Introduction to membrane lipids

Role of cell membrane homeostasis in the pathogenicity of pathogenic filamentous fungi

The cell membrane forms a fundamental part of all living cells and participates in a variety of physiological processes, such as material exchange, stress response, cell recognition, signal transduction, cellular immunity, apoptosis, and pathogenicity. Here, we review the mechanisms and functions of the membrane structure (lipid components of the membrane and the biosynthesis of unsaturated fatty acids), membrane proteins (transmembrane proteins and proteins contributing to membrane curvature), transcriptional regulation, and cell wall components that influence the virulence and pathogenicity of filamentous fungi.

Changes in Ion Transport across Biological Membranes Exposed to Particulate Matter

The cells of living organisms are surrounded by the biological membranes that form a barrier between the internal and external environment of the cells. Cell membranes serve as barriers and gatekeepers. They protect cells against the entry of undesirable substances and are the first line of interaction with foreign particles. Therefore, it is very important to understand how substances such as particulate matter (PM) interact with cell membranes. To investigate the effect of PM on the electrical properties of biological membranes, a series of experiments using a black lipid membrane (BLM) technique were performed. L-α-Phosphatidylcholine from soybean (azolectin) was used to create lipid bilayers. PM samples of different diameters (<4 (SRM-PM4.0) and <10 μm (SRM-PM10) were purchased from The National Institute of Standards and Technology (USA) to ensure the repeatability of the measurements. Lipid membranes with incorporated gramicidin A (5 pg/mL) ion channels were used to investigate the effect of PM on ion transport. The ionic current passing through the azolectin membranes was measured in ionic gradients (50/150 mM KCl on cis/trans side). In parallel, the electric membrane capacitance measurements, analysis of the conductance and reversal potential were performed. Our results have shown that PM at concentration range from 10 to 150 μg/mL reduced the basal ionic current at negative potentials while increased it at positive ones, indicating the interaction between lipids forming the membrane and PM. Additionally, PM decreased the gramicidin A channel activity. At the same time, the amplitude of channel openings as well as single channel conductance and reversal potential remained unchanged. Lastly, particulate matter at a concentration of 150 μg/mL did not affect the electric membrane capacity to any significant extent. Understanding the interaction between PM and biological membranes could aid in the search for effective cytoprotective strategies. Perhaps, by the use of an artificial system, we will learn to support the consequences of PM-induced damage.

Molecular regulation of lipid metabolism in Suaeda salsa

Suaeda salsa is remarkable for its high oil content and abundant unsaturated fatty acids. In this study, the regulatory networks on fatty acid and lipid metabolism were constructed by combining the de novo transcriptome and lipidome data. Differentially expressed genes (DEGs) associated with lipids biosynthesis pathways were identified in the S. salsa transcriptome. DEGs involved in fatty acid and glycerolipids were generally up-regulated in leaf tissues. DEGs for TAG assembly were enriched in developing seeds, while DEGs in phospholipid metabolic pathways were enriched in root tissues. Polar lipids were extracted from S. salsa tissues and analyzed by lipidomics. The proportion of galactolipid MGDG was the highest in S. salsa leaves. The molar percentage of PG was high in the developing seeds, and the other main phospholipids had higher molar percentage in roots of S. salsa. The predominant C36:6 molecular species indicates that S. salsa is a typical 18:3 plant. The combined transcriptomic and lipidomic data revealed that different tissues of S. salsa were featured with DEGs associated with specific lipid metabolic pathways, therefore, represented unique lipid profiles. This study will be helpful on understanding lipid metabolism pathway and exploring the key genes involved in lipid synthesis in S. salsa.

Eukaryotic Cell Membranes: Structure, Composition, Research Methods and Computational Modelling

This paper deals with the problems encountered in the study of eukaryotic cell membranes. A discussion on the structure and composition of membranes, lateral heterogeneity of membranes, lipid raft formation, and involvement of actin and cytoskeleton networks in the maintenance of membrane structure is included. Modern methods for the study of membranes and their constituent domains are discussed. Various simplified models of biomembranes and lipid rafts are presented. Computer modelling is considered as one of the most important methods. This is stated that from the study of the plasma membrane structure, it is desirable to proceed to the diverse membranes of all organelles of the cell. The qualitative composition and molar content of individual classes of polar lipids, free sterols and proteins in each of these membranes must be considered. A program to create an open access electronic database including results obtained from the membrane modelling of individual cell organelles and the key sites of the membranes, as well as models of individual molecules composing the membranes, has been proposed.

Expression pattern and the roles of phosphatidylinositol phosphatases in testis

Phosphoinositides (PIs) are relatively rare lipid components of the cellular membranes. Their homeostasis is tightly controlled by specific PI kinases and phosphatases. PIs play essential roles in cellular signaling, cytoskeletal organization, and secretory processes in various diseases and normal physiology. Gene targeting experiments strongly suggest that in mice with deficiency of several PI phosphatases such as Pten, Mtmrs, Inpp4b, and Inpp5b, spermatogenesis is affected, resulting in partial or complete infertility. Similarly, in men, loss of several of the PIP phosphatases is observed in infertility characterized by the lack of mature sperm. Using available gene expression databases, we compare expression of known PI phosphatases in various testicular cell types, infertility patients, and mouse age-dependent testicular gene expression, and discuss their potential roles in testis physiology and spermatogenesis.

ATP11B deficiency leads to impairment of hippocampal synaptic plasticity

Synaptic plasticity is known to regulate and support signal transduction between neurons, while synaptic dysfunction contributes to multiple neurological and other brain disorders; however, the specific mechanism underlying this process remains unclear. In the present study, abnormal neural and dendritic morphology was observed in the hippocampus following knockout of Atp11b both in vitro and in vivo. Moreover, ATP11B modified synaptic ultrastructure and promoted spine remodeling via the asymmetrical distribution of phosphatidylserine and enhancement of glutamate release, glutamate receptor expression, and intracellular Ca2+ concentration. Furthermore, experimental results also indicate that ATP11B regulated synaptic plasticity in hippocampal neurons through the MAPK14 signaling pathway. In conclusion, our data shed light on the possible mechanisms underlying the regulation of synaptic plasticity and lay the foundation for the exploration of proteins involved in signal transduction during this process.

A Protective Role for Triacylglycerols during Apoptosis

Triacylglycerols (TAGs) are one of the major constituents of the glycerolipid family. Their main role in cells is to store excess fatty acids, and they are mostly found within lipid droplets. TAGs contain acyl chains that vary in length and degree of unsaturation, resulting in hundreds of chemically distinct species. We have previously reported that TAGs containing polyunsaturated fatty acyl chains (PUFA-TAGs) accumulate via activation of diacylglycerol acyltransferases during apoptosis. In this work, we show that accumulation of PUFA-TAGs is a general phenomenon during this process. We further show that the accumulated PUFA-TAGs are stored in lipid droplets. Because membrane-residing PUFA phospholipids can undergo oxidation and form reactive species under increased levels of oxidative stress, we hypothesized that incorporation of PUFAs into PUFA-TAGs and their localization within lipid droplets during apoptosis limit the toxicity during this process. Indeed, exogenous delivery of a polyunsaturated fatty acid resulted in a profound accumulation of PUFA phospholipids and rendered cells more sensitive to oxidative stress, causing reduced viability. Overall, our results support the concept that activation of TAG biosynthesis protects cells from lipid peroxide-induced membrane damage under increased levels of oxidative stress during apoptosis. As such, targeting triacylglycerol biosynthesis in cancer cells might represent a new approach to promoting cell death during apoptosis.

Complex Relations Between Phospholipids, Autophagy, and Neutral Lipids

Research in the past decade has established the importance of autophagy to a large number of physiological processes and pathophysiological conditions. Originally characterized as a pathway responsible for protein turnover and recycling of amino acids in times of starvation, it has been recently recognized as a major regulator of lipid metabolism. Different lipid species play various roles in the regulation of autophagosomal biogenesis, both as membrane constituents and as signaling platforms. Distinct types of autophagy, in turn, facilitate specific steps in metabolic pathways of different lipid classes, best exemplified in recent studies on neutral lipid dynamics. We review the emerging notion of intricate links between phospholipids, autophagy, and neutral lipids.