CDKN1B/p27 is localized in mitochondria and improves respiration-dependent processes in the cardiovascular system-New mode of action for caffeine.

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.

Induction of a senescent like phenotype and loss of gap junctional intercellular communication by carbon nanoparticle exposure of lung epithelial cells.

Inhalation of combustion-derived particles is associated with the development of age-related diseases like chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis. In both diseases senescence of lung epithelial cells has been observed. Employing an in vitro system of repetitive exposure to pure carbon nanoparticles we asked whether this kind of particles are able to induce a senescent like phenotype, which might be accompanied by a loss of functionality at the level of gap junctional intercellular communication. Non-cytotoxic doses of carbon nanoparticles but not of bigger carbon particles led to an irreversible reduction of the proliferative capacity accompanied by the accumulation of the cell cycle blocking proteins p21 and p16 as well as a loss of both redox sensitive histone deacetylase SIRT1 and connexin-43. Gap junction intercellular communication detected by microinjection of fluorescent lucifer yellow was dramatically decreased after exposure. This loss of functionality was associated with a reduction of Connexin 43 at the plasma membrane. As the experimental system was chosen to study the effects of pure carbon nanoparticles in the absence of inflammatory cells, the data indicate that cumulative long-term exposure of the lung epithelium to low doses of combustion-derived nanoparticles might contribute to epithelial senescence and age-associated diseases of the airways.

Non-Canonical Activation of the Epidermal Growth Factor Receptor by Carbon Nanoparticles.

The epidermal growth factor receptor (EGFR) is an abundant membrane protein, which is essential for regulating many cellular processes including cell proliferation. In our earlier studies, we observed an activation of the EGFR and subsequent signaling events after the exposure of epithelial cells to carbon nanoparticles. In the current study, we describe molecular mechanisms that allow for discriminating carbon nanoparticle-specific from ligand-dependent receptor activation. Caveolin-1 is a key player that co-localizes with the EGFR upon receptor activation by carbon nanoparticles. This specific process mediated by nanoparticle-induced reactive oxygen species and the accumulation of ceramides in the plasma membrane is not triggered when cells are exposed to non-nano carbon particles or the physiological ligand EGF. The role of caveolae formation was demonstrated by the induction of higher order structures of caveolin-1 and by the inhibition of caveolae formation. Using an in vivo model with genetically modified mice lacking caveolin-1, it was possible to demonstrate that carbon nanoparticles in vivo trigger EGFR downstream signaling cascades via caveolin-1. The identified molecular mechanisms are, therefore, of toxicological relevance for inhaled nanoparticles. However, nanoparticles that are intentionally applied to humans might cause side effects depending on this phenomenon.