title: AFM stiffness nanotomography of normal, metaplastic and dysplastic human esophageal cells.
abstract: The mechanical stiffness of individual cells is important in tissue homeostasis, cell growth, division and motility, and the epithelial-mesenchymal transition in the initiation of cancer. In this work, a normal squamous cell line (EPC2) and metaplastic (CP-A) as well as dysplastic (CP-D) Barrett's Esophagus columnar cell lines are studied as a model of pre-neoplastic progression in the human esophagus. We used the combination of an atomic force microscope (AFM) with a scanning confocal fluorescence lifetime imaging microscope to study the mechanical properties of single adherent cells. Sixty four force indentation curves were taken over the nucleus of each cell in an 8 x 8 grid pattern. Analyzing the force indentation curves, indentation depth-dependent Young's moduli were found for all cell lines. Stiffness tomograms demonstrate distinct differences between the mechanical properties of the studied cell lines. Comparing the stiffness for indentation forces of 1 nN, most probable Young's moduli were calculated to 4.7 kPa for EPC2 (n = 18 cells), 3.1 kPa for CP-A (n = 10) and 2.6 kPa for CP-D (n = 19). We also tested the influence of nuclei and nucleoli staining organic dyes on the mechanical properties of the cells. For stained EPC2 cells (n = 5), significant stiffening was found (9.9 kPa), while CP-A cells (n = 5) showed no clear trend (2.9 kPa) and a slight softening was observed (2.1 kPa) in the case of CP-D cells (n = 16). Some force-indentation curves show non-monotonic discontinuities with segments of negative slope, resembling a sawtooth pattern. We found the incidence of these 'breakthrough events' to be highest in the dysplastic CP-D cells, intermediate in the metaplastic CP-A cells and lowest in the normal EPC2 cells. This observation suggests that the microscopic explanation for the increased compliance of cancerous and pre-cancerous cells may lie in their susceptibility to 'crumble and yield' rather than their ability to 'bend and flex'.
authors.affiliation: Department of Physics, Arizona State University, Tempe, AZ 85287, USA.
authors.forename: A
authors.initials: A
authors.lastname: Fuhrmann
authors.forename: J R
authors.initials: JR
authors.lastname: Staunton
authors.forename: V
authors.initials: V
authors.lastname: Nandakumar
authors.forename: N
authors.initials: N
authors.lastname: Banyai
authors.forename: P C W
authors.initials: PC
authors.lastname: Davies
authors.forename: R
authors.initials: R
authors.lastname: Ros
mesh_terms: D002460:Cell Line; D045744:Cell Line, Tumor; D055119:Elastic Modulus; D004938:Esophageal Neoplasms / Q000473:pathology*; D004947:Esophagus / Q000473:pathology*; D006801:Humans; D018625:Microscopy, Atomic Force / Q000379:methods*; D011230:Precancerous Conditions / Q000473:pathology*