Nicotinamide Mononucleotide Alleviates the Development of Fibrotic Cataract by Modulating the Nrf2/ <scp>FPN1</scp> Signaling Pathway

Cataract is the leading cause of blindness globally. Among them, fibrotic cataract accounts for a considerable proportion of the types of cataract onset, with oxidative stress and ferroptosis implicated in its pathogenesis. Nicotinamide mononucleotide (NMN), a precursor to NAD+, has shown potential in mitigating fibrosis in various organs. This study investigates the role of NMN in regulating ferroptosis and its therapeutic potential in fibrotic cataract. Clinical samples from ASC patients and controls were analyzed for ferroptosis markers using qPCR and biochemical assays. In vitro, TGF-β2-treated SRA01/04 cells were assessed for GSH, MDA, and Fe²⁺ levels, and the effects of NMN on cell viability, ROS levels, and GPX4, FTH1, Nrf2, and FPN1, ACSL4 protein expression were evaluated in SRA01/04 cells with/without NMN or Nrf2 inhibitor ML385. Additionally, we explored the impact of NMN on TNF-α, IL-6, and EMT using ELISA and Western blot. In vivo, an ASC mouse model received NMN, followed by H&E, Masson, ferroptosis-related markers, and protein expression. ASC patients showed that GPX4 and FTH1, GSH were downregulated, while ACSL4, MDA, and Fe²⁺ levels were upregulated. In vitro, NMN inhibits TGF-β2-induced upregulation of ferroptosis markers lipid ROS, MDA, and Fe²⁺ and prevents GSH downregulation in SRA01/04 cells; it reverses the EMT marker E-cadherin downregulation while suppressing collagen I, IV, and α-SMA expression. These protective effects are Nrf2-dependent, as ML385 deletes NMN's benefits. In vivo, NMN restores lens architecture, reduces fibrosis, and normalizes ferroptosis markers Fe²⁺, MDA reduction, and GSH restoration through Nrf2/FPN1 pathway activation. NMN alleviates the development of fibrotic cataract by modulating the Nrf2/FPN1 signaling pathway, inhibiting EMT and ferroptosis.