Abstract
Aging affects iron homeostasis and erythropoiesis, as evidenced by tissue iron loading in rodents and common anemia in the elderly. Since red pulp macrophages (RPMs) continuously process iron, their cellular functions might be susceptible to age-dependent decline, affecting organismal iron metabolism and red blood cell (RBCs) parameters. However, little is known about the effects of aging on the functioning of RPMs. To study aging RPMs, we employed 10-11-months-old female mice that show serum iron deficiency and iron overload primarily in spleens compared to young controls. We observed that this is associated with iron loading, oxidative stress, diminished lysosomal activity, and decreased erythrophagocytosis rate in RPMs. We uncovered that these impairments of RPMs lead to the retention of senescent RBCs in the spleen, their excessive local hemolysis, and the formation of iron- and heme-rich large extracellular protein aggregates, likely derived from damaged ferroptotic RPMs. We further found that feeding mice an iron-reduced diet alleviates iron accumulation and reactive oxygen species build-up in RPMs, improves their ability to clear and degrade erythrocytes, and limits ferroptosis. Consequently, this diet improves splenic RBCs fitness, limits hemolysis and the formation of iron-rich protein aggregates, and increases serum iron availability in aging mice. Using RPM-like cells, we show that diminished erythrophagocytic and lysosomal activities of RPMs can be attributed to a combination of increased iron levels and reduced expression of heme-catabolizing enzyme heme oxygenase 1 (HO-1). Taken together, we identified RPM dysfunction as an early hallmark of physiological aging and demonstrated that dietary iron reduction improves iron turnover efficacy.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
This is a significantly revised version of our manuscript updated with the data generated over last 2 months.
