Chronic alcohol exposure affects pancreatic acinar mitochondrial thiamin pyrophosphate uptake: studies with mouse 266-6 cell line and primary cells

Thiamin is essential for normal metabolic activity of all mammalian cells, including those of the pancreas. Cells obtain thiamin from their surroundings and enzymatically convert it into thiamin pyrophosphate (TPP) in the cytoplasm; TPP is then taken up by mitochondria via a specific carrier the mitochondrial TPP transporter (MTPPT; product of the SLC25A19 gene). Chronic alcohol exposure negatively impacts the health of pancreatic acinar cells (PAC), but its effect on physiological/molecular parameters of MTPPT is not known. We addressed this issue using mouse pancreatic acinar tumor cell line 266-6 and primary PAC of wild-type and transgenic mice carrying the SLC25A19 promoter that were fed alcohol chronically. Chronic alcohol exposure of 266-6 cells (but not to its nonoxidative metabolites ethyl palmitate and ethyl oleate) led to a significant inhibition in mitochondrial TPP uptake, which was associated with a decreased expression of MTPPT protein, mRNA, and activity of the SLC25A19 promoter. Similarly, chronic alcohol feeding of mice led to a significant inhibition in expression of MTPPT protein, mRNA, heterogeneous nuclear RNA, as well as in activity of SLC25A19 promoter in PAC. While chronic alcohol exposure did not affect DNA methylation of the Slc25a19 promoter, a significant decrease in histone H3 euchromatin markers and an increase in H3 heterochromatin marker were observed. These findings show, for the first time, that chronic alcohol exposure negatively impacts pancreatic MTPPT, and that this effect is exerted, at least in part, at the level of Slc25a19 transcription and appears to involve epigenetic mechanism(s).

Intracellular location of SNAP-25 in human neutrophils

Exocytosis plays an essential role in the physiological functions of human neutrophils. Although SNAP-25 is considered to play a key role in vesicle-membrane fusion, it has been detected almost exclusively in the neuronal system. Using different specific antibodies to SNAP-25, we have identified in the membrane fraction of resting human neutrophils an immunoreactive band with the same molecular mass observed in brain homogenates. Immunoblot analysis of subcellular fractions of neutrophils revealed that SNAP-25 protein was found in the granule membrane fraction, but not in the cytosolic and plasma membrane fractions. Granule localization for neutrophil SNAP-25 was further demonstrated by confocal and immunoelectron microscopy. Furthermore, SNAP-25 was mainly located in the morphologically defined neutrophil peroxidase-negative granules, which are mobilizable upon cell activation. In addition, the protein was specifically cleaved by botulinal neurotoxin A, as observed in brain homogenate. These findings reveal the presence of SNAP-25 in the granule membranes of human neutrophils.