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Abstract: γ-Aminobutyric acid (GABA) is a major inhibitory neurotransmitter and also presumed to be a neurotrophic factor. GABA is synthesized by glutamate decarboxylase (GAD). A mouse lacking a 67kDa isoform of GAD (GAD67) has a reduced GABA level in its brain at birth and does not survive postnatally because of cleft palate. In this study, to investigate the functional and developmental roles of GABA in the postnatal cerebellum, selective GAD67 deletion was achieved using a Cre-loxP strategy. In this mouse, GABA level was reduced to 16–44% in the cerebellum but not in the cerebrum. Inhibitory synaptic transmission to Purkinje cells was seriously impaired. However, the morphology of Purkinje cells and the density of synaptic terminals in the cerebellar cortex appeared unaffected, suggesting that GABA does not participate in cerebellar development substantially. [Copyright &y& Elsevier]

Abstract: Splenocytes of wild-type (Prnp +/+) and prion protein gene-deficient (Prnp −/−) mice were treated with various activation stimuli such as T cell mitogen concanavalin A (ConA), phorbol 12-myristate 13-acetate (PMA)+ionomycin (Io), or B cell mitogen lipopolysaccharide (LPS). Cellular prion protein (PrPC) expression was enhanced following ConA stimulation, but not PMA+Io or LPS in Prnp +/+ splenocytes. Rikn Prnp −/− splenocytes elicited lower cell proliferations than Prnp +/+ or Zrch I Prnp −/− splenocytes after LPS stimulation and showed sporadic nerve cells in the cerebral cortex and deeper structure. Around the degenerated nerve cells, mild vacuolation in the neuropil was observed. This neural alteration correlated well to the suppressed response of B cells in the spleen. The finding that discrete lesions within the central nervous systems induced marked modulation of immune function probably indicates the existence of a delicately balanced neural-endocrine network by PrPC and PrPLP/Doppel. [Copyright &y& Elsevier]

Abstract: The Prnd-encoded prion protein (PrP)-like protein, Doppel (Dpl), is a homologue of Prnp-encoded PrP, and is N-glycosylated protein with glycosylphosphatidylinositol anchor like PrP. Recently, ectopic expressions of Prnp/Prnd chimeric mRNAs have been identified as the cause of late-onset ataxia observed in several lines of Prnp-knockout mice such as ZrchII, Ngsk, Rcm0, and Rikn mice. However, it remains unclear whether the toxic effect of Dpl expression is a cell-autonomous mechanism but rather reflect a systemic process of heterogeneous cell population in the brain. In this study, the cell-autonomous role of Dpl was estimated by investigating PrP-deficient cells (HpL3-4)—the SV40 large T-antigen immortalized and Rikn Prnp −/− mice-derived neuronal cell line expressing Prnp/Prnd chimeric mRNAs. The reverse transcription polymerase chain reaction revealed that serum deprivation did not increase Prnp/Prnd chimeric mRNAs, which in fact was translated into a small amount of Dpl in HpL3-4 cells, whereas serum deprivation induced apoptotic cell death of HpL3-4 cells. Dpl overexpression enhanced apoptotic cell death, whereas the toxic effect of Dpl on apoptotic cell death was neutralized by PrP expression. These results indicate that Dpl elicited dose-dependently toxic effects on PrP-deficient cells without affecting on PrP-expressing cells, suggesting that the PrP–Dpl interaction can regulate cell death in a cell-autonomous manner. [Copyright &y& Elsevier]

Abstract: Cellular prion protein (PrPC) plays anti-apoptotic and anti-oxidative roles in apoptosis induced by serum deprivation in an immortalized prion protein gene (Prnp)-deficient neuronal cell line. The octapeptide repeat region (OR) and N-terminal half of the hydrophobic region (HR) of PrPC are indispensable for PrPC activity, but the mechanisms remain unclear. In the present study, elucidation of the mechanisms by which PrPC elicits the anti-oxidative activities was facilitated by evidence of stress-inducible protein 1 (STI1) mediating PrPC-dependent superoxide dismutase (SOD) activation. Immunoprecipitation revealed that PrPC was associated with STI1. The inhibitory peptides against PrPC–STI1 binding [STI1 pep.1 and PrP(113–132)] indicated toxic activity in PrPC-expressing cells by inhibiting SOD activity but not in Prnp−/− cells. Furthermore, OR and N-terminal half of the HR were required for the inhibitory effect of PrP(113–132) but not STI1 pep.1. These data are consistent with results established with a model where OR and N-terminal half of the HR mediate the action of STI1 upon cell survival and upregulation of SOD activity. [Copyright &y& Elsevier]

Abstract: Cellular prion protein PrPC contains two evolutionarily conserved domains among mammals; viz., the octapeptide repeat region (OR; amino acid residue 51–90) and the hydrophobic region (HR; amino acid residue 112–145). Accumulating evidence indicates that PrPC acts as an inhibitor of apoptosis and regulator of superoxide dismutase (SOD) activity. To further understand how PrPC activates SOD and prevents apoptosis, we provide evidence here that OR and N-terminal half of HR mediate PrPC-dependent SOD activation and anti-apoptotic function. Removal of the OR (amino acid residue 53–94) enhances apoptosis and decreases SOD activity. Deletion of the N-terminal half of HR (amino acids residue 95–132) abolishes its ability to activate SOD and to prevent apoptosis, whereas that of the C-terminal half of HR (amino acids residue 124–146) has little if any effect on the anti-apoptotic activity and SOD activation. These data are consistent with a model in which the anti-apoptotic and anti-oxidative function of PrPC is regulated by not only OR but also the N-terminal half of HR. [Copyright &y& Elsevier]

The function of cellular prion protein (PrPC), which is a copper binding protein, remains unclear. To elucidate the mechanisms in which PrPC is involved in neuroprotection, we compared death signals in prion protein gene-deficient (Prnp−/−) primary cerebellar granular neurons (CGNs) to those with wild-type (WT) CGNs. When copper was exposed to these CGNs, ZrchI, and Rikn Prnp−/− CGNs were more sensitized and underwent apoptotic cell death more readily than WT CGNs. Furthermore, the level of intracellular hydrogen peroxide (H2O2) in WT CGNs increased by copper toxicity, whereas those in ZrchI and Rikn Prnp−/− CGNs did not. These results suggest that PrPC modulates the intracellular H2O2 level as a copper-binding protein to protect CGNs from apoptotic cell death possibly due to inhibiting a Fenton reaction. [Copyright &y& Elsevier]

Prion protein (PrP) binds copper and exhibits superoxide dismutase-like activity, while the roles of PrP in copper homeostasis remain controversial. Using Zeeman graphite furnace atomic absorption spectroscopy, we quantified copper levels in immortalized PrP gene (Prnp)-deficient neuronal cells transfected with Prnp and/or Prnd, which encodes PrP-like protein (PrPLP/Dpl), in the presence or absence of oxidative stress induced by serum deprivation. In the presence of serum, copper levels were not significantly affected by the expression of PrP and/or PrPLP/Dpl, whereas serum deprivation induced a decrease in copper levels that was inhibited by PrP but not by PrPLP/Dpl. The inhibitory effect of PrP on the decrease of copper levels was prevented by overexpression of PrPLP/Dpl. These findings indicate that PrP specifically stabilizes copper homeostasis, which is perturbed under oxidative conditions, while PrPLP/Dpl overexpression prevents PrP function in copper homeostasis, suggesting an interaction of PrP and PrPLP/Dpl and distinct functions between PrP and PrPLP/Dpl on metal homeostasis. Taken together, these results strongly suggest that PrP, in addition to its antioxidant properties, plays a role in stabilizing cellular copper homeostasis under oxidative conditions. [Copyright &y& Elsevier]

Prion protein gene (Prnp)-deficient(Prnp−/−) neuronal cells are more susceptible to serum deprivation compared to Prnp+/+ neuronal cells. However, little is known about the cell death of Prnp−/− neuronal cells under serum deprivation. In this study, as a known neuroprotective agent we analyzed the effect of tumor necrosis factor-α (TNF-α) on the cell death of Prnp−/− neuronal cells. Although expression of Bcl-2 and Bcl-xL decreased in a time-dependent manner under serum deprivation, treatment with TNF-α protected Prnp−/− neuronal cells from serum deprivation with an increase in anti-apoptotic proteins Bcl-2 and Bcl-xL. Nuclear morphological analysis using fluorescence microscopy and flow cytometry analysis showed that gene transfer of bcl-2 or bcl-xL significantly inhibited apoptosis induced by serum deprivation. These findings indicate that TNF-α attenuated cell death of Prnp−/− neuronal cells by induction of Bcl-2 and Bcl-xL,and that decreases in Bcl-2 and Bcl-xL played crucial roles in the apoptosis of Prnp−/− neuronal cells. [Copyright &y& Elsevier]

Previous studies have reported a neuroprotective role for cellular prion protein (PrPC) against apoptosis induced by serum deprivation in an immortalized prion protein gene (Prnp)-deficient neuronal cell line, but the mechanisms remain unclear. In this study, to investigate the mechanisms by which PrPC prevents apoptosis, the authors compared apoptosis of Prnp−/− cells with that of Prnp−/− cells expressing the wild-type PrPC or PrPC lacking N-terminal octapeptide repeat region under serum-free conditions. Re-introduction of Prnp rescued cells from apoptosis, upregulated superoxide dismutase (SOD) activity, enhanced superoxide anion elimination, and inhibited caspase-3/9 activation. On the other hand, N-terminally truncated PrPC enhanced apoptosis accompanied by potentiation of superoxide production and caspase-3/9 activation due to inhibition of SOD. These results suggest that PrPC protects Prnp−/− cells from apoptosis via superoxide- and caspase-3/9-dependent pathways by upregulating SOD activity. Furthermore, the octapeptide repeat region of PrPC plays an essential role in regulating apoptosis and SOD activity. [Copyright &y& Elsevier]

The purpose of this report was to determine the effect of prion protein (PrP) gene disruption on T lymphocyte function. Previous studies have suggested that normal cellular prion protein (PrPc) binds to copper and Cu2+ is essential for interleukin-2 (IL-2) mRNA synthesis. In this study, IL-2 mRNA levels in a copper-deficient condition were investigated using T lymphocytes from prion protein gene-deficient (PrP0/0) and wild-type mice. Results showed that Cu2+ deficiency had no effect on PrPc expression in Con A-activated splenocytes. However, a delay in IL-2 gene expression was observed in PrP0/0 mouse T lymphocyte cultures using Con A and Cu2+–chelator. These results suggest that PrPc expression may play an important role in rapid Cu2+ transfer in T lymphocytes. The rapid transfer of Cu2+ in murine T lymphocytes could be one of the normal functions of PrPc. [Copyright &y& Elsevier]

A variety of secreted and membrane proteins play key roles in the formation of neuronal circuits in the central nervous system. Using the signal sequence trap method, we isolated and characterized a novel gene, Btcl1 (brain-specific transmembrane protein containing two CUB and an LDLa domains). BTCL1 has significant homology with neuropilin-1 and -2 in their CUB domains. Domain structure of BTCL1 indicates that BTCL1 belongs to a new class of brain-specific CUB domain-containing protein. On Northern blot analysis, Btcl1 mRNA was observed as a single transcript of 3.7 kb specifically in the brain. In situ hybridization analysis revealed that Btcl1 mRNA was highly expressed in the hippocampal CA3 region, olfactory bulb, and neocortex in the adult brain. Expression pattern of mRNA and structural similarity with neuropilin suggest that BTCL1 plays a role in the development and/or maintenance of neuronal circuitry. [Copyright &y& Elsevier]