TGF?2-Hepcidin Feed-Forward Loop in the Trabecular Meshwork Implicates Iron in Glaucomatous Pathology.

ABSTRACT: Purpose:Elevated levels of transforming-growth-factor (TGF)-?2 in the trabecular meshwork (TM) and aqueous humor are associated with primary open-angle glaucoma (POAG). The underlying mechanism includes alteration of extracellular matrix homeostasis through Smad-dependent and independent signaling. Smad4, an essential co-Smad, upregulates hepcidin, the master regulator of iron homeostasis. Here, we explored whether TGF-?2 upregulates hepcidin, implicating iron in the pathogenesis of POAG. Methods:Primary human TM cells and human and bovine ex vivo anterior segment organ cultures were exposed to bioactive TGF-?2, hepcidin, heparin (a hepcidin antagonist), or N-acetyl carnosine (an antioxidant), and the change in the expression of hepcidin, ferroportin, ferritin, and TGF-?2 was evaluated by semiquantitative RT-PCR, Western blotting, and immunohistochemistry. Increase in reactive oxygen species (ROS) was quantified with dihydroethidium, an ROS-sensitive dye. Results:Primary human TM cells and bovine TM tissue synthesize hepcidin locally, which is upregulated by bioactive TGF-?2. Hepcidin downregulates ferroportin, its downstream target, increasing ferritin and iron-catalyzed ROS. This causes reciprocal upregulation of TGF-?2 at the transcriptional and translational levels. Heparin downregulates hepcidin, and reduces TGF-?2-mediated increase in ferritin and ROS. Notably, both heparin and N-acetyl carnosine reduce TGF-?2-mediated reciprocal upregulation of TGF-?2. Conclusions:The above observations suggest that TGF-?2 and hepcidin form a self-sustained feed-forward loop through iron-catalyzed ROS. This loop is partially disrupted by a hepcidin antagonist and an anti-oxidant, implicating iron and ROS in TGF-?2-mediated POAG. We propose that modification of currently available hepcidin antagonists for ocular use may prove beneficial for the therapeutic management of TGF-?2-associated POAG.

SUBMITTER: Ashok A 

PROVIDER: S-EPMC7401420 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature