A CRAC-like motif in BAX sequence: relationship with protein insertion and pore activity in liposomes.

Several proteins that interact with cholesterol have a highly conserved sequence, corresponding to the cholesterol recognition/interaction amino acid consensus. Since cholesterol has been proposed to modulate both oligomerization and insertion of the pro-apoptotic protein BAX, we investigated the existence of such a motif in the BAX sequence. Residues 113 to 119 of the recombinant BAX α5-helix, LFYFASK, correspond with the sequence motif described for the consensus pattern, -L/V-(X)(1-5)-Y-(X)(1-5)-R/K. Functional characterization of the point mutations, K119A, Y115F, and L113A in BAX, was performed in liposomes supplemented with cholesterol, comparing binding, integration, and pore forming activities. Our results show that the mutations Y115F and L113A changed the cholesterol-dependent insertion observed in the wild type protein. In addition, substitutions in the BAX sequence modified the concentration dependency of carboxyfluorescein release in liposomes, although neither pore activity of the wild type or of any of the mutants significantly increased in cholesterol-enriched liposomes. Thus, while it is likely that the putative CRAC motif in BAX accounts for its enhanced insertion in cholesterol-enriched liposomes; the pore forming properties of BAX did not depend on cholesterol content in the membranes, albeit those mutations changed the pore channeling activity of the protein.

Adsorption of polyethylene microbeads and physiological effects on hydroponic maize.

About 90% of the plastic garbage remains in terrestrial ecosystems, and increasing evidence highlights the exposure of crops to plastic particles. However, the potential bioaccumulation of microplastics by plants and their effects on plants' physiology remains unexplored. Here, we evaluated the adsorption, potential uptake, and physiological effects of polyethylene (PE) microbeads in an experimental hydroponic culture of maize. Using isotope analysis, taking advantage of the different carbon isotope composition (δ13C) of fossil-derived PE and C4 plants (e.g., maize), we estimated that about 30% of the carbon in the rhizosphere of microplastic-exposed plants was derived from PE. Still, we did not find evidence of PE translocation to the shoots. Plastic bioaccumulation in the rhizosphere caused a significant decline in transpiration, nitrogen content, and growth. Our results indicate that plastic particles may accumulate in the rhizosphere, impairing water and nutrient uptake, and eventually reaching root eaters. Due to the implications for food production and livestock feeding, our findings encourage further research on the mechanism leading to the bioaccumulation of microplastics on the surface of belowground tissues.

Bax distribution into mitochondrial detergent-resistant microdomains is related to ceramide and cholesterol content in postischemic hearts.

*Diverse changes have been described in mitochondria of apoptotic cells: the phospholipid content is modified, ceramide and GD3 concentrations increase, the cristae structure is modified, and nonresident proteins are recruited into the mitochondrial membranes. In particular, Bax, a Bcl-2 family member protein, moves from the cytosol to the mitochondria, inducing cytochrome c release. Modifications of the content and distribution of specific lipids in the mitochondrial membranes, along with the well-known participation of the mitochondrial permeability transition pore in triggering apoptosis, led us to propose that lipid microdomains in mitochondria could coexist as structural elements with some of the mitochondrial permeability transition pore-forming proteins and with members of the Bcl-2 family. In this work, we demonstrated that Bax was associated preferentially with mitochondrial detergent-resistant membranes (mDRMs) in reperfused rat hearts, a well-known apoptotic model. Bax insertion into mDRMs correlated with cytochrome c release from such mitochondria. Bax location in mDRMs was associated with both the voltage-dependent anion channel and the adenine nucleotide translocator, two mitochondrial permeability transition pore-forming proteins. Interestingly, the voltage-dependent anion channel was more abundant in the mDRM fraction than in the Triton X-100-soluble fraction. Ceramide and cholesterol contents were higher in mDRMs from reperfused hearts. Our results suggest that membrane microenvironments enriched in cholesterol and ceramide in mitochondria favor Bax translocation to this organelle, fostering propagation of the apoptotic cascade.

Aspectos éticos clínicos: modelo de análisis en odontología / Clinical ethics aspects: an analysis model in dentistry

El estudio de los problemas éticos en las disciplinas de la salud plantea varias dificultades, siendo necesario tener las relaciones entre ética o filosofía de la moral, bioética y ética clínica. La tecnología ha modificado nuestras vidas y conjuntamente con algunas circunstancias de salud debe intervenir la ética con su interrogante. ¿cómo debe ser nuestro acto? ¿qué fin perseguimos en nuestras acciones? En todo conflicto entre lo que se debe hacer y lo que simplemente se puede hacer o se hace, son necesarias propuestas metodológicas para actuar desde lo racional con el planteo de los análisis de los problemas éticos-clínicos. Se deberá dar importancia a una adecuada formación profesional e investigación de los dilemas éticos que se imponen ante la necesidad del conocimiento y la prevención de las nuevas situaciones paradigmáticas que están surgiendo en los momentos actuales. La regulación del comportamiento de la práctica en salud actual presenta una problemática sumamente compleja; es por ello que no la podemos reducir sólo al orden de normativas. La ética y la moral intervendrán en la reflexión de lo correcto e incorrecto (conocimiento técnico-científico) del bien o del mal (principios éticos y conciencia moral), llevando a los profesionales de ala salud a los cuestionamientos de las obligaciones morales.