Dysregulation of Macrophage-Secreted Cathepsin B Contributes to HIV-1-Linked Neuronal Apoptosis

Abstract

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.

HIV-1 Tat Promotes Lysosomal Exocytosis in Astrocytes and Contributes to Astrocyte-mediated Tat Neurotoxicity

“…7B). Cathepsin B has been shown to be a potential neurotoxic factor (47)(48)(49). Consistent with these findings, an increased level of cathepsin B was detected in the supernatants of Tatexpressing astrocytes by Western blotting (Fig.…”

Cathepsin B Is Dispensable for Cellular Processing of Cathepsin B-Cleavable Antibody–Drug Conjugates

“…A noninternalizing ADC, coupled with various protease cleavable linkers, including the VC(S) linker, was also recently shown to still inhibit tumor growth in mouse xenografts (31). Aside from carboxylesterase 1c, extracellular cleavage may be carried out by secreted cathepsins and other degradative proteases in the tumor microenvironment (32)(33)(34). Previous work coupled with the data we report here point to multiple cleavage possibilities that can lead to payload release by protease-specific cleavable linkers.…”

A Proposal for the Evolution of Cathepsin and Silicatein in Sponges

“…Cathepsins can be lysosomal (B, C, F, H, K, L, O, S, W, and Z) and be activated by the acid pH of lysosomes (Turk et al 2001) or non-lysosomal (M, J, Q, R, S, and K). So far, lysosomal cathepsins have been largely studied (Bühling et al 2002) because of their implication in human disease (e.g., Sloane et al 1981;Sloane and Honn 1984;Lutgens et al 2007;Rodriguez-Franco et al 2012), remaining largely uninvestigated in other phyla. In mammals, the function of cathepsin B and L is often related to both extracellular degradation of collagen type I in bone and processing of hormones and antigenic proteins (Inui et al 1997; Mort and Buttle 1997;Söderström 1999;Horn et al 2005).…”