Characterization and quantification of endogenous amyloid fibrils in human semen
Virology
Final Report Abstract
Heterosexual transmission accounts for the majority of new HIV-1 infections. Despite recent advances in antiretroviral therapy regimens which effectively control the existing infections there is little progress in combating the spread of new infections. This challenge is mostly due to the lack of our understanding of the interactions between the virus and the complex host milieu in which infection takes place. In heterosexual transmissions semen plays an important role in the dissemination of the virus. When HIV-1 harboring semen is deposited onto the female genital tract, HIV-1 infects new target cells which are present in the genital mucosal tissue. There is an emerging understanding that semen which is one of the most complex of biological fluids is not a mere vehicle for HIV-1 dissemination but likely affects and influences the viral transmission. Increasing evidence suggests that semen contains peptides that affect the outcome of viral infections. SEVI or semen derived virus enhancer is one prominent example of such peptides. SEVI was discovered in a screen to identify factors present in semen derived peptide libraries. SEVI in amyloid form binds to virions via electrostatic and steric mechanisms and facilitates the fusion of viruses with target cells. So far, effect of SEVI on HIV-1 infection had been thoroughly characterized in cell culture based models. However, whether SEVI and other amyloid enhancer(s) are present in semen and if they play any potential role in HIV-1 infection/transmission is not known. In this project we set out to study human semen samples for the presence of amyloid fibrils using multiple state of art approaches. We showed that a large number of semen samples stain positive for amyloid specific diagnostic dyes. In select semen samples we could confirm the presence of amyloid fibrils by high resolution electron microscopy approaches and atomic force microscopy. In addition using antibodies specific for SEVI and semenogelin amyloids we showed that at least these peptides are present in amyloid form in the semen. We also found that dye stained amyloid structures readily interact with virus particles and enrich them locally. In conclusion, in this project we showed for the first time that semen is a unique biological fluid that contains amyloid fibrils which are capable of interacting with HIV-1. Future efforts should be directed to understand the role these amyloid fibrils have in sexual transmission in vivo using animal models and pursuing approaches that target amyloid-virus interactions for therapeutic interventions.
