To identify the pathways involved in phagocytosis by dendritic cells, I performed RNA sequencing of primary bone-marrow derived dendritic cells engulfing apoptotic human Jurkat cells (to undeniably distinguish phagocyte-derived RNA only) or after uptake of LPS-coated beads as a source of inflammatory trigger. My analysis revealed differential SLC programs that are initiated in dendritic cells during efferocytosis of apoptotic cells versus LPS-coated bead uptake. SLCs mediate transport of ions, aminoacids and small molecules across cellular membranes, are linked to >100 human diseases, and are also amenable for targeting by small molecules.
More particularly, SLCs associated with amino acid metabolism were upregulated and SLCs associated with oxidative phosphorylation (OXPHOS) were downregulated in efferocytic dendritic cells, while SLCs linked to intracellular pH regulation and nucleoside salvage/energy metabolism were upregulated upon ingesting pathogenic cargo. Using mouse models, I validated this SLC signature in DC subsets in vivo, in both tolerogenic and immunogenic conditions of phagocytosis.
Notably, efferocytic engulfment by dendritic cells indicated that an aminoacid transporter, which is highly expressed in skin-specific dendritic cell subsets, is upregulated in wounded skin in mice. Moreover, my in vitro studies show that switching off the gene function of the transporter specifically in dendritic cells, either by pharmacological inhibition or by gene deletion, promotes phagocytosis of dying cells. Therefore, I investigated whether this aminoacid transporter plays a role in the wound healing process, since removal of dead cells in the wounds by phagocytes, including dendritic cells, is essential for accelerating wound healing dynamics. My results demonstrated that topical administrator of a specific inhibitor of the transporter has both preventive and therapeutic effect in cutaneous wound healing in mouse models.
These results highlight dendritic cells and solute carrier transporters as critical players that regulate efferocytic clearance in the skin and open possibilities for more efficient treatment of chronic cutaneous wounds
