Acute periods of retinal ischemia impair subsequent supply of retinal blood flow and have been associated with several ocular diseases leading to visual impairment and blindness. Experimental evidence of diminished retinal blood flow after the initial retinal ischemia suggests that endothelial dysfunction may contribute to persistent retinal damage. Two important endothelium-derived factors involved in regulating retinal blood flow are vasodilator nitric oxide (NO) and vasoconstrictor endothelin-1 (ET-1). Our preliminary studies showed that retinal ischemia via elevated intraocular pressure (IOP) impaired bradykinin-induced NO-mediated dilation and enhanced ET-1-mediated constriction in pig retinal arterioles. Intravitreal administration of superoxide scavenger TEMPOL or endothelin-converting enzyme (ECE) inhibitor phosphoramidon before ischemia preserved vasodilation to bradykinin. Although these pilot studies suggest the involvement of ET-1 and oxidative stress in vascular dysfunction, their interrelationship and the signaling events contributing to the observed impairment remain to be elucidated. Herein, we hypothesize that ischemic insult activates the protein kinase C (PKC)-dependent vascular endothelin system, which leads to superoxide production via NAD(P)H oxidase and a subsequent increase in Rho/Rho kinase activation for the increased vascular tone and a reduced NO-mediated vasodilation. Since our long-term goal is to understand the signaling mechanisms responsible for physiological and pathophysiological regulation of retinal vasomotor function leading to future vascular therapy, the present application will serve the initial step toward this goal by identifying the causal factor and cellular mechanisms contributing to the impairment of vascular function following acute retinal ischemia. We will test the aforementioned hypothesis by pursuing three specific aims: (1) Determine whether enhanced ECE and PKC activities contribute to ischemia-induced dysfunction of retinal arterioles. (2) Determine whether activation of endothelin A/B receptors and vascular p38 mitogen-activated protein kinase/NAD(P)H oxidase signaling contributes to ischemia-induced dysfunction of retinal arterioles. (3) Determine whether enhanced vascular Rho/Rho kinase signaling contributes to ischemia-induced dysfunction of retinal arterioles. We will use both in-vivo and in-vitro approaches with various cellular/molecular techniques to integrate these three aims for elucidating the underlying mechanisms and signaling pathways responsible for the ischemia-induced arteriolar dysfunction in the retina. The results derived from these studies are essential to advance our understanding in the pathogenesis of retinal vascular disease associated with retinal ischemia and may suggest novel targets for future therapeutic interventions.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
7R01EY018420-05
Application #
8209194
Study Section
Hypertension and Microcirculation Study Section (HM)
Program Officer
Shen, Grace L
Project Start
2008-01-01
Project End
2013-12-31
Budget Start
2012-01-01
Budget End
2013-12-31
Support Year
5
Fiscal Year
2012
Total Cost
$316,440
Indirect Cost
$100,440
Name
Texas A&M University
Department
Surgery
Type
Schools of Medicine
DUNS #
835607441
City
College Station
State
TX
Country
United States
Zip Code
77845
Hein, Travis W; Xu, Wenjuan; Ren, Yi et al. (2013) Cellular signalling pathways mediating dilation of porcine pial arterioles to adenosine A?A receptor activation. Cardiovasc Res 99:156-63
Potts, Luke B; Bradley, Patrick D; Xu, Wenjuan et al. (2013) Role of endothelium in vasomotor responses to endothelin system and protein kinase C activation in porcine retinal arterioles. Invest Ophthalmol Vis Sci 54:7587-94
Hein, Travis W; Ren, Yi; Potts, Luke B et al. (2012) Acute retinal ischemia inhibits endothelium-dependent nitric oxide-mediated dilation of retinal arterioles via enhanced superoxide production. Invest Ophthalmol Vis Sci 53:30-6
Hein, Travis W; Rosa Jr, Robert H; Yuan, Zhaoxu et al. (2010) Divergent roles of nitric oxide and rho kinase in vasomotor regulation of human retinal arterioles. Invest Ophthalmol Vis Sci 51:1583-90
Hein, Travis W; Ren, Yi; Yuan, Zhaoxu et al. (2009) Functional and molecular characterization of the endothelin system in retinal arterioles. Invest Ophthalmol Vis Sci 50:3329-36
Hein, Travis W; Singh, Uma; Vasquez-Vivar, Jeannette et al. (2009) Human C-reactive protein induces endothelial dysfunction and uncoupling of eNOS in vivo. Atherosclerosis 206:61-8
Nagaoka, Taiji; Kuo, Lih; Ren, Yi et al. (2008) C-reactive protein inhibits endothelium-dependent nitric oxide-mediated dilation of retinal arterioles via enhanced superoxide production. Invest Ophthalmol Vis Sci 49:2053-60