My current interest in extracellular vesicles and their roles in infection build on my background in relevant areas of cell biology, biochemistry, and immunology. My graduate training with Dr. Christopher Nicchitta (Dept. of Cell Biology, Duke University) was focused on protein transport, folding, and trafficking in the secretory pathway. These projects stimulated my interest in immunology, and I applied my expertise in protein biochemistry to study antigen processing and presentation in the laboratory of Dr. Peter Cresswell (HHMI, Dept. of Immunobiology, Yale University). My post-doctoral studies were focused on tapasin, an ER chaperone that facilitates the assembly of MHC class I molecules. I developed in vitro assays to demonstrate the selective, tapasin-mediated loading of high affinity peptides onto MHC class I molecules, determined the crystal structure of tapasin in association with its partner protein ERp57, and identified key residues required for tapasin activity (Nat Immunol, 2007; Immunity, 2009; PNAS, 2011a). Taken together, my work elucidated the molecular mechanisms of tapasin function and MHC class I peptide loading. I also contributed to the discovery of UGT, an ER protein folding sensor, as a novel component of the MHC class I antigen processing pathway (PNAS, 2011a; PNAS,2011b).
In a desire to shift my research focus from fundamental immunology to an infection model, I launched a new research program upon my arrival at CWRU to study the immune response to Mycobacterium tuberculosis (Mtb). I have since developed several exciting, new research projects on the role of extracellular vesicles in the Mtb host-pathogen interaction.
A rapidly expanding area of research is the study of extracellular vesicles (EVs) and their clinical applications. Given the progress in recent years, it is now believed that all cell types secrete EVs for the purpose of intercellular communication. Molecular cargo, including proteins, lipids, and RNA, is specifically sorted into vesicles and trafficked via EVs to a recipient cell, thereby regulating the recipient cell function. Although this paradigm was elucidated in studies of exosomes (a type of EV released by mammalian cells), EV-mediated intercellular communication is a universal process that is conserved across kingdoms. Prokaryotes secrete 50–250 nm membrane vesicles in a manner that is regulated by environmental stress and is thought to promote survival. Since many types of host-derived stress are encountered during infection, this implies an important role for membrane vesicle secretion in bacterial virulence. Accordingly, membrane vesicles produced by gram-positive and gram-negative pathogens contain toxins, virulence factors, and other molecules that promote survival in the host. Most studies to date, however, have employed axenic (i.e., broth) culture models for vesicle purification and analysis. It is generally unknown if membrane vesicles are produced during bacterial infection, and, if so, whether they contribute to pathogenesis.
We predict that membrane vesicle secretion is particularly important for the success of Mycobacterium tuberculosis (Mtb), an intracellular pathogen that establishes latent infection and causes TB (tuberculosis). Mtb infects lung macrophages and creates a niche for survival within modified phagosomes. We recently reported the exciting discovery of bacterial membrane vesicle (BMV) production by Mtb within the phagosomes of infected macrophages and the subsequent release of BMVs from infected cells into the extracellular environment (J Immunol, 2015). These vesicles contained Mtb lipoproteins and lipoglycans which promote immune evasion and survival. Our findings suggest that 1) BMVs transport Mtb virulence factors to host targets within the infected macrophage, and 2) BMVs may also traffic beyond the site of infection to further promote TB pathogenesis. Our current efforts are aimed at A) determining the mechanisms of BMV biogenesis which are currently unknown, and B) developing in vitro and in vivo models to study the functions of BMVs during Mtb infection. These studies may lead to new strategies for TB diagnosis (serum BMVs as biomarkers) and treatment (drugs that inhibit BMV secretion).
- Athman JJ, Wang Y, McDonald D, Boom WH, Harding CV, and Wearsch PA (2015). Bacterial Membrane Vesicles Mediate the Release of Mycobacterium tuberculosis Lipoglycans and Lipoproteins from Infected Macrophages. J Immunol. 2015 Aug 1;195(3):1044-53. doi: 10.4049/jimmunol.1402894. Epub 2015 Jun 24.
- Richardson ET, Shukla S, Wearsch PA, Tsichlis P, Boom WH and Harding CV (2015). Toll-like receptor 2-dependent extracellular signal-regulated kinase signaling in Mycobacterium tuberculosis-infected macrophages drives anti-inflammatory responses and inhibits Th1 polarization of responding T cells. Infect Immun. 2015 Jun;83(6):2242-54. doi: 10.1128/IAI.00135-15. Epub 2015 Mar 16.
- ShuklaS, RichardsonET, AthmanJA, ShiL, WearschPA, McDonaldD, BanaeiN, BoomWH, JacksonM, and HardingCV (2014). Mycobacterium tuberculosis lipoprotein LprG binds lipoarabinomannan and determines its localization in the cell envelope to control phagolysosomal fusion. PLoS Pathogens, 10:e1004471.
- Reba SM, Li Q, Onwuzulike S, Ding X, Karim AF, Hernandez Y, Fulton SA, Harding CV, Lancioni CL, Nagy N, Rodriguez ME, Wearsch PA and Rojas RE (2014). TLR2 engagement on CD4+ T cells enhances effector functions and protective responses to Mycobacterium tuberculosis. Eur J Immunol. 44:1410-1421.
- Blum JP, Wearsch PA and Cresswell P (2013). Pathways of antigen processing. Annu Rev Immunol 31:443–473.
- Wearsch PA and Cresswell P (2013). In vitro reconstitution of the MHC class I peptide loading complex. Methods in Molecular Biology: Antigen Processing 960:67-80.
- Simmons DP*, Wearsch PA* Canaday DH, Meyerson HJ, Liu YC, Wang Y, Boom WH, Harding CV (2012). Type I interferon drives a dendritic cell maturation phenotype that allows continued class II MHC synthesis and antigen processing. J Immunol 188:3116-3126. *Co-first authorship
- Wearsch PA, Peaper DR and Cresswell P (2011) Essential glycan-dependent interactions optimize MHC class I peptide loading. Proc Natl Acad USA, 108:4950-4955.
- Zhang W, Wearsch PA, Zhu Y, Leonhardt RM and Cresswell P (2011) A role for UDP-glucose: glycoprotein glucosyltransferase in the regulation of MHC class I-restricted antigen processing. Proc Natl Acad USA, 108:4956-4961.
- Dong G*, Wearsch PA*, Peaper DR, Cresswell P and Reinisch KR (2009) Insight into MHC class I peptide loading from the structure of the tapasin/ERp57 heterodimer. Immunity 16:21-32. *Co-first authorship
- Wearsch PA, and Cresswell P (2007) Selective loading of high affinity peptides onto major histocompatibility complex class I molecules by the tapasin-ERp57 heterodimer. Nat Immunol 8:873-881.
- Peaper DR, Wearsch PA, and Cresswell P (2005) Tapasin and ERp57 form a stable disulfide-linked dimer within the MHC class I peptide-loading complex. EMBO J 24:3613-3623.
- Wearsch, PA, Jakob CA, Vallin A, Dwek RA, Rudd PM and Cresswell P (2004) Major histocompatibility complex class I molecules expressed with monoglucosylated N-linked glycans bind calreticulin independently of their assembly status. J Biol Chem 279:25112-25121.