Cell-specific coupling of the cloned human 5-HT1F receptor to multiple signal transduction pathways

We recently described the cloning of a fifth member of the 5-hydroxytryptamine (5-HT)₁ (serotonin₁) receptor class that inhibits adenylyl cyclase, namely the human 5-HT_1F receptor (Adham et al. 1993 a). In the present study we have examined in greater detail the functional coupling of the 5-HT_1F receptor in two different cell lines, NIH-3T3 and LM(tk^–) fibroblasts (receptor densities of 1.7 and 4.4 pmol/mg protein, respectively). The maximal inhibitory response elicited by 5-HT was significantly greater in NIH-3T3 as compared to LM(tk^–) cells, whereas the EC₅₀ values were comparable.To investigate the relationship between receptor occupancy and inhibition of cAMP accumulation mediated by 5-HT_1F receptors in NIH-3T3 cells (and hence the degree of receptor reserve), we used the irreversible receptor antagonist N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). The half-maximal response required only about 10% receptor occupancy, consistent with a receptor reserve of 90% (88±2.1%, n = 4) for 5-HT-induced inhibition of FSCA. Despite the presence of such a high degree of receptor reserve, a range of intrinsic activities was displayed by structurally diverse classes of compounds. For example, sumatriptan and lysergol were as efficacious as 5-HT itself and thus acted as full agonists, whereas metergoline and 1-NP behaved as partial agonists and as shown previously (Adham et al. 1993a), methiothepin was a silent antagonist (K_b = 438 nM).We have also investigated activation of additional signal transduction pathways by the 5-HT_1F receptor and found that the responses differ in the two cell lines with respect to stimulation of phospholipase C. For example, in NIH-3T3 cells no elevation of inositol phosphates (IP) of [Ca²⁺]_i was observed even at very high agonist concentrations (100 M). In contrast, in LM(tk^–) cells concentrations of 5-HT as low as 10 nM induced stimulation of IP and a rapid increase of [Ca²⁺]i. The 5-HT_1F receptor failed to alter arachidonic acid release in either cell line.The maximal increase in IP accumulation in LM(tk^–) cells was modest, averaging about 100% above basal. The increases of IP and [Ca²⁺]_i required 5-HT concentrations less than one order of magnitude greater than those inhibiting FSCA (EC₅₀ = 17, 55 and 8 nM, respectively), and both responses were blocked by 100 M methiothepin. All three responses (cAMP, IP, and [Ca²⁺]_i) were sensitive to pertussis toxin pre-treatment, suggesting the involvement of G_i/G_o protein(s) in these signal transduction pathways. [Ca²⁺]_i was also elevated by sumatriptan, which may provide a mechanism by which this drug causes constriction of the vasculature. In conclusion, these data indicate that the human 5-HT_1F receptor can couple to multiple effectors, and that this coupling is cell-type dependent.Abbreviations FSCA forskolin-stimulated cAMP accumulation - [Ca²⁺] intracellular free calcium concentration - AA arachidonic acid - EEDQ N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline - CHO chinese hamster ovary cell - LM(tk^–) mouse fibroblast cell - B_max maximal binding site density - K_i apparent dissociation constant obtained from competition binding studies - G protein guanine nucleotide-binding protein - HBS HEPES-buffered saline - IP inositol phosphates - IP₃ inositol 1,4,5 trisphosphate - PLC phospholipase C - K_b antagonist dissociation constant - K_d equilibrium dissociation constant - N-1F-6 stable NIH-3T3 cells expressing the cloned 5-HT_1F receptor - L-1F-3 stable LM(tk^–) cells expressing the cloned 5-HT_1F receptor - PTX pertussis toxin - BSA bovine serum albumin - METH methiothepin - SUMA sumatriptan - 5-MeO-DMT 5-methoxy-N,N-dimethyltryptamine - 1-NP 1-(1-napthyl)piperazine - 5-CT 5-carboxyamidotryptamine Correspondence to: N. Adham at the above address     

Increased nitric oxide production and gender-dependent changes in PPARα expression and signaling in the fetal lung from diabetic rats

The fetal lung is affected by maternal diabetes. Nuclear receptor PPARα regulates nitric oxide (NO) overproduction in different tissues. We aimed to determine whether fetal lung PPARα expression is altered by maternal diabetes, and if there are gender-dependent changes in PPARα regulation of NO production in the fetal lung. Fetal lungs from control and diabetic rats were explanted on day 21 of gestation and evaluated for PPARα expression and NO production. Fetuses were injected with the PPARα ligand LTB(4) on days 19, 20 and 21, and the fetal lung explanted on day 21 to evaluate PPARα and the inducible isoform of NO synthase (iNOS). Besides, pregnant rats were fed with olive oil- and safflower oil-supplemented diets, enriched in PPAR ligands, for evaluation of fetal lung NO production and PPARα expression. We found reduced PPARα concentrations only in the lung from male fetuses from the diabetic group when compared to controls, although maternal diabetes led to NO overproduction in both male and female fetal lungs. Fetal activation of PPARα led to changes in lung PPARα expression only in female fetuses, although this treatment increased iNOS expression in both male and female fetuses in the diabetic group. Diets supplemented with olive oil and not with safflower oil led to a reduction in NO production in male and female fetal lungs. In conclusion, there are gender-dependent changes in PPARα expression and signaling in the fetal lung from diabetic rats, although PPARα activation prevents maternal diabetes-induced lung NO overproduction in both male and female fetuses.     

Golgi phosphoprotein 4 (GPP130) is a sensitive and selective cellular target of manganese exposure

Chronic elevated exposure to manganese (Mn) is associated with neurocognitive and fine motor deficits in children. However, relatively little is understood about cellular responses to Mn spanning the transition between physiologic to toxic levels of exposure. Here, we investigated the specificity, sensitivity, and time course of the Golgi Phosphoprotein 4 (GPP130) response to Mn exposure in AF5 GABAergic neuronal cells, and we determined the extent to which GPP130 degradation occurs in brain cells in vivo in rats subchronically exposed to Mn. Our results show that GPP130 degradation in AF5 cells was specific to Mn, and did not occur following exposure to cobalt, copper, iron, nickel, or zinc. GPP130 degradation occurred without measurable increases in intracellular Mn levels and at Mn exposures as low as 0.54 µM. GPP130 protein was detectable by immunofluorescence in only ～15–30% of cells in striatal and cortical rat brain slices, and Mn‐exposed animals exhibited a significant reduction in both the number of GPP130‐positive cells, and the overall levels of GPP130 protein, demonstrating the in vivo relevance of this Mn‐specific response within the primary target organ of Mn toxicity. These results provide insight into specific mechanism(s) of cellular Mn regulation and toxicity within the brain, including the selective susceptibility of cells to Mn cytotoxicity. Synapse 67:205–215, 2013. © 2012 Wiley Periodicals, Inc.     

Cellular resolution anatomical and molecular atlases for prenatal human brains

Increasing interest in studies of prenatal human brain development, particularly using new single-cell genomics and anatomical technologies to create cell atlases, creates a strong need for accurate and detailed anatomical reference atlases. In this study, we present two cellular-resolution digital anatomical atlases for prenatal human brain at postconceptional weeks (PCW) 15 and 21. Both atlases were annotated on sequential Nissl-stained sections covering brain-wide structures on the basis of combined analysis of cytoarchitecture, acetylcholinesterase staining, and an extensive marker gene expression dataset. This high information content dataset allowed reliable and accurate demarcation of developing cortical and subcortical structures and their subdivisions. Furthermore, using the anatomical atlases as a guide, spatial expression of 37 and 5 genes from the brains, respectively, at PCW 15 and 21 was annotated, illustrating reliable marker genes for many developing brain structures. Finally, the present study uncovered several novel developmental features, such as the lack of an outer subventricular zone in the hippocampal formation and entorhinal cortex, and the apparent extension of both cortical (excitatory) and subcortical (inhibitory) progenitors into the prenatal olfactory bulb. These comprehensive atlases provide useful tools for visualization, segmentation, targeting, imaging, and interpretation of brain structures of prenatal human brain, and for guiding and interpreting the next generation of cell census and connectome studies.     

Dealing with treatment and transfer requests: how PGD-professionals discuss ethical challenges arising in everyday practice

How do professionals working in pre-implantation genetic diagnosis (PGD) reflect upon their decision making with regard to ethical challenges arising in everyday practice? Two focus group discussions were held with staff of reproductive genetic clinics: one in Utrecht (The Netherlands) with PGD-professionals from Dutch PGD-centres and one in Prague (Czech Republic) with PGD-professionals working in centres in different European countries. Both meetings consisted of two parts, exploring participants’ views regarding (1) treatment requests for conditions that may not fulfill traditional indications criteria for PGD, and (2) treatment and transfer requests involving welfare-of-the-child considerations. There was general support for the view that people who come for PGD will have their own good reasons to consider the condition they wish to avoid as serious. But whereas PGD-professionals in the international group tended to stress the applicants’ legal right to eventually have the treatment they want (whatever the views of the professional), participants in the Dutch group sketched a picture of shared decision-making, where professionals would go ahead with treatment in cases where they are able to understand the reasonableness of the request in the light of the couple’s reproductive history or family experience. In the international focus group there was little support for guidance stating that welfare-of-the child considerations should be taken into account. This was different in the Dutch focus group, where shared decision-making also had the role of reassuring professionals that applicants had adequately considered possible implications for the welfare of the child.     

Exploring the role of the complement system,endothelial injury,and microRNAs in thrombotic microangiopathy after kidney transplantation

ObjectiveWe investigated whether the recipient’s complement system function, kidney graft endothelial ultrastructural injury, and microRNA (miRNA) expression before transplantation may be associated with the risk of posttransplant de novo thrombotic microangiopathy (TMA).MethodsComplement system function assessment, histological and ultrastructural examination of preimplantation and kidney graft biopsies, and microRNA assessment were performed on kidney transplant recipients (KTRs) with de novo TMA.ResultsOn the basis of the clinical course, histological findings, and miRNA patterns, the following two de novo TMA phenotypes were observed: a self-limiting disease that was localized to the kidney graft and a systemic disease that progressed to graft failure without timely treatment. Decreased alternative complement pathway activity and ultrastructural endothelial injury before transplantation were confirmed in all five KTRs and four of five KTRs, respectively, but they did not correlate with de novo TMA severity.ConclusionsAlternative complement pathway abnormalities in KTRs and endothelial ultrastructural injury on preimplantation biopsy might be associated with de novo posttransplant TMA, although they did not predict posttransplant TMA severity (localized vs. systemic). The specific miRNA expression patterns in preimplantation kidney graft biopsies demonstrated a borderline statistically significant difference and might provide more accurate information on posttransplant TMA severity.     

Challenges and recommendations when selecting empirical antibiotics in patients with cirrhosis

There is abundant evidence that bacterial infections are severe complications in patients with cirrhosis,being the most frequent trigger of acute-on-chronic liver failure and causing death in one of every four patients during hospitalization.For these reasons,early diagnosis and effective treatment of infections are mandatory to improve patient outcomes.However,treating physicians are challenged in daily practice since diagnosing bacterial infections is not always straightforward.This situation ...