Interaction and interrelation of P2X7 and P2X4 receptor complexes in mouse lung epithelial cells

P2X4 and P2X7 receptors are ATP-gated ion channels that are co-expressed in alveolar epithelial type I cells. Both receptors are localized to the plasma membrane and partly associated with lipid rafts. Here we report on our study in an alveolar epithelial cell line of the molecular organization of P2X7R and P2X4R receptors and the effect of their knockdown. Native gel electrophoresis reveals three P2X7R complexes of ~430, ~580 and ~760 kDa. The latter two correspond exactly in size to signals of Cav-1, the structural protein of caveolae. Interestingly knockdown of P2rx7 affects protein levels, the intracellular distribution and the supramolecular organization of Cav-1 as well as of P2X4R, which is mainly detected in a complex of ~430 kDa. Our data suggest upregulation of P2X4R as a compensatory mechanism of P2X7R depletion.     

CD36 is a sensor of diacylglycerides

Toll-like receptor 2 (TLR2) is required for the recognition of numerous molecular components of bacteria, fungi and protozoa. The breadth of the ligand repertoire seems unusual, even if one considers that TLR2 may form heteromers with TLRs 1 and 6 (ref. 12), and it is likely that additional proteins serve as adapters for TLR2 activation. Here we show that an N-ethyl-N-nitrosourea-induced nonsense mutation of Cd36 (oblivious) causes a recessive immunodeficiency phenotype in which macrophages are insensitive to the R-enantiomer of MALP-2 (a diacylated bacterial lipopeptide) and to lipoteichoic acid. Homozygous mice are hypersusceptible to Staphylococcus aureus infection. Cd36(obl) macrophages readily detect S-MALP-2, PAM(2)CSK(4), PAM(3)CSK(4) and zymosan, revealing that some--but not all--TLR2 ligands are dependent on CD36. Already known as a receptor for endogenous molecules, CD36 is also a selective and nonredundant sensor of microbial diacylglycerides that signal via the TLR2/6 heterodimer.     

Mutations in CAV3 cause mechanical hyperirritability of skeletal muscle in rippling muscle disease.

Hereditary rippling muscle disease (RMD) is an autosomal dominant human disorder characterized by mechanically triggered contractions of skeletal muscle. Genome-wide linkage analysis has identified an RMD locus on chromosome 3p25. We found missense mutations in positional candidate CAV3 (encoding caveolin 3; ref. 5) in all five families analyzed. Mutations in CAV3 have also been described in limb-girdle muscular dystrophy type 1C (LGMD1C; refs. 6,7), demonstrating the allelism of dystrophic and non-dystrophic muscle diseases.     

Extensive surface diversity of a commensal microorganism by multiple DNA inversions.

The dynamic interactions between a host and its intestinal microflora that lead to commensalism are unclear. Bacteria that colonize the intestinal tract do so despite the development of a specific immune response by the host. The mechanisms used by commensal organisms to circumvent this immune response have yet to be established. Here we demonstrate that the human colonic microorganism, Bacteroides fragilis, is able to modulate its surface antigenicity by producing at least eight distinct capsular polysaccharides-a number greater than any previously reported for a bacterium-and is able to regulate their expression in an on-off manner by the reversible inversion of DNA segments containing the promoters for their expression. This means of generating surface diversity allows the organism to exhibit a wide array of distinct surface polysaccharide combinations, and may have broad implications for how the predominant human colonic microorganisms, the Bacteroides species, maintain an ecological niche in the intestinal tract.     

Perspectives on the prevention and treatment of infection for orthopedic tissue engineering applications

The emergence of orthopedic tissue engineering devices as viable clinical solutions demands that the field address significant clinical complications associated with the implantation of foreign materials in the body, especially infection. While tissue engi- neering has focused on the development of methods to regenerate and repair, until recently there has been a relative dearth of literature regarding the intersection of tissue engineering and infection. In particular, local delivery of antimicrobials has long been of clinical interest, but only recently has that been translated into the realm of tissue engineering. In this perspective, we briefly review major modes of local delivery for infection prevention and treatment and discuss possible strategies for preventing implant-associated infections.     

Oncogene-induced senescence is part of the tumorigenesis barrier imposed by DNA damage checkpoints

Recent studies have indicated the existence of tumorigenesis barriers that slow or inhibit the progression of preneoplastic lesions to neoplasia. One such barrier involves DNA replication stress, which leads to activation of the DNA damage checkpoint and thereby to apoptosis or cell cycle arrest, whereas a second barrier is mediated by oncogene-induced senescence. The relationship between these two barriers, if any, has not been elucidated. Here we show that oncogene-induced senescence is associated with signs of DNA replication stress, including prematurely terminated DNA replication forks and DNA double-strand breaks. Inhibiting the DNA double-strand break response kinase ataxia telangiectasia mutated (ATM) suppressed the induction of senescence and in a mouse model led to increased tumour size and invasiveness. Analysis of human precancerous lesions further indicated that DNA damage and senescence markers cosegregate closely. Thus, senescence in human preneoplastic lesions is a manifestation of oncogene-induced DNA replication stress and, together with apoptosis, provides a barrier to malignant progression.     

Increased methylation variation in epigenetic domains across cancer types

Tumor heterogeneity is a major barrier to effective cancer diagnosis and treatment. We recently identified cancer-specific differentially DNA-methylated regions (cDMRs) in colon cancer, which also distinguish normal tissue types from each other, suggesting that these cDMRs might be generalized across cancer types. Here we show stochastic methylation variation of the same cDMRs, distinguishing cancer from normal tissue, in colon, lung, breast, thyroid and Wilms' tumors, with intermediate variation in adenomas. Whole-genome bisulfite sequencing shows these variable cDMRs are related to loss of sharply delimited methylation boundaries at CpG islands. Furthermore, we find hypomethylation of discrete blocks encompassing half the genome, with extreme gene expression variability. Genes associated with the cDMRs and large blocks are involved in mitosis and matrix remodeling, respectively. We suggest a model for cancer involving loss of epigenetic stability of well-defined genomic domains that underlies increased methylation variability in cancer that may contribute to tumor heterogeneity.     

Iron deposits in the chronically inflamed central nervous system and contributes to neurodegeneration

Neurodegenerative disorders are characterized by the presence of inflammation in areas with neuronal cell death and a regional increase in iron that exceeds what occurs during normal aging. The inflammatory process accompanying the neuronal degeneration involves glial cells of the central nervous system (CNS) and monocytes of the circulation that migrate into the CNS while transforming into phagocytic macrophages. This review outlines the possible mechanisms responsible for deposition of iron in neurodegenerative disorders with a main emphasis on how iron-containing monocytes may migrate into the CNS, transform into macrophages, and die out subsequently to their phagocytosis of damaged and dying neuronal cells. The dying macrophages may in turn release their iron, which enters the pool of labile iron to catalytically promote formation of free-radical-mediated stress and oxidative damage to adjacent cells, including neurons. Healthy neurons may also chronically acquire iron from the extracellular space as another principle mechanism for oxidative stress-mediated damage. Pharmacological handling of monocyte migration into the CNS combined with chelators that neutralize the effects of extracellular iron occurring due to the release from dying macrophages as well as intraneuronal chelation may denote good possibilities for reducing the deleterious consequences of iron deposition in the CNS.     

A microbial symbiosis factor prevents intestinal inflammatory disease

Humans are colonized by multitudes of commensal organisms representing members of five of the six kingdoms of life; however, our gastrointestinal tract provides residence to both beneficial and potentially pathogenic microorganisms. Imbalances in the composition of the bacterial microbiota, known as dysbiosis, are postulated to be a major factor in human disorders such as inflammatory bowel disease. We report here that the prominent human symbiont Bacteroides fragilis protects animals from experimental colitis induced by Helicobacter hepaticus, a commensal bacterium with pathogenic potential. This beneficial activity requires a single microbial molecule (polysaccharide A, PSA). In animals harbouring B. fragilis not expressing PSA, H. hepaticus colonization leads to disease and pro-inflammatory cytokine production in colonic tissues. Purified PSA administered to animals is required to suppress pro-inflammatory interleukin-17 production by intestinal immune cells and also inhibits in vitro reactions in cell cultures. Furthermore, PSA protects from inflammatory disease through a functional requirement for interleukin-10-producing CD4+ T cells. These results show that molecules of the bacterial microbiota can mediate the critical balance between health and disease. Harnessing the immunomodulatory capacity of symbiosis factors such as PSA might potentially provide therapeutics for human inflammatory disorders on the basis of entirely novel biological principles.