Chronic Upregulation of Cleaved-Caspase-3 Associated with Chronic Myelin Pathology and Microvascular Reorganization in the Thalamus after Traumatic Brain Injury in Rats.

Andriy Glushakov,Cesar Borlongan,Alex Valadka,Ronald Hayes,Alexander Glushakov,Olena Glushakova,Sandra Acosta,Tetyana Korol

doi:10.3390/ijms19103151

Abstract

Traumatic brain injury (TBI) is associated with long-term disabilities and devastating chronic neurological complications including problems with cognition, motor function, sensory processing, as well as behavioral deficits and mental health problems such as anxiety, depression, personality change and social unsuitability. Clinical data suggest that disruption of the thalamo-cortical system including anatomical and metabolic changes in the thalamus following TBI might be responsible for some chronic neurological deficits following brain trauma. Detailed mechanisms of these pathological processes are not completely understood. The goal of this study was to evaluate changes in the thalamus following TBI focusing on cleaved-caspase-3, a specific effector of caspase pathway activation and myelin and microvascular pathologies using immuno- and histochemistry at different time points from 24 h to 3 months after controlled cortical impact (CCI) in adult Sprague-Dawley rats. Significant increases in cleaved-caspase-3 immunoreactivity in the thalamus were observed starting one month and persisting for at least three months following experimental TBI. Further, the study demonstrated an association of cleaved-caspase-3 with the demyelination of neuronal processes and tissue degeneration in the gray matter in the thalamus, as reflected in alterations of myelinated fiber integrity (luxol fast blue) and decreases in myelin basic protein (MBP) immunoreactivity. The immunofluorescent counterstaining of cleaved-caspase-3 with endothelial barrier antigen (EBA), a marker of blood-brain barrier, revealed limited direct and indirect associations of cleaved caspase-3 with blood-brain barrier damage. These results demonstrate for the first time a significant chronic upregulation of cleaved-caspase-3 in selected thalamic regions associated with cortical regions directly affected by CCI injury. Further, our study is also the first to report that significant upregulation of cleaved-caspase-3 in selected ipsilateral thalamic regions is associated with microvascular reorganization reflected in the significant increases in the number of microvessels with blood-brain barrier alterations detected by EBA staining. These findings provide new insights into potential mechanisms of TBI cell death involving chronic activation of caspase-3 associated with disrupted cortico-thalamic and thalamo-cortical connectivity. Moreover, this study offers the initial evidence that this upregulation of activated caspase-3, delayed degeneration of myelinated nerve fibers and microvascular reorganization with impaired blood-brain barrier integrity in the thalamus might represent reciprocal pathological processes affecting neuronal networks and brain function at the chronic stages of TBI.

Highlights

Traumatic brain injury (TBI) is a major public health problem affecting over 1.7 million Americans annually and causing 52,000 deaths and over 90,000 long-term disabilities [1,2,3,4]
Following experimental TBI, increases in cleaved-caspase-3 immunoreactivity were observed in selected brain regions with the most prominent upregulation detected in selected ipsilateral thalamic regions at sub-acute and chronic time points (Figure 1A)
Maximal increases in cleaved-caspase-3 immunoreactivity were observed in dorsal thalamic areas proximate to the hippocampal formation including the lateral posterior thalamic nucleus (LP), the laterodorsal thalamic nucleus (LD), the dorsal lateral geniculate nucleus (DLG) and the ventral lateral geniculate nucleus (VLG) (Figure 1B,C)

Summary

Introduction

Traumatic brain injury (TBI) is a major public health problem affecting over 1.7 million Americans annually and causing 52,000 deaths and over 90,000 long-term disabilities [1,2,3,4]. Chronic sleep disturbances are common after TBI, affecting about 50% of patients [6,7]. A wealth of clinical data has documented that TBI causes significant brain atrophy, which is associated with progressive neuronal degeneration and degeneration of the gray and white matter. This may disrupt brain connectivity within days after injury and continue for years [17,18,19]. A significant impairment in cerebral blood flow in the thalamic regions of patients with mild TBI as compared to healthy controls [27]

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