Blockade of Astrocytic Calcineurin/NFAT Signaling Helps to Normalize Hippocampal Synaptic Function and Plasticity in a Rat Model of Traumatic Brain Injury.

Increasing evidence suggests that the calcineurin (CN)-dependent transcription factor NFAT (Nuclear Factor of Activated T cells) mediates deleterious effects of astrocytes in progressive neurodegenerative conditions. However, the impact of astrocytic CN/NFAT signaling on neural function/recovery after acute injury has not been investigated extensively. Using a controlled cortical impact (CCI) procedure in rats, we show that traumatic brain injury is associated with an increase in the activities of NFATs 1 and 4 in the hippocampus at 7 d after injury. NFAT4, but not NFAT1, exhibited extensive labeling in astrocytes and was found throughout the axon/dendrite layers of CA1 and the dentate gyrus. Blockade of the astrocytic CN/NFAT pathway in rats using adeno-associated virus (AAV) vectors expressing the astrocyte-specific promoter Gfa2 and the NFAT-inhibitory peptide VIVIT prevented the injury-related loss of basal CA1 synaptic strength and key synaptic proteins and reduced the susceptibility to induction of long-term depression. In conjunction with these seemingly beneficial effects, VIVIT treatment elicited a marked increase in the expression of the prosynaptogenic factor SPARCL1 (hevin), especially in hippocampal tissue ipsilateral to the CCI injury. However, in contrast to previous work on Alzheimer's mouse models, AAV-Gfa2-VIVIT had no effects on the levels of GFAP and Iba1, suggesting that synaptic benefits of VIVIT were not attributable to a reduction in glial activation per se. Together, the results implicate the astrocytic CN/NFAT4 pathway as a key mechanism for disrupting synaptic remodeling and homeostasis in the hippocampus after acute injury. SIGNIFICANCE STATEMENT: Similar to microglia, astrocytes become strongly "activated" with neural damage and exhibit numerous morphologic/biochemical changes, including an increase in the expression/activity of the protein phosphatase calcineurin. Using adeno-associated virus (AAV) to inhibit the calcineurin-dependent activation of the transcription factor NFAT (Nuclear Factor of Activated T cells) selectively, we have shown that activated astrocytes contribute to neural dysfunction in animal models characterized by progressive/chronic neuropathology. Here, we show that the suppression of astrocytic calcineurin/NFATs helps to protect synaptic function and plasticity in an animal model in which pathology arises from a single traumatic brain injury. The findings suggest that at least some astrocyte functions impair recovery after trauma and may provide druggable targets for treating victims of acute nervous system injury.

Combining enriched environment and induced pluripotent stem cell therapy results in improved cognitive and motor function following traumatic brain injury.

PURPOSE: Despite advances towards potential clinically viable therapies there has been only limited success in improving functional recovery following traumatic brain injury (TBI). In rats, exposure to an enriched environment (EE) improves learning and fosters motor skill development. Induced pluripotent stem cells (iPSC) have been shown to survive transplantation and influence the recovery process. The current study evaluated EE and iPSC as a polytherapy for remediating cognitive deficits following medial frontal cortex (mFC) controlled cortical impact (CCI) injury. METHODS: Sixty adult male rats received a midline mFC CCI or sham injury and were randomly placed in either EE or standard environment (SE). Seven days post-injury rats received bilateral transplantation of iPSCs or media. Behavioral measures were conducted throughout the remainder of the study. Following behavioral analysis, brains were extracted and prepared for histological analysis. RESULTS: Open-field data revealed that combined therapy resulted in typical Sham/EE activity rearing patterns by the conclusion of the study. On the Vermicelli Handling task, rats with EE/iPSC polytherapy performed better than media-treated rats. Furthermore, rats treated with polytherapy performed equivalently to Sham/EE rats on the Morris water maze. Proficiency on the Rotarod was consistently better in EE when compared to SE counterparts. Confocal microscopy confirmed that iPSCs survived and migrated away from the transplantation site. CONCLUSIONS: Overall, EE or iPSC therapy improved cognition and motor performance, however, full cognitive restoration was seen only with the EE/iPSC treatment. These data suggest that EE/iPSC therapy should be explored as a potential, clinically relevant, treatment for TBI.

The impact of enriched environment and transplantation of murine cortical embryonic stem cells on recovery from controlled cortical contusion injury.

PURPOSE: The effectiveness of embryonic stem cell (eSC) therapy has been explored in many models of neurological disease and several research groups have shown that eSC treatment leads to improved outcomes in pre-clinical models of traumatic brain injury (TBI). Though functional recovery occurs, few surviving eSCs appear to develop neuronal characteristics; instead the majority of the surviving eSC express glial phenotypes. Additionally, researchers have shown that enriching the post-surgical environment of the subject promotes functional recovery following TBI. The purpose of the current project was to determine if post-surgical environmental enrichment (EE) impacts the survival, migration, and integration of eSCs in a rodent model of TBI and if the presence of these cells lead to improved outcomes. METHODS: In the current study, the medial frontal cortex (MFC) of rats was injured using a controlled cortical impact (CCI) device. Immediately following injury the rats were placed into either EE or standard environment (SE) housing and then seven days post-injury rats received either murine cortical eSC or media. Behavioral testing consisted of the Morris water maze (MWM), Barnes Maze (BM), and Rotarod tasks (RR). RESULTS: On the MWM task, TBI/eSC/EE animals performed as well as the Sham/SE and Sham/EE groups. The TBI/eSC/SE, TBI/Media/EE, and TBI/Media/SE groups were impaired compared to the controls. By the end of training on the BM there were no differences between the Sham, TBI/Media/EE, and TBI/eSC/EE groups. On the RR task all animals placed in the EE performed equally well and significantly better than their SE housed counterparts. By the end of training on the RR task, the TBI/eSC/EE group performed as well as the sham counterparts, and though not significant they also surpassed the performance of the injured animals that received enrichment or eSC treatment alone. CONCLUSIONS: Combing therapeutic strategies with enriching the post-injury environment is likely to be an important addition to determining the efficacy of pre-clinical therapies.