Sole Regulator Research Articles

The Crystal Structure of the Michaelis-Menten Complex of C1 Esterase Inhibitor and C1s Reveals Novel Insights into Complement Regulation.

The ancient arm of innate immunity known as the complement system is a blood proteolytic cascade involving dozens of membrane-bound and solution-phase components. Although many of these components serve as regulatory molecules to facilitate controlled activation of the cascade, C1 esterase inhibitor (C1-INH) is the sole canonical complement regulator belonging to a superfamily of covalent inhibitors known as serine protease inhibitors (SERPINs). In addition to its namesake role in complement regulation, C1-INH also regulates proteases of the coagulation, fibrinolysis, and contact pathways. Despite this, the structural basis for C1-INH recognition of its target proteases has remained elusive. In this study, we present the crystal structure of the Michaelis-Menten (M-M) complex of the catalytic domain of complement component C1s and the SERPIN domain of C1-INH at a limiting resolution of 3.94 Å. Analysis of the structure revealed that nearly half of the protein/protein interface is formed by residues outside of the C1-INH reactive center loop. The contribution of these residues to the affinity of the M-M complex was validated by site-directed mutagenesis using surface plasmon resonance. Parallel analysis confirmed that C1-INH-interfacing residues on C1s surface loops distal from the active site also drive affinity of the M-M complex. Detailed structural comparisons revealed differences in substrate recognition by C1s compared with C1-INH recognition and highlight the importance of exosite interactions across broader SERPIN/protease systems. Collectively, this study improves our understanding of how C1-INH regulates the classical pathway of complement, and it sheds new light on how SERPINs recognize their cognate protease targets.

At the crossroads: strigolactones mediate changes in cytokinin synthesis and signalling in response to nitrogen limitation.

Strigolactones (SLs) are key regulators of shoot growth and responses to environmental stimuli. Numerous studies have indicated that nitrogen (N) limitation induces SL biosynthesis, suggesting that SLs may play a pivotal role in coordinating systemic responses to N availability, but this idea has not been clearly demonstrated. Here, we generated triple knockout mutants in the SL synthesis gene TaDWARF17 (TaD17) in bread wheat and investigated their phenotypic and transcriptional responses under N limitation, aiming to elucidate the role of SLs in the adaptation to N limitation. Tad17 mutants display typical SL mutant phenotypes, and fail to adapt their shoot growth appropriately to N. Despite exhibiting an increased tillering phenotype, Tad17 mutants continued to respond to N limitation by reducing tiller number, suggesting that SLs are not the sole regulators of tillering in response to N availability. RNA-seq analysis of basal nodes revealed that the loss of D17 significantly altered the transcriptional response of N-responsive genes, including changes in the expression profiles of key N response master regulators. Crucially, our findings suggest that SLs are required for the transcriptional downregulation of cytokinin (CK) synthesis and signalling in response to N limitation. Collectively, our results suggest that SLs are essential for the appropriate morphological and transcriptional adaptation to N limitation in wheat, and that the repressive effect of SLs on shoot growth is partly mediated by their repression of CK synthesis.

Microbial communities overwhelm environmental controls in explaining nitrous oxide emission in acidic soils

Intensively fertilized acidic soils are global hotspots of nitrous oxide (N2O) emissions, contributing to net agronomic greenhouse gas outcomes. Identifying the key drivers of soil N2O emissions is hampered by the synergistic or antagonistic effects of multiple factors. Within a framework based on the predominant role of microbial communities producing N2O, the N2O emissions are affected either by proximal regulators: temporary soil property fluctuations affect N2O production transcriptionally, or by distal regulators: persistent genetic rearrangements in local microbial communities. The proximal regulators, individually or together, may spontaneously impact distal regulators. Here, we use acidic soils from tea (Camellia sinensis L.) plantations on a broader geographic scale as a model system. Based on amplicon sequencing and properties of 195 acidic (average pH = 5.0) soils, we determined the importance of proximal and distal regulation to N2O emissions. Microbial phylogenetic diversity as a distal regulator overwhelms mineral N content as a proximal regulator in explaining high N2O emissions. Low-abundance, diverse prokaryotic communities (e.g., Acidothermu) and specialized denitrifying fungal communities (e.g., Fusarium) were associated with high N2O emissions. Revisiting the impact of proximal regulators on distal regulators revealed that soil pH is the sole proximal regulator influencing the prokaryotic rare taxa that correlated with high N2O emissions. When considering proximal regulators together (here soil properties compiled as soil fertility index), the microbial diversity were independent of soil fertility. The microbial assembly was dominated by stochastic processes. Consequently, proximal regulators have a limited impact on distal regulators of N2O emissions from acidic soils. In conclusion, the framework underscored the importance of in situ microbial communities as distal regulators in explaining high N2O emissions from acidic soils.

Exogenous Cytokinin Induces Callus and Protocorm-Like-Bodies Formation in In Vitro Root Tips of Vanilla planifolia Andrews.

Vanilla is a popular flavouring essence derived from the pods of vanilla orchid plants. Due to the high demand for vanilla flavour, high yielding vanilla plantlets are necessary for establishing vanilla plantations. Clonal micropropagation is a viable technique for the mass production of high yielding vanilla plantlets. This study reports an efficient regeneration protocol by using cytokinin as the sole plant growth regulator to regenerate plantlets from the root tips of a commercial vanilla orchid species, Vanilla planifolia. Most studies to date have reported using seeds and nodes as starting explants for in vitro micropropagation of vanilla orchids. So far, regeneration from roots has not been very successful. Previous studies favoured the use of auxins only or high auxin to cytokinin ratios to induce callus, and sole cytokinins were used for direct shoot regeneration. However, it was sporadically observed in plantlets regeneration of V. planifolia that multiple shoots were regenerated from the tips of intact aerial roots submerged in media. This study therefore investigated the regeneration of excised vanilla root tips through the application of most commonly used auxins (1-naphthaleneacetic acid and 2,4-dichlorophenoxyacetic acid) and cytokinins (6-benzylaminopurine and thidiazuron). High auxin presence is known to promote callusing in in vitro plants. However, in this study, auxin treatment inhibits callusing in root tips. While cytokinin treatments, even at low levels, has promoted high rate of callusing. These callus cells regenerate into protocorm-like-body (PLB) shoots when cytokinin levels are increased to 0.5 mg/mL 6-benzylaminopurine (BAP) under light conditions. The findings of the study have the potential of providing large quantity of high yielding vanilla plantlets through clonal micropropagation.

Recent finding on sucrose synthase research: not the only key for starch and cellulose synthesis.

Sucrose synthase (SUS), an enzyme that breaks down sucrose, is known to play an important role in the production of UDP-glucose and ADP-glucose. An established and highly debated theory holds that SUS is necessary for providing UDP-glucose and ADP-glucose for the biosynthesis of cellulose and starch, respectively. This article is focused on two recent reports which refuted the long-held theory that SUS is the sole regulator in cellulose and starch synthesis.

Climate Change and Corporate Regulation in Angola: Reforming the Regulatory Framework for Climate Change Mitigation

Angola, like many African countries, continuously suffers the deleterious impacts of climate change despite its minimal global carbon contributions. Despite this, it has not taken active steps to institute a climate change regulatory framework or established any strong regulatory regime to aid the regulation of corporate activities and participation in mitigation projects in the country. This article examines the regulatory landscape of climate change and corporations in Angola and assesses the country’s ability to tackle the challenges posed by climate change. It examines the country's position in the international climate change arena and scrutinizes the contribution of corporations to Angola's carbon emissions. The absence of legislation on climate change in Angola creates a void which allows corporations in the country to avoid any responsibility for mitigation projects and activities. This article, therefore, analyses the strengths and weaknesses of the alternative regulatory frameworks such as judicial, market, and surrogate regulation that can operate to fill this void and the extent to which they curtail corporate excesses in climate change and incentivise participation in mitigation activities. In scrutinising the deficiencies of Angola’s climate change regulatory framework, the article adopts the dilute interventionism model which employs both prescriptive and facilitative measures to regulate corporations and mitigate the impact of climate change. It highlights the structure of the legislative framework, regulator, and technical expertise necessary for the successful implementation of the said model. Additionally, the article argues in favour of adopting a veto firewall protection to maintain the independence of the proposed sole independent regulator to be responsible for regulating the climate change activities of corporations in Angola.

Climate Change Regulations of Corporations in Tanzania: A Case for Dilute Interventionism and Veto Firewall Paradigm

Corporations operating in developing countries generally adopt an obstructionist approach to climate change and environmental regulation, particularly in states with weaker economic bargaining strength. Tanzania is one of the African states suffering the disproportionate impacts of climate change but with a weak regulatory capacity to restrain adverse corporate climate change impacting activities. This article critically analyses the climate change regulatory framework of corporations in Tanzania and proposes the implementation of the Dilute Interventionism Model as an innovative solution for regulating corporate activities in climate change mitigation in the country. The model combines prescriptive and facilitative measures in regulating corporations to mitigate the effects of climate change. The article also identifies the need for Veto Firewall protection to safeguard the independence of the sole independent regulator established to regulate the climate change activities of corporations in Tanzania. This article adopts the Dilute Interventionism Pyramid which depicts the steps required to implement the Dilute Interventionism Model in Tanzania. The challenges to the implementation of the Dilute Interventionism and Veto Firewall Paradigm in Tanzania are also discussed, including resistance from corporations, inadequate funding, and lack of technical capacity and the potential solutions to these challenges are briefly highlighted.

Climate Change and Corporate Regulation: A Critical Analysis of Egypt’s Legal and Regulatory Regime

Corporations operating in African states generally have apathy to climate change/environmental regulation, owing to their weak economic bargaining strength in these states. Egypt is one of the African states suffering the disproportionate impacts of climate change and although it has drawn up several climate policy documents, it has not yet enacted a Climate Change Act and has a weak regulatory capacity to restrain adverse corporate climate change-impacting activities. This article critically analyses the legal/ regulatory regime in Egypt for regulating corporate participation in climate change mitigation and its effectiveness in addressing climate change challenges. It critically analyses the implementation of the Dilute Interventionism Model. It evaluates the required legislative framework, regulator, and technical expertise necessary for its successful implementation. This paper also highlights the importance of the Veto Firewall protection to maintain the independence of the sole independent regulator responsible for regulating the climate change activities of corporations. This paper argues that the Dilute Interventionism Model, in conjunction with the veto firewall paradigm, provides a practical and effective approach to regulating corporations. However, successful implementation will require political will, corporate compliance, and technical capacity. This paper provides policymakers, stakeholders, and interested parties in Egypt and elsewhere with useful insights for addressing climate change challenges.

The evolution of financial reporting quality for companies listed on the Tadawul Stock Exchange in Saudi Arabia: New emerging markets' evidence

Motivated by the Saudi Arabian government's objective to diversify its economy away from oil and correct deficiencies associated with the Saudi stock market crash of 2006, a series of significant capital market infrastructure reforms were initiated that began with the 2007 reorganization of the Tadawul Stock Exchange (TSE) and the Capital Market Authority (CMA) as its sole regulator. This paper adds to the growing body of emerging market literature by providing new evidence of the effects of these initiatives on earnings quality for firms listed on the TSE. The results of tests of this study provide robust evidence that earnings quality increased during the 2007 to 2018 reform period. In particular, we document that relative to pre – reform years, reform period R squares, earnings response coefficients (ERCs) increased and discretionary accruals decreased. We rationalize these findings by asserting that improved regulatory oversight in juxtaposition with significant reform period investments into Saudi Arabia's capital markets infrastructure enhanced earnings quality (Jiambalvo et al., 2002; Latif et al., 2017; Zhong et al., 2017).

Deep longitudinal multi-omics analysis of Bordetella pertussis cultivated in bioreactors highlights medium starvations and transitory metabolisms, associated to vaccine antigen biosynthesis variations and global virulence regulation.

Bordetella pertussis is the bacterial causative agent of whooping cough, a serious respiratory illness. An extensive knowledge on its virulence regulation and metabolism is a key factor to ensure pertussis vaccine manufacturing process robustness. The aim of this study was to refine our comprehension of B. pertussis physiology during in vitro cultures in bioreactors. A longitudinal multi-omics analysis was carried out over 26 h small-scale cultures of B. pertussis. Cultures were performed in batch mode and under culture conditions intending to mimic industrial processes. Putative cysteine and proline starvations were, respectively, observed at the beginning of the exponential phase (from 4 to 8 h) and during the exponential phase (18 h 45 min). As revealed by multi-omics analyses, the proline starvation induced major molecular changes, including a transient metabolism with internal stock consumption. In the meantime, growth and specific total PT, PRN, and Fim2 antigen productions were negatively affected. Interestingly, the master virulence-regulating two-component system of B. pertussis (BvgASR) was not evidenced as the sole virulence regulator in this in vitro growth condition. Indeed, novel intermediate regulators were identified as putatively involved in the expression of some virulence-activated genes (vags). Such longitudinal multi-omics analysis applied to B. pertussis culture process emerges as a powerful tool for characterization and incremental optimization of vaccine antigen production.

Covid-19 Pandemic and Medicines Regulation in Ghana: Overview and Perspectives of Regulators

Background: The novel coronavirus SARS-CoV-2 pandemic, impacted health systems around the world resulting in a surge in demand for medicines and therapeutic interventions to combat the pandemic. Medicine regulatory agencies played a crucial role in ensuring the safety, quality, and efficacy of medicines. Regulatory agencies streamlined regulatory processes and made them flexible to tackle the urgent need for COVID-19 interventions. The COVID-19 pandemic prompted regulatory agencies on the importance of global regulatory collaboration and harmonization. Following the pandemic, regulatory agencies continually aim to ensure global alignment in regulatory standards, facilitate data sharing, and streamline regulatory processes to optimize their activities and preparedness for future emergencies. Objective: The objective of this study was to have an overview of medicines regulation following the emergence of the COVID-19 pandemic and regulator’s perspective on the associated regulatory adaptations. Method: The study was conducted through qualitative open-ended interviews. It was carried out within the head office of the Ghana Food and Drugs Authority; the sole regulator of medicines in the country. Interviews were audio-recorded with the consent of participants and transcribed for analysis. After transcription data was categorized into themes and analyzed using a generic thematic analysis method. Results: Ghana's medicines regulatory system, governed by the Food and Drugs Authority (FDA) developed a system which encompassed pre-market approval, post-market surveillance, pharmacovigilance activities, and approval of clinical trials, aimed at safeguarding public health. To address the urgent need for COVID-19 treatments and vaccines, regulators worldwide, including Ghana, implemented emergency use authorization (EUA) processes, demonstrated regulatory flexibility by adopting alternative assessment approaches and streamlining processes without compromising safety and quality standards. The Food and Drugs Authority along with other stakeholders and opinion leaders played a crucial role in disseminating accurate information and debunking myths and misconceptions about the pandemic to empower citizens with accurate information, dispel misinformation, and promote adherence to preventive measures. Conclusion: The importance of resourcefulness and the adoption of sustainable practices, working smarter, saving resources, embracing virtual trainings, and introducing dynamic assessment practices have been highlighted to have reshaped activities of the Authority. These lessons can serve as valuable guides in building a more efficient, collaborative, and environmentally conscious future as we continue to navigate the post pandemic world.

Običajno i pozitivno pravo u Srbiji

In order to fully and properly understand the essence of customary law, a joint explanatory endeavor of legal, ethnological, and sociological science is needed. During the last two centuries, the relationship between customary and positive law passed through two phases. The first phase was marked by the incredible strength and resistance of the customary law, which was deeply rooted in the patriarchal Serbian society. Its strength was such, that it managed to overpower the modern Austrian law during the creation of the Serbian Civil law code, despite the efforts and desires of the law code creator, Jovan Hadžić, to suppress it. Customary law became the sole regulator of marriage, family, and inheritance law, thus becoming a part of the positive law. The second phase took place after the Second World War. By promoting a new system of acceptable social and moral values, the new, revolutionary, socialistic law fiercely fought the customary law and rural traditions, labeling them as obsolete relicts of a class-divided society. However, customs showed their remarkable resilience, and found a way to survive this strife - quite ironically - by using the existing laws and legal loopholes, masking themselves sometimes like a chameleon. Maybe the best illustration of this conflict between positive and customary law can be found in the inheritance law, as it is a complex branch of law, which was shaped not only by laws, but also by the centuries-old traditions of our people. To be able to fully understand the customary inheritance law, one must first analyse the institutes of family, marriage, and kinship. Although many customs have already disappeared in the XXI century by overcoming the patriarchal notions in the modern society, some customs remained, but also some new have, due to various reasons, managed to emerge, making the topic of this paper quite contemporary

Hemp Growth in Vitro and in Vivo: A Comparison of Growing Media and Growing Environments across 10 Accessions

Micropropagation is a valuable production tool for the cultivation of hemp (Cannabis sativa), and development of optimal protocols is ongoing. The goal of this study was to evaluate a novel growing medium combination, consisting of Driver and Kuniyuki Walnut (DKW) medium as the nutrient source and glucose as the carbon source, and to investigate the link between in vitro and in vivo (i.e., greenhouse) plant performance. Among 10 accessions intended to represent a range of heterozygosity levels and various essential oil chemotypes, the DKW–glucose growing medium generally produced the most vigorous plantlets by all parameters evaluated in vitro (height, biomass, canopy area, vegetative growth rate, and regeneration rate). Across four growing media treatments, all of which included meta-topolin as the sole plant growth regulator, poor to no rooting was observed in vitro. Hybrids were more vigorous than nonhybrid selections in vitro, but not in vivo. No correlation was observed between in vitro and in vivo vigor, indicating that, with these media, plant performance in vitro is not predictive of that in vivo.

О РЕАКТИВНОСТИ ДЕТСКОГО ОРГАНИЗМА

The reactivity of the child’s body is highlighted in this article from the new positions considering the author’s article published in the Journal “PEDIATRIA. Journal named after G.N. Speransky” back in 1971. At the current level of knowledge, instead of the sole neuroendocrine regulation we shall talk about the integrative immune and neuroendocrine self-organization from the standpoint of genetics, immunology, personalized medical care, as well as the Orthodox ethics.

Physiological control of fetal heart rate variability during labour: implications and controversies.

The interpretation of fetal heart rate (FHR) patterns is the only available method to continuously monitor fetal well-being during labour. One of the most important yet contentious aspects of the FHR pattern is changes in FHR variability (FHRV). Some clinical studies suggest that loss of FHRV during labour is a sign of fetal compromise so this is reflected in practice guidelines. Surprisingly, there is little systematic evidence to support this observation. In this review we methodically dissect the potential pathways controlling FHRV during labour-like hypoxaemia. Before labour, FHRV is controlled by the combined activity of the parasympathetic and sympathetic nervous systems, in part regulated by a complex interplay between fetal sleep state and behaviour. By contrast, preclinical studies using multiple autonomic blockades have now shown that sympathetic neural control of FHRV was potently suppressed between periods of labour-like hypoxaemia, and thus, that the parasympathetic system is the sole neural regulator of FHRV once FHR decelerations are present during labour. We further discuss the pattern of changes in FHRV during progressive fetal compromise and highlight potential biochemical, behavioural and clinical factors that may regulate parasympathetic-mediated FHRV during labour. Further studies are needed to investigate the regulators of parasympathetic activity to better understand the dynamic changes in FHRV and their true utility during labour.

Shift in G1-Checkpoint from ATM-Alone to a Cooperative ATM Plus ATR Regulation with Increasing Dose of Radiation.

The current view of the involvement of PI3-kinases in checkpoint responses after DNA damage is that ATM is the key regulator of G1-, S- or G2-phase checkpoints, that ATR is only partly involved in the regulation of S- and G2-phase checkpoints and that DNA-PKcs is not involved in checkpoint regulation. However, further analysis of the contributions of these kinases to checkpoint responses in cells exposed to ionizing radiation (IR) recently uncovered striking integrations and interplays among ATM, ATR and DNA-PKcs that adapt not only to the phase of the cell cycle in which cells are irradiated, but also to the load of DNA double-strand breaks (DSBs), presumably to optimize their processing. Specifically, we found that low IR doses in G2-phase cells activate a G2-checkpoint that is regulated by epistatically coupled ATM and ATR. Thus, inhibition of either kinase suppresses almost fully its activation. At high IR doses, the epistatic ATM/ATR coupling relaxes, yielding to a cooperative regulation. Thus, single-kinase inhibition suppresses partly, and only combined inhibition suppresses fully G2-checkpoint activation. Interestingly, DNA-PKcs integrates with ATM/ATR in G2-checkpoint control, but functions in its recovery in a dose-independent manner. Strikingly, irradiation during S-phase activates, independently of dose, an exclusively ATR-dependent G2 checkpoint. Here, ATM couples with DNA-PKcs to regulate checkpoint recovery. In the present work, we extend these studies and investigate organization and functions of these PI3-kinases in the activation of the G1 checkpoint in cells irradiated either in the G0 or G1 phase. We report that ATM is the sole regulator of the G1 checkpoint after exposure to low IR doses. At high IR doses, ATM remains dominant, but contributions from ATR also become detectable and are associated with limited ATM/ATR-dependent end resection at DSBs. Under these conditions, only combined ATM + ATR inhibition fully abrogates checkpoint and resection. Contributions of DNA-PKcs and CHK2 to the regulation of the G1 checkpoint are not obvious in these experiments and may be masked by the endpoint employed for checkpoint analysis and perturbations in normal progression through the cell cycle of cells exposed to DNA-PKcs inhibitors. The results broaden our understanding of organization throughout the cell cycle and adaptation with increasing IR dose of the ATM/ATR/DNA-PKcs module to regulate checkpoint responses. They emphasize notable similarities and distinct differences between G1-, G2- and S-phase checkpoint regulation that may guide DSB processing decisions.

Regulations matter: their effects on actors of the nonindustrial timber value chain in the Southern Highlands of Tanzania

In recent years, non-industrial private forestry (NIPF) for timber production has gained economic importance in the Southern Highlands of Tanzania. Access to benefits accrued from NIPF represents an opportunity for poverty alleviation. Access and distribution of the benefits are affected by governance, which is an important aspect in this regard. This paper focuses on state regulations, which in the context of Africa and Tanzania in particular, have received scant attention in the value chain studies. The paper seeks to respond to three main questions: i) How is the timber value chain regulated? (ii) What strategies do the value chain actors use to gain access to benefits? And iii) how do regulations affect the incomes of the chain actors? Data for the study were collected from Njombe District through documentary analysis, focus group discussions, observations and in-depth interviews with key informants. The study findings show that while the government is the sole regulator of the chain, regulations are implemented differently at the sub-national level. Industrial and non-industrial private forestry are placed under the same regulatory framework despite their many differences. This has partly resulted in high transaction costs, which are unaffordable by the majority of actors in the NIPF value chain. Despite strict regulations and many taxes paid, the actors adopt different strategies such as using locally available materials and capitalizing on social networks in maximizing their incomes from the timber business. The regulations affect incomes of all actors, however, tree growers are the most-affected category. This is because tree growers possess limited capital to engage in high value chain activities and strict regulations aggravate the situation. The paper concludes that the contribution of non-industrial private forestry to poverty alleviation is stifled by cumbersome district and state regulations that limit actors' access to profitable markets.

Minimum Propulsion Power Assessment of a VLCC to Maintain the Maneuverability in Adverse Conditions

The International Maritime Organization (IMO) Guidelines for Determining Minimum Propulsion Power to Maintain the Maneuverability in Adverse Conditions is the sole regulation imposed on the routine design and approval of all new-built ships as a part of EEDI requirements. This study reviews the development of the guidelines and summarizes the recent amendments of MEPC76(2021). The present assessment is conducted for a new VLCC design following the new guidelines aiming at investigating the influence of alternative wave added resistance evaluation methods and the propeller design features on the assessment results. It is found that the most simple empirical formula method proposed by MEPC76 is not conservative enough, as could have been expected. On the other hand, spectral analysis methods based on empirically obtained and properly validated wave added resistance responses can produce consistent results. Moreover, discussions are made from the perspective of propeller design to meet the regulatory requirements. It is pointed out that the light running margin is a key design parameter, and propellers with larger light running margins are more advantageous for satisfying the minimum propulsion power regulation, thus ensuring the navigation safety in adverse conditions. These obtained insights and know-how can support the engineers in obtaining optimal design solutions.

The Mammalian Membrane Microenvironment Regulates the Sequential Attachment of Bacteria to Host Cells.

ABSTRACTPathogen attachment to host tissue is critical in the progress of many infections. Bacteria use adhesion in vivo to stabilize colonization and subsequently regulate the deployment of contact-dependent virulence traits. To specifically target host cells, they decorate themselves with adhesins, proteins that bind to mammalian cell surface receptors. One common assumption is that adhesin-receptor interactions entirely govern bacterial attachment. However, how adhesins engage with their receptors in an in vivo-like context remains unclear, in particular under the influence of a heterogeneous mechanical microenvironment. We here investigate the biophysical processes governing bacterial adhesion to host cells using a tunable adhesin-receptor system. By dynamically visualizing attachment, we found that bacterial adhesion to host cell surface, unlike adhesion to inert surfaces, involves two consecutive steps. Bacteria initially attach to their host without engaging adhesins. This step lasts about 1 min, during which bacteria can easily detach. We found that at this stage, the glycocalyx, a layer of glycosylated proteins and lipids, shields the host cell by keeping adhesins away from their receptor ligand. In a second step, adhesins engage with their target receptors to strengthen attachment for minutes to hours. The active properties of the membrane, endowed by the actin cytoskeleton, strengthen specific adhesion. Altogether, our results demonstrate that adhesin-ligand binding is not the sole regulator of bacterial adhesion. In fact, the host cell’s surface mechanical microenvironment mediates the physical interactions between host and bacteria, thereby playing an essential role in the onset of infection.

Physiologically relevant oxygen tensions differentially regulate hepatotoxic responses in HepG2 cells

This study evaluates the impact of physiologically relevant oxygen tensions on the response of HepG2 cells to known inducers and hepatotoxic drugs. We compared transcriptional regulation and CYP1A activity after a 48 h exposure at atmospheric culture conditions (20% O2) with representative periportal (8% O2) and perivenous (3% O2) oxygen tensions. We evaluated cellular responses in 2D and 3D cultures at each oxygen tension in parallel, using monolayers and a paper-based culture platform that supports cells suspended in a collagen-rich environment. Our findings highlight that the toxicity, potency, and mechanism of action of drugs are dependent on both culture format and oxygen tension. HepG2 cells in 3D environments at physiologic oxygen tensions better matched primary human hepatocyte data than HepG2 cells cultured under standard conditions. Despite altered transcriptional regulation with decreasing oxygen tensions, we did not observe the zonation patterns of drug-metabolizing enzymes found in vivo. Our approach demonstrates that oxygen is an important regulator of liver function but it is not the sole regulator. It also highlights the utility of the 3D paper-based culture platform for continued mechanistic studies of microenvironmental influences on cellular responses.