Sim-Ptychography Imaging of Hutchinson-Gilford Progeria Syndrome (HGPS) Cells

Abstract

Hutchinson-Gilford progeria syndrome (HGPS) is a genetic condition characterized by the rapid appearance of aging beginning in childhood. HGPS is caused by a mutation in the encoding gene of lamin-A, one important component of the nuclear lamina. Lamins provide shape and structural stability to the nucleus, and are involved in many cellular processes (DNA replication and repair, chromatin organization, etc). In HGPS the mutation of lamin-A results in a distorted nuclear lamina. It is crucial to understand if this mutation affects only the structure of the nucleus, or if other alterations occur. Optical microscopy is one of the most used tools to investigate biological processes, with high-resolution imaging commonly performed using fluorophores. However, live-cell imaging is not always compatible with labeling due to photobleaching and phototoxicity effects. Label-free imaging is therefore of great interest to study biological systems. One such method is ptychography, a computational approach able to retrieve the phase and amplitude of a sample by analyzing collected diffraction patterns. These phase maps contain information about thickness and refractive index, and allow quantification of cellular morphology. However, its limitation is the comparatively low achievable resolution. Previous work has shown the advantage of using structured illumination together with ptychography to increase the spatial resolution. For this reason, we couple ptychography with structured illumination microscopy (SIM) to perform high-resolution imaging. In this work, a ptychographic module was developed and mounted on a commercial SIM, to simultaneously collect ptychography and SIM data. We show how changes in the morphology of a HGPS nucleus affect the phase compared to normal cells, and how the SIM-ptychography approach can increase the resolution compared with conventional optical ptychography.