Regulation of Heme Oxygenase in HIV/HAND Pathogenesis

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Kolson, Dennis L. Project Summary HIV associated neurocognitive disorders (HAND) persist (~30% prevalence) worldwide in antiretroviral therapy (ART)-treated individuals despite a profound reduction in severe HAND (HIV-associated dementia/HAD). Biomarkers of oxidative stress in both systemic and CNS body compartments are strongly correlated with HAND, even in ART-treated individuals. Recently, we analyzed autopsied brains (>150 NNTC donors) and found a deficiency of a critical enzyme modulator of oxidative stress, heme oxygenase-1 (HO-1,) in those with HAND. This effect was independent of ART use and it correlated with brain macrophage activation and type I interferon responses. We further defined a link between brain HO-1 deficiency and HIV neuropathogenesis by showing that: i) HIV infection of monocyte-derived macrophages (MDM) consistently and selectively reduces HO-1 expression and increases neurotoxin (glutamate) release; ii) ART treatment of established HIV infection in MDM (HIV/MDM) does not prevent neurotoxin release, while iii) restoration of HO-1 expression in HIV/MDM does prevent neurotoxin release independent of ART and HIV replication. Our new preliminary studies also implicate dysregulation of brain HO-1 expression through a common HO-1 gene promoter sequence variation (GTn dinucleotide repeat length) and through regional variation in brain HO-1 expression in HAND pathogenesis. This HO-1 GTn dinucleotide repeat variation has previously been correlated with plasma markers of HIV disease progression (sCD14, HIV load) and our brain analyses demonstrate a strong correlation between HO-1 promoter GTn repeat length and the presence of HIV encephalitis. Additionally, our preliminary studies of autopsied rhesus macaque brains (n=18) demonstrated consistent regional (9 regions) brain differences in HO-1 expression levels, with lowest levels in deep brain structures where, in humans, HIV effects are particularly profound. Thus, our studies identify HIV-driven brain HO-1 deficiency as a major contributor to HAND pathogenesis, and they suggest that HO-1 promoter GTn repeat variation and brain regional HO-1 variation could be risk factors for HAND despite the use of ART. We hypothesize that HIV- induced brain HO-1 loss is a risk for HAND and that HO-1 promoter GTn repeat variation influences not only systemic HIV disease progression but also CNS disease progression and HAND. We further hypothesize that regional brain HO-1 levels contribute to selective regional vulnerability to HIV injury. We will: 1) Determine the correlation between HO-1 promoter GTn repeat variation and neurocognition in HIV+ subjects (CHARTER patient cohort); 2) Identify HO-1 variation associations with compartmental pathology and HIV disease markers (brain, spleen/NNTC autopsy cohort); and 3) Define the neuropathological in vitro responses of macrophages, astrocytes, endothelial cells relevant for blood-brain barrier function to HO-1 modulation and effects of the HO- 1 promoter GTn repeat variation on these responses. These studies can provide critical information for assessing cellular and clinical responses to HO-1-targeted therapies.