PDE2A2 regulates mitochondria morphology and apoptotic cell death via local modulation of cAMP/PKA signalling

cAMP/PKA signalling is compartmentalised with tight spatial and temporal control of signal propagation underpinning specificity of response. The cAMP-degrading enzymes, phosphodiesterases (PDEs), localise to specific subcellular domains within which they control local cAMP levels and are key regulators of signal compartmentalisation. Several components of the cAMP/PKA cascade are located to different mitochondrial sub-compartments, suggesting the presence of multiple cAMP/PKA signalling domains within the organelle. The function and regulation of these domains remain largely unknown. Here, we describe a novel cAMP/PKA signalling domain localised at mitochondrial membranes and regulated by PDE2A2. Using pharmacological and genetic approaches combined with real-time FRET imaging and high resolution microscopy, we demonstrate that in rat cardiac myocytes and other cell types mitochondrial PDE2A2 regulates local cAMP levels and PKA-dependent phosphorylation of Drp1. We further demonstrate that inhibition of PDE2A, by enhancing the hormone-dependent cAMP response locally, affects mitochondria dynamics and protects from apoptotic cell death.

Circulating cytokine levels and antibody responses to human Schistosoma haematobium: IL-5 and IL-10 levels depend upon age and infection status

Experimental schistosome infections induce strong parasite-specific Th2 responses. This study aims to relate human systemic cytokine and antibody levels to schistosome infection levels and history. Levels of anti-Schistosoma haematobium antibodies (directed against crude cercariae, egg and adult worm antigens) and plasma cytokines (IFN-γ, IL-2, IL-4, IL-5, IL-10, IL-13, IL-17, IL-21, and IL-23) were measured by ELISA in 227 Zimbabweans (6–60 years old) in a schistosome-endemic area and related to age and infection status. Egg-positive people had significantly higher levels of specific antibodies, IL-2, IFN-γ and IL-23. In contrast, egg-negative individuals had significantly higher circulating IL-10, IL-4, IL-13 and IL-21 that were detected with high frequency in all participants. Subjects with detectable plasma IL-17 produced few or no eggs. When analyzed by age, IL-4 and IL-10 increased significantly, as did schistosome-specific antibodies. However, when age was combined with infection status, IL-5 declined over time in egg-positive people, while increased with age in the egg-negative group. Older, lifelong residents had significantly higher IL-4 and IL-5 levels than younger egg-negative people. Thus, a mixed Th1/Th2 systemic environment occurs in people with patent schistosome infection, while a stronger Th2-dominated suite of cytokines is evident in egg-negative individuals.

T-cell regulation in helminth parasite infections: implications for inflammatory diseases

The field of infectious disease immunology is at an exciting intersection with new concepts in immune regulation meeting with the dynamics of infectious diseases. We discuss how the identification of regulatory mechanisms has already helped develop new models to understand helminth infections, which remain among the most prevalent chronic diseases in the world today. The epidemiological imbalance between helminth infections in developing countries, and intensifying allergies and autoimmune pathologies in the industrialised nations, seems to reflect a fundamental shift in regulation of immune responsiveness. Experimental studies have verified that helminths can downmodulate a range of immunopathological conditions, with the regulatory T cell being one of the most common mechanisms in play. We discuss further the context of host genetic predisposition, together with the impact of infection on the evolution of the human immune system, and suggest future strategies to harness our new understanding of helminth organisms in order to control both infectious and non-infectious immunological disorders.

Specificity of predominant IgG4 antibodies to adult and microfilarial stages of Brugia malayi

Human infections with filarial nematodes such as Brugia malayi are accompanied by unusually high titres of parasite-specific IgG4 antibodies. We have compared the profile of antigens recognised by filarial-specific IgG1 and IgG4 isotypes by Western blotting. Serum samples were collected from 120 subjects exposed to Brugia malayi, divided into three groups of asymptomatic amicrofilaraemic (endemic normal), microfilaraemic, and elephantiasis patients. Antigen preparations were tested from both adult B. malayi parasites, and from microfilariae; 24 distinct bands were analysed from the former, and 19 from the latter. Both qualitative scoring for band reactivity, and densitometric scanning of major bands, were employed. The consistent result was one of high and preferential IgG4 reactivity to a set of low molecular weight bands, of 15, 17, 20, 31 and 33 kDa; most of the 19 other bands showed higher reactivity with IgG4. Analysis of Western blot patterns showed an overall tendency for stronger IgG4 responses in microfilaraemic cases, and higher IgG1 responses in elephantiasis patients, consistent with published studies using ELISA on unfractionated parasite extracts. This study has defined an array of filarial antigens from each stage, and relative levels of IgG4 recognition, which will be important in unravelling distinct immune responses to this complex parasite.

A member of the TGF-beta receptor gene family in the parasitic nematode Brugia pahangi

The full length cDNA sequence of a Type I transforming growth factor-beta (TGF-beta) receptor has been isolated from the filarial parasitic nematode Brugia pahangi. This new gene, designated Bp-trk-1, encodes a predicted 645 amino acid sequence with an N-terminal hydrophobic stretch which may act as a signal peptide. The extracellular portion (residues 15-187) is cysteine-rich and has three potential N-glycosylation sites. At positions 250-255 the protein contains the glycine-serine rich motif characteristic of Type I receptors. The closest homologue is a Caenorhabditis elegans gene (Q09488) in cosmid C32D5.2 which shares 67% amino acid identity with Bp-trk-1 in the most conserved kinase domain (aa 259-482). Other type I receptors such as C. elegans daf-1 and Drosophila tkv show 38-53% identity in the same region. Some residues conserved in Drosophila and vertebrates are not present in the B. pahangi sequence. RT-PCR amplification has been used to show that the transcript is expressed in the three main stages of the B. pahangi life cycle: microfilariae, infective larvae and adults. The ligand remains unknown at this time but is likely to be most similar to that for C. elegans Q09488.

Secreted and surface antigens from larval stages of Wuchereria bancrofti, the major human lymphatic filarial parasite

Antigenic proteins of microfilariae and infective larvae of Wuchereria bancrofti have been identified by intrinsic and extrinsic radiolabelling, and specific immunoprecipitation with sera from filarial patients. From 125I surface-labelling experiments, the most prominent antigen on both stages is of relative molecular mass (Mr) 17 000, while a molecule of similar size is both synthesized and released in vitro following labelling with [35S]methionine. A second similarity between the two stages is the production and secretion of a Mr 21 000 component, which is, however, not detected on the worm surfaces. A series of additional proteins from larval W. bancrofti are described from each parasite compartment (secreted, surface and somatic) and the antigenicity and specificity of these components explored with serum from patients with filariasis due to W. bancrofti or Brugia species, and with onchocerciasis. Among additional molecules released in vitro we have found a Mr 51 000 antigen from both stages, and also several proteins which are not recognised by antibody from human filarial patients.