Mohamad Navab
Sep 1, 2000; 41:1495-1508
Articles

Mohamad Navab
Sep 1, 2000; 41:1481-1494
Articles

JL Dixon
Feb 1, 1993; 34:167-179
Reviews

Jason M. Ridlon
Feb 1, 2006; 47:241-259
Reviews

Deplatforming Trump puts big tech under fresh scrutiny Expert comment NCapeling 22 January 2021

The response of digital platforms to the US Capitol riots raises questions about online content governance. The EU and UK are starting to come up with answers.

The ‘deplatforming’ of Donald Trump – including Twitter’s announcement that it has permanently banned him due to ‘the risk of further incitement of violence’ after the riots in the US – shows once more not only the sheer power of online platforms but also the lack of a coherent and consistent framework for online content governance.

Taking the megaphone away from Trump during the Capitol riots seems sensible, but was it necessary or proportionate to ban him from the platform permanently? Or consistent with the treatment of other ‘strongmen’ world leaders such as Modi, Duterte and Ayatollah Ali Khamenei who have overseen nationalistic violence but whose accounts remain intact?

Such complex decisions on online expression should not made unilaterally by powerful and unregulated tech actors, but instead should be subject to democratic oversight and grounded in the obligations of states and responsibilities of companies under international human rights law.

The speed and scale of digital information has left governments across the world struggling with how to tackle online harms such as hate speech, extremist content and disinformation since the emergence of mass social media 15 years ago.

The US’s hallowed approach to the First Amendment, under which speech on public issues – even hate speech – occupies the highest rank and is entitled to special protection, has contributed to a reluctance to regulate Silicon Valley’s digital platforms. But the irony is that by not regulating them, the government harmed freedom of expression by leaving complex speech decisions in the hands of private actors.

Meanwhile at the other extreme is the growing number of illiberal and authoritarian governments using a combination of vague laws, censorship, propaganda, and internet blackouts to severely restrict online freedom of expression, control the narrative and, in some cases, incite atrocities.

Regulation is on the way

The happy medium – flexible online content regulation providing clarity, predictability, transparency, and accountability – has until now been elusive. But even before the deplatforming of Trump, 2021 was set to be the year when this approach finally gained some traction, at least in Europe.

The EU’s recently-published draft Digital Services Act puts obligations on dominant social media platforms to manage ‘systemic risks’, for example through requirements for greater transparency about their content decisions, algorithms used for recommendations, and online advertising systems.

The UK will shortly publish its Online Safety Bill, which will establish a new regulatory framework for tackling online harms, including the imposition of a duty of care and codes of conduct on Big Tech, to be overseen by an independent regulator (Ofcom).

Both proposals are based on a ‘co-regulatory’ model under which the regulator sets out a framework substantiated with rules by the private sector, with the regulator performing a monitoring function to ensure the rules are complied with.

Both also draw on international human rights standards and the work of civil society in applying these standards in relation to the online public square, with the aim of increasing control for users over what they see online, requiring transparency about tech companies’ policies in a number of areas, and strengthening the accountability of platforms when they fall foul of the regulation.

The procedure for both proposals has also been inclusive, involving extensive multi-stakeholder consultations with civil society organizations and Big Tech, and the proposals will be subject to scrutiny in 2021, notably from the EU and UK parliaments.

Both proposals are at an early stage, and it remains to be seen whether they go far enough – or indeed will have a chilling effect on online platforms. But as an attempt to initiate a dialogue on globally coherent principles, they are positive first steps. They also provide food for thought for the new Joe Biden administration in the US as it turns its attention to the regulation of Big Tech.

For some time civil society – most prominently David Kaye, the former UN Special Rapporteur on freedom of expression and opinion – have called for content regulation to be informed by universal international human rights law standards.

The EU and UK are peculiarly well-placed to take the lead in this area because European countries have for decades been on the receiving end of judgments from the European Court of Human Rights on the appropriate limits to freedom of expression in cases brought under the European Convention on Human Rights.

In deciding these cases, the court has to balance the right to freedom of expression against the restrictions imposed – for example in the context of incitement to violence, political debate, and satire. Deciding where to draw the line on what can and cannot be expressed in a civilised society which prizes freedom of expression is inevitably a difficult exercise.

International human rights law provides a methodology that inquires whether the interference to freedom of expression was prescribed by law and pursues a legitimate aim, and also whether it was necessary in a democratic society to achieve those aims – including whether the interference was necessary and proportionate (as for example in Delfi AS v Estonia, which involved a news portal failing to take down unlawful hate speech).

To be effective, online content regulation has to bite on tech companies, which is a challenge given the internet is global but domestic law normally applies territorially. The EU’s proposals have an extraterritorial element as they apply to any online platforms providing services in the EU regardless of where the platform is headquartered.

Further, both the EU and UK want to give the regulator strong enforcement powers – it is proposed for example that Ofcom will have powers to fine platforms up to ten per cent of their turnover for breaches.

Although the proposals would not apply directly to the deplatforming of Trump which occurred in the US, the philosophy behind the EU and UK approach is likely to have an impact beyond European shores in promoting a co-regulatory model that some of the bigger tech companies have been inviting for some time, reluctant as they are to ‘play God’ on content moderation decisions without reference to any regulatory framework.

In the absence of regulation, the standards of tech platforms such as Facebook and Twitter have already evolved over time in response to pressure from civil rights groups, users, and advertisers, including updated policies on protecting civic conversation and hate speech.

Facebook has also set up an independent Oversight Board, whose members include leading human rights lawyers, to review decisions on content including – at its own request – the decision to indefinitely suspend Trump from Facebook and Instagram. Decisions on the Board’s first tranche of cases are expected imminently.

Gatekeeper status is key

Online content regulation also needs to address the role of Big Tech as the ‘digital gatekeepers’, because their monopoly power extends not just to editorial control of the news and information we consume, but also to market access.

The decision of Apple, Google, and Amazon to stop hosting right-wing social network Parler after it refused to combat calls for violence during the US Capitol riots was understandable in the circumstances, but also underlined the unilateral ability of Big Tech to decide the rules of the market.

Again, it is Europe where efforts are underway to tackle this issue: the EU’s draft Digital Market Act imposes obligations on online gatekeepers to avoid certain unfair practices, and the UK’s new Digital Markets Unit will have powers to write and enforce a new code of practice on those technology companies with ‘substantial and enduring’ market power.

In the US, Biden’s team will be following these developments with interest, given the growing bipartisan support for strengthening US antitrust rules and reviving antitrust enforcement. The EU’s recently published proposals for an EU-US tech agenda include a transatlantic dialogue on the responsibility of tech platforms and strengthened cooperation between antitrust authorities on digital markets.

Ultimately a consistent – and global – approach to online content is needed instead of fragmented approaches by different companies and governments. It is also important the framework is flexible so that it is capable of applying not only to major democracies but also to countries where too often sweeping state regulation has been used as a pretext to curtail online expression online.

The pursuit of a pluralistic framework tailored to different political and cultural contexts is challenging, and international human rights law cannot provide all the answers but, as a universal framework, it is a good place to start. The raft of regulatory measures from the EU and UK means that, regardless of whether Trump regains his online megaphone, 2021 is set to be a year of reckoning for Big Tech.

Insights from Climate Policy: Engaging Subnational Governments in Global Platforms 10 June 2020 — 2:45PM TO 6:00PM Anonymous (not verified) 9 February 2021 Online

How have subnational governments shaped the global agenda and created momentum on climate change where national and international governance processes could not?

Can these advances be converted into meaningful collaboration channels for policy development? What works, or does not, when it comes to engagement with multilateral negotiation processes? What ingredients are necessary for success? What are the broader implications of these trends for inclusivity and innovation in international governance?

This event is part of the Inclusive Governance Initiative, which is examining how to build more inclusive models and mechanisms of global governance fit for purpose in today’s world.

Stop codon read-through (SCR) is a process of continuation of translation beyond a stop codon. This phenomenon, which occurs only in certain mRNAs under specific conditions, leads to a longer isoform with properties different from that of the canonical isoform. MTCH2, which encodes a mitochondrial protein that regulates mitochondrial metabolism, was selected as a potential read-through candidate based on evolutionary conservation observed in the proximal region of its 3' UTR. Here, we demonstrate translational read-through across two evolutionarily conserved, in-frame stop codons of MTCH2 using luminescence- and fluorescence-based assays, and by analyzing ribosome-profiling and mass spectrometry (MS) data. This phenomenon generates two isoforms, MTCH2x and MTCH2xx (single- and double-SCR products, respectively), in addition to the canonical isoform MTCH2, from the same mRNA. Our experiments revealed that a cis-acting 12-nucleotide sequence in the proximal 3' UTR of MTCH2 is the necessary signal for SCR. Functional characterization showed that MTCH2 and MTCH2x were localized to mitochondria with a long t1/2 (>36 h). However, MTCH2xx was found predominantly in the cytoplasm. This mislocalization and its unique C terminus led to increased degradation, as shown by greatly reduced t1/2 (<1 h). MTCH2 read-through–deficient cells, generated using CRISPR-Cas9, showed increased MTCH2 expression and, consistent with this, decreased mitochondrial membrane potential. Thus, double-SCR of MTCH2 regulates its own expression levels contributing toward the maintenance of normal mitochondrial membrane potential.

Expert

Rhodopsin is a canonical class A photosensitive G protein–coupled receptor (GPCR), yet relatively few pharmaceutical agents targeting this visual receptor have been identified, in part due to the unique characteristics of its light-sensitive, covalently bound retinal ligands. Rhodopsin becomes activated when light isomerizes 11-cis-retinal into an agonist, all-trans-retinal (ATR), which enables the receptor to activate its G protein. We have previously demonstrated that, despite being covalently bound, ATR can display properties of equilibrium binding, yet how this is accomplished is unknown. Here, we describe a new approach for both identifying compounds that can activate and attenuate rhodopsin and testing the hypothesis that opsin binds retinal in equilibrium. Our method uses opsin-based fluorescent sensors, which directly report the formation of active receptor conformations by detecting the binding of G protein or arrestin fragments that have been fused onto the receptor's C terminus. We show that these biosensors can be used to monitor equilibrium binding of the agonist, ATR, as well as the noncovalent binding of β-ionone, an antagonist for G protein activation. Finally, we use these novel biosensors to observe ATR release from an activated, unlabeled receptor and its subsequent transfer to the sensor in real time. Taken together, these data support the retinal equilibrium binding hypothesis. The approach we describe should prove directly translatable to other GPCRs, providing a new tool for ligand discovery and mutant characterization.

The Impact of Brexit on Energy Transformation in the UK and EU 28 March 2019 — 8:15AM TO 9:45AM Anonymous (not verified) 3 December 2018 Chatham House | 10 St James's Square | London | SW1Y 4LE

The UK’s decision to leave the EU will fundamentally reshape many of the UK’s policies and its relations with countries around the world. For energy and climate, the changes could be significant and will need to be managed carefully to secure ongoing investment, stable energy prices and ambitious climate objectives. The UK’s departure will also affect the balance of political support for climate and energy policies with the EU institutions and potentially impact upon regional initiatives.

This roundtable will discuss:

• The impact on the energy sector of Brexit during the transition period through until December 2020 including the operation of interconnectors and access to the Internal energy market, ongoing engagement in European research collaboration and the replacement of European financial resources.
• The possible opportunities and risks for the UK’s energy sector in 2021 and beyond.
• The implications of Brexit on the EU’s energy and climate policy.

The roundtable will discuss the role of the public and business in shaping the future deal as it will need to be ratified by the parliaments of all member states.

Attendance at this event is by invitation only.

Power Sector Transformation, New Market Dynamics and Geopolitical Implications 7 November 2018 — 8:00AM TO 9:30AM Anonymous (not verified) 6 December 2018 Chatham House | 10 St James's Square | London | SW1Y 4LE

The global electricity sector is experiencing profound change due to a confluence of technological innovation, environmental policies and regulatory reform. The effect is most obvious in the EU28, Australia and parts of North America.

However, this is just the beginning and the success of the next phase of electricity sector transformations hinges on enhancing system flexibility to facilitate unhindered low-cost deployment of renewables. It remains to be seen how utilities will seek to navigate this second phase of electricity transformations.

This session starts with a presentation and discussion that focuses on:

• Public and private sector risks of the transformation of the power sector, changes in generation mix and their implications for supply chain, employments and investment patterns.
• The role of government and the regulatory framework in light of changing market structure, new entrants and big data.
• Wider geopolitical issues including the implication for fossil fuel producers and the rise in demand for new materials and changes in land use.
• The possible implications on the power sector on the electrification of heat and transport.

The discussion then moves to the speed of transformation and what this means for existing and new market actors.

Food system transformation: A blind spot for climate and biodiversity action? 20 October 2022 — 12:00PM TO 1:00PM Anonymous (not verified) 5 October 2022 Chatham House and Online

How can COP27 and COP15 accelerate the agenda for sustainable food systems and land use?

Tackling the dual crises of climate change and biodiversity loss requires extraordinary levels of action at an unprecedented speed. Agriculture is the biggest user of land, the biggest source of methane emissions, a major contributor to total greenhouse gas emissions and the leading driver of biodiversity loss.

Anything short of a food system transformation puts climate and biodiversity objectives in peril. However, governments have not yet produced credible pathways and strong policies for tackling our growing ‘foodprint’ – the negative impacts of what we grow and eat.

In advance of COP27 in Sharm El-Sheikh for climate and COP15 in Montreal for biodiversity, Chatham House has published a new briefing paper which examines aligning food systems with climate and biodiversity targets.

The paper reviews the climate and biodiversity policy landscape to 2030, with a focus on land-based aspects and the inclusion of food and agriculture. The paper highlights serious conflicts between the impacts of the food system and goals to protect and restore biodiversity and mitigate climate change.

In light of this, opportunities for joined-up action on food, climate and biodiversity are identified, including three key steps for countries to take this decade to produce suitably ambitious and effective policies across the climate–biodiversity–food nexus.

This event brings together leading voices from the international policy arenas for climate and biodiversity to react to the briefing paper and discuss how COP27 and COP15 can accelerate the agenda for sustainable food systems and land use.

Daniel Le, Bao V. Le Hung, Stefano Morra, Chol Park and Zicheng Qian
Trans. Amer. Math. Soc. 377 (), 5749-5786.
Abstract, references and article information

Marko Voutilainen, Lauri Viitasaari and Pauliina Ilmonen
Theor. Probability and Math. Statist. 111 (), 181-197.
Abstract, references and article information

Yongqiang Liu, Laurentiu Maxim and Botong Wang
Proc. Amer. Math. Soc. 152 (), 5279-5288.
Abstract, references and article information

Rubén Medina and Andrés Quilis
Proc. Amer. Math. Soc. 152 (), 5137-5148.
Abstract, references and article information

YoungJu Choie, Winfried Kohnen and Yichao Zhang
Proc. Amer. Math. Soc. 152 (), 5025-5037.
Abstract, references and article information

Animals can sense the presence of microbes in their tissues and mobilize their own defenses by recognizing and responding to conserved microbial structures (often called microbe-associated molecular patterns (MAMPs)). Successful host defenses may kill the invaders, yet the host animal may fail to restore homeostasis if the stimulatory microbial structures are not silenced. Although mice have many mechanisms for limiting their responses to lipopolysaccharide (LPS), a major Gram-negative bacterial MAMP, a highly conserved host lipase is required to extinguish LPS sensing in tissues and restore homeostasis. We review recent progress in understanding how this enzyme, acyloxyacyl hydrolase (AOAH), transforms LPS from stimulus to inhibitor, reduces tissue injury and death from infection, prevents prolonged post-infection immunosuppression, and keeps stimulatory LPS from entering the bloodstream. We also discuss how AOAH may increase sensitivity to pulmonary allergens. Better appreciation of how host enzymes modify LPS and other MAMPs may help prevent tissue injury and hasten recovery from infection.

Chorismate mutase (CM), an essential enzyme at the branch-point of the shikimate pathway, is required for the biosynthesis of phenylalanine and tyrosine in bacteria, archaea, plants, and fungi. MtCM, the CM from Mycobacterium tuberculosis, has less than 1% of the catalytic efficiency of a typical natural CM and requires complex formation with 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase for high activity. To explore the full potential of MtCM for catalyzing its native reaction, we applied diverse iterative cycles of mutagenesis and selection, thereby raising kcat/Km 270-fold to 5 × 105 m−1s−1, which is even higher than for the complex. Moreover, the evolutionarily optimized autonomous MtCM, which had 11 of its 90 amino acids exchanged, was stabilized compared with its progenitor, as indicated by a 9 °C increase in melting temperature. The 1.5 Å crystal structure of the top-evolved MtCM variant reveals the molecular underpinnings of this activity boost. Some acquired residues (e.g. Pro52 and Asp55) are conserved in naturally efficient CMs, but most of them lie beyond the active site. Our evolutionary trajectories reached a plateau at the level of the best natural enzymes, suggesting that we have exhausted the potential of MtCM. Taken together, these findings show that the scaffold of MtCM, which naturally evolved for mediocrity to enable inter-enzyme allosteric regulation of the shikimate pathway, is inherently capable of high activity.

10 September 2020

Visual Abstract

Visual Abstract

Sophos X-Ops unveils five-year investigation tracking China-based groups targeting perimeter devices

Philipp Emanuel Geyer
Dec 17, 2020; 0:RA120.002359v1-mcp.RA120.002359
Research

Tuberculosis (TB), caused by the infection of Mycobacterium tuberculosis (MTB), is one of the leading causes of death worldwide, especially in children. However, the mechanisms by which MTB infects its cellular host, activates an immune response, and triggers inflammation remain unknown. Mitochondria play important roles in the initiation and activation of the nucleotide-binding oligomerization domain-like receptor with a pyrin domain 3 (NLRP3) inflammasome, where mitochondria-associated endoplasmic reticulum membranes (MAMs) may serve as the platform for inflammasome assembly and activation. Additionally, mitofusin 2 (MFN2) is implicated in the formation of MAMs, but, the roles of mitochondria and MFN2 in MTB infection have not been elucidated. Using mircroarry profiling of TB patients and in vitro MTB stimulation of macrophages, we observed an up-regulation of MFN2 in the peripheral blood mononuclear cells of active TB patients. Furthermore, we found that MTB stimulation by MTB-specific antigen ESAT-6 or lysate of MTB promoted MFN2 interaction with NLRP3 inflammasomes, resulting in the assembly and activation of the inflammasome and, subsequently, IL-1β secretion. These findings suggest that MFN2 and mitochondria play important role in the pathogen-host interaction during MTB infection.

AMP-activated protein kinase (AMPK) is a key regulator of energy metabolism that phosphorylates a wide range of proteins to maintain cellular homeostasis. AMPK consists of three subunits: α, β, and γ. AMPKα and β are encoded by two genes, the γ subunit by three genes, all of which are expressed in a tissue-specific manner. It is not fully understood, whether individual isoforms have different functions. Using RNA-Seq technology, we provide evidence that the loss of AMPKβ1 and AMPKβ2 lead to different gene expression profiles in human induced pluripotent stem cells (hiPSCs), indicating isoform-specific function. The knockout of AMPKβ2 was associated with a higher number of differentially regulated genes than the deletion of AMPKβ1, suggesting that AMPKβ2 has a more comprehensive impact on the transcriptome. Bioinformatics analysis identified cell differentiation as one biological function being specifically associated with AMPKβ2. Correspondingly, the two isoforms differentially affected lineage decision toward a cardiac cell fate. Although the lack of PRKAB1 impacted differentiation into cardiomyocytes only at late stages of cardiac maturation, the availability of PRKAB2 was indispensable for mesoderm specification as shown by gene expression analysis and histochemical staining for cardiac lineage markers such as cTnT, GATA4, and NKX2.5. Ultimately, the lack of AMPKβ1 impairs, whereas deficiency of AMPKβ2 abrogates differentiation into cardiomyocytes. Finally, we demonstrate that AMPK affects cellular physiology by engaging in the regulation of hiPSC transcription in an isoform-specific manner, providing the basis for further investigations elucidating the role of dedicated AMPK subunits in the modulation of gene expression.

Type I and III interferons induce expression of the “myxovirus resistance proteins” MxA in human cells and its ortholog Mx1 in murine cells. Human MxA forms cytoplasmic structures, whereas murine Mx1 forms nuclear bodies. Whereas both HuMxA and MuMx1 are antiviral toward influenza A virus (FLUAV) (an orthomyxovirus), only HuMxA is considered antiviral toward vesicular stomatitis virus (VSV) (a rhabdovirus). We previously reported that the cytoplasmic human GFP-MxA structures were phase-separated membraneless organelles (“biomolecular condensates”). In the present study, we investigated whether nuclear murine Mx1 structures might also represent phase-separated biomolecular condensates. The transient expression of murine GFP-Mx1 in human Huh7 hepatoma, human Mich-2H6 melanoma, and murine NIH 3T3 cells led to the appearance of Mx1 nuclear bodies. These GFP-MuMx1 nuclear bodies were rapidly disassembled by exposing cells to 1,6-hexanediol (5%, w/v), or to hypotonic buffer (40–50 mosm), consistent with properties of membraneless phase-separated condensates. Fluorescence recovery after photobleaching (FRAP) assays revealed that the GFP-MuMx1 nuclear bodies upon photobleaching showed a slow partial recovery (mobile fraction: ∼18%) suggestive of a gel-like consistency. Surprisingly, expression of GFP-MuMx1 in Huh7 cells also led to the appearance of GFP-MuMx1 in 20–30% of transfected cells in a novel cytoplasmic giantin-based intermediate filament meshwork and in cytoplasmic bodies. Remarkably, Huh7 cells with cytoplasmic murine GFP-MuMx1 filaments, but not those with only nuclear bodies, showed antiviral activity toward VSV. Thus, GFP-MuMx1 nuclear bodies comprised phase-separated condensates. Unexpectedly, GFP-MuMx1 in Huh7 cells also associated with cytoplasmic giantin-based intermediate filaments, and such cells showed antiviral activity toward VSV.

Priyanka Tripathi
Dec 30, 2020; 0:jlr.RA120001190v1-jlr.RA120001190
Research Articles

Daphne E.C. Boer
Dec 23, 2020; 0:jlr.RA120001043v1-jlr.RA120001043
Research Articles

Carlota Oleaga
Nov 17, 2020; 0:jlr.RA120000964v1-jlr.RA120000964
Research Articles

Yueming Hu
Dec 11, 2020; 0:jlr.RA120000919v1-jlr.RA120000919
Research Articles

Akemi Kakino
Nov 3, 2020; 0:jlr.RA120000767v1-jlr.RA120000767
Research Articles

For data that is being loaded from a SAS Stored Process Server, an insertion process might fail to a MySQL database with a warning, as well as an error message that says "During insert: Incorrect datetime value…"

An error might occur when you use the SAS 9 BULKLOAD= and BULKEXTRACT= options load data to or extract data from HP Neoview on the HP Itanium platform. The problem occurs because Hewlett-Packard changed the name of one of

     Lens and tear film lipids are as unique as the systems they reside in. The major lipid of the human lens is dihydrosphingomylein, found in quantity only in the lens. The lens contains a cholesterol to phospholipid molar ratio as high as 10:1, more than anywhere in the body. Lens lipids contribute to maintaining lens clarity, and alterations in lens lipid composition due to age are likely to contribute to cataract. Lens lipid composition reflects adaptations to the unique characteristics of the lens: no turnover of lens lipids or proteins; the lowest amount of oxygen than any other tissue and contains almost no intracellular organelles. The tear film lipid layer (TFLL) is also unique. The TFLL is a thin, 100 nm layer of lipid on the surface of tears covering the cornea that contributes to tear film stability. The major lipids of the TFLL are wax esters and cholesterol esters that are not found in the lens. The hydrocarbon chains associated with the esters are longer than those found anywhere in the body, as long as 32 carbons, and many are branched. Changes in the composition and structure of the 30,000 different moieties of TFLL contribute to the instability of tears. The focus of the current review is how spectroscopy has been used to elucidate the relationships between lipid composition, conformational order and function and the etiology of cataract and dry eye.

Adiponectin, an adipocyte-derived protein, has anti-atherogenic and anti-diabetic effects, but how it confers the anti-atherogenic effects is not well understood. To study the anti-atherogenic mechanisms of adiponectin, we examined whether it interacts with atherogenic low-density lipoprotein (LDL) to attenuate LDL’s atherogenicity. L5, the most electronegative subfraction of LDL, induces atherogenic responses similarly to copper-oxidized LDL (oxLDL). Unlike native LDL endocytosed via the LDL receptor, L5 and oxLDL are internalized by cells via the lectin-like oxidized LDL receptor-1 (LOX-1). Using enzyme-linked immunosorbent assays (ELISAs), we showed that adiponectin preferentially bound oxLDL but not native LDL. In Chinese hamster ovary (CHO) cells transfected with LOX-1 or LDL receptor, adiponectin selectively inhibited the uptake of oxLDL but not of native LDL, respectively. Furthermore, adiponectin suppressed the internalization of oxLDL in human coronary artery endothelial cells (HCAECs) and THP-1–derived macrophages. Western blot analysis of human plasma showed that adiponectin was abundant in L5 but not in L1, the least electronegative subfraction of LDL. Sandwich ELISAs with anti-adiponectin and anti–apolipoprotein B antibodies confirmed the binding of adiponectin to L5 and oxLDL. In LOX-1–expressing CHO cells, adiponectin inhibited cellular responses to oxLDL and L5, including nuclear factor-B activation and ERK phosphorylation. In HCAECs, adiponectin inhibited oxLDL-induced endothelin-1 secretion and ERK phosphorylation. Conversely, oxLDL suppressed the adiponectin-induced activation of adenosine monophosphate–activated protein kinase in COS-7 cells expressing adiponectin receptor AdipoR1. Our findings suggest that adiponectin binds and inactivates atherogenic LDL, providing novel insight into the anti-atherogenic mechanisms of adiponectin.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates cholesterol metabolism by inducing the degradation of hepatic low-density lipoprotein receptor (LDLR). Plasma PCSK9 has two main molecular forms: a 62-kDa mature form (PCSK9_62) and a 55-kDa, furin-cleaved form (PCSK9_55). PCSK9_55 is considered less active than PCSK9_62 in degrading LDLR. We aimed to identify the site of PCSK9_55 formation (intra- vs. extracellular) and to further characterize the LDLR-degradative function of PCSK9_55 relative to PCSK9_62. Co-expressing PCSK9_62 with furin in cell culture induced formation of PCSK9_55, most of which was found in the extracellular space. Under the same conditions we found that: i) adding a cell-permeable furin inhibitor preferentially decreased the formation of PCSK9_55 extracellularly; ii) using pulse-chase, we observed the formation of PCSK9_55 exclusively extracellularly in a time-dependent manner. A recombinant form of PCSK9_55 was efficiently produced but displayed impaired secretion that resulted in its intracellular trapping. However, the non-secreted PCSK9_55 was able to induce degradation of LDLR, though with 50% lower efficiency compared with PCSK9_62. Collectively, our data show that PCSK9_55 is generated in the extracellular space, and that intracellular PCSK9_55 is not secreted but retains the ability to degrade the LDLR through an intracellular pathway.

Apolipoproteins C-I, C-II and C-III interact with ApoE to regulate lipoprotein metabolism and contribute to Alzheimer’s disease pathophysiology. In plasma, apoC-I and C-II exist as truncated isoforms, while apoC-III exhibits multiple glycoforms. This study aimed to 1. delineate apoC-I, C-II and C-III isoform profiles in CSF and plasma in a cohort of non-demented older individuals (n = 61), and 2. examine the effect of APOE4 on these isoforms and their correlation with CSF Aβ42, a surrogate of brain amyloid accumulation. The isoforms of the apoCs were immunoaffinity enriched and measured with MALDI-TOF mass spectrometry, revealing a significantly higher percentage of truncated apoC-I and apoC-II in CSF compared to matched plasma, with positive correlation between CSF and plasma. A greater percentage of monosialylated and disialylated apoC-III isoforms was detected in CSF, accompanied by a lower percentage of the two non-sialylated apoC-III isoforms, with significant linear correlations between CSF and plasma. Furthermore, a greater percentage of truncated apoC-I in CSF, and apoC-II in plasma and CSF, was observed in individuals carrying at least one apoE E4 allele. Increased apoC-I and apoC-II truncations were  associated with lower CSF Aβ42. Finally, monosialylated apoC-III was lower, and disialylated apoC-III greater in the CSF of E4 carriers. Together, these results reveal distinct patterns of the apoCs isoforms in CSF, implying CSF-specific apoCs processing. These patterns were accentuated in APOE E4 allele carriers, suggesting an association between APOE4 genotype and Alzheimer’s disease pathology with apoCs processing and function in the brain.

Deficiency of glucocerebrosidase (GBA), a lysosomal β-glucosidase, causes Gaucher disease. The enzyme hydrolyzes β-glucosidic substrates and transglucosylates cholesterol to cholesterol-β-glucoside. Here we show that recombinant human GBA also cleaves β-xylosides and transxylosylates cholesterol. The xylosyl-cholesterol formed acts as acceptor for subsequent formation of di-xylosyl-cholesterol. Common mutant forms of GBA from patients with Gaucher disease with reduced β-glucosidase activity were similarly impaired in β-xylosidase, transglucosidase and transxylosidase activities, except for a slightly reduced xylosidase/glucosidase activity ratio of N370S GBA and a slightly reduced transglucosylation/glucosidase activity ratio of D409H GBA. XylChol was found to be reduced in spleen from Gaucher disease patients. The origin of newly identified XylChol in mouse and human tissues was investigated. Cultured human cells exposed to exogenous β-xylosides generated XylChol in a manner dependent on active lysosomal GBA but not the cytosol-facing β-glucosidase GBA2. We later sought an endogenous β-xyloside acting as donor in transxylosylation reactions, identifying xylosylated ceramide (XylCer) in cells and tissues that serve as donor in the formation of XylChol. UDP-glucosylceramide synthase (GCS) was unable to synthesize XylChol but could catalyse formation of XylCer. Thus, food-derived β-D-xyloside and XylCer are potential donors for the GBA-mediated formation of XylChol in cells. The enzyme GCS produces XylCer at a low rate. Our findings point to further catalytic versatility of GBA and prompt a systematic exploration of the distribution and role of xylosylated lipids.

Microtubules are polymers composed of αβ-tubulin subunits that provide structure to cells and play a crucial role in in the development and function of neuronal processes and cilia, microtubule-driven extensions of the plasma membrane that have sensory (primary cilia) or motor (motile cilia) functions. To stabilize microtubules in neuronal processes and cilia, α tubulin is modified by the posttranslational addition of an acetyl group, or acetylation. We discovered that acetylated tubulin in microtubules interacts with the membrane sphingolipid, ceramide. However, the molecular mechanism and function of this interaction are not understood. Here, we show that in human iPS cell-derived neurons, ceramide stabilizes microtubules, which indicates a similar function in cilia. Using proximity ligation assays, we detected complex formation of ceramide with acetylated tubulin in C. reinhardtii flagella and cilia of human embryonic kidney (HEK293T) cells, primary cultured mouse astrocytes, and ependymal cells. Using incorporation of palmitic azide and click chemistry-mediated addition of fluorophores, we show that a portion of acetylated tubulin is S-palmitoylated. S-palmitoylated acetylated tubulin is colocalized with ceramide-rich platforms (CRPs) in the ciliary membrane, and it is coimmunoprecipitated with Arl13b, a GTPase that mediates transport of proteins into cilia. Inhibition of S-palmitoylation with 2-bromo palmitic acid or inhibition of ceramide biosynthesis with fumonisin B1 reduces formation of the Arl13b-acetylated tubulin complex and its transport into cilia, concurrent with impairment of ciliogenesis. Together, these data show, for the first time, that CRPs mediate membrane anchoring and interaction of S-palmitoylated proteins that are critical for cilium formation, stabilization, and function. 

Bile acids, which are synthesized from cholesterol by the liver, are chemically transformed along the intestinal tract by the gut microbiota, and the products of these transformations signal through host receptors, affecting overall host health. These transformations include bile acid deconjugation, oxidation, and 7α-dehydroxylation. An understanding of the biogeography of bile acid transformations in the gut is critical because deconjugation is a prerequisite for 7α-dehydroxylation and because most gut microorganisms harbor bile acid transformation capacity. Here, we used a coupled metabolomic and metaproteomic approach to probe in vivo activity of the gut microbial community in a gnotobiotic mouse model. Results revealed the involvement of Clostridium scindens in 7α-dehydroxylation, of the genera Muribaculum and Bacteroides in deconjugation, and of six additional organisms in oxidation (the genera Clostridium, Muribaculum, Bacteroides, Bifidobacterium, Acutalibacter, and Akkermansia). Furthermore, the bile acid profile in mice with a more complex microbiota, a dysbiosed microbiota, or no microbiota was considered. For instance, conventional mice harbor a large diversity of bile acids, but treatment with an antibiotic such as clindamycin results in the complete inhibition of 7α-dehydroxylation, underscoring the strong inhibition of organisms that are capable of carrying out this process by this compound. Finally, a comparison of the hepatic bile acid pool size as a function of microbiota revealed that a reduced microbiota affects host signaling but not necessarily bile acid synthesis. In this study, bile acid transformations were mapped to the associated active microorganisms, offering a systematic characterization of the relationship between microbiota and bile acid composition.