Physiology/cell biology of pancreatic acinar mitochondrial vitamin B1 uptake

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DESCRIPTION (provided by applicant): Vitamin B1 (thiamin) is indispensable for normal function/health of pancreatic cells due to its critical role in oxidative energy metabolism, ATP production, and in maintaining normal cellular redox state. Low intracellular level of thiamin leads to acute energy failure and oxidative stress; it is also known to lead to impairment in the function of mitochondria. At the organ level, the pancreas contains high levels of thiamin, and deficiency of this vitamin leads to impairment in its functions. The pancreas cannot synthesis thiamin endogenously, and thus, must obtain the vitamin from circulation. The overall goal of this research program has been focused on developing a comprehensive understanding of the molecular mechanisms involved in thiamin entry into pancreatic acinar cells and the subsequent transport (compartmentalization) of its major metabolite thiamin pyrophosphate (TPP; which represent ~ 85-90% of total cellular thiamin and which is generated exclusively in the cytoplasm) into mitochondria (an organelle that contains and utilizes ~ 90% of cellular thiamin), how these process are regulated, and how they are affected by exposure to common external factors that are known to adversely affect normal pancreatic physiology/health. Studies during the previous funding period have focused exclusively on thiamin transport into pancreatic cells across cell membrane. Our focus in the current proposal is on transport of TPP into mitochondria of pancreatic acinar cells with special emphasis on how the process is being regulated at the transcriptional and post-transcriptional levels, how the involved mitochondrial TPP transporter (MTPPT; product of the SLC25A19 gene) is targeted to mitochondria, and which structural features of MTPPT are important for its function. We also aim at investigating the effect of chronic exposure to alcohol and to specific components of cigarette smoke (CS) (external factors known to adversely affect pancreatic health) on the uptake process. Thus, in new preliminary studies, we have cloned the 5'-regulatory region of the SLC25A19 gene, determined the minimal promoter needed for basal activity, and identified a number of putative cis- regulatory elements that may be needed for its activity. We also obtained evidence to show that the pancreatic acinar mitochondrial TPP uptake process is up-regulated in thiamin deficiency via transcriptional mechanism(s), that the process is also under possible regulation by specific intracellular regulatory pathway(s). Furthermore, information was obtained on how MTPPT is targeted to mitochondria. Moreover evidence were obtained to show that chronic exposure of pancreatic acinar cells to alcohol and to specific components of CS leads to a significant inhibition in pancreatic acinar mitochondrial TPP uptake process, and that the effect is mediated at the level of SLC25A19 transcription. Based on these preliminary findings, our working hypothesis in this proposal is that the pancreatic acinar mitochondrial TPP uptake process is a regulated event, that this regulation occurs at both transcriptional and post-transcriptional levels, that unique sequence(s) dictated targeting of MTPPT to mitochondria, and that chronic exposure of pancreatic acinar cells to alcohol and to specific components of CS impairs TPP uptake. Three specific aims are proposed to test this hypothesis. Results of these investigations are expected to provide valuable information regarding physiology/cell biology of an important pancreatic acinar mitochondrial uptake process, information that may also be applicable to other mitochondrial uptake systems. Furthermore, the results are of pathophysiological relevance as they may shed light onto the consequences of exposure of pancreatic acinar cells to common external factors that adversely affect pancreatic health, on mitochondrial physiology.