The role of shed PrP^c in the neuropathogenesis of HIV infection

HIV-1 enters the CNS soon after peripheral infection and causes chronic neuroinflammation and neuronal damage that leads to cognitive impairment in 40-70% of HIV-infected people. The nonpathogenic cellular isoform of the human prion protein (PrP^c) is an adhesion molecule constitutively expressed in the CNS. Previously, our laboratory showed that shed PrP^c (sPrP^c) is increased in the cerebrospinal fluid of HIV-infected people with cognitive deficits as compared with infected people with no impairment. In this article, we demonstrate that CCL2 and TNF-α, inflammatory mediators that are elevated in the CNS of HIV-infected people, increase shedding of PrP^c from human astrocytes by increasing the active form of the metalloprotease ADAM10.We show that the consequence of this shedding can be the production of inflammatory mediators, because treatment of astrocytes with rPrP^c increased secretion of CCL2, CXCL-12, and IL-8. Supernatants from rPrP^c-treated astrocytes containing factors produced in response to this treatment, but not rPrP^c by itself, cause increased chemotaxis of both uninfected and HIV-infected human monocytes, suggesting a role for sPrP^c in monocyte recruitment into the brain. Furthermore, we examined whether PrP^c participates in glutamate uptake and found that rPrP^c decreased uptake of this metabolite in astrocytes, which could lead to neurotoxicity and neuronal loss. Collectively, our data characterize mediators involved in PrP^c shedding and the effect of this sPrP^c on monocyte chemotaxis and glutamate uptake from astrocytes. We propose that shedding of PrP^c could be a potential target for therapeutics to limit the cognitive impairment characteristic of neuroAIDS.