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In myocardial infarction (MI), granulation tissue cells disappear via apoptosis to complete a final scarring with scanty cells. Blockade of this apoptosis was reported to improve post-MI ventricular remodeling and heart failure. However, the molecular biological mechanisms for the apoptosis are unknown. Fas and Fas ligand were overexpressed in the granulation tissue at the subacute stage of MI (1 week after MI) in mice, where apoptosis frequently occurred. In mice lacking functioning Fas (lpr strain) and in those lacking Fas ligand (gld strain), apoptotic rate of granulation tissue cells was significantly fewer compared with that of genetically controlled mice, and post-MI ventricular remodeling and dysfunction were greatly attenuated. Mice were transfected with adenovirus encoding soluble Fas (sFas), a competitive inhibitor of Fas ligand, on the third day of MI. The treatment resulted in suppression of granulation tissue cell apoptosis and produced a thick, cell-rich infarct scar containing rich vessels and bundles of smooth muscle cells with a contractile phenotype at the chronic stage (4 weeks after MI). This accompanied not only alleviation of heart failure but also survival improvement. However, the sFas gene delivery during scar tissue phase was ineffective, suggesting that beneficial effects of the sFas gene therapy owes to inhibition of granulation tissue cell apoptosis. The Fas/Fas ligand interaction plays a critical role for granulation tissue cell apoptosis after MI. Blockade of this apoptosis by interfering with the Fas/Fas ligand interaction may become one of the therapeutic strategies against chronic heart failure after large MI.

The morphogenesis of the photoreceptor cells in the retinas of C3H mice carrying the rd gene and C57BL mice carrying the normal gene was compared, and retinas of the C3H mutants (C3H-lpr/lpr, -lprcg/lprcg, and -lpr/lpr-gld/gld) defective in apoptosis through the Fas system were examined. In the C57BL retina, the inner and outer nuclear layers were separated at 8 days of age, and the photoreceptor inner and outer segments began to grow between 8-11 days after birth with their most rapid growth occurring between 14-17 days of age. In the C3H retina, the development was comparable to that of the C57BL retina at 8 days of age but the reduction in thickness of the outer nuclear and photoreceptor layers was noted at 11 days of age, and the outer nuclear layer became reduced to only a few nuclei in thickness at 14 days, being completely missing or reduced to a single row of cells at 20 days. The degeneration was by an apoptotic mechanism as confirmed morphologically and by the TUNEL method. In all the C3H mutant retinas examined over 24 days of age, the complete depletion of the outer nuclear layer or reduction to a single row comparable to 20-day-old C3H mice was seen. The rd gene action is therefore independent of Fas/Fas ligand-medicated apoptosis.

Retinal degeneration induced by a single intraperitoneal injection of N-methyl-N-nitrosourea (MNU) in male and female albino (GRS/A and DDD/1) and colored (C57BL) mice at 7 weeks of age was examined morphologically 1, 3, 7, 14 and 21 days after the treatment. A dose of 60 mg/kg body weight evoked progressive retinal degeneration in all mice. All albino and colored mice had a comparable progression of photoreceptor cell degeneration by an apoptotic mechanism, as confirmed by morphological and TUNEL methods. Apoptosis had already taken place 1 day after the treatment and was completed by Day 7. This process resulted in a thin remnant of retina with complete loss of photoreceptor cells-21 days after the treatment. During the course of apoptosis, the pigment epithelial cells were maintained in a continuous layer in all strains of mice. In colored mice, several layers of the swollen pigment-enriched cells were seen between the inner nuclear layer and the pigment epithelial layer 14 and 21 days after the treatment. In summary, the destruction of photoreceptor cells by the apoptotic process was the mechanism by which retinal degeneration was induced by MNU.

Retinal degeneration was induced by a single intraperitoneal injection of N-methyl-N-nitrosourea in female Sprague-Dawley albino rats at 50 days of age by two dose regimens, which were observed sequentially at 24, 48, and 72 hours and 7, 21, and 35 days after the treatment. After a dose of 75 mg/kg, methylnitrosourea evoked progressive retinal degeneration in all treated rats whereas a dose of 50 mg/kg was less effective. The 75-mg/kg-treated rats showed selective destruction of the photoreceptor cells by an apoptotic mechanism, as confirmed morphologically and by the terminal dUTP nick end labeling method. Apoptosis had already started at 24 hours after the treatment and was completed by day 7. During the photoreceptor degeneration, proliferation of glial fibrillary acidic protein and vimentin-positive Müller cells as detected by proliferating cell nuclear antigen labeling appeared at 48 hours and was prominent 72 hours after the treatment, and macrophage infiltration within the retina as recognized by ED1 positivity was maximal 7 and 21 days after the treatment. Retinal degeneration was also induced in female Brown-Norway colored rats in a similar dose-dependent manner. Pigment epithelium was discontinuous above Bruch's membrane, and migration of the swollen pigment epithelium toward the inner nuclear layer was seen 7 days after the treatment. Therefore, as also confirmed electron microscopically, the most striking change was the destruction of photoreceptor cells by the apoptotic process, followed by Müller cell proliferation, pigment epithelium migration, and macrophage infiltration for cell debris phagocytosis, resulting in a thin remnant of retina with attenuated inner nuclear cells in direct contact with Bruch's membrane or with the pigment epithelium and/or with the Müller cells 35 days after the treatment.