Unique Glycerophospholipid Signature in Retinal Stem Cells Correlates with Enzymatic Functions of Diverse Long-chain Acyl-CoA Synthetases

¹ Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
² Department of Pathology, Wake Forest University School of Medicine, Winston-Salem, NC, USA
³ Flow Cytometry Facility, Hospital for Sick Children, University of Toronto, Toronto, ON, Canada

^* To whom correspondence should be addressed. E-mail: jli7{at}caregroup.harvard.edu.

	Abstract

Lipidomics is an emerging research field that comprehensively characterizes lipid molecular species, their metabolic regulation and biological roles. We performed the first lipidomics study on glycerophospholipids (GPL) in adult mammalian retinal stem cells (RSC) and non-RSC control cells. A unique GPL signature identified by electrospray ionization tandem mass spectrometry showed new prominent peaks of 16:0 (sn-1)-18:0 (sn-2) or 16:0-16:0 saturated fatty acids, instead of 18:0-20:4 or 18:0-22:6 polyunsaturated essential fatty acids, at 720 m/z of phosphatidylethanolamine, 764 m/z of phosphatidylserine and 809 m/z of phosphatidylinositol in RSCs (sphere colony RSCs and enriched RSCs), but not in non-RSCs (retinal cells, ciliary cells, sphere colony-derived retinal cells and non-retinal cells). To seek whether the GPL signature was associated with long-chain acyl-CoA synthetase (LACS), a potential modulator of fatty acid profiles in de novo GPL synthesis, we analyzed gene expression, catabolic activity, substrate selectivity and inhibitor sensitivity of diverse LACSs. LACSs in RSCs mediated less utilization by GPLs of polyunsaturated essential fatty acids, including arachidonic acid [20:4 (n-6), a second messenger in cell signaling], which was accompanied by lower plasma membrane fluidity in proliferating RSCs compared to differentiated non-RSCs. These novel findings suggest that LACS-associated GPL signature and cell membrane fluidity may participate in regulating proliferation versus differentiation in RSCs, and perhaps other types of stem cells.