Faculty Bibliography

AIMS: Myocardial ischemia remains the prime cause of morbidity and mortality in the United States. Ischemic preconditioning (IPC) is a powerful form of endogenous protection against myocardial infarction. We studied alterations in KATPchannels surface density as a potential mechanism of IPC's protection. METHODS AND RESULTS: Using cardiac-specific knockout of Kir6.2 subunits, we demonstrate an essential role for sarcolemmal KATPchannels in the infarct-limiting effect of IPC in the mouse heart. With biochemical membrane fractionation, we demonstrated that sarcolemmal KATPchannel subunits are distributed both to the sarcolemma and intracellular endosomal compartments. Global ischemia causes a loss of sarcolemmal KATPchannel subunit distribution and internalization to endosomal compartments. Ischemia-induced internalization of KATPchannels was prevented by CaMKII inhibition. KATPchannel subcellular redistribution was also observed with immunohistochemistry. Ischemic preconditioning prior to the index ischemia reduces not only the infarct size, but also prevents KATPchannel internalization. Furthermore, not only did adenosine mimic IPC by preventing infarct size, but it also prevented ischemia-induced KATPchannel internalization via a PKC-mediated pathway. We show that preventing endocytosis with dynasore reduces both KATPchannel internalization and strongly mitigates infarct development. CONCLUSIONS: Our data demonstrate that plasticity of KATPchannel surface expression must be considered as a potentially important mechanism of the protective effects of IPC and adenosine.

Heart disease is a worldwide public health problem; assessment of cardiac function is an important part of the diagnosis and management of heart disease. Magnetic resonance imaging (MRI) of the heart can provide clinically useful information on cardiac function, although it is still not routinely used in clinical practice, in part because of limited imaging speed. New accelerated methods for performing cardiovascular MRI (CMR) have the potential to provide both increased imaging speed and robustness to CMR, as well as access to increased functional information. In this review, we will briefly discuss the main methods currently employed to accelerate CMR methods, such as parallel imaging, k-t undersampling and compressed sensing, as well as new approaches that extend the idea of compressed sensing and exploit sparsity to provide richer information of potential use in clinical practice.

OBJECTIVE: The purposes of this study were to examine the impact of 3 weeks of amphetamine administration on intrinsic connectome-wide connectivity patterns in adults with attention-deficit/hyperactivity disorder (ADHD) and explore the association between stimulant-induced symptom improvement and functional connectivity alteration. METHODS: Participants included 19 adults (age 20-55 years) diagnosed with ADHD using the Diagnostic and Statistical Manual of Mental Disorders, 4th ed., Text Revision (DSM-IV-TR) criteria (American Psychiatric Association 2000 ) per the Adult Clinician Diagnostic Scale taking part in amphetamine trials. For each patient, two 6-minute resting-state functional magnetic resonance imaging (R-fMRI) scans were acquired at baseline and after treatment. A fully data-driven multivariate analytic approach (i.e., multivariate distance matrix regression [MDMR]) was applied to R-fMRI data to characterize the distributed pharmacological effects in the entire functional connectome. Clinical efficacy was assessed using ADHD rating scale with adult prompts and the Adult Self-Report Scale v1.1 Symptom Checklist. We linked stimulant-induced functional connectivity changes to symptom amelioration using Spearman's correlation. RESULTS: Three weeks of administration of a stimulant significantly reduced ADHD symptoms. MDMR-based analyses on R-fMRI data highlighted the left dorsolateral prefrontal cortex (DLPFC, a key cognitive control region) and the medial prefrontal cortex (MPFC, the anterior core of default network) whose distributed patterns of functional connectivity across the entire brain were altered by psychostimulants. Follow-up intrinsic functional connectivity revealed that stimulants specifically decreased the positive functional connectivity between DLPFC-insula, DLPFC-anterior cingulate cortex, and MPFC-insula. Importantly, these functional connectivity changes are associated with symptom improvement. CONCLUSION: These results suggested that ADHD is associated with increased functional integration or decreased functional segregation between core regions of cognitive control, default, and salience networks. The apparent normalization of intrinsic functional interaction in these circuits (i.e., increased functional segregation) may underlie the clinical benefits produced by 3 weeks of amphetamine treatment.

Brain tauopathies are characterized by abnormal processing of tau protein. While somatodendritic tau mislocalization has attracted considerable attention in tauopathies, the role of tau pathology in axonal transport, connectivity and related dysfunctions remains obscure. We have previously shown using the squid giant synapse that presynaptic microinjection of recombinant human tau protein (htau42) results in failure of synaptic transmission. Here, we evaluated molecular mechanisms mediating this effect. Thus, the initial event, observed after htau42 presynaptic injection, was an increase in transmitter release. This event was mediated by calcium release from intracellular stores and was followed by a reduction in evoked transmitter release. The effect of htau42 on synaptic transmission was recapitulated by a peptide comprising the phosphatase-activating domain of tau, suggesting activation of phosphotransferases. Accordingly, findings indicated that htau42-mediated toxicity involves the activities of both GSK3 and Cdk5 kinases.

INTRODUCTION: Tau immunotherapy has emerged as a promising approach to clear tau aggregates from the brain. Our previous findings suggest that tau antibodies may act outside and within neurons to promote such clearance. METHODS: We have developed an approach using flow cytometry, a human neuroblastoma cell model overexpressing tau with the P301L mutation, and paired helical filament (PHF)-enriched pathologic tau to effectively screen uptake and retention of tau antibodies in conjunction with PHF. RESULTS: The flow cytometry approach correlates well with Western blot analysis to detect internalized antibodies in naive and transfected SH-SY5Y cells (r2 = 0.958, and r2 = 0.968, P = .021 and P = .016, respectively). In transfected cells, more antibodies are taken up/retained as pathologic tau load increases, both under co-treated conditions and when the cells are pretreated with PHF before antibody administration (r2 = 0.999 and r2 = 0.999, P = .013 and P = .011, respectively). DISCUSSION: This approach allows rapid in vitro screening of antibody uptake and retention in conjunction with pathologic tau protein before more detailed studies in animals or other more complex model systems.

OBJECTIVE: Absence seizures in patients with idiopathic generalized epilepsy (IGE) may in part be explained by a decrease in phasic GABAA (type-A gamma-aminobutyric acid) receptor function, but the mechanisms are only partly understood. Here we studied the relation between ictal and interictal spike-wave discharges (SWDs) and electroencephalography (EEG) gamma oscillatory activity (30-60 Hz) in patients with IGE. METHODS: EEG recordings were obtained of 14 children with IGE (mean age, 8.5 +/- 5 years) and 14 age- and sex-matched controls. Time-frequency analysis of each seizure and seizure-free control epochs was performed and cross-coherences of neocortical gamma oscillations were calculated to describe interictal and ictal characteristics of generalized seizures. RESULTS: SWDs were characterized with an abrupt increase of oscillatory activity of 3-4 and 13-60 Hz, peaking at 3-4 and 30-60 Hz, and with a simultaneous decrease in the 8-12 Hz frequency band. The rise in EEG gamma oscillations was short-lasting and decreased before activity declined at lower frequency ranges. Compared to control patients, patients with epilepsy also showed higher interictal values of mean coherence of gamma activity, but this interictal increase was not significant after post hoc analysis. SIGNIFICANCE: Our data support the hypothesis that gamma oscillatory activity increase concomitantly with rises in activity of lower EEG frequencies during absence seizures and that the activity starts to cease earlier than lower EEG frequencies. The data did not support a change in gamma activity preceding the 3-4 Hz SWDs. SWDs are hypothetically generated by the synchronous interaction between the thalamus and the cortex, whereas the production of gamma activity is the result of activity in local inhibitory networks. Thus, the modification of SWD by gamma activity may be understood in terms of the cellular and synaptic mechanisms involved.

Developmental disabilities, including attention-deficit hyperactivity disorder (ADHD), intellectual disability (ID), and autism spectrum disorders (ASD), affect one in six children in the USA. Recently, gene mutations in patched domain containing 1 (PTCHD1) have been found in ~1% of patients with ID and ASD. Individuals with PTCHD1 deletion show symptoms of ADHD, sleep disruption, hypotonia, aggression, ASD, and ID. Although PTCHD1 is probably critical for normal development, the connection between its deletion and the ensuing behavioural defects is poorly understood. Here we report that during early post-natal development, mouse Ptchd1 is selectively expressed in the thalamic reticular nucleus (TRN), a group of GABAergic neurons that regulate thalamocortical transmission, sleep rhythms, and attention. Ptchd1 deletion attenuates TRN activity through mechanisms involving small conductance calcium-dependent potassium currents (SK). TRN-restricted deletion of Ptchd1 leads to attention deficits and hyperactivity, both of which are rescued by pharmacological augmentation of SK channel activity. Global Ptchd1 deletion recapitulates learning impairment, hyper-aggression, and motor defects, all of which are insensitive to SK pharmacological targeting and not found in the TRN-restricted deletion mouse. This study maps clinically relevant behavioural phenotypes onto TRN dysfunction in a human disease model, while also identifying molecular and circuit targets for intervention.

The human monoclonal antibody denosumab inhibits osteoclast-mediated bone resorption by binding to receptor activator of nuclear factor kappaB ligand (RANKL), which is upregulated by tumor cells. Denosumab is indicated to prevent skeletal-related events (SREs) from osteoporosis and metastatic bone disease. We report a case of denosumab-induced hypocalcemia to highlight potential toxicity and treatment considerations. A 66-year-old man with prostate cancer, small cell lung cancer, and bone metastases presented with fatigue, weakness, and muscle spasm. Sixteen days prior, he received cycle 6 of cisplatin and etoposide, leuprolide, and denosumab (120 mg subcutaneously). His examination demonstrated a slight resting tremor, normal strength, and negative Chvostek sign. Laboratory analysis revealed hemoglobin, 8.0 g/dL; total calcium, 5.2 mg/dL (pre-denosumab, 8.9 mg/dL); and magnesium, 0.7 mg/dL. He initially received two units packed red blood cells, intravenous calcium and magnesium, and vitamin D. During his hospitalization, he required multiple doses of intravenous and oral calcium, magnesium, and vitamin D. Despite ongoing oral supplementation, his post-discharge serum calcium fluctuated significantly, requiring close monitoring and frequent dose adjustments. Denosumab's unique antiresorptive properties yield fewer SREs. The trade-off is increased hypocalcemia risk, which may be severe and require aggressive, prolonged supplementation and monitoring.

Alzheimer's disease, one of the most important brain pathologies associated with neurodegenerative processes, is related to overactivation of calpain-mediated proteolysis. Previous data showed a compelling efficacy of calpain inhibition against abnormal synaptic plasticity and memory produced by the excess of amyloid-beta, a distinctive marker of the disease. Moreover, a beneficial effect of calpain inhibitors in Alzheimer's disease is predictable by the occurrence of calpain hyperactivation leading to impairment of memory-related pathways following abnormal calcium influxes that might ensue independently of amyloid-beta elevation. However, molecules currently available as effective calpain inhibitors lack adequate selectivity. This work is aimed at characterizing the efficacy of a novel class of epoxide-based inhibitors, synthesized to display improved selectivity and potency towards calpain 1 compared to the prototype epoxide-based generic calpain inhibitor E64. Both functional and preliminary toxicological investigations proved the efficacy, potency, and safety of the novel and selective calpain inhibitors NYC438 and NYC488 as possible therapeutics against the disease.