Toll Like Receptor 4 is not targeted to the lysosome in Cystic Fibrosis airway epithelial cells.

1Keele University.
AJP Lung Cellular and Molecular Physiology (Impact Factor: 4.08). 01/2013; 304(5). DOI: 10.1152/ajplung.00372.2011
Source: PubMed


The innate immune response to bacterial infection is mediated through Toll-Like-Receptors, which trigger tightly regulated signaling cascades through transcription factors including Nuclear Factor-kappa B (NF-κB). LPS activation of TLR4 triggers internalisation of the receptor-ligand complex which is directed towards lysosomal degradation or endocytic recycling. Cystic Fibrosis (CF) patients display a robust and uncontrolled inflammatory response to bacterial infection, suggesting a defect in regulation. This study examined the intracellular trafficking of TLR4 in CF and non-CF airway epithelial cells following stimulation with LPS. We employed cells lines (16HBE14o-, CFBE41o- (CF) and CFTR-complemented CFBE41o-) and confirmed selected experiments in primary nasal epithelial cells from non-CF controls and CF patients (F508del homozygous). In control cells TLR4 expression (surface / cytoplasmic) was reduced after LPS, but remained unchanged in CF cells, and was accompanied by a heightened inflammatory response 24h after stimulation. All cells expressed markers of the early (EEA1) and late (Rab7b) endosomes at basal levels. Only CF cells displayed persistent expression of Rab7b following stimulation. Rab7 variants may directly internalize bacteria to the Golgi (recycling) or the lysosome (degradation). TLR4 co-localised with the lysosomal marker LAMP1 in 16HBE14o-, suggesting that TLR4 is targeted for lysosomal degradation in these cells. This co-localisation was not observed in CFBE41o- where persistent expression of Rab7 and release of pro-inflammatory cytokines was detected. Consistent with the apparent inability of CF cells to target TLR4 towards the lysosome, we observed persistent surface and cytoplasmic TLR4 expression in CFBE41o-. This defect may account for the prolonged inflammation associated with CF.

20 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: The innate immune system is a highly sensitive organ of perception sensing any cell stress and tissue injury. Its major type of response to all potential inciting and dangerous challenges is inflammation and tissue repair and, if needed, induction of a supportive adaptive immune response, the aim always being to maintain homeostasis. However, although initially beneficial, innate immunity-mediated, protection-intended repair processes become pathogenic when they are exaggerated and uncontrolled, resulting in permanent fibrosis which replaces atrophic or dying tissue and may lead to organ dysfunction or even failure. In this sense, atherosclerosis and organ fibrosis reflect classical disorders caused by an overreacting innate immune system. Strikingly, these two pathologies dominate the development of chronic allograft dysfunction as the main clinical problem still left in transplantation medicine. Growing evidence suggests that acute and chronic allograft injuries, including alloimmune-, isoimmune-, nonimmune-, and infection-mediated insults, not only lead to cell death-associated graft atrophy but also activate the innate immune system which, over time, leads to uncontrolled intragraft fibrogenesis, thereby compromising allograft function. Acute and chronic allograft injuries lead to induction of damage-associated molecular patterns (DAMPs) which, after recognition by pattern recognition receptors, activate cells of the innate immune system such as donor-derived intragraft fibroblasts and vascular cells as well as recipient-derived graft-invading macrophages and leukocytes. It is mainly the orchestrated action and function of these cells that slowly but steadily metamorphose the originally life-saving allograft into a poorly functioning organ of marginal viability.
    09/2013; 36(5):209-28. DOI:10.4103/2319-4170.117622
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Cystic fibrosis (CF) lung is a niche colonised by a diverse group of organisms, with a more limited number of species including P. aeruginosa dominating in adult patients. Whether all members of this microbial community play a direct or indirect role in pulmonary decline has yet to be fully elucidated, but investigations of their interactions with both co-colonising species and with host cells are beginning to shed light on their virulence potential. It is also emerging that some microbial species within this community adapt as chronic infection is established to survive the hostile environment of the lung, to minimise host clearance and to resist therapeutic intervention. Interactions of clearly defined CF pathogens with the host have been recently reviewed (Callaghan and McClean, 2012). This review highlights the recent developments in CF microbiology focussing on the cooperative, competitive and adaptive interactions of established and emerging pathogens in the lung microbiome.
    Environmental Microbiology 05/2014; 17(1). DOI:10.1111/1462-2920.12504 · 6.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Lung infection by Gram-negative bacteria is a major cause of morbidity and mortality in humans. Lipopolysaccharide (LPS), located in the outer membrane of the Gram-negative bacterial cell wall, is a highly potent stimulus of immune and structural cells via the TLR4/MD2 complex whose function is sequentially regulated by defined subsets of adaptor proteins. Regulatory mechanisms of lung-specific defense pathways point at the crucial role of resident alveolar macrophages, alveolar epithelial cells, the TLR4 receptor pathway, and lung surfactant in shaping the innate immune response to Gram-negative bacteria and LPS. During the past decade intracellular spatiotemporal localization of TLR4 emerged as a key feature of TLR4 function. Here, we briefly review lung cell type- and compartment-specific mechanisms of LPS-induced TLR4 regulation with a focus on primary resident hematopoietic and structural cells as well as modifying microenvironmental factors involved.
    Communicative & integrative biology 06/2014; 7(4):e29053. DOI:10.4161/cib.29053
Show more