Secretory Clusterin Inhibits Dopamine Neuron Apoptosis in MPTP Mice by Preserving Autophagy Activity.

Secretory clusterin (sCLU) plays an important role in the research progress of nervous system diseases. However, the physiological function of sCLU in Parkinson's disease (PD) are unclear. The purpose of this study was to examine the effects of sCLU-mediated autophagy on cell survival and apoptosis inhibition in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD. We found that MPTP administration induced prolonged pole-climbing time, shortened traction time and rotarod time, significantly decreased TH protein expression in the SN tissue of mice. In contrast, sCLU -treated mice took less time to climb the pole and had an extended traction time and rotating rod time. Meanwhile, sCLU intervention induced increased expression of the TH protein in the SN of mice. These results indicated that sCLU intervention could reduce the loss of dopamine neurons in the SN area and alleviate dyskinesia in mice. Furthermore, MPTP led to suppressed viability, enhanced apoptosis, an increased Bax/Bcl-2 ratio, and cleaved caspase-3 in the SN of mice, and these effects were abrogated by sCLU intervention. In addition, MPTP increased the levels of P62 protein, decreased Beclin1 protein, decreased the ratio of LC3B-II/LC3B-I, and decreased the numbers of autophagosomes and autophagolysosomes in the SN tissues of mice. These effects were also abrogated by sCLU intervention. Activation of PI3K/AKT/mTOR signaling with MPTP inhibited autophagy in the SN of MPTP mice; however, sCLU treatment activated autophagy in MPTP-induced PD mice by inhibiting PI3K/AKT/mTOR signaling. These data indicated that sCLU treatment had a neuroprotective effect in an MPTP-induced model of PD.

Exploring the translational potential of clusterin as a biomarker of early osteoarthritis.

BACKGROUND: Clusterin (CLU; also known as apolipoprotein J) is an ATP-independent holdase chaperone that prevents proteotoxicity as a consequence of protein aggregation. It is a ∼60 kDa disulfide-linked heterodimeric protein involved in the clearance of cellular debris and the regulation of apoptosis. CLU has been proposed to protect cells from cytolysis by complement components and has been implicated in Alzheimer's disease due to its ability to bind amyloid-ß peptides and prevent aggregate formation in the brain. Recent studies suggest that CLU performs moonlighting functions. CLU exists in two major forms: an intracellular form and a secreted extracellular form. The intracellular form of CLU may suppress stress-induced apoptosis by forming complexes with misfolded proteins and facilitates their degradation. The secreted form of CLU functions as an extracellular chaperone that prevents protein aggregation. METHODS: In this review, we discuss the published literature on the biology of CLU in cartilage, chondrocytes, and other synovial joint tissues. We also review clinical studies that have examined the potential for using this protein as a biomarker in synovial and systemic fluids of patients with rheumatoid arthritis (RA) or osteoarthritis (OA). RESULTS: Since CLU functions as an extracellular chaperone, we propose that it may be involved in cytoprotective functions in osteoarticular tissues. The secreted form of CLU can be measured in synovial and systemic fluids and may have translational potential as a biomarker of early repair responses in OA. CONCLUSION: There is significant potential for investigating synovial and systemic CLU as biomarkers of OA. Future translational and clinical orthopaedic studies should carefully consider the diverse roles of this protein and its involvement in other comorbidities. Therefore, future biomarker studies should not correlate circulating CLU levels exclusively to the process of OA pathogenesis and progression. Special attention should be paid to CLU levels in synovial fluid. THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE: There is significant potential for investigating synovial and systemic CLU as a predictive biomarker of osteoarthritis (OA) progression and response to novel treatments and interventions. Given that CLU plays diverse roles in other comorbidities such as rheumatoid arthritis (RA) and obesity, future translational and clinical orthopaedic biomarker studies should not directly correlate circulating CLU levels to the process of OA pathogenesis and progression. However, special attention should be paid to CLU levels in synovial fluid. The cytoprotective properties of CLU may support the implementation of regenerative strategies and new approaches for developing targeted therapeutics for OA.

Secretory Clusterin: A Promising Target for Chemoresistance of Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related deaths worldwide. Chemoresistance remains the major factor for limited efficacy of the HCC treatment. Thus, exploring the mechanisms underlying drug resistance is of great importance. Secretory clusterin (sCLU), a stressactivated and ATP-independent molecular chaperone, is up-regulated in numerous tumors and correlated with malignant phenotypes. For HCC, the implication of sCLU was previously addressed in tumor growth, metastasis, as well as early diagnosis and poor prognosis. Notably, accumulating studies have emphasized its vital role in drug resistance of HCC. Depletion of sCLU synergistically could enhance the sensitivity of HCC cells to a variety of chemotherapy agents. Herein, we summarized the potential mechanisms accounting for the sCLU-induced chemoresistance, including promoting apoptosis evasion, facilitating epithelial-mesenchymal transition (EMT), maintaining the viability of cancer stem cell (CSC), enhancing drug efflux capacity, and regulating autophagic activities. The current evidence suggest that targeting sCLU might be a promising approach in overcoming chemoresistance of HCC.

Targeting Clusterin Induces Apoptosis, Reduces Growth Ability and Invasion and Mediates Sensitivity to Chemotherapy in Human Osteosarcoma Cells.

OBJECTIVE: The aim of the study was to investigate the expression of sCLU in relation to the clinicopathological features and prognosis of patients with untreated High-Grade Osteosarcoma (HGOS) and to evaluate sCLU as a target for osteosarcoma (OS) therapies. METHODS: The expression of sCLU in 98 patients of HGOS enrolled from April 2005 to March 2015 at the affiliated hospital of Qingdao University was evaluated by immunohistochemistry. The sCLU expression, clinical data and survival were compared. siRNA-mediated sCLU gene silencing on cell apoptosis, viability, invasion and chemosensitivity to doxorubicin in U2OS cells in vitro was evaluated. RESULTS: sCLU expression was found in 59 (60%) of the 98 patients. A positive correlation was observed between sCLU expression and metastatic disease (P = 0.036) and a negative correlation between sCLU expression and response to chemotherapy (P = 0.002). Targeting sCLU expression in U2OS cells induced significant reduction in cellular growth and higher rates of spontaneous endogenous apoptosis. In addition, targeting sCLU expression inhibited the invasion of U2OS cells. Furthermore, targeting sCLU expression significantly sensitized to chemotherapeutic drug, doxorubicin. CONCLUSION: The overexpression of sCLU was significantly correlated with metastasis and chemosensitivity in patients with HGOS. sCLU may be a promising therapeutic or chemopreventive target for human OS treatment.

Secretory Clusterin as a Novel Molecular-targeted Therapy for Inhibiting Hepatocellular Carcinoma Growth.

BACKGROUND: Although secretory clusterin (sCLU) plays a crucial role in Hepatocellular Carcinoma (HCC) cells proliferation, Multiple Drug Resistance (MDR), metastasis and so on, its targeted effects and exact mechanism are still unknown. This review summarizes some new progress in sCLU as a molecular-targeted therapy in the treatment of HCC. METHODS: A systematic review of the published English-language literature about sCLU and HCC has been performed using the PubMed and bibliographic databases. Some valuable studies on sCLU in HCC progression were searched for relevant articles with the keywords: HCC, diagnosis, MDR, as molecular-targeted in treatment, and so on. RESULTS: The incidence of the positive rate of sCLU was significantly higher in HCC tissues as compared to the surrounding tissues at mRNA or protein level, gradually increasing with tumor-nodemetastasis staging (P<0.05). Also, the abnormal level of sCLU was related to poor differentiation degree, and considered as a useful marker for HCC diagnosis or independent prognosis for patients. Hepatic sCLU could be silenced at mRNA level by specific sCLU-shRNA or by OGX-011 to inhibit cancer cell proliferation with an increase in apoptosis, cell cycle arrest, reversal MDR, alteration of cell migration or invasion behaviors, and a decrease in GSK-3ß or AKT phosphorylation in vitro, as well as significant suppression of the xenograft growth by down-regulating ß-catenin, p-GSK3ß, and cyclinD1 expression in vivo. CONCLUSION: Abnormal hepatic sCLU expression should not only be a new diagnostic biomarker but also a novel promising target for inhibiting HCC growth.

Role of secretory clusterin in hepatocarcinogenesis.

Secretory clusterin (sCLU) is a small stress-induced cytoprotective chaperone protein. Its biological functions are similar to those of a heat-shock protein. The sCLU plays a crucial role in cell proliferation, multiple drug resistance, metastasis, and tumor progression. Abnormal sCLU expression in tumor tissues or sera of patients with primary hepatic cancer has been considered a useful biomarker for diagnosis and surveillance. However, the exact relationship between sCLU overexpression and malignant transformation of hepatocytes is still unknown. The present review examines some novel advances of the knowledge about the oncogenic role of sCLU in hepatocarcinogenesis.

Secreted Clusterin protein inhibits osteoblast differentiation of bone marrow mesenchymal stem cells by suppressing ERK1/2 signaling pathway.

Secreted Clusterin (sCLU, also known as Apolipoprotein J) is an anti-apoptotic glycoprotein involved in the regulation of cell proliferation, lipid transport, extracellular tissue remodeling and apoptosis. sCLU is expressed and secreted by mouse bone marrow-derived skeletal (stromal or mesenchymal) stem cells (mBMSCs), but its functional role in MSC biology is not known. In this study, we demonstrated that Clusterin mRNA expression and protein secretion in conditioned medium increased during adipocyte differentiation and decreased during osteoblast differentiation of mBMSCs. Treatment of mBMSC cultures with recombinant sCLU protein increased cell proliferation and exerted an inhibitory effect on the osteoblast differentiation while stimulated adipocyte differentiation in a dose-dependent manner. siRNA-mediated silencing of Clu expression in mBMSCs reduced adipocyte differentiation and stimulated osteoblast differentiation of mBMSCs. Furthermore, the inhibitory effect of sCLU on the osteoblast differentiation of mBMSCs was mediated by the suppression of extracellular signal-regulated kinase (ERK1/2) phosphorylation. In conclusion, we identified sCLU as a regulator of mBMSCs lineage commitment to osteoblasts versus adipocytes through a mechanism mediated by ERK1/2 signaling. Inhibiting sCLU is a possible therapeutic approach for enhancing osteoblast differentiation and consequently bone formation.

Tuning NF-κB activity: a touch of COMMD proteins.

NF-κB is an important regulator of immunity and inflammation, and its activation pathway has been studied extensively. The mechanisms that downregulate the activity of NF-κB have also received a lot of attention, particularly since its activity needs to be terminated to prevent chronic inflammation and subsequent tissue damage. The COMMD family has been identified as a new group of proteins involved in NF-κB termination. All ten COMMD members share the structurally conserved carboxy-terminal motif, the COMM domain, and are ubiquitously expressed. They seem to play distinct and non-redundant roles in various physiological processes, including NF-κB signaling. In this review, we describe the mechanisms and proteins involved in the termination of canonical NF-κB signaling, with a specific focus on the role of the COMMD family in the down-modulation of NF-κB.

The role of clusterin on pancreatic beta cell regeneration after exendin-4 treatment in neonatal streptozotocin administrated rats.

We investigated the effects of exendin-4 (Ex4) treatment on expression of clusterin and ß cell regeneration in the endocrine pancreas in neonatal streptozotocin (nSTZ) diabetic rats. Three groups were used: (1) n2-STZ group; on the second day after birth 100mg/kg STZ was given i.p. to two groups of newborn rats, (2) n2-STZ+Ex4 group; 3µg/kg/day Ex4 was given for 5 days starting on the third day, and (3) control group. In situ hybridization for mRNAs of insulin and clusterin, double immunostaining for insulin/clusterin and insulin/BrdU were carried out. Immunostaining for insulin, glucagon, somatostatin, clusterin, synaptophysin and pdx-1 was performed. In the n2-STZ+Ex4 group, BrdU/insulin and insulin/clusterin immunopositive cells were significantly increased in the islets of Langerhans in comparison to the other groups. The areas occupied by the insulin mRNA and peptide positive cells and also pdx-1 immunopositive cells were decreased in the n2-STZ diabetic group compared with the other groups. The clusterin mRNA and protein positive cells, and also the glucagon and somatostatin cells, were significantly increased in the islets of the n2-STZ and the n2-STZ+Ex4 groups compared with the control group. The results show that Ex4 treatment induces new beta cell clusters via up-regulation of clusterin, which might be effective on beta-cell proliferation and neogenesis.