Hyperinsulinemia-induced upregulation of adipocyte TPH2 contributes to peripheral serotonin production, metabolic dysfunction, and obesity
Brian I. Park, … , Michael D. Jensen, Andrew S. Greenberg
Brian I. Park, … , Michael D. Jensen, Andrew S. Greenberg
Published June 2, 2025
Citation Information: J Clin Invest. 2025;135(14):e190765. https://doi.org/10.1172/JCI190765.
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Research Article Endocrinology Metabolism

Hyperinsulinemia-induced upregulation of adipocyte TPH2 contributes to peripheral serotonin production, metabolic dysfunction, and obesity

Abstract

Tryptophan hydroxylase (TPH) is a rate-limiting enzyme for serotonin or 5-hydroxytryptamine (5-HT) synthesis. Previously, adipocyte TPH1 has been linked to increased adipose 5-HT, reduced brown adipose tissue (BAT) thermogenesis, and obesity. However, the role of TPH2, a neural isoform highly expressed in obese adipose tissue, is unknown. Here, we report that adipose tissue expression of TPH2 is dramatically elevated in mice with diet-induced obesity (DIO) and ob/ob mice, as well as in obese humans. In mice fed a high-fat diet, adipocyte TPH2 deficiency improved DIO-induced metabolic complications, enhanced BAT thermogenesis, and increased intestinal energy-harvesting efficiency without affecting adiposity. Conversely, TPH2 overexpression in epididymal adipocytes of chow-fed mice raised adipose and plasma 5-HT levels, suppressed BAT thermogenesis, and exacerbated obesity and metabolic dysfunction. We found that obesity-induced hyperinsulinemia upregulated adipocyte TPH2 expression via activation of mechanistic target of rapamycin complex 1 and SREBP1. In humans, TPH2 mRNA levels in subcutaneous adipose tissue, but not those of TPH1, are positively correlated with fasting plasma insulin concentrations. In summary, our study demonstrates that obesity-associated increases in adipocyte TPH2 can regulate distal tissue physiology and energy metabolism, suggesting that TPH2 could be a potential therapeutic target for obesity and its associated complications.

Authors

Brian I. Park, Andrew R. Reeves, Ying Zhu, Robin A. Wilson, Sophia C. Fernandes, Kimberly K. Buhman, Kelli A. Lytle, Michael D. Jensen, Andrew S. Greenberg

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Figure 1

Obesity dramatically upregulates adipocyte TPH2 expression in both mice and humans.

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Obesity dramatically upregulates adipocyte TPH2 expression in both mice ...
(A) eWAT 5-HT levels in chow- or HFD-fed mice for 6 weeks (n = 3 per group). (B) Plasma 5-HT levels in chow- or HFD-fed mice for 6 weeks (n = 6 per group). (C) mRNA levels of Tph1 and Tph2 of isolated epididymal white adipocytes in chow- or HFD-fed mice for 6 weeks (n = 4 for chow; n = 8 for HFD). (D) mRNA levels of Tph1 and Tph2 of isolated brown adipocytes in chow- or HFD-fed mice for 6 weeks (n = 4 for chow; n = 8 for HFD). (E) eWAT protein levels of TPH2 in chow- or HFD-fed mice for 6 weeks (n = 3 per group). (F) mRNA levels of TPH1 and TPH2 in human subcutaneous fat from lean and obese subjects (n = 6 per group). (G–I) Correlation between TPH2 expression in human subcutaneous fat and fasting plasma FFA (G),TG (H), and AST (I) levels of lean and obese individuals (n = 6 per group). Pearson’s r correlation coefficient with corresponding P values. Data are presented as mean ± SEM. For statistical analysis, 2-tailed Student’s t test (A–F) was used. *P < 0.05, **P < 0.01, ***P < 0.001.