Developmental changes and regional distribution of phospholipase D and base exchange enzyme activities in rat brain

The Potential Mechanism of Eriodictyol in Treating Alzheimer's Disease: A Study on Computer-assisted Investigational Strategies

BACKGROUND

At present, drug development for treating Alzheimer's disease (AD) is still highly challenging. Eriodictyol (ERD) has shown great potential in treating AD, but its molecular mechanism is unknown.

OBJECTIVE

We aimed to explore the potential targets and mechanisms of ERD in the treatment of AD through network pharmacology, molecular docking, and molecular dynamics simulations.

METHODS

ERD-related targets were predicted based on the CTD, SEA, PharmMapper, Swiss TargetPrediction, and ETCM databases, and AD-related targets were predicted through the TTD, OMIM, DrugBank, GeneCards, Disgenet, and PharmGKB databases. Protein-protein interaction, Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomics analyses (KEGG) were used to analyse the potential targets and key pathways of the anti-AD effect of ERD. Subsequently, potential DEGs affected by AD were analysed using the AlzData database, and their relationships with ERD were evaluated through molecular docking and molecular dynamics simulations.

RESULTS

A total of 198 ERD-related targets, 3716 AD-related targets, and 122 intersecting targets were identified. GO annotation analysis revealed 1497 biological processes, 78 cellular components, and 132 molecular functions of 15 core targets. KEGG enrichment analysis identified 168 signalling pathways. We ultimately identified 9 DEGs associated with AD through analysis of the AlzData data. Molecular docking results showed good affinity between the selected targets and ERD, with PTGS2, HSP90AA1, and BCL2. The interactions were confirmed by molecular dynamics simulations.

CONCLUSION

ERD exerts anti-AD effects through multiple targets, pathways, and levels, providing a theoretical foundation and valuable reference for the development of ERD as a natural anti-AD drug.

The Normal Human Adult Hypothalamus Proteomic Landscape: Rise of Neuroproteomics in Biological Psychiatry and Systems Biology

The human hypothalamus is central to the regulation of neuroendocrine and neurovegetative systems, as well as modulation of chronobiology and behavioral aspects in human health and disease. Surprisingly, a deep proteomic analysis of the normal human hypothalamic proteome has been missing for such an important organ so far. In this study, we delineated the human hypothalamus proteome using a high-resolution mass spectrometry approach which resulted in the identification of 5349 proteins, while a multiple post-translational modification (PTM) search identified 191 additional proteins, which were missed in the first search. A proteogenomic analysis resulted in the discovery of multiple novel protein-coding regions as we identified proteins from noncoding regions (pseudogenes) and proteins translated from short open reading frames that can be missed using the traditional pipeline of prediction of protein-coding genes as a part of genome annotation. We also identified several PTMs of hypothalamic proteins that may be required for normal hypothalamic functions. Moreover, we observed an enrichment of proteins pertaining to autophagy and adult neurogenesis in the proteome data. We believe that the hypothalamic proteome reported herein would help to decipher the molecular basis for the diverse range of physiological functions attributed to it, as well as its role in neurological and psychiatric diseases. Extensive proteomic profiling of the hypothalamic nuclei would further elaborate on the role and functional characterization of several hypothalamus-specific proteins and pathways to inform future research and clinical discoveries in biological psychiatry, neurology, and system biology.

Phospholipase D in brain function and Alzheimer's disease

Alzheimer's disease is the most common neurodegenerative disorder. Although lipids are major constituents of brain, their role in Alzheimer's disease pathogenesis is poorly understood. Much attention has been given to cholesterol, but growing evidence suggests that other lipids, such as phospholipids, might play an important role in this disorder. In this review, we will summarize the evidence linking phospholipase D, a phosphatidic acid-synthesizing enzyme, to multiple aspects of normal brain function and to Alzheimer's disease. The role of phospholipase D in signaling mechanisms downstream of beta-amyloid as well as in the trafficking and processing of amyloid precursor protein will be emphasized.

Metabolism and functions of phosphatidylserine in mammalian brain

Phosphatidylserine (PtdSer) is involved in cell signaling and apoptosis. The mechanisms regulating its synthesis and degradation are still not defined. Thus, its role in these processes cannot be clearly established at molecular level. In higher eukaryotes, PtdSer is synthesized from phosphatidylethanolamine or phosphatidylcholine through the exchange of the nitrogen base with free serine. PtdSer concentration in the nervous tissue membranes varies with age, brain areas, cells, and subcellular components. At least two serine base exchange enzymes isoforms are present in brain, and their biochemical properties and regulation are still largely unknown because their activities vary with cell type and/or subcellular fraction, developmental stage, and differentiation. These peculiarities may explain the apparent contrasting reports. PtdSer cellular levels also depend on its decarboxylation to phosphatidylethanolamine and conversion to lysoPtdSer by phospholipases. Several aspects of brain PtdSer metabolism and functions seem related to the high polyunsaturated fatty acids content, particularly docosahexaenoic acid (DHA).

Developmental changes in phospholipase D activity and mRNA levels in rat brain

Phospholipase D (PLD) activity and PLD1 mRNA levels were determined in rat brain at ages ranging from embryonic day (E) 19 to postnatal day (P) 49. Basal, oleate-, and phosphatidylinositol-4, 5-bisphosphate-stimulated PLD activity increased between E19 and P24 by approximately 3-fold and remained unaltered thereafter. A similar developmental pattern of mRNA levels of PLD1 isoform was found by Northern blotting. The development of PLD correlates with synaptogenesis and myelination suggesting that the enzyme might have an important function in these processes.

Phospholipase D hydrolyzes short-chain analogs of phosphatidylcholine in the absence of detergent

Phospholipase D is an important enzyme in signal transduction in neuronal tissue. A variety of assays have been used to measure phospholipase D activity in vitro. The most typical measure of phospholipase D activity is the production of phosphatidylethanol in the presence of ethanol. Phosphatidylethanol is a product of transphosphatidylation activity that is considered a unique property of phospholipase D. To support transphosphatidylation activity, high concentrations of ethanol may be required. Furthermore, most assays in the literature utilize a detergent. These extreme conditions, detergent and ethanol, may alter phospholipase D and hinder the study of its regulation. In this manuscript we describe an assay that eliminates these potentially confounding conditions. It utilizes high specific activity [3H]butanol as a nucleophilic receptor. This eliminates the need for high concentrations of alcohol. The substrate is an analog of phosphatidylcholine that contains short-chain fatty acids, 1,2-dioctanoyl-sn-glycero-3-phosphocholine. Phospholipase D readily hydrolyzes this substrate in the absence of detergent. This novel assay should be useful in the further characterization of phospholipase D.

Enzymology of mammalian phospholipases D: in vitro studies

The existence of multiple forms of phopholipase D was clearly established in a large number of biochemical studies that described and characterized the enzymological properties of the different PLD activities. This review summarizes the in vitro evidence showing differential subcellular localization and chromatographic properties of putative PLD isozymes, their phospholipid and alcohol substrate specificities, their modulation by various divalent cations, small G proteins and protein kinase c isozymes, and the role of phosphatidylinositol 4,5-bisphosphate as a cofactor of phospholipase D.

Brain ischemia decreases phosphatidylcholine-phospholipase D but not phosphatidylinositol-phospholipase C in rats

BACKGROUND AND PURPOSE

Phosphatidylcholine (PC)-phospholipase D (PLD) is an important intracellular signaling pathway in response to a variety of agonists, but little is known about the effects of brain ischemia on the PC-PLD system. We thus have examined the effects of global cerebral ischemia on PLD in rats.

METHODS

We have examined the effects of global ischemia (decapitation or four-vessel occlusion) on PLD and PLC activity in the membrane fraction of rat brains. We measured the PLD and PLC activity in detergent-mixed micelle assay systems using 3H-labeled exogenous substrate.

RESULTS

The results demonstrate that basal PLD activity showed a gradual decrease with increased duration (5 to 30 minutes) of ischemia by decapitation in the hippocampus; after 30 minutes of ischemia, PLD activity was significantly decreased compared with the control. Lineweaver-Burk plots showed that the apparent Vmax value of PLD in ischemia was one half of that in the control without changes in Km value. Ischemia by decapitation significantly decreased PLD activity in the brain stem as well as the hippocampus, whereas in four-vessel occlusion study, ischemia significantly decreased PLD activity in the hippocampus but not in the brain stem. Lowered temperature (30 degrees C and 22 degrees C) during ischemic incubation did not reverse the ischemia-induced PLD activity decrease. In contrast to PLD, ischemia by decapitation had no effect on basal phosphatidylinositol-phospholipase C activity or the amount of phospholipase C beta 1 in the membrane fractions from 30-minute ischemic hippocampus by immunoblots probed with the antibody.

CONCLUSIONS

These results suggest that PC-PLD is one of the target enzymes of ischemia; its decrease may cause a perturbation of PC hydrolysis and/or disorders of intracellular transduction of signals or choline metabolism for acetylcholine formation in brain.

Modulation of the serine base exchange enzyme activity of rat brain membranes by amphiphilic cations and amphiphilic anions

The biosynthesis of phosphatidylserine in mammalian tissues is catalyzed by the serine base exchange enzyme. The activity of this membrane-bound enzyme can be manipulated by amphiphiles. Amphiphilic cations, such as oleylamine, W-7, chlorpromazine, and didodecyldimethylamine, stimulate the serine base exchange activity. Amphiphilic anions, such as bis(2-ethylhexyl) hydrogen phosphate and cholesterol sulfate, inhibit the serine base exchange activity. These effects are more pronounced at pH 7.0 than at the pH optimum of 8.5 for this enzyme. Both the stimulators and the inhibitors alter the Vmax values without changing the Km value for serine, suggesting that their mechanism of action is related to interactions of the membrane-bound cosubstrate, phosphatidylethanolamine, with the membrane-bound enzyme. The optimal concentration of stimulator varies with the amount of membrane protein present; however, supraoptimal concentrations cause inhibitions. It is proposed that the amphiphilic cations enhance the interaction of the phosphorylethanolamine moiety of the membrane-bound cosubstrate with the enzyme and the amphiphilic anions interfere with such an interaction. Some of the pharmacological properties of these amphiphilic cations, employed clinically as antidepressants, may be mediated by modulation of the serine base exchange enzyme activity.

Effects of chlorpromazine on phosphatidylserine biosynthesis in rat pup brain exposed to ethanol in utero

Phosphatidylserine biosynthesis in rat pup brain was examined by assaying the serine base-exchange enzyme activity in the microsomal and plasma membrane fractions, and by measuring the incorporation of [3H]serine into phosphatidylserine in brain slices and in the intact brain. Chlorpromazine, either added in vitro into the incubation system or administered to animals via i.p. injection or feeding a liquid diet, gave rise to an increase in the phosphatidylserine biosynthesis activity. Ethanol administered in the form of a liquid diet to pregnant rats (day 11 birth) resulted in a decrease in phosphatidylserine biosynthesis in the newborn and developing brain. The ethanol-induced decrease in phosphatidylserine biosynthetic activity could be reversed by adding chlorpromazine to the ethanol diet. Results demonstrate that phosphatidylserine biosynthesis in the neonatal brain is affected in opposite directions by chlorpromazine and ethanol. This poses the possibility that chlorpromazine administration may be effective in alleviating the deleterious effects caused by the decreased phosphatidylserine biosynthesis in brain due to in utero ethanol exposure.

In vitro and in vivo ethanolamine metabolism in rat brain: effect of time and aging

The effect of the time in culture of foetal rat neurons and age on the incorporation of radioactive ethanolamine into methylated derivatives was investigated. Decreased incorporation of [3H]ethanolamine into its various methylated water-soluble and lipidic derivatives was observed in rat neurons cultures at 12 day in vitro (DIV) as compared to the 3rd and the 7th DIV. In vivo studies showed that there was a diminished labeling of methylated products in the older animals as compared to the younger ones. These in vitro and in vivo observations suggest a generalized decrease of N-methyltransferase activities during maturation and aging.

Sphingosine and unsaturated fatty acids modulate the base exchange enzyme activities of rat brain membranes

The base exchange enzymes catalyze the incorporation of L-serine, ethanolamine and choline into their corresponding phospholipids. The L-serine base enzyme activity was increased 120% by 0.1 mM sphingosine. There was a modest increase of the ethanolamine base exchange enzyme activity but the choline base exchange enzyme activity was unaffected. Na-arachadonate, Na-oleate and Na-linolenate at 0.2 mM concentration increased the activity of the L-serine and ethanolamine base exchange enzymes but inhibited the choline base exchange enzyme activity. A model is proposed suggesting that modulations of the L-serine base exchange enzyme may participate in the regulation of the calcium phospholipid-dependent protein kinase C.

Phospholipase D activity in subcellular membranes of rat ventricular myocardium

The phospholipase D (PL D), which catalyzes the formation of phosphatidic acid (PA), was studied in rat myocardium using 14C-labelled phosphatidylcholine (PC) as an exogenous substrate. Subcellular distribution experiments indicated the presence of PL D in particulate fractions only. Different procedures for the isolation of purified cardiac subcellular organelles showed the presence of PL D in sarcolemma (SL), sarcoplasmic reticulum (SR) and mitochondria with 14-, 11- and 5-fold enrichment when compared to the homogenate value, respectively. The activity of SL PL D was observed over a narrow acid pH range with an optimum at 6.5, and it showed a high specificity for PC while phosphatidylethanolamine and phosphatidylinositol showed a low rate of hydrolysis. Under optimal conditions, PA formation was linear for a 90-min period of incubation and the reaction rate was constant for 10 to 100 micrograms SL protein in the assay medium. The SR PL D displayed properties similar to those seen with the SL PL D. In membrane fractions PL D was also found to catalyze a transphosphatidylation reaction for the synthesis of phosphatidylglycerol. Assessment of the intramembranal levels of radioactive 1,2-diacylglycerol (DAG) in the absence or presence of KF suggested the presence of an active PA phosphohydrolase activity. This study indicates that a PC-specific PL D activity is localized in different membrane systems of the myocardium and may be associated with PA phosphohydrolase to act in a coordinated manner. The functional significance of PL D-dependent formation of PA in cardiac membranes is discussed.

Isolation and characterization of a phosphatidylinositol-glycan-anchor-specific phospholipase D from bovine brain

In recent years an increasing number of proteins has been shown to be membrane-anchored by a covalently attached PtdIns-glycan residue. In mammalian cells little is known about PtdIns-glycan-specific phospholipases which might play a role in the metabolism of PtdIns-glycan-anchored proteins. In order to identify PtdIns-glycan-specific phospholipases, a rapid and sensitive assay for such enzymes was developed using the PtdIns-glycan-anchored amphiphilic membrane form of acetylcholinesterase as substrate. The rate of product formation was monitored by the increase in soluble hydrophilic acetylcholinesterase in the aqueous phase after separation in Triton X-114. With this assay we established the presence of a PtdIns-glycan-specific phospholipase in bovine brain. This enzyme was soluble and could be partially purified by a heat step followed by chromatography on DEAE-cellulose and by gel filtration on Sepharose CL-6B. PtdIns-glycan-specific phospholipase had a high affinity for the PtdIns-glycan anchor of the substrate (Km = 52 nM) and did not degrade either PtdCho or PtdIns. Hydrophobic labeling of the anchor of the substrate with 3-trifluoromethyl-3-(m-[125I]iodophenyl)diazirine [( 125I]TID) caused a marked decrease in the cleavage rate and methylation of the amino group of the glucosamine residue of the anchor decreased the cleavage rate to zero. Using [125I]TID-labeled substrate, diradylglycerol phosphate was identified as the second product showing that the cleavage specificity of PtdIns-glycan-specific phospholipase was that of a phospholipase D. PtdIns-glycan-specific phospholipase D was inhibited by mercurials, omicron-phenanthroline and EGTA. It was stimulated by Ca2+ in micromolar concentrations indicating that PtdIns-glycan-phospholipase D is a Ca2(+)-regulated enzyme.

Enzymatic activities during differentiation of the human neuroblastoma cells, LA-N-1 and LA-N-2

The presence of 10(-5) M retinoic acid (RA) in the culture medium of LA-N-1, a catecholaminergic cell line, and LA-N-2, a cholinergic cell line, enhanced their morphological differentiation. Tyrosine hydroxylase (TH) activity of the LA-N-1 cells was increased in the RA-treated cells compared with control cultures at day 4 and remained elevated. Choline acetyltransferase (ChAT) activity in the LA-N-2 cells gradually increased until 8 days in vitro (DIV) both in the untreated control and the RA treated cultures. This activity in control and treated cells decreased gradually to a constant level of activity. The ChAT activity at 8 DIV of RA-treated LA-N-2 cells was increased 2.1-fold (P less than 0.001) as compared to the control cultures. This increase in ChAT activity was accompanied by a 73% decrease of acetylcholinesterase (AChE) activity in LA-N-2 cells by 8 DIV. AChE activity of LA-N-1 cells was unchanged during the time course of the experiment. Phospholipase-A2 (PL-A2) activity in RA-treated LA-N-2 cells was increased at day 4 as compared with the control cultures. There were no differences observed in phospholipase-D (PL-D), choline kinase and GPC-phosphodiesterases activities in RA-treated and -untreated LA-N-1 and LA-N-2 cells.