Physiology/Pathophysiology of Vitamin B1 Transport in Pancreatic Acinar Cells

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Vitamin B1 (thiamin) is indispensable for normal function/health of pancreatic cells due its critical roles in oxidative energy metabolism, ATP production, and in maintaining normal cellular redox state. Low intracellular level of thiamin leads to acute energy failure, oxidative stress, and impairment in mitochondrial function. At the organ level, the metabolically active pancreas maintains high levels of thiamin, and deficiency of the vitamin impairs its functions. The pancreas cannot synthesis thiamin endogenously; rather it obtains it from circulation. The overall goal of this research program since its inception has been focused on developing a comprehensive understanding of the molecular mechanisms involved in thiamin uptake by pancreatic acinar cells (PACs) and the subsequent transport (compartmentalization) of its major intracellular form, i. e., thiamin pyrophosphate (TPP), into mitochondria, how these processes are regulated, and how they are affected by exposure to external/internal factors that are known to adversely affect the normal physiology/health of the pancreas. We have addressed many of these issues, and in the current proposal aim at determining: i) the role of microRNAs in post-transcriptional regulation of THTR-1, THTR-2, and the mitochondrial TPP transporter (MTPPT) expression in PACS, and the uptake processes that they mediate; ii) whether THTR- 1 and THTR-2 of PACs have interacting partners that affect/regulate their physiology/cell biology; and iii) the effect of specific factors that PACs are exposed to under certain pathophysiological conditions [pro-inflammatory cytokines, and the bacterial lipopolysaccharide (LPS) and flagellin] on thiamin uptake and on transport of TPP into their mitochondria. Thus, in new preliminary studies evidence were obtained to suggest that microRNAs regulate THTR-1 expression and thiamin uptake by PACs, that THTR-1 has interacting partner(s), and that exposure of PACs to pro-inflammatory cytokines (especially those implicated in pancreatic disorders like IL- 6, TNF-α and IL-1β), as well as to LPS and flagellin, inhibit cellular thiamin uptake and transport of TPP into mitochondria. Based on these new findings, our working hypotheses are: i) microRNAs play an important role in post-transcriptional regulation of THTR-1, THTR-2, and MTPPT expression in PACs and the uptake events they mediate; ii) PACs THTR-1 and THTR-2 have interacting partners that affect/regulate their physiology/cell biology; and iii) pro- inflammatory cytokines, LPS and flagellin negatively impact PACs thiamin transport physiology. We plan to test these hypotheses by accomplishing two specific aims and will utilize state-of the art cellular/molecular approaches, human and mouse PACs, and appropriate transgenic mouse models. Results of these investigations should provide novel information regarding vitamin B1 cellular/molecular transport physiology in PACs and how internal/external factors affect the involved transport events. Such knowledge may ultimately assist in the designing of effective strategies to optimize pancreatic thiamin homeostasis, and thus, improve the health of the pancreas.