Sabetta Zackary, Krishna Gokul, Curry Tala, Adelson P David, Thomas Theresa Currier
bioRxiv. 2023 Feb 7:2023.02.06.527058. doi: 10.1101/2023.02.06.527058.
Traumatic brain injury (TBI) manifests late-onset and persisting clinical symptoms with implications for sex differences and increased risk for the development of age-related neurodegenerative diseases. Few studies have evaluated chronic temporal profiles of neuronal and glial pathology that include sex as a biological variable. After experimental diffuse TBI, late-onset and persisting somatosensory hypersensitivity to whisker stimulation develops at one-month post-injury and persists to at least two months post-injury in male rats, providing an model to evaluate the temporal profile of pathology responsible for morbidity. Whisker somatosensation is dependent on signaling through the thalamocortical relays of the whisker barrel circuit made up of glutamatergic projections between the ventral posteromedial nucleus of the thalamus (VPM) and primary somatosensory barrel cortex (S1BF) with inhibitory (GABA) innervation from the thalamic reticular nucleus (TRN) to the VPM. To evaluate the temporal profiles of pathology, male and female Sprague Dawley rats ( = 5-6/group) were subjected to sham surgery or midline fluid percussion injury (FPI). At 7-, 56-, and 168-days post-injury (DPI), brains were processed for amino-cupric silver stain and glial fibrillary acidic protein (GFAP) immunoreactivity, where pixel density of staining was quantified to determine the temporal profile of neuropathology and astrocyte activation in the VPM, S1BF, and TRN. FPI induced significant neuropathology in all brain regions at 7 DPI. At 168 DPI, neuropathology remained significantly elevated in the VPM and TRN, but returned to sham levels in the S1BF. GFAP immunoreactivity was increased as a function of FPI and DPI, with an FPI × DPI interaction in all regions and an FPI × Sex interaction in the S1BF. The interactions were driven by increased GFAP immunoreactivity in shams over time in the VPM and TRN. In the S1BF, GFAP immunoreactivity increased at 7 DPI and declined to age-matched sham levels by 168 DPI, while GFAP immunoreactivity in shams significantly increased between 7 and 168 days. The FPI × Sex interaction was driven by an overall greater level of GFAP immunoreactivity in FPI males compared to FPI females. Increased GFAP immunoreactivity was associated with an increased number of GFAP-positive soma, predominantly at 7 DPI. Overall, these findings indicate that FPI, time post-injury, sex, region, and aging with injury differentially contribute to chronic changes in neuronal pathology and astrocyte activation after diffuse brain injury. Thus, our results highlight distinct patterns of pathological alterations associated with the development and persistence of morbidity that supports chronic neuropathology, especially within the thalamus. Further, data indicate a convergence between TBI-induced and age-related pathology where further investigation may reveal a role for divergent astrocytic phenotypes associated with increased risk for neurodegenerative diseases.
创伤性脑损伤（TBI）表现出迟发性且持续存在的临床症状，这涉及性别差异以及与年龄相关的神经退行性疾病发生风险的增加。很少有研究评估将性别作为生物学变量的神经元和神经胶质病理的慢性时间变化情况。实验性弥漫性TBI后，雄性大鼠在损伤后1个月出现对触须刺激的迟发性且持续存在的体感超敏反应，并持续至损伤后至少2个月，这为评估导致发病的病理时间变化情况提供了一个模型。触须体感依赖于由丘脑腹后内侧核（VPM）与初级体感桶状皮质（S1BF）之间的谷氨酸能投射组成的触须桶状回路的丘脑皮质中继信号传递，同时有来自丘脑网状核（TRN）到VPM的抑制性（GABA）神经支配。为了评估病理的时间变化情况，将雄性和雌性Sprague Dawley大鼠（每组n = 5 - 6）进行假手术或中线液压冲击伤（FPI）。在损伤后7天、56天和168天（DPI），对大脑进行氨基铜银染色和胶质纤维酸性蛋白（GFAP）免疫反应性处理，对染色的像素密度进行定量，以确定VPM、S1BF和TRN中神经病理和星形胶质细胞激活的时间变化情况。FPI在7 DPI时在所有脑区均诱导出显著的神经病理变化。在168 DPI时，VPM和TRN中的神经病理变化仍显著升高，但S1BF中的神经病理变化恢复到假手术水平。GFAP免疫反应性随FPI和DPI而增加，在所有区域均存在FPI×DPI相互作用，在S1BF中存在FPI×性别相互作用。这些相互作用是由VPM和TRN中假手术组随时间GFAP免疫反应性增加所驱动的。在S1BF中，GFAP免疫反应性在7 DPI时增加，并在168 DPI时降至与年龄匹配的假手术水平，而假手术组的GFAP免疫反应性在7至168天之间显著增加。FPI×性别相互作用是由FPI雄性大鼠中GFAP免疫反应性总体水平高于FPI雌性大鼠所驱动的。GFAP免疫反应性增加与GFAP阳性体细胞数量增加相关，主要在7 DPI时。总体而言，这些发现表明FPI、损伤后时间、性别、区域以及损伤后的衰老对弥漫性脑损伤后神经元病理和星形胶质细胞激活的慢性变化有不同的贡献。因此，我们的结果突出了与支持慢性神经病理的发病发展和持续存在相关的病理改变的独特模式，尤其是在丘脑中。此外，数据表明TBI诱导的病理与年龄相关的病理之间存在趋同，进一步的研究可能揭示与神经退行性疾病风险增加相关的不同星形胶质细胞表型的作用。
