The PTEN/PI3K/Akt signaling pathway mediates HMGB1-induced cell proliferation by regulating the NF-κB/cyclin D1 pathway in mouse mesangial cells.

Our previous experiment confirmed that high-mobility group box chromosomal protein 1 (HMGB1) was involved in the pathogenesis of Lupus nephritis (LN) by upregulating the proliferation of the mouse mesangial cell line (MMC) through the cyclin D1/CDK4/p16 system, but the precise mechanism is still unknown. Therefore, in the present study, we demonstrated that HMGB1 induced the proliferation of MMC cells in a time- and concentration-dependent manner, downregulated phosphatase and tensin homolog deleted on chromosome ten (PTEN) expression, increased the level of Akt serine 473 phosphorylation, and induced p65 subunit nuclear translocation. The overexpression of PTEN prevented the upregulation of HMGB1-induced proliferation by blocking the activation of Akt. The knockdown of Akt by siRNA technology and blocking the nuclear factor-κB (NF-κB) pathway using pyrrolidine dithiocarbamate (PDTC) and SN50, inhibitors of NF-κB, both attenuated the HMGB1-induced proliferation by counteracting the activation of the cyclin D1. In addition, while sh-Akt partly blocked the nuclear translocation of the p65 subunit, PDTC did not affect the activation of the Akt induced by HMGB1 in MMC cells. These findings indicate that HMGB1 induced the proliferation of MMC cells by activating the PTEN/phosphoinositide-3-kinase (PI3K)/Akt/NF-κB signaling pathway.

Interplay between the Notch and PI3K/Akt pathways in high glucose-induced podocyte apoptosis.

Podocyte apoptosis contributes to the pathogenesis of diabetic nephropathy (DN). However, the mechanisms that mediate high glucose (HG)-induced podocyte apoptosis remain poorly understood. Conditionally immortalized mouse podocytes were cultured in HG medium. A chemical inhibitor or a specific short-hairpin RNA (shRNA) vector was used to inhibit the activation of the Notch pathway and the PI3K/Akt pathway in HG-treated podocytes. Western blotting and real-time PCR were used to evaluate the levels of Notch, PI3K/Akt, and apoptotic pathway signaling. The apoptosis rate of HG-treated podocytes was assessed by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling and annexin V/propidium iodide staining. In HG-treated podocytes, PI3K/Akt pathway activation prevented podocyte apoptosis in the early stage of HG stimulation and Notch pathway-induced podocyte apoptosis in the late stage of HG stimulation. The inhibition of the Notch pathway or the activation of the PI3K/Akt pathway prevented cell apoptosis in HG-treated podocytes. These findings suggest that the Notch and PI3K/Akt pathways may mediate HG-induced podocyte apoptosis.

High-fat diet causes increased serum insulin and glucose which synergistically lead to renal tubular lipid deposition and extracellular matrix accumulation.

Renal tubular lipid accumulation is associated with renal injury in the metabolic syndrome, but its mechanisms are not fully elucidated. The purpose of the present study was to investigate the exact mechanism of renal tubular lipid accumulation in the diet-induced metabolic syndrome. The in vivo experiments showed that a high-fat diet induced hyperglycaemia, hyperinsulinaemia and hypertriacylglycerolaemia, subsequent increases in sterol regulatory element binding protein-1 (SREBP-1) and transforming growth factor-ß1 (TGF-ß1), lipid droplet deposit in renal tubular cells and interstitial extracellular matrix accumulation in Wistar rats. A human renal proximal tubular epithelial cell line (HKC) was used to determine the direct role of insulin, and the results revealed that insulin induced SREBP-1, fatty acid synthase (FASN), TGF-ß1 expressions, lipid droplet and extracellular matrix deposits. Knockdown of SREBP-1 by RNA interference technology significantly inhibited FASN, TGF-ß1 up-regulation, lipid and extracellular matrix accumulation caused by insulin. In addition, we found that insulin and high glucose could synergistically increase SREBP-1, FASN, TGF-ß1 and fibronectin expressions in HKC cells. These results indicate that high-fat diet-induced increased serum insulin and glucose synergistically cause renal tubular lipid deposit and extracellular matrix accumulation via the SREBP-1 pathway.

[The effect of Janus kinase 2 inhibitor AG490 on renal tubular epithelial-myofibroblast transdifferentiation induced by interleukin-1ß].

OBJECTIVE: To investigate the effect of AG490, a Janus kinase 2 inhibitor, on epithelial-myofibroblast transdifferentiation induced by interleukin-1ß (IL-1ß). METHODS: Cultured human renal tubular epithelial cell line (HKCs) were divided into three groups: blank control group, IL-1ß (5 ng/ml) group and AG490 group (IL-1ß 5 ng/ml+AG490 10 µmol/L). The cells in all groups were collected at 24, 48, 72 hours after intervention. Immunocytochemistry and Western blotting analysis were used to determine the expressions of cytokeratin-18 (CK-18) and α-smooth muscle actin (α-SMA). RESULTS: The higher expression of CK-18 (1.25±0.08) and mild expression of α-SMA (0.17±0.01) were found in blank control group. In IL-1ß group, the protein level of CK-18 was gradually decreased with prolongation of stimulus (24 hours : 0.69±0.04, 48 hours: 0.52±0.03, 72 hours: 0.30±0.01), while the expression level of α-SMA was gradually increased (24 hours: 0.56±0.04, 48 hours: 1.05±0.07, 72 hours: 1.43±0.07), and the difference between blank control group and IL-1ß group was statistically significant (all P<0.05). The administration of AG490 could restore the expression of CK-18 (24 hours: 1.07±0.07, 48 hours: 0.93±0.06, 72 hours: 0.83±0.06), and inhibit the expression of α-SMA induced by IL-1ß (24 hours: 0.33± 0.01, 48 hours: 0.52±0.01, 72 hours: 0.61±0.04). There was significant difference between AG490 group and IL-1ß group (all P<0.05). The results of immunocytochemistry and that of Western blotting were identical. CONCLUSION: IL-1ß can induce the transdifferentiation of renal tubular epithelial cells, up-regulate the expression of α-SMA, induce the renal tubular epithelial cells to transform to myofibroblast, while AG490 can inhibit the effect of IL-1ß.

The regulatory effect of the p38 signaling pathway on valdecoxib-induced apoptosis of the Eca109 cell line.

Valdecoxib is a second generation selective COX-2 inhibitor that can induce cell apoptosis in a variety of cell types, but its precise regulatory mechanism is unknown. Apoptosis of Eca109 cells and p38 mRNA expression were investigted. The expression of p-p38MAPK, Fas and FasL proteins were detected by immunohistochemical staining and FCM. Valdecoxib increased the apoptosis rate of Eca109 cells. Fas and FasL protein expression was up-regulated in the valdecoxib groups, while SB203580 partly inhibited the valdecoxib-induced overexpression. Valdecoxib increased p38MAPK expression, while SB203580 inhibited the overexpression of this protein and the apoptosis rate decreased. The expression of Fas, FasL and p38MAPK protein were positively correlated with the apoptotic rate. In conclusion, valdecoxib activates the p38MAPK pathway, thus up-regulating expression of the Fas and FasL proteins, which may be one of the mechanisms through which valdecoxib induces apoptosis.

[Effects of fluvastatin on the expression of Janus kinase 2/signal transducers and activators of transcription (JAK/STAT) in glomerular mesangial cells under high concentration of glucose].

OBJECTIVE: To investigate the effects of fluvastatin on activation of Janus kinase 2 (JAK2) and signal transducers and activators of transcription 1, 3 (STAT1, 3) in glomerular mesangial cells(GMCs) under high concentration of glucose. METHODS: Rat GMCs were cultured in vitro, and they were treated with glucose and fluvastatin respectively. Tyrosine phosphorylation of JAK2 (p-JAK2) expression was detected by immunoprecipitation and Western blotting analysis. The protein expressions of JAK2, STAT1, p-STAT1, STAT3 and p-STAT3 were assessed by Western blotting. The protein synthesis of transforming growth factor-beta1 (TGF-beta1) and fibronectin (FN) in the supernatants of the GMCs were determined by enzyme-linked immunoadsorbent assay (ELISA). TGF-beta1 mRNA was assessed by reverse transcription and polymerase chain reaction (RT-PCR). RESULTS: Compared with low glucose control group, the expressions of p-JAK2 (802+/-124 vs.204+/-31), p-STAT1 (2,856.6+/-337.8 vs. 617.7+/-76.2), p-STAT3 (3,049.8+/-421.3 vs. 946.7+/-141.2) and TGF-beta1 mRNA were significantly up-regulated in GMCs under high glucose medium, and the concentration of TGF-beta1 in the supernatants [(2.87+/-0.34) microg/L vs. (1.20+/-0.11) microg/L] and FN [(6.34+/-0.61) mg/L vs. (3.24+/-0.26) mg/L, both P<0.01] were higher in the supernatants. The expression levels of p-JAK2 (412+/-67), p-STAT1 (1,178.4+/-137.1), p-STAT3 (1,572.6+/-181.2) and TGF-beta1 mRNA were significantly lower in fluvastatin group than those in high glucose group. The concentration of TGF-beta1 [(1.94+/-0.27) microg/L] and FN [(4.27+/-0.33)mg/L] in the supernatants in fluvastatin group were lower than those in high glucose control group (all P<0.05). CONCLUSION: Fluvastatin can inhibit overproduction of TGF-beta1 and FN in GMCs under high concentration of glucose, the underlying mechanism may partly be attributable to its influence on phosphorylation of JAK/STAT.

Protective effects of Schisandrin on high glucose-induced changes of RhoA and eNOS activity in human umbilical vein endothelial cells.

Schisandrin, derived from the Chinese medicinal herb Schisandra chinensis, has been found to confer protective effects on circulation systems. But the underlying molecular mechanisms remain unclear. The aim of this study was to investigate the effects of a high level of glucose on RhoA and eNOS activity in human umbilical vein endothelial cells(HUVECs) and how Schisandrin plays a role in mediating these effects. To find the optimal treatment time, HUVECs were cultured at a high glucose concentration (30 mM) for different lengths of time (0, 12, 24, and 48 h). Subsequently, the cells were randomized into five groups: a normal group, a high glucose group, and three high glucose groups that were given different doses (5, 10, and 20 µM) of Schisandrin. The cells were pretreated with Schisandrin for 24 h before stimulation with high glucose. The morphology of HUVECs in the various groups was assessed under a light microscope. Immunocytochemical staining was used to detect the level of p-MYPT1 expression. The levels of RhoA activity were determined using the RhoA Activation Assay Biochem Kit. The levels of eNOS activity were examined using a nitrate reduction test. The results showed that in the high glucose group, the activity of RhoA was increased and the activity of eNOS was reduced, thus decreasing the secretion of NO. However, after pretreatment with Schisandrin (10, 20 µM), the activity of RhoA was inhibited and the activity of eNOS increased, which led to an increase in NO production compared with the high glucose group. There was no evident difference between the 5 µM Schisandrin group and the high glucose group. Taken together, these findings indicate that Schisandrin can improve the function of endothelial cells by lowering the activity of RhoA/Rho kinase and raising both the activity of eNOS and the production of NO.

TLR2 Plays a Critical Role in HMGB1-Induced Glomeruli Cell Proliferation Through the FoxO1 Signaling Pathway in Lupus Nephritis.

The objective of this study was to examine the role and possible mechanisms of toll-like receptor 2 (TLR2) in high-mobility group box chromosomal protein 1 (HMGB1)-induced mouse mesangial cell (MMC) proliferation and glomeruli proliferation of MRL/Fas(lpr) mice. First, the expression of proliferating cell nuclear antigen (PCNA), TLR2 and Forkhead box protein O1 (FoxO1) messenger RNA (mRNA) and protein in the glomeruli of MRL/Fas(lpr) mice was quantified, and the correlation with cell proliferation of glomeruli was analyzed. Then, lipopolysaccharide (LPS), TLR2 neutralization antibody, and small hairpin TLR2 (shTLR2) were used to confirm the role of TLR2 in HMGB1-induced MMC proliferation. Furthermore, wild-type FoxO1 (WT-FoxO1) vector was used to investigate the effect of FoxO1 pathway on HMGB1-induced MMC proliferation. Finally, electroporation was used to knockdown TLR2 in the glomeruli of MRL/Fas(lpr) mice, and renal function, FoxO1, and PCNA expression were detected. The results showed that the TLR2 expression was upregulated and FoxO1 expression was decreased in the glomeruli of MRL/Fas(lpr) mice, and these effects were significantly correlated with cell proliferation of the glomeruli. In vitro, the TLR2 neutralization antibody and the WT-FoxO1 vector, both reduced the MMC proliferation levels induced by HMGB1. The TLR2 neutralization antibody also blocked the HMGB1-dependent activation of the FoxO1 pathway and cell proliferation. In addition, transfection with shTLR2 decreased the proliferation levels and PCNA expression induced by HMGB1. In vivo, treatment with shTLR2 significantly reduced the PCNA expression in the glomeruli of MRL/Fas(lpr) mice and improved renal function. In addition, treatment with shTLR2 or blocking of TLR2 also reduced the translocation of FoxO1. Thus, TLR2 plays a critical role in HMGB1-induced glomeruli cell proliferation through the FoxO1 signaling pathway in lupus nephritis.

[Protective effects of Lovastatin on early diabetic renal tissue and the possible mechanism].

OBJECTIVE: To investigate the protective effects of Lovastatin on renal function in experimental diabetic nephropathy in rats. and the function of cAMP-responsive element binding protein (CREB1) in this duration. METHODS: Diabetes was induced in male Wistar rats by intrapetitoneal injection of STZ (65 mg/kg). Three groups were divided as: Sham group, diabetic control group and Lovastatin treatment group. Lovastatin (20 mg/kg) was administered daily by gavage from the next day of the induction diabetes for 4 weeks. Upro, ucr in urine and Glu, Scr, BUN in serum were determined. Immunohistochemistry and computer image-pattern analysis system were used to analyze expression of PCNA and p-CREB1. Western blot were performed to valuate the expression of p-CREB1 with their specific corresponding antibodies. CREB1 mRNA was measured by RT-PCR. RESULTS: After Lovastatin treatment, renal function were ameliorative in diabetic rats. Decrements were also found in the expression of and PCNA, p-CREB1 and its mRNA in the treatment group compared with the diabetic group. CONCLUSION: Inhibition of glomerular cAMP-responsive element binding protein 1 may be responsible for the Lovastatin protective function that allevate the renal proliferation and hypertrophy in diabetic rats.

[Effect of losartan on expression of Janus kinase 2 and signal transducer and activator of transcription 3 in glomeruli of diabetic rats].

OBJECTIVE: To investigate the effects of losartan on Janus kinase 2 (JAK2) and signal transducer and activator of transcription 3 in glomeruli of diabetic rats. METHODS: Sixty Wistar male rats were randomly divided into control group (n=20), diabetes group (n=20), and losartan treatment group (n=20). Diabetes was induced by intraperitoneal injection of streptozotocin (STZ, 65 mg/kg). Losartan (10 mg/kg) was administered daily by gavage from the day following the induction of diabetes. The animals were sacrificed in the weeks 2 and 4 after STZ injection. The renal cortical tissues were obtained and glomeruli were isolated. The protein expressions of JAK2, STAT3 and tyrosine phosphorylated STAT3 (p-STAT3) were assessed respectively by Western blot. Immunoprecipitation and Western blot analysis were used to determine tyrosine phosphorylated JAK2 (p-JAK2). JAK2 and STAT3 mRNA were assayed by reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: Compared with the control group rats, the respective expression of JAK2, p-JAK2, STAT3, p-STAT3, JAK2 mRNA and STAT3 mRNA was significantly increased in the diabetic glomeruli without losartan treatment (all P<0.01). After treatment with losartan, the expression of p-JAK2 and p-STAT3 in the diabetic glomeruli was down-regulated (all P<0.05). However losartan had no effect on the expression of JAK2, STAT3, JAK2 mRNA and STAT3 mRNA in the diabetic glomeruli. CONCLUSION: JAK2 and STAT3 signal proteins may be involved in the kidney damage associated with diabetes. Regulation of phosphorylation of JAK2 and STAT3 may be responsible for the renal protective effects of losartan in diabetic rats.

[Tubular epithelial-myofibroblast transdifferentiation and expressions of hepatocyte growth factor and Smad7 in renal tissues of rat with experimental diabetes].

OBJECTIVE: To investigate the relationship of tubular epithelial-myofibroblast transdifferentiation and the expressions of hepatocyte growth factor (HGF) and Smad7, and to elucidate the role of HGF and Smad7 in diabetic nephropathy. METHODS: Diabetes was induced in male Wistar rats with right nephrectomy and streptozotocin (STZ) administration. The expressions of cytokeratin 18 (CK18), alpha-smooth muscle actin (alpha-SMA), HGF and Smad7 were assayed with immunohistochemistry. The expressions of alpha-SMA, HGF were assayed with flow cytometry. The expression of Smad7 was assessed by Western blot. RESULTS: Compared with those in kidneys of the control group, diabetic kidneys showed down-regulated expression of CK18 and up-regulated expression of alpha-SMA. The expressions of HGF and Smad7 were increased significantly in the kidneys of diabetic rats at first, then they decreased gradually, but were still higher than those of control. CONCLUSION: The tubular epithelial cells may undergo phenotypic alterations and change to myofibroblasts. The absence of up-regulation of HGF and Smad7 may be related with the transdifferentiation of tubular cells in this animal model.

[Effects of puerarin on renal function, expressions of MMP-2 and TIMP-2 in diabetic rats].

AIM: To investigate the effect of puerarin on expressions of MMP-2 and TIMP-2 in the kidney of diabetic rats. METHODS: Uninephrectomized male Wistar rats were used to induce diabetes by intraperitoneal injection of streptozocin (65 mg x kg(-1)). Puerarin was given daily by intraperitoneal injection from the third day of induction of diabetes for 16 weeks. Using in situ hybridization and immunohistochemistry to detect MMP-2, TIMP-2 mRNA expressions and MMP-2, TIMP-2, collagen IV and Laminin expressions in diabetic kidneys with image analysis system, Flow cytometry was used to detect the expressions of TGFbeta1, MMP-2 and TIMP-2. RESULTS: Compared with those in kidneys of control group, expressions of MMP-2 mRNA and proteins were lower, while the expressions of both TGFbeta1 and TIMP-2 were higher in the diabetic kidney (P < 0.05). The level of MMP-2 expression was advanced, while expression of TIMP-2 was reduced by puerarin treatment (P < 0.05). CONCLUSION: Puerarin showed some renal protective effect on diabetic nephropathy, partly through inhibition of excessive deposition of glomeruli extracellular matrix by up-regulating MMP-2 and down-regulating TIMP-2 expressions besides reducing the blood glucose.

[Effects of lovastatin on renal function and expression of phosphorylating-p38 mitogen-activated protein kinase in experimental diabetic nephropathy in rats].

OBJECTIVE: To investigate the effects of lovastatin on renal function, activity and expression of the p38 mitogen-activated protein kinase (MAPK) and cAMP responsive element-binding protein (CREB) in experimental diabetic nephropathy in rats. METHODS: Eighteen uninephrectomized male Wistar rats were randomly divided into three groups: control (n=6), diabetic (n=6) and lovastatin treatment group (n=6). Diabetes was induced by intraperitoneal injection of STZ (65 mg/kg). Lovastatin (20 mg/kg) was administered daily by gavage from the next day of the induction diabetes for 4 weeks. Four weeks later, animals were sacrificed and samples were collected to determine various parameters, including protein and creatinine in urine (Upro and UCr), and glucose (Glu), creatinine (SCr), blood urea nitrogen (BUN) in serum. Immunohistochemistry and computer image-pattern analysis system were used to analyze activation of P-p38 MAPK and P-CREB, the expression of transferase growth factor-beta(1) (TGF-beta(1)), fibronectin (FN), laminin (LN) in renal glomeruli were also measured. RESULTS: Expression of P-p38 MAPK and P-CREB in diabetic glomeruli in diabetic rats were higher than the controls, the same as the expression of TNF-beta(1), FN, LN(all P<0.01). After lovastatin treatment, expression of P-p38 MAPK, P-CREB and TGF-beta(1), FN, LN were markedly decreased compared with diabetic group(all P<0.01). CONCLUSION: Inhibition of glomerular p38 MAPK signal transduction pathway may be responsible for the decrement of extracellular matrix accumulation and renal protective effects of lovastatin in uninephrectomized rats.

[HMGB1/SREBP-1 mediated IFN-gamma-induced lipid deposition in mouse mesangial cells].

OBJECTIVE: To explore the possible mechanism of lipid deposition induced by interferon-gamma (IFN-gamma). METHODS: The mouse mesangial cells (MMC) were randomly divided into control group, stimulation group, stimulation + control vector group (sh-HMGB1) and stimulation+ specific sh-vector group (sh-SREBP-1). RT-PCR was used to detect the expression of HMGB1, SREBP-1 and fatty acid synthetase (FAS) mRNA; the protein expression was determined by Western blot. RESULTS: The Oil Red O staining revealed that the mouse mesangial cells showed significant lipid droplet in IFN-gamma group. IFN-gamma up-regulated the expression of HMGB1, SREBP-1, FAS mRNA and protein time-dependently; Transfection of MMC with HMGB1 siRNA resulted in the suppression of SREBP-1, FAS protein levels induced by IFN-gamma, following with decrease of lipid deposition. Stimulation with HMGB1 markedly induced expression of SREBP-1, FAS expression and peaked at 8 h, decreased at 12 h compared with that at 8 h. Sh-SREBP-1 decreased the lipid deposition induced by HMGB1 in MMC. CONCLUSION: IFN-gamma might induce lipid deposition in mouse mesangial cells partly by up-regulating the expression of HMGB1/SREBP-1/FAS.

High mobility group box 1 induces synoviocyte proliferation in rheumatoid arthritis by activating the signal transducer and activator transcription signal pathway.

Recently, it was discovered that high mobility group box chromosomal protein 1 (HMGB1) acts as a potent pro-inflammatory cytokine that is released into the extracellular milieu. Signal transducer and activator of transcription (STAT) proteins play an important role in cytokine signaling. Some investigators have reported preferential activation of STAT1, and others have reported preferential activation of STAT3 in response to endogenous interleukin-6 (IL-6) in patients with rheumatoid arthritis. Here, we show that expression of the HMGB1 protein is increased in the articular tissues of collagen-induced arthritis (CIA) rats, especially in cytoplasm and extracellular, following synoviocyte proliferation and STAT1 activation. In vitro, recombined human HMGB1 induced RSC-364 cell proliferation, activated STAT1 phosphorylation, increased the expression of cyclin D1 and CDK4 protein, and decreased the expression of p21 protein. In summary, our study suggests that HMGB1 plays an important role of cytokine in the pathogenesis of RA, which possibly induces synovial cell proliferation by activating the STAT1 signal pathway.

[The relationship between endoplasmic reticulum stress and its particular apoptosis way caspase-12 and apoptosis in renal cortex of diabetic rats].

OBJECTIVE: To investigate the expressions of 78-kDa glucose-regulated protein (GRP78) and Caspase-12 and their relationship with apoptosis in renal cortex of diabetic rats. METHODS: Uninephrectomized Wistar rats were used to induce diabetes by intraperitoneal injection of Streptozotocin (STZ 65 mg/kg). After 8 weeks, the expression and distribution of GRP78, Caspase-12, proliferating cell nuclear antigen (PCNA) were examined by immunohistochemistry. Flow cytometry was used to detect the levels of protein of GRP78 and Caspase-12. Apoptosis was evaluated by means of terminal deoxynucleotidyl transferase-mediated d-UDP nick-end labeling (TUNEL) and Flow cytometry. Serum creatinine, blood urea nitrogen and 24-hour urine protein excretion were checked. RESULTS: Compared with those in normal control group, the numbers of apoptosis and the expression of GRP78, Caspase-12 in glomerular and tubular cells were much higher in the diabetic kidneys at 8 weeks. There was no significant difference between group A and group B. CONCLUSION: Activation of endoplasmic reticulum stress may play an important role in the development of diabetic nephropathy.