Tissue-specific nonheritable influences drive endometrial immune system variation

Although human twin studies have revealed the combined contribution of heritable and environmental factors in shaping immune system variability in blood, the contribution of these factors to immune system variability in tissues remains unexplored. The human uterus undergoes constant regeneration and is exposed to distinct environmental factors. To assess uterine immune system variation, we performed a system-level analysis of endometrial and peripheral blood immune cells in monozygotic twins. Although most immune cell phenotypes in peripheral blood showed high genetic heritability, more variation was found in endometrial immune cells, indicating a stronger influence by environmental factors. Cytomegalovirus infection was identified to influence peripheral blood immune cell variability but had limited effect on endometrial immune cells. Instead, hormonal contraception shaped the local endometrial milieu and immune cell composition with minor influence on the systemic immune system. These results highlight that the magnitude of human immune system variation and factors influencing it can be tissue specific.

Preoperative immunological plasma markers TRAIL, CSF1 and TIE2 predict survival after resection for biliary tract cancer

Introduction

Systemic inflammatory markers have been validated as prognostic factors for patients with biliary tract cancer (BTC). The aim of this study was to evaluate specific immunologic prognostic markers and immune responses by analyzing preoperative plasma samples from a large prospectively collected biobank.

Methods

Expression of 92 proteins representing adaptive and innate immune responses was investigated in plasma from 102 patients undergoing resection for BTC 2009-2017 (perihilar cholangiocarcinoma n=46, intrahepatic cholangiocarcinoma n=27, gallbladder cancer n=29), by means of a high-throughput multiplexed immunoassay. Association with overall survival was analyzed by Cox regression, with internal validation and calibration. Tumor tissue bulk and single-cell gene expression of identified markers and receptors/ligands was analyzed in external cohorts.

Results

Three preoperative plasma markers were independently associated with survival: TRAIL, TIE2 and CSF1, with hazard ratios (95% confidence intervals) 0.30 (0.16-0.56), 2.78 (1.20-6.48) and 4.02 (1.40-11.59) respectively. The discrimination of a preoperative prognostic model with the three plasma markers was assessed with concordance-index 0.70, while the concordance-index of a postoperative model with histopathological staging was 0.66. Accounting for subgroup differences, prognostic factors were assessed for each type of BTC. TRAIL and CSF1 were prognostic factors in intrahepatic cholangiocarcinoma. In independent cohorts, TRAIL-receptor expression was higher in tumor tissue and seen in malignant cells, with TRAIL and CSF1 expressed by intra- and peritumoral immune cells. Intratumoral TRAIL-activity was decreased compared to peritumoral immune cells, while CSF1-activity was increased. The highest CSF1 activity was seen in intratumoral macrophages, while the highest TRAIL-activity was seen in peritumoral T-cells.

Discussion

In conclusion, three preoperative immunological plasma markers were prognostic for survival after surgery for BTC, providing good discrimination, even compared to postoperative pathology. TRAIL and CSF1, prognostic factors in intrahepatic cholangiocarcinoma, showed marked differences in expression and activity between intra- and peritumoral immune cells.

The Karolinska KI/K COVID-19 Immune Atlas: An open resource for immunological research and educational purposes

The Karolinska KI/K COVID-19 Immune Atlas project was conceptualized in March 2020 as a part of the academic research response to the developing SARS-CoV-2 pandemic. The aim was to rapidly provide a curated dataset covering the acute immune response towards SARS-CoV-2 infection in humans, as it occurred during the first wave. The Immune Atlas was built as an open resource for broad research and educational purposes. It contains a presentation of the response evoked by different immune and inflammatory cells in defined naïve patient-groups as they presented with moderate and severe COVID-19 disease. The present Resource Article describes how the Karolinska KI/K COVID-19 Immune Atlas allow scientists, students, and other interested parties to freely explore the nature of the immune response towards human SARS-CoV-2 infection in an online setting.

Mucosal-associated invariant T-cell tumor infiltration predicts long-term survival in cholangiocarcinoma

BACKGROUND AND AIMS

Cholangiocarcinoma (CCA) is a malignancy arising from biliary epithelial cells of intra- and extrahepatic bile ducts with dismal prognosis and few nonsurgical treatments available. Despite recent success in the immunotherapy-based treatment of many tumor types, this has not been successfully translated to CCA. Mucosal-associated invariant T (MAIT) cells are cytotoxic innate-like T cells highly enriched in the human liver, where they are located in close proximity to the biliary epithelium. Here, we aimed to comprehensively characterize MAIT cells in intrahepatic (iCCA) and perihilar CCA (pCCA).

APPROACH AND RESULTS

Liver tissue from patients with CCA was used to study immune cells, including MAIT cells, in tumor-affected and surrounding tissue by immunohistochemistry, RNA-sequencing, and multicolor flow cytometry. The iCCA and pCCA tumor microenvironment was characterized by the presence of both cytotoxic T cells and high numbers of regulatory T cells. In contrast, MAIT cells were heterogenously lost from tumors compared to the surrounding liver tissue. This loss possibly occurred in response to increased bacterial burden within tumors. The residual intratumoral MAIT cell population exhibited phenotypic and transcriptomic alterations, but a preserved receptor repertoire for interaction with tumor cells. Finally, the high presence of MAIT cells in livers of iCCA patients predicted long-term survival in two independent cohorts and was associated with a favorable antitumor immune signature.

CONCLUSIONS

MAIT cell tumor infiltration associates with favorable immunological fitness and predicts survival in CCA.

COVID-19-specific metabolic imprint yields insights into multiorgan system perturbations

Corona disease 2019 (COVID-19) affects multiple organ systems. Recent studies have indicated perturbations in the circulating metabolome linked to COVID-19 severity. However, several questions pertain with respect to the metabolome in COVID-19. We performed an in-depth assessment of 1129 unique metabolites in 27 hospitalized COVID-19 patients and integrated results with large-scale proteomic and immunology data to capture multiorgan system perturbations. More than half of the detected metabolic alterations in COVID-19 were driven by patient-specific confounding factors ranging from comorbidities to xenobiotic substances. Systematically adjusting for this, a COVID-19-specific metabolic imprint was defined which, over time, underwent a switch in response to severe acute respiratory syndrome coronavirus-2 seroconversion. Integration of the COVID-19 metabolome with clinical, cellular, molecular, and immunological severity scales further revealed a network of metabolic trajectories aligned with multiple pathways for immune activation, and organ damage including neurological inflammation and damage. Altogether, this resource refines our understanding of the multiorgan system perturbations in severe COVID-19 patients.

Continuous human uterine NK cell differentiation in response to endometrial regeneration and pregnancy

Immune cell differentiation is critical for adequate tissue-specific immune responses to occur. Here, we studied differentiation of human uterine natural killer cells (uNK cells). These cells reside in a tissue undergoing constant regeneration and represent the major leukocyte population at the maternal-fetal interface. However, their physiological response during the menstrual cycle and in pregnancy remains elusive. By surface proteome and transcriptome analysis as well as using humanized mice, we identify a differentiation pathway of uNK cells in vitro and in vivo with sequential acquisition of killer cell immunoglobulin-like receptors and CD39. uNK cell differentiation occurred continuously in response to the endometrial regeneration and was driven by interleukin-15. Differentiated uNK cells displayed reduced proliferative capacity and immunomodulatory function including enhanced angiogenic capacity. By studying human uterus transplantation and monozygotic twins, we found that the uNK cell niche could be replenished from circulation and that it was under genetic control. Together, our study uncovers a continuous differentiation pathway of human NK cells in the uterus that is coupled to profound functional changes in response to local tissue regeneration and pregnancy.

Innate lymphoid cell composition associates with COVID-19 disease severity

Objectives

The role of innate lymphoid cells (ILCs) in coronavirus disease 2019 (COVID‐19), caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), is unknown. Understanding the immune response in COVID‐19 could contribute to unravel the pathogenesis and identification of treatment targets. Here, we describe the phenotypic landscape of circulating ILCs in COVID‐19 patients and identified ILC phenotypes correlated to serum biomarkers, clinical markers and laboratory parameters relevant in COVID‐19.

Methods

Blood samples collected from moderately (n = 11) and severely ill (n = 12) COVID‐19 patients, as well as healthy control donors (n = 16), were analysed with 18‐parameter flow cytometry. Using supervised and unsupervised approaches, we examined the ILC activation status and homing profile. Clinical and laboratory parameters were obtained from all COVID‐19 patients, and serum biomarkers were analysed with multiplex immunoassays.

Results

Innate lymphoid cells were largely depleted from the circulation of COVID‐19 patients compared with healthy controls. Remaining circulating ILCs revealed decreased frequencies of ILC2 in severe COVID‐19, with a concomitant decrease of ILC precursors (ILCp) in all patients, compared with controls. ILC2 and ILCp showed an activated phenotype with increased CD69 expression, whereas expression levels of the chemokine receptors CXCR3 and CCR4 were significantly altered in ILC2 and ILCp, and ILC1, respectively. The activated ILC profile of COVID‐19 patients was associated with soluble inflammatory markers, while frequencies of ILC subsets were correlated with laboratory parameters that reflect the disease severity.

Conclusion

This study provides insights into the potential role of ILCs in immune responses against SARS‐CoV‐2, particularly linked to the severity of COVID‐19.

Innate Immune Responses to Acute Viral Infection During Pregnancy

Immunological adaptations in pregnancy allow maternal tolerance of the semi-allogeneic fetus but also increase maternal susceptibility to infection. At implantation, the endometrial stroma, glands, arteries and immune cells undergo anatomical and functional transformation to create the decidua, the specialized secretory endometrium of pregnancy. The maternal decidua and the invading fetal trophoblast constitute a dynamic junction that facilitates a complex immunological dialogue between the two. The decidual and peripheral immune systems together assume a pivotal role in regulating the critical balance between tolerance and defense against infection. Throughout pregnancy, this equilibrium is repeatedly subjected to microbial challenge. Acute viral infection in pregnancy is associated with a wide spectrum of adverse consequences for both mother and fetus. Vertical transmission from mother to fetus can cause developmental anomalies, growth restriction, preterm birth and stillbirth, while the mother is predisposed to heightened morbidity and maternal death. A rapid, effective response to invasive pathogens is therefore essential in order to avoid overwhelming maternal infection and consequent fetal compromise. This sentinel response is mediated by the innate immune system: a heritable, highly evolutionarily conserved system comprising physical barriers, antimicrobial peptides (AMP) and a variety of immune cells—principally neutrophils, macrophages, dendritic cells, and natural killer cells—which express pattern-receptors that detect invariant molecular signatures unique to pathogenic micro-organisms. Recognition of these signatures during acute infection triggers signaling cascades that enhance antimicrobial properties such as phagocytosis, secretion of pro-inflammatory cytokines and activation of the complement system. As well as coordinating the initial immune response, macrophages and dendritic cells present microbial antigens to lymphocytes, initiating and influencing the development of specific, long-lasting adaptive immunity. Despite extensive progress in unraveling the immunological adaptations of pregnancy, pregnant women remain particularly susceptible to certain acute viral infections and continue to experience mortality rates equivalent to those observed in pandemics several decades ago. Here, we focus specifically on the pregnancy-induced vulnerabilities in innate immunity that contribute to the disproportionately high maternal mortality observed in the following acute viral infections: Lassa fever, Ebola virus disease (EVD), dengue fever, hepatitis E, influenza, and novel coronavirus infections.

Natural killer cell immunotypes related to COVID-19 disease severity

Understanding innate immune responses in COVID-19 is important to decipher mechanisms of host responses and interpret disease pathogenesis. Natural killer (NK) cells are innate effector lymphocytes that respond to acute viral infections but might also contribute to immunopathology. Using 28-color flow cytometry, we here reveal strong NK cell activation across distinct subsets in peripheral blood of COVID-19 patients. This pattern was mirrored in scRNA-seq signatures of NK cells in bronchoalveolar lavage from COVID-19 patients. Unsupervised high-dimensional analysis of peripheral blood NK cells furthermore identified distinct NK cell immunotypes that were linked to disease severity. Hallmarks of these immunotypes were high expression of perforin, NKG2C, and Ksp37, reflecting increased presence of adaptive NK cells in circulation of patients with severe disease. Finally, arming of CD56bright NK cells was observed across COVID-19 disease states, driven by a defined protein-protein interaction network of inflammatory soluble factors. This study provides a detailed map of the NK cell activation landscape in COVID-19 disease.

Natural killer cell immunotypes related to COVID-19 disease severity

Understanding innate immune responses in COVID-19 is important to decipher mechanisms of host responses and interpret disease pathogenesis. Natural killer (NK) cells are innate effector lymphocytes that respond to acute viral infections but might also contribute to immunopathology. Using 28-color flow cytometry, we here reveal strong NK cell activation across distinct subsets in peripheral blood of COVID-19 patients. This pattern was mirrored in scRNA-seq signatures of NK cells in bronchoalveolar lavage from COVID-19 patients. Unsupervised high-dimensional analysis of peripheral blood NK cells furthermore identified distinct NK cell immunotypes that were linked to disease severity. Hallmarks of these immunotypes were high expression of perforin, NKG2C, and Ksp37, reflecting increased presence of adaptive NK cells in circulation of patients with severe disease. Finally, arming of CD56^bright NK cells was observed across COVID-19 disease states, driven by a defined protein-protein interaction network of inflammatory soluble factors. This study provides a detailed map of the NK cell activation landscape in COVID-19 disease.

29-Color Flow Cytometry: Unraveling Human Liver NK Cell Repertoire Diversity

Recent studies have demonstrated extraordinary diversity in peripheral blood human natural killer (NK) cells and have suggested environmental control of receptor expression patterns on distinct subsets of NK cells. However, tissue localization may influence NK cell differentiation to an even higher extent and less is known about the receptor repertoire of human tissue-resident NK cells. Advances in single-cell technologies have allowed higher resolution studies of these cells. Here, the power of high-dimensional flow cytometry was harnessed to unravel the complexity of NK cell repertoire diversity in liver since recent studies had indicated high heterogeneity within liver NK cells. A 29-color flow cytometry panel allowing simultaneous measurement of surface tissue-residency markers, activating and inhibitory receptors, differentiation markers, chemokine receptors, and transcription factors was established. This panel was applied to lymphocytes across three tissues (liver, peripheral blood, and tonsil) with different distribution of distinct NK cell subsets. Dimensionality reduction of this data ordered events according to their lineage, rather than tissue of origin. Notably, narrowing the scope of the analysis to the NK cell lineage in liver and peripheral blood separated subsets according to tissue, enabling phenotypic characterization of NK cell subpopulations in individual tissues. Such dimensionality reduction, coupled with a clustering algorithm, identified CD49e as the preferred marker for future studies of liver-resident NK cell subsets. We present a robust approach for diversity profiling of tissue-resident NK cells that can be applied in various homeostatic and pathological conditions such as reproduction, infection, and cancer.

Hernia of the umbilical cord associated with a patent omphalomesenteric duct

Congenital hernia of the cord is a different type of ventral abdominal wall defect in which the bowel usually herniates into the base of normally inserted umbilical cord through a patent umbilical ring. It is rare congenital anomaly with incidence of 1 in 5000. Although it was described as a distinct entity since 1920s it is often misdiagnosed as a small omphalocele. We present an unusal case of term male newborn with umbilical cord hernia associated with patent omphalomesenteric duct. The diagnose was made after birth despite antenatal ultrasound scans and it is managed successfully with uneventful recovery. If this is missdiagnosed, it could cause iatrogenic atresia of the ileum by clamping the umbilical cord after birth.

Molecular definition of group 1 innate lymphoid cells in the mouse uterus

Determining the function of uterine lymphocytes is challenging because of the dynamic changes in response to sex hormones and, during pregnancy, to the invading foetal trophoblast cells. Here we provide a genome-wide transcriptome atlas of mouse uterine group 1 innate lymphoid cells (ILCs) at mid-gestation. Tissue-resident Eomes+CD49a+ NK cells (trNK), which resemble human uterine NK cells, are most abundant during early pregnancy, and have gene signatures associated with TGF-β responses and interactions with trophoblast, epithelial, endothelial, smooth muscle cells, leucocytes and extracellular matrix. Conventional NK cells expand late in gestation and may engage in crosstalk with trNK cells involving IL-18 and IFN-γ. Eomes-CD49a+ ILC1s dominate before puberty, and specifically expand in second pregnancies when the expression of the memory cell marker CXCR6 is upregulated. These results identify trNK cells as the cellular hub of uterine group 1 ILCs, and mark CXCR6+ ILC1s as potential memory cells of pregnancy.

Negative CEA values in Metastatic Colorectal Carcinoma and the Likelihood of Complete Chemotherapy Response

Introduction

Experimental results reported in the literature have suggested that CEA might inhibit host defense mechanisms and that immunotolerance to CEA could play an important role in the development of metastases in colorectal carcinoma. It might therefore be assumed that negative CEA values during metastatic disease represent a favorable prognostic factor. Surprisingly, there are very few data available about negative CEA. The aim of this study was to determine the significance of negative initial CEA values in patients with metastatic colorectal carcinoma.

Patients and Methods

Initial CEA values were determined in 114 patients with metastatic colorectal carcinoma. The patients were divided into three groups according to these values: I (n=22) <5 ng/mL; II (n=33) 5-100 ng/mL; III (n=59) >100 ng/mL.

Results

Seven/114 complete responses (CR), 22/114 partial responses (PR), 45/114 instances of stable disease (SD) and 38/114 of progressive disease (PD) were registered, while two patients were not evaluable. There were six long-lasting CRs (median 24 months, range 10–37 months) in the CEA-negative patient subset, while in the CEA-positive subset there was only one CR, in a patient with an initial CEA level of 18 ng/mL. The mean initial CEA values in the different response categories were: CR: 4.0 ng/mL; PR: 436 ng/mL; SD: 1442 ng/mL; PD: 6071 ng/mL. The likelihood of response, in particular CR, was highly dependent upon CEA levels (Fisher's exact test, 0.00001). The median survival decreased significantly with increased values of CEA (p=0.006).

Conclusion

Negative CEA in metastatic disease was the main characteristic of the patient subset capable of attaining CR. When relapsing, all patients but one became CEA positive.

Multiple Levels of Control Determine How E4bp4/Nfil3 Regulates NK Cell Development

The transcription factor E4bp4/Nfil3 has been shown to have a critical role in the development of all innate lymphoid cell types including NK cells. In this study, we show that posttranslational modifications of E4bp4 by either SUMOylation or phosphorylation have profound effects on both E4bp4 function and NK cell development. We examined the activity of E4bp4 mutants lacking posttranslational modifications and found that Notch1 was a novel E4bp4 target gene. We observed that abrogation of Notch signaling impeded NK cell production and the total lack of NK cell development from E4bp4^-/- progenitors was completely rescued by short exposure to Notch peptide ligands. This work reveals both novel mechanisms in NK cell development by a transcriptional network including E4bp4 with Notch, and that E4bp4 is a central hub to process extrinsic stimuli.

Effect of inhibiting N-glycosylation on the stability and binding activity of the low density lipoprotein receptor

Tunicamycin, a specific inhibitor of N-glycosylation, was used to study the function of asparagine-linked oligosaccharides of the low density lipoprotein (LDL) receptor in cultured human skin fibroblasts. When cells were preincubated in the presence of 0.5 micrograms/ml of the drug the incorporation of [3H]mannose into the receptor was completely prevented and that of [3H]glucosamine was reduced to approximately 41% of the control value. The [35S]methionine radioactivity detected in receptor core protein of tunicamycin-treated cells was about 52% of that measured in the receptor of control cells. The decrease in the radioactivity was similar in both the mature receptor as well as in its precursor form, and it was significantly greater than that found in total protein. The rates of receptor degradation in control- and tunicamycin-treated cells were comparable. Neither cell surface appearance of the newly synthesized LDL receptor nor its recycling were affected by tunicamycin. However, the LDL receptor produced in tunicamycin-treated cells was smaller in molecular size, and it exhibited an about 50% lower binding capacity when compared with its counterpart synthesized in control cells. This indicates that there is a relationship between N-glycosylation and the ligand binding activity of the LDL receptor. The possible role of asparagine-linked oligosaccharides in optimizing the biological activity of the LDL receptor is discussed.

Calmodulin antagonists increase the amount of mRNA for the low-density-lipoprotein receptor in skin fibroblasts

The effects of calmodulin antagonists on the amount of LDL receptor (LDL-R) mRNA in cultured human fibroblasts was examined by hybridization with a fragment of LDL-R cDNA. In a 'Northern' blot the fragment hybridized to a 5.3-kilobase RNA, as expected for LDL-R mRNA. The concentration of this RNA was increased in preparations from cells that were treated with trifluoperazine or W-7 [N-(6-aminohexyl)-5-chloronaphthalene-1-sulphonamide]. The selectivity of the increase was established by using a probe for beta-actin mRNA. In dot-blot hybridization it was observed that the calmodulin antagonists cause 2-4-fold relative increase in the amount of LDL-R mRNA.

Calmodulin antagonists suppress cholesterol synthesis by inhibiting sterol delta 24 reductase

Preincubation of hepatoma cells and human skin fibroblasts in the presence of the calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide resulted in a dose-dependent suppression of [14C]mevalonolactone incorporation into cholesterol. At a calmodulin antagonist concentration of 25 mumol, the incorporation of [14C]mevalonolactone into cellular cholesterol was suppressed to about 30% (hepatoma cells) and 10% (human skin fibroblasts) of control values. When the total nonsaponifiable [14C]lipids were separated and analyzed by two-dimensional thin layer chromatography, an accumulation of [14C]desmosterol was observed along with reduced formation of [14C]cholesterol. However, when cells were preincubated in the presence of [14C]dihydrolanosterol, [14C]cholesterol formation was not inhibited by the calmodulin antagonists. About 25% of the cell-associated dihydrolanosterol radioactivity was converted to cholesterol in both control and calmodulin antagonist-pretreated cells. The data suggest that calmodulin antagonists prevent the conversion of desmosterol into cholesterol by inhibiting sterol delta 24 reductase and that the enzymes catalyzing sterol ring modifications are not affected by the inhibitors.

Calcium channel blockers stimulate LDL receptor synthesis in human skin fibroblasts

Human skin fibroblasts incubated in lipoprotein-deficient medium in the presence of 50-100 microM of the calcium channel blockers verapamil or diltiazem incorporated up to 2.5 times more [35S]methionine into immunoprecipitable LDL receptor protein than did control cells. Verapamil was found to be more potent in this regard than diltiazem. The calcium channel blockers did not influence the overall synthesis of cellular proteins or the half-life of the LDL receptor, and they were not able to prevent the suppression of LDL receptor synthesis caused by exogenous LDL or 25-hydroxycholesterol. The calcium channel blocker-induced stimulation of LDL receptor synthesis was accompanied by a corresponding increase in binding and internalization of [125I]LDL, but the degradation of internalized lipoprotein was slightly decreased. The results suggest that intracellular Ca2+ levels modulate LDL receptor metabolism in human skin fibroblasts.

Glucocorticoid-stimulated biosynthesis of low density lipoprotein receptor in cultured fibroblasts

Preincubation of human skin fibroblasts in the presence of 10(-6)-10(-5) mol/l glucocorticoids (dexamethasone) causes a concentration and time-dependent increase of receptor-mediated internalisation of [125I]LDL. This increase is due to a glucocorticoid-specific stimulation by 40-50% of LDL receptor synthesis as demonstrated by an increased incorporation of [35S]methionine into immune precipitated receptor protein. In contrast the rate of synthesis of total cell protein and of lysosomal cathepsin D is not significantly influenced by dexamethasone. The increased LDL receptor synthesis is accompanied by an enhanced synthesis of cholesterol from [2-3H]mevalonolactone and [1-14C]acetate. The glucocorticoid-induced enhancement of LDL receptor and cholesterol synthesis is abolished by preincubation of the cells with dexamethasone in combination with 25-hydroxycholesterol.

Sphingolipid-induced enhancement of receptor-mediated uptake of low density lipoproteins in normal and receptor-deficient human skin fibroblasts

(1) The receptor mediated endocytosis of homologous LDL by human skin fibroblasts can be significantly enhanced by prior incubation of the cells with sphingolipids. Gangliosides GM1 or GD1a, their desialylated derivatives and sphingosine stimulate binding and uptake to LDL by up to 40% of normal values. The effect is observed in normal fibroblasts, LDL receptor deficient fibroblasts or in tunicamycin-treated cells with a reduced number of functional receptors but is dependent on the time of preincubation of the cells and the concentration of the sphingolipid in the medium. (2) Detailed studies on the ganglioside effect revealed, that cell bound gangliosides intensify the LDL-induced suppression of [14C] acetate incorporation into cholesterol. (3) The receptor dependence and relative receptor specificity of the sphingolipid effect is evident from the fact that (a) after complete suppression of receptor synthesis gangliosides fail to stimulate uptake of LDL, that (b) fatty acids or lipids not containing sphingosine are without effect and that (c) the receptor specific internalisation of alpha 2-macroglobulin or epidermal growth factor is not influenced by exogenous sphingolipids.

Action of low-density lipoprotein and compactin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl-CoA reductase, on the synthesis of dolichol-linked oligosaccharides and low-density-lipoprotein receptor in human skin fibroblasts

To explore whether there is an inter-relationship between the rate of low-density (LD) lipoprotein binding to its receptor and the formation of dolichol-linked oligosaccharides, experiments were performed with human fibroblasts where the synthesis of lipoprotein receptor and dolichyl saccharides was under control of LD lipoprotein and compactin. Pretreatment of the cells with nonlabelled LD lipoprotein resulted in a suppression of both the binding of 125I-labelled LD lipoprotein to the receptor and the synthesis of dolichyl saccharides from [14C]acetate and [3H]mannose, but not from [3H]mevalonolactone. Compactin, in contrast, inhibited only the formation of dolichol-linked oligosaccharides. Mevalonolactone (1 microM) abolished the inhibitory effect of LD lipoprotein on dolichyl saccharide formation, but was not able to restore the receptor-binding capacity, thus suggesting that the synthesis of lipoprotein receptor is not coupled to the formation of dolichyl saccharides.

Effect of tunicamycin on the metabolism of low-density lipoproteins by control and low-density-lipoprotein-receptor-deficient human skin fibroblasts

Preincubation of normal human skin fibroblasts with tunicamycin, which inhibits N-glycosylation of glycoproteins, resulted in a dose-dependent and reversible inhibition of binding and internalization of homologous low-density lipoproteins by the cells. The degradation of the internalized lipoproteins was not affected by the drug. Comparative studies with fibroblasts deficient in low-density-lipoprotein receptors indicated that tunicamycin exerts its inhibitory effect only via the receptor-mediated high-affinity binding and uptake of lipoproteins. These results suggest that expression of low-density-lipoprotein receptors on the cell surface of human skin fibroblasts depends on intact N-glycosylation.

Homologous low density lipoprotein does not affect proteoglycan metabolism of cultured skin fibroblasts and arterial smooth muscle cells

The relevance of lipoprotein-glycosaminoglycan interactions on the proteoglycan metabolism was investigated. The following results were obtained: 1) Biosynthesis of [35S]proteoglycans by cultured human skin fibroblasts and their distribution to different compartments are neither affected by preincubation of the cells with homologous LDL nor by their presence. The internalisation of LDL was evidenced by a marked depression of [14C]cholesterol synthesis from [1-(14)C]-acetate. 2) Under the conditions of endocytosis experiments the formation of insoluble proteoglycan-LDL complexes is insignificant. Endocytosis and degradation of exogenous proteoglycans by skin fibroblasts or arterial smooth muscle cells proceed at normal rates in the presence of low or excess LDL concentrations. 3) From the results it may be concluded, that internalized LDL and their degradation products neither influence the synthesis and distribution of sulfated proteoglycans nor control expression and function of proteoglycan specific cell surface receptors.

Sialic-acid content of low-density lipoproteins controls their binding and uptake by cultured cells

The (high-affinity receptor)-mediated uptake of homologous low-density (low-rho) lipoproteins by cultured human arterial smooth muscle cells or human skin fibroblasts is controlled by the sialic acid content of low-rho lipoprotein particles. This conclusion is derived from the following results. 1. Gangliosides incubated with native low-rho lipoproteins associate with low-rho lipoprotein particles. Low-rho lipoproteins modified by associated GLac1, GGtet1, and GGtet2b + GGtet3 gangliosides are internalized by arterial smooth muscle cells at a rate up to 80% lower than native low-rho lipoproteins or those preincubated with desialized gangliosides. 2. The inhibitory effect of gangliosides is specific for high affinity uptake and not detectable on skin fibroblasts deficient in low-rho-lipoprotein receptor. 3. Desialyzed low-rho lipoproteins are internalized by smooth muscle cells up to 100% faster than native low-rho lipoproteins, the enhancement of uptake corresponding to the degree of desialization.

p-Chlorophenoxyisobutyrate enhanced retention of homologous lipoproteins by human aortic smooth muscle cells

Human aortic smooth muscle cells (SMC) specifically bind and take up indiscriminately both the lipid and protein moieties of homologous 25I-very low density lipoproteins (VLDL) and 125I-low density lipoproteins LDL). Sixty-five to 80% of absorbed lipids are incorporated into the cell lipids, preferentially into the phospholipid fraction. Twenty to 35% of the lipid bound and the protein moiety are eliminated from the cells. Half of the eliminated protein label is recovered as TCA soluble products. Five mM of p-chlorophenoxyisobutyrate (CPIB) raise the level of intracellular radioactivity derived from the lipid moieties of VLDL and LDL by about 40% via a reduced elimination. The processing of the protein moiety and lipoprotein binding to the cell surface are not affected by 5.0 mM of CPIB. CPIB lowers the incorporation of 14C-acetate, 14C-pyruvate, and 32phosphate radioactivity into fatty acids and phospholipids of aortic SMC. Five mM of CPIB reduce the overall palmitic acid synthesis by shifting from de novo synthesis to the mechanism of chain elongation, although the further elongation to saturated C18-C24 fatty acids is also depressed. The CPIB-enhanced retention of the lipid-derived lipoprotein radio-activity is interpreted as a compensatory mechanism providing cellular fatty acids which are deficient as a result of the CPIB inhibited synthetic processes.

Comparative studies on fatty acid synthesis in atherosclerotic and hypoxic human aorta

The oxygen and glucose uptake, lactate formation, ATP/ADP and NADH/NAD ratios and incorporation of [14C]acetate and [14C]linolenic acid into lipids of early fatty streaks and more advanced complicated atherosclerotic lesions of human aorta were determined during aerobic and hypoxic incubation. Compared with grossly normal appearing sections of the aorta in intima and media preparations of early fatty streaks the oxygen uptake was increased while that in further developed atheroma was slightly diminished. Under aerobic incubation conditions the metabolic state of fatty streaks and atheroma was characterized by increased lactate formation, NADH/NAD ratio and incorporation of [14C]acetate and [14C]linolenic acid into the lipids, but by a lowered ATP/ADP ratio. More pronounced changes in these metabolic parameters were observed when the aortic tissue segments were incubated under hypoxic conditions. The analysis by argentation TLC of fatty acid methylesters derived from total lipids of aerobically incubated fatty streaks revealed an increased incorporation of [14C]acetate into the highly unsaturated long-chain fatty acids. In developed atherosclerotic lesions and in hypoxia the incorporation of radioacetate into the polyunsaturated fatty acids and the formation of 20:4 fatty acid from [14C]linolenic acid were, in contrast to the above finding, decreased while the synthesis of eicosatrienoic acid was increased. This finding suggests a block in the desaturation step of linoleic into 20:4 fatty acid in further developed atheroma and in hypoxia. In aerobically incubated atherosclerotic lesions and in hypoxia the palmitic acid was synthesized mainly by chain elongation while in grossly normal areas of the aorta at least part of this acid was synthesized de novo.

Triglyceride lipase activity in bovine aorta

The cell-free supernatant from homogenized bovine aorta hydrolyzed triglycerides, beta-naphthylesters of lauric and stearic acid and Tween 20, 40 and 60. The rate of hydrolysis decreases as the acyl chain length of the substrates increases. The activity against triglycerides of short-chain fatty acids and monoacylesters could be partially separated from that of glycerol-trioleate lipase by ammonium sulfate fractionation. The activity of glycerol-trioleate lipase remained unaffected by heating for 5 min at 60 degrees C or by addition of bile acids, whereas the activity causing hydrolysis of triglycerides with short-chain fatty acids and monoacylesters decreases up to 60% by analogous treatment.

Comparative studies on the chemistry and the metabolism of arterial and venous tissue

Comparative studies of the chemistry and metabolism of human and bovine arterial and venous tissue had the following results (values for bovine tissue in parenthesis): 1. In arterial tissue the contents of collagen were 21% (37%) and of elastin 20% (31%) referred to the dry weight. In veins collagen amounted to 47% (30%) and elastin to 7% (18%). The mucopolysaccharide concentration was higher in arterial (1.2 and 1.5 resp.) than in venous tissue (0.4 and 0.2% resp.). Hyaluronate, chondroitin 6-sulphate (chondroitin 4-sulphate), dermatan sulphate and heparan sulphate were identified. In arterial tissue chondroitin sulphate was predominant with 59 % and 49 % resp. In human venous tissue the main component was dermatan sulphate (65%), in bovine veins it was hyaluronate (75%). No dermatan sulphate was found in bovine venous tissue. The number of cells was higher in arteries (4.5 × 10⁷ nuclei/g w. wt.) than in veins (2.8 × 10⁷). 2. On in vitro incubation bovine arterial tissue metabolized 73 %, venous tissue 32% of the added [U-^I4C] glucose within 12 h. In this period 2.8 and 2.4 mg lactate resp./g wet tissue were formed by arteries and veins. The specific radioactivity of lactate synthesized in arterial tissue reached that of the added [U-^I4C] glucose whereas lactate formed by veins had only 36 % of the specific activity of the [U-^I4C] glucose. The specific radioactivity of the acid mucopolysaccharides was 5–6 times higher in venous tissue than in arterial tissue. After labelling with ³⁵S-sulphate a 3-fold higher specific radioactivity of venous sulphated mucopolysaccharides was observed. 3. After incubation of bovine venous tissue in the presence of ^I4C-acetate the specific radioactivity of phospholipids was 45 % higher than that of arterial tissue in contrast to a 50 % lower labelling of cholesterol in venous tissue.