Prostaglandin Transporter OATP2A1/SLCO2A1 Is Essential for Body Temperature Regulation during Fever.

Prostaglandin E2 (PGE2) in the hypothalamus is a principal mediator of the febrile response. However, the role of organic anion transporting polypeptide 2A1 (OATP2A1/SLCO2A1), a prostaglandin transporter, in facilitating this response is unknown. Here, we investigated the effect of Slco2a1 deficiency on the body core temperature (Tc) and on the PGE2 concentration in hypothalamus interstitial fluid (Cisf) and CSF (Ccsf) of lipopolysaccharide (LPS; 100 µg/kg, i.p.)-treated mice of both sexes. Slco2a1-/- mice did not develop a febrile response. Ccsf was increased in Slco2a1+/+ and Slco2a1-/- mice, and Ccsf of Slco2a1-/- mice was well maintained at 5 h after LPS injection (1160 pg/ml) compared with Slco2a1+/+ mice (316 pg/ml). A microdialysis study revealed that Cisf peaked at 2 h after LPS injection in Slco2a1+/+ mice (841 pg/ml), whereas the increase in Cisf was negligible in Slco2a1-/- mice. The PGE2 plasma concentration in Slco2a1-/- mice (201 pg/ml) was significantly higher than that in Slco2a1+/+ mice (54 pg/ml) at 1 h after LPS injection, whereas the two groups showed similar PGE2 concentrations in the hypothalamus. Strong Oatp2a1 immunoreactivity was observed in F4/80-positive microglia and perivascular cells and in brain capillary endothelial cells. The changes in Tc and Cisf seen in LPS-injected Slco2a1+/+ mice were partially attenuated in monocyte-/macrophage-specific Slco2a1-/- (Slco2a1Fl/Fl/LysMCre/+) mice. Thus, OATP2A1 facilitates the LPS-induced febrile response by maintaining a high level of Cisf, possibly by regulating PGE2 secretion from F4/80-positive glial cells and/or facilitating PGE2 transport across the blood-brain barrier. These findings suggest that OATP2A1 is a useful therapeutic target for neuroinflammation.SIGNIFICANCE STATEMENT Fever is a physiological response caused by pyrogen-induced release of prostaglandin E2 (PGE2) in the hypothalamus, which plays a central role in regulating the set-point of body temperature. However, it is unclear whether the prostaglandin transporter OATP2A1/SLCO2A1 is involved in this response. We show here that LPS-induced fever is associated with increased PGE2 concentration in hypothalamus interstitial fluid (Cisf), but not in CSF (Ccsf), by means of a microdialysis study in global Slco2a1-knock-out mice and monocyte-/macrophage-specific Slco2a1-knock-out mice. The results suggest that OATP2A1 serves as a regulator of Cisf in F4/80-positive glial cells. OATP2A1 was detected immunohistochemically in brain capillary endothelial cells and, therefore, may also play a role in PGE2 transport across the blood-brain barrier.

Role of OATP2A1 in PGE(2) secretion from human colorectal cancer cells via exocytosis in response to oxidative stress.

Chronic inflammation induced by reactive oxygen species is associated with increased risk of developing colorectal cancer (CRC), and prostaglandin E2 (PGE2), which serves as a key mediator of inflammatory responses, plays an important role in CRC initiation and progression. Therefore, in the present study, we aimed to investigate the role of prostaglandin transporter OATP2A1/SLCO2A1 in the changes of PGE2 disposition in CRC cells in response to oxidative stress. H2O2 induced translocation of cytoplasmic OATP2A1 to plasma membranes in LoVo and COLO 320DM cells, but not in Caco-2 cells. The shift of subcellular OATP2A1 was abolished in the presence of anti-oxidant N-acetyl-L-cysteine or an inhibitor of protein kinase C, which evokes exocytosis. Exposure of LoVo cells to H2O2 caused an increase in the amount of extracellular PGE2 without changing the sum of intra- and extracellular PGE2. OATP2A1 knockdown decreased extracellular PGE2 in LoVo cells. In addition, extracellular PGE2 was significantly reduced by exocytosis inhibitor cytochalasin D, suggesting that H2O2-induced PGE2 release occurs in an exocytotic manner. Furthermore, mRNA expression of vascular endothelial growth factor (VEGF) was significantly reduced in LoVo cells by knockdown of OATP2A1. These results suggest that cytoplasmic OATP2A1 likely facilitates PGE2 loading into suitable intracellular compartment(s) for efficient exocytotic PGE2 release from CRC cells exposed to oxidative stress.

Prostaglandin transporter (OATP2A1/SLCO2A1) contributes to local disposition of eicosapentaenoic acid-derived PGE3.

Eicosapentaenoic acid (EPA)-derived prostaglandin E3 (PGE3) possesses an anti-inflammatory effect; however, information for transporters that regulate its peri-cellular concentration is limited. The present study, therefore, aimed to clarify transporters involved in local disposition of PGE3. PGE3 uptake was assessed in HEK293 cells transfected with OATP2A1/SLCO2A1, OATP1B1/SLCO1B1, OATP2B1/SLCO2B1, OAT1/SLC22A6, OCT1/SLC22A1 or OCT2/SLC22A2 genes, compared with HEK293 cells transfected with plasmid vector alone (Mock). PGE3 uptake by OATP2A1-expressing HEK293 cells (HEK/2A1) was the highest and followed by HEK/1B1, while no significantly higher uptake of PGE3 than Mock cells was detected by other transporters. Saturation kinetics in PGE3 uptake by HEK/2A1 estimated the Km as 7.202 ± 0.595 µM, which was 22 times higher than that of PGE2 (Km=0.331 ± 0.131 µM). Furthermore, tissue disposition of PGE3 was examined in wild-type (WT) and Slco2a1-deficient (Slco2a1(-/-)) mice after oral administration of EPA ethyl ester (EPA-E) when they underwent intraperitoneal injection of endotoxin (e.g., lipopolysaccharide). PGE3 concentration was significantly higher in the lung, and tended to increase in the colon, stomach, and kidney of Slco2a1(-/-), compared to WT mice. Ratio of PGE2 metabolite 15-keto PGE2 over PGE2 concentration was significantly lower in the lung and colon of Slco2a1(-/-) than that of WT mice, suggesting that PGE3 metabolism is downregulated in Slco2a1(-/-) mice. In conclusion, PGE3 was found to be a substrate of OATP2A1, and local disposition of PGE3 could be regulated by OATP2A1 at least in the lung.

OATP2A1/SLCO2A1-mediated prostaglandin E2 loading into intracellular acidic compartments of macrophages contributes to exocytotic secretion.

There is significant evidence that the inducible cyclooxygenase isoform (COX-2) regulates the pericellular concentration of PGE2; however, the mechanism of the secretory process remains unclear. The present study, therefore, aimed to evaluate the role of prostaglandin transporter (OATP2A1) in PGE2 secretion from macrophages. Immunofluorescence staining for Oatp2a1 (Slco2a1) was primarily detected in cytoplasmic domains, and was partially co-localized with anti-PGE2 antibody, LysoTracker®, and anti-lysosome-associated membrane protein (Lamp) 1 antibody in murine macrophage-derived RAW264 cells and peritoneal macrophages (PMs). PGE2 uptake by subcellular fraction containing light lysosomes was reduced significantly in the presence of an OATP inhibitor and in Slco2a1(+/-) PMs. Secretion of PGE2 and lysosome-specific N-acetyl-ß-d-glucosaminidase was enhanced in activated macrophagic cells, and diminished significantly under the Ca(2+)-depleted condition. The amount of PGE2 secreted from lipopolysaccharide-activated Slco2a1(-/-) PMs was significantly lower than that from PMs from wild type (WT) mice. Expression of Cox-2 and 15-hydroxyprostaglandin dehydrogenase (15-Pgdh) was unchanged between PMs from Slco2a1(-/-) and WT mice. These results suggest that OATP2A1 is involved in PGE2-loading into intracellular acidic compartments, including light lysosomes. Thus, OATP2A1 contributes to PGE2 secretion by macrophages via exocytosis induced by Ca(2+) influx, independently of PGE2 synthesis and metabolism.

Interplay between the prostaglandin transporter OATP2A1 and prostaglandin E2-mediated cellular effects.

Prostaglandins such as prostaglandin E2 (PGE2) play a pivotal role in physiological and pathophysiological pathways in gastric mucosa. Little is known about the interrelation of the prostaglandin E (EP) receptors with the prostaglandin transporter OATP2A1 in the gastric mucosa and gastric carcinoma. Therefore, we first investigated the expression of OATP2A1 and EP4 in normal and carcinoma gastric mucosa. Different PGE2-mediated cellular pathways and mechanisms were investigated using human embryonic kidney cells (HEK293) and the human gastric carcinoma cell line AGS stably transfected with OATP2A1. Colocalization and expression of OATP2A1 and EP4 were detected in mucosa of normal gastric tissue and of gastric carcinomas. OATP2A1 reduced the PGE2-mediated cAMP production in HEK293 and AGS cells overexpressing EP4 and OATP2A1. The expression of OATP2A1 in AGS cells resulted in a reduction of [(3)H]-thymidine incorporation which was in line with a higher accumulation of AGS-OATP2A1 cells in S-phase of the cell cycle compared to control cells. In contrast, the expression of OATP2A1 in HEK293 cells had no influence on the distribution in the S-phase compared to control cells. OATP2A1 also diminished the PGE2-mediated expression of interleukin-8 mRNA (IL-8) and hypoxia-inducible-factor 1α (HIF1α) protein in AGS-OATP2A1 cells. The expression of OATP2A1 increased the sensitivity of AGS cells against irinotecan which led to reduced cell viability. Taken together, these data show that OATP2A1 influences PGE2-mediated cellular pathways. Therefore, OATP2A1 needs to be considered as a key determinant for the understanding of the physiology and pathophysiology of prostaglandins in healthy and tumorous gastric mucosa.