Pathogenic leptospires modulate protein expression and post-translational modifications in response to mammalian host signals

Authors: Nally, Jarlath; GRASSMANN, ANDRE - Federal University Of Pelotas; PLANCHON, SEBASTIEN - Luxembourg Institute Of Science & Technology; SERGEANT, KJELL - Luxembourg Institute Of Science & Technology; RENAUT, JENNY - Luxembourg Institute Of Science & Technology; SESKU, JANKIRAM - University Of Texas At San Antonio; MCBRIDE, ALAN - Federal University Of Pelotas; CAIMANO, MELISSA - University Of Connecticut

Submitted to: Frontiers in Cellular and Infection Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2017
Publication Date: 8/9/2017
Citation: Nally, J.E., Grassmann, A.A., Planchon, S., Sergeant, K., Renaut, J., Sesku, J., McBride, A., Caimano, M.J. 2017. Pathogenic leptospires modulate protein expression and post-translational modifications in response to mammalian host signals. Frontiers in Cellular and Infection Microbiology. 7:362. https://doi.org/10.3389/fcimb.2017.00362.
DOI: https://doi.org/10.3389/fcimb.2017.00362

Interpretive Summary: Pathogenic species of Leptospira cause leptospirosis, a global disease that is transmitted from animals to humans. Leptospires survive in the kidney of domestic and wild animal species, from where they are excreted via urine; contact with infected urine, or water contaminated with infected urine, can result in disease since pathogenic leptospires can penetrate breaches of the skin, or mucosal surfaces. Pathogenic leptospires are inherently difficult to grow in the laboratory; they are cultured under conditions that are very different to those encountered during disease transmission. In order to understand how leptospires adapt to the host during infection and cause disease, it is important to try and replicate those environmental conditions that leptospires encounter during infection. In this study, a novel method of culturing leptospires in conditions encountered during host infection is used to identify proteins that leptospires express during infection compared to their growth in the laboratory. Our results demonstrate that leptospires modify their protein content during infection. Further, not only are protein amounts changed, but several proteins have specific modifications that are predicted to influence their function. These results provide novel insights which can help us to understand how leptospires can persist within animals. Finally, the identification of proteins expressed during infection, and their respective modifications, provide novel targets to study as protective vaccines and diagnostic antigens.

Technical Abstract: Pathogenic species of Leptospira cause leptospirosis, a bacterial zoonotic disease with a global distribution affecting over one million people annually. Reservoir hosts of leptospirosis, including rodents, dogs and cattle, exhibit little to no signs of disease but shed large numbers of organisms in their urine. Transmission occurs when mucosal surfaces or abraded skin come into contact with infected urine or urine-contaminated water or soil. Whilst little is known about how Leptospira adapt to persist within a reservoir host, in vitro studies suggest that leptospires alter their transcriptomic and proteomic profiles in response to environmental signals encountered during mammalian infection. We applied the dialysis membrane chamber (DMC) model to compare the whole cell proteome of in vivo derived leptospires with that of leptospires cultivated in vitro at 30oC and 37oC by 2-dimensional difference in gel electrophoresis (2-D DIGE). Of 1735 protein spots aligned across 9 DIGE gels, 202 protein spots were differentially expressed (p<0.05, fold change >1.25 or <-1.25) across all three conditions. Differentially expressed proteins were excised for identification by mass spectrometry. The greatest differences were detected when DMC-cultivated leptospires were compared with IV30- or IV37-cultivated leptospires, including the increased expression of multiple isoforms of Loa22, a known virulence factor. Unexpectedly, 20 protein isoforms of LipL32 and 7 isoforms of LipL41 were uniformly identified by DIGE as differentially expressed, suggesting that unique post-translational modifications are operative in response to mammalian host conditions. To test this hypothesis, a rat model of persistent renal colonization was used to isolate leptospires directly from the urine of experimentally infected rats. Comparison of urinary derived leptospires to IV30 leptospires by 2-D immunoblotting confirmed that modification of proteins with trimethyllysine and acetyllysine occurs to a different degree in response to mammalian host signals encountered during persistent renal colonization. These results provide novel insights into differential protein and post-translational modifications present in response to mammalian host signals which can be used to further define the unique equilibrium that exists between pathogenic leptospires and their reservoir host of infection.