Bile acid concentrations are controlled by a feedback regulatory pathway whereby activation of the farnesoid X receptor (FXR) represses transcription of both the CYP7A1 gene, encoding the rate-limiting enzyme in the classic bile acid synthesis pathway, and the CYP8B1 gene, required for synthesis of cholic acid. The tissue-specific roles of FXR were examined using liver-and intestinespecific FXR-null models. FXR deficiency in either liver (Fxr #L ) or intestine (Fxr #IE ) increased bile acid pool size. Treatment with the FXR-selective agonist GW4064 significantly repressed CYP7A1 in Fxr #L mice but not Fxr #IE mice, demonstrating that activation of FXR in intestine but not liver is required for short-term repression of CYP7A1 in liver. This intestinal-specific effect of FXR is likely mediated through induction of the hormone FGF15, which suppresses CYP7A1. In comparison to CYP7A1, FXR-mediated repression of CYP8B1 was more dependent on the presence of FXR in liver and less dependent on its presence in intestine. Consistent with these findings, recombinant FGF15 repressed CYP7A1 mRNA levels without affecting CYP8B1 expression.These data provide evidence that FXRmediated repression of bile acid synthesis requires the complementary actions of FXR in both liver and intestine and reveal mechanistic differences in feedback repression of CYP7A1 and CYP8B1.-Kim, I., S-H.

The farnesoid X receptor (FXR) controls the synthesis and transport of bile acids (BAs). Mice lacking expression of FXR, designated Fxr-null, have elevated levels of serum and hepatic BAs and an increase in BA pool size. Surprisingly, at 12 months of age, male and female Fxr-null mice had a high incidence of degenerative hepatic lesions, altered cell foci and liver tumors including hepatocellular adenoma, carcinoma and hepatocholangiocellular carcinoma, the latter of which is rarely observed in mice. At 3 months, Fxr-null mice had increased expression of the proinflammatory cytokine IL-1beta mRNA and elevated beta-catenin and its target gene c-myc. They also had increased cell proliferation as revealed by increased PCNA mRNA and BrdU incorporation. These studies reveal a potential role for FXR and BAs in hepatocarcinogenesis.

Pregnane X receptor (PXR) expression was shown to be protective in inflammatory bowel disease (IBD). However, the mechanism by which PXR provides protection remains unclear. Wild-type and Pxr-null mice were treated with the PXR agonist pregnenolone-16alpha-carbonitrile or vehicle and administered 2.5% dextran sulfate sodium (DSS) in drinking water to induce IBD. Typical clinical symptoms were evaluated on a daily basis. In vivo intestinal permeability assays and proinflammatory cytokine analysis were performed. PXR agonist-treated mice were protected from DSS-induced colitis compared with vehicle-treated mice, as defined by body weight loss, diarrhea, rectal bleeding, colon length, and histology. Pregnenolone-16alpha-carbonitrile did not decrease the severity of IBD in Pxr-null mice. PXR agonist treatment did not increase epithelial barrier function but did decrease mRNA expression of several NF-kappaB target genes in a PXR-dependent manner. The present study clearly demonstrates a protective role for PXR agonist in DSS-induced IBD. The data suggest that PXR-mediated repression of NF-kappaB target genes in the colon is a critical mechanism by which PXR activation decreases the susceptibility of mice to DSS-induced IBD.

Nicotine-induced attentional enhancement is of potential therapeutic value. To investigate the precise attentional function(s) affected and their neuronal mechanisms, the current functional magnetic resonance imaging (fMRI) study used an attention task in which subjects responded to stimuli of high (INT high ) or low intensity presented randomly in one of four peripheral locations. Central cues of varying precision predicted the target location. In some trials, the cue was not followed by a target, allowing separate analysis of blood oxygenation level-dependent (BOLD) responses to cue. Minimally deprived smokers underwent fast event-related fMRI twice: once with a nicotine patch (21 mg) and once with a placebo patch. Matched nonsmokers were scanned twice without a patch. Behaviorally, nicotine reduced omission errors and reaction time (RT) of valid and invalid cue trials and intra-individual variability of RT and did so preferentially in trials with INT high . The BOLD signal related to cue-only trials, regardless of cue precision, demonstrated nicotine-induced deactivation in anterior and posterior cingulate, angular gyrus, middle frontal gyrus, and cuneus. These regions overlapped with the so-called "default network," which activates during rest and deactivates with attention-demanding activities. Partial correlations controlling for nicotine plasma levels indicated associations of deactivation by nicotine in posterior cingulate and angular gyrus with performance improvements under INT high . Performance and regional activity in the absence of nicotine never differed between smokers and nonsmokers, ruling out a simple reversal of a deprivation-induced state. These findings suggest that nicotine improved attentional performance by downregulating resting brain function in response to task-related cues. Together with the selectivity of effects for INT high , this suggests a nicotine-induced potentiation of the alerting properties of external stimuli.

Biosensors based on the localized surface plasmon resonance (LSPR) of individual metallic nanoparticles promise to deliver modular, low-cost sensing with high-detection thresholds. However, they continue to suffer from relatively low sensitivity and figures of merit (FOMs). Herein we introduce the idea of sensitivity enhancement of LSPR sensors through engineering of the material dispersion function. Employing dispersion and shape engineering of chiral nanoparticles leads to remarkable refractive index sensitivities (1,091 nm RIU−1 at λ=921 nm) and FOMs (>2,800 RIU−1). A key feature is that the polarization-dependent extinction of the nanoparticles is now characterized by rich spectral features, including bipolar peaks and nulls, suitable for tracking refractive index changes. This sensing modality offers strong optical contrast even in the presence of highly absorbing media, an important consideration for use in complex biological media with limited transmission. The technique is sensitive to surface-specific binding events which we demonstrate through biotin–avidin surface coupling.

Carotid body (CB) glomus cells from rat express a TASK-like background K+ channel that is believed to play a critical role in the regulation of excitability and hypoxia-induced increase in respiration. Here we studied the kinetic behaviour of single channel openings from rat CB cells to determine the molecular identity of the 'TASK-like' K+ channels. In outside-out patches, the TASK-like background K+ channel in CB cells was inhibited >90% by a reduction of pH(o) from 7.3 to 5.8. In cell-attached patches with 140 mM KCl and 1 mM Mg2+ in the bath and pipette solutions, two main open levels with conductance levels of approximately 14 pS and approximately 32 pS were recorded at a membrane potential of -60 mV. The K+ channels showed kinetic properties similar to TASK-1 (approximately 14 pS), TASK-3 (approximately 32 pS) and TASK-1/3 heteromer (approximately 32 pS). The presence of three TASK isoforms was tested by reducing [Mg2+](o) to approximately 0 mM, which had no effect on the conductance of TASK-1, but increased those of TASK-1/3 and TASK-3 to 42 pS and 74 pS, respectively. In CB cells, the reduction of [Mg2+](o) to approximately 0 mM also caused the appearance of approximately 42 pS (TASK-1/3-like) and approximately 74 pS (TASK-3-like) channels, in addition to the approximately 14 pS (TASK-1-like) channel. The 42 pS channel was the most abundant, contributing approximately 75% of the current produced by TASK-like channels. Ruthenium red (5 microM) had no effect on TASK-1 and TASK-1/3, but inhibited TASK-3 by 87%. In CB cells, ruthenium red caused approximately 12% inhibition of TASK-like activity. Methanandamide reduced the activity of all three TASKs by 80-90%, and that of TASK-like channels in CB cell also by approximately 80%. In CB cells, hypoxia caused inhibition of TASK-like channels, including TASK-1/3-like channels. These results show that TASK-1, TASK-1/3 and TASK-3 are all functionally expressed in isolated CB cells, and that the TASK-1/3 heteromer provides the major part of the oxygen-sensitive TASK-like background K+ conductance.

Background-Hepatocyte nuclear factor 4α (HNF4α; NR2A1) is an orphan member of the nuclear receptor superfamily expressed in liver and intestine. While HNF4α expression is critical for liver function, its role in the gut and in the pathogenesis of inflammatory bowel disease (IBD) is unknown.

Transport of ferric citrate into cells of Escherichia coli K‐12 involves two energy‐coupled transport systems, one across the outer membrane and one across the cytoplasmic membrane. Previously, we have shown that ferric citrate does not have to enter the cytoplasm of E. coli K‐12 to induce transcription of the fec ferric citrate transport genes. Here we demonstrate that ferric citrate uptake into the periplasmic space between the outer and the cytoplasmic membranes is not required for fec gene induction. Rather, FecA and the TonB, ExbB and ExbD proteins are involved in induction of the fec transport genes independent of their role in ferric citrate transport across the outer membrane. The uptake of ferric citrate into the periplasmic space of fecA and tonB mutants via diffusion through the porin channels did not induce transcription of fec transport genes. Point mutants in FecA displayed the constitutive expression of fec transport genes in the absence of ferric citrate but still required TonB, with the exception of one FecA mutant which showed a TonB‐independent induction. The phenotype of the FecA mutants suggests a signal transduction mechanism across three compartments: the outer membrane, the periplasmic space and the cytoplasmic membrane. The signal is triggered upon the interaction of ferric citrate with FecA protein. It is postulated that FecA, TonB, ExbB and ExbD transfer the signal across the outer membrane, while the regulatory protein FecR transmits the signal across the cytoplasmic membrane to FecI in the cytoplasm. FecI serves as a sigma factor which facilitates binding of the RNA polymerase to the fec transport gene promoter upstream of fecA.(ABSTRACT TRUNCATED AT 250 WORDS)