Suitability and limitations of mesenchymal stem cells to elucidate human bone illness

Functional impairment of mesenchymal stem cells(MSCs),osteoblast progenitor cells,has been proposed to be a pathological mechanism contributing to bone disorders,such as osteoporosis(the most common bone disease)and other rare inherited skeletal dysplasias.Pathological bone loss can be caused not only by an enhanced bone resorption activity but also by hampered osteogenic differentiation of MSCs.The majority of the current treatment options counteract bone loss,and therefore bone fragility by blocking bone resorption.These socalled antiresorptive treatments,in spite of being effective at reducing fracture risk,cannot be administered for extended periods due to security concerns.Therefore,there is a real need to develop osteoanabolic therapies to promote bone formation.Human MSCs emerge as a suitable tool to study the etiology of bone disorders at the cellular level as well as to be used for cell therapy purposes for bone diseases.This review will focus on the most relevant findings using human MSCs as an in vitro cell model to unravel pathological bone mechanisms and the application and outcomes of human MSCs in cell therapy clinical trials for bone disease.

Short-Term Effects of Ozone on Mortality： Comparative Analysis of Urban and Suburban Zones in Madrid （Spain）

A large number of papers published in the last decades are related to the effect of ozone exposure on mortality worldwide. Several studies have been performed to investigate the effect of ozone on mortality in Madrid （Spain）, but the findings of these local reports were focused only on the Madrid city. The association of daily concentrations of ozone with daily mortality was investigated using autoregressive Poisson regression models. This study explores the effects of ozone on all causes except accidents, cardiovascular and respiratory short-term mortality in two areas of the Madrid region： an urban area constituted by the Madrid municipality and an industrial sub-urban area surrounding the city. Using three years of daily data （2003-2005）, it was analyzed the all-ages populations and the over-64 age groups. The average ozone concentrations over the study period were 54.07 ± 27.17 μg/m3 in the Madrid municipality and 70.09 ± 32.96 μg/m3 in the sub-urban municipalities surrounding the city. Our results in the all-ages group indicated that 0.69% of all causes except accidents, 1.15% of cardiovascular and 1.56% of respiratory daily deaths, respectively, could be attributed to exposure to ozone in the Madrid city, whereas 11.69% of daily respiratory deaths were attributable to ozone exposure in the Madrid sub-urban surroundings. Our results show a clear association between mortality and ozone exposure. The spatial heterogeneity of ozone effects on short-term mortality throughout the Madrid region may have implications for local environmental policies and also for social and health services planning.

The Study of Carbamoyl Phosphate Synthetase 1 Deficiency Sheds Light on the Mechanism for Switching On/Off the Urea Cycle

Carbamoyl phosphate synthetase i （CPS1） deficiency （CPS1D） is an inborn error of the urea cycle having autosomal （2q34） recessive inheritance that can cause hyperammonemia and neonatal death or mental retardation. We analyzed the effects on CPS1 activity, kinetic parameters and enzyme stability of missense mutations reported in patients with CPS1 deficiency that map in the 20-kDa C-terminal domain of the enzyme. This domain turns on or off the enzyme depending on whether the essential allosteric activator of CPS 1, N-acetyl- L-glutamate （NAG）, is bound or is not bound to it. To carry out the present studies, we exploited a novel system that allows the expression in vitro and the purification of human CPS1, thus permitting site-directed mutagenesis. These studies have clarified disease causation by individual mutations, identifying functionally important residues, and revealing that a number of mutations decrease the affinity of the enzyme for NAG. Patients with NAG affinity-decreasing mutations might benefit from NAG site saturation therapy with N-carbamyl-L- glutamate （a registered drug, the analog of NAG）. Our results, together with additional present and prior site-directed mutagenesis data for other residues mapping in this domain, suggest an NAG-triggered conformational change in the 134-~4 loop of the C-terminal domain of this enzyme. This change might be an early event in the NAG activation process. Molecular dynamics simulations that were restrained according to the observed effects of the mutations are consistent with this hypothesis, providing further backing for this structurally plausible signaling mechanism by which NAG could trigger urea cycle activation via CPS1.