1 In the spontaneously hypertensive rat (SHR) and aging Wistar-Kyoto rats (WKY), acetylcholine releases an endothelium-derived contracting factor (EDCF) produced by endothelial cyclooxygenase-1, which stimulates thromboxane A 2 receptors (TP receptors) on vascular smooth muscle. The purpose of the present study was to identify this EDCF by measuring changes in isometric tension and the release of various prostaglandins by acetylcholine. 2 In isolated aortic rings of SHR, U 46619, prostaglandin (PG) H 2 , PGF 2a , PGE 2 , PGD 2 , prostacyclin (PGI 2 ) and 8-isoprostane, all activate TP receptors of the vascular smooth muscle to produce a contraction (U 46619)8-isoprostane ¼ PGF 2a ¼ PGH 2 4PGE 2 ¼ PGD 2 4PGI 2 ). The contractions produced by PGH 2 and PGI 2 were fast and transient, mimicking endothelium-dependent contractions. PGI 2 did not relax isolated aortic rings of WKY and SHR. 3 Acetylcholine evoked the endothelium-dependent release of thromboxane A 2 , PGF 2a , PGE 2 , PGI 2 and most likely PGH 2 (PGI 2 )PGF 2a XPGE 2 4TXA 2 48-isoprostane, PGD 2 ). Dazoxiben abolished the production of thromboxane A 2 , but did not influence the endothelium-dependent contractions to acetylcholine. 4 The release of PGI 2 was significantly larger in the aorta of SHR than in WKY, and the former was more sensitive to the contractile effect of PGI 2 than the latter. The inhibition of PGI-synthase was associated with an increase in PGH 2 spillover and the enhancement of acetylcholine-induced endothelium-dependent contractions. 5 Thus, in the aorta of SHR and aging WKY, the endothelium-dependent contractions elicited by acetylcholine most likely involve the release of PGI 2 with a concomitant contribution of PGH 2 .

The effect of neutrophil elastase on the functional status of gelatinases was studied in an hamster model developed by intratracheal administration of lipopolysaccharide followed by in situ cell activation with phorbol myristate acetate. This resulted in the production in bronchoalveolar lavage fluids, in addition to the matrix metalloproteinase MMP-9, of a 75 kDa gelatinase associated with collagenolytic activity. Treatment in vivo with an elastase inhibitor abolished the latter activity. Since, in addition, elastase activates in vitro purified MMP-9 gelatinase into a similar 75 kDa entity, these data suggest that elastase may be a physiological activator of MMP-9 in vivo.

Autotaxin catalyzes the transformation of lyso-phosphatidylcholine in lyso-phosphatidic acid (LPA). LPA is a phospholipid possessing a large panel of activity, in particular as a motility factor or as a growth signal, through its G-protein coupled seven transmembrane receptors. Indirect evidence strongly suggests that autotaxin is the main, if not the only source of circulating LPA. Because of its central role in pathologic conditions, such as oncology and diabetes/obesity, the biochemical properties of autotaxin has attracted a lot of attention, but confirmation of its role in pathology remains elusive. One way to validate and/or confirm its central role, is to find potent and selective inhibitors. A systematic screening of several thousand compounds using a colorimetric assay and taking advantage of the phosphodiesterase activity of autotaxin that requires the enzymatic site than for LPA generation, led to the discovery of a potent nanomolar inhibitor, [4-(tetradecanoylamino)benzyl]phosphonic acid (S32826). This compound was inhibitory toward the various autotaxin isoforms, using an assay measuring the [ 14 C]lyso-phosphatidylcholine conversion into [ 14 C]LPA. We also evaluated the activity of S32826 in cellular models of diabesity and oncology. Nevertheless, the poor in vivo stability and/or bioavailability of the compound did not permit to use it in animals. S32826 is the first reported inhibitor of autotaxin with an IC 50 in the nanomolar range that can be used to validate the role of autotaxin in various pathologies in cellular models.

The mitochondrial uncoupling protein of brown adipose tissue (UCP1) was expressed in skeletal muscle and heart of transgenic mice at levels comparable with the amount found in brown adipose tissue mitochondria. These transgenic mice have a lower body weight, and when related to body weight, food intake and energy expenditure are increased. A specific reduction of muscle mass was observed but varied according to the contractile activity of muscles. Heart and soleus muscle are unaffected, indicating that muscles undergoing regular contractions, and therefore with a continuous mitochondrial ATP production, are protected. In contrast, the gastrocnemius and plantaris muscles showed a severely reduced mass and a fast to slow shift in fiber types promoting mainly IIa and IIx fibers at the expense of fastest and glycolytic type IIb fibers. These observations are interpreted as a consequence of the strong potential dependence of the UCP1 protonophoric activity, which ensures a negligible proton leak at the membrane potential observed when mitochondrial ATP production is intense. Therefore UCP1 is not deleterious for an intense mitochondrial ATP production and this explains the tolerance of the heart to a high expression level of UCP1. In muscles at rest, where ATP production is low, the rise in membrane potential enhances UCP1 activity. The proton return through UCP1 mimics the effect of a sustained ATP production, permanently lowering mitochondrial membrane potential. This very likely constitutes the origin of the signal leading to the transition in fiber types at rest. Uncoupling protein 1 (UCP1)1 is expressed exclusively in brown adipose tissue (reviewed in Refs. 1 and 2). Its presence in brown fat mitochondria is responsible for heat production by the mitochondria in brown adipocytes. UCP1 allows return of protons into the matrix without ATP synthesis, and therefore dissipates the proton electrochemical gradient built up after proton pumping by the respiratory complexes. When this gradient reaches high values this makes proton pumping and thus substrate oxidation less easy and therefore slows down respiration. Activity of UCP1 prevents this rise of the proton gradient and therefore allows respiration to occur at a high rate, without phosphorylation of ADP into ATP, and therefore energy is instantaneously released as heat. The essential role of the UCP1 in thermogenesis is illustrated by the cold intolerance of mice whose ucp1 gene has been disrupted (3). Recently, two genes coding for proteins highly homologous to UCP1 have been described (reviewed in Refs. 4 -6). Although there are experimental evidence supporting the hypothesis of an uncoupling activity of these proteins (7,8), their physiological relevance is still incompletely resolved (9 -11). We intended to obtain transgenic mice overexpressing the UCP1 in skeletal muscles, with the aim of examining the effects of the presence of this uncoupling protein on the pattern of myosin expression and metabolic characteristics of locomotor muscles. Two other reports pub...