Muller Cell Expression of Gliol Fibrillory Acidic Protein offer Genetic ...

No. 11 GFAP IN MULLER CELLS / Eisenfeld er ol. 1327
Fig. 4. Characterization of GFAP antibody in normal, constant light-damaged (A) and RCS (B) retinas. Lanes 1-3 are SDS-polyacrylamide
gels stained with Coomassie Blue. Lanes 4-6 are PAP stained immunoblots. Molecular weights calculated from protein standards are shown
on the left. A, Constant light-damaged retinas. Lanes (1, 4), normal retina; (2, 5) retina exposed to constant light for 7 days; (3, 6) retina
exposed to constant light for 3 days. B, RCS retinas; Lanes (1,4) normal retina; (2, 5) 40-day-old RCS retina; (3, 6) 70-day-old RCS retina.
several protein bands were seen in the Coomassie photo-oxidation and retinol-induced membranolysis. 18
shed outer segments. 1516 This leads to accumulation
References
of outer segment debris and subsequent photoreceptor
1. Bignami A and Dahl D: The radial glia of Muller in the rat
degeneration. The cause of photoreceptor death in
retina and their response to injury. An immunofluorescence
CL exposure is unknown, but several mechanisms
have been considered, including lipid peroxidation, 17 study with antibodies to the glial fibrillary acid (GFA) protein.
ExpEye Res 28:63, 1979.
Blue-stained acrylamide gels, anti-GFAP stained only
one or at most two adjacent bands. Using molecular
weight markers, the size of the anti-GFAP reacting
protein was estimated at 50,000 for CL-damaged
retinas and 47,000 for RCS retinas. The Tritoninsoluble
nature of the protein, as well as its apparent
molecular weight, indicate that the protein stained in
the immunofluorescence studies is GFAP.
The nitrocellulose blots showed that a small amount
These unrelated mechanisms leading to photoreceptor
death might result in a different time course of GFAP
accumulation in Muller cells.
(3) Finally, there might be a direct effect on other
cell types in the retina, leading to GFAP accumulation
in Muller cells. This would seem more likely in the
CL condition, where exposure to CL might have a
primary effect on Muller cells, resulting in a more
rapid accumulation of GFAP. This, of course, remains
of GFAP was present in both RCS-rdy + and the CL hypothetical at the present time.
control retinas. This was in accord with the immunocytochemical
staining of astrocytes in sections of
these retinas. Further, it appeared that the amount of
GFAP increased with progressive photoreceptor loss
in both the RCS and light damaged retinas, corroborating
the immunocytochemical observation of increased
GFAP in Miiller cells in both conditions.
Our results provide further evidence that Muller
cells express GFAP immunoreactivity following degeneration
of apparently a single cell type, the photoreceptor.
The time course of GFAP expression here
in Muller cells after CL damage is quite similar to
the increased anti-GFAP stainability in astrocytes at
48 hr following a stab wound of the brain 19 and in
Muller cells after optic nerve section or penetrating
Discussion
wounds of the eye. 1 The different time course of
Muller cell gliosis in the RCS rat, as well as the actual
The initial appearance of GFAP immunoreactivity
significance of increased GFAP expression in astrocytes
and Muller cells in pathologic conditions 820 are
was seen in Miiller cells from CL and RCS retinas
only after substantial loss of photoreceptors. This
topics for future study. This study has shown that
loss, as determined by measurements of the outer
retinas with environmentally and genetically caused
nuclear layer, reflected a 20% decrease in CL damaged
photoreceptor degeneration may provide useful models
for the elucidation of Muller cell functions, in-
retinas and a 61% decrease in RCS rats. There are
several possible explanations for this apparent difference
in the degree of photoreceptor loss before GFAP
cluding reaction to injury. The ability to induce
accumulation of GFAP in a cell type not normally
reactivity was detected.
expressing this protein should facilitate the study of
(1) The outer nuclear layer thickness measurements
the mechanisms of reactive gliosis in other parts of
indicated the degree of death and dropping out of
the central nervous system.
photoreceptor cells. Since the metabolic status of the
remaining photoreceptors was not monitored, even a
morphologically normal photoreceptor might already
Key words: Muller cells, glial fibrillary acidic protein,
photoreceptor degeneration, RCS rat, light damage
be altered functionally. Therefore, the outer nuclear
layer thickness might not be an accurate measure of
the state of degeneration. 14
(2) Although both conditions resulted ultimately
Acknowledgments
The authors wish to thank Dr. Larry Eng for the antiserum
to GFAP; Dr. Matthew La Vail for the RCS rats; Dr. J. C.
in the loss of photoreceptors, the etiologies of the two Saari for critical review of the manuscript; Mr. G. Garwin
and Ms. I. Klock for technical assistance; Mr. B. Clifton
forms of degeneration are thought to differ. In the
and Ms. D. Cannon for photographic help; and Ms. J. Seng
RCS rat, the genetic defect has been localized to the for secretarial assistance.
pigment epithelial cell, which is unable to phagocytose