HIV‐1 Infection of Trophoblasts Is Independent of gp120/CD4 Interactions but Relies on Heparan Sulfate Proteoglycans
Research Center in Infectious Diseases, Centre Hospitalier de l'Université Laval Research Center, and Faculty of Medicine, Laval University, Quebec, Canada
Mother‐to‐child transmission of human immunodeficiency virus type 1 (HIV‐1) is the leading cause of HIV infection in infants. Direct infection of trophoblasts—cells forming the placental barrier—may cause this transmission. Entry of HIV‐1 into trophoblasts is unusual for this retrovirus, because it is associated with endocytosis. However, given that trophoblasts express no or few receptors/coreceptors required for virus internalization, the mechanism underlying this event remains ambiguous. In the present study, we show that HIV‐1 entry and infection of polarized trophoblasts are independent not only of CD4 but also of envelope (Env) glycoproteins gp120 and gp41. Virus internalization, cytoplasmic release, reverse transcription, integration, and HIV‐1 gene expression occurred with both fusion‐incompetent and Env‐deficient viruses. Importantly, fusion‐independent infection was observed when we used viruses produced in a natural cellular reservoir (i.e., primary human cells). Finally, HIV‐1 requires heparan sulfate proteoglycans for uptake in trophoblasts. Together, our findings illustrate that HIV‐1 utilizes an unusual pathway for entering human polarized trophoblasts.
Received 12 July 2006; accepted 10 December 2006; electronically published 3 April 2007.
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Potential conflicts of interest: none reported.
Financial support: Canadian Institutes of Health Research (CIHR) HIV/AIDS Initiative (grant HOP‐67259 to M.J.T.); HIV/AIDS Research Program (CIHR Doctoral Research Award to G.V. and S.G.). M.J.T. holds the Canada Research Chair in Human Immuno‐Retrovirology (tier 1 level).
This work was performed by G.V. in partial fulfillment of her Ph.D. degree, Program of Microbiology‐Immunology, Faculty of Medicine, Laval University, Quebec, Canada.