Hepatic stellate cells (HSC) play an important role in the development of liver fibrosis. Here, we report that HSC express the stem/progenitor cell marker CD133 and exhibit properties of progenitor cells. CD133+ HSC of rats were selected by specific antibodies and magnetic cell sorting. Selected cells displayed typical markers of HSC, endothelial progenitor cells (EPC), and monocytes. In cell culture, CD133+ HSC transformed into alpha-smooth muscle actin positive myofibroblast-like cells, whereas application of cytokines known to facilitate EPC differentiation into endothelial cells led to the formation of branched tube-like structures and induced expression of the endothelial cell markers endothelial nitric oxide synthase and vascular-endothelial cadherin. Moreover, cytokines that guide stem cells to develop hepatocytes led to the appearance of rotund cells and expression of the hepatocyte markers alpha-fetoprotein and albumin. It is concluded that CD133+ HSC are a not yet recognized progenitor cell compartment with characteristics of early EPC. Their potential to differentiate into endothelial or hepatocyte lineages suggests important functions of CD133+ HSC during liver regeneration.

Significance: Oxidants were once principally considered perpetrators of injury and disease. However, this has become an antiquated view, with cumulative evidence showing that the oxidant hydrogen peroxide serves as a signaling molecule. Hydrogen peroxide carries vital information about the redox state of the cell and is crucial for homeostatic regulation during health and adaptation to stress. Recent Advances: In this review, we examine the contemporary concepts for how hydrogen peroxide is sensed and transduced into a biological response by introducing post-translational oxidative modifications on select proteins. Oxidant sensing and signaling by kinases are of particular importance as they integrate oxidant signals into phospho-regulated pathways. We focus on CAMKII, PKA, and PKG, kinases whose redox regulation has notable impact on cardiovascular function. Critical Issues: In addition, we examine the mechanism for regulating intracellular hydrogen peroxide, considering the net concentrations that may accumulate. The effects of endogenously generated oxidants are often modeled by applying exogenous hydrogen peroxide to cells or tissues. Here we consider whether model systems exposed to exogenous hydrogen peroxide have relevance to systems where the oxidant is generated endogenously, and if so, what concentration can be justified in terms of relevance to health and disease. Future Directions: Improving our understanding of hydrogen peroxide signaling and the sensor proteins that it can modify will help us develop new strategies to regulate intracellular signaling to prevent disease.

The ubiquitously expressed aryl hydrocarbon receptor (AhR) induces drug metabolizing enzymes as well as regulators of cell growth, differentiation and apoptosis. Certain AhR ligands promote atherosclerosis, an age-associated vascular disease. Therefore, we investigated the role of AhR in vascular functionality and aging. We report a lower pulse wave velocity in young and old AhR-deficient mice, indicative of enhanced vessel elasticity. Moreover, endothelial nitric oxide synthase (eNOS) showed increased activity in the aortas of these animals, which was reflected in increased NO production. Ex vivo, AhR activation reduced the migratory capacity of primary human endothelial cells. AhR overexpression as well as treatment with a receptor ligand, impaired eNOS activation and reduced S-NO content. All three are signs of endothelial dysfunction. Furthermore, AhR expression in blood cells of healthy human volunteers positively correlated with vessel stiffness. In the aging model Caenorhabditis elegans, AhR-deficiency resulted in increased mean life span, motility, pharynx pumping and heat shock resistance, suggesting healthier aging. Thus, AhR seems to have a negative impact on vascular and organismal aging. Finally, our data from human subjects suggest that AhR expression levels could serve as an additional, new predictor of vessel aging.

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Dietary antioxidants such as carotenoids, tocopherols, vitamin C or flavonoids exhibit biological activities that are not directly related to their antioxidant properties. The parent compounds and/or their metabolites have impact on cellular signaling pathways, influence the expression of certain genes or act as inhibitors of regulatory enzymes. Thus, they reveal additional biological effects which might be of importance in context with the prevention of degenerative diseases related to the consumption of a diet rich in antioxidants. This review focuses on known non-antioxidant properties of carotenoids, including retinoid-dependent signaling, stimulation of gap junctional communications, impact on the regulation of cell growth and induction of detoxifying enzymes, such as cytochrome P450-dependent monooxygenases.

COX-2 (cyclooxygenase-2) is a pivotal player in inflammatory processes, and ultraviolet radiation is a known stimulus for COX-2 expression in skin cells. Here, an induction of COX-2 expression in HaCaT human keratinocytes was observed only upon exposure of cells to UVB (280 -320 nm) but not to UVA radiation (320 -400 nm), as demonstrated by reverse transcription-PCR and Western blotting. Prostaglandin E 2 levels were elevated in cell culture supernatants of HaCaT cells exposed to UVB. COX-2 mRNA stability was dramatically increased by UVB irradiation. Both the stabilization of COX-2 mRNA and the enhancement of COX-2 steady-state mRNA and protein levels caused by UVB were prevented both by inhibition and small interfering RNA-induced depletion of p38 MAPK , a kinase strongly activated upon exposure to UVB, suggesting p38 MAPK -dependent mRNA stabilization as a mechanism of UVB-induced COX-2 expression. A dramatic decrease in COX-2 expression induced by UVB was elicited by small interfering RNA-based depletion of a stress-responsive mRNA stabilizing protein regulated by p38 MAPK , i.e. HuR; UVB-induced elevation of COX-2 mRNA and protein levels coincided with an accumulation of HuR in the cytoplasm and was attenuated in cells depleted of HuR. Moreover, UVB-induced generation of prostaglandin E 2 by HaCaT cells was blunted by HuR depletion, suggesting that stress kinases (such as p38 MAPK ) as well as HuR are excellent targets for approaches aiming at interfering with induction of COX-2 expression by UVB.Cyclooxygenases catalyze the rate-limiting step in prostaglandin biosynthesis, i.e. the conversion of arachidonic acid to prostaglandin (PG) 3 H 2 , which in turn is converted by various synthases to different prostaglandins or thromboxane A 2 , important mediators in inflammatory processes. Two genes coding for isoforms of cyclooxygenase (COX-1 and COX-2) are known (1). Although COX-1 and a COX-1 variant, termed COX-3 (2), are constitutively expressed, expression of COX-2 is strongly inducible by growth factors, cytokines, and other stimuli, resulting in the production of prostaglandins during inflammatory processes. One such potent stimulus for COX-2 induction is UV radiation. Both UVB (280 -320 nm) (3) and UVA (320 -400 nm) (4) were reported previously to enhance the expression of COX-2 in human keratinocytes, followed by an increased production of the inflammatory mediator PGE 2 , a major prostaglandin in skin. Analysis of the relative contributions of UV ranges to the effects of solar light on COX-2 levels demonstrated that UVB is a far more efficient inducer of COX-2 expression; for example, UVB and UVA-2 (320 -350 nm) but not UVA-1 (350 -400 nm) contributed to COX-2 induction by simulated solar light in artificial human epidermis (5). Several lines of evidence link COX-2 and PGE 2 to the development of UV-induced skin cancer, such as the findings that COX-2 and PGE 2 levels are elevated in skin cancer versus normal tissue, that PGE 2 is a promoting factor in skin carcinogenesis, and that depletion or inhib...

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We show that the cyclin-dependent kinase inhibitor 1B (CDKN1B)/p27, previously known as a cell cycle inhibitor, is also localized within mitochondria. The migratory capacity of endothelial cells, which need intact mitochondria, is completely dependent on mitochondrial p27. Mitochondrial p27 improves mitochondrial membrane potential, increases adenosine triphosphate (ATP) content, and is required for the promigratory effect of caffeine. Domain mapping of p27 revealed that the N-terminus and C-terminus are required for those improvements. Further analysis of those regions revealed that the translocation of p27 into the mitochondria and its promigratory activity depend on serine 10 and threonine 187. In addition, mitochondrial p27 protects cardiomyocytes against apoptosis. Moreover, mitochondrial p27 is necessary and sufficient for cardiac myofibroblast differentiation. In addition, p27 deficiency and aging decrease respiration in heart mitochondria. Caffeine does not increase respiration in p27-deficient animals, whereas aged mice display improvement after 10 days of caffeine in drinking water. Moreover, caffeine induces transcriptome changes in a p27-dependent manner, affecting mostly genes relevant for mitochondrial processes. Caffeine also reduces infarct size after myocardial infarction in prediabetic mice and increases mitochondrial p27. Our data characterize mitochondrial p27 as a common denominator that improves mitochondria-dependent processes and define an increase in mitochondrial p27 as a new mode of action of caffeine.