Download Lipoprotein lipase activity in tissues of the developing chick embryo

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Lipoprotein lipase activity
developing chick embryo
in
tissues
of
the
BRIAN K. SPEAKE, RAYMOND C. NOBLE and RUTH McCARTNEY
Drpartment
of
Biochemical
Sciences,
Scottish
Agricultural College, Auchincruive Ayr, Scotland,
KA6 5HW, U.K.
The lipids of the yolk provide the chick embryo
with over 90% of its energy needs as well as with
structural components and essential fatty acids
required for tissue growth and development.
The
transfer of lipid from the yolk to the embryo is
mediated by an extraembryonic structure, the highly
vascularised yolk sac membrane. Yolk lipid is taken
up into the cells of the yolk sac membrane, apparently
by phagocytosis, and is subsequently released as
plasma lipoprotein particles into adjacent blood
capillaries for delivery to the embA-yoniccirculation.
This process is especially intensive during the last 8
days of the 21 day developmental period [l].
Although chick embryo development is characterised
by
distinctive and often dramatic changes in
tissue-specific lipid composition {l], there is little
information regarding the mechanisms of uptake and
utilisation of yolk-derived lipid by the embryonic
tissues.
In adult mammals and l'rds, the initial
stages in the processing of triacylglycerol-rich
plasma 1 ipoproteins are catalysed by lipoprotein
lipase present at the luminal surface of the blood
Fatty acids
capillaries of specific tissues [2].
released by the action of this enzyme are thus made
available for utilisation by these particular tissues.
In the light of a previous report [3] suggesting a
role for lipoprotein lipase in chick embryo lipid
metabolism we have investigated several tissues of the
embryo for the presence of this enzyme at various
stages of development.
A preliminary study, using embryos at the 14th day
of development, indicated that lipoprotein lipase was
present at a high specific activity in adipose tissue
and heart. The enzyme was also detectable in skeletal
muscle, but was absent from brain and liver.
In
subsequent investigations the activity of the enzyme
in adipose tissue and heart was monitored throughout
the developmental period. Tissue from several embryos
(5-20,
depending on the developmental stage) was
pooled, homogenised in 10 vols. of 5mM sodium
barbital, pH7.5, containing 2VA (v/v) glycerol, 0.1%
(v/v) Triton X-100 and 50mM NaC1, and lipoprotein
lipase activity was determined [4].
A major increase in the activity (expressed as
unitddepot) of lipoprotein lipase in adipose tissue
occurs between days 12 and 16 of development (Table
1). concomitant with the beginning of the period of
lipid uptake from the yolk and also with a period of
intensive deposition of triacylglycerol into the
A further increase in enzyme level
adipocytes.
occurred after hatching, presumably induced by food
intake [2]. The biphasic nature of the developmental
changes in lipoprotein lipase levels was also apparent
when the enzyme activity was expressed as units/g
tissue, although the activity thus expressed decreased
between days 16 and 19 due to a rapid increase in the
tissue weight and lipid content over this period.
The activity of lipoprotein lipase in the heart,
expressed as units/g tissue increased from approx. 5
units at day 7 to approx 30 units at day 14.
Thereafter, increases in the enzyme's activity
occurred largely in parallel with the growth of the
heart, so that no major changes in activity/g tissue
took place.
Analysis of the fatty acid composition of +,he
triacylglycerol fraction of both adipose tissue and
heart, using gas-liquid chromatography, revealed the
presence of relatively high levels (up to 8% by weight
of total
fatty
acids) of
docosahexaenoic acid
295s
Table 1. Lipoprotein lipase activity of chick embryo
adipose tissue
Subcutaneous adipose tissue from the upper thigh area
and along the sides of the abdomen and thorax was used
as the source of the enzyme. The combined tissue from
both sides of a single embryo is referred to as a
depot. Units of enzyme activity refer to umoles fatty
acid released/h.
Each value represents the mean
(2S.D.) of 3 separate experiments.
Lipoprotein lipase activity
Days of
Development
12
16
19
5 days post-hatch
Units/g tissue wet wt.
32.4L16.9
73.7i 1.8
34.02 9.0
69.5i10.9
Unitddepot
1.120.3
22.2L0.8
21.2i4.2
65.7L7.1
(22:6,n-3) between days 12 and 16 of development.
Since
yolk
triacylglycerol
contains
negligible
proportions of this fatty acid it would appear that
certain modifications in lipid composition occur
during the conversion of yolk lipid droplets to plasma
lipoproteins by the yolk sac membrane [l].
In conclusion, the results suggest a major role
for
lipoprotein lipase in
the
tissue-specific
utilisation of yolk-derived lipid by the chick embryo.
SAC received financial support from the
Office Agriculture and Fisheries Department.
Scottish
1. Noble, R.C. & Cocchi, M. (1991) Prog. Lipid Res.
29, 107-140.
2. Speake, B.K., Parkin, S.M. & Robinson, D.S. (1985)
Biochem. SOC. Trans. 13, 29-31.
3. Bengtsson, G . , Hernell, 0. & Olivecrona, T. (1977)
Int. J. Biochem. 8, 587-539.
4. Parkin, S.M., Speake, B.K. & Robinson, D.S. (1982)
Biochem. J. 207. 485-495.