Abstract
Purpose :
Our lab and others have shown that retinal diseases like diabetic retinopathy and macular degeneration are associated with disrupted iron homeostasis resulting in retinal iron accumulation. However, our knowledge on how iron toxicity contributes to the retinopathy is limited. We reported recently that systemic iron overload causes upregulation of retinal renin angiotensin system (RAS). Literature evidences indicate that multiple genes of the RAS are targets of Wnt/β-catenin signaling. Interestingly, aberrant activation of Wnt/β-catenin signaling is observed in several degenerative diseases. In the present study, we explored if iron accumulation regulates canonical Wnt signaling in the retina.
Methods :
Retinal cells were treated with Ferric ammonium citrate to induce iron accumulation. Systemic iron overload was induced by treating mice with 1g/kg bodyweight of iron-dextran intraperitoneally once a week for 8 weeks. Retinal iron accumulation was induced by injecting 1 μL of 2.4mM holo-transferrin (or apo-transferrin for control mice) once intravitreally. Intracellular ROS generation was monitored by CM-H2DCFDA staining. Intracellular iron levels were estimated by inductively coupled plasma-mass spectrometry. Two-tailed Student's t-test was used for statistical analysis.
Results :
In-vitro and in-vivo iron treatment resulted in the activation of Wnt/β-catenin signaling and its downstream target genes including renin-angiotensin system in the retina. We confirmed further that iron induces Wnt signaling in the retina using TOPFlash T-cell factor/lymphoid enhancer factor promoter assay and Axin2-LacZ reporter mouse. Presence of iron chelator deferiprone or anti-oxidant N-acetyl cysteine reversed the iron mediated upregulation of Wnt/β-catenin signaling. In addition, treatment of retinal cells with peroxisome proliferator activated receptor (PPAR) alpha agonist, fenofibrate prevented iron induced β-catenin, RAS and oxidative stress signaling by chelating the iron.
Conclusions :
In summary, our study demonstrates that iron accumulation in the retina activates Wnt/β-catenin and RAS signaling in an oxidative stress dependent mechanism. In addition, we report a previously unidentified pharmacological effect of fenofibrate, an FDA approved lipid lowering drug, as an iron chelator making it an attractive drug for the treatment of many chronic diseases associated with iron overload.
This is a 2020 ARVO Annual Meeting abstract.