Pro- and anti-oxidant effects of polyunsaturated fatty acid supplementation in HepG2 cells

PUFA are bioactive nutrients thought to be effective in the prevention of many chronic diseases. PUFA susceptibility to free radical oxidation represents the other side of the coin, and the role of PUFA as pro- or anti-oxidants is still an unanswered question. In this study we supplemented HepG2 cells with different PUFA, and observed different effects on cytotoxicity, oxidation and modulation of antioxidant defenses. These were not simply related to the length of carbon chain, or to the number and position of double bonds. ARA supply evidenced the induction of oxidative damage, while DHA supplemented cells appeared richer in antioxidant defenses. To our knowledge, our study is the first evidencing the different pro- or anti-oxidant effect of different fatty acids when supplemented to cells. Overall, this points out the importance of not generalizing dietary recommendations considering PUFA as one category, but to extend them to the individual fatty acids.     

Global analysis of Cdc14 phosphatase reveals diverse roles in mitotic processes

Cdc14 phosphatase regulates multiple events during anaphase and is essential for mitotic exit in budding yeast. Cdc14 is regulated in both a spatial and temporal manner. It is sequestered in the nucleolus for most of the cell cycle by the nucleolar protein Net1 and is released into the nucleus and cytoplasm during anaphase. To identify novel binding partners of Cdc14, we used affinity purification of Cdc14 and mass spectrometric analysis of interacting proteins from strains in which Cdc14 localization or catalytic activity was altered. To alter Cdc14 localization, we used a strain deleted for NET1, which causes full release of Cdc14 from the nucleolus. To alter Cdc14 activity, we generated mutations in the active site of Cdc14 (C283S or D253A), which allow binding of substrates, but not dephosphorylation, by Cdc14. Using this strategy, we identified new interactors of Cdc14, including multiple proteins involved in mitotic events. A subset of these proteins displayed increased affinity for catalytically inactive mutants of Cdc14 compared with the wild-type version, suggesting they are likely substrates of Cdc14. We have also shown that several of the novel Cdc14-interacting proteins, including Kar9 (a protein that orients the mitotic spindle) and Bni1 and Bnr1 (formins that nucleate actin cables and may be important for actomyosin ring contraction) are specifically dephosphorylated by Cdc14 in vitro and in vivo. Our findings suggest the dephosphorylation of the formins may be important for their observed localization change during exit from mitosis and indicate that Cdc14 targets proteins involved in wide-ranging mitotic events.     

Homeodomain-interacting protein kinase-2 stabilizes p27(kip1) by its phosphorylation at serine 10 and contributes to cell motility

HIPK2 is a serine/threonine kinase that acts as a coregulator of an increasing number of factors involved in cell survival and proliferation during development and in response to different types of stress. Here we report on a novel target of HIPK2, the cyclin-dependent kinase inhibitor p27(kip1). HIPK2 phosphorylates p27(kip1) in vitro and in vivo at serine 10, an event that accounts for 80% of the total p27(kip1) phosphorylation and plays a crucial role in the stability of the protein. Indeed, HIPK2 depletion by transient or stable RNA interference in tumor cells of different origin was consistently associated with strong reduction of p27(kip1) phosphorylation at serine 10 and of p27(kip1) stability. An initial evaluation of the functional relevance of this HIPK2-mediated regulation of p27(kip1) revealed a contribution to cell motility, rather than to cell proliferation, but only in cells that do not express wild-type p53.     

Plant D-2-hydroxyglutarate dehydrogenase participates in the catabolism of lysine especially during senescence

D-2-Hydroxyglutarate dehydrogenase (D-2HGDH) catalyzes the specific and efficient oxidation of D-2-hydroxyglutarate (D-2HG) to 2-oxoglutarate using FAD as a cofactor. In this work, we demonstrate that D-2HGDH localizes to plant mitochondria and that its expression increases gradually during developmental and dark-induced senescence in Arabidopsis thaliana, indicating an enhanced demand of respiration of alternative substrates through this enzymatic system under these conditions. Using loss-of-function mutants in D-2HGDH (d2hgdh1) and stable isotope dilution LC-MS/MS, we found that the D-isomer of 2HG accumulated in leaves of d2hgdh1 during both forms of carbon starvation. In addition to this, d2hgdh1 presented enhanced levels of most TCA cycle intermediates and free amino acids. In contrast to the deleterious effects caused by a deficiency in D-2HGDH in humans, d2hgdh1 and overexpressing lines of D-2HGDH showed normal developmental and senescence phenotypes, indicating a mild role of D-2HGDH in the tested conditions. Moreover, metabolic fingerprinting of leaves of plants grown in media supplemented with putative precursors indicated that D-2HG most probably originates during the catabolism of lysine. Finally, the L-isomer of 2HG was also detected in leaf extracts, indicating that both chiral forms of 2HG participate in plant metabolism.     

The natural frequency of the foot-surface cushion during the stance phase of running

Researchers have reported on the stiffness of running in holistic terms, i.e. for the structures that are undergoing deformation as a whole rather than in terms of specific locations. This study aimed to estimate both the natural frequency and the viscous damping coefficient of the human foot-surface cushion, during the period between the heel strike and the mid-stance phase of running, using a purposely developed one degree-of-freedom inverted pendulum state space model of the leg. The model, which was validated via a comparison of measured and estimated ground reaction forces, incorporated a novel use of linearized and extended Kalman filter estimators. Investigation of the effect of variation of the natural frequency and/or the damping of the cushioning mechanism during running, using the said model, revealed the natural frequency of running on said foot-surface cushion, during the stance phase, to lie between 5 and 11 Hz. The "extended Kalman filter (EKF)" approach, that was used here for the first time to directly apply measured ground forces, may be widely applicable to the identification process of combined estimation of both unknown physiological state and mechanical characteristics of the environment in an inverse dynamic model.     

The Bantu expansion revisited: a new analysis of Y chromosome variation in Central Western Africa

The current distribution of Bantu languages is commonly considered to be a consequence of a relatively recent population expansion (3-5kya) in Central Western Africa. While there is a substantial consensus regarding the centre of origin of Bantu languages (the Benue River Valley, between South East Nigeria and Western Cameroon), the identification of the area from where the population expansion actually started, the relation between the processes leading to the spread of languages and peoples and the relevance of local migratory events remain controversial. In order to shed new light on these aspects, we studied Y chromosome variation in a broad dataset of populations encompassing Nigeria, Cameroon, Gabon and Congo. Our results evidence an evolutionary scenario which is more complex than had been previously thought, pointing to a marked differentiation of Cameroonian populations from the rest of the dataset. In fact, in contrast with the current view of Bantu speakers as a homogeneous group of populations, we observed an unexpectedly high level of interpopulation genetic heterogeneity and highlighted previously undetected diversity for lineages associated with the diffusion of Bantu languages (E1b1a (M2) sub-branches). We also detected substantial differences in local demographic histories, which concord with the hypotheses regarding an early diffusion of Bantu languages into the forest area and a subsequent demographic expansion and migration towards eastern and western Africa.