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

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

3D lid driven cavity flow by mixed boundary and finite element method

A numerical algorithm for the solution of the velocity-vorticity formulation of Navier-Stokes equations is presented. This formulation results in splitting of fluid flow into its kinematic and kinetic aspect. The Boundary Element Method (BEM) used for the solution of flow kinematics results in an implicit calculation of vorticity values at the boundary, whereas all transport equations are solved using Finite Element Method (FEM). The combination of both numerical techniques is proposed in order to increase the accuracy of computation of boundary vorticities, a weak point for a majority of numerical methods when dealing with velocity-vorticity formulation. Since the application of BEM results in fully populated system matrices, also the flow kinematics computation is done by combining BEM and FEM, the latter for computation of internal velocities, keeping the CPU time and computer storage requirements at the level close to Finite Element Method. To speed up the computation process and to distribute storage of integrals over several processors the algebraic parallelization of kinematics was performed. Lid driven flow in a cubic cavity was computed to show the robustness and versatility of the proposed numerical formulation. Results for Reynolds number value Re=100 and Re=1000 show good agreement with benchmark results