Toxicity of silver nanoparticles on different tissues in adult Danio rerio.

Although silver nanoparticles (AgNP) are among the most studied nanomaterials by virtue of their broad application in many areas, little is known about their overall toxicity to aquatic organisms after their contamination of the water environment. This study aimed to analyze the effect of the exposure (96 h) to different AgNP concentrations on Danio rerio (zebrafish) tissues. AgNP were synthesized and characterized by transmission electron microscopy (TEM), showing spherical AgNP of 30.00 ± 16.80 nm size. The effects of different AgNP concentrations (1, 3, and 5 µg L-1) on brain, muscle, gill, and liver tissues of zebrafish were investigated. The results show a significant decrease in brain and muscle acetylcholinesterase (AChE) activity. Liver and gill catalase (CAT) activity also decreased significantly. At the highest exposure concentration, muscle AChE was more inhibited (37.3%) than brain AChE (26.4%) and gill CAT was more inhibited (67.4%) than liver CAT (51.2%). D. rerio also showed gill morphological changes such as fusion of secondary lamellae, curvature, dilated marginal channel, and epithelial lifting. This study indicates that gill CAT together with morphological studies are potential biomarkers for AgNP.

Association between biomechanical alterations and migratory ability of semaphorin-3A-treated thymocytes.

BACKGROUND: Class 3 semaphorins are soluble proteins involved in cell adhesion and migration. Semaphorin-3A (Sema3A) was initially shown to be involved in neuronal guidance, and it has also been reported to be associated with immune disorders. Both Sema3A and its receptors are expressed by most immune cells, including monocytes, macrophages, and lymphocytes, and these proteins regulate cell function. Here, we studied the correlation between Sema3A-induced changes in biophysical parameters of thymocytes, and the subsequent repercussions on cell function. METHODS: Thymocytes from mice were treated in vitro with Sema3A for 30min. Scanning electron microscopy was performed to assess cell morphology. Atomic force microscopy was performed to further evaluate cell morphology, membrane roughness, and elasticity. Flow cytometry and/or fluorescence microscopy were performed to assess the F-actin cytoskeleton and ROCK2. Cell adhesion to a bovine serum albumin substrate and transwell migration assays were used to assess cell migration. RESULTS: Sema3A induced filopodia formation in thymocytes, increased membrane stiffness and roughness, and caused a cortical distribution of the cytoskeleton without changes in F-actin levels. Sema3A-treated thymocytes showed reduced substrate adhesion and migratory ability, without changes in cell viability. In addition, Sema3A was able to down-regulate ROCK2. CONCLUSIONS: Sema3A promotes cytoskeletal rearrangement, leading to membrane modifications, including increased stiffness and roughness. This effect in turn affects the adhesion and migration of thymocytes, possibly due to a reduction in ROCK2 expression. GENERAL SIGNIFICANCE: Sema3A treatment impairs thymocyte migration due to biomechanical alterations in cell membranes.

Triiodothyronine modulates differential homing of recent thymic emigrants to peripheral lymphoid organs.

The functioning of the immune system partially relies on T-cell exportation from the thymus, the major site of T-cell differentiation. Although the molecular mechanisms governing this process begin to be elucidated, it is not clear if thyroid hormones can alter the homing of recent thymic emigrants (RTE) to peripheral lymphoid organs. Herein, we investigated whether triiodothyronine (T(3)) could influence the homing of thymus-derived T cells. For that we used intrathymic injection of T(3) in combination with fluorescein isothiocyanate (FITC) to trace, 16 h later, FITC(+) cells, termed RTE, in peripheral lymphoid organs. We observed that T(3) stimulated thymocyte export, increasing the frequency of CD4(+) RTE and CD8(+) RTE in the subcutaneous and mesenteric lymph nodes. By contrast, the relative numbers of CD4(+) RTE in the spleen were decreased. T(3) also changed the differential distribution pattern of CD4(+) RTE, and to a lesser extent CD8(+) RTE in the peripheral lymphoid organs. Moreover, the expression of extracellular matrix (ECM) components, such as laminin and fibronectin, which are known to be involved in T-cell migration, increased in the lymph nodes but not in the spleen following intrathymic T(3) treatment. In conclusion, our data correspond to the first demonstration that in vivo treatment with thyroid hormone stimulates thymic T-cell homing and T-cell distribution in peripheral lymphoid organs.

Thymocyte migration: an affair of multiple cellular interactions?

Cell migration is a crucial event in the general process of thymocyte differentiation. The cellular interactions involved in the control of this migration are beginning to be defined. At least chemokines and extracellular matrix proteins appear to be part of the game. Cells of the thymic microenvironment produce these two groups of molecules, whereas developing thymocytes express the corresponding receptors. Moreover, although chemokines and extracellular matrix can drive thymocyte migration per se, a combined role for these molecules appears to contribute to the resulting migration patterns of thymocytes in their various stages of differentiation. The dynamics of chemokine and extracellular matrix production and degradation is not yet well understood. However, matrix metalloproteinases are likely to play a role in the breakdown of intrathymic extracellular matrix contents. Thus, the physiological migration of thymocytes should be envisioned as a resulting vector of multiple, simultaneous and/or sequential stimuli involving chemokines, adhesive and de-adhesive extracellular matrix proteins, as well as matrix metalloproteinases. Accordingly, it is conceivable that any pathological change in any of these loops may result in the alteration of normal thymocyte migration. This seems to be the case in murine infection by the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas' disease. A better knowledge of the physiological mechanisms governing thymocyte migration will provide new clues for designing therapeutic strategies targeting developing T cells

Thymocyte migration: an affair of multiple cellular interactions?

Cell migration is a crucial event in the general process of thymocyte differentiation. The cellular interactions involved in the control of this migration are beginning to be defined. At least chemokines and extracellular matrix proteins appear to be part of the game. Cells of the thymic microenvironment produce these two groups of molecules, whereas developing thymocytes express the corresponding receptors. Moreover, although chemokines and extracellular matrix can drive thymocyte migration per se, a combined role for these molecules appears to contribute to the resulting migration patterns of thymocytes in their various stages of differentiation. The dynamics of chemokine and extracellular matrix production and degradation is not yet well understood. However, matrix metalloproteinases are likely to play a role in the breakdown of intrathymic extracellular matrix contents. Thus, the physiological migration of thymocytes should be envisioned as a resulting vector of multiple, simultaneous and/or sequential stimuli involving chemokines, adhesive and de-adhesive extracellular matrix proteins, as well as matrix metalloproteinases. Accordingly, it is conceivable that any pathological change in any of these loops may result in the alteration of normal thymocyte migration. This seems to be the case in murine infection by the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas' disease. A better knowledge of the physiological mechanisms governing thymocyte migration will provide new clues for designing therapeutic strategies targeting developing T cells.

The thymus gland: a target organ for growth hormone.

Increasing evidence has placed hormones and neuropeptides among potent immunomodulators, in both health and disease. Herein, we focus on the effects of growth hormone (GH) upon the thymus. Exogenous GH enhances thymic microenvironmental cell-derived secretory products such as cytokines and thymic hormones. Moreover, GH increases thymic epithelial cell (TEC) proliferation in vitro, and exhibits a synergistic effect with anti-CD3 in stimulating thymocyte proliferation, which is in keeping with the data showing that transgenic mice overexpressing GH or GH-releasing hormone exhibit overgrowth of the thymus. GH also influences thymocyte traffic: it increases human T-cell progenitor engraftment into the thymus; augments TEC/thymocyte adhesion and the traffic of thymocytes in the lymphoepithelial complexes, the thymic nurse cells; modulates in vivo the homing of recent thymic emigrants, enhancing the numbers of fluroscein isothiocyanate (FITC)+ cells in the lymph nodes and diminishing them in the spleen. In keeping with the effects of GH upon thymic cells is the detection of GH receptors in both TEC and thymocytes. Additionally, data indicate that insulin-like growth factor (IGF)-1 is involved in several effects of GH in the thymus, including the modulation of thymulin secretion, TEC proliferation as well as thymocyte/TEC adhesion. This is in keeping with the demonstration of IGF-1 production and expression of IGF-1 by TEC and thymocytes. Also, it should be envisioned as an intrathymic circuitry, involving not only IGF-1, but also GH itself, as intrathymic GH expression is seen both in TEC and in thymocytes, and that thymocyte-derived GH could enhance thymocyte proliferation. Finally, the possibility that GH improve thymic functions, including thymocyte proliferation and migration, places this molecule as a potential therapeutic adjuvant in immunodeficiency conditions associated with thymocyte decrease and loss of peripheral T cells.

Is there a role for growth hormone upon intrathymic T-cell migration?

Intrathymic T-cell differentiation is essentially driven by the thymic microenvironment, a tridimensional network formed by thymic epithelial cells and to a lesser extent, dendritic cells, macrophages, fibroblasts, and extracellular matrix components. Thymocyte migration throughout the thymus is partially dependent on extracellular-matrix (ECM)-mediated interactions. Herein we investigated the putative role of growth hormone (GH) upon events related to intrathymic T-cell migration. We demonstrated that GH upregulates the expression of ECM ligands and receptors in distinct preparations of cultured thymic epithelial cells TECs). We also showed that adhesion of thymocytes to thymic epithelial cells was significantly increased by GH treatment, an effect that could be consistently abrogated when TECs were treated to antifibronectin, anti-VLA5, antilaminin, or anti-VLA6 antibodies before addition of thymocytes to the cultures. We also studied thymic nurse cells (TNCs), lymphoepithelial complexes that can be isolated ex vivo from the thymus. In this system, we had previously demonstrated that ECM ligands and receptors control both inward and outward thymocyte traffic. We then showed that GH enhances thymocyte release from TNCs, as well as the reconstitution of these lymphoepithelial complexes. Lastly, we evaluated the in vivo influence of GH on thymocyte exit. This was done by means of intrathymic injection of GH plus fluorescein isothiocyanate (FITC), and further analysis of recent thymic emigrants (FITC+ cells) in peripheral lymphoid organs, as defined by CD4/CD8-based cytofluorometric phenotyping. The proportions of FITC+ T cells appeared augmented in lymph nodes in GH-treated mice, as compared to controls. Taken together, these data indicate that GH stimulates intrathymic T-cell traffic, an effect that is at least partially mediated by extracellular matrix-mediated interactions.

Morphological action of tamoxifen in the endometrium of persistent estrous rats.

BACKGROUND: The aim of this study was to evaluate the action of tamoxifen on the endometrium in states of chronic anovulation. METHODS: Thirty-eight rats inducted to persistent estrous (testosterone propionate) confirmed by hormonal colpocytology were divided into a control and an experimental group; the latter received tamoxifen and had fragments of the uterine horns processed for morphological and morphometrical analysis. Data were analysed statistically by the Mann-Whitney and Student's t tests. RESULTS: Our findings revealed minor uterine weight, epithelial thickness; number of endometrial glands and low eosinophil counts in the group that received tamoxifen. These results were statistically significant. We often observed areas of metaplasic stratified squamous epithelium between cylindrical epithelial cells in both groups. CONCLUSIONS: Our results indicate that antiestrogenic effect of tamoxifen was only partial in persistent estrous, since there was no blocking against the squamous metaplasia of the endometrium.