Chronic HIV infection leads to the development of cognitive impairments, designated as HIV-associated neurocognitive disorders (HAND). The secretion of soluble neurotoxic factors by HIV-infected macrophages plays a central role in the neuronal dysfunction and cell death associated with HAND. One potentially neurotoxic protein secreted by HIV-1 infected macrophages is cathepsin B. To explore the potential role of cathepsin B in neuronal cell death after HIV infection, we cultured HIV-1ADA infected human monocyte-derived macrophages (MDM) and assayed them for expression and activity of cathepsin B and its inhibitors, cystatins B and C. The neurotoxic activity of the secreted cathepsin B was determined by incubating cells from the neuronal cell line SK-N-SH with MDM conditioned media (MCM) from HIV-1 infected cultures. We found that HIV-1 infected MDM secreted significantly higher levels of cathepsin B than did uninfected cells. Moreover, the activity of secreted cathepsin B was significantly increased in HIV-infected MDM at the peak of viral production. Incubation of neuronal cells with supernatants from HIV-infected MDM resulted in a significant increase in the numbers of apoptotic neurons, and this increase was reversed by the addition of either the cathepsin B inhibitor CA-074 or a monoclonal antibody to cathepsin B. In situ proximity ligation assays indicated that the increased neurotoxic activity of the cathepsin B secreted by HIV-infected MDM resulted from decreased interactions between the enzyme and its inhibitors, cystatins B and C. Furthermore, preliminary in vivo studies of human post-mortem brain tissue suggested an upregulation of cathepsin B immunoreactivity in the hippocampus and basal ganglia in individuals with HAND. Our results demonstrate that HIV-1 infection upregulates cathepsin B in macrophages, increases cathepsin B activity, and reduces cystatin-cathepsin interactions, contributing to neuronal apoptosis. These findings provide new evidence for the role of cathepsin B in neuronal cell death induced by HIV-infected macrophages.

Cognitive impairment remains a major complication of advanced human immunodeficiency virus (HIV) infection despite the widespread use of anti-retroviral therapy. Diagnosis is made by exclusion making biomarkers of great potential use. Thus, we used an integrated proteomics platform to assess cerebrospinal fluid protein profiles from 50 HIV-1 seropositive Hispanic women. Nine of 38 proteins identified were unique in those patients with cognitive impairment (CI). These proteins were linked to cell signaling, structural function, and antioxidant activities. This work highlights, in a preliminary manner, the utility of proteomic profiling for biomarker discovery for HIV-1 associated cognitive dysfunction.

Objective HIV-1-associated neurocognitive disorders (HAND) is triggered by immune activation of brain cells and remain prevalent during progressive viral infection despite antiretroviral therapy. Cathepsins and cystatins are lysosomal proteins secreted by macrophages and microglia, and may play important roles in neuroregulatory responses. Our laboratory has shown increased secretion and neurotoxicity of cathepsin B from in-vitro HIV-infected monocyte-derived macrophages, and increased expression in postmortem brain tissue with HIV encephalitis and HAND. We hypothesized that cystatin B and cathepsin B could represent potential biomarkers for HAND. Methods Monocytes, plasma, and cerebrospinal fluid (CSF) from retrospective samples from 63 HIV-seropositive Hispanic women were selected for this study. These were stratified as 27 normal, 14 asymptomatic, and 22 HIV dementia, and as 14 progressors and 17 nonprogressors. Samples were evaluated for cystatins B and C and cathepsin B expression and activity. Results Increased cathepsin B and cystatins B and C were found in plasma of HIV-seropositive women. Higher intracellular expression of cathepsin B and cystatin B were found in monocytes from women with HIV-associated dementia (P <0.05). Significant increase in cystatin B concentration in CSF was found in women with dementia compared with HIV-seropositive asymptomatic women. Conclusion These results demonstrate that dysregulation of cystatin B–cathepsin B system is operative in HIV-associated neurocognitive impairment and suggests that intracellular expression of cystatin B and cathepsin B in monocytes could be potential candidate biomarkers for HIV dementia, whereas increased cathepsin B and cystatins B and C in plasma are potential candidate markers of chronic HIV-1 activation.

Monocyte ingress into the brain during progressive human immunodeficiency virus (HIV-1) infection parallels the severity of cognitive impairments. Although activated monocyte phenotypes emerge during disease, the functional correlates of these cells remain unresolved. To this end, we studied the proteome of blood-derived monocytes obtained from Hispanic women with the most severe form of HIV-associated neurocognitive disorder, HIV-associated dementia (HAD). Monocytes isolated from peripheral blood mononuclear cells by CD14+ immunoaffinity column chromatography were >95% pure. Cells were recovered from five patients without evidence of cognitive impairment and four with HAD and analyzed by two-dimensional difference gel electrophoresis and tandem mass spectrometry. Importantly, ADP ribosylhydrolase, myeloperoxidase, thioredoxin, peroxiredoxin 3, NADPH, and GTPase activating protein were all downregulated in HAD. In regards to myeloperoxidase, thioredoxin, and peroxiredoxin 3 these changes were validated in an additional cohort of 30 patients by flow cytometry. We conclude that deficits in monocyte antioxidant proteins lead to neuronal damage through the loss of hydrogen peroxide scavenging capabilities, thus exposing neurons to apoptosis-inducing factors. Altered monocyte functions therefore may contribute to the development and progression of HAD.

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