Regulatory mechanisms of the protective function of alphaA- & alphaB-crystallins in retinal neurons and glia
Molecular Biology and Physiology of Neurons and Glial Cells
Final Report Abstract
Studies in animal models and in humans have shown that diabetic retinopathy is a complex disease characterized by vascular alterations, inflammation, and neuronal cell death, processes which involve upregulation of the two alpha (α)-crystallin proteins (αA and αB-crystallins) in retinal neurons and their supporting glial cells. We have demonstrated that this upregulation is a protective mechanism, as α-crystallins are protective in both cell types in vitro. We further demonstrated that α-crystallins’ protective function is impaired during diabetes over the time and thus cell death during diabetes occurs. In order to develop new treatments to prevent or reverse associated vision loss in diabetes, we were in this project particularly interested in investigating the exact mechanisms of α-crystallins protective function and its regulation in retinal neurons and Müller glial cells. Our goal was to confirm the potential of α-crystallins as novel therapies to prevent neurodegeneration in diseases like diabetes, glaucoma or age-related macular degeneration. During this project we found, that in particular αA-crystallin has an important role in the retina during diabetes, as loss of αA-crystallin but not αB-crystallin was associated with higher levels of retinal cell death in diabetic animals. Regarding the mechanisms of their protective function we found to our surprise, that αA-crystallins influence different signalling pathways in retinal neurons compared to Müller glial cells. Whereas they dampen the cell death rate in retinal neurons by directly influencing the endoplasmic reticulum stress (ER) response pathway, a pathway which is upregulated during diabetes, they had no effect on the ER stress response in Müller glial cells. Müller glial cells are important for neuronal cell survival by production and secretion of important factors for neuronal survival and they participate in the inflammatory response during diabetes. Thus we looked into the ability of Müller cells to secrete also αcrystallins. In fact, we found, that specifically secreted α-crystallin by these cells is able to reverse metabolic and inflammatory stress-induced neuronal cell death. Moreover, we could also demonstrate the ability of αA-crystallins to affect Müller glial cell activation in an antiinflammatory manner resulting in decreased production of inflammatory molecules and thus tempering of the immune response. In regard to the loss of α-crystallins’ protective function during diabetes, we discovered for the first time, that αA-crystallins completely devoted their protective effect (and their effect on the aforementioned molecular mechanisms), when crystallins are manipulated, mimicking what is seen during diabetes, with a reduced phosphorylation of αA-crystallin on a specific phosphorylation site within the protein. Thus in future manipulating this phosphorylation site might could prevent loss of function of αA- crystallins during diabetes und thus could account as an effective treatment modality to halt vision loss in patients with early stages of diabetes or other retinal diseases. The research was awarded with the 2017 “Kellogg Award for Excellence in Basic Research” at the annual Kellogg Eye Center Research Day (June 2nd 2017, Ann Arbor, MI, USA). The results were further published in an Ophthalmology newsletter (“Advances in Ophthalmology”), available online and in print, which is accessible by the broad public.
Publications
- (2018) A specific phosphorylation regulates the protective role of αA-crystallin in diabetes. JCI insight 3 (4)
Ruebsam, Anne; Dulle, Jennifer E.; Myers, Angela M.; Sakrikar, Dhananjay; Green, Katelyn M.; Khan, Naheed W.; Schey, Kevin; Fort, Patrice E.
(See online at https://doi.org/10.1172/jci.insight.97919) - (2017) A Triple Mutation of BetaB2- Crystallin is Necessary to Develop Cataract and Glaucoma. J Clin Exp Ophthalmol 8:690
Rübsam A, Dulle J, Garnai SJ, Pawar HS, Fort PE
(See online at https://doi.org/10.4172/2155-9570.1000690)
