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Aims: Catecholamine metabolism via monoamine oxidase (MAO) contributes to cardiac injury in models of ischemia and diabetes, but the pathogenic mechanisms involved are unclear. MAO deaminates norepinephrine (NE) and dopamine to produce H 2 O 2 and highly reactive "catecholaldehydes," which may be toxic to mitochondria due to the localization of MAO to the outer mitochondrial membrane. We performed a comprehensive analysis of catecholamine metabolism and its impact on mitochondrial energetics in atrial myocardium obtained from patients with and without type 2 diabetes. Results: Content and maximal activity of MAO-A and MAO-B were higher in the myocardium of patients with diabetes and they were associated with body mass index. Metabolomic analysis of atrial tissue from these patients showed decreased catecholamine levels in the myocardium, supporting an increased flux through MAOs. Catecholaldehyde-modified protein adducts were more abundant in myocardial tissue extracts from patients with diabetes and were confirmed to be MAO dependent. NE treatment suppressed mitochondrial ATP production in permeabilized myofibers from patients with diabetes in an MAO-dependent manner. Aldehyde dehydrogenase (ALDH) activity was substantially decreased in atrial myocardium from these patients, and metabolomics confirmed lower levels of ALDH-catalyzed catecholamine metabolites. Proteomic analysis of catechol-modified proteins in isolated cardiac mitochondria from these patients identified >300 mitochondrial proteins to be potential targets of these unique carbonyls. Innovation and Conclusion: These findings illustrate a unique form of carbonyl toxicity driven by MAO-mediated metabolism of catecholamines, and they reveal pathogenic factors underlying cardiometabolic disease. Importantly, they suggest that pharmacotherapies targeting aldehyde stress and catecholamine metabolism in heart may be beneficial in patients with diabetes and cardiac disease. Antioxid. Redox Signal. 35, 235-251.

Catecholamine stimulation of β-adrenergic receptors (βAR) in adipocytes activates the cAMP-dependent protein kinase to promote liberation of fatty acids as a fuel source. The adipocyte β3AR also activates extracellular signal-regulated kinases (ERK)-1 and -2 through direct recruitment and activation of Src kinase. This pathway together with cAMP-dependent protein kinase contributes to maximal β3AR-stimulated lipolysis. In a search for other molecules that might associate with β3AR upon agonist stimulation, we identified vimentin using a proteomics approach. Immunoprecipitation of β3AR from adipocytes in the absence or presence of the β3AR agonist CL316,243, followed by Western blotting for vimentin confirmed this specific interaction. Since vimentin has also been identified on lipid droplets, the functional consequences of blocking the expression or structural integrity of vimentin intermediate filaments on β3AR regulation of ERK activation and lipolysis was assessed. Following disruption of intermediate filaments with β,β′-iminodipropionitrile, as confirmed by confocal microscopy, β3AR-stimulated ERK activation was blocked, and lipolysis was reduced by more than 40%. Independently, depletion of vimentin by small hairpin RNA (shRNA) completely inhibited β3AR-mediated ERK activation and significantly reduced lipolysis. By contrast, disruption of actin-containing microfilaments by cytochalasin D or microtubules by nocodazole had no effect on either lipolysis or ERK activation. These results indicate that vimentin plays an essential role in the signal transduction pathway from β3AR to the activation ERK and its contribution to lipolysis. [ABSTRACT FROM AUTHOR]

Catecholamine-stimulated lipolysis is primarily a β-adrenergic and cAMP-dependent event. In previous studies we established that the β3-adrenergic receptor (β3AR) in adipocytes utilizes a unique mechanism to stimulate extracellular signal-regulated kinases 1 and 2 (ERK) by direct recruitment and activation of Src kinase. Therefore, we investigated the role of the ERK pathway in adipocyte metabolism and found that the β3AR agonist CL316,243 regulates lipolysis through both cAMP-dependent protein kinase (PKA) and ERK. Inhibition of PKA activity completely eliminated lipolysis at low (subnanomolar) CL316,243 concentrations and by 75-80% at higher nanomolar concentrations. The remaining 20-25% of PKA-independent lipolysis, as well as ERK activation, was abolished by inhibiting the activity of either Src (PP2 or small interfering RNA), epidermal growth factor receptor (EGFR with AG 1478 or small interfering RNA), or mitogen-activated protein kinase kinase 1 or 2 (MKK1/2 with PD098059). PD098059 inhibited lipolysis by 53% in mice as well. Finally, the effect of estradiol, a reported acute activator of ERK and lipolysis, was also totally prevented by PP2, AG1478, and PD098059. These results suggest that ERK activation by β3AR depends upon Src and epidermal growth factor receptor kinase activities and is responsible for the PKA-independent portion of the lipolytic response. Together these results illustrate the distinct and complementary roles for PKA and ERK in catecholamine-stimulated lipolysis. [ABSTRACT FROM AUTHOR]

The development of the metabolic syndrome in an increasing percentage of the populations of Western societies, particularly in the United States, requires valid models for establishing basic biochemical changes and performing preclinical studies on potential drug targets. The C57BL/6J mouse has become an important model for understanidng the interplay between genetic background and environmental challenges such as high-fat/high-calorie diets that predispose to the development of the metabolic syndrome. This review highlights metabolic and signal transduction features that are altered during the course of disease progression, many of which mirror the human situation. [Copyright &y& Elsevier]