A diffusible factor from normal retinal cells promotes rod photoreceptor survival in an in vitro model of retinitis pigmentosa

Abstract

Transgenic mice expressing a dominant mutation in the gene for the phototransduction molecule rhodopsin undergo retinal degeneration similar to that experienced by patients with the retinal degenerative disease, retinitis pigmentosa (RP). Although the mutation is thought to cause photoreceptor degeneration in a cell-autonomous manner, the fact that rod photoreceptor degeneration is slowed in chimeric wild-type/mutant mice suggests that cellular interactions are also important for maintaining photoreceptor survival. To more fully characterize the nature of the cellular interactions important for rod degeneration in the RP mutant mice, we have used an in vitro approach. We found that when the retinas of the transgenic mice were isolated from the pigmented epithelium and cultured as explants, the rod photoreceptors underwent selective degeneration with a similar time course to that observed in vivo. This selective rod degeneration also occurred when the cells were dissociated and cultured as monolayers. These data indicate that the mutant rod photoreceptors degenerate when removed from their normal cellular relationships and without contact with the pigmented epithelium, thus confirming the relative cell autonomy of the mutant phenotype. We next tested whether normal retinal cells could rescue the mutant photoreceptors in a coculture paradigm. Coculture of transgenic mouse with wild-type mouse or rat retinal cells significantly enhanced transgenic rod photoreceptor survival; this survival-promoting activity was diffusible through a filter, was heat labile, and not present in transgenic retinal cells. Several peptide growth factors known to be present in the retina were tested as the potential survival-promoting molecule responsible for the effects of the conditioned medium; however, none of them promoted survival of the photoreceptors expressing the Pro23His mutant rhodopsin. Nevertheless, we were able to demonstrate that the mutant photoreceptors could be rescued by an antagonist to a retinoic acid receptor, suggesting that the endogeneous survival-promoting activity may function through this pathway. These data thus confirm and extend the findings of previous work that local trophic interactions are important in regulating rod photoreceptor degeneration in retinitis pigmentosa. A diffusible factor found in normal but not transgenic retinal cells has a protective effect on the survival of rod photoreceptors from Pro23His mutant rhodopsin mice.

NRF2 promotes neuronal survival in neurodegeneration and acute nerve damage

“…Cone death in RP is unlikely to be caused only by oxidative stress. Rather, cone death is likely due to a combination of stress factors including, but not limited to, metabolic dysregulation (48), lack of trophic factors (72)(73)(74)(75)(76), and inflammation (77). While antioxidant gene therapy can be used as a standalone treatment, it can also supplement other gene therapies.…”

Retinal light damage: Mechanisms and protection

“…Retinas from light exposed transgenic rats expressing P23H rhodopsin also form all-trans retinoic acid (Duncan et al , 2006). Retinoids are well known transcriptional regulators, mediating both retinal cell differentiation and apoptosis during development (Kelly et al , 1994; Streichert et al , 1999; Soderpalm et al , 2000; Cveki and Wang, 2009). The formation of retinoic acids in the retinas of light exposed adult animals, then, links rhodopsin bleaching with transcriptional regulation.…”

Therapeutic Margins in a Novel Preclinical Model of Retinitis Pigmentosa

“…Our results suggest that complete, partial, and incomplete restoration of retinal function depend on the number of treated photoreceptors. Not achieving a minimum number of rescued rods is likely to cause nonautonomous death of rescued rods (Kedzierski et al, 1998;Streichert et al, 1999;Delyfer et al, 2005). Because many RP patients initially present with considerable degeneration (loss of peripheral rods and cones, cases may involve of the macula as well), then early treatment may produce favorable outcomes.…”