Protease detection in the biosensor era: A review.

Proteases have been proposed as potential biomarkers for several pathological conditions including cancers, multiple sclerosis and cardiovascular diseases, due to their ability to break down the components of extracellular matrix and basement membrane. The development of protease biosensors opened up the possibility to investigate the proteolytic activity of dysregulated proteases with higher efficiency over the traditional detection assays due to their quick detection capability, high sensitivity and selectivity, simple instrumentation and cost-effective fabrication processes. In contrast to the recently published review papers that primarily focused on one specific class of proteases or one specific detection method, this review article presents different optical and electrochemical detection methods that can be used to design biosensors for all major protease families.

Amyloid beta and its naturally occurring N-terminal variants are potent activators of human and mouse formyl peptide receptor 1.

Formyl peptide receptors (FPRs) may contribute to inflammation in Alzheimer's disease through interactions with neuropathological Amyloid beta (Aβ) peptides. Previous studies reported activation of FPR2 by Aβ, but further investigation of other FPRs and Aβ variants is needed. This study provides a comprehensive overview of the interactions of mouse and human FPRs with different physiologically relevant Aβ-peptides using transiently transfected cells in combination with calcium imaging.

Emerging contributions of formyl peptide receptors to neurodegenerative diseases.

Inflammation is a central element of many neurodegenerative diseases. Formyl peptide receptors (FPRs) can trigger several receptor-dependent signal transduction pathways that play a key role in neuroinflammation and neurodegeneration. They are chemotactic receptors that help to regulate pro- and anti-inflammatory responses in most mammals.

Chemosensory Cell-Derived Acetylcholine Drives Tracheal Mucociliary Clearance in Response to Virulence-Associated Formyl Peptides.

Mucociliary clearance through coordinated ciliary beating is a major innate defense removing pathogens from the lower airways, but the pathogen sensing and downstream signaling mechanisms remain unclear. We identified virulence-associated formylated bacterial peptides that potently stimulated ciliary-driven transport in the mouse trachea. This innate response was independent of formyl peptide and taste receptors but depended on key taste transduction genes.

Trpc5 deficiency causes hypoprolactinemia and altered function of oscillatory dopamine neurons in the arcuate nucleus.

Dopamine neurons of the hypothalamic arcuate nucleus (ARC) tonically inhibit the release of the protein hormone prolactin from lactotropic cells in the anterior pituitary gland and thus play a central role in prolactin homeostasis of the body. Prolactin, in turn, orchestrates numerous important biological functions such as maternal behavior, reproduction, and sexual arousal. Here, we identify the canonical transient receptor potential channel Trpc5 as an essential requirement for normal function of dopamine ARC neurons and prolactin homeostasis.

A calcium optimum for cytotoxic T lymphocyte and natural killer cell cytotoxicity.

Key Points: Cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells are required to eliminate cancer cells. We analysed the Ca dependence of CTL and NK cell cytotoxicity and found that in particular CTLs have a very low optimum of [Ca ] (between 122 and 334 nm) and [Ca ] (between 23 and 625 μm) for efficient cancer cell elimination, well below blood plasma Ca levels. As predicted from these results, partial down-regulation of the Ca channel Orai1 in CTLs paradoxically increases perforin-dependent cancer cell killing.

Organization and Plasticity of Sodium Channel Expression in the Mouse Olfactory and Vomeronasal Epithelia.

To understand the molecular basis of neuronal excitation in the mammalian olfactory system, we conducted a systematic analysis of the organization of voltage-gated sodium (Na) channel subunits in the main olfactory epithelium (MOE) and vomeronasal organ (VNO) of adult mice. We also analyzed changes in Na channel expression during development in these two systems and during regeneration of the MOE. Quantitative PCR shows that Na1.

Trpm5 expression in the olfactory epithelium.

The Ca-activated monovalent cation channel Trpm5 is a key element in chemotransduction of taste receptor cells of the tongue, but the extent to which Trpm5 channels are expressed in olfactory sensory neurons (OSNs) of the main olfactory epithelium (MOE) of adult mice as part of a specific pheromonal detection system is debated. Here, we used a novel Trpm5-IRES-Cre knockin strain to drive Cre recombinase expression, employed previously validated Trpm5 antibodies, performed in situ hybridization experiments to localize Trpm5 RNA, and searched extensively for Trpm5 splice variants in genetically-labeled, Trpm5-expressing MOE cells. In contrast to previous reports, we find no evidence for the existence in adult mouse OSNs of the classical Trpm5 channel known from taste cells.

The sensing of bacteria: emerging principles for the detection of signal sequences by formyl peptide receptors.

The ability to detect specific chemical signatures released by bacteria and other microorganisms is a fundamental feature of immune defense against pathogens. There is increasing evidence that chemodetection of such microorganism-associated molecular patterns (MAMPs) occurs at many places in the body including specific sets of chemosensory neurons in the mammalian nose. Formyl peptide receptors (FPRs) are a unique family of G protein-coupled receptors (GPCRs) that can detect the presence of bacteria and function as chemotactic receptors.

Strain-specific Loss of Formyl Peptide Receptor 3 in the Murine Vomeronasal and Immune Systems.

Formyl peptide receptor 3 (Fpr3, also known as Fpr-rs1) is a G protein-coupled receptor expressed in subsets of sensory neurons of the mouse vomeronasal organ, an olfactory substructure essential for social recognition. Fpr3 has been implicated in the sensing of infection-associated olfactory cues, but its expression pattern and function are incompletely understood. To facilitate visualization of Fpr3-expressing cells, we generated and validated two new anti-Fpr3 antibodies enabling us to analyze acute Fpr3 protein expression.

Recognition of bacterial signal peptides by mammalian formyl peptide receptors: a new mechanism for sensing pathogens.

Formyl peptide receptors (FPRs) are G-protein-coupled receptors that function as chemoattractant receptors in innate immune responses. Here we perform systematic structure-function analyses of FPRs from six mammalian species using structurally diverse FPR peptide agonists and identify a common set of conserved agonist properties with typical features of pathogen-associated molecular patterns. Guided by these results, we discover that bacterial signal peptides, normally used to translocate proteins across cytoplasmic membranes, are a vast family of natural FPR agonists.

Formyl peptide receptors from immune and vomeronasal system exhibit distinct agonist properties.

The formyl peptide receptor (Fpr) family is well known for its contribution to immune defense against pathogens in human and rodent leukocytes. Recently, several structurally related members of these receptors were discovered in sensory neurons of the mouse vomeronasal organ (VNO), key detectors of pheromones and related semiochemicals. Although the biological role of vomeronasal Fprs is not yet clear, the known contribution of other Fprs to host immune defense suggested that they could contribute to vomeronasal pathogen sensing.

Mammalian-specific OR37 receptors are differentially activated by distinct odorous fatty aldehydes.

The capacity of the mammalian olfactory system to detect an enormous collection of different chemical compounds is based on a large repertoire of odorant receptors (ORs). A small group of these ORs, the OR37 family, is unique due to a variety of special features. Members of this subfamily are exclusively found in mammals, they share a high degree of sequence homology and are highly conserved during evolution.

G protein G(alpha)o is essential for vomeronasal function and aggressive behavior in mice.

The rodent vomeronasal organ (VNO) mediates the regulation of species-specific and interspecies social behaviors. We have used gene targeting to examine the role of the G protein Gαo, encoded by the gene Gnao1, in vomeronasal function. We used the Cre-loxP system to delete Gαo in those cells that express olfactory marker protein, which includes all vomeronasal sensory neurons of the basal layer of the VNO sensory epithelium.

Loss-of-function mutations in sodium channel Nav1.7 cause anosmia.

Loss of function of the gene SCN9A, encoding the voltage-gated sodium channel Na(v)1.7, causes a congenital inability to experience pain in humans. Here we show that Na(v)1.

Oligomerization of TAS2R bitter taste receptors.

A family of 25 G protein-coupled receptors, TAS2Rs, mediates bitter taste in humans. Many of the members of this family are coexpressed in a subpopulation of taste receptor cells on the tongue, thereby allowing the possibility of receptor-receptor interactions with potential influences on their function. In this study, we used several experimental approaches to investigate whether TAS2Rs can form oligomers and if this has an effect on receptor function.

The molecular receptive ranges of human TAS2R bitter taste receptors.

Humans perceive thousands of compounds as bitter. In sharp contrast, only approximately 25 taste 2 receptors (TAS2R) bitter taste receptors have been identified, raising the question as to how the vast array of bitter compounds can be detected by such a limited number of sensors. To address this issue, we have challenged 25 human taste 2 receptors (hTAS2Rs) with 104 natural or synthetic bitter chemicals in a heterologous expression system.

The binding site for neohesperidin dihydrochalcone at the human sweet taste receptor.

Background: Differences in sweet taste perception among species depend on structural variations of the sweet taste receptor. The commercially used isovanillyl sweetener neohesperidin dihydrochalcone activates the human but not the rat sweet receptor TAS1R2+TAS1R3. Analysis of interspecies combinations and chimeras of rat and human TAS1R2+TAS1R3 suggested that the heptahelical domain of human TAS1R3 is crucial for the activation of the sweet receptor by neohesperidin dihydrochalcone.

A TAS1R receptor-based explanation of sweet 'water-taste'.

'Water-tastes' are gustatory after-impressions elicited by water following the removal of a chemical solution from the mouth, akin to colour after-images appearing on 'white' paper after fixation on coloured images. Unlike colour after-images, gustatory after-effects are poorly understood. One theory posits that 'water-tastes' are adaptation phenomena, in which adaptation to one taste solution causes the water presented subsequently to act as a taste stimulus.

Independent evolution of bitter-taste sensitivity in humans and chimpanzees.

It was reported over 65 years ago that chimpanzees, like humans, vary in taste sensitivity to the bitter compound phenylthiocarbamide (PTC). This was suggested to be the result of a shared balanced polymorphism, defining the first, and now classic, example of the effects of balancing selection in great apes. In humans, variable PTC sensitivity is largely controlled by the segregation of two common alleles at the TAS2R38 locus, which encode receptor variants with different ligand affinities.