Blockade of striatal adenosine A2A receptor reduces, through a presynaptic mechanism, quinolinic acid-induced excitotoxicity: possible relevance to neuroprotective interventions in neurodegenerative diseases of the striatum.

The aim of the present study was to evaluate whether, and by means of which mechanisms, the adenosine A2A receptor antagonist SCH 58261 [5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine] exerted neuroprotective effects in a rat model of Huntington's disease. In a first set of experiments, SCH 58261 (0.01 and 1 mg/kg) was administered intraperitoneally to Wistar rats 20 min before the bilateral striatal injection of quinolinic acid (QA) (300 nmol/1 microl). SCH 58261 (0.01 but not 1 mg/kg, i.p.) did reduce significantly the effects of QA on motor activity, electroencephalographic changes, and striatal gliosis. Because QA acts by both increasing glutamate outflow and directly stimulating NMDA receptors, a second set of experiments was performed to evaluate whether SCH 58261 acted by preventing the presynaptic and/or the postsynaptic effects of QA. In microdialysis experiments in naive rats, striatal perfusion with QA (5 mm) enhanced glutamate levels by approximately 500%. Such an effect of QA was completely antagonized by pretreatment with SCH 58261 (0.01 but not 1 mg/kg, i.p.). In primary striatal cultures, bath application of QA (900 microm) significantly increased intracellular calcium levels, an effect prevented by the NMDA receptor antagonist MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate]. In this model, bath application of SCH 58261 (15-200 nm) tended to potentiate QA-induced calcium increase. We conclude the following: (1) the adenosine A2A receptor antagonist SCH 58261 has neuroprotective effects, although only at low doses, in an excitotoxic rat model of HD, and (2) the inhibition of QA-evoked glutamate outflow seems to be the major mechanism underlying the neuroprotective effects of SCH 58261.

Structural characterization of PTX3 disulfide bond network and its multimeric status in cumulus matrix organization.

PTX3 is an acute phase glycoprotein that plays key roles in resistance to certain pathogens and in female fertility. PTX3 exerts its functions by interacting with a number of structurally unrelated molecules, a capacity that is likely to rely on its complex multimeric structure stabilized by interchain disulfide bonds. In this study, PAGE analyses performed under both native and denaturing conditions indicated that human recombinant PTX3 is mainly composed of covalently linked octamers. The network of disulfide bonds supporting this octameric assembly was resolved by mass spectrometry and Cys to Ser site-directed mutagenesis. Here we report that cysteine residues at positions 47, 49, and 103 in the N-terminal domain form three symmetric interchain disulfide bonds stabilizing four protein subunits in a tetrameric arrangement. Additional interchain disulfide bonds formed by the C-terminal domain cysteines Cys(317) and Cys(318) are responsible for linking the PTX3 tetramers into octamers. We also identified three intrachain disulfide bonds within the C-terminal domain that we used as structural constraints to build a new three-dimensional model for this domain. Previously it has been shown that PTX3 is a key component of the cumulus oophorus extracellular matrix, which forms around the oocyte prior to ovulation, because cumuli from PTX3(-/-) mice show defective matrix organization. Recombinant PTX3 is able to restore the normal phenotype ex vivo in cumuli from PTX3(-/-) mice. Here we demonstrate that PTX3 Cys to Ser mutants, mainly assembled into tetramers, exhibited wild type rescue activity, whereas a mutant, predominantly composed of dimers, had impaired functionality. These findings indicate that protein oligomerization is essential for PTX3 activity within the cumulus matrix and implicate PTX3 tetramers as the functional molecular units required for cumulus matrix organization and stabilization.

PTX3 interacts with inter-alpha-trypsin inhibitor: implications for hyaluronan organization and cumulus oophorus expansion.

Pentraxin 3 (PTX3) and heavy chains (HCs) of inter-alpha-trypsin inhibitor (IalphaI) are essential for hyaluronan (HA) organization within the extracellular matrix of the cumulus oophorus, which is critical for in vivo oocyte fertilization and female fertility. In this study, we examined the possibility that these molecules interact and cooperate in this function. We show that HCs and PTX3 colocalize in the cumulus matrix and coimmunoprecipitate from cumulus matrix extracts. Coimmunoprecipitation experiments and solid-phase binding assays performed with purified human IalphaI and recombinant PTX3 demonstrate that their interaction is direct and not mediated by other matrix components. PTX3 does not bind to IalphaI subcomponent bikunin and, accordingly, bikunin does not compete for the binding of PTX3 to IalphaI, indicating that PTX3 interacts with IalphaI subcomponent HC only. Recombinant PTX3-specific N-terminal region, but not the PTX3-pentraxin C-terminal domain, showed the same ability as full-length protein to bind to HCs and to enable HA organization and matrix formation by Ptx3(-/-) cumulus cell oocyte complexes cultured in vitro. Furthermore, a monoclonal antibody raised against PTX3 N terminus, which inhibits PTX3/IalphaI interaction, also prevents recombinant full-length PTX3 from restoring a normal phenotype to in vitro-cultured Ptx3(-/-) cumuli. These results indicate that PTX3 directly interacts with HCs of IalphaI and that such interaction is essential for organizing HA in the viscoelastic matrix of cumulus oophorus, highlighting a direct functional link between the two molecules.