Lysosomal enzyme trafficking factor LYSET enables nutritional usage of extracellular proteins.

Mammalian cells can generate amino acids through macropinocytosis and lysosomal breakdown of extracellular proteins, which is exploited by cancer cells to grow in nutrient-poor tumors. Through genetic screens in defined nutrient conditions, we characterized LYSET, a transmembrane protein (TMEM251) selectively required when cells consume extracellular proteins. LYSET was found to associate in the Golgi with GlcNAc-1-phosphotransferase, which targets catabolic enzymes to lysosomes through mannose-6-phosphate modification. Without LYSET, GlcNAc-1-phosphotransferase was unstable because of a hydrophilic transmembrane domain. Consequently, LYSET-deficient cells were depleted of lysosomal enzymes and impaired in turnover of macropinocytic and autophagic cargoes. Thus, LYSET represents a core component of the lysosomal enzyme trafficking pathway, underlies the pathomechanism for hereditary lysosomal storage disorders, and may represent a target to suppress metabolic adaptations in cancer.

miR-1 sustains muscle physiology by controlling V-ATPase complex assembly.

Muscle function requires unique structural and metabolic adaptations that can render muscle cells selectively vulnerable, with mutations in some ubiquitously expressed genes causing myopathies but sparing other tissues. We uncovered a muscle cell vulnerability by studying miR-1, a deeply conserved, muscle-specific microRNA whose ablation causes various muscle defects. Using Caenorhabditis elegans, we found that miR-1 represses multiple subunits of the ubiquitous vacuolar adenosine triphosphatase (V-ATPase) complex, which is essential for internal compartment acidification and metabolic signaling. V-ATPase subunits are predicted miR-1 targets in animals ranging from C. elegans to humans, and we experimentally validated this in Drosophila. Unexpectedly, up-regulation of V-ATPase subunits upon miR-1 deletion causes reduced V-ATPase function due to defects in complex assembly. These results reveal V-ATPase assembly as a conserved muscle cell vulnerability and support a previously unknown role for microRNAs in the regulation of protein complexes.

An inhibitor-mediated beta-cell dedifferentiation model reveals distinct roles for FoxO1 in glucagon repression and insulin maturation.

OBJECTIVE: The loss of forkhead box protein O1 (FoxO1) signaling in response to metabolic stress contributes to the etiology of type II diabetes, causing the dedifferentiation of pancreatic beta cells to a cell type reminiscent of endocrine progenitors. Lack of methods to easily model this process in vitro, however, have hindered progress into the identification of key downstream targets and potential inhibitors. We therefore aimed to establish such an in vitro cellular dedifferentiation model and apply it to identify novel agents involved in the maintenance of beta-cell identity. METHODS: The murine beta-cell line, Min6, was used for primary experiments and high-content screening. Screens encompassed a library of small-molecule drugs representing the chemical and target space of all FDA-approved small molecules with an automated immunofluorescence readout. Validation experiments were performed in a murine alpha-cell line as well as in primary murine and human diabetic islets. Developmental effects were studied in zebrafish and C. elegans models, while diabetic db/db mouse models were used to elucidate global glucose metabolism outcomes. RESULTS: We show that short-term pharmacological FoxO1 inhibition can model beta-cell dedifferentiation by downregulating beta-cell-specific transcription factors, resulting in the aberrant expression of progenitor genes and the alpha-cell marker glucagon. From a high-content screen, we identified loperamide as a small molecule that can prevent FoxO inhibitor-induced glucagon expression and further stimulate insulin protein processing and secretion by altering calcium levels, intracellular pH, and FoxO1 localization. CONCLUSIONS: Our study provides novel models, molecular targets, and drug candidates for studying and preventing beta-cell dedifferentiation.

Cell death induced autophagy contributes to terminal differentiation of skin and skin appendages.

In the adult mammalian skin, cells are constantly renewing, differentiating and moving upward, to finally die in a yet not fully understood manner. Here, we provide evidence that macroautophagy/autophagy has a dual role in the skin. In addition to its known catabolic protective role as an evolutionary conserved upstream regulator of lysosomal degradation, we show that autophagy induced cell death (CDA) occurs in epithelial lineage-derived organs, such as the inter-follicular epidermis, the sebaceous- and the Harderian gland. By utilizing GFP-LC3 transgenic and ATG7-deficient mice, we show that CDA is initiated during terminal differentiation at a stage when the cells have become highly resistant to apoptosis. In these transitional cells, the Golgi compartment expands, which accounts for the formation of primary lysosomes, and the nucleus starts to condense. During CDA a burst of autophagosome formation is observed, first the endoplasmic reticulum (ER) is phagocytosed followed by autophagy of the nucleus. By this selective form of cell death, most of the cytoplasmic organelles are degraded, but structural proteins remain intact. In the absence of autophagy, consequently, parts of the ER, ribosomes, and chromatin remain. A burst of autophagy was stochastically observed in single cells of the epidermis and collectively in larger areas of ductal cells, arguing for a coordinated induction. We conclude that autophagy is an integral part of cell death in keratinocyte lineage cells and participates in their terminal cell fate.Abbreviations: Atg7: autophagy related 7; BECN1: beclin 1; CDA: cell death-induced autophagy; Cre: Cre-recombinase; DAPI: 4',6-diamidino-2-phenylindole; ER: endoplasmatic reticulum; GFP: green fluorescent protein; HaGl: haderian gland; IVL: involucrin; KRT14: keratin 14; LD: lipid droplet; LSM: laser scanning microscope; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; PN: perinuclear space; RB: residual body; rER: rough endoplasmatic reticulum; SB: sebum; SG-SC: stratum granulosum - stratum corneum; SGl: sebaceous gland; SQSTM1: sequestosome 1; TEM: transmission electron microscopy; TUNEL: terminal deoxynucleotidyl transferase dUTP nick end labelling.

Extracellular Vesicles in Human Skin: Cross-Talk from Senescent Fibroblasts to Keratinocytes by miRNAs.

Extracellular vesicles (EVs) and their miRNA cargo are intercellular communicators transmitting their pleiotropic messages between different cell types, tissues, and body fluids. Recently, they have been reported to contribute to skin homeostasis and were identified as members of the senescence-associated secretory phenotype of human dermal fibroblasts. However, the role of EV-miRNAs in paracrine signaling during skin aging is yet unclear. Here we provide evidence for the existence of small EVs in the human skin and dermal interstitial fluid using dermal open flow microperfusion and show that EVs and miRNAs are transferred from dermal fibroblasts to epidermal keratinocytes in 2D cell culture and in human skin equivalents. We further show that the transient presence of senescent fibroblast derived small EVs accelerates scratch closure of epidermal keratinocytes, whereas long-term incubation impairs keratinocyte differentiation in vitro. Finally, we identify vesicular miR-23a-3p, highly secreted by senescent fibroblasts, as one contributor of the EV-mediated effect on keratinocytes in in vitro wound healing assays. To summarize, our findings support the current view that EVs and their miRNA cargo are members of the senescence-associated secretory phenotype and, thus, regulators of human skin homeostasis during aging.

Protein A- and Protein G-gold nanoparticle bioconjugates as nano-immunoaffinity platform for human IgG depletion in plasma and antibody extraction from cell culture supernatant.

Detection of disease-related biomarkers in plasma provides a possibility for early clinical diagnosis. However, highly abundant proteins in plasma, such as human immunoglobulin (hIgG) are a main impediment to biomarker discovery and analysis. Therefore, rapid and easy depletion of hIgG in the plasma is beneficial for biomarker discovery. In this work, citrate-capped gold nanoparticles (GNPs) were synthesized and conjugated with cysteine-tagged recombinant Protein A (rProtA) and Protein G (ProtG), respectively. The resultant protein-GNP bioconjugates were thoroughly characterized by surface plasmon resonance spectroscopy, hydrodynamic light scattering (DLS), electrophoretic light scattering (ELS) and rotary metal shadowing transmission electron microscopy (TEM) measurements. In order to quantitatively control the amount of the rProt A and ProtG on the GNP surface, binding studies and isotherm measurements have been performed. rProtA-GNP conjugate exhibited better binding capacities towards hIgG. Its surface coverage with rProtA molecules was determined by protein quantification after hydrolysis of the rProtA-GNP conjugate, GNP removal and subsequent amino acid assay by HPLC with fluorescence detection. Binding isotherms acquired with hIgG revealed their maximal capacity for depletion experiments. Depletion efficiency of around 90% could be achieved in a standard solution. With optimized amount of rProtA-GNP and ProtG-GNP, respectively, hIgG could be efficiently extracted from real samples (human plasma and hIgG-spiked cell culture supernatant). A benchmarking study with ProteinA-modified magnetic particles (Dynabeads) was performed as well. The results document that these rProtA-GNP and ProtG-GNP affinity nanoparticles could be a promising alternative to magnetic bead based immunoaffinity trapping and constitutes a flexible platform for both depletion of hIgG from human plasma and antibody affinity capture from cell culture supernatants in process control of biopharmaceuticals by simple solution handling (via pipetting) and centrifugation steps.

The structure and DNA-binding properties of Mgm101 from a yeast with a linear mitochondrial genome.

To study the mechanisms involved in the maintenance of a linear mitochondrial genome we investigated the biochemical properties of the recombination protein Mgm101 from Candida parapsilosis. We show that CpMgm101 complements defects associated with the Saccharomyces cerevisiae mgm101-1(ts) mutation and that it is present in both the nucleus and mitochondrial nucleoids of C. parapsilosis. Unlike its S. cerevisiae counterpart, CpMgm101 is associated with the entire nucleoid population and is able to bind to a broad range of DNA substrates in a non-sequence specific manner. CpMgm101 is also able to catalyze strand annealing and D-loop formation. CpMgm101 forms a roughly C-shaped trimer in solution according to SAXS. Electron microscopy of a complex of CpMgm101 with a model mitochondrial telomere revealed homogeneous, ring-shaped structures at the telomeric single-stranded overhangs. The DNA-binding properties of CpMgm101, together with its DNA recombination properties, suggest that it can play a number of possible roles in the replication of the mitochondrial genome and the maintenance of its telomeres.

Semi-solid fluorinated-DPPC liposomes: Morphological, rheological and thermic properties as well as examination of the influence of a model drug on their skin permeation.

The goal of this study was to investigate the influence of an incorporated model drug on the skin permeation of the vehicle itself as it may affect the microstructure and properties of the applied formulation via molecular interactions. For this purpose, we performed skin permeation studies using liposomes prepared with F-DPPC, a monofluorinated analog of dipalmitoylphosphatidylcholine (DPPC), with and without sodium fluorescein (SoFl) serving as model drug. Interestingly, the liposome preparation with F-DPPC yielded semi-solid opalescent systems. Hence, a thorough characterization was accomplished beforehand by electron microscopy imaging, rheological and thermoanalytical experiments. Freeze-fracture electron microscopy images confirmed the existence of globular shaped vesicles in the F-DPPC preparations and oscillatory rheological measurements proved the viscoelastic properties of F-DPPC and F-DPPC+SoFl liposomes in contrast to the viscous characteristics of DPPC liposomes. Thermoanalytical measurements revealed an increased phase transition temperature Tm of about 50 °C for F-DPPC and F-DPPC+SoFl liposomes compared to pure DPPC liposomes with a Tm of about 43° C. The similar Tm of F-DPPC+SoFl and F-DPPC liposomes as well as the similar skin permeation of the vehicle compound F-DPPC compared to its drug-free counterpart suggest an incorporation of sodium fluorescein into the aqueous core of F-DPPC liposomes.

Autophagy facilitates secretion and protects against degeneration of the Harderian gland.

The epithelial derived Harderian gland consists of 2 types of secretory cells. The more numerous type A cells are responsible for the secretion of lipid droplets, while type B cells produce dark granules of multilamellar bodies. The process of autophagy is constitutively active in the Harderian gland, as confirmed by our analysis of LC3 processing in GFP-LC3 transgenic mice. This process is compromised by epithelial deletion of Atg7. Morphologically, the Atg7 mutant glands are hypotrophic and degenerated, with highly vacuolated cells and pyknotic nuclei. The mutant glands accumulate lipid droplets coated with PLIN2 (perilipin 2) and contain deposits of cholesterol, ubiquitinated proteins, SQSTM1/p62 (sequestosome 1) positive aggregates and other metabolic products such as porphyrin. Immunofluorescence stainings show that distinct cells strongly aggregate both proteins and lipids. Electron microscopy of the Harderian glands reveals that its organized structure is compromised, and the presence of large intracellular lipid droplets and heterologous aggregates. We attribute the occurrence of large vacuoles to a malfunction in the formation of multilamellar bodies found in the less abundant type B Harderian gland cells. This defect causes the formation of large tertiary lysosomes of heterologous content and is accompanied by the generation of tight lamellar stacks of endoplasmic reticulum in a pseudo-crystalline form. To test the hypothesis that lipid and protein accumulation is the cause for the degeneration in autophagy-deficient Harderian glands, epithelial cells were treated with a combination of the proteasome inhibitor and free fatty acids, to induce aggregation of misfolded proteins and lipid accumulation, respectively. The results show that lipid accumulation indeed enhanced the toxicity of misfolded proteins and that this was even more pronounced in autophagy-deficient cells. Thus, we conclude autophagy controls protein and lipid catabolism and anabolism to facilitate bulk production of secretory vesicles of the Harderian gland.