Sox6 Is Necessary for Efficient Erythropoiesis in Adult Mice under Physiological and Anemia-Induced Stress Conditions

Abstract

BackgroundDefinitive erythropoiesis is a vital process throughout life. Both its basal activity under physiological conditions and its increased activity under anemia-induced stress conditions are highly stimulated by the hormone erythropoietin. The transcription factor Sox6 was previously shown to enhance fetal erythropoiesis together and beyond erythropoietin signaling, but its importance in adulthood and mechanisms of action remain unknown. We used here Sox6 conditional null mice and molecular assays to address these questions.Methodology/Principal Findings Sox6fl/flErGFPCre adult mice, which lacked Sox6 in erythroid cells, exhibited compensated anemia, erythroid cell developmental defects, and anisocytotic, short-lived red cells under physiological conditions, proving that Sox6 promotes basal erythropoiesis. Tamoxifen treatment of Sox6fl/flCaggCreER mice induced widespread inactivation of Sox6 in a timely controlled manner and resulted in erythroblast defects before reticulocytosis, demonstrating that impaired erythropoiesis is a primary cause rather than consequence of anemia in the absence of Sox6. Twenty five percent of Sox6fl/flErGFPCre mice died 4 or 5 days after induction of acute anemia with phenylhydrazine. The others recovered slowly. They promptly increased their erythropoietin level and amplified their erythroid progenitor pool, but then exhibited severe erythroblast and reticulocyte defects. Sox6 is thus essential in the maturation phase of stress erythropoiesis that follows the erythropoietin-dependent amplification phase. Sox6 inactivation resulted in upregulation of embryonic globin genes, but embryonic globin chains remained scarce and apparently inconsequential. Sox6 inactivation also resulted in downregulation of erythroid terminal markers, including the Bcl2l1 gene for the anti-apoptotic factor Bcl-xL, and in vitro assays indicated that Sox6 directly upregulates Bcl2l1 downstream of and beyond erythropoietin signaling.Conclusions/SignificanceThis study demonstrates that Sox6 is necessary for efficient erythropoiesis in adult mice under both basal and stress conditions. It is primarily involved in enhancing the survival rate and maturation process of erythroid cells and acts at least in part by upregulating Bcl2l1.

Sox6 enhances erythroid differentiation in human erythroid progenitors

“…This might reflect both the accelerated erythroid differentiation induced by Sox6 (Bcl-xL is known to increase in late erythroid differentiation) and a possible direct transcriptional activation on Bcl-xL, in agreement with what happens in mouse erythropoiesis. 12 In the latter case, the activation of Bcl-xL by Sox6, counteracting the parallel down-regulation imposed by SOCS3, might play a relevant role in ensuring the proper balance between proliferation and cell cycle withdrawal required for terminal maturation.…”

“…[1][2][3] In particular, Sox6, originally isolated from adult mouse testis, 4 is required for the development of the central nervous system, [5][6][7] for chondrogenesis, 8 and for cardiac and skeletal muscle formation. 9,10 Recently, Sox6 has been demonstrated to be crucial for definitive erythropoiesis, [11][12][13][14][15] a process in which committed progenitors progressively differentiate into burst-forming-unit erythroid cells and colonyforming-unit (CFU) erythroid cells, which in turn give rise to proerythroblasts and erythroblasts and finally to mature, enucleated red blood cells. These differentiation stages are accompanied by profound maturational changes: Within few cell divisions, in parallel with the accumulation of erythroid-specific markers (membrane proteins, enzymes required for the heme biosynthesis pathway, and globins), cells undergo chromatin condensation and enucleate.…”

“…18,19 Among them, Sox6 recently has been shown to stimulate erythroid cell survival, proliferation, and terminal maturation during definitive murine erythropoiesis. 11,12 Sox6-null mouse fetuses and pups are anemic and have defective red blood cells. Recently, Sox6 has been implicated in the silencing of embryonic globin genes; it directly silences the embryonic ⑀y-globin gene in definitive erythroid cells by binding to the ⑀y promoter, 13,14 and it cooperates with BCL11A in silencing ␥-globin expression, possibly via direct physical interaction.…”

Flicking the switch: adult hemoglobin expression in erythroid cells derived from cord blood and human induced pluripotent stem cells

“…Given its role in adult erythropoiesis and repression of embryonic/fetal hemoglobin expression, the SOX6 transcription factor is an attractive candidate. 16,17 Alternatively, post-translational modifications and subcellular localization of KLF1 could be involved. 18 Thus, the current work sheds some light on the conundrum that KLF1 is already a functional transcriptional activator in embryonic erythroid cells which do not express adult hemoglobin.…”

To respond or not to respond to hydroxyurea in thalassemia: a matter of stress adaptation?

“…Loss of function experiments showed that SOX6 is a gammaglobin repressor. 11,12 When over-expressed, however, it stimulates cell differentiation and the expression of all globin genes, although the gamma-globin gene is considerably less activated, presumably due to the specific repressive effect of SOX6. 13 In R-cells, SOX6 is over-expressed, particularly after HU administration.…”