Date of Award

8-1996

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Medical Sciences

Supervisor

Rolf J. Sebaldt

Abstract

The focus of my thesis was to investigate changes in the formation of
second messenger sn-1,2-diradylglycerol (DG) and phospholipids (PL) in murine
peritoneal macrophages in vitro and in vivo in response to varying concentrations
of the 3-olyunsaturated fatty acids ([symbol removed]3PUFA), eicosapentaenoic (EPA, 20:5[symbol removed]3) and docosahexaenoic (DHA, 22:6[symbol removed]3) acids. My findings establish for the first time that the incorporation of EPA and DHA into DG and membrane PL occurs
independently and dose-dependently, with EPA being incorporated to a greater
extent than DHA.

It was of interest to investigate the functional correlations of the substitution
of [symbol removed]3PUFA into DG and PL molecular species. DG is classically known as the physiological activator of protein kinase C (PKC). I investigated the effects on
PKC activation by pure species of diacylglycerol (DAG) with oleoyl, arachidonoyl,
eicosapentaenoyl or docosahexaenoyl at the sn-2 position. These results showed
that DG species with DHA or EPA incorporated at the sn-2 position activate PKC.
However, while DG with DHA at the sn-2 position activated PKC to a similar
extent as did DG with AA at the sn-2 position (representative of physiological DG),
DG with EPA at the sn-2 position activated PKC to a significantly lesser degree.
To the best of my knowledge, this is the first demonstration in the literature that the activation of PKC in vitro differs significantly among these molecular species
of DAG.

The immunoregulatory cytokine, interleukin-6 (IL-6), is produced in
response to tissue injury and inflammation and in vitro by LPS-stimulated
macrophages. I investigated the correlation of [symbol removed]3PUFA substitution into DC and
secretion of IL-6 by LPS-stimulated murine peritoneal macrophages. These results
show for the first time that IL-6 secretion is attenuated by [symbol removed]3PUFA, and to a
greater extent by DHA than by EPA.

I have obtained several novel findings that contribute to improved
understanding of the underlying mechanisms by which [symbol removed]3PUFA function at the
level of signal transduction. The ability to modify the fatty acid composition of the
signalling molecule, DG, with [symbol removed]3PUFA can now be used for future research to
further elucidate the functional ramifications of [symbol removed]3PUFA in cell signal
transduction.


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