Endogenous neurotoxic dopamine derivative covalently binds to Parkinson's disease‐associated ubiquitin C‐terminal hydrolase L1 and alters its structure and function

Parkinson's disease (PD) is a common neurodegenerative disease, but its pathogenesis remains elusive. A mutation in ubiquitin C‐terminal hydrolase L1 (UCH‐L1) is responsible for a form of genetic PD which strongly resembles the idiopathic PD. We previously showed that 1‐(3′,4′‐dihydroxybenzyl)‐1,2,3,4‐tetrahydroisoquinoline (3′,4′DHBnTIQ) is an endogenous parkinsonism‐inducing dopamine derivative. Here, we investigated the interaction between 3′,4′DHBnTIQ and UCH‐L1 and its possible role in the pathogenesis of idiopathic PD. Our results indicate that 3′,4′DHBnTIQ binds to UCH‐L1 specifically at Cys152 in vitro. In addition, 3′,4′DHBnTIQ treatment increased the amount of UCH‐L1 in the insoluble fraction of SH‐SY5Y cells and inhibited its hydrolase activity to 60%, reducing the level of ubiquitin in the soluble fraction of SH‐SY5Y cells. Catechol‐modified UCH‐L1 as well as insoluble UCH‐L1 were detected in the midbrain of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐treated PD model mice. Structurally as well as functionally altered UCH‐L1 have been detected in the brains of patients with idiopathic PD. We suggest that conjugation of UCH‐L1 by neurotoxic endogenous compounds such as 3′,4′DHBnTIQ might play a key role in onset and progression of idiopathic PD.

     

The inositol 5-phosphatase SHIP2 is an effector of RhoA and is involved in cell polarity and migration

Cell migration is essential for various physiological and pathological processes. Polarization in motile cells requires the coordination of several key signaling molecules, including RhoA small GTPases and phosphoinositides. Although RhoA participates in a front-rear polarization in migrating cells, little is known about the functional interaction between RhoA and lipid turnover. We find here that src-homology 2-containing inositol-5-phosphatase 2 (SHIP2) interacts with RhoA in a GTP-dependent manner. The association between SHIP2 and RhoA is observed in spreading and migrating U251 glioma cells. The depletion of SHIP2 attenuates cell polarization and migration, which is rescued by wild-type SHIP2 but not by a mutant defective in RhoA binding. In addition, the depletion of SHIP2 impairs the proper localization of phosphatidylinositol 3,4,5-trisphosphate, which is not restored by a mutant defective in RhoA binding. These results suggest that RhoA associates with SHIP2 to regulate cell polarization and migration.     

Probing Functional Properties of Nociceptive Axons Using a Microfluidic Culture System

Pathological changes in axonal function are integral features of many neurological disorders, yet our knowledge of the molecular basis of axonal dysfunction remains limited. Microfluidic chambers (MFCs) can provide unique insight into the axonal compartment independent of the soma. Here we demonstrate how an MFC based cell culture system can be readily adapted for the study of axonal function in vitro. We illustrate the ease and versatility to assay electrogenesis and conduction of action potentials (APs) in naïve, damaged or sensitized DRG axons using calcium imaging at the soma for pharmacological screening or patch-clamp electrophysiology for detailed biophysical characterisation. To demonstrate the adaptability of the system, we report by way of example functional changes in nociceptor axons following sensitization by neurotrophins and axotomy in vitro. We show that NGF can locally sensitize axonal responses to capsaicin, independent of the soma. Axotomizing neurons in MFC results in a significant increase in the proportion of neurons that respond to axonal stimulation, and interestingly leads to accumulation of Nav1.8 channels in regenerating axons. Axotomy also augmented AP amplitude following axotomy and altered activation thresholds in a subpopulation of regenerating axons. We further show how the system can readily be used to study modulation of axonal function by non-neuronal cells such as keratinocytes. Hence we describe a novel in vitro platform for the study of axonal function and a surrogate model for nerve injury and sensitization.     

Stimulating effects of low-power He-Ne laser on growth of Saccharomyces cerevisiae under high pressure

Summary A low-power He-Ne laser decreased the growth inhibitory effect of hydrostatic pressure (50 MPa) on Saccharomyces cerevisiae.     

Bioluminescence‐based cytotoxicity assay for simultaneous evaluation of cell viability and membrane damage in human hepatoma HepG2 cells

We have developed a bioluminescence‐based non‐destructive cytotoxicity assay in which cell viability and membrane damage are simultaneously evaluated using Emerald luciferase (ELuc) and endoplasmic reticulum (ER)‐targeted copepod luciferase (GLuc‐KDEL), respectively, by using multi‐integrase mouse artificial chromosome (MI‐MAC) vector. We have demonstrated that the time‐dependent concentration response curves of ELuc luminescence intensity and WST‐1 assay, and GLuc‐KDEL luminescence intensity and lactate dehydrogenase (LDH) activity in the culture medium accompanied by cytotoxicity show good agreement in toxicant‐treated ELuc‐ and GLuc‐KDEL‐expressing HepG2 stable cell lines. We have clarified that the increase of GLuc‐KDEL luminescence intensity in the culture medium reflects the type of cell death, including necrosis and late apoptosis, but not early apoptosis. We have also uncovered a strong correlation between GLuc‐KDEL luminescence intensity in the culture medium and the extracellular release of high mobility group box 1 (HMGB1), a representative damage‐associated molecular pattern (DAMP) molecule. The bioluminescence measurement assay using ELuc and GLuc‐KDEL developed in this study can simultaneously monitor cell viability and membrane damage, respectively, and the increase of GLuc‐KDEL luminescence intensity in the culture medium accompanied by the increase of cytotoxicity is an index of necrosis and late apoptosis associated with the extracellular release of DAMP molecules.     

Thermostable DNA helicase improves the sensitivity of digital PCR

DNA/RNA helicases, which catalyze the unwinding of duplex nucleic acids using the energy of ATP hydrolysis, contribute to various biological functions involving DNA or RNA. Euryarchaeota-specific helicase Tk-EshA (superfamily 2) from the hyperthermophilic archaeon Thermococcus kodakarensis has been used to decrease generation of mis-amplified products (noise DNAs) during PCR. In this study, we focused on another type (superfamily 1B) of helicase, Tk-Upf1 (TK0178) from T. kodakarensis, and compared its effectiveness in PCR and digital PCR with that of Tk-EshA. For this purpose, we obtained Tk-Upf1 as a recombinant protein and assessed its enzymatic characteristics. Among various double-stranded DNA (dsDNA) substrates (forked, 5′ overhung, 3′ overhung, and blunt-ended duplex), Tk-Upf1 had the highest unwinding activity toward 5′ overhung DNAs. Noise DNAs were also eliminated in the presence of Tk-Upf1 at concentrations 10-fold lower than those required to yield a comparable reduction with Tk-EshA. When a 5′ or 3′ overhung mis-annealed primer was included as a competitive primer along with specific primers, noise DNAs derived from the mis-annealed primer were eliminated in the presence of Tk-Upf1. In digital PCR, addition of Tk-EshA or Tk-Upf1 increased fluorescent intensities and improved separation between common and risk allele clusters, indicating that both helicases functioned as signal enhancers. In comparison with Tk-EshA, a smaller amount of Tk-Upf1 was required to improve the performance of digital PCR.     

Genome instability syndromes caused by impaired DNA repair and aberrant DNA damage responses

Maintenance of genome integrity is essential for all organisms because genome information regulates cell proliferation, growth arrest, and vital metabolic processes in cells, tissues, organs, and organisms. Because genomes are constantly exposed to intrinsic and extrinsic genotoxic stress, cellular DNA repair machinery and proper DNA damage responses (DDR) have evolved to quickly eliminate genotoxic DNA lesions, thus maintaining the genome integrity suitably. In human, germline mutations in genes involved not only in cellular DNA repair pathways but also in cellular DDR machinery frequently predispose hereditary diseases associated with chromosome aberrations. These genetic syndromes typically displaying mutations in DNA repair/DDR-related genes are often called “genome instability syndromes.” Common features of these hereditary syndromes include a high incidence of cancers and developmental abnormalities including short stature, microcephaly, and/or neurological deficiencies. However, precisely how impaired DNA repair and/or dysfunctional DDR pathologically promote(s) these syndromes are poorly understood. In this review article, we summarize the clinical symptoms of several representatives “genome instability syndromes” and propose the plausible pathogenesis thereof.