Palmitate Stimulates Expression of the von Willebrand Factor and Modulates Toll-like Receptors Level and Activity in Human Umbilical Vein Endothelial Cells (HUVECs).

An increased concentration of palmitate in circulation is one of the most harmful factors in obesity. The von Willebrand factor (vWF), a protein involved in haemostasis, is produced and secreted by the vascular endothelium. An increased level of vWF in obese patients is associated with thrombosis and cardiovascular disease.

Fluorescence evidence of annexin A6 translocation across membrane in model matrix vesicles during apatite formation.

Matrix vesicles (MVs) are 100-300 nm spherical structures released by mineralization competent cells to initiate formation of apatite, the mineral component in bones. Among proteins present in MVs, annexin A6 (AnxA6) is thought to be ubiquitously distributed in the MVs' lumen, on the surface of the internal and external leaflets of the membrane and also inserted in the lipid bilayer. To determine the molecular mechanism(s) that lead to the different locations of AnxA6, we hypothesized the occurrence of a pH drop during the mineralization.

Localization of Annexin A6 in Matrix Vesicles During Physiological Mineralization.

Annexin A6 (AnxA6) is the largest member of the annexin family of proteins present in matrix vesicles (MVs). MVs are a special class of extracellular vesicles that serve as a nucleation site during cartilage, bone, and mantle dentin mineralization. In this study, we assessed the localization of AnxA6 in the MV membrane bilayer using native MVs and MV biomimetics.

Src and ROCK Kinases Differentially Regulate Mineralization of Human Osteosarcoma Saos-2 Cells.

Osteoblasts initiate bone mineralization by releasing matrix vesicles (MVs) into the extracellular matrix (ECM). MVs promote the nucleation process of apatite formation from Ca and P in their lumen and bud from the microvilli of osteoblasts during bone development. Tissue non-specific alkaline phosphatase (TNAP) as well as annexins (among them, AnxA6) are abundant proteins in MVs that are engaged in mineralization.

Annexin A6 as a cholesterol and nucleotide binding protein involved in membrane repair and in controlling membrane transport during endo- and exocytosis.

Annexins, calcium- and membrane-binding proteins, have been extensively studied at the Nencki Institute since early 1990s, in terms of their structure, potential ligands and functions in the organism, with emphasis on mineralization processes in norm and pathology. The results of recently performed studies have revealed that annexins are playing essential roles in membrane organization. In this review we characterize the largest member of the annexin family of proteins, annexin A6 (AnxA6), in respect to its cholesterol and nucleotide binding properties, as well as intracellular pH sensing and ability to change membrane permeability to ions.

Activation of mammalian terget of rapamycin kinase and glycogen synthase kinase-3β accompanies abnormal accumulation of cholesterol in fibroblasts from Niemann-Pick type C patients.

Background: Niemann Pick type C (NPC) lysosomal disorder is linked to the disruption of cholesterol transport. Recent data suggest that the molecular background of this disease is more complex. It was found that accumulation of cholesterol and glycolipids in the late endosomal/lysosomal compartment of NPC1 cells may affect mitochondrial functions.

Matrix vesicles from chondrocytes and osteoblasts: Their biogenesis, properties, functions and biomimetic models.

Background: Matrix vesicles (MVs) are released from hypertrophic chondrocytes and from mature osteoblasts, the cells responsible for endochondral and membranous ossification. Under pathological conditions, they can also be released from cells of non-skeletal tissues such as vascular smooth muscle cells. MVs are extracellular vesicles of approximately 100-300nm diameter harboring the biochemical machinery needed to induce mineralization.

The roles of annexins in vascular endothelium dysfunction accompanying diabetes mellitus type 2.

Impairment in cellular transport, distribution and storage of cholesterol accompanies insulin resistance and diabetes mellitus type 2 as well as other diseases such as obesity, atherosclerosis, and non-alcoholic fatty liver disease. Diabetes mellitus type 2 is a metabolic disorder that is characterized by hyperglycemia in the context of insulin resistance and relative lack of insulin. Type 2 diabetes makes up about 90% of cases of diabetes.

[Annexins in mitochondria].

Annexins form a family of membrane- and calcium-binding proteins, widely distributed in vertebrates. Their interactions with membranes are regulated by changes of intracellular concentration of calcium ([Ca]), pH, and the presence of negatively charged phospholipids as well as cholesterol in membranes. As protein participating in membrane fusion and sensors of a [Ca] Annexins may regulate various signaling pathways including patways involving protein kinase C (PKC isoforms.

Two-Step Membrane Binding of NDPK-B Induces Membrane Fluidity Decrease and Changes in Lipid Lateral Organization and Protein Cluster Formation.

Nucleoside diphosphate kinases (NDPKs) are crucial elements in a wide array of cellular physiological or pathophysiological processes such as apoptosis, proliferation, or metastasis formation. Among the NDPK isoenzymes, NDPK-B, a cytoplasmic protein, was reported to be associated with several biological membranes such as plasma or endoplasmic reticulum membranes. Using several membrane models (liposomes, lipid monolayers, and supported lipid bilayers) associated with biophysical approaches, we show that lipid membrane binding occurs in a two-step process: first, initiation by a strong electrostatic adsorption process and followed by shallow penetration of the protein within the membrane.

Mitochondrial dysfunction in fibroblasts derived from patients with Niemann-Pick type C disease.

Mutations in the NPC1 or NPC2 genes lead to Niemann-Pick type C (NPC) disease, a rare lysosomal storage disorder characterized by progressive neurodegeneration. These mutations result in cholesterol and glycosphingolipid accumulation in the late endosomal/lysosomal compartment. Complications in the storage of cholesterol in NPC1 mutant cells are associated with other anomalies, such as altered distribution of intracellular organelles and properties of the plasma membrane.

[Participation of annexins in endocytosis and EGFR-mediated signal transduction].

Annexins are a family of membrane interacting proteins, widely distributed in vertebrates. Their involvement in the endosomal transport is due to annexin capability of binding cellular constituents such as membrane phospholipids and intracellular protein partners in a calcium dependent manner. Furthermore, annexins, through endosomal transport of particular receptors and specific cargo, may regulate various processes involved in signal transduction.

Exploring NMR methods as a tool to select suitable fluorescent nucleotide analogues.

Fluorescent analogues provide important tools for biochemical/biophysical research. However, the analogues contain chemical modifications much larger than those known to affect ligand-binding, such as the inversion of a carbon centre or substitution of an atom. We lack experimental tools and protocols to select the most appropriate fluorescent analogue.

Phospholipases of mineralization competent cells and matrix vesicles: roles in physiological and pathological mineralizations.

The present review aims to systematically and critically analyze the current knowledge on phospholipases and their role in physiological and pathological mineralization undertaken by mineralization competent cells. Cellular lipid metabolism plays an important role in biological mineralization. The physiological mechanisms of mineralization are likely to take place in tissues other than in bones and teeth under specific pathological conditions.

Interaction of AnxA6 with isolated and artificial lipid microdomains; importance of lipid composition and calcium content.

Niemann-Pick type C (NPC) disease is a lipid storage disorder characterized by accumulation of lipids in the late endosome/lysosome (LE/LY) compartment. In our previous report we isolated membranes of the LE/LY compartment from NPC L1 skin fibroblasts with a mutation in the NPC1 gene and found that they were characterized by low fluidity which likely contributed to the impaired function of membrane proteins involved in storage and turnover of cholesterol. In this report we isolated lipid microdomains (DRMs) from membranes of various cellular compartments and observed an increased amount of DRMs in the LE/LY compartment of NPC L1 cells in comparison to control cells, with no change in the DRM content in the plasma membrane.

[Participation of annexins in signal transduction, regulation of plasma membrane structure and membrane repair mechanisms].

Cell integrity, assured by plasma membrane continuity, is essential to maintain proper cell functioning and survival. Plasma membrane separates the cell interior from the extracellular milieu and constitutes a barrier due to which the spatial relationship between organelles and the internal membrane network as well as the chemical composition of the cytoplasm are preserved during the cellular life span. Therefore, all cellular processes including intracellular ion homeostasis, exchange of substances between the extracellular environment and the cytoplasm, maintenance of cellular shape, cellular movement, vesicular traffic, cell division and membrane biogenesis, as well as and cellular signaling depend on the integrity, structure and function of the plasma membrane.

Do annexins participate in lipid messenger mediated intracellular signaling? A question revisited.

Annexins are physiologically important proteins that play a role in calcium buffering but also influence membrane structure, participate in Ca²⁺-dependent membrane repair events and in remodelling of the cytoskeleton. Thirty years ago several peptides isolated from lung perfusates, peritoneal leukocytes, neutrophiles and renal cells were proven inhibitory to the activity of phospholipase A₂. Those peptides were found to derive from structurally related proteins: annexins AnxA1 and AnxA2.

Impaired dynamics of the late endosome/lysosome compartment in human Niemann-Pick type C skin fibroblasts carrying mutation in NPC1 gene.

The Niemann-Pick type C (NPC) disease is characterized by accumulation of lipids within the late endosome/lysosome (LE/LY) compartment as a result of dysfunctions of the NPC1 or NPC2 proteins and an altered distribution and/or functioning of proteins involved in the regulation of membrane dynamics. In our previous report we isolated membranes of the LE/LY compartment from NPC L1 skin fibroblasts with a mutation in the NPC1 gene (exon 8, R348X) and showed that annexin A6 (AnxA6) may contribute to the impaired dynamics of these membranes in a cholesterol-dependent manner and therefore to the overnormative storage of cholesterol. In this report we show that the LE/LY fraction isolated from NPC L1 cells is characterized by a 4-fold enrichment in cholesterol, 2.

[Store-operated calcium entry--are all elements of the system already identified?].

Store-operated Ca2+ entry (SOCE) is an ubiquitous mechanism leading to a transient increase of Ca2+ concentration in the cytoplasm ([Ca2+]c) of a leaving cell followed by refill of the internal stores with calcium. Discovery of STIM1 and STIM2 proteins located in the endoplasmic reticulum (ER) and playing a role of sensors of calcium, led to our understanding how the calcium signal from ER is propagated to calcium release-activated calcium channels (CRAC) located in the plasma membrane, resulting in their activation, flow of calcium into a cytoplasm and activation of calcium-dependent signaling. In light of controversies existing in identification of CRAC channels (such as Oral, TRPC and others), as well as identification of mechanisms of calcium entry that are independent of the presence of calcium in the internal calcium stores, in this review we discuss the newest theories about SOCE, proteins that are engaged in this mechanism as well as pathologies related to impaired SOCE.

[Calcium homeostasis in the animal cell--an outline].

Calcium ions are universal and versatile intracellular signalling molecule which is involved in regulation of many cellular functions in all living cells throughout all animal species. It results from unique properties of Ca2+ in comparison to other two- and monovalent cations commonly present inside and outside cells. On the other hand an excessive increase of intracellular Ca2+ accumulation may exert toxic effect leading to cell death.

Annexins as organizers of cholesterol- and sphingomyelin-enriched membrane microdomains in Niemann-Pick type C disease.

Growing evidence suggests that membrane microdomains enriched in cholesterol and sphingomyelin are sites for numerous cellular processes, including signaling, vesicular transport, interaction with pathogens, and viral infection, etc. Recently some members of the annexin family of conserved calcium and membrane-binding proteins have been recognized as cholesterol-interacting molecules and suggested to play a role in the formation, stabilization, and dynamics of membrane microdomains to affect membrane lateral organization and to attract other proteins and signaling molecules onto their territory. Furthermore, annexins were implicated in the interactions between cytosolic and membrane molecules, in the turnover and storage of cholesterol and in various signaling pathways.

[Pathogenesis of lipid storage diseases].

Lipidoses are rare genetic disorders characterized by defects of the digestive system that impair the way the body uses dietary fat. When the body is unable to properly digest fats, lipids such as cholesterol, sphingolipids or glycolipids may accumulate in body tissues in abnormal amounts. It has been also suggested that molecular mechanisms leading to development of human diseases, including obesity, diabetes type II and atherosclerosis, consist of impaired transport and storage of lipids, as well as disturbed structure and function of lipid membrane microdomains.

Annexin A6 is recruited into lipid rafts of Niemann-Pick type C disease fibroblasts in a Ca2+-dependent manner.

Niemann-Pick type C (NPC) disease is characterized by excessive accumulation of cholesterol in the late endosome/lysosome compartment. Some members of the annexin family of proteins such as annexin A2 (AnxA2) and annexin A6 (AnxA6) follow the same route as cholesterol during the endocytic pathway and are found, as AnxA6, attached to the membranes of the cholesterol storage compartment in NPC disease fibroblasts. Therefore, the purpose of this work was to test the hypothesis that AnxA6 participates in the NPC-induced changes in the organization of membrane microdomains resistant to solubilization by a nonionic detergent, Triton X-100, i.