Diabetic retinopathy is the major sight-threatening disease in the American working-aged population. It affects retinal vasculature and neurons. Our recent discovery of the powerful in vivo neuroprotective effects of a ligand for sigma receptor 1 (sR1) may offer a novel approach to treatment of neuronal death in this disease. We have observed remarkable preservation of retinal structure in the Ins2Akita/+ mouse model of diabetic retinopathy when the mice were treated with (+)-pentazocine ((+)-PTZ), a highly specific sR1 ligand. sR1, initially thought to be an opiate receptor, is now known to function as a molecular chaperone that binds the ER stress protein BiP (GRP78). Factors that trigger sR1-binding are only now being identified. We have preliminary data showing that oxidative stress, which is implicated in diabetic retinopathy, induces phosphorylation of serine in sR1 and increases its binding to BiP in retinal ganglion cells. Our data show that (+)-PTZ dephosphorylates sR1 and dissociates it from BiP. We have observed increased expression of BiP (and other ER stress genes) in retinas of Ins2Akita/+ mice, the expression of which is decreased when the mice are administered (+)-PTZ. In addition, (+)-PTZ upregulates the expression of xCT in the Ins2Akita/+ mouse retina. xCT is a key protein regulating synthesis of the antioxidant glutathione. Based on these data, Aim 1 will test the hypothesis that (+)-PTZ confers neuroprotection by minimizing oxidative stress/modulating the ER stress response and that it does so by regulating sR1 phosphorylation. (+)-PTZ is considered a highly specific ligand for sR1. Thus, we predict that (+)-PTZ neuroprotection is mediated solely through its interactions with sR1;however, this has not been tested. We have established a colony of sR1 knockout mice, the availability of which will permit us to determine definitively whether sR1 is required for (+)-PTZ to confer neuroprotection.
Aim 2 will test the hypothesis that (+)-PTZ mediates its neuroprotective effects solely through activation of sR1 and absence of sR1 will increase retinal vulnerability to diabetes-induced cellular stress. In addition to these mechanistic studies, we must make progress regarding the clinical applicability of our findings. Thus far, we have administered (+)-PTZ only at diabetes onset and observed robust retinal neuroprotection in the diabetic mice. We do not know whether (+)-PTZ can confer retinal neuroprotection if administered after diabetes onset. This is relevant clinically since it would be rare that treatment of humans with retinopathy would commence at disease onset. Identification of intervention strategies that are effective following the onset of disease are of paramount importance.
Aim 3 will test the hypothesis that administration of (+)-PTZ post-onset of diabetes can prevent neuronal cell death in diabetic retinopathy. Completion of these aims will allow us to achieve our long-range goal, which is to determine whether sR1 ligands hold promise for neuroprotection in human retinopathy.

Public Health Relevance

Diabetic retinopathy is the leading cause of blindness in working-aged Americans. It is a neurovascular disease characterized by alterations of retinal vessels and death of retinal neurons. The neuronal death associated with diabetic retinopathy involves inner retinal cells, most notably ganglion cells. We have exciting data showing that the drug, (+)-pentazocine, which targets a unique protein called sigma receptor 1, has profound neuroprotective effects against ganglion cell death in a mouse model of diabetic retinopathy. The proposed project will extend these findings to understand the mechanism of this protection with the ultimate goal of determining whether (+)- pentazocine may be useful clinically for retinopathy in humans.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY014560-06
Application #
8106216
Study Section
Biology and Diseases of the Posterior Eye Study Section (BDPE)
Program Officer
Shen, Grace L
Project Start
2003-04-01
Project End
2014-07-31
Budget Start
2011-08-01
Budget End
2012-07-31
Support Year
6
Fiscal Year
2011
Total Cost
$357,800
Indirect Cost
Name
Georgia Regents University
Department
Biology
Type
Schools of Medicine
DUNS #
966668691
City
Augusta
State
GA
Country
United States
Zip Code
30912
Chaudhary, Kapil; Promsote, Wanwisa; Ananth, Sudha et al. (2018) Iron Overload Accelerates the Progression of Diabetic Retinopathy in Association with Increased Retinal Renin Expression. Sci Rep 8:3025
Smith, Sylvia B; Wang, Jing; Cui, Xuezhi et al. (2018) Sigma 1 receptor: A novel therapeutic target in retinal disease. Prog Retin Eye Res 67:130-149
Mysona, Barbara; Kansara, Neil; Zhao, Jing et al. (2017) The Role of Sigma 1 Receptor as a Neuroprotective Target in Glaucoma. Adv Exp Med Biol 964:299-307
Wang, Jing; Cui, Xuezhi; Roon, Penny et al. (2017) The Role of Sigma1R in Mammalian Retina. Adv Exp Med Biol 964:267-284
Wang, Jing; Saul, Alan; Cui, Xuezhi et al. (2017) Absence of Sigma 1 Receptor Accelerates Photoreceptor Cell Death in a Murine Model of Retinitis Pigmentosa. Invest Ophthalmol Vis Sci 58:4545-4558
Smith, Sylvia B (2017) Introduction to Sigma Receptors: Their Role in Disease and as Therapeutic Targets. Adv Exp Med Biol 964:1-4
Saul, Alan B; Cui, Xuezhi; Markand, Shanu et al. (2017) Detailed electroretinographic findings in rd8 mice. Doc Ophthalmol 134:195-203
Promsote, Wanwisa; Powell, Folami Lamoke; Veean, Satyam et al. (2016) Oral Monomethyl Fumarate Therapy Ameliorates Retinopathy in a Humanized Mouse Model of Sickle Cell Disease. Antioxid Redox Signal 25:921-935
Wang, Jing; Saul, Alan; Roon, Penny et al. (2016) Activation of the molecular chaperone, sigma 1 receptor, preserves cone function in a murine model of inherited retinal degeneration. Proc Natl Acad Sci U S A 113:E3764-72
Wang, Jing; Cui, Xuezhi; Roon, Penny et al. (2016) Role of Sigma 1 Receptor in Retinal Degeneration of the Ins2Akita/+ Murine Model of Diabetic Retinopathy. Invest Ophthalmol Vis Sci 57:2770-81

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