Unveiling Leishmania invasion of fibroblasts: calcium signaling, lysosome recruitment and exocytosis culminate with actin-independent invasion

• Published in: bioRxiv
• Main Authors: Victor Soares Cavalcante-Costa, Costa-Reginaldo, Mariana, Queiroz-Oliveira, Thamires, Oliveira, Anny, Nat lia Couto, Anjos, Danielle, Santos, Jane, Andrade, Luciana, Maria F tima Horta, Castro-Gomes, Thiago
• Format: Paper
• Language: English
• Published: Cold Spring Harbor Cold Spring Harbor Laboratory Press 17.09.2018
• Subjects: Actin; Amastigotes; Apoptosis; Calcium signalling; Cytoskeleton; Dermis; Endocytosis; Exocytosis; Fibroblasts; Inoculation; Intracellular signalling; LAMP-1 protein; Leishmaniasis; Leukocytes (neutrophilic); Lysosomes; Macrophages; Parasites; Parasitic diseases; Phagocytes; Phagocytosis; Promastigotes; Tropical diseases
• DOI: 10.1101/420091

Intracellular parasites of the genus Leishmania are the causative agents of human leishmaniasis, a widespread emergent tropical disease. The parasite is transmitted by the bite of a sandfly vector that inoculates motile flagellated promastigote forms into the dermis of the mammalian host. After inoculation, parasites are ultimately captured by macrophages and multiply as round-shaped amastigote forms. Macrophages seem not to be the first infected cells since parasites were observed invading neutrophils first whose leishmania-containing apoptotic bodies were latter captured by macrophages, thereby becoming infected. The fact that Leishmania spp are able to live and replicate inside immune phagocytic cells and that macrophages are the main cell type found infected in chronicity created the perception that Leishmania spp are passive players waiting to be captured by phagocytes. However, several groups have described the infection of non-phagocytic cells in vivo and in vitro. The objective of this work was to study the cellular mechanisms involved in the invasion of non-professional phagocytes by Leishmania. We show that promastigotes of L.amazonensis actively induces invasion in fibroblasts without cytoskeleton activity, thus not through an induced type of phagocytosis as previously proposed. Inside fibroblasts parasites transformed in amastigotes, remained viable for at least two weeks and re-transformed in promastigotes when returned to insect vector conditions. Similarly to what was observed for T. cruzi, infection involves calcium signaling, recruitment and exocytosis of lysosomes and lysosome-triggered endocytosis. Conditions that alter lysosomal function such as cytochalasin-D and brefeldin-A treatment or the knockout of host cell lysosomal proteins LAMP-1 and 2 dramatically affected invasion. Likewise, triggering of lysosomal exocytosis and lysosome-dependent plasma membrane repair by low doses of streptolysin-O dramatically increased parasite entry. Together our results show that L.amazonensis promastigotes are able to take advantage of calcium-dependent lysosomal exocytosis and lysosome-induced endocytosis to invade and persist in non-phagocytic cells.