Mechanisms of improved erythroid progenitor growth with removal of chronic stress after trauma

Abstract

Background: Erythropoietic dysfunction after trauma and critical illness is associated with anemia, persistent inflammation, increased hematopoietic progenitor cell mobilization from the bone marrow, and reduced erythroid progenitor growth. Yet the duration and reversibility of these postinjury bone marrow changes remain unknown. This study sought to determine whether removal of chronic postinjury stress could induce improvements in erythroid progenitor growth.

Methods: Sprague-Dawley rats (n = 8-11/group) were assigned to the following: naïve, lung contusion and hemorrhagic shock, lung contusion and hemorrhagic shock plus daily chronic stress for 7 days followed by 7 days of routine handling to allow recovery (lung contusion and hemorrhagic shock + chronic stress 7), or lung contusion and hemorrhagic shock plus chronic stress for 14 days (lung contusion and hemorrhagic shock + chronic stress 14). Circulating CD117⁺CD71⁺ erythroid progenitors were detected by flow cytometry. Rodents were killed on day 14, and bone marrow erythroid progenitor growth and erythroid transcription factors were assessed. Differences were assessed by analysis of variance (P < .05).

Results: Compared to lung contusion and hemorrhagic shock + chronic stress 14, lung contusion and hemorrhagic shock + chronic stress 7 rodents had improved hemoglobin (8% ± 10% increase vs 6% ± 10% decrease) with fewer mobilized erythroid progenitors (898 × vs 1,524 cells), lower granulocyte-colony stimulating factor levels (3.1 ± 1.1 × pg/mL vs 5.9 ± 1.8 pg/mL), and improved erythroid progenitor growth. Cessation of stress had no impact on erythroid transcription factors GATA-1, GATA-2, LMO2, or KLF1.

Conclusion: Improvements in erythroid progenitor growth and reduced hematopoietic progenitor cell mobilization were seen 7 days after cessation of chronic stress and were associated with an improvement in hemoglobin. Early bone marrow erythropoietic functional recovery may result from resolution of hematopoietic progenitor mobilization rather than upregulation of pro-erythroid transcription factors. This study suggests that postinjury anemia is reversible and has the potential to improve with the cessation of stress.

Figure 1.

Schematic overview of experimental model. LCHS (lung contusion and hemorrhagic shock); LCHS+CS 7 (lung contusion and hemorrhagic shock plus 7 days of chronic restraint stress followed by 7 days of routine daily handling); LCHS+CS 14 (lung contusion and hemorrhagic shock plus 14 days of chronic restraint stress). POD, postoperative day.

Figure 2.

Impact of persistent versus resolved stress on hemoglobin. On day 14, LCHS+CS 7 did not see the reduction in hemoglobin seen in LCHS+CS 14 rats. LCHS (lung contusion and hemorrhagic shock); LCHS+CS 7 (lung contusion and hemorrhagic shock plus 7 days of chronic restraint stress followed by 7 days of routine daily handling); LCHS+CS 14 (lung contusion and hemorrhagic shock plus 14 days of chronic restraint stress).

Figure 3.

Impact of persistent versus resolved stress on bone marrow erythroid progenitor growth potential. CFU-GEMM, colony-forming unit-granulocyte, -erythrocyte, -monocyte, -megakaryocyte; BFU-E, burst-forming unit-erythroid; CFU-E, colony-forming unit-erythroid; LCHS, lung contusion and hemorrhagic shock; LCHS+CS 7, lung contusion and hemorrhagic shock plus 7 days of chronic restraint stress followed by 7 days of routine daily handling; LCHS+CS 14, lung contusion and hemorrhagic shock plus 14 days of chronic restraint stress.

Figure 4.

Traditional erythroid transcription is not affected by stress. On day 14, bone marrow KLF and LMO2 transcription remained significantly decreased in all groups (presented as fold change versus naïve) (A–B). Bone marrow transcription of erythroid commitment factor GATA-1 was decreased in LCHS cohort and unchanged in other cohorts (C). Bone marrow GATA-2 was unaffected by stress (D). ns, not significant.

Figure 5.

Impact of persistent versus resolved stress on CD71+CD117+ erythroid progenitor cell mobilization. Peripheral red cell-lysed rat blood cells labeled using APC anti-CD117 and FITC anti-CD71. APC (allophycocyanin); FITC (fluorescein) (A–B). On day 14, LCHS+CS 14 was associated with increased circulating CD71⁺CD117⁺ erythroid progenitors (C) and increased plasma G-CSF (D). These were not true in the LCHS+CS 7 cohort (C–D). G-CSF, granulocyte-colony stimulating factor; LCHS, lung contusion and hemorrhagic shock; LCHS+CS 7, lung contusion and hemorrhagic shock plus 7 days of chronic restraint stress followed by 7 days of routine daily handling; LCHS+CS 14, lung contusion and hemorrhagic shock plus 14 days of chronic restraint stress.