Decrypting the spatial relationship between peripheral chromatin and nuclear lamina in Hutchinson-Gilford Progeria Syndrome using super-resolution microscopy techniques.

The genetic condition known as Hutchinson-Gilford Progeria Syndrome (HGPS) causes the early onset of aging symptoms and premature death. HGPS is caused by a single nucleotide mutation in the LMNA gene, resulting in a truncated form of the protein Lamin A known as ΔLA50 or Progerin. This protein modification causes aberrant lamina network organization inducing nuclear and DNA structure abnormalities, leading to the loss of peripheral heterochromatin. In this study, we examine variations in chromatin compaction in a cellular model of HPGS using Expansion Microscopy (ExM). This super-resolution microscopy technique is based on embedding biological samples into a water-absorbant polymer network that, following mechanical homogenization, enables a four-fold linear expansion in water, allowing nanoscale biophysical studies using conventional microscopes. The image analysis of the HGPS cell model shows a significant variation in chromatin compaction that seems to disrupt its physical association with the nuclear lamina. Furthermore, this loss of compaction leads to a detectable spatial separation between the lamina network, mainly composed of the mutated form Progerin, and the peripheral heterochromatin. Therefore, to quantify this distance variation caused by Progerin-induced chromatin disorganization, we analyzed a batch of control cells expressing wild-typer lamin A and HGPS cells, finding a one-order of magnitude difference between the two sets. In order to validate these results, we perform super-resolution Stimulated Emission Depletion (STED) imaging. The next step will be performing Correlative Light Electron Microscopy (CLEM) on non-expanded cells to push the resolution of our analysis even forward and to investigate chromatin compaction on a nanoscale level.