Peter Tsai

Autistic-like behaviour and cerebellar dysfunction in Purkinje cell Tsc1 mutant mice

Autism spectrum disorders (ASDs) are highly prevalent neurodevelopmental disorders, but the underlying pathogenesis remains poorly understood. Recent studies have implicated the cerebellum in these disorders, with post-mortem studies in ASD patients showing cerebellar Purkinje cell (PC) loss, and isolated cerebellar injury has been associated with a higher incidence of ASDs. However, the extent of cerebellar contribution to the pathogenesis of ASDs remains unclear. Tuberous sclerosis complex (TSC) is a genetic disorder with high rates of comorbid ASDs that result from mutation of either TSC1 or TSC2, whose protein products dimerize and negatively regulate mammalian target of rapamycin (mTOR) signalling. TSC is an intriguing model to investigate the cerebellar contribution to the underlying pathogenesis of ASDs, as recent studies in TSC patients demonstrate cerebellar pathology and correlate cerebellar pathology with increased ASD symptomatology. Functional imaging also shows that TSC patients with ASDs display hypermetabolism in deep cerebellar structures, compared to TSC patients without ASDs. However, the roles of Tsc1 and the sequelae of Tsc1 dysfunction in the cerebellum have not been investigated so far. Here we show that both heterozygous and homozygous loss of Tsc1 in mouse cerebellar PCs results in autistic-like behaviours, including abnormal social interaction, repetitive behaviour and vocalizations, in addition to decreased PC excitability. Treatment of mutant mice with the mTOR inhibitor, rapamycin, prevented the pathological and behavioural deficits. These findings demonstrate new roles for Tsc1 in PC function and define a molecular basis for a cerebellar contribution to cognitive disorders such as autism.

A Critical Role of Erythropoietin Receptor in Neurogenesis and Post-Stroke Recovery

Erythropoietin (EPO) is the principal growth factor regulating the production of red blood cells. Recent studies demonstrated that exogenous EPO acts as a neuroprotectant and regulates neurogenesis. Using a genetic approach, we evaluate the roles of endogenous EPO and its classical receptor (EPOR) in mammalian neurogenesis. We demonstrate severe and identical embryonic neurogenesis defects in animals null for either the Epo or EpoR gene, suggesting that the classical EPOR is essential for EPO action during embryonic neurogenesis. Furthermore, by generating conditional EpoR knock-down animals, we demonstrate that brain-specific deletion of EpoR leads to significantly reduced cell proliferation in the subventricular zone and impaired post-stroke neurogenesis. EpoR conditional knockdown leads to a specific deficit in post-stroke neurogenesis through impaired migration of neuroblasts to the peri-infarct cortex. Our results suggest that both EPO and EPOR are essential for early embryonic neural development and that the classical EPOR is important for adult neurogenesis and for migration of regenerating neurons during post-injury recovery.

Hypotensive Resuscitation Strategy Reduces Transfusion Requirements and Severe Postoperative Coagulopathy in Trauma Patients With Hemorrhagic Shock: Preliminary Results of a Randomized Controlled Trial

BACKGROUND Trauma is a leading cause of death worldwide and is thus a major public health concern. Previous studies have shown that limiting the amount of fluids given by following a strategy of permissive hypotension during the initial resuscitation period may improve trauma outcomes. This study examines the clinical outcomes from the first 90 patients enrolled in a prospective, randomized controlled trial of hypotensive resuscitation, with the primary aim of assessing the effects of a limited transfusion and intravenous (IV) fluid strategy on 30-day morbidity and mortality. METHODS Patients in hemorrhagic shock who required emergent surgery were randomized to one of the two arms of the study for intraoperative resuscitation. Those in the experimental (low mean arterial pressure [LMAP]) arm were managed with a hypotensive resuscitation strategy in which the target mean arterial pressure (MAP) was 50 mm Hg. Those in the control (high MAP [HMAP]) arm were managed with standard fluid resuscitation to a target MAP of 65 mm Hg. Patients were followed up for 30 days. Intraoperative fluid requirements, mortality, postoperative complications, and other clinical data were prospectively gathered and analyzed. RESULTS Patients in the LMAP group received a significantly less blood products and total i.v. fluids during intraoperative resuscitation than those in the HMAP group. They had significantly lower mortality in the early postoperative period and a nonsignificant trend for lower mortality at 30 days. Patients in the LMAP group were significantly less likely to develop immediate postoperative coagulopathy and less likely to die from postoperatively bleeding associated with coagulopathy. Among those who developed coagulopathy in both groups, patients in the LMAP group had significantly lower international normalized ratio than those in the HMAP group, indicating a less severe coagulopathy. CONCLUSIONS Hypotensive resuscitation is a safe strategy for use in the trauma population and results in a significant reduction in blood product transfusions and overall IV fluid administration. Specifically, resuscitating patients with the intent of maintaining a target minimum MAP of 50 mm Hg, rather than 65 mm Hg, significantly decreases postoperative coagulopathy and lowers the risk of early postoperative death and coagulopathy. These preliminary results provide convincing evidence that support the continued investigation and use of hypotensive resuscitation in the trauma setting.

Copy number variation plays an important role in clinical epilepsy

To evaluate the role of copy number abnormalities detectable using chromosomal microarray (CMA) testing in patients with epilepsy at a tertiary care center.

Mechanisms of neurocognitive dysfunction and therapeutic considerations in tuberous sclerosis complex.

PURPOSE OF REVIEW Mendelian disorders that affect cognition provide a unique opportunity to study the mechanisms of neurodevelopmental disorders through the examination of genetic defects in animals and development of hypotheses that can be tested in human beings. Tuberous sclerosis complex (TSC) is a genetic disease that presents with epilepsy, autism, and intellectual disability. Here we review recent advances in our understanding of TSC pathogenesis and signaling pathways that may be modulated to treat the neurological symptoms. RECENT FINDINGS Accumulating evidence suggests that TSC patients have nontuber abnormalities that contribute to the development of the neurological phenotype- in particular, disorganization of axon tracts and deficient myelination. TSC mouse models have failed to replicate the human neuropathology entirely, but have shed light on the cellular abnormalities and the neurobehavioral phenotypes. Most importantly, cell culture and animal models have identified the mTORC1 pathway as a therapeutic target in this disease. SUMMARY Preclinical data strongly suggest that TSC is a disease of abnormal neuronal connectivity. The high incidence of neurodevelopmental deficits, early detection of the disease in very young ages, and availability of mTORC1 inhibitors make TSC a model for other Mendelian disorders of neurocognition and an avenue for the mechanism-based treatment trials of neurodevelopmental disorders.

Does the Level of Experience of Residents Affect Outcomes of Coronary Artery Bypass Surgery

BACKGROUND At our institution, coronary artery bypass grafting (CABG) operations are performed by staff surgeons or by first- or second-year cardiothoracic residents under the direct supervision of attending surgeons. We evaluated the influence of surgical seniority on outcomes. METHODS Using prospectively collected data from our departmental database, we identified all primary, isolated CABG operations (n = 1,042) performed between July 1997 and April 2007. Operations were then stratified according to the seniority of the primary surgeon: first-year cardiothoracic resident (CT1), second-year cardiothoracic resident (CT2), or staff surgeon. Data were examined for any association between seniority and surgical outcomes. RESULTS Staff, CT2, and CT1 surgeons performed 47 (4%), 610 (59%), and 385 (37%) cases, respectively. Efficiency was correlated with experience: for CT1, CT2, and staff surgeons, respectively, operative times averaged 345, 313, and 302 minutes; perfusion times averaged 118, 106, and 96 minutes; and cross-clamp times averaged 68, 58, and 57 minutes (p < 0.05 for all comparisons). The incidences of major morbidity (10.1%, 12.3%, 12.8%) and operative mortality (0.8%, 1.5%, 2.1%) were similar after operations performed by CT1, CT2, and staff surgeons, respectively (p > 0.15 for all). In univariate and multivariate analyses, the seniority of the primary surgeon did not independently predict morbidity or perioperative mortality. On follow-up (mean, 1,485 +/- 1,015 days), there was no significant difference in patient survival (log-rank, p = 0.64). CONCLUSIONS Lower academic seniority was associated with longer CABG operative times but did not affect outcomes. Thus, training residents to perform CABG is safe and is characterized by progressive improvement in their technical efficiency.

Cerebellar associative sensory learning defects in five mouse autism models

Sensory integration difficulties have been reported in autism, but their underlying brain-circuit mechanisms are underexplored. Using five autism-related mouse models, Shank3+/ΔC, Mecp2R308/Y, Cntnap2−/−, L7-Tsc1 (L7/Pcp2Cre::Tsc1flox/+), and patDp(15q11-13)/+, we report specific perturbations in delay eyeblink conditioning, a form of associative sensory learning requiring cerebellar plasticity. By distinguishing perturbations in the probability and characteristics of learned responses, we found that probability was reduced in Cntnap2−/−, patDp(15q11-13)/+, and L7/Pcp2Cre::Tsc1flox/+, which are associated with Purkinje-cell/deep-nuclear gene expression, along with Shank3+/ΔC. Amplitudes were smaller in L7/Pcp2Cre::Tsc1flox/+ as well as Shank3+/ΔC and Mecp2R308/Y, which are associated with granule cell pathway expression. Shank3+/ΔC and Mecp2R308/Y also showed aberrant response timing and reduced Purkinje-cell dendritic spine density. Overall, our observations are potentially accounted for by defects in instructed learning in the olivocerebellar loop and response representation in the granule cell pathway. Our findings indicate that defects in associative temporal binding of sensory events are widespread in autism mouse models. DOI: http://dx.doi.org/10.7554/eLife.06085.001

Neuronal Tsc1/2 complex controls autophagy through AMPK-dependent regulation of ULK1

Tuberous sclerosis complex (TSC) is a disorder arising from mutation in the TSC1 or TSC2 gene, characterized by the development of hamartomas in various organs and neurological manifestations including epilepsy, intellectual disability and autism. TSC1/2 protein complex negatively regulates the mammalian target of rapamycin complex 1 (mTORC1) a master regulator of protein synthesis, cell growth and autophagy. Autophagy is a cellular quality-control process that sequesters cytosolic material in double membrane vesicles called autophagosomes and degrades it in autolysosomes. Previous studies in dividing cells have shown that mTORC1 blocks autophagy through inhibition of Unc-51-like-kinase1/2 (ULK1/2). Despite the fact that autophagy plays critical roles in neuronal homeostasis, little is known on the regulation of autophagy in neurons. Here we show that unlike in non-neuronal cells, Tsc2-deficient neurons have increased autolysosome accumulation and autophagic flux despite mTORC1-dependent inhibition of ULK1. Our data demonstrate that loss of Tsc2 results in autophagic activity via AMPK-dependent activation of ULK1. Thus, in Tsc2-knockdown neurons AMPK activation is the dominant regulator of autophagy. Notably, increased AMPK activity and autophagy activation are also found in the brains of Tsc1-conditional mouse models and in cortical tubers resected from TSC patients. Together, our findings indicate that neuronal Tsc1/2 complex activity is required for the coordinated regulation of autophagy by AMPK. By uncovering the autophagy dysfunction associated with Tsc2 loss in neurons, our work sheds light on a previously uncharacterized cellular mechanism that contributes to altered neuronal homeostasis in TSC disease.

Safety and Efficacy of Antiplatelet and Antithrombotic Therapy in Acute Coronary Syndrome Patients With Chronic Kidney Disease

Chronic kidney disease (CKD) is prevalent and affects an ever-increasing proportion of patients presenting with acute coronary syndrome (ACS). Patients with CKD have a higher risk of ACS and significantly higher mortality, and are also predisposed to increased bleeding complications. Antiplatelet and antithrombotic drugs form the bedrock of management of patients with ACS. Most randomized trials of these drugs exclude patients with CKD, and current guidelines for management of these patients are largely based on these trials. We aim to review the safety and efficacy of these drugs in patients with CKD presenting with ACS.

Graded loss of tuberin in an allelic series of brain models of TSC correlates with survival, and biochemical, histological and behavioral features

Tuberous sclerosis complex (TSC) is a neurodevelopmental disorder with prominent brain manifestations due to mutations in either TSC1 or TSC2. Here, we describe novel mouse brain models of TSC generated using conditional hypomorphic and null alleles of Tsc2 combined with the neuron-specific synapsin I cre (SynIcre) allele. This allelic series of homozygous conditional hypomorphic alleles (Tsc2(c-del3/c-del3)SynICre(+)) and heterozygote null/conditional hypomorphic alleles (Tsc2(k/c-del3)SynICre(+)) achieves a graded reduction in expression of Tsc2 in neurons in vivo. The mice demonstrate a progressive neurologic phenotype including hunchback, hind limb clasp, reduced survival and brain and cortical neuron enlargement that correlates with a graded reduction in expression of Tsc2 in the two sets of mice. Both models also showed behavioral abnormalities in anxiety, social interaction and learning assays, which correlated with Tsc2 protein levels as well. The observations demonstrate that there are graded biochemical, cellular and clinical/behavioral effects that are proportional to the extent of reduction in Tsc2 expression in neurons. Further, they suggest that some patients with milder manifestations of TSC may be due to persistent low-level expression of functional protein from their mutant allele. In addition, they point to the potential clinical benefit of strategies to raise TSC2 protein expression from the wild-type allele by even modest amounts.