imaging

Question 1

new light microscopy study

Answer 1

Enos et al (1953) = looked at blood vessels of deceased US soldiers from Korean war
- Despite average age of only 22, histological analysis using LM revealed clear signs of lesions and arterial wall thickening = clear evidence that atherosclerosis begins early in life

Question 2

new EM studies

Answer 2

Kerr, Whiley and Currie (1972) = discovery of apoptosis = distinct type of cell death, characterised by nuclear condensation and cellular fragmentation and phagocytosis

Nixon (2005) = immunogold labelling and EM of biopsies from Alz brains = found autophagosomes not present in healthy brains = first evidence that autophagy is involved in neurodegeneration

Question 3

STED study

Answer 3

• STED has been used in an effective manner in order to evaluate the HIV-1 assembly site process. As the HIV-1 assembly site is a sub-diffraction sized (140nm) area of Gag protein multimerization, leading to the release of the viral particle from the plasma membrane. The role of how Env accumulated at the site was unclear.
o Chojnacki et al. 2013, demonstrated that Env exhibits a strong decrease in mobility at viral assembly sites identified by fluorescent Gag clusters, compared to nearby areas.
o Used a STED microscope in a biosafety 3 lab. Used a replication competent HIV strain which expressed GFP in the Gag protein, to allow for identification. Env proteins were identified using immunofluorescence of 2G12 anti-Env Abs conjugated to a human-Ab dye.
o STED scanning was used to evaluate the molecular dynamics of virion assembly by scanning for both two colours of gag and env and was able to demonstrate that the Env exhibited a decrease in env mobility at the Gag cluster sites, suggesting that Env is trapped in live HIV viruses upon assembly, with just a few Env molecules outside the assembly site.
 This is of interest in the molecular dynamics in infection, though there are questions regarding the addition of bulky GFP to Gag which could alter trafficking

Question 4

FDG-PET study

Answer 4

FDG-PET
 Non-invasive imaging modality that uses radioactively labelled glucose analogue that accumulates in metabolically active cells
 In a recent study in March this year (March 2020) in Nature, Tixier et al. identified an exciting new use for FDG-PET images of tumours: they showed that PET radiomics can reveal cancer transcriptomics!
o Their study included 45 patients with locally advanced head and neck cancer who had undergone FDG-PET scans at the time of diagnosis and transcriptome analysis using RNAs from both cancer and healthy tissues on microarrays
o Using Genomica software, they identified relationships between PET radiomics and genes involved in the cell cycle, disease, DNA repair, the immune system, metabolism, extracellular matrix organisation and signal transduction pathways
 This highlights the potential of FDG-PET radiomic features to infer tissue gene expression and the activity of various cellular pathways in head and neck cancers, and potentially other cancers too!
 The results of their study also reveal the exciting promise of radiomics to personalise treatments through targeting specific molecular pathways
• Limitations = poor temporal and spatial resolution (minutes/2-5mm), purely correlative and cannot prove causation without interventional studies

Question 5

MRS study

Answer 5

• Detects radio frequency electromagnetic signals produced by atomic nuclei within molecules = can be used to obtain in situ concentrations of certain chemicals in complex samples (e.g. living brain)
• General criticism = cannot detect intracellular vs extracellular
• Can be used to detect expression of 2-HG in gliomas
• Natsumeda et al (2014) = used MRS to detect levels of 2HG in 53 grade II and III mutant IDH1 gliomas
• Detectable in all mutant IDH1 gliomas, below detectable range in 37% of WT IDH gliomas
• Gliomas with high 2HG accumulation had better overall survival than gliomas with low 2HG accumulation
• 2HG accumulation correlates with IDH status and survival
Allows non-invasive detection of mutant IDH in tumours before surgery  useful as 2-HG degrades after formalin fixation and paraffin embedding, so accumulation is difficult to analyse ex vivo
Useful in determining treatment choice  evidence that patients with IDH-mutant tumours might benefit from aggressive surgery, also helps guide whether IDH inhibitors would give clinical benefit
Also good at monitoring infiltration of glioma into surrounding tissue, after bulk removed by surgery