A QTL on distal Chromosome 3 that influences the severity of light-induced damage to mouse photoreceptors

C57BL/6J-c^2J (c2J) albino mice showed much less damage to their photoreceptors after exposure to prolonged light than BALB/c mice and seven other albino strains tested. There were no gender differences, and preliminary studies suggested that the c2J relative protective effect was a complex trait. A genome-wide scan using dinucleotide repeat markers was carried out for the analysis of 194 progeny of the backcross (c2J × BALB/c)F₁× c2J and the thickness of the outer nuclear layer (ONL) of the retina was the quantitative trait reflecting retinal damage. Our results revealed a strong and highly significant quantitative trait locus (QTL) on mouse Chromosome (Chr) 3 that contributes almost 50% of the c2J protective effect, and three other very weak but significant QTLs on Chrs 9, 12, and 14. Interestingly, the Chrs 9 and 12 QTLs corresponded to relative susceptibility alleles in c2J (or relative protection alleles in BALB/c), the opposite of the relative protective effect of the QTLs on Chrs 3 and 14. We mapped the Rpe65 gene to the apex of the Chr 3 QTL (LOD score = 19.3). Northern analysis showed no difference in retinal expression of Rpe65 message between c2J and BALB/c mice. However, sequencing of the Rpe65 message revealed a single base change in codon 450, predicting a methionine in c2J and a leucine in BALB/c. When the retinas of aging BALB/c and c2J mice reared in normal cyclic light were compared, the BALB/c retinas showed a small but significant loss of photoreceptor cells, while the c2J retinas did not. Finding light damage-modifying genes in the mouse may open avenues of study for understanding age-related macular degeneration and other retinal degenerations, since light exposures may contribute to the course of these diseases. Received: 14 December 1999 / Accepted: 18 February 2000     

Effector CD4 T cells are biochemically distinct from the memory subset: evidence for long-term persistence of effectors in vivo.

Memory T cell responses are believed to be mediated by long-lived memory T cells that arise directly from a subset of short-lived, activated effector T cells that have reverted to the resting state. Although widely accepted, definitive proof that memory T cells arise from effectors is lacking because of the inability to reliably distinguish these subsets based on known phenotypic or functional parameters. We have used a biochemical approach to distinguish effector and memory CD4 T cell subsets and follow the differentiative fate of effector cells in vivo. When examined biochemically, effector and memory CD4 T cells are strikingly distinct and exhibit qualitative and quantitative differences in tyrosine phosphorylation. These effector-specific patterns were identical in effectors derived either from naive CD4 T cells (primary effectors) or memory CD4 T cells (memory effectors). To monitor the fate of effector cells in vivo, Ag-activated CD4+ TCR-transgenic T cells were transferred into irradiated BALB/c mice. These TCR-transgenic CD4 T cells persisted in adoptive hosts for several months, gave a recall response to Ag, yet exhibited effector-specific biochemical profiles. These results suggest that a subset of effector CD4 T cells can persist in vivo and contribute to long-term immunity by mediating secondary immune responses.     

Functional consequences of the sustained or transient activation by Bax of the mitochondrial permeability transition pore.

The overexpression of Bax kills cells by a mechanism that depends on induction of the mitochondrial permeability transition (MPT) (Pastorino, J. G., Chen, S.-T., Tafani, M., Snyder, J. W., and Farber, J. L. (1998) J. Biol. Chem. 273, 7770-7775). In the present study, purified, recombinant Bax opened the mitochondrial permeability transition pore (PTP). Depending on its concentration, Bax had two distinct effects. At a concentration of 125 nM, Bax caused the release of the intermembranous proteins cytochrome c and adenylate kinase and the release from the matrix of sequestered calcein, effects prevented by the inhibitor of the PTP cyclosporin A (CSA). At this concentration of Bax, there was no detectable mitochondrial swelling or depolarization. These effects of low Bax concentrations are interpreted as the consequence of transient, non-synchronous activation of the PTP followed by a prompt recovery of mitochondrial integrity. By contrast, Bax concentrations between 250 nM and 1 microM caused a sustained opening of the PTP with consequent persistent mitochondrial swelling and deenergization (the MPT). CSA prevented the MPT induced by Bax. Increasing concentrations of calcium caused a greater proportion of the mitochondria to undergo the MPT in the presence of Bax. Importantly, two known mediators of apoptosis, ceramide and GD3 ganglioside, potentiated the induction by Bax of the MPT. The data imply that Bax mediates the opening of the mitochondrial PTP with the resultant release of cytochrome c from the intermembranous space.     

Intermarriage and Jewish identity: The implications for pluralism and assimilation in American society*

Born across racial lines, Cedric Dover and Barack Obama both came to identify with the African American community. By contrasting the lives and ideas of two mixed-race individuals, one born in Calcutta and the other in Hawaii, this article examines cosmopolitanism, racial formation and the promise of the ‘post-racial’. A ‘Eurasian’ intellectual born in Calcutta in 1904, Dover developed a coloured cosmopolitanism that mirrors in revealing ways Obama's approach to race. Both men embraced blackness while transcending the boundaries of race and nation. Dover and Obama developed a conception of race as freedom – not freedom from race or of a particular race, but the freedom to embrace race without sacrificing other affiliations.     

Oxidative cell injury in the killing of cultured hepatocytes by allyl alcohol

The killing of cultured hepatocytes by allyl alcohol depended on the metabolism of this hepatotoxin by alcohol dehydrogenase to the reactive electrophile, acrolein. An inhibitor of alcohol dehydrogenase, pyrazole, prevented both the toxicity of allyl alcohol and the rapid depletion of GSH. Treatment of the hepatocytes with a ferric iron chelator, deferoxamine, or an antioxidant, N,N'-diphenyl-p-phenylenediamine (DPPD), prevented the cell killing but not the metabolism of allyl alcohol and the resulting depletion of GSH. Inhibition of glutathione reductase by 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) sensitized the hepatocytes to allyl alcohol, an effect that was not attributable to the reduction in GSH with BCNU. The cell killing with allyl alcohol was preceded by the peroxidation of cellular lipids as evidence by an accumulation of malondialdehyde in the cultures. Deferoxamine and DPPD prevented the lipid peroxidation in parallel with their protection from the cell killing. These data indicate that acrolein produces an abrupt depletion of GSH that is followed by lipid peroxidation and cell death. Such oxidative cell injury is suggested to result from the inability to detoxify endogenous hydrogen peroxide and the ensuing iron-dependent formation of a potent oxidizing species. Oxidative cell injury more consistently accounts for the hepatotoxicity of allyl alcohol than does the covalent binding of acrolein to cellular macromolecules.     

Oxygen tension within the arterial wall: relationship to altered bioenergetic metabolism and lipid accumulation

Oxygen tension (pO2) was measured in upper thoracic arteries and in muscular foci at the celiac bifurcation from atherosclerosis-susceptible White Carneau and atherosclerosis-resistant Show Racer pigeons at 6, 12, and 24 weeks of age. At each site the pO2 was measured within adventitial (outer), medial (middle), and subendothelial (inner) zones with polarographic oxygen microelectrodes while the animals were under dissociative anesthesia. The atherosclerosis-resistant Show Racer pigeons exhibited no significant age or site differences in pO2 levels. The medial pO2 was approximately 25 mm Hg, while the adventitial and subendothelial zones had pO2 levels of approximately 30 mm Hg. The pO2 profiles through the various zones of the arterial wall of 6-week-old atherosclerosis-susceptible White Carneau pigeons were similar to those of the Show Racers. However, significantly lower oxygen tension was found in the subendothelial zone from 12- and 24-week White Carneau celiac bifurcations (27 and 21 mm Hg) than in corresponding zones in Show Racer sites. Also, the medial zone in 24-week White Carneau celiac foci exhibited a significantly lower pO2 (20 mm Hg) than the medial zone of younger White Carneau. When correlated with previously described biochemical and morphological changes in White Carneau pigeons, the findings presented herein indicate that focal decreases in oxygen availability within arterial tissue occur after the onset of spontaneous atherogenesis, and probably result from decreased diffusion of oxygen into the arterial wall.     

Peroxidation-dependent and peroxidation-independent mechanisms by which acetaminophen kills cultured rat hepatocytes

Acetaminophen killed cultured hepatocytes prepared from male rats induced with 3-methylcholanthrene by two distinct mechanisms. With 0.5 to 5 mM acetaminophen, cell killing within 4 h depended on the inhibition of glutathione reductase by 1,3-bis(chloroethyl)-1-nitrosourea (BCNU) and was accompanied by the peroxidation of cellular lipids as assessed by the accumulation of malondialdehyde. The antioxidant diphenylphenylenediamine (DPPD) prevented both the peroxidation of lipids and the death of the cells. By contrast, DPPD had no effect on the metabolism of acetaminophen as assessed by the extent of the covalent binding of [3H]acetaminophen; by the rate and extent of the depletion of glutathione; and by the accumulation of acetaminophen metabolites in the culture medium. It is concluded that the peroxidation of the phospholipids of cellular membranes is the mechanism whereby 0.5 to 5 mM acetaminophen lethally injures cultured hepatocytes. With 10-20 mM acetaminophen, cell killing at 4 h still depended on BCNU. However, the amount of malondialdehyde in the cultures progressively decreased in parallel with the decreasing ability of DPPD to protect the cells. With 20 mM acetaminophen, there was no evidence of lipid peroxidation, and DPPD had no protective effect. Thus, a second mechanism of lethal cell injury with 10-20 mM acetaminophen is independent of lipid peroxidation and insensitive to antioxidants.