The role of mammalian target of rapamycin (mTOR) in macrophage polarization

Macrophages are key orchestrators of the innate immune response with a dynamic role in the promotion and resolution of inflammation. Macrophage polarization to a pro-inflammatory or anti-inflammatory phenotype must be tightly controlled to maintain appropriate responses to stimuli as well as to maintain tissue homeostasis. The nutrient and energy sensor Mammalian Target of Rapamycin (mTOR) integrates upstream signals from the PI3K/Akt pathway to orchestrate cellular protein, lipid, and glucose metabolism. This key metabolic pathway has been implicated in T-helper cell skewing and in the innate immune regulation. The mechanisms of innate immune regulation by mTOR are currently unclear as most studies use pharmacological inhibitors with potential off target effects. In this study, we use a novel model of TSC1 deficiency in myeloid lineage cells to elucidate a role for mTOR in macrophage polarization. We show, for the first time, that Tsc1-deficiency and constitutive mTORC1 activity in macrophages leads to a marked defect in M2 polarization when stimulated with the Th2 cytokine IL-4. Tsc1-deficient macrophages display attenuated Akt signaling in response to IL-4 consistent with negative feedback of mTORC1 on upstream IRS2/PI3K signaling, and we demonstrate that this parallel signaling pathway is critical for induction of a subset of M2 markers. Tsc1-deficient macrophages fail to upregulate the M2 genes Pgc-1!, Arg-1, Fizz-1, and Mgl1 in addition to other M2 markers despite normal STAT6 signaling in response to IL-4. Consistent with downregulation of Pgc-1!, Tsc1-deficient macrophages also display defects in fatty acid metabolism and mitchochondrial biogenesis. Furthermore, LPS stimulation in Tsc-1 deficient macrophages leads to an enhanced inflammatory response with increased production of pro-inflammatory cytokines. We believe that Tsc1-deficient macrophages are a model of constitutive mTORC1 activity akin to obesity, where chronic nutrient excess leads to increases in mTORC1 activity, attenuation of IRS/PI3K/Akt signaling, and defective M2 polarization of macrophages in metabolic tissues

Aberrant Cytoplasm Localization and Protein Stability of SIRT1 is Regulated by PI3K/IGF-1R Signaling in Human Cancer Cells

SIRT1, an NAD-dependent histone/protein deacetylase, has classically been thought of as a nuclear protein. In this study, we demonstrate that SIRT1 is mainly localized in the nucleus of normal cells, but is predominantly localized in the cytoplasm of the cancer / transformed cells we tested. We found this predominant cytoplasmic localization of SIRT1 is regulated by elevated mitotic activity and PI3K/IGF-1R signaling in cancer cells. We show that aberrant cytoplasmic localization of SIRT1 is due to increased protein stability and is regulated by PI3K/IGF-1R signaling. In addition, we determined that SIRT1 is required for PI3K-mediated cancer cell growth. Our study represents the first identification that aberrant cytoplasm localization is one of the specific alternations to SIRT1 that occur in cancer cells, and PI3K/IGF-1R signaling plays an important role in the regulation of cytoplasmic SIRT1 stability. Our findings suggest that the over-expressed cytoplasmic SIRT1 in cancer cells may greatly contribute to its cancer-specific function by working downstream of the PI3K/IGF-1R signaling pathway

The TSC-mTOR pathway regulates macrophage polarization

Macrophages are able to polarize to proinflammatory M1 or alternative M2 states with distinct phenotypes and physiological functions. How metabolic status regulates macrophage polarization remains not well understood, and here we examine the role of mTOR (Mechanistic Target of Rapamycin), a central metabolic pathway that couples nutrient sensing to regulation of metabolic processes. Using a mouse model in which myeloid lineage specific deletion of Tsc1 (Tsc1Δ/Δ) leads to constitutive mTOR Complex 1 (mTORC1) activation, we find that Tsc1Δ/Δ macrophages are refractory to IL-4 induced M2 polarization, but produce increased inflammatory responses to proinflammatory stimuli. Moreover, mTORC1-mediated downregulation of Akt signaling critically contributes to defective polarization. These findings highlight a key role for the mTOR pathway in regulating macrophage polarization, and suggest how nutrient sensing and metabolic status could be “hard-wired” to control of macrophage function, with broad implications for regulation of Type 2 immunity, inflammation, and allergy

mTORC1 suppresses PIM3 expression via miR-33 encoded by the SREBP loci

The mechanistic target of rapamycin complex 1 (mTORC1) is a central regulator of cell growth that is often aberrantly activated in cancer. However, mTORC1 inhibitors, such as rapamycin, have limited effectiveness as single agent cancer therapies, with feedback mechanisms inherent to the signaling network thought to diminish the anti-tumor effects of mTORC1 inhibition. Here, we identify the protein kinase and proto-oncogene PIM3 as being repressed downstream of mTORC1 signaling. PIM3 expression is suppressed in cells with loss of the tuberous sclerosis complex (TSC) tumor suppressors, which exhibit growth factor-independent activation of mTORC1, and in the mouse liver upon feeding-induced activation of mTORC1. Inhibition of mTORC1 with rapamycin induces PIM3 transcript and protein levels in a variety of settings. Suppression of PIM3 involves the sterol regulatory element-binding (SREBP) transcription factors SREBP1 and 2, whose activation and mRNA expression are stimulated by mTORC1 signaling. We find that PIM3 repression is mediated by miR-33, an intronic microRNA encoded within the SREBP loci, the expression of which is decreased with rapamycin. These results demonstrate that PIM3 is induced upon mTORC1 inhibition, with potential implications for the effects of mTORC1 inhibitors in TSC, cancers, and the many other disease settings influenced by aberrant mTORC1 signaling

Akt-mTORC1 signaling regulates Acly to integrate metabolic input to control of macrophage activation

Macrophage activation/polarization to distinct functional states is critically supported by metabolic shifts. How polarizing signals coordinate metabolic and functional reprogramming, and the potential implications for control of macrophage activation, remains poorly understood. Here we show that IL-4 signaling co-opts the Akt-mTORC1 pathway to regulate Acly, a key enzyme in Ac-CoA synthesis, leading to increased histone acetylation and M2 gene induction. Only a subset of M2 genes is controlled in this way, including those regulating cellular proliferation and chemokine production. Moreover, metabolic signals impinge on the Akt-mTORC1 axis for such control of M2 activation. We propose that Akt-mTORC1 signaling calibrates metabolic state to energetically demanding aspects of M2 activation, which may define a new role for metabolism in supporting macrophage activation

Pathways to Well-Being in Later Life: Socioeconomic and Health Determinants Across the Life Course of Australian Baby Boomers

In many countries like Australia and the United States, baby boomers are referred to as the 'lucky cohort', yet there has been little research on the origins and extent of inequalities within this cohort. This study uses path analysis to investigate direct and indirect effects of childhood and adult socioeconomic status and health on two subjective well-being measures: quality of life and life satisfaction. Retrospective life course data were obtained for 1,261 people aged 60 to 64 in the 2011-12 Life Histories and Health survey, a sub-study of the Australian 45 and Up Study. Supporting an accumulation model, the number of negative childhood and adult exposures were inversely related to both types of well-being. Consistent with a critical period model, childhood exposures had small but significant effects on subjective well-being and were relatively more important for quality of life than for life satisfaction. However, these childhood effects were largely indirect and significantly mediated by more proximal adult exposures, providing support for a pathway model. A key implication of this research is that the critical period for later life well-being is significant in adulthood rather than childhood, suggesting that there may be key opportunities for improving individuals' later life well-being far beyond the early, formative years. This research highlights the importance of understanding how earlier life exposures impact experiences in later life, and investing in health and socioeconomic opportunities to reduce inequalities across all stages of life

Selection, adaptation and advantage. Later-life health and wellbeing of English migrants to Australia

This study investigates the long-term impact of English adult migration to Australia by comparing health and wellbeing outcomes in later life of English migrants to their counterparts who remained in England (non-migrants) and to native-born Australians. It traces the influence of selection, adaptation and advantage as three mechanisms that can influence migrant health in later life. The analysis utilises data for a cohort aged 60–64 years from the Australian Life Histories and Health (LHH) survey (n = 1088), a sub-study of the Australian 45 and Up Study, in combination with a matched cohort from the English Longitudinal Study of Ageing (ELSA) (n = 1139). Social rather than health characteristics were found to play a role in the selection of English migrants. English migrants reported higher subjective quality of life than English non-migrants, and better physical health than the Australian-born, but their mental health outcomes did not significantly differ from the other cohorts. The comparatively better later-life outcomes for the English migrants can partly be linked to advantage, as they hold higher prestige jobs than the Australian-born at lower levels of education.This work was supported by the Australian Research Council [grant number DP 1096778], UK Medical Research Council [grant number G1001375/1] and UK Economic and Social Research Council [grant number G1001375/1]

Aberrant Cytoplasm Localization and Protein Stability of SIRT1 is Regulated by PI3K/IGF-1R Signaling in Human Cancer Cells

<p>SIRT1, an NAD-dependent histone/protein deacetylase, has classically been thought of as a nuclear protein. In this study, we demonstrate that SIRT1 is mainly localized in the nucleus of normal cells, but is predominantly localized in the cytoplasm of the cancer / transformed cells we tested. We found this predominant cytoplasmic localization of SIRT1 is regulated by elevated mitotic activity and PI3K/IGF-1R signaling in cancer cells. We show that aberrant cytoplasmic localization of SIRT1 is due to increased protein stability and is regulated by PI3K/IGF-1R signaling. In addition, we determined that SIRT1 is required for PI3K-mediated cancer cell growth. Our study represents the first identification that aberrant cytoplasm localization is one of the specific alternations to SIRT1 that occur in cancer cells, and PI3K/IGF-1R signaling plays an important role in the regulation of cytoplasmic SIRT1 stability. Our findings suggest that the over-expressed cytoplasmic SIRT1 in cancer cells may greatly contribute to its cancer-specific function by working downstream of the PI3K/IGF-1R signaling pathway.</p

Adapting data collection methods in the Australian Life Histories and Health Survey: a retrospective life course study

Objective: Ideally, life course data are collected prospectively through an ongoing longitudinal study. We report adaptive multimethod fieldwork procedures that gathered life history data by mail survey and telephone interview, comparable with the face-to-face methods employed in the English Longitudinal Study on Ageing (ELSA). Design: The Australian Life Histories and Health (LHH) Survey was a substudy of the Australian 45 and Up Study, with data collection methods modified from the ELSA Study. A self-complete questionnaire and life history calendar were completed by the participants, followed by a computer-assisted telephone interview recording key life events. Results: The LHH survey developed and tested procedures and instruments that gathered rich life history data within an ongoing Australian longitudinal survey on ageing. Data collection proved to be economical. The use of a self-complete questionnaire in conjunction with a life history calendar and coordinated computer-assisted telephone interview was successful in collecting retrospective life course information, in terms of being thorough, practical and efficient. This study has a diverse collection of data covering the life course, starting with early life experiences and continuing with socioeconomic and health exposures and outcomes during adult life. Conclusions: Mail and telephone methodology can accurately and economically add a life history dimension to an ongoing longitudinal survey. The method is particularly valuable for surveying widely dispersed populations. The results will facilitate understanding of the social determinants of health by gathering data on earlier life exposures as well as comparative data across geographical and societal contexts