SMAD2 and diabetic kidney disease: It alleviates diabetic nephropathy by inhibiting TGF-β1/Smad2/3 fibrotic pathways and ferroptosis (39–41, 113, 114), shields retinal cells via anti-apoptotic mechanisms (Bcl-2↑/Bax↓) (25, 61), and preserves testicular function through autophagy activation (115).