The role of innate cell PTP1B in susceptibility to infection

The immune system is a critical component for maintaining health. As the population ages they become more susceptible to infections due to changes in physiological and morphological functions of the immune system and the loss of its adaptability (immunosenescence).

Life-threatening infections have risen sharply in recent years, owing to the greater aged population as well as therapeutics used to combat age-induced disorders1,2. This emerging crisis has created the growing need to better understand the molecular mechanisms controlling protective immune responses to infection, naturally in health, and in aging.

The diminished immunological response to infection in ageing is especially related to a functional insufficiency of monocytes and macrophages. An essential component of the innate response to infection involves macrophages recognising pathogen cell wall components and engulfing and destroying cells through phagocytosis, cytokine/ROS production, antimicrobial peptides and activation of adaptive immune responses3.

Host immune cells express pattern recognition receptors that sense the pathogen-associated molecular patterns (PAMPs). However, the exact molecules and pathways controlling downstream cell signalling mechanisms and how these can be altered with age, are still unclear.

Based on our exciting new findings, we propose PTP1B as a major regulator of macrophage function and can direct the output of transcriptional responses induced by infection. PTP1B is an abundant, widely-expressed non-receptor protein tyrosine phosphatase that modulates important signalling pathways including an ability to dephosphorylate and inactivate the insulin receptor3 and regulate Jak/STAT immune mediated responses. PTP1B is implicated in the development of inflammation and insulin resistance associated with obesity during aging.

PTP1B is already a validated therapeutic target for age-associated diabetes and obesity, as well as HER2-positive breast cancer, and inhibitors are currently in Phase II clinical trials. However, how these new therapeutics could influence susceptibility to infection has not been documented. We have shown that, on activation with TLR4 agonists, PTP1B limits anti-inflammatory IL-10 production and signaling in macrophages and that myeloid PTP1B-deficient mice are protected against diet and age-induced obesity and insulin-resistance4.

In preliminary studies we have now found that loss of PTP1B, specifically in myeloid cells (LysM PTP1B-/-), significantly alters the susceptibility of these mice to a model of systemic fungal infection (Candida albicans) and that macrophages from these mice demonstrate abnormal inflammatory responses to infection. These data therefore indicate that PTP1B plays an important role in regulation of immune responses to infection.

Taking advantage of our well-established in vivo infection models and novel cutting edge technologies, the aim of the studentship is explore this hypothesis and to fully characterise cellular and immunological responses to models of bacterial (Staphylococcus aureus) and fungal (Candida albicans) infection in both macrophages and in mice deficient in PTP1B. Training will be provided in generating infection models in young and aged knockout mice and their analysis, primary macrophage isolation and culture, siRNA mediated gene knockdown, macrophage functional assays including lime lapse phagocytosis and cytokine/ROS production output and novel intracellular signalling analysis techniques. Our objectives are to:

1.Determine, in young and aged activated human and murine macrophages, the influence of PTP1B on cellular responses to C. albicans and S. aureus infection (including uptake and cytokine production).

2.Define the specific intracellular signalling pathways that are controlled by PTP1B on infection of macrophages with C. albicans and S. aureus.

3.Characterise the immunological response to systemic fungal infection in myeloid specific PTP1B knockout animals in terms of effects on cellular and cytokine inflammatory activities, and the effect of aging on these processes.

This studentship provides an exciting and unique opportunity to bring together areas of expertise in macrophage biology, cell signalling, ageing and bacterial and fungal infection to answer important questions on the basic biological and molecular mechanisms by which PTP1B can influence susceptibility to opportunistic pathogens.