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Effects of enhanced extracellular ammonia concentration on cultured mammalian retinal glial (Müller) cells
A Reichenbach1, J U Stolzenburg, H Wolburg
1Carl Ludwig Institute of Physiology, Leipzig University, Germany.
Abstract:
Müller (glial) cells of the neonatal rabbit retina were cultured as confluent monolayers and exposed to enhanced concentrations of ammonia (0.25, 0.5, 1, 3, 7, and 10 mM) in medium for various periods (30 min to 10 d). This caused, in a time- and dose-dependent manner, similar changes in the Müller cells as had previously been described in cultured astrocytes. The most conspicuous events were 1) an increasing size of cell nuclei, 2) an accumulation of phagocytotic vacuoles, and 3) a rearrangement of intermediate filaments. 4) A considerable number of cells died when higher ammonia concentrations were applied for more than 1 h. Simultaneous application of dibutyryl-cyclic adenosine monophosphate (dBcAMP) prevented almost completely both the increase in cell nucleus size and the changes of intermediate filaments, but only partly the early cell death of a subpopulation of cells, and the accumulation of phagocytotic vacuoles. Further changes evoked by enhanced ammonia concentration were 5) an accumulation of lipofuscin-like material ("fatty degeneration") revealed by lipophilic stain, 6) reduced immunoreactivity for cathepsin D, and increased immunoreactivity for 7) glial fibrillary acidic protein, 8) glutamine synthetase, and 9) bcl-2 protooncogene protein. These findings are discussed in respect to the possible underlying pathophysiological mechanisms.
Insights
High ammonia levels damage retinal Müller cells, causing cell death and structural changes. Dibutyryl-cyclic adenosine monophosphate (dBcAMP) partially protected cells from these ammonia-induced effects.
Area of Science:
- Neuroscience
- Cell Biology
- Ophthalmology
Background:
- Müller (glial) cells are crucial for retinal structure and function.
- Astrocytes exhibit specific responses to elevated ammonia concentrations.
- Understanding Müller cell response to ammonia is vital for retinal disease research.
Purpose of the Study:
- To investigate the effects of varying ammonia concentrations on cultured neonatal rabbit retinal Müller cells.
- To compare Müller cell responses to ammonia with those of astrocytes.
- To evaluate the protective potential of dibutyryl-cyclic adenosine monophosphate (dBcAMP) against ammonia toxicity.
Main Methods:
- Culturing neonatal rabbit retinal Müller cells as confluent monolayers.
- Exposing cells to a range of ammonia concentrations (0.25–10 mM) for diverse durations (30 min–10 d).
- Assessing cellular changes including nucleus size, vacuole accumulation, intermediate filament rearrangement, cell death, and protein expression.
Main Results:
- Ammonia exposure induced dose- and time-dependent increases in nucleus size, vacuole accumulation, and intermediate filament rearrangement.
- Higher ammonia concentrations led to significant cell death within 1 hour.
- dBcAMP partially mitigated nucleus enlargement, intermediate filament changes, and cell death, but not vacuole accumulation.
- Ammonia increased lipofuscin-like material, reduced cathepsin D, and elevated glial fibrillary acidic protein, glutamine synthetase, and bcl-2 protein expression.
Conclusions:
- Elevated ammonia concentrations induce significant pathological changes in Müller cells, mirroring astrocyte responses.
- dBcAMP offers partial protection against ammonia-induced Müller cell damage.
- These findings provide insights into the pathophysiological mechanisms of ammonia toxicity in the retina.
