Endocytosis at the maternal-fetal interface: balancing nutrient transport and pathogen defense

Endocytosis represents a category of regulated active transport mechanisms. These encompass clathrin-dependent and -independent mechanisms, as well as fluid phase micropinocytosis and macropinocytosis, each demonstrating varying degrees of specificity and capacity. Collectively, these mechanisms facilitate the internalization of cargo into cellular vesicles. Pregnancy is one such physiological state during which endocytosis may play critical roles. A successful pregnancy necessitates ongoing communication between maternal and fetal cells at the maternal-fetal interface to ensure immunologic tolerance for the semi-allogenic fetus whilst providing adequate protection against infection from pathogens, such as viruses and bacteria. It also requires transport of nutrients across the maternal-fetal interface, but restriction of potentially harmful chemicals and drugs to allow fetal development. In this context, trogocytosis, a specific form of endocytosis, plays a crucial role in immunological tolerance and infection prevention. Endocytosis is also thought to play a significant role in nutrient and toxin handling at the maternal-fetal interface, though its mechanisms remain less understood. A comprehensive understanding of endocytosis and its mechanisms not only enhances our knowledge of maternal-fetal interactions but is also essential for identifying the pathogenesis of pregnancy pathologies and providing new avenues for therapeutic intervention.

Intracellular Protein Adsorption Behavior and Biological Effects of Polystyrene Nanoplastics in THP-1 Cells

Micro(nano)plastics (MNPs) are emerging pollutants that can adsorb pollutants in the environment and biological molecules and ultimately affect human health. However, the aspects of adsorption of intracellular proteins onto MNPs and its biological effects in cells have not been investigated to date. The present study revealed that 100 nm polystyrene nanoplastics (NPs) could be internalized by THP-1 cells and specifically adsorbed intracellular proteins. In total, 773 proteins adsorbed onto NPs with high reliability were identified using the proteomics approach and analyzed via bioinformatics to predict the route and distribution of NPs following cellular internalization. The representative proteins identified via the Kyoto Encyclopedia of Genes and Genomes pathway analysis were further investigated to characterize protein adsorption onto NPs and its biological effects. The analysis revealed that NPs affect glycolysis through pyruvate kinase M (PKM) adsorption, trigger the unfolded protein response through the adsorption of ribophorin 1 (RPN1) and heat shock 70 protein 8 (HSPA8), and are chiefly internalized into cells through clathrin-mediated endocytosis with concomitant clathrin heavy chain (CLTC) adsorption. Therefore, this work provides new insights and research strategies for the study of the biological effects caused by NPs.

Orange-derived extracellular vesicles nanodrugs for efficient treatment of ovarian cancer assisted by transcytosis effect

Extracellular vesicles (EVs) have recently received much attention about the application of drug carriers due to their desirable properties such as nano-size, biocompatibility, and high stability. Herein, we demonstrate orange-derived extracellular vesicles (OEV) nanodrugs (DN@OEV) by modifying cRGD-targeted doxorubicin (DOX) nanoparticles (DN) onto the surface of OEV, enabling significantly enhancing tumor accumulation and penetration, thereby efficiently inhibiting the growth of ovarian cancer. The obtained DN@OEV enabled to inducement of greater transcytosis capability in ovarian cancer cells, which presented the average above 10-fold transcytosis effect compared with individual DN. It was found that DN@OEV could trigger receptor-mediated endocytosis to promote early endosome/recycling endosomes pathway for exocytosis and simultaneously reduce degradation in the early endosomes-late endosomes-lysosome pathway, thereby inducing the enhanced transcytosis. In particular, the zombie mouse model bearing orthotopic ovarian cancer further validated DN@OEV presented high accumulation and penetration in tumor tissue by the transcytosis process. Our study indicated the strategy in enhancing transcytosis has significant implications for improving the therapeutic efficacy of the drug delivery system.

Local problems need global solutions: The metabolic needs of regenerating organisms

The vast majority of species that belong to the plant or animal kingdom evolved with two main strategies to counter tissue damage-scar formation and regeneration. Whereas scar formation provides a fast and cost-effective repair to exit life-threatening conditions, complete tissue regeneration is time-consuming and requires vast resources to reinstall functionality of affected organs or structures. Local environments in wound healing are widely studied and findings have provided important biomedical applications. Less well understood are organismic physiological parameters and signalling circuits essential to maintain effective tissue repair. Here, we review accumulated evidence that positions the interplay of local and systemic changes in metabolism as essential variables modulating the injury response. We particularly emphasise the role of lipids and lipid-like molecules as significant components long overlooked.

Microtubule Targeting Agents in Disease: Classic Drugs, Novel Roles

Microtubule-targeting agents (MTAs) represent one of the most successful first-line therapies prescribed for cancer treatment. They interfere with microtubule (MT) dynamics by either stabilizing or destabilizing MTs, and in culture, they are believed to kill cells via apoptosis after eliciting mitotic arrest, among other mechanisms. This classical view of MTA therapies persisted for many years. However, the limited success of drugs specifically targeting mitotic proteins, and the slow growing rate of most human tumors forces a reevaluation of the mechanism of action of MTAs. Studies from the last decade suggest that the killing efficiency of MTAs arises from a combination of interphase and mitotic effects. Moreover, MTs have also been implicated in other therapeutically relevant activities, such as decreasing angiogenesis, blocking cell migration, reducing metastasis, and activating innate immunity to promote proinflammatory responses. Two key problems associated with MTA therapy are acquired drug resistance and systemic toxicity. Accordingly, novel and effective MTAs are being designed with an eye toward reducing toxicity without compromising efficacy or promoting resistance. Here, we will review the mechanism of action of MTAs, the signaling pathways they affect, their impact on cancer and other illnesses, and the promising new therapeutic applications of these classic drugs.

Amelioration of Diabetic Nephropathy by Targeting Autophagy via Rapamycin or Fasting: Relation to Cell Apoptosis/Survival

Autophagy has been demonstrated to have a beneficial effect on diabetic nephropathy (DN). Rapamycin, an inhibitor of mTOR, was shown to stimulate β-cell autophagy. However, its effects on preventing or ameliorating DN is unclear, and its effects are worth studying. As fasting is now an attractive protective strategy, we aim to compare its effect to rapamycin effects on pancreatic and renal cells. Twenty-eight adult male Wistar Albino rats were randomly divided into four groups, using streptozotocin (STZ) to induce diabetes mellitus (DM). Autophagy was induced by two ways; rapamycin or fasting. The extent of autophagy and apoptosis were investigated by measuring the level of LC3B and p53 proteins, respectively, in pancreatic and kidney tissues using Western blotting (WB) technique and imaging the renal cells under transmission electron microscope. The efflux transporter P-glycoprotein was quantified by WB as well. Rapamycin-induced autophagy occurred concurrently with apoptosis. On the other hand, fasting supported P-glycoprotein recovery and renal cell survival together with disabling β-cells apoptosis. In conclusion, this study provides a potential link between rapamycin or fasting for the cross-regulation of apoptosis and autophagy in the setting of cell stress as DN. Unlike rapamycin, fasting enhanced the active expression of ABCB1 efflux protein, providing insights on the potential ameliorative effects of fasting in DN that require further elucidation.

Endocytosis of abiotic nanomaterials and nanobiovectors: Inhibition of membrane trafficking

Humans are exposed to nanoscopical nanobiovectors (e.g. coronavirus SARS-CoV-2) as well as abiotic metal/carbon-based nanomaterials that enter cells serendipitously or intentionally. Understanding the interactions of cell membranes with these abiotic and biotic nanostructures will facilitate scientists to design better functional nanomaterials for biomedical applications. Such knowledge will also provide important clues for the control of viral infections and the treatment of virus-induced infectious diseases. In the present review, the mechanisms of endocytosis are reviewed in the context of how nanomaterials are uptaken into cells. This is followed by a detailed discussion of the attributes of man-made nanomaterials (e.g. size, shape, surface functional groups and elasticity) that affect endocytosis, as well as the different human cell types that participate in the endocytosis of nanomaterials. Readers are then introduced to the concept of viruses as nature-derived nanoparticles. The mechanisms in which different classes of viruses interact with various cell types to gain entry into the human body are reviewed with examples published over the last five years. These basic tenets will enable the avid reader to design advanced drug delivery and gene transfer nanoplatforms that harness the knowledge acquired from endocytosis to improve their biomedical efficacy. The review winds up with a discussion on the hurdles to be addressed in mimicking the natural mechanisms of endocytosis in nanomaterials design.

Lymphocystis Disease Virus (Iridoviridae) Enters Flounder (Paralichthys olivaceus) Gill Cells via a Caveolae-Mediated Endocytosis Mechanism Facilitated by Viral Receptors

In previous research, voltage-dependent anion channel protein 2 (VDAC2) and the receptor of activated protein C kinase 1 (RACK1) in flounder (Paralichthys olivaceus) were confirmed as functional receptors for lymphocystis disease virus (LCDV) entry; however, the underlying mechanism of VDAC2- and RACK1-mediated LCDV entry remains unclear. In this study, we elucidated the endocytosis pathway of LCDV entry into flounder gill (FG) cells by treatment with specific inhibitory agents, siRNAs, and co-localization analysis. LCDV entry was significantly inhibited by the disruption of caveolae-mediated endocytosis, dynamin, and microtubules, and the knockdown of caveoline-1 and dynamin expression, but was not inhibited by the disruption of clathrin-mediated endocytosis, micropinocytosis, or low-pH conditions. The disruption of caveolae-mediated and clathrin-mediated endocytosis was verified by the internalization of cholera toxin subunit B (CTB) and transferrin, respectively. Confocal immunofluorescence assay demonstrated that LCDV was co-localized with VDAC2 and RACK1, CTB was co-localized with VDAC2 and RACK1 and partially with LCDV, but transferrin was not co-localized with LCDV, VDAC2, or RACK1, indicating that LCDV utilized the same pathway as CTB, i.e., caveolae-mediated endocytosis. This was different from the pathway of transferrin, which used clathrin-mediated endocytosis. Furthermore, caveolin-1 was co-localized with LCDV, VDAC2, and RACK1, suggesting that caveolin-1 was involved in LCDV entry. These results revealed for the first time that LCDV entered into FG cells via caveolae-mediated endocytosis facilitated by VDAC2 and RACK1 receptors, relying on dynamin and microtubules in a pH-independent manner, which provided new insight into the molecular mechanisms of LCDV entry and potential for the development of antiviral agents, expanding our understanding of iridovirus infection.

Exosomes from mesenchymal stromal cells reduce murine colonic inflammation via a macrophage-dependent mechanism

Conventional treatments for inflammatory bowel disease (IBD) have multiple potential side effects. Therefore, alternative treatments are desperately needed. This work demonstrated that systemic administration of exosomes from human bone marrow-derived mesenchymal stromal cells (MSC-Exos) substantially mitigated colitis in various models of IBD. MSC-Exos treatment downregulated inflammatory responses, maintained intestinal barrier integrity, and polarized M2b macrophages but did not favor intestinal fibrosis. Mechanistically, infused MSC-Exos acted mainly on colonic macrophages, and macrophages from colitic colons acquired obvious resistance to inflammatory restimulation when prepared from mice treated with MSC-Exos versus untreated mice. The beneficial effect of MSC-Exos was blocked by macrophage depletion. Also, the induction of IL-10 production from macrophages was partially involved in the beneficial effect of MSC-Exos. MSC-Exos were enriched in proteins involved in regulating multiple biological processes associated with the anticolitic benefit of MSC-Exos. Particularly, metallothionein-2 in MSC-Exos was required for the suppression of inflammatory responses. Taken together, MSC-Exos are critical regulators of inflammatory responses and may be promising candidates for IBD treatment.

Bovine endometrium responds differentially to age-matched short and long conceptuses†

This study combined in vitro production of bovine blastocysts, multiple embryo transfer techniques, and a conceptus-endometrial explant co-culture system to test the hypothesis that bovine endometrium exposed to long vs. short day 15 conceptuses would exhibit a different transcriptome profile reflective of potential for successful pregnancy establishment. Bovine endometrial explants collected at the late luteal stage of the estrous cycle were cultured in RPMI medium for 6 h with nothing (control), 100 ng/mL recombinant ovine interferon tau (IFNT), a long day 15 conceptus, or a short day 15 conceptus. Transcriptional profiling of the endometrial explants found that exposure of endometrium to IFNT, long conceptuses, or short conceptuses altered (P < 0.05) expression of 491, 498, and 230 transcripts, respectively, compared to the control. Further analysis revealed three categories of differentially expressed genes (DEG): (i) commonly responsive to exposure to IFNT and conceptuses, irrespective of size (n = 223); (ii) commonly responsive to IFNT and long conceptuses only (n = 168); and genes induced by the presence of a conceptus but independent of IFNT (n = 108). Of those 108 genes, 101 were exclusively induced by long conceptuses and functional analysis revealed that regulation of molecular function, magnesium-ion transmembrane transport, and clathrin coat assembly were the principal gene ontologies associated with these DEG. In conclusion, bovine endometrium responds differently to age-matched conceptuses of varying size in both an IFNT-dependent and -independent manner, which may be reflective of the likelihood of successful pregnancy establishment.

Early endosome as a pathogenic target for antiphosphatidylethanolamine antibodies

Phosphatidylethanolamine (PE) is a major phospholipid species with important roles in membrane trafficking and reorganization. Accumulating clinical data indicate that the presence of circulating antibodies against PE is positively correlated with the symptoms of antiphospholipid syndromes (APS), including thrombosis and repeated pregnancy loss. However, PE is generally sequestered inside a normal resting cell, and the mechanism by which circulating anti-PE antibodies access cellular PE remains unknown. The studies presented here were conducted with synthetic PE-binding agents, plasma samples from patients with anti-PE autoimmunity, and purified anti-PE antibodies. The results suggest that the cellular vulnerability to anti-PE antibodies may be mediated by the binding of PE molecules in the membrane of the early endosome. Endosomal PE binding led to functional changes in endothelial cells, including declines in proliferation and increases in the production of reactive oxygen species, as well as the expression of inflammatory molecules. Collectively, our findings provide insight into the etiology of anti-PE autoimmunity and, because endosomes are of central importance in almost all types of cells, could have important implications for a wide range of biological processes.

GAPDH binds Akt to facilitate cargo transport in the early secretory pathway

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) undergoes numerous post-translational modifications, which impart new function and influence intracellular location. For example, atypical PKC ι/λ phosphorylates GAPDH that locates to vesicular tubular clusters and is required for retrograde membrane trafficking in the early secretory pathway. GAPDH is also required in the endocytic pathway; substitution of Pro²³⁴ to Ser (Pro²³⁴Ser) rendered CHO cells defective in endocytosis. To determine if GAPDH (Pro²³⁴Ser) could inhibit endoplasmic reticulum to Golgi trafficking, we introduced the recombinant mutant enzyme into several biochemical and morphological transport assays. The mutant protein efficiently blocked vesicular stomatitis virus-G protein transport. Because GAPDH binds to microtubules (MTs), we evaluated MT binding and MT intracellular distribution in the presence of the mutant. Although these properties were not changed relative to wild-type, GAPDH (Pro²³⁴Ser) altered Golgi complex morphology. We determined that the GAPDH point mutation disrupted association between the enzyme and the serine/threonine kinase Akt. Interestingly Rab1, which functions in anterograde-directed trafficking, stimulates GAPDH-Akt association with membranes in a quantitative binding assay. In contrast, Rab2 does not stimulate GAPDH-Akt membrane binding but instead recruits GAPDH-aPKC. We propose a mechanism whereby the association of GAPDH with Akt or with aPKC serves as a switch to discriminate between anterograde directed cargo and recycling cargo retrieved back to the ER, respectively.

Preparing the lethal hit: interplay between exo- and endocytic pathways in cytotoxic T lymphocytes

Cytotoxic T lymphocytes patrol our body in search for infected cells which they kill through the release of cytotoxic substances contained in cytotoxic granules. The fusion of cytotoxic granules occurs at a specially formed contact site, the immunological synapse, and is tightly controlled to ensure specificity. In this review, we discuss the contribution of two intracellular compartments, endosomes and cytotoxic granules, to the formation, function and disassembly of the immunological synapse. We highlight a recently proposed sequential process of fusion events at the IS upon target cell recognition. First, recycling endosomes fuse with the plasma membrane to deliver cargo required for the docking of cytotoxic granules. Second, cytotoxic granules arrive and fuse upon docking in a SNARE-dependent manner. Following fusion, membrane components of the cytotoxic granule are retrieved through endocytosis to ensure the fast, efficient serial killing of target cells that is characteristic of cytotoxic T lymphocytes.

ICAM-1 Binding Rhinoviruses A89 and B14 Uncoat in Different Endosomal Compartments

Human rhinovirus A89 (HRV-A89) and HRV-B14 bind to and are internalized by intercellular adhesion molecule 1 (ICAM-1); as demonstrated earlier, the RNA genome of HRV-B14 penetrates into the cytoplasm from endosomal compartments of the lysosomal pathway. Here, we show by immunofluorescence microscopy that HRV-A89 but not HRV-B14 colocalizes with transferrin in the endocytic recycling compartment (ERC). Applying drugs differentially interfering with endosomal recycling and with the pathway to lysosomes, we demonstrate that these two major-group HRVs productively uncoat in distinct endosomal compartments. Overexpression of constitutively active (Rab11-GTP) and dominant negative (Rab11-GDP) mutants revealed that uncoating of HRV-A89 depends on functional Rab11. Thus, two ICAM-1 binding HRVs are routed into distinct endosomal compartments for productive uncoating.

IMPORTANCE

Based on similarity of their RNA genomic sequences, the more than 150 currently known common cold virus serotypes were classified as species A, B, and C. The majority of HRV-A viruses and all HRV-B viruses use ICAM-1 for cell attachment and entry. Our results highlight important differences of two ICAM-1 binding HRVs with respect to their intracellular trafficking and productive uncoating; they demonstrate that serotypes belonging to species A and B, but entering the cell via the same receptors, direct the endocytosis machinery to ferry them along distinct pathways toward different endocytic compartments for uncoating.

Binding, internalization and fate of Huntingtin Exon1 fibrillar assemblies in mitotic and nonmitotic neuroblastoma cells

AIMS

The aggregation of Huntingtin (HTT) protein and of its moiety encoded by its Exon1 (HTTExon1) into fibrillar structures inside neurons is the molecular hallmark of Huntington's disease. Prion-like transmission of these aggregates between cells has been demonstrated. The cell-to-cell transmission mechanisms of these protein aggregates and the susceptibility of different kinds of neuronal cells to these toxic assemblies still need assessment.

METHODS

Here, we documented the binding to and internalization by differentiated and undifferentiated neuroblastoma cells of exogenous fibrillar HTTExon1 and polyglutamine (polyQ) polypeptides containing the same number of glutamines. We assessed the contribution of endocytosis to fibrillar HTTExon1 uptake, their intracellular localization and fate.

RESULTS

We observed that undifferentiated neuroblastoma cells were more susceptible to fibrillar HTTExon1 and polyQ than their differentiated counterparts. Furthermore, we demonstrated that exogenous HTTExon1 aggregates are mainly taken up by endocytosis and directed to lysosomal compartments in both mitotic and quiescent cells.

CONCLUSIONS

These data suggest that the rates of endocytic processes that differ in mitotic and quiescent cells strongly impact the uptake of exogenous HTTExon1 and polyQ fibrils. This may be either the consequence of distinct metabolisms or distributions of specific protein partners for amyloid-like assemblies at the surface of highly dividing versus quiescent cells. Our results highlight the importance of endocytic processes in the internalization of exogenous HTTExon1 fibrils and suggest that a proportion of those assemblies reach the cytosol where they can amplify by recruiting the endogenous protein after escaping, by yet an unknown process, from the endo-lysosomal compartments.