Purpose

Immunosuppression is frequently employed to enhance survival of xenografted human cells as part of translational proof-of-concept studies. However, the potential effects of this treatment are easily overlooked.

Methods

As part of baseline testing in the dark-eyed variant of the dystrophic Royal College of Surgeons (RCS) rat, we documented the time course of retinal degenerative changes versus Long Evans controls using bright field retinal imaging, fluorescein angiography, and histology and examined the impact of immunosuppression on visual function. Rats received either no treatment or systemic immunosuppression with oral cyclosporine A and injectable dexamethasone and subsequently underwent functional evaluation by optomotor response testing and electroretinography (ERG) at multiple intervals from P45 to P180.

Results

Immunosuppressed RCS animals demonstrated poorer performance on functional tests than age-matched untreated rats during the earlier stages of degeneration, including significantly lower spatial acuities on optomotor threshold testing and significantly lower b-wave amplitudes on scotopic and photopic ERGs. Retinal imaging documented the progression of degenerative changes in the RCS fundus and histologic evaluation of the RCS retina confirmed progressive thinning of the outer nuclear layer.

Conclusions

A standard regimen of cyclosporine A plus dexamethasone, administered to RCS rats, results in demonstrable systemic side effects and depressed scores on behavioral and electrophysiological testing at time points before P90. The source of the functional impairment was not identified. This finding has implications for the interpretation of data generated using this commonly used translational model.

Purpose

One of the leading causes of irreversible blindness worldwide, age-related macular degeneration (AMD) is a progressive disorder leading to retinal degeneration. While several treatment options exist for the exudative form of AMD, there are currently no FDA-approved treatments for the more common nonexudative (atrophic) form. Mounting evidence suggests that mitochondrial damage and retinal pigment epithelium (RPE) cell death are linked to the pathogenesis of AMD. Human retinal progenitor cells (hRPCs) have been studied as a potential restorative therapy for degenerative conditions of the retina; however, the effects of hRPC treatment on retinal cell survival in AMD have not been elucidated.

Methods

In this study, we used a cell coculture system consisting of hRPCs and AMD or age-matched normal cybrid cells to characterize the effects of hRPCs in protecting AMD cybrids from cellular and mitochondrial damage and death.

Results

AMD cybrids cocultured with hRPCs showed (1) increased cell viability; (2) decreased gene expression related to apoptosis, autophagy, endoplasmic reticulum (ER) stress, and antioxidant pathways; and (3) downregulation of mitochondrial replication genes compared to AMD cybrids without hRPC treatment. Furthermore, hRPCs cocultured with AMD cybrids showed upregulation of (1) neuronal and glial markers, as well as (2) putative neuroprotective factors, responses not found when hRPCs were cocultured with age-matched normal cybrids.

Conclusion

The current study provides the first evidence that therapeutic benefits may be obtainable using a progenitor cell-based approach for atrophic AMD. Our results suggest that bidirectional interactions exist between hRPCs and AMD cybrids such that hRPCs release trophic factors that protect the cybrids against the cellular and mitochondrial changes involved in AMD pathogenesis while, conversely, AMD cybrids upregulate the release of these neuroprotective factors by hRPCs while promoting hRPC differentiation. These in vitro data provide evidence that hRPCs may have therapeutic potential in atrophic AMD.