Lecture 22-Type 1 Diabetes Flashcards
1
Q
insulin was the first hormone to be?
A
cloned and produced recombinantly for therapeutic use
2
Q
insulin is made by
A
pancreatic islets
3
Q
3 types of cells in islets and function
A
beta cells- insulin
alpha cells- glucagon
gamma cells- somatostatin
4
Q
what part of proinsulin is cleaved?
A
C peptide- detected in blood
5
Q
A and B chain of proinsulin bond through
A
disulfide bonds
6
Q
C-peptide
A
detected in blood
- loss of C peptide, diagnosis for Type 1 diabetes
7
Q
4 classifications of diabetes
A
- T1D- immune mediated beta cell destruction (5-10%)
- T2D- insulin resistance and insulin deficiency (90-95%)
- other specific types (genetic factors affecting beta cell function or insulin action) (1-2%)
- gestational diabetes (in pregnancy, 3-5%)
8
Q
diabetes prevalence
A
- 2014-
- 8.5% adults over 18
- 140,000 cases of T1D in australia, more commonly diagnosed in children
- average 7 new cases/day Aus
- cost $570m- insulin injection and long term complications
- rising prevalence of T1D; 3-5% per year
9
Q
are islet autoantibodies involved in pathology?
A
no, even though they mark the presence
10
Q
islet autoantibodies and diagnosis of T1D
A
autoAbs precede diagnosis (95% newly diagnosed children have Ab)
11
Q
what do islet autoAbs mark? (2)
A
- mark the presence of autoimmune beta cell destruction
- evidence of disease specific b cell response
12
Q
what do islet cell autoAbs recognise?
A
a composite of islet antigens
13
Q
where are islet autoAbs found?
A
in serum not in the islets
14
Q
what can islet autoAbs be used to study?
A
- study natural history of disease
- identify individuals at risk (before diagnosis appearance)
- select high risk individuals for immune intervention and diagnosis
15
Q
less number of islet autoAbs in children=
A
less probability of getting disease
16
Q
what happens in presymptomatic T1D?
A
- env trigger
- development of autoAbs to islet Ags
- beta cell sensitivity to injury
- loss of first phase insulin response
17
Q
what happens in symptomatic t1D?
A
glucose intolerance
absence of C-peptide
18
Q
difference between stage 1 and 2 of natural history of T1D?
A
stage 1- normoglycemia
stage 2- dysglycemia
19
Q
how many susceptibility loci for T1D identified so far?
A
~53
20
Q
genes and diabetes
A
different combinations of genes increase risk for T1D
- many genes have immune cell function
- reveal new cellular pathways to be investigated for potential drug targets
21
Q
risk of T1D with twin
A
65% chance if you have identical twin with T1D
-risk of diabetes in autoAb positive twin is 89%
22
Q
proposed triggers of T1D
A
-infectious microbes/gut microbiome
-virus infection
-sunlight and vitD
-diet
controversial- independent studies have not consistently replicated findings
23
Q
type 1 IFN and T1D
A
increased IFNalpha detected in T1D pancreas
24
Q
what is IFN
A
potent activator of immune system
25
what triggers IFN production?
viral infection and innate immune activation
26
mice model of T1D
NOD mice
27
IFN stimulated genes in islets of NOD mice- expression
overexpressed
28
where do samples for study of T1D come from?
pancreatic organ donors with diabetes
| tissue from living donors
29
definition of insulitis
lymphocytic infiltration targeting islets of langerhans
30
two forms of insulitis
peri- immune cells are around outside of islet
| intra- immune cells in centre of islet
31
insulitis is often lobular- meaning
there is pathology in some lobes of pancreas and normal in other lobes
- feature of human disease that we dont see in mouse models
32
insulitis mainly affects
insulin positive islets
33
insulitis always accompanied by
pseudoatrophic islets devoid of beta cells
34
3 criteria for insulitis
1- fraction of infiltrated islets low (<10% islets)
2-should be lesions in >3 islets
3- >15 leucocyte common antigen (CD45)+cells/islet
35
what T cells are found within and around the islets in T1D pancreas?
CD4+, CD8+, CD68+
36
can you have insulin positive cells in pancreas even after diagnosis? implication?
yes- CD3+ T cells in diabetic individual 58 years after diagnosis
- if we dampen the anti-beta cell immune response, we can promote proliferation of these remaining beta cells so patient can make their own insulin
37
unmet clinical need for insulin injections
multiple injections per day
- but no currently approved therapies address underlying cause of disease
- approach that targets immune system is desirable
38
immune therapies for T1D
many tested in trials
- shown to slow progression of disease in trials
- but not in real treatment yet
- need new modulating therapy that can be used for large number of patients
39
T cells found in human islets are?
Beta cell antigen specific
| - recognise proteins produced by beta cells
40
how do autoreactive T cells in T1D develop?
- T cells escapes the negative selection in thymus,-->naive islet reactive T cells-->reach circulation (peripheral blood)
- pancreatic lymph node (activation and expansion of T cells)
- back to peripheral blood
- into pancreas (T cells gain effector function and expand, produce cytokines and cytotoxic molecules)
- go back to peripheral blood (detect cells in blood) or lymph node where there is upregulation of activation markers
41
tetramer staining for?
to detect autoantigen-specific T cells in islets
| - complex of 4MHC molecules together
42
catching T cells at the scene of the crime meaning
- isolating islets from T1D organ donors
- culture islets in presence of cytokines that promote growth of T cells
- many of the CD4 T cells recognised peptide in the islets and in peripheral blood
- also T cells that recognise B chain and A chain
43
main difference between human and mouse T1D
mouse- large proportion of islets affected and lots of immune cells
humans- not generally
44
NOD mouse model of autoimmune diabetes
- high risk HLA (env and genetic disposition)
- insulitis
- gradual increase of insulitis
- 4 months- diabetes development
45
immune modulation...
delays disease progression
46
immune suppression...
stops disease
47
how to CD8+T cells interact with beta cells?
T cell receptor (CD8+T cells) interact with peptide/MHCI on the beta cell
-autoreactive CD8+ T cells recognise and kill beta cells
48
upregulation of MHC class I correlates with?
number of CD8+ T cells in the islets
49
what is upregulated in T1D in humans?
HLA expression
50
what is upregulation of HLA mediated by?
by cytokine or IFN-gamma which signals through the JAK-STAT pathway
51
stat1 correlates with?
increase in HLA
52
how do we know stat1 is important for disease?
Stat1 KO mice dont develop disease- protected from autoimmune diabetes
- therefore target JAK/STAT pathway in T1D
53
JAKs are direct activators of ?
STAT proteins downstream of cytokines
54
JAK inhibitors in clinical use
few approved and used in clinics
| safety- reactivation of varicella zoster virus (can be prevented with vaccination)
55
STAT1 inhibitors in clinic?
not yet
56
what do JAK inhibitors do?
reduce the interaction between beta cells and T cells
| - but need to keep administering to keep glucose levels down in newly diagnosed diabetes
57
cadaveric islet allograft
isolated from organ donors
58
future transplants of beta cells
using stem cells- unlimited supply
| OR from other animals
59
when is T1D diagnosed in terms of beta cells?
when there is almost no beta cells remaining in pancreas
| - therefore need a source of new beta cells
60
autograft (pancreatitis)
disease of exocrine
| -remove pancreas, isoalte islets, reinfuse the islets so we dont have pancreatitis and T1D
61
how does islet transplantation occur?
- pancreas from organ donor
- islets isolated in lab
- sufficient quantity
- reinfused into portable circulation, go into liver, lodge in capillaries of liver
- sense glucose in the blood and secrete insulin into blood stream like normal pancreas
62
what is hypoglycemic unawareness? implications?
brain doesnt tell the patient that their blood sugar is low- can slip into coma
- need someone with them all the time
- excellent candidates for transplantation- life changing experience
63
4 main limitations to islet allotransplantation
- lack of sufficient donor pancreases (1-3 donors required per recipient)
- immunosuppression required
- eventual loss of graft function
- islet isolation is a process that is highly damaging to islets
64
examples of islet isolation being a process that is highly damaging to the islets
- long cold ischemia (pancreas sitting in ice from donor to lab)
- mechanical and enzymatic digestion
- disruption of ECM and BM (cells damaged)
- upregulation of hypoxia response genes (no blood supply)
* therefore putting back population of unhealthy cells into bloodstream
65
alternative sources of beta cells
- expansion/transdifferentiation (of glucagon cells to insulin producing cells)
- ESCs (need to ensure enough blood supply, otherwise wont survive)
- iPSCs
- adult stem cells
- xenotransplantation (using genetic modification in transgenic pigs_
66
future clinical trials focus
- immune suppression (repurpose drugs for T1D)
- regulatory T cells (grow in vitro, made antigen specific)
- antigen specific therapies (good for safety and due to lack of permanent remission with non-specific agents BUT difficult to tolerize memory T cells developed from primary immune response to the disease for proinsulin antigen)
- beta cell replacement (stem cells, xenotransplantation
