Edward Ross Pennington

Distinct membrane properties are differentially influenced by cardiolipin content and acyl chain composition in biomimetic membranes

Cardiolipin (CL) has a critical role in maintaining mitochondrial inner membrane structure. In several conditions such as heart failure and aging, there is loss of CL content and remodeling of CL acyl chains, which are hypothesized to impair mitochondrial inner membrane biophysical organization. Therefore, this study discriminated how CL content and acyl chain composition influenced select properties of simple and complex mitochondrial mimicking model membranes. We focused on monolayer excess area/molecule (a measure of lipid miscibility), bilayer phase transitions, and microdomain organization. In monolayer compression studies, loss of tetralinoleoyl [(18:2)4] CL content decreased the excess area/molecule. Replacement of (18:2)4CL acyl chains with tetraoleoyl [(18:1)4] CL or tetradocosahexaenoyl [(22:6)4] CL generally had little influence on monolayer excess area/molecule; in contrast, replacement of (18:2)4CL acyl chains with tetramyristoyl [(14:0)4] CL increased monolayer excess area/molecule. In bilayers, calorimetric studies showed that substitution of (18:2)4CL with (18:1)4CL or (22:6)4CL lowered the phase transition temperature of phosphatidylcholine vesicles whereas (14:0)4CL had no effect. Finally, quantitative imaging of giant unilamellar vesicles revealed differential effects of CL content and acyl chain composition on microdomain organization, visualized with the fluorescent probe Texas Red DHPE. Notably, microdomain areas were decreased by differing magnitudes upon lowering of (18:2)4CL content and substitution of (18:2)4CL with (14:0)4CL or (22:6)4CL. Conversely, exchanging (18:2)4CL with (18:1)4CL increased microdomain area. Altogether, these data demonstrate that CL content and fatty acyl composition differentially target membrane physical properties, which has implications for understanding how CL regulates mitochondrial activity and the design of CL-specific therapeutics.

Conservation of chemically degraded waterlogged wood with sugars

Abstract The effectiveness of two non-reducing sugars, both analogues of sucrose, to conserve degraded waterlogged wood was examined. The two sugars examined are trehalose and sucralose, both stable and relatively unreactive. The ability of these sugars to conserve a series of degraded tongue depressors was measured by determining the anti-shrink efficiency of each at various concentrations and comparing them to sucrose. The findings of this study indicate that both sucralose and trehalose may be effective conservation treatments for waterlogged archaeological wood and that at moderate concentrations the performance of both is comparable to sucrose. However, sucralose has a lower solubility, and concentrations higher than 60% w/v were not examined, whereas concentrations of up to 100% w/v of trehalose were studied. At these higher concentrations trehalose performed as well, if not better than sucrose, although there were crystalline deposits on the wood surface at these higher concentrations. With modifications and careful control, both of these sugars may be suitable conservation alternatives to sucrose due to their long-term stability and resistance to hydrolysis.

Docosahexaenoic acid lowers cardiac mitochondrial enzyme activity by replacing linoleic acid in the phospholipidome

Cardiac mitochondrial phospholipid acyl chains regulate respiratory enzymatic activity. In several diseases, the rodent cardiac phospholipidome is extensively rearranged; however, whether specific acyl chains impair respiratory enzyme function is unknown. One unique remodeling event in the myocardium of obese and diabetic rodents is an increase in docosahexaenoic acid (DHA) levels. Here, we first confirmed that cardiac DHA levels are elevated in diabetic humans relative to controls. We then used dietary supplementation of a Western diet with DHA as a tool to promote cardiac acyl chain remodeling and to study its influence on respiratory enzyme function. DHA extensively remodeled the acyl chains of cardiolipin (CL), monolyso-CL, phosphatidylcholine, and phosphatidylethanolamine. Moreover, DHA lowered enzyme activities of respiratory complexes I, IV, V, and I + III. Mechanistically, the reduction in enzymatic activities was not driven by a dramatic reduction in the abundance of supercomplexes. Instead, replacement of tetralinoleoyl-CL with tetradocosahexaenoyl-CL in biomimetic membranes prevented formation of phospholipid domains that regulate enzyme activity. Tetradocosahexaenoyl-CL inhibited domain organization due to favorable Gibbs free energy of phospholipid mixing. Furthermore, in vitro substitution of tetralinoleoyl-CL with tetradocosahexaenoyl-CL blocked complex IV binding. Finally, reintroduction of linoleic acid, via fusion of phospholipid vesicles to mitochondria isolated from DHA-fed mice, rescued the major losses in the mitochondrial phospholipidome and complexes I, IV, and V activities. Altogether, our results show that replacing linoleic acid with DHA lowers select cardiac enzyme activities by potentially targeting domain organization and phospholipid–protein binding, which has implications for the ongoing debate about polyunsaturated fatty acids and cardiac health.

Mechanical strength studies on degraded waterlogged wood treated with sugars

This study aims to measure the mechanical strength of chemically degraded wood samples and compare the values obtained with fresh wood and degraded wood treated with sugars. The mechanical strength of chemically degraded waterlogged wood samples was determined using a three-point bending system to generate load-deflection curves and subsequently calculate the modulus of elasticity and load to failure longitudinally. The values obtained allow us to compare the mechanical properties of white birch wood samples that were air dried after treatment with 60% w/v solutions of sucrose, trehalose, or sucralose. In addition, the same parameters were measured for fresh white birch wood samples and chemically degraded samples that were allowed to air dry without treatment. Fresh white birch was found to have a longitudinal modulus of elasticity of 11.5 GPa whereas this value decreased by 70% when the wood was degraded. Treatment with sugars increased the measured values of modulus of elasticity up to 36.9 GPa, a substantially higher value than for fresh wood. These data indicate that non-reducing sugars could be useful alternatives to polyethylene glycol for the conservation of waterlogged archaeological wood.

Docosahexaenoic acid regulates the formation of lipid rafts: A unified view from experiment and simulation

Docosahexaenoic acid (DHA, 22:6) is an n-3 polyunsaturated fatty acid (n-3 PUFA) that influences immunological, metabolic, and neurological responses through complex mechanisms. One structural mechanism by which DHA exerts its biological effects is through its ability to modify the physical organization of plasma membrane signaling assemblies known as sphingomyelin/cholesterol (SM/chol)-enriched lipid rafts. Here we studied how DHA acyl chains esterified in the sn-2 position of phosphatidylcholine (PC) regulate the formation of raft and non-raft domains in mixtures with SM and chol on differing size scales. Coarse grained molecular dynamics simulations showed that 1-palmitoyl-2-docosahexaenoylphosphatylcholine (PDPC) enhances segregation into domains more than the monounsaturated control, 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC). Solid state 2H NMR and neutron scattering experiments provided direct experimental evidence that substituting PDPC for POPC increases the size of raft-like domains on the nanoscale. Confocal imaging of giant unilamellar vesicles with a non-raft fluorescent probe revealed that POPC had no influence on phase separation in the presence of SM/chol whereas PDPC drove strong domain segregation. Finally, monolayer compression studies suggest that PDPC increases lipid-lipid immiscibility in the presence of SM/chol compared to POPC. Collectively, the data across model systems provide compelling support for the emerging model that DHA acyl chains of PC lipids tune the size of lipid rafts, which has potential implications for signaling networks that rely on the compartmentalization of proteins within and outside of rafts.

Mechanisms by Which Dietary Fatty Acids Regulate Mitochondrial Structure-Function in Health and Disease

Mitochondria are the energy-producing organelles within a cell. Furthermore, mitochondria have a role in maintaining cellular homeostasis and proper calcium concentrations, building critical components of hormones and other signaling molecules, and controlling apoptosis. Structurally, mitochondria are unique because they have 2 membranes that allow for compartmentalization. The composition and molecular organization of these membranes are crucial to the maintenance and function of mitochondria. In this review, we first present a general overview of mitochondrial membrane biochemistry and biophysics followed by the role of different dietary saturated and unsaturated fatty acids in modulating mitochondrial membrane structure-function. We focus extensively on long-chain n-3 (ω-3) polyunsaturated fatty acids and their underlying mechanisms of action. Finally, we discuss implications of understanding molecular mechanisms by which dietary n-3 fatty acids target mitochondrial structure-function in metabolic diseases such as obesity, cardiac-ischemia reperfusion injury, obesity, type 2 diabetes, nonalcoholic fatty liver disease, and select cancers.