Lipid second messengers generated from phosphatidic acid in isolated nuclei of rat cerebellum. Effect of nuclear agonists and ageing.

GAVEGLIO, V.L.; PASQUARÉ, S.J.; GIUSTO, N.M.

Buenos Aires

Workshop; Frontiers in Bioscience; 2012

MINCYT y Sociedad MAX PLANCK

Lipids are present not only in the nuclear envelope but also inside the nucleus as a component of chromatin. Nuclear lipid metabolism is different from either plasma membrane metabolism or that of other cellular organelles. It gives rise to several lipid second messengers that seem to be involved in the regulation of nuclear structure and gene expression. The purpose of the present research was therefore to study the metabolic pathways involved in the degradation of phosphatidic acid (PA) and its regulation in isolated nuclei from the central nervous system. This investigation would allow us to better understand the role of PA and the second messengers generated from it (diacylglycerol, monoacylglycerol, lysophosphatidic acid) in different nuclear processes. This study conducted in isolated nuclei from aged animalswill also allow us to analyze the effect of neurodegeneration on PA metabolism as a result of ageing. To this end, adult (4 mo) and aged (28 mo) rat cerebellums were homogenized and highly purified nuclei were isolated by sucrose-density ultracentrifugation. Using radiolabelled substrates we demonstrated the existence of lipid phosphate phosphatases (LPPs), diacylglycerol lipase (DAGL), monoacylglycerol lipase (MAGL), lysophosphatidate phosphohydrolase (LPAPase) and phospholipase (LPAase) as well as phosphatidic acidspecific phospholipase type A (PA-PLA) activities in rat cerebelar nuclei. We also characterized LPPs and DAGL enzymatic activities, and we analyzed the competitiveness between PA and other phosphorylated lipids by LPPs, as well as, their modulation by ions (Ca2+, Mg2+, F-) and detergents (Triton X-100, deoxycholate). These activities modulate changes in nuclear lipid composition, generating second messengers involved in intranuclear signalling. We further studied their regulation by nuclear agonists such as retinoic acid (RA), lysophosphatidic acid (LPA) and prostaglandin E2. The nuclear membranes incubated with a nuclear receptor (RAR) agonist, all-trans RA, were observed to produce a decrease in DAGL and MAGL activities while LPA was found to decrease LPPs and DAGL activities. In addition, we observed significant aged-related changes not only in the above-mentioned enzymatic activities involved in PA metabolism but also in its regulation by RA. Taken together, our results demonstrate an active PA metabolism related to signalling pathways in rat cerebellum nuclei. In line with these findings, further studies will be carried out on the regulation of these metabolic pathways by other nuclear agonists involved in neuronal inflammatory processes.