Reversible host cell remodeling underpins deformability changes in malaria parasite sexual blood stages

M Dearnley1, C Trang2, Y Zhang3, O Looker1, S Kenny1, K Klonis1, R Chandramohanadas2, S Zhang3, L Tilley1 and MWA Dixon1

  1. Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC 3010, Australia
  2. Pillar of Engineering Product Development, Singapore University of Technology & Design, Singapore 487372
  3. Department of Engineering Science and Mechanics, The Pennsylvania State University, PA 16802, USA

Survival of the human malaria parasite Plasmodium falciparum in the circulation of the host relies on its ability to drastically alter its red blood cell (RBC) host cell. The sexual blood stage (gametocyte) of the human malaria parasite Plasmodium falciparum undergoes remarkable biophysical changes as it prepares for transmission to mosquitoes. During maturation, mid-stage gametocytes show low deformability and sequester in the bone marrow and spleen cords, thus avoiding clearance during passage through splenic sinuses. Mature gametocytes exhibit increased deformability and reappear in the peripheral circulation, allowing uptake by mosquitoes. Here we define the reversible changes in erythrocyte membrane organization that underpin this biomechanical transformation. Using a combination of biophysical techniques such as ektocytometry, spleen mimic filtration assays along with super resolution microscopy and atomic force microscopy techniques we functionally assess the role that RBC membrane skeleton remodelling plays in this reversible shift in deformability. We show that the length of the spectrin cross-members and the membrane skeleton mesh size increases in immature un-deformable gametocytes and reverses upon transition to maturity. These changes are accompanied by relocation of actin from the erythrocyte membrane to the Maurer’s clefts, allowing for the visualised changes to the spectrin actin membrane skeleton. These changes are reversed in the late stage gametocyte allowing parasite survival within the host and disease transmission.