High salt intake induces adipogenesis by the modulation of MAPK/ERK1/2 pathway in both 3T3‐L1 adipocytes and co‐culture with macrophages
Authors: Park Hye‐Jin , Kim Jeoungyeon , Bak Sujeong , Lee Myoungsook 
Published: November 2023

Background

Obesity comes from an imbalance between energy intake and energy expenditure. And obesity is a major risk factor for diabetes, cardiovascular diseases, several forms of cancer, pulmonary, osteoarticular and metabolic diseases in the past decades.

Salt, an essential mineral, regulate the acid/base balance and have important physiological functions, such as metabolism, it maintains osmotic pressure. Physiological importance, as opposed to the high salt intake has been reported to induce variety mechanisms may be associated with cancer and chronic diseases such as, high blood pressure, heart disease and stroke, chronic renal failure, and osteoporosis. However, the underlying mechanisms is unknown.

In this study, we examined whether high salt intake induces adipogenesis, and investigated whether it was induced through the MAPK/ERK1/2 pathway in both 3T3‐L1 adipocytes and co‐culture with macrophages.

Methods

3T3‐L1 adipocytes was differentiated with MDI (1 uM dexamethasone, 0.5 mM 3‐isobutyl‐methyxanthine, 10 ug/ml insulin) with or without salt. 3T3‐L1 adipocytes at day 8 after the incubation of differentiation were co‐cultured with 2×106 RAW264.7 macrophages in trans‐well inserts with 0.45 um porous membrane to separate the adipocytes from the macrophages. After incubation 24h, Cell culture supernatants were collected, and the cells in the lower well were harvested. The biomarkers for adipocyte differentiation, transcription, insulin resistance, and adipocytokine were detected by western blot, qPCR and ELISA. Phenotypes of 3T3‐L1 were identified by expression of pro‐ or anti‐inflammatory responses such as MCP‐1, IL‐17A and F4/80, which were detected by fluorescence‐activated cell sorting (FACS) method.

Results

High salt concentration‐dependently increased transcription factor of adipogenesis (PPARγ, C/EBPα), insulin sensitivity (IRS‐1, GLUT4) and inflammation cytokines (IL‐17A, IL‐6, and MCP‐1) was increased in both 3T3‐L1 adipocytes and co‐culture with macrophages. According to induction of adipocytokines the protein and mRNA expression of LAR (leptin‐adiponectin ratio) was increased. And also, phosphorylation of ERK1/2 was increased by high salt. And pre‐treatment with U0126, a specific MEK1 inhibitor, blocked ERK1/2 phosphorylation and inhibited adipocyte differentiation.

Conclusions

Treatment of the concentrations of salt increased not only the enhancement of adipogenesis, insulin resistance, and also the production of inflammatory cytokines. And revealed that U0126, a specific MEK1 inhibitor, sequentially inhibited the activation of ERK1/2 pathway. These results represent that sodium increases adipogenesis via enhancement of MAPK/ERK1/2 pathway in both 3T3‐L1 adipocytes and co‐culture with macrophages.

Support or Funding Information

[Funds: This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (2014R1A2A1A11049611), This research was a part of the project titled ‘Development of An Individual Case‐Authorized Functional new Biomaterial from Marine organism resource’, funded by the Ministry of Oceans and Fisheries, Korea (PJT200598).]