Foxp3+ regulatory T (Treg) cells are key immune regulators during helminth infections, and identifying the mechanisms governing their induction is of principal importance for the design of treatments for helminth infections, allergies and autoimmunity. Little is yet known regarding the co-stimulatory environment that favours the development of Foxp3+ Treg-cell responses during helminth infections. As recent evidence implicates the co-stimulatory receptor ICOS in defining Foxp3+ Treg-cell functions, we investigated the role of ICOS in helminth-induced Foxp3+ Treg-cell responses. Infection of ICOS−/− mice with Heligmosomoides polygyrus or Schistosoma mansoni led to a reduced expansion and maintenance of Foxp3+ Treg cells. Moreover, during H. polygyrus infection, ICOS deficiency resulted in increased Foxp3+ Treg-cell apoptosis, a Foxp3+ Treg-cell specific impairment in IL-10 production, and a failure to mount putatively adaptive Helios−Foxp3+ Treg-cell responses within the intestinal lamina propria. Impaired lamina propria Foxp3+ Treg-cell responses were associated with increased production of IL-4 and IL-13 by CD4+ T cells, demonstrating that ICOS dominantly downregulates Type 2 responses at the infection site, sharply contrasting with its Type 2-promoting effects within lymphoid tissue. Thus, ICOS regulates Type 2 immunity in a tissue-specific manner, and plays a key role in driving Foxp3+ Treg-cell expansion and function during helminth infections.

Accumulating evidence points to reactive oxygen species (ROS) as important signaling molecules for cardiomyocyte differentiation in embryonic stem (ES) cells. Given that ES cells are normally maintained and differentiated in medium containing supraphysiological levels of glucose (25 mM), a condition which is known to result in enhanced cellular ROS formation, we questioned whether this high glucose concentration was necessary for cardiomyocyte lineage potential. We show here that ES cells cultured in physiological glucose (5 mM), maintained their general stemness qualities but displayed an altered mitochondrial metabolism, which resulted in decreased ROS production. Furthermore, ES and induced pluripotent stem (iPS) cells differentiated in lower glucose concentrations failed to generate cardiomyocyte structures; an effect mimicked with antioxidant treatments using catalase, N-acetyl cysteine and mitoubiquinone, under high glucose conditions in ES cells. Molecular analysis revealed that ES cells differentiated in 5 mM glucose had reduced expression of the pro-cardiac NOX4 gene and diminished phosphorylation of p38 mitogen-activated protein kinase (MAPK), together with specific changes in the cardiac transcriptional network. These outcomes could be reversed by supplementation of low glucose cultures with ascorbic acid, paradoxically acting as a pro-oxidant. Furthermore, forced expression of an upstream p38 MAPK kinase (MKK6) could bypass the requirement for ROS during differentiation to cardiomyocytes under low glucose conditions, illustrating a key role for p38 in the cardiac differentiation program. Together these data demonstrate that endogenous ROS control is important for cardiomyocyte formation from ES cells, and furthermore that supraphysiological glucose, by supplying ROS, is absolutely required.

Remodelling of mitochondrial metabolism is a hallmark of cancer. Mutations in the genes encoding succinate dehydrogenase (SDH), a key Krebs cycle component, are associated with hereditary predisposition to pheochromocytoma and paraganglioma, through mechanisms which are largely unknown. Recently, the jumonji-domain histone demethylases have emerged as a novel family of 2-oxoglutarate-dependent chromatin modifiers with credible functions in tumourigenesis. Using pharmacological and siRNA methodologies we show that increased methylation of histone H3 is a general consequence of SDH loss-of-function in cultured mammalian cells and can be reversed by overexpression of the JMJD3 histone demethylase. ChIP analysis revealed that the core promoter of IGFBP7, which encodes a secreted protein upregulated after loss of SDHB, showed decreased occupancy by H3K27me3 in the absence of SDH. Finally, we provide the first evidence that the chief (type I) cell is the major methylated histone-immunoreactive constituent of paraganglioma. These results support the notion that loss of mitochondrial function alters epigenetic processes and might provide a signature methylation mark for paraganglioma. FindingsForming part of complex II of the respiratory chain, succinate dehydrogenase (SDH) is situated at the intersection of the tricarboxylic acid (Krebs) cycle and oxidative phosphorylation. This combination of functions places SDH at the centre of two essential energy-producing metabolic processes of the cell. Recently, SDH genes have been considered as tumour suppressors since germ line inactivating mutations in the SDHB, C and D subunit genes can predispose individuals to hereditary paraganglioma (HPGL) [1,2] and phaeochromocytoma [3]. HPGL tumours can be found in the carotid body, a chemoreceptor organ consisting of several cell types [4]. The most predominant cell type in the carotid body is the chief (type I) cell; these cells, of neural crest origin, are arranged in rounded cell nests. The second prominent cell type is the type II gliallike (sustentacular) cell, which surrounds the nest of chief cells. Together, these cells form the striking cell ball of the paraganglion, traditionally referred to as "zellballen" [5].Although the mechanism(s) linking SDH deficiency to tumour formation remain poorly understood, an activation of the hypoxia pathway is frequently associated with SDH loss of function [6,7]. This results in the stabilization

Exposure to limiting oxygen in cells and tissues induce the stabilization and transcriptional activation of the hypoxia-inducible factor 1 alpha (HIF-1a) protein, a key regulator of the hypoxic response. Reactive oxygen species (ROS) generation has been implicated in the stabilization of HIF-1a during this response, but this is still a matter of some debate. In this study we utilize a mitochondria-targeted antioxidant, mitoubiquinone (MitoQ), and examine its effects on the hypoxic stabilization of HIF-1a. Our results show that under conditions of reduced oxygen (3% O 2 ), MitoQ ablated the hypoxic induction of ROS generation and destabilized HIF-1a protein. This in turn led to an abrogation of HIF-1 transcriptional activity. Normoxic stabilization of HIF-1a, on the other hand, was unchanged in the presence of MitoQ suggesting that ROS were not involved. This study strongly suggests that mitochondrial ROS contribute to the hypoxic stabilization of HIF-1a.