Ultrasensitive quantitative measurement of huntingtin phosphorylation at residue S13.

Huntington's disease (HD) is a progressive neurodegenerative disorder caused by an expansion of a CAG triplet repeat (encoding for a polyglutamine tract) within the first exon of the huntingtin gene. Expression of the mutant huntingtin (mHTT) protein can result in the production of N-terminal fragments with a robust propensity to form oligomers and aggregates, which may be causally associated with HD pathology. Several lines of evidence indicate that N17 phosphorylation or pseudophosphorylation at any of the residues T3, S13 or S16, alone or in combination, modulates mHTT aggregation, subcellular localization and toxicity. Consequently, increasing N17 phosphorylation has been proposed as a potential therapeutic approach. However, developing genetic/pharmacological tools to quantify these phosphorylation events is necessary in order to subsequently develop tool modulators, which is difficult given the transient and incompletely penetrant nature of such post-translational modifications. Here we describe the first ultrasensitive sandwich immunoassay that quantifies HTT phosphorylated at residue S13 and demonstrate its utility for specific analyte detection in preclinical models of HD.

Post-translational modifications clustering within proteolytic domains decrease mutant huntingtin toxicity.

Huntington's disease (HD) is caused in large part by a polyglutamine expansion within the huntingtin (Htt) protein. Post-translational modifications (PTMs) control and regulate many protein functions and cellular pathways, and PTMs of mutant Htt are likely important modulators of HD pathogenesis. Alterations of selected numbers of PTMs of Htt fragments have been shown to modulate Htt cellular localization and toxicity. In this study, we systematically introduced site-directed alterations in individual phosphorylation and acetylation sites in full-length Htt constructs. The effects of each of these PTM alteration constructs were tested on cell toxicity using our nuclear condensation assay and on mitochondrial viability by measuring mitochondrial potential and size. Using these functional assays in primary neurons, we identified several PTMs whose alteration can block neuronal toxicity and prevent potential loss and swelling of the mitochondria caused by mutant Htt. These PTMs included previously described sites such as serine 116 and newly found sites such as serine 2652 throughout the protein. We found that these functionally relevant sites are clustered in protease-sensitive domains throughout full-length Htt. These findings advance our understanding of the Htt PTM code and its role in HD pathogenesis. Because PTMs are catalyzed by enzymes, the toxicity-modulating Htt PTMs identified here may be promising therapeutic targets for managing HD.

Post-Translational Modifications (PTMs), Identified on Endogenous Huntingtin, Cluster within Proteolytic Domains between HEAT Repeats.

Post-translational modifications (PTMs) of proteins regulate various cellular processes. PTMs of polyglutamine-expanded huntingtin (Htt) protein, which causes Huntington's disease (HD), are likely modulators of HD pathogenesis. Previous studies have identified and characterized several PTMs on exogenously expressed Htt fragments, but none of them were designed to systematically characterize PTMs on the endogenous full-length Htt protein. We found that full-length endogenous Htt, which was immunoprecipitated from HD knock-in mouse and human post-mortem brain, is suitable for detection of PTMs by mass spectrometry. Using label-free and mass tag labeling-based approaches, we identified near 40 PTMs, of which half are novel (data are available via ProteomeXchange with identifier PXD005753). Most PTMs were located in clusters within predicted unstructured domains rather than within the predicted α-helical structured HEAT repeats. Using quantitative mass spectrometry, we detected significant differences in the stoichiometry of several PTMs between HD and WT mouse brain. The mass-spectrometry identification and quantitation were verified using phospho-specific antibodies for selected PTMs. To further validate our findings, we introduced individual PTM alterations within full-length Htt and identified several PTMs that can modulate its subcellular localization in striatal cells. These findings will be instrumental in further assembling the Htt PTM framework and highlight several PTMs as potential therapeutic targets for HD.

Abnormal molecular signatures of inflammation, energy metabolism, and vesicle biology in human Huntington disease peripheral tissues.

BACKGROUND: A major challenge in neurodegenerative diseases concerns identifying biological disease signatures that track with disease progression or respond to an intervention. Several clinical trials in Huntington disease (HD), an inherited, progressive neurodegenerative disease, are currently ongoing. Therefore, we examine whether peripheral tissues can serve as a source of readily accessible biological signatures at the RNA and protein level in HD patients. RESULTS: We generate large, high-quality human datasets from skeletal muscle, skin and adipose tissue to probe molecular changes in human premanifest and early manifest HD patients-those most likely involved in clinical trials. The analysis of the transcriptomics and proteomics data shows robust, stage-dependent dysregulation. Gene ontology analysis confirms the involvement of inflammation and energy metabolism in peripheral HD pathogenesis. Furthermore, we observe changes in the homeostasis of extracellular vesicles, where we find consistent changes of genes and proteins involved in this process. In-depth single nucleotide polymorphism data across the HTT gene are derived from the generated primary cell lines. CONCLUSIONS: Our 'omics data document the involvement of inflammation, energy metabolism, and extracellular vesicle homeostasis. This demonstrates the potential to identify biological signatures from peripheral tissues in HD suitable as biomarkers in clinical trials. The generated data, complemented by the primary cell lines established from peripheral tissues, and a large panel of iPSC lines that can serve as human models of HD are a valuable and unique resource to advance the current understanding of molecular mechanisms driving HD pathogenesis.

Generation and characterization of human induced pluripotent stem cells (iPSCs) from three male and three female patients with CDKL5 Deficiency Disorder (CDD).

CDKL5 Deficiency Disorder (CDD) is a rare X-linked monogenic developmental encephalopathy that is estimated to affect 1:42,000 live births. CDD is caused by pathogenic variants in the CDKL5 gene and is observed in both male and female patients. Here, we report the generation and characterization of induced pluripotent stem cells (iPSCs) derived from fibroblasts of six unrelated CDD patients-three males and three females. These patients are clinically diagnosed to present with classic CDD phenotypes, including refractory epilepsy and global developmental delay, and are being followed in a longitudinal clinical study.

Integrated genomics and proteomics define huntingtin CAG length-dependent networks in mice.

To gain insight into how mutant huntingtin (mHtt) CAG repeat length modifies Huntington's disease (HD) pathogenesis, we profiled mRNA in over 600 brain and peripheral tissue samples from HD knock-in mice with increasing CAG repeat lengths. We found repeat length-dependent transcriptional signatures to be prominent in the striatum, less so in cortex, and minimal in the liver. Coexpression network analyses revealed 13 striatal and 5 cortical modules that correlated highly with CAG length and age, and that were preserved in HD models and sometimes in patients. Top striatal modules implicated mHtt CAG length and age in graded impairment in the expression of identity genes for striatal medium spiny neurons and in dysregulation of cyclic AMP signaling, cell death and protocadherin genes. We used proteomics to confirm 790 genes and 5 striatal modules with CAG length-dependent dysregulation at the protein level, and validated 22 striatal module genes as modifiers of mHtt toxicities in vivo.

Complement activation in the peripheral nervous system following the spinal nerve ligation model of neuropathic pain.

Neuroinflammatory and neuroimmune mechanisms, as exemplified by infiltrating immune cells and activation of resident endothelial/glial cells, respectively, are known to be involved in the establishment and maintenance of chronic pain. An immune system pathway that may be involved in the activation of both immune and glial cells is complement. The complement pathway is made up of a large number of distinct plasma proteins which react with one another to opsonize pathogens and induce a series of inflammatory responses to help fight infection. Cleaved products and complexes produced by complement activation are responsible for a range of effects including mediation of immune infiltration, activation of phagocytes, opsonization/lysis of pathogens and injured cells, and production of vasoactive amines such as histamine and serotonin. Gene-expression microarray-analysis performed on the rat spinal nerve ligation (SNL) model of neuropathic pain revealed that multiple complement components including the C1 inhibitor, C1q alpha, beta, and gamma, C1r, C1s, C2, C3, C4, C7, and factors B, D, H, and P, were up-regulated while DAF was down-regulated. Regulation of C3 and DAF was confirmed by real-time RT-PCR and in situ hybridization. To test the hypothesis that complement plays a role in neuropathic pain, SNL rats were treated with cobra venom factor (CVF) to deplete plasma of complement component C3. Pain behavior was significantly attenuated in SNL rats treated with CVF as was complement activity at the ipsilateral dorsal root ganglia. Our results suggest the complement pathway might be a novel target for the development of neuropathic pain therapeutics.

Two populations of layer v pyramidal cells of the mouse neocortex: development and sensitivity to anesthetics.

Previous studies have shown that layer V pyramidal neurons projecting either to subcortical structures or the contralateral cortex undergo different morphological and electrophysiological patterns of development during the first three postnatal weeks. To isolate the determinants of this differential maturation, we analyzed the gene expression and intrinsic membrane properties of layer V pyramidal neurons projecting either to the superior colliculus (SC cells) or the contralateral cortex (CC cells) by combining whole cell recordings and single-cell RT-PCR in acute slices prepared from postnatal day (P) 5-7 or P21-30 old mice. Among the 24 genes tested, the calcium channel subunits alpha1B and alpha1C, the protease Nexin 1, and the calcium-binding protein calbindin were differentially expressed in adult SC and CC cells and the potassium channel subunit Kv4.3 was expressed preferentially in CC cells at both stages of development. Intrinsic membrane properties, including input resistance, amplitude of the hyperpolarization-activated current, and action potential threshold, differed quantitatively between the two populations as early as from the first postnatal week and persisted throughout adulthood. However, the two cell types had similar regular action potential firing behaviors at all developmental stages. Surprisingly, when we increased the duration of anesthesia with ketamine-xylazine or pentobarbital before decapitation, a proportion of mature SC cells, but not CC cells, fired bursts of action potentials. Together these results indicate that the two populations of layer V pyramidal neurons already start to differ during the first postnatal week and exhibit different firing capabilities after anesthesia.

Two types of nicotinic receptors mediate an excitation of neocortical layer I interneurons.

Nicotinic acetylcholine receptors are widely expressed in the neocortex but their functional roles remain largely unknown. Here we investigated the effect of nicotinic receptor activation on interneurons of layer I, which contains a high density of cholinergic fiber terminals. Ninety-seven of 101 neurons recorded in whole cell configuration in rat acute slices were excited by local pressure application of nicotinic agonists, acetylcholine (500 microM), 1,1-dimethyl-4-phenyl-piperazinium (500 microM) or choline (10 mM). Biocytin labeling confirmed that our sample included different morphological types of layer I interneurons. The responses to nicotinic agonists persisted in presence of glutamate and muscarinic receptor antagonists and on further addition of Cd(2+) or tetrodotoxin, indicating that they were mediated by direct activation of postsynaptic nicotinic receptors. The kinetics of the currents and their sensitivity to nicotinic receptor antagonists, methyllycaconitine (1-10 nM) or dihydro-beta-erythroidine (500 nM), suggested that early and late components of the responses were mediated by alpha7 and non-alpha7 types of receptors. Both components had inwardly rectifying I-V curves, which differed when intracellular spermine was omitted. Single-cell RT-PCR experiments identified alpha4, alpha7, and beta2 as the predominantly expressed mRNAs, suggesting that the receptors consisted of alpha7 homomers and alpha4beta2 heteromers. Finally, selective excitation of layer I interneurons through activation of their nicotinic receptors resulted in a tetrodotoxin-sensitive increase of inhibitory synaptic currents recorded in nonpyramidal cells but not in pyramidal cells of layer II/III. These results suggest that acetylcholine released in layer I may induce a disinhibition of the cortical network through activation of nicotinic receptors expressed by layer I interneurons.