Identifying the regulatory functions of nuclear lipid synthesis and storage pathways

• Grant number: 19/26521-3
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• Start date: March 01, 2020
• End date: February 28, 2021
• Field of knowledge: Biological Sciences - Morphology - Cytology and Cell Biology
• Principal Investigator: Aníbal Eugênio Vercesi
• Grantee: Gabriel de Gabriel Taffarello Dorighello
• Supervisor: Neale Ridgway
• Host Institution: Faculdade de Ciências Médicas (FCM). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil
• Institution abroad: Dalhousie University, Canada
• Associated to the scholarship: 17/02903-9 - Role of CETP expression in the macrophage redox state: possible consequences to inflammation and atherosclerosis, BP.PD

Abstract

The lipid droplets (LDs) store triglycerides (TG) and release fatty acids in response to nutrient and hormonal signals, effectively maintaining energy reserves and buffering the cell from fatty acid toxicity. The imbalance between the lipid biogenesis, cellular uptake and the energy storage cause hepatic steatosis and macrophage foam cell formation. Lipid synthesis and lipid droplets formation occurs in the cytoplasmic ER, but the ER also includes the inner nuclear membrane (INM). Associated with the INM are two key enzymes for phosphatidylcholine (PC) and diacylglycerol (DAG) synthesis, Choline-phosphate cytidylyltransferase a (CCTa) and Lipin1. Inhibition of Lipin1, in human U2OS cells, increased PC synthesis and nuclear membrane proliferation, but direct effects on CCTa were not reported. In contrast, Lipin1a expression in rat hepatoma cells was positively correlated with increased synthesis of TG, PC and PE. Hence, the relation between Lipin and CCTa in the INM lipid synthesis should be more studied. Additionally, the nLDs are present in many normal and transformed cell lines, rodent liver sections and yeast, which supports the concept that de novo phospholipid and TG synthesis occur in the nucleus. Corroborating with this concept, evidence indicates that choline/ethanolamine phosphotransferase (CEPT) and/or choline phosphotransferase (CPT) could synthesize PC in the INM: 1- Yeast homologues of CPT and CEPT were identified in the INM; 2- ~10% of epitope-tagged CEPT expressed in CHO cells was localized to the nuclear envelope (NE); 3- deuterated choline and fatty acid-labelled lipids were detected in the NE using nanoscale-secondary ion mass spectrometry. While this evidence is not conclusive, it implies that a subset of CEPT and/or CPT could be localized on the outer nuclear membrane and/or INM. Thus, the capacity of the INM to synthesize and store phospholipids and TG, and the potential relationship to genomic functions, is poorly understood and should be more studied. The objectives of this study are: 1- Evaluate if nuclear Lipin1 regulates CCT± translocation and activity at the INM and nLDs by modifying PA and DAG levels; 2- Determine if ER-localized CEPT/CPT and DGAT1/2 are also present on the INM. (AU)