Relative contribution of THTR-1 and THTR-2 in thiamin uptake by pancreatic acinar cells: studies utilizing Slc19a2 and Slc19a3 knockout mouse models.

Thiamin is essential for normal function of pancreatic acinar cells, and its deficiency leads to a reduction in pancreatic digestive enzymes. We have recently shown that thiamin uptake by rat pancreatic acinar cells is carrier-mediated and that both thiamin transporter (THTR)-1 and THTR-2 are expressed in these cells; little, however, is known about the relative contribution of these transporters toward total carrier-mediated thiamin uptake by these cells. We addressed this issue using a gene-specific silencing approach (siRNA) in mouse-derived pancreatic acinar 266-6 cells and Slc19a2 and Slc19a3 knockout mouse models. First we established that thiamin uptake by mouse pancreatic acinar cells is via a carrier-mediated process. We also established that these cells as well as native human pancreas express THTR-1 and THTR-2, with expression of the former (and activity of its promoter) being significantly higher than that of the latter. Using gene-specific siRNA against mouse THTR-1 and THTR-2, we observed a significant inhibition in carrier-mediated thiamin uptake by 266-6 cells in both cases. Similarly, thiamin uptake by freshly isolated primary pancreatic acinar cells of the Slc19a2 and Slc19a3 knockout mice was significantly lower than uptake by acinar cells of the respective littermates; the degree of inhibition observed in the former knockout model was greater than that of the latter. These findings demonstrate, for the first time, that both mTHTR-1 and mTHTR-2 are involved in carrier-mediated thiamin uptake by pancreatic acinar cells.