Abstract
Purpose: :
Fumaric acid & its esters (FAEs) are used to treat psoriasis, a chronic inflammatory skin disease characterized by keratinocyte proliferation. FAEs are emerging as treatment for multiple sclerosis, an inflammatory neurodegenerative disease. Proliferation, inflammation, and neurodegeneration are hallmarks of retinal disease, suggesting that FAEs may have therapeutic value in retinal degenerations. In diseased retinas, Müller glial cells (MCs), which play critical roles in sustaining healthy retinal function, undergo reactive gliosis, a highly proliferative state, to forestall tissue damage. A vitamin critical for DNA & RNA synthesis, which is needed to perform these cytoprotective functions, is folate. Folate is a lipophobic anion that cannot traverse the plasma membrane. It must be taken into cells by specific transport mechanisms. We discovered that PCFT plays a vital role in folate uptake in MCs (Bozard et al., 2010). In the current studies, we examined the effect of monomethylfumarate (MMF), the active metabolite of FAEs, on folate transport via PCFT in MCs.
Methods: :
MCs were isolated from 5-7 day mouse retinas per our method (Jiang et al, 2006). MCs were treated 18 h with 1 mM MMF & uptake of [3H]-methyltetrahydrofolate (MTF) in MCs was measured at pH 5.5. Dose-response & time-course analyses of MMF treatment were performed & substrate specificity analyzed. Kinetic parameters of PCFT transport activity were measured.
Results: :
[3H]-MTF uptake by MCs decreased by ~33 or 54% following 18h treatment with 250 µM or 1 mM MMF, respectively. Inhibition of PCFT activity was specific to derivatives of fumaric acid. Kinetic analysis revealed a decrease in Vmax from 7.2 to 2.2 pmol/mg protein/15 min in control cells vs. MCs treated 18 h with 1 mM MMF. Studies are underway to examine PCFT localization in MCs exposed to MMF.
Conclusions: :
This is the first report that a drug used in treatment of proliferative skin disorders can regulate folate uptake in MCs. The work lays the foundation to explore MMF as an antiproliferative agent against reactive gliosis in degenerating retina.
Keywords: retinal glia • Muller cells • proliferation