Human Immunodeficiency Virus-1 (HIV-1) swiftly infects the central nervous system (CNS) after infection through the migration of infected monocytes and macrophages into the brain (1). After the blood-brain barrier is breached, the virus infects resident microglia, which serve as a CNS reservoir (2). Viral replication and the subsequent immune response eventually leads to cognitive disorders, including dementia, memory defects and altered neuronal signaling (3) (4). The HIV-1 Tat protein is one of the main neurotoxins still produced in the CNS despite the use of combination antiretroviral therapy (cART) (5) (6). Indeed, Tat has been found to induce proinflammatory cytokine responses and neuronal apoptosis (7). Our laboratory utilizes a cortical injection of Tat into the murine CNS to mimic in part pathologic changes associated with HIV-1 associated neurocognitive disorders (HANDs), including sustained neuroinflammation and neurodegeneration within the CNS. Using this model, we have found microgliosis and engulfment of dendritic spines by resident microglia (8). Moreover, we have identified leucine rich repeat kinase 2 (LRRK2) as a novel kinase involved in microglial proinflammatory responses and phagocytosis in response to HIV-1 Tat. LRRK2 is an emerging target in neuroinflammation, as recent studies have linked LRRK2 kinase mutations to Parkinson's disease (9) (10) and microglial proinflammatory cytokine expression (11) (12). Therefore, I hypothesize that HIV-1 Tat increases microglial activation in a LRRK2 dependent manner, and that blocking LRRK2 activity will suppress microgliosis-dependent neurotoxicity during HANDs. In order to test this hypothesis, I will employ a broad analysis of microglial activation both in vitro and in vivo after LRRK2 inhibition using cutting-edge techniques, including in vitro microfluidic chambers and in vivo thin-skull two-photon microscopy. Using a genetic and pharmacologic approach, I will determine how LRRK2 kinase activity alters microglial inflammatory responses and will investigate the ability of a novel small molecule with previously validated high affinity for LRRK2 in cell-free assays, URMC-099, to inhibit microglial LRRK-2 kinase activity. These studies will not only advance our knowledge of how LRRK2 mediates microglial activation, but may help authenticate URMC-099 as an effective treatment for HANDs, as well other neurodegenerative conditions.
HIV-1 associated neurocognitive disorders (HANDs) are a serious and growing problem as the HIV infected population ages. This research will address the pathogenic activation of the Parkinson's disease associated signaling protein leucine-rich repeat kinase 2 (LRRK2) in HANDs. Inhibition of LRRK2 kinase activity may prove to be a novel therapeutic target for HANDs, thus having the potential to improve the lives of HIV positive individuals living with this devastating disease.
|Marker, Daniel F; Tremblay, Marie-Eve; Puccini, Jenna M et al. (2013) The new small-molecule mixed-lineage kinase 3 inhibitor URMC-099 is neuroprotective and anti-inflammatory in models of human immunodeficiency virus-associated neurocognitive disorders. J Neurosci 33:9998-10010|