Structure of the Lysinibacillus sphaericus Tpp49Aa1 pesticidal protein elucidated from natural crystals using MHz-SFX.

The Lysinibacillus sphaericus proteins Tpp49Aa1 and Cry48Aa1 can together act as a toxin toward the mosquito Culex quinquefasciatus and have potential use in biocontrol. Given that proteins with sequence homology to the individual proteins can have activity alone against other insect species, the structure of Tpp49Aa1 was solved in order to understand this protein more fully and inform the design of improved biopesticides. Tpp49Aa1 is naturally expressed as a crystalline inclusion within the host bacterium, and MHz serial femtosecond crystallography using the novel nanofocus option at an X-ray free electron laser allowed rapid and high-quality data collection to determine the structure of Tpp49Aa1 at 1.62 Å resolution. This revealed the packing of Tpp49Aa1 within these natural nanocrystals as a homodimer with a large intermolecular interface. Complementary experiments conducted at varied pH also enabled investigation of the early structural events leading up to the dissolution of natural Tpp49Aa1 crystals-a crucial step in its mechanism of action. To better understand the cooperation between the two proteins, assays were performed on a range of different mosquito cell lines using both individual proteins and mixtures of the two. Finally, bioassays demonstrated Tpp49Aa1/Cry48Aa1 susceptibility of Anopheles stephensi, Aedes albopictus, and Culex tarsalis larvae-substantially increasing the potential use of this binary toxin in mosquito control.

Water temperature at the time of the catch-and-release event is a better predictor of survival in Atlantic salmon (Salmo salar) than acute water temperature changes before and after.

Despite studies on the effect of catch-and-release on the survival of Atlantic salmon (Salmo salar) being widespread in the literature, studies to date have failed to evaluate the potential role of thermal history. Herein, we show that despite cooler conditions post-release, 4/18 (22%) salmon died when caught-and-released at water temperatures ≥20°C, whereas 1/13 (8%) salmon caught-and-released at water temperatures ≤20°C, but who encountered mean water temperatures ≥20°C post-release, died. We conclude water temperature at time of the catch-and-release event remains the most suitable predictor of post-release survival.

Think Human: exploring the exhibition of ergonomics to enhance education and engagement: establishing the CIEHF 75th anniversary exhibition.

The field of ergonomics and human factors (E/HF) has an urgent need for increased uptake of specialists to meet the growing demands of the sector and related industries employing ergonomists. In the absence of E/HF being part of the school curriculum, one way of achieving this is through public engagement activities. Specialists in E/HF are motivated by understanding people and interactions, inherent qualities in outreach and engagement, so we are well placed to practice what we preach by understanding our own users, the consumers of our science. In this paper, we present a curriculum map and museum exhibition model as part of ongoing work to develop a public exhibition, called 'Think Human', hosted at the Museum of Making in Derby, England, from September 2024, as part of ongoing work in timely celebration of the 75th anniversary of the UK's Chartered Institute of Ergonomics and Human Factors (CIEHF).

We present a framework for public engagement with ergonomics, exemplified through the development of a museum exhibition which draws on a model of user experience. With 14­18 year-old students being a key target audience, we map elements of the school curriculum onto the core ergonomics knowledge areas.

The Chartered Institute of Ergonomics and Human Factors at 75: perspectives on contemporary challenges and future directions for Ergonomics and Human Factors.

As the UK's Chartered Institute of Ergonomics and Human Factors (CIEHF) celebrates its 75th anniversary, it is worth reflecting on our discipline's contribution, current state, and critical future endeavours. We present the perspectives of 18 EHF professionals who were asked to respond to five questions regarding the impact of EHF, contemporary challenges, and future directions. Co-authors were in agreement that EHF's impact has been only limited to date and that critical issues require resolution, such as increasing the number of suitably qualified practitioners, resolving the research-practice gap, and increasing awareness of EHF and its benefits. Frequently discussed future directions include advanced emerging technologies such as artificial intelligence, the development of new EHF methods, and enhancing the quality and reach of education and training. The majority felt there will be a need for EHF in 75 years; however, many noted that our methods will need to adapt to meet new needs.Practitioner statement: This article provides the perspectives of 18 Ergonomics and Human Factors (EHF) professionals on the impact of EHF, contemporary challenges and critical future directions, and changes that are necessary to ensure EHF remains relevant in future. As such, it provides important guidance on future EHF research and practice.

Hydrogel cultures reveal Transient Receptor Potential Vanilloid 4 regulation of myofibroblast activation and proliferation in valvular interstitial cells.

As aortic valve stenosis develops, valve tissue becomes stiffer. In response to this change in environmental mechanical stiffness, valvular interstitial cells (VICs) activate into myofibroblasts. We aimed to investigate the role of mechanosensitive calcium channel Transient Receptor Potential Vanilloid type 4 (TRPV4) in stiffness induced myofibroblast activation. We verified TRPV4 functionality in VICs using live calcium imaging during application of small molecule modulators of TRPV4 activity. We designed hydrogel biomaterials that mimic mechanical features of healthy or diseased valve tissue microenvironments, respectively, to investigate the role of TRPV4 in myofibroblast activation and proliferation. Our results show that TRPV4 regulates VIC proliferation in a microenvironment stiffness-independent manner. While there was a trend toward inhibiting myofibroblast activation on soft microenvironments during TRPV4 inhibition, we observed near complete deactivation of myofibroblasts on stiff microenvironments. We further identified Yes-activated protein (YAP) as a downstream target for TRPV4 activity on stiff microenvironments. Mechanosensitive TRPV4 channels regulate VIC myofibroblast activation, whereas proliferation regulation is independent of the microenvironmental stiffness. Collectively, the data suggests differential regulation of stiffness-induced proliferation and myofibroblast activation. Our data further suggest a regulatory role for TRPV4 regarding YAP nuclear localization. TRPV4 is an important regulator for VIC myofibroblast activation, which is linked to the initiation of valve fibrosis. Although more validation studies are necessary, we suggest TRPV4 as a promising pharmaceutical target to slow aortic valve stenosis progression.

Distinguishing different surface interactions for nucleotides adsorbed onto hematite and goethite particle surfaces through ATR-FTIR spectroscopy and DFT calculations.

Geochemical interfaces can impact the fate and transport of aqueous species in the environment including biomolecules. In this study, we investigate the surface chemistry of adsorbed nucleotides on two different minerals, hematite and goethite, using infrared spectroscopy and density functional theory (DFT) calculations. Attenuated total reflectance-Fourier transform infrared spectroscopy is used to probe the adsorption of deoxyadenosine monophosphate (dAMP), deoxyguanosine monophosphate (dGMP), deoxycytidine monophosphate (dCMP), and deoxythymidine monophosphate (dTMP) onto either hematite or goethite particle surfaces. The results show preferential adsorption of the phosphate group to either surface. Remarkably, surface adsorption of the four nucleotides onto either hematite or goethite have nearly identical experimental spectra in the phosphate region (900 to 1200 cm-1) for each mineral surface yet are distinctly different between the two minerals, suggesting differences in binding of these nucleotides to the two mineral surfaces. The experimental absorption frequencies in the phosphate region were compared to DFT calculations for nucleotides adsorbed through the phosphate group to binuclear clusters in either a monodentate or bidentate bridging coordination. Although the quality of the fits suggests that both binding modes may be present, the relative amounts differ on the two surfaces with preferential bonding suggested to be monodentate coordination on hematite and bidentate bridging on goethite. Possible reasons for these differences are discussed.

Inner ear sensory system changes as extinct crocodylomorphs transitioned from land to water.

Major evolutionary transitions, in which animals develop new body plans and adapt to dramatically new habitats and lifestyles, have punctuated the history of life. The origin of cetaceans from land-living mammals is among the most famous of these events. Much earlier, during the Mesozoic Era, many reptile groups also moved from land to water, but these transitions are more poorly understood. We use computed tomography to study changes in the inner ear vestibular system, involved in sensing balance and equilibrium, as one of these groups, extinct crocodile relatives called thalattosuchians, transitioned from terrestrial ancestors into pelagic (open ocean) swimmers. We find that the morphology of the vestibular system corresponds to habitat, with pelagic thalattosuchians exhibiting a more compact labyrinth with wider semicircular canal diameters and an enlarged vestibule, reminiscent of modified and miniaturized labyrinths of other marine reptiles and cetaceans. Pelagic thalattosuchians with modified inner ears were the culmination of an evolutionary trend with a long semiaquatic phase, and their pelagic vestibular systems appeared after the first changes to the postcranial skeleton that enhanced their ability to swim. This is strikingly different from cetaceans, which miniaturized their labyrinths soon after entering the water, without a prolonged semiaquatic stage. Thus, thalattosuchians and cetaceans became secondarily aquatic in different ways and at different paces, showing that there are different routes for the same type of transition.

Environmental management on agricultural land: Cost benefit analysis of an integrated cropping system for provision of environmental public goods.

Agricultural land covers a significant portion of the earths land surface. Although the predominant function of agricultural land is food production, environmental public goods, such as biodiversity or soil maintenance, are also essential for long-term sustainability. In arable farms the type of cropping system used has a major impact on delivery of these environmental goods. Low input, integrated and regenerative cropping systems aim to improve environmental outcomes of arable farming, with the goal of reducing external inputs by supporting internal regulation of system processes. However, the production of environmental goods does not have an immediate market value to the farmer, and often comes at a cost, particularly in the early stages of transition to a more sustainable system. We estimate the on-farm costs and benefits of an integrated cropping system during the first six years of transition from intensive conventional management at the Centre for Sustainable Cropping in north east Scotland. Although integrated cropping had better environmental outcomes, all crops had higher financial margins in the conventional system compared to the integrated system, which suffered a loss of over £500 per ha per year across the full rotation. This indicates that financial incentives are likely to be important to allow farmers to transition towards a more environmentally friendly cropping system.

To automate or not to automate: advocating the 'cliff-edge' principle.

We reflect briefly on the last forty years or so of ergonomics and human factors research in automation, observing that many of the issues being discussed today are the same as all those decades ago. In this paper, we explicate one of the key arguments regarding the application of automation in complex safety-critical domains, which proposes restraining the capabilities of automation technology until it is able to fully and completely take over the task at hand. We call this the 'cliff-edge' principle of automation design. Instead, we espouse a use for the technology in a more problem-driven, human-centred way. These are not entirely new ideas and such a philosophy is already gaining traction in ergonomics and human factors. The point is that in a given system, tasks should be controlled either by human or by automation; anything in between only causes problems for system performance.

Human factors problems with automation have been with us for over forty years, and have changed little in that time. This brief review shows a groundswell of opinion that points to what we call the cliff-edge automation principle ­ restraining the full capabilities of technology until it is ready to fully and completely take over the task. This approach improves human performance in the system by keeping the person in the loop and in control. Researchers and practitioners in ergonomics and human factors should continue to push this message to the designers and manufacturers of automated systems.

Ontogenetic variation in the crocodylian vestibular system.

Crocodylians today live in tropical to subtropical environments, occupying mostly shallow waters. Their body size changes drastically during ontogeny, as do their skull dimensions and bite forces, which are associated with changes in prey preferences. Endocranial neurosensory structures have also shown to change ontogenetically, but less is known about the vestibular system of the inner ear. Here we use 30 high-resolution computed tomography (CT) scans and three-dimensional geometric morphometrics to investigate the size and shape changes of crocodylian endosseous labyrinths throughout ontogeny, across four stages (hatchling, juvenile, subadult and adult). We find two major patterns of ontogenetic change. First, the labyrinth increases in size during ontogeny, with negative allometry in relation to skull size. Second, labyrinth shape changes significantly, with hatchlings having shorter semicircular canal radii, with thicker diameters and an overall dorsoventrally shorter labyrinth than those of more mature individuals. We argue that the modification of the labyrinth during crocodylian ontogeny is related to constraints imposed by skull growth, due to fundamental changes in the crocodylian braincase during ontogeny (e.g. verticalisation of the basicranium), rather than changes in locomotion, diet, or other biological functions or behaviours.

Identification of Small Molecular Chaperones Binding P23H Mutant Opsin through an In Silico Structure-Based Approach.

N-terminal P23H opsin mutation accounts for most of retinitis pigmentosa (RP) cases. P23H functions and folding can be rescued by small chaperone ligands, which contributes to validate mutant opsin as a suitable target for pharmacological treatment of RP. However, the lack of structural details on P23H mutant opsin strongly impairs drug design, and new chemotypes of effective chaperones of P23H opsin are in high demand. Here, a computational-boosted workflow combining homology modeling with molecular dynamics (MD) simulations and virtual screening was used to select putative P23H opsin chaperones among different libraries through a structure-based approach. In vitro studies corroborated the reliability of the structural model generated in this work and identified a number of novel chemotypes of safe and effective chaperones able to promote P23H opsin trafficking to the outer cell membrane.

Examining Pathways of Iron and Sulfur Acquisition, Trafficking, Deployment, and Storage in Mineral-Grown Methanogen Cells.

Methanogens have a high demand for iron (Fe) and sulfur (S); however, little is known of how they acquire, deploy, and store these elements and how this, in turn, affects their physiology. Methanogens were recently shown to reduce pyrite (FeS2), generating aqueous iron sulfide (FeSaq) clusters that are likely assimilated as a source of Fe and S. Here, we compared the phenotypes of Methanococcus voltae grown with FeS2 or ferrous iron [Fe(II)] and sulfide (HS-). FeS2-grown cells are 33% smaller yet have 193% more Fe than Fe(II)/HS--grown cells. Whole-cell electron paramagnetic resonance revealed similar distributions of paramagnetic Fe, although FeS2-grown cells showed a broad spectral feature attributed to intracellular thioferrate-like nanoparticles. Differential proteomic analyses showed similar expression of core methanogenesis enzymes, indicating that Fe and S source does not substantively alter the energy metabolism of cells. However, a homolog of the Fe(II) transporter FeoB and its putative transcriptional regulator DtxR were up-expressed in FeS2-grown cells, suggesting that cells sense Fe(II) limitation. Two homologs of IssA, a protein putatively involved in coordinating thioferrate nanoparticles, were also up-expressed in FeS2-grown cells. We interpret these data to indicate that, in FeS2-grown cells, DtxR cannot sense Fe(II) and therefore cannot downregulate FeoB. We suggest this is due to the transport of Fe(II) complexed with sulfide (FeSaq), leading to excess Fe that is sequestered by IssA as a thioferrate-like species. This model provides a framework for the design of targeted experiments aimed at further characterizing Fe acquisition and homeostasis in M. voltae and other methanogens. IMPORTANCE FeS2 is the most abundant sulfide mineral in the Earth's crust and is common in environments inhabited by methanogenic archaea. FeS2 can be reduced by methanogens, yielding aqueous FeSaq clusters that are thought to be a source of Fe and S. Here, we show that growth of Methanococcus voltae on FeS2 results in smaller cell size and higher Fe content per cell, with Fe likely stored intracellularly as thioferrate-like nanoparticles. Fe(II) transporters and storage proteins were upregulated in FeS2-grown cells. These responses are interpreted to result from cells incorrectly sensing Fe(II) limitation due to assimilation of Fe(II) as FeSaq. These findings have implications for our understanding of how Fe/S availability influences methanogen physiology and the biogeochemical cycling of these elements.

An Uncultivated Virus Infecting a Nanoarchaeal Parasite in the Hot Springs of Yellowstone National Park.

The Nanoarchaeota are small cells with reduced genomes that are found attached to and dependent on a second archaeal cell for their growth and replication. Initially found in marine hydrothermal environments and subsequently in terrestrial geothermal hot springs, the Nanoarchaeota species that have been described are obligate ectobionts, each with a different host species. However, no viruses had been described that infect the Nanoarchaeota. Here, we identify a virus infecting Nanoarchaeota by the use of a combination of viral metagenomic and bioinformatic approaches. This virus, tentatively named Nanoarchaeota Virus 1 (NAV1), consists of a 35.6-kb circular DNA genome coding for 52 proteins. We further demonstrate that this virus is broadly distributed among Yellowstone National Park hot springs. NAV1 is one of the first examples of a virus infecting a single-celled organism that is itself an ectobiont of another single-celled organism.IMPORTANCE Here, we present evidence of the first virus found to infect Nanoarchaeota, a symbiotic archaean found in acidic hot springs of Yellowstone National Park, USA. Using culture-independent techniques, we provide the genome sequence and identify the archaeal host species of a novel virus, NAV1. NAV1 is the first example of a virus infecting an archaeal species that is itself an obligate symbiont and dependent on a second host organism for growth and cellular replication. On the basis of annotation of the NAV1 genome, we propose that this virus is the founding member of a new viral family, further demonstrating the remarkable genetic diversity of archaeal viruses.

Discovery and Characterization of Thermoproteus Spherical Piliferous Virus 1: a Spherical Archaeal Virus Decorated with Unusual Filaments.

We describe the discovery of an archaeal virus, one that infects archaea, tentatively named Thermoproteus spherical piliferous virus 1 (TSPV1), which was purified from a Thermoproteales host isolated from a hot spring in Yellowstone National Park (USA). TSPV1 packages an 18.65-kb linear double-stranded DNA (dsDNA) genome with 31 open reading frames (ORFs), whose predicted gene products show little homology to proteins with known functions. A comparison of virus particle morphologies and gene content demonstrates that TSPV1 is a new member of the Globuloviridae family of archaeal viruses. However, unlike other Globuloviridae members, TSPV1 has numerous highly unusual filaments decorating its surface, which can extend hundreds of nanometers from the virion. To our knowledge, similar filaments have not been observed in any other archaeal virus. The filaments are remarkably stable, remaining intact across a broad range of temperature and pH values, and they are resistant to chemical denaturation and proteolysis. A major component of the filaments is a glycosylated 35-kDa TSPV1 protein (TSPV1 GP24). The filament protein lacks detectable homology to structurally or functionally characterized proteins. We propose, given the low host cell densities of hot spring environments, that the TSPV1 filaments serve to increase the probability of virus attachment and entry into host cells.IMPORTANCE High-temperature environments have proven to be an important source for the discovery of new archaeal viruses with unusual particle morphologies and gene content. Our isolation of Thermoproteus spherical piliferous virus 1 (TSPV1), with numerous filaments extending from the virion surface, expands our understanding of viral diversity and provides new insight into viral replication in high-temperature environments.

Bacterial Viruses Subcommittee and Archaeal Viruses Subcommittee of the ICTV: update of taxonomy changes in 2021.

In this article, we - the Bacterial Viruses Subcommittee and the Archaeal Viruses Subcommittee of the International Committee on Taxonomy of Viruses (ICTV) - summarise the results of our activities for the period March 2020 - March 2021. We report the division of the former Bacterial and Archaeal Viruses Subcommittee in two separate Subcommittees, welcome new members, a new Subcommittee Chair and Vice Chair, and give an overview of the new taxa that were proposed in 2020, approved by the Executive Committee and ratified by vote in 2021. In particular, a new realm, three orders, 15 families, 31 subfamilies, 734 genera and 1845 species were newly created or redefined (moved/promoted).

Structural studies of Acidianus tailed spindle virus reveal a structural paradigm used in the assembly of spindle-shaped viruses.

The spindle-shaped virion morphology is common among archaeal viruses, where it is a defining characteristic of many viral families. However, structural heterogeneity intrinsic to spindle-shaped viruses has seriously hindered efforts to elucidate the molecular architecture of these lemon-shaped capsids. We have utilized a combination of cryo-electron microscopy and X-ray crystallography to study Acidianus tailed spindle virus (ATSV). These studies reveal the architectural principles that underlie assembly of a spindle-shaped virus. Cryo-electron tomography shows a smooth transition from the spindle-shaped capsid into the tubular-shaped tail and allows low-resolution structural modeling of individual virions. Remarkably, higher-dose 2D micrographs reveal a helical surface lattice in the spindle-shaped capsid. Consistent with this, crystallographic studies of the major capsid protein reveal a decorated four-helix bundle that packs within the crystal to form a four-start helical assembly with structural similarity to the tube-shaped tail structure of ATSV and other tailed, spindle-shaped viruses. Combined, this suggests that the spindle-shaped morphology of the ATSV capsid is formed by a multistart helical assembly with a smoothly varying radius and allows construction of a pseudoatomic model for the lemon-shaped capsid that extends into a tubular tail. The potential advantages that this novel architecture conveys to the life cycle of spindle-shaped viruses, including a role in DNA ejection, are discussed.

Peri-Procedural Aggressive Hydration for Post Endoscopic Retrograde Cholangiopancreatography (ERCP) Pancreatitis Prophylaxsis: Meta-analysis of Randomized Controlled Trials.

BACKGROUND: Periprocedural intravenous hydration is suggested to decrease the risk of post-ERCP pancreatitis (PEP). However, quality of evidence supporting this suggestion remains poor. Here we hypothesized that aggressive hydration(AH) could be an effective preventive measure. METHODS: Pubmed, EMBASE, CINAHL, Google Scholar, Clinical Trials. gov, Clinical Key, International Standard Randomized Trial Number registry as well as secondary sources were searched through January 2019 to identify randomized controlled studies comparing AH to standard hydration (SH) for prevention of PEP. Pooled odds ratio (OR) and 95% confidence intervals (CIs) were calculated using the random-effects model. RevMan 5.3 was used for analysis. RESULTS: A total of 9 RCTs, with 2094 patients, were included in the meta-analysis. AH reduced incidence of PEP by 56% compared to SH (OR = 0.44, CI:0.28-0.69; p = 0.0004). The incidence of post-ERCP hyperamylasemia also decreased with AH compared to SH (OR = 0.51; p = 0.001). Length of stay decreased by 1 day with AH (Mean Difference (MD): -0.89 d; p = 0.00002). There was no significant difference in adverse events related to fluid overload between two groups (OR:1.29; p = 0.81) and post-ERCP abdominal pain (OR:0.35; p = 0.17). Numbers of patient to be treated with AH to prevent one episode of PEP was 17. Final results of the meta-analysis were not affected by alternative effect measures or statistical models of heterogeneity. CONCLUSION: Aggressive hydration is associated with a significantly lower incidence of PEP and it appears to be an effective and safe strategy for the prevention of Post ERCP pancreatitis.

Trends in Hospitalization, Acute Kidney Injury, and Mortality in Patients With Spontaneous Bacterial Peritonitis.

GOALS: The purpose of our study was to evaluate trends of hospitalization, acute kidney injury (AKI) and mortality in cirrhotic patients with spontaneous bacterial peritonitis (SBP). BACKGROUND: SBP is a frequent bacterial infection in cirrhotic patients leading to increased morbidity and mortality. MATERIALS AND METHODS: A total of 4,840,643 patients hospitalized with cirrhosis from 2005 to 2014 were identified using the Nationwide Inpatient Sample database, of which 115,359 (2.4%) had SBP. We examined annual trends and used multivariable mixed-effects logistic regression analyses to obtain adjusted odds ratios by accounting for hospital level and patient level variables. RESULTS: We identified a striking increase in hospitalizations for SBP in cirrhotic patients (0.45% to 3.12%) and AKI in SBP patients (25.6% to 46.7%) from 2005 to 2014. Inpatient mortality decreased over the study period in patients with SBP (19.1% to 16.1%) and in patients with SBP plus AKI (40.9% to 27.6%). Patients with SBP had a higher inpatient mortality rate than those without SBP [15.5% vs. 6%, adjusted odd ratio (aOR): 2.02, P<0.001]. AKI was 2-fold more prevalent in cirrhotics with SBP than those without SBP (42.8% vs. 17.2%, aOR: 1.91, P<0.001) and concomitant AKI was associated with a 6-fold mortality increase (aOR: 5.84, P<0.001). Cirrhotic patients with SBP had higher hospitalization costs and longer length of stays than patients without SBP. CONCLUSIONS: Despite a higher hospitalization rate and prevalence of concomitant AKI, mortality in patients with SBP decreased during the study period. SBP is associated with high likelihood of development of AKI, which in turn, increases mortality.

Healthy human gut phageome.

The role of bacteriophages in influencing the structure and function of the healthy human gut microbiome is unknown. With few exceptions, previous studies have found a high level of heterogeneity in bacteriophages from healthy individuals. To better estimate and identify the shared phageome of humans, we analyzed a deep DNA sequence dataset of active bacteriophages and available metagenomic datasets of the gut bacteriophage community from healthy individuals. We found 23 shared bacteriophages in more than one-half of 64 healthy individuals from around the world. These shared bacteriophages were found in a significantly smaller percentage of individuals with gastrointestinal/irritable bowel disease. A network analysis identified 44 bacteriophage groups of which 9 (20%) were shared in more than one-half of all 64 individuals. These results provide strong evidence of a healthy gut phageome (HGP) in humans. The bacteriophage community in the human gut is a mixture of three classes: a set of core bacteriophages shared among more than one-half of all people, a common set of bacteriophages found in 20-50% of individuals, and a set of bacteriophages that are either rarely shared or unique to a person. We propose that the core and common bacteriophage communities are globally distributed and comprise the HGP, which plays an important role in maintaining gut microbiome structure/function and thereby contributes significantly to human health.

FXR activation by obeticholic acid or nonsteroidal agonists induces a human-like lipoprotein cholesterol change in mice with humanized chimeric liver.

Obeticholic acid (OCA) is a selective farnesoid X receptor (FXR) agonist that regulates bile acid and lipid metabolism. FXR activation induces distinct changes in circulating cholesterol among animal models and humans. The mechanistic basis of these effects has been elusive because of difficulties in studying lipoprotein homeostasis in mice, which predominantly package circulating cholesterol in HDLs. Here, we tested the effects of OCA in chimeric mice whose livers are mostly composed (≥80%) of human hepatocytes. Chimeric mice exhibited a human-like ratio of serum LDL cholesterol (LDL-C) to HDL cholesterol (HDL-C) at baseline. OCA treatment in chimeric mice increased circulating LDL-C and decreased circulating HDL-C levels, demonstrating that these mice closely model the cholesterol effects of FXR activation in humans. Mechanistically, OCA treatment increased hepatic cholesterol in chimeric mice but not in control mice. This increase correlated with decreased SREBP-2 activity and target gene expression, including a significant reduction in LDL receptor protein. Cotreatment with atorvastatin reduced total cholesterol, rescued LDL receptor protein levels, and normalized serum LDL-C. Treatment with two clinically relevant nonsteroidal FXR agonists elicited similar lipoprotein and hepatic changes in chimeric mice, suggesting that the increase in circulating LDL-C is a class effect of FXR activation.