Thesis Defense Announcement
To:  The George Mason University Community

Candidate: Akanksha Kaushal

Program: M.S. in Biology

Date:   Thursday April 14, 2016

Time:   11:00 am

Place:  George Mason University
             Science & Technology Campus<>

             Bull Run Hall, Room 130

Title: "The Role of Antimicrobial Peptides in Innate Immunity of Insects and Their Proposed Mode of Action"
Thesis Director: Dr. Monique van Hoek
Thesis Committee:  Dr. Kylene Kehn-Hall, Dr. Barney Bishop
A copy of the thesis will be available in the Gateway Library.  All are invited to attend the defense.

Antimicrobial peptides (AMPs) are components of both vertebrate and invertebrate innate immune systems that are expressed in response to exposure to bacterial antigens. Naturally occurring AMPs from many different species have been extensively studied and are being further studied and developed as potential therapeutics against antibiotic resistant microorganisms. In this thesis, a putative defensin from the bedbug Cimex lectularius (CL) is characterized for its antimicrobial activity against human skin flora including Gram-negative and Gram-positive bacteria. The bedbug defensin (CL-defensin), belonging to the family of insect defensins, is predicted to have a characteristic N-terminal loop, an -helix, and an antiparallel -sheet, which was supported by circular dichroism spectroscopy. CL-defensin was shown to be antimicrobial against Gram-positive bacteria commonly found on human skin however, it was ineffective against common skin Gram-negative bacteria. Our studies indicate that CL-defensin functions by depolarization of and pore-formation in the bacterial cytoplasmic membrane.

In addition, this thesis also focuses on characterizing antimicrobial activity of mosquito Aedes albopitctus' antimicrobial peptides against Francisella. Francisella tularensis is the cause of the zoonotic disease tularemia. In Sweden and Scandinavia, epidemiological studies have implicated mosquitoes as a vector. Prior laboratory research has demonstrated the presence of Francisella DNA in infected mosquitoes but has not definitively shown transmission of tularemia from a mosquito to a mammalian host. We hypothesize that antimicrobial peptides may play a role in mosquito host-defense to Francisella. We established that two Francisella species are susceptible to two mosquito-derived cecropins, a family of cationic, alpha-helical antimicrobial peptides, and less susceptible to a mosquito Defensin peptide. We also demonstrated induced gene expression of these peptides in Francisella infected C6/36 mosquito cell line.

Therefore, these studies successfully characterized antimicrobial activity of AMPs from two different insect species. These peptides could provide the basis for further studies and development into potential therapeutics against various bacteria.