Plasma Membrane Lipids: An Important Binding Site for All Lipoprotein Classes

Cholesterol is one of the main constituents of plasma membranes; thus, its supply is of utmost importance. This review covers the known mechanisms of cholesterol transfer from circulating lipoprotein particles to the plasma membrane, and vice versa. To achieve homeostasis, the human body utilizes cellular de novo synthesis and extracellular transport particles for supply of cholesterol and other lipids via the blood stream. These lipoprotein particles can be classified according to their density: chylomicrons, very low, low, and high-density lipoprotein (VLDL, LDL, and HDL, respectively). They deliver and receive their lipid loads, most importantly cholesterol, to and from cells by several redundant routes. Defects in one of these pathways (e.g., due to mutations in receptors) usually are not immediately fatal. Several redundant pathways, at least temporarily, compensate for the loss of one or more of them, but the defects trigger systemic diseases, such as atherosclerosis later on. Recently, intracellular membrane–membrane contact sites were shown to be involved in intracellular cholesterol transfer and the plasma membrane itself has been proposed to act as a binding site for lipoprotein-mediated cargo unloading.

A brief dive into the phenomenon of cisplatin resistance in non-small-cell lung cancer

Lung cancer is one of the most lethal types of cancer due to a lack of proper treatment. The rare presence of molecular therapy targets forces the use of platinum-based drugs. Cisplatin, approved by the USA as an anticancer therapy in the 1970s, is still one of the most prominent therapies against lung cancer. Unfortunately, the biggest limitation of cisplatin-based therapy is the development of cisplatin resistance. Cancer cells overcome the vast DNA damage caused by the drug in a variety of ways such as detoxication and extracellular transport of the drug, enhanced repair mechanisms, omitting apoptosis and epigenetic alterations. Chemotherapy resistance is an issue that so far cannot be dealt with. Nevertheless, better understanding of the molecular pathways behind cisplatin resistance brings hope for better therapy outcomes in lung cancer patients.

A human apolipoprotein L with detergent-like activity kills intracellular pathogens

Activation of cell-autonomous defense by the immune cytokine interferon-γ (IFN-γ) is critical to the control of life-threatening infections in humans. IFN-γ induces the expression of hundreds of host proteins in all nucleated cells and tissues, yet many of these proteins remain uncharacterized. We screened 19,050 human genes by CRISPR-Cas9 mutagenesis and identified IFN-γ–induced apolipoprotein L3 (APOL3) as a potent bactericidal agent protecting multiple non–immune barrier cell types against infection. Canonical apolipoproteins typically solubilize mammalian lipids for extracellular transport; APOL3 instead targeted cytosol-invasive bacteria to dissolve their anionic membranes into human-bacterial lipoprotein nanodiscs detected by native mass spectrometry and visualized by single-particle cryo–electron microscopy. Thus, humans have harnessed the detergent-like properties of extracellular apolipoproteins to fashion an intracellular lysin, thereby endowing resident nonimmune cells with a mechanism to achieve sterilizing immunity.

Selenoprotein P Regulates Synaptic Zinc and Reduces Tau Phosphorylation

Selenoprotein P (SELENOP1) is a selenium-rich antioxidant protein involved in extracellular transport of selenium (Se). SELENOP1 also has metal binding properties. The trace element Zinc (Zn2+) is a neuromodulator that can be released from synaptic terminals in the brain, primarily from a subset of glutamatergic terminals. Both Zn2+ and Se are necessary for normal brain function. Although these ions can bind together with high affinity, the biological significance of an interaction of SELENOP1 with Zn2+ has not been investigated. We examined changes in brain Zn2+ in SELENOP1 knockout (KO) animals. Timm-Danscher and N-(6-methoxy-8-quinolyl)-p-toluenesulphonamide (TSQ) staining revealed increased levels of intracellular Zn2+ in the SELENOP1−/− hippocampus compared to wildtype (WT) mice. Mass spectrometry analysis of frozen whole brain samples demonstrated that total Zn2+ was not increased in the SELENOP1−/− mice, suggesting only local changes in Zn2+ distribution. Unexpectedly, live Zn2+ imaging of hippocampal slices with a selective extracellular fluorescent Zn2+ indicator (FluoZin-3) showed that SELENOP1−/− mice have impaired Zn2+ release in response to KCl-induced neuron depolarization. The zinc/metal storage protein metallothionein 3 (MT-3) was increased in SELENOP1−/− hippocampus relative to wildtype, possibly in response to an elevated Zn2+ content. We found that depriving cultured cells of selenium resulted in increased intracellular Zn2+, as did inhibition of selenoprotein GPX4 but not GPX1, suggesting the increased Zn2+ in SELENOP1−/− mice is due to a downregulation of antioxidant selenoproteins and subsequent release of Zn2+ from intracellular stores. Surprisingly, we found increased tau phosphorylation in the hippocampus of SELENOP1−/− mice, possibly resulting from intracellular zinc changes. Our findings reveal important roles for SELENOP1 in the maintenance of synaptic Zn2+ physiology and preventing tau hyperphosphorylation.

Dual transcriptomics to determine interferon-gamma independent host response to intestinal Cryptosporidium parvum infection

Background: Protective immune responses to Cryptosporidium parvum, a zoonotic, gastrointestinal parasite, are primarily dependent on the presence of interferon-gamma (IFNγ). We discovered that treatment with soluble T. gondii antigen (STAg) reduces Cryptosporidium parvum shedding in the absence of IFNγ. To identify the protective IFNγ independent responses elicited by STAg, we conducted a transcriptomic analysis of intestinal sections of IFNγ-deleted, C. parvum infected or uninfected mice treated with STAg or PBS. Results: STAg treatment reduced oocyst shedding in C. parvum infected IFNγ deleted mice. Gene ontology analysis of the intestinal transcriptomes suggested that both C. parvum infection and STAg treatment changes the transcript abundance of genes involved in the host cell membrane, intracellular and extracellular transport, and immune responses. We found in high abundance 37 genes related to IFN type I response in infected mice treated with STAg. Among these genes, members of the oligoadenylate synthetase and Schlafen family were identified. Conclusions: STAg treatment of C. parvum infected mice induced both host immune and metabolism changes associated with a reduction in shedding. Several components of the type I interferon immune response were more abundant in the ileum of C. parvum infected in IFNγ-deleted mice. Future studies will explore the role of type I IFN mediated immune responses in controlling C. parvum infections. STAg treatment appears to only affects the host transcriptome while the parasite transcriptome remains unaffected. Several C. parvum genes, including mucin genes, are more abundant during infection of animals, which opens new avenues in C. parvum research.

Diet-Derived Exogenous miRNAs As Functional Food Components: Facts and New Perspectives

Exogenous miRNAs derived from dietary substances have been shown to be orally transferred to the mammalian system and proven to remain active to regulate host-gene expression. This way they have become an active area of research as functional food components and aspects for dietary supplementation. They are being studied as a new class of metabolically targeted therapeutics that work through diet manipulation and may hold promise for a therapeutic approach in reducing the risk of life-threatening diseases. However, a substantial amount of evidence also defies this dietary miRNA concept in terms of their absorption, bioavailability, cellular uptake and its physiological effects in the mammalian system. But recent advances in the identification of some unique sequence and structural characteristics of dietary miRNAs and a deeper understanding of their stability in host peripheral blood for its cellular uptake have strengthened the whole concept. The review comprehensively summarizes the mechanism for miRNA extracellular transport, absorption through the gastrointestinal tract (GI), stability in peripheral blood, and cellular uptake in mammalian cells. It recapitulates the shreds of evidence, related to the influence of dietary miRNAs on gene expression based on the source of the origin (plant vs animal), and compares their cross-kingdom behaviour in terms of their unique sequence and stem-loop structure properties that help them to get stabilized in the mammalian system. The review also summarizes the parameters required for maintaining the sustainable uptake and bioavailability of the dietary miRNAs with existing examples of successful in-vivo and in-vitro delivery of dietary miRNA for augmented therapy. Lastly, it provides an overview of the available and required databases, webserver, and tools that can be used for the successful identification of potential dietary miRNA candidates.

Soil bacterial populations are shaped by recombination and gene-specific selection across a meadow

Soil microbial diversity is often studied from the perspective of community composition, but less is known about genetic heterogeneity within species and how population structures are affected by dispersal, recombination, and selection. Genomic inferences about population structure can be made using the millions of sequencing reads that are assembled de novo into consensus genomes from metagenomes, as each read pair describes a short genomic sequence from a cell in the population. Here we track genome-wide population genetic variation for 19 highly abundant bacterial species sampled from across a grassland meadow. Genomic nucleotide identity of assembled genomes was significantly associated with local geography for half of the populations studied, and for a majority of populations within-sample nucleotide diversity could often be as high as meadow-wide nucleotide diversity. Genes involved in specialized metabolite biosynthesis and extracellular transport were characterized by elevated genetic diversity in multiple species. Microbial populations displayed varying degrees of homologous recombination and recombinant variants were often detected at 7-36% of loci genome-wide. Within multiple populations we identified genes with unusually high site-specific differentiation of alleles, fewer recombinant events, and lower nucleotide diversity, suggesting recent selective sweeps for gene variants. Taken together, these results indicate that recombination and gene-specific selection commonly shape local soil bacterial genetic variation.

Geobacter protein nanowires

The study of electrically conductive protein nanowires in Geobacter sulfurreducens has led to new concepts for long-range electron extracellular transport, as well as the development of sustainable conductive materials and electronic devices with novel functions. Until recently, electrically conductive pili (e-pili), assembled from the PilA pilin monomer, were the only known Geobacter protein nanowires. However, filaments comprised of the multi-heme c-type cytochrome, OmcS, are present in some preparations of G. sulfurreducens outer-surface proteins. The purpose of this review is to evaluate the available evidence on the in vivo expression of e-pili and OmcS filaments and their biological function. Abundant literature demonstrates that G. sulfurreducens expresses e-pili, which are required for long-range electron transport to Fe(III) oxides and through conductive biofilms. In contrast, there is no definitive evidence yet that wild-type G. sulfurreducens express long filaments of OmcS extending from the cells, and deleting the gene for OmcS actually increases biofilm conductivity. The literature does not support the concern that many previous studies on e-pili were mistakenly studying OmcS filaments. For example, heterologous expression of the aromatic-rich pilin monomer of G. metallireducens in G. sulfurreducens increases the conductivity of individual nanowires more than 5000-fold, whereas expression of an aromatic-poor pilin reduced conductivity more than 1000-fold. This more than million-fold range in nanowire conductivity was achieved while maintaining the 3 nm diameter consistent with e-pili, not OmcS. Purification methods that eliminate all traces of OmcS yield highly conductive e-pili. Substantial evidence suggests that OmcS is often associated with the outer cell surface and intermittently localized along e-pili in vivo. Future studies of G. sulfurreducens expression of protein nanowires need to be cognizant of the importance of maintaining environmentally relevant growth conditions because artificial laboratory culture conditions can rapidly select against e-pili expression. Principles derived from the study of e-pili have enabled identification of non-cytochrome protein nanowires in diverse bacteria and archaea. A similar search for cytochrome appendages is warranted. Both e-pili and OmcS filaments offer design options for the synthesis of protein-based ‘green’ electronics, which may be the primary driving force for the study of these structures in the near future.