Iron-dependent KDM4D activity controls the quiescence-activity balance of MSCs via the PI3K-Akt-Foxo1 pathway.

Iron deficiency is a prevalent nutritional deficit associated with organ damage and dysfunction. Recent research increasingly associates iron deficiency with bone metabolism dysfunction, although the precise underlying mechanisms remain unclear. Some studies have proposed that iron-dependent methylation-erasing enzyme activity regulates cell proliferation and differentiation under physiological or pathological conditions. However, it remains uncertain whether iron deficiency inhibits the activation of quiescent mesenchymal stem cells (MSCs) by affecting histone demethylase activity. In our study, we identified KDM4D as a key player in the activation of quiescent MSCs. Under conditions of iron deficiency, the H3K9me3 demethylase activity of KDM4D significantly decreased. This alteration resulted in increased heterochromatin with H3K9me3 near the PIK3R3 promoter, suppressing PIK3R3 expression and subsequently inhibiting the activation of quiescent MSCs via the PI3K-Akt-Foxo1 pathway. Iron-deficient mice displayed significantly impaired bone marrow MSCs activation and decreased bone mass compared to normal mice. Modulating the PI3K-Akt-Foxo1 pathway could reverse iron deficiency-induced bone loss.