PgmNr M5038: Mammalian Retinal Regeneration in Response to an α7 nAChR Agonist.

Authors:
M. K. Webster; H. B. Bach; C. L. Linn


Institutes
Western Michigan University, Kalamazoo, MI.


Abstract:

Irreversible vision loss due to disease, age or damage reduces quality of life worldwide and is a substantial burden on national healthcare. Previous studies in this lab have shown that α7 nicotinic acetylcholine receptor agonists are capable of providing neuroprotection in a glaucoma model. We seek to understand if and how the selective α7 nicotinic acetylcholine receptor agonist, PNU-282987, leads to proliferation of adult mammalian retinal neurons in Long Evans rats. To determine if PNU-282987 triggers proliferation of retinal neurons, animals were treated with 1 mM PNU-282987 and 1 mg/mL BrdU twice a day for varying amounts of time. Antiboides against BrdU revealed that new retinal neurons were generated in a dose and time dependent manner and double labeling using antibodies against specific retinal neurons demonstrated evidence of new photoreceptors, retinal ganglion cells as well as BrdU positive cells in the inner nuclear layer.

A well-established source of new retinal neurons in other vertebrate model organisms is the Müller glia. To determine if Müller glia are the source of new BrdU positive cells in PNU-282987 treated rat eyes, Müller glia and progenitor cells were examined for BrdU colabeling. This demonstrated that Müller glia are in fact BrdU positive and express the proliferation marker PCNA. Further, nestin, a neural progenitor cell marker, and PCNA positive cells were observed in the inner nuclear layer. This data supports the hypothesis that Müller glia give rise to new retinal progenitor cells and that these are the cells that then differentiate and gave rise to different types of mature neurons between 7 and 28 days after treatment with PNU-282987.

To begin to understand the gene pathways responsible for proliferation mediated by the selective α7 nicotinic acetylcholine receptor agonist, mRNA-seq was performed on animals treated with PNU-282987. Our pathway analysis demonstrated that after only 3 days of treatment there was significant changes in a number of key signaling pathways known to be involved in development and retinal regeneration in other vertebrate systems. As adult mammalian neurons do not typically regenerate or proliferate, we conclude that PNU-282987 is somehow reversing this process. Our results will have important implications for uncovering mechanisms to induce dedifferentiation and subsequent regeneration of the mammalian retina.