Soluble Amyloid Precursor Protein 770 Is Released from Inflamed Endothelial Cells and Activated Platelets: A NOVEL BIOMARKER FOR ACUTE CORONARY SYNDROME*

Most Alzheimer disease (AD) patients show deposition of amyloid β (Aβ) peptide in blood vessels as well as the brain parenchyma. We previously found that vascular endothelial cells express amyloid β precursor protein (APP) 770, a different APP isoform from neuronal APP695, and produce Aβ. Since the soluble APP cleavage product, sAPP, is considered to be a possible marker for AD diagnosis, sAPP has been widely measured as a mixture of these variants. We hypothesized that measurement of the endothelial APP770 cleavage product in patients separately from that of neuronal APP695 would enable discrimination between endothelial and neurological dysfunctions. Using our newly developed ELISA system for sAPP770, we observed that inflammatory cytokines significantly enhanced sAPP770 secretion by endothelial cells. Furthermore, we unexpectedly found that sAPP770 was rapidly released from activated platelets. We also found that cerebrospinal fluid mainly contained sAPP695, while serum mostly contained sAPP770. Finally, to test our hypothesis that sAPP770 could be an indicator for endothelial dysfunction, we applied our APP770 ELISA to patients with acute coronary syndrome (ACS), in which endothelial injury and platelet activation lead to fibrous plaque disruption and thrombus formation. Development of a biomarker is essential to facilitate ACS diagnosis in clinical practice. The results revealed that ACS patients had significantly higher plasma sAPP770 levels. Furthermore, in myocardial infarction model rats, an increase in plasma sAPP preceded the release of cardiac enzymes, currently used markers for acute myocardial infarction. These findings raise the possibility that sAPP770 can be a useful biomarker for ACS.     

Serum amyloid A (SAA)-induced remodeling of CSF-HDL

Inflammation is a risk factor for Alzheimer's disease. Serum amyloid A (SAA) is an acute phase protein that dissociates apolipoprotein AI (apoAI) from plasma HDL. In cerebrospinal fluid (CSF), the SAA concentration is much higher in subjects with Alzheimer's disease than in controls. CSF-HDL is rich in apoE, which plays an important role as a ligand for lipoprotein receptors in the central nervous system (CNS). To clarify whether SAA dissociates apoE from CSF-HDL, we added recombinant SAA to CSF and determined the apoE distribution in the CSF using native two-dimensional gel electrophoresis. We found that SAA dissociated apoE from CSF-HDL in a dose-dependent manner. This effect was more evident in apoE4 carriers than in apoE3 or apoE2 carriers. After a 24-h incubation at 37 degrees C, SAA continuously dissociated apoE from CSF-HDL. Amyloid beta (Abeta) fragments (1-42) were bound to large CSF-HDL but not to apoE dissociated by SAA. In conclusion, SAA dissociates apoE from CSF-HDL. We postulate that inflammation in the CNS may impair Abeta clearance due to the loss of apoE from CSF-HDL.     

Syntheses, structures, and mesomorphism of a series of Ni(II) salen complexes with 4-substituted long alkoxy chains

A series of nickel(II) salen complexes containing 4-substituted alkoxy chains of aromatic rings, [Ni((4-C_nH_2n + 1O)₂salen)] (n = 3 (1), 4 (2), 6 (3), 8 (4), 10 (5), 12 (6), 14 (7), 16 (8), 18 (9), and 20 (10)), and their parent complex, [Ni((4-HO)₂salen)] (11) (salen = N,N′-ethylenebis(salicylideneiminato)), have been prepared and mesomorphic properties have been investigated. An X-ray crystallographic analysis revealed that complex 11 · 2DMF has one-dimensional stacking structure supported by the π-π interaction between the six-membered chelate and aromatic rings with the NiNi distances of alternatively 3.3957 and 3.7224 Å and that complex 3 is formed by one-dimensional stacking by weak CH?O type hydrogen bonded interaction between the five-membered chelate ring and phenoxo atoms of the dramatically distorted salen moieties with the NiNi distance of 5.994 Å. Complexes 1-6 did not exhibit any mesophases. On the other hand, complexes 7-10 with longer alkoxy chains of n = 14-20 showed an unusual metallomesogen of a lamello-columnar mesophase within the smectic layers with an interlamellar distance of 31.1 Å (7), 33.6 Å (8), 37.1 Å (9), and 39.5 Å (10) and nearly constant stacking distance of 6.19-6.24 Å between the inter-dimers, irrespective of the variation of the alkoxy chain lengths by the X-ray diffraction measurements of the liquid crystal. The relationship between molecular assemblies and mesomorphic properties is discussed.     

MBNL and CELF proteins regulate alternative splicing of the skeletal muscle chloride channel CLCN1

The expression and function of the skeletal muscle chloride channel CLCN1/ClC-1 is regulated by alternative splicing. Inclusion of the CLCN1 exon 7A is aberrantly elevated in myotonic dystrophy (DM), a genetic disorder caused by the expansion of a CTG or CCTG repeat. Increased exon 7A inclusion leads to a reduction in CLCN1 function, which can be causative of myotonia. Two RNA-binding protein families—muscleblind-like (MBNL) and CUG-BP and ETR-3-like factor (CELF) proteins—are thought to mediate the splicing misregulation in DM. Here, we have identified multiple factors that regulate the alternative splicing of a mouse Clcn1 minigene. The inclusion of exon 7A was repressed by MBNL proteins while promoted by an expanded CUG repeat or CELF4, but not by CUG-BP. Mutation analyses suggested that exon 7A and its flanking region mediate the effect of MBNL1, whereas another distinct region in intron 6 mediates that of CELF4. An exonic splicing enhancer essential for the inclusion of exon 7A was identified at the 5′ end of this exon, which might be inhibited by MBNL1. Collectively, these results provide a mechanistic model for the regulation of Clcn1 splicing, and reveal novel regulatory properties of MBNL and CELF proteins.     

Mechanistic characterization of the sulfur-relay system for eukaryotic 2-thiouridine biogenesis at tRNA wobble positions

The wobble modification in tRNAs, 5-methoxycarbonylmethyl-2-thiouridine (mcm⁵s²U), is required for the proper decoding of NNR codons in eukaryotes. The 2-thio group confers conformational rigidity of mcm⁵s²U by largely fixing the C3′-endo ribose puckering, ensuring stable and accurate codon–anticodon pairing. We have identified five genes in Saccharomyces cerevisiae, YIL008w (URM1), YHR111w (UBA4), YOR251c (TUM1), YNL119w (NCS2) and YGL211w (NCS6), that are required for 2-thiolation of mcm⁵s²U. An in vitro sulfur transfer experiment revealed that Tum1p stimulated the cysteine desulfurase of Nfs1p, and accepted persulfide sulfurs from Nfs1p. URM1 is a ubiquitin-related modifier, and UBA4 is an E1-like enzyme involved in protein urmylation. The carboxy-terminus of Urm1p was activated as an acyl-adenylate (-COAMP), then thiocarboxylated (-COSH) by Uba4p. The activated thiocarboxylate can be utilized in the subsequent reactions for 2-thiouridine formation, mediated by Ncs2p/Ncs6p. We could successfully reconstitute the 2-thiouridine formation in vitro using recombinant proteins. This study revealed that 2-thiouridine formation shares a pathway and chemical reactions with protein urmylation. The sulfur-flow of eukaryotic 2-thiouridine formation is distinct mechanism from the bacterial sulfur-relay system which is based on the persulfide chemistry.