Huntingtin-associated Protein Research Articles

HAP40 modulates mutant Huntingtin aggregation and toxicity in Huntington’s disease mice

Huntington’s disease (HD) is a monogenic neurodegenerative disease, caused by the CAG trinucleotide repeat expansion in exon 1 of the Huntingtin (HTT) gene. The HTT gene encodes a large protein known to interact with many proteins. Huntingtin-associated protein 40 (HAP40) is one that shows high binding affinity with HTT and functions to maintain HTT conformation in vitro. However, the potential role of HAP40 in HD pathogenesis remains unknown. In this study, we found that the expression level of HAP40 is in parallel with HTT but inversely correlates with mutant HTT aggregates in mouse brains. Depletion of endogenous HAP40 in the striatum of HD140Q knock-in (KI) mice leads to enhanced mutant HTT aggregation and neuronal loss. Consistently, overexpression of HAP40 in the striatum of HD140Q KI mice reduced mutant HTT aggregation and ameliorated the behavioral deficits. Mechanistically, HAP40 preferentially binds to mutant HTT and promotes Lysine 48-linked ubiquitination of mutant HTT. Our results revealed that HAP40 is an important regulator of HTT protein homeostasis in vivo and hinted at HAP40 as a therapeutic target in HD treatment.

Research advances in huntingtin-associated protein 1 and its application prospects in diseases.

Huntingtin-associated protein 1 (HAP1) was the first protein discovered to interact with huntingtin. Besides brain, HAP1 is also expressed in the spinal cord, dorsal root ganglion, endocrine, and digestive systems. HAP1 has diverse functions involving in vesicular transport, receptor recycling, gene transcription, and signal transduction. HAP1 is strongly linked to several neurological diseases, including Huntington's disease, Alzheimer's disease, epilepsy, ischemic stroke, and depression. In addition, HAP1 has been proved to participate in cancers and diabetes mellitus. This article provides an overview of HAP1 regarding the tissue distribution, cell localization, functions, and offers fresh perspectives to investigate its role in diseases.

The use of L-asparaginase for the treatment of solid tumors: data from experimental studies and clinical trials

Drug therapy is one of the main strategies of cancer treatment. L-asparaginase, the enzyme that hydrolyzes asparagine, has been included in the treatment regimens for acute lymphoblastic leukemia and other hematological malignancies since more than 50 years ago, but its use for the treatment of solid tumors is still extremely limited. This review analyzes experimental data on the sensitivity of cell lines and xenografts of solid tumors to L-asparaginase, examines the results of clinical trials. Among the mechanisms of the cytotoxic effect of L-asparaginase on tumor cells, such processes as depletion of aspartic and glutamic acids, influence on the internal and external pathways of apoptosis, inhibition of cellular processes through a decrease in the activity of the mTOR protein, and weakening of the expression of the telomerase gene are discussed. Separately, molecular markers are considered, which can be used to suggest the effectiveness of future therapy with L-asparaginase in solid tumors. These markers include expression levels of asparagine synthetase and glutamine synthetase genes, degree of methylation of the ASNS gene promoter region, PTEN protein activity and autophagy, bone marrow environment of tumor cells, as well as expression of genes associated with asparaginase resistance (such as the μ1 opioid receptor gene and the huntingtin-associated protein 1 gene).

Huntingtin Interacting Proteins and Pathological Implications.

Huntington's disease (HD) is caused by an expansion of a CAG repeat in the gene that encodes the huntingtin protein (HTT). The exact function of HTT is still not fully understood, and previous studies have mainly focused on identifying proteins that interact with HTT to gain insights into its function. Numerous HTT-interacting proteins have been discovered, shedding light on the functions and structure of HTT. Most of these proteins interact with the N-terminal region of HTT. Among the various HTT-interacting proteins, huntingtin-associated protein 1 (HAP1) and HTT-interacting protein 1 (HIP1) have been extensively studied. Recent research has uncovered differences in the distribution of HAP1 in monkey and human brains compared with mice. This finding suggests that there may be species-specific variations in the regulation and function of HTT-interacting proteins. Understanding these differences could provide crucial insights into the development of HD. In this review, we will focus on the recent advancements in the study of HTT-interacting proteins, with particular attention to the differential distributions of HTT and HAP1 in larger animal models.

Huntingtin-associated protein 1 ameliorates neurological function rehabilitation by facilitating neurite elongation through TrKA-MAPK pathway in mice spinal cord injury.

Huntingtin-associated protein 1 (HAP1) is a neuronal protein closely associated with microtubules and might facilitate neurological function rehabilitation. This study aimed to investigate the effects of HAP1 on SCI and the underlying mechanisms. the spinal cord injury (SCI) mouse model was induced by Allen's method. Then recombinant-HAP1 (r-HAP1) was administrated by intrathecal injection, and the BMS, Thermal nociceptive thresholds, tactile nociceptive thresholds, and neurofibrillary regeneration were identified to inspect the therapy outcome. Then NSCs were isolated from mice on embryonic day 14.5 and induced to differentiate into neurons. The efficiency of axon growth was calculated. Signaling pathway array was conducted to examine the signaling pathways in NSCs treated with r-HAP1. Antagonists and activators of TrkA were used to confirm the role of TrkA of HAP1 intervention both in vitro and in vivo. r-HAP1 ameliorates the neurological function rehabilitation after SCI, and benefits the regain of Tuj in injury spinal cord. Also significantly enhances neurite growth during neuronal differentiation of NSCs; Signaling pathway array and Western blot revealed that r-HAP1 significantly activates the phosphorylation of TrkA-MAPK/ERK in NSCs. TrkA selective inhibitor GW441756 blocks r-HAP1 on TrkA-MAPK/ERK signaling pathway and detracts from axonal growth after neuronal differentiation. TrkA selective activator gambogic amide can mimic the function of r-HAP1 by activating the foregoing pathway. ERK activator U-46619 reverses the blocking effect of GW441756 on r-HAP1. HAP1 activates the TrkA-MAPK signaling pathway and is conducive to neurite elongation during NSC neuronal differentiation; by which to improve the prognosis of spinal cord injury in mice.

P-334 Transcriptomic patterns in early-secretory and mid-secretory endometrium in a natural menstrual cycle immediately before in vitro fertilization and embryo transfer

Abstract Study question To evaluate endometrial transcriptomic patterns in early-secretory phase (ESP) and mid-secretory phase (MSP) in a natural menstrual cycle before IVF-ET Summary answer Endometial ranscriptomic patterns in ESP and MSP immediately before IVF-ET appear to differ according to IVF-ET outcome, which may be implicated in endometrial receptivity. What is known already Biologic processes and molecular participants in the transition from ESP to MSP endometrium underscore the complex events in preparing for embryo implantation. Previously reported genes with altered expression during endometrial transition from the ES phase to the MS phase were frequently involved in ion binding, cell cycle regulation, transport of signaling proteins, or immune modulation. Although several studies have compared gene expression in the receptive phase and pre-receptive phases in an attempt to identify a molecular signature characteristic of a receptive endometrium, a consensus has not been reached regarding the genes accounting for transcriptomic differences between phases. Study design, size, duration Differentially expressed genes (DEGs) in the MSP, compared to the ESP, were identified using NanoString nCounter data in both the pregnant and non-pregnant groups. Participants/materials, setting, methods A total of 30 patients whose endometrial tissues were obtained in a natural menstrual cycle immediately before IVF-ET were included. Endometrial dating was histologically confirmed as ESP (cycle day 16 to 18) or MSP (cycle day 19 to 21) according to Noyes criteria. The patients were divided into two groups depending on IVF-ET outcome: pregnant (n = 14; 7 in ESP and 7 in MSP) or non-pregnant (n = 16; 8 in ESP and 8 in MSP). Main results and the role of chance A total of 14 DEGs were identified when comparing the ES phase and MS phase endometrium in the pregnant group. A total of 12 DEGs were identified when comparing the ES phase and MS phase endometrium in the non-pregnant group Nine genes were upregulated in the MS phase endometrium, compared to the ES phase endometrium, in both the pregnant and non-pregnant groups: adrenoceptor alpha 2A (ADRA2A), interleukin 1 receptor-associated kinase 2 (IRAK2), a disintegrin and metalloproteinase with thrombospondin repeats 15 (ADAMTS15), serpin family E member 1 (SERPINE1), integrin subunit beta 3 (ITGB3), transmembrane protein 252 (TMEM252), huntingtin associated protein 1 (HAP1), C2 calcium-dependent domain containing 4A (C2CD4A), and integrin subunit alpha 2 (ITGA2). Four genes were upregulated in the MS phase endometrium, compared to the ES phase endometrium, only in the pregnant group: TMEM37, galactosidase beta 1 like 2 (GLB1L2), Rho family GTPase 3 (RND3), and cytochrome P450 family 24 subfamily A member 1 (CYP24A1). One gene (ADAMTS8) was downregulated and one gene (monoamine oxidase A [MAOA]) was upregulated in the MS phase endometrium, compared to the ES phase endometrium, only in the non-pregnant group. Limitations, reasons for caution Firstly, since our sample size was relatively small, our results should be considered preliminary. Secondly, because endometrial tissue samples wee not obtained in IVF-ET cycle, they may not reflect changes in an actual pregnancy cycle.Thirdly, there may have been embryonic effects on implantation that were not accounted for. Wider implications of the findings TMEM37, GLB1L2, RND3, and CYP24A1 were upregulated only in the pregnant group; ADAMTS8 was downregulated while MAOA was upregulated only in the non-pregnant group.These novel DEGs, which have not been previously studied, may have functional significance during the WOI and serve as potential biomarkers of endometrial receptivity. Trial registration number not applicable

Huntingtin-associated protein 1-associated intracellular trafficking in neurodegenerative diseases.

Huntingtin-associated protein 1 (HAP1), the first identified HTT-binding partner, is highly expressed in the central nervous system, and has been found to associated with neurological diseases. Mounting evidence suggests that HAP1 functions as a component of cargo-motor molecules to bind various proteins and participates in intracellular trafficking. It is known that the failure of intracellular transport is a key contributor to the progression of neurodegenerative disorders (NDs) including Alzheimer's disease (AD), Huntington's disease (HD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), spinal and bulbar muscular atrophy (SBMA) and spinocerebellar ataxia (SCA). The link between HAP1 and various NDs is supported by growing evidence. This review aims to provide a comprehensive overview of the intracellular trafficking function of HAP1 and its involvement in NDs.

Immunohistochemical Distribution and Neurochemical Characterization of Huntingtin-Associated Protein 1 Immunoreactive Neurons in the Adult Mouse Lingual Ganglia

Huntingtin-associated protein 1 (HAP1) is a determinant marker for the stigmoid body (STB), a neurocytoplasmic physiological inclusion. STB/HAP1 enriched areas in the brain/spinal cord are usually protected from neurodegenerative diseases, whereas the regions with tiny amounts or no STB/HAP1 are affected. In addition to the brain/spinal cord, HAP1 is highly expressed in the myenteric/submucosal plexuses of the enteric nervous system in the gastrointestinal tract. The tongue is attached to the pharynx by the hyoid bone as an extension of the gastrointestinal system. To date, the immunohistochemical distribution and neurochemical characterization of HAP1 have not been elucidated in the lingual ganglia. Using immunohistochemistry and light microscopy, our current study demonstrates the expression and immunohistochemical phenotype of HAP1 in the lingual ganglia of adult mice. We showed that HAP1 was profoundly distributed in the intralingual ganglion (ILG) and the ganglia near the root of the tongue (which we coined as "lingual root ganglion"; LRG). Neurons in ILG and LRG exhibited high coexpression of HAP1 with NOS or ChAT. Furthermore, most HAP1-immunoreactive neurons contained SP, CGRP, and VIP immunoreactivity in both ILG and LRG. The current results might serve as an essential base for future studies to elucidate the pathological/physiological functions of HAP1 in the lingual ganglia.

Neurochemical phenotypes of huntingtin-associated protein 1 in reference to secretomotor and vasodilator neurons in the submucosal plexuses of rodent small intestine

Huntingtin-associated protein 1(HAP1) is an immunohistochemical marker of the stigmoid body (STB). Brain and spinal cord regions with lack of STB/HAP1 immunoreactivity are always neurodegenerative targets, whereas STB/HAP1 abundant regions are usually spared from neurodegeneration. In addition to the brain and spinal cord, HAP1 is abundantly expressed in the excitatory and inhibitory motor neurons in myenteric plexuses of the enteric nervous system (ENS). However, the detailed expression of HAP1 and its neurochemical characterization in submucosal plexuses of ENS are still unknown. In this study, we aimed to clarify the expression and neurochemical characterization of HAP1 in the submucosal plexuses of the small intestine in adult mice and rats. HAP1 was highly expressed in the submucosal plexuses of both rodents. The percentage of HAP1-immunoreactive submucosal neurons was not significantly varied between the intestinal segments of these rodents. Double immunofluorescence results revealed that almost all the cholinergic secretomotor neurons containing ChAT/ CGRP/ somatostatin/ calretinin, non-cholinergic secretomotor neurons containing VIP/NOS/TH/calretinin, and vasodilator neurons containing VIP/calretinin expressed HAP1. Our current study is the first to clarify that STB/HAP1 is expressed in secretomotor and vasodilator neurons of submucosal plexuses, suggesting that STB/HAP1 might modulate or protect the secretomotor and vasodilator functions of submucosal neurons in ENS.

Huntingtin-associated protein 1 is a potential tumor suppressor for gastric cancer

Gastric cancer is heterogeneous cancer and the causes of this disease are complex. New diagnostic and therapeutic targets are urgently needed to explore. Huntingtin-associated protein 1 (HAP1) is directly related to Huntington's disease (HD). However, patients with Huntington's disease have a lower incidence of cancer. Therefore, we are committed to studying the correlation between HAP1 and gastric carcinogenesis and development. Immunohistochemical staining, western blot analysis, and RT-qPCR were conducted to explore the localization and expression of HAP1 in gastric cancer. To study the biological significance of HAP1, we overexpressed HAP1 in both MKN28 and AGS cell lines by lentivirus infection. To explore the role of HAP1 in cell proliferation, the cells counting assay, EdU incorporation assay, and colony formation assay were carried out. We performed the wound healing assay and transwell assay to study the cell migration and invasion. To further investigate whether HAP1 could regulate gastric cancer cell death during glucose deprivation, Annexin V-FITC/PI staining was performed. In our study, we elucidated that HAP1 was downregulated in gastric cancer. What's more, overexpressing HAP1 inhibited cell proliferation, cell migration and invasion, and triggered apoptosis during glucose deprivation. More importantly, the antitumor properties and mechanisms of HAP1 have been elucidated further in gastric cancer. Taken together, the available evidence implies that HAP1 may serve as a potential tumor suppressor, making it a significant target in preventing and treating gastric cancer. This research provides a theoretical basis for the early diagnosis, clinical targeted therapy, and prognosis evaluation of gastric cancer.

Differential expression and roles of Huntingtin and Huntingtin-associated protein 1 in the mouse and primate brains.

Huntingtin-associated protein 1 (HAP1) is the first identified protein whose function is affected by its abnormal interaction with mutant huntingtin (mHTT), which causes Huntington disease. However, the expression patterns of Hap1 and Htt in the rodent brain are not correlated. Here we found that the primate HAP1, unlike the rodent Hap1, is correlatively expressed with HTT in the primate brains. CRISPR/Cas9 targeting revealed that HAP1 deficiency in the developing human neurons did not affect neuronal differentiation and gene expression as seen in the mouse neurons. However, deletion of HAP1 exacerbated neurotoxicity of mutant HTT in the organotypic brain slices of adult monkeys. These findings demonstrate differential HAP1 expression and function in the mouse and primate brains, and suggest that interaction of HAP1 with mutant HTT may be involved in mutant HTT-mediated neurotoxicity in adult primate neurons.

Huntingtin and Its Partner Huntingtin-Associated Protein 40: Structural and Functional Considerations in Health and Disease.

Since the discovery of the mutation causing Huntington’s disease (HD) in 1993, it has been debated whether an expanded polyglutamine (polyQ) stretch affects the properties of the huntingtin (HTT) protein and thus contributes to the pathological mechanisms responsible for HD. Here we review the current knowledge about the structure of HTT, alone (apo-HTT) or in a complex with Huntingtin-Associated Protein 40 (HAP40), the influence of polyQ-length variation on apo-HTT and the HTT-HAP40 complex, and the biology of HAP40. Phylogenetic analyses suggest that HAP40 performs essential functions. Highlighting the relevance of its interaction with HTT, HAP40 is one of the most abundant partners copurifying with HTT and is rapidly degraded, when HTT levels are reduced. As the levels of both proteins decrease during disease progression, HAP40 could also be a biomarker for HD. Whether declining HAP40 levels contribute to disease etiology is an open question. Structural studies have shown that the conformation of apo-HTT is less constrained but resembles that adopted in the HTT-HAP40 complex, which is exceptionally stable because of extensive interactions between HAP40 and the three domains of HTT. The complex— and to some extent apo-HTT— resists fragmentation after limited proteolysis. Unresolved regions of apo-HTT, constituting about 25% of the protein, are the main sites of post-translational modifications and likely have major regulatory functions. PolyQ elongation does not substantially alter the structure of HTT, alone or when associated with HAP40. Particularly, polyQ above the disease length threshold does not induce drastic conformational changes in full-length HTT. Therefore, models of HD pathogenesis stating that polyQ expansion drastically alters HTT properties should be reconsidered.

Mapping of STB/HAP1 Immunoreactivity in the Mouse Brainstem and its Relationships with Choline Acetyltransferase, with Special Emphasis on Cranial Nerve Motor and Preganglionic Autonomic Nuclei

Huntingtin-associated protein 1 (HAP1) is a core component of stigmoid body (STB) and is known as a neuroprotective interactor with causal agents for various neurodegenerative diseases. Brain regions rich in STB/HAP1 immunoreactivity are usually spared from cell death, whereas brain regions with negligible STB/HAP1 immunoreactivity are the major neurodegenerative targets. Recently, we have shown that STB/HAP1 is abundantly expressed in the spinal preganglionic sympathetic/parasympathetic neurons but absent in the motoneurons of spinal cord, indicating that spinal motoneurons are more vulnerable to neurodegenerative diseases. In light of STB/HAP1 neuroprotective effects, it is also essential to clarify the distribution of STB/HAP1 in another major neurodegenerative target, the brainstem. Here, we examined the expression and detailed immunohistochemical distribution of STB/HAP1 and its relationships with choline acetyltransferase (ChAT) in the midbrain, pons, and medulla oblongata of adult mice. Abundant STB/HAP1 immunoreactive neurons were disseminated in the periaqueductal gray, Edinger-Westphal nucleus, raphe nuclei, locus coeruleus, pedunculopontine tegmental nucleus, superior/inferior salivatory nucleus, and dorsal motor nucleus of vagus. Double-label immunohistochemistry of HAP1 with ChAT (or with urocortin-1 for Edinger-Westphal nucleus centrally projecting population) confirmed that STB/HAP1 was highly present in parasympathetic preganglionic neurons but utterly absent in cranial nerve motor nuclei throughout the brainstem. These results suggest that due to deficient putative STB/HAP1-protectivity, cranial nerve motor nuclei might be more vulnerable to certain neurodegenerative stresses than STB/HAP1-expressing brainstem nuclei, including preganglionic parasympathetic nuclei. Our current results also lay a basic foundation for future studies that seek to clarify the physiological/pathological roles of STB/HAP1 in the brainstem.

Uncovering a Genetic Polymorphism Located in Huntingtin Associated Protein 1 in Modulation of Central Pain Sensitization Signaling Pathways.

Fibromyalgia syndrome (FMS) is characterized by widespread pain and increased sensitivity to nociceptive stimulus or tenderness. While familial aggregation could suggest a potential hereditary component in FMS development, isolation of genetic determinants has proven difficult due to the multi-factorial nature and complexity of the syndrome. Central sensitization is thought to be one of the key mechanisms leading to FMS in a subset of patients. Enhanced central pain signaling can be measured using the Nociceptive Flexion Reflex (NFR) or RIII threshold. We performed a genome-wide association study (GWAS) using an array to genotype 258,756 human genetic polymorphisms in 225 FMS patients and 77 healthy volunteers and searched for genetic variants associated with a lowered NFR threshold. We have identified a potential association between a single nucleotide polymorphism resulting in a common non-synonymous coding mutation in the Huntingtin associated protein 1 (HAP1) gene (rs4796604, MAF = 0.5) and the NFR threshold (p = 4.78E−06). The Hap1 protein is involved in trafficking and is particularly enriched in neurons. Our results suggest a possible involvement of the neuronal trafficking protein HAP1 in modulating pain signaling pathways and thus participate in the establishment of the NFR threshold.

HAP1 interacts with 14–3-3 to regulate epileptic seizure via GABAAR-mediated inhibitory synaptic transmission in pentylenetetrazole rat model

Disruption of γ-aminobutyric acid type A receptors (GABAARs) synaptic clustering and a decrease number in the plasma membrane are thought to contribute to the alteration in the balance between excitatory and inhibitory neurotransmission in the epilepsy. Thus, it is important to elucidate the molecular mechanisms that regulate the stabilities of surface GABAARs populations as well as their concentrations at inhibitory synapses. However, the mechanism that delivers GABAARs to plasma membrane has not been conclusively determined. Our previous research indicated that huntingtin-associated protein 1 (HAP1), a major facilitator of pathological variations in membrane trafficking, modulates epileptic seizure by regulating GABAARs-mediated inhibitory synaptic transmission in pentylenetetrazole (PTZ)-induced epileptic rats. However, a detailed molecular interaction networks comprising GABAARs and HAP1 is necessary for studying and investigating new treatment targets for epilepsy. In this study, we indicate that HAP1 specifically interacts with 14–3–3, a protein that functions as a chaperone, forming a cargo adaptor complex to regulate surface GABAARs expression and the inhibitory post-synaptic current amplitudes. Disrupting the HAP1/14–3–3 complex decreases the strength of GABAARs-mediated inhibitory synaptic transmission in epilepsy. Taken together, HAP1/14–3–3 complex is linked to inhibitory synaptic transmission in evoking seizures, therefore, it is a possible drug target for epilepsy.

Visualization of three-dimensional stigmoid body in FFPE and ultrathin sections of mouse.

Huntingtin-associated protein 1 (HAP1) is abundantly expressed in the neurons of the central nervous system and forms unique intracytoplasmic inclusions of unknown function called 'stigmoid bodies' (STBs). Transmission electron microscopy has revealed that the STBs are aggregates of granules containing cavities with a diameter of 0.5-3 µm. Small STBs fuse to form larger STBs, the size of which is said to vary depending on the developmental growth stage and brain region. Light microscopy can only reveal that these STBs have similar circular shapes due to its limited resolution. Therefore, light microscopy is only fit for the study of the STB distribution and quantitative changes. We, herein, suggest the adoption of correlative light and electron microscopy, which combines confocal laser scanning microscopy and scanning electron microscopy as the method allowing us to identify the huntingtin-associated protein 1-positive STBs in formalin-fixed paraffin-embedded (FFPE) sections. This approach allows us to study the three-dimensional morphology of immunolabeled objects in histopathological specimens. The STBs in FFPE sections of murine hypothalami reflected the transmission electron microscopic images of Epon-embedded STBs, although we were not able to observe any organelle covering the STBs of the FFPE sections. Furthermore, we were able to reconstruct the three-dimensional structure of the STB, and we identified it to be of spherical form, covered with mitochondria and rough endoplasmic reticulum, and bearing a cluster of cavities in the centre. In the future, we might gain new insights by comparing the three-dimensional structure of the STB between different neurons and under a variety of conditions.

Immunohistochemical expression and neurochemical phenotypes of huntingtin-associated protein 1 in the myenteric plexus of mouse gastrointestinal tract.

Huntingtin-associated protein 1 (HAP1) is a neural huntingtin interactor and being considered as a core molecule of stigmoid body (STB). Brain/spinal cord regions with abundant STB/HAP1 expression are usually spared from neurodegeneration in stress/disease conditions, whereas the regions with little STB/HAP1 expression are always neurodegenerative targets. The enteric nervous system (ENS) can act as a potential portal for pathogenesis of neurodegenerative disorders. However, ENS is also a neurodegenerative target in these disorders. To date, the expression of HAP1 and its neurochemical characterization have never been examined there. In the current study, we determined the expression of HAP1 in the ENS of adult mice and characterized the morphological relationships of HAP1-immunoreactive (ir) cells with the markers of motor neurons, sensory neurons, and interneurons in the myenteric plexus using Western blotting and light/fluorescence microscopy. HAP1-immunoreaction was present in both myenteric and submucosal plexuses of ENS. Most of the HAP1-ir neurons exhibited STB in their cytoplasm. In myenteric plexus, a large number of calretinin, calbindin, NOS, VIP, ChAT, SP, somatostatin, and TH-ir neurons showed HAP1-immunoreactivity. In contrast, most of the CGRP-ir neurons were devoid of HAP1-immunoreactivity. Our current study is the first to clarify that HAP1 is highly expressed in excitatory motor neurons, inhibitory motor neurons, and interneurons but almost absent in sensory neurons in myenteric plexus. These suggest that STB/HAP1-ir neurons are mostly Dogiel type I neurons. Due to lack of putative STB/HAP1 protectivity, the sensory neurons (Dogiel type II) might be more vulnerable to neurodegeneration than STB/HAP1-expressing motoneurons/interneurons (Dogiel type I) in myenteric plexus.

Biological functions and potential therapeutic applications of huntingtin-associated protein 1: progress and prospects.

Huntington disease (HD) is a single-gene autosomal dominant inherited neurodegenerative disease caused by a polyglutamine expansion of the protein huntingtin (HTT). Huntingtin-associated protein 1 (HAP1) is the first protein identified as an interacting partner of huntingtin, which is directly associated with HD. HAP1 is mainly expressed in the nervous system and is also found in the endocrine system and digestive system, and then involves in the occurrence of the related endocrine diseases, digestive system diseases, and cancer. Understanding the function of HAP1 could help elucidate the pathogenesis that HTT plays in the disease process. Therefore, this article attempts to summarize the latest research progress of the role of HAP1 and its application for diseases in recent years, aiming to clarify the functions of HAP1 and its interacting proteins, and provide new research ideas and new therapeutic targets for the treatment of cancer and related diseases.

HAP40 protein levels are huntingtin-dependent and decrease in Huntington disease

The huntingtin-associated protein 40 (HAP40) is an abundant interactor of huntingtin (HTT). In complexes of these proteins, HAP40 tightly binds to HTT in a cleft formed by two larger domains rich in HEAT repeats, and a smaller bridge domain connecting the two.We show that HAP40 steady-state protein levels are directly dependent on HTT (both normal and mutant HTT) and that HAP40 is strongly stabilized by the interaction with HTT resulting in an at least 5-fold increase in HAP40's half-life when bound to HTT. Cellular HAP40 protein levels were reduced in primary fibroblasts and lymphoblasts of Huntington Disease (HD) patients and in brain tissue of a full-length HTT mouse model of HD, concomitant with decreased soluble HTT levels in these cell types. This data and our previous demonstration of coevolution between HTT and HAP40 and evolutionary conservation of their interaction suggest that HAP40 is an obligate interaction partner of HTT. Our observation of reduced HAP40 levels in HD invites further studies, whether HAP40 loss-of-function contributes to the pathophysiology of HD.

Pathological polyQ expansion does not alter the conformation of the Huntingtin-HAP40 complex

The abnormal amplification of a CAG repeat in the gene coding for huntingtin (HTT) leads to Huntington's disease (HD). At the protein level, this translates into the expansion of a polyglutamine (polyQ) stretch located at the HTT N terminus, which renders HTT aggregation prone by unknown mechanisms. Here we investigated the effects of polyQ expansion on HTT in a complex with its stabilizing interaction partner huntingtin-associated protein 40 (HAP40). Surprisingly, our comprehensive biophysical, crosslinking mass spectrometry and cryo-EM experiments revealed no major differences in the conformation of HTT-HAP40 complexes of various polyQ length, including 17QHTT-HAP40 (wild type), 46QHTT-HAP40 (typical polyQ length in HD patients), and 128QHTT-HAP40 (extreme polyQ length). Thus, HTT polyQ expansion does not alter the global conformation of HTT when associated with HAP40.