Cell cycle and mitosis progression during ZIKA virus infection: The viral non-structural protein NS5 as a master regulator of the APC/cyclosome?

Alterations in cell cycle regulation contribute to Zika virus (ZIKV)-associated pathogenesis and may have implications for the development of therapeutic avenues. As a matter of fact, ZIKV alters cell cycle progression at multiple stages, including G1, S, G2, and M phases. During a cell cycle, the progression of mitosis is particularly controlled to avoid any abnormalities in cell division. In this regard, the critical metaphase-anaphase transition is triggered by the activation of anaphase-promoting complex/cyclosome (APC/C) by its E3 ubiquitin ligase subunit Cdc20. Cdc20 recognizes substrates by interacting with a destruction box motif (D-box). Recently, the ZIKV nonstructural protein 5 (NS5), one of the most highly conserved flavivirus proteins, has been shown to localize to the centrosome in each pole and to spindle fibers during mitosis. Inducible expression of NS5 reveals an interaction of this viral factor with centrosomal proteins leading to an increase in the time required to complete mitosis. By analyzing the NS5 sequence, we discovered the presence of a D-box. Taken together, these data support the idea that, in addition to its role in viral replication, NS5 plays a critical role in the control of the cell cycle of infected cells and, more specifically, in the regulation of the mitotic spindle. Here we propose that the NS5 protein may interfere with the metaphase-anaphase progression, and thus cause the observed delay in mitosis via the regulation of APC/C.

Porphyromonas gingivalis lipopolysaccharides act exclusively through TLR4 with a resilience between mouse and human.

Porphyromonas gingivalis is a key bacterium in chronic periodontitis, which is associated with several chronic inflammatory diseases. Lipopolysaccharides from P. gingivalis (Pg LPS) can activate multiple cell types via the production of pro-inflammatory cytokines. The receptors for Pg LPS have initially been reported as TLR2, contrasting with the well-studied TLR4 receptor for E. coli LPS; this observation remains controversial since synthetic Pg lipid A activates TLR4 but not TLR2. Despite this observation, the dogma of Pg LPS-mediated TLR2 activation remains the basis of many hypotheses and result interpretations. In the present work, we aimed at determining whether TLR4 or TLR2, or both, mediate Pg LPS pro-inflammatory activity using Pg LPS with different grades of purity, instead of synthetic lipid A from Pg LPS. Here we show that Pg LPS 1) acts exclusively through TLR4, and 2) are differently recognized by mouse and human TLR4 both in vitro and in vivo. Taken together, our results suggest that Pg LPS activity is mediated exclusively through TLR4 and only weakly induces proinflammatory cytokine secretion in mouse models. Caution should be taken when extrapolating data from mouse systems exposed to Pg or Pg LPS to humans.

Soluble HMGB1 is a novel adipokine stimulating IL-6 secretion through RAGE receptor in SW872 preadipocyte cell line: contribution to chronic inflammation in fat tissue.

Low-grade inflammation (LGI) is a central phenomenon in the genesis of obesity and insulin-resistance characterized by IL-6 in human serum. Whereas this LGI was initially thought to be mainly attributed to macrophage activation, it is now known that pre-adipocytes and adipocytes secrete several adipokines including IL-6 and participate to LGI and associated pathologies. In macrophages, HMGB1 is a nuclear yet secreted protein and acts as a cytokine to drive the production of inflammatory molecules through RAGE and TLR2/4. In this paper we tested the secretion of HMGB1 and the auto- and paracrine contribution to fat inflammation using the human preadipocyte cell line SW872 as a model. We showed that 1) human SW872 secreted actively HMGB1, 2) IL-6 production was positively linked to high levels of secreted HMGB1, 3) recombinant HMGB1 boosted IL-6 expression and this effect was mediated by the receptor RAGE and did not involve TLR2 or TLR4. These results suggest that HMGB1 is a major adipokine contributing to LGI implementation and maintenance, and can be considered as a target to develop news therapeutics in LGI associated pathologies such as obesity and type II diabetes.

Citrus fruit extracts reduce advanced glycation end products (AGEs)- and H2O2-induced oxidative stress in human adipocytes.

Diabetes is a reactive oxygen species (ROS)-mediated pathology, with a worldwide prevalence estimated to double by 2030. A major effort has been launched to find therapeutic means to improve health conditions of diabetic patients. Recent data show that supplemental natural antioxidants represent a potential strategy as adjunct therapy. Despite the major role of adipocytes in the etiology of diabetes, little is known about the effect of natural antioxidants on adipocyte response to oxidative stress. Using a diabetes-like oxidative stress model, the potential protective effect of antioxidative flavedo, albedo, and pulp extracts of (1) tangor Elendale (Citrus reticulata × Citrus sinensis) and (2) tangelo Minneola (C. reticulata × Citrus paradisis) was investigated on human adipocytes. Besides the retardation of free-radical-induced hemolysis of human erythrocytes, non-cytotoxic concentrations of tangelo and tangor flavedo extracts significantly reduced the levels of protein carbonyls in response to advanced glycation end products (AGEs) generated by albumin glycation in SW872 cells. Flavedo extracts lowered carbonyl accumulation in H2O2-treated adipocytes, while tangelo and tangor flavedo, albedo, and pulp extracts suppressed ROS production in SW872 cells with or without the addition of H2O2. Our results clearly show that Mauritian Citrus fruit extracts represent an important source of antioxidants, with a novel antioxidative role at the adipose tissue level.