Abstract
Glaucoma is a group of disorders associated with retinal ganglion cell (RGC) degeneration and death. There is a clear contribution of mitochondrial dysfunction and oxidative stress toward glaucomatous RGC death. Mitochondrial uncoupling protein 2 (Ucp2) is a well-known regulator of oxidative stress that increases cell survival in acute models of oxidative damage. The impact of Ucp2 on cell survival during sub-acute and chronic neurodegenerative conditions, however, is not yet clear. Herein, we test the hypothesis that increased Ucp2 expression will improve RGC survival in a mouse model of glaucoma. We show that increasing RGC but not glial Ucp2 expression in transgenic animals decreases glaucomatous RGC death, but also that the PPAR-γ agonist rosiglitazone (RSG), an endogenous transcriptional activator of Ucp2, does not significantly alter RGC loss during glaucoma. Together, these data support a model whereby increased Ucp2 expression mediates neuroprotection during a long-term oxidative stressor, but that transcriptional activation alone is insufficient to elicit a neuroprotective effect, motivating further research in to the post-transcriptional regulation of Ucp2.
Highlights
Glaucoma is a group of disorders associated with retinal ganglion cell (RGC) degeneration and death (Quigley, 2011) and, after cataracts, is the most frequent cause of blindness worldwide (Resnikoff and Keys, 2012)
We treated primary cortical astrocytes with FCCP at a low concentration to uncouple mitochondria without completely dissipating the m, and found that 10 nM FCCP depolarized the mitochondrial membrane potential ( m) to 88±4% of control levels, whereas m was 34±2% of control in astrocytes treated with 10 μM FCCP, a concentration routinely used to maximally depolarize mitochondria (10 μM; Figure 1A); 10 nM FCCP added to MitoSox loaded cells did not significantly alter mitochondrial superoxide generation, so we tested the hypothesis that uncoupling will reduce ROS production by dysfunctional mitochondria
AA significantly increased the rate of MitoSox oxidation (p < 0.001, FIGURE 4 | Effects of Thy1-creERT2 and Gfap-creERT2 on retinal Cre recombinase localization and uncoupling protein 2 (Ucp2) expression. (A) Gene diagram of transgenic Ucp2 and cre recombinase variants used in the present study. (B) Expression of Ucp2 in control and transgenic mice (n = 3). (C) Hoechst 33258-labeled frozen sections of Ucp2KI; GFAP-creERT2 and Ucp2KI; Thy1-creERT2 retinas, showing the endogenous fluorescence of EGFP and YFP, respectively
Summary
Glaucoma is a group of disorders associated with retinal ganglion cell (RGC) degeneration and death (Quigley, 2011) and, after cataracts, is the most frequent cause of blindness worldwide (Resnikoff and Keys, 2012). IOP reduction does not reduce glaucomatous visual field loss in roughly half of patients (Leske et al, 2004), necessitating development of adjuvant therapeutic modalities, including neuroprotective molecules that can protect RGCs. The molecular mechanisms of glaucoma pathogenesis are multifactorial, but are frequently connected to an increase in damaging free radicals in the eye (Izzotti et al, 2003; Saccà and Izzotti, 2008), retina (Tezel et al, 2005), and optic nerve head (Malone and Hernandez, 2007; Feilchenfeld et al, 2008), termed oxidative stress. The early transcriptional responses of DBA2/J mouse RGCs to elevated IOP strongly suggest mitochondrial abnormalities in RGCs early in the disease (Williams et al, 2017), which appears to persist in multiple animal models (Coughlin et al, 2015; Takihara et al, 2015; Ito and Di Polo, 2017) as well as in human glaucoma (Abu-Amero et al, 2006; Piotrowska-Nowak et al, 2018)
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