Impaired iron recycling from erythrocytes is an early iron-dependent hallmark of aging
Aging affects iron homeostasis, as evidenced by tissue iron loading and toxicity and common anemia in the elderly. Iron needs in mammals are met primarily by iron-recycling from senescent red blood cells (RBCs), a task chiefly accomplished by splenic red pulp macrophages (RPMs) via erythrophagocytosis. Given that RPMs continuously process iron, their cellular functions might be susceptible to age-dependent decline, a condition that has been largely unexplored to date. Here, we found that 10-11-months-old female mice exhibit iron loading, diminished lysosomal activity, and decreased erythrophagocytosis rate in RPMs. These impairments lead to the retention of senescent hemolytic RBCs in the spleen, and the formation of undegradable iron- and heme-rich extracellular protein aggregates, likely derived from ferroptotic RPMs. We further found that feeding mice an iron-reduced diet alleviates iron accumulation in RPMs, enhances their ability to clear erythrocytes, and limits ferroptosis. Consequently, this diet ameliorates hemolysis of splenic RBCs and the formation of iron-rich aggregates, increasing serum iron availability in aging mice. Using RPM-like cells, we show that the diminished iron-recycling capacity of RPMs is underlain by iron accumulation and reduced expression of heme-catabolizing enzyme heme oxygenase 1 (HO-1). Taken together, we identified RPM collapse as an early hallmark of aging and demonstrated that dietary iron reduction improves iron turnover efficacy.