Dysfunction of SERCA pumps as novel mechanism of methylglyoxal cytotoxicity

A novel pathway of methylglyoxal (MGX)-induced apoptosis via sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) is presented. Interaction of SERCA1 with MGX was investigated by molecular docking and experimentally in a cell-free system. MGX concentration- and time-dependently decreased SERCA1 activity. A significant increase of sarcoplasmic reticulum (SR) carbonylation was found in the concentration range of 1-10 mM caused by MGX and a decrease of thiol groups at the concentrations of 5 and 40 mM. Affinities of SERCA1 to ATP and Ca²⁺ were not influenced by MGX, however decreases of V_max related to both binding sites were observed. Molecular docking indicated binding of MGX at the cytosolic region of SERCA1, inducing conformational changes in the cytosolic-transmembrane interface. This interaction resulted in conformational changes in the cytosolic region (FITC fluorescence decrease) as well as in the transmembrane region of SERCA1 (Trp fluorescence decrease) without direct binding to the cytosolic ATP or transmembrane Ca²⁺ binding sites. Regarding the MGX inhibitory effect in a cell-free system and similarities of SERCA1 to its other isoforms, proapoptotic properties of MGX may be expected in cellular systems. At cellular level, MGX induced a decrease of SERCA2b expression in the pancreatic INS-1E β-cell line. This was accompanied by cell viability decrease, increase in apoptosis, impaired insulin secretion and elevation of basal intracellular Ca²⁺ levels. Decreased expression of SERCA2b may contribute to induction of apoptosis of pancreatic β-cells.