Biomedical subjects

Bernat Soria

Publications and source records attributed to Bernat Soria.

25 records · Page 2Linked to original sources

PubMed2003

Mitochondrial dysfunction is involved in apoptosis induced by serum withdrawal and fatty acids in the beta-cell line INS-1.

The potential toxic effects of high extracellular concentrations of fatty acids were tested in beta(INS-1)-cells cultured in the absence of serum, a condition known to alter cell survival in various systems. This may in part mimic the situation in type 1 or 2 diabetes where beta-cells are already insulted by various stressful conditions, such as cytokines and oxidative stress. Serum removal caused, over a 36-h period, oxidative stress and an early impairment of mitochondrial function, as revealed by increased superoxide production and markedly reduced mitochondrial membrane potential, but a lack of cytochrome c and apoptosis-inducing factor release in the cytosol. The fatty acids palmitate and oleate considerably accelerated the apoptosis process in serum-starved cells, as revealed by fluorescence-activated cell sorting analysis, morphological changes, chromatin condensation, DNA laddering, poly(ADP-ribose) polymerase cleavage, cytochrome c and apoptosis-inducing factor release, and increased levels of Bax and cytosolic caspase-2. The fatty acids also increased nitric oxide production, apparently independently of inducible nitric oxide synthase induction. Under the same experimental conditions, elevated glucose alone had only a marginal effect on beta-cell apoptosis. Together the results indicate that elevated concentrations of fatty acids are particularly efficient in accelerating the rate of apoptosis of already stressed beta(INS-1)-cells displaying altered mitochondrial function, and that the mitochondrial arm of the apoptosis process is involved in beta-cell lipotoxicity.

Apoptosis↗

PubMed2002

Low doses of the endocrine disruptor bisphenol-A and the native hormone 17beta-estradiol rapidly activate transcription factor CREB.

Endocrine-disrupting chemicals (EDCs) are hormone-like agents present in the environment that alter the endocrine system of wildlife and humans. Most EDCs have potencies far below those of the natural hormone 17beta-E2 when acting through the classic estrogen receptors (ERs). Here, we show that the environmental estrogen Bisphenol-A and the native hormone 17beta-E2 activate the transcription factor, cAMP-responsive element binding protein (CREB) with the same potency. Phosphorylated CREB (P-CREB) was increased after only a 5-minute application of either BPA or 17beta-E2 in a calcium-dependent manner. The effect was reproduced by the membrane-impermeable molecule E2 conjugated to horseradish peroxidase (E-HRP). The increase in P-CREB was not modified by the anti-estrogen ICI 182,780. Therefore, low-dose of BPA activates the transcription factor CREB via an alternative mechanism, involving a non-classical membrane estrogen receptor. Because these effects are elicited at concentrations as low as 10(-9) M, this observation is of environmental and public health relevance.

Animals↗

PubMed2002

Nuclear KATP channels trigger nuclear Ca(2+) transients that modulate nuclear function.

Glucose, the principal regulator of endocrine pancreas, has several effects on pancreatic beta cells, including the regulation of insulin release, cell proliferation, apoptosis, differentiation, and gene expression. Although the sequence of events linking glycemia with insulin release is well described, the mechanism whereby glucose regulates nuclear function is still largely unknown. Here, we have shown that an ATP-sensitive K(+) channel (K(ATP)) with similar properties to that found on the plasma membrane is also present on the nuclear envelope of pancreatic beta cells. In isolated nuclei, blockade of the K(ATP) channel with tolbutamide or diadenosine polyphosphates triggers nuclear Ca(2+) transients and induces phosphorylation of the transcription factor cAMP response element binding protein. In whole cells, fluorescence in situ hybridization revealed that these Ca(2+) signals may trigger c-myc expression. These results demonstrate a functional K(ATP) channel in nuclei linking glucose metabolism, nuclear Ca(2+) signals, and nuclear function.

Adenosine Triphosphate↗

PubMed2002

Direct visualization by confocal fluorescent microscopy of the permeation of myristoylated peptides through the cell membrane.

To study the permeability through the cellular membrane of synthetic peptides containing an hydrophobic moiety, we used a 13-mer myristoylated peptide labeled with a N-terminal fluorescent probe. After 2 h of incubation, the subcellular distribution was analyzed in intact chromaffin cells by confocal fluorescent microscopy. Our results demonstrate that myristoylated peptides diffuse into intact cells, showing an heterogeneous distribution, but they do not reach the cellular nucleous, at least during the time range used.

Acylation↗

PubMed2002

A nonclassical estrogen membrane receptor triggers rapid differential actions in the endocrine pancreas.

Glucose homeostasis in blood is mainly maintained by insulin released from beta-cells and glucagon released from alpha-cells, both integrated within the pancreatic islet of Langerhans. The secretory processes in both types of cells are triggered by a rise in intracellular calcium concentration ([Ca2+](i)). In this study, rapid effects of the natural hormone E2 on [Ca2+](i) were studied in both types of cells within intact islets using laser scanning confocal microscopy. alpha- And beta-cells showed opposite [Ca2+](i) responses when stimulated with physiological concentrations of 17beta-E2. Although the estrogen produced an increase in the frequency of glucose-induced [Ca2+](i) oscillations in insulin-releasing beta-cells, it prevented the low glucose-induced [Ca2+](i) oscillations in glucagon-releasing alpha-cells. The effects of 17beta-E2 on alpha-cells were mimicked by the cGMP permeable analog 8bromo-cGMP and blocked by the cGMP-dependent protein kinase (PKG) inhibitor KT5823. Evidence indicated that these were membrane actions mediated by a nonclassical ER. Both effects were rapid in onset and were reproduced by 17beta-E2 linked to horseradish peroxidase, a cell-impermeable molecule. Furthermore, these actions were not blocked by the specific ER blocker ICI 182,780. Competition studies performed with 17beta-E2 linked to horseradish peroxidase binding in alpha-cells supported the idea that the membrane receptor involved is neither ERalpha nor ERbeta. Additionally, the binding site was shared by the neurotransmitters epinephrine, norepinephrine, and dopamine and had the same pharmacological profile as the receptor previously described for beta-cells. Therefore, rapid estrogen actions in islet cells are initiated by a nonclassical estrogen membrane receptor.

Alkaloids↗

PubMed1991

Inactivation of Delayed Potassium Current in Cultured Bovine Chromaffin Cells.

Potassium currents of cultured bovine chromaffin cells in the presence of CdCl2 (0.5 mM) or CoCl2 (2 - 4 mM) may be described as a component that follows an n4 kinetics over the first 100 ms. However, during prolonged voltage clamp steps (5 - 20 s) this current reaches a peak and then declines to a non-zero steady-state level. In the absence of potassium accumulation, slow decay has been attributed to slow inactivation of the K+ conductance. Slow inactivation of calcium-independent potassium currents responds to the following: (i) the inactivation has a time course that may be fitted by a sum of two exponentials; (ii) inactivation is use-dependent (increasing frequency or duration of depolarizing pulses increases the extent of inactivation). Use-dependent inactivation does not appear when short (100 ms) hyperpolarizing prepulses are applied; (iii) at a membrane potential of - 60 mV, approximately 20% of the channels are inactivated; (iv) recovery from inactivation is very slow. At a holding potential of - 70 mV it takes about 20 s to reach the original value. The rate of inactivation recovery is voltage-dependent. The more hyperpolarized the membrane potential, the faster the recovery. The presence of use-dependent inactivation with slow recovery could be relevant for the stimulus - secretion coupling modulation in chromaffin cells.

Journal Article↗

PubMedDate not supplied

Isolation and characterization of residual undifferentiated mouse embryonic stem cells from embryoid body cultures by fluorescence tracking.

The differentiation of mouse embryonic stem (ES) cells can be induced in vitro after leukemia inhibitory factor (LIF) withdrawal and further enhanced by the formation of "embryoid body" (EB) aggregates. This strategy is being used in order to optimize differentiation protocols that would result in functional cells for experimental cell replacement therapies. However, this study presents the possibility for residual undifferentiated cells to survive after standard in vitro procedures. Mouse ES cells were stably transfected with the enhanced green fluorescent protein (EGFP), under the control of the Oct4 promoter, a transcription factor that is expressed in undifferentiated ES cells but down-regulated on differentiation. Residual fluorescent cells were isolated from EBs that were cultured in standard conditions in absence of LIF. These residual cells displayed recurrent gain of chromosomes 8 and 9. Residual fluorescent cells, further expanded in absence of LIF and cultured as EBs, still displayed a significant Oct4 expression in comparison with parental transfected ES cells. Consequently, these residual cells have an intrinsic resistance to differentiate. The behavior of these cells, observed in vitro, can be overcome in vivo, as they were able to induce teratomas in subcutaneously injected nude mice. Residual undifferentiated cells displayed slight levels of VASA and DAZL expression. These results demonstrate that mouse ES cells cultured in vitro, in standard conditions, can spontaneously acquire recurrent karyotypical changes that may promote an undifferentiated stage, being selected in standard culture conditions in vitro.

Animals↗