AAV-mediated and pharmacological induction of Hsp70 expression stimulates survival of retinal ganglion cells following axonal injury

We evaluated the effect of AAV2- and 17-AAG (17-N -allylamino-17-demethoxygeldanamycin)-mediated upregulation of Hsp70 expression on the survival of retinal ganglion cells (RGCs) injured by optic nerve crush (ONC). AAV2-Hsp70 expression in the retina was primarily observed in the ganglion cell layer. Approximately 75% of all transfected cells were RGCs. RGC survival in AAV2-Hsp70 injected animals was increased by an average of 110% 2 weeks after the axonal injury compared to the control. The increase in cell numbers was not even across the retinas with a maximum effect of approximately 306% observed in the inferior quadrant. 17-AAG-mediated expression of Hsp70 has been associated with cell protection in various models of neurodegenerative diseases. We show here that a single intravitreal injection of 17-AAG (0.2 ug/ul) results in an increased survival of ONC injured RGCs by approximately 49% compared to the vehicle-treated animals. Expression of Hsp70 in retinas of 17-AAG-treated animals was upregulated approximately by 2-fold compared to control animals. Our data support the idea that the upregulation of Hsp70 has a beneficial effect on the survival of injured RGCs, and the induction of this protein could be viewed as a potential neuroprotective strategy for optic neuropathies.

Dnmt1-dependent DNA methylation is essential for photoreceptor terminal differentiation and retinal neuron survival

Epigenetic regulation of the genome is critical for the emergence of diverse cell lineages during development. To understand the role of DNA methylation during retinal network formation, we generated a mouse retinal-specific Dnmt1 deletion mutation from the onset of neurogenesis. In the hypomethylated Dnmt1-mutant retina, neural progenitor cells continue to proliferate, however, the cell cycle progression is altered, as revealed by an increased proportion of G1 phase cells. Despite production of all major retinal neuronal cell types in the Dnmt1-mutant retina, various postmitotic neurons show defective differentiation, including ectopic cell soma and aberrant dendritic morphologies. Specifically, the commitment of Dmnt1-deficient progenitors towards the photoreceptor fate is not affected by DNA hypomethylation, yet the initiation of photoreceptor differentiation is severely hindered, resulting in reduction and mislocalization of rhodopsin-expressing cells. In addition to compromised neuronal differentiation, Dnmt1 deficiency also leads to rapid cell death of photoreceptors and other types of neurons in the postnatal retina. These results indicate that Dnmt1-dependent DNA methylation is critical for expansion of the retinal progenitor pool, as well as for maturation and survival of postmitotic neurons.