ERK1/2 Activation in Macrophages Promotes Leishmania Internalization and Pathogenesis

The obligate intracellular protozoan parasite Leishmania binds several host cell receptors to trigger its uptake by phagocytic cells, ultimately resulting in visceral or cutaneous leishmaniasis. After Leishmania engages receptors on macrophages and other phagocytes, a series of signaling pathways in the host cell are activated during its internalization, which are critical for establishment and persistence of Leishmania infection. Thus, preventing Leishmania internalization by phagocytes could be a novel therapeutic strategy for leishmaniasis. However, the host cellular machinery that mediates promastigote and amastigote uptake is poorly understood. Here, using small-molecule inhibitors of Mitogen-activated protein kinases/Extracellular signal regulated kinases (MAPK/ERK), we demonstrate that ERK1/2 mediates efficient Leishmania amazonensis uptake and phagocytosis of beads by macrophages. We find that inhibition of MEK1/2 or ERK1/2 leads to inefficient amastigote uptake by macrophages. Moreover, using inhibitors and primary macrophages lacking spleen tyrosine kinase (SYK) or Abl family kinases, we show that SYK and Abl family kinases mediate Raf, MEK, and ERK1/2 activity and are necessary for efficient uptake. Finally, we demonstrate that trametinib, a MEK1/2 inhibitor used clinically to treat certain cancers, significantly reduces disease severity and parasite burden in Leishmania-infected mice, even if it is started after lesions develop. Our results show that maximal Leishmania infection requires MAPK/ERK and highlight the potential for MAPK/ERK-mediated signaling pathways to be novel therapeutic targets for leishmaniasis. One sentence summary An Abl2-SYK-Raf-MEK-ERK pathway facilitates Leishmania uptake by phagocytic cells and promotes disease severity in Leishmania-infected mice.