Long-lasting, sex- and age-specific effects of social stressors on corticosterone responses to restraint and on locomotor responses to psychostimulants in rats

Many neural systems are undergoing marked development over adolescence, which may heighten an animal's vulnerability to stressors. One consequence may be altered sensitivity to drugs of abuse. We previously reported that social stressors in adolescence increased behavioral sensitization to nicotine in adulthood in female, but not male, rats. Here we examined whether social stressors in adolescence alter the functioning of the hypothalamic-pituitary-adrenal (HPA) axis by examining corticosterone release in response to restraint in adulthood. To further assess effects of social stressors on behavioral sensitivity to psychostimulants, we examined locomotor activity in response to nicotine and to amphetamine. In a second set of experiments, we investigated whether the same procedure of social stressors administered in adulthood produces effects similar to that observed when administered in adolescence. Rats underwent daily 1 h isolation followed by pairing with a new cage mate on either postnatal days 33-48 (pubertal stress: PS) or days 65-80 (adult stress: AS). Three weeks later rats tested for either: (a) corticosterone levels were measured in response to restraint, or (b) locomotor sensitization to nicotine (0.25 mg/kg; 5 days) followed by an amphetamine challenge (0.5 mg/kg) 24 h later. Effects of social stressors were evident only in females. PS females had increased locomotor activity to amphetamine compared to controls, and AS females had increased corticosterone release compared to controls. No effect of the social stressors was found in males at either age except for reduced weight gain during the stress procedure. Thus, females are more susceptible to the enduring effects of these moderate social stressors than are males. However, in terms of behavioral sensitivity to drugs of abuse, females may be more susceptible to stressors during adolescence than adulthood, although the reverse appears to be true for HPA function.     

The absence of ABCA1 decreases soluble ApoE levels but does not diminish amyloid deposition in two murine models of Alzheimer disease

ABCA1, a cholesterol transporter expressed in the brain, has been shown recently to be required to maintain normal apoE levels and lipidation in the central nervous system. In addition, ABCA1 has been reported to modulate beta-amyloid (Abeta) production in vitro. These observations raise the possibility that ABCA1 may play a role in the pathogenesis of Alzheimer disease. Here we report that the deficiency of ABCA1 does not affect soluble or guanidine-extractable Abeta levels in Tg-SwDI/B or amyloid precursor protein/presenilin 1 (APP/PS1) mice, but rather is associated with a dramatic reduction in soluble apoE levels in brain. Although this reduction in apoE was expected to reduce the amyloid burden in vivo, we observed that the parenchymal and vascular amyloid load was increased in Tg-SwDI/B animals and was not diminished in APP/PS1 mice. Furthermore, we observed an increase in the proportion of apoE retained in the insoluble fraction, particularly in the APP/PS1 model. These data suggested that ABCA1-mediated effects on apoE levels and lipidation influenced amyloidogenesis in vivo.     

Apoptosis induced by the kinase inhibitor BAY 43-9006 in human leukemia cells involves down-regulation of Mcl-1 through inhibition of translation

BAY 43-9006 is a kinase inhibitor that induces apoptosis in a variety of tumor cells. Here we report that treatment with BAY 43-9006 results in marked cytochrome c and AIF release into the cytosol, caspase-9, -8, -7, and -3 activation, and apoptosis in human leukemia cells (U937, Jurkat, and K562). Pronounced apoptosis was also observed in blasts from patients with acute myeloid leukemia. These events were accompanied by ERK1/2 inactivation and caspase-independent down-regulation of Mcl-1. Inducible expression of a constitutively active MEK1 construct did not prevent Mcl-1 down-regulation, suggesting that this event is not related to MEK/ERK pathway inactivation. Furthermore, BAY 43-9006 did not induce major changes in Mcl-1 mRNA levels monitored by real-time PCR or Mcl-1 promoter activity demonstrated by luciferase reporter assays, but it did enhance Mcl-1 down-regulation in actinomycin D-treated cells. Inhibition of protein synthesis by cycloheximide or proteasome function with MG132 and pulse-chase studies with [35S]methionine demonstrated that BAY 43-9006 did not diminish Mcl-1 protein stability, nor did it enhance Mcl-1 ubiquitination, but instead markedly attenuated Mcl-1 translation in association with the rapid and potent dephosphorylation of the eIF4E translation initiation factor. Finally, ectopic expression of Mcl-1 in leukemic cells markedly inhibited BAY 43-9006-mediated cytochrome c cytosolic release, caspase-9, -7, and -3 activation, as well as cell death, indicating that Mcl-1 operates upstream of cytochrome c release and caspase activation. Together, these findings demonstrate that BAY 43-9006 mediates cell death in human leukemia cells, at least in part, through down-regulation of Mcl-1 via inhibition of translation.     

Naturally occurring capsid substitutions render HIV-1 cyclophilin A independent in human cells and TRIM-cyclophilin-resistant in Owl monkey cells

In this study, we asked if a naturally occurring HIV-1 variant exists that circumvents CypA dependence in human cells. To address this issue, we sought viruses for CypA independence using Debio-025, a cyclosporine A (CsA) analog that disrupts CypA-capsid interaction. Surprisingly, viral variants from the Main group replicate even in the presence of the drug. Sequencing analyses revealed that these viruses encode capsid substitutions within the CypA-binding site (V86P/H87Q/I91V/M96I). When we introduced these substitutions into viruses that normally rely on CypA for replication, these mutants no longer depended on CypA, suggesting that naturally occurring capsid substitutions obviate the need for CypA. This is the first demonstration that isolates from the Main group naturally develop CypA-independent strategies to replicate in human cells. Surprisingly, we found that these capsid substitutions render HIV-1 capable of infecting Owl monkey (OMK) cells that highly restrict HIV-1. OMK cell resistance to HIV-1 is mediated via TRIM-Cyp, which arose from a retrotransposition of CypA into the TRIM5 alpha gene. Interestingly, saturation experiments suggest that the Pro86/Gln87/Val91/Ile96 capsid core is "invisible" to TRIM-Cyp. This study demonstrates that specific capsid substitutions can release HIV-1 from both CypA dependence in human cells and TRIM-Cyp restriction in monkey cells.     

Loss of RPA1 induces Chk2 phosphorylation through a caffeine-sensitive pathway

RPA is an important component of DNA replication, repair and recombination, but its involvement in the signaling of cell-cycle checkpoints is not well understood. In this study, we show that knockdown of RPA1 by siRNA duplexes induces ATM (Ser1981) and Chk2 (Thr68), but not Chk1 (Ser345) phosphorylation and results in p21 upregulation in HeLa cells. However, the induction of Chk2 (Thr68) phosphorylation and p21 expression by RPA1 siRNA transfection can be completely blocked by the ATM inhibitor caffeine. Moreover, transfection of siRNAs targeting ATM dramatically reduces Chk2 (Thr68) phosphorylation in RPA1 knockdown cells. Taken together, these results suggest that loss of RPA1 activates the Chk2 signaling pathway in an ATM-dependent manner.     

The dimycocerosate ester polyketide virulence factors of mycobacteria

Recent advances in the study of mycobacterial lipids indicate that the class of outer membrane lipids known as dimycocerosate esters (DIMs) are major virulence factors of clinically relevant mycobacteria including Mycobacterium tuberculosis and Mycobacterium leprae. DIMs are a structurally intriguing class of polyketide synthase-derived wax esters discovered over seventy years ago, yet, little was known until recently about their biosynthesis. Availability of several mycobacterial genomes has accelerated progress toward clarifying steps in the DIM biosynthetic pathway and it is our belief that reviewing the bases of our current knowledge will clarify outstanding issues and help direct future endeavors.     

Cyanobacterial Photosystem I lacks specificity in its interaction with cytochrome c<Subscript>6</Subscript> electron donors

In cyanobacteria, plastocyanin and cytochrome c ₆, the alternate donor proteins to Photosystem I, can be acidic, neutral or basic; the role of electrostatics in their interaction with photosystem I varies accordingly. In order to elucidate whether these changes in the electron donors’ properties correlate with complementary changes in the docking site of the corresponding photosystem, we have investigated the kinetics of reactions between three cytochrome c ₆ with isoelectric points of 5.6, 7.0 and 9.0, with Photosystem I particles from the same three genera of cyanobacteria which provided the cytochromes. The model systems compared here thus sample the full range of charge properties observed in cytochromes c ₆: acidic, basic and neutral. The rate constants and dependence on ionic strength for photosystem I reduction were distinctive for each cytochrome c ₆, but independent of Photosystem I. We conclude that the specific structural features of each cytochrome c ₆ dictate their different kinetic behaviours, whereas the three photosystems are relatively indiscriminate in docking with the electron donors.     

Testing simple indices of habitat proximity

Simple measures of habitat proximity made primarily on the basis of land cover are widely used in the ecological literature to infer habitat connectivity, or the potential for animal movement among resource patches. However, such indices rarely have been tested against observations of animal movement or against more detailed biological models. We developed a priori expectations as to the types of study systems and organisms for which various habitat proximity indices would be best suited. We then used data from three study systems and four species to test which, if any, of the indices were good predictors of population-level responses. Our a priori expectations about index performance were not upheld. The indices that consider both habitat area and distance from the focal patch were highly correlated with each other, suggesting that they do index similar quantities. However, none of the indices performed well in predicting population response variables. The results suggest that the pattern of habitat cover alone may be insufficient to predict the process of animal movement.