Phosphatidylserine enrichment in the nuclear membrane regulates key enzymes of phosphatidylcholine synthesis.

Phosphatidylserine (PS) is an important anionic phospholipid that is synthesized within the endoplasmic reticulum (ER). While PS shows the highest enrichment and serves important functional roles in the plasma membrane (PM) but its role in the nucleus is poorly explored. Using three orthogonal approaches, we found that PS is also uniquely enriched in the inner nuclear membrane (INM) and the nuclear reticulum (NR).

Non-vesicular phosphatidylinositol transfer plays critical roles in defining organelle lipid composition.

Phosphatidylinositol (PI) is the precursor lipid for the minor phosphoinositides (PPIns), which are critical for multiple functions in all eukaryotic cells. It is poorly understood how phosphatidylinositol, which is synthesized in the ER, reaches those membranes where PPIns are formed. Here, we used VT01454, a recently identified inhibitor of class I PI transfer proteins (PITPs), to unravel their roles in lipid metabolism, and solved the structure of inhibitor-bound PITPNA to gain insight into the mode of inhibition.

Roles of Phosphatidylinositol 4-Phosphorylation in Non-vesicular Cholesterol Trafficking.

Cholesterol (Chol) is an essential component of all eukaryotic cell membranes that affects the function of numerous peripheral as well as integral membrane proteins. Chol is synthesized in the ER, but it is selectively enriched within the plasma membrane (PM) and other endomembranes, which requires Chol to cross the aqueous phase of the cytoplasm. In addition to the classical vesicular trafficking pathways that are known to facilitate the bulk transport of membrane intermediates, Chol is also transported via non-vesicular lipid transfer proteins that work primarily within specialized membrane contact sites.

LIPID transfer proteins regulate store-operated calcium entry via control of plasma membrane phosphoinositides.

The ER-resident proteins STIM1 together with the plasma membrane (PM)-localized Orai1 channels constitute the molecular components of the store-operated Ca entry (SOCE) pathway. Prepositioning of STIM1 to the peripheral ER close to the PM ensures its efficient interaction with Orai1 upon a decrease in the ER luminal Ca concentration. The C-terminal polybasic domain of STIM1 has been identified as mediating the interaction with PM phosphoinositides and hence positions the molecule to ER-PM contact sites.

Metabolic routing maintains the unique fatty acid composition of phosphoinositides.

Phosphoinositide lipids (PPIn) are enriched in stearic- and arachidonic acids (38:4) but how this enrichment is established and maintained during phospholipase C (PLC) activation is unknown. Here we show that the metabolic fate of newly synthesized phosphatidic acid (PA), the lipid precursor of phosphatidylinositol (PI), is influenced by the fatty acyl-CoA used with preferential routing of the arachidonoyl-enriched species toward PI synthesis. Furthermore, during agonist stimulation the unsaturated forms of PI(4,5P) are replenished significantly faster than the more saturated ones, suggesting a favored recycling of the unsaturated forms of the PLC-generated hydrolytic products.

Osseointegration of Plasma Jet Treated Titanium Implant Surface in an Animal Model.

Osseointegration of titanium implant is important for the success of both dental and medical implants. Previous studies have attempted to improve osseointegration by considering the use of plasma jet technology, where information with animal models and parameters related to osseointegration is still lacking. Therefore, this study investigated the effects of non-thermal atmospheric pressure plasma jet (NTAPPJ) treatment on titanium implants in terms of osseointegration in mongrel dogs.

Myelination of peripheral nerves is controlled by PI4KB through regulation of Schwann cell Golgi function.

Better understanding myelination of peripheral nerves would benefit patients affected by peripheral neuropathies, including Charcot-Marie-Tooth disease. Little is known about the role the Golgi compartment plays in Schwann cell (SC) functions. Here, we studied the role of Golgi in myelination of peripheral nerves in mice through SC-specific genetic inactivation of phosphatidylinositol 4-kinase beta (PI4KB), a Golgi-associated lipid kinase.

PHOSPHOINOSITIDES AND CALCIUM SIGNALING. A MARRIAGE ARRANGED IN ER-PM CONTACT SITES.

Calcium (Ca) ions are critically important in orchestrating countless regulatory processes in eukaryotic cells. Consequently, cells tightly control cytoplasmic Ca concentrations using a complex array of Ca-selective ion channels, transporters, and signaling effectors. Ca transport through various cellular membranes is highly dependent on the intrinsic properties of specific membrane compartments and conversely, local Ca changes have profound effects on the membrane lipid composition of such membrane sub-domains.

ORP3 phosphorylation regulates phosphatidylinositol 4-phosphate and Ca dynamics at plasma membrane-ER contact sites.

Oxysterol-binding protein (OSBP)-related proteins (ORPs) mediate non-vesicular lipid transfer between intracellular membranes. Phosphoinositide (PI) gradients play important roles in the ability of OSBP and some ORPs to transfer cholesterol and phosphatidylserine between the endoplasmic reticulum (ER) and other organelle membranes. Here, we show that plasma membrane (PM) association of ORP3 (also known as OSBPL3), a poorly characterized ORP family member, is triggered by protein kinase C (PKC) activation, especially when combined with Ca increases, and is determined by both PI(4,5) and PI4 After activation, ORP3 efficiently extracts PI4 and to a lesser extent phosphatidic acid from the PM, and slightly increases PM cholesterol levels.

Integrated regulation of the phosphatidylinositol cycle and phosphoinositide-driven lipid transport at ER-PM contact sites.

Among the structural phospholipids that form the bulk of eukaryotic cell membranes, phosphatidylinositol (PtdIns) is unique in that it also serves as the common precursor for low-abundance regulatory lipids, collectively referred to as polyphosphoinositides (PPIn). The metabolic turnover of PPIn species has received immense attention because of the essential functions of these lipids as universal regulators of membrane biology and their dysregulation in numerous human pathologies. The diverse functions of PPIn lipids occur, in part, by orchestrating the spatial organization and conformational dynamics of peripheral or integral membrane proteins within defined subcellular compartments.

Lipid Dynamics at Contact Sites Between the Endoplasmic Reticulum and Other Organelles.

Phospholipids are synthesized primarily within the endoplasmic reticulum and are subsequently distributed to various subcellular membranes to maintain the unique lipid composition of specific organelles. As a result, in most cases, the steady-state localization of membrane phospholipids does not match their site of synthesis. This raises the question of how diverse lipid species reach their final membrane destinations and what molecular processes provide the energy to maintain the lipid gradients that exist between various membrane compartments.

Phosphatidylinositol 4,5-bisphosphate controls Rab7 and PLEKHM1 membrane cycling during autophagosome-lysosome fusion.

The small GTPase Rab7 is a key organizer of receptor sorting and lysosomal degradation by recruiting of a variety of effectors depending on its GDP/GTP-bound state. However, molecular mechanisms that trigger Rab7 inactivation remain elusive. Here we find that, among the endosomal pools, Rab7-positive compartments possess the highest level of PI4P, which is primarily produced by PI4K2A kinase.

Lipid synthesis and transport are coupled to regulate membrane lipid dynamics in the endoplasmic reticulum.

Structural lipids are mostly synthesized in the endoplasmic reticulum (ER), from which they are actively transported to the membranes of other organelles. Lipids can leave the ER through vesicular trafficking or non-vesicular lipid transfer and, curiously, both processes can be regulated either by the transported lipid cargos themselves or by different secondary lipid species. For most structural lipids, transport out of the ER membrane is a key regulatory component controlling their synthesis.

Schwann-Cell-Specific Deletion of Phosphatidylinositol 4-Kinase Alpha Causes Aberrant Myelination.

Active membrane remodeling during myelination relies on phospholipid synthesis and membrane polarization, both of which are known to depend on inositol phospholipids. Here, we show that sciatic nerves of mice lacking phosphatidylinositol 4-kinase alpha (PI4KA) in Schwann cells (SCs) show substantially reduced myelin thickness with grave consequences on nerve conductivity and motor functions. Surprisingly, prolonged inhibition of PI4KA in immortalized mouse SCs failed to decrease plasma membrane phosphatidylinositol 4,5-bisphosphate (PI(4,5)P) levels or PI 3-kinase (PI3K) activation, in spite of large reductions in plasma membrane PI4P levels.

Provision of oral hygiene services as a potential method for preventing periodontal disease and control hypertension and diabetes in a community health centre in Korea.

This study aimed to evaluate the effects of a community-based oral hygiene service on general and periodontal health indicators of patients with hypertension and type 2 diabetes mellitus visiting a community health centre in Korea. The study used a one-group pretest-posttest and interrupted time-series design. A total of 151 participants (45% male), with a mean age of 63 ± 8.

Lenz-Majewski mutations in PTDSS1 affect phosphatidylinositol 4-phosphate metabolism at ER-PM and ER-Golgi junctions.

Lenz-Majewski syndrome (LMS) is a rare disease characterized by complex craniofacial, dental, cutaneous, and limb abnormalities combined with intellectual disability. Mutations in thePTDSS1gene coding one of the phosphatidylserine (PS) synthase enzymes, PSS1, were described as causative in LMS patients. Such mutations render PSS1 insensitive to feedback inhibition by PS levels.

Phosphatidylinositol and phosphatidic acid transport between the ER and plasma membrane during PLC activation requires the Nir2 protein.

Phospholipase C (PLC)-mediated hydrolysis of the limited pool of plasma membrane (PM) phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] requires replenishment from a larger pool of phosphatidylinositol (PtdIns) via sequential phosphorylation by PtdIns 4-kinases and phosphatidylinositol 4-phosphate (PtdIns4P) 5-kinases. Since PtdIns is synthesized in the endoplasmic reticulum (ER) and PtdIns(4,5)P2 is generated in the PM, it has been postulated that PtdIns transfer proteins (PITPs) provide the means for this lipid transfer function. Recent studies identified the large PITP protein, Nir2 as important for PtdIns transfer from the ER to the PM.

Phosphatidylinositol-Phosphatidic Acid Exchange by Nir2 at ER-PM Contact Sites Maintains Phosphoinositide Signaling Competence.

Sustained agonist-induced production of the second messengers InsP3 and diacylglycerol requires steady delivery of phosphatidylinositol (PtdIns) from its site of synthesis in the ER to the plasma membrane (PM) to maintain PtdIns(4,5)P2 levels. Similarly, phosphatidic acid (PtdOH), generated from diacylglycerol in the PM, has to reach the ER for PtdIns resynthesis. Here, we show that the Drosophila RdgB homolog, Nir2, a presumed PtdIns transfer protein, not only transfers PtdIns from the ER to the PM but also transfers PtdOH to the opposite direction at ER-PM contact sites.

Distinct properties of the two isoforms of CDP-diacylglycerol synthase.

CDP-diacylglycerol synthases (CDS) are critical enzymes that catalyze the formation of CDP-diacylglycerol (CDP-DAG) from phosphatidic acid (PA). Here we show in vitro that the two isoforms of human CDS, CDS1 and CDS2, show different acyl chain specificities for its lipid substrate. CDS2 is selective for the acyl chains at the sn-1 and sn-2 positions, the most preferred species being 1-stearoyl-2-arachidonoyl-sn-phosphatidic acid.

Inositol lipid regulation of lipid transfer in specialized membrane domains.

The highly dynamic membranous network of eukaryotic cells allows spatial organization of biochemical reactions to suit the complex metabolic needs of the cell. The unique lipid composition of organelle membranes in the face of dynamic membrane activities assumes that lipid gradients are constantly generated and maintained. Important advances have been made in identifying specialized membrane compartments and lipid transfer mechanisms that are critical for generating and maintaining lipid gradients.

A highly dynamic ER-derived phosphatidylinositol-synthesizing organelle supplies phosphoinositides to cellular membranes.

Polyphosphoinositides are lipid signaling molecules generated from phosphatidylinositol (PtdIns) with critical roles in vesicular trafficking and signaling. It is poorly understood where PtdIns is located within cells and how it moves around between membranes. Here we identify a hitherto-unrecognized highly mobile membrane compartment as the site of PtdIns synthesis and a likely source of PtdIns of all membranes.

Dual roles for the Drosophila PI 4-kinase four wheel drive in localizing Rab11 during cytokinesis.

Successful completion of cytokinesis relies on addition of new membrane, and requires the recycling endosome regulator Rab11, which localizes to the midzone. Despite the critical role of Rab11 in this process, little is known about the formation and composition of Rab11-containing organelles. Here, we identify the phosphatidylinositol (PI) 4-kinase III beta four wheel drive (Fwd) as a key regulator of Rab11 during cytokinesis in Drosophila melanogaster spermatocytes.

Live cell imaging with protein domains capable of recognizing phosphatidylinositol 4,5-bisphosphate; a comparative study.

Background: Phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] is a critically important regulatory phospholipid found in the plasma membrane of all eukaryotic cells. In addition to being a precursor of important second messengers, PtdIns(4,5)P2 also regulates ion channels and transporters and serves the endocytic machinery by recruiting clathrin adaptor proteins. Visualization of the localization and dynamic changes in PtdIns(4,5)P2 levels in living cells is critical to understanding the biology of PtdIns(4,5)P2.

Phosphoinositide signaling: new tools and insights.

Phosphoinositides constitute only a small fraction of cellular phospholipids, yet their importance in the regulation of cellular functions can hardly be overstated. The rapid metabolic response of phosphoinositides after stimulation of certain cell surface receptors was the first indication that these lipids could serve as regulatory molecules. These early observations opened research areas that ultimately clarified the plasma membrane role of phosphoinositides in Ca(2+) signaling.