Interactions of nanoparticles with pulmonary structures and cellular responses

Combustion-derived and synthetic nano-sized particles (NSP) have gained considerable interest among pulmonary researchers and clinicians for two main reasons: 1) Inhalation exposure to combustion-derived NSP was associated with increased pulmonary and cardiovascular morbidity and mortality as suggested by epidemiological studies. Experimental evidence has provided a mechanistic picture of the adverse health effects associated with inhalation of combustion-derived and synthetic NSP. 2) The toxicological potential of NSP contrasts with the potential application of synthetic NSP in technological as well as medicinal settings with the latter including the use of NSP as diagnostics or therapeutics. In order to shed light on this paradox, this article aims to highlight recent findings about the interaction of inhaled NSP with the structures of the respiratory tract including surfactant and alveolar macrophages and epithelial cells. Cellular responses to NSP exposure include the generation of reactive oxygen species and the induction of an inflammatory response. Furthermore, this review places special emphasis on methodological differences between experimental studies and the caveats associated with the dose metrics and points out ways to overcome inherent methodological problems. Key words: electron tomography, surfactant, translocation, oxidative stress, inflammation.

Arabidopsis WEE1 kinase controls cell cycle arrest in response to activation of the DNA integrity checkpoint

Upon the incidence of DNA stress, the ataxia telangiectasia-mutated (ATM) and Rad3-related (ATR) signaling kinases activate a transient cell cycle arrest that allows cells to repair DNA before proceeding into mitosis. Although the ATM-ATR pathway is highly conserved over species, the mechanisms by which plant cells stop their cell cycle in response to the loss of genome integrity are unclear. We demonstrate that the cell cycle regulatory WEE1 kinase gene of Arabidopsis thaliana is transcriptionally activated upon the cessation of DNA replication or DNA damage in an ATR- or ATM-dependent manner, respectively. In accordance with a role for WEE1 in DNA stress signaling, WEE1-deficient plants showed no obvious cell division or endoreduplication phenotype when grown under nonstress conditions but were hypersensitive to agents that impair DNA replication. Induced WEE1 expression inhibited plant growth by arresting dividing cells in the G2-phase of the cell cycle. We conclude that the plant WEE1 gene is not rate-limiting for cycle progression under normal growth conditions but is a critical target of the ATR-ATM signaling cascades that inhibit the cell cycle upon activation of the DNA integrity checkpoints, coupling mitosis to DNA repair in cells that suffer DNA damage.

Microvascular endowment in the developing chicken embryo lung

In the current study, the contribution of the major angiogenic mechanisms, sprouting and intussusception, to vascular development in the avian lung has been demonstrated. Sprouting guides the emerging vessels to form the primordial vascular plexus, which successively surrounds and encloses the parabronchi. Intussusceptive angiogenesis has an upsurge from embryonic day 15 (E15) and contributes to the remarkably rapid expansion of the capillary plexus. Increased blood flow stimulates formation of pillars (the archetype of intussusception) in rows, their subsequent fusion and concomitant delineation of slender, solitary vascular entities from the disorganized meshwork, thus crafting the organ-specific angioarchitecture. Morphometric investigations revealed that sprouting is preponderant in the early period of development with a peak at E15 but is subsequently supplanted by intussusceptive angiogenesis by the time of hatching. Quantitative RT-PCR revealed that moderate levels of basic FGF (bFGF) and VEGF-A were maintained during the sprouting phase while PDGF-B remained minimal. All three factors were elevated during the intussusceptive phase. Immunohistoreactivity for VEGF was mainly in the epithelial cells, whereas bFGF was confined to the stromal compartment. Temporospatial interplay between sprouting and intussusceptive angiogenesis fabricates a unique vascular angioarchitecture that contributes to the establishment of a highly efficient gas exchange system characteristic of the avian lung.

Evidence and structural mechanism for late lung alveolarization

According to the current view, the formation of new alveolar septa from preexisting ones ceases due to the reduction of a double- to a single-layered capillaries network inside the alveolar septa (microvasculature maturation postnatal days 14-21 in rats). We challenged this view by measuring stereologically the appearance of new alveolar septa and by studying the alveolar capillary network in three-dimensional (3-D) visualizations obtained by high-resolution synchrotron radiation X-ray tomographic microscopy. We observed that new septa are formed at least until young adulthood (rats, days 4-60) and that roughly half of the new septa are lifted off of mature septa containing single-layered capillary networks. At the basis of newly forming septa, we detected a local duplication of the capillary network. We conclude that new alveoli may be formed in principle at any time and at any location inside the lung parenchyma and that lung development continues into young adulthood. We define two phases during developmental alveolarization. Phase one (days 4-21), lifting off of new septa from immature preexisting septa, and phase two (day 14 through young adulthood), formation of septa from mature preexisting septa. Clinically, our results ask for precautions using drugs influencing structural lung development during both phases of alveolarization.