Architecture of the outbred brown fat proteome defines regulators of metabolic physiology.

Brown adipose tissue (BAT) regulates metabolic physiology. However, nearly all mechanistic studies of BAT protein function occur in a single inbred mouse strain, which has limited the understanding of generalizable mechanisms of BAT regulation over physiology. Here, we perform deep quantitative proteomics of BAT across a cohort of 163 genetically defined diversity outbred mice, a model that parallels the genetic and phenotypic variation found in humans. We leverage this diversity to define the functional architecture of the outbred BAT proteome, comprising 10,479 proteins. We assign co-operative functions to 2,578 proteins, enabling systematic discovery of regulators of BAT. We also identify 638 proteins that correlate with protection from, or sensitivity to, at least one parameter of metabolic disease. We use these findings to uncover SFXN5, LETMD1, and ATP1A2 as modulators of BAT thermogenesis or adiposity, and provide OPABAT as a resource for understanding the conserved mechanisms of BAT regulation over metabolic physiology.

Mitochondrial TNAP controls thermogenesis by hydrolysis of phosphocreatine.

Adaptive thermogenesis has attracted much attention because of its ability to increase systemic energy expenditure and to counter obesity and diabetes1-3. Recent data have indicated that thermogenic fat cells use creatine to stimulate futile substrate cycling, dissipating chemical energy as heat4,5. This model was based on the super-stoichiometric relationship between the amount of creatine added to mitochondria and the quantity of oxygen consumed. Here we provide direct evidence for the molecular basis of this futile creatine cycling activity in mice. Thermogenic fat cells have robust phosphocreatine phosphatase activity, which is attributed to tissue-nonspecific alkaline phosphatase (TNAP). TNAP hydrolyses phosphocreatine to initiate a futile cycle of creatine dephosphorylation and phosphorylation. Unlike in other cells, TNAP in thermogenic fat cells is localized to the mitochondria, where futile creatine cycling occurs. TNAP expression is powerfully induced when mice are exposed to cold conditions, and its inhibition in isolated mitochondria leads to a loss of futile creatine cycling. In addition, genetic ablation of TNAP in adipocytes reduces whole-body energy expenditure and leads to rapid-onset obesity in mice, with no change in movement or feeding behaviour. These data illustrate the critical role of TNAP as a phosphocreatine phosphatase in the futile creatine cycle.

Polarization sensitive optical side leakage radiometry for distributed characterization of anti-resonant hollow-core fibers.

A novel technique referred to as optical side leakage radiometry is proposed and experimentally demonstrated for non-destructive and distributed characterization of anti-resonant hollow-core optical fibers with high spatial resolution. Through in-depth analysis of the leakage light collection, we discover a unique polarization dependence, which is validated by our experiment. By leveraging this effect and employing Fourier filtering, this method enables accurate quantification of propagation attenuations for fundamental and higher order modes (with the uncertainty of <1 dB/km), identification of localized defects (with the resolution of ∼5 cm), and measurement of ultra-low spectral phase birefringence (at the level of 10-7) in two in-house-fabricated nested antiresonant nodeless hollow-core fibers. Such a fiber characterization approach, boasting unprecedently high accuracy and a potentially wide dynamic range, holds the potential to become an indispensable diagnosis tool for monitoring and assisting the manufacture of high-quality anti-resonant hollow-core fiber.

Selectively gas-filled anti-resonant hollow-core fibers for broadband high-purity LP11 mode guidance.

An anti-resonant hollow-core fiber capable of propagating the LP11 mode with high purity and over a wide wavelength range is proposed and demonstrated. The suppression of the fundamental mode relies on the resonant coupling with specific gas selectively filled into the cladding tubes. After a length of 2.7 m, the fabricated fiber shows a mode extinction ratio of over 40 dB at 1550 nm and above 30 dB in a wavelength range of 150 nm. The loss of the LP11 mode is measured to be 2.46 dB/m at 1550 nm. We discuss the potential application of such fibers in high-fidelity high-dimensional quantum state transmission.

Accurate modeling and measurement of pressure-induced group velocity dispersion variations in anti-resonant hollow-core fibers.

Precise control of group velocity dispersion (GVD) by pressure in a gas-filled hollow-core fiber (HCF) is of essential importance for many gas-based nonlinear optical applications. To accurately calculate the pressure-induced dispersion variations (∂ß2/∂p) in anti-resonant types of HCF, an analytical model combining the contribution of the gas material, capillary waveguide, and cladding resonances is developed, with an insightful physical picture. Broadband (∼1000 nm) GVD measurements in a single-shot manner realize accuracy and precision as low as 0.1 ps2/km and 2 × 10-3 ps2/km, respectively, and validate our model. Consistent with our model, a pronounced negative ∂ß2/∂p is observed experimentally for the first time, to our knowledge. Our model can also be extended to other HCFs with cladding resonances in predicting ∂ß2/∂p, such as in photonic bandgap types of HCF.

Phase-resolved all-fiber reflection-based s-NSOM for on-chip characterization.

We report on a phase-resolved, reflection-based, scattering-type near-field scanning optical microscope technique with a convenient all-fiber configuration. Exploiting the flexible positioning of the near-field probe, our technique renders a heterodyne detection for phase measurement and point-to-point frequency-domain reflectometry for group index and loss measurement of waveguides on a chip. The important issue of mitigating the measurement errors due to environmental fluctuations along fiber-optic links has been addressed. We perform systematic measurements on different types of silicon waveguides which demonstrate the accuracy and precision of the technique. With a phase compensation approach on the basis of a common-path interferometer, the phase drift error is suppressed to ∼ 0.013°/s. In addition, characterizations of group index, group velocity dispersion, propagation loss, insertion loss, and return loss of component waveguides on a chip are all demonstrated. The measurement accuracy of the propagation loss of a ∼ 0.2 cm long nano-waveguide reaches ±1 dB/cm. Our convenient and versatile near-field characterization technique paves the way for in-detail study of complex photonic circuits on a chip.

Air flowing induced thermo-optic effect for thermal sensitivity reduction in anti-resonant hollow core fibers.

The signal propagation delay through an optical fiber changes with environmental temperature, imposing a fundamental limit on performances in many fiber-optic applications. It has been shown that the thermal coefficient of delay (TCD) in hollow core fibers (HCFs) can be 20 times lower than in standard single-mode fibers (SSMFs). To further reduce TCD over a broad wavelength range at room temperature, so that to enrich fiber-optic applications in time- synchronization scenarios, the thermal expansion effect of silica glass must be compensated for. Exploiting the thermo-optic effect of air inside an anti-resonant hollow core fiber (ARF) can be a feasible solution. Nevertheless, an accurate description of the air flow in the course of temperature variation is highly needed to predict the influence of this effect. This work develops an analytical model for quantitatively calculating this temperature-induced air-flowing effect. Across a range of parameters of core diameter, fiber length, and temperature change rate, the experimentally measured propagation delay changes agree well with our model. The resultant low thermal sensitivity is also validated in non-steady conditions and in a practically usable SSMF-ARF-SSMF chain. Our model indicates that a >40-fold TCD reduction relative to SSMFs can be realized in a 60-m-long, 50-µm-diameter ARF, and further TCD reduction should be possible by properly engineering the gas type and the ambient pressure.

Four-ray interference model for complete characterization of tubular anti-resonant hollow-core fibers.

We propose a comprehensive four-ray interference model based on simple geometric optics that can be employed to characterize all the structural parameters of an anti-resonant hollow-core fiber with tubular cladding structures in a non-invasive and fast way. Combining this model with white-light side-scattering spectroscopy, the outer and the inner radii of the jacket tube can be measured with sub-micron accuracy. The improved illumination source and collimator enable fast spectrum acquisition and identification of the key interference peaks of the four rays. A fitting-based estimate of the interference peaks fully exploits a wealth of spectra acquired at different rotation angles and can help to retrieve the diameter of the cladding tubes with high resolution of 0.17 µm, which exceeds the diffraction limit of the probe light. We also report for the first time, to the best of our knowledge, the polarization and the transverse mode dependences in the side-scattering interference spectra, with which the glass wall thicknesses of the cladding tubes can be estimated on the basis of our four-ray interference model as well.

Connector-style hollow-core fiber interconnections.

To go beyond the fundamental limits imposed by latency, nonlinearity, and laser damage threshold in silica glass fibers, the hollow-core fiber (HCF) technique has been intensively investigated for decades. Recent breakthroughs in ultralow-loss HCF clearly imply that long-haul applications of HCF in communications and lasers are going to appear. Nevertheless, up to now, the HCF technique as a whole is still hampered by the limited length of a single span and the lack of HCF-based functional devices. To resolve these two issues, it is of importance to develop ultralow-loss and plug-and-play HCF interconnections. In this work, we report on HCF interconnections with the lowest-ever insertion losses (0.10 dB for HCF to standard single-mode fiber (SMF) and 0.13 dB for HCF to itself in the 1.5 µm waveband) and in a pluggable means. Two fiber mode-field adapters, one based on a graded-index multi-mode fiber (GIF) and the other utilizing a thermally expanded core (TEC) SMF, have been tested and compared. An extra insertion loss arising from imperfect refractive index distribution in a commercial GIF is observed. Our HCF interconnections also realize a back-reflection of <-35 dB over a 100 nm bandwidth as well as other critical metrics in favor of practical applications. Our technique is viable for any type of HCF.

Hollow-core conjoined-tube fiber for penalty-free data transmission under offset launch conditions.

Three types of hollow-core fibers, i.e., photonic-bandgap fiber, negative-curvature fiber, and conjoined-tube fiber, are compared in terms of data transmission performance. Their group velocity dispersions and group indices are measured in detail by using low-coherence interferometry. Whilst all three fibers show good performance with an optimized central launch, they behave differently under offset launch for 10 Gbit/s on-off keying transmission. We use a Q2-factor analysis method to gain insight into the data transmission over a hollow-core fiber. The low-loss, low-intermodal crosstalk conjoined-tube fiber shows great resilience to bending and offset launch compared to the other two hollow-core fibers, enabling genuine penalty-free data transmission in realistic environments.

Diameter measurement of optical nanofiber based on high-order Bragg reflections using a ruled grating.

A convenient method using a commercially available ruled grating for precise and overall diameter measurement of optical nanofibers (ONFs) is presented. We form a composite Bragg reflector with a micronscale period by dissolving aluminum coating, slicing the grating along ruling lines, and mounting it on an ONF. The resonant wavelengths of high-order Bragg reflections possess fiber diameter dependence, enabling nondestructive measurement of the ONF diameter profile. This method provides an easy and economic diagnostic tool for wide varieties of ONF-based applications.

Imaging of guided waves using an all-fiber reflection-based NSOM with self-compensation of a phase drift.

A phase-resolved reflection-based near-field scanning optical microscopy (NSOM) technique with an original all-fiber configuration is presented. Our system consists of an intrinsically phase-stable common-path interferometer. The reflection from the waveguide input facet or from an integrated fiber Bragg grating is used as the reference beam. This arrangement effectively suppresses the phase drift caused by environmental fluctuations. By raster scanning a silicon atomic force microscope probe, we measure the complex near fields of the propagating and stationary waves in silicon nanowaveguides. Our robust, align-free, cost-effective, and shot-noise-limited near-field imaging technique paves the way for versatile optical characterizations of nanophotonic structures on a chip.

Full control of far-field radiation via photonic integrated circuits decorated with plasmonic nanoantennas.

We theoretically develop a hybrid architecture consisting of photonic integrated circuit and plasmonic nanoantennas to fully control optical far-field radiation with unprecedented flexibility. By exploiting asymmetric and lateral excitation from silicon waveguides, single gold nanorod and cascaded nanorod pair can function as component radiation pixels, featured by full 2π phase coverage and nanoscale footprint. These radiation pixels allow us to design scalable on-chip devices in a wavefront engineering fashion. We numerically demonstrate beam collimation with 30° out of the incident plane and nearly diffraction limited divergence angle. We also present high-numerical-aperture (NA) beam focusing with NA ≈0.65 and vector beam generation (the radially-polarized mode) with the mode similarity greater than 44%. This concept and approach constitutes a designable optical platform, which might be a future bridge between integrated photonics and metasurface functionalities.

Structure and unfolding of the third type III domain from human fibronectin.

Fibronectin is a modular extracellular matrix protein that is essential for vertebrate development. The third type III domain (3FN3) in fibronectin interacts with other parts of fibronectin and with anastellin, a protein fragment that causes fibronectin aggregation. 3FN3 opens readily both as an isolated domain in solution and when part of fibronectin in stretched fibrils, and it was proposed that this opening is important for anastellin binding. We determined the structure of 3FN3 using nuclear magnetic resonance spectroscopy, and we investigated its stability, folding, and unfolding. Similar to most other FN3 domains, 3FN3 contains two antiparallel ß-sheets that are composed of three (A, B, and E) and four (C, D, F, and G) ß-strands, respectively, and are held together by a conserved hydrophobic interface. cis-trans isomerization of P847 at the end of ß-strand C leads to observable conformational heterogeneity in 3FN3, with a cis peptide bond present in almost one-quarter of the molecules. The chemical stability of 3FN3 is relatively low, but the folding rate constant in the absence of denaturant is in the same range as those of other, more stable FN3 domains. Interestingly, the unfolding rate constant in the absence of denaturant is several orders of magnitude higher than the unfolding rate constants of other FN3 domains investigated to date. This unusually fast rate is comparable to the rate of binding of 3FN3 to anastellin at saturating anastellin concentrations, consistent with the model in which 3FN3 has to unfold to interact with anastellin.

Structural and functional characterization of the acidic region from the RIZ tumor suppressor.

RIZ (retinoblastoma protein-interacting zinc finger protein), also denoted PRDM2, is a transcriptional regulator and tumor suppressor. It was initially identified because of its ability to interact with another well-established tumor suppressor, the retinoblastoma protein (Rb). A short motif, IRCDE, in the acidic region (AR) of RIZ was reported to play an important role in the interaction with the pocket domain of Rb. The IRCDE motif is similar to a consensus Rb-binding sequence LXCXE (where X denotes any amino acid) that is found in several viral Rb-inactivating oncoproteins. To improve our understanding of the molecular basis of binding of Rb to RIZ, we investigated the interaction between purified recombinant AR and the pocket domain of Rb using nuclear magnetic resonance spectroscopy, isothermal titration calorimetry, and fluorescence anisotropy experiments. We show that AR is intrinsically disordered and that it binds the pocket domain with submicromolar affinity. We also demonstrate that the interaction between AR and the pocket domain is mediated primarily by the short stretch of residues containing the IRCDE motif and that the contribution of other parts of AR to the interaction with the pocket domain is minimal. Overall, our data provide clear evidence that RIZ is one of the few cellular proteins that can interact directly with the LXCXE-binding cleft on Rb.

A comprehensive landscape of the zinc-regulated human proteome.

Zinc is an essential micronutrient that regulates a wide range of physiological processes, principally through Zn 2+ binding to protein cysteine residues. Despite being critical for modulation of protein function, for the vast majority of the human proteome the cysteine sites subject to regulation by Zn 2+ binding remain undefined. Here we develop ZnCPT, a comprehensive and quantitative mapping of the zinc-regulated cysteine proteome. We define 4807 zinc-regulated protein cysteines, uncovering protein families across major domains of biology that are subject to either constitutive or inducible modification by zinc. ZnCPT enables systematic discovery of zinc-regulated structural, enzymatic, and allosteric functional domains. On this basis, we identify 52 cancer genetic dependencies subject to zinc regulation, and nominate malignancies sensitive to zinc-induced cytotoxicity. In doing so, we discover a mechanism of zinc regulation over Glutathione Reductase (GSR) that drives cell death in GSR-dependent lung cancers. We provide ZnCPT as a resource for understanding mechanisms of zinc regulation over protein function.

Ergothioneine boosts mitochondrial respiration and exercise performance via direct activation of MPST.

Ergothioneine (EGT) is a diet-derived, atypical amino acid that accumulates to high levels in human tissues. Reduced EGT levels have been linked to age-related disorders, including neurodegenerative and cardiovascular diseases, while EGT supplementation is protective in a broad range of disease and aging models in mice. Despite these promising data, the direct and physiologically relevant molecular target of EGT has remained elusive. Here we use a systematic approach to identify how mitochondria remodel their metabolome in response to exercise training. From this data, we find that EGT accumulates in muscle mitochondria upon exercise training. Proteome-wide thermal stability studies identify 3-mercaptopyruvate sulfurtransferase (MPST) as a direct molecular target of EGT; EGT binds to and activates MPST, thereby boosting mitochondrial respiration and exercise training performance in mice. Together, these data identify the first physiologically relevant EGT target and establish the EGT-MPST axis as a molecular mechanism for regulating mitochondrial function and exercise performance.

Regulatory T cells shield muscle mitochondria from interferon-γ-mediated damage to promote the beneficial effects of exercise.

Exercise enhances physical performance and reduces the risk of many disorders such as cardiovascular disease, type 2 diabetes, dementia, and cancer. Exercise characteristically incites an inflammatory response, notably in skeletal muscles. Although some effector mechanisms have been identified, regulatory elements activated in response to exercise remain obscure. Here, we have addressed the roles of Foxp3+CD4+ regulatory T cells (Tregs) in the healthful activities of exercise via immunologic, transcriptomic, histologic, metabolic, and biochemical analyses of acute and chronic exercise models in mice. Exercise rapidly induced expansion of the muscle Treg compartment, thereby guarding against overexuberant production of interferon-γ and consequent metabolic disruptions, particularly mitochondrial aberrancies. The performance-enhancing effects of exercise training were dampened in the absence of Tregs. Thus, exercise is a natural Treg booster with therapeutic potential in disease and aging contexts.

Isolation of extracellular fluids reveals novel secreted bioactive proteins from muscle and fat tissues.

Proteins are secreted from cells to send information to neighboring cells or distant tissues. Because of the highly integrated nature of energy balance systems, there has been particular interest in myokines and adipokines. These are challenging to study through proteomics because serum or plasma contains highly abundant proteins that limit the detection of proteins with lower abundance. We show here that extracellular fluid (EF) from muscle and fat tissues of mice shows a different protein composition than either serum or tissues. Mass spectrometry analyses of EFs from mice with physiological perturbations, like exercise or cold exposure, allowed the quantification of many potentially novel myokines and adipokines. Using this approach, we identify prosaposin as a secreted product of muscle and fat. Prosaposin expression stimulates thermogenic gene expression and induces mitochondrial respiration in primary fat cells. These studies together illustrate the utility of EF isolation as a discovery tool for adipokines and myokines.

Bias for Treatment Effect by Measurement Error in Pretest in ANCOVA Analysis.

This paper investigated consequences of measurement error in the pretest on the estimate of the treatment effect in a pretest-posttest design with the analysis of covariance (ANCOVA) model, focusing on both the direction and magnitude of its bias. Some prior studies have examined the magnitude of the bias due to measurement error and suggested ways to correct it. However, none of them clarified how the direction of bias is affected by measurement error. This study analytically derived a formula for the asymptotic bias for the treatment effect. The derived formula is a function of the reliability of the pretest, the standardized population group mean difference for the pretest, and the correlation between pretest and posttest true scores. It revealed a concerning consequence of ignoring measurement errors in pretest scores: treatment effects could be overestimated or underestimated, and positive treatment effects can be estimated as negative effects in certain conditions. A simulation study was also conducted to verify the derived bias formula.