Lysosomal Dysfunction Caused by Cellular Accumulation of Silica Nanoparticles

Abstract

Nanoparticles (NPs) are widely used as components of drugs or cosmetics and hold great promise for biomedicine, yet their effects on cell physiology remain poorly understood. Here we demonstrate that clathrin-independent dynamin 2-mediated caveolar uptake of surface-functionalized silica nanoparticles (SiNPs) impairs cell viability due to lysosomal dysfunction. We show that internalized SiNPs accumulate in lysosomes resulting in inhibition of autophagy-mediated protein turnover and impaired degradation of internalized epidermal growth factor, whereas endosomal recycling proceeds unperturbed. This phenotype is caused by perturbed delivery of cargo via autophagosomes and late endosomes to SiNP-filled cathepsin B/L-containing lysosomes rather than elevated lysosomal pH or altered mTOR activity. Given the importance of autophagy and lysosomal protein degradation for cellular proteostasis and clearance of aggregated proteins, these results raise the question of beneficial use of NPs in biomedicine and beyond. Nanoparticles (NPs)2 are widely used as components of drugs or cosmetics and hold great promise as tools in biomedicine to improve the detection and treatment of diseases (1). For example, nanoparticle technology has enabled improvements in cancer treatment, ranging from improved efficacy of drug delivery (2) to enhanced immunogenicity of cancer vaccines (3). Moreover, NPs are used as biosensors and biomarkers (4, 5) or for DNA/drug delivery (6). Hence, it is necessary to understand the mechanisms of interaction of NPs with living cells and tissues to assess the biological consequences associated with their application in biomedicine (7). At present, the risks associated with the biomedical application of NPs at the cellular and organismic levels remain incompletely understood (1). Among the phenotypic changes reported to be associated with the biomedical application of NPs are cellular stress responses (i.e. redox imbalance, oxidative stress), DNA damage, and altered gene expression (8,9). Which of these phenotypes can be considered a direct consequence of cellular NP association or uptake and the underlying molecular mechanisms have remained in many cases unknown.Upon cellular application, NPs initially interact with the plasma membrane, often followed by their internalization into the cell interior (10 -12) via clathrin-dependent as well as clathrin-independent endocytosis routes (i.e. via caveolae), which may require the membrane-severing GTPase dynamin (13,14). Due to the questionable specificity of many commonly used pharmacological tools toward these pathways (15) the precise mechanisms of cellular uptake of NPs often have remained elusive. After cell entry NPs are delivered to the endolysosomal system (16), where they may accumulate. Lysosomes play essential roles in cell physiology ranging from the degradation of malfunctional or aggregated proteins (e.g. via autophagy) or lipids to nutrient signaling and cellular growth control (17). For example, internalized growth factors such as EGF are sorted to la...

Silica nanoparticles induce autophagosome accumulation via activation of the EIF2AK3 and ATF6 UPR pathways in hepatocytes

“…SiNPs have been shown to induce autophagy in various cell lines, such as HCT-116 human colon cancer cells, HepG2 human hepatoma cells, HUVECs, and RAW 264.7 murine macrophage cells [3,[19][20][21]. Moreover, our group and others have also reported that SiNPs induce autophagy dysfunction via lysosomal impairment and inhibition of autophagosome degradation [5,22]. Based on the aforementioned clues, we speculated that SiNPinduced autophagy dysfunction occurs via 2 mechanisms: first, through autophagy induction and enhanced autophagosome synthesis, and second, by autophagic degradation blockage.…”

Amorphous silica nanoparticles trigger vascular endothelial cell injury through apoptosis and autophagy via reactive oxygen species-mediated MAPK/Bcl-2 and PI3K/Akt/mTOR signaling

“…Lysosome is one of the major intracellular storage sites for SiNPs that enter into cells. 58 SiNPs accumulation in lysosomes has been suggested as a mechanism of cytotoxicity in lung epithelial cells, and its overload leading to delayed clearance and particle persistence can negatively impact lysosome function. 59 It has been reported that internalized SiNPs could cause destabilization of lysosomes and permeabilization of lysosome membranes, 60 resulting in ROS generation, cytosolic acidification, and eventually cellular death.…”

Macrophages participate in local and systemic inflammation induced by amorphous silica nanoparticles through intratracheal instillation

“…Lysosomes play an important role in cell physiology, including in the degradation of exogenous elements or of endogenous damaged organelles, as well as in nutrient signaling and regulation of cell growth. 19 The presence of a large number of secondary lysosomes may indicate the unstable status of the tissues. Previous studies have shown that nanoparticles can penetrate organs following ingestion, injection, skin application, or inhalation through systemic circulation.…”