Pig testis extract augments adiponectin expression and secretion through the peroxisome proliferator-activated receptor signaling pathway in 3T3-L1 adipocytes

Adiponectin is a key molecule whose upregulation may ameliorate symptoms of type 2 diabetes mellitus and disorders of lipid metabolism. Several plant-derived components have been shown to enhance adiponectin secretion; however, there have been no reports on the effects of animal-derived products. Therefore, in the current study, we investigated whether hot-water extracts of specific livestock by-products induce the expression of adiponectin in mouse 3T3-L1 adipocytes. Out of the 11 extracts tested, pig testis extract (PTE) was found to enhance adiponectin expression and secretion by 3T3-L1 cells. Furthermore, simultaneous treatment with PTE and daidzein, a soy phytoestrogen, synergistically enhanced adiponectin secretion. Moreover, pretreatment with an estrogen receptor β antagonist (PHTPP) diminished adiponectin secretion from daidzein-treated cells but not from PTE-treated cells. Transcriptome analyses revealed that both daidzein and PTE regulate the peroxisome proliferator-activated receptor signaling pathway, although differences in the regulation of gene expression were observed between PTE- and daidzein-treated cells. These results suggest that PTE ameliorates lipid metabolic dysfunction by promoting adipocyte differentiation and enhancing adiponectin secretion via a mechanism different from that of daidzein.