Qing Su

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common chronic liver disease worldwide. Although gut microbiota dysbiosis and aberrant bile acid metabolism are central to MASLD pathogenesis, the critical keystone species and precise molecular mechanisms remain elusive. Here, we performed an integrated analysis of 14 public 16S rRNA datasets (275 controls, 352 patients), combining multi-method differential abundance screening, machine learning, and network analysis to pinpoint MASLD-specific microbial signatures. We further validated the therapeutic potential of candidate secondary bile acids (SBAs) in a HepG2 steatosis model. MASLD patients displayed significantly reduced microbial diversity and a distinct community structure. Bifidobacterium longum emerged as the top discriminative putative keystone species, showing marked depletion and reduced network centrality. The secondary bile acid biosynthesis pathway was downregulated and positively correlated with B. longum abundance. Mechanistically, in vitro assays demonstrated that two SBAs, 23-nor-deoxycholic acid (23-NCA) and sodium taurodeoxycholate (TDCA-Na), alleviated hepatocellular lipid accumulation and inflammation, concomitant with TGR5 upregulation, AMPK activation, and p38 MAPK inhibition. In conclusion, depletion of the putative keystone species B. longum is associated with downregulated predicted genomic potential for secondary bile acid biosynthesis, while candidate SBAs protect hepatocytes in association with the activation of the hepatic TGR5–AMPK signaling axis in vitro. These findings offer a mechanistic basis for therapeutic strategies targeting the microbiota-bile acid axis.

BACKGROUND: Hypertension is a leading risk factor for all-cause mortality worldwide, affecting ≈1.3 billion people. Imbalanced gut microbiota contributes to blood pressure elevation. We recently reported sex differences in the responses of gut microbiota to environmental stimuli, such as salt, with male gut microbiota being more vulnerable to induce high blood pressure than female microbiota. In this study, we investigated the mechanisms by which gut microbiota regulate blood pressure in a sex-dependent manner. METHODS: Antibiotic treatment, gonadectomy, sex hormone replenishment, and treatment with trimethylamine N-oxide or its blocker were performed in male and female spontaneously hypertensive rats. RESULTS: We observed sex differences in gut microbiota composition and sex-specific blood pressure responses to antibiotic treatment in pubertal spontaneously hypertensive rats. In gonadectomized rats treated with sex hormones, we found that the male sex hormone dihydrotestosterone elevated blood pressure, reshaped gut microbiota, and increased levels of microbiota-derived metabolites, trimethylamine and treatment with trimethylamine N-oxide. The accumulation of treatment with trimethylamine N-oxide in plasma and the paraventricular nucleus of the hypothalamus was associated with inflammation and sympathetic activation. CONCLUSIONS: These findings underscore the mechanistic role of dihydrotestosterone in gut microbiota-mediated sex-specific blood pressure regulation and suggest that targeting the gut microbiota-treatment with trimethylamine N-oxide pathway may provide new therapeutic strategies for male hypertension.

Objects: Taurine exhibits protective effects in the context of cardiovascular pathophysiology. A range of evidence suggests that hypertension activates inflammatory responses and oxidative stress in the paraventricular nucleus (PVN), elevating the arterial tone and sympathetic activity, while it induces gut–brain axis dysfunction in the context of hypertension. However, the mechanism underlying taurine’s anti-hypertensive effects via the gut–brain axis remains unclear. Method: Male spontaneously hypertensive rats (SHRs) were administered 3% taurine in their drinking water for eight weeks, with their arterial pressure measured weekly. Molecular techniques were employed to investigate taurine’s effects on the hypertensive gut and PVN. Additionally, 16S rRNA gene sequencing was used to analyze the gut microbiota composition, and untargeted metabolomics was applied to assess the fecal metabolites following taurine supplementation. Results: Taurine supplementation not only reduced the blood pressure, sympathetic activity, and inflammatory and oxidative stress in the PVN but also improved the cardiac pathology and microbiota composition while alleviating gut inflammation in hypertensive rats. The untargeted metabolite analysis indicated that the primary effect of the taurine intervention in SHRs was exerted on tryptophan metabolism. The levels of serum metabolites such as kynurenine, L-tryptophan, serotonin (5-HT), and 5-hydroxyindole-3-acetic acid (5-HIAA) were altered in hypertensive rats following taurine treatment. Conclusions: Taurine supplementation restored the microbiota balance, strengthened the mucosal barrier, reduced intestinal inflammation, and stimulated tryptophan metabolism. The metabolites derived from the gut microbiota likely crossed the brain barrier and reached the paraventricular nucleus, thereby reducing the inflammatory responses and oxidative stress in the PVN via gut–brain communication, leading to decreased sympathetic nerve activity and blood pressure in the studied hypertensive rats.

Background: Numerous studies have indicated that a high salt diet inhibits brain Na⁺/K⁺-ATPase (NKA) activity, and affects oxidative stress and inflammation in the paraventricular nucleus (PVN). Furthermore, Na⁺/K⁺-ATPase alpha 2-isoform (NKA α2) may be a target in the brain, taking part in the development of salt-dependent hypertension. Therefore, we hypothesized that NKA α2 regulates oxidative stress and inflammation in the PVN in the context of salt-induced hypertension. Methods: Part I: We assessed NKA subunits (NKA α1, NKA α2, and NKA α3), Na⁺/K⁺-ATPase activity, oxidative stress, and inflammation in a high salt group (8% NaCl) and normal salt group (0.3% NaCl). Part II: NKA α2 short hairpin RNA (shRNA) was bilaterally microinjected into the PVN of salt-induced hypertensive rats to knockdown NKA α2, and we explored whether NKA α2 regulates downstream signaling pathways related to protein kinase C γ (PKC γ)-dependent oxidative stress and toll-like receptor 4 (TLR4)-induced inflammation in the PVN to promote the development of hypertension. Results: High salt diet increased NKA α1 and NKA α2 protein expression in the PVN but had no effect on NKA α3 compared to the normal salt diet. Na⁺/K⁺-ATPase activity and ADP/ATP ratio was lower, but NAD(P)H activity and NF-κB activity in the PVN were higher after a high salt diet. Bilateral PVN microinjection of NKA α2 shRNA not only improved Na⁺/K⁺-ATPase activity and ADP/ATP ratio but also suppressed PKC γ-dependent oxidative stress and TLR4-dependent inflammation in the PVN, thus decreasing sympathetic activity in rats with salt-induced hypertension. Conclusions: NKA α2 in the PVN elicits PKC γ/Rac1/NAD (P)H-dependent oxidative stress and TLR4/MyD88/NF-κB-induced inflammation in the PVN, thus increasing MAP and sympathetic activity during the development of salt-induced hypertension.

Inflammation has been implicated in the development of cardiovascular disease. We determined whether nod-like receptor with pyrin domain containing 3 (NLRP3) involved in the process of prehypertension, central blockade of NLRP3 decreased inflammation reaction, regulated neurohormonal excitation, and delayed the progression of prehypertension. Prehypertensive rats were induced by 8% salt diet. The rats on high-salt diet for 1 month were administered a specific NLRP3 blocker in the hypothalamic paraventricular nucleus (PVN) for 4 weeks. ELISA, western blotting, immunohistochemistry, and flow cytometry were used to measure NLRP3 cascade proteins, pro-inflammation cytokines (PICs), chemokine ligand 2 (CCL2), C-X-C chemokine receptor type 3 (CXCR3), vascular cell adhesion molecule 1 (VCAM-1), neurotransmitters, and leukocytes count detection, respectively. NLRP3 expression in PVN was increased significantly in prehypertensive rats, accompanied by increased number of microglia, CD4+, CD8+ T cell, and CD8+ microglia. Expressions of PICs, CCL2, CXCR3, and VCAM-1 significantly increased. The balance between 67-kDa isoform of glutamate decarboxylase (GAD67) and tyrosine hydroxylase (TH) was damaged. Plasma norepinephrine (NE) in prehypertensive rats was increased and gamma-aminobutyric acid (GABA) was reduced. NLRP3 blockade significantly decreased blood pressure, reduced PICs, CCL2, VCAM-1 expression in PVN, and restored neurotransmitters. Blood pressure and inflammatory markers were upregulated after termination of central blockage NLRP3. Salt-induced prehypertension is partly due to the role of NLRP3 in PVN. Blockade of brain NLRP3 attenuates prehypertensive response, possibly via downregulating the cascade reaction triggered by inflammation and restoring the balance of neurotransmitters.

Heart failure (HF) is a serious cardiovascular disease and is characterized by exaggerated sympathetic activity. In this paper, we review these limited studies, with particular emphasis on examining the role of the paraventricular nucleus (PVN) in the neurohumoral excitation in HF. The PVN is an important neuroendocrine and preautonomic output nucleus, and is considered as the important central site for integration of sympathetic nerve activity. Accumulating evidences demonstrate that a number of neurohumoral processes are involved in the pathophysiology of HF, such as renin-angiotensin system (RAS), proinflammatory cytokines (PICs), neurotransmitters, and reactive oxygen species (ROS). Recent studies about neurohumoral regulation indicate that angiotensin II type1 receptor (AT1-R) is the important product mediated by cytoplasmic nuclear factor-kappa B (NF-κB) which is up-regulated along with elevated PICs and angiotensin II (ANG II) in the PVN of HF rats. These findings suggest that the NF-κB mediates the cross-talk between RAS and PICs in the PVN in HF. The further studies indicate that the interaction between AT1-R and NF-κB in the PVN contributes to oxidative stress and sympathoexcitation by modulating neurotransmitters in heart failure, and the superoxide activates NF-κB in the PVN and contributes to neurohumoral excitation. In conclusion, the neurohumoral excitation in HF is based on the interaction of RAS, PICs, ROS, NF-κB and neurotransmitters in the PVN; and the activated NF-κB in the PVN modulates the neurotransmitters and contributes to sympathoexcitation in rats with heart failure.