Strain Magnitude and Strain Rate Influence Stretch-Induced Injury of PC12 Cells

The acceleration-deceleration associated with external impact to head causes the mechanical deformation of brain tissue, resulting in neuronal damage. However, the correlation between the deformation and the neuronal damage has not been understood sufficiently. In this study, we investigated the effects of various magnitudes and rates of strain on cytotoxicity, mortality and morphology of Rat pheochromocytoma cell line, PC12 cells using the shock machine. PC12 cells were seeded in poly-L-lysine-coated polycarbonate dishes and neurites were elongated by the addition of neuron growth factor. The dishes were weighted at the bottom of 0.2 mm thickness in order to strain it by loading acceleration induced by the shock machine. The magnitude of acceleration was 500 G and the duration of acceleration was 1 ms. Then, PC12 cells were subjected to strain magnitudes (up to 2.2%) and strain rates (up to 19.0 (-1)). After exposure to impact, lactate dehydrogenase (LDH) was measured as cytotoxicity and cell viability was measured by the dye exclusion method with trypan blue dye as cell mortality. Morphology of neurites in PC12 cells were observed by phase contrast microscopy. As a result, cytotoxicity and cell mortality increased with increase in strain magnitude and strain rate. In addition, swelling and beading of neurites in PC12 cells increased with increase in strain magnitudes or strain rates. These results suggested that stretch-induced injury of PC12 cells is dependent on strain magnitude and strain rate, but, in order to elucidate neuronal damage caused by an interaction between strain magnitude and strain rate, more quantitative studies are required, such as various combination of strain magnitude and strain rate.