Increased palmitate intake: higher acylcarnitine concentrations without impaired progression of β-oxidation

Palmitic acid (PA) is associated with higher blood concentrations of medium-chain acylcarnitines (MCACs), and we hypothesized that PA may inhibit progression of FA β-oxidation. Using a cross-over design, 17 adults were fed high PA (HPA) and low PA/high oleic acid (HOA) diets, each for 3 weeks. The [1-¹³C]PA and [13-¹³C]PA tracers were administered with food in random order with each diet, and we assessed PA oxidation (PA OX) and serum AC concentration to determine whether a higher PA intake promoted incomplete PA OX. Dietary PA was completely oxidized during the HOA diet, but only about 40% was oxidized during the HPA diet. The [13-¹³C]PA/[1-¹³C]PA ratio of PA OX had an approximate value of 1.0 for either diet, but the ratio of the serum concentrations of MCACs to long-chain ACs (LCACs) was significantly higher during the HPA diet. Thus, direct measurement of PA OX did not confirm that the HPA diet caused incomplete PA OX, despite the modest, but statistically significant, increase in the ratio of MCACs to LCACs in blood.     

DBA/2J Genetic Background Exacerbates Spontaneous Lethal Seizures but Lessens Amyloid Deposition in a Mouse Model of Alzheimer’s Disease

Alzheimer’s disease (AD) is a leading cause of dementia in the elderly and is characterized by amyloid plaques, neurofibrillary tangles (NFTs) and neuronal dysfunction. Early onset AD (EOAD) is commonly caused by mutations in amyloid precursor protein (APP) or genes involved in the processing of APP including the presenilins (e.g. PSEN1 or PSEN2). In general, mouse models relevant to EOAD recapitulate amyloidosis, show only limited amounts of NFTs and neuronal cell dysfunction and low but significant levels of seizure susceptibility. To investigate the effect of genetic background on these phenotypes, we generated APP^swe and PSEN1^de9 transgenic mice on the seizure prone inbred strain background, DBA/2J. Previous studies show that the DBA/2J genetic background modifies plaque deposition in the presence of mutant APP but the impact of PSEN1^de9 has not been tested. Our study shows that DBA/2J.APP^swePSEN1^de9 mice are significantly more prone to premature lethality, likely to due to lethal seizures, compared to B6.APP^swePSEN1^de9 mice—70% of DBA/2J.APP^swePSEN1^de9 mice die between 2-3 months of age. Of the DBA/2J.APP^swePSEN1^de9 mice that survived to 6 months of age, plaque deposition was greatly reduced compared to age-matched B6.APP^swePSEN1^de9 mice. The reduction in plaque deposition appears to be independent of microglia numbers, reactive astrocytosis and complement C5 activity.     

Interaction of pulmonary surfactant protein A with phospholipid liposomes: a kinetic study on head group and fatty acid specificity.

Recent work on surfactant protein A (SP-A) has shown that Ca(2+) induces an active conformation, SP-A, which binds rapidly to liposomes and mediates their aggregation. Employing sensitive real time assays, we have now studied the lipid binding characteristics of the SP-A liposome interaction. From the final equilibrium level of the resonant mirror binding signal, an apparent dissociation constant of ca. K(d)=5 microM is obtained for the complex between SP-A and dipalmitoylphosphatidylcholine (DPPC) liposomes. At nanomolar SP-A concentrations, this complex is formed with a subsecond (0.3 s) reaction time, as measured by light-scattering signals evoked by photolysis of caged Ca(2+). With palmitoyloleoylphosphatidylcholine (POPC), the complex formation proceeds at half the rate, compared to DPPC, leading to a lower final equilibrium level of SP-A lipid interaction. Distearoylphosphatidylcholine (DSPC) shows a stronger interaction than DPPC. Regarding the phospholipid headgroups, phosphatidylinositol (PI) and sphingomyelin (SM) interact comparable to DPPC, while less interaction is seen with phosphatidylethanolamine (PE) or with phosphatidylglycerol (PG). Thus both headgroup and fatty acid composition determine SP-A phospholipid interaction. However, the protein does not exhibit high specificity for either the polar or the apolar moiety of phospholipids.     

Solution structure and backbone dynamics of Calsensin, an invertebrate neuronal calcium-binding protein

Calsensin is an EF-hand calcium-binding protein expressed by a subset of peripheral sensory neurons that fasciculate into a single tract in the leech central nervous system. Calsensin is a 9-kD protein with two EF-hand calcium-binding motifs. Using multidimensional NMR spectroscopy we have determined the solution structure and backbone dynamics of calcium-bound Calsensin. Calsensin consists of four helices forming a unicornate-type four-helix bundle. The residues in the third helix undergo slow conformational exchange indicating that the motion of this helix is associated with calciumbinding. The backbone dynamics of the protein as measured by (15)N relaxation rates and heteronuclear NOEs correlate well with the three-dimensional structure. Furthermore, comparison of the structure of Calsensin with other members of the EF-hand calcium-binding protein family provides insight into plausible mechanisms of calcium and target protein binding.     

Differential regulation of platelet-derived growth factor stimulated migration and proliferation in osteoblastic cells

Osteoblastic migration and proliferation in response to growth factors are essential for skeletal development, bone remodeling, and fracture repair, as well as pathologic processes, such as metastasis. We studied migration in response to platelet-derived growth factor (PDGF, 10 ng/ml) in a wounding model. PDGF stimulated a twofold increase in migration of osteoblastic MC3T3-E1 cells and murine calvarial osteoblasts over 24-48 h. PDGF also stimulated a tenfold increase in 3H-thymidine (3H-TdR) incorporation in MC3T3-E1 cells. Migration and DNA replication, as measured by BrdU incorporation, could be stimulated in the same cell. Blocking DNA replication with aphidicolin did not reduce the distance migrated. To examine the role of mitogen-activated protein (MAP) kinases in migration and proliferation, we used specific inhibitors of p38 MAP kinase, extracellular signal regulated kinase (ERK), and c-Jun N-terminal kinase (JNK). For these signaling studies, proliferation was measured by carboxyfluorescein diacetate succinimidyl ester (CFSE) using flow cytometry. Inhibition of the p38 MAP kinase pathway by SB203580 and SB202190 blocked PDGF-stimulated migration but had no effect on proliferation. Inhibition of the ERK pathway by PD98059 and U0126 inhibited proliferation but did not inhibit migration. Inhibition of JNK activity by SP600125 inhibited both migration and proliferation. Hence, the stimulation of migration and proliferation by PDGF occurred by both overlapping and independent pathways. The JNK pathway was involved in both migration and proliferation, whereas the p38 pathway was predominantly involved in migration and the ERK pathway predominantly involved in proliferation.     

Sesquiterpene lactones from Centaurea repens

Six sesquiterpene lactones have been isolated and characterized from Centaurea repens. They are identified as cynaropicrin, repin, janerin, aguerin B, repdiolide and epoxyrepdiolide.     

Autoinhibition of the kinesin-2 motor KIF17 via dual intramolecular mechanisms

Long-distance transport in cells is driven by kinesin and dynein motors that move along microtubule tracks. These motors must be tightly regulated to ensure the spatial and temporal fidelity of their transport events. Transport motors of the kinesin-1 and kinesin-3 families are regulated by autoinhibition, but little is known about the mechanisms that regulate kinesin-2 motors. We show that the homodimeric kinesin-2 motor KIF17 is kept in an inactive state in the absence of cargo. Autoinhibition is caused by a folded conformation that enables nonmotor regions to directly contact and inhibit the enzymatic activity of the motor domain. We define two molecular mechanisms that contribute to autoinhibition of KIF17. First, the C-terminal tail interferes with microtubule binding; and second, a coiled-coil segment blocks processive motility. The latter is a new mechanism for regulation of kinesin motors. This work supports the model that autoinhibition is a general mechanism for regulation of kinesin motors involved in intracellular trafficking events.     

Further Mathematical Modelling of Mating Sex Ratios & Male Strategies with Special Relevance to Human Life History

Influential models of male reproductive strategies have often ignored the importance of mate guarding, focusing instead on trade-offs between fitness gained through care for dependants in a pair bond versus fitness from continued competition for additional mates. Here we follow suggestions that mate guarding is a distinct alternative strategy that plays a crucial role, with special relevance to the evolution of our own lineage. Human pair bonding may have evolved in concert with the evolution of our grandmothering life history, which entails a shift to male-biased sex ratios in the fertile ages. As that sex ratio becomes more male biased, payoffs for mate-guarding increase due to partner scarcity. We present an ordinary differential equation model of mutually exclusive strategies (dependant care, multiple mating, and mate guarding), calculate steady-state frequencies and perform bifurcation analysis on parameters of care and guarding efficiency. Mate guarding triumphs over alternate strategies when populations are male biased, and guarding is fully efficient. When guarding does not ensure complete certainty of paternity, and multiple maters are able to gain some paternity from guarders, multiple mating can coexist with guarding. At female-biased sex ratios, multiple mating takes over, unless the benefit of care to the number of surviving offspring produced by the mates of carers is large.