Plasmodium parasites, the causative agent of malaria, are transmitted to a vertebrate host by the infective bite of an Anopheles mosquito. Development of the parasite in the mosquito is an obligatory step in its life cycle and offers us an additional target in the effort to curb disease transmission.
Glycobiological Analysis of Plasmodium development in the Anopheles mosquito.
Discovery of novel interventions in the fight against malaria requires a pioneering approach to examine cell-cell interactions among the transmission stages of the parasite (i.e., sporozoite and ookinete) and their respective mammalian or mosquito host cells. Glycobiology offers such a unique approach. In model systems, glycans and glycoconjugates have been shown to be important structural components of cell walls and the extracellular matrix, modifiers of protein solubility (secretion) and stability (protection from enzyme degradation), modulators of glycoprotein trafficking both intra- and extracellularly (e.g., by modifying porosity of the glycocalyx), mediators of cell-cell and cell-matrix adhesion and intra- and extracellular signaling. Yet, despite their clear importance in cell biology, an appreciation of glycan posttranslational modification of critical proteins involved in host-pathogen interactions, especially in the context of malaria parasite development, remains undervalued.
In addition to using transgenic technologies (parasite) and RNAi (mosquito), we are also applying mass spectrometry and lectin/glycan arrays to answer some of the fundamental questions concerning how protein-glycan interactions mediate cell invasion across different parasite developmental stages (but most especially in the mosquito). Recent and on-going work have examined the role of glycosyltransferases, glycoconjugates (glycoproteins and proteoglycans) on the mosquito midgut surface as well as identified novel ookinete (parasite) lectin-like molecules.
Cell-cell adhesion in parasite transmission from man to mosquito.
Microbial pathogens have been shown to subvert normal host cell glycoconjugates for initial attachment and subsequent invasion. The working hypothesis is that cell adhesion/invasion is believed to be co-receptor mediated, wherein initial adhesion and recognition of the host cell membrane is achieved through protein-glycan recognition and invasion entails recognition of a second ligand, such as a host cell surface protein. My work, along with several others, has contributed greatly to the body of knowledge on the characterization of mosquito midgut carbohydrate ligands for Plasmodium ookinetes. To date, several protein and glycans have been identified as potential transmission-blocking vaccine candidates. We continue to dissect the role of protein-glycan interactions during midgut invasion that, in turn, can lead to the discovery of new adhesion ligands and adhesins on the mosquito midgut and ookinete, respectively. Implicit in this thrust is the development of a pan-malaria transmission-blocking vaccine, a goal of considerable interest to several multilateral malaria vaccine initiatives. In fact, antibodies against one anopheline midgut antigen, a membrane alanyl aminopeptidase (APN) have been tested in standard membrane feeding assays in both Cameroon and Thailand to assess their efficacy in blocking the development of naturally circulating strains of Plasmodium falciparum. and Plasmodium vivax. The results suggest that the concept of a pan-malaria mosquito-based transmission-blocking vaccine may be viable. Feasibility studies that may ultimately lead to process development of this mosquito antigen as a vaccine target are underway.
However, inherent limitations exist with the use of mosquito midgut antigens as transmission-blocking vaccine targets. First and foremost is the lack of natural boosting since the human immune system will not be exposed to mosquito midgut antigens. Given this problem, in collaboration with Dr. Hai-Quan Mao (JHU Biomedical Engineering), we have been applying the use of biodegradeable micro and nanoparticle technology as a platform for temperature-stable (no cold chain necessary), single-immunization (slow antigen release), needle-free vaccine delivery.
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Martinez-Barnetche, J., Gomez-Barreto, R., Ovilla-Munoz, M., Tellez-Sosa, J., Garcia-Lopez, D.E., Dinglasan, R.R., Ubaida Mohien, C., MacCallum, R.M., Redmond, S., Gibbons, J.G., Rokas, A., Machado, C.M., Cazares-Raga, F., Gonzalez-Ceron, L., Hernandez-Martinez, S., Rodriguez-Lopez, M.H. Transcriptome of the adult female malaria mosquito vector Anopheles albimanus. BMC Genomics, 2012. 13, 207.
Mathias, D.K., Plieskatt, J.L., Armistead, J.S., Bethony, J.M., Abdul-Majid, K.B., McMillan, A., Angov, E., Aryee, M.J., Zhan, B., Gillespie, P., Keegan, B., Jariwala, A. R., Rezende, W., Bottazzi, M.E., Scorpio, D.G., Hotez, P.J., Dinglasan, R.R. Expression, immunogenicity, histopathology, and potency of a mosquito-based malaria transmission-blocking recombinant vaccine. Infection and Immunity. 2012, 80, 1606. PMID: 22311924.
Parish, L.A., Colquhoun, D.R., Ubaida-Mohien, C., Lyashkov, A., Graham, D.R., Dinglasan, R.R. Ookinete-Interacting Proteins on the Microvillar Surface are Partitioned into Detergent Resistant Membranes of Anopheles gambiae Midguts. Journal of Proteome Research. 2011. Epub ahead of print. PMID:21905706