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Open Access Research article

Generation of choline for acetylcholine synthesis by phospholipase D isoforms

Di Zhao1, Michael A Frohman3 and Jan Krzysztof Blusztajn12*

Author Affiliations

1 Departments of Pathology and Laboratory Medicine, Boston University, School of Medicine, Boston, MA, USA

2 Department of Psychiatry, Boston University School of Medicine, Boston, MA, USA

3 Department of Pharmacology and the Center for Developmental Genetics, SUNY at Stony Brook, Stony Brook, New York, USA

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BMC Neuroscience 2001, 2:16  doi:10.1186/1471-2202-2-16

Published: 19 October 2001

Abstract

This article is dedicated to the memory of Sue Kim Hanson, a graduate student in the department of Pathology and Laboratory Medicine at Boston University School of Medicine, who perished in the terrorist attacks of September 11, 2001.

Background

In cholinergic neurons, the hydrolysis of phosphatidylcholine (PC) by a phospholipase D (PLD)-type enzyme generates some of the precursor choline used for the synthesis of the neurotransmitter acetylcholine (ACh). We sought to determine the molecular identity of the relevant PLD using murine basal forebrain cholinergic SN56 cells in which the expression and activity of the two PLD isoforms, PLD1 and PLD2, were experimentally modified. ACh levels were examined in cells incubated in a choline-free medium, to ensure that their ACh was synthesized entirely from intracellular choline.

Results

PLD2, but not PLD1, mRNA and protein were detected in these cells and endogenous PLD activity and ACh synthesis were stimulated by phorbol 12-myristate 13-acetate (PMA). Introduction of a PLD2 antisense oligonucleotide into the cells reduced PLD2 mRNA and protein expression by approximately 30%. The PLD2 antisense oligomer similarly reduced basal- and PMA-stimulated PLD activity and ACh levels. Overexpression of mouse PLD2 by transient transfection increased basal- (by 74%) and PMA-stimulated (by 3.2-fold) PLD activity. Moreover, PLD2 transfection increased ACh levels by 26% in the absence of PMA and by 2.1-fold in the presence of PMA. Overexpression of human PLD1 by transient transfection increased PLD activity by 4.6-fold and ACh synthesis by 2.3-fold in the presence of PMA as compared to controls.

Conclusions

These data identify PLD2 as the endogenous enzyme that hydrolyzes PC to generate choline for ACh synthesis in cholinergic cells, and indicate that in a model system choline generated by PLD1 may also be used for this purpose.