Metabolite-based inter-kingdom communication controls intestinal tissue recovery following chemotherapeutic injury.

Cytotoxic chemotherapies have devastating side effects, particularly within the gastrointestinal tract. Gastrointestinal toxicity includes the death and damage of the epithelium and an imbalance in the intestinal microbiota, otherwise known as dysbiosis. Whether dysbiosis is a direct contributor to tissue toxicity is a key area of focus. Here, from both mammalian and bacterial perspectives, we uncover an intestinal epithelial cell death-Enterobacteriaceae signaling axis that fuels dysbiosis. Specifically, our data demonstrate that chemotherapy-induced epithelial cell apoptosis and the purine-containing metabolites released from dying cells drive the inter-kingdom transcriptional re-wiring of the Enterobacteriaceae, including fundamental shifts in bacterial respiration and promotion of purine utilization-dependent expansion, which in turn delays the recovery of the intestinal tract. Inhibition of epithelial cell death or restriction of the Enterobacteriaceae to homeostatic levels reverses dysbiosis and improves intestinal recovery. These findings suggest that supportive therapies that maintain homeostatic levels of Enterobacteriaceae may be useful in resolving intestinal disease.

Identification of molecular phenotypes and biased signaling induced by naturally occurring mutations of the human calcium-sensing receptor.

More than 200 naturally occurring mutations have been identified in the human CaSR, which have been linked to diseases involving dysregulation of extracellular Ca(2+) homeostasis. These mutations have classically been termed "loss-" or "gain-of-function" mutations, which is an oversimplification given that amino acid changes can alter numerous molecular properties of a receptor. We thus sought to characterize the effects of 21 clinically relevant mutations, the majority located in the heptahelical domains and extracellular loop regions of the CaSR, using flow cytometry to measure cell surface receptor expression levels, and measurements of intracellular Ca(2+) mobilization and ERK1/2 phosphorylation to monitor receptor signaling. We identified distinct molecular phenotypes caused by these naturally occurring amino acid substitutions, which included combinations of loss- and gain-of-expression and changes in intrinsic signaling capacity. Importantly, we also identified biased signaling in the response of the CaSR to different mutations across the two pathways, indicating that some mutations resulted in receptor conformations that differentially altered receptor-coupling preferences. These findings have important implications for understanding the causes of diseases linked to the CaSR. A full appreciation of the molecular effects of these amino acid changes may enable the development of therapeutics that specifically target the molecular determinant of impairment in the receptor.

Positive and negative allosteric modulators promote biased signaling at the calcium-sensing receptor.

The calcium-sensing receptor (CaSR) is a G protein-coupled receptor whose function can be allosterically modulated in a positive or negative manner by calcimimetics or calcilytics, respectively. Indeed, the second-generation calcimimetic, cinacalcet, has proven clinically useful in the treatment of chronic kidney disease patients with secondary hyperparathyroidism but is not widely used in earlier stages of renal disease due to the potential to predispose such patients to hypocalcaemia and hyperphosphatemia. The development of a biased CaSR ligand that is more selective for specific signaling pathway(s) leading only to beneficial effects may overcome this limitation. The detection of such stimulus-bias at a G protein-coupled receptor requires investigation across multiple signaling pathways and the development of methods to quantify the effects of allosteric ligands on orthosteric ligand affinity and cooperativity at each pathway. In the current study, we determined the effects of the calcimimetics, NPS-R568 or cinacalcet, and the calcilytic, NPS-2143, on Ca(o)(2+)-mediated intracellular Ca(2+) mobilization, ERK1/2 phosphorylation, and plasma membrane ruffling in a stably transfected human embryonic kidney 293-TREx c-myc-CaSR cell line and applied a novel analytical model to quantify these modulator effects. We present quantitative evidence for the generation of stimulus bias by both positive and negative allosteric modulators of the CaSR, manifested as greater allosteric modulation of intracellular Ca(2+) mobilization relative to ERK1/2 phosphorylation, and a higher affinity of the modulators for the state of the CaSR mediating plasma membrane ruffling relative to the other two pathways. Our findings provide the first evidence that an allosteric modulator used in clinical practice exhibits stimulus bias.

The role of transmembrane domain 3 in the actions of orthosteric, allosteric, and atypical agonists of the M4 muscarinic acetylcholine receptor.

Despite the discovery of a diverse range of novel agonists and allosteric modulators of the M(4) muscarinic acetylcholine (ACh) receptor (mAChR), little is known about how such ligands activate the receptor. We used site-directed mutagenesis of conserved residues in transmembrane 3 (TMIII), a key region involved in G protein-coupled receptor activation, to probe the binding and function of prototypical orthosteric mAChR agonists, allosteric modulators, and "atypical" agonists. We found that most mutations did not affect the binding of the allosteric modulators, with the exception of W108(3.28)A and L109(3.29)A (which may contribute directly to the interface between allosteric and orthosteric sites) and mutation D112(3.32)N (which may cause a global disruption of a hydrogen bond network). Although numerous mutations affected signaling, we did not identify amino acids that were important for the functional activity of any one class of agonist (orthosteric, allosteric, or atypical) to the exclusion of any others, suggesting that TMIII is key for the transmission of stimulus irrespective of the agonist. We also identified two key residues, Trp108(3.28) and Asp112(3.32), that are essential for the transmission of binding cooperativity between 3-amino-5-chloro-6-methoxy-4-methyl-thieno[2,3-b]pyridine- 2-carboxylic acid cyclopropylamide (LY2033298) and ACh. Finally, we found that LY2033298 was able to rescue functionally impaired signaling of ACh at the majority of mutants tested in a manner that was inversely correlated with the ACh signaling efficacy, indicating that a key part of the mechanism of the positive cooperativity mediated by LY2033298 on the endogenous agonist involves a global drive of the receptor toward an active conformation.

Problem based learning - 'Bringing everything together' - A strategy for Graduate Nurse Programs.

This article discusses a case study that was initiated by a Graduate Nurse Coordinator of an acute care inpatient hospital in Australia. It outlines the conceptualisation and creative implementation of a structured group problem based learning activity which was a component of a Graduate Nurse Program. The learning activity was based on the beliefs that knowledge acquisition today is an active process and should focus on the learner developing strategies to obtain, review and manage information. The learning activity implemented in this case study was valuable as it recognised the benefits that can be gained for the Graduate Nurse by ensuring the context of their teaching and learning activities is grounded in practical experiences. The learning activity aimed to prepare Graduate Nurses to cope with the multiple challenges faced as they enter the nursing profession by enhancing their skills of inquiry, problem solving and reasoning. The evaluation of this case study found that the incorporation of structured group problem based learning did promote the achievement of these educational outcomes with Graduate Nurses displaying critical thinking, clinical judgment and knowledge acquisition skills. An unexpected benefit of this activity for Graduate Nurses was the enhancement of clinical practice behaviours, such as communication and interactive skills. This case study describes the positive outcomes not only for Graduates Nurses in the application of their learning but also the wider benefits which can be gained for the organisation, patient care standards and the health care team. It is anticipated that this article will be an inspiration to others who are interested in implementing innovative teaching strategies into Graduate Nurse Programs.