May 16, 2011
Biting back: Research could lead to mosquitoes being susceptible to diseases they transmit
Mosquitoes are becoming more resistant to current pesticides. That's troubling to Kansas State University biologist Kristin Michel, as it means malaria and other mosquito-borne diseases will continue spreading. A recent grant from the National Institutes of Health may change all that.
Michel, an assistant professor of biology, is using the nearly $1.5 million grant for the four-year study, "The function(s) of serpin-2 in mosquito immunity and physiology." Findings from this investigation into the role of the serpin-2 molecule in Anopheles gambiae -- the African malaria mosquito -- could stop the transmission of malaria and other mosquito-spread diseases by making mosquitoes susceptible to the very diseases they transmit.
As principal investigator, Michel and her laboratory team are focusing on definitively understanding the role of serpin-2 in the mosquito's body. Serpins are a group of similarly structured proteins that can inhibit a group of enzymes that break down proteins called proteases. Serpin-2 controls certain proteases that create immunity against bacteria and fungi in the mosquito.
"Current insecticides used for controlling vector-borne diseases are chemicals that target an insect's nervous system," Michel said. "Because serpin-2 relates to a mosquito's immunity, it could act as a novel insecticide target."
Attacking this molecule could avoid or disrupt a response from the mosquito's immune system that would otherwise protect the insect, she said.
The idea for the research came from a previous project conducted by Michel and fellow K-State researchers. By removing serpin-2 from the mosquitoes' bodies, the researchers noticed melanization is affected. In insects melanin is used to encompass foreign objects that enter their body, like bacteria and parasites. This process prevents the insect's immune system from constantly fighting the foreign body. It also causes pseudo-tumors in the mosquitoes once serpin-2 is removed.
"We don't really quite understand yet why this happens, but we do know that the mosquito's immune response is totally overamplified," Michel said. "Instead of melanizing parasites or bacteria, the mosquito's body attacks itself, getting melanotic pseudo-tumors throughout it."
These pseudo-tumors appear as black dots on the insect's thorax and abdomen. Afflicted mosquitoes that do not initially die from the tumors steadily lose interest in blood feeding over time.
"So what we're going to do with this grant is to find out which proteases -- since it's most likely more than one -- are being inhibited by serpin-2 for this whole process to occur," Michel said. "Right now we have very little information about the cloud of proteases that float around in the insect, with regards to what they do and how they interact."
Finding the proteases will require lots of detective work as more than 50 proteases are potentially being inhibited by serpin-2. However, Michel said, the most time-consuming portion may be collecting enough material from the mosquitoes to sample, as one mosquito yields about 0.1 microliters of bodily material.
Several co-investigators are also lending their expertise to the study. Michael Kanost, university distinguished professor and head of the department of biochemistry, is helping with expression of proteases and in vitro testing. Christopher Culbertson, associate professor of chemistry, is building microfluidics technology that will allow for better plasma analysis from the mosquitoes, potentially helping with the sample sizes. Scott Lovell, director of the protein structure laboratory at the University of Kansas, will use X-ray crystallography to visualize how serpin-2 binds to the proteases it inhibits.
"By the end of the study we really hope to say serpin-2 is a perfect target for an insecticide that prevents the mosquito's immunity," Michel said. "The next step will be then to find such chemicals. That's where we're hoping to take this research."