In recent years, the gut microbiota has been increasingly recognized for its influence on various central nervous system diseases mediated by microglia, yet the underlying mechanisms remain unclear. As key metabolites of the gut microbiota, short-chain fatty acids (SCFAs) have emerged as a focal point in understanding microglia-related interactions. In this review, we further refine the connection between the gut microbiota and microglia by introducing the concept of the “SCFAs-microglia” pathway. We summarize current knowledge on this pathway, recent discoveries regarding its role in neurological diseases, and potential pharmacological strategies targeting it. Finally, we outlined the current challenges and limitations in this field of research. We hope this review provides new insights into the role of the gut microbiota in neuroimmune regulation.

Ulcerative colitis (UC) has attracted much attention for its negative influence on quality of life and increased risk of colorectal cancer. Chemical and biological drugs are currently the usual treatment for UC. These drugs always induce severe side effects, or patients might become resistant to these therapies. Therefore, new therapeutic options for UC are urgently needed. In this study, we discovered the inhibitory activity of the intestinal tryptophan metabolite indole-3-carboxaldehyde (3-IAld) in dextran sulfate sodium salt (DSS)-induced UC mice by targeting the TLR4/NF-κB/p38 signaling pathway. This compound effectively protected against colon length shortening and damage induced by DSS in the colon, notably reducing the severity of inflammation. The production of inflammatory factors of TNF-α, IL-6, and IL-1β was significantly attenuated when treating with 3-IAld in vivo and vitro. This might be attributed to inhibition of the TLR4/NF-kB/p38 signaling pathway. Moreover, 3-IAld could up-regulate the expression of ZO-1 and Occludin in vivo and vitro. Meanwhile, liquid chromatography mass spectrometry (LC-MS) results showed that 3-IAld could balance the aspartate and glutamate metabolism and the lysine degradation metabolism in the serum of DSS-induced colitis mice. In conclusion, 3-IAld ameliorated the intestinal barrier dysfunction and inflammatory response in DSS-induced UC mice, balanced amino acid metabolism, and inhibited the activation of the TLR4/NF-kB/p38 signaling pathway, thereby protecting mice with colitis.

Burdock (Arctium lappa) is a popular vegetable in China and Japan that is consumed for its general health benefits. The principal active component of burdock is arctigenin, which shows a range of bioactivities in vivo and in vitro. Here, we investigated the potential anti-tumor effects of arctigenin using two human hepatocellular carcinoma (HCC) cell lines, HepG2 and Hep3B, and sought to elucidate its potential mechanisms of action. Our results showed that arctigenin treatment inhibited cell growth in both HepG2 and Hep3B cell lines (IC₅₀ of 4.74 nM for HepG2 cells, and of 59.27 nM for Hep3B cells). In addition, migration, invasion, and colony formation by HepG2 cells were significantly inhibited by arctigenin. By contrast, treatment of Hep3B cells with arctigenin did not alter these parameters. Arctigenin also significantly reduced the levels of gankyrin mRNA and protein in HepG2 cells, but not in Hep3B cells. A luciferase assay indicated that arctigenin targeted the -450 to -400 region of the gankyrin promoter. This region is also the potential binding site for both C/EBPα and PPARα, as predicted and confirmed by an online software analysis and ChIP assay. Additionally, a co-immunoprecipitation (Co-IP) assay showed that binding between C/EBPα and PPARα was increased in the presence of arctigenin. However, arctigenin did not increase the expression of C/EBPα or PPARα protein. A binding screening assay and liquid chromatography–mass spectrometry (LC–MS) were performed to identify the mechanisms by which arctigenin regulates gankyrin expression. The results suggested that arctigenin could directly increase C/EBPα binding to the gankyrin promoter (-432 to -422 region), but did not affect PPARα binding. Expression of gankyrin, C/EBPα, and PPARα were analyzed in tumor tissues of patients using real-time PCR. Both C/EBPα and PPARα showed negative correlations with gankyrin. In tumor-bearing mice, arctigenin had a significant inhibitory effect on HCC growth. In conclusion, our results suggested that arctigenin could inhibit liver cancer growth by directly recruiting C/EBPα to the gankyrin promoter. PPARα subsequently bound to C/EBPα, and both had a negative regulatory effect on gankyrin expression. This study has identified a new mechanism of action of arctigenin against liver cancer growth.

Although colon (COAD) and rectal adenocarcinoma (READ) combined to refer to colorectal cancer (CRC), substantial clinical evidence urged that CRC should be treated as two different cancers due to compared with READ, COAD showed higher morbidity and worse 5-year survival. This study has tried to screen for the crucial gene that caused the worse prognosis and investigate its mechanism for mediating tumor growth and metastases in COAD. Meanwhile, the potential anti-COAD compound implicated in this mechanism was identified and testified from 1,855 food-borne chemical kits. This study aims to bring a new perspective to the development of new anti-COAD drugs and personalized medicine for patients with COAD. The survival-related hub genes in COAD and READ were screened out from The Cancer Genome Atlas (TCGA) database and the results showed that HIGD1A, lower expressed in COAD than in READ, was associated with poor prognosis in COAD patients, but not in READ. Over-expressed HIGD1A suppressed CRC cell proliferation, invasion, and migration in vitro and in vivo. Meanwhile, the different expressed microRNA profiles between COAD and READ showed that miR-501-3p was highly expressed in COAD and inhibited HIGD1A expression by targeting 3'UTR of HIGD1A. MiR-501-3p mimics promoted cell proliferation and metastasis in CRC cells. In addition, Procyanidin C1 (PCC1), a kind of natural polyphenol has been verified as a potential miR-501-3p inhibitor. In vitro and in vivo, PCC1 promoted HIGD1A expression by suppressing miR-501-3p and resulted in inhibited tumor growth and metastasis. The present study verified that miR-501-3p/HIGD1A axis mediated tumor growth and metastasis in COAD. PCC1, a flavonoid that riched in food exerts anti-COAD effects by inhibiting miR-501-3p and results in the latter losing the ability to suppress HIGD1A expression. Subsequently, unfettered HIGD1A inhibited tumor growth and metastasis in COAD.