Parkinson's disease (PD) is the most common neurodegenerative movement disorder afflicting >500,000 patients in the United States alone. This age-related progressive disorder is typified by invariant loss of dopaminergic substantia nigra neurons (DAN), dystrophic neurites, the presence of α-synuclein (SYN) positive intracytoplasmic inclusions (Lewy bodies) in the remaining DAN, and activated microglia. As such, microglial activation and resultant increase in proinflammatory molecules have moved to the forefront of PD research as a potential pathobiologic mechanism of disease. Herein, we present data demonstrating early microglial activation in mice that over-express wild-type SYN, the release of SYN from a SYN overexpressing MN9D cell line, and dose-dependent SYN-mediated activation of primary microglial cultures with consequent increases in proinflammatory molecules. Furthermore, we provide evidence that the CD36 scavenger receptor and downstream kinases are involved in SYN-mediated microglial activation. Together, our data suggest an early role for SYN and inflammation in PD pathogenesis.

Post-ischemic neurodegeneration remains the principal cause of mortality following cardiac resuscitation. Recent studies have implicated gastrointestinal ischemia in the sepsis-like response associated with the post-cardiac arrest syndrome (PCAS). However, the extent to which the resulting low-grade endotoxemia present in up to 86% of resuscitated patients affects cerebral ischemia-reperfusion injury has not been investigated. Here we report that a single injection of low-dose lipopolysaccharide (50 μg/kg, IP) delivered after global cerebral ischemia (GCI) induces blood-brain barrier permeability, microglial activation, cortical injury, and functional decline in vivo, compared to ischemia alone. And while GCI was sufficient to induce neutrophil (PMN) activation and recruitment to the post-ischemic CNS, minimal endotoxemia exhibited synergistic effects on markers of systemic inflammation including PMN priming, lung damage, and PMN burden within the lung and other non-ischemic organs including the kidney and liver. Our findings predict that acute interventions geared towards blocking the effects of serologically occult endotoxemia in survivors of cardiac arrest will limit delayed neurodegeneration, multi-organ dysfunction and potentially other features of PCAS. This work also introduces lung-brain coupling as a novel therapeutic target with broad effects on innate immune priming and post-ischemic neurodegeneration following cardiac arrest and related cerebrovascular conditions.

Lung and brain development is often altered in infants born preterm and exposed to excess oxygen, and this can lead to impaired lung function and neurocognitive abilities later in life. Oxygen-derived reactive oxygen species and the ensuing inflammatory response are believed to be an underlying cause of disease because over-expression of some anti-oxidant enzymes is protective in animal models. For example, neurodevelopment is preserved in mice that ubiquitously express human extracellular superoxide dismutase (EC-SOD) under control of an actin promoter. Similarly, oxygen-dependent changes in lung development are attenuated in transgenic SftpcEC−SOD mice that over-express EC-SOD in pulmonary alveolar epithelial type II cells. But whether anti-oxidants targeted to the lung provide protection to other organs, such as the brain is not known. Here, we use transgenic SftpcEC−SOD mice to investigate whether lung-specific expression of EC-SOD also preserves neurodevelopment following exposure to neonatal hyperoxia. Wild type and SftpcEC−SOD transgenic mice were exposed to room air or 100% oxygen between postnatal days 0–4. At 8 weeks of age, we investigated neurocognitive function as defined by novel object recognition, pathologic changes in hippocampal neurons, and microglial cell activation. Neonatal hyperoxia impaired novel object recognition memory in adult female but not male mice. Behavioral deficits were associated with microglial activation, CA1 neuron nuclear contraction, and fiber sprouting within the hilus of the dentate gyrus (DG). Over-expression of EC-SOD in the lung preserved novel object recognition and reduced the observed changes in neuronal nuclear size and myelin basic protein fiber density. It had no effect on the extent of microglial activation in the hippocampus. These findings demonstrate pulmonary expression of EC-SOD preserves short-term memory in adult female mice exposed to neonatal hyperoxia, thus suggesting anti-oxidants designed to alleviate oxygen-induced lung disease such as in preterm infants may also be neuroprotective.

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Introduction: Cardiac arrest induces a robust systemic inflammatory response that exacerbates CNS injury and is characterized in part by neutrophil (PMN) migration to the brain. Tetracyclines have been shown to reduce inflammation after stroke, and here we test the effects of the tetracycline derivative 9-tert-butyl doxycycline (9TB) on PMN activation, trafficking, and ischemic neuroprotection in a mouse model of global ischemia-reperfusion. Hypothesis: Inhibition of PMN activation by 9TB will decrease PMN extravasation in the CNS and mitigate ischemia-reperfusion injury. Methods: Transient global cerebral ischemia was induced in LysM-EGFP mice by 3-vessel occlusion (3VO). Mice were given 50 μg/kg lipopolysaccharide (LPS) to simulate endotoxemia observed after cardiac arrest and daily injections of 25 mg/kg 9TB or vehicle control. Blood was collected 4 hours after 3VO/LPS for fluorescence-activated cell sorting (FACS) analysis of PMN activation. Brain and spleen immunohistochemistry were performed after 3 days to assess injury and PMN burden. Results: Expression of the PMN activation marker CD11b was increased 4 hours after 3VO/LPS compared to sham (mean fluorescence intensity = 55,516 vs. 6,537) and lower in 3VO/LPS animals treated with 9TB (MFI = 36,445). While sham-treated groups showed little PMN infiltration into the brain (7.5 PMN/mm2 ± 2.2 vs. 1.9 PMN/mm2 ± 1.3; NS), 9TB treatment of shams increased splenic PMN sequestration (81.4 ± 8.3 vs. 38.0 ± 7.5; p<0.001). This effect was enhanced with 3VO/LPS (112.2 ± 8.9 vs. 37.3 ± 0.1; p<0.0001). 3VO/LPS animals receiving 9TB exhibited lower cortical PMN counts (19.3 PMN/mm2 ± 13.6) compared to those receiving vehicle (46.5 PMN/mm2 ± 5.5; p<0.05). Daily 9TB after 3VO/LPS also decreased cortical injury compared to vehicle-treated controls (9.7% ± 6.8 vs. 32.2% ± 6.4; p<0.05) with no difference between sham groups (5.5% ± 0.9 vs. 6.8% ± 5.8; NS). PMN burden was positively correlated with neuronal injury (Pearson’s r=0.8621, p<0.01). Conclusions: 9TB treatment rapidly inhibits PMN activation and reduces PMN migration and CNS injury when delivered acutely following cerebral ischemia-reperfusion. Future studies are required to link ischemic neuroprotection with the observed effects on PMN activity.