The juxtamembrane region of synaptotagmin 1 interacts with dynamin 1 and regulates vesicle fission during compensatory endocytosis in endocrine cells.

Synaptotagmin 1 (Syt1) is a synaptic vesicle protein that is important for the kinetics of both exocytosis and endocytosis, and is thus a candidate molecule to link these two processes. Although the tandem Ca(2+)-binding C2 domains of Syt1 have important roles in exocytosis and endocytosis, the function of the conserved juxtamembrane (jxm) linker region has yet to be determined. We now demonstrate that the jxm region of Syt1 interacts directly with the pleckstrin homology (PH) domain of the endocytic protein dynamin 1. By using cell-attached capacitance recordings with millisecond time resolution to monitor clathrin-mediated endocytosis of single vesicles in neuroendocrine chromaffin cells, we find that loss of this interaction prolongs the lifetime of the fission pore leading to defects in the dynamics of vesicle fission. These results indicate a previously undescribed interaction between two major regulatory proteins in the secretory vesicle cycle and that this interaction regulates endocytosis.

Memory and synaptic deficits in Hip14/DHHC17 knockout mice.

Palmitoylation of neurotransmitter receptors and associated scaffold proteins regulates their membrane association in a rapid, reversible, and activity-dependent fashion. This makes palmitoylation an attractive candidate as a key regulator of the fast, reversible, and activity-dependent insertion of synaptic proteins required during the induction and expression of long-term plasticity. Here we describe that the constitutive loss of huntingtin interacting protein 14 (Hip14, also known as DHHC17), a single member of the broad palmitoyl acyltransferase (PAT) family, produces marked alterations in synaptic function in varied brain regions and significantly impairs hippocampal memory and synaptic plasticity. The data presented suggest that, even though the substrate pool is overlapping for the 23 known PAT family members, the function of a single PAT has marked effects upon physiology and cognition. Moreover, an improved understanding of the role of PATs in synaptic modification and maintenance highlights a potential strategy for intervention against early cognitive impairments in neurodegenerative disease.

Hip14l-deficient mice develop neuropathological and behavioural features of Huntington disease.

Palmitoylation, the dynamic post-translational addition of the lipid, palmitate, to proteins by Asp-His-His-Cys-containing palmitoyl acyltransferase (PAT) enzymes, modulates protein function and localization and plays a key role in the nervous system. Huntingtin-interacting protein 14 (HIP14), a well-characterized neuronal PAT, has been implicated in the pathogenesis of Huntington disease (HD), a fatal neurodegenerative disease associated with motor, psychiatric and cognitive symptoms, caused by a CAG expansion in the huntingtin gene (HTT). Mice deficient for Hip14 expression develop neuropathological and behavioural features similar to HD, and the catalytic activity of HIP14 is impaired in HD mice, most likely due to the reduced interaction of HIP14 with HTT. Huntingtin-interacting protein 14-like (HIP14L) is a paralog of HIP14, with identical domain structure. Together, HIP14 and HIP14L are the major PATs for HTT. Here, we report the characterization of a Hip14l-deficient mouse model, which develops adult-onset, widespread and progressive neuropathology accompanied by early motor deficits in climbing, impaired motor learning and reduced palmitoylation of a novel HIP14L substrate: SNAP25. Although the phenotype resembles that of the Hip14(-/-) mice, a more progressive phenotype, similar to that of the YAC128 transgenic mouse model of HD, is observed. In addition, HIP14L interacts less with mutant HTT than the wild-type protein, suggesting that reduced HIP14L-dependent palmitoylation of neuronal substrates may contribute to the pathogenesis of HD. Thus, both HIP14 and HIP14L may be dysfunctional in the disease.

Wild-type HTT modulates the enzymatic activity of the neuronal palmitoyl transferase HIP14.

Huntington disease (HD) is caused by polyglutamine expansion in the huntingtin (HTT) protein. Huntingtin-interacting protein 14 (HIP14), one of 23 DHHC domain-containing palmitoyl acyl transferases (PATs), binds to HTT and robustly palmitoylates HTT at cysteine 214. Mutant HTT exhibits reduced palmitoylation and interaction with HIP14, contributing to the neuronal dysfunction associated with HD. In this study, we confirmed that, among 23 DHHC PATs, HIP14 and its homolog DHHC-13 (HIP14L) are the two major PATs that palmitoylate HTT. Wild-type HTT, in addition to serving as a palmitoylation substrate, also modulates the palmitoylation of HIP14 itself. In vivo, HIP14 palmitoylation is decreased in the brains of mice lacking one HTT allele (hdh+/-) and is further reduced in mouse cortical neurons treated with HTT antisense oligos (HTT-ASO) that knockdown HTT expression by ∼95%. Previously, it has been shown that palmitoylation of DHHC proteins may affect their enzymatic activity. Indeed, palmitoylation of SNAP25 by HIP14 is potentiated in vitro in the presence of wild-type HTT. This influence of HTT on HIP14 activity is lost in the presence of CAG expansion. Furthermore, in both brains of hdh+/- mice and neurons treated with HTT-ASO, we observe a significant reduction in palmitoylation of endogenous SNAP25 and GluR1, synaptic proteins that are substrates of HIP14, suggesting wild-type HTT also influences HIP14 enzymatic activity in vivo. This study describes an important biochemical function for wild-type HTT modulation of HIP14 palmitoylation and its enzymatic activity.

Altered palmitoylation and neuropathological deficits in mice lacking HIP14.

Huntingtin interacting protein 14 (HIP14, ZDHHC17) is a huntingtin (HTT) interacting protein with palmitoyl transferase activity. In order to interrogate the function of Hip14, we generated mice with disruption in their Hip14 gene. Hip14-/- mice displayed behavioral, biochemical and neuropathological defects that are reminiscent of Huntington disease (HD). Palmitoylation of other HIP14 substrates, but not Htt, was reduced in the Hip14-/- mice. Hip14 is dysfunctional in the presence of mutant htt in the YAC128 mouse model of HD, suggesting that altered palmitoylation mediated by HIP14 may contribute to HD.

Strength in numbers: growth of Canadian clinician investigator training in the 21st century.

PURPOSE: Enhancing clinician-investigator (CI) training at Canadian medical schools is urgently needed to bolster the dwindling work force of medical professionals carrying out patient-oriented research in a wide array of medical fields. The purpose of this study is to obtain, from the 15 Canadian medical schools that offer one or more CI training programs, data on the number of trainees, funding levels, attrition rates or other important metrics to evaluate the outcomes of such training efforts. METHODS: All Canadian CI programs were surveyed to collect demographic information for the academic year 2010-2011 and compared this to historical data collected by the Association of Faculties of Medicine of Canada (AFMC) and MD/PhD program funding data from the Canadian Institutes of Health Research (CIHR). RESULTS: Over the past decade, enrolment in Canadian CI training programs has increased approximately four-fold. Program-specific funding (CIHR) has also increased, but nearly 50% of MD/PhD trainees are still not supported through dedicated CIHR funding. CONCLUSION: It is too early to know to what extent this increase in both CI and funding will sustain the workforce of Canadian researchers carrying out patient-oriented research. Monitoring of CI training demographics across Canada, beyond this baseline study, will be essential to measure outcomes from CI training programs and to guide response from funding bodies and policy-makers.

Comparison of the National Institutes of Health Stroke Scale with disability outcome measures in acute stroke trials.

BACKGROUND AND PURPOSE: Acute stroke trials typically use disability scales as their primary end point. Neurologic impairment scales such as the National Institutes of Health Stroke Scale (NIHSS) are possibly more sensitive to change in patient status. We aimed to compare a range of potential NIHSS end points with modified Rankin Scale (mRS) and Barthel Index (BI) end points. METHODS: We simulated a total of 6000 clinical trials, each with 1400 patients. We estimated statistical power for a range of NIHSS end points, including prognosis-adjusted and fixed dichotomized end points. These end points were compared with the BI and mRS dichotomized at 95 and 1, respectively. RESULTS: The most powerful fixed end point was the NIHSS dichotomized at 1. For prognosis-adjusted outcome, we found greatest power if we defined success as achieving a score of < or =1 or improvement by at least 11 points from baseline. We are more likely to achieve a statistically significant result by using this prognosis-adjusted end point instead of NIHSS < or =1 (odds ratio, 2.8; 95% confidence interval [CI], 2.5 to 3.2). Use of the optimal NIHSS prognosis-adjusted end point rather than BI > or =95 could justify a reduction in sample size of approximately 68% (95% CI, 67% to 69%) without loss of statistical power. CONCLUSIONS: The NIHSS neurologic scale appears more sensitive than the BI or mRS, allowing smaller sample sizes or greater statistical power. The use of an NIHSS prognosis-adjusted end point could allow therapeutic effects from drugs to be more easily identified.

Improving trial power through use of prognosis-adjusted end points.

BACKGROUND AND PURPOSE: The stroke patient population is heterogeneous, leading to wide variation in outcome caused by differences in age, initial severity, and presence of concomitant disease. Setting an identical recovery target for all patients in intervention trials may conceal individually important therapeutic treatment effects. Instead, a variable end point that takes severity or likely prognosis into account may be more informative. METHODS: We used data from the Glycine Antagonist in Neuroprotection (GAIN) International trial to assess statistical power of various primary end points for intervention trials. We selected prognosis-adjusted cut points based on Barthel Index (BI) or Rankin Scale (RS) using a prognostic model, or assigned a fixed end point within subgroups of patients defined by their Oxford category or National Institutes of Health Stroke Scale (NIHSS) score. We simulated a treatment effect and estimated statistical power with standard formulae. RESULTS: Assignment of end points using a prognostic model for individual patients increased statistical power, when compared with assigning end points using only the Oxford classification. For the BI, power was increased from 60% to 88% (equivalent to a 49% reduction in sample size if power remains unchanged). With the RS end points, power was increased from 84% to 92% (or a 24% reduction in sample size). Versus a fixed end point for all patients, model-based methods increased power by 22 percentage points for BI> or =95 and 14 percentage points for RS< or =1 (effective sample size reductions 43% and 34%). CONCLUSIONS: Prognosis-adjusted end points can increase statistical power compared with fixed end points. Assessment is based on realistic goals for individual patients and yet trial results remain generalizable.

Strengthening acute stroke trials through optimal use of disability end points.

BACKGROUND AND PURPOSE: Suboptimal choices of primary end point for acute stroke trials may have contributed to inconclusive results. The Barthel Index (BI) and Rankin Scale (RS) have been widely used and analyzed in various ways. We sought to investigate the most powerful end point for use in acute stroke trials. METHODS: Data from the Glycine Antagonist in Neuroprotection (GAIN) International Trial were used to simulate 24 000 clinical trials exploring various patterns and magnitudes of treatment effect and thus to estimate the statistical power for a range of end points based on the BI or RS. RESULTS: RS end points were more powerful than BI end points. End points dichotomized toward the favorable extreme of either scale or adjusted according to baseline prognosis ("patient-specific" end point) were among the most powerful. Combining RS and BI in a "global" end point was also successful. Improvements in statistical power indicated that using a RS end point instead of BI > or =60 could reduce the sample size by up to 84% (95% CI, 80% to 87%), 73% (95% CI, 68% to 79%) for a patient-specific BI end point, or 81% (95% CI, 76% to 85%) for a global end point. CONCLUSIONS: The RS and global end points are preferable to BI end points; the position of the cut point is also important. Better choices of end point substantially strengthen trial power for a given trial size or allow reduced sample sizes without loss of statistical power.

Putting proteins in their place: palmitoylation in Huntington disease and other neuropsychiatric diseases.

Post-translational modification of proteins by the lipid palmitate is critical for protein localization and function. Palmitoylation is regulated by the opposing enzymes palmitoyl acyltransferases (PATs) and acyl protein thioesterases, which add and remove palmitate from proteins, respectively. Palmitoylation is particularly important for a number of processes including neuronal development and synaptic activity in the central nervous system. Dysregulated palmitoylation contributes to neuropsychiatric disease. In total six PATs (HIP14, HIP14L, ZDHHC8, ZDHHC9, ZDHHC12, and ZDHHC15) and one thioesterase (PPT1) have been implicated in Huntington disease (HD), Alzheimer disease, schizophrenia, mental retardation, and infantile and adult onset forms of neuronal ceroid lipofuscinosis. Currently there is no genetic link between PATs and Alzheimer disease pathogenesis but palmitoylation of amyloid precursor protein-processing enzyme, γ-secretase, influences ß-amyloid generation. Several lines of evidence point to a role for palmitoylation by HIP14 in the pathogenesis of HD; HIP14 is dysfunctional in the presence of the HD mutation and Hip14-deficient mice develop features of HD. Wildtype huntingtin (the protein mutated in HD) enhances the PAT activity of HIP14 and mutant HTT interacts less with HIP14. Therefore, it may be that loss of the positive modulation of HIP14 activity due to reduced interaction with huntingtin is important in the disease mechanism. Preliminary evidence suggests a closely related PAT to HIP14, HIP14L, may also play a role in the pathogenesis of HD. In order to design rational therapeutic approaches to restore palmitoylation in neuropsychiatric disease, it will be critical to better understand the relationships between PATs and thioesterases with their regulators and substrates.

Low levels of human HIP14 are sufficient to rescue neuropathological, behavioural, and enzymatic defects due to loss of murine HIP14 in Hip14-/- mice.

Huntingtin Interacting Protein 14 (HIP14) is a palmitoyl acyl transferase (PAT) that was first identified due to altered interaction with mutant huntingtin, the protein responsible for Huntington Disease (HD). HIP14 palmitoylates a specific set of neuronal substrates critical at the synapse, and downregulation of HIP14 by siRNA in vitro results in increased cell death in neurons. We previously reported that mice lacking murine Hip14 (Hip14-/-) share features of HD. In the current study, we have generated human HIP14 BAC transgenic mice and crossed them to the Hip14-/- model in order to confirm that the defects seen in Hip14-/- mice are in fact due to loss of Hip14. In addition, we sought to determine whether human HIP14 can provide functional compensation for loss of murine Hip14. We demonstrate that despite a relative low level of expression, as assessed via Western blot, BAC-derived human HIP14 compensates for deficits in neuropathology, behavior, and PAT enzyme function seen in the Hip14-/- model. Our findings yield important insights into HIP14 function in vivo.

Human Sco1 and Sco2 function as copper-binding proteins.

The function of human Sco1 and Sco2 is shown to be dependent on copper ion binding. Expression of soluble domains of human Sco1 and Sco2 either in bacteria or the yeast cytoplasm resulted in the recovery of copper-containing proteins. The metallation of human Sco1, but not Sco2, when expressed in the yeast cytoplasm is dependent on the co-expression of human Cox17. Two conserved cysteines and a histidyl residue, known to be important for both copper binding and in vivo function in yeast Sco1, are also critical for in vivo function of human Sco1 and Sco2. Human and yeast Sco proteins can bind either a single Cu(I) or Cu(II) ion. The Cu(II) site yields S-Cu(II) charge transfer transitions that are not bleached by weak reductants or chelators. The Cu(I) site exhibits trigonal geometry, whereas the Cu(II) site resembles a type II Cu(II) site with a higher coordination number. To identify additional potential ligands for the Cu(II) site, a series of mutant proteins with substitutions in conserved residues in the vicinity of the Cu(I) site were examined. Mutation of several conserved carboxylates did not alter either in vivo function or the presence of the Cu(II) chromophore. In contrast, replacement of Asp238 in human or yeast Sco1 abrogated the Cu(II) visible transitions and in yeast Sco1 attenuated Cu(II), but not Cu(I), binding. Both the mutant yeast and human proteins were nonfunctional, suggesting the importance of this aspartate for normal function. Taken together, these data suggest that both Cu(I) and Cu(II) binding are critical for normal Sco function.