The synthesis of Retinal Ganglion Cell Phospholipids is under control of an Endogenous Circadian Clock. Daily Variations in Phospholipid Synthesizing Enzyme Activities

E. GARBARINO-PICO,; A.R. CARPENTIERI,; P. CASTAGNET,; S. PASQUARÉ,; M. GIUSTO, N.; B.L. CAPUTTO,; MARIO EDUARDO GUIDO

JOURNAL OF NEUROSCIENCE RESEARCH

WILEY-LISS, DIV JOHN WILEY & SONS INC

Año: 2004 vol. 76 p. 642 - 652

0360-4012

Retinal ganglion cells (RGCs) are major components of the vertebrate circadian system. They send information to the brain synchronizing the entire organism to the light-dark cycles. We recently reported that chicken RGCs display daily variations in the biosynthesis of glycerophospholipids in constant darkness (DD). It was unclear if this rhythmicity was driven by this population itself or by other retinal cells. Here we show that RGCs present circadian oscillations in the labeling of 32P-phospholipids both in vivo in constant light (LL) and in cultures of immunopurified embryonic cells. In vivo, there was greater 32P-orthophosphate incorporation into total phospholipids during the subjective day. Phosphatidylinositol (PI) was the utmost 32P-labeled lipid at all times examined displaying maximum levels during the subjective day and dusk. In addition, a significant daily variation was found in the activity of distinct enzymes of the pathway of phospholipid biosynthesis and degradation such as lysophospholipid acyltransferases (AT II), phosphatidate phosphohydrolase (PAP) and diacylglycerol lipase (DGL) in cell preparations obtained in DD, exhibiting differential but coordinated temporal profiles. Furthermore, cultures of immunopurified RGCs synchronized by medium exchange, displayed a circadian fluctuation in the phospholipid labeling. The results demonstrate that chicken RGCs contain circadian oscillators capable of generating metabolic oscillations in the biosynthesis of phospholipids autonomously.