New Atomic Force Microscopy Based Astrocyte Cell Shape Index
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New Atomic Force Microscopy Based Astrocyte Cell Shape Index Volkan Mujdat Tiryaki1, Usienemfon Adia-Nimuwa1, Steven Allen Hartz1, Kan Xie1, Virginia M. Ayres1, Ijaz Ahmed2, and David I. Shreiber 2 1 Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI 48824, USA 2 Department of Biomedical Engineering, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
ABSTRACT A new three-dimensional cell shape index using the AFM height images of cells cultured on cell substrates was defined. The new cell shape index revealed quantitative cell spreading information of cells that is not included in the conventional cell shape index. The quantitative morphometry of rat cerebral cortical astrocytes cultured on four different kinds of cell substrates were investigated using the conventional and the new cell shape index, and the results were compared. The new cell shape index showed the quantitative astrocyte spreading and stellation behavior that agrees with the AFM height images of astrocytes.
INTRODUCTION In vivo, cells have different morphologies depending on their type, e.g., astrocytes have a stellate morphology in the central nervous system (CNS) [1], and endothelial cells are elongated in the circulatory system [2]. When cells are cultured on substrates, they may adopt a similar morphology to their shape in vivo. A cell shape index (CSI) is a measurement of the morphological differentiation that is induced by the biochemical and physical environment of the cell. It is a quantitative cell morphology evaluation method that can be used to compare the morphology of cells in vitro and in vivo. The field of measuring cell morphology changes is known as quantitative morphometry [3]. Stellation is an important process for astrocytes, and CSI can be used to quantify the astrocyte stellation response. Conventional CSI is the ratio of perimeter squared to the cell projection area [1]: CSI = P2 / (4 π A)
(1)
where P is cell perimeter, and A is the cell projection area. This equation describes stellation as a cell’s departure from a circular cross section since: (2 π r)2 / 4 π (πr2) = 1
(2)
This definition for CSI was created for use with two-dimensional optical microscopy images and does not include three-dimensional aspects such as cell spreading. Our recent work indicates that cell spreading behavior may be an important part of an astrocyte’s response to its nanophysical environment, and that it can vary as much as 50% as a function of culture surface
properties [4]. In this study, the cell spreading behavior was observed as a result of an atomic force microscopy (AFM) investigation of astrocyte morphological responses to four culture environments that supplied the cells with different nanophysical cues. We are especially interested in astrocyte responses to polyamide nanofibrillar scaffolds because they have demonstrated promise for CNS repair in in vivo and in vitro investigations [5,6]. As only external cues were used to trigger cell responses, astrocyte responses t
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