Article

Diabetologia

, Volume 54, Issue 3, pp 669-680

Epicatechin blocks pro-nerve growth factor (proNGF)-mediated retinal neurodegeneration via inhibition of p75 neurotrophin receptor proNGF expression in a rat model of diabetes

  • M. M. H. Al-GayyarAffiliated withClinical and Experimental Therapeutics, College of Pharmacy, University of GeorgiaVeterans Affairs Medical CenterDepartment of Biochemistry, Faculty of Pharmacy, University of Mansoura
  • , S. MatragoonAffiliated withClinical and Experimental Therapeutics, College of Pharmacy, University of GeorgiaVeterans Affairs Medical Center
  • , B. A. PillaiAffiliated withClinical and Experimental Therapeutics, College of Pharmacy, University of GeorgiaVeterans Affairs Medical Center
  • , T. K. AliAffiliated withClinical and Experimental Therapeutics, College of Pharmacy, University of GeorgiaVeterans Affairs Medical CenterMedical Center of Little Rock
  • , M. A. AbdelsaidAffiliated withClinical and Experimental Therapeutics, College of Pharmacy, University of GeorgiaVeterans Affairs Medical Center
  • , A. B. El-RemessyAffiliated withClinical and Experimental Therapeutics, College of Pharmacy, University of GeorgiaDepartment of Pharmacology and Toxicology, Medical College of GeorgiaDepartment of Ophthalmology, Medical College of GeorgiaVeterans Affairs Medical Center Email author 

Abstract

Aims/hypothesis

Accumulation of pro-nerve growth factor (NGF), the pro form of NGF, has been detected in neurodegenerative diseases. However, the role of proNGF in the diabetic retina and the molecular mechanisms by which proNGF causes retinal neurodegeneration remain unknown. The aim of this study was to elucidate the role of proNGF in neuroglial activation and to examine the neuroprotective effects of epicatechin, a selective inhibitor of tyrosine nitration, in an experimental rat model of diabetes.

Methods

Expression of proNGF and its receptors was examined in retinas from streptozotocin-induced diabetic rats, and in retinal Müller and retinal ganglion cells (RGCs). RGC death was assessed by TUNEL and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays in diabetic retinas and cell culture. Nitrotyrosine was determined using Slot-blot. Activation of the tyrosine kinase A (TrkA) receptor and p38 mitogen-activated protein kinase (p38MAPK) was assessed by western blot.

Results

Diabetes-induced peroxynitrite impaired phosphorylation of TrkA-Y490 via tyrosine nitration, activated glial cells and increased expression of proNGF and its receptor, p75 neurotrophin receptor (p75NTR), in vivo and in Müller cells. These effects were associated with activation of p38MAPK, cleaved poly-(ADP-ribose) polymerase and RGC death. Treatment of diabetic animals with epicatechin (100 mg kg−1 day−1, orally) blocked these effects and restored neuronal survival. Co-cultures of RGCs with conditioned medium of activated Müller cells significantly reduced RGC viability (44%). Silencing expression of p75NTR by use of small interfering RNA protected against high glucose- and proNGF-induced apoptosis in RGC cultures.

Conclusions/interpretation

Diabetes-induced peroxynitrite stimulates p75NTR and proNGF expression in Müller cells. It also impairs TrkA receptor phosphorylation and activates the p75NTR apoptotic pathway in RGCs, leading to neuronal cell death. These effects were blocked by epicatechin, a safe dietary supplement, suggesting its potential therapeutic use in diabetic patients.

Keywords

Diabetes Epicatechin Neuroprotection Peroxynitrite p75NTR proNGF