Behavioural characteristics and sex differences of a treatment-resistant depression model: Chronic mild stress in the Wistar-Kyoto rat

MKP1 may be involved in the occurrence of depression by regulating hippocampal autophagy in rats

BACKGROUND

Mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP1) is upregulated in the hippocampus of patients with depression, while pharmacological inhibition of hippocampal MKP1 can mitigate depression-like behaviors in rodents. In addition, MAPK signaling regulates autophagy, and antidepressants were recently shown to target autophagic signaling pathways. We speculated that MKP1 contributes to depression by enhancing hippocampal autophagy through dephosphorylation of the MAPK isoform ERK1/2.

METHODS

We established a rat depression model by exposure to chronic unpredictable mild stress (CUMS), and then examined depression-like behaviors in the sucrose preference test (SPT) and forced swimming test (FST) as well as expression changes in hippocampal MKP1, ERK1/2, phosphorylated ERK1/2, and autophagy-related proteins LC3II by Western blotting and immunostaining. These same measurements were repeated in rats exposed to CUMS following hippocampal infusion of a MKP1-targeted shRNA. Finally, the effects of MKP1 expression level on autophagy we examined in rat GMI-R1 microglia.

RESULTS

CUMS-exposed rats demonstrated anhedonia in the SPT and helplessness in the FST, two core depression-like behaviors. Expression levels of MKP1 and LC3II were upregulated in the hippocampus of CUMS rats, suggesting enhanced autophagy, while pERK/ERK was downregulated. Knockdown of hippocampal MKP1 mitigated depression-like behaviors, downregulated hippocampal LC3II expression, and upregulated hippocampal pERK/ERK. Similarly, MKP1 knockdown in GMI-R1 cells upregulated pERK/ERK and reduced the number of LC3II autophagosomes, while MKP1 overexpression had the opposite effects.

CONCLUSION

Enhanced hippocampal autophagy via MKP1-mediated ERK dephosphorylation may contribute to the development of depression.