Luminal Plasma Membrane Research Articles

Obesity-Induced Infertility in Male Mice Is Associated With Disruption of Crisp4 Expression and Sperm Fertilization Capacity.

Approximately 15% of human couples of reproductive age have impaired fertility, and the male component accounts for about half of these cases. The etiology is usually unknown, but high correlation with the increase in obesity rates is documented. In this study, we show that diet-induced and genetically obese mice display copulatory behavior comparable to controls, but the number of females impregnated by obese males is remarkably low. Screening for changes in gene expression in the male reproductive tract showed decreased Crisp4 expression in testis and epididymis of obese mice. Lack of CRISP4 in the luminal membrane of epididymal cells indicated inadequate secretion. Consistent with CRISP4 action in acrosome reaction, sperm from mice fed a high-fat diet (HFD) had decreased fertilization capacity. CRISP4 treatment of sperm from HFD mice prior to in vitro fertilization improved fertilization rate. In leptin-deficient obese and infertile mice, leptin's effect to restore CRISP4 expression and function required gonadal hormones. Our findings indicate that the obesity-induced decline in sperm motility and fertilization capacity results in part from the disruption of epididymal CRISP4 expression and secretion.

β1-Integrin Accumulates in Cystic Fibrosis Luminal Airway Epithelial Membranes and Decreases Sphingosine, Promoting Bacterial Infections

SummaryChronic pulmonary colonization with bacterial pathogens, particularly Pseudomonas aeruginosa, is the primary cause of morbidity and mortality in patients with cystic fibrosis (CF). We observed that β1-integrins accumulate on the luminal membrane of upper-airway epithelial cells from mice and humans with CF. β1-integrin accumulation is due to increased ceramide and the formation of ceramide platforms that trap β1-integrins on the luminal pole of bronchial epithelial cells. β1-integrins downregulate acid ceramidase expression, resulting in further accumulation of ceramide and consequent reduction of surface sphingosine, a lipid that kills bacteria. Interrupting this vicious cycle by triggering surface β1-integrin internalization via anti-β1-integrin antibodies or the RGD peptide ligand—or by genetic or pharmacological correction of ceramide levels—normalizes β1-integrin distribution and sphingosine levels in CF epithelial cells and prevents P. aeruginosa infection in CF mice. These findings suggest a therapeutic avenue to ameliorate CF-associated bacterial infections.

CK2 is a key regulator of SLC4A2-mediated Cl\u2212/HCO3\u2212 exchange in human airway epithelia

Transepithelial bicarbonate secretion by human airway submucosal glands and surface epithelial cells is crucial to maintain the pH-sensitive innate defence mechanisms of the lung. cAMP agonists stimulate HCO3− secretion via coordinated increases in basolateral HCO3− influx and accumulation, as well as CFTR-dependent HCO3− efflux at the luminal membrane of airway epithelial cells. Here, we investigated the regulation of a basolateral located, DIDS-sensitive, Cl−/HCO3− exchanger, anion exchanger 2 (AE2; SLC4A2) which is postulated to act as an acid loader, and therefore potential regulator of HCO3− secretion, in human airway epithelial cells. Using intracellular pH measurements performed on Calu-3 cells, we demonstrate that the activity of the basolateral Cl−/HCO3− exchanger was significantly downregulated by cAMP agonists, via a PKA-independent mechanism and also required Ca2+ and calmodulin under resting conditions. AE2 contains potential phosphorylation sites by a calmodulin substrate, protein kinase CK2, and we demonstrated that AE2 activity was reduced in the presence of CK2 inhibition. Moreover, CK2 inhibition abolished the activity of AE2 in primary human nasal epithelia. Studies performed on mouse AE2 transfected into HEK-293T cells confirmed almost identical Ca2+/calmodulin and CK2 regulation to that observed in Calu-3 and primary human nasal cells. Furthermore, mouse AE2 activity was reduced by genetic knockout of CK2, an effect which was rescued by exogenous CK2 expression. Together, these findings are the first to demonstrate that CK2 is a key regulator of Cl−-dependent HCO3− export at the serosal membrane of human airway epithelial cells.

Effects on P-Glycoprotein Expression after Blood-Brain Barrier Disruption Using Focused Ultrasound and Microbubbles.

Many blood-borne substances attempting to pass through the luminal membrane of brain endothelial cells are acted upon by a variety of metabolizing enzymes or are actively expelled back into the capillary lumen by embedded efflux transporters, such as Permeability-glycoprotein (Pgp). Overexpression of this protein has also been linked to multidrug resistance in cancer cells. Previous studies have shown that focused ultrasound (FUS), when combined with a microbubble agent, has ability to temporarily disrupt blood-brain barrier (BBBD). In this work, we investigated whether modulation of Pgp expression is part of the FUS-induced effects. We found that ultrasound can temporarily suppress Pgp expression. When BBBD was produced at 0.55 MPa, Pgp was suppressed up to 48 hours and restored by 72 hours. At 0.81 MPa, suppression can last 72 hours or longer. These findings support the idea that microbubble-enhanced FUS disrupts the functional components of the BBB through suppression of drug efflux.

Spatiotemporal Changes in P-glycoprotein Levels in Brain and Peripheral Tissues Following Ischemic Stroke in Rats.

P-glycoprotein (P-gp) is known to transport a diverse array of xenobiotics, including therapeutic drugs. A member of the ATP-binding cassette (ABC) transporter family, P-gp is a protein encoded by the gene Mdr1 in humans and Abcb1 in rodents (represented by 2 isoforms Abcb1a and Abcb1b). Lining the luminal and abluminal membrane of brain capillary endothelial cells, P-gp is a promiscuous efflux pump extruding a variety of exogenous toxins and drugs. In this study, we measured dynamic changes in Abcb1a and Abcb1b transcripts and P-gp protein in the brain, liver, and kidney after experimental stroke. P-glycoprotein has been shown to increase in brain endothelial cells following hypoxia in vitro or after exposure to proinflammatory cytokines. Using a rat model of ischemic stroke, we hypothesized that P-gp expression will be increased in the brain, liver, and kidney in response to neuroinflammation following ischemic stroke. Adult Sprague Dawley rats underwent middle cerebral artery occlusion (MCAO) for 90 minutes and were killed at 4, 14, 24, and 48 hours postreperfusion onset to determine the time course of P-gp expression. To mimic ischemia occurring at the blood-brain barrier, rat brain endothelial (RBE4) cells were subjected to hypoxia and low glucose (HLG) for 16 hours. Immunoblotting analyses showed P-gp increases in brain and liver following 90-minute MCAO, as well as in cultured RBE4 cells after 16-hour HLG treatment, but fluctuated in the kidney depending on the time point. The relative roles of each isoform in the protein expression were analyzed with quantitative reverse transcriptase polymerase chain reaction. Ischemic stroke leads to significant increases in P-gp levels not only in the brain but also in the liver. The increase in P-gp could dramatically reduce the bioavailability and efficacy of neuroprotective drugs. Therefore, P-gp represents a big hurdle to drug delivery to the ischemic brain.

The renal effects of SGLT2 inhibitors and a mini-review of the literature.

Sodium-glucose linked transporter 2 (SGLT2) inhibitors are a new and promising class of antidiabetic agents which target renal tubular glucose reabsorption. Their action is based on the blockage of SGLT2 sodium-glucose cotransporters that are located at the luminal membrane of tubular cells of the proximal convoluted tubule, inducing glucosuria. It has been proven that they significantly reduce glycated hemoglobin (HbA1c), along with fasting and postprandial plasma glucose in patients with type 2 diabetes mellitus (T2DM). The glucosuria-induced caloric loss as well as the osmotic diuresis significantly decrease body weight and blood pressure, respectively. Given that SGLT2 inhibitors do not interfere with insulin action and secretion, their efficacy is sustained despite the progressive β-cell failure in T2DM. They are well tolerated, with a low risk of hypoglycemia. Their most frequent adverse events are minor: genital and urinal tract infections. Recently, it was demonstrated that empagliflozin presents a significant cardioprotective effect. Although the SGLT2 inhibitors' efficacy is affected by renal function, new data have been presented that some SGLT2 inhibitors, even in mild and moderate renal impairment, induce significant HbA1c reduction. Moreover, recent data indicate that SGLT2 inhibition has a beneficial renoprotective effect. The role of this review paper is to explore the current evidence on the renal effects of SGLT2 inhibitors.

Intelligent Design of Brain-penetrant Compounds Based on Transporter- Conscious Drug Design

In drug discovery and development, central nervous system (CNS) drugs should be delivered into brain. Nonetheless, drug permeability into brain may be blocked by the blood-brain barrier (BBB) due to the imperviousness of the tight junction between endothelial cells in CNS and excretion by MDR1 (P-gp) expressing in the apical (luminal) membrane of endothelial cells. However, SLC transporter-mediated transport at the BBB can solve this permeable problem. It is well-known that compounds possessing N-containing groups are transported into brain across the BBB. This transportation was suggested to be associated with amine transporters. Thus, transporter-consciously designed drugs which possess N-containing groups as transporter recognition unit can be effectively delivered into brain across the BBB. In this paper, possibility of CNS drugs based on transporter-conscious drug design is described.

β3-Adrenoreceptors in the thick ascending limb of Henle and in principal cells of the collecting duct work to concentrate urine

β3-Adrenoreceptors and their importance to increase sodium reabsorption in the thick ascending loop of Henle and to increase water reabsorption in principal cells of the collecting duct are, forthe first time, described here. This is anintegrated brain response to dehydration perceived by osmosensitive cells in the hypothalamus and triggering through vasopressin axonal and dendritic release a coordinated responseimplicating vasopressin V2 receptors and β3-adrenoreceptors on the luminal membrane of cortical collectingduct cells.

P-glycoprotein traffics from the nucleus to the plasma membrane in rat brain endothelium during inflammatory pain

P-glycoprotein (PgP), a drug efflux pump in blood–brain barrier endothelial cells, is a major clinical obstacle for effective central nervous system drug delivery. Identifying PgP regulatory pathways that can be exploited clinically is critical for improving central nervous system drug delivery. We previously found that PgP activity increases in rat brain microvessels concomitant with decreased central nervous system drug delivery in response to acute peripheral inflammatory pain. In the current study, we tested the hypothesis that PgP traffics to the luminal plasma membrane of the microvessel endothelial cells from intracellular stores during peripheral inflammatory pain. Using immunofluorescence microscopy, we detected PgP in endothelial cell nuclei and in the luminal plasma membrane in control animals. Following peripheral inflammatory pain, luminal PgP staining increased while staining in the nucleus decreased. Biochemical analysis of nuclear PgP content confirmed our visual observations. Peripheral inflammatory pain also increased endothelial cell luminal staining of polymerase 1 and transcript release factor/cavin1 and serum deprivation response protein/cavin2, two caveolar scaffold proteins, without changing caveolin1 or protein kinase C delta binding protein/cavin3 location. Our data (a) indicate that PgP traffics from stores in the nucleus to the endothelial cell luminal membrane in response to peripheral inflammatory pain; (b) provide an explanation for our previous observation that peripheral inflammatory pain inhibits central nervous system drug uptake; and (c) suggest a novel regulatory mechanism for PgP activity in rat brain.

CD34 Promotes Pathological Epi-Retinal Neovascularization in a Mouse Model of Oxygen-Induced Retinopathy.

The sialomucins CD34 and podocalyxin (PODXL) are anti-adhesive molecules expressed at the luminal membrane of endothelial cells of small blood vessels and facilitate vascular lumen formation in the developing mouse aorta. CD34 transcript and protein levels are increased during human angiogenesis, its expression is particularly enriched on endothelial tip cell filopodia and CD34 is a marker for tip cells in vitro. Here, we investigated whether CD34 merely marks endothelial tip cells or has a functional role in tip cells and angiogenesis. We assessed that silencing CD34 in human microvascular endothelial cells has little effect on endothelial cell migration or invasion, but has a significant effect on vascular-endothelial growth factor-induced angiogenic sprouting activity in vitro. In vivo, the absence of CD34 reduced the density of filopodia on retinal endothelial tip cells in neonatal mice, but did not influence the overall architecture of the retinal vascular network. In oxygen-induced retinopathy, Cd34-/- mice showed normal intra-retinal regenerative angiogenesis but the number of pathological epi-retinal neovascular tufts were reduced. We conclude that CD34 is not essential for developmental vascularization in the retina, but its expression promotes the formation of pathological, invasive vessels during neovascularization.

Distribution of organic anion transporters NaDC3 and OAT1-3 along the human nephron.

The initial step in renal secretion of organic anions (OAs) is mediated by transporters in the basolateral membrane (BLM). Contributors to this process are primary active Na(+)-K(+)-ATPase (EC 3.6.3.9), secondary active Na(+)-dicarboxylate cotransporter 3 (NaDC3/SLC13A3), and tertiary active OA transporters (OATs) OAT1/SLC22A6, OAT2/SLC22A7, and OAT3/SLC22A8. In human kidneys, we analyzed the localization of these transporters by immunochemical methods in tissue cryosections and isolated membranes. The specificity of antibodies was validated with human embryonic kidney-293 cells stably transfected with functional OATs. Na(+)-K(+)-ATPase was immunolocalized to the BLM along the entire human nephron. NaDC3-related immunostaining was detected in the BLM of proximal tubules and in the BLM and/or luminal membrane of principal cells in connecting segments and collecting ducts. The thin and thick ascending limbs, macula densa, and distal tubules exhibited no reactivity with the anti-NaDC3 antibody. OAT1-OAT3-related immunostaining in human kidneys was detected only in the BLM of cortical proximal tubules; all three OATs were stained more intensely in S1/S2 segments compared with S3 segment in medullary rays, whereas the S3 segment in the outer stripe remained unstained. Expression of NaDC3, OAT1, OAT2, and OAT3 proteins exhibited considerable interindividual variability in both male and female kidneys, and sex differences in their expression could not be detected. Our experiments provide a side-by-side comparison of basolateral transporters cooperating in renal OA secretion in the human kidney.

Hydronephrosis and Urinary Bladder Hypertrophy in ROMK Bartter's Mouse

The renal outer medullary potassium channel (ROMK; Kir1.1) plays an important role in Na+ and K+ homeostasis. ROMK knockout mice (KO) show a similar phenotype to Bartter's syndrome of salt wasting and dehydration due to reduced Na‐2Cl‐K‐cotransporter activity. ROMK KO mice also show hydronephrosis; however, the mechanism of this phenotype has not been understood. We investigated ROMK expression and regulation by high and low K intake in mouse bladder, by Western blot and immunofluorescence (IF) staining. We also compared the bladder weight, bladder capacity, and thickness of urothelium and smooth muscle layer between WT and ROMK KO mice. Western blotting detected ROMK expression at 45~48 kDA, and IF staining showed that the luminal membrane of umbrella cells were strongly stained in WT compared to KO mice. The expression of ROMK in the luminal membrane disappeared and signal intensity of the detrusor muscle was decreased by low potassium diet (LK) in WT mice. In contrast, there was no significant change in ROMK intensity, but the thickness of urothelium was increased after mice were treated with HK diet. The thickness of urothelium was 168.1±25.8 μm in normal K (NK) and was 300.7±83.6 μm (p<0.001) in the HK treated group compared with NK in WT mice at the same age. The bladder weight, bladder capacity and the thickness of urothelium in ROMK KO showed average increases 2~4 fold greater than WT at both 2 months and 12 months of age. The thickness of the urothelium was 648.8±33.2 μm vs 302.7±16.5 μm (p<0.001) and the detrusor muscle 1940.7±98.9 μm vs 1308.2±102.1 μm (p=0.013) respectively in 12‐month ROMK KO mice. In conclusion, ROMK expressed in the urinary bladder can be regulated by K+ intake; significant enlargement and hypertrophy of the bladder may contribute to hydronephrosis in ROMK KO mice.Support or Funding InformationNIH RO1 DK099284 and PO1 DK 17433

Aβ40 Reduces P-Glycoprotein at the Blood–Brain Barrier through the Ubiquitin–Proteasome Pathway

Failure to clear amyloid-β (Aβ) from the brain is in part responsible for Aβ brain accumulation in Alzheimer's disease (AD). A critical protein for clearing Aβ across the blood-brain barrier is the efflux transporter P-glycoprotein (P-gp) in the luminal plasma membrane of the brain capillary endothelium. P-gp is reduced at the blood-brain barrier in AD, which has been shown to be associated with Aβ brain accumulation. However, the mechanism responsible for P-gp reduction in AD is not well understood. Here we focused on identifying critical mechanistic steps involved in reducing P-gp in AD. We exposed isolated rat brain capillaries to 100 nm Aβ40, Aβ40, aggregated Aβ40, and Aβ42. We observed that only Aβ40 triggered reduction of P-gp protein expression and transport activity levels; this occurred in a dose- and time-dependent manner. To identify the steps involved in Aβ-mediated P-gp reduction, we inhibited protein ubiquitination, protein trafficking, and the ubiquitin-proteasome system, and monitored P-gp protein expression, transport activity, and P-gp-ubiquitin levels. Thus, exposing brain capillaries to Aβ40 triggers ubiquitination, internalization, and proteasomal degradation of P-gp. These findings may provide potential therapeutic targets within the blood-brain barrier to limit P-gp degradation in AD and improve Aβ brain clearance. The mechanism reducing blood-brain barrier P-glycoprotein (P-gp) in Alzheimer's disease is poorly understood. In the present study, we focused on defining this mechanism. We demonstrate that Aβ40 drives P-gp ubiquitination, internalization, and proteasome-dependent degradation, reducing P-gp protein expression and transport activity in isolated brain capillaries. These findings may provide potential therapeutic avenues within the blood-brain barrier to limit P-gp degradation in Alzheimer's disease and improve Aβ brain clearance.

THE ONTOGENY OF P-GLYCOPROTEIN IN THE DEVELOPING HUMAN BLOOD BRAIN BARRIER: IMPLICATION FOR OPIOID TOXICITY IN NEONATES

Neonates have been shown to have a heightened sensitivity to the central depressive effects of opioids compared to older infants and adults. The limited development of P-glycoprotein (P-gp), located on the luminal membrane of the brain endothelial cells, may limit the ability of the neonate to efflux morphine from the brain back to the systemic circulation. Presently, little is known about blood brain barrier P-gp expression during human development. The objective of the study was to determine the ontogeny of P-gp in the human BBB. Postmortem cortex samples from gestational age (GA) 20–26 weeks, GA 36–40 weeks, postnatal age (PNA) 0–3 months, PNA 3–6 months, and adults were immunostained for P-gp. Analysis was carried out by spinning disc confocal microscopy. The intensity of P-gp staining in adults was significantly higher compared to at GA 20–26 weeks (p=0.0002), GA 36–40 weeks (p=0.0002), and PNA 0–3 months (p=0.0044). P-gp intensity at GA 20–26 weeks (p=0.0011), GA 36–40 weeks (p=0.0013), and PNA 0–3 months (p=0.0173) was significantly lower compared to at PNA 3–6 months. P-gp expression in the BBB is limited at birth, increases with postnatal maturation, and reaches adult levels at approximately 3–6 months of age. Given the immaturity of BBB P-gp after birth, morphine may concentrate in the brain. This provides mechanistic support to life threatening opioid toxicity seen with maternal codeine use during breastfeeding.

Nanoparticles as Alternative Strategies for Drug Delivery to the Alzheimer Brain: Electron Microscopy Ultrastructural Analysis.

One of the biggest problems and challenges for the development of new drugs and treatment strategies against Alzheimer Disease (AD) is the crossing of target drugs into the blood brain barrier. The use of nanoparticles in drug delivery therapy holds much promise in targeting remote tissues, and as a result many studies have attempted to study the ultrastructural localization of nanoparticles in various tissues. However, there are currently no in vivo studies demonstrating the ultrastructural distribution of nanoparticles in the brain. The aim of this study was to address how intraperitoneal injection of silver nanoparticles in the brain leads to leaking on the inter-endothelial contact and luminal plasma membrane, thus elucidating the possibility of penetrating into the most affected areas in the Alzheimer brain (vascular endothelium, perivascular, neuronal and glial cells). Our results show that the silver nanoparticles reached the brain and were found in hippocampal areas, indicating that they can be conjugated and used to deliver the drugs into the cell cytoplasm of the damaged brain cells. The present study can be useful for the development of novel drug delivering therapy and useful in understanding the delivery, distribution and effects of silver nanoparticles in AD brain tissue at cellular and subcellular level.

Fatty Acid-Binding Protein 5 Facilitates the Blood–Brain Barrier Transport of Docosahexaenoic Acid

The brain has a limited ability to synthesize the essential polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA) from its omega-3 fatty acid precursors. Therefore, to maintain brain concentrations of this PUFA at physiological levels, plasma-derived DHA must be transported across the blood-brain barrier (BBB). While DHA is able to partition into the luminal membrane of brain endothelial cells, its low aqueous solubility likely limits its cytosolic transfer to the abluminal membrane, necessitating the requirement of an intracellular carrier protein to facilitate trafficking of this PUFA across the BBB. As the intracellular carrier protein fatty acid-binding protein 5 (FABP5) is expressed at the human BBB, the current study assessed the putative role of FABP5 in the brain endothelial cell uptake and BBB transport of DHA in vitro and in vivo, respectively. hFAPB5 was recombinantly expressed and purified from Escherichia coli C41(DE3) cells and the binding affinity of DHA to hFABP5 assessed using isothermal titration calorimetry. The impact of FABP5 siRNA on uptake of (14)C-DHA into immortalized human brain microvascular endothelial (hCMEC/D3) cells was assessed. An in situ transcardiac perfusion method was optimized in C57BL/6 mice and subsequently used to compare the BBB influx rate (Kin) of (14)C-DHA between FABP5-deficient (FABP5(-/-)) and wild-type (FABP5(+/+)) C57BL/6 mice. DHA bound to hFABP5 with an equilibrium dissociation constant of 155 ± 8 nM (mean ± SEM). FABP5 siRNA transfection decreased hCMEC/D3 mRNA and protein expression of FABP5 by 53.2 ± 5.5% and 44.8 ± 13.7%, respectively, which was associated with a 14.1 ± 2.7% reduction in (14)C-DHA cellular uptake. By using optimized conditions for the in situ transcardiac perfusion (a 1 min preperfusion (10 mL/min) followed by perfusion of (14)C-DHA (1 min)), the Kin of (14)C-DHA was 0.04 ± 0.01 mL/g/s. Relative to FABP5(+/+) mice, the Kin of (14)C-DHA decreased 36.7 ± 12.4% in FABP5(-/-) mice. This study demonstrates that FABP5 binds to DHA and is involved in the brain endothelial cell uptake and subsequent BBB transport of DHA, confirming the importance of this cytoplasmic carrier protein in the CNS exposure of this PUFA essential for neuronal function.

Flozins, inhibitors of type 2 renal sodium-glucose co-transporter – not only antihyperglycemic drugs

Abstract The kidneys play a crucial role in the regulation of the carbohydrate metabolism. In normal physiological conditions, the glucose that filters through the renal glomeruli is subsequently nearly totally reabsorbed in the proximal renal tubules. Two transporters are engaged in this process: sodium-glucose co-transporter type 1 (SGLT1), and sodium-glucose co-transporter type type 2 (SGLT2) - this being located in the luminal membrane of the renal tubular epithelial cells. It was found that the administration of dapagliflozin, a selective SGLT2 inhibitor, in patients with type 2 diabetes, is associated with the reduction of HbA1c concentration by 0.45-1.11%. Additional benefits from the treatment with dapagliflozin are the reduction of arterial blood pressure and a permanent reduction of body weight. This outcome is related to the effect of osmotic diuresis and to the considerable loss of the glucose load by way of urine excretion. Dapagliflozin may be successfully applied in type 2 diabetes monotherapy, as well as in combined therapy (including insulin), where it is equally effective as other oral anti-diabetic drugs. Of note: serious adverse effects of dapagliflozin administration are rarely observed. What is more, episodes of severe hypoglycaemia related with the treatment occur only sporadically, most often in the course of diabetes polytherapy. The most frequent effects of the SGLT2 inhibitors are inseparably associated with the mechanism of their action (the glucuretic effect), and cover urogenital infections with a mild clinical course. At present, clinical trials are being continued of the administration of several subsequent drugs from this group, the most advanced of these being the use of canagliflozin and empagliflozin.

Abstract 2037: The butyrate transporter SLC5A8 is a tumor suppressor in colon linked to dietary fiber content

Abstract Dietary fiber has long been known to protect against colonic inflammation and colon cancer. Short-chain fatty acids (SCFA) such as butyrate generated in colonic lumen by bacterial fermentation of dietary fiber mediate most of these protective effects, but the underlying molecular mechanisms are poorly understood. We examined the role of the plasma membrane transporter Slc5a8 in the beneficial effects of these bacterial metabolites against colitis and colon cancer. Slc5a8 is expressed on the luminal membrane of colonic epithelial cells and also in mucosal immune cells including the antigen-presenting dendritic cells. The transporter mediates the entry of SCFAs into colonic epithelium from the lumen and also into dendritic cells in the lamina propria. We interrogated the role of the transporter in colon by comparing the function of dendritic cells and progression of experimentally induced colitis and colon cancer between wild type mice and Slc5a8-null mice. Since the amount of SCFAs generated in colonic lumen depends on the fiber content in the diet, we used two different diets, one with optimal fiber content (FC diet) and the other with no fiber (FF diet). These studies have shown that Slc5a8 is obligatory for butyrate-dependent inhibition of histone deacetylases in colonic epithelium and dendritic cells and also for the maintenance of the intestinal barrier function; but this obligatory need for the transporter is evident only when the mice are fed FF diet. The transporter is dispensable with FC diet. Compared to wild type mice, Slc5a8-null mice exhibit increased susceptibility to dextran sulfate sodium-induced colitis and azoxymethane/dextran sulfate sodium-induced colon cancer, again only with FF diet and not with FC diet. Butyrate induces the immunosuppressive enzymes indoleamine dioxygenase 1 (IDO1) and aldehyde dehydrogenase 1A2 (Aldh1A2) in dendritic cells in an Slc5a8-dependent manner. This is corroborated by the decreased expression of these two enzymes in the colon of germ-free mice compared to conventional mice. IDO1 and Aldh1A2 play a critical role in dendritic cells to maintain an immunosuppressive phenotype. Butyrate, which induces the expression of both enzymes, promotes the ability of dendritic cells to convert naive T cells into FoxP3-positive immunosuppressive Tregs and also their ability to suppress interferon-gamma-secreting pro-inflammatory T cells. As such, Slc5a8-null mice have decreased Tregs and increased IFN-gamma-positive T cells in colon. We conclude that Slc5a8 may be dispensable in colon under dietary conditions associated with high fiber content when the luminal concentrations of SCFAs are high, but the transporter is indispensable for protection against colonic inflammation and colon cancer with a diet containing suboptimal fiber which results in decreased concentrations of SCFAs in the lumen. Thus, Slc5a8 is a conditional tumor suppressor in colon linked to dietary fiber content. Citation Format: Vadivel Ganapathy, Ashish Gurav, Nagendra Singh. The butyrate transporter SLC5A8 is a tumor suppressor in colon linked to dietary fiber content. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2037. doi:10.1158/1538-7445.AM2015-2037

Abstract 6: Continuous Plasma S1p-dependent Signaling by Apically Polarized S1Pr1 Supports Endothelial Barrier Function

Sphingosine-1-phosphate, generated by sphingosine kinases (Sphk1 and 2), acts at its receptor S1Pr1 to maintain vascular homeostasis. The gradient of S1P concentration (low micromolar in plasma vs. low nanomolar in tissue) suggests two non-mutually exclusive models via which S1P maintains the endothelial barrier: 1) plasma S1P communicates continuously with the endothelium to maintain vascular integrity and regulate vascular leak, or 2) compartmentalization of S1P and S1Pr1 enables sensing of plasma extravasation and a dynamic response to leak. To distinguish between these models, we examined endothelial responses to apical vs. basolateral application of S1P in vitro and S1Pr1 subcellular localization in vivo. Addition of S1P to the upper (apical) chamber of transwells containing EA.hy926 endothelial monolayers triggered ERK activation. Surprisingly, addition of these agonists to the lower (basolateral) chamber was without effect. Similar results were obtained with the S1Pr1 agonist SEW2871, but the PAR1 agonist SFLLRN triggered ERK activation from either chamber. By immunofluorescence staining and surface biotinylation of EA.hy926 cells, S1Pr1 protein was present predominantly on the apical surface. Similarly, staining of mouse trachea microvessels revealed S1Pr1 on CD31-positive membranes apical, but not basal, to the endothelial cell nucleus. S1Pr1 staining co-localized with the apical membrane marker podocalyxin but not the basal marker β1-integrin. The level of S1Pr1 protein in endothelial cells in mice lacking plasma S1P (Sphk1 flox/-; Sphk2 -/-; Mx-1 cre) was twice that in littermate controls. Deletion of S1Pr1 from the endothelium (S1Pr1 flox/-; Cdh5 Cre) resulted in a 6-fold increase in vascular permeability compared to littermate controls. Preliminary data suggests that S1Pr1 inactivation alters the phosphorylation state of VE-cadherin. These results suggest that S1Pr1 is polarized to the luminal membrane of endothelial cells where it is continuously activated but only partially downregulated by plasma S1P and that ongoing activation of S1Pr1 by S1P in plasma is required to maintain endothelial barrier function.

CYR61 (CCN1) overexpression induces lung injury in mice.

Cysteine-rich protein-61 (CYR61), also known as connective tissue growth factor, CYR61, and nephroblastoma overexpressed gene 1 (CCN1), is a heparin-binding protein member of the CCN family of matricellular proteins. Gene expression profiles showed that Cyr61 is upregulated in human acute lung injury (ALI), but its functional role is unclear. We hypothesized that CYR61 contributes to ALI in mice. First, we demonstrated that CYR61 expression increases after bleomycin-induced lung injury. We then used adenovirus-mediated gene transfer to determine whether CYR61 overexpression in the lungs was sufficient to cause ALI. Mice instilled with CYR61 adenovirus showed greater weight loss, increased bronchoalveolar lavage total neutrophil counts, increased protein concentrations, and increased mortality compared with mice instilled with empty-vector adenovirus. Immunohistochemical studies in lungs from humans with idiopathic pulmonary fibrosis revealed CYR61 expression on the luminal membrane of alveolar epithelial cells in areas of injury. We conclude that CYR61 is upregulated in ALI and that CYR61 overexpression exacerbates ALI in mice.