Translocation of Lysosomal Cathepsin D Caused by Oxidative Stress or Proteasome Inhibition in Primary Cultured Neurons and Astrocytes

Abstract

Proteins produced by eukaryotic cells frequently undergo various post-translational modifications, such as phosphorylation, acetylation, ubiquitination, and glycosylation. The modified proteins perform various functions involved in signal transduction, localization, and degradation signals. Among them, glycosylation is the most common protein modification in mammals.2) In the biosynthesis of N-linked glycoprotein, sugar chains are added to nascent polypeptides and processed by various enzymes in the endoplasmic reticulum and Golgi apparatus, and the complete glycoproteins are transported to their target organelles or secreted extracellularly by means of vesicular traffic. Therefore, with some exceptions, 3) N-linked glycoproteins can not be found in the cytosol [4][5][6] ; however, we have reported the accumulation of N-glycoproteins in the cytosol in both Alzheimer's disease 7) and normal aging of the rat brain. 8) In a normally aging rat brain, accumulated N-glycoproteins were detected by two-dimensional polyacrylamide gel electrophoresis and lectin blot, and one protein was identified as cathepsin D, a lysosomal protease.8) Cathepsin D is a major intracellular aspartic protease. In the rat brain, cathepsin D was detected in both neurons and glial cells. Increased cathepsin D has been reported in aging, 9-11) Alzheimer's disease, 12,13) and dystrophy 14) ; however, the physiological and pathological significance is poorly understood. In addition, the mechanism of cathepsin D accumulation in cytosol in the aging process remains elusive. 8)Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are constantly produced in various cells and tissues. The concentrations of these reactive species are determined by redox balance between the rates of production from endogenous and exogenous origins and the rates of clearance by various antioxidant systems; however, the redox balance gradually degenerates with aging, finally resulting in oxidative stress, 15,16) which is thought to cause the dysfunction of various subcellular components, including lysosomes.This suggests that oxidative stress may induce changes in the intracellular distribution of cathepsin D.The accumulation of cathepsin D in the cytosol may be also induced by the dysfunction of protein degradation systems. Protein degradation systems are categorized into lysosomal and non-lysosomal systems, such as proteasomes. Proteasome protein degradation is known to eliminate misfolded/unassembled (glyco)proteins in the cytosol; therefore, the decline of proteasome activity may lead to the accumulation of cathepsin D in the cytosol.It is important to elucidate the mechanism of cathepsin D accumulation in the cytosol of the rat brain during aging; however, it is difficult to examine the whole brain because it is too complicated. Therefore, we used primary cultured neurons and astrocytes derived from the brain, and examined whether oxidative stress and proteasome inhibition induced the accumulation of cathepsin D in the cytosol and also induced apoptosis...

Functional Analysis of the Cathepsin D Gene Response to SGIV Infection in the Orange-Spotted Grouper, Epinephelus coioides

“…However, studies have shown that in mammals, the mature CD contains a light chain and a heavy chain, which rely on hydrophobic interaction to form a β-sheet structure, while CD from fish and other non-mammalians has single-chain molecules due to the lack of amino acid residues necessary to generate a two-chain form [30,31]. To investigate the function of Ec-CD, we examined the subcellular localization of Ec-CD using a green fluorescent protein, and the results showed that green fluorescence representing Ec-CD was excluded from the nucleus, as is consistent with previous reports [5]. Cathepsins are a concern with the immune response to pathogen invasion [32].…”

“…Viruses 2022, 14, 1680 2 of 16 regulating cell cycle progression [5][6][7]. Moreover, much research has investigated the role of CD in disease.…”

Upregulation of cathepsin D in the caudate nucleus of primates with experimental parkinsonism

“…Therefore, these hyperactive neurons are prone to more oxidative stress [ 4 ]. Intriguingly, oxidative stress is thought to activate lysosomes and release Cat D into the cytosol in non-neuronal cells [ 22 - 26 ]. Although oxidative stress has been described as a main trigger for the loss of DA neurons in SN pars compacta region in PD [ 27 ], its link to PD-related changes in other parts of the brain are less well studied.…”

Activation of Asparaginyl Endopeptidase Leads to Tau Hyperphosphorylation in Alzheimer Disease

“…Acidic conditions in AD brains increase the lysosomal protease activity and lysosomal membrane permeability (51,55). Lysosomal enzyme activity in the cytosol has been previously described, such as cytosolic cathepsins in both pathological (56,57) and physiological (44) apoptotic mechanisms. AEP is predominantly localized in lysosomes but is overexpressed in many types of tumors and associated with enhanced tissue invasion and metastasis.…”