Chlamydomonas reinhardtii Cell Wall-Derived Hydroxyproline-Rich Glycoproteins Enhance Intestinal Epithelial Iron Absorption via PHD Inhibition and HIF2α Activation

Targeting host intestinal iron absorption pathways offers a promising alternative antianemia strategy to conventional iron supplementation/fortification. Here, hydroxyproline-rich glycoproteins featuring repetitive X-Hypn and (X-Hyp)n motifs were isolated from the Chlamydomonas reinhardtii cell walls. In polarized Caco-2 cell monolayers, the protein fraction, rather than the polysaccharide fraction, significantly promoted iron reduction, apical uptake, and transepithelial transport. LC-MS analysis revealed the intracellular accumulation of Hyp-Hyp, Pro-Hyp, and Ser-Hyp (0.10–0.18 μg/mg protein). Thermodynamic and docking simulations indicated these peptides effectively inhibited prolyl hydroxylase (PHD) by binding to its active site via entropy-driven hydrophobic/electrostatic interactions and steric hindrance. This increased hypoxia-inducible factor 2α (HIF2α) stability and upregulated essential iron transporters (DMT1, Dcytb, FPN, and HEPH). Furthermore, oral administration of the glycoproteins in rats acutely enhanced duodenal HIF2α stability and iron-transporter transcription. Overall, C. reinhardtii cell wall-derived hydroxyproline-rich peptides may stimulate intestinal iron absorption via PHD-HIF2α signaling, offering a sustainable nutritional intervention for iron deficiency.