Abstract MP103: Methylglyoxal Modifications on Myofilament Proteins Caused by Diabetes Block Heart Failure Drug Targets Through Changing Tropomyosin Position

Abstract

We previously discovered methylglyoxal (MG), a glycolysis byproduct, modifies arginine and lysine residues on myofilament proteins to a greater extent in patients with diabetes and heart failure than non-failing controls. These modifications reduced myofilament calcium sensitivity (pCa 50 ), maximal calcium activated force (F max ) and cross-bridge cycling dynamics. We hypothesized that compensating for these modifications might slow or halt the development of diabetic cardiomyopathy. We attempted to pharmacologically compensate for the negative functional effects of MG using omecamtiv mecarbil (OM), a myosin activator currently in clinical trials. As reported previously, we found that OM increased pCa 50 and decreased F max in normal myocytes. However, in myocytes pretreated with MG, OM had no effect of pCa 50 but still decreased F max . These data suggest OM may have less, or potentially detrimental effects in diabetic patients.To understand why MG might block the actions of sarcomere drug targets, we aimed to further elucidate the molecular mechanisms of MG. We utilized a computer model of sarcomere contraction to predict what molecular effects of MG would explain the functional data we collected. The model predicted a simultaneous increase in cross-bridge detachment rate and a decrease in the closed-to-blocked tropomyosin transition rate could explain the data. Stopped flow experiments measuring myofilament kinetics indicated a decreased transition rate between “closed” and “blocked” tropomyosin state but did not indicate a difference in the cross-bridge detachment rate upon treatment with MG. This finding further explained the observation that MG blocks OM’s effects - since a myosin activator would not necessarily be effective if MG affected tropomyosin position on actin. We hypothesize that a residue we found to be modified by MG on actin, K291 would be important for the molecular mechanism observed, since it is located in a critical position for the interaction between actin and tropomyosin. In this study, we have elucidated the mechanism of MG’s detrimental myofilament impact and found that that these modifications reduce the efficacy of OM. This mechanistic understanding will help drive future identification of therapeutic targets.