The intracellular trafficking pathway of transferrin

Aptamer-Targeted Dendrimersomes Assembled from Azido-Modified Janus Dendrimers "Clicked" to DNA

Amphiphilic Janus dendrimers (JDs), synthetic alternatives to lipids, have the potential to expand the scope of nanocarrier delivery systems. JDs self-assemble into vesicles called dendrimersomes, encapsulate both hydrophobic cargo and nucleic acids, and demonstrate enhanced stability in comparison to lipid nanoparticles (LNPs). Here, we report the ability to enhance the cellular uptake of Janus dendrimersomes using DNA aptamers. Azido-modified JDs were synthesized and conjugated to alkyne-modified DNAs using copper-catalyzed azide alkyne cycloaddition. DNA-functionalized JDs form nanometer-sized dendrimersomes in aqueous solution via thin film hydration. These vesicles, now displaying short DNAs, are then hybridized to transferrin receptor binding DNA aptamers. Aptamer-targeted dendrimersomes show improved cellular uptake as compared to control vesicles via fluorescence microscopy and flow cytometry. This work demonstrates the versatility of using click chemistry to conjugate functionalized JDs with biologically relevant molecules and the feasibility of targeting DNA-modified dendrimersomes for drug delivery applications.

The proteasome modulates endocytosis specifically in glomerular cells to promote kidney filtration

Kidney filtration is ensured by the interaction of podocytes, endothelial and mesangial cells. Immunoglobulin accumulation at the filtration barrier is pathognomonic for glomerular injury. The mechanisms that regulate filter permeability are unknown. Here, we identify a pivotal role for the proteasome in a specific cell type. Combining genetic and inhibitor-based human, pig, mouse, and Drosophila models we demonstrate that the proteasome maintains filtration barrier integrity, with podocytes requiring the constitutive and glomerular endothelial cells the immunoproteasomal activity. Endothelial immunoproteasome deficiency as well as proteasome inhibition disrupt the filtration barrier in mice, resulting in pathologic immunoglobulin deposition. Mechanistically, we observe reduced endocytic activity, which leads to altered membrane recycling and endocytic receptor turnover. This work expands the concept of the (immuno)proteasome as a control protease orchestrating protein degradation and antigen presentation and endocytosis, providing new therapeutic targets to treat disease-associated glomerular protein accumulations.

A paintbrush for delivery of nanoparticles and molecules to live cells with precise spatiotemporal control

Delivery of very small amounts of reagents to the near-field of cells with micrometer spatial precision and millisecond time resolution is currently out of reach. Here we present μkiss as a micropipette-based scheme for brushing a layer of small molecules and nanoparticles onto the live cell membrane from a subfemtoliter confined volume of a perfusion flow. We characterize our system through both experiments and modeling, and find excellent agreement. We demonstrate several applications that benefit from a controlled brush delivery, such as a direct means to quantify local and long-range membrane mobility and organization as well as dynamical probing of intercellular force signaling.

DMT1-dependent endosome-mitochondria interactions regulate mitochondrial iron translocation and metastatic outgrowth

Transient early endosome (EE)-mitochondria interactions can mediate mitochondrial iron translocation, but the associated mechanisms are still elusive. We showed that Divalent Metal Transporter 1 (DMT1) sustains mitochondrial iron translocation via EE-mitochondria interactions in triple-negative MDA-MB-231, but not in luminal A T47D breast cancer cells. DMT1 silencing increases labile iron pool (LIP) levels and activates PINK1/Parkin-dependent mitophagy in MDA-MB-231 cells. Mitochondrial bioenergetics and the iron-associated protein profile were altered by DMT1 silencing and rescued by DMT1 re-expression. Transcriptomic profiles upon DMT1 silencing are strikingly different between 2D and 3D culture conditions, suggesting that the environment context is crucial for the DMT1 knockout phenotype observed in MDA-MB-231 cells. Lastly, in vivo lung metastasis assay revealed that DMT1 silencing promoted the outgrowth of lung metastatic nodules in both human and murine models of triple-negative breast cancer cells. These findings reveal a DMT1-dependent pathway connecting EE-mitochondria interactions to mitochondrial iron translocation and metastatic fitness of breast cancer cells.

Two in one: the emerging concept of bifunctional antibodies

Therapeutic antibodies have become indispensable for treating a wide range of diseases, and their significance in drug discovery has expanded considerably over the past few decades. Bifunctional antibodies are now emerging as a promising new drug modality to address previously unmet needs in antibody therapeutics. Distinct from traditional antibodies that operate through an 'occupancy-based' inhibition mechanism, these innovative molecules recruit the protein of interest to a 'biological effector,' initiating specific downstream consequences such as targeted protein degradation or posttranslational modifications. In this review, we emphasize the potential of bifunctional antibodies to tackle diverse biomedical challenges.

Cancer Cell Targeting Via Selective Transferrin Receptor Labeling Using Protein-Derived Carbon Dots

Carbon dot (CD) nanoparticles offer tremendous advantages as fluorescent probes in bioimaging and biosensing; however, they lack specific affinity for biomolecules, limiting their practical applications in selective targeting. Nanoparticles with intrinsic affinity for a target have applications in imaging, cytometry, therapeutics, etc. Toward that end, we report the transferrin receptor (CD71) targeting CDs, synthesized for the first time. The formation of these particles is truly groundbreaking, as direct tuning of nanoparticle affinity was achieved by simple and careful precursor selection of a protein, which has the targeting characteristic of interest. We hypothesized that the retention of the original protein's peptides on the nanoparticle surface provides the CDs with some of the function of the precursor protein, enabling selective binding to the protein's receptor. This was confirmed with FTIR (Fourier transform infrared) data and subsequent affinity-based cell assays. These transferrin (Tf)-derived CDs have been shown to possess an affinity for CD71, a cancer biomarker that is ubiquitously expressed in nearly every cancer cell line due to its central role mediating the uptake of cellular iron. The CDs were tested using the human leukemia cell line HL60 and demonstrated the selective targeting of CD71 and specific triggering of transferrin-mediated endocytosis via clathrin-coated pits. The particle characterization results reflect a carbon-based nanoparticle with bright violet fluorescence and 7.9% quantum yield in aqueous solution. These unpresented CDs proved to retain the functional properties of the precursor protein. Indicating that this process can be repeated for other disease biomarkers for applications ranging from biosensing and diagnostic bioimaging to targeted therapeutics.

Recent Advances in Delivery of Peptide and Protein Therapeutics to the Brain

The classes of neuropharmaceuticals known as proteins and peptides serve as diagnostic tools and are involved in specific communication in the peripheral and central nervous systems. However, due to tight junctions resembling epithelial cells found in the blood-brain barrier (BBB) in vivo, they are typically excluded from transport from the blood to the brain. The drugs having molecular weight of less than 400 Dalton are able to cross the BBB via lipid-mediated free diffusion. However, large molecule therapeutics are devoid of these characteristics. As an alternative, these substances may be carried via chimeric peptide drug delivery systems, and assist in transcytosis through BBB with the aid of linker strategies. With their recent developments, several forms of nanoparticles, including poly (ethylene glycol)-poly(ε-caprolactone) copolymers, nanogels, liposomes, nanostructured lipid carriers, poly (D, L-lactide-co-glycolide) nanoparticles, chitosan, and solid lipid nanoparticles, have also been considered for their therapeutic applications. Moreover, the necessity for physiologic optimization of current drug delivery methods and their carriers to deliver therapeutic doses of medication into the brain for the treatment of various neurologic illnesses has also been emphasized. Therapeutic use of proteins and peptides has no neuroprotective impact in the absence of all these methods. Each tactic, however, has unique drawbacks and considerations. In this review, we discuss different drug delivery methods for therapeutic distribution of pharmaceuticals, primarily neuroproteins and neuropeptides, through endothelial capillaries via blood-brain barrier. Finally, we have also discussed the challenges and future perspective of protein and peptide therapeutics delivery to the brain. SIGNIFICANCE STATEMENT: Very few reports on the delivery of therapeutic protein and peptide nanoformulations are available in the literature. Herein, we attempted to discuss these nanoformulations of protein and peptide therapeutics used to treat brain diseases.

p97/VCP Promotes the Recycling of Endocytic Cargo

The endocytic pathway is of central importance for eukaryotic cells, as it enables uptake of extracellular materials, membrane protein quality control and recycling, as well as modulation of receptor signaling. While the ATPase p97 (VCP, Cdc48) has been found to be involved in the fusion of early endosomes and endolysosomal degradation, its role in endocytic trafficking is still incompletely characterized. Here, we identify myoferlin (MYOF), a ferlin family member with functions in membrane trafficking and repair, as a hitherto unknown p97 interactor. The interaction of MYOF with p97 depends on the cofactor PLAA previously linked to endosomal sorting. Besides PLAA, shared interactors of p97 and MYOF comprise several proteins involved in endosomal recycling pathways, including Rab11, Rab14, and the transferrin receptor CD71. Accordingly, a fraction of p97 and PLAA localizes to MYOF-, Rab11-, and Rab14-positive endosomal compartments. Pharmacological inhibition of p97 delays transferrin recycling, indicating that p97 promotes not only the lysosomal degradation, but also the recycling of endocytic cargo.

Molecular Mechanisms of Ferroptosis and Its Role in Viral Pathogenesis

Ferroptosis is a novelty form of regulated cell death, and it is mainly characterized by iron accumulation and lipid peroxidation in the cells. Its underlying mechanism is related to the amino acid, iron, and lipid metabolisms. During viral infection, pathogenic microorganisms have evolved to interfere with ferroptosis, and ferroptosis is often manipulated by viruses to regulate host cell servicing for viral reproduction. Therefore, this review provides a comprehensive overview of the mechanisms underlying ferroptosis, elucidates the intricate signaling pathways involved, and explores the pivotal role of ferroptosis in the pathogenesis of viral infections. By enhancing our understanding of ferroptosis, novel therapeutic strategies can be devised to effectively prevent and treat diseases associated with this process. Furthermore, unraveling the developmental mechanisms through which viral infections exploit ferroptosis will facilitate development of innovative antiviral agents.

Neuron-specific gene NSG1 binds to and positively regulates sortilin ectodomain shedding via a metalloproteinase-dependent mechanism

Increasing evidence suggests that aberrant regulation of sortilin ectodomain shedding can contribute to amyloid-β pathology and frontotemporal dementia, although the mechanism by which this occurs has not been elucidated. Here, we probed for novel binding partners of sortilin using multiple and complementary approaches and identified two proteins of the neuron-specific gene (NSG) family, NSG1 and NSG2, that physically interact and colocalize with sortilin. We show both NSG1 and NSG2 induce subcellular redistribution of sortilin to NSG1- and NSG2-enriched compartments. However, using cell surface biotinylation, we found only NSG1 reduced sortilin cell surface expression, which caused significant reductions in uptake of progranulin, a molecular determinant for frontotemporal dementia. In contrast, we demonstrate NSG2 has no effect on sortilin cell surface abundance or progranulin uptake, suggesting specificity for NSG1 in the regulation of sortilin cell surface expression. Using metalloproteinase inhibitors and A disintegrin and metalloproteinase 10 KO cells, we further show that NSG1-dependent reduction of cell surface sortilin occurred via proteolytic processing by A disintegrin and metalloproteinase 10 with a concomitant increase in shedding of sortilin ectodomain to the extracellular space. This represents a novel regulatory mechanism for sortilin ectodomain shedding that is regulated in a neuron-specific manner. Furthermore, this finding has implications for the development of strategies for brain-specific regulation of sortilin and possibly sortilin-driven pathologies.

Amelioration effects of the soybean lecithin-gallic acid complex on iron-overload-induced oxidative stress and liver damage in C57BL/6J mice

CONTEXT

Gallic acid (GA) and lecithin showed important roles in antioxidant and drug delivery, respectively. A complex synthesized from GA and soybean lecithin (SL-GAC), significantly improved bioavailability of GA and pharmacological activities. However, the antioxidant activity of SL-GAC and its effect on iron-overload-induced liver injury remains unexplored.

OBJECTIVE

This study investigates the antioxidant properties of SL-GAC in vitro and in mice, and its remediating effects against liver injury by iron-overloaded.

MATERIALS AND METHODS

In vitro, free radical scavenging activity, lipid peroxidation inhibition, and ferric reducing power of SL-GAC were measured by absorbance photometry. In vivo, C57BL/6J mice were randomized into 4 groups: control, iron-overloaded, iron-overloaded + deferoxamine, and iron-overloaded + SL-GAC. Treatments with deferoxamine (150 mg/kg/intraperitioneally) and SL-GAC (200 mg/kg/orally) were given to the desired groups for 12 weeks, daily. Iron levels, oxidative stress, and biochemical parameters were determined by histopathological examination and molecular biological techniques.

RESULTS

In vitro, SL-GAC showed DPPH and ABTS free radicals scavenging activity with IC₅₀ values equal to 24.92 and 128.36 μg/mL, respectively. In C57BL/6J mice, SL-GAC significantly reduced the levels of serum iron (22.82%), liver iron (50.29%), aspartate transaminase (25.97%), alanine transaminase (38.07%), gamma glutamyl transferase (42.11%), malondialdehyde (19.82%), total cholesterol (45.96%), triglyceride (34.90%), ferritin light chain (18.51%) and transferrin receptor (27.39%), while up-regulated the levels of superoxide dismutase (24.69%), and glutathione (11.91%).

CONCLUSIONS

These findings encourage the use of SL-GAC to treat liver injury induced by iron-overloaded. Further in vivo and in vitro studies are needed to validate its potential in clinical medicine.

Infection of liver sinusoidal endothelial cells with Muromegalovirus muridbeta1 involves binding to neuropilin-1 and is dynamin-dependent

Liver sinusoidal endothelial cells (LSEC) are scavenger cells with a remarkably high capacity for clearance of several blood-borne macromolecules and nanoparticles, including some viruses. Endocytosis in LSEC is mainly via the clathrin-coated pit mediated route, which is dynamin-dependent. LSEC can also be a site of infection and latency of betaherpesvirus, but mode of virus entry into these cells has not yet been described. In this study we have investigated the role of dynamin in the early stage of muromegalovirus muridbeta1 (MuHV-1, murid betaherpesvirus 1, murine cytomegalovirus) infection in mouse LSECs. LSEC cultures were freshly prepared from C57Bl/6JRj mouse liver. We first examined dose- and time-dependent effects of two dynamin-inhibitors, dynasore and MitMAB, on cell viability, morphology, and endocytosis of model ligands via different LSEC scavenger receptors to establish a protocol for dynamin-inhibition studies in these primary cells. LSECs were challenged with MuHV-1 (MOI 0.2) ± dynamin inhibitors for 1h, then without inhibitors and virus for 11h, and nuclear expression of MuHV-1 immediate early antigen (IE1) measured by immune fluorescence. MuHV-1 efficiently infected LSECs in vitro. Infection was significantly and independently inhibited by dynasore and MitMAB, which block dynamin function via different mechanisms, suggesting that initial steps of MuHV-1 infection is dynamin-dependent in LSECs. Infection was also reduced in the presence of monensin which inhibits acidification of endosomes. Furthermore, competitive binding studies with a neuropilin-1 antibody blocked LSEC infection. This suggests that MuHV-1 infection in mouse LSECs involves virus binding to neuropilin-1 and occurs via endocytosis.

Hypoxia Modulates Cellular Endocytic Pathways and Organelles with Enhanced Cell Migration and 3D Cell Invasion

Hypoxia, a decrease in cellular or tissue level oxygen content, is characteristic of most tumors and has been shown to drive cancer progression by altering multiple subcellular processes. We hypothesized that the cancer cells in a hypoxic environment might have slower proliferation rates and increased invasion and migration rates with altered endocytosis compared to the cancer cells in the periphery of the tumor mass that experience normoxic conditions. We induced cellular hypoxia by exposing cells to cobalt chloride, a chemical hypoxic mimicking agent. This study measured the effect of hypoxia on cell proliferation, migration, and invasion. Uptake of fluorescently labeled transferrin, galectin3, and dextran that undergo endocytosis through major endocytic pathways (Clathrin-mediated pathway (CME), Clathrin-independent pathway (CIE), Fluid phase endocytosis (FPE)) were analyzed during hypoxia. Also, the organelle changes associated with hypoxia were studied with organelle trackers. We found that the proliferation rate decreased, and the migration and invasion rate increased in cancer cells in hypoxic conditions compared to normoxic cancer cells. A short hypoxic exposure increased galectin3 uptake in hypoxic cancer cells, but a prolonged hypoxic exposure decreased clathrin-independent endocytic uptake of galectin 3. Subcellular organelles, such as mitochondria, increased to withstand the hypoxic stress, while other organelles, such as Endoplasmic reticulum (ER), were significantly decreased. These data suggest that hypoxia modulates cellular endocytic pathways with reduced proliferation and enhanced cell migration and invasion.

IgG and insulin enhance endocytosis in THP-1 cells via activation of phosphatidylinositol 3-kinase (PI3K)

Extracellular substances, including membrane-impermeable nutrients, are taken up by cells via endocytosis. Endocytosis is also an important pathway for antigen uptake by antigen-presenting cells such as monocytes, macrophages, dendritic cells, and B cells. In this study, we investigated the regulatory mechanism of endocytosis in THP-1 cells, a monocytic leukemia cell line. We analyzed the effect of IgG and insulin, which are abundant in the serum and play important roles in immunity and metabolism, respectively, on the endocytic activity in THP-1 cells. The results indicated that IgG and insulin enhance pinocytosis and phagocytosis via activation of phosphatidylinositol 3-kinase (PI3K). Our results suggest that IgG and insulin contribute to the maintenance of endocytic activity and are important for antigen presentation and nutrient uptake.

Comprehensive analysis of sex differences in the function and ultrastructure of hippocampal presynaptic terminals

Sex differences in the brain, encompassing variations in specific brain structures, size, cognitive function, and synaptic connections, have been identified across numerous species. While previous research has explored sex differences in postsynaptic structures, synaptic plasticity, and hippocampus-dependent functions, the hippocampal presynaptic terminals remain largely uninvestigated. The hippocampus is a critical structure responsible for multiple brain functions. This study examined presynaptic differences in cultured hippocampal neurons derived from male and female mice using a combination of biochemical assays, functional analyses measuring exocytosis and endocytosis of synaptic vesicle proteins, ultrastructural analyses via electron microscopy, and presynaptic Ca2+-specific optical probes. Our findings revealed that female neurons exhibited a higher number of synaptic vesicles at presynaptic terminals compared to male neurons. However, no significant differences were observed in presynaptic protein expression, presynaptic terminal ultrastructure, synaptic vesicle exocytosis and endocytosis, or presynaptic Ca2+ alterations between male and female neurons.

Loss of polarity regulators initiates gasdermin-E-mediated pyroptosis in syncytiotrophoblasts

The syncytiotrophoblast is a human epithelial cell that is bathed in maternal blood on the maternal-facing surface of the human placenta. It therefore acts as a barrier and exchange interface between the mother and fetus. Syncytiotrophoblast dysfunction is a feature of pregnancy pathologies, like preeclampsia. Dysfunctional syncytiotrophoblasts display a loss of microvilli, which is a marker of aberrant apical-basal polarization, but little data exist about the regulation of syncytiotrophoblast polarity. Atypical PKC isoforms are conserved polarity regulators. Thus, we hypothesized that aPKC isoforms regulate syncytiotrophoblast polarity. Using human placental explant culture and primary trophoblasts, we found that loss of aPKC activity or expression induces syncytiotrophoblast gasdermin-E-dependent pyroptosis, a form of programmed necrosis. We also establish that TNF-α induces an isoform-specific decrease in aPKC expression and gasdermin-E-dependent pyroptosis. Therefore, aPKCs are homeostatic regulators of the syncytiotrophoblast function and a pathogenically relevant pro-inflammatory cytokine leads to the induction of programmed necrosis at the maternal-fetal interface. Hence, our results have important implications for the pathobiology of placental disorders like preeclampsia.

A Comparison of Cellular Uptake Mechanisms, Delivery Efficacy, and Intracellular Fate between Liposomes and Extracellular Vesicles

A key aspect for successful drug delivery via lipid-based nanoparticles is their internalization in target cells. Two prominent examples of such drug delivery systems are artificial phospholipid-based carriers, such as liposomes, and their biological counterparts, the extracellular vesicles (EVs). Despite a wealth of literature, it remains unclear which mechanisms precisely orchestrate nanoparticle-mediated cargo delivery to recipient cells and the subsequent intracellular fate of therapeutic cargo. In this review, internalization mechanisms involved in the uptake of liposomes and EVs by recipient cells are evaluated, also exploring their intracellular fate after intracellular trafficking. Opportunities are highlighted to tweak these internalization mechanisms and intracellular fates to enhance the therapeutic efficacy of these drug delivery systems. Overall, literature to date shows that both liposomes and EVs are predominantly internalized through classical endocytosis mechanisms, sharing a common fate: accumulation inside lysosomes. Studies tackling the differences between liposomes and EVs, with respect to cellular uptake, intracellular delivery and therapy efficacy, remain scarce, despite its importance for the selection of an appropriate drug delivery system. In addition, further exploration of functionalization strategies of both liposomes and EVs represents an important avenue to pursue in order to control internalization and fate, thereby improving therapeutic efficacy.

Cardiac iron metabolism during aging - Role of inflammation and proteolysis

Iron is the most abundant trace element in the human body. Since iron can switch between its 2-valent and 3-valent form it is essential in various physiological processes such as energy production, proliferation or DNA synthesis. Especially high metabolic organs such as the heart rely on iron-associated iron-sulfur and heme proteins. However, due to switches in iron oxidation state, iron overload exhibits high toxicity through formation of reactive oxygen species, underlining the importance of balanced iron levels. Growing evidence demonstrates disturbance of this balance during aging. While age-associated cardiovascular diseases are often related to iron deficiency, in physiological aging cardiac iron accumulates. To understand these changes, we focused on inflammation and proteolysis, two hallmarks of aging, and their role in iron metabolism. Via the IL-6-hepcidin axis, inflammation and iron status are strongly connected often resulting in anemia accompanied by infiltration of macrophages. This tight connection between anemia and inflammation highlights the importance of the macrophage iron metabolism during inflammation. Age-related decrease in proteolytic activity additionally affects iron balance due to impaired degradation of iron metabolism proteins. Therefore, this review accentuates alterations in iron metabolism during aging with regards to inflammation and proteolysis to draw attention to their implications and associations.

Loss of miR-144/451 alleviates β-thalassemia by stimulating ULK1-mediated autophagy of free α-globin

Most cells can eliminate unstable or misfolded proteins through quality control mechanisms. In the inherited red blood cell disorder β-thalassemia, mutations in the β-globin gene (HBB) lead to a reduction in the corresponding protein and the accumulation of cytotoxic free α-globin, which causes maturation arrest and apoptosis of erythroid precursors and reductions in the lifespan of circulating red blood cells. We showed previously that excess α-globin is eliminated by Unc-51-like autophagy activating kinase 1 (ULK1)-dependent autophagy and that stimulating this pathway by systemic mammalian target of rapamycin complex 1 (mTORC1) inhibition alleviates β-thalassemia pathologies. We show here that disrupting the bicistronic microRNA gene miR-144/451 alleviates β-thalassemia by reducing mTORC1 activity and stimulating ULK1-mediated autophagy of free α-globin through 2 mechanisms. Loss of miR-451 upregulated its target messenger RNA, Cab39, which encodes a cofactor for LKB1, a serine-threonine kinase that phosphorylates and activates the central metabolic sensor adenosine monophosphate-activated protein kinase (AMPK). The resultant enhancement of LKB1 activity stimulated AMPK and its downstream effects, including repression of mTORC1 and direct activation of ULK1. In addition, loss of miR-144/451 inhibited the expression of erythroblast transferrin receptor 1, causing intracellular iron restriction, which has been shown to inhibit mTORC1, reduce free α-globin precipitates, and improve hematological indices in β-thalassemia. The beneficial effects of miR-144/451 loss in β-thalassemia were inhibited by the disruption of Cab39 or Ulk1 genes. Together, our findings link the severity of β-thalassemia to a highly expressed erythroid microRNA locus and a fundamental, metabolically regulated protein quality control pathway that is amenable to therapeutic manipulation.

Transferrin-Targeted Liposomes in Glioblastoma Therapy: A Review

Glioblastoma (GBM) is a highly aggressive brain tumor, and its treatment is further complicated by the high selectivity of the blood-brain barrier (BBB). The scientific community is urgently seeking innovative and effective therapeutic solutions. Liposomes are a promising new tool that has shown potential in addressing the limitations of chemotherapy, such as poor bioavailability and toxicity to healthy cells. However, passive targeting strategies based solely on the physicochemical properties of liposomes have proven ineffective due to a lack of tissue specificity. Accordingly, the upregulation of transferrin receptors (TfRs) in brain tissue has led to the development of TfR-targeted anticancer therapeutics. Currently, one of the most widely adopted methods for improving drug delivery in the treatment of GBM and other neurological disorders is the utilization of active targeting strategies that specifically target this receptor. In this review, we discuss the role of Tf-conjugated liposomes in GBM therapy and present some recent studies investigating the drug delivery efficiency of Tf-liposomes; in addition, we address some challenges currently facing this approach to treatment and present some potential improvement possibilities.

Application of In vitro transcytosis models to brain targeted biologics

The blood brain barrier (BBB) efficiently limits the penetration of biologics drugs from blood to brain. Establishment of an in vitro BBB model can facilitate screening of central nervous system (CNS) drug candidates and accelerate CNS drug development. Despite many established in vitro models, their application to biologics drug selection has been limited. Here, we report the evaluation of in vitro transcytosis of anti-human transferrin receptor (TfR) antibodies across human, cynomolgus and mouse species. We first evaluated human models including human cerebral microvascular endothelial cell line hCMEC/D3 and human colon epithelial cell line Caco-2 models. hCMEC/D3 model displayed low trans-epithelial electrical resistance (TEER), strong paracellular transport, and similar transcytosis of anti-TfR and control antibodies. In contrast, the Caco-2 model displayed high TEER value and low paracellular transport. Anti-hTfR antibodies demonstrated up to 70-fold better transcytosis compared to control IgG. Transcytosis of anti-hTfR.B1 antibody in Caco-2 model was dose-dependent and saturated at 3 μg/mL. Enhanced transcytosis of anti-hTfR.B1 was also observed in a monkey brain endothelial cell based (MBT) model. Importantly, anti-hTfR.B1 showed relatively high brain radioactivity concentration in a non-human primate positron emission tomography study indicating that the in vitro transcytosis from both Caco-2 and MBT models aligns with in vivo brain exposure. Typically, brain exposure of CNS targeted biologics is evaluated in mice. However, antibodies, such as the anti-human TfR antibodies, do not cross-react with the mouse target. Therefore, validation of a mouse in vitro transcytosis model is needed to better understand the in vitro in vivo correlation. Here, we performed transcytosis of anti-mouse TfR antibodies in mouse brain endothelial cell-based models, bEnd3 and the murine intestinal epithelial cell line mIEC. There is a good correlation between in vitro transcytosis of anti-mTfR antibodies and bispecifics in mIEC model and their mouse brain uptake. These data strengthen our confidence in the predictive power of the in vitro transcytosis models. Both mouse and human in vitro models will serve as important screening assays for brain targeted biologics selection in CNS drug development.

Polymer/Nanoceria Hybrid Polyplexes for Gene and Antioxidant Delivery

Various diseases, including cancers and inflammatory diseases, are characterized by a disruption of redox homeostasis, suggesting the need for synergistic treatments involving co-delivery of gene therapies and free radical scavengers. In this report, polyethylenimine (PEI), nanoceria (NC), and DNA were complexed to form nanoparticles providing simultaneous delivery of a gene and an antioxidant. NC was coated in citric acid to provide stable, 4 nm particles that electrostatically bound PEI/DNA polyplexes. The resulting ternary particles transfected HeLa cells with similar efficiency to that of ternary polyplexes comprising 15 kDa poly-l-α-glutamic acid/PEI/DNA while providing smaller particle sizes by more than 100 nm. NC/PEI/DNA polyplexes exhibited enhanced radical-scavenging activity compared to free NC, and oxidative stress from the superoxide-generating agent, menadione, could be completely reversed by the delivery of NC/PEI/DNA polyplexes. Transfection by NC/PEI/DNA polyplexes was demonstrated to occur efficiently through caveolin-mediated endocytosis and macropinocytosis. Co-delivery of genes encoding reactive oxygen species-scavenging proteins, transcription factors, growth factors, tumor suppressors, or anti-inflammatory genes with NC, therefore, may be a promising strategy in synergistic therapeutics.

Effects of the Natural Flavonoid Quercetin on Arenavirus Junín Infection

There is no specific chemotherapy approved for the treatment of pathogenic arenaviruses that cause severe hemorrhagic fever (HF) in the population of endemic regions in America and Africa. The present study reports the effects of the natural flavonoid quercetin (QUER) on the infection of A549 and Vero cells with Junín virus (JUNV), agent of the Argentine HF. By infectivity assays, a very effective dose-dependent reduction of JUNV multiplication was shown by cell pretreatment at 2-6 h prior to the infection at non-cytotoxic concentrations, with 50% effective concentration values in the range of 6.1-7.5 µg/mL. QUER was also active by post-infection treatment but with minor efficacy. Mechanistic studies indicated that QUER mainly affected the early steps of virus adsorption and internalization in the multiplication cycle of JUNV. Treatment with QUER blocked the phosphorylation of Akt without changes in the total protein expression, detected by Western blot, and the consequent perturbation of the PI3K/Akt pathway was also associated with the fluorescence redistribution from membrane to cytoplasm of TfR1, the cell receptor recognized by JUNV. Then, it appears that the cellular antiviral state, induced by QUER treatment, leads to the prevention of JUNV entry into the cell.

Characterization of K562 cells: uncovering novel chromosomes, assessing transferrin receptor expression, and probing pharmacological therapies

Human erythroleukemic K562 cells represent the prototypical cell culture model of chronic myeloid leukemia (CML). The cells are pseudo-triploid and positive for the Philadelphia chromosome. Therefore, K562 cells have been widely used for investigating the BCR/ABL1 oncogene and the tyrosine kinase inhibitor, imatinib-mesylate. Further, K562 cells overexpress transferrin receptors (TfR) and have been used as a model for targeting cytotoxic therapies, via receptor-mediated endocytosis. Here, we have characterized K562 cells focusing on the karyotype of cells in prolonged culture, regulation of expression of TfR in wildtype (WT) and doxorubicin-resistant cells, and responses to histone deacetylase inhibition (HDACi). Karyotype analysis indicates novel chromosomes and gene expression analysis suggests a shift of cultured K562 cells away from patient-derived leukemic cells. We confirm the high expression of TfR on K562 cells using immunofluorescence and cell-surface receptor binding radioassays. Importantly, high TfR expression is observed in patient-derived cells, and we highlight the persistent expression of TfR following doxorubicin acquired resistance. Epigenetic analysis indicates that permissive histone acetylation and methylation at the promoter region regulates the transcription of TfR in K562 cells. Finally, we show relatively high expression of HDAC enzymes in K562 cells and demonstrate the chemotoxic effects of HDACi, using the FDA-approved hydroxamic acid, vorinostat. Together with a description of morphology, infrared spectral analysis, and examination of metabolic properties, we provide a comprehensive characterization of K562 cells. Overall, K562 cell culture systems remain widely used for the investigation of novel therapeutics for CML, which is particularly important in cases of imatinib-mesylate resistance.

De novo missense variants in phosphatidylinositol kinase PIP5KIγ underlie a neurodevelopmental syndrome associated with altered phosphoinositide signaling

Phosphoinositides (PIs) are membrane phospholipids produced through the local activity of PI kinases and phosphatases that selectively add or remove phosphate groups from the inositol head group. PIs control membrane composition and play key roles in many cellular processes including actin dynamics, endosomal trafficking, autophagy, and nuclear functions. Mutations in phosphatidylinositol 4,5 bisphosphate [PI(4,5)P2] phosphatases cause a broad spectrum of neurodevelopmental disorders such as Lowe and Joubert syndromes and congenital muscular dystrophy with cataracts and intellectual disability, which are thus associated with increased levels of PI(4,5)P2. Here, we describe a neurodevelopmental disorder associated with an increase in the production of PI(4,5)P2 and with PI-signaling dysfunction. We identified three de novo heterozygous missense variants in PIP5K1C, which encodes an isoform of the phosphatidylinositol 4-phosphate 5-kinase (PIP5KIγ), in nine unrelated children exhibiting intellectual disability, developmental delay, acquired microcephaly, seizures, visual abnormalities, and dysmorphic features. We provide evidence that the PIP5K1C variants result in an increase of the endosomal PI(4,5)P2 pool, giving rise to ectopic recruitment of filamentous actin at early endosomes (EEs) that in turn causes dysfunction in EE trafficking. In addition, we generated an in vivo zebrafish model that recapitulates the disorder we describe with developmental defects affecting the forebrain, including the eyes, as well as craniofacial abnormalities, further demonstrating the pathogenic effect of the PIP5K1C variants.

Reconstitution of morphogen shuttling circuits

Developing tissues form spatial patterns by establishing concentration gradients of diffusible signaling proteins called morphogens. The bone morphogenetic protein (BMP) morphogen pathway uses a family of extracellular modulators to reshape signaling gradients by actively "shuttling" ligands to different locations. It has remained unclear what circuits are sufficient to enable shuttling, what other patterns they can generate, and whether shuttling is evolutionarily conserved. Here, using a synthetic, bottom-up approach, we compared the spatiotemporal dynamics of different extracellular circuits. Three proteins-Chordin, Twsg, and the BMP-1 protease-successfully displaced gradients by shuttling ligands away from the site of production. A mathematical model explained the different spatial dynamics of this and other circuits. Last, combining mammalian and Drosophila components in the same system suggests that shuttling is a conserved capability. Together, these results reveal principles through which extracellular circuits control the spatiotemporal dynamics of morphogen signaling.

An Alternative Mechanism of Subcellular Iron Uptake Deficiency in Cardiomyocytes

BACKGROUND

Systemic defects in intestinal iron absorption, circulation, and retention cause iron deficiency in 50% of patients with heart failure. Defective subcellular iron uptake mechanisms that are independent of systemic absorption are incompletely understood. The main intracellular route for iron uptake in cardiomyocytes is clathrin-mediated endocytosis.

METHODS

We investigated subcellular iron uptake mechanisms in patient-derived and CRISPR/Cas-edited induced pluripotent stem cell-derived cardiomyocytes as well as patient-derived heart tissue. We used an integrated platform of DIA-MA (mass spectrometry data-independent acquisition)-based proteomics and signaling pathway interrogation. We employed a genetic induced pluripotent stem cell model of 2 inherited mutations (TnT [troponin T]-R141W and TPM1 [tropomyosin 1]-L185F) that lead to dilated cardiomyopathy (DCM), a frequent cause of heart failure, to study the underlying molecular dysfunctions of DCM mutations.

RESULTS

We identified a druggable molecular pathomechanism of impaired subcellular iron deficiency that is independent of systemic iron metabolism. Clathrin-mediated endocytosis defects as well as impaired endosome distribution and cargo transfer were identified as a basis for subcellular iron deficiency in DCM-induced pluripotent stem cell-derived cardiomyocytes. The clathrin-mediated endocytosis defects were also confirmed in the hearts of patients with DCM with end-stage heart failure. Correction of the TPM1-L185F mutation in DCM patient-derived induced pluripotent stem cells, treatment with a peptide, Rho activator II, or iron supplementation rescued the molecular disease pathway and recovered contractility. Phenocopying the effects of the TPM1-L185F mutation into WT induced pluripotent stem cell-derived cardiomyocytes could be ameliorated by iron supplementation.

CONCLUSIONS

Our findings suggest that impaired endocytosis and cargo transport resulting in subcellular iron deficiency could be a relevant pathomechanism for patients with DCM carrying inherited mutations. Insight into this molecular mechanism may contribute to the development of treatment strategies and risk management in heart failure.

Affibody Molecules Intended for Receptor-Mediated Transcytosis via the Transferrin Receptor

The development of biologics for diseases affecting the central nervous system has been less successful compared to other disease areas, in part due to the challenge of delivering drugs to the brain. The most well-investigated and successful strategy for increasing brain uptake of biological drugs is using receptor-mediated transcytosis over the blood-brain barrier and, in particular, targeting the transferrin receptor-1 (TfR). Here, affibody molecules are selected for TfR using phage display technology. The two most interesting candidates demonstrated binding to human TfR, cross-reactivity to the murine orthologue, non-competitive binding with human transferrin, and binding to TfR-expressing brain endothelial cell lines. Single amino acid mutagenesis of the affibody molecules revealed the binding contribution of individual residues and was used to develop second-generation variants with improved properties. The second-generation variants were further analyzed and showed an ability for transcytosis in an in vitro transwell assay. The new TfR-specific affibody molecules have the potential for the development of small brain shuttles for increasing the uptake of various compounds to the central nervous system and thus warrant further investigations.

The endosomal-lysosomal system in ADC design and cancer therapy

INTRODUCTION

This discourse delves into the intricate connections between the endosomal-lysosomal system and antibody-drug conjugates (ADCs), shedding light on an essential yet less understood dimension of targeted therapy. While ADCs have revolutionized cancer treatment, resistance remains a formidable challenge, often involving diverse and overlapping mechanisms.

AREAS COVERED

This discourse highlights the roles of various components within the endosomal machinery, including Rab proteins, in ADC resistance development. It also explores how the transferrin-transferrin receptor and epidermal growth factor-epidermal growth factor receptor complexes, known for their roles in recycling and degradation process, respectively, can offer valuable insights for ADC design. Selected strategies to enhance lysosomal targeting are discussed, and potentially offer solutions to improve ADC efficacy.

EXPERT OPINION

By harnessing these different insights that connect ADCs with the endosomal-lysosomal system, the field may benefit to shape the next-generation of ADC design for increased efficacy and improved patient outcomes.

Targeted intracellular delivery of antitubercular bioactive(s) to Mtb infected macrophages via transferrin functionalized nanoliposomes

The packaging of antimicrobials/chemotherapeutics into nanoliposomes can enhance their activity while minimizing toxicity. However, their use is still limited owing to inefficient/inadequate loading strategies. Several bioactive(s) which are non ionizable, and poorly aqueous soluble cannot be easily encapsulated into aqueous core of liposomes by using conventional means. Such bioactive(s) however could be encapsulated in the liposomes by forming their water soluble molecular inclusion complex with cyclodextrins. In this study, we developed Rifampicin (RIF) - 2-hydroxylpropyl-β-cyclodextrin (HP-β-CD) molecular inclusion complex. The HP-β-CD-RIF complex interaction was assessed by using computational analysis (molecular modeling). The HP-β-CD-RIF complex and Isoniazid were co-loaded in the small unilamellar vesicles (SUVs). Further, the developed system was functionalized with transferrin, a targeting moiety. Transferrin functionalized SUVs (Tf-SUVs) could preferentially deliver their payload intracellularly in the endosomal compartment of macrophages. In in vitro study on infected Raw 264.7 macrophage cells revealed that the encapsulated bioactive(s) could eradicate the pathogen more efficiently than free bioactive(s). In vivo studies further revealed that the Tf-SUVs could accumulate and maintain intracellular bioactive(s) concentrations in macrophages. The study suggests Tf-SUVs as a promising module for targeted delivery of a drug combination with improved/optimal therapeutic index and effective clinical outcomes.

A PPIX-binding probe facilitates discovery of PPIX-induced cell death modulation by peroxiredoxin

While heme synthesis requires the formation of a potentially lethal intermediate, protoporphyrin IX (PPIX), surprisingly little is known about the mechanism of its toxicity, aside from its phototoxicity. The cellular protein interactions of PPIX might provide insight into modulators of PPIX-induced cell death. Here we report the development of PPB, a biotin-conjugated, PPIX-probe that captures proteins capable of interacting with PPIX. Quantitative proteomics in a diverse panel of mammalian cell lines reveal a high degree of concordance for PPB-interacting proteins identified for each cell line. Most differences are quantitative, despite marked differences in PPIX formation and sensitivity. Pathway and quantitative difference analysis indicate that iron and heme metabolism proteins are prominent among PPB-bound proteins in fibroblasts, which undergo PPIX-mediated death determined to occur through ferroptosis. PPB proteomic data (available at PRIDE ProteomeXchange # PXD042631) reveal that redox proteins from PRDX family of glutathione peroxidases interact with PPIX. Targeted gene knockdown of the mitochondrial PRDX3, but not PRDX1 or 2, enhance PPIX-induced death in fibroblasts, an effect blocked by the radical-trapping antioxidant, ferrostatin-1. Increased PPIX formation and death was also observed in a T-lymphoblastoid ferrochelatase-deficient leukemia cell line, suggesting that PPIX elevation might serve as a potential strategy for killing certain leukemias.

Engineering Therapeutics to Detoxify Hemoglobin, Heme, and Iron

Hemolysis (i.e., red blood cell lysis) can increase circulatory levels of cell-free hemoglobin (Hb) and its degradation by-products, namely heme (h) and iron (Fe). Under homeostasis, minor increases in these three hemolytic by-products (Hb/h/Fe) are rapidly scavenged and cleared by natural plasma proteins. Under certain pathophysiological conditions, scavenging systems become overwhelmed, leading to the accumulation of Hb/h/Fe in the circulation. Unfortunately, these species cause various side effects such as vasoconstriction, hypertension, and oxidative organ damage. Therefore, various therapeutics strategies are in development, ranging from supplementation with depleted plasma scavenger proteins to engineered biomimetic protein constructs capable of scavenging multiple hemolytic species. In this review, we briefly describe hemolysis and the characteristics of the major plasma-derived protein scavengers of Hb/h/Fe. Finally, we present novel engineering approaches designed to address the toxicity of these hemolytic by-products.

Orthogonal Versatile Interacting Peptide Tags for Imaging Cellular Proteins

Genetic tags are transformative tools for investigating the function, localization, and interactions of cellular proteins. Most studies today are reliant on selective labeling of more than one protein to obtain comprehensive information on a protein's behavior in situ. Some proteins can be analyzed by fusion to a protein tag, such as green fluorescent protein, HaloTag, or SNAP-Tag. Other proteins benefit from labeling via small peptide tags, such as the recently reported versatile interacting peptide (VIP) tags. VIP tags enable observations of protein localization and trafficking with bright fluorophores or nanoparticles. Here, we expand the VIP toolkit by presenting two new tags: TinyVIPER and PunyVIPER. These two tags were designed for use with MiniVIPER for labeling up to three distinct proteins at once in cells. Labeling is mediated by the formation of a high-affinity, biocompatible heterodimeric coiled coil. Each tag was validated by fluorescence microscopy, including observation of transferrin receptor 1 trafficking in live cells. We verified that labeling via each tag is highly specific for one- or two-color imaging. Last, the self-sorting tags were used for simultaneous labeling of three protein targets (i.e., TOMM20, histone 2B, and actin) in fixed cells, highlighting their utility for multicolor microscopy. MiniVIPER, TinyVIPER, and PunyVIPER are small and robust peptide tags for selective labeling of cellular proteins.

Out of the ESCPE room: Emerging roles of endosomal SNX-BARs in receptor transport and host-pathogen interaction

Several functions of the human cell, such as sensing nutrients, cell movement and interaction with the surrounding environment, depend on a myriad of transmembrane proteins and their associated proteins and lipids (collectively termed "cargoes"). To successfully perform their tasks, cargo must be sorted and delivered to the right place, at the right time, and in the right amount. To achieve this, eukaryotic cells have evolved a highly organized sorting platform, the endosomal network. Here, a variety of specialized multiprotein complexes sort cargo into itineraries leading to either their degradation or their recycling to various organelles for further rounds of reuse. A key sorting complex is the Endosomal SNX-BAR Sorting Complex for Promoting Exit (ESCPE-1) that promotes the recycling of an array of cargos to the plasma membrane and/or the trans-Golgi network. ESCPE-1 recognizes a hydrophobic-based sorting motif in numerous cargoes and orchestrates their packaging into tubular carriers that pinch off from the endosome and travel to the target organelle. A wide range of pathogens mimic this sorting motif to hijack ESCPE-1 transport to promote their invasion and survival within infected cells. In other instances, ESCPE-1 exerts restrictive functions against pathogens by limiting their replication and infection. In this review, we discuss ESCPE-1 assembly and functions, with a particular focus on recent advances in the understanding of its role in membrane trafficking, cellular homeostasis and host-pathogen interaction.

Role of serotype and virulence determinants of Streptococcus pyogenes biofilm bacteria in internalization and persistence in epithelial cells in vitro

Streptococcus pyogenes causes a multitude of local and systemic infections, the most common being pharyngitis in children. Recurrent pharyngeal infections are common and are thought to be due to the re-emergence of intracellular GAS upon completion of antibiotic treatment. The role of colonizing biofilm bacteria in this process is not fully clear. Here, live respiratory epithelial cells were inoculated with broth-grown or biofilm bacteria of different M-types, as well as with isogenic mutants lacking common virulence factors. All M-types tested adhered to and were internalized into epithelial cells. Interestingly, internalization and persistence of planktonic bacteria varied significantly between strains, whereas biofilm bacteria were internalized in similar and higher numbers, and all strains persisted beyond 44 hours, showing a more homogenous phenotype. The M3 protein, but not the M1 or M5 proteins, was required for optimal uptake and persistence of both planktonic and biofilm bacteria inside cells. Moreover, the high expression of capsule and SLO inhibited cellular uptake and capsule expression was required for intracellular survival. Streptolysin S was required for optimal uptake and persistence of M3 planktonic bacteria, whereas SpeB improved intracellular survival of biofilm bacteria. Microscopy of internalized bacteria showed that planktonic bacteria were internalized in lower numbers as individual or small clumps of bacteria in the cytoplasm, whereas GAS biofilm bacteria displayed a pattern of perinuclear localization of bacterial aggregates that affected actin structure. Using inhibitors targeting cellular uptake pathways, we confirmed that planktonic GAS mainly uses a clathrin-mediated uptake pathway that also required actin and dynamin. Clathrin was not involved in biofilm internalization, but internalization required actin rearrangement and PI3 kinase activity, possibly suggesting macropinocytosis. Together these results provide a better understanding of the potential mechanisms of uptake and survival of various phenotypes of GAS bacteria relevant for colonization and recurrent infection.

A deep dive into future therapies for microcytic anemias and clinical considerations

INTRODUCTION

Microcytic anemias (MA) have frequent or rare etiologies. New discoveries in understanding and treatment of microcytic anemias need to be reviewed.

AREAS COVERED

Microcytic anemias with a focus on the most frequent causes and on monogenic diseases that are relevant for understanding biocellular mechanisms of MA. All treatments except gene therapy, with a focus on recent advances. PubMed search with references selected by expert opinion.

EXPERT OPINION

As the genetic and cellular backgrounds of dyserythropoiesis will continue to be clarified, collaboration with bioengineering of treatments acting specifically at the protein domain level will continue to provide new therapies in hematology as well as oncology and neurology.

An Aptamer That Rapidly Internalizes into Cancer Cells Utilizes the Transferrin Receptor Pathway

Strategies to direct drugs specifically to cancer cells have been increasingly explored, and significant progress has been made toward such targeted therapy. For example, drugs have been conjugated into tumor-targeting antibodies to enable delivery directly to tumor cells. Aptamers are an attractive class of molecules for this type of drug targeting as they are high-affinity/high-specificity ligands, relatively small in size, GMP manufacturable at a large-scale, amenable to chemical conjugation, and not immunogenic. Previous work from our group revealed that an aptamer selected to internalize into human prostate cancer cells, called E3, can also target a broad range of human cancers but not normal control cells. Moreover, this E3 aptamer can deliver highly cytotoxic drugs to cancer cells as Aptamer-highly Toxic Drug Conjugates (ApTDCs) and inhibit tumor growth in vivo. Here, we evaluate its targeting mechanism and report that E3 selectively internalizes into cancer cells utilizing a pathway that involves transferrin receptor 1 (TfR 1). E3 binds to recombinant human TfR 1 with high affinity and competes with transferrin (Tf) for binding to TfR1. In addition, knockdown or knockin of human TfR1 results in a decrease or increase in E3 cell binding. Here, we reported a molecular model of E3 binding to the transferrin receptor that summarizes our findings.

Efficient Delivery of Biological Cargos into Primary Cells by Electrodeposited Nanoneedles via Cell-Cycle-Dependent Endocytosis

Nanoneedles are a useful tool for delivering exogenous biomolecules to cells. Although therapeutic applications have been explored, the mechanism regarding how cells interact with nanoneedles remains poorly studied. Here, we present a new approach for the generation of nanoneedles, validated their usefulness in cargo delivery, and studied the underlying genetic modulators during delivery. We fabricated arrays of nanoneedles based on electrodeposition and quantified its efficacy of delivery using fluorescently labeled proteins and siRNAs. Notably, we revealed that our nanoneedles caused the disruption of cell membranes, enhanced the expression of cell-cell junction proteins, and downregulated the expression of transcriptional factors of NFκB pathways. This perturbation trapped most of the cells in G2 phase, in which the cells have the highest endocytosis activities. Taken together, this system provides a new model for the study of interactions between cells and high-aspect-ratio materials.

Purification Analysis, Intracellular Tracking, and Colocalization of Extracellular Vesicles Using Atomic Force and 3D Single-Molecule Localization Microscopy

Extracellular vesicles (EVs) play a key role in cell-cell communication and thus have great potential to be utilized as therapeutic agents and diagnostic tools. In this study, we implemented single-molecule microscopy techniques as a toolbox for a comprehensive characterization as well as measurement of the cellular uptake of HEK293T cell-derived EVs (eGFP-labeled) in HeLa cells. A combination of fluorescence and atomic force microscopy revealed a fraction of 68% fluorescently labeled EVs with an average size of ∼45 nm. Two-color single-molecule fluorescence microscopy analysis elucidated the 3D dynamics of EVs entering HeLa cells. 3D colocalization analysis of two-color direct stochastic optical reconstruction microscopy (dSTORM) images revealed that 25% of EVs that experienced uptake colocalized with transferrin, which has been linked to early recycling of endosomes and clathrin-mediated endocytosis. The localization analysis was combined with stepwise photobleaching, providing a comparison of protein aggregation outside and inside the cells.

Characterization of PGua4, a Guanidinium-Rich Peptoid that Delivers IgGs to the Cytosol via Macropinocytosis

To investigate the structure-cellular penetration relationship of guanidinium-rich transporters (GRTs), we previously designed PGua4, a five-amino acid peptoid containing a conformationally restricted pattern of eight guanidines, which showed high cell-penetrating abilities and low cell toxicity. Herein, we characterized the cellular uptake selectivity, internalization pathway, and intracellular distribution of PGua4, as well as its capacity to deliver cargo. PGua4 exhibits higher penetration efficiency in HeLa cells than in six other cell lines (A549, Caco-2, fibroblast, HEK293, Mia-PaCa2, and MCF7) and is mainly internalized by clathrin-mediated endocytosis and macropinocytosis. Confocal microscopy showed that it remained trapped in endosomes at low concentrations but induced pH-dependent endosomal membrane destabilization at concentrations ≥10 μM, allowing its diffusion into the cytoplasm. Importantly, PGua4 significantly enhanced macropinocytosis and the cellular uptake and cytosolic delivery of large IgGs following noncovalent complexation. Therefore, in addition to its peptoid nature conferring high resistance to proteolysis, PGua4 presents characteristics of a promising tool for IgG delivery and therapeutic applications.

Standardized Preclinical In Vitro Blood-Brain Barrier Mouse Assay Validates Endocytosis-Dependent Antibody Transcytosis Using Transferrin-Receptor-Mediated Pathways

The presence of the blood-brain barrier (BBB) creates a nigh-on impenetrable obstacle for large macromolecular therapeutics that need to be delivered to the brain milieu to treat neurological disorders. To overcome this, one of the strategies used is to bypass the barrier with what is referred to as a "Trojan Horse" strategy, where therapeutics are designed to use endogenous receptor-mediated pathways to piggyback their way through the BBB. Even though in vivo methodologies are commonly used to test the efficacy of BBB-penetrating biologics, comparable in vitro BBB models are in high demand, as they benefit from being an isolated cellular system devoid of physiological factors that can on occasion mask the processes behind BBB transport via transcytosis. We have developed an in vitro BBB model (In-Cell BBB-Trans assay) based on the murine cEND cells that help delineate the ability of modified large bivalent IgG antibodies conjugated to the transferrin receptor binder scFv8D3 to cross an endothelial monolayer grown on porous cell culture inserts (PCIs). Following the administration of bivalent antibodies into the endothelial monolayer, a highly sensitive enzyme-linked immunosorbent assay (ELISA) is used to determine the concentration in the apical (blood) and basolateral (brain) chambers of the PCI system, allowing for the evaluation of apical recycling and basolateral transcytosis, respectively. Our results show that antibodies conjugated to scFv8D3 transcytose at considerably higher levels compared to unconjugated antibodies in the In-Cell BBB-Trans assay. Interestingly, we are able to show that these results mimic in vivo brain uptake studies using identical antibodies. In addition, we are able to transversely section PCI cultured cells, allowing for the identification of receptors and proteins that are likely involved in the transcytosis of the antibodies. Furthermore, studies using the In-Cell BBB-Trans assay revealed that transcytosis of the transferrin-receptor-targeting antibodies is dependent on endocytosis. In conclusion, we have designed a simple, reproducible In-Cell BBB-Trans assay based on murine cells that can be used to rapidly determine the BBB-penetrating capabilities of transferrin-receptor-targeting antibodies. We believe that the In-Cell BBB-Trans assay can be used as a powerful, preclinical screening platform for therapeutic neurological pathologies.

Rab21 regulates caveolin-1-mediated endocytic trafficking to promote immature neurite pruning

Transmembrane proteins are internalized by clathrin- and caveolin-dependent endocytosis. Both pathways converge on early endosomes and are thought to share the small GTPase Rab5 as common regulator. In contrast to this notion, we show here that the clathrin- and caveolin-mediated endocytic pathways are differentially regulated. Rab5 and Rab21 localize to distinct populations of early endosomes in cortical neurons and preferentially regulate clathrin- and caveolin-mediated pathways, respectively, suggesting heterogeneity in the early endosomes, rather than a converging point. Suppression of Rab21, but not Rab5, results in decreased plasma membrane localization and total protein levels of caveolin-1, which perturbs immature neurite pruning of cortical neurons, an in vivo-specific step of neuronal maturation. Taken together, our data indicate that clathrin- and caveolin-mediated endocytic pathways run in parallel in early endosomes, which show different molecular regulation and physiological function.

Ferritin But Not Iron Increases in Retina Upon Systemic Iron Overload in Diabetic and Iron-Dextran Injected Mice

Purpose

Iron overload causes oxidative damage in the retina, and it has been involved in the pathogeny of diabetic retinopathy, which is one of the leading causes of blindness in the adult population worldwide. However, how systemic iron enters the retina during diabetes and the role of blood retinal barrier (BRB) in this process remains unclear.

Methods

The db/db mouse, a well-known model of type 2 diabetes, and a model of systemic iron overload induced by iron dextran intraperitoneal injection, were used. Perls staining and mass spectrophotometry were used to study iron content. Western blot and immunohistochemistry of iron handling proteins were performed to study systemic and retinal iron metabolism. BRB function was assessed by analyzing vascular leakage in fundus angiographies, whole retinas, and retinal sections and by studying the status of tight junctions using transmission electron microscopy and Western blot analysis.

Results

Twenty-week-old db/db mice with systemic iron overload presented ferritin overexpression without iron increase in the retina and did not show any sign of BRB breakdown. These findings were also observed in iron dextran-injected mice. In those animals, after BRB breakdown induced by cryopexy, iron entered massively in the retina.

Conclusions

Our results suggested that BRB protects the retina from excessive iron entry in early stages of diabetic retinopathy. Furthermore, ferritin overexpression before iron increase may prepare the retina for a potential BRB breakdown and iron entry from the systemic circulation.

ATP9A deficiency causes ADHD and aberrant endosomal recycling via modulating RAB5 and RAB11 activity

ATP9A, a lipid flippase of the class II P4-ATPases, is involved in cellular vesicle trafficking. Its homozygous variants are linked to neurodevelopmental disorders in humans. However, its physiological function, the underlying mechanism as well as its pathophysiological relevance in humans and animals are still largely unknown. Here, we report two independent families in which the nonsense mutations c.433C>T/c.658C>T/c.983G>A (p. Arg145*/p. Arg220*/p. Trp328*) in ATP9A (NM_006045.3) cause autosomal recessive hypotonia, intellectual disability (ID) and attention deficit hyperactivity disorder (ADHD). Atp9a null mice show decreased muscle strength, memory deficits and hyperkinetic movement disorder, recapitulating the symptoms observed in patients. Abnormal neurite morphology and impaired synaptic transmission are found in the primary motor cortex and hippocampus of the Atp9a null mice. ATP9A is also required for maintaining neuronal neurite morphology and the viability of neural cells in vitro. It mainly localizes to endosomes and plays a pivotal role in endosomal recycling pathway by modulating small GTPase RAB5 and RAB11 activation. However, ATP9A pathogenic mutants have aberrant subcellular localization and cause abnormal endosomal recycling. These findings provide strong evidence that ATP9A deficiency leads to neurodevelopmental disorders and synaptic dysfunctions in both humans and mice, and establishes novel regulatory roles for ATP9A in RAB5 and RAB11 activity-dependent endosomal recycling pathway and neurological diseases.

Cell surface protein aggregation triggers endocytosis to maintain plasma membrane proteostasis

The ability of cells to manage consequences of exogenous proteotoxicity is key to cellular homeostasis. While a plethora of well-characterised machinery aids intracellular proteostasis, mechanisms involved in the response to denaturation of extracellular proteins remain elusive. Here we show that aggregation of protein ectodomains triggers their endocytosis via a macroendocytic route, and subsequent lysosomal degradation. Using ERBB2/HER2-specific antibodies we reveal that their cross-linking ability triggers specific and fast endocytosis of the receptor, independent of clathrin and dynamin. Upon aggregation, canonical clathrin-dependent cargoes are redirected into the aggregation-dependent endocytosis (ADE) pathway. ADE is an actin-driven process, which morphologically resembles macropinocytosis. Physical and chemical stress-induced aggregation of surface proteins also triggers ADE, facilitating their degradation in the lysosome. This study pinpoints aggregation of extracellular domains as a trigger for rapid uptake and lysosomal clearance which besides its proteostatic function has potential implications for the uptake of pathological protein aggregates and antibody-based therapies.

Uptake of severe acute respiratory syndrome coronavirus 2 spike protein mediated by angiotensin converting enzyme 2 and ganglioside in human cerebrovascular cells

Introduction

There is clinical evidence of neurological manifestations in coronavirus disease-19 (COVID-19). However, it is unclear whether differences in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)/spike protein (SP) uptake by cells of the cerebrovasculature contribute to significant viral uptake to cause these symptoms.

Methods

Since the initial step in viral invasion is binding/uptake, we used fluorescently labeled wild type and mutant SARS-CoV-2/SP to study this process. Three cerebrovascular cell types were used (endothelial cells, pericytes, and vascular smooth muscle cells), in vitro.

Results

There was differential SARS-CoV-2/SP uptake by these cell types. Endothelial cells had the least uptake, which may limit SARS-CoV-2 uptake into brain from blood. Uptake was time and concentration dependent, and mediated by angiotensin converting enzyme 2 receptor (ACE2), and ganglioside (mono-sialotetrahexasylganglioside, GM1) that is predominantly expressed in the central nervous system and the cerebrovasculature. SARS-CoV-2/SPs with mutation sites, N501Y, E484K, and D614G, as seen in variants of interest, were also differentially taken up by these cell types. There was greater uptake compared to that of the wild type SARS-CoV-2/SP, but neutralization with anti-ACE2 or anti-GM1 antibodies was less effective.

Conclusion

The data suggested that in addition to ACE2, gangliosides are also an important entry point of SARS-CoV-2/SP into these cells. Since SARS-CoV-2/SP binding/uptake is the initial step in the viral penetration into cells, a longer exposure and higher titer are required for significant uptake into the normal brain. Gangliosides, including GM1, could be an additional potential SARS-CoV-2 and therapeutic target at the cerebrovasculature.

Clathrin-Mediated Albumin Clearance in Alveolar Epithelial Cells of Murine Precision-Cut Lung Slices

A hallmark of acute respiratory distress syndrome (ARDS) is an accumulation of protein-rich alveolar edema that impairs gas exchange and leads to worse outcomes. Thus, understanding the mechanisms of alveolar albumin clearance is of high clinical relevance. Here, we investigated the mechanisms of the cellular albumin uptake in a three-dimensional culture of precision-cut lung slices (PCLS). We found that up to 60% of PCLS cells incorporated labeled albumin in a time- and concentration-dependent manner, whereas virtually no uptake of labeled dextran was observed. Of note, at a low temperature (4 °C), saturating albumin receptors with unlabeled albumin and an inhibition of clathrin-mediated endocytosis markedly decreased the endocytic uptake of the labeled protein, implicating a receptor-driven internalization process. Importantly, uptake rates of albumin were comparable in alveolar epithelial type I (ATI) and type II (ATII) cells, as assessed in PCLS from a SftpcCre^ERT2/+: tdTomato^flox/flox mouse strain (defined as EpCAM⁺CD31^-CD45^-tdTomatoSPC^-T1α⁺ for ATI and EpCAM⁺CD31^-CD45^-tdTomatoSPC⁺T1α^- for ATII cells). Once internalized, albumin was found in the early and recycling endosomes of the alveolar epithelium as well as in endothelial, mesenchymal, and hematopoietic cell populations, which might indicate transcytosis of the protein. In summary, we characterize albumin uptake in alveolar epithelial cells in the complex setting of PCLS. These findings may open new possibilities for pulmonary drug delivery that may improve the outcomes for patients with respiratory failure.

Coordinated reprogramming of renal cancer transcriptome, metabolome and secretome associates with immune tumor infiltration

BACKGROUND

Clear cell renal cell carcinoma (ccRCC) is the most common subtype of renal cancer. The molecules (proteins, metabolites) secreted by tumors affect their extracellular milieu to support cancer progression. If secreted in amounts detectable in plasma, these molecules can also serve as useful, minimal invasive biomarkers. The knowledge of ccRCC tumor microenvironment is fragmentary. In particular, the links between ccRCC transcriptome and the composition of extracellular milieu are weakly understood. In this study, we hypothesized that ccRCC transcriptome is reprogrammed to support alterations in tumor microenvironment. Therefore, we comprehensively analyzed ccRCC extracellular proteomes and metabolomes as well as transcriptomes of ccRCC cells to find molecules contributing to renal tumor microenvironment.

METHODS

Proteomic and metabolomics analysis of conditioned media isolated from normal kidney cells as well as five ccRCC cell lines was performed using mass spectrometry, with the following ELISA validation. Transcriptomic analysis was done using microarray analysis and validated using real-time PCR. Independent transcriptomic and proteomic datasets of ccRCC tumors were used for the analysis of gene and protein expression as well as the level of the immune infiltration.

RESULTS

Renal cancer secretome contained 85 proteins detectable in human plasma, consistently altered in all five tested ccRCC cell lines. The top upregulated extracellular proteins included SPARC, STC2, SERPINE1, TGFBI, while downregulated included transferrin and DPP7. The most affected extracellular metabolites were increased 4-hydroxy-proline, succinic acid, cysteine, lactic acid and downregulated glutamine. These changes were associated with altered expression of genes encoding the secreted proteins (SPARC, SERPINE1, STC2, DPP7), membrane transporters (SLC16A4, SLC6A20, ABCA12), and genes involved in protein trafficking and secretion (KIF20A, ANXA3, MIA2, PCSK5, SLC9A3R1, SYTL3, and WNTA7). Analogous expression changes were found in ccRCC tumors. The expression of SPARC predicted the infiltration of ccRCC tumors with endothelial cells. Analysis of the expression of the 85 secretome genes in > 12,000 tumors revealed that SPARC is a PanCancer indicator of cancer-associated fibroblasts' infiltration.

CONCLUSIONS

Transcriptomic reprogramming of ccRCC supports the changes in an extracellular milieu which are associated with immune infiltration. The proteins identified in our study represent valuable cancer biomarkers detectable in plasma.

IFITM3 regulates fibrinogen endocytosis and platelet reactivity in nonviral sepsis

Platelets and megakaryocytes are critical players in immune responses. Recent reports suggest infection and inflammation alter the megakaryocyte and platelet transcriptome to induce altered platelet reactivity. We determined whether nonviral sepsis induces differential platelet gene expression and reactivity. Nonviral sepsis upregulated IFN-induced transmembrane protein 3 (IFITM3), an IFN-responsive gene that restricts viral replication. As IFITM3 has been linked to clathrin-mediated endocytosis, we determined whether IFITM3 promoted endocytosis of α-granule proteins. IFN stimulation enhanced fibrinogen endocytosis in megakaryocytes and platelets from Ifitm+/+ mice, but not Ifitm-/- mice. IFITM3 overexpression or deletion in megakaryocytes demonstrated IFITM3 was necessary and sufficient to regulate fibrinogen endocytosis. Mechanistically, IFITM3 interacted with clathrin and αIIb and altered their plasma membrane localization into lipid rafts. In vivo IFN administration increased fibrinogen endocytosis, platelet reactivity, and thrombosis in an IFITM-dependent manner. In contrast, Ifitm-/- mice were completely rescued from IFN-induced platelet hyperreactivity and thrombosis. During murine sepsis, platelets from Ifitm+/+ mice demonstrated increased fibrinogen content and platelet reactivity, which was dependent on IFN-α and IFITMs. Platelets from patients with nonviral sepsis had increases in platelet IFITM3 expression, fibrinogen content, and hyperreactivity. These data identify IFITM3 as a regulator of platelet endocytosis, hyperreactivity, and thrombosis during inflammatory stress.

Pseudokinase NRP1 facilitates endocytosis of transferrin in the African trypanosome

Trypanosoma brucei causes human African trypanosomiasis (HAT) and nagana in cattle. During infection of a vertebrate, endocytosis of host transferrin (Tf) is important for viability of the parasite. The majority of proteins involved in trypanosome endocytosis of Tf are unknown. Here we identify pseudokinase NRP1 (Tb427tmp.160.4770) as a regulator of Tf endocytosis. Genetic knockdown of NRP1 inhibited endocytosis of Tf without blocking uptake of bovine serum albumin. Binding of Tf to the flagellar pocket was not affected by knockdown of NRP1. However the quantity of Tf per endosome dropped significantly, consistent with NRP1 promoting robust capture and/or retention of Tf in vesicles. NRP1 is involved in motility of Tf-laden vesicles since distances between endosomes and the kinetoplast were reduced after knockdown of the gene. In search of possible mediators of NRP1 modulation of Tf endocytosis, the gene was knocked down and the phosphoproteome analyzed. Phosphorylation of protein kinases forkhead, NEK6, and MAPK10 was altered, in addition to EpsinR, synaptobrevin and other vesicle-associated proteins predicted to be involved in endocytosis. These candidate proteins may link NRP1 functionally either to protein kinases or to vesicle-associated proteins.