration ([Ca2+]i), p38 mitogen-activated protein kinases (MAPK) phosphorylation and hypoxia inducible factor 1 α subunit (HIF-1α) expression. However, BAPTA-AM (an intracellular calcium chelator), SB 203580 (an inhibitor of p38) and HIF-1α antisense significantly inhibited the [Ca2+]i, p38 MAPK phosphorylation and HIF-1α expression respectively. Our results also showed that p38 MAPK phosphorylation was reduced by BAPTA-AM, and HIF-1α expression was inhibited by SB203580 and BAPTA-AM, suggesting that calcium, p38 MAPK and HIF-1α are in the same signal transduction pathways during LOGD. Noticeably, reduced BPRP expression by LOGD can be recovered by SB203580, BAPTA-AM and HIF-1α antisense. Conclusion: All together, our observations suggest that calcium, p38 MAPK activation and HIF-1α are necessary for LOGD-reduced BPRP expression in PC12 cells.

Nordihydroguaiaretic acid impairs prostate cancer cell migration and tumor metastasis by suppressing neuropilin 1

Tumor metastasis is a major cause leading to the deaths of cancer patients. Nordihydroguaiaretic acid (NDGA) is a natural product that has been demonstrated to show therapeutic values in multiple diseases. In this study, we report that NDGA can inhibit cell migration and tumor metastasis via a novel mechanism. NDGA suppresses NRP1 function by downregulating its expression, which leads to attenuated cell motility, cell adhesion to ECM and FAK signaling in cancer cells. Moreover, due to its cross-cell type activity on NRP1 suppression, NDGA also impairs angiogenesis function of endothelial cells and fibronectin assembly by fibroblasts, both of which are critical to promote metastasis. Based on these comprehensive effects, NDGA effectively suppresses tumor metastasis in nude mice model. Our findings reveal a novel mechanism underlying the anti-metastasis function of NDGA and indicate the potential value of NDGA in NRP1 targeting therapy for selected subtypes of cancer.

Epinephrine increases phosphorylation of MAP-2c in rat pheochromocytoma cells (PC12 Cells) via a protein kinase C- and mitogen activated protein kinase-dependent mechanism.

Adrenoceptors mediate effects of endogenous catecholamines and have been shown to affect the neuronal development. Microtubule-associated protein-2 (MAP-2) is an important cytoskeleton protein whose phosphorylation in response to extracellular signal is involved in the regulation of neurite outgrowth and neuronal plasticity. The present study was designed to determine the effect of activation of adrenoceptor by epinephrine on MAP-2 phosphorylation in differentiation PC12 cells and, if so, to explore the mediating mechanism. We found that epinephrine could significantly increase the phosphorylation of MAP-2c at ser136 in a dose- and time-dependent manner in differentiated PC12 cells as well as microtubule arrays. Differentiated PC12 cells express alpha 2A-adrenoceptor, whose antagonists could block these mentioned effects of epinephrine, and clonidine which is the agonist of alpha 2-adrenoceptor could mimic the effect of epinephrine. Moreover phosphorylation of ERK and PKC was induced by epinephrine, and ERK and PKC specific inhibitors concentration-dependently prevented epinephrine-induced phosphorylation of MAP-2c at ser136. In addition, pretreatment of PC12 cells with epinephrine partly inhibited 30 microM nocodazole induced neurites retraction. These findings suggest that epinephrine induces phosphorylation of MAP-2c at ser136 through a alpha 2-adrenoceptor mediated, ERK/PKC-dependent signaling pathway, which may contribute to the stabilization of neurites.