May  2004 Issue 

   

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AFM Study Shows Old Cells Lose Their Elasticity

The reason our skin becomes more leathery and thick as we age  might be due to a loss of elasticity in the cells, according to Igor  Sokolov of Clarkson University, who presented his latest research  findings during a session on bioimaging techniques at the APS March  Meeting in Montreal.

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.

silica sphere

A 5Ám silica sphere glued to a standard AFM cantilever was  used to obtain stable and repeatable measurements over the  area of individual cell.

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.


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