MAPK/ERK Activation in Macrophages PromotesLeishmaniaInternalization and Pathogenesis

Abstract

ABSTRACTThe obligate intracellular protozoan parasiteLeishmaniabinds several host cell receptors to trigger its uptake by phagocytic cells, ultimately resulting in visceral or cutaneous leishmaniasis. AfterLeishmaniaengages 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 ofLeishmaniainfection. Thus, preventingLeishmaniainternalization by phagocytes could be a novel therapeutic strategy for leishmaniasis. However, the host cellular machinery that mediates promastigote and amastigote uptake is not well understood. Here, using small-molecule inhibitors of Mitogen-activated protein kinases/Extracellular signal regulated kinases (MAPK/ERK), we demonstrate that ERK1/2 mediatesLeishmania amazonensisuptake and (to a lesser extent) 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 inLeishmania-infected mice, even if it is started significantly after lesions develop. Our results show that maximalLeishmaniainfection requires MAPK/ERK and highlight the potential for MAPK/ERK-mediated signaling pathways to be novel therapeutic targets for leishmaniasis.Author (lay) summary:Leishmaniais a single-celled parasite that causes skin ulcers or a disseminated disease in humans. Our goal is to identify new drugs to treatLeishmaniainfection.Leishmaniamust live inside human immune cells to cause disease. IfLeishmaniais not able to enter human immune cells, it dies. Our studies demonstrate howLeishmaniainfection stimulates a set of proteins called MAP kinases, which pass signals from one protein to the next within mammalian immune cells. The resulting signals allowLeishmaniato enter into these immune cells and survive within its host. Importantly, a drug that prevents these signals from MAP kinases, called trametinib, decreases the development of skin ulcers when it is given to mice that are infected withLeishmania. Our findings suggest thatLeishmaniacould be treated with drugs that act on kinases found in humans rather than the parasites themselves.One sentence summary:An Abl2-SYK-Raf-MEK-ERK pathway facilitatesLeishmaniauptake by phagocytic cells and promotes disease severity inLeishmania-infected mice.