K. E. Galicia1,2, H. Wang2, R. Gonzalez1,2, M. Choudhry1,2, J. Kubasiak1,2 1Loyola University Medical Center, Department Of Surgery, MAYWOOD, ILLINOIS, USA 2Loyola University Chicago, Burn And Shock Trauma Research Institute, Maywood, IL, USA
Introduction: Hematopoiesis proceeds in a tiered pattern of differentiation, beginning with hematopoietic stem cells (HSC) and ultimately leading to the production of erythroid, myeloid, and lymphoid lineages (Figure 1A). Lineage commitment can be pathologically altered; this is well-characterized in hematologic disorders like leukemia. However, in the setting of burn injury, changes in lineage commitment are much less understood. Evidence suggests that burn injury induces a myeloid predominance associated with poor patient prognosis and increased likelihood of shock and infection. This study aims to further profile HSC of the bone marrow niche following burn injury in a murine model.
Methods: C57BL/6 male mice were randomly assigned to receive either burn or sham injury. Using a prefabricated template exposing ~12% total body surface area (TBSA) on the animal’s dorsal surface, mice were subjected to burn injury via immersion into a ~85°C water bath for ~7 seconds. Mice were then euthanized at 6 hours, and 1, 2, 3, 7, and 10 days post-burn. Bone marrow was collected from bilateral hindlimbs and processed to determine HSC populations via flow cytometry. Flow cytometry gating was performed with markers CD48, CD150, and CD135, using FlowJo Software (v10.6). Event counts and frequencies were analyzed with multiple unpaired t-tests and linear mixed-effect regression.
Results: Following burn injury, mice demonstrate significantly increased percent population of CD48-150- Short-Term (ST)-HSC/Multipotent Progenitor (MPP)1 at 1, 2, 3, and 7 days relative to sham (all p<0.05), with subsequent return to baseline by 10 days (Figure 1B). In contrast, CD48-150+ Long-Term (LT)-HSC appear largely unaffected by burn injury, differing only at 3 days relative to sham (20.1% vs 11.8%; p=0.01; Figure 1C). Among burn mice, CD48+150+ MPP2 is significantly decreased relative to CD48+150- MPP3 at 6 hours and 2, 3, 7, and 10 days (all p<0.05). In fact, the difference in percent population between MPP2 and MPP3 progressively increases from 33% to 50% over the course of 10 days post-burn. Finally, CD135+150- MPP4 appears largely unaffected by burn injury, differing only at 1 day relative to sham (14.9% vs 7.6%; p=0.001; Figure 1D).
Conclusion: Burn injury results in ST-HSC/MPP1 proliferation that subsides by 10 days. Subsequent lineage commitment displays a myeloid predominance with a shift toward MPP3 and eventual Granulocyte-Monocyte Progenitor (GMP) production. Further research is in progress to correlate these bone marrow niche changes to potential HSC alterations in the peripheral blood, spleen, and skin.
