Paul Sabatier University

About: Paul Sabatier University is a education organization based out in Toulouse, France. It is known for research contribution in the topics: Population & Adipose tissue. The organization has 15431 authors who have published 23386 publications receiving 858364 citations.

Height-diameter allometry of tropical forest trees

Abstract: . Tropical tree height-diameter (H:D) relationships may vary by forest type and region making large-scale estimates of above-ground biomass subject to bias if they ignore these differences in stem allometry. We have therefore developed a new global tropical forest database consisting of 39 955 concurrent H and D measurements encompassing 283 sites in 22 tropical countries. Utilising this database, our objectives were: 1. to determine if H:D relationships differ by geographic region and forest type (wet to dry forests, including zones of tension where forest and savanna overlap). 2. to ascertain if the H:D relationship is modulated by climate and/or forest structural characteristics (e.g. stand-level basal area, A). 3. to develop H:D allometric equations and evaluate biases to reduce error in future local-to-global estimates of tropical forest biomass. Annual precipitation coefficient of variation (PV), dry season length (SD), and mean annual air temperature (TA) emerged as key drivers of variation in H:D relationships at the pantropical and region scales. Vegetation structure also played a role with trees in forests of a high A being, on average, taller at any given D. After the effects of environment and forest structure are taken into account, two main regional groups can be identified. Forests in Asia, Africa and the Guyana Shield all have, on average, similar H:D relationships, but with trees in the forests of much of the Amazon Basin and tropical Australia typically being shorter at any given D than their counterparts elsewhere. The region-environment-structure model with the lowest Akaike's information criterion and lowest deviation estimated stand-level H across all plots to within amedian −2.7 to 0.9% of the true value. Some of the plot-to-plot variability in H:D relationships not accounted for by this model could be attributed to variations in soil physical conditions. Other things being equal, trees tend to be more slender in the absence of soil physical constraints, especially at smaller D. Pantropical and continental-level models provided less robust estimates of H, especially when the roles of climate and stand structure in modulating H:D allometry were not simultaneously taken into account.

Liver PPARα is crucial for whole-body fatty acid homeostasis and is protective against NAFLD

Abstract: Objective Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor expressed in tissues with high oxidative activity that plays a central role in metabolism. In this work, we investigated the effect of hepatocyte PPARα on non-alcoholic fatty liver disease (NAFLD). Design We constructed a novel hepatocyte-specific PPARα knockout ( Pparα hep−/−) mouse model. Using this novel model, we performed transcriptomic analysis following fenofibrate treatment. Next, we investigated which physiological challenges impact on PPARα. Moreover, we measured the contribution of hepatocytic PPARα activity to whole-body metabolism and fibroblast growth factor 21 production during fasting. Finally, we determined the influence of hepatocyte-specific PPARα deficiency in different models of steatosis and during ageing. Results Hepatocyte PPARα deletion impaired fatty acid catabolism, resulting in hepatic lipid accumulation during fasting and in two preclinical models of steatosis. Fasting mice showed acute PPARα-dependent hepatocyte activity during early night, with correspondingly increased circulating free fatty acids, which could be further stimulated by adipocyte lipolysis. Fasting led to mild hypoglycaemia and hypothermia in Pparα hep−/− mice when compared with Ppar α−/− mice implying a role of PPARα activity in non-hepatic tissues. In agreement with this observation, Pparα −/− mice became overweight during ageing while Ppar αhep−/− remained lean. However, like Ppar α−/− mice, Ppar αhep−/− fed a standard diet developed hepatic steatosis in ageing. Conclusions Altogether, these findings underscore the potential of hepatocyte PPARα as a drug target for NAFLD.

Bioinorganic chemistry of copper and zinc ions coordinated to amyloid-β peptide

Abstract: In the present perspective, we give a critical review on the coordination chemistry of the metal ions copper and zinc to the amyloid-β (Aβ) peptide; such complexes have been linked to Alzheimer's disease. We focus on two main issues: the identification of the coordination sphere of the Cu(II) and Zn(II) ions and the affinity of these metal ions towards the peptide. With the aim to come up with as few as possible valuable structural models and binding affinity values, we critically review the divergent propositions reported in the literature and take into account the experimental differences and the limits of the methods used in the published studies. We propose that: (i) the conditional dissociation constant of the Cu(Aβ) complexes lies in the range of 10 pM to 100 nM, with a preference for the region between 100 pM to 1 nM. (ii) Two most likely coordination modes for the predominant form of the Cu(Aβ) complexes at physiological pH can be retained, both being 3N1O distorted square planar. In the first model, the Cu(II) ion is coordinated by the Nτ atoms of the three His residues and the carboxylate of the Asp1. In the second model, both the N-terminus and the carboxylate functions of Asp1 are ligated together with the Nτ of His6 and of His13 (or His14). An equilibrium between these two forms at room temperature, and a preferentially freezing out of the second one would explain most of the divergences in the published results (in particular, between those obtained by EPR and NMR). (iii) The apparent dissociation constants of Zn(Aβ) in various buffers are in the range of 1 to 20 μM (a 10 times lower conditional dissociation constant can be estimated. (iv) For the Zn(II) coordination, the implication of the three His and the Asp1 residues is consensual. The Asp1 can be coordinated by the carboxylate and/or the N-terminus functions. Additional ligands are possible, such as Glu11 or H2O.