Heme-regulated eIF2α kinase plays a crucial role in protecting erythroid cells against Pb-induced hemolytic stress.

Abstract

Lead (Pb) is a heavy metal with considerable environmental contamination. It is toxic to diverse cells and has been reported to cause a wide array of detrimental health problems including neurological disorders and anemia. In light of the mechanisms underlying Pb-induced anemia, the current understanding is still limited, in spite of efforts for years. Our previous studies recognized a protective role for the heme-regulated eIF2α kinase (Hri) in erythroid cells against oxidative stress exerted by arsenic and cadmium. Whether Hri is involved in Pb-induced hemolytic stress has not been scrutinized. In the current study, to more stringently address this question, we looked into erythropoiesis upon Pb(NO3)2 exposure by using an in vivo mouse model and ex vivo cultured E14.5 fetal liver cells. Diagnoses of hemolytic anemia, decreased red cell count, reduced hemoglobin concentration, and elevated bilirubin level were observed in Hri knockout (Ko) mice only, upon low-dose Pb administration. Significantly different from Ko mice, wild type (Wt) mice did not develop hemolytic anemia. Enforced extramedullary and medullary erythropoieses were found in Ko mice with Pb exposure. However, anemia was not compensated in Hri-deficient mice, as in vivo and ex vivo results manifested that expanded Hri-null erythroid precursors experienced blocked differentiation and enhanced apoptosis, leading to ineffective erythropoiesis under Pb exposure. Additionally, Pb treatment also promoted hepcidin expression and consequentially increased splenic iron storage, resulting in restrained iron availability for erythropoiesis. All considered, Hri-null erythroid precursors were prone to Pb-induced hemolytic stress. Hri deficiency gave rise to ineffective erythropoiesis and reduced iron availability for erythropoiesis under Pb stimulation, and these events together exacerbated Pb-induced hemolytic anemia. It is thus conceivable that this study delineated an indispensable function of Hri in maintaining red cell membrane integrity and guiding erythroid cell differentiation under Pb exposure. Our findings therefore deciphered a crucial role for Hri in protecting erythroid cells against Pb-induced toxicity.