Lecture 17 - T1D Research Flashcards
What are the limitations of studying T1D in humans
Not possible to take pancreatic biopsies from at-risk individuals prior to or once diagnosed with T1D (whatever functional beta cells they have left - not a viable option to do surgery on the pancreas)
- Difficult to determine what’s happening during disease development
- Need access to key tissues and cells, but only have access to:
o Peripheral blood of living individuals
o Cadaveric donor pancreatic specimens - Difficult to identify and confirm genetic and environmental factors:
o Need controlled breeding allows us to test the effect of different genes
o Need controlled isolation allows us to test the effect of different environmental factors
What is the NOD mouse?
Nonobese diabetic (NOD) mouse
Spontaneously develop diabetes
Higher rates in females than males (humans about same)
Has to do with sex hormones in mice, if you castrate males then they get higher rates similar to females, giving testosterone to females will lower rates
> lymphocytes mediate specific destruction of insulin-producing Beta cells
How does T1D arise in the NOD mouse?
Very consistent development of diabetes in NOD mouse
> day 20: immune cell invasion of pancreas
day 40-120: increasing insulitis and beta cell destruction, progressive loss of insulin
day 120-death (200): clinical diagnosis (hyperglycemia), residual to no insulin secretion
What is peri-insulitis?
When insulin is in the peripheral/outside of the cell
What are the genetic factor similarities between mouse and human?
Mouse genetic studies identified > 30 T1D susceptibility loci
Humans >40 alleles that increase risk of T1D
Many of the genetic susceptibility loci overlap between mouse and humans
Mouse T1D loci termed Idd, Human T1D loci termed IDDM
We find more genes in heterogenous humans, because we could have different combinations of loci, mouse are all basically clones
What are the immunological abnormalities in NOD mouse: thymus?
- Thymus:
o Abnormality is the impaired deletion of autoreactive T cells
o Causes beta-cell specific T cells to escape into the periphery
What are the immunological abnormalities in NOD mouse: macrophages?
o Less efficient at clearing dying cells/beta cells
o Produces higher levels of inflammatory cytokines
o This causes an increase in inflammation in islet and exposure of beta cell antigens
What are the immunological abnormalities in NOD mouse: dendritic cells?
o Defective maturation an responses to certain stimuli
o Fails to eliminate autoreactive T cells in the periphery
o Causes enhanced activation of beta-cell specific T cells
What are the immunological abnormalities in NOD mouse: T cells?
o Enhanced propensity to proliferative and produce pro-inflammatory cytokines (esp. IFN-gamma)
o Regulatory T cells are less effective at suppressing autoreactive CD4+ and C8+ T cells in the periphery
o Causes increased numbers and enhanced activation of beta-cell specific T cells
What are the genetic factors: Idd1 and IDDM1?
- A similar amino acid change for the MHC/HLA class II molecule associated with T1D
High risk allele genotype for beta chain
>human HLA (DQ2 or DQ8) = DQB1 *0201 or *0302
>Mouse MHC = NOD H2-Ag7 - Beta chain position 57 (peptide cleft where beta cell is presented with B-cell receptor)
>human = code for alanine
>mouse = code for serine
>both associated with increased T1D risk
What are the salt bridge changes in NOD mice and humans during the amino acid change for MHC/HLA class II molecule
Salt bridge DISRUPTED when aspartic acid at position 57 is changed to serine or alanine
>associated with susceptibility to T1DM
Salt bridge FORMED between aspartic acid at position 57 in beta chain and arginine on alpha chain
>associated with resistance to T1DM
How can aspartic acid changes be proven to affect T1D development?
Use gene editing in NOD mouse
>CRISPR-Cas9 mutagenesis to change MHC amino acid
> show that changing 1 aa from serine to aspartic acid is protective
NOD MICE WITH ASPARTIC ACID ARE PROTECTED
What are the environmental factors that are similar between human and mouse?
- Positive correlation between equatorial distance and incidence of T1D – decreased temperature = increased diabetes incidence
- Correlation does not equal causation
Different diabetes incidence rates for different countries - definitely has environmental factors that affect incidence
What effect does the environmental factor of temperature have on T1D?
Higher temperature reduces incidence of diabetes in NOD mice
what does this mean for humans? temp does it affect? prob not cause weather is seasonal and doesnt always stay 24 degrees but** (add in)
What effect does the environmental factor of microbial pathogens have on T1D?
- Can move NOD mice from a facility that has microbial pathogens to one that doesn’t
- Mice in conventional dirty breeding facilities have lower incidence of diabetes
>T1D incidence in NOD mice is affected by microbial pathogens –> link to the theory that early exposure of pathogens tempers the immune system and reduces incidence of T1D