Inhibitor of apoptosis protein survivin regulates vascular injury

Survivin (also termed Birc5) belongs to the family of genes known as inhibitors of apoptosis, and it has been implicated in both prevention of cell death and control of mitosis. The survivin pathway is exploited in cancer, but its potential role in vascular injury is unknown. Here, we show that balloon-mediated arterial injury in rabbits resulted in expression of survivin in vascular cells. Serum or PDGF-AB stimulated survivin expression in cultured smooth-muscle cells (SMCs), which suppressed apoptosis and prevented caspase activation. Adenoviral delivery of a phosphorylation-defective survivin mutant reversed the cytoprotective effect of PDGF in SMCs without affecting mitotic progression, suppressed neointimal formation in wire-injured mouse femoral arteries, and induced vascular cell apoptosis in vivo. These data identify survivin as a critical regulator of SMC apoptosis after acute vascular injury. Disrupting the survivin pathway may provide a novel therapy to limit pathological vessel-wall remodeling.     

The meso-angioblast: a multipotent,self-renewing cell that originates from the dorsal aorta and differentiates into most mesodermal tissues

We have previously reported the origin of a class of skeletal myogenic cells from explants of dorsal aorta. This finding disagrees with the known origin of all skeletal muscle from somites and has therefore led us to investigate the in vivo origin of these cells and, moreover, whether their fate is restricted to skeletal muscle, as observed in vitro under the experimental conditions used. To address these issues, we grafted quail or mouse embryonic aorta into host chick embryos. Donor cells, initially incorporated into the host vessels, were later integrated into mesodermal tissues, including blood, cartilage, bone, smooth, skeletal and cardiac muscle. When expanded on a feeder layer of embryonic fibroblasts, the clonal progeny of a single cell from the mouse dorsal aorta acquired unlimited lifespan, expressed hemo-angioblastic markers (CD34, Flk1 and Kit) at both early and late passages, and maintained multipotency in culture or when transplanted into a chick embryo. We conclude that these newly identified vessel-associated stem cells, the meso-angioblasts, participate in postembryonic development of the mesoderm, and we speculate that postnatal mesodermal stem cells may be derived from a vascular developmental origin.     

The role of [Delta]1-pyrroline-5-carboxylate dehydrogenase in proline degradation

In response to stress, plants accumulate Pro, requiring degradation after release from adverse conditions. Delta1-Pyrroline-5-carboxylate dehydrogenase (P5CDH), the second enzyme for Pro degradation, is encoded by a single gene expressed ubiquitously. To study the physiological function of P5CDH, T-DNA insertion mutants in AtP5CDH were isolated and characterized. Although Pro degradation was undetectable in p5cdh mutants, neither increased Pro levels nor an altered growth phenotype were observed under normal conditions. Thus AtP5CDH is essential for Pro degradation but not required for vegetative plant growth. External Pro application caused programmed cell death, with callose deposition, reactive oxygen species production, and DNA laddering, involving a salicylic acid signal transduction pathway. p5cdh mutants were hypersensitive toward Pro and other molecules producing P5C, such as Arg and Orn. Pro levels were the same in the wild type and mutants, but P5C was detectable only in p5cdh mutants, indicating that P5C accumulation may be the cause for Pro hypersensitivity. Accordingly, overexpression of AtP5CDH resulted in decreased sensitivity to externally supplied Pro. Thus, Pro and P5C/Glu semialdehyde may serve as a link between stress responses and cell death.     

Nitroarginine methyl ester and canavanine lower intracellular reduced glutathione

In rat glial cells, arginine analogs N(G)-nitroarginine methyl ester (both D- and L-stereoisomer) and L-canavanine lower the intracellular levels of reduced glutathione, stimulate the pentose phosphate pathway, increase the level of malonyldialdehyde, and increase the leakage of lactate dehydrogenase. These effects are not related to the inhibition of nitric oxide synthase and depend on the oxidation of intracellular thiols; indeed, there are no signs of lipoperoxidation and cytotoxicity in cells previously loaded with glutathione. Furthermore, these arginine analogs elicit an oxidative burst in N11 cells and decrease the detectable level of both glutathione and dithiothreitol in cell-free experiments. These effects were not observed with the arginine analog N(G)-monomethyl-L-arginine, suggesting that the substituting moiety in (or near) the guanidine group could modify the reactivity of the arginine analogs with thiol compounds.     

CD40-induced aggregation of MHC class II and CD80 on the cell surface leads to an early enhancement in antigen presentation

Ligation of CD40 on B cells increases their ability to present Ag and to activate MHC class II (MHC-II)-restricted T cells. How this occurs is not entirely clear. In this study we demonstrate that CD40 ligation on Ag-presenting B cells (APC) for a short period between 30 min and 3 h has a rapid, augmenting effect on the ability of a B cell line and normal B cells to activate T cells. This is not due to alterations in Ag processing or to an increase in surface expression of CD80, CD86, ICAM-1, or MHC-II. This effect is particularly evident with naive, resting T lymphocytes and appears to be more pronounced under limiting Ag concentrations. Shortly after CD40 ligation on a B cell line, MHC-II and CD80 progressively accumulated in cholesterol-enriched microdomains on the cell surface, which correlated with an initial enhancement in their Ag presentation ability. Moreover, CD40 ligation induced a second, late, more sustained enhancement of Ag presentation, which correlates with a significant increase in CD80 expression by APC. Thus, CD40 signaling enhances the efficiency with which APC activate T cells by at least two related, but distinct, mechanisms: an early stage characterized by aggregation of MHC-II and CD80 clusters, and a late stage in which a significant increase in CD80 expression is observed. These results raise the possibility that one important role of CD40 is to contribute to the formation of the immunological synapse on the APC side.     

Activation of peroxisome proliferator-activated receptors α and γ1 inhibits human smooth muscle cell proliferation

Atherosclerotic lesions occur as a result of excess lipid deposition within the vascular tissues. The peroxisome proliferator-activated receptors (PPARs) present in adipose and hepatic tissues have been shown to promote fatty acid oxidation and lipid storage. An immunohistochemical assessment of PPAR and PPAR revealed both proteins were also present in the medial and intimal layers of human arteries, predominately in regions containing smooth muscle cells. In agreement with this observation, smooth muscle cells isolated from these vessels were found by RT-PCR to express both PPAR and PPAR1. The functionality of these receptors was tested with selective PPAR agonists. Mitogenic stimulation of smooth muscle cell proliferation was blocked by 15d-PGJ₂, a PPAR agonist, as well as by WY14643, a PPAR agonist. These data indicate PPAR activation by selective agonists could influence lesion progression directly, as well as indirectly through reductions in serum lipoprotein and triglyceride levels.