Intronless Pabpc6 encodes a testis-specific, cytoplasmic poly(A)-binding protein but is dispensable for spermatogenesis in the mouse†.

Besides ubiquitous poly(A)-binding protein, cytoplasmic 1 (PABPC1), testis-specific PABPC2/PABPt (in humans, referred to as PABPC3), and female and male germline-specific PABPC1L/ePAB, have been reported in the mouse testis. Recent in silico analysis additionally identified testis-specific Pabpc6 in the mouse. In this study, we characterized PABPC6 and its mutant mice. PABPC6 was initially detectable in the cytoplasm of pachytene spermatocytes, increased in abundance in round spermatids, and decreased in elongating spermatids. PABPC6 was capable of binding to poly(A) tails of various mRNAs and interacting with translation-associated factors, including EIF4G, PAIP1, and PAIP2. Noteworthy was that PABPC6, unlike PABPC1, was barely associated with translationally active polysomes and enriched in chromatoid bodies of round spermatids. Despite these unique characteristics, neither synthesis of testicular proteins nor spermatogenesis was affected in the mutant mice lacking PABPC6, suggesting that PABPC6 is functionally redundant with other co-existing PABPC proteins during spermatogenesis.

Novel cell line development strategy for monoclonal antibody manufacturing using translational enhancing technology.

Chinese hamster ovary (CHO) cells are widely used for constructing expression systems to produce therapeutic proteins. However, the establishment of high-producer clones remains a laborious and time-consuming process, despite various progresses having been made in cell line development. We previously developed a new strategy for screening high monoclonal antibody (mAb)-producing cells using flow cytometry (FCM). We also reported that p180 and SF3b4 play key roles in active translation on the endoplasmic reticulum, and that the productivity of secreted alkaline phosphatase was enhanced by the overexpression of p180 and SF3b4. Here, we attempted to apply the translational enhancing technology to high mAb-producing cells obtained after high-producer cell sorting. A high mAb-producing CHO clone, L003, which showed an mAb production level of >3 g/L in fed-batch culture, was established from a high mAb-producing cell pool fractionated by FCM. Clones generated by the overexpression of p180 and SF3b4 in L003 cells were evaluated by fed-batch culture. The specific productivity of clones overexpressing these two factors was ∼3.1-fold higher than that of parental L003 cells in the early phase of the culture period. Furthermore, the final mAb concentration was increased to 9.5 g/L during 17 days of fed-batch culture after optimizing the medium and culture process. These results indicate that the overexpression of p180 and SF3b4 would be promising for establishing high-producer cell lines applicable to industrial production.

Silibinin ameliorates STZ-induced impairment of memory and learning by up- regulating insulin signaling pathway and attenuating apoptosis.

Alzheimer's disease (AD) is a neurodegenerative disease, mainly characterized by cognitive dysfunction and memory impairment. Due to its pathological similarities to type 2 diabetes mellitus (T2DM), such as ß-amyloid deposition, oxidative stress, inflammation, disordered glucose metabolism, impaired signaling pathways of insulin and insulin-like growth factor-1 (IGF-1), we speculate that AD is another form of brain diabetes. Clarifying the relationship between T2DM and AD is important for us to better understand the exact pathological mechanisms of AD. Silibinin, a polyphenolic flavonoid extracted from the seeds of Silybum marianum, exerts hepatoprotective, anti- diabetic and neuroprotective effects. Streptozotocin (STZ), which is used to disrupt the insulin signal transduction pathway, could well mimic the sporadic AD models by intracerebroventricular (ICV) injection. Therefore, we selected ICV injection of STZ (ICV-STZ) to investigate the neuroprotective effects of silibinin in rats and to make a foundation for further exploring the relationship between AD and T2DM. ICV-STZ obviously caused memory damage, sharply reduced the number of nissl bodies and destroyed morphological structure of hippocampal neuronal cells, while silibinin attenuated the damages. Moreover, silibinin significantly decreased STZ-induced tau hyperphosphorylation (ser404) in hippocampus and cerebral cortex, markedly inhibited apoptosis of neurons induced by STZ, and up-regulated insulin signal transduction pathway. Silibinin exerts neuroprotective effect in STZ-treated rats, indicating the potential of silibinin for the treatment of AD patients with T2DM in future.

Silibinin protects rat pancreatic ß-cell through up-regulation of estrogen receptors' signaling against amylin- or Aß1-42 -induced reactive oxygen species/reactive nitrogen species generation.

Amylin and amyloid-ß (Aß) were found to induce reactive oxygen species (ROS) and reactive nitrogen species (RNS) in rat pancreatic ß-cell line, INS-1 cells, leading to cell death. In this study, we report on reciprocal relationship between the expression of estrogen receptors (ERs) α and ß (ERα and ERß) and generation of ROS/RNS in amylin/Aß1-42 -treated INS-1 cells. That is, pharmacological activation of ERs in INS-1 cells significantly decreases ROS/RNS generation, but blockage of ERs increases ROS/RNS generation. Silibinin is a natural polyphenolic flavonoid isolated from milk thistle with phytoestrogen activities, also known as silybin. Treatment with silibinin down-regulated ROS/RNS production induced by treatment with amylin/Aß1-42 in the cells. Silencing ERs expression with siRNAs targeting ERs showed that the protective effect of silibinin was markedly weakened, indicating that silibinin protection is largely attributed to activation of ERs' signaling. The binding of silibinin to ERs implies that the protective effect of silibinin on amylin/Aß1-42 -treated INS-1 cells owes to down-regulation of ROS/RNS through the activation of ERs phosphorylation. Amylin and Aß1-42 cotreatment enhanced furthermore ROS/RNS generation and cytotoxicity through further down-regulation of ERs phosphorylation, and this was reversed by silibinin. Silibinin also protects INS-1 cells from amylin and Aß1-42 cotreatment. These results indicate that protective effect of silibinin is mediated by enhancement of ERs phosphorylation that depresses ROS/RNS generation in amylin/Aß1-42 -treated INS-1 cells.

Silibinin ameliorates amylin-induced pancreatic ß-cell apoptosis partly via upregulation of GLP-1R/PKA pathway.

The objective was to investigate the mechanism of the protective effect of silibinin on amylin/Aß1-42-induced INS-1 cell apoptosis, with special reference to the roles of glucagon-like peptide-1 receptor (GLP-1R) and protein kinase A (PKA). The effects of silibinin on apoptosis, insulin secretion, GLP-1R, and PKA expression in the INS-1 cells treated with amylin/Aß1-42 were examined. INS-1 cells exposed to amylin showed increased TUNEL-positive ratio, reduced expression of GLP-1R and PKA. GLP-1R antagonists or PKA inhibitor enhanced the expression of apoptosis-associated proteins and TUNEL-positive ratio. Silibinin exerted antiapoptotic effect on and upregulation of GLP-1R and PKA. However, Aß1-42-induced INS-1 cell apoptosis, GLP-1R, and PKA expressions were not changed. Our results indicate that down-regulation of GLP-1R and PKA contributes to INS-1 cell apoptosis induced with amylin. Silibinin protects INS-1 cells from amylin-induced apoptosis through activation of GLP-1R/PKA signaling. Silibinin's inhibition of the toxic effects of Aß1-42 is independent of GLP-1R/PKA pathway.

Estrogen Receptors Are Involved in the Neuroprotective Effect of Silibinin in Aß1-42-Treated Rats.

Alzheimer's disease (AD) is a progressive neurodegenerative disease that is characterized by a cascade of pathologic changes. A widely discussed theory indicates that amyloid ß (Aß) peptides are the causative agents of AD. Silibinin, a flavonoid derived from milk thistle, is well known for its hepato-protective activities and we have reported the neuroprotective effects of silibinin. In this study, we investigated the role of estrogen receptors (ERs) in silibinin's neuroprotective effect on Aß1-42-injected rats. Results of Morris water maze and novel object-recognition tests demonstrated that silibinin significantly attenuated Aß1-42-induced memory impairment. Silibinin attenuated ERs and PI3K-Akt pathways, as well as modulated mitogen-activated protein kinases in the hippocampus of Aß1-42-injected rats. Taken together, silibinin is a potential candidate in the treatment of Alzheimer's disease.

Silibinin ameliorates anxiety/depression-like behaviors in amyloid ß-treated rats by upregulating BDNF/TrkB pathway and attenuating autophagy in hippocampus.

Depression is one of the most frequent psychiatric disorders of Alzheimer's disease (AD). Depression and anxiety are associated with increased risk of developing AD. Silibinin, a flavonoid derived from milk thistle (Silybum marianum), has been used as a hepato-protectant in the clinical treatment of liver diseases. In this study, the effect of silibinin on Aß-induced anxiety/depression-like behaviors in rats was investigated. Silibinin significantly attenuated anxiety/depression-like behaviors caused by Aß1-42-treatment as shown in tail suspension test (TST), elevated plus maze (EPM) and forced swimming tests (FST). Moreover, silibinin was able to attenuate the neuronal damage in the hippocampus of Aß1-42-injected rats. Silibinin-treatment up-regulated the function through BDNF/TrkB pathway and attenuated autophagy in the hippocampus. Our study provides a new insight into the protective effects of silibinin in the treatment of anxiety/depression.

Selective propagation of mouse-passaged scrapie prions with long incubation period from a mixed prion population using GT1-7 cells.

In our previous study, we demonstrated the propagation of mouse-passaged scrapie isolates with long incubation periods (L-type) derived from natural Japanese sheep scrapie cases in murine hypothalamic GT1-7 cells, along with disease-associated prion protein (PrPSc) accumulation. We here analyzed the susceptibility of GT1-7 cells to scrapie prions by exposure to infected mouse brains at different passages, following interspecies transmission. Wild-type mice challenged with a natural sheep scrapie case (Kanagawa) exhibited heterogeneity of transmitted scrapie prions in early passages, and this mixed population converged upon one with a short incubation period (S-type) following subsequent passages. However, when GT1-7 cells were challenged with these heterologous samples, L-type prions became dominant. This study demonstrated that the susceptibility of GT1-7 cells to L-type prions was at least 105 times higher than that to S-type prions and that L-type prion-specific biological characteristics remained unchanged after serial passages in GT1-7 cells. This suggests that a GT1-7 cell culture model would be more useful for the economical and stable amplification of L-type prions at the laboratory level. Furthermore, this cell culture model might be used to selectively propagate L-type scrapie prions from a mixed prion population.

Silibinin ameliorates Aß25-35-induced memory deficits in rats by modulating autophagy and attenuating neuroinflammation as well as oxidative stress.

Alzheimer's disease (AD) is a progressive, neurodegenerative disease. Accumulating evidence suggests that inflammatory response, oxidative stress and autophagy are involved in amyloid ß (Aß)-induced memory deficits. Silibinin (silybin), a flavonoid derived from the herb milk thistle, is well known for its hepatoprotective activities. In this study, we investigated the neuroprotective effect of silibinin on Aß25-35-injected rats. Results demonstrated that silibinin significantly attenuated Aß25-35-induced memory deficits in Morris water maze and novel object-recognition tests. Silibinin exerted anxiolytic effect in Aß25-35-injected rats as determined in elevated plus maze test. Silibinin attenuated the inflammatory responses, increased glutathione (GSH) levels and decreased malondialdehyde (MDA) levels, and upregulated autophagy levels in the Aß25-35-injected rats. In conclusion, silibinin is a potential candidate for AD treatment because of its anti-inflammatory, antioxidant and autophagy regulating activities.

Heterogeneity of abnormal prion protein (PrP(Sc)) in murine scrapie prions determined by PrP(Sc)-specific monoclonal antibodies.

In prion diseases, abnormal prion protein (PrP(Sc)) is considered as the main component of the infectious agent. Delineation of PrP(Sc) conformation is expected to be a critical factor in understanding properties of prions. However, practical methods to differentiate between conformers of PrP(Sc) are inadequate. Here, we used two PrP(Sc)-specific monoclonal antibodies (mAbs), 3B7 and 3H6, and found that mAb 3H6 detected a limited portion of PrP(Sc) in five mice-adapted prion strains. The quantity of mAb 3H6-precipitated PrP(Sc) was significantly lesser in 22L compared to other strains. This result provides a direct evidence of the conformational heterogeneity of PrP(Sc) within the prion strains. Conformation-specific probes, like these mAbs, have the potential to be powerful tools for investigating conformational variations in PrP(Sc).

Different antigenicities of the N-terminal region of cellular and scrapie prion proteins.

Limited information is available about conformational differences between the abnormal isoform of prion protein (PrP(Sc) ) and cellular prion protein (PrP(C) ) under native conditions. To clarify conformational differences between these two isoforms, PrP-deficient mice were immunized with brain homogenates of normal and scrapie-infected animals. All mice generated anti-PrP antibodies. Peptide array analysis of these serum samples revealed a distinctive epitope of PrP(Sc) consisting of QGSPGGN (PrP41-47) at the N-terminus. This study demonstrated a conformational dissimilarity at the N-terminus between PrP(Sc) and PrP(C) , a finding that may provide novel information about conformational features of PrP(Sc) .

Sensitivity and specificity of a commercial BSE kit for the detection of ovine scrapie.

To examine the sensitivity of a commercially available bovine spongiform encephalopathy (BSE) kit (NippIBL) for the detection of ovine scrapie, 50 scrapie-positive ovine samples from the UK, and 54 scrapie-negative ovine samples from Japan were obtain and tested using this kit. The sensitivity and specificity of NippIBL for ovine samples were 96% and 100%, respectively. The detection limit of the abnormal isoform of prion protein (PrP(Sc) ) of NippIBL was examined using diluted scrapie-positive samples. The sensitivity of NippIBL to ovine scrapie was 3-10 times superior to that of another commercial BSE diagnosis kit. Thus, the NippIBL kit proved more effective for the detection of ovine scrapie.

Tracing conformational transition of abnormal prion proteins during interspecies transmission by using novel antibodies.

Conformational differences in abnormal prion proteins (PrP(Sc)) have been postulated to produce different prion phenotypes. During the interspecies transmission of prions, the conformation of PrP(Sc) may change with passage; however, little is known about the mechanism of PrP(Sc) transition. In this study, novel PrP(Sc)-specific monoclonal antibodies (mAbs) were developed that could detect the PrP(Sc) of mouse but not that of sheep. By using these mAbs, we attempted to examine PrP(Sc) accumulated in mice inoculated with sheep scrapie serially up to five passages. The presence of PrP(Sc) in the mice was confirmed at all passages; however, mAb-bound PrP(Sc) conformer was detected only from the third passage onward. The generated mAb enabled tracing of a particular conformer during adaptation in sheep-to-mice transmission of prion, suggesting that the conformational transition of PrP(Sc) was caused by propagation of this conformer. Such mAbs capable of discriminating conformational differences may allow us to address questions concerning PrP(Sc) conformation and strain diversity.

Lactoferrin induces cell surface retention of prion protein and inhibits prion accumulation.

Prion diseases are fatal neurodegenerative disorders, and the conformational conversion of normal cellular prion protein (PrP(C)) into its pathogenic, amyloidogenic isoform (PrP(Sc)) is the essential event in the pathogenesis of these diseases. Lactoferrin (LF) is a cationic iron-binding glycoprotein belonging to the transferrin (TF) family, which accumulates in the amyloid deposits in the brain in neurodegenerative disorders, such as Alzheimer's disease and Pick's disease. In the present study, we have examined the effects of LF on PrP(Sc) formation by using cell culture models. Bovine LF inhibited PrP(Sc) accumulation in scrapie-infected cells in a time- and dose-dependent manner, whereas TF was not inhibitory. Bioassays of LF-treated cells demonstrated prolonged incubation periods compared with non-treated cells indicating a reduction of prion infectivity. LF mediated the cell surface retention of PrP(C) by diminishing its internalization and was capable of interacting with PrP(C) in addition to PrP(Sc). Furthermore, LF partially inhibited the formation of protease-resistant PrP as determined by the protein misfolding cyclic amplification assay. Our results suggest that LF has multifunctional antiprion activities.

Microglial cell line established from prion protein-overexpressing mice is susceptible to various murine prion strains.

Several lines of evidence suggest that microglia have important roles in the pathogenesis of prion diseases. Here, we establish a novel microglial cell line (MG20) from neonatal tga20 mice that overexpress murine prion protein. After exposure to Chandler scrapie, we observed the replication and accumulation of disease-associated forms of the prion protein in MG20 cells up to the 15th passage. Furthermore, MG20 cells were susceptible to ME7, Obihiro scrapie, and bovine spongiform encephalopathy agents. Thus, MG20 cell lines persistently infected with various murine prion strains provide a useful model for the study of the pathogenesis of prion diseases.