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 #
5R01EY014560-08
Application #
8512726
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
2013-08-01
Budget End
2014-07-31
Support Year
8
Fiscal Year
2013
Total Cost
$342,000
Indirect Cost
$114,000
Name
Georgia Regents University
Department
Biology
Type
Schools of Medicine
DUNS #
966668691
City
Augusta
State
GA
Country
United States
Zip Code
30912
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
Zhao, Jing; Mysona, Barbara A; Qureshi, Azam et al. (2016) (+)-Pentazocine Reduces NMDA-Induced Murine Retinal Ganglion Cell Death Through a σR1-Dependent Mechanism. Invest Ophthalmol Vis Sci 57:453-61
Shanmugam, Arul K; Mysona, Barbara A; Wang, Jing et al. (2016) Progesterone Receptor Membrane Component 1 (PGRMC1) Expression in Murine Retina. Curr Eye Res 41:1105-1112
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
Ha, Y; Liu, H; Xu, Z et al. (2015) Endoplasmic reticulum stress-regulated CXCR3 pathway mediates inflammation and neuronal injury in acute glaucoma. Cell Death Dis 6:e1900
Wang, Jing; Shanmugam, Arul; Markand, Shanu et al. (2015) Sigma 1 receptor regulates the oxidative stress response in primary retinal Müller glial cells via NRF2 signaling and system xc(-), the Na(+)-independent glutamate-cystine exchanger. Free Radic Biol Med 86:25-36
Shanmugam, Arul; Wang, Jing; Markand, Shanu et al. (2015) Sigma receptor 1 activation attenuates release of inflammatory cytokines MIP1γ, MIP2, MIP3α, and IL12 (p40/p70) by retinal Müller glial cells. J Neurochem 132:546-58
Ibrahim, Ahmed S; Elshafey, Sally; Sellak, Hassan et al. (2015) A lipidomic screen of hyperglycemia-treated HRECs links 12/15-Lipoxygenase to microvascular dysfunction during diabetic retinopathy via NADPH oxidase. J Lipid Res 56:599-611
Zhao, Jing; Ha, Yonju; Liou, Gregory I et al. (2014) Sigma receptor ligand, (+)-pentazocine, suppresses inflammatory responses of retinal microglia. Invest Ophthalmol Vis Sci 55:3375-84
Tawfik, Amany; Markand, Shanu; Al-Shabrawey, Mohamed et al. (2014) Alterations of retinal vasculature in cystathionine-β-synthase heterozygous mice: a model of mild to moderate hyperhomocysteinemia. Am J Pathol 184:2573-85

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