Abstract
Purpose:
Stem cell based therapies, have been shown to hold real promise in the treatment of degenerative diseases of the retina. However, the efficiency of such strategies is still considerably low. Tissue repair mechanisms are conserved at the organism level and enhance the regenerative process. We hypothesized that promoting tissue repair may also enhance the efficiency of cell engraftment in the retina. Key components of the retinal repair network have been identified in Drosophila involving interactions between the damaged retina and hemocytes. We have used the Drosophila to identify hemocyte derived factors that can promote tissue repair in the retina and have tested the conservation of their function in the mammalian retina. Our work focused on Mesencephalic Astrocyte-derived Neurotrophic Factor (MANF).
Methods:
We have used UV induced retinal damage in flies and light induced retinal damage in mouse as model systems to test the effects of MANF. MANF was overexpressed in flies using the UAS/Gal4 system. In mice, recombinant protein was delivered by intravitreal injection.
Results:
We have identified MANF as a hemocyte derived protein in Drosophila that can promote tissue repair in the fly retina, using RNAseq. We show that MANF is expressed in hemocytes of Drosophila larvae, it is secreted to the hemolymph and induced in response to stress in a Pvf-1/PvR dependent manner. Hemocyte specific MANF expression is sufficient to reduce tissue loss after UV and genetically-induced photoreceptor apoptosis. Moreover, stress induced MANF results in changes in the hemocyte population correlating with increased lamellocyte differentiation. We have tested the conservation of the pathway in mammalian retinal repair. As in flies, MANF is induced in microglia/macrophages invading the retina following light damage and this correlates with reduced tissue loss. Importantly, intravitreal delivery of MANF recombinant protein is sufficient to limit cell death following light damage and promotes alterations in macrophages/microglia.
Conclusions:
MANF is a conserved neuroprotective factor in the retina. MANF acts as an immune-modifying factor to limit cell loss following acute damage. . This work will serve as a proof of concept to the use of tissue repair promoting factors as co-adjutants in stem cell regenerative therapies.
Keywords: 595 microglia •
688 retina •
615 neuroprotection