Rapid Suppression of Mitochondrial Permeability Transition by Methylglyoxal

Abstract

Methylglyoxal (MG) (pyruvaldehyde) is a reactive carbonyl compound produced in glycolysis. MG can form covalent adducts on proteins resulting in advanced glycation end products that may alter protein function. Here we report that MG covalently modifies the mitochondrial permeability transition pore (PTP), a high conductance channel involved in the signal transduction of cell death processes. Incubation of isolated mitochondria with MG for a short period of time (5 min), followed by removal of excess free MG, prevented both ganglioside GD3-and Ca 2؉ -induced PTP opening and the ensuing membrane depolarization, swelling, and cytochrome c release. Under these conditions MG did not significantly interfere with mitochondrial substrate transport, respiration, or oxidative phosphorylation. The suppression of permeability transition was reversible following extended incubation in MG-free medium. Of the 29 physiological carbonyl and dicarbonyl compounds tested only MG and its analogue glyoxal were able to specifically alter the behavior of the PTP. Using a set of arginine-containing peptides, we found that the major MG-derived arginine adduct formed, following a short time exposure to MG, was the 5-hydro-5-methylimidazol-4-one derivative. These findings demonstrate that MG rapidly modifies the PTP covalently and stabilizes the PTP in the closed conformation. This is probably due to the formation of an imidazolone adduct on an arginine residue involved in the control of PTP conformation (Linder, M. D., Morkunaite-Haimi, S., Kinnunen, P. J. K., Bernardi, P., and Eriksson, O. (2002) J. Biol. Chem. 277, 937-942). We deduce that the permeability transition constitutes a potentially important physiological target of MG.

Proteomic studies identified a single nucleotide polymorphism in glyoxalase I as autism susceptibility factor

“…These AGE's may have altered or compromised function at crucial stages during neurogenesis. Methylglyoxal has been shown to target several proteins involved in the regulation of cell growth and differentiation [Godbout et al, 2002;Sakamoto et al, 2002;Speer et al, 2003]. Overexpression of Glo1 in cells treated with phorbol esters [Gillespie, 1981] and cancer tissues [Thornalley, 1995] have also led to the suggestion that Glo1 activity is related to cell growth.…”

Antimelanoma Activity of Apoptogenic Carbonyl Scavengers

“…The apoptogenicity of carbonyl scavengers on human melanoma cell lines suggests that covalent trapping of RCS may be part of the apoptogenic mechanism of action observed with these agents. Recently, MG modulation of regulatory mechanisms of apoptosis, such as MPT pore opening and Hsp 27 oligomerization, have been demonstrated as part of an emerging cancer cell survival pathway that interferes with apoptosis by glycolytic formation of RCS (Speer et al, 2003;Johans et al, 2005;Wondrak et al, 2005). The possibility of a functional antagonism between carbonyl scavengers and RCS-mediated cell survival was further examined by inducing carbonyl scavenger-triggered apoptosis after external addition of the RCS phenylglyoxal (PG) as summarized in Fig.…”

“…4. PG is a membrane-permeable RCS that irreversibly inhibits MPT pore opening in isolated mitochondria (Speer et al, 2003), thereby potentially mimicking the effects of elevated intracellular MG. Indeed, PG pretreatment antagonized carbonyl scavenger-induced G361 melanoma cell apoptosis (Fig.…”

“…In addition to the established role of AGE-receptor for advanced glycation end product signaling in many human malignancies, increasing evidence supports the hypothesis that RCS, originating from increased tumor cell glycolysis and mitochondrial oxidative stress, are small molecule antiapoptotic effectors (Sakamoto et al, 2002;Speer et al, 2003;Johans et al, 2005). The ␣-dicarbonyl MG forms from glycolytic triose phosphates by spontaneous phosphate elimina-tion (Thornalley, 1995), and intracellular MG levels are elevated under conditions of increased glycolytic flux, such as hyperglycemia (Shinohara et al, 1998) and aerobic glycolysis associated with malignant transformation (Kawase et al, 1996).…”

“…Recent evidence suggests that covalent modification of arginine residues by MG targets specific proteins involved in apoptosis, such as mitochondrial permeability transition (MPT) pore proteins (Johans et al, 2005) and heat shock protein 27 (Hsp 27) (Sakamoto et al, 2002). MG modification of MPT pore proteins interferes with pore opening, inhibiting mitochondrial swelling, loss of transmembrane potential, and subsequent release of proapoptotic factors such as cytochrome c and apoptosis-inducing factor in response to apoptotic stimuli such as high Ca 2ϩ and ganglioside GD3 (Speer et al, 2003;Johans et al, 2005). In various human cancer cell lines, post-translational MG-mediated arginine-pyrimidine formation occurs at a single arginine residue of Hsp 27 with induction of Hsp 27 oligomerization essential for repression of cytochrome c-mediated apoptosome assembly (Bruey et al, 2000).…”