Signals for the maintenance of epithelial homeostasis are provided in part by commensal bacteria metabolites, that promote tissue homeostasis in the gut and remote organs as microbiota metabolites ...enter the bloodstream. In our study, we investigated the effects of bile acid metabolites, 3-oxolithocholic acid (3-oxoLCA), alloisolithocholic acid (AILCA) and isolithocholic acid (ILCA) produced from lithocholic acid (LCA) by microbiota, on the regulation of innate immune responses connected to the expression of host defense peptide cathelicidin in lung epithelial cells. The bile acid metabolites enhanced expression of cathelicidin at low concentrations in human bronchial epithelial cell line BCi-NS1.1 and primary bronchial/tracheal cells (HBEpC), indicating physiological relevance for modulation of innate immunity in airway epithelium by bile acid metabolites. Our study concentrated on deciphering signaling pathways regulating expression of human cathelicidin, revealing that LCA and 3-oxoLCA activate the surface G protein-coupled bile acid receptor 1 (TGR5, Takeda-G-protein-receptor-5)-extracellular signal-regulated kinase (ERK1/2) cascade, rather than the nuclear receptors, aryl hydrocarbon receptor, farnesoid X receptor and vitamin D3 receptor in bronchial epithelium. Overall, our study provides new insights into the modulation of innate immune responses by microbiota bile acid metabolites in the gut-lung axis, highlighting the differences in epithelial responses between different tissues.
We demonstrate plasmonic nanowire-based thermo-optic variable optical attenuators operating in the 1525-1625 nm wavelength range. The devices have a footprint as low as 1 mm, extinction ratio ...exceeding 40 dB, driving voltage below 3 V, and full modulation bandwidth of 1 kHz. The polarization dependent loss is shown to be critically dependent on the nanowire geometry but devices with polarization-dependent loss as low as +/-2.5 dB PDL over most of the attenuation range have been fabricated. We propose an even more compact device design to reduce insertion loss to approximately 1 dB.
We demonstrate the feasibility of fabricating thermo-optic plasmonic devices for variable optical attenuation and/or low-frequency (kHz) signal modulation. Results of finite-element simulations and ...experimental characterization of prototype devices indicate that a plasmonic device can reach specifications similar to or better than commercially available thermo-optic integrated optical components. Specifically, we have considered the insertion loss, power consumption, footprint, polarization-dependent loss, extinction ratio, and frequency response of the plasmonic devices, in addition to fabrication and material-related issues. The most serious fabrication challenge is to realize metallic nanowire waveguides with a sufficiently accurate cross-section to ensure low polarization-dependent loss at high extinction ratios.
We have investigated the potential of using gold nanowires embedded in a dielectric cladding environment as polarization-independent long-range surface plasmon polariton waveguides at telecom ...wavelengths. We performed finite-element analysis on various symmetric and close-to-symmetric cross-sectional geometries and evaluated the effects of cladding thickness on the propagation and coupling loss. The calculations confirm that fabrication of polarization-independent waveguides with reasonable tolerances is feasible and that straight-waveguide insertion losses around 1.5 dB for short (0.5 mm) devices can be realized when coupling to and from conventional dielectric waveguide geometries.
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