By stimulating the phosphorylation of c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (p38 MAPK), signal transducer and activator of transcription 3 (STAT3) and NF-κB, the 5-HT degradation system can upregulate pro-apoptotic factors such as Bcl-2 Associated X-protein (Bax), cleaved-caspase 3 and cleaved-caspase 9, and downregulate anti-apoptotic factors like Bcl-2, which ultimately results in apoptosis, secretion of TNF-α and IL-1β, and the progression of liver diseases 281,282. Here, STAT3 is linked to liver disorder.