Type 2 Diabetes Impairs Anti-Inflammatory Macrophage Differentiation in Diabetic Foot Ulcers

Background: Diabetic (DM) patients have a 30-fold increased risk of developing diabetic foot ulcers (DFUs), with 43% of non-healing DFUs requiring a lower extremity amputation (LEA). Non-healing DFUs is associated with impaired macrophage differentiation. Bone marrow (BM) hematopoietic stem cells (HSCs) differentiate into monocytes, which enter the circulation to become pro-inflammatory macrophages (M1) or anti-inflammatory macrophages (M2). In murine studies, DM HSCs transplantation was sufficient for impaired wound healing and skewed differentiation towards M1 when compared to non-DM control mice. This study suggests a causal relationship between DM BM-derived HSCs and impaired wound healing. However, it is unclear if these results translate to humans. We hypothesize that human DM BM-derived HSCs would be skewed towards M1 and away from M2 when compared to non-DM BM-derived HSCs. Methods: BM was collected from patients undergoing LEAs. Comparative analysis was made between DM patients with non-healing DFUs and from non-DM patients. Organoid BM samples were cultured for CD34+ HSC expansion. In vitro differentiation was performed using CD34+ HSCs induced to differentiated into monocytes (M-CSF) and subsequently to M1 (IFNy) or M2 (IL-4 and IL-13). Differentiated cells were quantified using flow cytometry and compared using student t-test statistical analysis. Results: HSCs derived from DM and non-DM BM yielded comparable percentages of monocytes, M1, and M2. We found no difference in the efficiency of monocyte or M1 differentiation between groups. Interestingly, M2 differentiated at a lower efficiency from DM HSCs than from non-DM HSCs (0.685 versus 1.15, respectively; p = 0.047). Conclusions: HSCs derived from DM BM have a comparable efficiency to differentiate towards monocytes and M1, however a decreased efficiency to differentiate towards M2 when compared to HSCs derived from non-DM BM in vitro . This finding suggests that the mechanism of non-healing DFUs involves dysfunction of BM-derived HSC/monocytes. In DFUs, monocytes may be skewed towards M1 differentiation because of reduced M2 differentiation capacity, thus favoring a pro-inflammatory state and preventing healing.