Glycogen in rat adipose tissue: Sequential synthesis and random degradation

Vol.

95, No.

August

3, 1980

BIOCHEMICAL

AND

BIOPHYSICAL

RESEARCH

COMMUNICATIONS

Pages 1031-1036

14, 1980

GLYCOGEN IN RAT ADIPOSE TISSUE : SEQUENTIAL SYNTHESIS AND RANDOM DEGRADATION Pierre Laboratoirw ad International U. C. L. 75.39,

Received

Devos

and

Henri-Gery

Hers

de CXmie Physiologique, lfniversite de Louvain Institute of Cellular and .kfoZecuZar Pathology, 75 avenue Hippocrate, B-1230 Brussels (Belgium)

June 26,198O

Slil4MA PY < : In the adipose tissue like in the liver, glycogen molecules are synthesized in a molecular order such that some molecules are completed before others start to grow. In the adipose tissue, the degradation of glycogen occurs at random, whereas, in the liver, molecules that were synthesized last are degraded first and vice versa. This difference in the catabolism of glycogen between the two tissues may be related to the fact that glycogen is in the form of monomeric beta particles in the adipose tissue and of polymeric alpha particles in the liver.

Labeling in a period the

(2)

livers,

labeled

remain

after

synthesized.

last

are

observed

is

also first

~TL vizlo,

in

In the

liver,

Imade up of subunits

and the

been done in

by a partially Furthermore,

and vice

versa.

hepatocytes

glycogen

is

called

beta

present particles

This

in the form

glycogen

pulse-labeling

degradation

ordered

of glycogen

were

of large

in

synthesized

degradation

The beta

of the

the case of the

and in a cell-free

(4,5).

of synthesis

purified

that

to grow.

of glycogen

these

the molecules

and result

chains

the amount

the phosphorolytic thus

(1)

start

external

has also

(3).

foetal

stage

in

ordered;

isolated

others

increase

catalyzed

that

the

precursor

sequential,withthe

at an early

internal

fold

aerogenes

is

before

incorporated

of glycogen

degraded

in both

synthesized

in the

have revealed liver

has shown that

observation

of Aerohacter

experiments the adult

units

a several

synthesis

of a radioactive

of glycogen

completely

A similar

administration

synthesis

distributed

polysaccharide

synthase

are

glucosyl

equally

"de novo"

synthesis the

some molecules

Indeed,

by pulse

of sustained

adult

that

of glycogen

system alpha particle

was (2). particles, seems to

Vol.

95, No.

3, 1980

correspond

to the

glycogen these

tree-like

molecule.

molecules

determining It

BIOCHEMICAL

thus

the appears

order

in which

adipose

tissue

experimentation. present

(7,8)

adipose

adipose

when starved

under normal animals

this

glycogen

This

experimental

glycogen

in

the

course

release

of radioactivity

showed,

however,

was extremely in the

that

slow

brown

is

the

tissue

in the liver. be found

The

type

of

revealed

concentration but

that

(6) is

in

glycogen

and the brown very

increases

low in the

enormously

one or two days of refeeding,

in order

at which for

tissue

but

was therefore

however,

was formed

labeling

or random

experiments

glucose could

(9).

of

an ordered

Preliminary

of radioactive

adipose

it

pulse

to detect

degradation.

incorporation

which

this

of

in

particles.

in the white

appropriate

the

association

would

have

the same rate

of synthesis

in the white

adipose

After

therefore

during

for

the

factor

of beta

conditions

at about

model

both

glycogen

refed.

is degraded

form

studies

nutritional

are

order

model

particles

Furthermore,

tissue.

tissue

in the

ultrastructural

of beta

the

of glycogen

a similar

as an appropriate

Indeed, in the form

if

COMMUNICATIONS

considered that

and degradation

is present

was chosen

usually

may be an important

to check

glycogen

is

RESEARCH

hypothesize

particle

of synthesis

BIOPHYSICAL

which

therefore

an alpha

of interest

tissues

is

structure

One could into

AND

into

be easily

glycogen measured

chosen.

METHODS Male Wistar rats weighing about 100 g, were fasted for three days and then refed. They received, by intraperitoneal injection, 2 ug (6.106 cpm) of [U-I4Clglucose dissolved in 0.5 ml of 0.15 M NaCl, either 10 min (early labeling) or 21 hrs (late labeling) after initiation of refeeding. Preliminary experiments had revealed that the content of glycogen in the brown adipose tissue as well as in the liver is maximal at approximately The experimental schedule was set up 24 hrs after initation of refeeding. At each time indicated in fig. 1, four rats of each series were accordingly. killed by decapitation and glycogen was isolated from the liver and the The methods used for the isolation interscapular brown adipose tissue. and the analysis of glycogen as well as the source of materials were as previously described (2).

RESULTS AND DISCUSSION After rats

one day of refeeding,

previously

fasted

for

3 days,

the interscapular weighed

1032

brown

approximately

adipose

tissue

300 mg and

of contained

Vol.

95, No.

BIOCHEMICAL

3, 1980

ADIPOSE

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

TISSUE

LIVER

LATE

,

0

25 TIME

50

75

AFTER

INITIATION

OF

REFEEDING

(HRS)

Glycogen synthesis and degradation in the brown adipose tissue upon refeeding of fasted rats. The highest concentrations of glycogen that were registered (100 % values) were 5 % (w/w) of the wet weight in the liver and 1 % in the adipose tissue. Arrows indicate the time at which LU-14Clglucose was administered. The radioactivity incorporated in glycogen was, for the early and late labeling respectively, 1200 and 150 cmp per mg of liver glycogen and 2300 and 2100 cpm per mg of adipose tissue glycogen. Beta amylolysis of the latter glycogen revealed no significant difference between the percentage of 12C (mass of polysaccharide) and 14C remaining in the beta dextrin both in the case of early labeling and at times 21, 26 and 4 6 hrs.

an in t e liver %i=+

about

3 mg of glycogen

admin istered refeeding

in period

same amount conditions the

same in

to analyze

the

and as much as 1 % of the radioactivity form

or 21 hrs

of [U-14C later

of radioactivity indicates

that

distribution

(left

part

either

the

of

rate

in the

of synthesis periods.

radioactivity

1033

at the

of Fig.

was incorporated

the two experimental the

glucose,

1).

had been

beginning The fact

of the that

the

two experimental

of glycogen

Beta

that

amylolysis

on the inner

was approximately was used

as a tool

and the outer

Vol.

95, No.

chains

3, 1980

BIOCHEMICAL

of the polysaccharide.

of the beta

dextrin

originated.

It

observation

study

of the synthesis

works

of Gahan and Conrad system

synthase

attached

to the same glycogen discussion

in the

liver

rat

affinity

for

its

(1,2)

and also

with

the

indicates

glycogen, is

can be found

previous

by a partially

This

synthesis

it

of our

of glycogen

its

mechanism

which

results

product,

until

radioactivity

from

~~UYXJWZ~S (3).

molecule

of this

specific

the

synthesis

COMMUNICATIONS

that

and remains terminated.

A

in a previous

(2).

The degradation the second of Fig.

last

same animals

in great

removal

degradation

previous

activity

than

of synthesis refeeding

(2),

There degradation

is

in

right

part

of Fig.

of glycogen

liver,

glycogen

molecules

their

destruction

occurs

to the

fact

that

tissue

whereas

liver;

it

(2).

It liver This

later. known

suggests

is

also

soon

during

be sustained

the

in

and the adipose

are

orderly

at random.

degraded This is in

is

and the with

initiation

of

the high

4 to 6 hrs

a much longer

tissue in

: indeed, the adipose

presumably

alpha dependent

form in particles on the

rate of

period.

the patterns

a monoparticulate

degradation

1034

since

is

tissue,

much more radio-

the

first

first. of the

in agreement

after

whereas

form of the more complex

the ordered

In this

that

between

difference

liver

last

are

during

difference

liver

1.

was to be expected

a remarkable the

in the

noticeable

glycogen

to occur

not

in the that

is

first

the left

synthesized

incorporated

incorportated

the polysaccharide it

units

during

glycogen

glycogen

observed

can obviously therefore

of the those

into

(1 % per hr)

of the

with

the

occured

As shown in

contrast

data

21 hours

tissue

degradation

degradation

of the units

published

adipose

of refeeding.

of the glucose

was incorporated

refeeding

initiation

any delayed

and illustrated

the preferential

the brown

was no preferential

nor

are

in

days after

1, there

results

delayed

of glycogen

and third

synthesized

our

the

with

from Aerobacter

has a high

RESEARCH

of the glycogen

on the de notio

glycogen

These

that

in agreement

of glycogen

enzymatic

part

revealed

is

purified

publication

BIOPHYSICAL

was the same as that

This

more extensive

AND

of in

the

tissue related theadipose in the alpha

Vol.

95, No.

BIOCHEMICAL

3, 1980

AND

BIOPHYSICAL

RESEARCH

COMMUNICATIONS

OUTER

CHAINS

INNER

CHAINS

INTRAMOLECULAR ORGANIZATION K

/ ORDERED BETA-PARTICLES @

HYPOTHETICAL BETWEEN

LINKS

ALPHA

PARTICLES

ORDERED ALPHA-PARTICLES

The glycogen molecule, corresponding to a beta particle, is e up of inner and outer chains; the major part of the outer chains corresponding to approximately 50 % of the mass of glycogen can be removed by beta-amylolysis. The alpha particle is made up of a large number (as a mean, approximately 30) of beta sub-units; it is not known at the present time if these subunits are linked covalently or not.One may hypothetize that these beta units are synthetized in a defined order (arrows) inside of an alpha particle and degraded in the reverse order. There may also be an This order in the synthesis and degradation of the alpha particles. second hypothesis requires that there exists a link either physical or dynamic, between several alpha particles.

+ma

structure.

As

more

discussed

two ways

may

be

the

alpha

particles

in

a defined

order

and

several

alpha

particles

are

attached

to

2)

explained

extensively

indicate

in

the

second

way

in

the

random

number

the

of

alpha

of

through

the no

the

fact

process

of

morphological

degraded each

in

by

(see

not

cannot the

Fig.

revealed

by

in

their

completely

adipose

tissue There

for

biochemical

1035

such and

observation

synthesized

inside

reverse

direction;

a link 2).

which In

would

of

the

liver

be

is

that

hydrolytic

however,

to

autophagic

morphological

favor

(10).

discarded

an

would

a glycogen-poor

size

is,

of

ulstrastructural

and

be

autophagy.

this

the

other

a glycogen-rich

evidence of

are

as

and

in

particles

degradation

particles

glycogen

(2),

beta

that,

which

combination

the

between

interpretation

knowledge, contrast,

and

difference

degradation

lysosomal

In

is

the

Another

our

synthesis

interpretation

examination, is

for

: 1)

previously

and the

process data

the

indicate

best

of

Vol.

95, No.

that

autophagy

neonatal

BIOCHEMICAL

3, 1980

liver

AND

may be responsible and also

in the

for liver

BIOPHYSICAL

RESEARCH

the glycogenolysis of adult

rats

which

treated

with

COMMUNICATIONS

occurs

in the

phlorizin(11).

ACKNOWLEDGETdENTS This work wtzs supported by the "Fends de la Reckercke Scientij'ique M&iYcale 'I and by the U.S. Public Hea2tk Service (Grmt AM 92351.

REFERENCES Devos, P., Devos, P., Gahan, L.C., Luft, J.H. Drochmans, 6. Gutman, A., 427-439 7. Napolitano, 685-692. 8. Suter, E.R. 9. Tuerkischer, 10. Devos, P., 11. Devos, P.,

:: d: 5.

and Hers, H.G. (1974) Biochem. J. 140, 331-340. and Hers, H.G. (1979) Eur. J. Biochem. 99, 161-167. and Conrad, H.E. (1968) Biochemistry 7, 3979-3990. (1956) J. Biophys. Biochem. Cytol. 2, 799-801. P. (1962) J. Ultrastructure Res. 6, 141-163. E. (1967) Isr. J. Med. SC. 3, Schramm, H., and Shafrir, L.,

and Fawcett,

D. (1958)

J. Biophys.

Biochem.

Cytol.

(1969) Lab. Invest. 21, 246-258. E., and Wertheimer, E. (1942) J. Physiol. 100, 385-409. Van Hoof, F., Baudhuin, P., and Hers, H.G., in preparation. and Hers, H.G. (1980) Biochem. J., in press.

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