Marshall T. Bell

Toll-Like Receptor 4–Dependent Microglial Activation Mediates Spinal Cord Ischemia–Reperfusion Injury

Background— Paraplegia continues to complicate thoracoabdominal aortic interventions. The elusive mechanism of spinal cord ischemia–reperfusion injury has delayed the development of pharmacological adjuncts. Microglia, the resident macrophages of the central nervous system, can have pathological responses after a variety of insults. This can occur through toll-like receptor 4 (TLR-4) in stroke models. We hypothesize that spinal cord ischemia–reperfusion injury after aortic occlusion results from TLR-4–mediated microglial activation in mice. Methods and Results— TLR-4 mutant and wild-type mice underwent aortic occlusion for 5 minutes, followed by 60 hours of reperfusion when spinal cords were removed for analysis. Spinal cord cytokine production and microglial activation were assessed at 6 and 36 hours after surgery. Isolated microglia from mutant and wild-type mice were subjected to oxygen and glucose deprivation for 24 hours, after which the expression of TLR-4 and proinflammatory cytokines was analyzed. Mice without functional TLR-4 demonstrated decreased microglial activation and cytokine production and had preserved functional outcomes and neuronal viability after thoracic aortic occlusion. After oxygen and glucose deprivation, wild-type microglia had increased TLR-4 expression and production of proinflammatory cytokines. Conclusions— The absence of functional TLR-4 attenuated neuronal injury and microglial activation after thoracic aortic occlusion in mice. Furthermore, microglial upregulation of TLR-4 occurred after oxygen and glucose deprivation, and the absence of functional TLR-4 significantly attenuated the production of proinflammatory cytokines. In conclusion, TLR-4–mediated microglia activation in the spinal cord after aortic occlusion is critical in the mechanism of paraplegia after aortic cross-clamping and may provide targets for pharmacological intervention.

Spinal cord protection via alpha-2 agonist-mediated increase in glial cell-line–derived neurotrophic factor

OBJECTIVES Delayed paraplegia secondary to ischemia-reperfusion injury is a devastating complication of thoracoabdominal aortic surgery. Alpha-2 agonists have been shown to attenuate ischemia-reperfusion injury, but the mechanism for protection has yet to be elucidated. A growing body of evidence suggests that astrocytes play a critical role in neuroprotection by release of neurotrophins. We hypothesize that alpha-2 agonism with dexmedetomidine increases glial cell-line-derived neurotrophic factor in spinal cord astrocytes to provide spinal cord protection. METHODS Spinal cords were isolated en bloc from C57BL/6 mice, and primary spinal cord astrocytes and neurons were selected for and grown separately in culture. Astrocytes were treated with dexmedetomidine, and glial cell-line-derived neurotrophic factor was tested for by enzyme-linked immunosorbent assay. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used to assess neuronal viability. RESULTS Spinal cord primary astrocytes treated with dexmedetomidine at 1 μmol/L and 10 μmol/L had significantly increased glial cell-line-derived neurotrophic factor production compared with control (P < .05). Neurons subjected to oxygen glucose deprivation had significant preservation (P < .05) of viability with use of dexmedetomidine-treated astrocyte media. Glial cell-line-derived neurotrophic factor neutralizing antibody eliminated the protective effects of the dexmedetomidine-treated astrocyte media (P < .05). CONCLUSIONS Astrocytes have been shown to preserve neuronal viability via release of neurotrophic factors. Dexmedetomidine increases glial cell-derived neurotrophic factor from spinal cord astrocytes via the alpha-2 receptor. Treatment with alpha-2 agonist dexmedetomidine may be a clinical tool for use in spinal cord protection in aortic surgery.

Spinal Cord Ischemia-Reperfusion Injury Induces Erythropoietin Receptor Expression

BACKGROUND Paraplegia remains a devastating complication of aortic surgery, occurring in up to 20% of complex thoracoabdominal repairs. Erythropoietin (EPO) attenuates this injury in models of spinal cord ischemia. Upregulation of the beta-common receptor (βcR) subunit of the EPO receptor is associated with reduced damage in murine models of neural injury. This receptor activates anti-apoptotic pathways including signaling transducer and activator of transcription 3 (STAT3). We hypothesized that spinal cord ischemia-reperfusion injury upregulates the βcR subunit with a subsequent increase in activated STAT3. METHODS Adult male C57/BL6 mice received an intraperitoneal injection of 0.5 mL of EPO (10 U/kg) or 0.9% saline after induction of anesthesia. Spinal cord ischemia was induced through sternotomy and 4-minute thoracic aortic cross-clamp. Sham mice underwent sternotomy without cross-clamp placement. Four groups were studied: ischemic and sham groups, each with and without EPO treatment. After 4 hours of reperfusion, spinal cords were harvested and homogenized. The βcR subunit expression and STAT3 activation were evaluated by immunoblot. RESULTS Ischemia reperfusion increased βcR subunit expression in spinal cords of ischemia + saline and ischemia + EPO mice compared with shams (3.4 ± 1.39 vs 1.31 ± 0.3, p = 0.01 and 3.80 ± 0.58 vs 1.56 ± 0.32, p = 0.01). Additionally, both ischemic groups demonstrated increased STAT3 activation compared with shams (1.35 ± 0.14 vs 1.09 ± 0.07, p = 0.01 and 1.66 ± 0.35 vs 1.08 ± 0.17, p = 0.02). CONCLUSIONS Ischemia-reperfusion injury induces EPO receptor βcR subunit expression and early downstream anti-apoptotic signaling through STAT3 activation. Further investigation into the role of the βcR subunit is warranted to determine tissue protective functions of EPO. Elucidation of mechanisms involved in spinal cord protection is essential for reducing delayed paraplegia.

Interruption of spinal cord microglial signaling by alpha-2 agonist dexmedetomidine in a murine model of delayed paraplegia

BACKGROUND Despite investigation into preventable pharmacologic adjuncts, paraplegia continues to complicate thoracoabdominal aortic interventions. The alpha 2a adrenergic receptor agonist, dexmedetomidine, has been shown to preserve neurologic function and neuronal viability in a murine model of spinal cord ischemia reperfusion, although the mechanism remains elusive. We hypothesize that dexmedetomidine will blunt postischemic inflammation in vivo following thoracic aortic occlusion with in vitro demonstration of microglial inhibition following lipopolysaccharide (LPS) stimulation. METHODS Adult male C57BL/6 mice underwent 4 minutes of aortic occlusion. Mice received 25 μg/kg intraperitoneal dexmedetomidine (n = 8) or 0.9% normal saline (n = 7) at reperfusion and 12-hour intervals postoperatively until 48 hours. Additionally, sham mice (n = 3), which had aortic arch exposed with no occlusion, were included for comparison. Functional scoring was done at 6 hours following surgery and 12-hour intervals until 60 hours when spinal cords were removed and examined for neuronal viability and cytokine production. Additional analysis of microglia activation was done in 12 hours following surgery. Age- and sex-matched mice had spinal cord removed for microglial isolation culture. Cells were grown to confluence and stimulated with toll-like receptor-4 agonist LPS 100 ng/mL in presence of dexmedetomidine or vehicle control for 24 hours. Microglia and media were then removed for analysis of protein expression. RESULTS Dexmedetomidine treatment at reperfusion significantly preserved neurologic function with mice in treatment group having a Basso Score of 6.3 in comparison to 2.3 in ischemic control group. Treatment was associated with a significant reduction in microglia activation and in interleukin-6 production. Microglial cells in isolation when stimulated with LPS had an increased production of proinflammatory cytokines and markers of activation. Treatment with dexmedetomidine significantly attenuated microglial activation and proinflammatory cytokine production in vitro with a greater than twofold reduction in tumor necrosis factor-α. CONCLUSIONS Alpha 2a agonist, dexmedetomidine treatment at reperfusion preserved neurologic function and neuronal viability. Furthermore, dexmedetomidine treatment resulted in an attenuation of microglial activation and proinflammatory cytokine production both in vivo and in vitro following LPS stimulation. This finding lends insight into the mechanism of paralysis following thoracic aortic interventions and may guide future pharmacologic targets for attenuating spinal cord ischemia and reperfusion.

Clinical indicators of paraplegia underplay universal spinal cord neuronal injury from transient aortic occlusion.

Paraplegia following complex aortic intervention relies on crude evaluation of lower extremity strength such as whether the patient can lift their legs or flex the ankle. Little attention has been given to the possible long-term neurologic sequelae following these procedures in patients appearing functionally normal. We hypothesize that mice subjected to minimal ischemic time will have functional and histological changes despite the gross appearance of normal function. Male mice underwent 3 min of aortic occlusion (n=14) or sham surgery (n=4) via a median sternotomy. Neurologic function was graded by Basso Motor Score (BMS) preoperatively and at 24h intervals after reperfusion. Mice appearing functionally normal and sham mice were placed on a walking beam and recorded on high-definition, for single-frame motion analysis. After 96 hrs, spinal cords were removed for histological analysis. Following 3 min of ischemia, functional outcomes were split evenly with either mice displaying almost normal function n=7 or near complete paraplegia n=7. Additionally, single-frame motion analysis revealed significant changes in gait. Histologically, there was a significant stepwise reduction of neuronal viability, with even the normal function ischemic group demonstrating significant loss of neurons. Despite the appearance of normal function, temporary ischemia induced marked cyto-architectural changes and neuronal degeneration. Furthermore high-definition gait analysis revealed significant changes in gait and activity following thoracic aortic occlusion. These data suggest that all patients undergoing procedures, even with short ischemic times, may have spinal cord injury that is not evident clinically.

Cancer Stem Cell Phenotype Is Supported by Secretory Phospholipase A2 in Human Lung Cancer Cells

BACKGROUND Lung cancer stem cells (CSCs) are a subpopulation of cells that drive growth, invasiveness, and resistance to therapy. Inflammatory eicosanoids are critical to maintain this malignant subpopulation. Secretory phospholipase A2 group IIa (sPLA2) is an important mediator of the growth and invasive potential of human lung cancer cells and regulates eicosanoid production. We hypothesized that sPLA2 plays a role in the maintenance of lung CSCs. METHODS Cancer stem cells from lung adenocarcinoma cell lines H125 and A549 were isolated using aldehyde dehydrogenase activity and flow cytometry. Protein and mRNA levels for sPLA2 were compared between sorted cells using Western blotting and quantitative reverse transcriptase-polymerase chain reaction techniques. Chemical inhibition of sPLA2 and short-hairpin RNA knockdown of sPLA2 were used to evaluate effects on tumorsphere formation. RESULTS Lung CSCs were isolated in 8.9%±4.1% (mean±SD) and 4.1%±1.6% of H125 and A549 cells respectively. Both sPLA2 protein and mRNA expression were significantly elevated in the CSC subpopulation of H125 (p=0.002) and A549 (p=0.005; n=4). Knockdown of sPLA2 significantly reduced tumorsphere formation in H125 (p=0.026) and A549 (p=0.001; n=3). Chemical inhibition of sPLA2 resulted in dose-dependent reduction in tumorsphere formation in H125 (p=0.003) and A549 (p=0.076; n=3). CONCLUSIONS Lung CSCs express higher levels of sPLA2 than the non-stem cell population. Our findings that viral knockdown and chemical inhibition of sPLA2 reduce tumorsphere formation in lung cancer cells demonstrate for the first time that sPLA2 plays an important role in CSCs. These findings suggest that sPLA2 may be an important therapeutic target for human lung cancer.

Reproducable Paraplegia by Thoracic Aortic Occlusion in a Murine Model of Spinal Cord Ischemia-reperfusion

BACKGROUND Lower extremity paralysis continues to complicate aortic interventions. The lack of understanding of the underlying pathology has hindered advancements to decrease the occurrence this injury. The current model demonstrates reproducible lower extremity paralysis following thoracic aortic occlusion. METHODS Adult male C57BL6 mice were anesthetized with isoflurane. Through a cervicosternal incision the aorta was exposed. The descending thoracic aorta and left subclavian arteries were identified without entrance into pleural space. Skeletonization of these arteries was followed by immediate closure (Sham) or occlusion for 4 min (moderate ischemia) or 8 min (prolonged ischemia). The sternotomy and skin were closed and the mouse was transferred to warming bed for recovery. Following recovery, functional analysis was obtained at 12 hr intervals until 48 hr. RESULTS Mice that underwent sham surgery showed no observable hind limb deficit. Mice subjected to moderate ischemia for 4 min had minimal functional deficit at 12 hr followed by progression to complete paralysis at 48 hr. Mice subjected to prolonged ischemia had an immediate paralysis with no observable hind-limb movement at any point in the postoperative period. There was no observed intraoperative or post operative mortality. CONCLUSION Reproducible lower extremity paralysis whether immediate or delayed can be achieved in a murine model. Additionally, by using a median sternotomy and careful dissection, high survival rates, and reproducibility can be achieved.

Spontaneous Pulmonary Torsion Secondary to Left Upper Lobe Malignancy

Journal of Thoracic Oncology ® • Volume 10, Number 11, November 2015 CASE REPORT A 72-year-old man with known left upper lobe moderately differentiated mucinous adenocarcinoma presented with shortness of breath 3 weeks after diagnosis, during ongoing work-up. Work-up to date demonstrated no evidence of metastatic disease. He was presumed to have postobstructive pneumonia and antibiotics started. Prior imaging was suspicious for pericardial invasion, so dedicated gated cardiac magnetic resonance imaging was performed. This demonstrated findings suggestive of pulmonary torsion (Fig. 1). Chest computed tomography was performed immediately thereafter and confirmed 180° torsion of the left upper lobe (Fig. 2). The patient was emergently taken for thoracic exploration. Obstruction of the left mainstem bronchus due to rotation was demonstrated upon flexible bronchoscopy. Upon entering the left hemi-thorax via thoracotomy, a 180° counterclockwise axial rotation of the lung around the hilum was identified. Anatomy was notable for the upper lobe being distended and