Background: The phosphatase and tensin homolog (PTEN)/phosphatidylinositol-3-kinase (PI3K)/AKT signaling pathway is central for cell cycle control, differentiation, migration, and metabolism. Unrestricted growth of adipose tissue in particular is frequently seen in humans with germline PTEN and mosaic activating PIK3CA mutations, respectively.
Objective and hypotheses: We assume that adipocytes from affected tissue show hyperproliferation and modified differentiation ultimately leading to adipose tissue overgrowth. We aimed to study preadipocytes in vitro, which were derived from affected regions of pediatric mutation carriers. Moreover, we established a PTEN knockdown in SGBS preadipocytes to mimic hyperactive PI3K/AKT signaling.
Method: We used paraffin embedded lipoma tissue samples for histological analysis. Size of adipocytes was measured using automated image analysis. After cell culturing of mutant preadipocytes, AKT- and p70S6-kinase phosphorylation was determined by western blot analysis. Oil-Red-O-staining of cellular lipids was followed by a photometric quantification. Gene expression was analyzed using qRT-PCR. PTEN knockdown was performed using siRNA.
Results: Adipocytes from PTEN or PIK3CA mutation carriers (n=6) were found to be significantly larger compared to controls (n=5). Contrary to expectation, cell proliferation was not enhanced, despite higher basal AKT (Ser473) and p70S6-kinase phosphorylation. We found an increase of lipid accumulation and PPAR-gamma mRNA expression in PIK3CA mutant adipocytes during differentiation, which was absent in PTEN mutant or PTEN knockdown adipocytes.
Conclusion: Mutations in PTEN or PIK3CA lead to hypertrophic adipocytes with constitutive phosphorylation of AKT, but no increase of proliferation.
10 - 12 Sep 2016
European Society for Paediatric Endocrinology