Initial autophagic protection switches to disruption of autophagic flux by lysosomal instability during cadmium stress accrual in renal NRK-52E cells

• Published in: Archives of toxicology Vol. 91; no. 10; pp. 3225 - 3245
• Main Authors: Lee, W.-K., Probst, S., Santoyo-Sánchez, M. P., Al-Hamdani, W., Diebels, I., von Sivers, J.-K., Kerek, E., Prenner, E. J., Thévenod, F.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-10-2017; Springer Nature B.V
• Subjects: Animals; Apoptosis; Apoptosis - drug effects; Apoptosis - physiology; Autophagy; Autophagy - drug effects; Bcl-2 protein; Biomedical and Life Sciences; Biomedicine; Cadmium; Cadmium - administration & dosage; Cadmium - toxicity; Cathepsins; Cell death; Cell Line; Cell survival; Cellular stress response; Disruption; Dose-Response Relationship, Drug; Endoplasmic reticulum; Endoplasmic Reticulum Stress - drug effects; Environmental Health; Exposure; Fluctuations; Fluidity; Flux; Inorganic Compounds; Isoquinolines - pharmacology; Kidney Tubules, Proximal - cytology; Lysosomal Membrane Proteins - metabolism; Lysosomes - drug effects; Lysosomes - metabolism; Lysosomes - pathology; Machinery and equipment; Membrane fluidity; Microtubule-Associated Proteins - metabolism; Mortality; Occupational Medicine/Industrial Medicine; Phagocytosis; Pharmacology/Toxicology; Phenols - pharmacology; Poly(ADP-ribose) polymerase; Rapamycin; Rats; Rodents; Signal transduction; Sirolimus - pharmacology; Sphingomyelin; Stability; Stress; Stresses; Switches; Toxicity; Unfolded Protein Response - drug effects; Lysosomal membrane permeabilization; Laurdan; Transition metal toxicity; Lysenin; Unfolded protein response
• ISSN: 0340-5761; 1432-0738
• DOI: 10.1007/s00204-017-1942-9

The renal proximal tubule (PT) is the major target of cadmium (Cd
2+
) toxicity where Cd
2+
causes stress and apoptosis. Autophagy is induced by cell stress, e.g., endoplasmic reticulum (ER) stress, and may contribute to cell survival or death. The role of autophagy in Cd
2+
-induced nephrotoxicity remains unsettled due to contradictory results and lack of evidence for autophagic machinery damage by Cd
2+
. Cd
2+
-induced autophagy in rat kidney PT cell line NRK-52E and its role in cell death was investigated. Increased LC3-II and decreased p62 as autophagy markers indicate rapid induction of autophagic flux by Cd
2+
(5–10 µM) after 1 h, accompanied by ER stress (increased p-PERK, p-eIF2α, CHOP). Cd
2+
exposure exceeding 3 h results in p62/LC3-II accumulation, but diminished effect of lysosomal inhibitors (bafilomycin A1, pepstatin A +E-64d) on p62/LC3-II levels, indicating decreased autophagic flux and cargo degradation. At 24 h exposure, Cd
2+
(5–25 µM) activates intrinsic apoptotic pathways (Bax/Bcl-2, PARP-1), which is not evident earlier (≤6 h) although cell viability by MTT assay is decreased. Autophagy inducer rapamycin (100 nM) does not overcome autophagy inhibition or Cd
2+
-induced cell viability loss. The autophagosome–lysosome fusion inhibitor liensinine (5 μM) increases CHOP and Bax/Bcl-2-dependent apoptosis by low Cd
2+
stress, but not by high Cd
2+
. Lysosomal instability by Cd
2+
(5 μM; 6 h) is indicated by increases in cellular sphingomyelin and membrane fluidity and decreases in cathepsins and LAMP1. The data suggest dual and temporal impact of Cd
2+
on autophagy: Low Cd
2+
stress rapidly activates autophagy counteracting damage but Cd
2+
stress accrual disrupts autophagic flux and lysosomal stability, possibly resulting in lysosomal cell death.