生物标记物之警示信号

寻找生物标记——能对阿尔茨海默氏症的侵入发出警告信号的标记物——的工作一直在进行着。而开展这项研究的目的旨在赢得对这一疾病治疗的主动权．探索阿尔茨海默氏症防治的新模式     

Requirement for mast cell growth factor for primordial germ cell survival in culture.

Mast-cell growth factor (MGF) is encoded by the murine steel (Sl) locus and is a ligand for the tyrosine kinase receptor protein encoded by the proto-oncogene c-kit at the murine dominant white spotting (W) locus. Mutations at both these loci affect mast cells, primordial germ cells (PGCs), haemopoietic stem cells and melanocytes. In many Sl and W mutants, the rapid proliferation of PGC that normally occurs between day 7 and 13.5 of embryonic development fails to occur. As c-kit is expressed in PGCs while MGF is expressed in the surrounding mesenchyme, MGF might promote the proliferation of PGCs. Here we report that MGF is essential for PGC survival in culture, but does not stimulate PGC proliferation. Moreover, whereas both the transmembrane and soluble proteolytic cleavage forms of MGF stimulate mast-cell proliferation, soluble MGF has a relatively limited ability to support survival of PGCs in culture, thus explaining the sterility in mice carrying the steel-dickie (Sld) mutation, which encodes only a soluble form of MGF, and providing a functional role for a transmembrane growth factor.     

Characterization of the human cysteinyl leukotriene CysLT1 receptor.

The cysteinyl leukotrienes-leukotriene C4(LTC4), leukotriene D4(LTD4) and leukotriene E4(LTE4)-are important mediators of human bronchial asthma. Pharmacological studies have determined that cysteinyl leukotrienes activate at least two receptors, designated CysLT1 and CysLT2. The CysLT1-selective antagonists, such as montelukast (Singulair), zafirlukast (Accolate) and pranlukast (Onon), are important in the treatment of asthma. Previous biochemical characterization of CysLT1 antagonists and the CysLT1 receptor has been in membrane preparations from tissues enriched for this receptor. Here we report the molecular and pharmacological characterization of the cloned human CysLT1 receptor. We describe the functional activation (calcium mobilization) of this receptor by LTD4 and LTC4, and competition for radiolabelled LTD4 binding to this receptor by the cysteinyl leukotrienes and three structurally distinct classes of CysLT1-receptor antagonists. We detected CysLT1-receptor messenger RNA in spleen, peripheral blood leukocytes and lung. In normal human lung, expression of the CysLT1-receptor mRNA was confined to smooth muscle cells and tissue macrophages. Finally, we mapped the human CysLT1-receptor gene to the X chromosome.     

Interleukin-2 signals during priming are required for secondary expansion of CD8+ memory T cells

Although interleukin-2 (IL-2) was initially characterized as the primary T-cell growth factor following in vitro activation, less is known about its role in shaping T-cell responses to acute infections in vivo. The use of IL-2- or IL-2-receptor-deficient mice is problematic owing to their early development of autoimmunity, attributable to the central role of IL-2 in the generation, maintenance and function of CD4+CD25+ regulatory T cells. To bypass these inherent difficulties, we have studied the effect of IL-2 on T-cell responses to acute infections by adopting a mixed chimaera strategy in which T cells lacking the high-affinity IL-2 receptor could be studied in an otherwise healthy mouse containing a full complement of regulatory T cells. Here we show that although IL-2 signalling to pathogen-specific CD8+ T cells affects the number of developing effector and memory cells very little, it is required for the generation of robust secondary responses. This is not due to an altered T-cell-receptor repertoire development or selection, and does not reflect an acute requirement for IL-2 during secondary activation and expansion. Rather, we demonstrate a previously unappreciated role for IL-2 during primary infection in programming the development of CD8+ memory T cells capable of full secondary expansion. These results have important implications for the development of vaccination or immunotherapeutic strategies aimed at boosting memory T-cell function.     

The arrangement of the three cone classes in the living human eye

Human colour vision depends on three classes of receptor, the short- (S), medium- (M), and long- (L) wavelength-sensitive cones. These cone classes are interleaved in a single mosaic so that, at each point in the retina, only a single class of cone samples the retinal image. As a consequence, observers with normal trichromatic colour vision are necessarily colour blind on a local spatial scale. The limits this places on vision depend on the relative numbers and arrangement of cones. Although the topography of human S cones is known, the human L- and M-cone submosaics have resisted analysis. Adaptive optics, a technique used to overcome blur in ground-based telescopes, can also overcome blur in the eye, allowing the sharpest images ever taken of the living retina. Here we combine adaptive optics and retinal densitometry to obtain what are, to our knowledge, the first images of the arrangement of S, M and L cones in the living human eye. The proportion of L to M cones is strikingly different in two male subjects, each of whom has normal colour vision. The mosaics of both subjects have large patches in which either M or L cones are missing. This arrangement reduces the eye's ability to recover colour variations of high spatial frequency in the environment but may improve the recovery of luminance variations of high spatial frequency.     

Haematopoietic stem cells do not transdifferentiate into cardiac myocytes in myocardial infarcts

The mammalian heart has a very limited regenerative capacity and, hence, heals by scar formation. Recent reports suggest that haematopoietic stem cells can transdifferentiate into unexpected phenotypes such as skeletal muscle, hepatocytes, epithelial cells, neurons, endothelial cells and cardiomyocytes, in response to tissue injury or placement in a new environment. Furthermore, transplanted human hearts contain myocytes derived from extra-cardiac progenitor cells, which may have originated from bone marrow. Although most studies suggest that transdifferentiation is extremely rare under physiological conditions, extensive regeneration of myocardial infarcts was reported recently after direct stem cell injection, prompting several clinical trials. Here, we used both cardiomyocyte-restricted and ubiquitously expressed reporter transgenes to track the fate of haematopoietic stem cells after 145 transplants into normal and injured adult mouse hearts. No transdifferentiation into cardiomyocytes was detectable when using these genetic techniques to follow cell fate, and stem-cell-engrafted hearts showed no overt increase in cardiomyocytes compared to sham-engrafted hearts. These results indicate that haematopoietic stem cells do not readily acquire a cardiac phenotype, and raise a cautionary note for clinical studies of infarct repair.     

Crystal structure of human cytochrome P450 2C9 with bound warfarin

Cytochrome P450 proteins (CYP450s) are membrane-associated haem proteins that metabolize physiologically important compounds in many species of microorganisms, plants and animals. Mammalian CYP450s recognize and metabolize diverse xenobiotics such as drug molecules, environmental compounds and pollutants. Human CYP450 proteins CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 are the major drug-metabolizing isoforms, and contribute to the oxidative metabolism of more than 90% of the drugs in current clinical use. Polymorphic variants have also been reported for some CYP450 isoforms, which has implications for the efficacy of drugs in individuals, and for the co-administration of drugs. The molecular basis of drug recognition by human CYP450s, however, has remained elusive. Here we describe the crystal structure of a human CYP450, CYP2C9, both unliganded and in complex with the anti-coagulant drug warfarin. The structure defines unanticipated interactions between CYP2C9 and warfarin, and reveals a new binding pocket. The binding mode of warfarin suggests that CYP2C9 may undergo an allosteric mechanism during its function. The newly discovered binding pocket also suggests that CYP2C9 may simultaneously accommodate multiple ligands during its biological function, and provides a possible molecular basis for understanding complex drug-drug interactions.     

Prion disease: horizontal prion transmission in mule deer

Epidemics of contagious prion diseases can be perpetuated by horizontal (animal to animal) and maternal (dam to offspring, before or after birth) transmission, but the relative importance of each mechanism is unclear. Here we compare the incidence of chronic wasting disease (CWD) in captive mule deer (Odocoileus hemionus) that is attributable to horizontal or maternal transmission. We find that horizontal transmission is remarkably efficient, producing a high incidence of disease (89%) in a cohort of deer in which maternal transmission was improbable. Our results indicate that horizontal transmission is likely to be important in sustaining CWD epidemics.