Targeting Trim69 alleviates high fat diet (HFD)-induced hippocampal injury in mice by inhibiting apoptosis and inflammation through ASK1 inactivation.

The prevalence of obesity is growing, and high fat diet (HFD)-induced obesity can alter the brain and cognition. However, the link between HFD, hippocampal function, and inflammation is still not fully understood. Tripartite motif (TRIM) family has been implicated in various cellular processes, such as apoptosis, neurogenesis, and innate immune responses. Trim69, a member of TRIM family, was investigated in the present study to determine its role in HFD-induced hippocampal damage. Here, we first found that hippocampal Trim69 expression was markedly down-regulated in wild-type (WT) mice challenged with HFD. Trim69 knockout (KO) mice exhibited an exaggerated version of the metabolic disorder after HFD challenge, as evidenced by their increased body weight and elevated insulin resistance. HFD-induced hippocampal injury was further aggravated by Trim69 deletion, as confirmed by the reduced survival of neurons and increased level of apoptotic cell death. In addition, the inflammatory response triggered by HFD was more pronounced in the hippocampi of Trim69-KO mice after blockage of the activation of the nuclear factor kappa B (NF-κB) signaling pathway. Phosphorylation of mitogen-activated protein kinase (MAPK) kinase 4 (MKK4), MKK7, and c-Jun N-terminal kinase (JNK) in the hippocampi of HFD-challenged mice was intensified by the loss of Trim69. Hippocampal-apoptosis-signal-regulating kinase 1 (ASK1) phosphorylation was also found to be up-regulated by HFD, especially in mice with Trim69 deletion. Of note, we found that Trim69 directly interacted with and deubiquitinated ASK1 in microglial cells. Microglial cell-specific suppression of Trim69 exacerbated inflammation and apoptosis in response to lipopolysaccharide (LPS). Trim69 over-expression markedly alleviated LPS-induced inflammatory response and apoptotic cell death in microglial cells. Together, these results indicated that Trim69 might be a functionally essential inhibitor of ASK1 activation during the pathogenesis of hippocampal inflammation and apoptosis, and it could serve as a novel molecular target for obesity-associated brain damage.