Abstract
Purpose :
In diabetes, matrix metalloproteinase 9 (MMP-9) is activated in the retinal vasculature, and this damages the mitochondria and its DNA (mtDNA), resulting in free radical production and accelerated capillary cell apoptosis. Patients with diabetic retinopathy also have increased circulating levels of a thiol-containing non-protein amino acid, homocysteine, and high homocysteine is considered to increase oxidative stress. Our aim was to investigate the role of homocysteine in the development of diabetic retinopathy.
Methods :
Wistar rats (male), normal, or streptozotocin-induced diabetic, were administered homocysteine (400ug/kg/day) for 30 days. Homocysteine levels in the plasma and retina were quantified by a competitive ELISA method. Gene transcripts of cystathionine β-synthase (CBS, enzyme responsible for removal of homocysteine from the methionine cycle), MMP-9 and its tissue inhibitor TIMP1, activity of MMP-9 (fluorescence assay), ROS levels (2′,7′-dichlorofluorescein diacetate method) and mtDNA damage (mtDNA-encoded cytochrome b) were quantified in retinal microvessels.
Results :
Compared to normal control rats, homocysteine levels were elevated by ~3 fold in the plasma and retina of diabetic rats, and CBS levels were significantly decreased in their retinal vasculature. Administration of homocysteine to normal rats increased MMP-9 (activity and mRNA) and ROS levels, and decreased TIMP1 and cytochrome b transcripts. Homocysteine administration to diabetic rats further elevated ROS and MMP-9 (activity and mRNA) and reduced TIMP1 and cytochrome b; the values obtained from diabetic rats, with and without homocysteine, were significantly different from each other.
Conclusions :
In diabetes, increased homocysteine in the retina activates MMP-9 and impairs MMP-9/TIMP1 ratio, which facilitates mitochondrial damage. Thus, strategies targeting homocysteine metabolism have potential to protect diabetes-induced mitochondrial damage, and impede the development of diabetic retinopathy.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.