Modulation by Sphingosine of Phosphorylation of Substrate Proteins by Protein Kinase C in Nuclei from Cow Mammary Gland

Fumonisin distorts the cellular membrane lipid profile: A mechanistic insight

Monitoring modifications in membrane lipids in association with external stimuli/agents, including fumonisins (FUMs), is a widely employed approach to assess cellular metabolic response/status. FUMs are prevalent fusariotoxins worldwide that have diverse structures with varying toxicity across species; nevertheless, they can induce metabolic disturbances and disease, including cancer. The capacity of FUMs to disrupt membrane lipids, demonstrated across numerous species and organs/tissues, is ascribed to a multitude of factors/events, which range from direct to indirect effects. Certain events are well established, whereas the potential consequences of others remain speculative. The most notable effect is their resemblance to sphingoid bases, which impacts the synthesis of ceramides leading to numerous changes in lipids' composition that are not limited to sphingolipids' composition of the membranes. The next plausible scenario involves the induction of oxidative stress, which is considered an indirect/secondary effect of FUMs. Additional modes of action include modifications of enzyme activities and nuclear signals related to lipid metabolism, although these are likely not yet fully comprehended. This review provides in-depth insight into the current state of these events and their potential mechanistic actions in modifying membrane lipids, with a focus on long-chain fatty acids. This paper also presents a detailed description of the reported modifications to membrane lipids by FUMs.

Review of Eukaryote Cellular Membrane Lipid Composition, with Special Attention to the Fatty Acids

Biological membranes, primarily composed of lipids, envelop each living cell. The intricate composition and organization of membrane lipids, including the variety of fatty acids they encompass, serve a dynamic role in sustaining cellular structural integrity and functionality. Typically, modifications in lipid composition coincide with consequential alterations in universally significant signaling pathways. Exploring the various fatty acids, which serve as the foundational building blocks of membrane lipids, provides crucial insights into the underlying mechanisms governing a myriad of cellular processes, such as membrane fluidity, protein trafficking, signal transduction, intercellular communication, and the etiology of certain metabolic disorders. Furthermore, comprehending how alterations in the lipid composition, especially concerning the fatty acid profile, either contribute to or prevent the onset of pathological conditions stands as a compelling area of research. Hence, this review aims to meticulously introduce the intricacies of membrane lipids and their constituent fatty acids in a healthy organism, thereby illuminating their remarkable diversity and profound influence on cellular function. Furthermore, this review aspires to highlight some potential therapeutic targets for various pathological conditions that may be ameliorated through dietary fatty acid supplements. The initial section of this review expounds on the eukaryotic biomembranes and their complex lipids. Subsequent sections provide insights into the synthesis, membrane incorporation, and distribution of fatty acids across various fractions of membrane lipids. The last section highlights the functional significance of membrane-associated fatty acids and their innate capacity to shape the various cellular physiological responses.

Mammalian sphingoid bases: Biophysical, physiological and pathological properties

Sphingoid bases encompass a group of long chain amino alcohols which form the essential structure of sphingolipids. Over the last years, these amphiphilic molecules were moving more and more into the focus of biomedical research due to their role as bioactive molecules. In fact, free sphingoid bases interact with specific receptors and target molecules and have been associated with numerous biological and physiological processes. In addition, they can modulate the biophysical properties of biological membranes. Several human diseases are related to pathological changes in the structure and metabolism of sphingoid bases. Yet, the mechanisms underlying their biological and pathophysiological actions remain elusive. Within this review, we aimed to summarize the current knowledge on the biochemical and biophysical properties of the most common sphingoid bases and to discuss their importance in health and disease.

Mammalian sphingoid bases: Biophysical, physiological and pathological properties

Sphingoid bases encompass a group of long chain amino alcohols which form the essential structure of sphingolipids. Over the last years, these amphiphilic molecules were moving more and more into the focus of biomedical research due to their role as bioactive molecules. In fact, free sphingoid bases interact with specific receptors and target molecules, and have been associated with numerous biological and physiological processes. In addition, they can modulate the biophysical properties of biological membranes. Several human diseases are related to pathological changes in the structure and metabolism of sphingoid bases. Yet, the mechanisms underlying their biological and pathophysiological actions remain elusive. Within this review, we aimed to summarize the current knowledge on the biochemical and biophysical properties of the most common sphingoid bases and to discuss their importance in health and disease.

Changes in cerebral membrane lipid composition and fluidity during thioacetamide-induced hepatic encephalopathy

Lipids are an essential structural and functional component of cellular membranes. Changes in membrane lipid composition are known to affect the activities of many membrane-associated enzymes, endocytosis, exocytosis, membrane fusion and neurotransmitter uptake, and have been implicated in the pathophysiology of many neurodegenerative disorders. In the present study, we investigated changes in the lipid composition of membranes isolated from the cerebral cortex of rats treated with thioacetamide (TAA), a hepatotoxin that induces fulminant hepatic failure (FHF) and thereon hepatic encephalopathy (HE). HE refers to acute neuropsychiatric changes accompanying FHF. The estimation of membrane phospholipids, cholesterol and fatty acid content in cerebral cortex membranes from TAA-treated rats revealed a decrease in cholesterol, phosphatidylserine, sphingomyelin, a monounsaturated fatty acid, namely oleic acid, and the polyunsaturated fatty acids gamma-linolenic acid, decosa hexanoic acid and arachidonic acid compared with controls. Assessment of membrane fluidity with pyrene, 1,6-diphenyl-1,3,5-hexatriene and 1-[4-(trimethylammonio)phenyl]-6-phenyl-1,3,5-hexatriene revealed a decrease in the annular membrane fluidity, whereas the global fluidity was unaffected. The level of the thiobarbituric acid reactive species marker for lipid peroxidation also increased in membranes from TAA-treated rats, thereby indicating the prevalence of oxidative stress. Results from the present study demonstrate gross alterations in cerebral cortical membrane lipid composition and fluidity during TAA-induced HE, and their possible implications in the pathogenesis of this condition are also discussed.

Similarities of cow mammary gland cytosolic 21-kDa protein, the substrate for protein kinase C, to the 20-kDa myosin light chain from smooth muscle

In the cytosol of cow mammary gland, several proteins are phosphorylated in the presence of the protein kinase C (PKC) cofactors 1-oleoyl-2-acetyl-sn-glycerol (OAG), phosphatidylserine (PS) and Ca2+. Of the substrates, the 21-kDa protein is inferred to be a 20-kDa regulatory myosin light chain (MLC20) from smooth muscle because of its molecular mass, its distribution in the cytosol, its association with melittin and sphingosine (the PKC modulators), and phosphorylation by PKC as well as by Ca2+/calmodulin-dependent myosin light chain kinase (MLCK). The present study was undertaken to examine whether the 21-kDa protein could be identified as MLC20, by adding cow uterine MLC20 to the reaction mixture containing cytosol with or without the PKC cofactors and/or calmodulin. In the absence of MLC20, the 21-kDa protein was phosphorylated when the PKC cofactors and calmodulin were added to the reaction mixture. Phosphorylation of the 21-kDa protein was inhibited by melittin or sphingosine, and the inhibition was reversed by PS, but not by calmodulin. When MLC20 was included in the reaction mixture, it was phosphorylated in the presence of the PKC cofactors, and the phosphorylated MLC20 band overlapped that of the 21-kDa protein. The indistinguishably overlapped band of the two proteins was inhibited by melittin and by sphingosine, and their inhibition was reversed by PS, not by calmodulin. It is suggested that the 21-kDa protein is the smooth muscle MLC20 and also that the 21-kDa MLC20 is phosphorylated by PKC, but not by MLCK.