Expression Of Key Transporters Research Articles

Ion Transport Basis of Diarrhea, Paneth Cell Metaplasia, and Upregulation of Mechanosensory Pathway in Anti-CD40 Colitis Mice.

Anti-Cluster of differentiation (CD)-40-induced colitis, driven by innate inflammatory responses in the intestine, is a potent animal model exhibiting IBD pathophysiology including diarrhea. However, the ion transport basis of diarrhea and some key mucosal pathways (Paneth cells, stem cell niche, and mechanosensory) in this model have not been investigated. Mucosal scrapings and intestinal tissue from control and CD40 antibody (150µg) treated Rag2-/- mice were examined for gut inflammation, Paneth cell numbers, expression of key transporters, tight/adherens junction proteins, stem cell niche, and mechanosensory pathway via hematoxylin and eosin staining, quantitative polymerase chain reaction, and western blotting. Compared with control, anti-CD40 antibody treatment resulted in a significant loss of body weight (P < .05) and diarrhea at day 3 postinjection. Distal colonic tissues of anti-CD40 mice exhibited increased inflammatory infiltrates, higher claudin-2 expression, and appearance of Paneth cell-like structures indicative of Paneth cell metaplasia. Significantly reduced expression (P < .005) of downregulated in adenoma (key Cl- transporter), P-glycoprotein/multidrug resistantance-1 (MDR1, xenobiotic transporter), and adherens junction protein E-cadherin (~2-fold P < .05) was also observed in the colon of anti-CD40 colitis mice. Interestingly, there were also marked alterations in the stem cell markers and upregulation of the mechanosensory YAP-TAZ pathway, suggesting the activation of alternate regeneration pathway post-tissue injury in this model. Our data demonstrate that the anti-CD40 colitis model shows key features of IBD observed in the human disease, hence making it a suitable model to investigate the pathophysiology of ulcerative colitis (UC).

Organic Anion and Cation SLC22 “Drug” Transporter (Oat1, Oat3, and Oct1) Regulation during Development and Maturation of the Kidney Proximal Tubule

Proper physiological function in the pre- and post-natal proximal tubule of the kidney depends upon the acquisition of selective permeability, apical-basolateral epithelial polarity and the expression of key transporters, including those involved in metabolite, toxin and drug handling. Particularly important are the SLC22 family of transporters, including the organic anion transporters Oat1 (originally identified as NKT) and Oat3 as well as the organic cation transporter Oct1. In ex vivo cultures of metanephric mesenchyme (MM; the embryonic progenitor tissue of the nephron) Oat function was evident before completion of nephron segmentation and corresponded with the maturation of tight junctions as measured biochemically by detergent extractability of the tight junction protein, ZO-1. Examination of available time series microarray data sets in the context of development and differentiation of the proximal tubule (derived from both in vivo and in vitro/ex vivo developing nephrons) allowed for correlation of gene expression data to biochemically and functionally defined states of development. This bioinformatic analysis yielded a network of genes with connectivity biased toward Hnf4α (but including Hnf1α, hyaluronic acid-CD44, and notch pathways). Intriguingly, the Oat1 and Oat3 genes were found to have strong temporal co-expression with Hnf4α in the cultured MM supporting the notion of some connection between the transporters and this transcription factor. Taken together with the ChIP-qPCR finding that Hnf4α occupies Oat1, Oat3, and Oct1 proximal promoters in the in vivo differentiating rat kidney, the data suggest a network of genes with Hnf4α at its center plays a role in regulating the terminal differentiation and capacity for drug and toxin handling by the nascent proximal tubule of the kidney.

Acclimation of ion regulatory capacities in gills of marine fish under environmental hypercapnia

The preservation of ion balance and pH despite environmental fluctuations is essential for the maintenance of vital cellular functions. While several ion transporters contribute to acid-base regulation in fish, the involvement and expression of key transporters under hypercapnia remain to be established. Here, two members of the HCO(3)(-) transporter family (Na(+)/HCO(3)(-) cotransporter NBC1 and Cl(-)/HCO(3)(-) exchanger AE1) were described for the first time in gills of marine fish. Benthic eelpout Zoarces viviparus were acclimated to 10,000 ppm CO(2). Hypercapnia did not affect whole animal oxygen consumption over a period of 4 days. During a time series of 6 wk NBC1 mRNA levels first decreased by about 40% (8 to 24 h) but finally increased about threefold over control. mRNA expression of AE1 decreased transiently by 50% at day 4 but recovered to control levels only. Reduced mRNA levels were also found for two Na(+)/H(+) exchangers (NHE1A, NHE1B) during the first days (by 50-60% at days 1 and 2), followed by restoration of control levels. This pattern was mirrored in a slight decrease of NHE1 protein contents and its subsequent recovery. In contrast, Na(+)-K(+)-ATPase mRNA and protein contents, as well as maximum activity, rose steadily from the onset of hypercapnia, and reached up to twofold control levels at the end. These results indicate shifting acclimation patterns between short- and long-term CO(2) exposures. Overall, ion gradient-dependent transporter mRNA levels were transiently downregulated in the beginning of the disturbance. Upregulation of NBC1 on long timescales stresses the importance of this transporter in the hypercapnia response of marine teleosts. Long-term rearrangements include Na(+)-K(+)-ATPase at higher densities and capacities, indicating a shift to elevated rates of ion and acid-base regulation under environmental hypercapnia.

Mitochondrial transport proteins of the brain

In this study, cellular distribution and activity of glutamate and gamma-aminobutyric acid (GABA) transport as well as oxoglutarate transport across brain mitochondrial membranes were investigated. A goal was to establish cell-type-specific expression of key transporters and enzymes involved in neurotransmitter metabolism in order to estimate neurotransmitter and metabolite traffic between neurons and astrocytes. Two methods were used to isolate brain mitochondria. One method excludes synaptosomes and the organelles may therefore be enriched in astrocytic mitochondria. The other method isolates mitochondria derived from all regions of the brain. Immunological and enzymatic methods were used to measure enzymes and carriers in the different preparations, in addition to studying transport kinetics. Immunohistochemistry was also employed using brain slices to confirm cell type specificity of enzymes and carriers. The data suggest that the aspartate/glutamate carriers (AGC) are expressed predominantly in neurons, not astrocytes, and that one of two glutamate/hydroxyl carriers is expressed predominantly in astrocytes. The GABA carrier and the oxoglutarate carrier appear to be equally distributed in astrocytes and neurons. As expected, pyruvate carboxylase and branched-chain aminotransferase were predominantly astrocytic. Insofar as the aspartate/glutamate exchange carriers are required for the malate/aspartate shuttle and for reoxidation of cytosolic NADH, the data suggest a compartmentation of glucose metabolism in which astrocytes catalyze glycolytic conversion of glucose to lactate, whereas neurons are capable of oxidizing both lactate and glucose to CO(2) + H(2)O.

Nuclear Receptor Ligands: Rational and Effective Therapy for Chronic Cholestatic Liver Disease?

p r f c t p p f c he regulation of genes that are essential to many hepatic metabolic and transport functions are medited in large part by the action of small molecules that unction as nuclear receptor ligands.1 This process has een labeled chemical genomics.2 These ligands bind to heir specific nuclear receptors, activating the receptor hat then binds to specific elements in a gene’s promoter esulting in stimulation or inhibition of gene expresion.3 In the liver many drugs, metabolites, and herbal ompounds exert their biologic properties as ligands for uclear receptors.4,5 Some familiar examples of drugs hat activate nuclear receptors include phenobarbital and t John’s wort. Both drugs induce hepatic drug metablizing enzymes by acting as ligands for the pregnane X eceptor (PXR), which binds to specific response eleents in the promoter of cytochrome P-450 3A CYP3A), a major hepatic microsomal drug–metabolizng enzyme. This induction then indirectly affects the etabolism and systemic effects of a wide variety of other ompounds metabolized by CYP3A. An extract of 4 ifferent plants, Yin Zhi Huang, has been used tradiionally for treating neonatal jaundice in China and is a igand for the constitutive androstane receptor (CAR) hat up-regulates the expression of several different liver ransporters and enzymes involved in the hepatic clearnce of serum bilirubin.5 Indeed, more than 10% of edically useful drugs are known to exert their biologic ehavior by binding to ligand-binding domains on speific nuclear receptors.4 Table 1 shows some of the most mportant nuclear receptors and their physiologic ligands hat determine the hepatic transport and metabolism of variety of xenobiotics and endogenous substrates. In this issue of GASTROENTEROLOGY, Marschall et al6 eport that rifampicin and ursodeoxycholic acid (UDCA), wo well-known drugs used in the treatment of cholesatic liver disease, each stimulate the transcription of a istinct set of genes that together decrease bile acid ptake, enhance bile acid detoxification and excretion, nd stimulate the clearance of bilirubin. Rifampicin inreased the expression of CYP3A4, uridine 5=-glucuonosyl transferase (UGT1A1), and multidrug-resisance–associated protein (MRP2) whereas UDCA timulated the bile salt export pump (BSEP), and mulidrug resistance protein (MDR3), and MRP4. Although hese effects were observed in patients undergoing choecystectomy who otherwise were healthy, these separate ut complementary effects on gene and protein expresion are predicted to have beneficial effects if they ocurred in patients with cholestatic liver disease. These ndings thus suggest that there is therapeutic benefit rom combining drugs such as rifampicin and UDCA hat target nuclear receptors that have coordinated effects n the transcriptional regulation of hepatobiliary excreory mechanisms.7 How does this occur? The hepatic clearance of bile acids and bilirubin can be ivided into 4 phases that include the following: phase 0, epatic uptake; phase I, metabolism (eg, hydroxylation); hase II, detoxification (eg, conjugation); and phase III, xcretion. Nuclear receptors and their ligands that are he major determinants of the functional expression of enes that determine these pathways are shown in Figure , together with enzymes that control bile acid synthesis. In the enterohepatic circulation, the hepatic uptake of onjugated bile acids (phase 0) is mediated predominantly y the sodium taurocholate cotransporting polypeptide TCP (SLC10A1), whereas unconjugated bile acid uptake s facilitated by several organic anion transporting polypepides (OATPs) on the sinusoidal membrane, but predomi-