Cbln1 is essential for synaptic integrity and plasticity in the cerebellum

Cbln1 is a cerebellum-specific protein of previously unknown function that is structurally related to the C1q and tumor necrosis factor families of proteins. We show that Cbln1 is a glycoprotein secreted from cerebellar granule cells that is essential for three processes in cerebellar Purkinje cells: the matching and maintenance of pre- and postsynaptic elements at parallel fiber-Purkinje cell synapses, the establishment of the proper pattern of climbing fiber-Purkinje cell innervation, and induction of long-term depression at parallel fiber-Purkinje cell synapses. Notably, the phenotype of cbln1-null mice mimics loss-of-function mutations in the orphan glutamate receptor, GluR delta2, a gene selectively expressed in Purkinje neurons. Therefore, Cbln1 secreted from presynaptic granule cells may be a component of a transneuronal signaling pathway that controls synaptic structure and plasticity.

The structure and proteolytic processing of Cbln1 complexes

The hexadecapeptide cerebellin is present in the brains of many vertebrate species and is derived from a larger protein, Cbln1 (cerebellin 1 precursor protein). Although cerebellin has features of a neuropeptide, Cbln1 belongs to the C1q/tumor necrosis factor superfamily of secreted proteins, suggesting that it is the biologically active molecule and the proteolytic events that generate cerebellin serve another function. Therefore, we assessed whether Cbln1 undergoes proteolytic processing and determined what consequences the cleavage events necessary to produce cerebellin have on the structure of Cbln1. Substantial degradation of Cbln1 was evident in the synaptic compartment of cerebellum and lysates of cultured cerebellar neurons and cells transfected with Cbln1 expression vectors. However, only uncleaved Cbln1 containing the cerebellin motif was released and assembled into hexameric complexes. Using yeast two hybrid and mammalian expression systems we show that the cleavages required to produce cerebellin influence the subunit stoichiometry of Cbln1 complexes. Cleavage at the N-terminus of the cerebellin sequence in Cbln1 yields trimeric complexes by separating the trimer-mediating C-terminal C1q domain from conserved N-terminal cysteine residues that mediate higher order oligomerization. Cleavage at the C-terminus of the cerebellin motif disrupts the C1q domain and abolishes subunit interactions. Functional implications of these data are discussed.

Selective O2 oxidation of air-sensitive lanthanocene thiolates and thioether chelate

Two unusual regioselective O2 oxidation reactions of air-sensitive lanthanocene thiolates and a thioether chelate are described, revealing a novel oxygenation pattern of thiolate ligands.

Influence of cytosolic and mitochondrial Ca2+, ATP, mitochondrial membrane potential, and calpain activity on the mechanism of neuron death induced by 3-nitropropionic acid

3-Nitropropionic acid (3NP), an irreversible inhibitor of succinate dehydrogenase, induces both rapid necrotic and slow apoptotic death in rat hippocampal neurons. Low levels of extracellular glutamate (10 microM) shift the 3NP-induced cell death mechanism to necrosis, while NMDA receptor blockade results in predominantly apoptotic death. In this study, we examined the 3NP-induced alterations in free cytosolic and mitochondrial calcium levels, ATP levels, mitochondrial membrane potential, and calpain and caspase activity, under conditions resulting in the activation of apoptotic and necrotic pathways. In the presence of 10 microM glutamate, 3NP administration resulted in a massive elevation in [Ca(2+)](c) and [Ca(2+)](m), decreased ATP, rapid mitochondrial membrane depolarization, and a rapid activation of calpain but not caspase activity. In the presence of the NMDA receptor antagonist MK-801, 3NP did not induce a significant elevation of [Ca(2+)](c) within the 24h time period examined, nor increase [Ca(2+)](m) within 1h. ATP was maintained at control levels during the first hour of treatment, but declined 64% by 16h. Calpain and caspase activity were first evident at 24h following 3NP administration. 3NP treatment alone resulted in a more rapid decline in ATP, more rapid calpain activation (within 8h), and elevated [Ca(2+)](m) as compared to the results obtained with added MK-801. Together, the results demonstrate that 3NP-induced necrotic neuron death is associated with a massive calcium influx through NMDA receptors, resulting in mitochondrial depolarization and calpain activation; while 3NP-induced apoptotic neuron death is not associated with significant elevations in [Ca(2+)](c), nor with early changes in [Ca(2+)](m), mitochondrial membrane potential, ATP levels, or calpain activity.

Calpain facilitates the neuron death induced by 3-nitropropionic acid and contributes to the necrotic morphology

3-Nitropropionic acid (3NP), an irreversible inhibitor of succinate dehydrogenase, has been used to model features of neurodegenerative disorders including Huntington disease, as well as acute neuronal insults such as cerebral ischemia. 3NP induces rapid necrosis and delayed apoptosis in primary cultures of rat hippocampal neurons. Low levels of extracellular glutamate shift the cell death mechanism to necrosis, whereas antagonism of NMDA receptors results in predominately apoptotic death. In the present study, the involvement of cysteine proteases in the morphologic and biochemical alterations accompanying 3NP-induced neuron death was investigated. Immunoblots of spectrin breakdown products indicated Ca(2+)-dependent cysteine protease (calpain) activation within the 8 hours of 3NP administration, whereas caspase-3 activation was not evident until 16 to 48 hours after treatment. The NMDA receptor antagonist MK-801 (dizocilpine) decreased 3NP-induced calpain activity, but did not alter caspase-3 activity. Similar to MK-801, calpain inhibitors (Z-Val-Phe.H and Z-Leu-Phe-CONHEt) shifted the cell death morphology towards apoptosis and delayed, but did not prevent, the 3NP-induced cell death. Together, the results indicate that following 3NP administration, increased calpain activity precedes caspase-3 activation, contributes to the necrotic morphology, and facilitates and accelerates the cell death.

[In vitro modulation of the invasive and metastatic potentials of human hepatocellular carcinoma by interlukin-2]

OBJECTIVE

To investigate the effects of interlukin-2 (IL-2) on the in vitro invasiveness and the expression of several cell surface antigens related to invasive and metastatic potentials of human hepatocellular carcinoma (HCC) QGY-7701 cell line.

METHODS

QGY-7701 cells were incubated with high concentration of IL-2 or low concentration of IL-2 in different time. The expression of ICAM-1, CD(44) and HLA-I of the tumor cells was determined by fluorescence-activated cell sorter (FACS) analysis The tumor cell binding affinity to extracellular matrix components was measured by cell attachment assay. The degree of homotypic aggregation was quantified by cell aggregation assay.

RESULTS

IL-2 treatment exhibited enhanced expression of ICAM-1 (from 8.3% to 20.5% after high concentration of IL-2 treatment and 17.3% after low concentration of IL-2 treatment) and HLA-I (from 9.8% to 25.4% and 22.1%, respectively after high and low concentration of IL-2 treatment), suppression of CD(44) (from 26.4% to 12.5% and 11.6%, respectively) on HCC cell line and decreased binding affinity to type IV collagen (from 23.5% to 12.4%, 32.3% to 13.8%, 45.7% to 19.6% at 20 min, 40 min and 60 min, respectively after high concentration of IL-2 treatment, and 9.6%, 12.5% and 17.9%, respectively after low concentration of IL-2 treatment) and fibronectin (from 18.6% to 14.1%, 31.2% to 18.4%, 44.5% to 20.5% at 20 min, 40 min and 60 min, respectively after high concentration of IL-2 treatment, and 14.6%, 17.1% and 18.9%, respectively after low concentration of IL-2 treatment) and the degree of homotypic aggregation (from 58.3% to 26.5%, 85.4% to 37.6%, 88.6% to 42.3% at 20 min, 40 min and 60 min, respectively after high concentration of IL-2 treatment, and 25.0%, 36.4% and 42.6%, respectively after low concentration of IL-2 treatment)of HCC cells.

CONCLUSIONS

IL-2 may directly alter tumor properties associated with invasive and metastatic phenotypes of HCC cells, and can inhibit the invasive and metastatic potentials of HCC cells.

Differential changes of synaptic transmission in spiny neurons of rat neostriatum following transient forebrain ischemia

Spiny neurons in neostriatum are vulnerable to cerebral ischemia. To reveal the mechanisms underlying the postischemic neuronal damage, the spontaneous activities, evoked postsynaptic potentials and membrane properties of spiny neurons in rat neostriatum were compared before and after transient forebrain ischemia using intracellular recording and staining techniques in vivo. In control animals the membrane properties of spiny neurons were about the same between the left and right neostriatum but the inhibitory synaptic transmission was stronger in the left striatum. After severe ischemia, the spontaneous firing and membrane potential fluctuation of spiny neurons dramatically reduced. The cortically evoked initial excitatory postsynaptic potentials were suppressed after ischemia indicated by the increase of stimulus threshold and the rise time of these components. The paired-pulse facilitation test indicated that such suppression might involve presynaptic mechanisms. The inhibitory postsynaptic potentials in spiny neurons were completely abolished after ischemia and never returned to the control levels. A late depolarizing postsynaptic potential that was elicited from approximately 5% of the control neurons by cortical stimulation could be evoked from approximately 30% of the neurons in the left striatum and approximately 50% in the right striatum after ischemia. The late depolarizing postsynaptic potential could not be induced after acute thalamic transection. The intrinsic excitability of spiny neurons was suppressed after ischemia evidenced by the significant increase of spike threshold and rheobase as well as the decrease of repetitive firing rate following ischemia. The membrane input resistance and time constant increased within 6 h following ischemia and the amplitude of fast afterhyperpolarization significantly increased after ischemia. These results indicate the depression of excitatory monosynaptic transmission, inhibitory synaptic transmission and excitability of spiny neurons after transient forebrain ischemia whereas the excitatory polysynaptic transmission in neostriatum was potentiated. The facilitation of excitatory polysynaptic transmission is stronger in the right neostriatum than in the left neostriatum after ischemia. The suppression of inhibitory component and the facilitation of excitatory polysynaptic transmission may contribute to the pathogenesis of neuronal injury in neostriatum after transient cerebral ischemia.

Enhanced excitatory synaptic transmission in spiny neurons of rat striatum after unilateral dopamine denervation

The synaptic transmission and intrinsic membrane properties of spiny neurons in rat neostriatum were studied after unilateral dopamine depletion using in vivo intracellular recording and staining techniques. Two to four weeks after dopamine denervation, the spontaneous firing rate of spiny neurons increased and the spontaneous membrane potential fluctuation stayed at a more depolarized state for longer periods of time. The amplitude of cortically evoked initial excitatory postsynaptic potentials increased and a late excitatory postsynaptic potential that was occasionally found in control neurons was elicited from 23% of spiny neurons after dopamine denervation. No significant changes in intrinsic membrane properties of spiny neurons were observed after dopamine denervation. These results suggest that dopamine inhibits excitatory synaptic transmission of spiny neurons in naïve animals.

[Purification and characterization of 2-carbonyl reductase from marine bacteria Bacillus sp]

ANADPH-dependent 2-Oxoaldehyde reductase was isolated and purified from a marine bacteria Bacillus sp. The purification procedure involved ammonium sulfate fractionation and Q Sepharose FF, Hydroxyapatite, Sephadex G-100 column chromatographies. The specific activity of the purified enzyme was increased by 141.1 folds over crude extract and the recovery yield was 11.4%. 2-Oxoaldehyde compounds were found to be speciall good substrates. The optimum pH of the enzyme activity was 6.2-6.6. The Km coefficient for 3-deoxyglucosone was 2.5 mmol/L. The molecular weight of the enzyme was estimated to be 33 kD The enzyme activity is stable below 30 degrees C and pH 5.0-8.0. EDTA, beta-mercaptoethanol and dithiothreitol enhanced the enzyme activity. On the other hand, the enzyme activity was partially lost by idoacetic acid or N-ethylmaleimide.

[A histopathologic and immunohistochemical study of 68 cases of hemangioblastoma]

The aim of this study was to evaluate the histologic characteristics of hemangioblastoma (HB) and investigate the histogenesis of its stromal cells. Sixty-eight cases of hemangioblastoma were studied by light microscopy and thirty-three cases were examined by immunohistochemical stainning. Forty-eight of the 68 patients were males and 20 were females. The average age was 37. Fifty-two cases (76.6%) had been present for two months to one year before the diagnosis was made. Sixty cases (88.2%) arose in the cerebellum. Fifty cases (73.5%) appeared as cystic nodules. Histologically, the 68 cases of HB were further categorized into three subtypes: typical (30 cases), cellular (21 cases) and reticular (17 cases). In 33 cases, the stromal cell were positive for NSE, but negative for F-VIII, UEA-1, GFAP and EMA. In summary, there are three essential histologic categories of hemangioblastoma, and its stromal cells may well have the characters of neuroendocrine differentiation.

Cbln3, a novel member of the precerebellin family that binds specifically to Cbln1

Precerebellin (Cbln1) is the precursor of the brain-specific hexadecapeptide cerebellin. Although cerebellin has properties of a conventional neuropeptide, its function is controversial because Cbln1 has structural features characteristic of circulating atypical collagens. Cbln1 is related to the three subunits of the complement C1q complex. Therefore, we hypothesized that Cbln1 participated in analogous heteromeric complexes with precerebellin-related proteins. Using LexA-Cbln1 as bait in a yeast two-hybrid screen, we isolated a cDNA encoding a novel Cbln1-related protein, designated Cbln3. The gene encoding cbln3 had the same intron-exon structure as cbln1 but mapped to a different mouse chromosome (14). The deduced amino acid sequence of Cbln3 was 55% identical to Cbln1 and also contained a C1q signature domain and signal sequence for secretion. In addition to binding avidly to Cbln3, Cbln1 also formed homomeric complexes. In contrast, Cbln3 homomeric association was weak. These interactions exhibited specificity because C1qB bound to neither Cbln1 nor Cbln3. Like cbln1, cbln3 was expressed in the cerebellum and dorsal cochlear nucleus in which it was detected in granule neurons. Because Cbln1 and Cbln3 are coexpressed in the brain and interact avidly, they may function as a secreted heteromeric complex in vivo.

The effect of coriaria lactone on NMDA receptor mediated currents in rat hippocampal CA1 neurons

To investigate the exact mechanism of epileptogenesis induced by coriaria lactone (CL), the effect of CL on NMDA receptor mediated current (IAsp) in rat hippocampal CA1 neurons was investigated by using nystatin perforated whole-cell patch clamp. 10(-6)-10(-4) mol/L Asp acted on NMDA receptors and elicited an inward current (IAsp) at a holding potential (VH) of -40 mV in presence of 10(-6) mol/L glycine and absence of Mg2+ extracellularly. CL enhanced NMDA receptor mediated current induced by Asp, but had no effect on threshold concentration, EC50, Hill coefficient as well as maximal-effect concentration and reversal potential of IAsp. The effect had no relationship with holding potential. These results showed that CL could enhance NMDA receptor mediated current to increase [Ca2+]i of neurons by acting on Gly site, thereby inducing epilepsy.