Junyang Jung

Two-Photon Absorbing Dyes with Minimal Autofluorescence in Tissue Imaging: Application to in Vivo Imaging of Amyloid-β Plaques with a Negligible Background Signal

Fluorescence imaging of tissues offer an essential means for studying biological systems. Autofluorescence becomes a serious issue in tissue imaging under excitation at UV-vis wavelengths where biological molecules compete with the fluorophore. To address this critical issue, a novel class of fluorophores that can be excited at ∼900 nm under two-photon excitation conditions and emits in the red wavelength region (≥600 nm) has been disclosed. The new π-extended dipolar dye system shows several advantageous features including minimal autofluorescence in tissue imaging and pronounced solvent-sensitive emission behavior, compared with a widely used two-photon absorbing dye, acedan. As an important application of the new dye system, one of the dyes was developed into a fluorescent probe for amyloid-β plaques, a key biomarker of Alzheimers disease. The probe enabled in vivo imaging of amyloid-β plaques in a disease-model mouse, with negligible background signal. The new dye system has great potential for the development of other types of two-photon fluorescent probes and tags for imaging of tissues with minimal autofluorescence.

Toward a selective, sensitive, fast-responsive, and biocompatible two-photon probe for hydrogen sulfide in live cells.

Hydrogen sulfide has emerged as an exciting endogenous gasotransmitter in addition to nitric oxide and carbon dioxide. Noninvasive detection methods for hydrogen sulfide thus become indispensable tools for studying its diverse roles in biological systems. Accordingly, fluorescent probes for hydrogen sulfide have received great attention in recent years. A practically useful fluorescent probe for bioimaging of hydrogen sulfide should be selective, sensitive, fast-responsive, biocompatible, observable in the biological optical window, and capable of deep-tissue imaging. These sensing properties, however, are extremely difficult to achieve at the same time. Disclosed here is the two-photon fluorescent probe that meets all of these criteria. The probe belongs to a Michael acceptor system, which raised a serious selectivity issue over the competing biothiols such as cysteine and glutathione. We have addressed the selectivity issue by optimizing the electronic and steric interactions between biothiols and the probe, in addition to achieving very high sensitivity, fast-response, and biocompatibility. Also, the sensing mechanism suggested in the literature was revised. The probe thus enables us to image the endogenously produced hydrogen sulfide with negligible interference from other biothiols in live cells. The excellent sensing properties of the probe combined with its capability of bioimaging thus make it a practically useful tool for further studying biological roles of hydrogen sulfide.

Clinical and Functional Anatomy of the Urethral Sphincter

Continence and micturition involve urethral closure. Especially, insufficient strength of the pelvic floor muscles including the urethral sphincter muscles causes urinary incontinence (UI). Thus, it is most important to understand the main mechanism causing UI and the relationship of UI with the urethral sphincter. Functionally and anatomically, the urethral sphincter is made up of the internal and the external sphincter. We highlight the basic and clinical anatomy of the internal and the external sphincter and their clinical meaning. Understanding these relationships may provide a novel view in identifying the main mechanism causing UI and surgical techniques for UI.

Physiological Importance of Hydrogen Sulfide: Emerging Potent Neuroprotector and Neuromodulator

Hydrogen sulfide (H2S) is an emerging neuromodulator that is considered to be a gasotransmitter similar to nitrogen oxide (NO) and carbon monoxide (CO). H2S exerts universal cytoprotective effects and acts as a defense mechanism in organisms ranging from bacteria to mammals. It is produced by the enzymes cystathionine β-synthase (CBS), cystathionine ϒ-lyase (CSE), 3-mercaptopyruvate sulfurtransferase (MST), and D-amino acid oxidase (DAO), which are also involved in tissue-specific biochemical pathways for H2S production in the human body. H2S exerts a wide range of pathological and physiological functions in the human body, from endocrine system and cellular longevity to hepatic protection and kidney function. Previous studies have shown that H2S plays important roles in peripheral nerve regeneration and degeneration and has significant value during Schwann cell dedifferentiation and proliferation but it is also associated with axonal degradation and the remyelination of Schwann cells. To date, physiological and toxic levels of H2S in the human body remain unclear and most of the mechanisms of action underlying the effects of H2S have yet to be fully elucidated. The primary purpose of this review was to provide an overview of the role of H2S in the human body and to describe its beneficial effects.

Role of Gasotransmitters in Oxidative Stresses, Neuroinflammation, and Neuronal Repair

To date, three main gasotransmitters, that is, hydrogen sulfide (H2S), carbon monoxide (CO), and nitric oxide (NO), have been discovered to play major bodily physiological roles. These gasotransmitters have multiple functional roles in the body including physiologic and pathologic functions with respect to the cellular or tissue quantities of these gases. Gasotransmitters were originally known to have only detrimental and noxious effects in the body but that notion has much changed with years; vast studies demonstrated that these gasotransmitters are precisely involved in the normal physiological functioning of the body. From neuromodulation, oxidative stress subjugation, and cardiovascular tone regulation to immunomodulation, these gases perform critical roles, which, should they deviate from the norm, can trigger the genesis of a number of neurodegenerative diseases such as Alzheimers disease (AD) and Parkinsons disease (PD). The purpose of this review is to discuss at great length physical and chemical properties and physiological actions of H2S, NO, and CO as well as shedding light on recently researched molecular targets. We particularly put emphasis on the roles in neuronal inflammation and neurodegeneration and neuronal repair.

Possible ATP release through lysosomal exocytosis from primary sensory neurons.

The adenosine triphosphate (ATP) plays important roles under physiological and pathological conditions such as traumatic brain injury, neuroinflammation and neuropathic pain. In the present study, we set out to study the role of lysosomal vesicles on ATP release from the dorsal root ganglion neurons. We found that the lysosomal vesicles, which contain the quinacrine-positive fluorescence and express the vesicular nucleotide transporter (VNUT), were localized within the soma and growth cone of the cultured dorsal root ganglion neurons. In addition, the number of the quinacrine staining was decreased by application of lysosomal exocytosis activators, and this decrease was suppressed by the metformin and vacuolin-1, which suppressed lysosomal exocytosis. Thus, these findings suggest that ATP release via the lysosomal exocytosis may be one of the pathways for ATP release in response to stimulation.

Alterations in Nitric Oxide Synthase in the Aged CNS

Aging is associated with neuronal loss, gross weight reduction of the brain, and glial proliferation in the cortex, all of which lead to functional changes in the brain. It is known that oxidative stress is a critical factor in the pathogenesis of aging; additionally, growing evidence suggests that excessive nitric oxide (NO) production contributes to the aging process. However, it is still unclear how NO plays a role in the aging process. This paper describes age-related changes in the activity of NADPH-diaphorase (NADPH-d), a marker for neurons containing nitric oxide synthase (NOS), in many CNS regions. Understanding these changes may provide a novel perspective in identifying the aging mechanism.

Nitric Oxide: Exploring the Contextual Link with Alzheimer’s Disease

Neuronal inflammation is a systematically organized physiological step often triggered to counteract an invading pathogen or to rid the body of damaged and/or dead cellular debris. At the crux of this inflammatory response is the deployment of nonneuronal cells: microglia, astrocytes, and blood-derived macrophages. Glial cells secrete a host of bioactive molecules, which include proinflammatory factors and nitric oxide (NO). From immunomodulation to neuromodulation, NO is a renowned modulator of vast physiological systems. It essentially mediates these physiological effects by interacting with cyclic GMP (cGMP) leading to the regulation of intracellular calcium ions. NO regulates the release of proinflammatory molecules, interacts with ROS leading to the formation of reactive nitrogen species (RNS), and targets vital organelles such as mitochondria, ultimately causing cellular death, a hallmark of many neurodegenerative diseases. AD is an enervating neurodegenerative disorder with an obscure etiology. Because of accumulating experimental data continually highlighting the role of NO in neuroinflammation and AD progression, we explore the most recent data to highlight in detail newly investigated molecular mechanisms in which NO becomes relevant in neuronal inflammation and oxidative stress-associated neurodegeneration in the CNS as well as lay down up-to-date knowledge regarding therapeutic approaches targeting NO.

Extracellular ATP inhibits Schwann cell dedifferentiation and proliferation in an ex vivo model of Wallerian degeneration

After nerve injury, Schwann cells proliferate and revert to a phenotype that supports nerve regeneration. This phenotype-changing process can be viewed as Schwann cell dedifferentiation. Here, we investigated the role of extracellular ATP in Schwann cell dedifferentiation and proliferation during Wallerian degeneration. Using several markers of Schwann cell dedifferentiation and proliferation in sciatic explants, we found that extracellular ATP inhibits Schwann cell dedifferentiation and proliferation during Wallerian degeneration. Furthermore, the blockage of lysosomal exocytosis in ATP-treated sciatic explants is sufficient to induce Schwann cell dedifferentiation. Together, these findings suggest that ATP-induced lysosomal exocytosis may be involved in Schwann cell dedifferentiation.

Hydrogen sulfide is essential for Schwann cell responses to peripheral nerve injury.

Hydrogen sulfide (H2S) functions as a physiological gas transmitter in both normal and pathophysiological cellular events. H2S is produced from substances by three enzymes: cystathionine β‐synthase (CBS), cystathionine γ‐lyase (CSE), and 3‐mercaptopyruvate sulfurtransferase (MST). In human tissues, these enzymes are involved in tissue‐specific biochemical pathways for H2S production. For example, CBS and cysteine aminotransferase/MST are present in the brain, but CSE is not. Thus, we examined the expression of H2S production‐related enzymes in peripheral nerves. Here, we found that CSE and MST/cysteine aminotransferase, but not CBS, were present in normal peripheral nerves. In addition, injured sciatic nerves in vivo up‐regulated CSE in Schwann cells during Wallerian degeneration (WD); however, CSE was not up‐regulated in peripheral axons. Using an ex vivo sciatic nerve explant culture, we found that the inhibition of H2S production broadly prevented the process of nerve degeneration, including myelin fragmentation, axonal degradation, Schwann cell dedifferentiation, and Schwann cell proliferation in vitro and in vivo. Thus, these results indicate that H2S signaling is essential for Schwann cell responses to peripheral nerve injury.