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Item Coronary perivascular adipose tissue and vascular smooth muscle function: influence of obesity(2016-03-22) Noblet, Jillian Nicole; Tune, Johnathan D.Factors released from coronary perivascular adipose tissue (PVAT), which surrounds large coronary arteries, have been implicated in the development of coronary disease. However, the precise contribution of coronary PVAT-derived factors to the initiation and progression of coronary vascular dysfunction remains ill defined. Accordingly, this investigation was designed to delineate the mechanisms by which PVAT-derived factors influence obesity-induced coronary smooth muscle dysfunction. Isometric tension studies of coronary arteries from lean and obese swine demonstrated that both lean and obese coronary PVAT attenuate vasodilation via inhibitory effects on smooth muscle K+ channels. Specifically, lean coronary PVAT attenuated KCa and KV7 channel-mediated dilation, whereas obese coronary PVAT impaired KATP channel-mediated dilation. Importantly, these effects were independent of alterations in underlying smooth muscle function in obese arteries. The PVAT-derived factor calpastatin impaired adenosine dilation in lean but not obese arteries, suggesting that alterations in specific factors may contribute to the development of smooth muscle dysfunction. Further studies tested the hypothesis that leptin, which is expressed in coronary PVAT and is upregulated in obesity, acts as an upstream mediator of coronary smooth muscle dysfunction. Long-term administration (3 day culture) of obese concentrations of leptin markedly altered the coronary artery proteome, favoring pathways associated with calcium signaling and cellular proliferation. Isometric tension studies demonstrated that short-term (30 min) exposure to leptin potentiated depolarization-induced contraction of coronary arteries and that this effect was augmented following longer-term leptin administration (3 days). Inhibition of Rho kinase reduced leptin-mediated increases in coronary artery contractions. Acute treatment was associated with increased Rho kinase activity, whereas longer-term exposure was associated with increases in Rho kinase protein abundance. Alterations in Rho kinase signaling were also associated with leptin-mediated increases in coronary vascular smooth muscle proliferation. These findings provide novel mechanistic evidence linking coronary PVAT with vascular dysfunction and further support a role for coronary PVAT in the pathogenesis of coronary disease.Item Leptin augments coronary vasoconstriction and smooth muscle proliferation via a Rho-kinase-dependent pathway(Springer, 2016-05) Noblet, Jillian N.; Goodwill, Adam G.; Sassoon, Daniel J.; Kiel, Alexander M.; Tune, Johnathan D.; Department of Cellular & Integrative Physiology, IU School of MedicineLeptin has been implicated as a key upstream mediator of pathways associated with coronary vascular dysfunction and disease. The purpose of this investigation was to test the hypothesis that leptin modifies the coronary artery proteome and promotes increases in coronary smooth muscle contraction and proliferation via influences on Rho kinase signaling. Global proteomic assessment of coronary arteries from lean swine cultured with obese concentrations of leptin (30 ng/mL) for 3 days revealed significant alterations in the coronary artery proteome (68 proteins) and identified an association between leptin treatment and calcium signaling/contraction (four proteins) and cellular growth and proliferation (35 proteins). Isometric tension studies demonstrated that both acute (30 min) and chronic (3 days, serum-free media) exposure to obese concentrations of leptin potentiated depolarization-induced contraction of coronary arteries. Inhibition of Rho kinase significantly reduced leptin-mediated increases in coronary artery contractions. The effects of leptin on the functional expression of Rho kinase were time-dependent, as acute treatment increased Rho kinase activity while chronic (3 day) exposure was associated with increases in Rho kinase protein abundance. Proliferation assays following chronic leptin administration (8 day, serum-containing media) demonstrated that leptin augmented coronary vascular smooth muscle proliferation and increased Rho kinase activity. Inhibition of Rho kinase significantly reduced these effects of leptin. Taken together, these findings demonstrate that leptin promotes increases in coronary vasoconstriction and smooth muscle proliferation and indicate that these phenotypic effects are associated with alterations in the coronary artery proteome and dynamic effects on the Rho kinase pathway.Item Local metabolic hypothesis is not sufficient to explain coronary autoregulatory behavior(Springer Nature, 2018-08-02) Kiel, Alexander M.; Goodwill, Adam G.; Baker, Hana E.; Dick, Gregory M.; Tune, Johnathan D.; Cellular and Integrative Physiology, School of MedicineThe local metabolic hypothesis proposes that myocardial oxygen tension determines the degree of autoregulation by increasing the production of vasodilator metabolites as perfusion pressure is reduced. Thus, normal physiologic levels of coronary venous PO2, an index of myocardial oxygenation, are proposed to be required for effective autoregulation. The present study challenged this hypothesis through determination of coronary responses to changes in coronary perfusion pressure (CPP 140-40 mmHg) in open-chest swine in the absence (n = 7) and presence of euvolemic hemodilution (~ 50% reduction in hematocrit), with (n = 5) and without (n = 6) infusion of dobutamine to augment MVO2. Coronary venous PO2 decreased over similar ranges (~ 28-15 mmHg) as CPP was lowered from 140 to 40 mmHg in each of the groups. However, coronary venous PO2 was not associated with changes in coronary blood flow (r = - 0.11; P = 0.29) or autoregulatory gain (r = - 0.29; P = 0.12). Coronary zero-flow pressure (Pzf) was measured in 20 mmHg increments and determined to be directly related to vascular resistance (r = 0.71; P < 0.001). Further analysis demonstrated that changes in coronary blood flow remained minimal at Pzf > 20 mmHg, but progressively increased as Pzf decreased below this threshold value (r = 0.68; P < 0.001). Coronary Pzf was also positively correlated with autoregulatory gain (r = 0.43; P = 0.001). These findings support that coronary autoregulatory behavior is predominantly dependent on an adequate degree of underlying vasomotor tone, independent of normal myocardial oxygen tension.