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

Spinal afferent innervation in flat-mounts of the rat stomach: anterograde tracing

The dorsal root ganglia (DRG) project spinal afferent axons to the stomach. However, the distribution and morphology of spinal afferent axons in the stomach have not been well characterized. In this study, we used a combination of state-of-the-art techniques, including anterograde tracer injection into the left DRG T7-T11, avidin-biotin and Cuprolinic Blue labeling, Zeiss M2 Imager, and Neurolucida to characterize spinal afferent axons in flat-mounts of the whole rat stomach muscular wall. We found that spinal afferent axons innervated all regions with a variety of distinct terminal structures innervating different gastric targets: (1) The ganglionic type: some axons formed varicose contacts with individual neurons within myenteric ganglia. (2) The muscle type: most axons ran in parallel with the longitudinal and circular muscles and expressed spherical varicosities. Complex terminal structures were observed within the circular muscle layer. (3) The ganglia-muscle mixed type: some individual varicose axons innervated both myenteric neurons and the circular muscle, exhibiting polymorphic terminal structures. (4) The vascular type: individual varicose axons ran along the blood vessels and occasionally traversed the vessel wall. This work provides a foundation for future topographical anatomical and functional mapping of spinal afferent axon innervation of the stomach under normal and pathophysiological conditions.

Mapping the Organization and Morphology of Calcitonin Gene-Related Peptide (CGRP)-IR Axons in the Whole Mouse Stomach

Nociceptive afferent axons innervate the stomach and send signals to the brain and spinal cord. Peripheral nociceptive afferents can be detected with a variety of markers [e.g., substance P (SP) and calcitonin gene-related peptide (CGRP)]. We recently examined the topographical organization and morphology of SP-immunoreactive (SP-IR) axons in the whole mouse stomach muscular layer. However, the distribution and morphological structure of CGRP-IR axons remain unclear. We used immunohistochemistry labeling and applied a combination of imaging techniques, including confocal and Zeiss Imager M2 microscopy, Neurolucida 360 tracing, and integration of axon tracing data into a 3D stomach scaffold to characterize CGRP-IR axons and terminals in the whole mouse stomach muscular layers. We found that: 1) CGRP-IR axons formed extensive terminal networks in both ventral and dorsal stomachs. 2) CGRP-IR axons densely innervated the blood vessels. 3) CGRP-IR axons ran in parallel with the longitudinal and circular muscles. Some axons ran at angles through the muscular layers. 4) They also formed varicose terminal contacts with individual myenteric ganglion neurons. 5) CGRP-IR occurred in DiI-labeled gastric-projecting neurons in the dorsal root and vagal nodose ganglia, indicating CGRP-IR axons were visceral afferent axons. 6) CGRP-IR axons did not colocalize with tyrosine hydroxylase (TH) or vesicular acetylcholine transporter (VAChT) axons in the stomach, indicating CGRP-IR axons were not visceral efferent axons. 7) CGRP-IR axons were traced and integrated into a 3D stomach scaffold. For the first time, we provided a topographical distribution map of CGRP-IR axon innervation of the whole stomach muscular layers at the cellular/axonal/varicosity scale.

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.

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

BACKGROUND

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.

METHODS AND RESULTS

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.

CONCLUSIONS

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.

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.

Quantification of CGRP-immunoreactive myenteric neurons in mouse colon

Quantitative data of biological systems provide valuable baseline information for understanding pathology, experimental perturbations, and computational modeling. In mouse colon, calcitonin gene-related peptide (CGRP) is expressed by myenteric neurons with multiaxonal (Dogiel type II) morphology, characteristic of intrinsic primary afferent neurons (IPANs). Analogous neurons in other species and gut regions represent 5-35% of myenteric neurons. We aimed to quantify proportions of CGRP-immunopositive (CGRP+) myenteric neurons. Colchicine-treated wholemount preparations of proximal, mid, and distal colon were labeled for HuC/D, CGRP, nitric oxide synthase (NOS), and peripherin (Per). The pan-neuronal markers (Hu+/Per+) co-labeled 94% of neurons. Hu+/Per- neurons comprised ∼6%, but Hu-/Per+ cells were rare. Thus, quantification was based on Hu+ myenteric neurons (8576 total; 1225 ± 239 per animal, n = 7). CGRP+ cell bodies were significantly larger than the average of all Hu+ neurons (329 ± 13 vs. 261 ± 12 μm² , p < .0001). CGRP+ neurons comprised 19% ± 3% of myenteric neurons without significant regional variation. NOS+ neurons comprised 42% ± 2% of myenteric neurons overall, representing a lower proportion in proximal colon, compared to mid and distal colon (38% ± 2%, 44% ± 2%, and 44% ± 3%, respectively). Peripherin immunolabeling revealed cell body and axonal morphology in some myenteric neurons. Whether all CGRP+ neurons were multiaxonal could not be addressed using peripherin immunolabeling. However, of 118 putatively multiaxonal neurons first identified based on peripherin immunoreactivity, all were CGRP+ (n = 4). In conclusion, CGRP+ myenteric neurons in mouse colon were comprehensively quantified, occurring within a range expected of a putative IPAN marker. All Per+ multiaxonal neurons, characteristic of Dogiel type II/IPAN morphology, were CGRP+.

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.