Airan Liu

Amelioration of neurodegenerative changes in cellular and rat models of diabetes-related Alzheimer's disease by exendin-4.

Growing evidence suggests that type 2 diabetes mellitus (DM) is associated with age-dependent Alzheimer’s disease (AD), the latter of which has even been considered as type 3 diabetes. Several physiopathological features including hyperglycemia, oxidative stress, and dysfunctional insulin signaling relate DM to AD. In this study, high glucose-, oxidative stress-induced neuronal injury and intracerebroventricular-streptozotocin (ICV-STZ) animals as the possible models for diabetes-related AD were employed to investigate the effects of exendin-4 (Ex-4), a long-acting glucagon-like peptide-1 (GLP-1) receptor agonist, on diabetes-associated Alzheimer-like changes as well as the molecular mechanisms involved. Our study demonstrated that GLP-1/Ex-4 could exert a protective effect against reduced viability of PC12 cells caused by high glucose and that this protective effect was mediated via the PI3-kinase pathway. In addition, GLP-1/Ex-4 ameliorated oxidative stress-induced injury in PC12 cells. In rat models, bilateral ICV-STZ administration was used to produce impaired insulin signaling in the brain. Fourteen days following ICV-STZ injection, rats treated with twice-daily Ex-4 had better learning and memory performance in the Morris water maze test compared with rats treated with saline. Additionally, histopathological evaluation confirmed the protective effects of Ex-4 treatment on hippocampal neurons against degeneration. Furthermore, we demonstrated that Ex-4 reversed ICV-STZ-induced tau hyperphosphorylation through downregulation of GSK-3β activity, a key kinase in both DM and AD. Our findings suggests that Ex-4 can protect neurons from diabetes-associated glucose metabolic dysregulation insults in vitro and from ICV-STZ insult in vivo, and that Ex-4 may prove of therapeutic value in the treatment of AD especially DM-related AD.

Activation of canonical wnt pathway promotes differentiation of mouse bone marrow-derived MSCs into type II alveolar epithelial cells, confers resistance to oxidative stress, and promotes their migration to injured lung tissue in vitro

The differentiation of mesenchymal stem cells (MSCs) into type II alveolar epithelial (AT II) cells in vivo and in vitro, is critical for reepithelization and recovery in acute lung injury (ALI), but the mechanisms responsible for differentiation are unclear. In the present study, we investigated the role of the canonical wnt pathway in the differentiation of mouse bone marrow‐derived MSCs (mMSCs) into AT II cells. Using a modified co‐culture system with murine lung epithelial‐12 (MLE‐12) cells and small airway growth media (SAGM) to efficiently drive mMSCs differentiation, we found that GSK 3β and β‐catenin in the canonical wnt pathway were up‐regulated during differentiation. The levels of surfactant protein (SP) C, SPB, and SPD, the specific markers of AT II cells, correspondingly increased in mMSCs when Wnt3a or LiCl was added to the co‐culture system to activate wnt/β‐catenin signaling. The expression of these factors was depressed to some extent by inhibiting the pathway with the addition of DKK 1. The differentiation rate of mMSCs also depends on their abilities to accumulate and survive in inflammatory tissue. Our results suggested that the activation of wnt/β‐catenin signaling promoted mMSCs migration towards ALI mouse‐derived lung tissue in a Transwell assay, and ameliorated the cell death and the reduction of Bcl‐2/Bax induced by H2O2, which simultaneously caused reduced GSK 3β and β‐catenin in mMSCs. These data supports a potential mechanism for the differentiation of mMSCs into AT II cells involving canonical wnt pathway activation, which may be significant to their application in ALI. J. Cell. Physiol. 228: 1270–1283, 2013.

Interaction between mesenchymal stem cells and endothelial cells restores endothelial permeability via paracrine hepatocyte growth factor in vitro

IntroductionMesenchymal stem cells (MSCs) have potent stabilising effects on vascular endothelium injury, inhibiting endothelial permeability in lung injury via paracrine hepatocyte growth factor (HGF). Recently, it has been indicated that MSCs secrete more factors by MSC-endothelial cell (MSC-EC) interactions. We hypothesised that MSC-EC interactions restore endothelial permeability induced by lipopolysaccharide (LPS) via paracrine HGF.MethodsWe investigated the endothelial permeability induced by LPS under two co-culture conditions. Human pulmonary microvascular endothelial cells (HPMECs) were added into the upper chambers of cell-culture inserts, while two different co-culture conditions were used in the lower side of the transwells, as follows: (1) MSC-EC interaction group: MSCs and HPMECs contact co-culture; (2) MSC group: MSCs only. The endothelial paracellular and transcellular permeabilities in the upper side of transwells were detected. Then the concentration of HGF was measured in the culture medium by using an enzyme-linked immunosorbent assay kit, followed by neutralisation of HGF with anti-HGF antibody in the co-culture medium. In addition, adherens junction and cytoskeleton protein expressions were measured by Western blot and immunofluorescence. HPMEC proliferation was analysed by bromodeoxyuridine incorporation assay.ResultsThe paracellular permeability significantly increased after LPS stimulation in a dose-dependent and time-dependent manner. Meanwhile, MSC-EC interaction more significantly decreased endothelial paracellular and transcellular permeability induced by LPS. Moreover, HGF levels in the MSC-EC interaction group were much higher than those of the MSC group. However, neutralising HGF with anti-HGF antibody inhibited the role of MSC-EC interaction in improving endothelial permeability. Compared with the MSC group, MSC-EC interaction increased vascular endothelial (VE)-cadherin and occludin protein expression, reduced caveolin-1 protein expression in HPMECs, and restored remodelling of F-actin and junctional localisation of VE-cadherin. Furthermore, the proliferation ratio in the MSC-EC interaction group was higher than that of the MSC group. However, the effects of MSCs were significantly blocked by anti-HGF antibody.ConclusionsThese data suggested that MSC-EC interaction decreased endothelial permeability induced by LPS, which was attributed mainly to HGF secreted by MSCs. The main mechanisms by which HGF restored the integrity of endothelial monolayers were remodelling of endothelial intercellular junctions, decreasing caveolin-1 protein expression, and inducing proliferation in HPMECs.

Glucagon-like peptide-1 protects hippocampal neurons against advanced glycation end product-induced tau hyperphosphorylation

We have previously demonstrated that glucagon-like peptide-1 (GLP-1) receptor agonist ameliorated neurodegenerative changes in rat models of diabetes-related Alzheimers disease (AD), and protected neurons from glucose toxicity in vitro. Herein, we investigated the effects of GLP-1 receptor mediates on cell toxicity and tau hyperphosphorylation induced by advanced glycation end products (AGEs), which are associated with glucose toxicity, and the molecular mechanism in PC12 cells and the primary hippocampal neurons. Our study demonstrated that the similar protection effects of GLP-1 existed in PC12 cells treated with glucose-bovine serum albumin (BSA) in hyperglycemic conditions or with glycoaldehyde-BSA alone. Additionally, glucose-BSA alone did not induce significant cytotoxicity in PC12 cells, but resulted in tau hyperphosphorylation in primary hippocampal neurons in 24h. And we found that GLP-1 could reduce cell tau phosphorylation induced by high glucose or glucose-BSA. Furthermore, our data in the present study suggested that GLP-1 regulated tau phosphorylation induced by AGEs through a signaling pathway involving glycogen synthase kinase 3β (GSK-3β), similarly to the GSK-3β inhibitor, lithium chloride. Our findings suggest that GLP-1 can protect neurons from diabetes-associated AGE insults in vitro, and provide new evidence for a potential therapeutic value of GLP-1 receptor agonist in the treatment of AD especially diabetes-related AD.

Wnt5a through Noncanonical Wnt/JNK or Wnt/PKC Signaling Contributes to the Differentiation of Mesenchymal Stem Cells into Type II Alveolar Epithelial Cells In Vitro

The differentiation of mesenchymal stem cells (MSCs) into type II alveolar epithelial (AT II) cells is critical for reepithelization and recovery in acute respiratory distress syndrome (ARDS), and Wnt signaling was considered to be the underlying mechanisms. In our previous study, we found that canonical Wnt pathway promoted the differentiation of MSCs into AT II cells, however the role of the noncanonical Wnt pathway in this process is unclear. It was disclosed in this study that noncanonical Wnt signaling in mouse bone marrow–derived MSCs (mMSCs) was activated during the differentiation of mMSCs into AT II cells in a modified co-culture system with murine lung epithelial-12 cells and small airway growth media. The levels of surfactant protein (SP) C, SPB and SPD, the specific markers of AT II cells, increased in mMSCs when Wnt5a was added to activate noncanonical Wnt signaling, while pretreatment with JNK or PKC inhibitors reversed the promotion of Wnt5a. The differentiation rate of mMSCs also depends on their abilities to accumulate and survive in inflammatory tissue. We found that the Wnt5a supplement promoted the vertical and horizontal migration of mMSCs, ameliorated the cell death and the reduction of Bcl-2/Bax induced by H2O2. The effect of Wnt5a on the migration of mMSCs and their survival after H2O2 exposure were partially inhibited with PKC or JNK blockers. In conclusion, Wnt5a through Wnt/JNK signaling alone or both Wnt/JNK and Wnt/PKC signaling promoted the differentiation of mMSCs into AT II cells and the migration of mMSCs; through Wnt/PKC signaling, Wnt5a increased the survival of mMSCs after H2O2 exposure in vitro.

Activation of Wnt/β-catenin signalling promotes mesenchymal stem cells to repair injured alveolar epithelium induced by lipopolysaccharide in mice

IntroductionMesenchymal stem cells (MSCs) have potential for re-epithelization and recovery in acute respiratory distress syndrome (ARDS). In a previous in vitro study, the results showed that the canonical Wnt/β-catenin pathway promoted the differentiation of MSCs into type II alveolar epithelial cells, conferred resistance to oxidative stress, and promoted their migration, suggesting that the Wnt/β-catenin pathway might be one of the key mechanisms underling the therapeutic effect of mouse MSCs in ARDS.MethodsMouse MSCs stable transfected with β-catenin or green fluorescent protein control were transplanted intratracheally into the ARDS mice induced by lipopolysaccharide. Lung tissue injury and repair assessment were examined using haematoxylin and eosin staining, lung injury scoring, Masson’s trichrome staining and fibrosis scoring. Homing and differentiation of mouse MSCs were assayed by labelling and tracing MSCs using NIR815 dye, immunofluorescent staining, and Western immunoblot analysis. The inflammation and permeability were evaluated by detecting the cytokine and protein measurements in bronchoalveolar lavage fluid using enzyme-linked immunosorbent assay.ResultsIn this study, β-catenin-overexpressing MSC engraftment led to more significant effects than the GFP controls, including the retention of the MSCs in the lung, differentiation into type II alveolar epithelial cells, improvement in alveolar epithelial permeability, and the pathologic impairment of the lung tissue.ConclusionThese results suggest that the activation of canonical Wnt/β-catenin pathway by mouse MSCs by overexpressing β-catenin could further improve the protection of mouse MSCs against epithelial impair and the therapeutic effects of mouse MSCs in ARDS mice.

Mesenchymal Stem Cells Overexpressing Angiotensin-Converting Enzyme 2 Rescue Lipopolysaccharide-Induced Lung Injury.

Bone marrow-derived mesenchymal stem cells (MSCs), which have beneficial effects in acute lung injury (ALI), can serve as a vehicle for gene therapy. Angiotensin-converting enzyme 2 (ACE2), a counterregulatory enzyme of ACE that degrades angiotensin (Ang) II into Ang 1–7, has a protective role against ALI. Because ACE2 expression is severely reduced in the injured lung, a therapy targeted to improve ACE2 expression in lung might attenuate ALI. We hypothesized that MSCs overexpressing ACE2 would have further benefits in lipopolysaccharide (LPS)-induced ALI mice, when compared with MSCs alone. MSCs were transduced with ACE2 gene (MSC-ACE2) by a lentiviral vector and then infused into wild-type (WT) and ACE2 knockout (ACE2-/y) mice following an LPS-induced intratracheal lung injury. The results demonstrated that the lung injury of ALI mice was alleviated at 24 and 72 h after MSC-ACE2 transplantation. MSC-ACE2 improved the lung histopathology and had additional anti-inflammatory effects when compared with MSCs alone in both WT and ACE2-/y ALI mice. MSC-ACE2 administration also reduced pulmonary vascular permeability, improved endothelial barrier integrity, and normalized lung eNOS expression relative to the MSC group. The beneficial effects of MSC-ACE2 could be attributed to its recruitment into the injured lung and enhanced local expression of ACE2 protein without changing the serum ACE2 levels after MSC-ACE2 transplantation. The biological activity of the increased ACE2 protein decreased the Ang II amount and increased the Ang 1–7 level in the lung when compared with the ALI and MSC-only groups, thereby inhibiting the detrimental effects of accumulating Ang II. Therefore, compared to MSCs alone, the administration of MSCs overexpressing ACE2 resulted in a further improvement in the inflammatory response and pulmonary endothelial function of LPS-induced ALI mice. These additional benefits could be due to the degradation of Ang II that accompanies the targeted overexpression of ACE2 in the lung.

Stable Genetic Alterations of β-Catenin and ROR2 Regulate the Wnt Pathway, Affect the Fate of MSCs

The Wnt pathways have been shown to be critical for the fate of mesenchymal stem cells (MSCs) in vitro, but their roles in MSCs in vivo remain poorly characterized due to the lack of stable alterations in their signaling. In the present study, we constructed long‐term and stable mMSCs lines with activated and inactivated β‐catenin (the key molecule of the canonical Wnt signaling pathway) or ROR2 (the key molecule of the noncanonical Wnt5a/ROR2 signaling pathway) modifications with lentiviral vectors. We found that the transduction efficiencies mediated by the lentiviral vectors were 92.61–97.04% and were maintained over 20 passages of mMSCs. Transfection by lentiviral vectors not only regulated the mRNA and protein expression of β‐catenin or ROR2 but also regulated nuclear β‐catenin accumulation or the Wnt5a/JNK and Wnt5a/PKC pathways belonging to the canonical Wnt and noncanonical Wnt5a/ROR2 pathways, respectively. β‐Catenin or ROR2 gene overexpression promoted mMSC proliferation, migration and differentiation into osteoblasts, while inhibiting the adipogenic differentiation of mMSCs. In contrast, inactivation of the β‐catenin or ROR2 genes resulted in the opposite effects. Therefore, these results confirm that lentiviral vector transduction can facilitate sustained and efficient gene modification of the Wnt pathway in mMSCs. This study provides a method to investigate the effects of the Wnt pathway on the fate of mMSCs in vivo and for the further improvement of MSC‐based therapies. J. Cell. Physiol. 229: 791–800, 2014.

Therapeutic Effects of Bone Marrow-Derived Mesenchymal Stem Cells in Models of Pulmonary and Extrapulmonary Acute Lung Injury.

Bone marrow-derived mesenchymal stem cells (MSCs) offer a promising therapy for acute lung injury (ALI). However, whether the same MSC treatments possess similar potential for different ALI models is not fully clear. The present study evaluated the distribution and therapeutic effects of intravenous MSC administration for the treatment of intratracheal lipopolysaccharide (LPS)-induced intrapulmonary ALI and intravenous LPS/zymosan-induced extrapulmonary ALI, matched with lung injury severity, at 30 min and 1, 3, and 7 days. We found that MSC transplantation attenuated lung injury and inhibited lung inflammation in both ALI models. The benefits of MSCs were more significant in the intrapulmonary ALI mice. In vivo and ex vivo fluorescence imaging showed that MSCs primarily homed into the lung. However, more MSCs were recruited into the lungs of the intrapulmonary ALI mice than those of the extrapulmonary ALI mice over the time course. A few MSCs were also detected in the liver and spleen at days 3 and 7. In addition, the two ALI models showed different extrapulmonary organ dysfunction. A lower percentage of cell apoptosis and SDF-1α levels was found in the liver and spleen of the intrapulmonary ALI mice than in those of the extrapulmonary ALI mice. These results suggested that the two ALI models were accompanied with different degrees of extrapulmonary organ damage, which resulted in differences in the trafficking and accumulation of MSCs to the injured lung and consequently accounted for different therapeutic effects of MSCs for lung repair in the two ALI models. These data suggest that intravenous administration of MSCs has a greater potential for the treatment of intrapulmonary ALI than extrapulmonary ALI matched with lung injury severity; these differences were due to more recruitment of MSCs in the lungs of intrapulmonary ALI mice than those of extrapulmonary ALI mice. This finding may contribute to the clinical use of MSCs for the treatment of ALI.

The Vascular Endothelial Growth Factors-Expressing Character of Mesenchymal Stem Cells Plays a Positive Role in Treatment of Acute Lung Injury In Vivo

Recently, mesenchymal stem cells (MSC) have been proved to be beneficial in acute respiratory distress syndrome (ARDS). Vascular endothelial growth factor (VEGF) is an important angiogenesis factor that MSC release. However, the precise role of VEGF-expressing character of MSC in the MSC treatment for ARDS remains obscure. Here, we firstly knocked down the gene VEGF in MSC (MSC-ShVEGF) with lentiviral transduction. Then we injected the MSC-ShVEGF to rats with lipopolysaccharide-induced acute lung injury (ALI) via the tail vein. Data showed that MSC transplantation significantly increased VEGF levels in the lung, reduced lung permeability, protected lung endothelium from apoptosis, facilitated VE-cadherin recovery, controlled inflammation, and attenuated lung injury. However, VEGF gene knockdown in MSC led to relatively insufficient VEGF expression in the injured lung and significantly diminished the therapeutic effects of MSC on ALI, suggesting an important role of VEGF-expressing behavior of MSC in the maintenance of VEGF in the lung and the MSC treatment for ALI. Hence, we conclude that MSC restores the lung permeability and attenuates lung injury in rats with ALI in part by maintaining a “sufficient” VEGF level in the lung and the VEGF-expressing character of MSC plays a positive role in the therapeutic effects of MSC on ARDS.