Molecular Mechanism of Stimulation of Na-K-ATPase by Leukotriene D4 in Intestinal Epithelial Cells.

Niraj Nepal,Balasubramanian Palaniappan,Soudamani Singh,Uma Sundaram,Subha Arthur,Molly R Butts

doi:10.3390/ijms22147569

Niraj Nepal, Balasubramanian Palaniappan + Show 4 more

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https://doi.org/10.3390/ijms22147569

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Abstract

Na-K-ATPase provides a favorable transcellular Na gradient required for the functioning of Na-dependent nutrient transporters in intestinal epithelial cells. The primary metabolite for enterocytes is glutamine, which is absorbed via Na-glutamine co-transporter (SN2; SLC38A5) in intestinal crypt cells. SN2 activity is stimulated during chronic intestinal inflammation, at least in part, secondarily to the stimulation of Na-K-ATPase activity. Leukotriene D4 (LTD4) is known to be elevated in the mucosa during chronic enteritis, but the way in which it may regulate Na-K-ATPase is not known. In an in vitro model of rat intestinal epithelial cells (IEC-18), Na-K-ATPase activity was significantly stimulated by LTD4. As LTD4 mediates its action via Ca-dependent protein kinase C (PKC), Ca levels were measured and were found to be increased. Phorbol 12-myristate 13-acetate (PMA), an activator of PKC, also mediated stimulation of Na-K-ATPase like LTD4, while BAPTA-AM (Ca chelator) and calphostin-C (Cal-C; PKC inhibitor) prevented the stimulation of Na-K-ATPase activity. LTD4 caused a significant increase in mRNA and plasma membrane protein expression of Na-K-ATPase α1 and β1 subunits, which was prevented by calphostin-C. These data demonstrate that LTD4 stimulates Na-K-ATPase in intestinal crypt cells secondarily to the transcriptional increase of Na-K-ATPase α1 and β1 subunits, mediated via the Ca-activated PKC pathway.

Highlights

The primary function of the mammalian small intestine is the absorption of nutrients vital for the survival
The crypt cell brush border membrane (BBM) transporter SN2 requires a favorable Na-gradient, which is maintained by the Na-K-ATPase, an integral transmembrane protein located on the basolateral membrane (BLM) of these cells
It was postulated in this study that the stimulation of glutamine absorption mediated by SN2 in crypt cells might compensate for the decreased B0AT1 mediated glutamine absorption in the absorptive villus cells, to meet the overall nutritional demand of the enterocytes

Summary

Introduction

The primary function of the mammalian small intestine is the absorption of nutrients vital for the survival. The process of nutrient absorption occurs through a monolayer of epithelial cells (innermost layer of the mucosa), called enterocytes, present in the small intestine These enterocytes are further divided into immature enterocytes (crypt cells) and mature enterocytes (villus cells). It has been shown that inhibition of the formation of leukotrienes in this animal model of IBD reverses the stimulation of Na-K-ATPase activity and subsequently SN2 activity in crypt cells [3]. It is unknown how LTD4 may stimulate Na-K-ATPase in crypt cells during chronic intestinal inflammation

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