Kv7.2 regulates the function of peripheral sensory neurons

The Kv7 (KCNQ) family of voltage‐gated K⁺ channels regulates cellular excitability. The functional role of Kv7.2 has been hampered by the lack of a viable Kcnq2‐null animal model. In this study, we generated homozygous Kcnq2‐null sensory neurons using the Cre‐Lox system; in these mice, Kv7.2 expression is absent in the peripheral sensory neurons, whereas the expression of other molecular components of nodes (including Kv7.3), paranodes, and juxtaparanodes is not altered. The conditional Kcnq2‐null animals exhibit normal motor performance but have increased thermal hyperalgesia and mechanical allodynia. Whole‐cell patch recording technique demonstrates that Kcnq2‐null sensory neurons have increased excitability and reduced spike frequency adaptation. Taken together, our results suggest that the loss of Kv7.2 activity increases the excitability of primary sensory neurons. J. Comp. Neurol. 522:3262–3280, 2014. © 2014 Wiley Periodicals, Inc.     

Falkor,a novel cell growth regulator isolated by a functional genetic screen

A novel cell growth regulator, named Falkor, was identified using a functional approach to mammalian gene cloning, the Genetic Supressor Elements (GSE) method. In this screen, expression of the C-terminal domain of Falkor conferred cells with resistance to cisplatin-induced growth arrest. Expression of the C-terminus of Falkor, but not of the full-length protein, enhanced cell growth both following genotoxic stress and under normal conditions suggesting a general role for this protein in cell growth control. This effect of the C-terminus fragment was abrogated by over-expression of the full-length Falkor, suggesting that the fragment counteracts the function of the full-length protein. Falkor is encoded by a 2-kb mRNA which is present at different levels in various tissues, and is localized in the nucleus of cells. The C-terminal domain of Falkor, isolated from the GSE library, has significant homology to a known human and rat cell growth regulator, SM-20, and to the C. elegans protein EGL-9, recently shown to modify the Hypoxia Inducible Factor-1alpha. The homology suggests that these proteins share a functional domain that is conserved among a family of growth regulation proteins.     

Altered expression of ion channel isoforms at the node of Ranvier in P0-deficient myelin mutants

To elucidate the impact of myelinating Schwann cells on the molecular architecture of the node of Ranvier, we investigated the nodal expression of voltage-gated sodium channel (VGSC) isoforms and the localization of paranodal and juxtaparanodal membrane proteins in a severely affected Schwann cell mutant, the mouse deficient in myelin protein zero (P0). The abnormal myelin formation and compaction was associated with immature nodal cluster types of VGSC. Most strikingly, P0-deficient motor nerves displayed an ectopic nodal expression of the Na(v)1.8 isoform, where it is coexpressed with the ubiquitous Na(v)1.6 channel. Furthermore, Caspr was distributed asymmetrically or was even absent in the mutant nerve fibers. The potassium channel K(v)1.2 and Caspr2 were not confined to juxtaparanodes, but often protruding into the paranodes. Thus, deficiency of P0 leads to dysregulation of nodal VGSC isoforms and to altered localization of paranodal and juxtaparanodal components of the nodal complex.     

Correlation between cathepsin D serum concentration and carotid intima-media thickness in hemodialysis patients

Aim  

Cardiovascular (CV) disease is the leading cause of death in hemodialysis (HD) patients, and approximately half of mortalities in HD patients are attributed to CV disease. Atherosclerosis is the most frequent cause of CV complications in patients with end-stage renal disease (ESRD). Based on recent studies, cathepsin D has been suggested as a potential marker of atherosclerosis, and we hypothesized that there is an association between serum concentration of cathepsin D and carotid intima-media thickness (CIMT) in hemodialysis patients.     

The tyrosine phosphatase Shp2 (PTPN11) directs Neuregulin-1/ErbB signaling throughout Schwann cell development

The nonreceptor tyrosine phosphatase Shp2 (PTPN11) has been implicated in tyrosine kinase, cytokine, and integrin receptor signaling. We show here that conditional mutation of Shp2 in neural crest cells and in myelinating Schwann cells resulted in deficits in glial development that are remarkably similar to those observed in mice mutant for Neuregulin-1 (Nrg1) or the Nrg1 receptors, ErbB2 and ErbB3. In cultured Shp2 mutant Schwann cells, Nrg1-evoked cellular responses like proliferation and migration were virtually abolished, and Nrg1-dependent intracellular signaling was altered. Pharmacological inhibition of Src family kinases mimicked all cellular and biochemical effects of the Shp2 mutation, implicating Src as a primary Shp2 target during Nrg1 signaling. Together, our genetic and biochemical analyses demonstrate that Shp2 is an essential component in the transduction of Nrg1/ErbB signals.     

Glial M6B stabilizes the axonal membrane at peripheral nodes of Ranvier

Glycoprotein M6B and the closely related proteolipid protein regulate oligodendrocyte myelination in the central nervous system, but their role in the peripheral nervous system is less clear. Here we report that M6B is located at nodes of Ranvier in peripheral nerves where it stabilizes the nodal axolemma. We show that M6B is co‐localized and associates with gliomedin at Schwann cell microvilli that are attached to the nodes. Developmental analysis of sciatic nerves, as well as of myelinating Schwann cells/dorsal root ganglion neurons cultures, revealed that M6B is already present at heminodes, which are considered the precursors of mature nodes of Ranvier. However, in contrast to gliomedin, which accumulates at heminodes with or prior to Na⁺ channels, we often detected Na⁺ channel clusters at heminodes without any associated M6B, indicating that it is not required for initial channel clustering. Consistently, nodal cell adhesion molecules (NF186, NrCAM), ion channels (Nav1.2 and Kv7.2), cytoskeletal proteins (AnkG and βIV spectrin), and microvilli components (pERM, syndecan3, gliomedin), are all present at both heminodes and mature nodes of Ranvier in Gpm6b null mice. Using transmission electron microscopy, we show that the absence of M6B results in progressive appearance of nodal protrusions of the nodal axolemma, that are often accompanied by the presence of enlarged mitochondria. Our results reveal that M6B is a Schwann cell microvilli component that preserves the structural integrity of peripheral nodes of Ranvier.     

Paranodal permeability in "myelin mutants"

Fluorescent dextran tracers of varying sizes have been used to assess paranodal permeability in myelinated sciatic nerve fibers from control and three "myelin mutant" mice, Caspr-null, cst-null, and shaking. We demonstrate that in all of these the paranode is permeable to small tracers (3 kDa and 10 kDa), which penetrate most fibers, and to larger tracers (40 kDa and 70 kDa), which penetrate far fewer fibers and move shorter distances over longer periods of time. Despite gross diminution in transverse bands (TBs) in the Caspr-null and cst-null mice, the permeability of their paranodal junctions is equivalent to that in controls. Thus, deficiency of TBs in these mutants does not increase the permeability of their paranodal junctions to the dextrans we used, moving from the perinodal space through the paranode to the internodal periaxonal space. In addition, we show that the shaking mice, which have thinner myelin and shorter paranodes, show increased permeability to the same tracers despite the presence of TBs. We conclude that the extent of penetration of these tracers does not depend on the presence or absence of TBs but does depend on the length of the paranode and, in turn, on the length of "pathway 3," the helical extracellular pathway that passes through the paranode parallel to the lateral edge of the myelin sheath.