Proceedings of The Physiological Society

Physiology 2016 (Dublin, Ireland) (2016) Proc Physiol Soc 37, PCB072

Poster Communications

Smooth muscle cells-generated methylglyoxal is responsible for cardiac and myocyte dysfunctions in diabetes mellitus

K. R. Bidasee1, F. Alomar4, G. Rozanski3, J. Singh2

1. Pharmacology and Experimental Neuroscience, University of Nebraska Medical center, Omaha, Nebraska, United States. 2. School of Forensic and Investigative Science, University of Central Lancashire, Preston, United Kingdom. 3. Cellular and Integrative Physiology, University of Nebraska Medical center, Omaha, Nebraska, United States. 4. Department of Pharmacology, University of Dammam, Dammam, Dammam, Saudi Arabia.

Heart failure is a common pathophysiology in individuals with diabetes mellitus (DM). This defect has been attributed in part to disruption of sarcoplasmic reticulum (SR) Ca2+ cycling in cardiac myocytes arising from post-translational modification and dysregulation of ryanodine receptor Ca2+ release channels (RyR2) and sarco(endo)plasmic reticulum Ca2+ATPase (SERCA2) by the di-carbonyl species (RCS). The most potent SR-dysregulating RCS is the diffusible methylglyoxal (MG), but its source remains elusive. This study which received ethical clearance from UCLan and the University of Nebraska Medical Center, Omaha, tests the hypothesis that smooth muscle cells in the microvasculature (cSMCs) of the heart are responsible for generating the MG that perturbs SR Ca2+ cycling in myocytes. DM was induced in young adult male Sprague-Dawley rats via a single intravenous injection of streptozotocin (STZ) (45 mg/kg in 0.1 ml in citrate buffer, n = 36). Control animals received citrate buffer injection only (Con, n = 24). One week after STZ injection, DM animals were divided into three groups. One group was injected with an adeno-associated virus (AAV2/9) to selectively increase expression of the MG-degrading enzyme glyoxalase-I in cSMCs (1.7×1012 viron particles/kg), another was injected with AAV2/9 to increase expression of the non-selective green fluorescent protein (GFP), and the third group remain untreated. After 7-8 weeks of DM, body mass, heart rate, ejection fraction and fractional shortening were significantly lower than in Con [415 ± 10g vs 275 ± 15g; 367.1 ± 10.1 bpm vs 289.1 ± 8.1 bpm; 79.1 ± 1.9% vs 70.9 ± 1.9% and 49.1 ± 1.7% vs 41.9 ± 1.9%, respectively]. Contraction and relaxation kinetics were also significantly lower [cell length, 115.8 ± 3.0 μm vs 110.7 ± 4.2 μm; contractile velocity, 75.0 ± 6.3 μm/s vs 132 ± 10.2 μm/s; relengthening velocity 60.9 ± 5.8 vs 117.9 ± 9.1, p<0.05], as was mean Ca2+ transient amplitude [1.1± 0.1 vs 3.0 ± 0.2 FU, p<0.05]. The MG-generating enzyme vascular adhesion protein 1 and MG were increase 5-fold and 3.6 in cSMCs of DM hearts, and the MG-degrading enzyme glyoxalase-I (Glo-I) was 50% lower. RyR2 and SERCA2a activities were also compromised. Increasing expression of Glo-I in cSMCs of DM to near Con levels, attenuated impairments in heart rate [320.1 ± 5.1 bpm], ejection fraction [74.4 ± 0.7%] and fractional shortening [47.5 ± 0.5%]. It also improved contractile velocity [101.4 ± 8.2 μm/s, relengthening velocity [98.3 ± 5.4], Ca2+ transient amplitude [2.5 ± 0.2 FU], and the activities of RyR2 and SERCA2. Gene transfer of GFP did not improve cardiac or myocyte function in DM animals. These data are the first to show that MG generated in cSMCs during DM is diffusing and dysregulating SR Ca2+ cycling proteins in myocytes.

Where applicable, experiments conform with Society ethical requirements