Dynamic simulation of cardiolipin remodeling: greasing the wheels for an interpretative approach to lipidomics

Lipidomics is providing new insight into the metabolic syndrome and its sequelae

PURPOSE OF REVIEW

The metabolic syndrome incorporating obesity, hypertension, dyslipidaemia and elevated plasma glucose has reached epidemic proportions in many Western countries leading to a dramatic increase in insulin resistance, steatosis and type 2 diabetes. Lipidomics presents a new set of tools to unravel the relationship between hyper-caloric diets and other environmental and genetic factors with the metabolic syndrome and disease progression.

RECENT FINDINGS

Plasma lipidomic studies are providing detailed characterisation of the dyslipidaemia associated with obesity and the metabolic syndrome. Combined with lipoprotein fractionation and dynamic modelling we are gaining a new comprehension of lipoprotein composition structure and function. At the population level genome-wide association studies are identifying potential loci linking lipid metabolism with disease pathogenesis. Analysis of tissue, cell and even organelle lipidomes are unravelling the complex relationships between lipotoxicity, inflammation, oxidative stress and cellular function.

SUMMARY

The global view of lipid metabolism offered by lipidomics is accelerating our understanding of disease processes and identifying new avenues of research into metabolic syndrome and its sequelae. The ongoing identification and validation of lipid biomarkers will likely see their introduction into clinical practice for improved quantification of disease risk, earlier identification of disease and improved patient management in the near future.

Cardiac and skeletal muscle defects in a mouse model of human Barth syndrome

Barth syndrome is an X-linked genetic disorder caused by mutations in the tafazzin (taz) gene and characterized by dilated cardiomyopathy, exercise intolerance, chronic fatigue, delayed growth, and neutropenia. Tafazzin is a mitochondrial transacylase required for cardiolipin remodeling. Although tafazzin function has been studied in non-mammalian model organisms, mammalian genetic loss of function approaches have not been used. We examined the consequences of tafazzin knockdown on sarcomeric mitochondria and cardiac function in mice. Tafazzin knockdown resulted in a dramatic decrease of tetralinoleoyl cardiolipin in cardiac and skeletal muscles and accumulation of monolysocardiolipins and cardiolipin molecular species with aberrant acyl groups. Electron microscopy revealed pathological changes in mitochondria, myofibrils, and mitochondrion-associated membranes in skeletal and cardiac muscles. Echocardiography and magnetic resonance imaging revealed severe cardiac abnormalities, including left ventricular dilation, left ventricular mass reduction, and depression of fractional shortening and ejection fraction in tafazzin-deficient mice. Tafazzin knockdown mice provide the first mammalian model system for Barth syndrome in which the pathophysiological relationships between altered content of mitochondrial phospholipids, ultrastructural abnormalities, myocardial and mitochondrial dysfunction, and clinical outcome can be completely investigated.

Metabolic management of brain cancer

Malignant brain tumors are a significant health problem in children and adults. Conventional therapeutic approaches have been largely unsuccessful in providing long-term management. As primarily a metabolic disease, malignant brain cancer can be managed through changes in metabolic environment. In contrast to normal neurons and glia, which readily transition to ketone bodies (β-hydroxybutyrate) for energy under reduced glucose, malignant brain tumors are strongly dependent on glycolysis for energy. The transition from glucose to ketone bodies as a major energy source is an evolutionary conserved adaptation to food deprivation that permits the survival of normal cells during extreme shifts in nutritional environment. Only those cells with a flexible genome and normal mitochondria can effectively transition from one energy state to another. Mutations restrict genomic and metabolic flexibility thus making tumor cells more vulnerable to energy stress than normal cells. We propose an alternative approach to brain cancer management that exploits the metabolic flexibility of normal cells at the expense of the genetically defective and metabolically challenged tumor cells. This approach to brain cancer management is supported from recent studies in mice and humans treated with calorie restriction and the ketogenic diet. Issues of implementation and use protocols are presented for the metabolic management of brain cancer.