Week 17 Flashcards
UCP-1
Uncoupling protein -1, expressed by brown and beige adipocytes in their mitochondria. Serves to allow proton leakage across the mitochondrial membrane, thus generating heat at the expense of ATP
Types of adipose tissue
Visceral or subcutaneous
White, brown or beige
Beta adrenergic stimulation of adipose tissue
leads to increased lipolysis
adipocytokines secreted by adipose tissue
leptin
adipsin
adiponectin
How do Beta cells sense glucose concentrations?
They express cell surface GLUT2, which imports glucose from circulation and glucokinase, which phosphorylates it so that it cannot re-exit the cell (leading to glucose 6-phosphate)
Increased glycolytic flux within the B cell leads to glycolysis and ATP/ADP ratio increase that is sensed by the cell and leads to depolarization and release of insulin.
What are some metabolic assays for monitoring insulin sensitivity in muscles?
muscle uptake of radio-labelled glucose
-AKT phosphorylation in response to insulin
Tools to assess glucose metabolism
- Glucose Tolerance Test (feed glucose and track clearance, can also track insulin secretion)
- Insulin tolerance test (injection of insulin)
Clamps
Hyperglycemic clamp technique
The plasma glucose concentration is acutely raised to 125 mg/dl above basal levels by a continuous infusion of glucose. This hyperglycemic plateau is maintained by adjustment of a variable glucose infusion, based on the rate of insulin secretion and glucose metabolism. Because the plasma glucose concentration is held constant, the glucose infusion rate is an index of insulin secretion and glucose metabolism. The hyperglycemic clamps are often used to assess insulin secretion capacity.
Hyperinsulinemic-euglycemic clamp technique
The plasma insulin concentration is acutely raised and maintained at 100 μU/ml by a continuous infusion of insulin. Meanwhile, the plasma glucose concentration is held constant at basal levels by a variable glucose infusion. When the steady-state is achieved, the glucose infusion rate equals glucose uptake by all the tissues in the body and is therefore a measure of tissue insulin sensitivity. The hyperinsulinemic clamps are often used to measure insulin resistance.
Which types of diabetes can each clamp type test for?
Hyperglycemic clamp assesses insulin secretion capacity, and is thus used for T1D.
Hyperinsulinemic-euglycemic clamp measures insulin resistance and therefore is used to assess T2D.
Cachexia
a “wasting” disorder that causes extreme weight loss and muscle wasting, and can include loss of body fat.
Metabolic state of ATMs in obesity
In obesity, ATMs adopt a metabolic activation state with prominent lysosomal activity, with the main purpose to clear dead adipocytes.
Adipose tissue macrophages in obesity
ATMs expand to over 50% of cell in obese adipose tissue, due to increased proliferation and trafficking of blood monocytes
Enriched in visceral fat
ATMs have inflammatory phenotype in obesity
How was a role for TNFa discovered in adipose tissue?
Mice were put on a glycemic clamp (?) and treated with antibodies that prevented TNFa signaling. These mice were significantly more sensitive to insulin.
Experiment showing a role for macrophages in insulin resistance
Mice were created that specifically lacked JNK signaling in macrophages (downstream of TNFa and IL1B).
These mice showed similar obesity during HFD to WT mice, but showed increased insulin sensitivity when tested on hyperinsulinemic-euglycemic clamp studies
How do ATMs control thermogenesis?
alternatively-activated ATMs respond to IL-4 in BAT to promote thermogenesis
How do eosinophils control glucose metabolism?
Adipose tissue eosinophils are the main source of IL-4 in the tissue and there is a lack of alternatively-activated macrophages in the adipose in their absence. Eosinophil-deficient mice on HFD have impaired insulin sensitivity.
What are the main producers of IL-4 in adipose?
Eosinophils
How do eosinophils control thermogenesis?
Eosinophils promote the beige adipose tissue through IL-4 and ATMs, which leads to heat generation as opposed to lipid storage.
How do T cells influence adipose tissue?
In obese fat depots, CD8 T cells are increased and lead to the recruitment of macrophages from circulating monocytes. In lean fat depots, most T cells are CD4 and/or Tregs.
Depletion of CD8 T cells decreases inflammatory parameters in adipose and improves glucose control
Roles of Tregs in adipose tissue
Visceral-AT specific Tregs have been found to correlate with lean adipoe deposits. These Tregs uniquely express PPARg, accumulate with age, and are responsible for the effects of the diabetes drug pioglitazone
Tregs in aged adipose may promote insulin resistance though
pioglitazone
Pioglitazone selectively stimulates the nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR-γ) and to a lesser extent PPAR-α. It modulates the transcription of the genes involved in the control of glucose and lipid metabolism in the muscle, adipose tissue, and the liver.
This has been shown to rely on adipose tissue resident Tregs.
What do VAT Tregs require?
VAT Tregs are highly enriched in particular TCR variable gene expression, require Foxp3 for VAT ressidency, express PPARg, and rely on IL-33 signaling for maintenance.
Mast cells in adipose tissue
Increased mast cells in obese adipose tissue. Mast cell KOs had decreased adiposity and increased glucose homeostasis
Treatment with mast cell stabilizers led to similar results as mast cell KO mice.
Role of ILC2s. in adipose
ILC2s are decreased in obesity. They seem to promote the browning of adipoe tissue through IL-33, which promoted ucp-1 expression in adipocytes.
Role of cytokines in promoting insulin secretion
Fractalkine/CX3CR1 system regulates insulin secretion from beta cells. Chemokine may be produced locally within islets.
Adipsin
Another name for complement factor D, this protease is dysregulated in type 2 diabetes. It was shown that adipsin can help to generate C3a to stimulate beta cell insulin secretion via ATP-coupled respiration and cytosolic calcium flux.
Chronic adipsin treatment is effective in a mouse model of type 2 diabetes.
Humans with higher levels of adipsin appearto be protected from diabetes.
What is the role of IL-33 in pancreatic islets?
mesenchymal cells of the islets produce IL-33 that acts on resident ILC2s, leading to their production of IL-13 and CSF2 that pushes local DCs and Mqs to make Retinoic acid sensed by B cells to increase their insulin secretion
Injection of IL-33 into mice was able to rescue diabetic phenotypes.
Role of the inflammasome in adipose tissue
NLRP3 KO mice had increased insulin sensitivity and fewer inflammatory ATMs
anti IL-1B humanized mAb approved for use in rheumatic disorders
Canakinumab
Role of inflammation in cardiovascular disease
Decreasing IL-1B and therefore other inflammatory markers such as IL-6 and CRP waws able to reduce the number of cardiovascular events within patients that had prior myocardial infarction
How might COVID affect insulin resistance?
Some studies have shown that SARS-CoV-2 is able to directly infect islets of the pancreas, but the extent to which this happens in vivo is unclear.
It does appear though that the virus is able to infect adipose tissue quite well, and this correlates with a decrease in the levels of adiponectin, which is an insulin-sensitizing adipokine.
Leptin
adipokine that blunts insulin secretion by Beta cells by causing a K+ leak
adiponectin
Adipokine that sensitizes skeletal muscle and liver cells to insulin; anti-diabetic. Also has anti-apoptotic effects on Beta cells.
Wound repair phases
Haemostasis
inflammation
proliferation
dermal remodeling
clot/eschar contents
fibrin, fibrinogen, vitronectin and thrombospondin
Haemostasis
platelets activate upon recognition of subendothelial matrix and degranulate, releasing chemokines and cytokines. They also contribute to the formation of clots.
Cytokines that attract neutrophils to damaged vessel walls
IL-1, TNFa.
How are nuetrophils removed from a healing wound?
They are mostly extruded by adherence to the fibrin scab. Others undergo apoptosis.
re-epithelialization in wound healing
changes in matrix tension and presence of cytokines and growth factors activate keratinocytes to undergo a partial epithelial-mesenchymal transition, where they migrate laterally across the wound to reform the epidermal layer.
Cytokines produced by ILCs that contribute to wound repair
Amphiregulin from ILC2s
and IL-22 from ILC3s.
How do ILC3s contribute to tissue repair in the intestine?
Besides their production of IL-22, they contribute in an IL-22 independent manner through the amplification of the Hippo-Yap1 sigaling in intestinal crypts, which promotes intestinal stem cell maintenance.
Tuft cell : ILC2 circuit in intestinal epithelium
Succinate (metabolite) is sensed by tuft cells, which then produce IL-25. IL-25 is sensed by the ILC2s, which in turn make IL-13 to promote Goblet/Tuft cell hyperplasia
How do T cells contribute to intestinal epithelial integrity?
Tregs can produce amphiregulin & make IL-4 and IL-14, which promote Goblet cell / tuft cell differentiation
Dual role of IL-22 in colon cancer
Deficiency of IL-22 might lead to delayed colonic repair and increased intestinal inflammation, thereby promoting tumour development. However, the increased availability of IL-22 in Il22bp2/2 mice during the recovery phase caused prolonged epithelial proliferation, thereby also promoting the development of intestinal tumours
IL-22BP
IL22 binding protein that negatively regulates IL22 bioavailability
How does type 1 / type 2, or type 3 immunity contribute to wound healing?
Type 1 is thought to function mostly in microbial clearance, which prevents further inflammation and tissue damage
Type 2 is thought to most directly promote tissue repair through amphiregulin, IL-13, etc.
Type 3 is thought to promote protection from tissue damage through IL-22 (increased AMPs)
Role of IL-22 in intestinal GVHD
IL-22R is highly expressed on intestinal stem cells, and IL-22 produced by ILC3s signaling seems to protect these cells and thus epithelial integrity during GVHD in the gut
Intestinal stem cell marker
Lgr5+
Cellular composition of the ISC compartment in crypts
Paneth cells and Olfm4+ crypt base columnar (CBC) cells interspersed with one another.
Paneth cells provide an epithelail stem cell niche by providing ISC growth factors.
Why is it thought that allogeneic donor T cell target the ISC compartment of the gut specifically?
MAdCAM-1 expression was found to be predominantly expressed by endothelium surrounding the crypt base, thus driving T cell infiltration overwhelingly to this area with a4B7.
Signals from Paneth cells that regulate ISC compartment in crypts
Wnt3
EGF
NotchL
Afferent vs efferent neurons
Afferent (sensory) neurons report information from the periphery to the CNS
Efferent is the opposite.
Spinal vs visceral sensory nerves
Sensory neurons are also classified as spinal, with cell bodies located in the dorsal root ganglia (DRG) and projecting to the spinal cord, and vagal (visceral), with cell bodies located in the nodose and jugular ganglia and projecting to the brainstem
DAM
Disease-associated microglia that ere discovered in massive parallel scRNA seq of AD mouse models.
Role of complement cascade in neuronal development
Synaptic pruning requires the binding of complement proteins C1q to the targeted synapses, as well as complement receptors expressed by the microglia that prune them.
MIA disease model
the rodent maternal immune ac-
tivation (MIA) model of this phenomeno, off- spring from pregnant mice infected with virus or injected intraperitoneally with synthetic double- stranded RNA (dsRNA) [poly(I:C)], a mimic of viral infection, exhibit behavioral symptoms reminiscent of ASD: social deficits, abnormal communication, and repetitive behaviors
This has been shown to be dependent on IL17a in the CNS
How does innervation of the intestine change from proximal to distal?
Nerves in the proximal intestine are more geared towards digestion and nutrient absorption, while distal gut is geared more towards peristalsis, etc.
This is due to the different microbial loads sensed by the immune system; germ free mice do not have this compartmentalization.
The number and density of neurons is similarly affected by microbe presence.
What are two bacterial products that can be sensed by sensory neurons?
N-formyl peptide is sensed by FPR1
alpha-hemolysin is also sensed
Both are from streptococcal aureus
Neuronal loss in Salmonella infection
Mice had ~30% gut neuronal loss specifically in the region that Salmonella infection takes place. This loss led to long-term dysmotility in the gut, and was able to be reversed by restoring the gut microbiota to a pre-infection state.
How do muscularis macrophages prevent neuronal loss in the gut?
MMs can sense norepinephrine released by neurons and in response turn on a tissue-protective program.
Treatment of mice with a B-2-adrenergic agonist during Stm infection could prevent neuronal loss in mice.
Mice that were lacking B2AR in myeloid compartments had increased neuronal loss after infection
nervous system : macrophage interactions in the gut.
Rapid changes in MM gene expression, in particular the gene Arg1, were found to be mediated by stimulation of MM adrenergic receptor beta 2 (ADRB2) through sympathetic, extrinsic EAN activation. Current work started to ascribe a role to this sympathetic-MM-iEAN circuit during the course of inflammation.
Effect of Sympathetic neuron-derived norepinephrine in the BM
shown to increase HSC mobilization into the blood, via regulation of CXCL12 expression in bone marrow mesenchymal stem cells
intrinsic versus extrinsic neurons
tissue-associated neurons are classified as intrinsic (cell bodies that lie within the tissue) versus extrinsic (cell bodies that lie outside of the tissue, including the sympathetic and the parasympathetic autonomic nervous system)
EAN
Enteric-associated neurons
VEGF
vascular endothelial growth factor - the major mediator of vascular permeability during the initiation phase, VEGF stimulates formation of new blood vessels during resolution and healing
Effect of chronic IFNg on CD8 T cells
Although IFN-g has an important immunostimulatory func- tion mediated by upregulation of MHC-I molecules and their associated anti- gen-processing and antigen-presentation machinery (Zhou, 2009), its continuous production induces PD-L1 and leads to exhaustion of chronically stimulated effector CD8+ T cells
Three steps of cancer immunoediting hypothesis
Elimination phase
Equilibrium phase
Escape phase
Three ways that transformed cells can escape immunosurveillance through the loss of tumor antigen expression
(i) through emergence of tumor cells that lack expression of strong rejection antigens,
(ii) through loss of major histocompatibility complex (MHC) class I proteins that present these antigens to tumor-specific T cells, or
(iii) through loss of an- tigen processing function within the tumor cell that is needed to produce the antigenic peptide epitope and load it onto the MHC class I mol- ecule.
How does chronic inflammation contribute to tumor progression?
It contributes to cancer initiation by generating geno- toxic stress, to cancer promotion by inducing cel- lular proliferation, and to cancer progression by enhancing angiogenesis and tissue invasion
Three lines of evidence for cancer immunoediting hypothesis in humans
Immunodeficiency is associated with a higher risk for cancer
Spontaneous immune responses occur in cancer patients against tumor antigens
Intratumoral infiltration of lymphocytes expressing IFNgand TNFa is positively assoiaited with cancer patient prognosis.
Six hallmarks of tumor development
sustaining proliferative signaling, evading growth suppressors, resisting cell death, enabling replicative immortality, inducing angiogenesis, and activating invasion and metastasis
How was perforin shown to play a role in cancer imunosurveillance?
Perforin deficiency was shown to result in accelerated tumor growth in a mouse model of breast cancer
Cytotoxic cells discovered by Ming’s lab in cancerous tissue
ILC1ls and ILTC1s are Tissue-resident Lymphocyte that expand in cancerous lesions (shown through parabiosis experiment). These cells are dependent on IL-15 signaling.
Why do tumors grown in immunodeficient backgrounds show better rejection in new immunocompent hosts as compared to WT control?
The tumors that arose in immunocompetent hosts had the selective pressure of the immune system to promote only weakly immunogenic tumors, while tumors in immunodeficient hosts would be a mix of weakly and strongly immunogenic tumors - the strongly immunogenic tumors will be switftly rejected.
What is some evidence that the adaptive immune system can provide an equilibrium state in tumor immunosurveillance?
Mice were injected with a tumor-promoting chemical, and the mice that showed indolent tumor growth were selected for the next arm of the experiment. These mice recieved either anti-CD4/CD8 or an isotype control antibody, and the mice with depleted T cells had increased tumor growth.
What is some evidence for tumor-specific antigens having a role in immunosurveillance?
You can immunize mice with irradiated tumor cells and then implant viable cells of the same lineage. These mice should reject the tumor, whereas injection of viable tumor cells from a separate lineage will lead to tumor growth in vaccinated mice.
Additionally, exome sequencing in chemically-induced tumor models showed a correlation of particular mutant epitopes with tumor rejection.
Cytokines needed for the maintenance of Tmems
IL-7 and IL-15.
Terminally exhausted T cell phenotype
PD-1-hi
Eomes-hi
Tbet-lo
Tcf1-negative
Three contributors to T cell exhaustion
Persistent antigen stimulation (viral infection, cancer) Negative costimulation (PD-1 / CTLA-4 / Lag3) Chronic inflammation (IFN-I, TGFB, IL10)
What is required for checkpoint blockade therapy to be successful?
Will only work if there is insufficient immunosuveillance. If the tumor is completely non-immunogenic, there is likely little immunosuppression in the TME.
1st FDA-approved checkpoint inhibitor for tumor treatment
anti-CTLA-4 (2011)
Aryl hydrocarbon receptor expression, ligands, and function
ligand-activated transcription factor with a large variety of ligands (some bacterial products)
In gut ILC3s, ligation of AhR leads to production of IL-22
