Mechanisms of viral seeding and inflammation of the CNS: Potential therapeutics and biomarkers for neuroAIDS
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HIV associated neurocognitive disorders (HAND) develop in >50% of HIV infected individuals despite successful antiretroviral therapy (ART). It is mediated, in part, by ongoing neuroinflammation and neuronal damage, facilitated by release of viral proteins from viral reservoirs within the central nervous system (CNS) that are present even in people on ART. HIV is detected within the CNS 4-7 days following peripheral infection, after entry into the brain of infected monocytes that transmigrate across the BBB in response to chemokines, including CCL2 and CXCL12. Monocytes are heterogeneous, characterized by their expression of the LPS receptor, CD14, and the FcyIII receptor, CD16. The majority of monocytes in healthy people are CD14+CD16-, while 5-10% are mature CD14+CD16+ monocytes. Mature CD14+CD16+ monocytes are highly susceptible to HIV infection, and are significantly increased in the periphery of HIV infected individuals, comprising 20-60% of monocytes. These monocytes from infected people are heterogeneous, consisting of cells that are infected with HIV, HIV+CD14+CD16+ monocytes, and cells that have been exposed to virus, viral proteins, and inflammatory factors, but are not infected, HIVexpCD14+CD16 + monocytes. Once HIV+CD14+CD16 +monocytes enter the CNS they release virus that can infect other CNS cell types, and also may differentiate into infected resident macrophages. The junctional proteins JAM-A and ALCAM are essential to BBB transmigration, as well as the chemokine receptors on monocytes, CCR2, the receptor for CCL2, and CXCR4 and CXCR7, receptors for CXCL12. To develop therapeutics that can limit viral (re)seeding of the CNS, we examined the roles of these proteins in entry of HIV+and HIVexpCD14+CD16 + monocytes into the CNS. In addition, to characterize a biomarker to detect individuals with HAND, we examined CCR2 on CD14+CD16 + monocytes in PBMC from infected people and correlated it with neuroinflammation and neuronal damage as detected by magnetic resonance imaging / spectroscopy (MRI / MRS), with peripheral blood HIV DNA, and with neurocognitive testing.;The hypotheses of this work are that 1) chemokine receptors and junctional proteins mediate preferential transmigration of HIV+CD14+CD16+monocytes across the BBB, and are therapeutic targets to limit (re)seeding of CNS viral reservoirs, and 2) CCR2 on CD14+CD16+ monocytes is a biomarker for HAND..;We demonstrated that HIV+CD14+CD16 + monocytes preferentially transmigrate across our human BBB model to CCL2 in comparison to HIVexpCD14+CD16 + monocytes, and that this is mediated, in part, by increased JAM-A and ALCAM on these monocytes. Using anti-JAM-A and anti-ALCAM antibodies, and Cenicriviroc, a CCR2/CCR5 dual inhibitor, we showed that all three blocking agents preferentially blocked the transmigration of HIV+CD14 +CD16+ monocytes, indicating that JAM-A, ALCAM, and CCR2 are essential to their transmigration and may be therapeutic targets for HAND. We showed that CCR2 is increased on CD14+CD16 + monocytes in PBMC from HIV infected people with HAND, and not on those from infected people with impairment due to other causes than HIV (NPI-O), or from those without cognitive impairment. In addition, we demonstrated that increased CCR2 on CD14+CD16+ monocytes correlates with increased HIV DNA from peripheral blood PBMC, and that PBMC HIV DNA is higher in those with HAND. Using MRI / MRS, we determined that increased CCR2 correlates with decreased neuronal activity in the basal ganglia, a brain region affected in HAND. This provides strong evidence that CCR2 may be a biomarker for HAND.;We demonstrated that CD14+CD16+ monocytes from uninfected and HIV infected people express CXCR7, and that it mediates their chemotaxis and transmigration to CXCL12. We showed that CCX771, a CXCR7 antagonist, reduces transmigration across the BBB of these mature monocytes, but not of CD14+CD16- monocytes. This suggests that it may reduce entry of CD14+CD16+ monocytes into the CNS, thereby limiting neuroinflammation, neuronal damage, and subsequent HAND.
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