A 5µm silica sphere glued to a standard AFM cantilever was used to obtain stable and repeatable measurements over the area of individual cell.
Sokolov is using atomic force microscopy to study individual human epithelial cells, which are found in skin as well as in other tissues that line the surfaces of the body, including blood vessels, kidneys, liver, brain, eyes, etc.
Sokolov and his colleagues used fast aging in in-vitro epithelial cells under laboratory conditions, and then probed the elasticity of such cells. However, a typical rigid AFM probe is too sharp to measure the cells quickly while they are alive, and is not gentle enough to get reliable statistical data. So Sokolov added a five-micron silica ball to the AFM tip. This ball presses slowly against the cell being studied and records how much deformation is caused by the pressure being applied.
Sokolov discovered that epithelial cells tend to be more rigid in old (close to senescence) cells than in young ones, which helps explain why skin often looks and feels more leathery as we age.
Previously, researchers believed the culprit was only the biochemical "glue" that holds epithelial tissue together rather than the cells themselves. This loss of elasticity has been implicated in the pathogenesis of many progressive diseases of aging including hardening of the arteries, joint stiffness, cataracts, Alzheimer's and dementia. Sokolov's findings could inspire the search for new treatments.
What causes this loss of elasticity? Sokolov hypothesized that the secret lay in the cell cytoskeleton, the most rigid part of the cell, and imaged it using AFM. He discovered that older cells have a higher surface density of cytoskeleton with more fibers per unit area.
Among the other interesting new bioimaging techniques described at the meeting was a new approach to facial recognition, developed by researchers at the State University of New York, Stony Brook. Most face recognition techniques use still images, and are sensitive to lighting, shadows, or such appearance modifications as makeup, natural aging, or cosmetic surgery.
According to E Guan, the group is using a technique called digital image speckle correlation (DISC) to trace the motion of the underlying musculature of a person's face. Human skin has a natural pattern of pores that is easily visible with high-resolution digital cameras.
Guan and his cohorts took two photos of a subject, showing a small change in expression, such as a slight smile. With DISC, they were able to analyze these digital images and recognize the underlying muscle structure, which is unique to individuals and is not affected by lighting or makeup. Because the motion pattern can be associated to an individual, "suspects" can be identified via a facial "print" using conventional fingerprint scanning technology.
The method could also prove useful for diagnosing nerve-related diseases like Bell's palsy, or skin disorders, based on asymmetry of facial expressions or abnormal stiffness of the skin.
It is extremely difficult for biologists to probe living cells because most optical techniques rely on forms of ionizing radiation, which can damage or destroy delicate structures, even causing mutations that morph into cancerous cells. Hence, most studies of proteins to date have been conducted using dead cells.
Eric Nelson of the University of Louisville is one of a number of researchers looking for new methods to study living cells. He is using a technique called Fluorescence Redistribution After Photobleach-ing (FRAP) to glean clues about how proteins function and how they move around a cell.
Nelson focused on RAD-18, a protein that has recently been found to help initiate the repair of damaged DNA. He has discovered that within the nucleus of cells, this protein tends to congregate in and bind to certain areas, suggesting the existence of DNA-repair factories within the cell. The FRAP studies also revealed that proteins move more freely in low density regions than in high density nucleic regions, probably because those in low-density regions are bound and do not diffuse. Future experiments will be aimed at determining the underlying relocation mechanisms for RAD-18
©1995 - 2017, AMERICAN PHYSICAL SOCIETY
APS encourages the redistribution of the materials included in this newspaper provided that attribution to the source is noted and the materials are not truncated or changed.
Associate Editor: Jennifer Ouellette