Inhibition of Fas-mediated apoptotic cell death of murine T lymphocytes in a mouse model of immunosenescence in linkage to deterioration in cell membrane raft function

Epithelial raft cultures for investigations of virus growth, pathogenesis and efficacy of antiviral agents

The organotypic epithelial raft cultures, originally developed to study keratinocytes differentiation, represent a novel approach to the study of viruses able to infect epithelial cells. Organotypic epithelial raft cultures accurately reproduce the process of epithelial differentiation in vitro and can be prepared from normal keratinocytes, explanted epithelial tissue, or established cell lines. This culture system permits cells to proliferate and fully differentiate at the air-liquid interface on a dermal-equivalent support. Normal primary human keratinocytes (PHKs) stratify and fully differentiate in a manner similar to the normal squamous epithelial tissues, while transformed cell lines exhibit dysplastic morphologies similar to the (pre)neoplastic lesions seen in vivo. This three-dimensional (3D) culture system provides an essential tool for investigations of virus growth, virus-host cell interactions, for the genetic analysis of viral proteins and regulatory sequences, and for the evaluation of antiviral agents. The 3D epithelial cultures have proven a breakthrough in the research on papillomaviruses, since their life cycle is strictly linked to the differentiation of the host epithelium. In the last years, several reports have shown the usefulness of the 3D epithelial cultures for the study of other viruses that target at least during a part of their life cycles epithelial cells. The 3D epithelial cultures allow the analysis of virus-host cell interactions in stratified epithelia that more closely resemble the in vivo situation. In this review we describe the advances on research on 3D epithelial cultures for the study of virus growth and pathogenesis of different families of viruses, including papilloma-, herpes-, pox-, adeno-, and parvoviruses.

Rapid phase change of lipid microdomains in giant vesicles induced by conversion of sphingomyelin to ceramide

To understand the role of sphingomyelinase (SMase) in the function of biological membranes, we have investigated the effect of conversion of sphingomyelin (SM) to ceramide (Cer) on the assembly of domains in giant unilamellar vesicles (GUVs). The GUVs were prepared from mixture of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), N-palmitoly-D-erythro-sphingosine (C16Cer), N-palmitoyl-D-erythro-sphingosylphosphorylcholine (C16SM) and cholesterol. The amounts of DOPC, sum of C16Cer and C16SM, and cholesterol were kept constant (the ratio of these four lipids is shown as 1:X:1-X:1 (molar ratio), i.e., X is C16Cer/(C16Cer+C16SM)). Shape and distribution of domains formed in the GUVs were monitored by a fluorescent lipid, Texas Red 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (0.1 mol%). In GUVs containing low C16Cer (X=0 and 0.25), round-shaped domains labeled by the fluorescent lipid were present, suggesting coexistence of liquid-ordered and disordered domains. In GUVs containing intermediate Cer concentration (X=0.5), the fluorescent domain covered most of GUV surface, which was surrounded by gel-like domains. Differential scanning calorimetry of multilamellar vesicles prepared in the presence of higher Cer concentration (X>or=0.5) suggested existence of a Cer-enriched gel phase. Video microscopy showed that the enzymatic conversion of SM to Cer caused rapid change in the domain structure: several minutes after the SMase addition, the fluorescent region spread over the GUV surface, within which regions with darker contrast existed. Image-based measurement of generalized polarization (GP) of 6-dodecanoyl-2-dimethylaminonaphthalene (Laurdan), which is related to the acyl chain ordering of the lipids, was performed. Before the SMase treatment domains with high (0.65) and low (below 0.4) GP values coexisted, presumably reflecting the liquid-ordered and disordered domains; after the SMase treatment regions with intermediate GP values (0.5) and smaller regions with higher GP values (0.65) were present. Generation of Cer thus caused a phase transition from liquid-ordered and disordered phases to a gel and liquid phase.