Effects Of Erythropoietin On Transmembrane Transport Of Folic Acid In Caco - 2 Cells And Its Mechanism

The development of recombinant erythropoietin (EPO) therapy represents a great advance in the treatment of renal anemia. Besides the direct stimulation of erythropoiesis, EPO may also play a regulatory role in maintaining the homeostasis of hematopoietic nutrients. It has been reported that EPO can stimulate intestinal iron absorption. However, the involvement of EPO in intestinal folate absorption remains elusive. Folate absorption in instine occurs via carrier-mediated process that involves the uptake transporters reduced folate carrier (RFC), apical proton coupled folate transporter (PCFT), and an efflux transporter multidrug resistance-associated protein2(MRP2). On the other hand, after successfully binding to an EPO receptor (EPOR), EPO can activate three main signaling pathways:the janus protein tyrosine kinase2(JAK-2) pathway, extracellular signal regulated kinases (ERK) pathway, and phosphatidylinositol3kinase/Akt (PI3K/Akt) pathway, which subsequently modulate downstream gene expression. We assume that EPO may regulate folate transporter expression and consequent folate absorption via these EPO signaling pathways.Thus, in this study, human intestinal-derived Caco-2cells expressing endogenous RFC, PCFT, MRP2and EPOR were used as an in vitro enterocyte model to clarify the possible role of EPO in intestinal folate absorption. The results of transport studies indicated that transporter-mediated uptake of folic acid was enhanced by EPO treatment in a dose-dependent manner, which was associated with the significant up-regulation of reduced folate carrier (RFC) and apical proton coupled folate transporter (PCFT). The efflux of folic acid was enhanced only by the high dose of EPO treatment, which was companied with the significant up-regulation of apical multidrug resistance-associated protein2(MRP2). The expression levels of all these transporters were up-regulated by EPO treatment in a dose-and time-dependent manner. Transporter expression in response to blocking EPO induced activation of JAK-2, ERK and PI3K/Akt was changed to different extent. As a conclusion, EPO can modulate intestinal folate absorption in vitro:enhanced uptake of folic acid may be associated with the up-regulation of PCFT and RFC, as well as the alteration on the subcellular distribution of PCFT; enhanced efflux of folic acid may be associated with the up-regulation of MRP2; JAK-2, ERK and PI3/Akt play distinct roles in regulating the expression of folate transporters.