An in vitro model for uniaxial stretching of cultured neural cells: The roles of mechanical deformation and Bcl-2 proteins on axonal injury

Traumatic brain injury (TBI) is a significant health-care problem in our society and quite often leads to permanent disability or death. Today, over 5.3 million Americans are living with some sort of brain injury related disability (Brain Injury Association). Severe mechanical impact loading as well as non-impact inertial loading to the head may result in large intracranial deformations of the brain tissues and into numerous injuries and biological responses. Macroscopic shear deformation of brain tissue during head injury often translates to a localized stretching of individual neurons and their processes. It is therefore critical to perform uniaxial stretching of the neurons with strains and strain rates that mimic head injury conditions. A unique in vitro injury device has been developed with the capability of stretching cultured neural cells at strains above 100% and strain rates above 100s−1. The effect of strain on the development of axonal injury has been well documented. However, the effect of strain rate on axonal injury has not yet been considered. This study investigates the affects of both strain and strain rate on the death of cultured neurons. Differentiated neurons were uniaxially stretch injured at predetermined strain and strain rates. Our results indicate an equal and possibly a slightly higher strain rate dependence on cell death than strain alone.; Mechanical stretch injury to neural cells has largely been described as a necrotic cell death however, studies now indicate that apoptosis may also be present following TBI. We have investigated whether Bax and BClX _L protein overexpression participate in cell death pathways following stretch injury and whether apoptosis is a factor in in vitro models of axonal injury. Bax overexpression produced significant cell death and little neurite development throughout the differentiation of neural precursor cells. Although morphologically correct neural cultures could not be obtained from the YFP-Bax cells, continued experiments did not produce identifiable Bax translocation as a result of stretch injury. Alternatively, BClX _L overexpression provided significant protection to neural cells throughout differentiation and in response to a wide range of apoptotic insults in the differentiated state. BClX_L overexpression did not however, protect against stretch injury.