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WISP2 regulates preadipocyte commitment and PPARγ activation by BMP4.

ABSTRACT: Inability to recruit new adipose cells following weight gain leads to inappropriate enlargement of existing cells (hypertrophic obesity) associated with inflammation and a dysfunctional adipose tissue. We found increased expression of WNT1 inducible signaling pathway protein 2 (WISP2) and other markers of WNT activation in human abdominal s.c. adipose tissue characterized by hypertrophic obesity combined with increased visceral fat accumulation and insulin resistance. WISP2 activation in the s.c. adipose tissue, but not in visceral fat, identified the metabolic syndrome in equally obese individuals. WISP2 is a novel adipokine, highly expressed and secreted by adipose precursor cells. Knocking down WISP2 induced spontaneous differentiation of 3T3-L1 and human preadipocytes and allowed NIH 3T3 fibroblasts to become committed to the adipose lineage by bone morphogenetic protein 4 (BMP4). WISP2 forms a cytosolic complex with the peroxisome proliferator-activated receptor γ (PPARγ) transcriptional activator zinc finger protein 423 (Zfp423), and this complex is dissociated by BMP4 in a SMAD-dependent manner, thereby allowing Zfp423 to enter the nucleus, activate PPARγ, and commit the cells to the adipose lineage. The importance of intracellular Wisp2 protein for BMP4-induced adipogenic commitment and PPARγ activation was verified by expressing a mutant Wisp2 protein lacking the endoplasmic reticulum signal and secretion sequence. Secreted Wnt/Wisp2 also inhibits differentiation and PPARγ activation, albeit not through Zfp423 nuclear translocation. Thus adipogenic commitment and differentiation is regulated by the cross-talk between BMP4 and canonical WNT signaling and where WISP2 plays a key role. Furthermore, they link WISP2 with hypertrophic obesity and the metabolic syndrome.

SUBMITTER: Hammarstedt A

PROVIDER: S-EPMC3574913 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundPolycystic ovary syndrome (PCOS) is the most common cause of anovulatory infertility in women. Rhamnocitrin (Rha) has anti-inflammatory and antioxidant actions. The WNT1-inducible-signaling pathway protein 2 (Wisp2) and nuclear factor (NF)-κB are involved in fibrosis in many diseases. We aimed to elucidate the role of Rha in fibrosis of PCOS and the underlying mechanisms.MethodsDehydroepiandrosterone (DHEA)-incubated ovarian granulosa KGN cells were treated by Rha. Cell proliferation was detected with cell counting kit-8 (CCK-8) and 5-ethynyul-2'-deoxyuridine (EdU) staining. The levels of Wisp2 and transforming growth factor-β1 (TGF-β1) in supernatant were measured by enzyme-linked immunosorbent assay (ELISA). We observed α-smooth muscle actin (α-SMA) protein by immunofluorescence (IF). The levels of fibrosis factors were determined using Western blot. We observed p65 nuclear translocation with confocal microscopy. We used Wisp2 overexpression and knockdown in cells treated with DHEA or Rha to validate Wisp2 function. Interaction between Wisp2 and NF-κB, as well as Wisp2 and PPARγ, were assessed by co-immunoprecipitation assay, luciferase reporter assay and chromatin immunoprecipitation (ChIP).ResultsThe results showed that Rha elevated the reduced proliferation of DHEA-treated cells. In addition, Rha reversed the decreased Wisp2 and the increased TGF-β1 in supernatant. The proteins CTGF, α-SMA, Collagen I, TGF-β1, p-Smad2, and p-Smad3 were up-regulated while Wisp2, Sirt1, and PPARγ were down-regulated by DHEA treatment, which were reversed by Rha. Meanwhile, DHEA up-regulated p-IKBa and p-p65 and promoted p65 nuclear translocation, which were inhibited by Rha. These effects of Rha were antagonized by Wisp2 knockdown and were mimicked by Wisp2 overexpression. We confirmed the protein interaction between Wisp2 and NF-κB, along with Wisp2 and PPARγ.ConclusionsWisp2-mediated PPARγ/NF-κB/TGF-β1/Smad2/3 signaling contributes to Rha-improved ovarian granulosa cells fibrosis, suggesting Rha as a novel agent for the treatment of PCOS.

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WISP2 regulates preadipocyte commitment and PPARγ activation by BMP4.

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