Angiotensin-(1-7) attenuates high glucose-induced proximal tubular epithelial-to-mesenchymal transition via inhibiting ERK1/2 and p38 phosphorylation

Genetic variants in the renin-angiotensin-aldosterone system: Impact on cancer risk, prognosis, and therapeutic directions

Although renin-angiotensin-aldosterone system (RAAS) is known to maintain blood pressure and electrolyte balance, it has recently been linked to a number of biological processes such as angiogenesis, tumorigenesis, metastasis, and cellular proliferation, increasing the risk of cancer development and progression. Multiple genetic variants have been found to affect the genes encoding RAAS components, altering gene transcription and protein expression. This review provides an up-to-date insight into the role of RAAS in carcinogenesis, as well as the impact of RAAS genetic variants on the risk of cancer development, progression, and patient survival and outcomes, as well as response to treatment. This paves the way for the application of precision medicine in cancer risk assessment and management by implementing preventative programs in individuals at risk and guiding the therapeutic direction in cancer patients.

Exogenous Ang-(1-7) inhibits autophagy via HIF-1α/THBS1/BECN1 axis to alleviate chronic intermittent hypoxia-enhanced airway remodelling of asthma

Obstructive sleep apnoea (OSA)-induced chronic intermittent hypoxia (CIH) has been considered a risk factor for severe asthma. Airway remodelling, which could be modulated by autophagy, plays a key role in severe asthma. However, the extent of autophagy's involvement in CIH-potentiated airway remodelling remains largely unexplored. Furthermore, we had found that angiotensin-(1-7) [Ang-(1-7)] has therapeutic effects on airway remodelling in asthma, but the underlying mechanism is either unclear. This study aimed to explore how CIH aggravates asthma and mechanism of protective effects of Ang-(1-7) on airway remodelling, with a focus on autophagy. We observed that CIH promoted epithelial-to-mesenchymal transition (EMT), indicated by elevated EMT and fibrotic markers such as Snail and Collagen IV, both in vitro and in vivo. CIH intensified cell autophagy, evident from increased LC3B expression and reduced p62 levels. Ang-(1-7) reversed the CIH-enhanced expression of Snail, Collagen IV, and LC3B. To explore how CIH enhanced autophagy in cellular and animal model of asthma, overexpression of hypoxia-inducible factor 1-alpha (HIF-1α) and Thrombospondin 1 (THBS1) were identified in CIH-exposure mice lung compared with normal mice lung tissues from the GEO database. Finally, through chromatin immunoprecipitation and immunoprecipitation assays, we verified that Ang-(1-7) inhibits CIH-induced binding of HIF-1α to the promoter of THBS1, and also disrupts the protein-protein interaction between THBS1 and the autophagy-associated protein Beclin 1 (BECN1), ultimately leading to autophagy inhibition. Our findings suggest that exogenous Ang-(1-7) can inhibit autophagy via HIF-1α/THBS1/BECN1 axis, thereby alleviating CIH-enhanced airway remodelling in asthma. These findings imply the potential therapeutic effect of Ang-(1-7) in asthma with OSA.

Efficacy of the monocarbonyl curcumin analog C66 in the reduction of diabetes-associated cardiovascular and kidney complications

Curcumin is a polyphenolic compound derived from turmeric that has potential beneficial properties for cardiovascular and renal diseases and is relatively safe and inexpensive. However, the application of curcumin is rather problematic due to its chemical instability and low bioavailability. The experimental results showed improved chemical stability and potent pharmacokinetics of one of its analogs – (2E,6E)-2,6-bis[(2-trifluoromethyl)benzylidene]cyclohexanone (C66). There are several advantages of C66, like its synthetic accessibility, structural simplicity, improved chemical stability (in vitro and in vivo), presence of two reactive electrophilic centers, and good electron-accepting capacity. Considering these characteristics, we reviewed the literature on the application of C66 in resolving diabetes-associated cardiovascular and renal complications in animal models. We also summarized the mechanisms by which C66 is preventing the release of pro-oxidative and pro-inflammatory molecules in the priming and in activation stage of cardiomyopathy, renal fibrosis, and diabetic nephropathy. The cardiovascular protective effect of C66 against diabetes-induced oxidative damage is Nrf2 mediated but mainly dependent on JNK2. In general, C66 causes inhibition of JNK2, which reduces cardiac inflammation, fibrosis, oxidative stress, and apoptosis in the settings of diabetic cardiomyopathy. C66 exerts a powerful antifibrotic effect by reducing inflammation-related factors (MCP-1, NF-κB, TNF-α, IL-1β, COX-2, and CAV-1) and inducing the expression of anti-inflammatory factors (HO-1 and NEDD4), as well as targeting TGF-β/SMADs, MAPK/ERK, and PPAR-γ pathways in animal models of diabetic nephropathy. Based on the available evidence, C66 is becoming a promising drug candidate for improving cardiovascular and renal health.

The Role of PKC-MAPK Signalling Pathways in the Development of Hyperglycemia-Induced Cardiovascular Complications

Cardiovascular disease is the most common cause of death among diabetic patients worldwide. Hence, cardiovascular wellbeing in diabetic patients requires utmost importance in disease management. Recent studies have demonstrated that protein kinase C activation plays a vital role in the development of cardiovascular complications via its activation of mitogen-activated protein kinase (MAPK) cascades, also known as PKC-MAPK pathways. In fact, persistent hyperglycaemia in diabetic conditions contribute to preserved PKC activation mediated by excessive production of diacylglycerol (DAG) and oxidative stress. PKC-MAPK pathways are involved in several cellular responses, including enhancing oxidative stress and activating signalling pathways that lead to uncontrolled cardiac and vascular remodelling and their subsequent dysfunction. In this review, we discuss the recent discovery on the role of PKC-MAPK pathways, the mechanisms involved in the development and progression of diabetic cardiovascular complications, and their potential as therapeutic targets for cardiovascular management in diabetic patients.

Angiotensin (1-7) Inhibits Ang II-mediated ERK1/2 Activation by Stimulating MKP-1 Activation in Vascular Smooth Muscle Cells

The renin–angiotensin system (RAS) exerts profound physiological effects on blood pressure regulation and fluid homeostasis, mainly by modulating renal, cardiovascular, and central nervous systems. Angiotensin (Ang)-(1-7), an end-product of RAS, is recognized by its cardiovascular protective properties through stimulation of the Mas receptor, including vasodilation, anti-inflammatory, and antihypertensive actions, and consequently, counter-regulating the well-known Ang II-elicited actions. The overall hypothesis of this study is that Ang-(1-7) inhibits Ang II-induced ERK1/2 activation in vascular smooth muscle cells (VSMCs), via regulation of mitogen-activated protein phosphatase-1 (MKP-1) activity. Aortas from male Wistar rats were incubated with Ang-(1-7) or vehicle. Concentration-response curves to Ang II were performed in endothelium-denuded aortas, in the presence or absence of ERK1/2 (PD98059) inhibitor or Mas receptor (A-779) antagonist. Expression of proteins was assessed by western blot, and immunohistochemistry was conducted in VSMCs. Ang-(1-7) incubation decreased Ang II-induced contractile response in aortas, and this effect was not observed in the presence of PD98059 or A-779. Stimulation of VSMCs with Ang-(1-7) prevented Ang II-induced ERK1/2 phosphorylation, but not C-Raf-activation. Furthermore, Ang II decreased MKP-1 phosphorylation in VSMCs. Interestingly, simultaneous incubation of Ang-(1-7) with Ang II favored MKP-1 phosphorylation, negatively modulating ERK1/2 activation in VSMCs. The results suggest that Ang-(1-7) counter-regulates actions evoked by Ang II overproduction, as observed in cardiovascular diseases, mainly by modulating MKP-1 activity. This evidence suggests that the role of Ang-(1-7) in MKP-1-regulation represents a target for new therapeutic development.

Ang-(1-7) treatment attenuates lipopolysaccharide-induced early pulmonary fibrosis

Early pulmonary fibrosis is the leading cause of poor prognosis in patients with acute respiratory distress syndrome (ARDS). However, whether the renin-angiotensin system (RAS) can serve as a therapeutic target is unknown. In this study, an animal model of early pulmonary fibrosis was established via the LPS three-hit regimen. Afterwards, the animals were treated with intraperitoneal injections of Ang-(1-7), AVE0991, or A779 once per day for 20 days. The plasma and BALF AngII levels of the animals were increased, while there were no significant changes in Ang-(1-7) levels in lung tissue after LPS treatment. Furthermore, the AT1R protein levels were significantly increased and the Mas levels were significantly decreased on days 14 and 21. Administration of Ang-(1-7) downregulated LPS-induced AT1R mRNA expression, which was upregulated by A779. The expression of Mas mRNA responded in the opposite direction relative to AT1R. Moreover, LPS caused decreased levels of Mas and E-cadherin and increased AT1R, Vimentin, and Src phosphorylation levels. Ang-(1-7) or AVE0991 blocked these effects but was counteracted by A779 treatment. Our findings suggested that AngII and AT1R levels exhibit opposite dynamic trends during LPS-induced early pulmonary fibrosis, as do Ang-(1-7) and Mas. Ang-(1-7) exerts protective effects against early pulmonary fibrosis, mainly by regulating the balance between AngII and AT1R and between Ang-(1-7) and Mas and by inhibiting Src kinase activation.

A Nucleoside/Nucleobase-Rich Extract from Cordyceps Sinensis Inhibits the Epithelial-Mesenchymal Transition and Protects against Renal Fibrosis in Diabetic Nephropathy

Cordyceps Sinensis, a traditional Chinese medicine and a healthy food, has been used for the treatment of kidney disease for a long time. The aim of present study was to isolate a nucleoside/nucleobase-rich extract from Cordyceps Sinensis (CS-N), determine the contents of nucleosides and nucleobases, and explore its anti-diabetic nephropathy activity. CS-N was isolated and purified by using microporous resin and glucan columns and the unknown compounds were identified by using HPLC-DAD and LC-MS. The effects of CS-N on the epithelial-mesenchymal transition (EMT), extracellular matrix (ECM) depositions, and the MAPK signaling pathway were evaluated in streptozotocin (STZ)-induced diabetic mice and high glucose (HG)-exposed HK-2 cells. CS-N significantly attenuated the abnormity of renal functional parameters, ameliorated histopathological changes, and inhibited EMT and ECM accumulation by regulating p38/ERK signaling pathways. Our findings indicate that CS-N exerts a therapeutic effect on experimental diabetic renal fibrosis by mitigating the EMT and the subsequent ECM deposition with inhibition of p38 and ERK signaling pathways.

A potential role of the renin-angiotensin-aldosterone system in epithelial-to-mesenchymal transition-induced renal abnormalities: Mechanisms and therapeutic implications

Epithelial-to-mesenchymal transition (EMT) is an orchestrated event where epithelial cells progressively undergo biochemical changes and transition into mesenchymal-like cells by gradually losing their epithelial characteristics. EMT plays a crucial pathologic role in renal abnormalities, especially renal fibrosis. A number of bench studies suggest the potential involvement of renin-angiotensin-aldosterone system (RAAS) in renal EMT process and associated renal abnormalities. EMT appears to be an important pathologic mechanism for the deleterious renal effects of angiotensin II and aldosterone, the two major RAAS components. Mechanistically, the renal RAAS-TGF-β-Smad3 signalling pathway plays an important pathologic role in EMT-associated renal abnormalities. Intriguingly, the RAAS antagonists such as losartan, telmisartan, eplerenone, and spironolactone have the potential to prevent renal EMT in bench studies. This review describes the key mechanistic role of RAAS overactivation in EMT-induced renal abnormalities. Moreover, drugs interrupting the RAAS at different levels in the cascade ameliorating the EMT-associated renal abnormalities are described.

AngII induces HepG2 cells to activate epithelial-mesenchymal transition

The present study aimed to determine whether HepG2 can induce epithelial-mesenchymal transition (EMT) via angiotensin II (AngII) simulation. The expression levels of EMT markers vimentin and E-cadherin in cancer tissues and adjacent tissues of patients with hepatocellular carcinoma (HCC) were detected by immunohistochemistry. In addition, HepG2 cells were stimulated with AngII, and the gene and protein expression levels of vimentin and E-cadherin were measured by reverse transcription-quantitative polymerase chain reaction and western blot analyses, respectively, whereas cell migration and invasion were assessed using Transwell assays. The AngII inhibitor Ang1-7 and the Ang1-7 inhibitor A779 were added to the system to further evaluate AngII-induced EMT. Compared with that in normal tissue, the expression level of vimentin in HCC tissue was increased, whereas that of E-cadherin was decreased. EMT occurred 48 h following AngII stimulation. The transcription level of E-cadherin in HepG2 cells was decreased, whereas that of vimentin was increased. In addition, the migration and invasion abilities of the cells were increased simultaneously. Ang1-7 partly inhibited AngII-induced EMT. When stimulated at an appropriate time, HepG2 cells have the ability to undergo EMT.

Angiotensin‑(1‑7) prevents lipopolysaccharide‑induced hepatocellular inflammatory response by inhibiting the p38MAPK/AP‑1 signaling pathway

The pathological mechanism of lipopolysaccharide (LPS)‑induced liver injury involves a number of inflammatory mediators and cytokines. Angiotensin (Ang)‑(1‑7), a ligand for the proto‑oncogene Mas (Mas) receptor, antagonizes the actions of Ang II in the renin angiotensin system and exerts an anti‑inflammatory effect on LPS‑induced macrophages. The present study investigated the potential role of Ang‑(1‑7) in the regulation of inflammatory responses in LPS‑induced hepatocytes using the rat liver BRL cell line. The results of the present study demonstrated that the inflammatory mediator, tumor necrosis factor (TNF)‑α, its upstream transcriptional regulatory factor activator protein (AP)‑1 and p38 mitogen activated protein kinase (MAPK) which were detected by reverse transcription‑quantitative polymerase chain reaction and western blotting were upregulated in LPS‑induced hepatic cells in a time‑dependent manner, peaking 12 h following LPS stimulation. By contrast, treatment with Ang‑(1‑7) significantly attenuated the expression of TNF‑α, AP‑1 and p38MAPK in a concentration‑dependent manner. The anti‑inflammatory effect of Ang‑(1‑7) was reversed by the Mas receptor selective antagonist, A779, in BRL cells. Furthermore, the p38MAPK inhibitor, SB 203580, abolished the protective effects of Ang‑(1‑7), suggesting the involvement of the p38MAPK pathway in the anti‑inflammatory activity of Ang‑(1‑7). The results of the present study indicated that Ang‑(1‑7) may serve an anti‑inflammatory role in LPS‑induced hepatocyte injury via the regulation of the p38MAPK/AP‑1 signaling pathway.

The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7)

The renin-angiotensin system (RAS) is a key player in the control of the cardiovascular system and hydroelectrolyte balance, with an influence on organs and functions throughout the body. The classical view of this system saw it as a sequence of many enzymatic steps that culminate in the production of a single biologically active metabolite, the octapeptide angiotensin (ANG) II, by the angiotensin converting enzyme (ACE). The past two decades have revealed new functions for some of the intermediate products, beyond their roles as substrates along the classical route. They may be processed in alternative ways by enzymes such as the ACE homolog ACE2. One effect is to establish a second axis through ACE2/ANG-(1-7)/MAS, whose end point is the metabolite ANG-(1-7). ACE2 and other enzymes can form ANG-(1-7) directly or indirectly from either the decapeptide ANG I or from ANG II. In many cases, this second axis appears to counteract or modulate the effects of the classical axis. ANG-(1-7) itself acts on the receptor MAS to influence a range of mechanisms in the heart, kidney, brain, and other tissues. This review highlights the current knowledge about the roles of ANG-(1-7) in physiology and disease, with particular emphasis on the brain.

Up-regulation of angiotensin-converting enzyme in response to acute ischemic stroke via ERK/NF-κB pathway in spontaneously hypertensive rats

Cerebral ischemic stroke is usually caused by a temporary or permanent decrease in blood supply to the brain. Despite general progress in diagnosis and treatment, the prognosis of stroke is still unsatisfactory, and more detailed potential mechanisms are needed to investigate underlying the pathological process. Here, we showed that serum angiotensin-converting enzyme (ACE) concentration was positively correlated with infarct volume after acute ischemic stroke (AIS). Moreover, using a permanent middle cerebral artery occlusion rat model, we indicated for the first time that increased ACE expression in response to AIS was regulated by the ERK/NF-κB pathway in peri-infarct regions. More importantly, we disclosed that angiotensin II type 1 receptors were implicated in up-regulation of ACE expression in peri-infarct regions. These findings offer insight into ACE expression and activity in response to stroke, and further our understanding of ACE mechanisms.

Protective effects of probucol on Ox-LDL-induced epithelial-mesenchymal transition in human renal proximal tubular epithelial cells via LOX‑1/ROS/MAPK signaling

Oxidized low-density lipoprotein (Ox-LDL), as a strong oxidant, results in renal injury through multiple mechanisms. The aim of the present study was to determine the injury effects of Ox‑LDL and the potential protective effects of the antioxidant reagent probucol on epithelial‑mesenchymal transition (EMT) in human renal proximal tubular epithelial cells (HK‑2) and to further explore the role and interrelation of lectin‑like oxidized low‑density lipoprotein receptor‑1 (LOX‑1), reactive oxygen species (ROS) and mitogen‑activated protein kinase (MAPK) pathway. In the present study, concentrations of 0‑100 µg/ml Ox‑LDL were used to induce HK‑2 cell EMT. Then, probucol (20 µmol/l) and the LOX‑1 inhibitor, polyinosinic acid (250 µg/ml), were also used to pretreat HK‑2 cells. Intracellular ROS activity was evaluated using the specific probe 2',7'‑dichlorodihydrofluorescein diacetate (DCFH‑DA). Concentration of nitric oxide (NO) was determined using a biochemical colorimetric method. Expression of E‑cadherin, α‑smooth muscle actin (SMA), LOX‑1, NADPH oxidase 4 (NOX4), cytochrome b‑245 α chain (p22phox), extracellular signal‑regulated kinase (ERK), and p38 MAPK protein levels were examined by western blotting. The results revealed that Ox‑LDL induced the expression of LOX‑1 and α‑SMA and reduced the expression of E‑cadherin in a dose‑dependent manner, and these effects were inhibited by polyinosinic acid or probucol pretreatment. Stimulation with 50 µg/ml Ox‑LDL induced the expression of NOX4 and p22phox and increased intracellular ROS activity, but NO production in the cell supernatants was not affected. The Ox‑LDL‑mediated increases in Nox4 and p22phox expression and in ROS activity were inhibited by probucol pretreatment. Further investigations into the underlying molecular pathways demonstrated that ERK and p38 MAPK were activated by Ox‑LDL stimulation and then inhibited by probucol pretreatment. The findings of the present study therefore suggest that Ox‑LDL induced EMT in HK‑2 cells, the mechanism of which may be associated with LOX‑1‑related oxidative stress via the ERK and p38 MAPK pathways. Notably, pretreatment with probucol inhibited the Ox‑LDL‑induced oxidative stress by reducing the expression of LOX‑1, and blocked the progression of EMT.

Angiotensin Ⅱ induces epithelial-mesenchymal transition in hepatocellular carcinoma cells

AIM

To detect the expression of molecules of the renin-angiotensin system (RAS) in hepatocellular carcinoma (HCC) and explore whether angiotensin Ⅱ (Ang Ⅱ) induces epithelial-mesenchymal transition (EMT) in SSMC7721 cells.

METHODS

Fifty-six HCC tissues were collected, and immunohistochemistry and Western blot were used to assess the expression of angiotensin converting enzyme 1 (ACE1), ACE2, vimentin, E-cadherin proteins in these tissues. Ang II was then used to stimulate SSMC7721 cells to detect whether EMT markers such as vimentin and E-cadherin were induced.

RESULTS

Compared with normal tissues, the expression of ACE1 and AT1 in HCC tumor tissues were higher. Ang II up-regulated the expression of vimentin but down-regulated the expression of E-cadherin in SSMC7721 cells.

CONCLUSION

The RAS may play a role in HCC metastasis.

High glucose induced endothelial to mesenchymal transition in human umbilical vein endothelial cell

BACKGROUND

Studies have shown that endothelial-to-mesenchymal transition (EndMT) could contribute to the progression of diabetic nephropathy, diabetic renal fibrosis, and cardiac fibrosis. The aim of this study was to investigate the influence of high glucose and related mechanism of MAPK inhibitor or specific antioxidant on the EndMT.

METHODS

In vitro human umbilical vein endothelial cells (HUVEC) were cultured with 11mM, 30mM, 60mM and 120mM glucose for 0, 24, 48, 72 and 168h. Endothelial cell morphology was observed with microscope, and RT-PCR was used to detect mRNA expression of endothelial markers VE-cadherin and CD31, mesenchymal markers α-SMA and collagen I, and transforming growth factor TGF-β1. Immunofluorescence staining was performed to detect the expression of CD31 and α-SMA. The concentration of TGF-β1 in the supernatant was detected by ELISA. ERK1/2 phosphorylation level was detected by Western blot analysis.

RESULTS

High glucose induced EndMT and increased the TGF-β1 level in HUVEC cells. Cells in high glucose for 7 days showed a significant decrease in mRNA expression of CD31 and VE-cadherin, and a significant increase in that of α-SMA and collagen I, while lost CD31 staining and acquired α-SMA staining. ERK signaling pathway blocker PD98059 significantly attenuated the high glucose-induced increase in the ERK1/2 phosphorylation level. PD98059 and NAC both inhibited high glucose-induced TGF-β1 expression and attenuated EndMT marker protein synthesis.

CONCLUSION

High glucose could induce HUVEC cells to undergo EndMT. NAC and ERK signaling pathway may play important role in the regulation of the TGF-β1 biosynthesis during high glucose-induced EndMT.

Angiotensin(1-7) attenuated Angiotensin II-induced hepatocyte EMT by inhibiting NOX-derived H2O2-activated NLRP3 inflammasome/IL-1β/Smad circuit

Epithelial-mesenchymal transition (EMT) is correlated with NAPDH oxidase (NOX)-derived reactive oxygen species (ROS). The ROS-induced NOD-like receptor pyrin domain containing-3 (NLRP3) inflammasome is a novel mechanism of EMT. Angiotensin II (AngII) induces EMT by regulating intracellular ROS. Nevertheless, it has not been reported whether AngII could induce hepatocyte EMT. Angiotensin-(1-7) [Ang-(1-7)] can inhibit the effects of AngII via a counter-regulatory mechanism. However, whether Ang-(1-7) attenuated the effects of AngII on hepatocyte EMT remains unclear. The aim of this study was to determine whether Ang-(1-7) attenuated AngII-induced hepatocyte EMT by inhibiting the NOX-derived ROS-mediated NLRP3 inflammasome/IL-1ß/Smad circuit. In vivo, two animal models were established. In the first model, rats were infused AngII. In the second model, Ang-(1-7) was constantly infused into double bile duct ligated (BDL) rats. In vitro, hepatocytes were pretreated with antioxidant, NLRP3 siRNA, NOX4 siRNA, or Ang-(1-7) before exposure to AngII. In vitro, AngII induced hepatocyte EMT, which was inhibited by N-acetylcysteine (NAC), diphenylene iodonium (DPI), and NOX4 siRNA. NLRP3 inflammasome, which was activated by hydrogen peroxide (H2O2), mediated AngII-induced hepatocyte EMT. Ang-(1-7) suppressed AngII-induced EMT by inhibiting the NOX-derived H2O2-activated NLRP3 inflammasome/IL-1ß/Smad circuit. In vivo, infusion of AngII induced activation of H2O2-correlated NLRP3 inflammasome in rat livers and accumulation of α-collagen I (Col1A1) in hepatocytes. Infusion of Ang-(1-7) alleviated BDL-induced liver fibrosis and inhibited the expression of Col1A1 and the activation of NLRP3 inflammasome in hepatocytes. Ang-(1-7) attenuated AngII-induced hepatocyte EMT by inhibiting the NOX-derived H2O2-activated NLRP3 inflammasome/IL-1ß/Smad circuit.

Hyperglycemia Promotes the Epithelial-Mesenchymal Transition of Pancreatic Cancer via Hydrogen Peroxide

Diabetes mellitus (DM) and pancreatic cancer are intimately related, as approximately 85% of patients diagnosed with pancreatic cancer have impaired glucose tolerance or even DM. Our previous studies have indicated that high glucose could promote the invasive and migratory abilities of pancreatic cancer cells. We therefore explored the underlying mechanism that hyperglycemia modulates the metastatic potential of pancreatic cancer. Our data showed that streptozotocin- (STZ-) treated diabetic nude mice exhibit larger tumor size than that of the euglycemic mice. The number of nude mice that develop liver metastasis or ascites is much more in the STZ-treated group than that in the euglycemic group. Hyperglycemic mice contain a higher plasma H₂O₂-level than that from euglycemic mice. The injection of polyethylene glycol-conjugated catalase (PEG-CAT), an H₂O₂ scavenger, may reverse hyperglycemia-induced tumor metastasis. In addition, hyperglycemia could also modulate the expression of epithelial-mesenchymal transition- (EMT-) related factors in pancreatic tumor tissues, as the E-cadherin level is decreased and the expression of mesenchymal markers N-cadherin and vimentin as well as transcription factor snail is strongly increased. The injection of PEG-CAT could also reverse hyperglycemia-induced EMT. These results suggest that the association between hyperglycemia and poor prognosis of pancreatic cancer can be attributed to the alterations of EMT through the production of hydrogen peroxide.

Attenuation of hyperglycemia-induced apoptotic signaling and anti-angiogenic milieu in cultured cytotrophoblast cells

OBJECTIVE

Preeclampsia (preE) is a hypertensive disorder that occurs 20% in diabetic pregnancy. We have shown that hyperglycemia impairs cytotrophoblast cell (CTB) function. In this study, we assess apoptotic and anti-angiogenic signaling in excess glucose-induced CTBs.

STUDY DESIGN

Human extravillous CTBs (Sw. 71) were treated with 100, 150, 200, 300, or 400 mg/dL glucose for 48 h. Some cells were pretreated with a p38 inhibitor (SB203580) or a peroxisome proliferator-activated receptor gamma (PPARγ) ligand (rosiglitazone) or with D-mannitol. Cell lysates were utilized to measure p38 MAPK phosphorylation, PPARγ, Bcl-2-associated-X protein (Bax), anti-apoptotic Bcl-2, caspase-9, and cyclooxygenase-2 (Cox-2) expression by western blot. Levels of the vascular endothelial growth factor (VEGF), placental growth factor (PlGF), soluble fms-like tyrosine kinase-1 (sFlt-1), soluble endoglin (sEng), and interleukin 6 (IL-6) were measured in culture media using ELISA kits. Statistical comparisons were performed using analysis of variance with Duncan's post hoc test.

RESULTS

p38 phosphorylation and PPARγ were upregulated (p < 0.05) in CTBs treated with ≥150 mg/dL glucose compared to basal (100 mg/dL). Expressions of Bax/Bcl-2, Cox-2, and caspase-9 were upregulated (p < 0.05) in CTBs treated with ≥150 mg/dL glucose. Secretion of sFlt-1, sEng, and IL-6 was increased while VEGF and PIGF were decreased in CTB-treated ≥150 mg/dl of glucose (*p < 0.01 for each). SB203580 or rosiglitazone pretreatment significantly attenuated hyperglycemia-induced apoptotic and anti-angiogenic signaling. D-Mannitol had no effect.

CONCLUSION

Hyperglycemia induced apoptotic and anti-angiogenic signaling in CTBs. The observed diminution of hyperglycemia-induced signaling by SB203580 or rosiglitazone pretreatment suggests the involvement of apoptotic and anti-angiogenic signaling in CTB dysfunction.

CD36 is involved in high glucose-induced epithelial to mesenchymal transition in renal tubular epithelial cells

The epithelial-to-mesenchymal transition (EMT) plays an important role in the progression of diabetic nephropathy. Our recent study showed that ROS mediated high glucose (HG)-induced EMT in renal tubular epithelial cells. CD36, a class-B scavenger receptor, has been reported to mediate the production of ROS in chronic kidney disease. In the present study, we examined the effect of inhibition of CD36 with CD36 siRNA or sulfosuccinimidyl-oleate (SSO), a CD36 antagonist, on HG-induced EMT in HK-2 cells. HG induced CD36 expression in a time-dependent manner in HK-2 cells. HG was shown to induce EMT at 72 h. This was blocked by knockdown of CD36 or treatment with SSO. Meanwhile, we also found that knockdown of CD36 or treatment with SSO inhibited HG-induced ROS generation, activation of ERK1/2 and Smad2, expression of TGF-β1 and synthesis of fibronectin. These data suggest that inhibition of CD36 prevented HG-induced EMT in HK-2 cells, highlighting CD36 as a potential therapeutic target for diabetic nephropathy.

Novel curcumin analog C66 prevents diabetic nephropathy via JNK pathway with the involvement of p300/CBP-mediated histone acetylation

Glomerulosclerosis and interstitial fibrosis represent the key events in development of diabetic nephropathy (DN), with connective tissue growth factor (CTGF), plasminogen activator inhibitor-1 (PAI-1) and fibronectin 1 (FN-1) playing important roles in these pathogenic processes. To investigate whether the plant metabolite curcumin, which exerts epigenetic modulatory properties when applied as a pharmacological agent, may prevent DN via inhibition of the JNK pathway and epigenetic histone acetylation, diabetic and age-matched non-diabetic control mice were administered a 3-month course of curcumin analogue (C66), c-Jun N-terminal kinase inhibitor (JNKi, sp600125), or vehicle alone. At treatment end, half of the mice were sacrificed for analysis and the other half were maintained without treatment for an additional 3 months. Renal JNK phosphorylation was found to be significantly increased in the vehicle-treated diabetic mice, but not the C66- and JNKi-treated diabetic mice, at both the 3-month and 6-month time points. C66 and JNKi treatment also significantly prevented diabetes-induced renal fibrosis and dysfunction. Diabetes-related increases in histone acetylation, histone acetyl transferases' (HATs) activity, and the p300/CBP HAT expression were also significantly attenuated by C66 or JNKi treatment. Chromatin immunoprecipitation assays showed that C66 and JNKi treatments decreased H3-lysine9/14-acetylation (H3K9/14Ac) level and p300/CBP occupancy at the CTGF, PAI-1 and FN-1 gene promoters. Thus, C66 may significantly and persistently prevent renal injury and dysfunction in diabetic mice via down-regulation of diabetes-related JNK activation and consequent suppression of the diabetes-related increases in HAT activity, p300/CBP expression, and histone acetylation.

Hyperglycemia impairs cytotrophoblast function via stress signaling

OBJECTIVE

Diabetes mellitus is a risk factor for preeclampsia. Cytotrophoblast (CTB) invasion is facilitated from the conversion of plasminogen to plasmin by urokinase plasminogen activator (uPA), regulated by plasminogen activator inhibitor 1 (PAI-1), and may be inhibited in preeclampsia. This study assessed signaling mechanisms of hyperglycemia-induced CTB dysfunction.

STUDY DESIGN

Human CTBs were treated with 45, 135, 225, 495, or 945 mg/dL glucose for 48 hours. Some cells were pretreated with a p38 inhibitor (SB203580) or a peroxisome proliferator-activated receptor-gamma (PPAR-γ) ligand (rosiglitazone). Expression of uPA, PAI-1, and PPAR-γ levels and p38 mitogen-activated protein kinase phosphorylation were measured by Western blot in cell lysates. Messenger ribonucleic acid of uPA and PAI-1 was measured by quantitative polymerase chain reaction. Levels of interleukin-6, angiogenic (vascular endothelial growth factor [VEGF], placenta growth factor [PlGF]) and antiangiogenic factors (soluble fms-like tyrosine kinase-1 [sFlt-1], soluble endoglin [sEng]) were measured in the media by enzyme-linked immunosorbent assay kits. Statistical comparisons were performed using analysis of variance with a Duncan's post-hoc test.

RESULTS

Both uPA and PAI-1 protein and messenger ribonucleic acid were down-regulated (P < .05) in CTBs treated with 135 mg/dL glucose or greater compared with basal (45 mg/dL). The sEng, sFlt-1, and interleukin-6 were up-regulated, whereas the VEGF and PlGF were down-regulated by 135 mg/dL glucose or greater. p38 phosphorylation and PPAR-γ were up-regulated (P < .05) in hyperglycemia-treated CTBs. The SB203580 or rosiglitazone pretreatment showed an attenuation of glucose-induced down-regulation of uPA and PAI-1.

CONCLUSION

Hyperglycemia disrupts the invasive profile of CTB by decreasing uPA and PAI-1 expression; down-regulating VEGF and PlGF; and up-regulating sEng, sFlt-1, and interleukin-6. Attenuation of CTB dysfunction by SB203580 or rosiglitazone pretreatment suggests the involvement of stress signaling.

Angiotensin-(1-7) abolishes AGE-induced cellular hypertrophy and myofibroblast transformation via inhibition of ERK1/2

Angiotensin-(1-7) (Ang-(1-7))/AT7-Mas receptor axis is an alternative pathway within the renin-angiotensin system (RAS) that generally opposes the actions of Ang II/AT1 receptor pathway. Advanced glycated end product (AGEs) including glucose- and methylglyoxal-modified albumin (MGA) may contribute to the development and progression of diabetic nephropathy in part through activation of the Ang II/AT1 receptor system; however, the influence of AGE on the Ang-(1-7) arm of the RAS within the kidney is unclear. The present study assessed the impact of AGE on the Ang-(1-7) axis in NRK-52E renal epithelial cells. MGA exposure for 48 h significantly reduced the intracellular levels of Ang-(1-7) approximately 50%; however, Ang I or Ang II expression was not altered. The reduced cellular content of Ang-(1-7) was associated with increased metabolism of the peptide to the inactive metabolite Ang-(1-4) [MGA: 175±9 vs.

CONTROL

115±11 fmol/min/mg protein, p<0.05, n=3] but no change in the processing of Ang I to Ang-(1-7). Treatment with Ang-(1-7) reversed MGA-induced cellular hypertrophy and myofibroblast transition evidenced by reduced immunostaining and protein expression of α-smooth muscle actin (α-SMA) [0.4±0.1 vs. 1.0±0.1, respectively, n=3, p<0.05]. Ang-(1-7) abolished AGE-induced activation of the MAP kinase ERK1/2 to a similar extent as the TGF-β receptor kinase inhibitor SB58059; however, Ang-(1-7) did not attenuate the MGA-stimulated release of TGF-β. The AT7-Mas receptor antagonist D-Ala(7)-Ang-(1-7) abolished the inhibitory actions of Ang-(1-7). In contrast, AT1 receptor antagonist losartan did not attenuate the MGA-induced effects. We conclude that Ang-(1-7) may provide an additional therapeutic approach to the conventional RAS blockade regimen to attenuate AGE-dependent renal injury.

Angiotensin-converting enzyme 2/angiotensin-(1-7)/Mas axis protects against lung fibrosis by inhibiting the MAPK/NF-κB pathway

Accumulating evidence has demonstrated that up-regulation of the angiotensin (Ang)-converting enzyme (ACE)/AngII/AngII type 1 receptor (AT1R) axis aggravates pulmonary fibrosis. The recently discovered ACE2/Ang-(1-7)/Mas axis, which counteracts the activity of the ACE/AngII/AT1R axis, has been shown to protect against pulmonary fibrosis. However, the mechanisms by which ACE2 and Ang-(1-7) attenuate pulmonary fibrosis remain unclear. We hypothesized that up-regulation of the ACE2/Ang-(1-7)/Mas axis protects against bleomycin (BLM)-induced pulmonary fibrosis by inhibiting the mitogen-activated protein kinase (MAPK)/NF-κB pathway. In vivo, Ang-(1-7) was continuously infused into Wistar rats that had received BLM or AngII. In vitro, human fetal lung-1 cells were pretreated with compounds that block the activities of AT1R, Mas (A-779), and MAPKs before exposure to AngII or Ang-(1-7). The human fetal lung-1 cells were infected with lentivirus-mediated ACE2 before exposure to AngII. In vivo, Ang-(1-7) prevented BLM-induced lung fibrosis and AngII-induced lung inflammation by inhibiting the MAPK phosphorylation and NF-κB signaling cascades. However, exogenous Ang-(1-7) alone clearly promoted lung inflammation. In vitro, Ang-(1-7) and lentivirus-mediated ACE2 inhibited the AngII-induced MAPK/NF-κB pathway, thereby attenuating inflammation and α-collagen I production, which could be reversed by the Mas inhibitor, A-779. Ang-(1-7) inhibited AngII-induced lung fibroblast apoptotic resistance via inhibition of the MAPK/NF-κB pathway and activation of the BCL-2-associated X protein/caspase-dependent mitochondrial apoptotic pathway. Ang-(1-7) alone markedly stimulated extracellular signal-regulated protein kinase 1/2 phosphorylation and the NF-κB cascade. Up-regulation of the ACE2/Ang-(1-7)/Mas axis protected against pulmonary fibrosis by inhibiting the MAPK/NF-κB pathway. However, close attention should be paid to the proinflammatory effects of Ang-(1-7).

Inhibition of MAPK-mediated ACE expression by compound C66 prevents STZ-induced diabetic nephropathy

A range of in vitro, experimental and clinical intervention studies have implicated an important role for hyperglycaemia-induced activation of the renin-angiotensin system (RAS) in the development and progression of diabetic nephropathy (DN). Blockade of RAS by angiotensin converting enzyme (ACE) inhibitors is an effective strategy in treating diabetic kidney diseases. However, few studies demonstrate the mechanism by which hyperglycaemia up-regulates the expression of ACE gene. Our previous studies have identified a novel curcumin analogue, (2E,6E)-2,6-bis(2-(trifluoromethyl)benzylidene)cyclohexanone (C66), which could inhibit the high glucose (HG)-induced phosphorylation of mitogen-activated protein kinases in mouse macrophages. In this study, we found that the renal protection of C66 in diabetic mice was associated with mitogen-activated protein kinase (MAPK) inactivation and ACE/angiotensin II (Ang II) down-regulation. Generally, MAPKs have been considered as a downstream signalling of Ang II and a mediator for Ang II-induced pathophysiological actions. However, using C66 and specific inhibitors as small molecule probes, in vitro experiments demonstrate that the MAPK signalling pathway regulates ACE expression under HG stimulation, which contributes to renal Ang II activation and the development of DN. This study indicates that C66 is a potential candidate of DN therapeutic agents, and more importantly, that reduction in ACE expression by MAPKs inhibition seems to be an alternative strategy for the treatment of DN.

Knockdown of thioredoxin-interacting protein ameliorates high glucose-induced epithelial to mesenchymal transition in renal tubular epithelial cells

Epithelial to mesenchymal transition (EMT) of tubular cells contributes to the renal accumulation of matrix protein that is associated with diabetic nephropathy. Both high glucose and transforming growth factor-β (TGF-β) are able to induce EMT in cell culture. In this study, we examined the role of the thioredoxin-interacting protein (TXNIP) on EMT induced by high glucose or TGF-β1 in HK-2 cells. EMT was assessed by the expression of α-smooth muscle actin (α-SMA) and E-cadherin and the induction of a myofibroblastic phenotype. High glucose (30mM) was shown to induce EMT at 72h. This was blocked by knockdown of TXNIP or antioxidant NAC. Meanwhile, we also found that knockdown of TXNIP or antioxidant NAC inhibited high glucose-induced generation of reactive oxygen species (ROS), phosphorylation of p38 MAPK and ERK1/2 and expression of TGF-β1. HK-2 cells that were exposed to TGF-β1 (4ng/ml) also underwent EMT. The expression of TXNIP gene and protein was increased in HK-2 cells treated with TGF-β1. Transfection with TXNIP shRNA was able to attenuate TGF-β1 induced-EMT. These results suggested that knockdown of TXNIP antagonized high glucose-induced EMT by inhibiting ROS production, activation of p38 MAPK and ERK1/2, and expression of TGF-β1, highlighting TXNIP as a potential therapy target for diabetic nephropathy.

Glucose dependence of glycogen synthase activity regulation by GSK3 and MEK/ERK inhibitors and angiotensin-(1-7) action on these pathways in cultured human myotubes

Glycogen synthase (GS) is activated by glucose/glycogen depletion in skeletal muscle cells, but the contributing signaling pathways, including the chief GS regulator GSK3, have not been fully defined. The MEK/ERK pathway is known to regulate GSK3 and respond to glucose. The aim of this study was to elucidate the GSK3 and MEK/ERK pathway contribution to GS activation by glucose deprivation in cultured human myotubes. Moreover, we tested the glucose-dependence of GSK3 and MEK/ERK effects on GS and angiotensin (1-7) actions on these pathways. We show that glucose deprivation activated GS, but did not change phospho-GS (Ser640/1), GSK3β activity or activity-activating phosphorylation of ERK1/2. We then treated glucose-replete and -depleted cells with SB415286, U0126, LY294 and rapamycin to inhibit GSK3, MEK1/2, PI3K and mTOR, respectively. SB415286 activated GS and decreased the relative phospho-GS (Ser640/1) level, more in glucose-depleted than -replete cells. U0126 activated GS and reduced the phospho-GS (Ser640/1) content significantly in glucose-depleted cells, while GSK3β activity tended to increase. LY294 inactivated GS in glucose-depleted cells only, without affecting relative phospho-GS (Ser640/1) level. Rapamycin had no effect on GS activation. Angiotensin-(1-7) raised phospho-ERK1/2 but not phospho-GSK3β (Ser9) content, while it inactivated GS and increased GS phosphorylation on Ser640/1, in glucose-replete cells. In glucose-depleted cells, angiotensin-(1-7) effects on ERK1/2 and GS were reverted, while relative phospho-GSK3β (Ser9) content decreased. In conclusion, activation of GS by glucose deprivation is not due to GS Ser640/1 dephosphorylation, GSK3β or ERK1/2 regulation in cultured myotubes. However, glucose depletion enhances GS activation/Ser640/1 dephosphorylation due to both GSK3 and MEK/ERK inhibition. Angiotensin-(1-7) inactivates GS in glucose-replete cells in association with ERK1/2 activation, not with GSK3 regulation, and glucose deprivation reverts both hormone effects. Thus, the ERK1/2 pathway negatively regulates GS activity in myotubes, without involving GSK3 regulation, and as a function of the presence of glucose.

Interaction between TGF-β and ACE2-Ang-(1-7)-Mas pathway in high glucose-cultured NRK-52E cells

Transforming growth factor-β (TGF-β) is pivotal in diabetic nephropathy (DN). Angiotensin converting enzyme-2 (ACE2) converts angiotensin II (Ang II) to angiotensin 1-7 (Ang-(1-7)), which binds to Mas. Proximal tubular ACE2 is decreased in DN. ACE2 deficiency exacerbates whereas ACE2 overexpression attenuates DN. Thus, we investigated the mechanism of high glucose-decreased ACE2 in terms of the interaction between TGF-β and ACE2-Ang-(1-7)-Mas in NRK-52E cells. We found that high glucose increased TGF-β1. SB431542 attenuated high glucose-inhibited ACE2 and Mas and Ang-(1-7) conversion from Ang II while attenuating high glucose-induced fibronectin. TGF-β1 also decreased ACE2 and Mas and Ang-(1-7) conversion from Ang II. A779 attenuated Ang-(1-7)-decreased TGF-β1 and Ang-(1-7)-activated JAK2-STAT3. Moreover, A779, LY294002 and AG490 attenuated Ang-(1-7)-inhibited TGF-β1. The combination of Ang-(1-7) and Mas attenuated TGF-β1 (but not high glucose)-induced fibronectin. Thus, high glucose decreases ACE2 via TGF-βR in NRK-52E cells. Additionally, there is a negative feedback function between TGF-β and ACE2, and the combined inhibition of TGF-β and activation of the ACE2-Ang-(1-7)-Mas may be useful for treating diabetic renal fibrosis.

Angiotensin-converting enzyme 2, angiotensin-(1-7) and Mas: new players of the renin-angiotensin system

Angiotensin (Ang)-(1-7) is now recognized as a biologically active component of the renin-angiotensin system (RAS). Ang-(1-7) appears to play a central role in the RAS because it exerts a vast array of actions, many of them opposite to those attributed to the main effector peptide of the RAS, Ang II. The discovery of the Ang-converting enzyme (ACE) homolog ACE2 brought to light an important metabolic pathway responsible for Ang-(1-7) synthesis. This enzyme can form Ang-(1-7) from Ang II or less efficiently through hydrolysis of Ang I to Ang-(1-9) with subsequent Ang-(1-7) formation by ACE. In addition, it is now well established that the G protein-coupled receptor Mas is a functional binding site for Ang-(1-7). Thus, the axis formed by ACE2/Ang-(1-7)/Mas appears to represent an endogenous counterregulatory pathway within the RAS, the actions of which are in opposition to the vasoconstrictor/proliferative arm of the RAS consisting of ACE, Ang II, and AT(1) receptor. In this brief review, we will discuss recent findings related to the biological role of the ACE2/Ang-(1-7)/Mas arm in the cardiovascular and renal systems, as well as in metabolism. In addition, we will highlight the potential interactions of Ang-(1-7) and Mas with AT(1) and AT(2) receptors.

Angiotensin-(1-7) in kidney disease: a review of the controversies

Ang-(1-7) [angiotensin-(1-7)] is a biologically active heptapeptide component of the RAS (renin-angiotensin system), and is generated in the kidney at relatively high levels, via enzymatic pathways that include ACE2 (angiotensin-converting enzyme 2). The biological effects of Ang-(1-7) in the kidney are primarily mediated by interaction with the G-protein-coupled receptor Mas. However, other complex effects have been described that may involve receptor-receptor interactions with AT(1) (angiotensin II type 1) or AT(2) (angiotensin II type 2) receptors, as well as nuclear receptor binding. In the renal vasculature, Ang-(1-7) has vasodilatory properties and it opposes growth-stimulatory signalling in tubular epithelial cells. In several kidney diseases, including hypertensive and diabetic nephropathy, glomerulonephritis, tubulointerstitial fibrosis, pre-eclampsia and acute kidney injury, a growing body of evidence supports a role for endogenous or exogenous Ang-(1-7) as an antagonist of signalling mediated by AT(1) receptors and thereby as a protector against nephron injury. In certain experimental conditions, Ang-(1-7) appears to paradoxically exacerbate renal injury, suggesting that dose or route of administration, state of activation of the local RAS, cell-specific signalling or non-Mas receptor-mediated pathways may contribute to the deleterious responses. Although Ang-(1-7) has promise as a potential therapeutic agent in humans with kidney disease, further studies are required to delineate its signalling mechanisms in the kidney under physiological and pathophysiological conditions.