Lysophospholipid metabolism and signalling - role of lysophospholipases

Bioactive fats (lipids) influence many biological processes including cell growth, death, and migration. Lysophosphatidic acid (LPA) is a bioactive lysophospholipid that is mainly produced by the lysophospholipid degrading enzyme (lysophospholipase), autotaxin. Our work established a connection between the autotaxin-LPA pathway and energy metabolism in mammals. We showed that autotaxin is influenced by nutrients and insulin and that the autotaxin-LPA pathway hinders the function of mitochondria, the powerhouses of the cell. It remains unclear how this pathway precisely influences mitochondrial maintenance and function. Lipid phosphate phosphatase 3 (LPP3) is a lysophospholipase that breaks down LPA. LPP3 is essential for embryo formation and is best known for its role in blood vessel development and function. LPP3 is present in tissues with high energy metabolism including muscle and adipose and was implicated in sugar metabolism. However, the relationship between LPP3, mitochondrial function and energy metabolism is largely unexplored. The overall goal of this research is to examine the role of autotaxin and LPP3 in mammalian energy metabolism and mitochondrial maintenance and function. Using cultured mammalian fat and muscle cells exposed to LPA and fat and muscle tissue from mice with reduced autotaxin levels, we will test whether the autotaxin-LPA pathway affects the fusion and fission of mitochondria. This process, termed mitochondrial dynamics, is linked to mitochondrial energy metabolism and function. Mitochondrial structure will be assessed by electron microscopy. Proteins involved in mitochondrial dynamics will be measured using immunoblotting technique. Fluorescence microscopy will allow us to visualize mitochondrial fusion and fission in live cells. By blocking distinct LPA receptors, we will determine which receptors are involved in autotaxin-LPA mediated changes in mitochondrial dynamics. We will also assess whether autotaxin-LPA alters mitochondrial degradation through mitophagy. Using mice and rats, we will determine whether LPP3 levels and activity change in response to feeding/fasting. We will employ cultured fat and muscle cells to assess how different energy substrates and starvation affect LPP3. We will also monitor changes in LPP3 localization to cellular compartments using microscopy. The effect of increased and decreased LPP3 on nutrient uptake and oxidation will be examined using labeled substrates and mitochondrial respirometry. Mice with muscle and fat-specific increases in LPP3 will be used to verify whether LPP3 changes energy metabolism in these tissues in the living organism. Comprehensive metabolite analysis will be performed by mass spectrometry. Mitochondrial dynamics and degradation will also be assessed. This research will provide new insight into the biological role of autotaxin and LPP3 and elucidate how these lysophospholipases impact energy metabolism and mitochondrial maintenance and function.