Abstract:

Wound healing is a very complex process that needs the participation of several cell types either resident or recruited from the bone marrow. My PhD work is focused on the identification of novel therapeutic strategies for the treatment of delayed healing, which remains a significant global health concern. First, we explored the potential of fetal microchimeric cells (FMC) to improve maternal wound healing. We found that skin healing was similarly improved in post-partum mice and in pregnant mice, through increased proliferation and angiogenesis. Besides, we showed that the chronic ulcers of post-partum SAD-1 mice (model of sickle cell disease) healed more quickly than those of virgin mice. This was associated with the recruitment of fetal cells in maternal wounds where they harbored markers of leukocytes and endothelial cells. Taken together, these results indicate that healing capacities of FMC are maintained long after delivery. Then, we investigated the pathogenic role of neutrophil extracellular traps (NET) in sickle cell disease (SCD) ulcers, using a humanized mice model (TOWNES mice). We observed that young TOWNES SCD mice displayed a significant delay in skin healing, along with a reduced neo-epidermis formation and angiogenesis in sickle cell mice (SS) compared to control mice (AA). SS mice skin did not show any major architectural difference compared to AA mice. However, SS mice displayed more circulating neutrophils at steady state, due to an increase in hematopoietic stem and progenitor cells (HSPC) in bone marrow with higher clonogenicity capacities. Neutrophils in SS mice were more activated and released more NET. In agreement, neutrophils and NET were increased in the wound bed of SS mice. Reducing neutrophil counts with short-term hydroxyurea treatment improved wound healing in SS mice, similar to treatment with NET inhibitors (Dnase I or PAD4 inhibitor). To show that delayed healing was due to defects in bone marrow-recruited cells, we grafted AA mice with AA (control, AA => AA) or SS bone marrow (SS => AA). Skin healing was significantly delayed in SS => AA mice, but this was partially rescued by PAD4 inhibitor treatment. Overall, this work demonstrated the pathogenic role of neutrophils and NET in SCD chronic ulcers by using a humanized mouse model of SCD. Lastly, we investigated the role of mineralocorticoid receptor (MR) in glucocorticoid (GC)-induced impaired wound healing. Our results found that persistent GC stimulation of the MR is responsible for the cutaneous side effects and that this can be cured by MR blockade. Then, we identified a significant role of MR signaling in the inflammation and impaired vascular density that is associated with GC-induced delayed wound healing. Importantly, we showed that the myeloid MR plays a critical role in promoting local inflammation. Knocking down MR in myeloid cells, especially in macrophages, promoted anti-inflammatory macrophage polarization and dermal angiogenesis, thus increasing tissue repair. This suggests that MR inhibitors could be effective to prevent GC-induced delayed wound healing. Overall, my doctoral research has contributed to a better understanding of the various mechanisms that lead to wound healing defects. This has enabled the development of potential new therapeutic approaches, which could be developed into drugs or medications in the future to treat delayed wound healing.