The thrombin receptor PAR4 supports visceral adipose tissue inflammation
Sonja Kleeschulte1, Vivien Fischinger2, Lisa Öhlke3
1Department of Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Düsseldorf, Germany.
Abstract:
Thrombin inhibition suppresses adiposity, WAT inflammation and metabolic dysfunction in mice. Protease-activated receptor (PAR)1 does not account for thrombin-driven obesity, so we explored the culprit role of PAR4 in this context. Male WT and PAR-4-/- mice received a high fat diet (HFD) for 8 weeks, WT controls received standard chow. Body fat was quantified by NMR. Epididymal WAT was assessed by histology, immunohistochemistry, qPCR and lipase activity assay. 3T3-L1 preadipocytes were differentiated ± thrombin, acutely stimulated ± PAR4 activating peptide (AP) and assessed by immunoblot, qPCR and U937 monocyte adhesion. Epicardial adipose tissue (EAT) from obese and lean patients was assessed by immunoblot. PAR4 was upregulated in mouse WAT under HFD. PAR4-/- mice developed less visceral adiposity and glucose intolerance under HFD, featuring smaller adipocytes, fewer macrophages and lower expression of adipogenic (leptin, PPARγ) and pro-inflammatory genes (CCL2, IL-1β) in WAT. HFD-modified activity and expression of lipases or perilipin were unaffected by PAR4 deletion. 3T3-L1 adipocytes differentiated with thrombin retained Ki67 expression, further upregulated IL-1β and CCL2 and were more adhesive for monocytes. In mature adipocytes, PAR4-AP increased phosphorylated ERK1/2 and AKT, upregulated Ki67, CCl2, IL-β and hyaluronan synthase 1 but not TNF-α mRNA, and augmented hyaluronidase-sensitive monocyte adhesion. Obese human EAT expressed more PAR4, CD68 and CD54 than lean EAT. PAR4 upregulated in obesity supports adipocyte hypertrophy, WAT expansion and thrombo-inflammation. The emerging PAR4 antagonists provide a therapeutic perspective in this context beyond their canonical antiplatelet action.
Insights
Protease-activated receptor 4 (PAR4) drives obesity and inflammation in white adipose tissue (WAT). Inhibiting PAR4 in mice reduced visceral adiposity and improved glucose tolerance, suggesting PAR4 antagonists as a potential therapy.
Area of Science:
- Biochemistry
- Physiology
- Immunology
Background:
- Thrombin inhibition reduces adiposity and inflammation.
- Protease-activated receptor 1 (PAR1) does not mediate thrombin-driven obesity.
- The role of PAR4 in obesity and metabolic dysfunction requires investigation.
Purpose of the Study:
- To investigate the role of PAR4 in high-fat diet-induced obesity, adipose tissue inflammation, and metabolic dysfunction.
- To assess the impact of PAR4 deletion on adiposity, glucose tolerance, and adipose tissue characteristics in mice.
- To examine the effects of thrombin and PAR4 activation on adipocytes and monocyte adhesion in vitro, and PAR4 expression in human adipose tissue.
Main Methods:
- Wild-type (WT) and PAR-4 knockout (PAR-4-/-) mice were fed a high-fat diet (HFD) or standard chow for 8 weeks.
- Body fat was measured using NMR; epididymal white adipose tissue (WAT) was analyzed by histology, immunohistochemistry, qPCR, and lipase activity assays.
- 3T3-L1 preadipocytes and mature adipocytes were treated with thrombin or a PAR4-activating peptide (AP); human epicardial adipose tissue (EAT) from obese and lean individuals was analyzed.
Main Results:
- PAR4 was upregulated in mouse WAT under HFD. PAR4-/- mice exhibited reduced visceral adiposity and improved glucose tolerance, with smaller adipocytes and lower expression of adipogenic and pro-inflammatory genes in WAT.
- Thrombin-treated 3T3-L1 adipocytes showed increased IL-1β and CCL2 expression and enhanced monocyte adhesion. PAR4-AP stimulation of mature adipocytes increased phosphorylated ERK1/2 and AKT, upregulated Ki67, CCL2, IL-1β, and hyaluronan synthase 1, and augmented monocyte adhesion.
- Obese human EAT displayed higher expression of PAR4, CD68, and CD54 compared to lean EAT.
Conclusions:
- Upregulated PAR4 in obesity contributes to adipocyte hypertrophy, WAT expansion, and thrombo-inflammation.
- PAR4 plays a significant role in high-fat diet-induced obesity and associated metabolic dysfunction.
- PAR4 antagonists represent a promising therapeutic strategy for obesity and related inflammatory conditions, extending beyond their antiplatelet effects.
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