Bioenergetika imunitnho systmu a imunosupresivn mechanismy APCs

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Bioenergetika imunitního systému a
imunosupresivní mechanismy APCs

• Pokroky v imunologii
• Brezen 2006
• Karel Drbal

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Cellular energy metabolism

• ATP is the principal immediate donor of free
  energy. Turnover is very high an ATP molecule is
  typically consumed within a minute of its
  formation

Buttgereit ImmunolToday 21192
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Energy supply and immune functions (examples)

• Energy deficit in Late stages of septic and
  haemorrhagic shock inflammation is followed by
  marked immunosuppression of T cells
• increased mitochondrial deficit with ageing gt
  loss of T cell function
• apoptosis x necrosis x autophagy type of cell
  death might be determined by the intensity and
  duration of cell damage and ATP absence/presence

Buttgereit ImmunolToday 21192
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Energy supply and immune functions (2)
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Growth factors costimulation regulate nutrient
uptake

• The mitogenic stimulation of thymocytes or naive
  T cells induces an almost 20-fold increase in
  glucose uptake within 1 hour (glucose catabolism
  required for cell cycle entry)

• AEROBIC GLYCOLYSIS

METABOLIC SWITCH
OXIDATIVE PHOSPHORYLATION
only for survival
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T cell quiescence

• Self-maintenance of quiescent T cells is a highly
  regulated and energetically demanding process.
• Quiescence is maintained, in part, by regulated
  protein turnover, which consumes a large amount
  of ATP.
• survival-promoting cytokines induce transcription
  factors to maintain actively the expression of
  inhibitors of the genes that are involved in
  cellular activation (IkB)
• family of E3 UBIQUITIN LIGASES functions to
  maintain peripheral T cells, by potentiating the
  rapid degradation of protein kinases such as
  those that are activated by antigen- or
  cytokine-receptor ligation

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Terms

• GLYCOLYSIS
• A metabolic process that occurs in the cytosol
  and breaks down one molecule of glucose into two
  molecules of pyruvate, resulting in the
  production of ATP. Pyruvate is converted to
  lactate, which regenerates the NAD that is
  required as an electron acceptor in this
  catabolic process. Alternatively, pyruvate can be
  oxidized in the tricarboxylic-acid cycle, and NAD
  can be regenerated in one of two mitochondrial
  shuttles that end with electron donation to the
  electron-transport chain.
• OXIDATIVE PHOSPHORYLATION
• A metabolic process that encompasses two sets of
  reactions. The first reaction involves the
  conversion of intermediate molecules (pyruvate
  and fatty acids) to acetyl coenzyme A
  (acetyl-CoA) and the degradation of acetyl-CoA to
  carbon dioxide in the tricarboxylic-acid cycle,
  yielding free electrons that are carried by NADH
  and FADH2. The second reaction involves the
  transfer of electrons from NADH and FADH2 to the
  electron-transport chain, resulting in the
  movement of protons out of the mitochondrial
  matrix. The resulting electrochemical potential
  is used by the F1F0 ATP synthase to synthesize
  ATP.
• CATABOLIC METABOLISM
• The breakdown of complex substances into simpler
  ones. This often allows cells to capture the
  released reduction equivalents and channel them
  into ATP production. Examples include the
  oxidation of fatty acids and amino acids.
• ANABOLIC METABOLISM
• The synthesis of complex macromolecules from
  simpler intermediates at the expense of ATP.
  Examples include the synthesis of nucleotides
  from ribose-5-phosphate, lipids from acetyl
  coenzyme A, and proteins from amino acids.
• AEROBIC GLYCOLYSIS
• A metabolic process that is preferentially
  induced in proliferating lymphocytes and is also
  characteristic of neoplastic and transformed
  cells. In contrast to anaerobic conditions (such
  as in skeletal muscle and inflamed tissues), in
  which glycolysis is the main source of ATP,
  lymphocytes in the peripheral blood are not
  exposed to low oxygen concentrations however,
  they continue to excrete excess pyruvate as
  lactate rather than fully oxidizing it in the
  tricarboxylic-acid cycle.

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The PI3K pathway regulates energy metabolism

• Stimuli
• cytokines (both PI3K and JAK pathways)
• costimulation - CD28/CTLA4-B7 (mainly PI3K
  pathway)
• Genes involved in coordination of catabolic and
  anabolic metabolism
• TSC1 (tuberous sclerosis1), TSC2,
• RHEB (RAS homologue enriched in brain),
• RICTOR (rapamycin-insensitive companion of TOR)
• RAPTOR (regulatory associated protein of TOR),
• PTEN (phosphatase and tensin homologue) and
• PP2A (protein phosphatase 2A)
• and the core kinases of this pathway AKT/PKB,
  AMPK, PIM2 and TOR.

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Inhibition of the PI3K pathway by rapamycin

• potent inhibitor of energy metabolism
• G1 arrest
• suppresses cap-dependent translation
• stimulus- or cell-type specific
• selective accumulation of CD4CD25 regulatory T
  cells
• does not phenocopy the effects of growth-factor
  or nutrient deprivation
• alternative pathway of metabolism regulation
• JAK induced expression of PIM1, PIM2 oncogenic
  kinases
• immunotherapeutics
• patients with autoimmune or infectious diseases
  or for those who are undergoing solid-organ
  transplantation

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Effects of other drugs on cellular metabolism

• Glucocorticoids (major side-effects !)
• Lazaroids (free radical scavengers and membrane
  stabilizers)
• Cyclosporine A and FK506 (cyclophilin-targeted
  immunosuppressants)
• Channel blockers - promising! (voltage-gated K
  channel Kv1.3, Ca2-activated (KCa) channels)

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APCs regulate uptake of essential amino acids in
T cells

• Cysteine redox regulation of cysteine membrane
  transport
• APCs regulate T-cell proliferation by controlling
  the availability of the amino acid cysteine,
  which is present only at a low concentration in
  blood plasma (intracellular reduced cysteine and
  extracellular oxidized di-cystine equilibrium is
  defined by redox conditions both inside and
  outside the cell) but lymphocytes lack specific
  cystine transporters and cannot synthesize
  cysteine. The activation of dendritic cells or
  macrophages by ligation of CD40 or by treatment
  with LPS or TNF increases cystine uptake and
  cysteine production by these cells, and it also
  promotes the secretion of thioredoxin, which
  reduces extracellular cystine to cysteine,
  thereby making cysteine available to nearby
  lymphocytes.
• Tryptophan catabolism (deprivation toxic
  metabolites)
• APCs can also control the T-cell response by
  regulating the extracellular concentration of
  tryptophan. Tryptophan is enzymatically degraded
  by indoleamine 2,3-dioxygenase (IDO), which is
  expressed at high concentrations in placenta and
  potentiates fetal tolerance during embryonic
  development. Induction of IDO activity in
  macrophages depletes extracellular tryptophan,
  and tryptophan metabolites can suppress the
  immune response by inducing either T-cell death,
  through the generation of reactive oxygen
  species, or T-cell anergy, by activating the
  stress responsive kinase GCN2. Macrophages
  themselves escape growth limitation that is
  caused by tryptophan catabolism, in part, by
  upregulating expression of tryptophanyl tRNA
  synthetase.
• Arginine catabolism (deprivation toxic
  metabolites)
• increased metabolism of L-arginine by myeloid
  cells can result in the impairment of lymphocyte
  responses to antigen during immune responses and
  tumour growth
• arginase and nitric-oxide synthase (use
  L-arginine as substrate) are crucial components
  of this lymphocyte-suppression pathway

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Overview of IDO/tryptophan pathways
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Myeloid suppressor cells-T cell relationship (IDO)

• Myeloid cell differentiation Pro-inflammatory
  signals (such as CD40 ligand, TNF, LPS)
  versusTolerogenic signals (such as
  CTLA4CD80/CD86 ligation by regulatory T cells)
• Production of major anti-inflammatory T cell
  suppressive mediators
• prostaglandin E2, eicosanoids and cytokines
  (IL-10, TGFb)
• Reactive free radicals (ROS, RNOS) are also
  suppressive for T cells
• Novel mechanism of essential AA deprivation by
  IDO (indoleamine 2,3 dioxygenase), ARG (arginase)
  and NOS (nitric oxide synthase)
• ancient antibacterial mechanisms where
  macrophages inhibit microbial infections by
  producing IDO, which catabolizes tryptophan
  for single-celled organisms, nutrient depletion
  is a common biological strategy to control
  proliferation of competing cells (also iron
  chelator lactoferrin)
• local veto for T cell response tolerance
  induction at feto-maternal barrier (IDO
  expression in placenta)
• IFNg , regulatory T cells CTLA4 gt induced Mf IDO
  expression
• treatment with 1-methyl-tryptophan (a
  pharmacological inhibitor of IDO) induced rapid
  and uniform rejection of allogeneic conceptus a
  few days after implantation.
• T cell has a cell-cycle regulatory checkpoint for
  available free tryptophan

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Mutual NOS-IDO regulation

• inflammation (IFNg) induced NO synthetase (iNOS)
  produce NO which inhibits IDO activity
• binds to the heme complex of IDO
• some tryptophan metabolites inhibit iNOS activity
• iNOS and IDO gene expression is coordinated by
  proinflammatory cytokines
• Tryptophan-tRNA synthetase is the only tRNA
  synthetase gene inducible by IFNg
• allows cells that produce IDO to access lower
  tryptophan concentrations during inflammation in
  order to survive.
• ? is there a special reason why tryptophan
  catabolism might be used to regulate T-cell
  proliferation?
• tryptophan is the most energetically expensive
  amino acid to synthesize.

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IDO regulate immune response

• chronic infection
• chronic lentiviral infection (HIV) occur despite
  initially potent antiviral T-cell responses.
• chronic inflammation
• provoke sustained IDO production
• autoimmunity
• the only amino acid whose metabolism has been
  linked with autoimmunity
• cancer
• tumor-resident macrophages suppress infiltrated T
  cells (similar to placenta)

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L-arginine overview

• conditionally essential AA
• metabolized by the enzymes ARG (arginase)
  producing urea and L-ornithine and iNOS
  (inducible nitric oxide synthase) which give rise
  to nitric oxide (NO) and L-citrulline

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L-arginine T cell suppression-ARG

• ARG dependent
• MSC consumed l-arginine from the extracellular
  environment, and they inhibited re-expression of
  the ?-chain of CD3 after its TCR-signalling-induce
  d internalization
• amino-acid loss and urea have been shown to alter
  the translation of various mRNAs in other cell
  types, through the kinase pathways that involve
  general control non-depressible 2 (GCN2) and
  mammalian target of rapamycin (mTOR)

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L-arginine T cell suppression-iNOS

• NOS dependent
• NO is known to negatively regulate
  intracellular-signalling proteins either
  directly, by S-nitrosylation of crucial cysteine
  residues, or indirectly, by activation of soluble
  guanylate cyclase and cyclic-GMP-dependent
  protein kinase
• block cytokine-JAK-STAT pathway
• production of reactive free radicals

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L-arginine T cell suppression

• NOS ARG dependent
• radicals (ROS, RNOS)!!! (most potent
  peroxynitrite ONOO-)
• induction of T cell death

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ROS, RNOS

• REACTIVE OXYGEN SPECIES (ROS). Aerobic organisms
  derive their energy from the reduction of oxygen
  (O2). The metabolism of O2, and in particular its
  reduction through the mitochondrial
  electrontransfer chain, generates by-products
  such as superoxide (O2), hydrogen peroxide
  (H2O2) and hydroxyl radicals (OH). These three
  species and the unstable intermediates that are
  formed by lipid peroxidation are referred to as
  ROS. ROS can damage important intracellular
  targets, such as DNA, carbohydrates or proteins.
• REACTIVE NITROGEN OXIDE SPECIES (RNOS). Nitric
  oxide (NO) chemistry is complex because of the
  extreme reactivity of NO, which can result in the
  formation of different reactive nitrogen
  intermediates (RNI) depending on the amount of NO
  that is produced by cells. At low concentrations,
  NO reacts directly with metals and radicals. At
  higher concentrations, indirect effects prevail,
  and these include several oxidation or
  nitrosylation reactions with oxygen (O2) that
  result in the production of various moieties. NO
  and related RNI are effective antimicrobial
  agents and signal-transducing molecules. The term
  RNOS, although less frequently used, more
  specifically indicates this family of molecules
  than does the term RNI.

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