Transforming growth factor-β enhances matrix metalloproteinase-2 expression and activity through AKT in fibroblasts derived from angiofibromas in patients with tuberous sclerosis complex

Abstract

Patients with tuberous sclerosis complex (TSC) develop fibrous tumours in the brain, skin, kidney, heart and lungs due to TSC1/2 mutations. In the skin, patients develop angiofibromas that have vascular and fibrotic components in which transforming growth factor (TGF)-β and matrix metalloproteinase (MMP)-2 are important. To investigate if the TGF-β axis and MMP-2 play an important role in the pathogenesis of TSC angiofibromas. Samples from TSC angiofibromas and normal skin were measured for expression of TGF-β and MMP-2 by immunohistochemistry and real-time polymerase chain reaction. Fibroblasts grown from TSC angiofibromas (TSC fibroblasts) were incubated with TGF-β. Expression of ERK, AKT and S6K was measured by Western blotting, and MMP-2 expression and activity were determined by enzyme-linked immunosorbent assay and gelatin zymography, respectively. There was an increase in the expression of TGF-β and MMP-2 in TSC tumours compared with those in normal skin. The baseline expression of MMP-2 was increased in conditioned medium from TSC fibroblasts. In addition, TGF-β enhanced MMP-2 production and activity, which could be abrogated by pretreatment with an AKT inhibitor (LY294002) but not with rapamycin. Finally, there was a significant colocalization of TGF-β and MMP-2 in the TSC tumours. There is an increase of MMP-2 as a result of TGF-β acting through AKT in TSC tumour cells. This regulation of the TGF-β-AKT-MMP-2 axis is independent of mammalian target of rapamycin (mTOR) signalling. In addition to targeting the mTOR pathway, targeting TGF-β simultaneously could block dysregulated tissue remodelling in TSC tumours.