Huntingtin-associated protein-1 (HAP1) was initially identified as an interacting partner of huntingtin, the Huntington disease protein. Unlike huntingtin that is ubiquitously expressed throughout the brain and body, HAP1 is enriched in neurons, suggesting that its dysfunction could contribute to Huntington disease neuropathology. Growing evidence has demonstrated that HAP1 and huntingtin are anterogradely transported in axons and that the abnormal interaction between mutant huntingtin and HAP1 may impair axonal transport. However, the exact role of HAP1 in anterograde transport remains unclear. Here we report that HAP1 interacts with kinesin light chain, a subunit of the kinesin motor complex that drives anterograde transport along microtubules in neuronal processes. The interaction of HAP1 with kinesin light chain is demonstrated via a yeast two-hybrid assay, glutathione S-transferase pull down, and coimmunoprecipitation. Furthermore, HAP1 is colocalized with kinesin in growth cones of neuronal cells. We also demonstrated that knocking down HAP1 via small interfering RNA suppresses neurite outgrowth of PC12 cells. Analysis of live neuronal cells with fluorescence microscopy and fluorescence recovery after photobleaching demonstrates that suppressing the expression of HAP1 or deleting the HAP1 gene inhibits the kinesin-dependent transport of amyloid precursor protein vesicles. These studies provide a molecular basis for the participation of HAP1 in anterograde transport in neuronal cells.Huntingtin-associated protein-1 (HAP1) 2 was the first protein identified to interact with huntingtin (htt), the Huntington disease (HD) protein (1, 2). Htt contains a polyglutamine (polyQ) stretch in its N terminus, and expansion of this glutamine repeat (Ͼ37 glutamines) causes selective neurodegeneration. However, the underlying mechanisms of the specific neuropathology of HD remain unclear, especially in light of the widespread expression of htt. It is believed that the expanded polyQ confers an abnormal protein conformation and affects the function of other neuronal proteins (3). This idea, or the theory of gain of function, is strongly supported by the fact that polyQ expansion causes htt to abnormally interact with other proteins (4, 5). HAP1 is a good candidate for htt-mediated pathology, because its binding to the N-terminal region of htt is enhanced by expanded polyQ tracts, and its expression is enriched in the brain (1).The critical role of HAP1 in neuronal function has been demonstrated in HAP1 knock-out mice. Deletion of the mouse HAP1 gene leads to retarded growth, depressed feeding behavior, and postnatal death of these mice (6 -8). This phenotype may be caused by the degeneration of hypothalamic neurons that control feeding behavior (7). Several studies have suggested that HAP1 is involved in neuronal transport of organelles or molecules. HAP1 is required for vesicular transport of brain-derived neurotrophic factor along microtubules, and mutant htt impairs this transport concomitant with its increased interacti...

Objective:To evaluate safety (primary objective) and efficacy of increasing doses (400 U up to 800 U) of incobotulinumtoxinA (Xeomin, Merz Pharmaceuticals GmbH) for patients with limb spasticity.Methods:In this prospective, single-arm, dose-titration study (NCT01603459), patients (18–80 years) with spasticity due to cerebral causes, who were clinically deemed to require total doses of 800 U incobotulinumtoxinA, received 3 consecutive injection cycles (ICs) with 400 U, 600 U, and 600–800 U incobotulinumtoxinA, respectively, each followed by 12–16 weeks' observation. Outcomes included adverse events (AEs), antibody testing, Resistance to Passive Movement Scale (REPAS; based on the Ashworth Scale), and Goal Attainment Scale.Results:In total, 155 patients were enrolled. IncobotulinumtoxinA dose escalation did not lead to an increased incidence of treatment-related AEs (IC1: 4.5%; IC2: 5.3%; IC3: 2.9%). No treatment-related serious AEs occurred. The most frequent AEs overall were falls (7.7%), nasopharyngitis, arthralgia, and diarrhea (6.5% each). Five patients (3.2%) discontinued due to AEs. No patient developed secondary nonresponse due to neutralizing antibodies. Mean (SD) REPAS score improvements from each injection to 4 weeks postinjection increased throughout the study (IC1: −4.6 [3.9]; IC2: −5.9 [4.2]; IC3: −7.1 [4.8]; p < 0.0001 for all). The proportion of patients achieving ≥3 (of 4) treatment goals also increased (IC1: 25.2%; IC2: 50.7%; IC3: 68.6%).Conclusion:Escalating incobotulinumtoxinA doses (400 U up to 800 U) did not compromise safety or tolerability, enabled treatment in a greater number of muscles/spasticity patterns, and was associated with increased treatment efficacy, improved muscle tone, and goal attainment.ClinicalTrials.gov identifier:NCT01603459.Classification of evidence:This study provides Class IV evidence that, for patients with limb spasticity, escalating incobotulinumtoxinA doses (400 U up to 800 U) increases treatment efficacy without compromising safety or tolerability.