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Electrical Impedance as a Novel Biomarker of Myotube Atrophy and Hypertrophy

Tracking physiological changes in skeletal muscle thickness is a direct and unbiased approach in screening therapeutic compounds that prevent skeletal muscle atrophy or induce hypertrophy.
In a recent study (1), Rakhilin et al. used the xCELLigence system from Roche (SIX: RO, ROG; OTCQX: RHHBY) as a novel method to evaluate changes in myotube thickness via measuring cellular electrical impedance. They showed that both qualitative and quantitative changes in electrical impedance as a function of cellular adhesion in real time correlate well with variation in myotube thickness caused by atrophy or hypertrophy agents. Conversely, pharmacologically blocking myotube hypertrophy prevents changes in electrical impedance. According to the study, impedance can be used as a reliable and sensitive biomarker for myotube atrophy or hypertrophy. In drug screening it might be beneficial in finding novel treatments preventing muscle atrophy and other diseases associated with any morphological change in cell shape.
In the past, an accurate cell thickness estimate often was challenging due to a couple of reasons. One is the extreme heterogeneity of the myotube cellular population and therefore the lack of a regular distribution of perturbed myotubes. Another reason is the fact that differentiated myotubes form a confluent layer, which makes it difficult to estimate parameters of individual cells. Furthermore, most of the atrophy or hypertrophy-induced changes in cell thickness are relatively small (less than twofold) and therefore hard to detect with low statistical error. Electrical impedance measurement now overcomes these hurdles and offers a reliable method to determine cell thickness.
Rakhilin et al. measured the modulation of electrical impedance in C2C12 myotubes in real time with Roche-s xCELLigence system (former RT-CES from ACEA Biosciences, Inc., San Diego, CA). In the system, cells were cultured on an electrode array that is fabricated on a glass surface and embedded into the bottom of the 96-well plate. In operation, a 96-well plate is mounted to the device station and placed inside a CO2 incubator. A computer analyzes changes in impedance every few minutes, depending on the program settings.
The molecular mechanisms driving changes in myotube adhesion are quite complex and likely involve both reversible transient short-term (0-20 h) components due to G-protein-coupled receptor (GPCR ) activation and relatively stable long-term (>20 h) components. Rakhilin et al. studied changes in C2C12 diameter caused by IG F-1-driven hypertrophy, which peaks at 20 to 48 h after cell treatment. Within that period of time, changes in myotube thickness correlated perfectly with modulation of cell index or impedance. Furthermore, rapamycin-induced inhibition of IG F-1-induced hypertrophy in C2C12 cells also decreased impedance, indicating a direct relationship between cell thickness and impedance. The partial nature of impedance inhibition might be explained by incomplete blocking of the IG F-1 signaling pathway exclusively via mTOR. Hence, modulation of impedance at 20 to 48 h after compound addition may be used as a biomarker of myotube thickness.
(1) S. Rakhilin, G. Turner, M. Katz, R. Warden, J. Irelan, Y. A. Abassi and D. J. Glass: Electrical Impedance as a Novel Biomarker of Myotube Atrophy and Hypertrophy J Biomol Screen published online 14 April 2011; DOI: 10.1177/1087057111401392.
Online version: http://jbx.sagepub.com/content/early/2011/04/01/1087057111401392

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