B10 - Molecular causes for lipomatosis associated with hyperactivation of the PTEN/PI3K/AKT/mTOR pathway

Severe lipomatosis or adipose tissue overgrowth frequently occurs in children and adolescents with germline mutations in PTEN (phosphatase and tensin homolog), which encodes a major negative regulator of PI3 kinase growth factor signalling. In order to analyse molecular causes of lipoma formation associated with defects in PTEN, we will use a lipoma animal model with conditional Pten knockout in osteo-chondroprogenitor cells (collaboration with N. Klöting). In addition to the in vivo model, we will establish suitable cell models by downregulating PTEN or overexpressing a constitutively active PI3 kinase in adipose-derived mesenchymal stem cells.

We anticipate relevant dysregulations in signalling pathways, which link to adipogenesis and proliferation of (pre)adipocytes/lipoma cells. Target-specific pharmaceuticals will be tested that could reverse pathological adipogenesis and adipose tissue overgrowth. A better understanding of this prototypic monogenic orphan disease will not only provide treatment options for the affected patients but also inform on basic mechanisms of adipocyte differentiation and proliferation and add to the functional and molecular understanding of the pathogenesis of obesity.

Figure: 1A: Schematic overview of the phosphatidylinositol 3-kinase(PI3K)/AKT/mammalian target of rapamycin (mTOR) signalling pathway which is constitutively active under conditions of phosphatase and tensin homolog (PTEN) haploinsufficiency caused by PTEN germline mutations. 1B: Adipose tissue sections from a lipoma of a patient with PTEN mutation (left) and age-matched control (right). Scale bar = 100 µm 1C: Quantification of adipocyte size in adipose tissue sections of patients with PTEN or PI3K mutations and age-matched controls.

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Anna Kirstein, PhD student