Constipation in Tg2576 mice model for Alzheimer's disease associated with dysregulation of mechanism involving the mAChR signaling pathway and ER stress response

Generally-healthy individuals with aberrant bowel movement frequencies show enrichment for microbially-derived blood metabolites associated with reduced kidney function

Bowel movement frequency (BMF) has been linked to changes in the composition of the human gut microbiome and to many chronic conditions, like metabolic disorders, neurodegenerative diseases, chronic kidney disease (CKD), and other intestinal pathologies like irritable bowel syndrome and inflammatory bowel disease. Lower BMF (constipation) can lead to compromised intestinal barrier integrity and a switch from saccharolytic to proteolytic fermentation within the microbiota, giving rise to microbially-derived toxins that may make their way into circulation and cause damage to organ systems. However, the connections between BMF, gut microbial metabolism, and the early-stage development and progression of chronic disease remain underexplored. Here, we examined the phenotypic impact of BMF variation in a cohort of generally-healthy, community dwelling adults with detailed clinical, lifestyle, and multi-omic data. We showed significant differences in microbially-derived blood plasma metabolites, gut bacterial genera, clinical chemistries, and lifestyle factors across BMF groups that have been linked to inflammation, cardiometabolic health, liver function, and CKD severity and progression. We found that the higher plasma levels of 3-indoxyl sulfate (3-IS), a microbially-derived metabolite associated with constipation, was in turn negatively associated with estimated glomerular filtration rate (eGFR), a measure of kidney function. Causal mediation analysis revealed that the effect of BMF on eGFR was significantly mediated by 3-IS. Finally, we identify self-reported diet, lifestyle, and psychological factors associated with BMF variation, which indicate several common-sense strategies for mitigating constipation and diarrhea. Overall, we suggest that aberrant BMF is an underappreciated risk factor in the development of chronic diseases, even in otherwise healthy populations.

Cholinergic Receptor Muscarinic 1 Co-Localized with Mitochondria in Cultured Dorsal Root Ganglion Neurons, and Its Deletion Disrupted Mitochondrial Ultrastructure in Peripheral Neurons: Implications in Alzheimer's Disease

Background

Loss of Cholinergic Receptor Muscarinic 1 (CHRM1) has been linked to the pathogenesis of Alzheimer's disease (AD). Our recent study found significantly lower CHRM1 protein levels in AD patient cortices, linked to reduced survival. Furthermore, using knockout mice (Chrm1-/-) we demonstrated that deletion of Chrm1 alters cortical mitochondrial structure and function, directly establishing a connection between its loss and mitochondrial dysfunction in the context of AD. While CHRM1's role in the brain has been extensively investigated, its impact on peripheral neurons in AD remains a crucial area of research, especially considering reported declines in peripheral nerve conduction among AD patients.

Objective

The objective was to characterize Chrm1 localization and mitochondrial deficits in Chrm1-/- dorsal root ganglion (DRG) neurons.

Methods

Recombinant proteins tagged with Green or Red Fluorescent Protein (GFP/RFP) were transiently expressed to investigate the localization of Chrm1 and mitochondria, as well as mitochondrial movement in the neurites of cultured primary mouse DRG neurons, using confocal time-lapse live cell imaging. Transmission electron microscopy was performed to examine the ultrastructure of mitochondria in both wild-type and Chrm1-/- DRGs.

Results

Fluorescence imaging revealed colocalization and comigration of N-terminal GFP-tagged Chrm1 and mitochondrial localization signal peptide-tagged RFP-labelled mitochondria in the DRGs neurons. A spectrum of mitochondrial structural abnormalities, including disruption and loss of cristae was observed in 87% neurons in Chrm1-/- DRGs.

Conclusions

This study suggests that Chrm1 may be localized in the neuronal mitochondria and loss of Chrm1 in peripheral neurons causes sever mitochondrial structural aberrations resembling AD pathology.

Slow gut transit increases the risk of Alzheimer's disease: An integrated study of the bi-national cohort in South Korea and Japan and Alzheimer's disease model mice

INTRODUCTION

Although the association between Alzheimer's disease (AD) and constipation is controversial, its causality and underlying mechanisms remain unknown.

OBJECTIVES

To investigate the potential association between slow gut transit and AD using epidemiological data and a murine model.

METHODS

We conducted a bi-national cohort study in South Korea (discovery cohort, N=3,130,193) and Japan (validation cohort, N=4,379,285) during the pre-observation period to determine the previous diagnostic history (2009-2010) and the follow-up period (2011-2021). To evaluate the causality, we induced slow gut transit using loperamide in 5xFAD transgenic mice. Changes in amyloid-beta (Aβ) and other markers were examined using ELISA, qRT-PCR, RNA-seq, and behavioral tests.

RESULTS

Constipation was associated with an increased risk of AD in the discovery cohort (hazard ratio, 2.04; 95% confidence interval [CI], 2.01-2.07) and the validation cohort (hazard ratio; 2.82; 95% CI, 2.61-3.05). We found that loperamide induced slower gut transit in 5xFAD mice, increased Aβ and microglia levels in the brain, increased transcription of genes related to norepinephrine secretion and immune responses, and decreased the transcription of defense against bacteria in the colonic tissue.

CONCLUSION

Impaired gut transit may contribute to AD pathogenesis via the gut-brain axis, thus suggesting a cyclical relationship between intestinal barrier disruption and Aβ accumulation in the brain. We propose that gut transit or motility may be a modifiable lifestyle factor in the prevention of AD, and further clinical investigations are warranted.

Compositional changes in fecal microbiota in a new Parkinson's disease model: C57BL/6-Tg(NSE-haSyn) mice

BACKGROUND

The gut-brain axis (GBA) in Parkinson's disease (PD) has only been investigated in limited mice models despite dysbiosis of the gut microbiota being considered one of the major treatment targets for neurodegenerative disease. Therefore, this study examined the compositional changes of fecal microbiota in novel transgenic (Tg) mice overexpressing human α-synuclein (hαSyn) proteins under the neuron-specific enolase (NSE) to analyze the potential as GBA model.

RESULTS

The expression level of the αSyn proteins was significantly higher in the substantia nigra and striatum of NSE-hαSyn Tg mice than the Non-Tg mice, while those of tyrosine hydroxylase (TH) were decreased in the same group. In addition, a decrease of 72.7% in the fall times and a 3.8-fold increase in the fall number was detected in NSE-hαSyn Tg mice. The villus thickness and crypt length on the histological structure of the gastrointestinal (GI) tract decreased in NSE-hαSyn Tg mice. Furthermore, the NSE-hαSyn Tg mice exhibited a significant increase in 11 genera, including Scatolibacter, Clostridium, Feifania, Lachnoclostridium, and Acetatifactor population, and a decrease in only two genera in Ligilactobacillus and Sangeribacter population during enhancement of microbiota richness and diversity.

CONCLUSIONS

The motor coordination and balance dysfunction of NSE-hαSyn Tg mice may be associated with compositional changes in gut microbiota. In addition, these mice have potential as a GBA model.

The Pathological Effects of Circulating Hydrophobic Bile Acids in Alzheimer's Disease

Recent clinical studies have revealed that the serum levels of toxic hydrophobic bile acids (deoxy cholic acid, lithocholic acid [LCA], and glycoursodeoxycholic acid) are significantly higher in patients with Alzheimer's disease (AD) and amnestic mild cognitive impairment (aMCI) when compared to control subjects. The elevated serum bile acids may be the result of hepatic peroxisomal dysfunction. Circulating hydrophobic bile acids are able to disrupt the blood-brain barrier and promote the formation of amyloid-β plaques through enhancing the oxidation of docosahexaenoic acid. Hydrophobic bile acid may find their ways into the neurons via the apical sodium-dependent bile acid transporter. It has been shown that hydrophobic bile acids impose their pathological effects by activating farnesoid X receptor and suppressing bile acid synthesis in the brain, blocking NMDA receptors, lowering brain oxysterol levels, and interfering with 17β-estradiol actions such as LCA by binding to E2 receptors (molecular modelling data exclusive to this paper). Hydrophobic bile acids may interfere with the sonic hedgehog signaling through alteration of cell membrane rafts and reducing brain 24(S)-hydroxycholesterol. This article will 1) analyze the pathological roles of circulating hydrophobic bile acids in the brain, 2) propose therapeutic approaches, and 3) conclude that consideration be given to reducing/monitoring toxic bile acid levels in patients with AD or aMCI, prior/in combination with other treatments.

Similarities and differences in constipation phenotypes between Lep knockout mice and high fat diet-induced obesity mice

CRISPR-Cas9-mediated leptin (Lep) knockout (KO) mice exhibited prominent phenotypes for constipation, even though they were not compared with other model animals. This study compared the stool excretion, gastrointestinal motility, histological structure, mucin secretion, and enteric nerve function in Lep KO and high fat diet (HFD)-treated mice to determine if there were differences in their phenotypes for constipation. Most obesity phenotypes, including fat weight, adipocyte size, expression of lipolytic proteins (HSL, perilipin, and ATGL), and glucose concentrations, were detected similarly in the Lep KO and HFD-treated mice. They showed a similar decrease in the excretion parameters, including the stool number, weight, and water content, while the same pattern was detected in the gastrointestinal motility and intestinal length. A similar decrease in the mucosal layer thickness, muscle thickness, ability for mucin secretion, and expression of water channel (aquaporin 3 and 8) genes was detected in the mid-colon of the Lep KO and HFD-treated mice, but the alteration rate in some levels was greater in the HFD-treated group than the Lep KO mice. On the other hand, the levels of c-kit, nNOS, NSE, and PGP9.5 expression for the enteric neurons and intestitial cells of Cajal (ICC) were remarkably lower in the mid-colon of the HFD-treated mice than in the Lep KO mice, but the level of most proteins in both groups remained lower than those in the control group. A similar alteration pattern in the expression of muscarinic acetylcholine receptors (mAChRs) and serotonin receptors was detected in the Lep KO and HFD-treated mice. These results suggest that most phenotypes for obesity-induced constipation were similarly detected in the Lep KO and HFD-treated mice, but there was a difference in the regulatory function of the enteric nervous system (ENS).

Dysbiosis of Fecal Microbiota in Tg2576 Mice for Alzheimer's Disease during Pathological Constipation

Tg2576 transgenic mice for Alzheimer's disease (AD) exhibited significant phenotypes for neuropathological constipation, but no research has been conducted on the association of the fecal microbiota with dysbiosis. The correlation between fecal microbiota composition and neuropathological constipation in Tg2576 mice was investigated by examining the profile of fecal microbiota and fecal microbiota transplantation (FMT) in 9-10-month-old Tg2576 mice with the AD phenotypes and constipation. Several constipation phenotypes, including stool parameters, colon length, and histopathological structures, were observed prominently in Tg2576 mice compared to the wild-type (WT) mice. The fecal microbiota of Tg2576 mice showed decreases in Bacteroidetes and increases in the Firmicutes and Proteobacteria populations at the phylum level. The FMT study showed that stool parameters, including weight, water content, and morphology, decreased remarkably in the FMT group transplanted with a fecal suspension of Tg2576 mice (TgFMT) compared to the FMT group transplanted with a fecal suspension of WT mice (WFMT). The distribution of myenteric neurons and the interstitial cells of Cajal (ICC), as well as the enteric nervous system (ENS) function, remained lower in the TgFMT group. These results suggest that the neuropathological constipation phenotypes of Tg2576 mice may be tightly linked to the dysbiosis of the fecal microbiota.

What Are the Key Gut Microbiota Involved in Neurological Diseases? A Systematic Review

There is a growing body of evidence highlighting there are significant changes in the gut microbiota composition and relative abundance in various neurological disorders. We performed a systematic review of the different microbiota altered in a wide range of neurological disorders (Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), amyotrophic lateral sclerosis, and stroke). Fifty-two studies were included representing 5496 patients. At the genus level, the most frequently involved microbiota are Akkermansia, Faecalibacterium, and Prevotella. The overlap between the pathologies was strongest for MS and PD, sharing eight genera (Akkermansia, Butyricicoccus, Bifidobacterium, Coprococcus, Dorea, Faecalibacterium, Parabacteroides, and Prevotella) and PD and stroke, sharing six genera (Enterococcus, Faecalibacterium, Lactobacillus, Parabacteroides, Prevotella, and Roseburia). The identification signatures overlapping for AD, PD, and MS raise the question of whether these reflect a common etiology or rather common consequence of these diseases. The interpretation is hampered by the low number and low power for AD, ALS, and stroke with ample opportunity for false positive and false negative findings.

Exercise Training Prevents the Loss of Wall Thickness and Lowers Expression of Alzheimer's Related Proteins in 3xTg Mouse Jejunum

Growing evidence has demonstrated the benefits of regular exercise on cardiovascular, neural, and cognitive function in humans with Alzheimer's disease (AD). However, the consequences of AD on gastrointestinal morphology and the effects of regular exercise, which plays an important role against the development of certain gastrointestinal-related diseases, are still poorly understood. Therefore, to assess the changes in intestinal structure in a mouse model of AD and the impact of exercise, 2-month-old 3xTg-AD male mice were subjected to treadmill running 5 days per week for a period of 5 months. Jejunum from 3xTg-AD mice analyzed by histochemical methods revealed significant alterations in morphology. Compared to age-matched wild-type (WT) mice, villi length and crypt depth were increased, and collagen content of jejunum was elevated in 3xTg-AD mice. Jejunum wall dimensions, expressed as total wall thickness, outer longitudinal thickness, and inner circular thickness were decreased in 3xTg-AD compared to WT. Smooth muscle actin expression in jejunal wall was decreased in 3xTg-AD. Most of these aberrations were improved with exercise. Western blot expression of cyclin dependent kinase 5 (CDK5, involved in neural cell death and hyperphosphorylation of tau), was elevated in 3xTg-AD jejunum. This was associated with a 4-fold increase in tau5 expression. Exercise prevented the increase in expression of CDK5 and tau5. Expression of caspase 3 (an apoptotic marker) was elevated in 3xTg-AD jejunum and exercise prevented this. The results of our study indicate that the abnormalities in jejunum of the 3xTg mouse model of AD were prevented with exercise training.

GSH-AuNP anti-oxidative stress, ER stress and mitochondrial dysfunction in amyloid-beta peptide-treated human neural stem cells

Amyloid-beta (Aβ) peptides have a role in the pathogenesis of Alzheimer's disease (AD) and are thought to promote oxidative stress, endoplasmic reticulum (ER) stress and mitochondrial deficiency, causing neuronal loss in the AD brain. The potential applications of glutathione conjugated gold nanoparticles (GSH-AuNPs) suggest they might have therapeutic value. Several studies have demonstrated that the effects of nanoparticles could provide protective roles in AD. Here, we showed that GSH-AuNPs mediate the viability of human neural stem cells (hNSCs) with Aβ, which was correlated with decreased caspase 3 and caspase 9. Importantly, hNSCs co-treated with GSH-AuNPs were significantly protected from Aβ-induced oxidative stress, as detected using the DCFH-DA, DHE, and MitoSOX staining assays. Furthermore, hNSCs co-treated with GSH-AuNPs were significantly protected from the Aβ-induced reduction in the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and Nrf2 downstream antioxidant target genes (SOD-1, SOD-2, Gpx, Catalase, and HO-1). In addition, GSH-AuNPs rescued the expression levels of ER stress-associated genes (Bip, CHOP, and ASK1) in Aβ-treated hNSCs. GSH-AuNPs normalized ER calcium and mitochondrial cytochrome c homeostasis in Aβ-treated hNSCs. Furthermore, treatment with GSH-AuNPs restored the levels of ATP, D-loop, mitochondrial mass, basal respiration, ATP-linked reparation, maximal respiration capacity, COX activity, mitochondrial membrane potential, and mitochondrial genes (PGC1α, NRF-1 and Tfam) in Aβ-treated hNSCs. Taken together, these findings extend our understanding of the protective effects of GSH-AuNPs against oxidative stress, ER stress and mitochondrial dysfunction in hNSCs with Aβ.

Prevalence of Constipation in Elderly and Its Association With Dementia and Mild Cognitive Impairment: A Cross-Sectional Study

Background

Constipation and dementia have similar epidemiological characteristics. Changes in intestinal flora and characteristics of the brain-gut axis play roles in the pathogeneses of the two diseases, suggesting that there may be a close connection between the two. Most of the studies on constipation in dementia patients have focused on the population with α-synucleinopathies [Parkinson’s disease dementia (PDD), dementia with Lewy bodies (DLB)]. Few studies have reported the prevalence of constipation in all-cause dementia and mild cognitive impairment (MCI) populations.

Objective

To assess the prevalence of constipation in patients with all-cause dementia and MCI subtypes and to explore the association between constipation with dementia and MCI subtypes.

Methods

From May 2019 to December 2019, we conducted a population-based cross-sectional survey. A total of 11,743 participants aged 65 or older from nine cities in China were surveyed. Participants underwent a series of clinical examinations and neuropsychological measurements. Constipation, dementia, MCI and MCI subtype were diagnosed according to established criteria through standard diagnostic procedures.

Results

The overall age- and sex-adjusted prevalence of constipation in individuals aged 65 years and older was 14.8% (95% CI, 14.6–15.0). The prevalence rates of constipation were19.2% (95% CI, 17.3–21.0), 19.1% (95% CI, 16.8–21.5), 14.4% (95% CI, 12.8–15.9), and 13.8% (95% CI, 13.0–14.6) in the dementia, non-amnestic (na)-MCI, amnestic (a)-MCI and normal cognition populations, respectively. Multivariate logistic regression analysis showed that higher prevalence of constipation was associated with dementia (p = 0.0.032, OR = 1.18, 95% CI: 1.02–1.38) and na-MCI (p = 0.003, OR = 1.30, 95% CI: 1.09–1.54).

Conclusion

The present study found a high prevalence of constipation in elderly individuals in China, and higher in patients with dementia and na-MCI.

Dysbiosis of Fecal Microbiota From Complement 3 Knockout Mice With Constipation Phenotypes Contributes to Development of Defecation Delay

Significant phenotypes for constipation were detected in complement 3 (C3) knockout (KO) mice, although no research has been conducted on an association with alteration of gut microbiota. To investigate the effects of dysbiosis on fecal microbiota from C3 KO mice with constipation, the composition of fecal microbiota was characterized in mid-colons of 16-week-old C3 KO mice, and their function for defecation delay development was examined after fecal microbiota transplantation (FMT) of C3 KO mice. Some significant alterations in constipation phenotypes, including stool parameters and histopathological structure, were detected in 16-week-old C3 KO mice compared to those of wild-type (WT) mice. Fecal microbiota of C3 KO mice exhibited decreases in Anaerocolumna, Caecibacterium, Christensenella, Kineothrix, and Oscillibacter populations and increases in Prevotellamassilia, Reuthenibacterium, Prevotella, Eubacterium, Culturomica, Bacteroides, and Muribaculum populations. In FMT study, key stool parameters, including weight and water content, were remarkably declined in a transplanted KO (KFMT) group of antibiotics-induced depletion of microbiota (AiDM)-WT and AiDM-KO mice, and a similar change was observed in fecal morphology. However, intestine length decreased in only the KFMT group of AiDM-WT mice compared with that of AiDM-KO mice. The mucosal layer and muscle thickness were commonly decreased in the KFMT group of AiDM-WT and AiDM-KO mice, and significant alterations in the crypt structure of Lieberkuhn and molecular regulators, including AQP8, C-kit, and 5-HT, were observed in the same group. Taken together, results of the present study indicate that dysbiosis of fecal microbiota from C3 KO mice with constipation phenotypes has a key role in the induction and regulation of defecation delay.

Berberine Improves Behavioral and Cognitive Deficits in a Mouse Model of Alzheimer's Disease via Regulation of β-Amyloid Production and Endoplasmic Reticulum Stress

Alzheimer's disease (AD) is a neurodegenerative disease characterized by β-amyloid (Aβ), neurofibrillary tangles, and neuronal cell death. Aggressive Aβ accumulation accelerates senile plaque formation and perturbs endoplasmic reticulum (ER) function. Aβ accumulation-induced changes stimulate the unfolded protein response (UPR), which can trigger neuronal apoptosis. Protein kinase RNA-like endoplasmic reticulum kinase (PERK), whose activation is stress-dependent, increases the phosphorylation of eukaryotic translation initiation factor-2α (eIF2α). eIF2α promotes the synthesis of β-site APP cleavage enzyme 1 (BACE1), which in turn facilitates Aβ generation and subsequent neuronal apoptosis. In this study, we investigated whether berberine could improve cognitive deficits in the triple-transgenic mouse model of Alzheimer's disease (3 × Tg AD) mice. Our results revealed that berberine treatment may inhibit PERK/eIF2α signaling-mediated BACE1 translation, thus reducing Aβ production and resultant neuronal apoptosis. Further, berberine may have neuroprotective effects, via attenuation of ER stress and oxidative stress. In sum, our study demonstrates the therapeutic potential of berberine for treating AD.

Deficiency of complement component 3 may be linked to the development of constipation in FVB/N-C3em1Hlee /Korl mice

Alterations in complement component 3 (C3) expression has been reported to be linked to several bowel diseases including Crohn's disease, inflammatory bowel disease, and ulcerative colitis; however, the association with constipation has never been investigated. In this study, we aimed to investigate the correlation between C3 regulation and constipation development using a C3 deficiency model. To achieve these, alterations in stool excretion, transverse colon histological structure, and mucin secretion were analyzed in FVB/N-C3em1Hlee /Korl (C3 knockout, C3 KO) mice with the deletion of 11 nucleotides in exon 2 of the C3 gene. The stool excretion parameters, gastrointestinal transit, and intestine length were remarkably decreased in C3 KO mice compared with wild-type (WT) mice, although there was no specific change in feeding behavior. Furthermore, C3 KO mice showed a decrease in mucosal and muscle layer thickness, alterations in crypt structure, irregular distribution of goblet cells, and an increase of mucin droplets in the transverse colon. Mucin secretion was suppressed, and they accumulated in the crypts of C3 KO mice. In addition, the constipation phenotypes detected during C3 deficiency were confirmed in FVB/N mice treated with C3 convertase inhibitor (rosmarinic acid (RA)). Similar phenotypes were observed with respect to stool excretion parameters, gastrointestinal transit, intestine length, alterations in crypt structure, and mucin secretion in RA-treated FVB/N mice. Therefore, the results of the present study provide the first scientific evidence that C3 deficiency may play an important role in the development of constipation phenotypes in C3 KO mice.

Molecular Characterization of Constipation Disease as Novel Phenotypes in CRISPR-Cas9-Generated Leptin Knockout Mice with Obesity

(1) Background: We characterized a novel animal model with obesity-induced constipation because constipation is rarely known in genetically engineered mice (GEM); (2) Methods: The changes in the constipation parameters and mechanisms were analyzed in CRISPR-Cas9-mediated leptin (Lep) knockout (KO) mice from eight to 24 weeks; (3) Results: Significant constipation phenotypes were observed in the Lep KO mice since 16 weeks old. These mice showed a significant decrease in the gastrointestinal motility, mucosal layer thickness and ability for mucin secretion as well as the abnormal ultrastructure of Lieberkühn crypts in the transverse colon. The density or function of the enteric neurons, intestinal Cajal cells (ICC), smooth muscle cells, and the concentration of gastrointestinal (GI) hormones for the GI motility were remarkably changed in Lep KO mice. The downstream signaling pathway of muscarinic acetylcholine receptors (mAChRs) were activated in Lep KO mice, while the expression of adipogenesis-regulating genes were alternatively reduced in the transverse colon of the same mice; (4) Conclusions: These results provide the first strong evidence that Lep KO mice can represent constipation successfully through dysregulation of the GI motility mediated by myenteric neurons, ICC, and smooth muscle cells in the transverse colon during an abnormal function of the lipid metabolism.