Retinoic acid receptor signalling directly regulates osteoblast and adipocyte differentiation from mesenchymal progenitor cells

Low and high serum retinol levels are associated with increased fracture risk and poor bone health. We recently showed retinoic acid receptors (RARs) are negative regulators of osteoclastogenesis. Here we show RARs are also negative regulators of osteoblast and adipocyte differentiation. The pan-RAR agonist, all-trans retinoic acid (ATRA), directly inhibited differentiation and mineralisation of early osteoprogenitors and impaired the differentiation of more mature osteoblast populations. In contrast, the pan-RAR antagonist, IRX4310, accelerated differentiation of early osteoprogenitors. These effects predominantly occurred via RARγ and were further enhanced by an RARα agonist or antagonist, respectively. RAR agonists similarly impaired adipogenesis in osteogenic cultures. RAR agonist treatment resulted in significant upregulation of the Wnt antagonist, Sfrp4. This accompanied reduced nuclear and cytosolic β-catenin protein and reduced expression of the Wnt target gene Axin2, suggesting impaired Wnt/β-catenin signalling. To determine the effect of RAR inhibition in post-natal mice, IRX4310 was administered to male mice for 10 days and bones were assessed by µCT. No change to trabecular bone volume was observed, however, radial bone growth was impaired. These studies show RARs directly influence osteoblast and adipocyte formation from mesenchymal cells, and inhibition of RAR signalling in vivo impairs radial bone growth in post-natal mice.     

Molecular assays for detecting Aphanomyces invadans in ulcerative mycotic fish lesions

The pathogenic oomycete Aphanomyces invadans is the primary etiological agent in ulcerative mycosis, an ulcerative skin disease caused by a fungus-like agent of wild and cultured fish. We developed sensitive PCR and fluorescent peptide nucleic acid in situ hybridization (FISH) assays to detect A. invadans. Laboratory-challenged killifish (Fundulus heteroclitus) were first tested to optimize and validate the assays. Skin ulcers of Atlantic menhaden (Brevoortia tyrannus) from populations found in the Pamlico and Neuse River estuaries in North Carolina were then surveyed. Results from both assays indicated that all of the lesioned menhaden (n = 50) collected in September 2004 were positive for A. invadans. Neither the FISH assay nor the PCR assay cross-reacted with other closely related oomycetes. These results provided strong evidence that A. invadans is the primary oomycete pathogen in ulcerative mycosis and demonstrated the utility of the assays. The FISH assay is the first molecular assay to provide unambiguous visual confirmation that hyphae in the ulcerated lesions were exclusively A. invadans.     

Dynamin function is important for chemokine receptor‐induced cell migration

The HIV viral entry co‐receptors CCR5 and CXCR4 function physiologically as typical chemokine receptors. Activation leads to cytosolic signal transduction that results in a variety of cellular responses such as cytoskeletal rearrangement and chemotaxis (CTX). Our aim was to investigate the signalling pathways involved in CC and CXC receptor‐mediated cell migration. Inhibition of dynamin I and II GTPase with dynasore completely inhibited CCL3‐stimulated CTX in THP‐1 cells, whereas the dynasore analogue Dyngo‐4a, which is a more potent inhibitor, showed reduced ability to inhibit CC chemokine‐induced CTX. In contrast, dynasore was not able to block cell migration via CXCR4. The same activation/inhibition pattern was verified in activated T lymphocytes for different CC and CXC chemokines. Cell migration induced by CC and CXC receptors does not rely on active internalization processes driven by dynamin because the blockade of internalization does not affect migration, but it might rely on dynamin interaction with the cytoskeleton. We identify here a functional difference in how CC and CXC receptor migration is controlled, suggesting that specific signalling networks are being employed for different receptor classes and potentially specific therapeutic targets to prevent receptor migration can be identified. Copyright © 2015 John Wiley & Sons, Ltd.     

Effects of short-term chemical ablation of the GIP receptor on insulin secretion, islet morphology and glucose homeostasis in mice

Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone secreted by endocrine K-cells in response to nutrient absorption. In this study we have utilized a specific and enzymatically stable GIP receptor antagonist, (Pro3)GIP, to evaluate the contribution of endogenous GIP to insulin secretion and glucose homeostasis in mice. Daily injection of (Pro3)GIP (25 nmol/kg body weight) for 11 days had no effect on food intake or body weight. Non-fasting plasma glucose concentrations were significantly raised (p<0.05) by day 11, while plasma insulin concentrations were not significantly different from saline treated controls. After 11 days, intraperitoneal glucose tolerance was significantly impaired in the (Pro3)GIP treated mice compared to control (p<0.01). Glucose-mediated insulin secretion was not significantly different between the two groups. Insulin sensitivity of 11-day (Pro3)GIP treated mice was slightly impaired 60 min post injection compared with controls. Following a 15 min refeeding period in 18 h fasted mice, food intake was not significantly different in (Pro3)GIP treated mice and controls. However, (Pro3)GIP treated mice displayed significantly elevated plasma glucose levels 30 and 60 min post feeding (p<0.05, in both cases). Postprandial insulin secretion was not significantly different and no changes in pancreatic insulin content or islet morphology were observed in (Pro3)GIP treated mice. The observed biological effects of (Pro3)GIP were reversed following cessation of treatment for 9 days. These data indicate that ablation of GIP signaling causes a readily reversible glucose intolerance without appreciable change of insulin secretion.     

Encapsulation of Pseudomonas sp. ADP cells in electrospun microtubes for atrazine bioremediation

Electrospun hollow polymeric microfibers (microtubes) were evaluated as an encapsulation method for the atrazine degrading bacterium Pseudomonas sp. ADP. Pseudomonas sp. ADP cells were successfully incorporated in a formulation containing a core solution of polyethylene oxide dissolved in water and spun with an outer shell solution made of polycaprolactone and polyethylene glycol dissolved in a chloroform and dimethylformamide. The resulting microtubes, collected as mats, were partially collapsed with a ribbon-like structure. Following encapsulation, the atrazine degradation rate was low (0.03?±?0.01?mg atrazine/h/g fiber) indicating that the electrospinning process negatively affected cell activity. Atrazine degradation was restored to 0.5?±?0.1?mg atrazine/h/g fiber by subjecting the microtubes to a period of growth. After 3 and 7?days growth periods, encapsulated cells were able to remove 20.6?±?3 and 47.6?±?5.9?mg atrazine/g mat, respectively, in successive batches under non-growth conditions (with no additional electron donor) until atrazine was detected in the medium. The loss of atrazine degrading capacity was regained following an additional cell-growth period.     

The Role of Climatic Factors in the Expression of an Intrasexual Signal in the Paper Wasp Polistes dominulus

Within a species, variation in the use of sexual signals is observed between different populations. For intersexual traits, differences in the environmental conditions experienced by populations can play an important role in driving variation in male ornaments and female preferences. However, little is known about the factors maintaining variation in intrasexual traits used in competition. In this study, we investigate the role of climatic conditions in maintaining variation in the expression of an intrasexual signal in the paper wasp Polistes dominulus. The results of an experiment in which pupae were housed under different temperature and humidity conditions revealed a strong effect of temperature during pupal development on the expression of the signal. Furthermore, a comparison of survival and body weight between wasps reared at different temperatures indicates that signal expression exhibits phenotypic plasticity in response to developmental temperature. The effect of temperature on signal expression is consistent with patterns of signal expression observed across populations in the wild and suggests that climatic conditions may act to constrain signal expression in some populations but not in others, driving variation in signal use within P. dominulus. Environmental conditions may therefore be important in defining the scope for intrasexual signalling in animal populations and, in doing so, may play a role in maintaining variation in intrasexual traits in the face of sexual selection.