Adult stress, glucocorticoids and disease susceptibility

Question 1

What is most stressed caused by?

Answer 1

Much depression has a genetic component/stress induced (precipitating factor often).

Question 2

What is stress?

Answer 2

a severe mental disorder, with or without organic damage, characterized by derangement of personality and loss of contact with reality and causing deterioration of normal social functioning

Question 3

Why can depression be thought of as an adaptation?

Answer 3

epression an adaptation of some kind/ pathological change/ adaptive change that has gone wrong→ It is probably multiple disorders, thus symptoms for it are quite broad (there is no biochemical test).
10% of world population have it at some point→ suggests that it is adaptive in some way

Question 4

Why evolutionarily might depression be beneficial?

Answer 4

Evolutionarily: Depression is a way to manage unachievable goals, to stop you wasting valuable resources. In youths, way to engender pity for you from adults and gain from this but does not work as well in adulthood, opposite happens.

Question 5

What is the first theory for depression and evidence? Hint one pharmacological, one looking at human studies

Answer 5

1. Deficiency of monoamine transmitters at certain sites in the brain (eg noradrenaline, dopamine). Theory first came about from drugs: selective serotonin uptake inhibitors, tricyclic antidepressants (block serotonin reuptake transporter), monoamine oxidase inhibitors (block the break down of serotonin) and they looked at mechanism of action.
   If look at suicide post mortems – find decreased amount of serotonin metabolites in the CSF.

Question 6

What do tricyclic antidepressants do?

Answer 6

They block the serotonin re-uptake transporter

Question 7

What do monoamine oxidase inhibitors do?

Answer 7

block the breakdown of serotonin

Question 8

What is the problem with theory 1?

Answer 8

However if you give something that directly increases serotonin such as L-tryptophan they do not relieve depression. There must be other factors contributing.

Question 9

Which other monoamine is important?

Answer 9

Other monoamines important – dopamine is particularly important for loss of pleasure in life and psychomotor symptoms. Dopaminergic neurons are very stress sensitive. Lisdexamfetamine is particularly good at increasing dopamine in brain, currently being looked at a treatment for stress.

Question 10

What is the second theory for stress? Evidence

Answer 10

2. Neurotrophic model – eg brain derived neurotrophic factors are used to regulate cell death and synapses →adult brain plasticity and adaptability. They seem particularly important in the hippocampus as Small hippocampal volumes are linked to depression. If you chronically stress animal, hippocampal size decreases and there is less neurotrophic factors→ dysregulation of plasticity.

Question 11

Which area of the brain can repair and regrow?

Answer 11

One of the few sites of the brain that can repair and regrow is the hippocampus, means that you can have recovery from depression. Important for consolidation of memories (very important as protective against depression, past experiences that modify how you respond to stress) and emotions.

Question 12

What is the third theory?

Answer 12

Ca 1, 2 and 3 and dentate gyrus are different areas of the hippocampus. Cortisol has damaging effects in Ca1, not Ca 2, Ca3 region it induces neuronal atrophy and thus has a negative effect on synapses.

Question 13

What is cortisols role in depression at physiological levels?

Answer 13

At physiological levels, serotonin and cortisol work together to increase nerve transmission and increase serotonin machinery. • Enhanced transmission via ↑ Ca2+
Impede access to incoming information and induce atrophy Regulate neurogenesis: Inhibit proliferation, Decrease survival

Question 14

What are SSRIs dependent on?

Answer 14

Looking at the SSRIs you find that the effects are lost in 5HT1a knock out mice, particularly if targeted to the hippocampus. SSRIs seem to depend on serotonin production in the hippocampus, especially dentate gyrus.

Question 15

What biological findings are there is depressed people?

Answer 15

Most consistent biological finding is increased cortisol, in about 50% of depressed patients (in plasma, urine and CSF). If you conduct a Dex/CRF (treat with steroid such as dexamethasone then give CRF – in healthy you kickstart negative feedback so CRF will not cause much ACTH release) and in stressed patients the feedback is impaired and you get a high cortisol response.
About 50% of cushings have depression. Long term of treatment with IFN alpha (stimulates steroids) – 50% get depression. Cortisol synthesis inhibitors decrease the incidence of depression.

Question 16

What can chronic depression lead to?

Answer 16

Stress can be a good thing as long is it an acute stress, improves memory consolidation. Chronic impairs retrieval of emotional information and the working memory. Memory serves to put working stamp on experiences.

Question 17

How do anti-depressants generally work?

Answer 17

Antidepressants may work by improving neurogenesis (time lag) and also be resensitizing the GR and negative feedback. For the serotonin may be direct effect or the effects on cortisol.

Question 18

What are risk factors for depression?

Answer 18

Risk factors for depression – being female (some argument that females may be better at admitting to depression in surveys). Oestrogen is an anti depressant whereas progesterone seems to increase serotonin breakdown. Thought to be linked to the menstrual cycle and the withdrawal of oestrogen during the cycle so lose protective effects. Also women have increased limbic activation to perceived stress (focus on negative stressors) – NEUROTIC. Stress diathesis model (due to increased emotions, are more predisposed to being stressed).
Other risk factors include genetics (eg offspring of those with major depression 2-3 times more likely to become depressed themselves). Eg a polymorphism in the gene that controls the glucocorticoid receptor. Environmental factors and psychological factors (eg parentals such as divorce or abuse) in childhood and in utero.

Question 19

What is the definition of neurotic?

Answer 19

Also women have increased limbic activation to perceived stress (focus on negative stressors) – NEUROTIC

Question 20

What are the stress hormones and what do they generally do?

Answer 20

Stress hormones include cortisol, the catecholamines, vasopressin, growth hormone and prolactin.
• raising blood glucose concentration for immediate use by muscle and other tissues
• raising arterial blood pressure to get more nutrients (including oxygen) to specific tissues (e.g. muscle, brain). This will be associated with
• altered blood distribution, e.g. blood shifted from (temporarily) non-essential to essential tissues.
• attenuation of normal inflammatory responses
• heightened central activities

Question 21

What to the majority of patients with cushings have? Hypothesised mechanism behind this? But why is there another theory?

Answer 21

HT. Thought to be due to saturation of 11bHSD2 so act on the MR receptor. However, dexamethasone causes increase in BP and is selective for GR.

Question 22

What do human aortic endothelial cells express? Evidence

Answer 22

ACTH-R and 11bHSD2. Shown by RNA PCR. ACTH inhibits 11bHSD2 and increases the amount of local cortisol available. Cell culture study, using agonist and antagonist of ACTH. More agonist, more cortisol production

Question 23

What major cardiovascular risk factor are glucocorticoids linked to and evidence?

Answer 23

Atherosclerosis. Mice generated that were apo E lipoprotein deficient (highly susceptible to atherosclerosis) and given 11bHSD1 inhibitor plus high fat diet which blocked the amount of atherosclerosis

Question 24

Which type of molecule do glucocorticoids effect?

Answer 24

Inhibit Vasodilatory prostaglandins (in turn increases the actions of vasoconstrictors e.g. catecholamines)

Question 25

Example of action on prostaglandins

Answer 25

Annexin 1 released from cell and has an autocrine effect, inhibits actions of phospholipase c (important for generation of prostaglandins)

Question 26

How do GC affect the RAS system?

Answer 26

Increase synthesis of angiotensinogen. • In the VSMC the angiotensin II receptor is of the AT 1 type.
• Dexamethasone increased the number of AT 1 receptors in vascular smooth muscle cells, so with more receptors, get more Angiotensin-II activity
• This effect was blocked when a GR specific antagonist was added
• Dexamethasone caused relative increase of AT1 receptor mRNA- lots of their actions seem to be at genomic level

Question 27

What is another action that glucocorticoids may have? Think blood vessels

Answer 27

They may inhibit vasodilatory NO synthase. 3x20 patients on either valsartan (AT2 antagonist), diuretic or placebo and NO synthase inhibitor. Those on valsartan had decreased blood flow compared to others.

Question 28

What hormone do GC act on?

Answer 28

They increase erythropoietin that makes the blood more viscous and decreases NO synthase

Question 29

What is there evidence that glucocorticoids may have a direct effect on?

Answer 29

Heart

Question 30

What do GC do to the catecholamines?

Answer 30

Acutely cortisol decreases the effects of the catecholamines. Rats stressed through immobilisation. Raised catecholamine effects were attenuated by cortisol injection. Increased conversion of noradrenalin to adrenaline through PMNt
o Chronic: Chronic amounts of glucocorticoids causes a significant increase in catecholamines. Very different acute and chronic effect

Question 31

What is produced in the adrenal cortex and what are their role in immunity?

Answer 31

Through HPA activation, glucocorticoids and DHEA (precursor to sex steroids) are produced from the adrenal cortex.
• Glucocorticoids – NEGATIVE effect on immune function.↑ glucose metabolism ↑ cardiovascular function
• DHEA – POSITIVE effect on immune function

Question 32

What produced in the adrenal gland has a positive role in immunity? How is it found? What happens with age?

Answer 32

DHEA. DHEAS is the sulfated version of DHEA (conversion is reversibly catalyzed by sulfotransferase (usually in liver, small intestines and adrenals).
In blood, most DHEA is found as DHEAS and there are no diurnal variation in DHEAS levels. Decreases with age

Question 33

What can increase DHEA?

Answer 33

Exercise increases DHEA production. DHEA-S has been found to be significantly higher in older men who are endurance trained (Tissandier et al. 2001). DHEA-S (Tremblay et al. 2004) have been shown to increase in response to acute exercise in younger adults.

Question 34

What happens to cortisol with age and the ration?

Answer 34

Conversely, Cortisol production increases with age.
Control of immune function relies on the DHEA:cortisol ration (better to have high for better immune function), thus the detrimental affect of stress increase with age.

Question 35

What are potential mechanisms for why DHEA increases with exercise

Answer 35

Increased secretion rate by the adrenal cortex as a result of ACTH stimulation (Johnson et al.1997)
Decreased metabolic clearance due to a reduction in hepatic blood flow during exercise

Question 36

Which experimental model are used to look at GC and imflammation?

Answer 36

• ARTHRITIS SUSCEPTIBLE – LEWIS RATS

* NOT SUSCEPTIBLE TO ARTHRITIS – FISCHER RATS

Question 37

What did lewis and Fischer rats show about GC?

Answer 37

• When given adjuvant to induce arthritis, Lewis rats had much higher incidence and susceptibility compared to Fischer rats.
• Then give a glucocorticoid receptor antagonist (RU486) to Fischer as well as the arthritis causing adjuvant. At high doses of antagonist, many Fischer rats develop arthritis and worsened severity. Blocking steroids increases the susceptibility to drug induced arthritis.
• With Lewis rats, give dexamethasone in combination to adjuvant. High dose dexamethasone decreased the incidence and severity of arthritis→ Glucocorticoids thus have a protective function. In control rats, all animals developed arthritis.
• Lewis rats have a much blunted response to stress, when given a stressful stimulus. Brain analysis shows reduced CRH mRNA in the PVN.

Question 38

What do inflammatory mediators do? What are examples?

Answer 38

Cytokines – IL-1, IL-2, IL-6, IL-8, TNF-α. Waves of cytokines are released after a stressful stimulus. 
Eicosanoids / PAF
Amines – histamine, 5-HT
Peptides – bradykinin
Nitric oxide
Enzymes – PLA2, COX2
THEY ACTIVATE THE HPA AXIS

Question 39

How can you see the effect on inflammatory mediators?

Answer 39

Inject virus, increase in corticosterone ( control) . After stress, IL1 levels significantly increase. Then Give virus with antibody to IL1, and the stress response mounted is significantly reduced.

Question 40

How can the effect of GC on inflammation in the HYPOTHALAMUS BE SEEN?

Answer 40

Hypothalamus. Control – give IL1 and you get an increase in ACTH, CRH mRNA and cFos.. If you give a CRH antagonist, then the ACTH released is reduced. Using arachidonic acid to block the signaling cascade in the hypothalamus and pituitary gland also causes a significant reduction in corticosterone release.

Question 41

What evidence is there that glucocorticoids do not mediate immune function

Answer 41

• Stress induced changes of the immune system can occur in Adrenalectomised or hypohysectomised animals
• Changes in immune function occur in the absence of a detectable changes in glucocorticoid levels
• Increase in glucocorticoids levels can occur in the absence of detectable changes in immune function

Question 42

What is an example of immunosuppression?

Answer 42

• Tail shock paradigm with rats: A single shock session (with 16 tail shocks being delivered on a variable basis every 2–6 min)
• Associated with a very robust suppression of both splenic and peripheral blood T cell proliferative responses
• 3 or 5 daily equivalent shock sessions
• The response of splenic T cells returned to that of the control but T cell proliferative responses in the peripheral blood remained dramatically suppressed.

Question 43

What is a season example of GC?

Answer 43

• Hungry season from July to December, then wet season and harvest for the rest of the year
• If born in hungry season then have increased mortality from infection related disease
• These children also have reduced thymic size from the reduced immune function and the reduced thymic output
• Hungry season babies have a reduced life span.

Question 44

What way does glucocorticoids mediate anti-inflammatory actions?

Answer 44

Through Annexin1

Question 45

Describe the characteristics of annexin 1?

Answer 45

• Glucocorticoid-regulated
• Anti-inflammatory
• Anti-proliferative, pro-apoptotic
• Neuroprotective
• Modulator of neuroendocrine function

Question 46

What family does annexin1 belong to?

Answer 46

Annexin I belongs to the annexin family of Ca2+-dependent phospholipid-binding proteins.

Question 47

What is the mechanism of action of annexin 1?

Answer 47

Annexin A1 both suppresses phospholipase A2 and COX level, thereby BLOCKING EICASANOID PRODUCTION, and inhibits various leukocyte inflammatory events (epithelial adhesion, emigration, chemotaxis and phagocytosis).

Question 48

Resting state, what are levels of annexing like?

Answer 48

In resting conditions, human and mouse immune cells such as neutrophils and macrophages contain high levels of annexin A1 in their cytoplasm

Question 49

What happens when annexing 1 is activated?

Answer 49

Following cell, annexin A1 is promptly mobilized to the cell surface and secreted. Annexin A1 promotes neutrophil detachment and apoptosis, and phagocytosis of apoptotic neutrophils by macrophages.

Question 50

What effect does annexin1 have on innate immunity?

Answer 50

In vitro and in vivo analyses show that exogenous and endogenous annexin A1 counter-regulate the activities of innate immune cells, in particular extravasation and the generation of proinflammatory mediators, and this ensures that a sufficient level of activation is reached but not exceeded.

Question 51

What effect does anxa 1 have one immune function?

Answer 51

A) Dexamethasone increases the expression of ANXA1 in the rat anterior pituitary gland, measured by western blot. Detected at cell surface, close to endocrine cells
b)Translocation of annexin 1 from the cytoplasm to the cell surface where it is retained by a Ca2+-dependent manner.

Question 52

Where is annexin1 found in?

Answer 52

Annexin 1 is localized to folliculostellate cells in the anterior pituitary gland
(Not present in the corticotrophs, but collects where folliculostellate cells come into contact with endocrine cells)
Cell sorting identified annexin 1 binding sites on approximately 80% of the pituitary endocrine cells, including
Corticotrophs
Somatotrophs
Lactotrophs
Gonadotrophs

Question 53

What does annexin1 require?

Answer 53

Reversal of the inhibitory effects of Annexin and dexamethasone on forskolin-stimulated ACTH release in vitro by PKC blockade (nhibitor of PKC caused ACTH release to increase, even when ANXA and Dex administered)

Question 54

What evidence is there that leptin is involved in immunity?

Answer 54

Leptin belongs to the family of long-chain helical cytokines
The leptin receptor ,OBR, is a member of the class I cytokine receptor family - which includes receptors for IL-6, IL-12, OSM and prolactin.  

Ob/ob mouse is immune deficient

Question 55

What does leptin do for immunity?

Answer 55

Leptin induces a proliferation of peripheral blood leukocytes and CD4+ cells. Responder CD4+ cells are leptin targets (rather than mediator cells).

Question 56

Where is the leptin receptor found?

Answer 56

Leptin receptor in hypothalamus & purified CD4+T cells.
Leptin enhances T-cell responses primarily by binding to its receptor on T cells – rather than through a direct effect on the stimulator cell.

Question 57

What happens if you give leptin to leptin deficient mouse?

Answer 57

ob/ob T cells never exposed to leptin.
Leptin increases both proliferation and IL-2 production.
ob/ob responder T cells are more sensitive to exogenous leptin.

Question 58

What is a clinical link for evidence of leptin and food?

Answer 58

• Starvation associated with a higher frequency of infectious diseases

Question 59

What experiment was done to look at the effects of leptin?

Answer 59

• Investigated the capacity of leptin replacement to reverse the inhibitory effects of starvation on T-cell priming.
• Measured by the delayed-type hypersensitivity (DTH) response.
• Apply stress to the ear and measure the inflammation that occurs in terms of change in body weight
• One group starving, the other starving and given exogenous leptin. If fed then have normal immune function and increase inflammation in ear hence weight goes up. Starved with no leptin does not mount an immune response unlike starved and then given exogenous leptin
• Starvation of mice for 48 hours led to a 69% reduction in the mean DTH (immune/0 response.
• This inhibition was completely reversed by injection of leptin during the period of starvation.

Question 60

What human evidence is there for the effects of leptin?

Answer 60

Prior to treatment, the two patients tested (B and C) showed selective CD4+ T cell lymphopenia and severely impaired lymphocyte function.
After recombinant leptin replacement, both the immunophenotype and the T cell responsiveness were significantly improved and in some experiments reached the levels observed in normal age-matched controls.
Leptin is a key molecule in both CD4+ T cell development and function in humans, as testified by the increased proportion of CD4+ naive T cells and the restored IFN-γ secretion, respectively.

Question 61

What is a potential future use for leptin?

Answer 61

Give to anorexia nervosa patients to improve immune function