Paratypoides faecalices of the intestines alleviate cardiovascular disease by promoting the degradation of branched-chain amino acids

Cardiovascular disease (CVD) is becoming increasingly prevalent worldwide, causing more than 17 million deaths
each year.
Atherosclerosis is characterized by plaque formation in the vessel wall, endothelial dysfunction, and inflammation of the arterial wall and is the main cause of
CVD.
The pathogenesis of atherosclerosis is complex and involves chronic inflammation, stromal changes, and dyslipidemia
.
Obesity, smoking, diabetes, hypertension, intestinal dysbiosis, sleep disturbances, physical inactivity, environmental stress, and family history are all defined as risk factors
for the development and progression of atherosclerosis.
At present, the clinical treatment of atherosclerosis mainly includes lipid- or hypoglycemic drugs, anti-inflammatory drugs and changes to a healthier lifestyle
.

In recent years, the rapid development of omics technology has expanded our understanding of atherosclerosis, and the key role of the gut microbiota in CVD is being explored and elucidated
.
Some metabolites of intestinal microbial origin show anti-atherosclerotic or pro-atherosclerotic effects
.
For example, short-chain fatty acids (SCFAs) and secondary bile acids improve atherosclerosis, while another example is trimethylamine-N-oxide derived from intestinal trimethylamine, which has been shown to accelerate the formation
of atherosclerotic lesions.
However, there are still many unknown associations between intestinal flora and CVD, and studying the effect of intestinal flora on CVD will help develop anti-atherosclerotic therapies
that target intestinal flora.

On October 17, 2022, the Liu Hongwei/Liu Shuangjiang team of the Institute of Microbiology of the Chinese Academy of Sciences published an article entitled "Gut Parabacteroides merdae protects against cardiovascular damage by enhancing branched-chain amino acid catabolism" in Nature Metabolism.
Parabacteroides faecalices merdae (P.
faecals) was found in the intestine.
merdae) porA gene can degrade branched-chain amino acids (BCAAs) into SCFAs, reduce the level of BCAAs in the intestine and plasma, reduce the activity of mTORC1 pathway and IgA level of arterial plaque macrophages, and improve the symptoms of atherosclerosis in
mice.
This study revealed the important role of intestinal microbiota-driven BCAA catabolism in maintaining cardiovascular health, providing a new target for intestinal
microbiota-based anti-atherosclerotic therapy.

GMD relieves atherosclerosis in ApoE knockout mice on a high-fat diet

Ganoderma lucidum heteroterpene derivatives (GMD) have the effect of targeting the intestinal flora to alleviate hyperlipidemia and obesity, but the mechanism is not clear
.
To explore whether GMD relieves atherosclerosis, the authors fed ApoE knockout mice a high-fat diet to induce atherosclerosis, and then treated the mice with GMD (5 mg/kg and 10 mg/kg) and atorvastatin for 9 weeks
, respectively.
The results showed that GMD significantly improved total cholesterol, LDL, cholesterol, total triglycerides and free fatty acids in mice
.
GMD mice also had significantly reduced
plasma levels of ox-LDL, MDA, HS-CRP, LPS and inflammatory factors.
Ultrasound testing showed that GMD significantly improved aortic arch thickness and blood flow
.
Pathological examination showed that the area of aortic root lesions and common aortic lesions in the GMD group was significantly reduced, while the collagen content of aortic plaque increased
.
In summary, GMD has an anti-atherosclerotic effect
.

GMD can modulate the gut flora of high-fat diet ApoE knockout mice

Previous research by the authors has shown that GMD is a powerful inhibitor of α-glucosidase that delays the breakdown of carbohydrates in the gut, alters the distribution of carbohydrates in the digestive tract, and regulates the modification
of gut microbes.

In this study, the authors analyzed the effect of GMD on the gut microbiome of ApoE knockout mice on a high-fat diet by 16S rRNA sequencing, and found that P.
Species such as merdae, Bacteroides acidifacios and Bacteroides testinalis differ significantly in
composition and abundance.
Functional analysis showed that BCAA degradation and amino acid metabolism were significantly enhanced
in the intestinal flora of mice in the GMD treatment group.
Abundance analysis showed that P.
Merdae was 420 times more abundant than the control, the largest
variation at the species level.
Analysis based on two gut microbiota validation cohorts showed that P.
vD patients compared to healthy controls.
The abundance of merdae was significantly reduced, while BCAAs were higher
.
More importantly, statin therapy could not alter P.
Abundance of merdae
.
In summary, P.
merdae may be a key factor
in mediating GMD to relieve atherosclerosis.

P.
merdae relieves atherosclerosis in high-fat diet ApoE knockout mice

To further explore P.
The role of merdae in relieving atherosclerosis, the author will P.
merdae, high-temperature inactivated P.
Merdae or PBS gave gavage
to ApoE knockout mice on a high-fat diet for 4 weeks.
On day 3 after 4 weeks of treatment, P.
merdae mice in feces.
The content of merdae was significantly increased, and the body weight, plasma TC level, total TG level and LDL-C level of mice were improved.
P.
merdae treatment also significantly reduced the area of aortic root lesions, fat deposition in plaque area and necrotic core area of mice, and increased the level of plaque collagen.
P.
merdae-treated mice also had reduced
plasma LPS, ox-LDL, hs-CRP, and hepatic steatosis levels.
And the high-temperature inactivated P.
Merdae had no effect
on body weight, hyperlipidaemia, and lesion size.
16S rRNA sequencing found that, as with GMD treatment, P.
merdae gavage significantly increased the abundance of Akkermansia and Parabacteroides in the gut of high-fat diet ApoE knockout mice, enhancing the BCAA degradation pathway
.
This indicates that P.
Merdae relieves atherosclerosis
.

P.
merdae promotes the degradation of BCAAs in the mouse intestine

BCAAs are known to be converted into branched-chain short-chain fatty acids (BSCFAs)
in the gut.
The authors found that GMD or P.
The levels of BCAAs in feces and plasma of merdae-treated mice were reduced, while the levels of BSCFAs (including isobutyric acid, isovaleric acid, and 2-methylbutyric acid) in feces were significantly increased, indicating that GMD and P.
Merdae promotes the degradation
of BCAAs in the gut.

To confirm P.
Merdae's ability to decompose BCAAs, the authors cultured in vitro with yeast extract, peptone, and fatty acid (YCFA) media, and BSCFAs
such as isobutyrate, isovalerate, and 2-methylbutyric acid were detected in the medium 24 hours after culture.
This indicates that P.
Merdae has the ability
to convert BCAAs into BSCFAs.
To determine P.
The authors performed a pangenomic analysis using gutSMASH to identify a homologous gene that can catalyze BCAAs into the porA gene
of BSCFAs.
Further, the authors construct a P.
porA deficiency.
The merdae mutant strain (PMΔPorA), GC-MS analysis confirmed that PMΔPorA was unable to convert BCAAs into BSCFAs
.
In the validation cohort, CVD patients had significantly lower
levels of P.
merdae and porA genes compared to healthy controls.
This indicates that P.
The porA gene in merdae plays a role
in converting BCAAs into BSCFAs.

Next, to test whether porA gene-dependent BCAA degradation is P.
A key factor in merdae's anti-atherosclerotic effect, the authors transplanted either the PMΔPorA strain or wild-type strain (PMWT) into ApoE knockout mice
on a high-fat diet.
Experiments showed that the deletion of the porA gene did not affect P.
Merdae's colonization ability, but as predicted, plasma and fecal BCAAs levels in mice in the PMΔPorA group were much higher than in the PMWT group, and the PMΔPorA strain did not improve lipid levels, inflammation levels, and atherosclerosis symptoms
in the mice.
It is worth noting that there was no difference
in the expression levels of BCAA key catabolic genes BCAT2, BCKD E1α, BCKD E1β, BCKD E2 and PP2Cm in liver, fat and muscle between PMΔPorA group and PMWT group.
This showed that the porA of P.
merdae is a key gene
to promote intestinal BCAA catabolism and improve atherosclerosis in mice.

P.
merdae inhibits the mTORC1 signaling pathway

Elevated plasma BCAAs are positively correlated with insulin resistance, and dietary restriction of BCAAs may improve obesity and insulin sensitivity
.
In this study, the authors observed that ApoE-knockout mice on a high-fat diet were transplanted with wild-type P.
There was an improvement in hyperglycemia and glucose tolerance after merdae, whereas transplantation of PMPorA did not
.
Overactivation of the mTORC1 pathway is associated with
atherosclerosis and insulin resistance.
BCAAs are mTORC1 agonists, and supplementation with BCAAs activates the mTORC1 pathway, exacerbating inflammation and oxidative stress
in endothelial cells.

The author is interested in wild-type P.
Immunofluorescence staining of mouse aortic roots in merdae group and PMΔPorA group compared the activation of mTORC1 pathway in atherosclerotic plaque macrophages, and found that P.
Mice in the merdae group showed lower levels of
S6 phosphorylation.
This suggests that the BCAA-mTORC1 pathway mediates P.
Merdae anti-atherosclerosis
.
In addition, the authors found wild-type P.
Plaque macrophages in merdae-treated mice secreted significantly lower levels of IgA than PMΔPorA-treated mice, confirming that previously reported BSCFAs regulate IgA secretion
.

summary

Obesity, dyslipidemia, and bowel dysregulation are cardiovascular disease-related factors
.
GMD has been shown to alleviate obesity and hyperlipidemia
by modulating the gut microbiota of obese mice.
In this study, the authors found that GMD prevented obesity-related atherosclerosis
by increasing the abundance of parabacteria in the gut and enhancing branched-chain amino acid catabolism.
16S rRNA sequencing found that GMD could significantly increase P.
Abundance of merdae
.
Transplant P.
Merdae can also enhance intestinal BCAA degradation and relieve atherosclerosis
.
Mechanically, the porA gene in P.
merdae can degrade BCAAs into SCFAs, reduce the level of BCAAs in the intestine and plasma, reduce the activity of mTORC1 pathway and IgA level of arterial plaque macrophages, and improve the symptoms of atherosclerosis in
mice.
After knocking out porA, P.
merdae does not relieve atherosclerosis
.
This study has discovered a new mechanism by which intestinal flora regulates CVD, providing a new target for CVD treatment
.

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