Changes Induced in Astrocyte Cathepsin D by Cytokines and Leupeptin

Abstract

Cathepsin D is widely, but unevenly, distributed among cells and is capable of degrading a number of neural peptides and proteins. The present study was undertaken to examine the level of cathepsin D in astrocytes that might be relevant to its induction in inflammatory demyelination. Primary astrocytes were cultured from neonatal rat cerebrums according to the method of McCarthy and de Vellis. Based on staining for cell markers, cultures were greater than 95% astrocytes and less than 3% microglia. Under serum-free conditions, leupeptin induced a 1.4- to 2.0-fold increase, maximal by 48 hours, in cathepsin D protein quantified by a radioimmunoassay. Cathepsin D enzymatic activity, inhibitable by pepstatin, also increased. Northern blot analysis demonstrated that leupeptin also increased cathepsin D mRNA expression. Kinetic analysis indicated that maximal cathepsin D mRNA levels are detected 24 h after stimulation with leupeptin. Exposure of astrocytes under the same conditions to rat recombinant interferon-gamma, human recombinant tumor necrosis factor-alpha, human recombinant interleukin-1 beta, lipopolysaccharide, calcium ionophore, or a combination of these reagents did not increase the level of cathepsin D above controls. These results indicate that astrocytic cathepsin D mRNA and protein can be induced by selected materials. Furthermore, the effects attributed to leupeptin as a proteinase inhibitor may be modified by its ability to increase cathepsin D activity.

Lysosomal cathepsin D is upregulated in Alzheimer's disease neocortex and may be a marker for neurofibrillary degeneration

“…Besides direct action on abnormally aggregated peptides, catD or its zymogen (pro‐catD) may regulate other cellular responses implicated in AD pathogenesis and progression, including cytokine secretion and initiation of apoptosis . Conversely, pro‐inflammatory cytokines like tumor necrosis factor and interferon‐γ, known to be activated in AD by misfolded and aggregated peptides , may upregulate pro‐catD and increase catD activities . Therefore, follow‐up studies are needed to better characterize the intertwining relationships between protein misfolding, neuroinflammatory responses and catD upregulation in AD.…”

Role of Ca2+ and calmodulin‐dependent enzymes in the regulation of glycine transport in Müller glia

“…1990), glia contains several Ca 2+ ‐activated proteases, capable of irreversibly altering glial cytoskeleton (Legrand et al . 1991; Whitaker et al . 1991).…”

Glial calcium

“…For example, Ca2+ influx causes nonspecific Ca2+-activated proteolysis in rat optic nerve, spinal cord and peripheral nerve glial cells (Schlaepfer and Zimmerman, 1981). In fact, glia contain several Ca2+activated proteases including the lysosomal protease cathepsin D (Whitaker et al, 1991), the actin-severing and capping protein, gelsolin (Legrand et al, 1991), and several Ca2 ' -activated neutral proteases (CANP) (Banik et al, 1991;Perlmutter et al, 1988Perlmutter et al, ,1990. Myelin basic protein, proteolipid protein and neurofilament protein serve as specific substrates for CANP (Banik et al, 1985).…”