Mechanisms involved in renal cell adaptation to stress by thallium

MOREL GOMEZ, EMANUEL; FERNANDEZ , MARIA DEL CARMEN; VERSTRAETEN, SANDRA

Salta

Congreso; LV Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular y XIV PABMB Congress; 2019

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB) y Asociación Panamericana de Bioquímica y Biología Molecular (PABMB)

Thallium (Tl) is a non-essential toxic heavy metal that contaminates the environment (water, air and soils). Human intoxication with Tl affects several organs and tissues through still poorly understood mechanisms, in which the kidney is a main target of Tl toxicity. Tl has two oxidation states, the monovalent [Tl(I)] and trivalent [Tl(III)] cations, the latter being a strong oxidant. We previously demonstrated that Tl decreased the number of proliferating renal epithelial (MDCK) cells, altered their lipid metabolism and induced changes in cellular complexity and morphology. Other non-essential metals (cadmium, lead and mercury) give way to trigger diverse cellular processes in response to stress, such as endoplasmic reticulum (ER) stress, autophagy and paraptosis. Hence, the present study seeks to investigate if some of these molecular mechanisms are likely to mediate Tl effects on MDCK cells. Confluent cell cultures were incubated for 3, 6, 24 or 48 h in the absence orpresence of Tl(I) or Tl(III) (100 µM). Expression levels of proteins involved in autophagy and ER stress were analyzed by Western blot. Tl(I) and Tl(III) increased XBP-1(s) expression at 6 and 24 h of cell exposure and increased those of IRE-1, ATF-6, beclin-1 and sequestrin-1 at 24 and 48 h of treatment. The involvement of MAPK expression in ER stress and paraptosis was next analyzed. Tl increased p-JNK/JNK ratio without changing in p-ERK/ERK ratio after 3 h of treatment. RT-PCR analysis indicated that both Tl(I) and Tl(III) increased prohibitin (a positive paraptosis modulator) expression after 24 h of treatment without affecting the expression of phosphatidylethanolamine-binding protein(a negative paraptosis modulator) expression. Phase-contrast and transmission electron microscopy evidenced cytoplasmic vacuolation compatible with paraptosis-like death. Tl also induced changes in LC3 intracellular distribution, as evidenced by fluorescence microscopy. To sum up, current results provide evidence that Tl might induce two cellular responses: in early stages of exposure, cells activate ER stress and autophagy as adaptative and pro-survival responses. In advanced stages of exposure, severe ER stress leads to cytoplasm vacuolation and paraptosis. Considering that Tl impairs human health at different levels, including alterations in the kidneys, our findings contribute to further understand the biochemical mechanisms underlying Tl toxicity in humans. However, additional studies are required to investigate further the adaptation and survival mechanisms that are involved in Tl intoxication.