The Athar Chishti Lab
Pathophysiology of Malaria and Sickle Cell Disease
Our primary research interest is to understand the assembly and regulation of the mammalian cytoskeleton. We study the function of cytoskeletal and signaling proteins in diseases that afflict blood cells, including malaria and sickle cell disease.
Host Parasite Interactions
We are investigating the mechanisms of malaria pathogenesis in red blood cells (RBCs) / erythrocytes, with the goal of developing novel diagnostics, therapeutics, and vaccine targets. Because of emerging drug resistance and the lack of an effective vaccine, there is an urgent need to identify new drugs and vaccine targets against malaria. The identification of the malaria parasite proteins (ligand) and their cognate host proteins (receptor) is essential for the development of an effective multi-subunit vaccine. Using a multidisciplinary approach, we identified an essential role of RBC membrane complex containing Band 3 (anion exchanger-1) and Glycophorin A (GPA) during the parasite invasion of RBCs (Fig.1A). Currently, we are employing the phage-display cDNA libraries to identify additional components of the parasite protein complex for new drug/vaccine targets against malaria.
Figure 1. (A) RBC invasion by the malaria parasite Plasmodium falciparum. (B) Visualization of spiral knobs in malaria parasite-infected human RBCs.
A distinctive feature of Plasmodium falciparum, the most lethal human malaria parasite, is the adhesion of infected RBCs (iRBCs) to organs such as the brain and placenta. Sequestration occurs in major organs, including the brain, where human cerebral malaria begins with excessive adhesion of iRBCs to host endothelial cells lining the blood vessels thus resulting in decreased microcirculatory flow and reduced oxygen supply. The attachment of iRBCs to blood vessels is mediated by surface bumps known as “knobs” on the surface of iRBCs. Using electron microscopy, we have isolated these knobs and provided the first evidence of the existence of a unique spiral shaped morphology (Fig.1B) mediated by the parasite derived histidine-rich protein termed KAHRP. Currently, we are developing novel peptides that can disrupt the KAHRP interactions as potential therapeutics against cerebral malaria.
Calpain-1 and Sickle Cell Disease
Our lab has a long-standing interest in the biology of Calpain-1, a calcium-dependent cysteine protease that regulates multiple signaling and cytoskeletal functions in platelets, erythrocytes, neurons, and many other cells. We generated the first mouse model of calpain-1 deficiency, and identified several calpain substrates including Dematin, PTP1B, and Talin. Using genetically altered mouse models, we investigated their role in platelet secretion, adhesion, motility, and apoptosis pathways. Currently, we are evaluating the function of calpain-1 and its substrates in lipid reorganization, glucose homeostasis, and malaria infection. These studies led to the development of calpain-1 null humanized mouse model of sickle cell disease (Townes Model). This unique mouse model is currently under investigation for the development of new therapeutic strategies to attenuate pain, thrombosis, and adhesion phenotypes in sickle cell disease.
Scaffolding Proteins and Kinesins
Cell polarity is a fundamental process and its loss leads to developmental abnormalities. Our lab is investigating the role of membrane-associated guanylate kinase homologues (MAGUKs) in signaling pathways regulated by kinesin motors. MAGUKs are scaffolding proteins composed of PDZ, SH3, and GUK domains (Fig. 2) that are essential for the maintenance of cell polarity. Our lab provided the first evidence of MAGUKs-Cytoskeleton interactions via the FERM domain of Protein 4.1. While investigating MAGUKs, we discovered a new mechanism for the intracellular transport of PIP3, a product of phosphatidylinositol 3-kinase, mediated by a kinesin-3 family motor protein termed GAKIN or KIF13B. Using p55/MPP1, GAKIN/KIF13B, and KIF13A deficient mouse models, developed in our laboratory, we are currently investigating the mechanism of intracellular protein and lipid transport in disorders of development and inflammation.
Figure 2. Domain organization of selected MAGUKs