Oral batyl alcohol supplementation rescues decreased cardiac conduction in ether phospholipid-deficient mice.

Plasmalogens (Pls) are a class of membrane phospholipids which serve a number of essential biological functions. Deficiency of Pls is associated with common disorders such as Alzheimer's disease or ischemic heart disease. A complete lack of Pls due to genetically determined defective biosynthesis gives rise to rhizomelic chondrodysplasia punctata (RCDP), characterized by a number of severe disabling pathologic features and death in early childhood. Frequent cardiac manifestations of RCDP include septal defects, mitral valve prolapse, and patent ductus arteriosus. In a mouse model of RCDP, reduced nerve conduction velocity was partially rescued by dietary oral supplementation of the Pls precursor batyl alcohol (BA). Here, we examine the impact of Pls deficiency on cardiac impulse conduction in a similar mouse model (Gnpat KO). In-vivo electrocardiographic recordings showed that the duration of the QRS complex was significantly longer in Gnpat KO mice than in age- and sex-matched wild-type animals, indicative of reduced cardiac conduction velocity. Oral supplementation of BA for 2 months resulted in normalization of cardiac Pls levels and of the QRS duration in Gnpat KO mice but not in untreated animals. BA treatment had no effect on the QRS duration in age-matched wild-type mice. These data suggest that Pls deficiency is associated with increased ventricular conduction time which can be rescued by oral BA supplementation.

Membrane deformation and separation.

Biological membranes are highly dynamic (e.g., during cell division, organelle biosynthesis, vesicular transport, and neurotransmitter release). They can be shaped into protein-coated transport vesicles or tubules and undergo regulated fusion. The life of transport vesicles depends on highly specific and tightly regulated protein machineries, which not only shape the donor membrane into nascent budding structures but also help to overcome the energy barrier to break the bilayers apart in order to pinch off nascent vesicles. Ultimately, vesicular membranes have to fuse with a target lipid bilayer, a process that again requires remodeling. Here, we highlight recent insights into mechanisms that lead to membrane deformation in the process of vesicular budding.

ArfGAP1 activity and COPI vesicle biogenesis.

Golgi-derived coat protein I (COPI) vesicles mediate transport in the early secretory pathway. The minimal machinery required for COPI vesicle formation from Golgi membranes in vitro consists of (i) the hetero-heptameric protein complex coatomer, (ii) the small guanosine triphosphatase ADP-ribosylation factor 1 (Arf1) and (iii) transmembrane proteins that function as coat receptors, such as p24 proteins. Various and opposing reports exist on a role of ArfGAP1 in COPI vesicle biogenesis. In this study, we show that, in contrast to data in the literature, ArfGAP1 is not required for COPI vesicle formation. To investigate roles of ArfGAP1 in vesicle formation, we titrated the enzyme into a defined reconstitution assay to form and purify COPI vesicles. We find that catalytic amounts of Arf1GAP1 significantly reduce the yield of purified COPI vesicles and that Arf1 rather than ArfGAP1 constitutes a stoichiometric component of the COPI coat. Combining the controversial reports with the results presented in this study, we suggest a novel role for ArfGAP1 in membrane trafficking.