Gut Akkermansia Muciniphila Ameliorates HIV-1 gp120-Induced Neuronal Pyroptosis By Regulating Kyna Level in Brain Via Blood-Brain Barrier

Backgrounds:

HIV-1 gp120 is a critical virulence factor implicated in HIV-associated neurocognitive disorders (HAND), causing significant neuronal damage. Our previous research has demonstrated elevated transcription of pyroptosis-related genes and increased expression of gasdermin D (GSDMD) in neurons of HIV-1 gp120 transgenic mice (Tgm), leading to pyroptosis upon GSDMD cleavage. Akkermansia muciniphila (A.m.), a promising next generation probiotic, has shown neuroprotective effects in various neurodegenerative diseases, albeit its mechanism remains unclear. Previous studies have indicated that A.m. promotes tryptophan degradation, enhances kynurenine (KYN) production, and may influence the generation of kynurenic acid (KYNA) through blood -brain barrier (BBB), a known neuroprotective metabolite in the brain. Therefore, this study aims to investigate the protective effects and underlying mechanisms of orally administered A.m. against HIV-1 gp120-induced neuronal pyroptosis in mice.

Methods:

Akkermansia muciniphila (A.m., ATCC BAA-835) was purchased from the Guangdong Microbial Culture Collection Center (GDMCC). Bacteria were harvested during logarithmic growth on the third day of anaerobic culture and quantified to 1×10⁹/mL by absorbance. Ten-month-old HIV-1 gp120 transgenic mice (Tgm) and C57BL/6J mice (wild type, WT) were randomly divided into 4 groups (n=10) and orally gavaged daily with 200 μL of either PBS or A.m. for 6 weeks. Mice were sacrificed thereafter, and serum, cerebrospinal fluid, and brain tissue were collected for subsequent experiments. Serum KYN levels and cerebrospinal fluid KYNA levels were measured by ELISA, while neuronal counts and GSDMD expression levels in the brain were assessed by immunohistochemistry. SPSS 20.0 software was used for statistical analysis. P<0.05 were considered statistically significant.

Results:

Compared to the Tgm+PBS group, 6 weeks of oral gavage with A.m. significantly reduced neuronal damage in the brains of Tgm mice. Immunohistochemistry staining with NeuN, a marker for neurons, revealed a significant increase in the number of neurons in the cerebral cortex and hippocampus of Tgm mice following A.m. gavage. Further immunohistochemical analysis of GSDMD expression levels in the brains of each group indicated a significant reduction in GSDMD expression in Tgm mice after A.m. gavage. These findings collectively suggest that A.m. gavage mitigates neuronal loss and GSDMD expression induced by HIV-1 gp120. In additional ELISA experiments, we found significant increases in kynurenine (KYN) levels in serum and kynurenic acid (KYNA) levels in cerebrospinal fluid via BBB after A.m. gavage across all groups, indicating that A.m. gavage enhances the generation of KYN from tryptophan degradation in serum and elevates protective KYNA levels at the blood-brain barrier. The increase in brain KYNA levels may represent a potential mechanism by which A.m. gavage exerts its neuroprotective effects.

Conclusions:

After 6 weeks of daily gavage with A.m. (200 μL/day), there was a significant reduction in neuronal loss and pyroptosis-related GSDMD expression in Tgm mice. Evidence from serum and cerebrospinal fluid strongly suggests that the neuroprotective effects of intestinal A.m. are likely mediated through the regulation of KYNA generation by using orally administered A.m. in the gut-blood-brain way. (Acknowledgements: This study was supported by National Natural Science Foundation of China, No. 82172259 to H. Cao and Grant from School of Public Health of Southern Medical University, China, Grant No. GW202329 to H. Cao and Undergraduate Training Program for Innovation and Entrepreneurship of SMU, No.202312121328. Corresponding author: Hong Cao, gzhcao@smu.edu.cn)

No relevant conflicts of interest to declare.