Circadian expression and specific localization of synaptotagmin17 in the suprachiasmatic nucleus, the master circadian oscillator in mammals

The localization and function of synaptotagmin (syt)17 in the suprachiasmatic nucleus (SCN) of the brain, which is the master circadian oscillator, were investigated. The Syt17 mRNA-containing neurons were mainly situated in the shell region while SYT17 immunoreactive cell bodies and neural fibers were detected in the core and shell of the SCN and the subparaventricular zone (SPZ). Further, electron microscopy analysis revealed SYT17 in the rough endoplasmic reticulum (rER), Golgi apparatus (G), and large and small vesicles of neurons. Syt17 mRNA expression in the SCN showed a circadian rhythm, and light exposure at night suppressed its expression. In addition, the free running period of locomotor activity rhythm was shortened in Syt17-deletion mutant mice. These findings suggest that SYT17 is involved in the regulation of circadian rhythms.

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.

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.

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.

Expression of huntingtin-associated protein 1 in adult mouse dorsal root ganglia and its neurochemical characterization in reference to sensory neuron subpopulations

•

This study is the first to examine HAP1-expression in dorsal root ganglia (DRG).

•

HAP1 is highly co-expressed with the markers of nociceptive/proprioceptive neurons.

•

HAP1 is completely lacking in the touch-sensitive DRG neurons.

•

HAP1 may play an important role in modulating nociceptive/proprioceptive functions.

•

It will be of great interest to clarify the pathophysiological role of HAP1 in DRG.

Huntingtin-associated protein 1 (HAP1) is a polyglutamine (polyQ) length-dependent interactor with causal agents in several neurodegenerative diseases and has been regarded as a protective factor against neurodegeneration. In normal rodent brain and spinal cord, HAP1 is abundantly expressed in the areas that are spared from neurodegeneration while those areas with little HAP1 are frequent targets of neurodegeneration. We have recently showed that HAP1 is highly expressed in the spinal dorsal horn and may participate in modification/protection of certain sensory functions. Neurons in the dorsal root ganglia (DRG) transmits sensory stimuli from periphery to spinal cord/brain stem. Nevertheless, to date HAP1 expression in DRG remains unreported. In this study, the expression of HAP1 in cervical, thoracic, lumbar and sacral DRG in adult male mice and its relationships with different chemical markers for sensory neurons were examined using Western blot and immunohistochemistry. HAP1-immunoreactivity was detected in the cytoplasm of DRG neurons, and the percentage of HAP1-immunoreactive (ir) DRG neurons was ranged between 28–31 %. HAP1-immunoreactivity was comparatively more in the small cells (47–58 %) and medium cells (40–44 %) than that in the large cells (9–11 %). Double-immunostaining for HAP1 and markers for nociceptive or mechanoreceptive neurons showed that about 70–80 % of CGRP-, SP-, CB-, NOS-, TRPV1-, CR- and PV-ir neurons expressed HAP1. In contrast, HAP1 was completely lacking in TH-ir neurons. Our current study is the first to clarify that HAP1 is highly expressed in nociceptive/proprioceptive neurons but absent in light-touch-sensitive TH neurons, suggesting the potential importance of HAP1 in pain transduction and proprioception.

Androgen Affects the Dynamics of Intrinsic Plasticity of Pyramidal Neurons in the CA1 Hippocampal Subfield in Adolescent Male Rats

Androgen receptor (AR) is abundantly expressed in the preoptico-hypothalamic area, bed nucleus of stria terminalis, and medial amygdala of the brain where androgen plays an important role in regulating male sociosexual, emotional and aggressive behaviors. In addition to these brain regions, AR is also highly expressed in the hippocampus, suggesting that the hippocampus is another major target of androgenic modulation. It is known that androgen can modulate synaptic plasticity in the CA1 hippocampal subfield. However, to date, the effects of androgen on the intrinsic plasticity of hippocampal neurons have not been clearly elucidated. In this study, the effects of androgen on the expression of AR in the hippocampus and on the dynamics of intrinsic plasticity of CA1 pyramidal neurons were examined using immunohistochemistry, Western blotting and whole-cell current-clamp recording in unoperated, sham-operated, orchiectomized (OCX), OCX + testosterone (T) or OCX + dihydrotestosterone (DHT)-primed adolescent male rats. Orchiectomy significantly decreased AR-immunoreactivity, resting membrane potential, action potential numbers, afterhyperpolarization amplitude and membrane resistance, whereas it significantly increased action potential threshold and membrane capacitance. These effects were successfully reversed by treatment with either aromatizable androgen T or non-aromatizable androgen DHT. Furthermore, administration of the AR-antagonist flutamide in intact rats showed similar changes to those in OCX rats, suggesting that androgens affect the excitability of CA1 pyramidal neurons possibly by acting on the AR. Our current study potentially clarifies the role of androgen in enhancing the basal excitability of the CA1 pyramidal neurons, which may influence selective neuronal excitation/activation to modulate certain hippocampal functions.

Muscarinic Acetylcholine Receptors Chrm1 and Chrm3 Are Essential for REM Sleep

Sleep regulation involves interdependent signaling among specialized neurons in distributed brain regions. Although acetylcholine promotes wakefulness and rapid eye movement (REM) sleep, it is unclear whether the cholinergic pathway is essential (i.e., absolutely required) for REM sleep because of redundancy from neural circuits to molecules. First, we demonstrate that synaptic inhibition of TrkA+ cholinergic neurons causes a severe short-sleep phenotype and that sleep reduction is mostly attributable to a shortened sleep duration in the dark phase. Subsequent comprehensive knockout of acetylcholine receptor genes by the triple-target CRISPR method reveals that a similar short-sleep phenotype appears in the knockout of two Gq-type acetylcholine receptors Chrm1 and Chrm3. Strikingly, Chrm1 and Chrm3 double knockout chronically diminishes REM sleep to an almost undetectable level. These results suggest that muscarinic acetylcholine receptors, Chrm1 and Chrm3, are essential for REM sleep.

Distribution of HAP1-immunoreactive Cells in the Retrosplenial-retrohippocampal Area of Adult Rat Brain and Its Application to a Refined Neuroanatomical Understanding of the Region

Huntingtin-associated protein 1 (HAP1) is a neural interactor of huntingtin in Huntington's disease and interacts with gene products in a number of other neurodegenerative diseases. In normal brains, HAP1 is expressed abundantly in the hypothalamus and limbic-associated regions. These areas tend to be spared from neurodegeneration while those with little HAP1 are frequently neurodegenerative targets, suggesting its role as a protective factor against apoptosis. In light of the relationship between neurodegenerative diseases and deterioration of higher nervous activity, it is important to definitively clarify HAP1 expression in a cognitively important brain region, the retrosplenial-retrohippocampal area. Here, HAP1 expression was evaluated immunohistochemically over the retrosplenial cortex, the subicular complex, and the entorhinal and perirhinal cortices. HAP1-immunoreactive (ir) cells were classified into five discrete groups: (1) a distinct retrosplenial cell cluster exclusive to the superficial layers of the granular cortex, (2) a conspicuous, thin line of cells in layers IV/V of the "subiculum-backing cortex," (3) a group of highly immunoreactive cells associated with the medial entorhinal-subicular corner, (4) pericallosal cells just below layer VI and adjacent to the white matter, and (5) other sporadic, widely-disseminated HAP1-immunoreactive cells. HAP1 was found to be the first marker for the complex subiculum-backing cortex and a precise marker for several subfields in the retrosplenial-retrohippocampal area, verified through comparative staining with other neurochemicals. HAP1 may play an important role in protecting these cortical structures and functions for higher nervous activity by increasing the threshold to neurodegeneration and decreasing vulnerability to stress or aging.

Regional circadian period difference in the suprachiasmatic nucleus of the mammalian circadian center

The suprachiasmatic nucleus (SCN) is the mammalian circadian rhythm center. Individual oscillating neurons have different endogenous circadian periods, but they are usually synchronized by an intercellular coupling mechanism. The differences in the period of each oscillating neuron have been extensively studied; however, the clustering of oscillators with similar periods has not been reported. In the present study, we artificially disrupted the intercellular coupling among oscillating neurons in the SCN and observed regional differences in the periods of the oscillating small-latticed regions of the SCN using a transgenic rat carrying a luciferase reporter gene driven by regulatory elements from a per2 clock gene (Per2::dluc rat). The analysis divided the SCN into two regions--aregion with periods shorter than 24 h (short-period region, SPR) and another with periods longer than 24 h (long-period region, LPR). The SPR was located in the smaller medial region of the dorsal SCN, whereas the LPR occupied the remaining larger region. We also found that slices containing the medial region of the SCN generated shorter circadian periods than slices that contained the lateral region of the SCN. Interestingly, the SPR corresponded well with the region where the SCN phase wave is generated. We numerically simulated the relationship between the SPR and a large LPR. A mathematical model of the SCN based on our findings faithfully reproduced the kinetics of the oscillators in the SCN in synchronized conditions, assuming the existence of clustered short-period oscillators.

Angiopoietin-like 2, a circadian gene, improves type 2 diabetes through potentiation of insulin sensitivity in mice adipocytes

Angiopoietin-like (Angptl)2, a member of the Angptl protein family, is predominantly secreted from adipose tissue and the heart. Here, we demonstrate that the expression of Angptl2 in epididymal adipose tissue of C57BL/6J mice shows pulsatility and circadian rhythmicity and that the rhythmicity was disrupted in high-fat-fed and leptin receptor-deficient diabetic db/db mice with insulin resistance. To investigate whether the reduction in Angptl2 expression was related to the progression of diabetes, we treated db/db mice with recombinant Angptl2 for 4 wk during the peak period of Angptl2 expression in C57BL/6J mice. Angptl2-treated mice showed decreases in plasma glucose, insulin, triglyceride, and fatty acid levels and an increase in plasma adiponectin, a therapeutic regulator of insulin resistance, leading to improvements in glucose tolerance. In cultured adipocytes, recombinant Angptl2 increased adiponectin expression and stimulated insulin sensitivity partially by reducing the levels of tribbles homolog 3, a specific Akt kinase inhibitory protein. Conversely, Angptl2 small interfering RNA reduced adiponectin expression, resulting in insulin resistance. In preadipocytes, treatment with Angptl2 small interfering RNA inhibited differentiation to adipocytes and reduced adiponectin expression. Taken together, our results suggest that replenishment of Angptl2 stimulates insulin sensitivity and improves the type 2 diabetic state.

FRNK, the autonomously expressed C-terminal region of focal adhesion kinase, is uniquely regulated in vascular smooth muscle: analysis of expression in transgenic mice

FRNK, the autonomously expressed carboxyl-terminal region of focal adhesion kinase (FAK), is expressed in tissues that are rich in vascular smooth muscle cells (VSMCs). Here we report the generation of transgenic mice harboring the putative FRNK promoter fused to LacZ and examine the promoter activity in situ via expression of beta-galactosidase. The transgenic mice exhibited expression of beta-galactosidase predominantly in arterial VSMCs in large and small blood vessels of major organs. Upregulation of beta-galactosidase activity was observed in tunica media following carotid injury, indicating that the FRNK promoter is activated in VSMCs in response to injury. Robust expression of beta-galactosidase in blood vessels was also detected in the developing embryo. However, expression was also observed in the midline, the nose and skin epidermis, indicating distinct transcriptional regulation of the FRNK promoter in embryogenesis. To analyze FRNK expression in vitro, we identified a 116 bp sequence in the FRNK promoter that was sufficient to function as an enhancer when fused to the minimal actin promoter and expressed in cultured smooth muscle cells. Mutation of AP-1 and NF-E2 binding consensus sequences within this element abrogated enhancer activity, supporting the involvement of this promoter element in VSMC expression of FRNK.