Through unknown mechanisms, insulin activates the sterol regulatory element-binding protein (SREBP1c) transcription factor to promote hepatic lipogenesis. We find that this induction is dependent on ...the mammalian target of rapamycin (mTOR) complex 1 (mTORC1). To further define the role of mTORC1 in the regulation of SREBP1c in the liver, we generated mice with liver-specific deletion of TSC1 (LTsc1KO), which results in insulin-independent activation of mTORC1. Surprisingly, the LTsc1KO mice are protected from age- and diet-induced hepatic steatosis and display hepatocyte-intrinsic defects in SREBP1c activation and de novo lipogenesis. These phenotypes result from attenuation of Akt signaling driven by mTORC1-dependent insulin resistance. Therefore, mTORC1 activation is not sufficient to stimulate hepatic SREBP1c in the absence of Akt signaling, revealing the existence of an additional downstream pathway also required for this induction. We provide evidence that this mTORC1-independent pathway involves Akt-mediated suppression of Insig2a, a liver-specific transcript encoding the SREBP1c inhibitor INSIG2.
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► mTORC1 is required for proper activation of hepatic SREBP1c by insulin ► LTsc1KO mice reveal that mTORC1 activation is not sufficient to induce hepatic SREBP1c ► An mTORC1-independent pathway is also required for hepatic SREBP1c induction by Akt ► Akt signaling suppresses Insig2a, a liver-specific inhibitor of SREBP1c
The signaling pathways imposing hormonal control over adipocyte differentiation are poorly understood. While insulin and Akt signaling have been found previously to be essential for adipogenesis, the ...relative importance of their many downstream branches have not been defined. One direct substrate that is inhibited by Akt-mediated phosphorylation is the tuberous sclerosis complex 2 (TSC2) protein, which associates with TSC1 and acts as a critical negative regulator of the mammalian target of rapamycin (mTOR) complex 1 (mTORC1). Loss of function of the TSC1-TSC2 complex results in constitutive mTORC1 signaling and, through mTORC1-dependent feedback mechanisms and loss of mTORC2 activity, leads to a concomitant block of Akt signaling to its other downstream targets.
We find that, despite severe insulin resistance and the absence of Akt signaling, TSC2-deficient mouse embryo fibroblasts and 3T3-L1 pre-adipocytes display enhanced adipocyte differentiation that is dependent on the elevated mTORC1 activity in these cells. Activation of mTORC1 causes a robust increase in the mRNA and protein expression of peroxisome proliferator-activated receptor gamma (PPARgamma), which is the master transcriptional regulator of adipocyte differentiation. In examining the requirements for different Akt-mediated phosphorylation sites on TSC2, we find that only TSC2 mutants lacking all five previously identified Akt sites fully block insulin-stimulated mTORC1 signaling in reconstituted Tsc2 null cells, and this mutant also inhibits adipogenesis. Finally, renal angiomyolipomas from patients with tuberous sclerosis complex contain both adipose and smooth muscle-like components with activated mTORC1 signaling and elevated PPARgamma expression.
This study demonstrates that activation of mTORC1 signaling is a critical step in adipocyte differentiation and identifies TSC2 as a primary target of Akt driving this process. Therefore, the TSC1-TSC2 complex regulates the differentiation of mesenchymal cell lineages, at least in part, through its control of mTORC1 activity and PPARgamma expression.
To achieve cell entry, many nonenveloped viruses must transform from a dormant to a primed state. In contrast to the membrane fusion mechanism of enveloped viruses (e.g., influenza virus), this ...membrane penetration mechanism is poorly understood. Here, using single-particle cryo-electron microscopy, we report a 3.3 Å structure of the primed, infectious subvirion particle of aquareovirus. The density map reveals side-chain densities of all types of amino acids (except glycine), enabling construction of a full-atom model of the viral particle. Our structure and biochemical results show that priming involves autocleavage of the membrane penetration protein and suggest that Lys84 and Glu76 may facilitate this autocleavage in a nucleophilic attack. We observe a myristoyl group, covalently linked to the N terminus of the penetration protein and embedded in a hydrophobic pocket. These results suggest a well-orchestrated process of nonenveloped virus entry involving autocleavage of the penetration protein prior to exposure of its membrane-insertion finger.
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► A 3.3Å structure of a primed nonenveloped virus is obtained by cryo-EM ► Atomic models are built from the cryo-EM density alone for six protein conformers ► Autocleavage occurs in the membrane penetration protein during priming ► A membrane-insertion “finger” is buried in a hydrophobic pocket during priming
Human cytomegalovirus (HCMV) enters host by glycoprotein B (gB)-mediated membrane fusion upon receptor-binding to gH/gL-related complexes, causing devastating diseases such as birth defects. Although ...an X-ray crystal structure of the recombinant gB ectodomain at postfusion conformation is available, the structures of prefusion gB and its complex with gH/gL on the viral envelope remain elusive. Here, we demonstrate the utility of cryo electron tomography (cryoET) with energy filtering and the cutting-edge technologies of Volta phase plate (VPP) and direct electron-counting detection to capture metastable prefusion viral fusion proteins and report the structures of glycoproteins in the native environment of HCMV virions. We established the validity of our approach by obtaining cryoET in situ structures of the vesicular stomatitis virus (VSV) glycoprotein G trimer (171 kD) in prefusion and postfusion conformations, which agree with the known crystal structures of purified G trimers in both conformations. The excellent contrast afforded by these technologies has enabled us to identify gB trimers (303kD) in two distinct conformations in HCMV tomograms and obtain their in situ structures at up to 21 Å resolution through subtomographic averaging. The predominant conformation (79%), which we designate as gB prefusion conformation, fashions a globular endodomain and a Christmas tree-shaped ectodomain, while the minority conformation (21%) has a columnar tree-shaped ectodomain that matches the crystal structure of the "postfusion" gB ectodomain. We also observed prefusion gB in complex with an "L"-shaped density attributed to the gH/gL complex. Integration of these structures of HCMV glycoproteins in multiple functional states and oligomeric forms with existing biochemical data and domain organization of other class III viral fusion proteins suggests that gH/gL receptor-binding triggers conformational changes of gB endodomain, which in turn triggers two essential steps to actuate virus-cell membrane fusion: exposure of gB fusion loops and unfurling of gB ectodomain.
We present results from an analysis of all data taken by the bicep2/Keck CMB polarization experiments up to and including the 2015 observing season. This includes the first Keck Array observations at ...220 GHz and additional observations at 95 and 150 GHz. The Q and U maps reach depths of 5.2, 2.9, and 26 μK_{CMB} arcmin at 95, 150, and 220 GHz, respectively, over an effective area of ≈400 square degrees. The 220 GHz maps achieve a signal to noise on polarized dust emission approximately equal to that of Planck at 353 GHz. We take auto and cross spectra between these maps and publicly available WMAP and Planck maps at frequencies from 23 to 353 GHz. We evaluate the joint likelihood of the spectra versus a multicomponent model of lensed-ΛCDM+r+dust+synchrotron+noise. The foreground model has seven parameters, and we impose priors on some of these using external information from Planck and WMAP derived from larger regions of sky. The model is shown to be an adequate description of the data at the current noise levels. The likelihood analysis yields the constraint r_{0.05}<0.07 at 95% confidence, which tightens to r_{0.05}<0.06 in conjunction with Planck temperature measurements and other data. The lensing signal is detected at 8.8σ significance. Running a maximum likelihood search on simulations we obtain unbiased results and find that σ(r)=0.020. These are the strongest constraints to date on primordial gravitational waves.
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•A novel rotating UVC-LED device was invented to improve air quality.•Efficacy of static irradiation was 53–79 % lower in poorly- than well-mixed rooms.•Using moving irradiation in a ...poorly-mixed room could enhance efficacy by 22–50 %.•A more compact and safe disinfection system is possible with UVC-LED.
The potential of inactivating indoor bacteria aerosols using a novel rotating ultraviolet-C (UV-C) light-emitting-diode (LED) system was investigated. The system was installed in the upper level of a full scale chamber and its effectiveness against aerosolized E. coli, S. marcescens, and S. epidermidis under the well-mixed with stationary UV-LED scenario was initially tested. The estimated susceptibility values were 1.068, 1.148, and 0.156 m2/J for E. coli, S. marcescens, and S. epidermidis, respectively. Three additional scenarios of experiments were conducted, in which E. coli was aerosolized into the test chamber and then allowed to decay under (i) poorly-mixed condition with stationary system, (ii) well-mixed with rotating system, and (iii) poorly-mixed conditions with rotating system. Our results showed no significant difference between the performance of stationary and rotating UR-UVGI-LED systems under a well-mixed condition. While the performance of the stationary UR-UVGI-LED system under a poorly-mixed condition decreased by 52.90–79.38 % compared to a well-mixed condition, rotating the UR-UVGI-LED system under a poorly-mixed condition, compared to the stationary system, enhanced its performance by 22.36–49.86 %. Thus, our proposed rotating irradiation offers great potential for application in environments where bioaerosols are unevenly distributed in a built environment.
Cost-effective and safe air disinfection methods are urgently needed in various environmental public settings. A novel UVC-based disinfection system was designed and tested to provide a promising ...solution because of its effective inactivation of indoor bioaerosols at a low cost. UVC light-emitting diodes (UVC-LEDs) were utilized as the irradiation source. This system has the unique feature of rotating the UVC-LEDs to generate a “scanning irradiation” zone. Escherichia coli was aerosolized into an experimental chamber, exposed to UVC-LEDs, and sampled using an impactor. Effects of air mixing (well-mixed vs. poorly-mixed), transmission range (short vs. long), and irradiation mode (stationary vs. rotating) were evaluated. The system performs significantly well under the poorly-mixed condition. The results obtained from the short disinfection range indicate that the rotating UVC was approximately 70.5 % more effective than the stationary UVC for the poorly-mixed case. Further, we evaluated the performance of the long disinfection range under a poorly-mixed situation, and the disinfection efficacy was 84.6 % higher for the rotating irradiation than that of the stationary. About 0.59–1.34 J/m2 UV dose can be used to obtain one-log inactivation of E. coli. In conclusion, the novel rotating upper-room UVC-LED system is effective in reducing indoor pathogen transmission, and our findings are highly significant to a growing field where LEDs are applied for disinfection.
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•Upper-room UVC-LED could mitigate both short-range and long-range transmissions.•New UVC-LED achieved ACHeq up to 41 h−1 for the short disinfection range scenario.•Stationary & rotating UV irradiation had equal efficacy under well-mixed room air.•With poor air mixing, rotating UV was 70–85 % more effective than stationary UV.
The mammalian target of rapamycin (mTOR) complex 1 (mTORC1) is a nutrient-sensitive protein kinase that is aberrantly activated in many human cancers. Whether dysregulation of mTORC1 signaling in ...normal tissues increases the risk for cancer, however, is unknown. We focused on hepatocellular carcinoma, which has been linked to environmental factors that affect mTORC1 activity, including diet. Ablation of the gene encoding TSC1 (tuberous sclerosis complex 1), which as part of the TSC1-TSC2 complex is an upstream inhibitor of mTORC1, results in constitutively increased mTORC1 signaling, an effect on this pathway similar to that of obesity. We found that mice with liver-specific knockout of Tsc1 developed sporadic hepatocellular carcinoma with heterogeneous histological and biochemical features. The spontaneous development of hepatocellular carcinoma in this mouse model was preceded by a series of pathological changes that accompany the primary etiologies of this cancer in humans, including liver damage, inflammation, necrosis, and regeneration. Chronic mTORC1 signaling led to unresolved endoplasmic reticulum stress and defects in autophagy, factors that contributed to hepatocyte damage and hepatocellular carcinoma development. Therefore, we conclude that increased activation of mTORC1 can promote carcinogenesis and may thus represent a key molecular link between cancer risk and environmental factors, such as diet.
This study investigated the effectiveness of different polarities of ionizers in inactivating bioaerosols in a duct flow condition. Three bacteria species—Escherichia coli (E. coli), Salmonella ...typhimurium (S. typhimurium), and Staphylococcus epidermidis (S. epidermidis)—were aerosolized into the duct under three airstream velocities, ranging from 3.0 to 6.5 m/s. The positive ionizer showed better disinfection performance than the negative ionizer by 29%–41%. Our results showed an inverse correlation between air velocity and the disinfection efficiencies. As the velocity was increased from 3.0 to 6.5 m/s, the corresponding disinfection efficiencies of positive ionizer decreased from 88.5% to 44.0%, 49.0% to 38.7%, and 35.1% to 19.8% for E. coli, S. typhimurium, and S. epidermidis, respectively. For the negative ionizer, the corresponding disinfection efficiencies decreased from 62.9% to 35.4%, 54.2% to 30.0%, and 42.9% to 30.2% for E. coli, S. typhimurium, and S. epidermidis, respectively. The positive ionizer was further tested at three relative humidity levels (50%, 70%, and 90%) and three temperature (17.5 °C, 21.0 °C, and 25.0 °C) levels. From 50% to 90% relative humidity, the disinfection efficiencies decreased from 46.0% to 23.6%, 35.2% to 22.5%, and 24.8% to 20.7%, for E. coli, S. typhimurium, and S. epidermidis, respectively. At the same time, the efficacy of the ionizer increased as temperature decreased. Therefore, from a temperature of 17.5 °C to 25.0 °C, our results show that the disinfection efficiencies decreased from 56.0% to 32%, 38.8% to 22.6%, and 24.8% to 21.5%, for E.coli, S. typhimurium, and S. epidermidis, respectively. The ozone emission rates of both ionizers were measured and found to be very small.
•Both polarities of ions were effective against gram positive and negative bacteria.•Positive ions showed 28.8–40.9% higher disinfection efficacy than negative ions.•Increasing humidity and temperature significantly decreased disinfection of ionizer.•Ozone emission rates of ionizers were lower than most electrostatic precipitators.
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