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Sabrina Kuespert, Ernst Tamm, Rudolf Fuchshofer; Disruption of the homeostatic balance between TGF-β and BMPs in the outflow tissues of the CTGF-based Glaucoma mouse model. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4008.
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To investigate the homeostatic balance between TGF-β2 and its endogenous antagonists, the bone morphogenetic proteins (BMPs), in CTGF-overexpressing mice (Junglas et al., Am J. Path. 2012) with primary open-angle glaucoma (POAG).
2 month-old βB1-Crystallin-CTGF mice and wild-type littermates were analyzed. The amounts of BMPs, TGF-β2 and their mRNA expression, as well as that of other molecules involved in their respective signaling pathways (pSmad 1/5/8; pSmad 2/3; Smad 6/7, Gremlin) were analyzed by immunoblotting, immunohistochemistry and real-time RT-PCR. Cultured human trabecular meshwork (HTM) cells were treated under serum free conditions with different concentrations of CTGF (5 ng-100 ng) for 24 h. Changes in the expression pattern of TGF-β2 were determined by Western blot analysis and real-time RT-PCR. Blocking of the CTGF pathway was performed with an inhibitor against MEK1/2 (UO126).
CTGF overexpression in βB1-Crystallin-CTGF with POAG leads to a significant decrease of BMP synthesis and signaling in aqueous humor outflow tissues when compared to wild-type littermates. In contrast, the expression of TGF-β2 and activity of its signaling were enhanced in 2-month-old transgenic mice. The examination of the inhibitory Smads showed that Smad6 was significantly enhanced in transgenic mice, whereas Smad7 was unaffected. Gremlin, a specific BMP inhibitor, was also significantly increased in CTGF overexpressing mice with POAG. In vitro, CTGF treatment led to an induction of TGF-β2 via the ERK1/2 pathway.
CTGF is a key modulator in the pathogenesis of POAG leading to changes in the homeostatic balance between TGF-β and BMPs. The shift towards the TGF-β pathway is initiated by an increased TGF-β expression versus a reduced BMP synthesis. In addition, an upstream blockage of BMPs by Gremlin and an enhanced downstream inhibition by Smad6 was observed in the transgenic animals. The effects appear to involve the ERK1/2 pathway. Modification of CTGF signaling seems to be a promising strategy to treat POAG.
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