Open AccessN-Methyl-D-aspartate receptor activation, novel mechanism of homocysteine-induced blood–retinal barrier dysfunction
Author(s) -
Amany Tawfik,
Riyaz Mohamed,
Dina Kira,
Suhib Alhusban,
Mohamed AlShabrawey
Publication year - 2020
Publication title -
journal of molecular medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.708
H-Index - 139
eISSN - 1432-1440
pISSN - 0946-2716
DOI - 10.1007/s00109-020-02000-y
Subject(s) - occludin , retinal , blood–retinal barrier , cystathionine beta synthase , biology , homocysteine , hyperhomocysteinemia , tight junction , endocrinology , medicine , microbiology and biotechnology , biochemistry , diabetic retinopathy , methionine , diabetes mellitus , amino acid
Elevated levels of amino acid homocysteine (Hcy) recognized as hyperhomocysteinemia (HHcy) was reported in several human visual disorders, such as diabetic retinopathy (DR) and age-related macular degeneration (AMD). Breakdown of blood-retinal barrier (BRB) is concomitant with vision loss in DR and AMD. We previously reported that HHcy alters BRB. Here, we tested the hypothesis that HHcy alters BRB via activation of N-methyl-D-aspartate receptor (NMDAR). Human retinal endothelial cells subjected to high level of Hcy and mouse model of HHcy were used. We injected Hcy intravitreal and used a mouse model of HHcy that lacks cystathionine-β-synthase (CBS). RT-PCR, western blot, and immunofluorescence showed that retinal endothelial cells (RECs) express NMDAR at the gene and protein levels both in vitro and in vivo and this was increased by HHcy. We assessed BRB function and retinal morphology using fluorescein angiogram and optical coherence tomography (OCT) under HHcy with and without pharmacological inhibition of NMDAR by (MK801) or in mice lacking endothelial NMDAR (NMDAR E-/- mouse). Additionally, retinal albumin leakage and tight junction proteins ZO-1 and occludin were assessed by western blotting analysis. Inhibition or elimination of NMDAR was able to improve the altered retinal hyperpermeability and morphology under HHcy as indicated by significant decrease in retinal albumin leakage and restoration of tight junction proteins ZO-1 and occludin. Our findings underscore a potential role for endothelial NMDAR in mediating Hcy-induced breakdown of BRB and subsequently as a potential therapeutic target in retinal diseases associated with HHcy such as DR and AMD. KEY MESSAGES: • Elevated levels of homocysteine (Hcy) are defined as hyperhomocysteinemia (HHcy). • HHcy is implicated in diabetic retinopathy and age-related macular degeneration. • HHcy alters BRB via activation of N-methyl-D-aspartate receptor.