Apoptotic cell death of photoreceptor cells in mice deficient for the adhesion molecule on glia (AMOG, the β2-subunit of the Na,K-ATPase)

Abstract

Disruption of the gene for the adhesion molecule on glia (AMOG, the beta 2-subunit of the Na, K-ATPase) in mice results in swelling and subsequent degeneration of astrocyte endfeet in the brainstem and in cell death of photoreceptor cells in the retina. In the present study, we demonstrate that photoreceptor cells in the mutant develop normally during the first postnatal week. Compared to wild-type mice, a slightly increased density of degenerating photoreceptor cells became apparent in 9-day-old mutants and numerous degenerating photoreceptor cells were present in the retina of 16-day-old AMOG/beta 2-deficient mice. In situ labelling of degenerating cells by terminal dUTP nick end labelling and electron microscopic analysis revealed apoptotic cell death of photoreceptor cells. Massive degeneration of photoreceptor cells in the mutant at postnatal day 16 correlated with elevated levels of glial fibrillary acidic protein in retinal astrocytes and with expression of this protein by Muller cells. No evidence was found for degeneration of other retinal cell types or for glial cell death in the optic nerve. Our observations demonstrate that the pathological death of cells induced by disruption of the AMOG/beta 2 gene results from activation of an intrinsic death program, similar to what has been shown to occur during normal development.

Na,K-ATPase Subunit β1knock-inPrevents Lethality of β2 Deficiency in Mice

“…In ␤2-deficient mice, apoptotic death of photoreceptor cells in the retina was observed during the last days of the mutant's life (Molthagen et al, 1996), whereas in wild-type animals, apoptotic cell death in the retina occurs predominantly until the second postnatal week and after this time only sporadic cell loss is observed (Chang et al, 1993;Portera-C ailliau et al, 1994). Using the TUN EL method to analyze apoptotic cell death in retinae of ␤2/␤1 k nock-in mice, we observed a progressive degeneration of photoreceptor cells, although it was less than in ␤2-deficient mice [this study and Molthagen et al (1996)]. Thus, apoptotic cell death of photoreceptor cells in the retina was delayed considerably in the k nock-in mice compared with ␤2-deficient mice.…”

“…To visualize degenerating cells in the retina, fragmented DNA of apoptotic cells was detected using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUN EL) technique (Gavrieli et al, 1992). Briefly, cryosections through central regions of the retinae from 17-d-old, 4-month-old, and 9-monthold wild-type (␤2/␤1 ϩ/ϩ ) and ␤2/␤1 k nock-in mice (␤2/␤1 ki / ki ) were mounted onto silan-coated coverslips and processed as described (Molthagen et al, 1996). Sections were finally mounted onto slides and analyzed with a fluorescence microscope (Axiophot, Z eiss).…”

“…Degeneration of photoreceptor cells in central regions of the retinae of 17-d-old, 4-month-old, and 9-month-old wild-type and ␤2/␤1 k nock-in mice was visualized using a modified TUNEL method (Molthagen et al, 1996). In retinae of 17-d-old wild-type mice, only a few degenerating cells were visible in the outer nuclear layer (Fig.…”

“…Mice deficient in ␤2 exhibit lack of motor coordination at 15 d of age and subsequent tremor and paralysis of extremities, and they die at 17-18 d after birth (Magyar et al, 1994). Morphological analysis of the C NS of 17-d-old ␤2-deficient mice revealed enlarged ventricles, swollen astrocytic end feet in the brain stem, thalamus, and spinal cord, and apoptotic photoreceptor cell death in the retina during the second postnatal week (Magyar et al, 1994;Molthagen et al, 1996).…”

Neuropathology in Drosophila Membrane Excitability Mutants

“…Mutations of the ATPase b2 subunit in mice also cause neurodegeneration (Magyar et al 1994;Molthagen et al 1996). Pharmacological disruption of the Na 1 /K 1 ATPase has been shown to cause membrane depolarization resulting in increased intracellular calcium, ultimately leading to necrosis (Chatterjee and Roy 1965;Lees et al 1990).…”