Signaling and regulatory mechanisms of integrinα3β1 on the apoptosis of cultured rat podocytes

Effects of Genistein on Common Kidney Diseases

Genistein is a naturally occurring phytoestrogen (soy or soybean products) that is classified as an isoflavone, and its structure is similar to that of endogenous estrogens; therefore, genistein can exert an estrogen-like effect via estrogen receptors. Additionally, genistein is a tyrosine kinase inhibitor, which enables it to block abnormal cell growth and proliferation signals through the inhibition of tyrosine kinase. Genistein is also an angiogenesis inhibitor and an antioxidant. Genistein has effects on kidney cells, some of the kidney’s physiological functions, and a variety of kidney diseases. First, genistein exerts a protective effect on normal cells by reducing the inflammatory response, inhibiting apoptosis, inhibiting oxidative stress, inhibiting remodeling, etc., but after cell injury, the protective effect of genistein decreases or even has the opposite effect. Second, genistein can regulate renin intake to maintain blood pressure balance, regulate calcium uptake to regulate Ca²⁺ and Pi balances, and reduce vasodilation to promote diuresis. Third, genistein has beneficial effects on a variety of kidney diseases (including acute kidney disease, kidney cancer, and different chronic kidney diseases), such as reducing symptoms, delaying disease progression, and improving prognosis. Therefore, this paper reviews animal and human studies on the protective effects of genistein on the kidney in vivo and in vitro to provide a reference for clinical research in the future.

Mutation of Beclin1 acetylation site at K414 alleviates high glucose-induced podocyte impairment in the early stage of diabetic nephropathy by inhibiting hyperactivated autophagy

BACKGROUND

Our group recently reported that a mutation of the novel Beclin1 K414R acetylation site impacts the stability of Beclin1 protein, which decreases autophagy in adipocytes and further impedes adipocyte differentiation and lipolysis. This study was to explore whether Beclin1 acetylation plays a role in the early renal injury induced by high glucose and to further investigate the K414R mutation site in podocytes.

METHODS

Male Sprague-Dawley rats were randomized to con (control) and diabetic nephropathy (DN) groups. The DN group was induced by a single 55 mg/kg intraperitoneal injection of streptozotocin and fed a high-fat and high-sugar diet (the con group received an equal volume of the vehicle and fed a plain diet), after 3 days of induction, blood glucose levels were measured to confirm the onset of diabetes. Then, at weeks 0 and 4, the biochemical index was assayed and renal cortex tissues were harvested. MPC5 podocytes were cultured in vitro. Beclin1 (K414R)-pLVX-ZsGreen1-N1(wild-type or mutant) lentiviral plasmids were transfected into podocytes. Western blot or immunoprecipitation was used to test proteins or the acetylation levels respectively, and immunohistochemistry was used to analyze morphological changes of podocytes. Immunofluorescence was used to detect the aggregation of LC3 puncta.

RESULTS

The acetylation level of Beclin1 was upregulated with podocyte injury exacerbated in high glucose at 24 h and that a mutation at K414R could inhibit hyperactivated autophagy, which ameliorated podocyte impairment.

CONCLUSION

These findings suggest that the acetylation site at K414 is a critical molecule and drug target and that further research into this area is warranted.

Macrophage migration inhibitory factor regulates integrin-β1 and cyclin D1 expression via ERK pathway in podocytes

AIMS

Macrophage migration inhibitory factor (MIF) is found to increase in proliferative glomerulonephritis. MIF binds to the MIF receptor (CD74) that activates MAP kinase (ERK and p38). Integrins and cyclinD1 regulate cell proliferation, differentiation and adhesion. This study evaluates whether MIF can regulate integrin-β1/cyclin D1 expression and cell adhesion of podocytes.

MAIN METHODS

Expression of integrin-β1 mRNA/protein and cyclin D1 mRNA under stimulation of MIF was evaluated by real-time PCR and Western blotting. MIF receptor (CD74) and MAP kinase under MIF treatment were examined to determine which pathway regulated integrin-β1 and cyclin D1 expression. Cell adhesion was evaluated under MIF treatment and/or anti-integrin-β1 antibody by cell adhesion assay.

KEY FINDINGS

Protein levels of integrin-β1 were up-regulated under MIF treatment in a dosage-dependent manner. CD74 protein levels were not changed after MIF treatment. Integrin-β1 and cyclin D1 mRNA levels were up-regulated after MIF 100 ng/ml treatment. ERK inhibitor U0126 reduced MIF-induced the increase in integrin-β1 mRNA and protein expression following MIF stimulation. However, p38 inhibitor SB 203580 did not inhibit MIF-induced increase in integrin-β1 mRNA and protein expression following MIF stimulation. MIF-induced increase in cyclin D1 mRNA level also was inhibited only by U0126 following MIF stimulation. Podocyte adhesion was increased after MIF treatment, but, anti-integrin-β1 antibody decreased MIF-enhanced podocyte adhesion.

SIGNIFICANCE

MIF increases integrin-β1 and cyclin D1 expression through the ERK pathway in podocytes, and the up-regulated expression of integrin-β1 increases podocyte adhesion. These results provide further understanding for the role of MIF in developing proliferative glomerulonephritis.

Correlation Between Single-Nucleotide Polymorphisms Within miR-30a and Related Target Genes and Risk or Prognosis of Nephrotic Syndrome

This study was aimed to figure out the association of single-nucleotide polymorphisms (SNPs) within miR-30a and its downstream molecules (i.e., Notch1, Snail1, p53, CD73, and TET1) with susceptibility to and prognosis of nephrotic syndrome (NS). In the aggregate, 265 patients and 281 healthy controls were gathered, and related laboratory indicators were examined. The miR-30a, Notch1, Snail1, TET1, p53, and CD73 expressions were also evaluated by quantitative real-time polymerase chain reaction (qRT-PCR), immunohistochemistry, or enzyme-linked immunosorbent assay. Besides, the SNPs were genotyped by RT-PCR with aid of ABI-PRISM^™ 377 DNA sequencing instrument. As a result, the NS patients were correlated with remarkably higher 24-h protein excretion, random urine protein/creatinine (UPCR), and serum creatinine, along with lower estimated glomerular filtration rate and serum albumin, when compared with normal subjects (p < 0.05). Furthermore, significant correlations were present between miR-30a expression and the expressions of Notch1 (r_s = -0.350), p53 (r_s = -0.339), CD73 (r_s = -0.300), TET1 (r_s = -0.249), and Snail1 (r_s = -0.829) (all p < 0.05). The SNPs of miR-30a [i.e., rs2222722 (C>T)], Notch1 [i.e., rs3124599 (G>A), rs3124591 (C>T), and rs139994842 (G>A)], Snail1 [i.e., rs6020178 (T>C)], p53 [i.e., rs1042522 (C>G)], and CD73 [i.e., rs9444348 (G>A) and rs4431401 (T>C)] were significantly correlated with both differed NS risk and altered hormone sensitivity to NS (all p < 0.05). Moreover, haplotype AC of CD73 and haplotype ATG of Notch1 were the helpful factors against NS (p < 0.05), yet haplotype GT of CD73 functioned oppositely (p < 0.05). The haplotype AT of CD73 was beneficial to the NS patients for that the carriers could be treated with hormones without severe complications (p < 0.05). Conclusively, the SNPs situated within miR-30a and its downstream molecules (i.e., Notch1, Snail1, p53, CD73, and TET1) could become the promising biomarkers for both NS diagnosis and prediction of NS prognosis.

Hepatitis B Virus X Protein Reduces Podocyte Adhesion via Downregulation of α3β1 Integrin

BACKGROUND/AIMS

Hepatitis B virus (HBV)-associated glomerulonephritis (HBV-GN) is characterized by a reduced number of podocytes due to apoptosis and shedding from the basement membrane. However, the pathological mechanism of HBV-GN is unclear. We previously showed that hepatitis B virus X protein (HBx) promotes apoptosis in tubular epithelial cells. In this study, we transfected podocytes with HBx and examined the effects on adhesion and apoptosis of these cells.

METHODS

Podocytes were transfected with pc-DNA3.1 (+)-HBx. One control group was not transfected and another control group was transfected with empty plasmids. Podocyte adhesion was assessed by a fluorescence assay, apoptosis was measured by flow cytometry and fluorescence microscopy, and expression of α3β1 integrin was determined by western blotting and the reverse transcription polymerase chain reaction (RT-PCR). Activity of caspase-8 was measured by a spectrophotometric assay.

RESULTS

Relative to controls, podocytes with pc-DNA3.1(+)-HBx had reduced cell adhesion, increased apoptosis, reduced expression of α3β1 integrin, and increased caspase-8 activity. β1 integrin blockage reduced podocyte adhesion, but increased apoptosis and caspase-8 activity. Treatment of transfected podocytes with a caspase-8 inhibitor (Z-IETD-FMK) had no effect on the HBx-mediated integrin downregulation and reduced podocyte adhesion, suggesting that α3β1 integrin downregulaton is sufficient to alter cell adhesion.

CONCLUSIONS

Our in vitro results indicate that HBx reduced podocyte adhesion and expression of α3β1 integrin, and increased apoptosis. Moreover, HBx-mediated downregulation of α3β1 integrin expression is sufficient to reduce podocyte adhesion. HBx-induced apoptosis of podocytes may contribute to HBV-GN.

Calcineurin inhibitors cyclosporin A and tacrolimus protect against podocyte injury induced by puromycin aminonucleoside in rodent models

Podocyte injury and the appearance of proteinuria are features of minimal-change disease (MCD). Cyclosporin A (CsA) and tacrolimus (FK506) has been reported to reduce proteinuria in patients with nephrotic syndrome, but mechanisms remain unknown. We, therefore, investigated the protective mechanisms of CsA and FK506 on proteinuria in a rat model of MCD induced by puromycin aminonucleoside (PAN) and in vitro cultured mouse podocytes. Our results showed that CsA and FK506 treatment decreased proteinuria via a mechanism associated to a reduction in the foot-process fusion and desmin, and a recovery of synaptopodin and podocin. In PAN-treated mouse podocytes, pre-incubation with CsA and FK506 restored the distribution of the actin cytoskeleton, increased the expression of synaptopodin and podocin, improved podocyte viability, and reduced the migrating activities of podocytes. Treatment with CsA and FK506 also inhibited PAN-induced podocytes apoptosis, which was associated with the induction of Bcl-xL and inhibition of Bax, cleaved caspase 3, and cleaved PARP expression. Further studies revealed that CsA and FK506 inhibited PAN-induced p38 and JNK signaling, thereby protecting podocytes from PAN-induced injury. In conclusion, CsA and FK506 inhibit proteinuria by protecting against PAN-induced podocyte injury, which may be associated with inhibition of the MAPK signaling pathway.

Maintaining human fetal pancreatic stellate cell function and proliferation require β1 integrin and collagen I matrix interactions

Pancreatic stellate cells (PaSCs) are cells that are located around the acinar, ductal, and vasculature tissue of the rodent and human pancreas, and are responsible for regulating extracellular matrix (ECM) turnover and maintaining the architecture of pancreatic tissue. This study examines the contributions of integrin receptor signaling in human PaSC function and survival. Human PaSCs were isolated from pancreata collected during the 2nd trimester of pregnancy and identified by expression of stellate cell markers, ECM proteins and associated growth factors. Multiple integrins are found in isolated human PaSCs, with high levels of β1, α3 and α5. Cell adhesion and migration assays demonstrated that human PaSCs favour collagen I matrix, which enhanced PaSC proliferation and increased TGFβ1, CTGF and α3β1 integrin. Significant activation of FAK/ERK and AKT signaling pathways, and up-regulation of cyclin D1 protein levels, were observed within PaSCs cultured on collagen I matrix. Blocking β1 integrin significantly decreased PaSC adhesion, migration and proliferation, further complementing the aforementioned findings. This study demonstrates that interaction of β1 integrin with collagen I is required for the proliferation and function of human fetal PaSCs, which may contribute to the biomedical engineering of the ECM microenvironment needed for the efficient regulation of pancreatic development.

Albumin overload down-regulates integrin-β1 through reactive oxygen species-endoplasmic reticulum stress pathway in podocytes

Proteinuria is a major hallmark of glomerular nephropathy and endoplasmic reticulum (ER) stress plays an important role in glomerular nephropathy. The protein levels of integrin-β1 in podocytes are found to be negative correlation with amount of proteinuria. This study investigated whether urinary protein, particularly albumin, induced ER stress that consequently reduced integrin-β1 expression. All experiments were performed using primary cultured rat podocyte. Protein and mRNA expression were measured by western blotting and semiquantified reverse transcriptase polymerase chain reaction. Albumin uptake was found at 1 h after albumin addition. Albumin reduced precursor and mature forms of integrin-β1, but did not change mRNA levels of integrin-β1. Albumin induced reactive oxygen species (ROS) generation and ER stress. Antioxidant (N-acetylcysteine) suppressed albumin-induced ER stress and decrements in precursor and mature forms of integrin-β1. Then, ER stress inhibitors (4-phenylbutyrate and salubrinal) also inhibited albumin-induced decrements in precursor and mature forms of integrin-β1. The potent ER stress inducers (thapsigargin and tunicamycin) directly decreased precursor and mature forms of integrin-β1 and led appearance of unglycosylated core protein of integrin-β1. Our results show that in proteinuric disease, albumin decreases precursor and mature forms of integrin-β1 through ROS-ER stress pathway in podocytes.

Cyclin D1 expression in podocytes: regulated by mitogens in collaboration with integrin-extracellular matrix interaction through extracellular signal-regulated kinase

Cyclin D1 plays significant roles in cell cycle entry and migration. We have documented that both integrin α3β1 expressions and the number of podocytes were reduced in focal segmental glomerulosclerosis. We wondered whether integrin-extracellular matrix (ECM) interaction was involved in the regulation of cyclin D1 expression, and the possible signaling pathways in mitogen-stimulating podocytes. Cultured podocytes were divided into serum (mitogens/growth factors)-starved and serum-stimulated groups. Reverse transcription polymerase chain reaction was used to detect cyclin D1 mRNA, and Western blot analysis was used to measure protein concentrations of cyclin D1 and extracellular signal-regulated kinase (ERK) activation (p-ERK/ERK). The integrin-ECM interaction was blocked by anti-β1-integrin monoclonal antibody or RGDS (Arg-Gly-Asp-Ser). The MEK inhibitor, U0126, was used to inhibit ERK activation. The results showed that there was little cyclin D1 protein in serum-starved groups, but it was abundant in serum-stimulated groups. Both cyclin D1 mRNA and protein levels were reduced in serum-stimulated podocytes after blocking integrin-ECM interaction. ERK activation in serum-stimulated podocytes was significantly decreased after blocking integrin-ECM interaction. Cyclin D1 mRNA and protein concentrations in serum-stimulated podocytes were reduced after blocking ERK activation by U0126. We demonstrate that integrin-ECM interaction collaborates with mitogens to activate ERK/mitogen-activated protein kinase pathways which are essential for cyclin D1 expression in podocytes.

Extracellular signal-regulated kinase plays a proapoptotic role in podocytes after reactive oxygen species treatment and inhibition of integrin-extracellular matrix interaction

The effect of reactive oxygen species (ROS) and blocking integrin-extracellular matrix (ECM) interaction on apoptosis in podocytes, and the related signal transduction pathways remain unclear. Primary cultured rat podocytes were exposed to ROS. Integrin-ECM interaction was inhibited with anti-β1-integrin monoclonal antibody (mAb) or RGDS (Arg-Gly-Asp-Ser). Extracellular signal-regulated kinase (ERK) activation was evaluated with Western blotting. U0126 was used to inhibit ERK activation. Terminal deoxynucleotidyl transferase-mediated dUTP-peroxidase nick end-labeling of DNA (TUNEL) was used to evaluate apoptosis. We found that ROS-treated podocytes exhibited increased apoptosis, and both anti-β1-integrin mAb and RGDS induce apoptosis. Addition of ROS to either anti-β1-integrin mAb or RGDS enhanced apoptosis in both conditions. ERK activation was increased by either ROS or blocking integrin-ECM interaction. Preincubation with U0126 decreased apoptosis induced by ROS, anti-β1-integrin mAb or RGDS, respectively. Our study demonstrated that ROS and blocking integrin-ECM interaction induce podocyte apoptosis, which is mediated by ERK activation.

Integrin {alpha}3, but not {beta}1, regulates islet cell survival and function via PI3K/Akt signaling pathways

β1-integrin is a well-established regulator of β-cell activities; however, the role of its associated α-subunits is relatively unknown. Previously, we have shown that human fetal islet and INS-1 cells highly express α3β1-integrin and that collagens I and IV significantly enhance their survival and function; in addition, blocking β1 function in the fetal islet cells decreased adhesion on collagen I and increased apoptosis. The present study investigates the effect of blocking α3. Using α3 blocking antibody or small interfering RNA, the effects of α3-integrin blockade were examined in isolated human fetal or adult islet cells or INS-1 cells, cultured on collagens I or IV. In parallel, β1 blockade was analyzed in INS-1 cells. Perturbing α3 function in human islet or INS-1 cells resulted in significant decreases in cell function (adhesion, spreading, proliferation and Pdx1 and insulin expression/secretion), primarily on collagen IV. A significant decrease in focal adhesion kinase and ERK1/2 phosphorylation and increased caspase3 cleavage were observed on both collagens. These effects were similar to changes after β1 blockade. Interestingly, only α3 blockade reduced expression of phospho-Akt and members of its downstream signaling cascades (glycogen synthase kinase β and X-linked inhibitor of apoptosis), demonstrating a specific effect of α3 on the phosphatidylinositol 3-kinase/Akt pathway. These results suggest that α3- as well as β1-integrin-extracellular matrix interactions are critical for modulating β-cell survival and function through specialized signaling cascades and enhance our understanding of how to improve islet microenvironments for cell-based treatments of diabetes.

The activation of extracellular signal-regulated kinase is responsible for podocyte injury

Podocyte and its slit diaphragm play an important role in maintaining normal glomerular filtration barrier function and structure. Podocyte apoptosis and slit diaphragm injury leads to proteinuria and glomerulosclerosis. However, the molecular mechanism of podocyte injury remains poorly understood. The family of mitogen-activated protein kinases including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase, and p38 signal pathways, are implicated in the progression of various glomerulopathies. However, the role of the activated signal pathway(s) in podocyte injury is elusive. This study examined phosphorylation of ERK in rat puromycin aminonucleoside (PAN) nephropathy as well as conditionally immortalized mouse podocyte treated with PAN in vitro. The effect of treatment with U0126, an inhibitor of ERK, was also investigated. In PAN nephropathy, the phosphorylation of ERK was marked. In podocyte injury, the marked and sustained activation of ERK pathway was also observed before the appearance of significant podocyte apoptosis. Pretreatment with U0126 to podocyte completely inhibited ERK activation, with complete suppression podocyte apoptosis and ameliorated nephrin protein expression along with the phosphorylation of nephrin in podocyte injury. In cultured podocyte, PAN induced actin recorganition, and U0126 inhibited such change. However, U0126 did not recovery the phosphorylation change of neph1 in podocyte injury. We concluded that the sustained activation of ERK along with the phosphorylation of neph1 might be necessary for podocyte injury. The study here suggested that ERK might become a potential target for therapeutic intervention to prevent podocytes from injury which will result in proteinuria.

Mechanical forces and TGFbeta1 reduce podocyte adhesion through alpha3beta1 integrin downregulation

BACKGROUND

Podocyturia is a marker of diabetic nephr- opathy, a possible determinant of its progression and a powerful risk factor for cardiovascular disease. A reduction in podocyte adhesion to the glomerular basement membrane (GBM) via downregulation of alpha3beta1 integrin expression, the main podocyte anchoring dimer to the GBM, may represent one of the mechanisms of podocyturia in glomerular disease. This study investigated the role of mechanical forces and transforming growth factor beta1 (TGFbeta1) in podocyte adhesion and integrin expression.

METHODS

Conditionally immortalized murine podocytes were exposed to mechanical stretch and/or TGFbeta1 for 48 h. Podocyte adhesion, apoptosis and alpha3beta1 integrin expression were assessed.

RESULTS

Stretch and TGFbeta1 significantly reduced podocyte adhesion and alpha3beta1 integrin expression, events paralleled by increased apoptosis. Blockade of beta1 integrin, with a specific antibody, demonstrated a reduced podocyte adhesion indicating that beta1 integrin downregulation was required for the loss of podocyte adhesion. This was linked to an increase in podocyte apoptosis. The role of apoptosis in podocyte adhesion was further investigated using caspase-3 inhibitors. Podocyte apoptosis inhibition did not affect stretch- and TGFbeta1-mediated integrin downregulation and the loss of podocyte adhesion, suggesting that alpha3beta1 integrin downregulation is sufficient to alter cell adhesion. Although stretch significantly increased podocyte TGFbeta type I, II and III receptors but not podocyte TGFbeta1 secretion, the combination of stretch and TGFbeta1 did not show any additive or synergistic effects on podocyte adhesion and alpha3beta1 integrin expression.

CONCLUSIONS

These results suggest that downregulation of alpha3beta1 integrin expression, by mechanical forces or TGFbeta1, is per se sufficient to reduce podocyte adhesion. Apoptosis may represent a parallel important determinant of the podocyte loss from the GBM.

Signaling and regulatory mechanisms of integrin alphavbeta6 on the apoptosis of colon cancer cells

Considerable researches have been done about integrin alphanubeta6 and carcinomas, but little information has been shown about the relationship between integrin alphanubeta6 and apoptosis. In this study, we investigated the apoptosis and its related signal pathways to integrin alphavbeta6 in colon cancer cells. After we blocked the function of integrin alphavbeta6 in HT29 cells used the monoclonal antibody, the apoptotic cells increased markedly. Meanwhile, cytochrome C released from mitochondria into cytosol, Bcl-2 decreased while Bax increased significantly, and Fas and Fas-ligand had no change. The activities of caspase-3 and caspase-9 increased, while caspase-8 remained no change. Moreover, the expression of phosphorylated extracellular signal-related kinase (P-ERK) decreased. We confirmed that integrin alphavbeta6 acted as an important role in inhibiting apoptosis in colon cancer cells, and the signaling involved the mitochondrial pathway.