How to Delay Non-Alcoholic Fatty Liver Disease?

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How to Delay Non-Alcoholic Fatty Liver Disease?

How to Delay Non-Alcoholic Fatty Liver Disease?

Recent studies have shown that “mitochondria” play a role in the development of various diseases such as tumors, cardiovascular diseases, neurodegenerative diseases, diabetes, and autoimmune diseases, making it one of the hot research topics.

Additionally, the number of applications for the National Natural Science Foundation related to “intestinal bacteria” has been steadily increasing in recent years. So, how can these two major research areas be combined to generate new insights?

We bring you an interpretation of an article from the research team at the University of León in Spain. The team demonstrated that targeting mitochondrial dysfunction may delay the progression of non-alcoholic fatty liver disease (NASH) by improving the gut-liver axis.

The study, titled “Enhanced mitochondrial activity reshapes a gut microbiota profile that delays NASH progression,” was published in the Hepatology journal.

How to Delay Non-Alcoholic Fatty Liver Disease?

I. Background of the Study

Previous research has indicated that mitochondrial dysfunction, oxidative stress, and changes in the gut microbiota can promote the progression of NASH. Moreover, studies have shown that mitochondrial function and the gut microbiota may mutually regulate each other. Therefore, targeting mitochondrial dysfunction could act as a firewall to maintain a normal gut-liver axis, thus delaying or even preventing the progression of NASH.

MCJ, a methylated controlled J protein, is a mitochondrial protein associated with the function of mitochondrial electron transport chain complex I and inhibits its function. Research has reported that the lack of MCJ can disrupt the mutual regulation between host mitochondria and the gut microbiota during ulcerative colitis, affecting the severity of the disease. Therefore, MCJ gene knockout mice provide a reliable model for studying the impact of liver mitochondria on gut microbiota imbalance and gut-liver axis changes in NASH.

The aim of this study was to assess the impact of MCJ deficiency on a NASH diet mouse model, considering changes in the composition of the gut microbiota as a driving force. Furthermore, the researchers aimed to determine whether the observed liver-protective phenotype in MCJ knockout (MCJ-KO) mice could be transferred to germ-free (GF) mice through cecal microbiota transplantation (CMT).

II. Research Methods

Model A: Selection of Donor Mice

Wild-type (WT) and MCJ-KO male mice with a C57BL/6 background were raised in the CIC bioGUNE animal facility. The animals were fed a control diet or a high-fat diet (CDA-HFD) containing 60% kcal fat, L-amino acids, 0.1% methionine, and lacking choline for 6 weeks. One mouse from each experimental group in Model A was selected as the donor of gut microbiota.
Model B: Gut Microbiota Transplantation

Six-week-old GF male C57BL/6J mice were raised in a specific pathogen-free animal facility at the University of León. After an adaptation period, 100μl of donor cecal content was transplanted once by oral gavage to the animals. Based on four different types of donor-transplanted microbiota and diet, the mice were divided into eight groups.
Sample Collection

Liver, intestine, brown adipose tissue, epididymal white adipose tissue (WAT), feces, and cecal content were collected from mice in Models A and B, immediately immersed in liquid nitrogen, and stored at -80°C for analysis. Blood was collected and centrifuged to obtain plasma.

III. Research Results

After 6 weeks of feeding with CDA-HFD, mice showed increased intestinal permeability, and serum fluorescein isothiocyanate (FITC)-dextran levels increased compared to the control group. Moreover, FITC-dextran permeability was significantly reduced in MCJ-KO mice fed with CDA-HFD, suggesting a potential protective effect.

Analysis of tight junction proteins showed that mRNA levels of Occludin and Zonula occludens 1 (Zo-1) were significantly decreased, indicating improved intestinal barrier integrity in mice lacking MCJ, which could prevent bacterial and microbial product translocation. In summary, the lack of MCJ can protect intestinal barrier integrity, reduce bacterial product translocation, and regulate inflammation in NASH.

To investigate whether the protective effect observed in CDA-HFD-fed MCJ-KO mice is attributed to specific microbial community features, the researchers performed CMT on GF mice and fed them a CDA-HFD for 3 weeks. Histological evaluation showed that CDA-HFD diet led to early non-alcoholic fatty liver disease (NAFLD) stages in transplanted GF mice, with increased liver fat deposition, early inflammation, and ballooning. Furthermore, the expression of pro-inflammatory factors such as Ccr5, Il-1β, Il-6, and Tnf was significantly downregulated after CMT from MCJ-KO donors. In conclusion, GF mice receiving CMT from MCJ-KO donors and fed with CDA-HFD exhibited a slowed progression of NASH. Therefore, the liver-protective effect observed in MCJ-KO mice can be transferred through gut microbiota transplantation.

Next, the authors conducted histological and gene expression studies in CDA-HFD-fed GF mice to determine the effects of CMT from MCJ-KO donors on intestinal barrier integrity and the gut-liver axis. Histological analysis of ileum tissue showed no significant differences. However, relative expression of Claudin-1 and Zo-1 increased in GF mice from MCJ-KO donors, along with decreased liver mRNA levels of Nlrp3 and Tlr-4. Thus, the ability of MCJ deficiency to counteract these gene upregulations was observed after CMT, confirming the results obtained in Model A.

Analyzing the operational taxonomic units (OTU) at the genus level for each donor to recipient group in GF mice (relative abundance >0.01%) through Venn diagrams, it was found that the gut microbiota profile was associated with the MCJ-KO genotype and transferred to CDA-HFD-fed GF mice through CMT.

The lack of MCJ can enhance lipid β-oxidation and improve liver fat deposition in a diet-induced NAFLD model. Therefore, the purpose of the study was to confirm the same effect in MCJ-KO mice (Model A). The results showed that in CDA-HFD-fed MCJ-KO mice, the measurement of liver NAD+, NADH, and their ratio demonstrated a significant increase in the availability of NAD+. Further research revealed that the increased availability of NAD+ in the liver of MCJ-KO mice could be transferred through CMT, thereby increasing liver fatty acid oxidation and reducing NAS scores and hepatic lipid accumulation.

IV. Conclusion

In summary, this study suggests that specific microbial community features from MCJ-deficient mice and their specific metabolism can delay the progression of NASH in a diet-induced NAFLD model.

Moreover, this liver-protective effect can be transferred through gut microbiota transplantation.

Currently, there are no effective treatments for NASH, but its prevalence is increasing year by year, severely affecting patients’ lives.

Finding effective alternative methods is urgently needed. This study indicates that the lack of MCJ and the improved mitochondrial activity it leads to establish a unique protective microbial community, capable of slowing the progression of the disease in a rigorous NASH lean diet model.

Overall, these results emphasize the importance of mitochondrial-microbiota interactions in NASH and suggest a treatment strategy based on microbiota transplantation, paving the way for different approaches.