Clusterin overexpression protects against western diet-induced obesity and NAFLD.

Obesity is a significant risk factor for various metabolic diseases and is closely related to non-alcoholic fatty liver disease (NAFLD) characterized by inflammation and oxidative stress. Clusterin is a multi-functional protein that is up-regulated in the pathogenesis of various metabolic diseases, including obesity and NAFLD. Our previous studies indicated that hepatocyte-specific overexpression of clusterin alleviates methionine choline-deficient (MCD) diet-induced non-alcoholic steatohepatitis (NASH) by activating nuclear factor erythroid 2-related factor 2 (Nrf2). Here we generated transgenic mice with whole-body clusterin overexpression (wCLU-tg) and investigated the role of clusterin in Western diet-induced obesity and NAFLD. We confirmed that obesity parameters and the spectrum of NAFLD of wCLU-tg mice were improved compared to wild type mice. Contrarily, clusterin deficiency deteriorated metabolic disruptions. We also found that clusterin activates target molecules for obesity and NAFLD, namely Nrf2 and AMPK, suggesting that clusterin protects against Western diet-induced obesity and NAFLD by activating Nrf2 and AMPK.

Hepatocyte-specific clusterin overexpression attenuates diet-induced nonalcoholic steatohepatitis.

Clusterin is a multifunctional glycoprotein that plays important roles and is up-regulated in liver diseases such as hepatitis and hepatocellular carcinoma. However, little is known about the significance of clusterin in the pathogenesis of non-alcoholic steatohepatitis (NASH). The aim of this study is to examine the role of clusterin in progression of steatohepatitis in mice fed a methionine and choline deficient (MCD) diet. We generated hepatocyte-specific clusterin overexpression (hCLU-tg) mice, and hCLU-tg mice showed lower levels of hepatic triglycerides, less infiltration of macrophages and reduction of TNF-α, activation of Nrf-2 than wild-type littermates fed the MCD diet. Also, sustained clusterin expression in liver ameliorated hepatic fibrogenesis by reducing the activation of hepatic stellate cells by MCD diet. Sustained expression of clusterin in liver functioned as a preconditioning stimulus and prevented MCD diet-induced severe steatohepatitis injury via Nrf2 activation. These results demonstrate a novel function of clusterin as an immune preconditioning regulator in various inflammatory diseases including steatohepatitis.

Toll-like receptor 4 signaling is required for clusterin-induced tumor necrosis factor-α secretion in macrophage.

Clusterin is a secretory glycoprotein that is up-regulated in areas of inflammation and under increased levels of oxidative stress. Previously, we demonstrated that clusterin activates NF-κB, and up-regulates the expression of MMP-9 and TNF-α. In this research, we extend our previous findings by reporting that such clusterin-induced macrophage response is mediated via TLR4 signaling. Specifically, we found that TNF-α induced by clusterin was significantly abrogated by pretreatment of TLR4-signaling inhibitors and anti-TLR4 neutralizing antibody. Additionally, a primary culture of macrophages derived from TLR4-signal defective and knockout mice were unresponsive to clusterin, resulting in no TNF-α secretion, whereas macrophages carrying wild-type TLR4 responded to clusterin and induced TNF-α. Moreover, clusterin increased NF-κB promoter activity in HEK-Blue hTLR4 cells, but not in HEK-Blue Null2 cells. To confirm that clusterin elicits TLR4 signal transduction, recombinant clusterin was generated and purified from cell culture. Interestingly, we found that the recombinant clusterin with C-terminal HA-tag induces TNF-α secretion at a significantly lower level compared to an intact form of clusterin without C-terminal HA-tag. Removal of HA-tag from the recombinant clusterin restored its activity, suggesting that C-terminal HA-tag partially masks the domain involved in TLR4 signaling. Furthermore, clusterin enhanced TLR4 mobilization into lipid raft of plasma membrane, and TNF-α and MMP-9 secretion stimulated by clusterin was diminished by pretreatment with methyl-ß-cyclodextrin (MßCD), which was used to disrupt lipid raft. In conclusion, clusterin-induced TNF-α and MMP-9 up-regulation is most likely mediated via TLR4 recruitment into lipid rafts, and these data describe a novel role of clusterin as an endogenous regulator for TLR4 signaling.

Secretory clusterin inhibits osteoclastogenesis by attenuating M-CSF-dependent osteoclast precursor cell proliferation.

Secretory clusterin (sCLU)/apolipoprotein J is a multifunctional glycoprotein that is ubiquitously expressed in various tissues. Reduced sCLU in the joints of patients with bone erosive disease is associated with disease activity; however, its exact role has yet to be elucidated. Here, we report that CLU is expressed and secreted during osteoclastogenesis in mouse bone marrow-derived macrophages (BMMs) that are treated with receptor activator of nuclear factor kappa-B ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). CLU-deficient BMMs obtained from CLU(-/-) mice exhibited no significant alterations in OC differentiation in comparison with BMMs obtained from wild-type mice. In contrast, exogenous sCLU treatment significantly inhibited OC formation in both BMMs and OC precursor cultures. The inhibitory effect of sCLU was more prominent in BMMs than OC precursor cultures. Interestingly, treating BMMs with sCLU decreased the proliferative effects elicited by M-CSF and suppressed M-CSF-induced ERK activation of OC precursor cells without causing apoptotic cell death. This study provides the first evidence that sCLU reduces OC formation by inhibiting the actions of M-CSF, thereby suggesting its protective role in bone erosion.

Deficiency of clusterin exacerbates high-fat diet-induced insulin resistance in male mice.

The present study examined the role of clusterin in insulin resistance in high fat-fed wild-type and clusterin knockout (KO) mice. The plasma levels of glucose and C-peptide and islet size were increased in clusterin KO mice after an 8-week high-fat diet. In an ip glucose tolerance test, the area under the curve for glucose was not different, whereas the area under the curve for insulin was higher in clusterin KO mice. In a hyperinsulinemic-euglycemic clamp, the clamp insulin levels were higher in clusterin KO mice after the high-fat diet. After adjusting for the clamp insulin levels, the glucose infusion rate, suppression of hepatic glucose production, and glucose uptake were lower in clusterin KO mice in the high fat-fed group. The plasma levels of clusterin and clusterin mRNA levels in the skeletal muscle and liver were increased by the high-fat diet. The mRNA levels of the antioxidant enzymes were lower, and the mRNA levels of nicotinamide adenine dinucleotide phosphate oxidase (NOX) 1 and cytokines and protein carbonylation were higher in the skeletal muscle and liver in clusterin KO mice after the high-fat diet. Palmitate-induced gene expressions of NOX1 and cytokines were higher in the primary cultured hepatocytes of clusterin KO mice compared with the wild-type mice. Clusterin inhibited the gene expression and reactive oxygen species generation by palmitate in the hepatocytes and C2C12. AKT phosphorylation by insulin was reduced in the hepatocytes of clusterin KO mice. These results suggest that clusterin plays a protective role against high-fat diet-induced insulin resistance through the suppression of oxidative stress and inflammation.

Clusterin stimulates the chemotactic migration of macrophages through a pertussis toxin sensitive G-protein-coupled receptor and Gßγ-dependent pathways.

Clusterin induces the expression of various chemotactic cytokines including tumor necrosis factor-α (TNF-α) in macrophages and is involved in the cell migration. According to the results of this study, clusterin induced the directional migration (chemotaxis) of macrophages based on a checkerboard analysis. The chemotactic activity of clusterin was prevented by pretreatment with pertussis toxin (PTX), indicating that the Gαi/o-protein coupled receptor (GPCR) was involved in the chemotactic response of clusterin. Clusterin-stimulated chemotaxis was abrogated in a dose-dependent manner by pretreatment with gallein (a Gßγ inhibitor), indicating the involvement of Gßγ released from the GPCR. In addition, inhibitors of phospholipase C (PLC, U73122) and phosphoinositide 3-kinase (PI3K, LY294002), the key targets of Gßγ binding and activation, suppressed chemotactic migration by clusterin. The phosphorylation of Akt induced by clusterin was blocked by pretreatment with gallein or LY294002 but not with U73122, indicating that Gßγ released from the PTX-sensitive Gi protein complex activated PLC and PI3K/Akt signaling pathways separately. The activation of cellular MAP kinases was essential in that their inhibitors blocked clusterin-induced chemotaxis, and Gßγ was required for the activation of MAP kinases because gallein reduced their phosphorylations induced by clusterin. In addition, the inflammation-induced migration of macrophages was greatly reduced in clusterin-deficient mice based on a thioglycollate-induced peritonitis model system. These results suggest that clusterin stimulates the chemotactic migration of macrophages through a PTX-sensitive GPCR and Gßγ-dependent pathways and describe a novel role of clusterin as a chemoattractant of monocytes/macrophages, suggesting that clusterin may serve as a molecular bridge between inflammation and its remodeling of related tissue by recruiting immune cells.

Anti-apoptotic effect of clusterin on cisplatin-induced cell death of retinoblastoma cells.

Clusterin is a cytoprotective chaperone protein that is known to protect various retinal cells. It was also reported to be overexpressed in several types of malignant tumors, whose chemoresistance correlates with the expression of clusterin. Herein, we investigated the effect of clusterin on cisplatin-induced cell death of retinoblastoma cells. Firstly, evaluation of clusterin expression demonstrated that it was highly expressed in human retinoblastoma tissues and cell lines (SNUOT-Rb1 and Y79) particularly in the area between viable cells around vessels and necrotic zones in the relatively avascular area in human retinoblastoma tissues. Furthermore, the effects of cisplatin on retinoblastoma cells were evaluated. Cisplatin (1 µg/ml) significantly affected cell viability of SNUOT-Rb1 cells by inducing caspase-3-dependent apoptosis. Notably, the cell death due to cisplatin was prevented by 5 µg/ml of clusterin administered 4 h prior to cisplatin treatment by inhibiting cisplatin-induced apoptosis. Furthermore, overexpression of clusterin exerted its anti-apoptotic effect on cisplatin-induced apoptosis, and effectively prevented cisplatin-induced cell death. These data suggest that clusterin, found to be expressed in human retinoblastoma, may exert anti-apoptotic effects on cisplatin-induced apoptosis and prevent cell death. Therefore, clusterin can contribute to cisplatin resistance of retinoblastoma.

Clusterin induces the secretion of TNF-α and the chemotactic migration of macrophages.

Tumor associated macrophages are known to be closely linked with tumor progression and metastasis. On the other hand, clusterin is overexpressed in several tumor types and regarded as a putative tumor-promoting factor due to this overexpression and the subsequent induction of chemoresistance. In our previous study, clusterin was found to induce the expression of matrix metalloproteinase-9 (MMP-9) in macrophages, and MMP-9 is known to be essential for tumor cell migration and invasion via basement membrane breakdown. Because paracrine interactions between tumor cells and surrounding macrophages regulate metastasis, these findings raise the possibility that clusterin promotes the secretion of cytokines in macrophages in addition to MMP-9. Here, we demonstrate that clusterin upregulates the expressions of chemotactic cytokines, that is, monocyte chemotactic protein-1 (MCP-1), macrophage inflammatory protein-1ß (MIP-1ß), regulated upon activation, normal T cell expressed and secreted (RANTES), and tumor necrosis factor-α (TNF-α) in Raw264.7 macrophages. In particular, clusterin stimulated TNF-α secretion via the activations of ERK, JNK, and PI3K/Akt pathways in a time and dose-dependent manner. Furthermore, clusterin-induced TNF-α secretion was found to play a critical role in the chemotactic migration of Raw264.7 macrophages. It was also found that clusterin acts directly as a chemoattractant for macrophages. Together, these results suggest that clusterin stimulates the expression and secretion of TNF-α, which plays a critical role in promoting macrophage chemotaxis, via ERK, JNK, and PI3K/Akt pathways. Collectively, these findings describe a novel function for clusterin as an inducer of TNF-α in macrophages and their chemotactic migration, and suggest that clusterin has a tumor-promoting effect.

Over-expression of human clusterin increases stress resistance and extends lifespan in Drosophila melanogaster.

Clusterin is a disulfide-linked heterodimeric glycoprotein that has been implicated in a variety of biological processes. Its expression has been shown to be elevated during cellular senescence and normal aging, but it is uncertain whether clusterin protects against aging or whether its expression is a consequence of aging. To investigate the functions of clusterin during organismal aging, we established transgenic Drosophila alleles to induce the expression of the secretory form of human clusterin (hClu(S)) using the Gal4/UAS system. hClu(S) protein (~60 kDa) was detected in both adult homogenates and larval hemolymphs of flies ubiquitously overexpressing hClu(S) (da-Gal4>UAS-hClu(S)) and in motoneurons (D42-Gal4>UAS-hClu(S)). Interestingly, the mean lifespans of these hClu(S)-overexpressing flies were significantly greater than those of control flies that exhibited no hClu(S) induction. hClu(S)-overexpressing flies also showed significantly greater tolerance to heat shock, wet starvation, and oxidative stress. Furthermore, amounts of reactive oxygen species (ROS) in whole bodies were significantly lower in hClu(S)-overexpressing flies. In addition, clusterin was found to prevent the inactivation of glutamine synthetase (GS) by metal-catalyzed oxidation (MCO) in vitro, and this protection was only supported by thiol-reducing equivalents, such as, DTT or GSH, and not by ascorbate (a non-thiol MCO system). Furthermore, this protection against GS inactivation by clusterin was abolished by reacting clusterin with N-ethylmaleimide, a sulfhydryl group-modifying agent. Taken together, these results suggest that a disulfide-linked form of clusterin functions as an antioxidant protein via its cysteine sulfhydryl groups to reduce ROS levels and delay the organismal aging in fruit flies.

Clusterin attenuates the development of renal fibrosis.

Upregulation of clusterin occurs in several renal diseases and models of nephrotoxicity, but whether this promotes injury or is a protective reaction to injury is unknown. Here, in the mouse unilateral ureteral obstruction model, obstruction markedly increased the expression of clusterin, plasminogen activator inhibitor-1 (PAI-1), type I collagen, and fibronectin. Compared with wild-type mice, clusterin-deficient mice exhibited higher levels of PAI-1, type I collagen, and fibronectin and accelerated renal fibrosis in response to obstruction. In cultured rat tubular epithelium-like cells, adenovirus-mediated overexpression of clusterin inhibited the expression of TGF-ß-stimulated PAI-1, type I collagen, and fibronectin. Clusterin inhibited TGF-ß-stimulated Smad3 activity via inhibition of Smad3 phosphorylation and its nuclear translocation. Moreover, intrarenal delivery of adenovirus-expressing clusterin upregulated expression of clusterin in tubular epithelium-like cells and attenuated obstruction-induced renal fibrosis. In conclusion, clusterin attenuates renal fibrosis in obstructive nephropathy. These results suggest that upregulation of clusterin during renal injury is a protective response against the development of renal fibrosis.

Clusterin induces matrix metalloproteinase-9 expression via ERK1/2 and PI3K/Akt/NF-κB pathways in monocytes/macrophages.

Most solid tumor tissues possess a significant population of macrophages, which are known to be closely linked with tumor progression and metastasis. Clusterin has been reported to be overexpressed in various tumors and to have a tumor-promoting role. As clusterin induction and macrophage infiltration occur concurrently at the tumor site, it raises a possibility that clusterin may regulate the function of macrophages via facilitating ECM remodeling. Here, we demonstrate for the first time the expression of MMP-9 by clusterin in human primary monocytes as well as human and murine macrophage cell lines, THP-1, and Raw264.7. MMP-9 expression was accompanied by increased enzymatic activity, as revealed by gelatin zymography. The MMP-9 activity promoted by clusterin was found to be dependent on the activation of ERK1/2 and PI3K/Akt but not p38 or JNK pathways. Inhibition of PI3K activity did not affect the activation of ERK1/2 and vice versa, indicating that the two pathways were independently operated to stimulate MMP-9 activity. Moreover, clusterin facilitated nuclear translocation of NF-κB p65 along with IκB-α degradation and phosphorylation, which was critical for MMP-9 expression. As NF-κB is a central regulator of inflammation, clusterin may provide a molecular link between inflammation and cancer via up-regulating NF-κB and MMP-9. Collectively, these data highlight a novel role of clusterin as a stimulator for MMP-9 expression in macrophages, which may contribute to the tissue reorganization by serving as a modulator for ECM degradation.

Methylation of eukaryotic elongation factor 2 induced by basic fibroblast growth factor via mitogen-activated protein kinase.

Protein arginine methylation is important for a variety of cellular processes including transcriptional regulation, mRNA splicing, DNA repair, nuclear/cytoplasmic shuttling and various signal transduction pathways. However, the role of arginine methylation in protein biosynthesis and the extracellular signals that control arginine methylation are not fully understood. Basic fibroblast growth factor (bFGF) has been identified as a potent stimulator of myofibroblast dedifferentiation into fibroblasts. We demonstrated that symmetric arginine dimethylation of eukaryotic elongation factor 2 (eEF2) is induced by bFGF without the change in the expression level of eEF2 in mouse embryo fibroblast NIH3T3 cells. The eEF2 methylation is preceded by ras-raf-mitogen-activated protein kinase kinase (MEK)-extracellular signal-regulated kinase (ERK1/2)- p21Cip/WAF1 activation, and suppressed by the mitogenactivated protein kinase (MAPK) inhibitor PD98059 and p21Cip/WAF1 short interfering RNA (siRNA). We determined that protein arginine methyltransferase 7 (PRMT7) is responsible for the methylation, and that PRMT5 acts as a coordinator. Collectively, we demonstrated that eEF2, a key factor involved in protein translational elongation is symmetrically arginine-methylated in a reversible manner, being regulated by bFGF through MAPK signaling pathway.

Essential role of clusterin in pancreas regeneration.

Based on our previous observations that clusterin induction accompanies pancreas regeneration in the rat, we sought to determine if regeneration might be impaired in mice that lacked clusterin. We studied the impact of absent clusterin on morphogenic and functional features of regenerating pancreas. Clusterin induction was accompanied in the regenerating pancreas by a robust development of new lobules with ductules, acini, and endocrine islets in wild type after partial pancreatectomy. In clusterin knock-out mice, however, pancreatectomy resulted in a poor formation of regenerating lobule. In particular, regeneration of beta-cells was also significantly reduced and was associated with persistent hyperglycemia. Duct cells obtained from pancreatectomized clusterin knock-out mice exhibited impaired beta-cell formation in vitro; this was restored by administration of exogenous clusterin. We suggest that clusterin plays a critical role to promote both exocrine and endocrine regeneration following pancreas injury, as well as for in vitro beta-cell regeneration.

Clusterin protects H9c2 cardiomyocytes from oxidative stress-induced apoptosis via Akt/GSK-3ß signaling pathway.

Clusterin is a secretory glycoprotein, which is highly up-regulated in a variety of normal and injury tissues undergoing apoptosis including infarct region of the myocardium. Here, we report that clusterin protects H9c2 cardiomyocytes from H2O2-induced apoptosis by triggering the activation of Akt and GSK-3ß. Treatment with H2O2 induces apoptosis of H9c2 cells by promoting caspase cleavage and cytochrome c release from mitochondria. However, co-treatment with clusterin reverses the induction of apoptotic signaling by H2O2, thereby recovers cell viability. The protective effect of clusterin on H2O2-induced apoptosis is impaired by PI3K inhibitor LY294002, which effectively suppresses clusterin-induced activation of Akt and GSK-3ß. In addition, the protective effect of clusterin is independent on its receptor megalin, because inhibition of megalin has no effect on clusterin-mediated Akt/GSK-3ß phosphoylation and H9c2 cell viability. Collectively, these results suggest that clusterin has a role protecting cardiomyocytes from oxidative stress and the Akt/GSK-3ß signaling mediates anti-apoptotic effect of clusterin.

Clusterin synergizes with IL-2 for the expansion and IFN-γ production of natural killer cells.

CLU is a secreted, multifunctional protein implicated in several immunologic and pathologic conditions. As the level of serum CLU was shown to be elevated during inflammatory responses, we questioned if CLU might interact with circulating lymphocytes leading to functional consequences. To assess this possibility directly, mouse splenocytes and purified NK cells were cultured with varying dose of CLU, and its effect on cell proliferation was examined. Our data showed that CLU up-regulated DNA synthesis and expansion of NK cells significantly in response to a suboptimal, but not maximal, dose of IL-2, and CLU alone did not exhibit such effects. This CLU-mediated synergy required the co-presence of CLU at the onset of IL-2 stimulation and needed a continuous presence during the rest of the culture. Importantly, NK cells stimulated with CLU showed increased formation of cell clusters and a CD69 activation receptor, representing a higher cellular activation status compared with those from the control group. Furthermore, these NK cells displayed elevated IFN-γ production upon RMA/S tumor target exposures, implying that CLU regulates not only NK cell expansion but also effector function of NK cells. Collectively, our data present a previously unrecognized function of CLU as a novel regulator of NK cells via providing costimulation required for cell proliferation and IFN-γ secretion. Therefore, the role of CLU on NK cells should be taken into consideration for the previously observed, diverse functions of CLU in chronic inflammatory and autoimmune conditions.

Nestin action during insulin-secreting cell differentiation.

Nestin, which was initially identified as a marker of neural stem cells, has been reported in regenerating pancreas as well as in early embryonic stem (ES) cell derivatives. However, little is known about its specific roles in stem cells as a functional regulator. We investigated the source of the action of nestin in ES and adult pancreatic ductal stem (PDS) cells in regard to the neogenesis of insulin-secreting beta-cells. In ES cells, suppression of nestin by gene silencing led to an increased expression of the pluripotency-associated genes, including Oct 4, Nanog, and SSEA-1, before embryoid body (EB) formation, whereas it reduced endodermal and pancreatic transcription factors in EBs. Inhibition of nestin expression in adult PDS cells caused a low expression of pancreatic transcription factors and islet hormones, leading to poor beta-cell development and insulin secretion. These data may indicate not only that nestin is a simple stem cell marker, but also that it constitutes a functional factor at the time of stem cell differentiation. We suggest that nestin plays pivotal roles as an intermediate regulator governing both stemness and differentiation of stem cells in the process of their differentiation into insulin-secreting cells.

Protective effect of clusterin on blood-retinal barrier breakdown in diabetic retinopathy.

Purpose. To investigate whether clusterin attenuates blood-retinal barrier (BRB) breakdown in diabetic retinopathy. Methods. Mice with streptozotocin-induced diabetes and advanced glycation end product-treated human retinal microvascular endothelial cells (HRMECs) were used to determine the effect of clusterin on vascular permeability and tight junction protein expression, through perfusion of retinal vessels with FITC-bovine serum albumin, a [(3)H]sucrose permeability assay, a cell viability assay, Western blot analysis, immunocytochemistry, immunohistochemistry, and terminal deoxynucleotidyl transferase biotin-dUTP nick-end labeling. Results. Up to 20 mug/mL of clusterin, which is 20 times the effective therapeutic concentration, did not affect the viability of the HRMECs. Moreover, it caused no toxicity in the retina. It effectively inhibited vascular endothelial growth factor-induced hyperpermeability in the HRMECs and the retinas. The antipermeability activity of clusterin was related to the restoration of tight junction proteins. Finally, it was shown to reduce leakage from the vessels in the diabetic retinas and to restore the expression of the tight junction proteins. Conclusions. The data suggest that clusterin, a well-known antipermeability factor naturally secreted by cells, may have therapeutic potential in the treatment of diabetic BRB breakdown.

Protective effect of clusterin from oxidative stress-induced apoptosis in human retinal pigment epithelial cells.

PURPOSE: Oxidative stress to retinal pigment epithelial (RPE) cells is thought to play a critical role in the pathogenesis of age-related macular degeneration (AMD). This study was conducted to investigate whether clusterin protects human RPE cells from ROS-induced apoptosis through a PI3K/Akt survival pathway. METHODS: The preventive effect of clusterin on reactive oxygen species (ROS) production and RPE cell death induced by hydrogen peroxide was determined in ARPE-19 cells. The ability of clusterin to protect RPE cells against ROS-mediated apoptosis was assessed by caspase-3 activity and DAPI staining. Furthermore, the protective effect of clusterin via the PI3K/Akt pathway was determined by Western blot analysis. RESULTS: Clusterin prevented ARPE-19 cells from H(2)O(2)-induced cell death and ROS production. H(2)O(2)-induced oxidative stress increased caspase-3 activity, which was significantly inhibited by clusterin, as determined by the abrogation of apoptotic bodies. Interestingly, clusterin induced Akt phosphorylation in human RPE cells under oxidative stress, which contributed to cell viability in ARPE-19 cells. This cell survival by clusterin was blocked by a PI3K inhibitor. CONCLUSIONS: Clusterin may play a protective role in responding to the local redox environment of human RPE cells, which contributes to the cell survival via the PI3K/Akt pathway. Therefore, clusterin could be considered for the preventive approach to AMD.

Protective role of clusterin/apolipoprotein J against neointimal hyperplasia via antiproliferative effect on vascular smooth muscle cells and cytoprotective effect on endothelial cells.

OBJECTIVE: Clusterin is induced in vascular smooth muscle cells (VSMCs) during atherosclerosis and injury-induced neointimal hyperplasia. However, its functional roles in VSMCs and endothelial cells remain controversial and elusive. This study was undertaken to clarify the role of clusterin in neointimal hyperplasia and elucidate its mechanism of action. METHODS AND RESULTS: Adenovirus-mediated overexpression of clusterin (Ad-Clu) repressed TNF-alpha-stimulated expression of MCP-1, fractalkine, ICAM-1, VCAM-1, and MMP-9, leading to inhibition of VSMC migration. Both Ad-Clu and secreted clusterin suppressed VSMC proliferation by inhibiting DNA synthesis, but not by inducing apoptosis. Ad-Clu upregulated p53 and p21(cip1/waf1) but downregulated cyclins D and E, leading to suppression of pRb phosphorylation and subsequent induction of G1 arrest in VSMCs. Clusterin deficiency augmented VSMC proliferation in vitro and accelerated neointimal hyperplasia in vivo, but concomitantly impaired reendothelialization in wire-injured murine femoral arteries. Moreover, Ad-Clu significantly reduced neointimal thickening in balloon-injured rat carotid arteries. Clusterin also diminished TNF-alpha-induced apoptosis of human umbilical vein endothelial cells and restored endothelial nitric oxide synthase expression suppressed by TNF-alpha. CONCLUSIONS: These results suggest that upregulation of clusterin during vascular injury may be a protective response against, rather than a causative response to, the development of neointimal hyperplasia.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces calcium influx through T-type calcium channel and enhances lysosomal exocytosis and insulin secretion in INS-1 cells.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has been associated with diabetes in several epidemiological studies. However, the diabetogenic action of TCDD on pancreatic cells is unclear. Here, we investigated the direct toxic effects of TCDD on a rat insulin-secreting beta cell line. We found that TCDD enhances exocytosis of MTT formazan and lysosomal proteins such as beta-hexosaminindase and Lamp-1. This TCDD-induced exocytosis was abrogated by T-type calcium channel blockers (mibefradil, flunarizine) but not by an aryl hydrocarbon receptor antagonist (alpha-naphtoflavone). Indeed, cytosolic calcium levels were increased by TCDD. Furthermore, TCDD stimulated insulin secretion, which was inhibited by flunarizine. Taken together, our results suggest that TCDD-induced calcium influx via T-type channels regulates vesicular trafficking, such as lysosomal and secretory granule exocytosis, and that TCDD might exert adverse effects on beta cells by continuous insulin release followed by beta cell exhaustion. This could contribute to the link between TCDD exposure and the risk of developing diabetes.