ApoE isoform- and microbiota-dependent progression of neurodegeneration in a mouse model of tauopathy

Tau-mediated neurodegeneration is a hallmark of Alzheimer's disease. Primary tauopathies are characterized by pathological tau accumulation and neuronal and synaptic loss. Apolipoprotein E (ApoE)-mediated neuroinflammation is involved in the progression of tau-mediated neurodegeneration, and emerging evidence suggests that the gut microbiota regulates neuroinflammation in an APOE genotype-dependent manner. However, evidence of a causal link between the microbiota and tau-mediated neurodegeneration is lacking. In this study, we characterized a genetically engineered mouse model of tauopathy expressing human ApoE isoforms reared under germ-free conditions or after perturbation of their gut microbiota with antibiotics. Both of these manipulations reduced gliosis, tau pathology, and neurodegeneration in a sex- and ApoE isoform-dependent manner. The findings reveal mechanistic and translationally relevant interrelationships between the microbiota, neuroinflammation, and tau-mediated neurodegeneration.

Increased Type I interferon signaling and brain endothelial barrier dysfunction in an experimental model of Alzheimer's disease

Blood-brain barrier (BBB) dysfunction is emerging as a key pathogenic factor in the progression of Alzheimer's disease (AD), where increased microvascular endothelial permeability has been proposed to play an important role. However, the molecular mechanisms leading to increased brain microvascular permeability in AD are not fully understood. We studied brain endothelial permeability in female APPswe/PS1∆E9 (APP/PS1) mice which constitute a transgenic mouse model of amyloid-beta (Aβ) amyloidosis and found that permeability increases with aging in the areas showing the greatest amyloid plaque deposition. We performed an unbiased bulk RNA-sequencing analysis of brain endothelial cells (BECs) in female APP/PS1 transgenic mice. We observed that upregulation of interferon signaling gene expression pathways in BECs was among the most prominent transcriptomic signatures in the brain endothelium. Immunofluorescence analysis of isolated BECs from female APP/PS1 mice demonstrated higher levels of the Type I interferon-stimulated gene IFIT2. Immunoblotting of APP/PS1 BECs showed downregulation of the adherens junction protein VE-cadherin. Stimulation of human brain endothelial cells with interferon-β decreased the levels of the adherens junction protein VE-cadherin as well as tight junction proteins Occludin and Claudin-5 and increased barrier leakiness. Depletion of the Type I interferon receptor in human brain endothelial cells prevented interferon-β-induced VE-cadherin downregulation and restored endothelial barrier integrity. Our study suggests that Type I interferon signaling contributes to brain endothelial dysfunction in AD.

Microbiome Medicine: Microbiota in Development and Management of Cardiovascular Diseases

The gut microbiome consists of the trillions of bacteria and other microbes whose metabolic activities and interactions with the immune system go beyond the gut itself. We are all aware that bacteria and other microorganisms have a significant impact on our health. Also, health of the bacteria directly reflects the health status of the body where they reside. Eventually, alterations in the microbiome at different sites of a body is associated with many different diseases such as obesity, IBD, malnutrition, CVD, etc. Microbiota directly or indirectly affects the heart with formation of plaques in the blood vessels and cell wall become prone to the lesion development. This ultimately leads to heighten the overall inflammatory status via increased bacterial translocation. Metabolites derived from the gut microbial metabolism of choline, phosphatidylcholine, and L-carnitine directly contribute to CVD pathology. These dietary nutrients have trimethylamine (TMA) moiety, which participates in the development of atherosclerotic heart disease. The objective of this review was to examine various metabolic pathways regulated by the gut microbiome that appear to alter heart function and lead to the development and progression of cardiovascular diseases, as well as how to target the gut microbiome for a healthier heart. In this review, we had also discussed about various clinical drugs having crosstalk between microbiota and heart and clinical trials for gut-heart microbiome.

Alcohol Feeding in Mice Promotes Colonic Hyperpermeability and Changes in Colonic Organoid Stem Cell Fate

BACKGROUND

Alcohol increases intestinal permeability to proinflammatory microbial products that promote liver disease, even after a period of sobriety. We sought to test the hypothesis that alcohol affects intestinal stem cells using an in vivo model and ex vivo organoids generated from jejunum and colon from mice fed chronic alcohol.

METHODS

Mice were fed a control or an alcohol diet. Intestinal permeability, liver steatosis-inflammation, and stool short-chain fatty acids (SCFAs) were measured. Jejunum and colonic organoids and tissue were stained for stem cell, cell lineage, and apical junction markers with assessment of mRNA by PCR and RNA-seq. ChIP-PCR analysis was carried out for Notch1 using an antibody specific for acetylated histone 3.

RESULTS

Alcohol-fed mice exhibited colonic (but not small intestinal) hyperpermeability, steatohepatitis, and decreased butyrate/total SCFA ratio in stool. Stem cell, cell lineage, and apical junction marker staining in tissue or organoids from jejunum tissue were not impacted by alcohol. Only chromogranin A (Chga) was increased in jejunum organoids by qPCR. However, colonic tissue and organoid staining exhibited an alcohol-induced significant decrease in cytokeratin 20+  (Krt20+) absorptive lineage enterocytes, a decrease in occludin and E-cadherin apical junction proteins, an increase in Chga, and an increase in the Lgr5 stem cell marker. qPCR revealed an alcohol-induced decrease in colonic organoid and tissue Notch1, Hes1, and Krt20 and increased Chga, supporting an alteration in stem cell fate due to decreased Notch1 expression. Colonic tissue ChIP-PCR revealed alcohol feeding suppressed Notch1 mRNA expression (via deacetylation of histone H3) and decreased Notch1 tissue staining.

CONCLUSIONS

Data support a model for alcohol-induced colonic hyperpermeability via epigenetic effects on Notch1, and thus Hes1, suppression through a mechanism involving histone H3 deacetylation at the Notch1 locus. This decreased enterocyte and increased enteroendocrine cell colonic stem cell fate and decreased apical junctional proteins leading to hyperpermeability.

Circadian rhythm disruption promotes alcohol-induced liver and brain injury

Alcoholic liver disease (ALD) progression to cirrhosis and development of hepatic encephalopathy (HE) are characterized by hepatic and brain inflammation involving innate immune cells. Identifying the risk factors and immune mechanisms involved in susceptibility to liver and brain injury are significant unmet needs. Circadian rhythm disruption promotes alcohol-induced liver pathology. We aim to investigate whether circadian rhythm disruption also primes brain inflammation by impacting trafficking and inflammatory potential of recruited and resident mononuclear phagocytes (MP).

Alcohol (EtOH) is delivered to C57BL/6 mice per a modified NIAAA model of alcoholic liver disease whereby chronic alcohol consumption (20% EtOH v/v in drinking water, 4 wks (Meadows-Cook diet)) is combined with three once daily binges of alcohol. Tissue was assessed via H&E and IHC for α-smooth muscle actin (αSMA) and collagen I (Col I) (liver) and allograft inflammatory factor 1 (Iba-1) (brain). All features associated with human alcoholic liver injury including steatosis, hepatic inflammation and early fibrogenesis were present. Brain mononuclear phagocytes analysed by flow cytometry revealed an increase in recruited and resident MP in response to the alcohol treatment. Moreover, in the steady-state, hepatic and brain MP populations demonstrate circadian oscillations.

Thus, circadian rhythm disruption may modulate alcohol-induced alterations in mononuclear phagocyte trafficking and function similarly in brain and liver.

Alterations in lysosomal and proteasomal markers in Parkinson's disease: relationship to alpha-synuclein inclusions

We explored the relationship between ubiquitin proteasome system (UPS) and lysosomal markers and the formation of alpha-synuclein (alpha-syn) inclusions in nigral neurons in Parkinson disease (PD). Lysosome Associated Membrane Protein 1(LAMP1), Cathepsin D (CatD), and Heat Shock Protein73 (HSP73) immunoreactivity were significantly decreased within PD nigral neurons when compared to age-matched controls. This decrease was significantly greater in nigral neurons that contained alpha-syn inclusions. Immunoreactivity for 20S proteasome was similarly reduced in PD nigral neurons, but only in cells that contained inclusions. In aged control brains, there is staining for alpha-syn protein, but it is non-aggregated and there is no difference in LAMP1, CatD, HSP73 or 20S proteasome immunoreactivity between alpha-syn positive or negative neuromelanin-laden nigral neurons. Targeting over-expression of mutant human alpha-syn in the rat substantia nigra using viral vectors revealed that lysosomal and proteasomal markers were significantly decreased in the neurons that displayed alpha-syn-ir inclusions. These findings suggest that alpha-syn aggregation is a key feature associated with decline of proteasome and lysosome and support the hypothesis that cell degeneration in PD involves proteosomal and lysosomal dysfunction, impaired protein clearance, and protein accumulation and aggregation leading to cell death.