Aberrant adenosine signaling in patients with focal cortical dysplasia

AUTHORS

Mengyi Guo, Jing Zhang, Jing Wang, Xiongfei Wang, Qing Gao, Chongyang Tang, Jiahui Deng, Zhonghua Xiong, Xiangru Kong, Yuguang Guan, Jian Zhou, Detlev Boison, Guoming Luan, Tianfu Li

ABSTRACT

Focal cortical dysplasia (FCD), a common malformation of cortical development, is frequently associated with pharmacoresistant epilepsy in both children and adults. Adenosine is an inhibitory modulator of brain activity and a prospective anti-seizure agent with potential for clinical translation. Our previous results demonstrated that the major adenosine-metabolizing enzyme adenosine kinase (ADK) was upregulated in balloon cells (BCs) within FCD type IIB lesions, suggesting that dysfunction of the adenosine system is implicated in the pathophysiology of FCD. In our current study, we therefore performed a comprehensive analysis of adenosine metabolism and signaling in surgically resected cortical specimens from patients with FCD type I and type II via immunohistochemistry and immunoblot analysis. Adenosine metabolism was assessed by quantifying the levels of the key enzymes of adenosine metabolism, i.e., ADK, adenosine deaminase (ADA), and 5’-ectonucleotidase (CD73). Adenosine signaling was assessed by quantifying the levels of adenosine A2A receptor (A2AR) and putative downstream mediators of adenosine, namely, glutamate transporter-1 (GLT-1) and mammalian target of rapamycin (mTOR). Within lesions in FCD specimens, we found that the adenosine-metabolizing enzymes ADK and ADA, as well as the adenosine-producing enzyme CD73, were upregulated. We also observed an increase in A2AR expression, as well as a decrease in GLT-1 levels and an increase in mTOR levels, in FCD specimens compared with control tissue. These results suggest that dysregulation of the adenosine system is a common pathologic feature of both FCD type I and type II. The adenosine system might therefore be a therapeutic target for the treatment of epilepsy associated with FCD.

Distinct and dementia-related synaptopathy in the hippocampus after military blast exposures

AUTHORS

Michael F. Almeida, Thuvan Piehler, Kelly E. Carstens, Meilan Zhao, Mahsa Samadi, Serena M. Dudek, Christopher J. Norton, Catherine M. Parisian, Karen L.G. Farizatto, Ben A. Bahr

ABSTRACT

Explosive shockwaves, and other types of blast exposures, are linked to injuries commonly associated with military service and to an increased risk for the onset of dementia. Neurological complications following a blast injury, including depression, anxiety, and memory problems, often persist even when brain damage is undetectable. Here, hippocampal explants were exposed to the explosive 1,3,5-trinitro-1,3,5-triazinane (RDX) to identify indicators of blast-induced changes within important neuronal circuitries. Highly controlled detonations of small, 1.7-gram RDX spherical charges reduced synaptic markers known to be downregulated in cognitive disorders, but without causing overt neuronal loss or astroglial responses. In the absence of neuromorphological alterations, levels of synaptophysin, GluA1, and synapsin IIb were significantly diminished within 24 hr, and these synaptic components exhibited progressive reductions following blast exposure as compared to their stable maintenance in control explants. In contrast, labeling of the synapsin IIa isoform remained unaltered, while neuropilar staining of other markers decreased, including synapsin IIb and neural cell adhesion molecule (NCAM) isoforms, along with evidence of NCAM proteolytic breakdown. NCAM180 displayed a distinct decline after the RDX blasts, whereas NCAM140 and NCAM120 exhibited smaller or no deterioration, respectively. Interestingly, the extent of synaptic marker reduction correlated with AT8-positive tau levels, with tau pathology stochastically found in CA1 neurons and their dendrites. The decline in synaptic components was also reflected in the size of evoked postsynaptic currents recorded from CA1 pyramidals, which exhibited a severe and selective reduction. The identified indicators of blast-mediated synaptopathy point to the need for early biomarkers of explosives altering synaptic integrity with links to dementia risk, to advance strategies for both cognitive health and therapeutic monitoring.

Genetic Approach to Elucidate the Role of Cyclophilin D in Traumatic Brain Injury Pathology

AUTHORS

Ryan D. Readnower, William Brad Hubbard, Olivia J. Kalimon, James W. Geddes, Patrick G. Sullivan

ABSTRACT

Cyclophilin D (CypD) has been shown to play a critical role in mitochondrial permeability transition pore (mPTP) opening and the subsequent cell death cascade. Studies consistently demonstrate that mitochondrial dysfunction, including mitochondrial calcium overload and mPTP opening, is essential to the pathobiology of cell death after a traumatic brain injury (TBI). CypD inhibitors, such as cyclosporin A (CsA) or NIM811, administered following TBI, are neuroprotective and quell neurological deficits. However, some pharmacological inhibitors of CypD have multiple biological targets and, as such, do not directly implicate a role for CypD in arbitrating cell death after TBI. Here, we reviewed the current understanding of the role CypD plays in TBI pathobiology. Further, we directly assessed the role of CypD in mediating cell death following TBI by utilizing mice lacking the CypD encoding gene Ppif. Following controlled cortical impact (CCI), the genetic knockout of CypD protected acute mitochondrial bioenergetics at 6 h post-injury and reduced subacute cortical tissue and hippocampal cell loss at 18 d post-injury. The administration of CsA following experimental TBI in Ppif-/- mice improved cortical tissue sparing, highlighting the multiple cellular targets of CsA in the mitigation of TBI pathology. The loss of CypD appeared to desensitize the mitochondrial response to calcium burden induced by TBI; this maintenance of mitochondrial function underlies the observed neuroprotective effect of the CypD knockout. These studies highlight the importance of maintaining mitochondrial homeostasis after injury and validate CypD as a therapeutic target for TBI. Further, these results solidify the beneficial effects of CsA treatment following TBI.

Ultrasound-mediated blood-brain barrier disruption improves anti-pyroglutamate3 Aβ antibody efficacy and enhances phagocyte infiltration into brain in aged Alzheimer’s disease-like mice

AUTHORS

Qiaoqiao Shi, Tao Sun, Yongzhi Zhang, Chanikarn Power, Camilla Hoesch, Shawna Antonelli, Maren K. Schroeder, Barbara J. Caldarone, Nadine Taudte, Mathias Schenk, Thore Hettmann, Stephan Schilling, Nathan J. McDannold, Cynthia A. Lemere

ABSTRACT

Pyroglutamate-3 amyloid-β (pGlu3 Aβ) is an N-terminally modified, toxic form of amyloid-β that is present in cerebral amyloid plaques and vascular deposits. Using the Fc-competent murine anti-pGlu3 Aβ monoclonal antibody (mAb), 07/2a, we present here a nonpharmacological approach using focused ultrasound (FUS) with intravenous (i.v.) injection of microbubbles (MB) to facilitate i.v. delivery of the 07/2a mAb across the blood brain barrier (BBB) in order to improve Aβ removal and restore memory in aged APP/PS1 mice, an Alzheimer’s disease (AD)-like model of amyloidogenesis.

Compared to sham-treated controls, aged APP/PS1 mice treated with 07/2a immediately prior to FUS-mediated BBB disruption (mAb + FUS-BBBD combination treatment) showed significantly better spatial learning and memory in the Water T Maze. FUS-BBBD treatment alone improved contextual fear learning and memory in aged WT and APP/PS1 mice, respectively. APP/PS1 mice given the combination treatment had reduced Aβ42 and pGlu3 Aβ hippocampal plaque burden compared to PBS-treated APP/PS1 mice.

Hippocampal synaptic puncta density and synaptosomal synaptic protein levels were also higher in APP/PS1 mice treated with 07/2a just prior to BBB disruption. Increased Iba-1+ microglia were observed in the hippocampi of AD mice treated with 07/2a with and without FUS-BBBD, and APP/PS1 mice that received hippocampal BBB disruption and 07/2a showed increased Ly6G+ monocytes in hippocampal CA3. FUS-induced BBB disruption did not increase the incidence of microhemorrhage in mice with or without 07/2a mAb treatment.

Our findings suggest that FUS is useful tool that may enhance delivery of an anti-pGlu3 Aβ mAb for immunotherapy. FUS-mediated BBB disruption in combination with the 07/2a mAb also appears to facilitate monocyte infiltration in this AD model. Overall, these effects resulted in greater sparing of synapses and improved cognitive function without causing overt damage, suggesting the possibility of FUS as a noninvasive method to increase the therapeutic efficacy in AD patients.