Contributed by Guest Blogger: Brittany Sider ’11
MicroRNA (miRNA) molecules, first characterized in the early 1990s, have been implicated in a variety of different biological mechanisms. It took almost a decade for researchers to detect and understand the role of miRNAs in regulation of translation. Since then, research has focused on how we can scientifically manipulate these regulating molecules to our advantage in order to further understand biological underpinnings of certain diseases, as well as potential miRNA-based therapies.
The ability of the influenza virus to undergo frequent and substantial genomic mutations forces us to continually monitor its prevalence, and modify yearly vaccines to target the prevailing viral strains. Recently, live attenuated influenza vaccines (LAIVs, e.g. FluMist) have been proven effective, and have been distributed to a large portion of the eligible population to combat the seasonal flu. These vaccines are manipulated to become much more temperature-sensitive, and therefore are only capable of replicating in temperatures found in the nose. The inability of these attenuated viruses to replicate in the respiratory tract (due to higher temperatures) allows the vaccinated individual to produce antibodies to the influenza strains in the vaccine from the infection in the nasal passage. Therefore, the individual can produce the correct immune response without the virus spreading to the respiratory tract and causing symptoms.
In 2009, a group of researchers from Mount Sinai School of Medicine found that using microRNA response elements (MREs) can supplement the effectiveness of LAIVs. In the study, the MREs for the miR-124 (neural tissue-specific) and miR-93 (a ubiquitous miRNA) were inserted into open reading frames of influenza A nucleoprotein coding regions. The investigators vaccinated mice with miR-93-seeded strains, and then inoculated them with a lethal dose of influenza A/PR/8/34 H1N1 21 days later. This resulted in 100% survival of the subjects, as well as a robust immune response. In an attempt to attribute these results to other influenza strains, the same experiment was done with H5N1 (MREs were inserted into the vaccine specific for H5N1, and methods were repeated). Subjects who had received mock vaccinations 21 days prior to being inoculated with H5N1 displayed rapid weight loss, as well as 100% mortality. On the other hand, mice that had received the MRE-containing H5N1 strain did not display any signs of disease. Furthermore, serum from these subjects exhibited neutralizing activity against the wild-type H5N1, and a wide array of antibody responses (high levels of IgM, IgG1, IgG2a and IgG2b).
The results from this study lead the researchers to believe that MRE-containing LAIVs can be used, and potentially be even more effective than currently available LAIVs in protecting against influenza A outbreaks. In addition, this technology provides the potential to control for the degree of attenuation of the vaccine by manipulating the number of MREs/miRNAs. Lastly, FluMist – although proven to be equally as effective as injected vaccines – has some age exclusions. Perhaps the addition of MREs/miRNAs could expand the target demographic of this method of vaccination.
Contributed by Guest Blogger: M. Aradi ’14
It has been recently discovered that exosomes are used by virally infected cells and cancer cells to manipulate their environment. The Epstein-Barr Virus, or EBV, significantly affects cell growth and leads to types of malignant cancer. The major oncogenic protein of EBV has been found to be LMP1, as it is often expressed with EBV cancers. Viruses use the exosomal pathway to leave cells and evade immune responses. It has been observed that LMP1 contributes to cell growth through the exosomal pathway. Exosomes generally transfer mRNA, micro RNA (miRNA) and proteins to other cells to affect cell proliferation, cell to cell communication and tumor cell invasion. LMP1’s most important target is the cellular EFGR protein, which is a cell growth-signaling receptor. EFGR is secreted from cells in exosomes, and then is taken up by epithelial cells where it functions for cell-growth pathways. It has also been discovered that cells infected with EBV release exosomes that contain LMP1, which inhibits T-cell functions.
The question was: What are the effects of LMP1 on exosomal composition and biochemical properties that support EBV cell infection? The test included two groups of EBV cells; first group contained low levels of LMP1, and the second group had higher expression levels of LMP1. The two group exosomes were tested for uptake potential by other cells, and it was found that the second group exosomes had a higher level of uptake. This shows that LMP1 plays a role in controlling exosomal proteins involved in cell adhesion and interaction. The two groups were exposed to epithelial cells and were observed for how the host cell signaling pathways were affected. It was found that the LMP1 exosomes induced higher levels of cell growth signaling pathways in recipient cells, showing that LMP1 contains protein factors that induce cell growth necessary for tumor growth and metastasis.
Although the study revealed certain key mechanisms of LMP1 function with EBV, further questions involve which specific exosomal proteins are manipulated by LMP1? How do LMP1 and EFGR interact to successfully induce cell growth? Which structure or pathway could possibly be targeted to prevent the spread of EBV and its tumor-inducing factors in efforts to cure cancer?
Contributed by Guest Blogger: C. Romero ’14
Recent research has shown that microRNA miR-275 in the Aedes aegypti mosquito is necessary for blood digestion and egg development. A. aegypti is the most common vector of arboviruses, or ARthropod-BOrne viruses, which include the dengue fever and yellow fever viruses that infect millions and kill thousands each year. Mosquitoes require vertebrate blood to produce eggs, making them good vectors for human diseases. Blood feeding and egg maturation occur in cycles, where blood feeding is required to trigger a step in the process of egg production. In A. aegypti, researchers from University of California, Riverside led by Alexander Raikhel found that miR-275 plays a critical role in this regulatory system.
MicroRNA is a relatively recent discovery, having been first identified in 1993. It appears as if their primary function is post-transcriptional regulation, in which microRNA sequences bind to complementary mRNA. The outcome has come to be known as translational repression or gene silencing, where mRNA is kept from reaching ribosomes and producing proteins, thus interrupting gene expression.
The researchers developed a RNA inhibitor specific to the microRNA molecule, known as an antagomir, to bind to miR-275 before it could silence its corresponding mRNA. By injecting female A. aegypti with this antagomir, blood digestion, fluid excretory function and egg production were all severely inhibited.
This discovery opens new doors to control of the spread of arboviruses, where removal of a single tiny molecule can limit the mosquito’s function at a fundamental level.
Many new questions arise from this research, some of which are already pending investigation by Raikhel’s UC Riverside team. The researchers plan on looking into the particular mRNA that miR-275 targets, and thus find the genes that regulate the blood-meal-mediated egg maturation cycle and see what role they play. Raikhel also plans on looking into the mechanism that underlies the activation of miR-275.
Further off, however, are considerations of how to bring this finding into the real world with a new mosquito control method. New innovations in microRNA research will surely bring us closer to harnessing its power, much as the scientific community has done in DNA genetics.