Suicidality in middle aged and older patients with schizophrenia and depressive symptoms: relationship to functioning and Quality of Life.

BACKGROUND: Suicidality is a health concern in patients with schizophrenia. We examined the hypotheses: (1) Middle aged and older patients with schizophrenia, depressive symptoms and suicidality would exhibit worse quality of life and worse everyday functioning, social skills and medication management relative to those without suicidality; (2) higher levels of suicidality would be significantly associated with worse functioning, worse quality of life and older age. METHODS: We examined 146 outpatients with schizophrenia and depression. Patients were at least 40 years old and were diagnosed with schizophrenia or schizoaffective disorder and had two or more depressive symptoms based on DSM-IV criteria for major depression. We assessed suicidality with the Intersept Suicide Scale (ISS) and functioning with the UCSD Performance-based Skills Assessment (UPSA), Social Skills Performance Assessment (SSPA), and Medication Management Ability Assessment (MMAA). Quality of life was assessed with the Heinrichs Quality of Life Scale (QLS). RESULTS: The mean age of patients was 52.4+ 6.9 years. Subjects with suicidality (ISS scores > 0) had lower QLS scores compared to those without suicidality. However, there were no differences in UPSA, SSPA nor MMAA scores between the two groups. In addition, based on Spearman's rho correlational analysis, there were significant associations of QLS scores with ISS scores (r = - 0.236) and with MMAA "total errors" scores (r = 0.174). Logistic regression demonstrated that only QLS scores predicted suicidality. CONCLUSION: Thirty-six percent of our sample had at least mild degrees of suicidality. Lower quality of life appears to be an important predictor of suicidality.

Expression of the DMT1 (NRAMP2/DCT1) iron transporter in mice with genetic iron overload disorders.

Iron overload is highly prevalent, but its molecular pathogenesis is poorly understood. Recently, DMT1 was shown to be a major apical iron transporter in absorptive cells of the duodenum. In vivo, it is the only transporter known to be important for the uptake of dietary non-heme iron from the gut lumen. The expression and subcellular localization of DMT1 protein in 3 mouse models of iron overload were examined: hypotransferrinemic (Trf(hpx)) mice, Hfe knockout mice, and B2m knockout mice. Interestingly, in Trf(hpx) homozygotes, DMT1 expression was strongly induced in the villus brush border when compared to control animals. This suggests that DMT1 expression is increased in response to iron deficiency in the erythron, even in the setting of systemic iron overload. In contrast, no increase was seen in DMT1 expression in animals with iron overload resembling human hemochromatosis. Therefore, it does not appear that changes in DMT1 levels are primarily responsible for iron loading in hemochromatosis.

Genes that modify the hemochromatosis phenotype in mice.

Hereditary hemochromatosis (HH) is a prevalent human disease caused by a mutation in HFE, which encodes an atypical HLA class I protein involved in regulation of intestinal iron absorption. To gain insight into the pathogenesis of hemochromatosis, we have bred Hfe knockout mice to strains carrying other mutations that impair normal iron metabolism. Compound mutant mice lacking both Hfe and its interacting protein, beta-2 microglobulin (B2m), deposit more tissue iron than mice lacking Hfe only, suggesting that another B2m-interacting protein may be involved in iron regulation. Hfe knockout mice carrying mutations in the iron transporter DMT1 fail to load iron, indicating that hemochromatosis involves iron flux through DMT1. Similarly, compound mutants deficient in both Hfe and hephaestin (Heph) show less iron loading than do Hfe knockout mice, indicating that iron absorption in hemochromatosis involves the function of Heph as well. Finally, compound mutants lacking Hfe and the transferrin receptor accumulate more tissue iron than do mice lacking Hfe alone, consistent with the idea that interaction between these two proteins contributes to the control of normal iron absorption. In addition to providing insight into the pathogenesis of HH, our results suggest that each of these genes might be a candidate modifier of the human hemochromatosis phenotype.

The C282Y mutation causing hereditary hemochromatosis does not produce a null allele.

Targeted mutagenesis was used to produce two mutations in the murine hemochromatosis gene (Hfe) locus. The first mutation deletes a large portion of the coding sequence, generating a null allele. The second mutation introduces a missense mutation (C282Y) into the Hfe locus, but otherwise leaves the gene intact. This mutation is identical to the disease-causing mutation in patients with hereditary hemochromatosis. Mice carrying each of the two mutations were bred and analyzed. Homozygosity for either mutation results in postnatal iron loading. The effects of the null mutation are more severe than the effects of the C282Y mutation. Mice heterozygous for either mutation accumulate more iron than normal controls. Interestingly, although liver iron stores are greatly increased, splenic iron is decreased. We conclude that the C282Y mutation does not result in a null allele.

Polyomavirus VP1 phosphorylation: coexpression with the VP2 capsid protein modulates VP1 phosphorylation in Sf9 insect cells.

The polyomavirus virion has an outer capsid comprised of 72 pentamers of the VP1 protein associated with the minor virion proteins, VP2 and VP3, and the viral minichromosome. To investigate the interaction between VP1 and VP2/VP3, we mapped VP1 phosphorylation sites and assayed VP1 recognition by anti-peptide antibodies after coexpression of VP1 with VP2 or VP3 by using recombinant baculovirus vectors. VP1, expressed either alone or with VP3, was phosphorylated on serine residues, which are not modified during polyomavirus infection of mouse cells. When VP1 was coexpressed with VP2, the nonphysiologic serine phosphorylation of VP1 was decreased, and a tryptic peptide containing Thr-63, a site modified during virus infection of mouse cells, was phosphorylated. An anti-peptide antibody directed against the VP1 BC loop domain containing Thr-63 recognized VP1 expressed alone but not VP1 coexpressed with VP2 or VP3. The change in phosphorylation resulting from coexpression of two structural proteins identifies the potential of the baculovirus system for studying protein-protein interactions and defines a functional role for the VP1-VP2 interaction.

Expression of the polyomavirus VP2 and VP3 proteins in insect cells: coexpression with the major capsid protein VP1 alters VP2/VP3 subcellular localization.

During polyomavirus infection the capsid proteins are synthesized in the cytoplasm and transported into the nucleus were virion assembly occurs. Expression of the major capsid protein VP1 in Sf9 insect cells results in the accumulation of capsid-like particles in the nucleus, independent of the presence of the minor capsid proteins VP2 and VP3 or the viral DNA (Montross et al., J. Virol. 65, 4991-4998, 1991). Sf9 cells infected with baculovirus vectors expressing the polyomavirus minor capsid proteins VP2 and VP3 were examined. VP2 was myristylated in Sf9 cells, as seen during polyomavirus infection of mouse cells. Immunoprecipitation of lysates from co-infected cells demonstrated an association between VP1 and VP2. As determined by immunogold electron microscopy, when expressed alone VP2 was associated with membrane structures in the cytoplasm and VP3 was diffusely localized in the cytoplasm. When co-infected with a VP1 expressing baculovirus, both VP2 and VP3 became predominantly localized to the nucleus in association with capsid-like structures. Thus, the polyomavirus capsid proteins interact in vivo and alter their subcellular localization as a consequence.

Nuclear assembly of polyomavirus capsids in insect cells expressing the major capsid protein VP1.

Polyomavirus normally assembles in the nucleus of infected mouse cells. Sf9 insect cells expressing the polyomavirus major capsid protein VP1 were examined by electron microscopy. Capsidlike particles of apparently uniform size were found in the nucleus. Immunogold electron microscopy demonstrated abundant VP1 in the cytoplasm which was not assembled into any recognizable higher-order structure. Cytoplasmic VP1 assembled after the cells were treated with the calcium ionophore ionomycin. Purified VP1 aggregates were shown by negative staining and cryoelectron microscopy to consist predominantly of particles similar to the empty T = 7 viral capsid. Thus, polyomavirus VP1 can assemble in vivo into capsids independent of other viral proteins or DNA. Nuclear assembly may result from increased available calcium in this subcellular compartment.

Characterization of the DNA-binding properties of the polyomavirus capsid protein VP1.

The major capsid protein of polyomavirus, VP1, has been expression cloned in Escherichia coli, and the recombinant VP1 protein has been purified to near homogeneity (A. D. Leavitt, T. M. Roberts, and R. L. Garcea, J. Biol. Chem. 260:12803-12809, 1985). With this recombinant protein, a nitrocellulose filter transfer assay was developed for detecting DNA binding to VP1 (Southwestern assay). In optimizing conditions for this assay, dithiothreitol was found to inhibit DNA binding significantly. With recombinant VP1 proteins deleted at the carboxy and amino termini, a region of the protein affecting DNA binding was identified within the first 7 amino acids (MAPKRKS) of the VP1 amino terminus. Southwestern analysis of virion proteins separated by two-dimensional gel electrophoresis demonstrated equivalent DNA binding among the different VP1 isoelectric focusing subspecies, suggesting that VP1 phosphorylation does not modulate this function. By means of partial proteolysis of purified recombinant VP1 capsomeres for assessing structural features of the protein domain affecting DNA binding, a trypsin-sensitive site at lysine 28 was found to eliminate VP1 binding to DNA. The binding constant of recombinant VP1 to polyomavirus DNA was determined by an immunoprecipitation assay (R. D. G. McKay, J. Mol. Biol. 145:471-488, 1981) to be 1 x 10(-11) to 2 x 10(-11) M, which was not significantly different from its affinity for plasmid DNA. McKay analysis of deleted VP1 proteins and VP1-beta-galactosidase fusion proteins indicated that the amino terminus was both necessary and sufficient for DNA binding. As shown by electron microscopy, DNA inhibited in vitro capsomere self-assembly into capsidlike structures (D. M. Salunke, D. L. D. Caspar, and R. L. Garcea, Cell 46:895-904, 1986). Thus, VP1 is a high-affinity, non-sequence-specific DNA-binding protein with the binding function localized near its trypsin-accessible amino terminus. The inhibitory effects of disulfide reagents on DNA binding and of DNA on capsid assembly suggest possible intermediate steps in virion assembly.