In Vitro Research
With High Validity to Predict in Vivo Behavior
BMSEED’s MEASSuRE is an integrated in vitro model for TBI, SCI, and other stretch/compression-induced injuries.
1) The Mechanics Module reproduces the biomechanics of a TBI, SCI, or concussion pulling the stretchable microelectrode array (MEA) over an indenter to deform, i.e., injure, the cells. Multiple injuries can be produced for investigating the effects of repeated concussions and the link to neurodegerative diseases.
2) The Electrophysiology Module enables electrophysiological measurements before and after stretching (the injury) using the microelectrodes on the stretchable microelectrode array (MEA). Notably, the electrodes stretch with the cells during the injury, i.e., post-injury electrophysiology (cell health) can be readily normalized to pre-injury level.
3) The Imaging Module enables visualization of cells and cellular processes during the injury using optical and fluorescence imaging, e.g., to verify cell adhesion to the substrate or measure the flow of Ca ions.
Every year more than 1.7 million Americans sustain a traumatic brain injury (TBI) or concussion, 220,000 are hospitalized, and 66,000 die. In addition, 12,000-20,000 Americans sustain a spinal cord injury (SCI) annually. Despite the billions of dollars spent on research and drug development over the past decades, little is known about the mechanisms of neurotraumatic injuries, and ALL 30 clinical trials for neuroprotective drugs have failed. Additionally, epidemiological data suggest that a history of traumatic brain injury (TBI) is a significant environmental risk factor in developing Alzheimer’s Disease (AD). Evidence of a link between AD and TBI is that amyloid beta (Abeta) plaques similar to those observed in the early stages of AD have been found in 30% of patients who die acutely after a TBI. Furthermore, repetitive concussions, or mild TBI (mTBI), may lead to permanent degenerative changes including AD, chronic traumatic encephalopathy, and dementia.
In most cases, the primary biomechanical mechanism of the cell damage in a TBI, concussion, and SCI is a pathological stretch of the brain tissue during the impact. In vitro TBI models for early screening of novel therapeutics need the capability to assess the subtle but important changes in health and function of the injured neurons. Electrophysiology is a great method to assess changes in cellular health and function because the technique directly measures what is most critical to the function of neurons: the generation and transmission of electrical signals.
MEASSuRE enables functional drug screening, reproduction of the biomechanics of the injury, and measuring cell health and function before and after the injury with stretchable microelectrodes.
Pathological Cell Stretching
Neurotrauma
MEASSuRE reproduces the biomechanics of TBI and SCI. Changes in the health and function of the injured neurons can be readily assessed by comparing the post-injury electrophysiology to pre-injury level. The effectiveness of neuroprotective treatments to minimize the damage after injury can therefore be readily assessed.
Concussion
MEASSuRE will allow researchers and physicians to develop improved concussion protocols that are based on the electrophysiology of the underlying injury rather than cognitive tests.
Muscle Injury and Pain
MEASSuRE will allow the investigation of the mechanism of those muscle injuries that are caused by excessive tension or compression, and the evaluation of drugs to speed up recovery.
Stem Cell Repair Mechanism
Stem cells are involved in repair processes after injury in different parts of the body, e.g., in the brain after a traumatic brain injury. The mechanism of the activation of the mechanoreceptors is not understood. MEASSuRE will be a useful tool to elucidate and study this mechanism.
Alzheimer’s Disease
Neurodegenerative diseases such as Alzheimer’s disease have common pathological pathways with TBI, e.g., the build-up of amyloid-plaques. Therefore, MEASSuRE might be a valuable tool for the early evaluation of the efficacy of drug candidates against Alzheimer’s disease.
Example for the use of MEASSuRE:
Assessing Long Term Potentiation in Organotypic Hippocampal Slice Cultures (OHSCs) after TBI
After injury, induction of LTP through high frequency stimulation does not increase magnitude of response that is seen in sham injured OHSCs
OHSC-based in vitro models maintain the structure of the hippocampus and provide a platform to study the interactions of multiple cell types. Long term potentiation (LTP) is a cellular in vitro correlate of learning and memory which is based on synaptic plasticity. Long term potentiation is decreased after repeated mild injury. This study demonstrates how the use of stretchable microelectrode arrays (sMEAs) in the MEASSuRE platform is critical in detecting the impairment of LTP, i.e., the reduction in synaptic plasticity, after a TBI.
Methods
OHSCs derived from hippocampi of P8-10 Sprague-Dawley rats were placed on the sMEAs and kept in an incubator for at least 10 days. Spontaneous activity and stimulus response (SR) curves were recorded with the Electrophysiology Module of MEASSuRE. The slices (one per sMEA) were then subjected to moderate biaxial stretch injury (average strain: 16.2%, strain rate: 16.8 s-1) with the Mechanics Module of MEASSuRE, or sham injury as control. The actual tissue strains were confirmed with high-speed video recorded with the Imaging Module of MEASSuRE. 24 hours after injury, a second recording of spontaneous activity and SR curves. To measure plasticity, long term potentiation was induced with 3 rounds of 100 pulses at 100Hz separated by 10 seconds applied once at i50. LTP percentage values were calculated as the magnitude of the responses measured 50-60 minutes after plasticity induction, normalized to the last 10 minutes of baseline.
Results
There was no change in the overall firing rate, the magnitude of the spontaneous activity, SR parameters, or the average number of bursts before and after injury. However, there was a decrease in the spike length of the average burst after injury (7.78 ± 0.71 vs 5.94 ± 0.16, N = 10-12 slices, *p<0.05). LTP deficits 24 hours after injury were robust (48.06 ± 13.50 vs -3.62 ± 2.79%, N=4 slices **p<0.01, see Figure) compared to baseline.
Conclusions
Stretchable microelectrode arrays (sMEAs) provide a unique way to study electrical activity in the same OHSCs before and after injury. In this example, a large LTP deficits after injury was detected, which can be used as a model to assess therapeutics for TBI in vitro.