Andreas Rüegg

Active Caspase-1 Is a Regulator of Unconventional Protein Secretion

Mammalian cells export most proteins by the endoplasmic reticulum/Golgi-dependent pathway. However, some proteins are secreted via unconventional, poorly understood mechanisms. The latter include the proinflammatory cytokines interleukin(IL)-1beta, IL-18, and IL-33, which require activation by caspase-1 for biological activity. Caspase-1 itself is activated by innate immune complexes, the inflammasomes. Here we show that secretion of the leaderless proteins proIL-1alpha, caspase-1, and fibroblast growth factor (FGF)-2 depends on caspase-1 activity. Although proIL-1alpha and FGF-2 are not substrates of the protease, we demonstrated their physical interaction. Secretome analysis using iTRAQ proteomics revealed caspase-1-mediated secretion of other leaderless proteins with known or unknown extracellular functions. Strikingly, many of these proteins are involved in inflammation, cytoprotection, or tissue repair. These results provide evidence for an important role of caspase-1 in unconventional protein secretion. By this mechanism, stress-induced activation of caspase-1 directly links inflammation to cytoprotection, cell survival, and regenerative processes.

Nodal-chain metals

The band theory of solids is arguably the most successful theory of condensed-matter physics, providing a description of the electronic energy levels in various materials. Electronic wavefunctions obtained from the band theory enable a topological characterization of metals for which the electronic spectrum may host robust, topologically protected, fermionic quasiparticles. Many of these quasiparticles are analogues of the elementary particles of the Standard Model, but others do not have a counterpart in relativistic high-energy theories. A complete list of possible quasiparticles in solids is lacking, even in the non-interacting case. Here we describe the possible existence of a hitherto unrecognized type of fermionic excitation in metals. This excitation forms a nodal chain—a chain of connected loops in momentum space—along which conduction and valence bands touch. We prove that the nodal chain is topologically distinct from previously reported excitations. We discuss the symmetry requirements for the appearance of this excitation and predict that it is realized in an existing material, iridium tetrafluoride (IrF4), as well as in other compounds of this class of materials. Using IrF4 as an example, we provide a discussion of the topological surface states associated with the nodal chain. We argue that the presence of the nodal-chain fermions will result in anomalous magnetotransport properties, distinct from those of materials exhibiting previously known excitations.

Topological insulators from complex orbital order in transition-metal oxides heterostructures

Topological band insulators which are dynamically generated by electron-electron interactions have been theoretically proposed in two- and three-dimensional lattice models. We present evidence that the two-dimensional version can be stabilized in digital (111) heterostructures of transition-metal oxides as a result of purely local interactions. The topological phases are accompanied by spontaneous ordering of complex orbitals and we discuss their stability with respect to the Hunds rule coupling, Jahn-Teller interaction, and inversion-symmetry breaking terms. As main competitors we identify spin-nematic and magnetic phases.

Interaction-driven topological insulators on the kagome and the decorated honeycomb lattices

We study the spinless and spinful extended Hubbard models with repulsive interactions on the kagome and the decorated honeycomb (star) lattice. Using Hartree-Fock mean-field theory, we show that interaction-driven insulating phases with nontrivial topological invariants (Chern number or

Topological order and semions in a strongly correlated quantum spin Hall insulator.

{Z}_{2}

Slave-boson mean-field theory of the Mott transition in the two-band Hubbard model

invariant) exist for an experimentally reasonable range of parameters. These phases occur at filling fractions which involve either Dirac points or quadratic band crossing points in the noninteracting limit. We present comprehensive mean-field phase diagrams for these lattices and discuss the competition between topologically nontrivial phases and numerous other ordered states, including various charge, spin, and bond orderings. Our results suggest that

Weyl semimetal from spontaneous inversion symmetry breaking in pyrochlore oxides

{Z}_{2}

Bound states of conical singularities in graphene-based topological insulators.

topological insulators should be found in a number of systems with either little or no intrinsic spin-orbit coupling.

Z 2 -slave-spin theory for strongly correlated fermions

We provide a self-consistent mean-field framework to study the effect of strong interactions in a quantum spin Hall insulator on the honeycomb lattice. We identify an exotic phase for large spin-orbit coupling and intermediate Hubbard interaction. This phase is gapped and does not break any symmetry. Instead, we find a fourfold topological degeneracy of the ground state on the torus and fractionalized excitations with semionic mutual braiding statistics. Moreover, we argue that it has gapless edge modes protected by time-reversal symmetry but a trivial Z(2) topological invariant. Finally, we discuss the experimental signatures of this exotic phase. Our work highlights the important theme that interesting phases arise in the regime of strong spin-orbit coupling and interactions.

Electronic structure of (LaNiO 3 ) 2 /(LaAlO 3 ) N heterostructures grown along [111]

Abstract.We apply the slave-boson approach of Kotliar and Ruckenstein to the two-band Hubbard model with an Ising like Hunds rule coupling and bands of different widths. On the mean-field level of this approach we investigate the Mott transition and observe both separate and joint transitions of the two bands depending on the choice of the inter- and intra-orbital Coulomb interaction parameters. The mean-field calculations allow for a simple physical interpretation and can confirm several aspects of previous work. Beside the case of two individually half-filled bands we also examine what happens if the original metallic bands possess fractional filling either due to finite doping or due to a crystal field which relatively shifts the atomic energy levels of the two orbitals. For appropriate values of the interaction and of the crystal field we can observe a band insulating state and a ferromagnetic metal.