Trem2 promotes foamy macrophage lipid uptake and survival in atherosclerosis

Atherosclerosis is driven by the expansion of cholesterol-loaded 'foamy' macrophages in the arterial intima. Factors regulating foamy macrophage differentiation and survival in plaque remain poorly understood. Here we show, using trajectory analysis of integrated single-cell RNA sequencing data and a genome-wide CRISPR screen, that triggering receptor expressed on myeloid cells 2 (Trem2) is associated with foamy macrophage specification. Loss of Trem2 led to a reduced ability of foamy macrophages to take up oxidized low-density lipoprotein (oxLDL). Myeloid-specific deletion of Trem2 showed an attenuation of plaque progression, even when targeted in established atherosclerotic lesions, and was independent of changes in circulating cytokines, monocyte recruitment or cholesterol levels. Mechanistically, we link Trem2-deficient macrophages with a failure to upregulate cholesterol efflux molecules, resulting in impaired proliferation and survival. Overall, we identify Trem2 as a regulator of foamy macrophage differentiation and atherosclerotic plaque growth and as a putative therapeutic target for atherosclerosis.

Profiling the myeloid compartment of PBMC in active tuberculosis reveals substantial changes in CD14+ cells and upregulation of CD16 in pro-inflammatory dendritic cells

Tuberculosis (TB) is the second leading infectious killer after COVID-19 worldwide. Gene expression analysis of whole blood and peripheral blood mononuclear cells (PBMC) from TB infected versus uninfected donors suggests that myeloid cells contribute to the immune signature of TB infection. In this study, we carried out the largest cellular and molecular profiling of the circulating myeloid compartment in the context of Mycobacterium tuberculosis (Mtb) infection to date. Using flow cytometry and RNA sequencing, we isolated and interrogated the transcriptomic profile of myeloid cell subsets isolated from PBMC in a cohort of active TB (ATB) patients with paired sampling at diagnosis and mid-treatment, as well as from Mtb sensitized (IGRA+) and unsensitized (IGRA−) healthy individuals. We identified an increased frequency of CD14+CD16− and CD14+CD16+ myeloid cells in ATB at diagnosis with upregulated expression of interferon signaling genes that significantly overlapped with previously reported blood TB signatures. In CD14+CD16+ cells, there was an additional increased expression of MHC-II related genes, which could be traced down to a subset of pro-inflammatory dendritic cells (DCs), namely CD14+CD163+ DC3. This cell population significantly upregulated CD16 in ATB at diagnosis, thus displaying a CD14+CD16+ phenotype, similarly to intermediate monocytes. This result also suggests CD16 might play an important role in inflammatory DC function in ATB. Thus, our study demonstrates quantitative and qualitative changes in CD14+ myeloid cells that are contributing to blood TB signatures. Additionally, it reveals phenotypic overlaps between subsets of monocytes and DCs in human blood that may hold disease relevance.

Supported by a grant from NIH (U19 AI118626)

Single-cell profiling reveals distinct subsets of CD14+ monocytes drive blood immune signatures of active tuberculosis

Introduction

Previous studies suggest that monocytes are an important contributor to tuberculosis (TB)-specific immune signatures in blood.

Methods

Here, we carried out comprehensive single-cell profiling of monocytes in paired blood samples of active TB (ATB) patients at diagnosis and mid-treatment, and healthy controls.

Results

At diagnosis, ATB patients displayed increased monocyte-to-lymphocyte ratio, increased frequency of CD14+CD16- and intermediate CD14+CD16+ monocytes, and upregulation of interferon signaling genes that significantly overlapped with previously reported blood TB signatures in both CD14+ subsets. In this cohort, we identified additional transcriptomic and functional changes in intermediate CD14+CD16+ monocytes, such as the upregulation of inflammatory and MHC-II genes, and increased capacity to activate T cells, reflecting overall increased activation in this population. Single-cell transcriptomics revealed that distinct subsets of intermediate CD14+CD16+ monocytes were responsible for each gene signature, indicating significant functional heterogeneity within this population. Finally, we observed that changes in CD14+ monocytes were transient, as they were no longer observed in the same ATB patients mid-treatment, suggesting they are associated with disease resolution.

Discussion

Together, our study demonstrates for the first time that both intermediate and classical monocytes individually contribute to blood immune signatures of ATB and identifies novel subsets and associated gene signatures that may hold disease relevance.

Siderophore-mediated zinc acquisition enhances enterobacterial colonization of the inflamed gut

Zinc is an essential cofactor for bacterial metabolism, and many Enterobacteriaceae express the zinc transporters ZnuABC and ZupT to acquire this metal in the host. However, the probiotic bacterium Escherichia coli Nissle 1917 (or "Nissle") exhibits appreciable growth in zinc-limited media even when these transporters are deleted. Here, we show that Nissle utilizes the siderophore yersiniabactin as a zincophore, enabling Nissle to grow in zinc-limited media, to tolerate calprotectin-mediated zinc sequestration, and to thrive in the inflamed gut. We also show that yersiniabactin's affinity for iron or zinc changes in a pH-dependent manner, with increased relative zinc binding as the pH increases. Thus, our results indicate that siderophore metal affinity can be influenced by the local environment and reveal a mechanism of zinc acquisition available to commensal and pathogenic Enterobacteriaceae.

Crucial questions in cell biology and in neurobiology

Forty-two proper questions about the research methods, the structure, physiology, biochemistry, pathology and theory of cell biology and 27 more about neurobiology are listed. These have not hitherto been addressed in the literature, other than in my previous publications. The answers to some of them show anomalies in current views, or draw attention to control experiments, which have never been done. Progress will be limited until these important questions are addressed.

Limitations of clinical and biological histology

Histology, including histochemistry, histopathology, electron microscopy and immunocytochemistry, can be considered as two disciplines--clinical and biological. The former is used to make a clinical diagnosis, based on empirical comparisons between, on the one hand, the clinical health of a normal subject with the histological appearances of the organs, and on the other hand, the clinical disease or syndrome of a patient, with the different histological appearances of the organs believed by the clinicians to be affected. It is intended that biological histology should be the most accurate description possible of the structure and chemistry of the living tissue in the intact healthy organism.

A study of 131 patients with schizophrenia and provision for them

One hundred and thirty-one patients came to the Institute of Biological Psychiatry at Bangor, accompanied by 161 healthy blood relatives, spouses and friends. A history was taken and a diagnosis of schizophrenia was made using DSM IIIR criteria. The patients were examined to see if they had any concurrent physical disease. Venous blood samples were taken for measurements of chemical constituents believed to be involved in schizophrenia. The population of patients is described, and the views of the patients and their relatives were noted. Recommendations are made about how provision for patients might be improved.

Abdominal pumping

This article reviews the author's experience with a form of interposed abdominal compression cardiopulmonary resuscitation (IAC-CPR) in the United Kingdom. The development of the technique based upon animal resuscitation, including the use of phasic compression (abdominal pumping) for the resuscitation of rats from 30 minutes of cardiac arrest due to hypothermia, is reviewed. A simple technique for clinical use is described. The technique uses a hard-covered book or bean-shaped board applied to the abdomen below the umbilicus and compressed alternately with cardiac massage while respiration is assisted. Anecdotal clinical results suggests that further controlled clinical investigation is warranted.

The possible pain experienced during execution by different methods

The physiology and pathology of different methods of capital punishment are described. Information about this physiology and pathology can be derived from observations on the condemned persons, postmortem examinations, physiological studies on animals undergoing similar procedures, and the literature on emergency medicine. It is difficult to know how much pain the person being executed feels or for how long, because many of the signs of pain are obscured by the procedure or by physical restraints, but one can identify those steps which are likely to be painful. The general view has been that most of the methods used are virtually painless, and lead to rapid dignified death. Evidence is presented which shows that, with the possible exception of intravenous injection, this view is almost certainly wrong.

Fatty acid levels in the brains of schizophrenics and normal controls

Essential fatty acids are important constituents of the brain. There is evidence that levels in blood of certain essential fatty acids and their eicosanoid derivatives may be abnormal. We now report that in the frontal cortex of schizophrenic patients there are significant differences from normal in the fatty acid composition of phosphatidylethanolamine. These differences from normal were not found in the cerebellar cortex.

A new hypothesis for electrical transmission in the mammalian central nervous system

It has been previously shown that the anatomical synapse does not exist in the living central nervous system, and that receptors are unlikely to be unique molecules sited on particular locations in or on the cell membrane. These conclusions and the rapidity of action of intravenously administered substances necessitated the adumbration of a new electrical hypothesis for the mechanism whereby signals pass from one part of the brain and spinal cord to another. The hypothesis proposed implies some testable predictions.

The effects of transmitters on the affinity of the insoluble fraction of ox brain for Na+ and K+

The insoluble fraction of ox-brain, which had previously been shown to have a non-linear affinity for Na+ and K+, was prepared. Acetylcholine (1 x 10(-8) mol/l and 1 x 10(-7) mol/l) reduced the affinity of the fraction for Na+ and K+ to zero, while at 1 x 10(-6) mol/l, the affinity for the cations was almost as high as in the absence of the transmitter; the affinities for Na+ and K+ were particularly high, when the supernatant concentrations of these ions exceeded 80-100 mM. Addition of eserine (3 x 10(-5) mol/l) considerably modified the response of the fraction to acetylcholine (1 x 10(-5) mol/l). Atropine (1 x 10(-8) mol/l) in the absence or presence of acetylcholine (1 x 10(-5), or 1 x 10(-4) mol/l) reduced the affinity of the fraction for Na+ and K+ to zero. Epinephrine (3 x 10(-10) mol/l) lowered the affinity for Na+ and K+, while ergotamine itself (1 x 10(-5) mol/l) reduced it to zero. The addition of both epinephrine and ergotamine at the latter concentrations restored the affinity of the fractions for Na+ and K+ to what it had been in the absence of the transmitter or antagonist, previously reported. Norepinephrine (3 x 10(-10) mol/l), or ouabain (1 x 10(-7) mol/l) reduced the affinity of the fraction for Na+ and K+ to zero. Thus, the transmitters and antagonists altered the affinity of the insoluble fraction for Na+ and K+ non-linearity, dependent upon their concentrations, the concentrations of the cations, and the interaction of transmitter and antagonist.

Critique of current views on receptors, and a new general theory of receptor location and action in vivo

The Davson-Danielli model of the cell membrane accounted for nearly all the space within it by suggesting that it was composed of structural proteins and lipids; this would leave virtually no space for the large number of enzymes, carriers, antigens, antibodies, and receptors for hormones, transmitters, drugs and toxins, generally believed to be present within the membranes. The sizes of many of the structural proteins, lipids, enzymes and receptors, have been measured by electron microscopic techniques, and are too large to be located within or next to the Robertson 'unit' membrane or the Singer-Nicolson membrane, without producing bulges; these are never seen by transmission electron microscopy, and rarely by freezing techniques. If they were present but unstained, gaps should appear in the membranes corresponding to the measured dimensions of these macromolecules; such gaps are not seen. It has been assumed that the substances react with receptors located only at the cell membrane, but, in the intact organism, they pass through many cellular phases before having any effect; one hundred and five phases in the passage from the blood to the brain are identified. It is suggested that the receptor is the sum total of all the reactions between the substances added and each of the phase reacting to a differing degree. Experiments which could assess the relative validity of the currently accepted and new ones proposed are listed.

The anatomical synapse in mammals by light and electron microscopy

The original descriptions of synapses by light microscopy are examined, and their widths and numbers per neuron soma are compared in light and electron micrographs. Electron micrographs show the synaptic cleft very frequently normal to the plane of section. It is rare to find any connection of the synaptic knobs to any dendrite of another axon, and the granular appearance on the surface of unfixed mammalian neurons can be shown to be due to intracellular particles- probably mitochondria. It is concluded that the anatomical synapse is an artifact. This raises questions about the nature of chemical transmission and the vesicle hypothesis. It may require a reinterpretation of transmission, but does not affect physiological or pharmacological findings about the effects of transmitters.

Reduction in mortality from upper gastrointestinal haemorrhage

A study of 2377 cases of haemorrhage from the upper gastrointestinal tract shows a significant fall in mortality rate--from 15.5% in the period of retrospective study from 1961 to 1970 to 7% in the prospective study from 1972 to 1982. The fall in mortality rate from non-variceal bleeding was from 12.8% to 5%. In the second five years of the prospective study, the total mortality rate was 5.8%, with 4.5% for non-variceal haemorrhage. This improvement occurred despite a significant rise in the proportion of patients of 60 years of age and over, and was particularly evident in patients with bleeding chronic gastric ulcers. There was also a significant reduction in mortality in the 60 years and over age group in the latter five years of the prospective study. The data suggest that there were three aspects of management which were important in the reduction of mortality. These were early fibreoptic endoscopic diagnosis, improved resuscitation and postoperative care, and early control of bleeding from oesophageal varices by balloon tamponade and surgery in selected cases. These complicated procedural aspects of management are best applied in a special unit for the treatment of patients with haemorrhage from the upper gastrointestinal tract. It is concluded that there has been significant progress in the treatment of this problem during the last decade.

Dying and death, with special reference to brain death. A bibliography

A bibliography of dying and death has been made, with special reference to the brain. It does not claim to be comprehensive. Short references have been omitted unless they contained new information not published elsewhere. When books or papers have been written in other languages, their titles have been translated, and their original languages indicated. It has not always been possible to find the complete page references to these.

Some fundamental theoretical and practical problems associated with neurochemical techniques in mammalian studies

The assumptions inherent in (i) a pharmacokinetic experiment in vivo, (ii) a subcellular fractionation, (iii) a chemical assay in an isolated neuron, are listed as three examples of well known neurochemical techniques. From these lists of assumptions a number of general hiatuses in knowledge of the effect of preparation of tissue on the results of experiment have been identified. The importance and different kinds of control experiments are discussed. Comment is made on how the different parameters to which measurements are referred may affect the result of the experiments. Optimal techniques are preferably non-disruptive and non-invasive. A few new techniques are proposed.

Preparation of an insoluble fraction of ox brain and its affinity for Na+ and K+

A water insoluble fraction was prepared from ox cerebrum by homogenization in water, dialysis against water, washing with water and drying in air at 293 degrees K. The fraction represented 15.5 +/- 3% (n = 8) of the weight of the fresh brain; it contained means of 81% (n = 6) of the lipid, found in freshly dried ox brain samples, and 46% (n = 5) (biuret method) or 51% (n = 3) (6) of the protein, respectively. The Na+ and K+ concentrations were measured by atomic emission flame photometry, firstly, in prepared media, and then after 4 ml of the same media had been mixed with 1 g of the insoluble fraction at 310 degrees K for 20 min; the concentration in the fraction was calculated from that found in the medium. The concentration in the medium (mM) after incubation was compared with that calculated to be in the fraction, (mumol/g). When the insoluble fraction was mixed with Krebs Ringer saline containing bicarbonate and glucose, modified so that the ratios of NaCl and KCl varied-(although together they always added up to 150 mM)-there was a mean of 2.6 times as much Na+ or K+ in the fraction (mumol/g) as in the media (mM) when the latter contained up to 80 mM Na+ or K+. When the concentration of the cations in the media exceeded this value, the concentration of Na+ in the fraction rose considerably, while the concentration of K+ fell to zero. When only Ca2+ or only Mg2+ was omitted from the Krebs-Ringer bicarbonate glucose saline, the fraction did not take up Na+ or K+ from the medium at any concentration. On electron microscopy the fraction was granular and amorphous and contained myelin figures. The fraction did not take up any significant volume of oxygen measured manometrically either in the modified Krebs-Ringer solutions or in a mitochondrial substrate.

Artefacts in electron microscopy and the consequences for biological and medical research

It has been previously shown that the endoplasmic reticulum, the Golgi apparatus, the lysosomes, the nuclear pores, and the cristae of the mitochondria could not exist in living cells. Therefore, study of them in all life sciences, or any apparent correlation between their 'structure' and 'function' should be abandoned. The consequences to biological and medical research of such conclusions are considered. Semantic and logical analyses of experiments should always be done, and all the assumptions inherent in them should be identified and tested. Research should be more directed to studies on whole living animals, rather than to metal deposits, precipitation patterns, homogenates, or tissue fixed or subjected to other powerful physical and chemical agents known to change them drastically.

Area changes in slices of rat brain during preparation for histology or electron microscopy

Cerebral slices cut from rat brain, either 2-3 mm or 0.27 mm thick, were used to study the effect of embedding and freezing. Paraffin wax sections 6 micrometer thick were mounted and stained with haematoxylin and eosin or Marsland et al.'s (1954) silver stain, and their areas were examined at each step. Embedding in paraffin wax of slices 2-3 mm thick, or in Epon of slices 0.27 mm thick, caused a diminution of their areas by 20-30%. Staining of paraffin wax sections did not alter their areas. Glycerol alone at 15% concentration had no effect on the areas, but at 30% concentration they were diminished by approximately 20%. Diminution of the areas of glycerol treated slices 0.27 mm thick also occurred when they were transferred to liquid N2 or to isopentane, but the areas increased after glycerol was replaced by Freon 12. It was concluded that embedding or freezing cerebral slices caused changes in their areas, but that staining of sections after they had been embedded, sectioned and mounted did not.

The unit membrane, the endoplasmic reticulum, and the nuclear pores are artefacts

It is shown on the basis of solid geometry that the trilaminar appearance of membranes described by Robertson must be an artefact, although the membranes themselves are not. However, considerations of solid geometry as well as observations on living cells indicate that the endoplasmic reticulum and nuclear pores are artefacts resulting from preparation for electron microscopy. Suggestions for their genesis are proposed.