Effects of lipophosphoglycan on macrophage actin dynamics
2002 (English)Licentiate thesis, comprehensive summary (Other academic)
Leishmania donovani is a blood-borne tropicial parasite, which infects humans through bites by Phlebotomine sandflies. The parasite survives and multiplies inside macrophages in inner organs, and causes the deadly disease visceral leishmaniasis (Kala-Azar). Lipophosphoglycan (LPG) is the major surface component of Leishmania donovani promastigotes. LPG comprises a membrane-anchoring
lysophosphatidylinositol moiety and an extracellular chain of repeating disaccharide phosphates. The repeats are crucial for parasite survival inside macrophages following phagocytosis. LPG has several effects on the host cell including inhibition of protein kinase C (PKC) activity, and inhibition of phagosomal maturation, a process requiring depolymerization of periphagosomal F-actin. Confocal microscopy and image analysis was used to follow F-actin dynamics in single macrophages during phagocytosis of L. donovani promastigotes and LPG-coated particles. F-actin did not depolymerize, but instead progressively polymerized around phagosomes with LPG-containing prey. This directly correlated with reduced translocation of PKCα to the phagosome and blocked phagosomal maturation. It was also found that LPG inhibited cortical actin turnover, which may be the underlying cause of the reduced uptake of LPG-containing prey. Free calcium was necessary for phagocytosis, periphagosomal F-actin breakdown and phagosomal maturation in macrophages interacting with unopsonized prey. LPG required free calcium to exert its inhibitory effects on these processes. We also studied F -actin turnover in macrophages overexpressing dominant-negative (DN) PKCα. DN PKCα macrophages showed increased amounts of cortical F-actin, decreased phagocytic capacity, inhibition of periphagosomal F-actin breakdown and defective phagosomal maturation. When DN PKCa macrophages interacted with LPG-containing prey, phagocytosis was almost completely blocked.
Together, our results indicate that blockage of F-actin breakdown through inhibition of PKCa by LPG reduces phagocytosis and is instrumental for the inhibition of phagosomal maturation induced by L. donovani promastigotes.
Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 2002. , 42 p.
Linköping Studies in Health Sciences. Thesis, ISSN 1100-6013 ; 58
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:liu:diva-26683Local ID: 11250ISBN: 91-7373-190-0OAI: oai:DiVA.org:liu-26683DiVA: diva2:247233
2002-12-10, Hälsouniversitetet, Linköping, 10:15 (Swedish)
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