SOCS8 deficiency models MAFLD-like progression in the zebrafish gut‒liver axis

To understand the progression of metaflammation, elucidating the age-dependent role of SOCS8 deficiency in socs8 −/− zebrafish is crucial, as this may serve as a disease model for metabolic disorders because of the gradual dysregulation of immunity, metabolism, and the gut microbiota observed in this species. Thus, both juvenile (1-month-old) and adult (3-month-old) mutant socs8 −/− as well as wild-type zebrafish were tested for changes in growth, histopathology, transcriptomes, and microbiota composition. Histological analysis revealed a marked increase in oil droplets and a reduction in hepatocyte nuclear density for the comparison between socs8 −/− and wild type fish, indicative of metabolic dysfunction-associated fatty liver disease (MAFLD). The liver in 1-month-old (1 ​mo) socs8 −/− zebrafish had changes in “arginine and proline metabolism”, alongside an increased percentage of M0 and M2 macrophages. This suggests a protective response from macrophages, which is consistent with the GO term of “negative regulation of leukocyte differentiation”. The enhanced fatty acid metabolism in 1 ​mo may serve as an indicator of free fatty acid-induced hepatotoxicity associated with simple steatosis but not with liver dysfunction. These findings aligned with the higher growth of 1 ​mo socs8 −/− fish. In 3-month-old (3 ​mo) socs8 −/− fish, the GO terms “steroid hormone biosynthesis” and “steroid metabolic process” indicated the presence of endoplasmic reticulum stress, which contributes to the development of steatohepatitis. DNA repair pathways and associated terms indicated hepatocyte death. The presence of increased dendritic cells, along with expanded activated dendritic cells in nonalcoholic steatohepatitis (NASH), indicated that the 3 ​mo socs8 −/− model may represent the late stage of MAFLD. In the gut, imaging results from larvae and single-cell sequencing of intestinal mucosa cells from 3 ​mo socs8 −/− fish revealed a consistent accumulation of lymphocytes, with the number of innate immune cells higher in larvae but lower in adult fish, compared to wide type fish. In the 1 ​mo socs8 −/− fish, enhanced mucin secretion, suggested by a greater number of goblet cells and upregulated “SNARE interactions in vesicular transport”, was in line with “mannose type O-glycan biosynthesis”. The same group had upregulated IL-13 and its receptors, aligning with the GO term “wound healing” and the idea that innate lymphocytes producing IL-13 may function as regulators of immunity and tissue remodeling. The enriched pathways “arachidonic acid metabolism” and “intestinal immune network for IgA production” at 1 month, indicating enhanced proliferation of intestinal epithelial cells and improved host‒microbe interactions, respectively. Comparing 1 ​mo socs8 −/− with wide type fish, higher levels of Prevotella indicate enhanced glucose metabolism due to their role in polysaccharide breakdown. Meanwhile, lower levels of Veillonella indicate oxidative stress, potentially associated with a reduced lumen at one month. Intestinal bacterial overgrowth in 3 ​mo socs8 −/− fish (compared to 1 ​mo socs8 −/− ) contributes to the exacerbation of liver dysfunction. Compared 3 ​mo socs8 −/− with wide type fish, despite an increase in T/NK cells, elevated fatty acid metabolism may impair the function of intestinal lymphocytes. Therefore, the symptoms observed in the gut‒liver axis suggest that socs8 −/− zebrafish may serve as a model for MAFLD.