Abstract
HIV-associated neurocognitive disorders prevail in 20–50 percent of infected individuals. Macrophages transmigrate through the blood brain barrier during HIV-1 infection, triggering neuronal dysfunction. HIV-infected macrophages secrete cathepsin B (CATB), and serum amyloid p component (SAPC), inducing neuronal apoptosis by an unknown mechanism. We hypothesized that HIV infection facilitates CATB/SAPC secretion from macrophages followed by neuronal internalization, promoting dysfunction. SK-N-SH neuronal cells were exposed to active recombinant histidine-tagged cathepsin B (His-CATB). His-CATB entry was tracked by intracellular flow cytometry, and neuronal dysfunction was verified by western blot. Macrophage-derived extracellular vesicles (EVs) were tested for the presence of CATB and SAPC. Neurons internalized His-CATB, an effect that was partially decreased by pre-treatment with anti-CATB antibody. Pre-treatment with CATB and SAPC antibodies decreased cleavage of caspase-3 and restored synaptophysin in neurons. Neurons exposed to macrophage-conditioned media differentially internalized His-CATB, dependent on the HIV replication levels. Finally, CATB and SAPC were secreted in EVs. We report for the first time that CATB is secreted from macrophages both free and in EVs, and is internalized by neurons. Moreover, HIV-replication levels modulate the amount of CATB neuronal uptake, and neuronal dysfunction can be decreased with CATB antibodies. In conclusion, the CATB/SAPC complex represents a novel target against HIV-associated neurocognitive disorders.
Highlights
Cathepsin B (CATB), a lysosomal cysteine protease, is secreted by HIV-infected monocyte-derived macrophages (MDM)[6] and interacts with serum amyloid p component (SAPC) at the extracellular level[7]
We observed that cathepsin B (CATB) and SAPC are secreted from MDM in extracellular vesicles (EVs) labeled with exosome markers, which could represent an alternate mechanism of internalization and neurotoxicity
Pre-treatment of media with anti-CATB antibody decreased the percentage of PE-positive neurons to 34.9%, while CA074 inhibitor had no effect in internalization (60.1%) (Fig. 1B)
Summary
Cathepsin B (CATB), a lysosomal cysteine protease, is secreted by HIV-infected monocyte-derived macrophages (MDM)[6] and interacts with serum amyloid p component (SAPC) at the extracellular level[7]. Both proteins induce apoptosis of SK-N-SH neuroblastoma cells that is reduced when the MDM supernatants or macrophage-conditioned media (MCM) is pre-treated with anti-CATB or anti-SAPC antibodies[7]. These two proteins are increased in post-mortem brain samples from deep frontal white matter of patients diagnosed with HIV-associated neurocognitive disorders (HAND) compared to tissues from patients with normal cognition. We observed that CATB and SAPC are secreted from MDM in EVs labeled with exosome markers, which could represent an alternate mechanism of internalization and neurotoxicity
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