Pathogenesis and Treatment of Autoimmune Heart Disease
|Figure 1. Inflamed heart heavily infested with T. cruzi amastigote pseudocysts (large nests of tiny round parasites).|
A large number of heart infections and other processes that damage the heart, such as heart attacks and cancer treatments, can cause autoimmune myocarditis in some people. In autoimmune myocarditis, the immune system attacks the heart by mistake. This is true of Chagas heart disease, caused by infection with the parasite Trypanosoma cruzi (T. cruzi), which is found throughout the Americas including the United States.
The Engman Lab is interested in several questions related to the cardiac autoimmunity of Chagas disease: How does autoimmunity develop? Is autoimmunity important? Can we prevent or treat autoimmunity?
Mechanisms of Host Cell Invasion by the Parasite Trypanosoma cruzi
T. cruzi survives in the human host by invading host cells and hiding inside, especially cells in the heart. To enter a host cell, the parasite tricks the host cell cytoskeleton to attract lysosomes, small acidic vesicles that fuse with the newly forming parasite-containing vacuole. As more lysosomes fuse, the vacuole becomes more acidic, eventually activating a pore-forming protein on the T. cruzi surface that permits the parasite to escape into the cytoplasm, where it replicates.
|Figure 2. The image at the left shows three cardiac myoblasts infected with T. cruzi: two are filled with nonflagellated amastigotes (A placed in host cell nucleus) and the cell in the center is filled with elongated, flagellated trypomastigotes (T). The image at the right shows a host cell being invaded by a T. cruzi trypomastigote, which binds to host microtubules and recruits lysosomes to the parasitophorous vacuole, which fuse and acidify the vacuole, activating a surface pore-forming protein that promotes escape of the parasite and differentiation to the dividing amastigote forms shown in the left panel.|
Structure and Function of Calcium-Acyl Switch Proteins
|Figure 3. Calflagin in the flagellar membrane of a single (top) and dividing (bottom) trypanosome, with microtubules throughout the cell and prominently in the basal bodies at the origin of each flagellum.|
Calcium-acyl switch proteins (CASP) regulate other proteins by binding and releasing them in a calcium-dependent manner. The CASP adopts a different conformation depending on whether it is bound to calcium. In one conformation, the fatty acid (acyl) is extended and inserts into a cell membrane. In the other, the fatty acid is sequestered and the protein comes off the membrane. Many CASPs bind to and inhibit membrane proteins and thereby confer calcium regulation on them via the calcium-acyl switch mechanism. Cilia are rich in CASPs. The Engman Lab is interested in the structures, biochemistry and functions of CASPs in ciliary environmental sensing and development. One of the ciliary CASPs we study is called calflagin.
Molecular Determinants of Protein Trafficking to Ciliary Membranes
Cilia are threadlike projections of a cell that are important for all of our senses (vision, hearing, smell, taste, and touch), clearing the respiratory tract of foreign particles, and normal human development. They serve as environmental sensors in single-celled organisms as well as in animals. The ciliary membrane is highly enriched in lipid rafts, microdomains containing high concentrations of sterols and sphingolipids that serve as platforms for the assembly of signaling complexes. Proteins destined for the ciliary membrane often have fatty acid modifications, such as calflagin (see Figure 3), and the interaction of these fatty acids with the ciliary lipid rafts is essential for proper targeting. The Engman Laboratory is interested in molecularly characterizing signaling complexes containing lipid rafts and signaling proteins, particularly those seen in the electron micrograph in Figure 4, of cilia extracted with detergent to reveal these signaling particles associated with the ciliary axoneme (A) (molecular motor) but not on the paraflagellar rod (P) or subpellicular microtubules (T).
|Figure 4. A scanning electron micrograph of flagella extracted with ice-cold Triton X-100, revealing detergent-resistant particles aligned on the flagellar axoneme (A) and axoneme-associated membrane particles (M) but not on paraflagellar rod (P) or subpellicular microtubules (T).|