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Host Defense I > Bone & Fat > Flashcards

Bone & Fat Flashcards

1
Q

What is the role of DKK-1?

A

DKK-1 is negative regulator of WNT/beta catenin pathway; binding to a Wnt receptor

(TNFalpha will promote it) blocks Wnt activation of preosteoblast to mature osteoblast - this will bind to receptor for Wnt and inhibit Wnt action on maturation of osteoblast. in mature osteoblast

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2
Q

What is the role of Osteoprotegerin?

A

OPG: Osteoprotegerin; inhibits RANKL which is essential for formation of osteoclasts

Osteoprotegerin (OPG) protects the skeleton from excessive bone resorption by binding to RANKL and preventing it from binding to its receptor, RANK

OPG (osteoprotegerin) mainly from OB is a decoy soluble receptor

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3
Q

What do mesenchymal stem cells give rise to? Hematopoietic stem cells?

A

mesenchymal SC- give rise to pre-OB and chondrocyte

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4
Q

What does Wnt do?

A

Wnt suppress osteoclast-mediated bone resorption by down regulate expression of RANKL, and upregulation of OPG

urges MSC toward preosteoblast… and inhibits other lineages like chondrocytes

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5
Q

What family are RANK and RANKL members of?

A

TNF superfamily

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6
Q

What does bone mass and skeletal integrity depend upon?

A

Thus, RANKL/OPG ratio is an important determinant of bone mass and skeletal integrity

The ratio between OPG and RANKL determines bone formation

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7
Q

Where is RANK expressed?

What is RANKL?

A

RANK expressed on pre-OC and OC: receptor

RANKL is the cytokine

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8
Q

What do OB release?

A

OB releases M-CSF that promotes OC survival and proliferation

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9
Q

Which cells can express RANKL?

A

RANKL can be expressed by many innate and adaptive immune cells, including neutrophils, monocytes, DC, T and B cells

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10
Q

What cytokines induce RANKL?

Which will suppress/reduce expression of RANKL?

A

Proinflammatory cytokines IL1,IL6, IL8, TNFα and especially Th17 induce RANKL and promote OC differentiation

Th2 - IL4, IL10, IL13 will reduce expression

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11
Q

What effect will sex hormones have?

A

Sex hormones: maintain bone homeostasis

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12
Q

Describe how T cells are involved in bone modeling particularly in a dominant Th1 or Th17 response.

When might Th17 response be inhibited?

A

A dominant Th1 response in and around bone is associated with INFγ and activates macrophages. Result: pro-clastogenic and bone resorption

TH17 cells, if dominant, are potent OC activators

A normal Th1 or TH2 response or balanced Th1/Th2 responses would strongly inhibit IL 17. Result: a good thing

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13
Q

In what clinical scenario might you see increased IL23? What would this indicate? Describe the Th response and mechanisms.

A

Rheumatoid Arthritis

Increased IL23-stimulus unknown- appears in high levels in synovium of a joint

Th17 cells infiltrate the synovium

IL17 activates neighboring OC and they proliferate

The RANK/RANKL/OPG balance is pro-bone loss and causes bone erosions and loss of joint function

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14
Q

What is Denosumab? Describe its action.

A

Denosumab is an human monoclonal antibody for treatment of osteoporosis.

is good at binding and soaking up the RANKL …by doing that you push balance back toward OB rather than OC.

Blocking RANKL with a monoclonal antibody (Denosumab) can lead to decreased bone loss

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15
Q

What is Pannus?

A

Pannus is inflammatory synovial tissue: source of cytokines that mediate bone loss.

(RA?)
Slide 16

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16
Q

Describe role of estrogen in pre and post menopausal women.

A

Premenopausal state: estrogen promotes normal OB & OC function

Post menopausal state: OPG/RANKL balance is altered

Blocking RANKL with a monoclonal antibody (Denosumab) can lead to decreased bone loss

17
Q

Does an inflammatory state increase or decrease with an increase in adipose tissue?

A

high level of adipose tissue- more toward inflammatory state

Obesity is firmly linked to major adverse health outcomes, especially DM-2 and insulin resistance
Adipose tissue is the largest endocrine organ that produces a wide array of hormones that act like cytokines and vice-versa
Any stimulus that increases inflammation in adipose tissue is a bad thing

18
Q

Can white adipose tissue be classified as an endocrine organ?

A

Super endocrine organ and critical for homeostasis

Produces hormones, chemokines and cytokines

Regulates energy storage and expenditure, body mass and immune responses

Composed of pre-adipocytes, adipocytes, stromal/vascular cells and macrophages

19
Q

What are M1 and M2? Describe roles. Where are they?

Describe cytokines released and which Th response for each.

A

WAT Communicators: Macrophages

M1 is pro-inflammatory
M2 is anti-inflammatory

M1: Th1 response, IL1, IL6, IL8, and TNFa
M2: Th2, IL4, IL10, IL13

20
Q

What are Osteopontin and Resistin? Where are they? What are they? Describe their roles/what they produce.

A

These are Macrophage-Derived Cytokines in WAT

Osteopontin: A pro-inflammatory and a potent chemotactic signal for monocytes and macrophages

Resistin: antagonist of adiponectin

Produce the usual suspects: IL1,6,8, TNFα

Adiponectin is produced from adipocytes and has anti-inflammatory function – insulin sensitizer

21
Q

Describe action of adiponectin and resistin.

A

Adiponectin is produced from adipocytes and has anti-inflammatory function – insulin sensitizer

Resistin: antagonist of adiponectin

22
Q

Adipocytes of WAT produce adipocytokines that act like cytokines & hormones and have broad spectrum effects

Describe the effects (pro-inflammatory or anti-inflammatory)

Leptin
Adiponectin
Visfatin

Describe macrophage inhibitory factor cytokine.

A

Leptin is pro-inflammatory

Adiponectin is anti-inflammatory

Macrophage inhibitory factor cytokine is TNF- like but promotes adiponectin release

Visfatin is pro-inflammatory and pro angiogenic

Most abundant are leptin and adiponectin
Leptin: appetite control, CNS
Adiponectin: insulin sentisizer

23
Q

What cytokine is an insulin sensitizer? Where is it produced? Describe its function.

A

Adiponectin is produced from adipocytes and has anti-inflammatory function – insulin sensitizer

24
Q

How can expanding fat in adipocytes make WAT pro-inflammatory?

A

Expanding fat in adipocytes triggers a very dangerous signaling program that makes WAT very pro-inflammatory by recruiting a large number of monocytes and macrophages into it

The portal vein carries the problem into the liver and (probably) also into atheromatous plaques

25
Q

How does adipose tissue differ in lean vs obese individuals?

Describe levels of Tregs.
How will Wnt5a, SFRP5, adiponectin, MAC and TNFa change in obese individuals?

A

Macrophages regulate adipogenesis through WNT5a and TNF-like cytokines.
SFRP5: Secreted Frizzled-Related Protein 5; Frizzled is membrane receptor for WNT proteins. SFPR5 increases in obesity and metabolic syndrome.

Obese: CD8 and Th1, recruit Mac
Mac increase in obesity
Obese: more wnt5a, TNFa, SFRP5 and less adiponectin

White adipose tissue in Obese: increased macrophage infiltration

T cells: lean more Tregs

26
Q

Describe a fatty artery as a “local obesity”
What will cholesterol attract?
Describe the action of macrophages.

A

Cholesterol in the plaque attracts M1 pro-inflammatory macrophages

Macrophages secrete the chemokine CCL2 to attract monocytes and then prohibit them from exiting

Big plaque to ruptured plaque is clinical problem of huge dimensions

27
Q

What secretes CCL2 and what happens when it is secreted?

A

Cholesterol in the plaque attracts M1 pro-inflammatory macrophages

Macrophages secrete the chemokine CCL2 to attract monocytes and then prohibit them from exiting

Big plaque to ruptured plaque is clinical problem of huge dimensions

28
Q

How are innate immune responses in the brain suppressed? (What cells and what cytokines?)

A

Innate immune responses in the brain are held in active suppression by microglia and Il-10 and TGF- β

29
Q

Describe the 2 subsets of microglia in the CNS.

Do they act more like M1 or M2?
MHC?
What are they derived from?

A

2 subsets of microglia in CNS:

migrate early in development and have DC and macrophage characteristics and act like M2 Macrophages

They are highly branched and display little MHC

Other subset is perivascular and derived from circulating monocytes

30
Q

What cells compose the innate immune cells of CNS?

A

Microglia
Astrocytes
Oligodendroytes

31
Q

How will DAMPS/PAMPS be recognized in CNS? What responses will be initiated?

A

Activation of the glial system by DAMPS/PAMPS converts the M2 to M1 and then they secrete pro-inflammatory cytokines

They upregulate MHC and change morphology

IFNgamma, TNFalpha, IL17 to endothelial cell and astrocyte…which work as inflammation amplifiers, activation of NF-kB and IL6

Slide 37

32
Q

What cytokines may be an important cause of delirium or long term traumatic brain damage?

A

Pro- inflammatory cytokines, especially IL-6, have potent effects on neural function and survival

May be important cause of delirium, long term traumatic brain damage

Host Defense I (24 decks)

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