1,721,010 research outputs found
CD95 Stimulation and ceramide have a different impact on the morphology and physiology of mitochondria and endoplasmic reticulum.
No full textStimulation with C2 ceramide (1) or with antibodies to the death receptor CD95/Fas/APO-1 (2) induces apoptosis in a wide variety of cell types. Both stimuli cause cytochrome c release, caspase activation and DNA fragmentation. Less known are the effects of these apoptotic agents on organelles such as mitochondria and endoplasmic reticulum (ER). We studied the modifications occurring to mitochondria and ER in HeLa cells during the onset of apoptosis, showing that ceramide and CD95 stimulation have a different impact on morphology and physiology of mitochondria and ER. In C2 ceramide-stimulated cells, mitochondria were fragmented, spherical and smaller than in control cells; these changes occurred as early as 30 min from the stimulation and were not detected in anti-CD95 treated cells where the mitochondrial network did not apparently change its morphology even after several hours. This could be due to a direct damaging effect of ceramide on mitochondrial structures but also to the fact that ceramide itself induces a rapid Ca2+ release from the ER (3). In addition, ceramide induced a dramatic reduction in the mitochondrial Ca2+ response upon stimulation of the ER with histamine, while on the contrary, anti-CD95-stimulated HeLa cells showed a histamine-induced Ca2+ response similar to that of unstimulated control cells. The reduction in mitochondrial Ca2+ response in cells treated with C2 ceramide did not depend on a diminished capacity of mitochondria to take-up Ca2+ released by the ER but primarily on the fact that [Ca2+]ER was lower in ceramide-treated cells. Morphological changes occurring to the ER during ceramide treatment are under investigation. These findings suggest that Ca2+ is involved in the apoptotic pathway of C2 ceramide and show that different apoptotic stimuli have a different impact on the morphology and physiology of mitochondria and ER.
Bibliography:
1) Okazaki T, Kondo T, Kitano T, Tashima M. Diversity and complexity of ceramide signalling in apoptosis. Cell Signal 1998, 10:685-92.
2) Sharma K, Wang RX, Zhang LY, Yin DL, Luo XY, Solomon JC, Jiang RF, Markos K, Davidson W, Scott DW, Shi YF. Death the Fas way: regulation and pathophysiology of CD95 and its ligand. Pharmacol Ther 2000, 88:333-47.
3) Pinton P, Ferrari D, Rapizzi E, Di Virgilio F, Pozzan T, Rizzuto R. The Ca2+ concentration of the endoplasmic reticulum is a key determinant of ceramide-induced apoptosis: significance for the molecular mechanism of Bcl-2 action. EMBO 2001, 20:2690 2701
Scleral fixated intraocular lenses - An angiographic study
No full textPurpose: We reviewed the results, complications, and fluorescein angiographic (FA) findings in eyes that had undergone transscleral fixation of posterior chamber intraocular lenses (IOLs). Methods: Posterior chamber IOL implantation with scleral fixation was performed on 18 patients. Three patients were aphakic, 14 had an intraoperative posterior capsule rupture during cataract surgery, and one was operated on for a retained lens nucleus and dislocated IOL in the vitreous. Follow-up examinations measured visual acuity, intraocular pressure, and IOL decentration and tilting. In 14 patients, iris and retinal FA were performed. Results: No major complications were noted during the procedure. Mean best-corrected visual acuity was 20/70 preoperatively and 20/30 postoperatively after a mean follow-up of 9.8 months. Fourteen patients achieved a visual acuity of 20/40 or better. Macular epiretinal membranes were diagnosed after surgery in five eyes but only one eye showed significant distortion of the fovea (macular pucker). Iris FA revealed no major vascular abnormalities. Fluorescein angiography showed cystoid macular edema in six cases. Light-induced retinal lesions occurred in six eyes. Conclusions: Transscleral fixation of posterior chamber IOLs provided adequate visual acuity in most patients. Incomplete visual recovery after surgery may be related to the occurrence of macular edema and epiretinal membranes. Light-induced retinal injury was the major irreversible intraoperative complication
Sphingosine 1-phosphate receptors modulate intracellular Ca2+ homeostasis
No full textLigation of sphingosine 1-phosphate (S1P) to a set of specific receptors named S1P receptors (S1PRs) regulates important biological processes. Although the ability of S1P to increase cytosolic Ca2+ in various cell types is well known, the role of the individual S1PRs has not been fully characterized. Here, we provide a complete analysis of S1P-dependent intracellular Ca2+ homeostasis in HeLa cells. Overexpression of S1P2, or S1P3, but not S1P1, leads to a significant increase in cytosolic and mitochondrial [Ca2+] in response to S1P challenge. Moreover, cells ectopically expressing S1P2, or S1P3 exhibited an appreciable decrease of the free Ca2+ concentration in the endoplasmic reticulum, dependent on stimulation of receptors by S1P endogenously present in the culture medium which was accompanied by a reduced susceptibility to C2-ceramide-induced cell death. These results demonstrate a differential contribution of individual S1PRs to Ca2+ homeostasis and its possible implication in the regulation of cell survival
Anti-ribosomal P protein antibodies detected by immunoblotting in patients with connective tissue diseases: their specificity for SLE and association with IgG anticardiolipin antibodies
No full textI.F. 3.59
The Ca2+ concentration in the endoplasmic reticulum is a key determinant of ceramide-induced apoptosis: significance for the molecular mechanism of Bcl-2 action
No full textThe mechanism of action of the anti-apoptotic oncogene Bcl-2 is still largely obscure. We have recently shown that the overexpression of Bcl-2 in HeLa cells reduces the Ca2+ concentration in the endoplasmic reticulum ([Ca2+]er) by increasing the passive Ca2+ leak from the organelle. To investigate whether this Ca2+ depletion is part of the mechanism of action of Bcl-2, we mimicked the Bcl-2 effect on [Ca2+]er by different pharmacological and molecular approaches. All conditions that lowered [Ca2+]er protected HeLa cells from ceramide, a Bcl-2-sensitive apoptotic stimulus, while treatments that increased [Ca2+]er had the opposite effect. Surprisingly, ceramide itself caused the release of Ca2+ from the endoplasmic reticulum and thus [Ca2+] increased both in the cytosol and in the mitochondrial matrix, paralleled by marked alterations in mitochondria morphology. The reduction of [Ca2+]er levels, as well as the buffering of cytoplasmic [Ca2+] changes, prevented mitochondrial damage and protected cells from apoptosis. It is therefore concluded that the Bcl-2-dependent reduction of [Ca2+]er is an important component of the anti-apoptotic program controlled by this oncogene
Nuclear poly(ADP-ribose) polymerase I rapidly triggers mitochondrial dysfunction
No full textTo obtain further information on time course and mechanisms of cell death after poly(ADP-ribose) polymerase-1 (PARP-1) hyperactivation, we used HeLa cells exposed for 1 h to the DNA alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine. This treatment activated PARP-1 and caused a rapid drop of cellular NAD(H) and ATP contents, culminating 8-12 h later in cell death. PARP-1 antagonists fully prevented nucleotide depletion and death. Interestingly, in the early 60 min after challenge with N-methyl-N'-nitro-N-nitrosoguanidine, mitochondrial membrane potential and superoxide production significantly increased, whereas cellular ADP contents decreased. Again, these events were prevented by PARP-1 inhibitors, suggesting that PARP-1 hyperactivity leads to mitochondrial state 4 respiration. Mitochondrial membrane potential collapsed at later time points (3 h), when mitochondria released apoptosis-inducing factor and cytochrome c. Using immunocytochemistry and targeted luciferase transfection, we found that, despite an exclusive localization of PARP-1 and poly(ADP-ribose) in the nucleus, ATP levels first decreased in mitochondria and then in the cytoplasm of cells undergoing PARP-1 activation. PARP-1 inhibitors rescued ATP (but not NAD(H) levels) in cells undergoing hyper-poly(ADP-ribosyl)ation. Glycolysis played a central role in the energy recovery, whereas mitochondria consumed ATP in the early recovery phase and produced ATP in the late phase after PARP-1 inhibition, further indicating that nuclear poly(ADP-ribosyl)ation rapidly modulates mitochondrial functioning. Together, our data provide evidence for rapid nucleus-mitochondria cross-talk during hyper-poly(ADP-ribosyl)ation-dependent cell death
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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