Adiponectin and AdipoR1 regulate PGC-1alpha and mitochondria by Ca(2+) and AMPK/SIRT1.

Adiponectin is an anti-diabetic adipokine. Its receptors possess a seven-transmembrane topology with the amino terminus located intracellularly, which is the opposite of G-protein-coupled receptors. Here we provide evidence that adiponectin induces extracellular Ca(2+) influx by adiponectin receptor 1 (AdipoR1), which was necessary for subsequent activation of Ca(2+)/calmodulin-dependent protein kinase kinase beta (CaMKKbeta), AMPK and SIRT1, increased expression and decreased acetylation of peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha), and increased mitochondria in myocytes. Moreover, muscle-specific disruption of AdipoR1 suppressed the adiponectin-mediated increase in intracellular Ca(2+) concentration, and decreased the activation of CaMKK, AMPK and SIRT1 by adiponectin. Suppression of AdipoR1 also resulted in decreased PGC-1alpha expression and deacetylation, decreased mitochondrial content and enzymes, decreased oxidative type I myofibres, and decreased oxidative stress-detoxifying enzymes in skeletal muscle, which were associated with insulin resistance and decreased exercise endurance. Decreased levels of adiponectin and AdipoR1 in obesity may have causal roles in mitochondrial dysfunction and insulin resistance seen in diabetes.

High-throughput development of a hybrid-type fluorescent glutamate sensor for analysis of synaptic transmission.

Fluorescent sensors are powerful tools for visualizing cellular molecular dynamics. We present a high-throughput screening system, designated hybrid-type fluorescence indicator development (HyFInD), to identify optimal position-specific fluorophore labeling in hybrid-type sensors consisting of combinations of ligand-binding protein mutants with small molecular fluorophores. We screened sensors for glutamate among hybrid molecules obtained by the reaction of four cysteine-reactive fluorescence probes with a set of cysteine-scanning mutants of the 274 amino acid S1S2 domain of AMPA-type glutamate receptor GluA2 subunit. HyFInD identified a glutamate-responsive probe (enhanced glutamate optical sensor: eEOS) with a dynamic range >2400 %, good photostability, and high selectivity. When eEOS was specifically tethered to neuronal surfaces, it reliably visualized the spatiotemporal dynamics of glutamate release at single synapses, revealing synapse-to-synapse heterogeneity of short-term plasticity.

Acidic-pH-activatable fluorescence probes for visualizing exocytosis dynamics.

Live imaging of exocytosis dynamics is crucial for a precise spatiotemporal understanding of secretion phenomena, but current approaches have serious limitations. We designed and synthesized small-molecular fluorescent probes that were chemically optimized for sensing acidic intravesicular pH values, and established that they can be used to sensitively and reliably visualize vesicular dynamics following stimulation. This straightforward technique for the visualization of exocytosis as well as endocytosis/reacidification processes with high spatiotemporal precision is expected to be a powerful tool for investigating dynamic cellular phenomena involving changes in the pH value.

Imaging extrasynaptic glutamate dynamics in the brain.

Glutamate is the major neurotransmitter in the brain, mediating point-to-point transmission across the synaptic cleft in excitatory synapses. Using a glutamate imaging method with fluorescent indicators, we show that synaptic activity generates extrasynaptic glutamate dynamics in the vicinity of active synapses. These glutamate dynamics had magnitudes and durations sufficient to activate extrasynaptic glutamate receptors in brain slices. We also observed crosstalk between synapses--i.e., summation of glutamate released from neighboring synapses. Furthermore, we successfully observed that sensory input from the extremities induced extrasynaptic glutamate dynamics within the appropriate sensory area of the cerebral cortex in vivo. Thus, the present study clarifies the spatiotemporal features of extrasynaptic glutamate dynamics, and opens up an avenue to directly visualizing synaptic activity in live animals.

Enzymatic production of RNAi libraries from cDNAs.

RNA interference (RNAi) induced by small interfering (siRNA) or short hairpin RNA (shRNA) is an important research approach in mammalian genetics. Here we describe a technology called enzymatic production of RNAi library (EPRIL) by which cDNAs are converted by a sequence of enzymatic treatments into an RNAi library consisting of a vast array of different shRNA expression constructs. We applied EPRIL to a single cDNA source and prepared an RNAi library consisting of shRNA constructs with various RNAi efficiencies. High-throughput screening allowed us to rapidly identify the best shRNA constructs from the library. We also describe a new selection scheme using the thymidine kinase gene for obtaining efficient shRNA constructs. Furthermore, we show that EPRIL can be applied to constructing an RNAi library from a cDNA library, providing a basis for future whole-genome phenotypic screening of genes.

Cell surface-anchored fluorescent aptamer sensor enables imaging of chemical transmitter dynamics.

A fluorescent aptamer sensor was applied to the analysis of extracellular chemical transmitter dynamics. We utilized a tocopherol-labeled aptamer, which allowed the direct anchoring of the fluorescent aptamer on the cell surface while retaining its performance as a fluorescent sensor. The fast-responsive fluorescent DNA aptamer sensor, which targets adenine compounds, was anchored on the surface of brain astrocytes. Fluorescence imaging of the aptamer-anchored astrocytes enabled the real-time monitoring of release of adenine compounds as a gliotransmitter, which was synchronized with calcium wave propagation in neighboring cells.

In vivo Fluorescence Imaging of Extracellular ATP in the Mouse Cerebral Cortex with a Hybrid-type Optical Sensor.

Adenosine 5'-triphosphate (ATP) works as an extracellular signaling molecule for cells in the brain, such as neurons and glia. Cellular communication via release of ATP is involved in a range of processes required for normal brain functions, and aberrant communication is associated with brain disorders. To investigate the mechanisms underlying these cellular processes, various techniques have been developed for the measurement of extracellular ATP. To monitor the dynamics of extracellular ATP signaling with high spatiotemporal resolution, we recently developed a hybrid-type ATP optical sensor (ATPOS) that enables in vivo fluorescence imaging of extracellular ATP dynamics in the brain. ATPOS is synthesized by labeling an ATP-binding protein, Bacillus FoF1-ATP synthase ε subunit, with a small-molecular fluorescent dye Cy3. Injection of ATPOS into the cerebral cortex of living mice enables visualization of the wave-like propagation of extracellular ATP release in response to electrical stimulation. The protocol described here should be useful for visualizing ATP signaling in diverse processes involved in intercellular communication in the brain.

Quantitative modeling of regular retinal microglia distribution.

Microglia are resident immune cells in the central nervous system, showing a regular distribution. Advancing microscopy and image processing techniques have contributed to elucidating microglia's morphology, dynamics, and distribution. However, the mechanism underlying the regular distribution of microglia remains to be elucidated. First, we quantitatively confirmed the regularity of the distribution pattern of microglial soma in the retina. Second, we formulated a mathematical model that includes factors that may influence regular distribution. Next, we experimentally quantified the model parameters (cell movement, process formation, and ATP dynamics). The resulting model simulation from the measured parameters showed that direct cell-cell contact is most important in generating regular cell spacing. Finally, we tried to specify the molecular pathway responsible for the repulsion between neighboring microglia.

Real-time in vivo imaging of extracellular ATP in the brain with a hybrid-type fluorescent sensor.

Adenosine 5' triphosphate (ATP) is a ubiquitous extracellular signaling messenger. Here, we describe a method for in-vivo imaging of extracellular ATP with high spatiotemporal resolution. We prepared a comprehensive set of cysteine-substitution mutants of ATP-binding protein, Bacillus FoF1-ATP synthase ε subunit, labeled with small-molecule fluorophores at the introduced cysteine residue. Screening revealed that the Cy3-labeled glutamine-105 mutant (Q105C-Cy3; designated ATPOS) shows a large fluorescence change in the presence of ATP, with submicromolar affinity, pH-independence, and high selectivity for ATP over ATP metabolites and other nucleotides. To enable in-vivo validation, we introduced BoNT/C-Hc for binding to neuronal plasma membrane and Alexa Fluor 488 for ratiometric measurement. The resulting ATPOS complex binds to neurons in cerebral cortex of living mice, and clearly visualized a concentrically propagating wave of extracellular ATP release in response to electrical stimulation. ATPOS should be useful to probe the extracellular ATP dynamics of diverse biological processes in vivo.

Biologists often refer to a small molecule called adenosine triphosphate ­ or ATP for short ­ as 'the currency of life'. This molecule carries energy all through the body, and most cells and proteins require ATP to perform their various roles. Nerve cells (also known as neurons) in the brain release ATP when activated, and use this molecule to send signals to other active neurons or other cells in the brain. But ATP can also signal danger in the brain. A molecule derived from ATP is involved in transmitting the pain signals of migraines and severe headaches; and ATP levels can become imbalanced after strokes, when parts of the brain are deprived of blood. Despite its importance, ATP remains difficult to visualize in the body, and monitoring the molecule in the active brain in real time is challenging. To address this issue, Kitajima et al. designed an optical sensor that could monitor ATP in the healthy brain, and was sensitive enough to detect when and where it was released. First, Kitajima et al. made several potential sensors by attaching various fluorescent tags to different locations on a protein that binds ATP. Next each sensor was tested to determine whether it could bind ATP tightly and get bright upon binding. This is important because previous sensors could not detect ATP release in the brains of living animals. To illustrate the new sensors' potential, Kitajima et al. used the sensor to image ATP in the brains of live mice. A 'wave' of ATP was seen spreading through the brain after neurons were stimulated with a small electric pulse, mimicking a sudden migraine or stroke. The results confirm that this new sensor is suitable for imaging how ATP signals in the brain, and it may help resolve the underlying mechanisms of migraines and strokes. This sensor could also be used to understand other cellular process which rely on ATP to carry out their role.

Glutamatergic neurotransmission in the procerebrum (olfactory center) of a terrestrial mollusk.

The terrestrial slug Limax has the ability to learn odor associations. This ability depends on the function of the procerebrum, the secondary olfactory center in the brain. Among the various neurotransmitters that are thought to be involved in the function of the procerebrum, glutamate is one of the most important molecules. However, the existence and function of glutamate in this system have been proposed solely on the basis of a few lines of indirect evidence from pharmacological experiments. In the present study, we demonstrated the existence and release of glutamate as a neurotransmitter in the procerebrum of Limax, by using three different techniques: 1) immunohistochemistry of glutamate, 2) in situ hybridization to mRNA of the vesicular glutamate transporter, and 3) real-time imaging of glutamate release within the procerebrum using the glutamate optical sensor EOS2. The release of glutamate within the cell mass layer of the procerebrum was synchronized with oscillation of the local field potential and had the same physiological properties as this oscillation; both were blocked by a serotonin antagonist and were propagated in an apical to basal direction in the procerebrum. Our observations suggest strongly that the oscillation of the local field potential is driven by the glutamate released by bursting neurons in the procerebrum.

Artificial control of subtype-specific platelet-derived growth factor-receptor signaling.

Platelet-derived growth factor (PDGF) signaling controls various physiological functions via two receptor subtypes: PDGF receptor (PDGFR) alpha and PDGFRbeta. Nevertheless, our understanding of their roles is limited because of a lack of pharmacological tools to discriminate subtype-specific signaling. We developed a chimeric receptor by combining ligand-binding-domain truncated PDGFRbeta with anti-fluorescein single chain antibody, expecting the control of PDGFRbeta-specific signaling by oligomerized fluorescein as an artificial agonist. Results show that calcium mobilization, Cdc42 activation, and cell migration were elicited specifically by the artificial ligand in cells expressing the chimeric receptor. Our method is expected to be useful to understand the subtype-specific roles of PDGFRs in various cellular functions.

The Altered Supramolecular Structure of Dopamine D2 Receptors in Disc1-deficient Mice.

Disc1 is a susceptibility gene for psychiatric disorders including schizophrenia. It has been suggested that excess transmission through dopamine type 2 receptors (D2Rs) in the striatum is an underlying mechanism of pathogenesis. In this study, we used super-resolution microscopy to study the distribution of D2Rs at the nanoscale in mice lacking exons 2 and 3 of Disc1 (Disc1-deficient mice). We found that D2Rs in the nucleus accumbens (NAc) of wild-type mice form nanoclusters (~ 20,000 nm2), and that Disc1-deficient mice have larger and more D2R nanoclusters than wild-type mice. Interestingly, administration of clozapine reduced the size and spatial distribution of the nanoclusters only in Disc1-deficient mice. Moreover, we observed that medium spiny neurons in the NAc of Disc1-deficient mice had reduced spine density on their dendrites than did wild-type mice, and this was also reversed by clozapine administration. The altered D2R nanoclusters might be morphological representations of the altered dopaminergic transmission in disease states such as schizophrenia.

Synaptic weight set by Munc13-1 supramolecular assemblies.

The weight of synaptic connections, which is controlled not only postsynaptically but also presynaptically, is a key determinant in neuronal network dynamics. The mechanisms controlling synaptic weight, especially on the presynaptic side, remain elusive. Using single-synapse imaging of the neurotransmitter glutamate combined with super-resolution imaging of presynaptic proteins, we identify a presynaptic mechanism for setting weight in central glutamatergic synapses. In the presynaptic terminal, Munc13-1 molecules form multiple and discrete supramolecular self-assemblies that serve as independent vesicular release sites by recruiting syntaxin-1, a soluble N-ethylmaleimide-sensitive-factor attachment receptor (SNARE) protein essential for synaptic vesicle exocytosis. The multiplicity of these Munc13-1 assemblies affords multiple stable states conferring presynaptic weight, potentially encoding several bits of information at individual synapses. Supramolecular assembling enables a stable synaptic weight, which confers robustness of synaptic computation on neuronal circuits and may be a general mechanism by which biological processes operate despite the presence of molecular noise.

High-throughput screening system to identify small molecules that induce internalization and degradation of HER2.

Overexpression of growth factor receptors in cancers, e.g., human epidermal growth factor receptor 2 (HER2) in ovarian and breast cancers, is associated with aggressiveness. A possible strategy to treat cancers that overexpress those receptors is blockade of receptor signaling by inducing receptor internalization and degradation. In this study, we developed a cell-based high-throughput screening (HTS) system to identify small molecules that induce HER2 internalization by employing our recently developed acidic-pH-activatable probe in combination with protein labeling technology. Our HTS system enabled facile and reliable quantification of HER2 internalization with a Z' factor of 0.66 and a signal-to-noise ratio of 44.6. As proof of concept, we used the system to screen a ∼155,000 small-molecule library and identified three hits that induced HER2 internalization and degradation via at least two distinct mechanisms. This HTS platform should be adaptable to other disease-related receptors in addition to HER2.

Optical glutamate sensor for spatiotemporal analysis of synaptic transmission.

Imaging neurotransmission is expected to greatly improve our understanding of the mechanisms and regulations of synaptic transmission. Aiming at imaging glutamate, a major excitatory neurotransmitter in the CNS, we developed a novel optical glutamate probe, which consists of a ligand-binding domain of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor glutamate receptor GluR2 subunit and a small molecule fluorescent dye. We expected that such fluorescent conjugates might report the microenvironmental changes upon protein conformational changes elicited by glutamate binding. After more than 100 conjugates were tested, we finally obtained a conjugate named E (glutamate) optical sensor (EOS), which showed maximally 37% change in fluorescence intensity upon binding of glutamate with a dissociation constant of 148 nm. By immobilizing EOS on the cell surface of hippocampal neuronal culture preparations, we pursued in situ spatial mapping of synaptically released glutamate following presynaptic firing. Results showed that a single firing was sufficient to obtain high-resolution images of glutamate release, indicating the remarkable sensitivity of this technique. Furthermore, we monitored the time course of changes in presynaptic activity induced by phorbol ester and found heterogeneity in presynaptic modulation. These results indicate that EOS can be generally applicable to evaluation of presynaptic modulation and plasticity. This EOS-based glutamate imaging method is useful to address numerous fundamental issues about glutamatergic neurotransmission in the CNS.

NO signalling decodes frequency of neuronal activity and generates synapse-specific plasticity in mouse cerebellum.

Nitric oxide (NO) is an intercellular messenger regulating neuronal functions. To visualize NO signalling in the brain, we generated a novel fluorescent NO indicator, which consists of the heme-binding region (HBR) of soluble guanylyl cyclase and the green fluorescent protein. The indicator (HBR-GFP) was expressed in the Purkinje cells of the mouse cerebellum and we imaged NO signals in acute cerebellar slices upon parallel fibre (PF) activation with a train of burst stimulations (BS, each BS consisting of five pulses at 50 Hz). Our results showed that the intensity of synaptic NO signal decays steeply with the distance from the synaptic input near PF-Purkinje cell synapses and generates synapse-specific long-term potentiation (LTP). Furthermore, the NO release level has a bell-shaped dependence on the frequency of PF activity. At an optimal frequency (1 Hz), but not at a low frequency (0.25 Hz) of a train of 60 BS, NO release as well as LTP was induced. However, both NO release and LTP were significantly reduced at higher frequencies (2-4 Hz) of BS train due to cannabinoid receptor-mediated retrograde inhibition of NO generation at the PF terminals. These results suggest that synaptic NO signalling decodes the frequency of neuronal activity to mediate synaptic plasticity at the PF-Purkinje cell synapse.

Intracellular delivery of glutathione S-transferase into mammalian cells.

Protein transduction domains (PTDs) derived from human immunodeficiency virus Tat protein and herpes simplex virus VP22 protein are useful for the delivery of non-membrane-permeating polar or large molecules into living cells. In the course of our study aiming at evaluating PTD, we unexpectedly found that the fluorescent-dye-labeled glutathione S-transferase (GST) from Schistosoma japonicum without known PTDs was delivered into COS7 cells. The intracellular transduction of GST was also observed in HeLa, NIH3T3, and PC12 cells, as well as in hippocampal primary neurons, indicating that a wide range of cell types is permissive for GST transduction. Furthermore, we showed that the immunosuppressive peptide VIVIT fused with GST successfully inhibits NFAT activation. These results suggest that GST is a novel PTD which may be useful in the intracellular delivery of biologically active molecules, such as small-molecule drugs, bioactive peptides, or proteins.