Manxiang Li

LKB1/AMPK/mTOR signaling pathway in non-small-cell lung cancer.

Links between cancer and metabolism have been suggested for a long time but compelling evidence for this hypothesis came from the recent molecular characterization of the LKB1/AMPK signaling pathway as a tumor suppressor axis. Besides the discovery of somatic mutations in the LKB1 gene in certain type of cancers, a critical emerging point was that the LKB1/AMPK axis remains generally functional and could be stimulated by pharmacological molecules such as metformin in cancer cells. In addition, AMPK plays a central role in the control of cell growth, proliferation and autophagy through the regulation of mTOR activity, which is consistently deregulated in cancer cells. Targeting of AMPK/mTOR is thus an attractive strategy in the development of therapeutic agents against non-small-cell lung cancer (NSCLC). In this review, the LKB1/AMPK/mTOR signaling pathway is described, highlighting its protective role, and opportunities for therapeutic intervention, and clinical trials in NSCLC.

Activation of AMPK by metformin inhibits TGF-β-induced collagen production in mouse renal fibroblasts.

AIMS To clarify whether activation of adenosine monophosphate-activated protein kinase (AMPK) by metformin inhibits transforming growth factor beta (TGF-β)-induced collagen production in primary cultured mouse renal fibroblasts and further to address the molecular mechanisms. MAIN METHODS Primary cultured mouse renal fibroblasts were stimulated with TGF-β1 and the sequence specific siRNA of Smad3 or connective tissue growth factor (CTGF) was applied to investigate the involvement of these molecular mediators in TGF-β1-induced collagen type I production. Cells were pre-incubated with AMPK agonist metformin or co-incubated with AMPK agonist metformin and AMPK inhibitor Compound C before TGF-β1 stimulation to clarify whether activation of AMPK inhibition of TGF-β1-induced renal fibroblast collagen type I expression. KEY FINDINGS Our results demonstrate that TGF-β1 time- and dose-dependently induced renal fibroblast collagen type I production; TGF-β1 also stimulated Smad3-dependent CTGF expression and caused collagen type I generation; this effect was blocked by knockdown of Smad3 or CTGF. Activation of AMPK by metformin reduced TGF-β1-induced collagen type I production by suppression of Smad3-driven CTGF expression. SIGNIFICANCE This study suggests that activation of AMPK might be a novel strategy for the treatment of chronic kidney disease (CKD) partially by inhibition of renal interstitial fibrosis (RIF).

Statins suppress MMP2 secretion via inactivation of RhoA/ROCK pathway in pulmonary vascular smooth muscles cells.

Recent studies have shown that statins ameliorate hypoxia-induced pulmonary hypertension in animal models. Yet, the underlying molecular mechanisms have not been completely understood. Here, we investigated the hypothesis that statins regulate vascular remodeling by modulation of matrix metalloproteinases (MMP) secretion in primary cultured pulmonary artery smooth muscle cells (PASMCs). Angiotensin II induced a concentration-dependent MMP2 secretion. A 2.75 fold increase was achieved by 100 nM angiotensin II stimulation for 24 h in primary cultured PASMCs (P<0.01 versus control), which was reversed by silencing Ras homolog gene family member A (RhoA) or inhibition of its downstream Rho-associated kinase (ROCK). There was no effect of angiotensin II on the expression of tissue inhibitors of matrix metalloproteinases (TIMPs). Pre-exposure of cells to simvastatin concentration-dependently blocked angiotensin II-stimulated MMP2 release. MMP2 release was reduced to1.34 fold increase in the presence of 10 microM simvastatin (P<0.01 versus angiotensin II-stimulated cells). We further revealed that simvastatin suppression of RhoA activation mediated its inhibitory effect on angiotensin II-triggered MMP2 release. Similarly, simvastatin suppressed endothelin-1-induced MMP2 release through RhoA/ROCK pathway. These results indicated a novel statins-regulation of RhoA/ROCK signaling against pulmonary vascular remodeling, and suggest that statins could prove useful in targeting this pathway in pulmonary hypertension and other disease conditions.

Heme oxygenase‐1/p21WAF1 mediates peroxisome proliferator‐activated receptor‐γ signaling inhibition of proliferation of rat pulmonary artery smooth muscle cells

Activation of peroxisome proliferator‐activated receptor (PPAR)‐γ suppresses proliferation of rat pulmonary artery smooth muscle cells (PASMCs), and therefore ameliorates the development of pulmonary hypertension in animal models. However, the molecular mechanisms underlying this effect remain largely unknown. This study addressed this issue. The PPARγ agonist rosiglitazone dose‐dependently stimulated heme oxygenase (HO)‐1 expression in PASMCs, 5 μm rosiglitazone inducing a 12.1‐fold increase in the HO‐1 protein level. Cells pre‐exposed to rosiglitazone showed a dose‐dependent reduction in proliferation in response to serotonin; this was abolished by pretransfection of cells with sequence‐specific small interfering RNA against HO‐1. In addition, rosiglitazone stimulated p21WAF1 expression in PASMCs, a 2.34‐fold increase in the p21WAF1 protein level being achieved with 5 μm rosiglitazone; again, this effect was blocked by knockdown of HO‐1. Like loss of HO‐1, loss of p21WAF1 through siRNA transfection also reversed the inhibitory effect of rosiglitazone on PASMC proliferation triggered by serotonin. Taken together, our findings suggest that activation of PPARγ induces HO‐1 expression, and that this in turn stimulates p21WAF1 expression to suppress PASMC proliferation. Our study also indicates that rosiglitazone, a medicine widely used in the treatment of type 2 diabetes mellitus, has potential benefits for patients with pulmonary hypertension.

Activation of PPAR-γ ameliorates pulmonary arterial hypertension via inducing heme oxygenase-1 and p21WAF1: An in vivo study in rats

AIMS Our previous study has indicated that activation of PPAR-γ inhibits the proliferation of rat pulmonary artery smooth muscle cells (PASMCs) in vitro through inducing the expression of heme oxygenase-1 (HO-1), which in turn up-regulates the p21(WAF1) expression. In the present study, we intended to determine whether similar mechanisms have been involved in activation of PPAR-γ inhibition of development of rat PAH model. MATERIAL AND METHODS Rat pulmonary arterial hypertension (PAH) model was established by subcutaneous injection of monocrotaline (MCT). Rosiglitazone was administered to activate PPAR-γ. Zinc protoporphyria IX (ZnPP-IX), was used to confirm the role of HO-1 in mediating PPAR-γ function. Parameters including the right ventricle systolic pressure (RVSP), the right ventricular hypertrophy (RVH) and the percentage of medial wall thickness were used to evaluate the development of PAH. Immunoblotting was used to determine the expression of HO-1 and p21(WAF1). KEY FINDINGS Rosiglitazone significantly decreased the RVSP and inhibited the RVH in MCT-induced rat PAH model, and partially inhibited the pulmonary vascular remodeling. These effects were coupled with the sequential increase of HO-1 and p21(WAF1) expressions by rosiglitazone. SIGNIFICANCE Activation of PPAR-γ benefits PAH by inhibiting proliferation of PASMCs and reducing pulmonary vascular remodeling. The present study suggests that enhancing PPAR-γ activity might have potential value in clinical treatment of PAH.

Statins inhibit pulmonary artery smooth muscle cell proliferation by upregulation of HO-1 and p21WAF1

Simvastatin is a 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor, which has been shown to ameliorate the development of pulmonary hypertension in animal model by suppression of pulmonary artery smooth muscle cells (PASMCs) proliferation, yet its underlying molecular mechanisms are not completely understood. In this study, we show that simvastatin dose-dependently inhibited serotonin-stimulated PASMCs proliferation. This was accompanied with the parallel induction of heme oxyganase-1 (HO-1) and upregulation of p21WAF1. More importantly, we found that Tin-protoporphyrin (SnPP), a selective inhibitor of HO-1, could block the effect of simvastatin on inhibition of cell proliferation in response to serotonin and abolish simvastatin-induced p21WAF1 expression. The inhibitive effect of simvastatin on cell proliferation was also significantly suppressed by silencing p21WAF1 with siRNA transfection. The extent of effect of SnPP on inhibition of cell proliferation was similar to that of lack of p21WAF1 by siRNA transfection. Taken together, our study suggests that simvastatin inhibits PASMCs proliferation by sequential upregulation of HO-1 and p21WAF1 to benefit pulmonary hypertension.

Activation of AMPK inhibits pulmonary arterial smooth muscle cells proliferation

ABSTRACT The aims of the present study were to examine the effect of AMPK activation on pulmonary arterial smooth muscle cells (PASMCs) proliferation and to address its potential mechanisms. ET-1 dose and time-dependently induced PASMCs proliferation, and this effect was suppressed by a selective AMPK activator metformin. The results of the study further indicated that the proliferation of PASMCs stimulated by ET-1 was associated with the increase of Skp2 and decrease of p27, and metformin reversed ET-1-induced Skp2 elevation and raised p27 protein level. Our study suggests that activation of AMPK suppresses PASMCs proliferation and has potential value in negatively modulating pulmonary vascular remodeling and therefore could prevent or treat the development of pulmonary arterial hypertension (PAH).

Endothelin-1 induces hypoxia inducible factor 1α expression in pulmonary artery smooth muscle cells

Endothelin‐1 (ET‐1) dose‐dependently increased HIF1α expression in pulmonary artery smooth muscle cells (PASMCs). Inhibition of protein synthesis did not affect ET‐1‐induced HIF1α expression. The maximum effect of ET‐1 was similar to that caused by proteasome inhibitor MG132. Further study indicates that ET‐1 also dose‐dependently stimulated calcineurin activation, specific calcineurin inhibitor cyclosporine A (CsA), abolished ET‐1‐induced HIF1α elevation, and reversed ET‐1‐induced RACK1 (receptor of activated protein kinase C 1) de‐phosphorylation. Endothelin receptor A was found to specifically mediate the effects of ET‐1. To examine whether RACK1 is particularly involved in proteasome‐dependent HIF1α degradation, RACK1 was silenced by siRNA transfection. Cells lacking RACK1 exhibited significant elevation of HIF1α protein level. Taken together, our study suggests that ET‐1 suppressed proteasome‐dependent HIF1α degradation by calcineurin‐dependent RACK1 de‐phosphorylation.

Inhibition of cGMP phosphodiesterase 5 suppresses matrix metalloproteinase-2 production in pulmonary artery smooth muscles cells

1. It has been shown that the beneficial effects of phosphodiesterase (PDE) 5 inhibition on pulmonary hypertension (PH) are associated with the induction of vascular relaxation and suppression of the proliferation of pulmonary artery smooth muscle cells (PASMC). In the present study, we investigated whether PDE5 inhibition affects the production and/or secretion of matrix metalloproteinases (MMPs) in PASMC, resulting in extracellular matrix remodelling in the pulmonary vasculature and, thus, the development of PH.

The PPARγ agonist, rosiglitazone, attenuates airway inflammation and remodeling via heme oxygenase-1 in murine model of asthma

Aim:Rosiglitazone is one of the specific PPARγ agonists showing potential therapeutic effects in asthma. Though PPARγ activation was considered protective in inhibiting airway inflammation and remodeling in asthma, the specific mechanisms are still unclear. This study was aimed to investigate whether heme oxygenase-1 (HO-1) related pathways were involved in rosiglitazone-activated PPARγ signaling in asthma treatment.Methods:Asthma was induced in mice by multiple exposures to ovalbumin (OVA) in 8 weeks. Prior to every OVA challenge, the mice received rosiglitazone (5 mg/kg, po). After the mice were sacrificed, the bronchoalveolar lavage fluid (BALF), blood samples and lungs were collected for analyses. The activities of HO-1, MMP-2 and MMP-9 in airway tissue were assessed, and the expression of PPARγ, HO-1 and p21 proteins was also examined.Results:Rosiglitazone administration significantly attenuated airway inflammation and remodeling in mice with OVA-induced asthma, which were evidenced by decreased counts of total cells, eosinophils and neutrophils, and decreased levels of IL-5 and IL-13 in BALF, and by decreased airway smooth muscle layer thickness and reduced airway collagen deposition. Furthermore, rosiglitazone administration significantly increased PPARγ, HO-1 and p21 expression and HO-1 activity, decreased MMP-2 and MMP-9 activities in airway tissue. All the therapeutic effects of rosiglitazone were significantly impaired by co-administration of the HO-1 inhibitor ZnPP.Conclusion:Rosiglitazone effectively attenuates airway inflammation and remodeling in OVA- induced asthma of mice by activating PPARγ/HO-1 signaling pathway.