Epigenetic Regulation of Wnt signaling to mediate Müller Cell Survival and Proliferation

Abstract

Purpose: : Histone Lysine Methyltransferases (HKMTases) catalyze histone lysine methylation (HKM) on terminal tails of histone H3 and represent an important epigenetic mechanism that regulates cell specific gene expression, development and survival. Müller cells, via gliosis and proliferation, play an active role in many types of retinal disorders. In this study we investigated the relationship between HKMTases and wnt signaling in mediating Müller cell survival and proliferation

Methods: : Müller cells were isolated from the retinas of mice at the age of postnatal day 0 and cultured in the defined media. Inhibitors of the HMTases Ezh2 and G9a, Dzneb and Bix, were applied to the culture media in the presence and absence of Wnt3a. An in situ cell death detection kit (TUNEL) was used to quantify cell survival, and 5 bromo deoxyurdinine (BrdU) incorporation assays were used to assess cell proliferation. Effects of HMTase inhibitors and Wnt3a on Müller cell survival and proliferationwere examined.

Results: : Inhibition of HMTases significantly increased Müller cell apoptosis and decreased cell proliferation. There was a dose dependent effect of Dzneb and Bix on Müller cell survival. While addition of Wnt3a alone did not affect Müller cell survival and proliferation, it reversed the effects of Dznep and Bix

Conclusions: : Müller cell survival and proliferation are epigenetically regulated by the HKMTases Ezh2 and G9a. Our results furher suggest that Wnt3a is downstream signal of Ezh2 and G9a that may regulate Müller cell survival and proliferation. Aberrant proliferation and reactive gliosis of Müller glia is associated with many diseases including vitreoretinal interface disorders such as epiretinal membrane, proliferative vitreoretinopathy following retinal detachment, exuberant fibrosis in various forms of macular degenerations. Moreover, Müller glia have been suggested as a reservoir of endogeneous neurogenic progenitor cells amenable to retinal repair following retinal neurodegeneration. By regulating vital retinal glial functions, the HKMTases emerge as a potential therapeutic target to modulate Müller glial proliferation and survival in a variety of retinal disorders.

Keywords: Muller cells • cell survival • proliferation