SiO-induced thermal instability and interplay between graphite and SiO in graphite/SiO composite anode.

Silicon monoxide (SiO), which exhibits better cyclability compared to silicon while delivering higher capacity than that of graphite, is an adequate material for the development of lithium-ion batteries (LIBs) having higher energy densities. However, incorporating silicon-based materials including SiO into stable graphite anode inevitably degrades not only cycle life but also calendar life of LIBs, while little is known about their aging mechanisms. Here, SiO-induced thermal instability of the graphite/SiO composite anode is investigated. We reveal that under thermal exposure, SiO accelerates the loss of lithium inventory and concomitantly facilitates the lithium de-intercalation from graphite. This self-discharge phenomenon, which is weakly observed in the graphite anode without SiO, is the result of preferential parasitic reaction on the SiO interface and spontaneous electron and lithium-ion migration to equilibrate the electron energy imbalance between graphite and SiO. Understanding this underlying electron-level interplay between graphite and SiO in the composite anode will contribute toward improving shelf life of SiO-containing LIBs in actual operating conditions.

Cdo promotes neuronal differentiation via activation of the p38 mitogen-activated protein kinase pathway.

Neural basic helix-loop-helix transcription factors (bHLHs) control many aspects of neurogenesis, such as proliferation, fate determination, and differentiation. We have previously shown that the promyogenic cell surface receptor Cdo modulates the Cdc42 and p38 mitogen-activated protein kinase (MAPK) pathways via a direct association with two scaffold-type proteins, JLP and Bnip-2, to regulate activities of myogenic bHLH factors and myogenic differentiation. We report here that Cdo uses similar regulatory mechanisms to promote neuronal differentiation. Expression of JLP, a scaffold protein for p38MAPK, and Bnip-2, a regulator of Cdc42, is increased during differentiation of C17.2 neural precursor cells and P19 embryonal carcinoma cells. These molecules regulate Cdc42 and p38MAPK activities, which increase in a Cdo-dependent manner during neuronal differentiation of C17.2 cells and retinoic acid-treated P19 cells. Furthermore, enhancement or reduction of Cdc42 and p38MAPK activities enhances or reduces, respectively, neuronal differentiation of these cell lines. Cdc42 and p38MAPK activities also promote heterodimerization of neurogenin1 and E47, suggesting that one way they promote neurogenesis is via regulation of neural bHLH factor activities. These results imply that a conserved intracellular signaling mechanism initiated by Cdo regulates the activities of tissue-specific bHLH factors and therefore functions as a key regulator of differentiation of several different cell lineages.

A Cdo-Bnip-2-Cdc42 signaling pathway regulates p38alpha/beta MAPK activity and myogenic differentiation.

The p38alpha/beta mitogen-activated protein kinase (MAPK) pathway promotes skeletal myogenesis, but the mechanisms by which it is activated during this process are unclear. During myoblast differentiation, the promyogenic cell surface receptor Cdo binds to the p38alpha/beta pathway scaffold protein JLP and, via JLP, p38alpha/beta itself. We report that Cdo also interacts with Bnip-2, a protein that binds the small guanosine triphosphatase (GTPase) Cdc42 and a negative regulator of Cdc42, Cdc42 GTPase-activating protein (GAP). Moreover, Bnip-2 and JLP are brought together through mutual interaction with Cdo. Gain- and loss-of-function experiments with myoblasts indicate that the Cdo-Bnip-2 interaction stimulates Cdc42 activity, which in turn promotes p38alpha/beta activity and cell differentiation. These results reveal a previously unknown linkage between a cell surface receptor and downstream modulation of Cdc42 activity. Furthermore, interaction with multiple scaffold-type proteins is a distinctive mode of cell surface receptor signaling and provides one mechanism for specificity of p38alpha/beta activation during cell differentiation.

Activation of p38alpha/beta MAPK in myogenesis via binding of the scaffold protein JLP to the cell surface protein Cdo.

The p38 mitogen-activated protein kinase (MAPK) pathway plays an important role in cell differentiation, but the signaling mechanisms by which it is activated during this process are largely unknown. Cdo is an immunoglobulin superfamily member that functions as a component of multiprotein cell surface complexes to promote myogenesis. In this study, we report that the Cdo intracellular region interacts with JLP, a scaffold protein for the p38alpha/beta MAPK pathway. Cdo, JLP, and p38alpha/beta form complexes in differentiating myoblasts, and Cdo and JLP cooperate to enhance levels of active p38alpha/beta in transfectants. Primary myoblasts from Cdo(-/-) mice, which display a defective differentiation program, are deficient in p38alpha/beta activity, and the expression of an activated form of MKK6 (an immediate upstream activator of p38) rescues the ability of Cdo(-/-) cells to differentiate. These results document a novel mechanism of signaling during cell differentiation: the interaction of a MAPK scaffold protein with a cell surface receptor.

Cdo functions at multiple points in the Sonic Hedgehog pathway, and Cdo-deficient mice accurately model human holoprosencephaly.

Holoprosencephaly (HPE), a common defect of human forebrain development, is associated with haploinsufficiency for genes encoding Sonic Hedgehog (SHH) pathway components. Clinical expression of HPE is extremely variable, but it is rarely associated with defects in other SHH-dependent structures, such as limbs. Here we report that mice lacking the transmembrane protein Cdo, previously implicated in myogenesis, display HPE with strain-specific severity and without limb defects, modeling human HPE and implicating modifier genes as a cause of variability. Shh target gene expression is reduced in the developing forebrains of Cdo-/- mice, and Cdo positively regulates Shh signaling in vitro. Our data suggest that Cdo enhances pathway activity in multiple ways, including at signal reception and via a parallel mechanism required at the level of Gli transcription factors. Specific Cdo domains required for its promyogenic effect are dispensable for its Shh signaling role, suggesting that Cdo has multiple, independent functions.

Cortical thinning and hydrocephalus in mice lacking the immunoglobulin superfamily member CDO.

CDO is a cell surface immunoglobulin superfamily member that positively regulates myogenic differentiation in vitro and in vivo and signals to posttranslationally activate myogenic basic helix-loop-helix (bHLH) transcription factors. The Cdo gene is also expressed in the dorsal aspect and midline structures of the developing central nervous system, and mice lacking CDO on the C57BL/6 background display holoprosencephaly with approximately 80% penetrance, resulting in perinatal lethality. We report here that a fraction of Cdo-/- mice from this background have additional defects in brain development, including hydrocephalus and cortical thinning. Primary neural progenitor cultures from E14.5 Cdo-/- mutants display reduced proliferation, which may underlie the thinning. The cortical preplate and cortices of mutant animals also show reduced staining for beta-tubulin III, indicating defective neuronal differentiation. CDO levels are strongly increased in cultured C17.2 neuronal precursor cells stimulated to differentiate; modulation of CDO levels in these cells by overexpression or interfering RNA approaches enhances or diminishes differentiation, respectively. Cotransfection of CDO enhances the activity of the neurogenic bHLH factor, neurogenin1, in reporter assays and enhances heterodimerization of neurogenin1 and E47. These results indicate that CDO promotes neuronal differentiation and support the hypothesis that CDO coordinates differentiation of multiple cell lineages by regulating the activity of tissue-specific bHLH factors.

Netrins and neogenin promote myotube formation.

Differentiation of skeletal myoblasts into multinucleated myotubes is a multistep process orchestrated by several families of transcription factors, including myogenic bHLH and NFAT proteins. The activities of these factors and formation of myotubes are regulated by signal transduction pathways, but few extracellular factors that might initiate such signals have been identified. One exception is a cell surface complex containing promyogenic Ig superfamily members (CDO and BOC) and cadherins. Netrins and their receptors are established regulators of axon guidance, but little is known of their function outside the nervous system. We report here that myoblasts express the secreted factor netrin-3 and its receptor, neogenin. These proteins stimulate myotube formation and enhance myogenic bHLH- and NFAT-dependent transcription. Furthermore, neogenin binds to CDO in a cis fashion, and myoblasts lacking CDO are defective in responding to recombinant netrin. It is proposed that netrin-3 and neogenin may promote myogenic differentiation by an autocrine mechanism as components of a higher order complex of several promyogenic cell surface proteins.

Heat-shock protein 25 (Hspb1) regulates manganese superoxide dismutase through activation of Nfkb (NF-kappaB).

We previously demonstrated that overexpression of HSP25 (now known as Hspb1) conferred increased resistance to ionizing radiation (Radiat Res. 154, 421-428, 2000). In the present study, L929 cells overexpressing Hspb1 were shown to have increased expression of the manganese superoxide dismutase gene (now known as SOD2) and its enzyme activity. To elucidate Hspb1-induced pathways leading to activation of these antioxidant enzymes, the production of the tumor necrosis factor alpha (Tnf) and interleukin 1 beta (Il1b) genes was examined. Increased expression of Tnf and Il1b resulting from Hspb1 overexpression was detected by RT-PCR. Increased activation of Nfkb (degradation of Ikb, a member of the Nfkb family) was also found in Hspb1-overexpressing cells. When treated with Tnf, Nfkb activation and SOD2 gene expression were increased more by Hspb1 overexpression. Moreover, transfection with the Hspb1 antisense gene abrogated all of the Hspb1-mediated phenomena. To further elucidate the exact relationship between induction of SOD2 and Nfkb activation, a dominant negative I-kBalpha (now known as Nfkb1a) construct was transfected into Hspb1-overexpressing cells. The dominant negative Nfkb1a inhibited Hspb1-mediated SOD2 gene expression. In addition, Hspb1-mediated radioresistance was blocked by dominant negative Nfkb1a transfection. When the SOD2 gene was transfected into L929 cells, a somewhat increased radioresistance was detected by a clonogenic survival assay compared to control cells. Hspb1 produced Tnf and Il1b and facilitated SOD2 gene expression through Nfkb activation, possibly resulting in Hspb1-mediated radioresistance.